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Sökning: L773:1386 1425 OR L773:1873 3557

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1.
  • Hammarstrom, L., et al. (författare)
  • A biomimetic approach to artificial photosynthesis : Ru(II)-polypyridine photo-sensitisers linked to tyrosine and manganese electron donors
  • 2001
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 57:11, s. 2145-2160
  • Forskningsöversikt (refereegranskat)abstract
    • The paper describes recent advances towards the construction of functional rr mics of the oxygen evolving complex in photosystem II (PSII) that are coupled to photoinduced charge separation. Some key principles of PSII and artificial systems for light-induced charge accumulation are discussed. Systems are described where biomimetic electron donors - manganese complexes and tyrosine - have been linked to a Ru(II)-polypyridine photosensitiser. Oxidation of the donors by intramolecular electron transfer from the photo-oxidised Ru(III) complex has been studied using optical flash photolysis and EPR experiments. A step-wise electron transfer Mn-2(III,III) --> tyrosine --> Ru(III) has been demonstrated, in analogy to the reaction on the donor side of PSII Electron transfer from the tyrosine to Ru(III) was coupled to tyrosine deprotonation. This resulted in a large reorganisation energy and thus a slow reaction rate, unless the tyrosine was hydrogen bonded or already deprotonated. A comparison with analogous reactions in PSH is made. Finally, light-induced oxidation of a manganese dimer linked to a Ru(II)-photosensitiser has been observed. Preliminary results suggest the possibility of photo-oxidising manganese dimers in several steps, which is an important advancement towards water oxidation.
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2.
  • Holmgren, Allan, et al. (författare)
  • Fourier transform infrared and Raman study of Alizarin Red S adsorbed at the fluorite-water interface
  • 1999
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 55:9, s. 1721-1730
  • Tidskriftsartikel (refereegranskat)abstract
    • The adsorption of 1,2-dihydroxyanthraqinone-3-sulphonate (ARS) onto the surface of fluorite mineral was studied using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and Fourier transform (FT) Raman spectroscopy. The FT-Raman method proved to be more appropriate for this study when ARS was adsorbed from alkaline solution. At pH 6 both DRIFT and Raman spectra indicate non-precipitated ARS on the fluorite surface. At higher pH Raman spectra indicate ARS to be attached to the fluorite surface through the quinoid group at the 9-position and the α-phenolic oxygen.
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3.
  • Kalinin, Stanislav V., et al. (författare)
  • Partial Donor-Donor Energy Migration (PDDEM) as a Fluorescence Spectroscopic Tool for Measuring Distances in Biomacromolecules
  • 2002
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 58:5, s. 1087-1097
  • Tidskriftsartikel (refereegranskat)abstract
    • A theoretical model is presented, tested and applied for determining the rates of energy migration and distances within pairs of chemically identical fluorophores, so-called donors (D), which are exposed to different physical properties. The model is a general extension of the recently developed donor–donor energy migration (DDEM) model [J. Chem. Soc., Faraday Trans. 92 (1996)1563; J. Chem. Phys. 105 (1996) 10896] that applies to examining structure-function of biomacromolecules, such as proteins. Most fluorescent groups of the same kind incorporated at different positions (α and β) in a macromolecule exhibit shifts of the absorption and/or emission spectra, as well as different relaxation rates of the photophysics. As a consequence, the energy migration between the Dα and Dβ groups will be partially reversible. We refer to this case, as the partial donor–donor energy migration (PDDEM). The models of PPDEM presented can be used for analysing time-resolved fluorescence relaxation, as well as fluorescence depolarisation experiments. To explore the limitations of the PDDEM model, we have generated and re-analysed synthetic data that mimic time-correlated single photon counting (TCSPC) experiments. It was found that slow and fast rates of energy migration are most accurately recovered from the fluorescence relaxation and the depolarisation experiments, respectively. At comparable transfer and fluorescence rates, both kinds of experiments are equally useful. Real experiments on PDDEM were performed on an asymmetrically quenched bichromophoric molecule (1,32-dihydroxy-dotriacontane-bis-(Rhodamine 101) ester), that spans across the lipid bilayer of a vesicle. The depolarisation data were analysed by the PDDEM model and provide a distance between Rhodamine 101 groups, which agrees with independent studies
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4.
  • Kloo, Lars A., et al. (författare)
  • Spectroscopic characterisation of indium(III) chloride and mixed ligand complexes
  • 2002
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 58:5, s. 953-957
  • Tidskriftsartikel (refereegranskat)abstract
    • Acidic solutions of InCl3 plus InBr3 contain mixed halide complexes and solvent extraction yields the four-coordinate anions InClnBr4-n- whose v(In-Cl) and v(In-Br) modes are reported. Two solid products of InCl3 with 15-crown-5 have been identified; crystallisation from aqueous HCl gave a molecular adduct containing InCl3(H2O)(2), whereas the ionic complex [InCl2(15-crown-5)][InCl4] was produced under anhydrous conditions. The vibrational spectra are assigned.
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5.
  • Lund, Anders, et al. (författare)
  • New materials for ESR dosimetry
  • 2002
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 58:6, s. 1301-1311
  • Tidskriftsartikel (refereegranskat)abstract
    • New materials for electron spin resonance (ESR) dosimetry have been investigated with the aim to find systems more sensitive than L-alanine accepted as a standard for high dose determinations. Among the investigated systems ammonium tartrate, 2-methylalanine, salts of formic acids and dithionates have been found to be more sensitive than alanine by a factor 2-10. The lower limit applies to tissue equivalent materials, while much higher sensitivities were obtained with formates and dithionates containing heavier atoms. The increased sensitivity was mainly attributed to suitable ESR properties of the room temperature stable radicals as regards spectral shape (narrow lines, little or no hyperfine structure) and microwave saturation properties (short relaxation times). The radical structures have when necessary been clarified by ENDOR spectroscopy, while the saturation properties have been screened by pulsed ESR measurements.
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6.
  • Minaev, Boris F. (författare)
  • Ab initio study of the ground state properties of molecular oxygen
  • 2004
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 60:5, s. 1027-1041
  • Tidskriftsartikel (refereegranskat)abstract
    • The electric and magnetic properties of the ground state of oxygen molecule are calculated by multiconfiguration self-consisted field (MCSCF) method and compared with experimental data: the quadrupole moment, polarizability, the O-17 nuclear quadrupole coupling constant, magnetizability tensor, nuclear spin-rotation Coupling constant and rotational g factor. The last two constants are calculated for all possible isotope modifications. The rotational, ESR and NMR spectra are discussed. Fermi-contact hyperfine coupling parameter is additionally estimated by different methods. The NMR chemical shielding tensor for (OO)-O-17-O-16 species at high temperature limit (without electron spin contribution) is predicted. Potential energy curves for 10 excited bound states and the internuclear distance dependence of the studied properties are also presented.
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7.
  • Minaev, B., et al. (författare)
  • Physical properties and spectra of IO, IO- and HOI studied by ab initio methods
  • 2002
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 58:5, s. 1039-1053
  • Tidskriftsartikel (refereegranskat)abstract
    • Structure and properties of the IO, IO- and HOI species, which are of potential importance for the ozone destruction catalytic cycle in the troposphere, have been calculated together with the EPR, NMR and UV-visible spectra by ab initio methodology with account of spin-orbit coupling (SOC) effects. Multi-configuration self-consistent field calculations with linear and quadratic response techniques and the multi-reference configuration interaction method have been employed. Photodissociation of these species, crucial for the catalytic ozone-destruction cycle, is critically reviewed and analyzed. Calculations predict that the singlet-triplet (S-T) transition to the lowest triplet state (X(1)A' --> (3)A) should be responsible for the weak long-wavelength tail absorption ( similar to450-560 nm) and photodissociation of the HOI molecule. The second, more intense, band around 400 nm is produced by two overlapping S-S and S-T transitions. In order to check this assignement of the HOI photodissociation the isoelectronic IO- anion and IO radical have been studied by the same methods. Comparison with the EPR spectrum of the 10 radical indicates that the methods are reliable which gives credit to the accuracy of the HOI spectral interpretation. NMR spectra of HOI and IO- molecules,and some other properties are calculated for the first time.
