| 1. |
- Andersson, August, et al.
(författare)
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Magnetic resonance investigations of lipid motion in isotropic bicelles
- 2005
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 21:7, s. 7702-7709
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of DMPC in different isotropic bicelles have been investigated by NMR and EPR methods. The local dynamics were obtained by interpretation of 13C NMR relaxation measurements of DMPC in the bicelles, and these results were compared to EPR spectra of spin-labeled lipids. The overall size of the bicelles was investigated by PFG NMR translational diffusion measurements. The dynamics and relative sizes were compared among three different bicelles: [DMPC]/[DHPC] = 0.25, [DMPC]/[DHPC] = 0.5, and [DMPC]/[CHAPS] = 0.5. The local motion is found to depend much more strongly on the choice of the detergent, rather than the overall size of the bicelle. The results provide an explanation for differences in apparent dynamics for different peptides, which are bound to bicelles. This in turn determines under what conditions reasonable NMR spectra can be observed. A model is presented in which extensive local motion, in conjunction with the overall size, affects the spectral properties. An analytical expression for the size dependence of the bicelles, relating the radius of the bilayer region with physical properties of the detergent and the lipid, is also presented.
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| 2. |
- Carlsson, F, et al.
(författare)
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Protein-polyelectrolyte cluster formation and redissolution: A Monte Carlo study
- 2003
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Ingår i: Journal of The American Ceramic Society. - : American Chemical Society (ACS). - 0002-7820 .- 1551-2916. ; 125:10, s. 3140-9
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous solutions of proteins and oppositely charged polyelectrolytes were studied at different polyelectrolyte chain length, ionic strength, and protein-protein interaction potential as a function of the polyelectrolyte concentration. One of the protein models used represented lysozyme in aqueous environment. The model systems were solved by Monte Carlo simulations, and their properties were analyzed in terms of radial distribution functions, structure factors, and cluster composition probabilities. In the system with the strongest electrostatic protein-polyelectrolyte interaction the largest clusters were formed near or at equivalent amount of net protein charge and polyelectrolyte charge, whereas in excess of polyelectrolyte a redissolution appeared. Shorter polyelectrolyte chains and increased ionic strength lead to weaker cluster formation. An inclusion of nonelectrostatic protein-protein attraction promoted the protein-polyelectrolyte cluster formation.
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| 3. |
- Halthur, Tobias, et al.
(författare)
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Stability of Polypeptide Multilayers As Studied by in Situ Ellipsometry : Effects of Drying and Post-Buildup Changes in Temperature and pH
- 2004
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 126, s. 17009-17015
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Tidskriftsartikel (refereegranskat)abstract
- Polyelectrolyte multilayers (PEM) of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) with an initial layer of polyethyleneimine (PEI) were built on silica and titanium surfaces using the layer-by-layer (LbL) technique. The stability of the film during drying/rewetting, temperature cycles, and pH shifts was studied in situ by means of ellipsometry. The film thickness was found to decrease significantly (approximately 70%) upon drying, but the original film thickness was regained upon rewetting, and the buildup could be continued. The thickness in the dry state was found to be extremely sensitive to ambient humidity, needing several hours to equilibrate. Changes in temperature and pH were also found to influence the multilayer thickness, leading to swelling and deswelling of as much as 8% and 10-20% respectively. The film does not necessarily regain its original thickness as the pH is shifted back, but instead shows clear signs of hysteresis.
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| 4. |
- Tyrode, Eric, et al.
