| 1. |
- Hammarstrom, L., et al.
(författare)
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A biomimetic approach to artificial photosynthesis : Ru(II)-polypyridine photo-sensitisers linked to tyrosine and manganese electron donors
- 2001
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 57:11, s. 2145-2160
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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)
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Fourier transform infrared and Raman study of Alizarin Red S adsorbed at the fluorite-water interface
- 1999
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 55:9, s. 1721-1730
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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)
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Partial Donor-Donor Energy Migration (PDDEM) as a Fluorescence Spectroscopic Tool for Measuring Distances in Biomacromolecules
- 2002
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 58:5, s. 1087-1097
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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)
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Spectroscopic characterisation of indium(III) chloride and mixed ligand complexes
- 2002
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 58:5, s. 953-957
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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)
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New materials for ESR dosimetry
- 2002
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 58:6, s. 1301-1311
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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)
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Ab initio study of the ground state properties of molecular oxygen
- 2004
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 60:5, s. 1027-1041
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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)
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Physical properties and spectra of IO, IO- and HOI studied by ab initio methods
- 2002
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 58:5, s. 1039-1053
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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)
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On-line and in situ monitoring of oxygen concentration and gas temperature in a reheating furnace utilizing tunable diode-laser spectroscopy
- 2001
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - Amsterdam : Elsevier. - 1386-1425 .- 1873-3557. ; 58:11, s. 2449-2455
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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)
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Fluorescence correlation spectroscopy of flavins and flavoenzymes : photochemical and photophysical aspects
- 2001
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 57:11, s. 2135-2144
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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)
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Noninvasive in situ identification and band assignments of some pharmaceutical excipients inside USP vials with FT-near-infrared spectroscopy
- 2009
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 72:4, s. 890-896
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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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