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8.
  • Sandström, Lars (författare)
  • On-line and in situ monitoring of oxygen concentration and gas temperature in a reheating furnace utilizing tunable diode-laser spectroscopy
  • 2001
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - Amsterdam : Elsevier. - 1386-1425 .- 1873-3557. ; 58:11, s. 2449-2455
  • Tidskriftsartikel (refereegranskat)abstract
    • Increased demands on energy savings and quality control in metallurgical processes have created incentives for new methods to monitor and control the process. In this paper we will present a field trial that shows the potential of tunable diode-laser spectroscopy (TDLS) for simultaneous contact free measuring and monitoring of the oxygen concentration as well as the gas temperature in a reheating furnaceduring production. The field trials were carried out at an oil-fueled reheating furnace during 7 weeks of production. The tunable diode-laserspectrometer was measuring in situ across the preheating zone and the soaking zone in the furnace. During the campaign the oxygenconcentration and the gas temperature in the furnace environment were simultaneously monitored and instantaneous variations in these parameters could easily be recorded and subsequently correlated to actual changes in the process. Furthermore, the much shorter response-time of the TDLS technique compared with conventional measurement methods such as thermocouples and extractive gas analyzers was also demonstrated during the trials. The results show the potential for the TDLS technique to be used for energy savings as well as product quality improvements by controlling the burners in the reheating furnace. The results show that it would be possible to control and optimize the oxygenconcentration with TDLS in the control loop of the reheating furnace. © 2002 Elsevier Science B.V. All rights reserved.
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9.
  • van den Berg, P. A. W., et al. (författare)
  • Fluorescence correlation spectroscopy of flavins and flavoenzymes : photochemical and photophysical aspects
  • 2001
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 57:11, s. 2135-2144
  • Tidskriftsartikel (refereegranskat)abstract
    • Fluorescence Correlation Spectroscopy (FCS) was used to investigate the excited-state properties of flavins and flavoproteins in solution at the single molecule level. Flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD) and lipoamide dehydrogenase served as model systems in which the flavin cofactor is either free in solution (FMN, FAD) or enclosed in a protein environment as prosthetic group (lipoamide dehydrogenase). Parameters such as excitation light intensity, detection time and chromophore concentration were varied in order to optimize the autocorrelation traces. Only in experiments with very low light intensity ( < 10 kW/cm(2)), FMN and FAD displayed fluorescence properties equivalent to those found with conventional fluorescence detection methods. Due to the high triplet quantum yield of FMN, the system very soon starts to build up a population of non-fluorescent molecules, which is reflected in an apparent particle number far too low for the concentration used. Intramolecular photoreduction and subsequent photobleaching may well explain these observations. The effect of photoreduction was clearly shown by titration of FMN with ascorbic acid. While titration of FMN with the quenching agent potassium iodide at higher concentrations ( > 50 mM of I-) resulted in quenched flavin fluorescence as expected, low concentrations of potassium iodide led to a net enhancement of the de-excitation rate from the triplet state., thereby improving the fluorescence signal. FCS experiments on FAD exhibited an improved photostability of FAD as compared to FMN: As a result of stacking of the adenine and flavin moieties, FAD has a considerably lower triplet quantum yield. Correlation curves of lipoamide dehydrogenase yielded correct values for the diffusion time and number of molecules at low excitation intensities. However, experiments at higher light intensities revealed a process which can be explained by photophysical relaxation or photochemical destruction of the enzyme. As the time constant of the process induced at higher light intensities resembles the diffusion time constant of free flavin, photodestruction with the concomitant release of the cofactor offers a reasonable explanation.
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10.
  • Ali, Hassan, et al. (författare)
  • Noninvasive in situ identification and band assignments of some pharmaceutical excipients inside USP vials with FT-near-infrared spectroscopy
  • 2009
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 72:4, s. 890-896
  • Tidskriftsartikel (refereegranskat)abstract
    • For the manufacture of dosage forms all ingredients must be reliably identified. In this paper, the suitability of FT-NIR spectroscopy to identify potassium sorbate, sodium starch glycollate, calcium ascorbate, calcium carbonate, candelilla wax, maltosextrin, monohydrated and anhydrous lactose inside USP vials was investigated. Differentiation between the anhydrous and monohydrated forms of lactose was found to be possible by studying the regions of the near-infrared spectrum corresponding to the combination and first overtone stretching frequencies of water. The results show unequivocally the potential of FT-NIR spectroscopy for rapid, in situ and non-destructive identification of pharmaceutical excipients
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11.
  • Ali, Hassan, et al. (författare)
  • Vibrational spectroscopic study of fluticasone propionate
  • 2009
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 72:2, s. 244-247
  • Tidskriftsartikel (refereegranskat)abstract
    • Fluticasone propionate is a synthetic glucocorticoid with potent anti-inflammatory activity that has been used effectively in the treatment of chronic asthma. The present work reports a vibrational spectroscopic study of fluticasone propionate and gives proposed molecular assignments on the basis of ab initio calculations using BLYP density functional theory with a 6-31G* basis set and vibrational frequencies predicted within the quasi-harmonic approximation. Several spectral features and band intensities are explained. This study generated a library of information that can be employed to aid the process monitoring of fluticasone propionate.
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12.
  • Ali, Hassan, et al. (författare)
  • Vibrational spectroscopic study of terbutaline hemisulphate
  • 2009
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 72:4, s. 715-719
  • Tidskriftsartikel (refereegranskat)abstract
    • The Raman spectrum of terbutaline hemisulphate is reported for the first time, and molecular assignments are proposed on the basis of ab initio BLYP DFT calculations with a 6-31G* basis set and vibrational frequencies predicted within the quasi-harmonic approximation; these predictions compare favourably with the observed vibrational spectra. Comparison with previously published infrared data explains several spectral features. The results from this study provide data that can be used for the preparative process monitoring of terbutaline hemisulphate, an important β2 agonist drug in various dosage forms and its interaction with excipients and other components
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13.
  • Becker, Hans-Christian, et al. (författare)
  • Size- and solvent-dependent kinetics for cis-trans isomerization in donor-acceptor systems
  • 2009
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 72:5, s. 1014-1019
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated, using time-resolved and steady-state optical spectroscopy, the cis-trans isomerization dynamics in a series of charge transfer. donor-acceptor compounds. The number of donor (dithiafulvene) and acceptor (p-nitrophenyl) moieties as well as their spatial arrangement around a central ethynylethene core has been varied in a systematic way, All compounds in the series are weakly fluorescent. We show that the fluorescence spectrum red-shifts within a few picoseconds, a shift which occurs concurrently with a blue-shift of the transient absorption spectrum. The kinetics following the initial relaxation are in all cases multi-exponential, and the time constants correlate with molecular size and solvent viscosity. We interpret the data as a result of conformational change where the conjugation through the central double bond is broken upon excitation into the charge-transfer transition, and the time for rotation around this bond is dependent on the molecular interactions between solute and solvent. (C) 2009 Elsevier B.V. All Fights reserved.
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14.