(författare)
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Adsorption of CTAB on hydrophilic silica studied by linear and nonlinear optical spectroscopy
- 2008
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Ingår i: Journal of The American Ceramic Society. - : American Chemical Society. - 0002-7820 .- 1551-2916 .- 0002-7863 .- 1520-5126. ; 130:51, s. 17434–17445-
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Tidskriftsartikel (refereegranskat)abstract
- Vibrational sum-frequency spectroscopy (SFS) and total internal reflection Raman scattering (TIR Raman) have been used to study the adsorption of hexadecyltrimethylammonium bromide (CTAB) to hydrophilic silica. These two complementary techniques permit the determination of the adsorbed amount with a sensitivity of 1% of the maximum surface coverage, changes in the average tilt of the adsorbed molecules, the presence of asymmetric aggregates in the adsorbed film, and the structure and orientation of the water molecules in the interfacial region. The TIR Raman spectra show a monotonic increase with CTAB concentration with no measurable changes in the relative intensities of the different polarization combinations probed, implying that no significant changes occur in the conformational order of the hydrocarbon chain. In the sum-frequency (SF) spectra, no detectable peaks from the surfactant headgroup and hydrophobic chain were observed at any surface coverage. Major changes are observed in the water bands of the SF spectra, as the originally negatively charged silica surface becomes positively charged with an increase in the adsorbed amount, inducing a change in the polar orientation of the water molecules near the surface. The detection limits for hydrocarbons chains in the SF spectra were estimated by comparison with the SF spectrum of a disordered octadecyltrichlorosilane monolayer. The simulations demonstrate that the asymmetry in the adsorbed CTAB layer at any concentration is less than 5% of a monolayer. The results obtained pose severe constraints on the possible structural models, in particular at concentrations below the critical micellar concentration where information is scarce. The formation of hemimicelles, monolayers and other asymmetric aggregates is ruled out, with centrosymmetric aggregates forming from early on in the adsorption process.
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| 5. |
- Tyrode, Eric, et al.
(författare)
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Hydration State of Non-ionic Surfactant Monolayers at the Liquid/Vapor Interface : Structure Determination by Vibrational Sum Frequency Spectroscopy
- 2005
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 127, s. 16848-16859
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Tidskriftsartikel (refereegranskat)abstract
- The OH stretching region of water molecules in the vicinity of nonionic surfactant monolayers has been investigated using vibrational sum frequency spectroscopy (VSFS) under the polarization combinations ssp, ppp, and sps. The surface sensitivity of the VSFS technique has allowed targeting the few water molecules present at the surface with a net orientation and, in particular, the hydration shell around alcohol, sugar, and poly(ethylene oxide) headgroups. Dramatic differences in the hydration shell of the uncharged headgroups were observed, both in comparison to each another and in comparison to the pure water surface. The water molecules around the rigid glucoside and maltoside sugar rings were found to form strong hydrogen bonds, similar to those observed in tetrahedrally coordinated water in ice. In the case of the poly(ethylene oxide) surfactant monolayer a significant ordering of both strongly and weakly hydrogen bonded water was observed. Moreover, a band common to all the surfactants studied, clearly detected at relatively high frequencies in the polarization combinations ppp and sps, was assigned to water species located in proximity to the surfactant hydrocarbon tail phase, with both hydrogen atoms free from hydrogen bonds. An orientational analysis provided additional information on the water species responsible for this band.
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| 6. |
- Abad, JM, et al.
(författare)
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Immobilization of peroxidase glycoprotein on gold electrodes modified with mixed epoxy-boronic acid monolayers
- 2002
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 124:43, s. 12845-12853
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Forskningsöversikt (refereegranskat)abstract
- The development of bioelectronic enzyme applications requires the immobilization of active proteins onto solid or colloidal substrates such as gold. Coverage of the gold surface with alkanethiol self-assembled monolayers (SAMS) reduces nonspecific adsorption of proteins and also allows the incorporation onto the surface of ligands with affinity for complementary binding sites on native proteins. We present in this work a strategy for the covalent immobilization of glycosylated proteins previously adsorbed through weak, reversible interactions, on tailored SAMS. Boronic acids, which form cyclic esters with saccharides, are incorporated into SAMS to weakly adsorb the glycoprotein onto the electrode surface through their carbohydrate moiety. To prevent protein release from the electrode surface, we combine the affinity motif of boronates with the reactivity of epoxy groups to covalently link the protein to heterofunctional boronateepoxy SAMS. The principle underlying our strategy is the increased immobilization rate achieved by the weak interaction-induced proximity effect between slow reacting oxyrane groups in the SAM and nucleophilic residues from adsorbed proteins, which allows the formation of very stable covalent bonds. This approach is exemplified by the use of phenylboronates-oxyrane mixed monolayers as a reactive support and redox-enzyme horseradish peroxidase as glycoprotein for the preparation of peroxidase electrodes. Quartz crystal microbalance, atomic force microscopy, and electrochemical measurements are used to characterize these enzymatic electrodes. These epoxy-boronate functional monolayers; are versatile, stable interfaces, ready to incorporate glycoproteins by incubation under mild conditions.