  • Bezvikonnyi, Oleksandr, et al. (författare)
  • Effects of carbazolyl and diphenylamino substituents bearing methoxy groups on the performance of hole-transporting materials in OLEDs
  • 2024
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier. - 1386-1425 .- 1873-3557. ; 321
  • Tidskriftsartikel (refereegranskat)abstract
    • Newly designed and synthesized derivatives of pentaphenylbenzene with methoxy-substituted carbazolyl or diphenylamino moieties were investigated to estimate their applicability as hole transport materials. Both the compounds exhibit high thermal stability. The intramolecular charge transfer is blocked for the film of the compound containing diphenylamino groups. The intermolecular charge transfer is induced in the film of carbazolyl-containing compound. The derivative of pentaphenylbenzene and diphenylamine exhibits higher hole drift mobility (2.4.10-3 cm2/V.s at the electric field of 5.5.105 V/cm) and by 0.1 eV lower ionization potential than the carbazolyl-containing compound. Both the compounds were utilized as hole-transporting materials in a series of organic light emitting diodes (OLEDs) based on of thermally activated delayed fluorescence. With the maximum values of external quantum efficiency of 25.9 % and power efficiency of 43.4 lm/W, OLEDs containing the layers of the synthesized compounds outperformed the device based on TCTA by 4 %, without the change in spectral properties. Variable angle spectroscopic ellipsometry revealed the moderate average roughness of the films of the compound deposited by the thermal vacuum evaporation technique with an arithmetic mean deviation of not more than 0.8 nm. The prominent hole transport characteristics of the compounds make them good candidates for utilization in optoelectronic devices.
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15.
  • Bondesson, Laban, et al. (författare)
  • Hydrogen bonding effects on infrared and Raman spectra of drug molecules
  • 2007
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 66:2, s. 213-224
  • Tidskriftsartikel (refereegranskat)abstract
    • Infrared and Raman spectra of three drug molecules, aspirin, caffeine and ibuprofen, in gas phase and in aqueous solution have been simulated using hybrid density functional theory. The long range solvent effect is modelled by the polarizable continuum model, while the short range hydrogen bonding effects are taken care of by the super-molecular approach with explicit inclusion of water molecules. The calculated spectra are found to compare well with available experimental results. The agreement obtained make grounds for proposing theoretical modeling as a tool for characterizing changes in the bonding environments of drug molecules in terms of particular variations in their IR and Raman spectra.
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16.
  • Danilczuk, M., et al. (författare)
  • Ammonium Dithionate – a New Material for Highly Sensitive EPR Dosimetry
  • 2008
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Institutionen för fysik, kemi och biologi. - 1386-1425 .- 1873-3557. ; 69:1, s. 18-21
  • Tidskriftsartikel (refereegranskat)abstract
    • Polycrystalline ammonium dithionate has been examined for its radiation response in the low dose range (< 5 Gy) using EPR technique. The •SO3- radical ion was detected as a single EPR line with a peak-to-peak derivative width of ca. 0.44 mT in irradiated samples and its intensity was found to vary linearly with dose. At equal and moderate settings of microwave power and modulation amplitude ammonium dithionate was at least 7 times more sensitive than L-alanine which is the most common EPR dosimeter standard. Pulse experiments were performed on the powder samples to obtain the longitudinal relaxation time. These and microwave saturation experiments served to indicate the optimal microwave power to be applied during measurements as an EPR dosimeter for best sensitivity of this material. It is thus claimed that ammonium dithionate has excellent potential to become an EPR dosimeter with a low limit of the measurable dose for cases where tissue equivalence is not required or can be corrected for.
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17.
  • Danilczuk, M., et al. (författare)
  • Conduction electron spin resonance of small silver particles
  • 2006
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 63:1, s. 189-191
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron spin resonance (ESR) spectroscopy has been used to study the conduction electron spin resonance (CESR) of small silver particles stabilized in dehydrated Ag-rho zeolite. Silver particles were produced by hydrogen reduction at elevated temperatures and diameter of the stabilized particles was calculated based on the linewidth of CESR signal using Kawabata theory. © 2005 Elsevier B.V. All rights reserved.
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18.
  • de Oliveira, Maria I. A., et al. (författare)
  • Optical properties of organosilicon compounds containing sigma-electron delocalization by quasiparticle self-consistent GW calculations
  • 2021
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Pergamon Press. - 1386-1425 .- 1873-3557. ; 245
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate theoretically the electronic and optical absorption properties of two sub-classes of oligosilanes: (i) Si(CH3)(4), Si-4(CH3)(8), and Si-8(CH3)(8) that contain Si dot, ring and cage, respectively, and exhibit typical Si-C and Si-Si bonds; and (ii) persilastaffanes Si7H6(CH3)(6) and Si12H6(CH3)(12), which contain extended delocalized s-electrons in Si-Si bonds over three-dimensional Si frameworks. Our modeling is performed within the GW approach up to the partially self-consistent GW(0) approximation, which is more adequate for reliably predicting the optical band gaps of materials. We examine how the optical properties of these organosilicon compounds depend on their size, geometric features, and Si/C composition. Our results indicate that the present methodology offers a viable way of describing the optical excitations of tailored functional Si-C-based clusters and molecular optical tags with potential use as efficient light absorbers/emitters in molecular optical devices. (C) 2020 The Author(s). Published by Elsevier B.V.
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19.
  • Eddahaoui, K., et al. (författare)
  • Vibrational Spectra and Factor Group Analysis of M0.50TiOPO4 Oxyphosphates (M = Mg, Zn, Ni, Co, Fe and Cu)
  • 2012
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier. - 1386-1425 .- 1873-3557. ; 99, s. 81-89
  • Tidskriftsartikel (refereegranskat)abstract
    • Raman spectra of a series of orthophosphates M0.50TiO(PO4) (M = Mg, Zn, Ni, Co, Fe, and Cu) have been recorded in crystalline state. Factor group analysis has been performed for space group P21/c and assignments of the internal modes of the [PO4] tetrahedra and [TiO6] octahedra have been made.Graphical abstract
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20.
  • Exley, Christopher, et al. (författare)
  • Silicon species in seawater
  • 2014
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier. - 1386-1425 .- 1873-3557. ; 117, s. 820-821
  • Tidskriftsartikel (refereegranskat)
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21.
  • Gorji, Reyhaneh, et al. (författare)
  • Applications of optical sensing and imaging spectroscopy in indoor farming : A systematic review
  • 2024
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Pergamon-Elsevier Science LTD. - 1386-1425 .- 1873-3557. ; 322
  • Tidskriftsartikel (refereegranskat)abstract
    • As demand for food continues to rise, innovative methods are needed to sustainably and efficiently meet thegrowing pressure on agriculture. Indoor farming and controlled environment agriculture have emerged aspromising approaches to address this challenge. However, optimizing fertilizer usage, ensuring homogeneousproduction, and reducing agro-waste remain substantial challenges in these production systems. One potentialsolution is the use of optical sensing technology, which can provide real-time data to help growers makeinformed decisions and enhance their operations. optical sensing can be used to analyze plant tissues, evaluatecrop quality and yield, measure nutrients, and assess plant responses to stress. This paper presents a systematicliterature review of the current state of using spectral-optical sensors and hyperspectral imaging for indoorfarming, following the PRISMA 2020 guidelines. The study surveyed existing studies from 2017 to 2023 toidentify gaps in knowledge, provide researchers and farmers with current trends, and offer recommendations andinspirations for possible new research directions. The results of this review will contribute to the development ofsustainable and efficient methods of food production.
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22.
  • Guo, Ming, et al. (författare)
  • Comparison of the interaction between lactoferrin and isomeric drugs
  • 2017
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier. - 1386-1425 .- 1873-3557. ; 173, s. 593-607
  • Tidskriftsartikel (refereegranskat)abstract
    • The binding properties of pentacyclic triterpenoid isomeric drugs, i.e. ursolic acid (UA) and oleanolic acid (OA), to bovine lactoferrin (BLF) have been studied by molecule modeling, fluorescence spectroscopy, UV-visible absorbance spectroscopy and infrared spectroscopy (IR). Molecular docking, performed to reveal the possible binding mode or mechanism, suggested that hydrophobic interaction and hydrogen bonding play important roles to stabilize the complex. The results of spectroscopic measurements showed that the two isomeric drugs both strongly quenched the intrinsic fluorescence of BLF through a static quenching procedure although some differences between UM and OA binding strength and non-radiation energy transfer occurred within the molecules. The number of binding sites was 3.44 and 3.10 for UA and OA, respectively, and the efficiency of Forster energy transfer provided a distance of 0.77 and 1.21 nm for UA and OA, respectively. The conformation transformation of BLF affected by the drugs conformed to the "all-or-none" pattern. In addition, the changes of the ratios of alpha-helices, beta-sheets and beta-turns of BLF during the process of the interaction were obtained. The results of the experiments in combination with the calculations showed that there are two modes of pentacyclic triterpenoid binding to BLF instead of one binding mode only governed by the principle of the lowest bonding energy.
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23.
  • Guo, Zhiming, et al. (författare)
  • Chemometrics coupled 4-Aminothiophenol labelled Ag-Au alloy SERS off-signal nanosensor for quantitative detection of mercury in black tea
  • 2020
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 242
  • Tidskriftsartikel (refereegranskat)abstract
    • Black tea like other food crops is prone to mercury ion (Hg2+) contamination right from cultivation to industrial processing. Due to the dangerous health effects posed even in trace contents, sensitive detection and quantification sensors are required. This study employed the surface-enhanced Raman scattering (SERS) enhancement property of 4-aminothiophenol (4-ATP) as a signal turn off approach functionalized on Ag-Au alloyed nanopartide to firstly detect Hg2+ in standard solutions and spiked tea samples. Different chemometric algorithms were applied on the acquired SERS and inductively coupled plasma-mass spectrometry (ICP-MS) chemical reference data to select effective wavelengths and spectral variables in order to develop models to predict the Hg2+. Results indicated that Ag-Au/4-ATP SERS sensor combined with ant colony optimization partial least squares (ACO-PLS) exhibited the best correlation efficient and minimum errors for Hg2+ standard solutions (R-c = 0.984, R-p = 0.974, RMSEC = 0.157 mu g/mL, RMSEP = 0.211 mu g/mL) and spiked tea samples (R-c = 0.979, R-p = 0.963, RMSEC = 0.181 mu g/g and RMSEP = 0210 mu g/g). The limit of detection of the proposed sensor was 4.12 x 10(-7) mu g/mL for Hg2+ standard solutions and 2.83 x 10(-5) mu g/g for Hg2+ spiked tea samples. High stability and reproducibility with relative standard deviation of 1.14% and 0.84% were detected. The potent strong relationship between the SERS sensor and the chemical reference method encourages the application of the developed chemometrics coupled SERS system for future monitoring and evaluation of Hg2+ in tea.
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24.
  • Hellström, Pär, et al. (författare)
  • A theoretical and experimental study of vibrational properties of alkyl xanthates
  • 2006
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 65:3-4, s. 887-895
  • Tidskriftsartikel (refereegranskat)abstract
    • Geometrical structure and vibrational modes of potassium and sodium ethyl/heptyl xanthates were studied, using both theoretical and experimental methods. Both Hartree-Fock and density functional theory were used. The experimental method used was infrared absorption spectroscopy (FTIR). Our work showed that vibrational frequencies calculated with density functional theory, using the local density approximation, are in very good agreement with experiments. The results were not improved by using the more sophisticated and computationally demanding B3LYP functional.
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25.
  • Hu, Jiwen, et al. (författare)
  • Rapid detection of mercury (II) ions and water content by a new rhodamine B-based fluorescent chemosensor
  • 2020
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1386-1425 .- 1873-3557. ; 241
  • Tidskriftsartikel (refereegranskat)abstract
    • A rhodamine B-based sensor (RS) was designed and synthesized by a combination of the spirolacton rhodamine B (fluorophore) and multidentate chelates (ionophore) with high affinity towards Hg2+. In the presence of Hg2+, the resulting red-orange fluorescence (under UV light) and naked eye red color of IDS are supposed to be used for quantitative and qualitative measurement of Hg2+. Further fluorescent titration and analysis demonstrate that RS can selectively detect Hg2+ within 1 s with a low limit of detection (LOD) of 16 nM in acetonitrile media, meanwhile, the association constant (K-a) was calculated to be 0.32 x 10(5) M-1. More importantly, the resultant complex (RSHg) of RS and Hg2+ has also been successfully applied to detect limited water content in acetonitrile solution. (C) 2020 Published by Elsevier B.V.
  •  
26.
  • Hu, Jiwen, et al. (författare)
  • Ratiometric fluorogenic determination of endogenous hypochlorous acid in living cells
  • 2019
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1386-1425 .- 1873-3557. ; 219, s. 232-239
  • Tidskriftsartikel (refereegranskat)abstract
    • Hypochlorous acid (HClO) is one of the most important ROS (reactive oxygen species) and common pollutant in tap-water. However, the determination of HClO with fast response and high sensitivity/selectivity is still an urgent demanding. Here we fabricated a ratiometric fluorescent probe RC based on TBET (through-bond energy transfer) on the platform of coumarin and rhodamine with the thiosemicarbazide group as the linker. This probe could display the characteristic fluorescence emission of coumarin. Upon addition of HClO, the linker was reacted into an oxadiazole, resulting in the opening of spiro-ring of rhodamine. The resultant then gives ratiometric fluorogenic changes. The probe exhibits fast response and high selectivity and sensitivity towards HClO with a low limit of detection (similar to 140 nM). Eventually, RC is successfully applicated for determining spiked HClO in water samples and imaging endogenous HClO in living cells. (C) 2019 Published by Elsevier B.V.
  •  
27.
  • Hu, Jiwen, et al. (författare)
  • Selective colorimetric detection of copper (II) by a protein-based nanoprobe
  • 2021
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1386-1425 .- 1873-3557. ; 252
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, we report a novel protein-based nanoprobe (PNP) that can be employed for quantitative analysis of Cu2+ in pure water medium and real samples. Structurally, the proposed nanoprobe comprises a biofriendly protein (hen egg-white lysozyme (HEWL)) and a Cu2+-specific chromogenic agent, where HEWL acts as a nanocarrier encapsulating a structurally tailored rhodamine B derivate. The resulting PNP exhibits a hydrodynamic diameter of similar to 106 nm and efficiently disperses in water, enabling the detection of Cu2+ in pure aqueous systems without the aid of any organic co-solvents. The high sensitivity and selectivity of PNP allow the colorimetric detection of Cu2+ in the presence of other metal interferents with a low detection limit of 160 nM. The satisfying recovery of trace level Cu2+ in environmental samples demonstrate the great potential of employing PNP for the determination of Cu2+ in actual applications. Most importantly, the simple co-grinding method employing proteins and chromogenic agents provides a novel strategy to generate sensing systems that are useful detection of pollutants in aqueous samples. (C) 2021 Elsevier B.V. All rights reserved.
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28.
  •  
29.
  • Jafari, Mohammad Javad, et al. (författare)
  • Antimicrobial susceptibility testing using infrared attenuated total reflection (IR-ATR) spectroscopy to monitor metabolic activity
  • 2024
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1386-1425 .- 1873-3557. ; 304
  • Tidskriftsartikel (refereegranskat)abstract
    • Fast and accurate detection of antimicrobial resistance in pathogens remains a challenge, and with the increase in antimicrobial resistance due to mis- and overuse of antibiotics, it has become an urgent public health problem. We demonstrate how infrared attenuated total reflection (IR-ATR) can be used as a simple method for assessment of bacterial susceptibility to antibiotics. This is achieved by monitoring the metabolic activities of bacterial cells via nutrient consumption and using this as an indicator of bacterial viability. Principal component analysis of the obtained spectra provides a tool for fast and simple discrimination of antimicrobial resistance in the acquired data. We demonstrate this concept using four bacterial strains and four different antibiotics, showing that the change in glucose concentration in the growth medium after 2 h, as monitored by IR-ATR, can be used as a spectroscopic diagnostic technique, to reduce detection time and to improve quality in the assessment of antimicrobial resistance in pathogens.
  •  
30.
  •  
31.
  • Karaush, N. N., et al. (författare)
  • Identification of tautomeric intermediates of a novel thiazolylazonaphthol dye - A density functional theory study
  • 2018
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Pergamon Press. - 1386-1425 .- 1873-3557. ; 203, s. 324-332
  • Tidskriftsartikel (refereegranskat)abstract
    • The recently synthesized thiazolylazo dye, 1-(5-benzy1-1,3-thiazol-2-yl)diazenyllnaphthalene-2-ol called shortly BnTAN, is studied by density functional theory (DFT) in three tautomeric forms in order to explain the available H-1 NMR, UV-Vis and FTIR spectra. An experimentally observed IR band at 1678 cm(-1), assigned to the C=O bond stretching vibration, supports the notion that BnTAN retains in the less stable keto-form even in the solid state due to an ultrafast single-coordinate intramolecular proton transfer. This finding is also in a good agreement with an X-ray crystallography analysis which indicates an intermediate position of the proton between the OH and -N=N-groups. Calculations also show that some experimentally observed H-I NMR signals could be considered as being averaged values between theoretically calculated chemical shifts for the corresponding protons in the keto- and enol-tautomers. At the same time the UV-Vis spectra are almost insensitive to the tautomerization processes as the main single band absorption at 500 nm is present in all tautomers according to our TD DFT simulations. The minor differences in spectral features of the long-wavelength visible region are also noted and discussed with respect to the manifestation of the less stable tautomer form.
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32.
  • Komaguchi, K, et al. (författare)
  • An ESR and ENDOR study of irradiated 6Li-formate
  • 2007
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 66:3, s. 754-760
  • Tidskriftsartikel (refereegranskat)abstract
    • Lithium formate (6LiOOCH·H2O), 95% 6Li enrichment, combined with an exchange of crystallization water with D2O was investigated. The ESR spectrum of the radiation induced free radicals stable at room temperature consists of a singlet with a narrow line width, 0.92 mT. 6Li has smaller magnetic moment and nuclear spin, which resulted in the narrower line width accompanied with an increase in peak amplitude. In comparison with lithium formate with natural isotopic composition, 6Li (7.5%, I = 1) and 7Li (92.5%, I = 3/2), the sensitivity was increased by a factor of two. With optimised spectrometer settings 6Li formate had seven times higher sensitivity compared to alanine. Therefore this material is proposed as a dosimeter material in a dose range down to 0.1 Gy. The g and the 13C-hyperfine (hf) tensors of the CO2- radical anion, major paramagnetic products, were evaluated to be g = (2.0037, 1.9975, 2.0017), and A(13C) = (465.5, 447.5, 581.3) MHz for polycrystalline samples at room temperature. Furthermore, the 1H-hf and 6Li-hf tensors observed for the surroundings of CO2- by ENDOR technique were in fairly good agreement with DFT calculations. The CO2- radicals are found to be so stable that the formate is applicable to the ESR dosimetry, because of fully relaxing in a fully relaxed geometrical structure of the CO2- component and remaining tight binding with the surroundings after the H atom detachment from HCO2-. © 2006 Elsevier B.V. All rights reserved.
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33.
  • Komaguchi, K., et al. (författare)
  • ESR and theoretical studies of trimer radical cations of coronene
  • 2006
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 63:1, s. 76-84
  • Tidskriftsartikel (refereegranskat)abstract
    • Highly resolved ESR spectra of monomer, dimer and trimer radical cations of coronene (C24H12) were observed at room temperature for a solution of 1,1,1,3,3,3-hexafluoro-2-propan-2-ol (HFP) containing thallium(III) trifluoroacetate as oxidant. The spectra consisting of multiple lines with isotropic 1H-hyperfine splitting (hfs) constants of 0. 0766 mT (24H) and 0.013 mT (6H) were attributable to a mixture of the dimer with the trimer radical cations, (C24H12)2+ and (C24H12)3+. For (C24H12)2+, the 1H-hfs constant agreed well with the reported value, 0.077 mT. However, for (C 24H12)3+, the values were significantly different from the reported ones, 0.117 mT (12H) and 0.020 mT (24H), by Ohya Nishiguchi et al. [H. Ohya-Nishiguchi, H. Ide, N. Hirota, Chem. Phys. Lett. 66 (1979) 581], but rather similar to those reported by Willigen et al. [H. van Willigen, E. De Boer, J.T. Cooper, W.F. Forbes, J. Chem . Phys. 49 (1968) 1190]. In conflict with Willigen's report, however, no ESR line broadening which has been ascribed to a low stationary concentration of (C 24H12)3+ was detected. Based on ab initio MO calculations for benzene as a compact model of C24H 12, the structure of (C24H12)3+ was investigated in terms of the observed 1H-hfs constants. A staggered sandwich C2v structure was suggested being at the "global" minimum for the benzene trimer cation. In the structure, the unpaired electron spin is predominantly localized to the central ring, which is qualitatively in agreement with the previous ESR results of (C 24H12)3+ by Ohya-Nishiguchi et al. In addition, as a "local" minimum, the benzene trimer was indicated to have a slipped sandwich Cs structure, which is less stable by ca. 19 kJ mol-1 than the "global" minimum. In this structure, the unpaired electron spin was nearly equally distributed on both the central and one of the two side C24H12 molecules. The observed 1H-hfs constants were possibly attributable to the (C 24H12)3+ cation with the analogous slipped sandwich Cs structure.
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34.
  • Lahrich, S., et al. (författare)
  • Elaboration, Rietveld refinements and vibrational spectroscopic study of Na1-xKxCaPb3(PO4)3 lacunar apatites (0 < x < 1)
  • 2015
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 145, s. 493-499
  • Tidskriftsartikel (refereegranskat)abstract
    • Synthesis of apatites, Na1-xKxCaPb3(PO4)(3) 0 <= x <= 1, with anion vacancy were carried out using solid state reactions. The solid solution of apatite-type structure crystallize in the hexagonal system, space group P6(3)/m (No. 176). Rietveld refinements showed that around 90% of Pb2+ cations are located in the (6h) sites, the left amount of Pb2+ cations are located in the (4f) sites; 27-31% of Ca2+ cations are located in the (6h) sites, the left amount of Ca2+ cations are located in the (4f) sites. The ninefold coordination sites (4f) are also occupied by the K+ and Na+ monovalent ions. The structure can be described as built up from [PO4](3-) tetrahedra and Pb2+/Ca2+ of sixfold coordination cavities (6h positions), which delimit void hexagonal tunnels running along [001]. These tunnels are connected by cations of mixed sites (4f) which are half occupied by Pb2+/Ca2+ and half by Na+/K+ mixed cations. The assignment of the observed frequencies in the Raman and infrared spectra is discussed on the basis of a unit cell group analysis and by comparison with other apatites. Vibrational spectra of all the compositions are similar and show some linear shifts of the frequencies as a function of the composition toward lower values due the substitutions of Na+ by K+ with a larger radius.
  •  
35.
  • Li, Junfeng, et al. (författare)
  • A theoretical study on vibronic spectra and photo conversation process of protonated naphthalenes
  • 2018
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Pergamon Press. - 1386-1425 .- 1873-3557. ; 205, s. 520-527
  • Tidskriftsartikel (refereegranskat)abstract
    • The equilibrium structures and vibrational frequencies of the ground state and several singlet low-lying excited states of alpha-and beta-protonated naphthalenes (alpha-and beta-HN+) have been studied by time -dependent density -functional theory (TD-DFT). Within the Franck -Condon approximation, vibronic absorption spectra of alpha-HN+ and beta-HN+, together with the vibronic emission spectrum of alpha-HN+, have been calculated. The obtained good agreement between the theoretical and experimental spectra enables to correctly assign vibronic features in both absorption and emission spectra. Moreover, the non -radiative deactivation pathway from the low-lying excite states to the ground state in alpha-HN+ and beta-HN+, as well as the photo-induce proton transfer pathway, are investigated at the CASPT2/CASSCF/6-31G* level. Our study is helpful for understanding the photochemical behavior of these important polycyclic aromatic hydrocarbon molecules.
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36.
  • Li, Junfeng, et al. (författare)
  • The correct assignment of vibrationally-resolved absorption spectra of protonated anthracene isomers
  • 2021
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier. - 1386-1425 .- 1873-3557. ; 244
  • Tidskriftsartikel (refereegranskat)abstract
    • The assignment of experimental optical absorption spectra of protonated anthracene has been under debate for years. It is complicated by the presence of rich vibronic spectral features and the possible co-occurrence of two isomers, 9H-An(+) and 1H-An(+). In this study, the vibrationally resolved absorption spectra of 9H-An(+) and 1H-An(+) have been calculated using time-dependent density functional theory. The calculated vibronic spectra profiles of 9H-An(+) and 1H-An(+) are in excellent agreementwith the corresponding experimental results and provide unambiguously spectra assignments. It shows that the previously reported assignments based on vertical excitation energy are largelywrong. The onset located at 493.8 nmof the experimental spectrumcan be assigned to the S-0 -> S-1 transition of 9H-An(+), while the origin band located at 453.5 nmcorresponds to the S-0 -> S-2 transition of 1H-An(+).
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37.
  • Li, Suyang, et al. (författare)
  • One-pot fabrication of Mo1-xWxS2 alloy nanosheets as SERS substrates with highly Raman enhancement effect and long-term stability
  • 2022
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 279, s. 121465-
  • Tidskriftsartikel (refereegranskat)abstract
    • A new Mo1-xWxS2 two-dimensional nanosheets were prepared by the one-pot method. After certain Mo atoms in MoS2 were replaced by W ones in a hydrothermal reduction procedure, Mo1-xWxS2 was formed on the Mo foil. Well enhanced Mo1-xWxS2 nanosheets were prepared when the sodium tungstate concentration got under control. Various characterizations were carried out, which indicate that Mo1-xWxS2 nanosheets with good crystallinity. Compared with MoS2, the Raman intensity of Rhodamine 6G (10-6 M) was amplified by 1.7 times with Mo1-xWxS2 nanosheets as the substrate. The characteristic Raman peaks could still be clearly distinguished until the concentration of Rhodamine 6G (R6G), Methylene blue (MB) and Crystal violet (CV) down to 10-8, 10-8 and 10- 7 M, respectively. With abundant edge active sites that facilitate charge transfer, Mo1-xWxS2 nanosheets could better enhance SERS signals of target detection molecules and get a good linear relationship exists within the concentration and Raman peak strength. In addition, R6G SERS detection also shows excellent reproducibility and long-term stability of this TMDs SERS substrate.
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38.
  • Lindgren, Matteus, 1980-, et al. (författare)
  • A combined molecular dynamic simulation and Urea 14N NMR relaxation study of the Urea - lysozyme system
  • 2010
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier. - 1386-1425 .- 1873-3557. ; 75:3, s. 953-9
  • Tidskriftsartikel (refereegranskat)abstract
    • Urea in the lysozyme solvation shell has been studied by utilizing a combination of urea , water NMR relaxation experiments and a molecular dynamics simulation of the urea–lysozyme system. Samples with lysozyme in the native fold in water as well as in 3 M urea have been studied, as well as denatured lysozyme in a 8.5 M urea solvent. The spin relaxation rates of the samples with folded protein show a clear field dependence, which is consistent with a few urea molecules having long residence times on the protein surface and preferentially located in pockets and grooves on the protein. By combining the 3 M urea NMR relaxation data and data from the MD simulation, a full parameter set of the relaxation model is found which can successfully predict the experimental relaxation rates of the 3 M urea sample. However, in the parameter fitting it is evident that the rotational dynamics of urea in the MD simulation is slightly too fast to be consistent with the NMR relaxation rates, perhaps a result of the fast dynamics of the TIP3P water model. The relaxation rates of urea in the proximity of the unfolded lysozyme lack field dependence, which can be interpreted as a loss of pockets and grooves on the denatured protein. The extracted model parameters from the 3 M sample are adjusted and tested on a simple model of the unfolded protein sample and are seen to be in agreement with the relaxation rates. It is shown that the combination of NMR relaxation and MD simulations can be used to create a microscopic picture of the solvent at the protein interface, which can be used for example in the study of chemical denaturation.
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39.
  • Lund, Anders, et al. (författare)
  • Automatic fitting procedures for EPR spectra of disordered systems: matrix diagonalization and perturbation methods applied to fluorocarbon radicals
  • 2008
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier. - 1386-1425 .- 1873-3557. ; 69:5, s. 1294-1300
  • Tidskriftsartikel (refereegranskat)abstract
    • Two types of automatic fitting procedures for EPR spectra of disordered systems have been developed, one based on matrix diagonalisation of a general spin Hamiltonian, the other on 2nd order perturbation theory. The first program is based on a previous Fortran code complemented with a newly written interface in Java to provide user-friendly in- and output. The second is intended for the special case of free radicals with several relatively weakly interacting nuclei, in which case the general method becomes slow. A least squares’ fitting procedure utilizing analytical or numerical derivatives of the theoretically calculated spectrum with respect to the g-and hyperfine structure (hfs) tensors was used to refine those parameters in both cases. ‘Rigid limit’ ESR spectra from radicals in organic matrices and in polymers, previously studied experimentally at low temperature, were analysed by both methods. Fluoro-carbon anion radicals could be simulated, quite accurately with the exact method, whereas automatic fitting on e.g. the c-C4F8- anion radical is only feasible with the 2nd order approximative treatment. Initial values for the 19F hfs tensors estimated by DFT calculations were quite close to the final. For neutral radicals of the type XCF2CF2• the refinement of the hfs tensors by the exact method worked better than the approximate. The reasons are discussed. The ability of the fitting procedures to recover the correct magnetic parameters of disordered systems was investigated by fittings to synthetic spectra with known hfs tensors. The exact and the approximate methods are concluded to be complementary, one being general, but limited to relatively small systems, the other being a special treatment, suited for S=½ systems with several moderately large hfs.
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40.
  • Lund, Anders, et al. (författare)
  • Automatic fitting to 'powder' EPR spectra of coupled paramagnetic species employing Feynman's theorem
  • 2006
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 63:4, s. 830-835
  • Tidskriftsartikel (refereegranskat)abstract
    • A previous automatic fitting procedure of EPR spectra has been extended with the purpose to characterise coupled paramagnetic complexes in powders and frozen solutions. The theoretical EPR spectra were obtained by matrix diagonalization of a general spin Hamiltonian. A least-squares fitting procedure using analytical derivatives of the calculated spectrum with respect to the spectroscopic, fine structure, nuclear quadrupole, electron-electron, and hyperfine coupling tensors was used to refine those parameters. The powder spectra of matrix isolated CF3 and RCF2CF2 radicals, previously measured at low temperature, were reanalysed with this method. A theoretically modeled complex consisting of a Cu2+ ion, featuring an axially symmetric g-tensor and 63Cu hyperfine structure anisotropy, and a free radical located at different orientations, with respect to the symmetry axis of the Cu2+ ion, was examined in order to investigate the possibility to recover the magnetic parameters of the separate units and the magnetic couplings between them. © 2005 Elsevier B.V. All right reserved.
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41.
  • Lund, Anders, et al. (författare)
  • Monomer- and polymer radicals of vinyl compounds: EPR and DFT studies of geometric and electronic structures in the adsorbed state
  • 2012
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier. - 1386-1425 .- 1873-3557. ; 98, s. 367-377
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron paramagnetic resonance (EPR) spectroscopy was applied to study the paramagnetic species formed from styrene, 1,1-diphenylethylene, alpha-methylstyrene, beta-methylstyrene and methylmethacrylate adsorbed on amorphous silica gel after gamma-irradiation at 77 K. Radicals formed by the hydrogen atom addition at the vinyl group of the monomers were observed in all samples. The hydrogen atoms were shown to originate to a large extent from the adsorbent by using silica gel with deuterated silanol groups. An EPR spectrum assigned to a propagating radical was observed at increased temperature for samples containing methylmethacrylate (MMA). The structures of the adsorption complexes, the respective hyperfine splitting constants and the adsorption energies were calculated by applying OFF quantum chemical methods. The reaction between an MMA molecule and the MMA radical and the structure of the propagating radical was modeled. The calculated hyperfine splitting constants for all radicals confirmed the assignment of the experimental spectra.
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42.
  • Lund, Eva, et al. (författare)
  • Compounds of Li-6 and natural Li for EPR dosimetry in photon/neutron mixed radiation fields
  • 2004
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 60:6, s. 1319-1326
  • Tidskriftsartikel (refereegranskat)abstract
    • Formates and dithionates of Li-6, enriched and Li-7 in natural composition of Li offer a possibility to measure the absorbed dose from photons and thermal neutrons in a mixed radiation field for instance at a boron neutron capture therapy (BNCT) facility. Tests with formates and dithionates of enriched 6Li and lithium compounds with natural composition have been performed at the BNCT facility at Studsvik, Sweden. Irradiations have been performed at 3 cm depth in a Perspex phantom in a fluence rate of thermal neutrons 1.8 x 10(9) n cm(-2) s(-1). The compounds were also irradiated in a pure X-ray field from a 4 MV linear accelerator at 5 cm depth in a phantom with accurately determined absorbed doses. The signal intensity and shape was investigated within 3 h after the irradiation. A single line spectrum attributed to the CO2- radical was observed after irradiation of lithium formate. An increase in line width occurring after neutron irradiation in comparison with photon irradiation of the Li-6 sample was attributed to dipolar broadening between CO2- radicals trapped in the tracks of the alpha particles. A spectrum due to the SO3- radical anion was observed after irradiation of lithium dithionate. The signal amplitude increased using the Li-6 in place of the Li with natural composition of isotopes, in studies with low energy X-ray irradiation. Due to the decreased line width, caused by the difference in g(N) and I between the isotopes, the sensitivity with Li-6 dithionate may be enhanced by an order of magnitude compared to alanine dosimetry. After comprehensive examination of the different combinations of compounds with different amounts of Li-6 and Li-7 regarding dosimetry, radiation chemistry and EPR properties these dosimeter material might be used for dose determinations at BNCT treatments and for biomedical experiments. Interesting properties of the radical formation might be visible due to the large difference in ionization density of neutrons compared to photons. (C) 2003 Elsevier B.V. All rights reserved.
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43.
  • Maia Paiva, Eduardo, et al. (författare)
  • Low-frequency Raman spectrophotometer with wide laser illumination on the sample : A tool for pharmaceutical analytical analysis
  • 2020
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier. - 1386-1425 .- 1873-3557. ; 228
  • Tidskriftsartikel (refereegranskat)abstract
    • This work describes an optical configuration for a Raman spectrophotometer, which permits variation of the laser spot size from 3 to 3000 μm, maintaining a high Raman photons throughput and allowing acquisitions with a short integration time. In addition, the instrument can acquire spectra from the low to middle frequency vibrational range (10 to 2000 cm−1), on the Stokes and anti-Stokes sides. One of the features of this new optical configuration is the non-use of beam splitters to redirect the scattered light to the detector, which would sacrifice the laser power. The quantitative and qualitative analytical performances of the Raman spectrophotometer were evaluated using chemometric models to predict the concentrations of different active pharmaceutical ingredients (APIs) in mixtures with polymorphs and excipients, as well as by analysis of an API mixture employing hyperspectral imaging. This new optical configuration was shown to be versatile for pharmaceutical purposes and could be used in applications such as the characterization of new drugs or the quality control of raw materials and processes, using normal Raman measurements or SERS (surface-enhanced Raman scattering).
  •  
44.
  • Maia Paiva, Eduardo, et al. (författare)
  • Near-infrared spectra of liquid and gas samples by diffuse reflectance employing benchtop and handheld spectrophotometers
  • 2022
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier. - 1386-1425 .- 1873-3557. ; 264
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper describes a new method to obtain NIR spectra of liquid and gas samples by diffuse reflectance, which is especially suitable for handheld spectrophotometers, since most of these instruments are designed to acquire spectrum using this geometry. The core of the method is a diffuse reflectance cell, which consists of a vial containing a mixture of the liquid or gas sample (rare medium) and a powder (dense medium). Using this strategy, no adaptation is required to measure spectra with most portable NIR spectrometers. This new method was used to obtain NIR spectra of several liquids and gases, which were compared with traditional transmittance spectra. As a proof of concept, measurements of biodiesel/vegetable oil/diesel blends were used to build multivariate calibrations to predict the contents of biodiesel and vegetable oil in diesel blends using benchtop and handheld FT-NIR spectrophotometers. This low-cost method was demonstrated to be suitable for overcoming problems related to the handling of viscous samples and expand the applications with portable NIR instruments.
  •  
45.
  • Malyshev, Dmitry, et al. (författare)
  • Laser induced degradation of bacterial spores during micro-Raman spectroscopy
  • 2022
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier. - 1386-1425 .- 1873-3557. ; 265
  • Tidskriftsartikel (refereegranskat)abstract
    • Micro-Raman spectroscopy combined with optical tweezers is a powerful method to analyze how the biochemical composition and molecular structures of individual biological objects change with time. In this work we investigate laser induced effects in the trapped object. Bacillus thuringiensis spores, which are robust organisms known for their resilience to light, heat, and chemicals are used for this study. We trap spores and monitor the Raman peak from CaDPA (calcium dipicolinic acid), which is a chemical protecting the spore core. We see a correlation between the amount of laser power used in the trap and the release of CaDPA from the spore. At a laser power of 5 mW, the CaDPA from spores in water suspension remain intact over the 90 min experiment, however, at higher laser powers an induced effect could be observed. SEM images of laser exposed spores (after loss of CaDPA Raman peak was confirmed) show a notable alteration of the spores' structure. Our Raman data indicates that the median dose exposure to lose the CaDPA peak was ∼60 J at 808 nm. For decontaminated/deactivated spores, i.e., treated in sodium hypochlorite or peracetic acid solutions, the sensitivity on laser power is even more pronounced and different behavior could be observed on spores treated by the two chemicals. Importantly, the observed effect is most likely photochemical since the increase of the spore temperature is in the order of 0.1 K as suggested by our numerical multiphysics model. Our results show that care must be taken when using micro-Raman spectroscopy on biological objects since photoinduced effects may substantially affect the results.
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46.
  • Malyshev, Dmitry, et al. (författare)
  • pH induced changes in Raman, UV-Vis absorbance, and fluorescence spectra of dipicolinic acid (DPA)
  • 2022
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier. - 1386-1425 .- 1873-3557. ; 271
  • Tidskriftsartikel (refereegranskat)abstract
    • Dipicolinic acid (DPA) is an essential component for the protection of DNA in bacterial endospores and is often used as a biomarker for spore detection. Depending upon the pH of the solution, DPA exists in different ionic forms. Therefore, it is important to understand how these ionic forms influence spectroscopic response. In this work, we characterize Raman and absorption spectra of DPA in a pH range of 2.0–10.5. We show that the ring breathing mode Raman peak of DPA shifts from 1003 cm−1 to 1017 cm−1 and then to 1000 cm−1 as pH increases from 2 to 5. The relative peak intensities related to the different ionic forms of DPA are used to experimentally derive the pKa values (2.3 and 4.8). We observe using UV–vis spectroscopy that the changes in the absorption spectrum of DPA as a function of pH correlate with the changes observed in Raman spectroscopy, and the same pKa values are verified. Lastly, using fluorescence spectroscopy and exciting a DPA solution at between 210–330 nm, we observe a shift in fluorescence emission from 375 nm to 425 nm between pH 2 and pH 6 when exciting at 320 nm. Our work shows that the different spectral responses from the three ionic forms of DPA may have to be taken into account in, e.g., spectral analysis and for detection applications.
  •  
47.
  • Manoun, B., et al. (författare)
  • High temperature and composition induced phase transitions in LiZnV1-xAsxO4 phenacites : Crystal structure and Raman spectroscopy studies
  • 2015
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 151, s. 956-964
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, using techniques of X-ray diffraction and Raman spectroscopy, we report the composition and high-temperature induced phase transition in the system LiZnV1-xAsxO4 (0 <= x <= 1). Both techniques showed that the increase of arsenic amount induced a structural transition from R-3 LiZnVO4 type to LiZnAsO4 type belonging to R3 space group, the transition occurring between x = 0.7 and x = 0.8. Furthermore, increasing temperature for the compositions (0.8 <= x <= 1) manifests a transition from the LiZnAsO4 structural type with R3 space group to the R-3 LiZnVO4 structural type. For this series, the transition from the space group R3 to the centro-symmetric space group R-3 shows considerable changes in the compositional and temperature dependencies of the bands: spectral positions of all the observed Raman bands exhibit shifts linearly proportional to the temperature increase, with points of shift-rate changes revealing a symmetry change. The Raman-spectra based temperature-composition phase diagram confirms the results obtained using the method of Rietveld refinements, thus showing the R-3 to R3 transition occurring between x = 0.7 and 0.8.
  •  
48.
  • Minaev, Boris (författare)
  • Ab initio study of low-lying triplet states of the lithium dimer
  • 2005
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 62:4-5, s. 790-799
  • Tidskriftsartikel (refereegranskat)abstract
    • Observation of Bose-Einstein condensation in Li-7(2) initiated the interest in the scattering length of two ground state lithium atoms when they approach each other as a radical pair triplet a(3)Sigma(u)(+) state. But some properties of this state are still unknown. In present work, a number of low-lying triplet states of lithium molecule are calculated by multi-configuration self-consistent field (MCSCF) and response techniques with account of spin-orbit coupling, spin-spin coupling and some other magnetic perturbations. The singlet-triplet transition probabilities to the ground state are also presented. Most results are connected with the weakly bound lowest triplet a(3)Sigma(u)(+) state, whose radiative lifetime and spin-splitting are unknown so far in spite of its great importance in Bose-Einstein condensation. Calculations indicate that this state has a very small spin-splitting, lambda(ss) = -0.01 cm(-1), which is negligible in comparison with the line-width in experimental Fourier transform C spectra published so far. Similar splitting is obtained for the upper state of the 1(3)Sigma(g)(+)-a(3)Sigma(u)(+) transition. This is in agreement with experimental rovibronic analysis of the 1(3)Sigma(g)(+)- a(3)Sigma(u)(+) band system in which the triplet structure was not resolved. The radiative lifetime of the a(3)Sigma(u)(+) state is predicted to exceed 10 h.
  •  
49.
  • Minaev, Boris, et al. (författare)
  • Calculation of the fine structure and intensity of the singlet-triplet transitions in the imidogen radical
  • 2005
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 61:6, s. 1105-1112
  • Tidskriftsartikel (refereegranskat)abstract
    • The singlet-triplet transition moments are calculated for the NH radical by multiconfiguration self-consistent field (MCSCF) method with a quadratic response (QR) technique. The band systems in the visible region (b(l) Sigma(+)-> X-3 Sigma(-) and a(1) Delta -> X-3 Sigma(-)) of the NH radical are analyzed in comparison with previous ab initio treatments and with the recent experimental data in attempt to solve some discrepancies. The b(1)Sigma(+)-> X-3 Sigma(-)(Omega) transition moments ratio for the two spin sublevels Omega = 1 and Omega = 0 of the ground state is well reproduced and the radiative lifetime of the b(1) Sigma(+) state (tau(b) = 58 ms) is obtained in a good agreement with the experimental value tau(b)= 53((+1 7)(-13)) 3[1 3 ms. The A(3) Pi X-3 Sigma-transition some improvement is achieved in comparison with the previous ab initio results, but the calculated radiative lifetime (tau(a) = 3.9 s) is still much lower than the recent measurement provides (tau(a)= 12.5 s). The zero field splitting and spin-rotation coupling constants are calculated for the ground state by different methods and advantage of the density functional theory is stressed.
  •  
50.
  • Minaev, Boris, et al. (författare)
  • Density functional theory study of vibronic structure of the first absorption Qx band in free-base porphin
  • 2006
  • Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 65:2, s. 308-323
  • Tidskriftsartikel (refereegranskat)abstract
    • Harmonic vibrational frequencies and vibronic intensities in the first S-0 -> S-1 (pi pi*) absorption band of free-base porphin (H2P) are investigated by hybrid density functional theory (DFT) with the standard B3LYP functional. The S-0-S-1 transition probability is calculated using time-dependent DFT with account of Franck-Condon (FC) and Herzberg-Teller (HT) contributions to the electric-dipole transition moments including displacements along all 108 vibrational modes. Two weak wide bands observed in the gas phase absorption spectra of the H2P molecule at 626 and 576 nm are interpreted as the 0-0 band of the X(1)A(g)-> B-3u transition and the 0-1 band with largest contributions from the nu(10)(a(g)) = 1610 cm(-1) and nu(19)(b(1g)) = 1600 cm(-1) modes, respectively, in agreement with previous tentative assignments. Both bands are induced by the HT mechanism, while the FC contributions are negligible. A number of fine structure bands, including combination of two vibrational quanta, are obtained and compared with available spectra from supersonic jet and Shpolskij matrices. Both absorption and fluorescence spectra are interpreted on ground of the linear coupling model and a good fulfillment of the mirror-symmetry rule.
  •  
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