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| 7. |
- Abdellah, Mohamed, et al.
(författare)
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Time-Resolved IR Spectroscopy Reveals a. Mechanism with TiO2 as a Reversible Electron Acceptor in a TiO2-Re Catalyst System for CO2 Photoreduction
- 2017
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 139:3, s. 1226-1232
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Tidskriftsartikel (refereegranskat)abstract
- Attaching the phosphonated molecular catalyst [(ReBr)-Br-I(bpy)-(CO)(3)](0) to the wide-bandgap semiconductor TiO2 strongly enhances the rate of visible-light-driven reduction of CO2 to CO in dimethylformamide with triethanolamine (TEOA) as sacrificial electron donor. Herein, we show by transient mid-IR spectroscopy that the mechanism of catalyst photoreduction is initiated by ultrafast electron injection into TiO2, followed by rapid (ps-ns) and sequential two-electron oxidation of TEOA that is coordinated to the Re center. The injected electrons can be stored in the conduction band of TiO2 on an ms-s time scale, and we propose that they lead to further reduction of the Re catalyst and completion of the catalytic cycle. Thus, the excited Re catalyst gives away one electron and would eventually get three electrons back. The function of an electron reservoir would represent a role for TiO2 in photocatalytic CO2 reduction that has previously not been considered. We propose that the increase in photocatalytic activity upon heterogenization of the catalyst to TiO2 is due to the slow charge recombination and the high oxidative power of the Re-II species after electron injection as compared to the excited MLCT state of the unbound Re catalyst or when immobilized on ZrO2, which results in a more efficient reaction with TEOA.
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| 8. |
- Abelein, Axel, et al.
(författare)
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Ionic Strength Modulation of the Free Energy Landscape of A beta(40) Peptide Fibril Formation
- 2016
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 138:21, s. 6893-6902
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Tidskriftsartikel (refereegranskat)abstract
- Protein misfolding and formation of cross-beta structured amyloid fibrils are linked to, many neurodegenerative disorders. Although recently developed,quantitative approaches have started to reveal the molecular nature of self-assembly and fibril formation of proteins and peptides, it is yet unclear how these self-organization events are precisely modulated by microenvironmental factors, which are known to strongly affect the macroscopic aggregation properties. Here, we characterize the explicit effect of ionic strength on the microscopic aggregation rates of amyloid beta peptide (A beta 40) self-association, implicated in Alzheimer's disease. We found that physiological ionic strength accelerates A beta 40 aggregation kinetics by promoting surface-catalyzed secondary nucleation reactions. This promoted catalytic effect can be assigned to shielding of electrostatic repulsion between Monomers on the fibril surface or between the fibril surface itself and monomeric peptides. Furthermore, we observe the formation of two different beta-structured states with =similar but distinct spectroscopic features, which can be assigned to an off-pathway immature state (F-beta*) and a mature stable State (F-beta), where salt favors formation of the F-beta fibril morphology. Addition of salt to preformed F-beta* accelerates transition to F-beta, underlining the dynamic nature of A beta 40 fibrils in solution. On the basis of,these results we suggest a model where salt decreases the free-energy barrier for A beta 40 folding to the F-beta state, favoring the buildup of the mature fibril morphology while omitting competing, energetically less favorable structural states.
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| 9. |
- Abrahamsson, Maria, et al.
(författare)
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A 3.0 mu s room temperature excited state lifetime of a bistridentate Ru-II-polypyridine complex for rod-like molecular arrays
- 2006
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 128:39, s. 12616-12617
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Tidskriftsartikel (refereegranskat)abstract
- A bistridentate RuII-polypyridine complex [Ru(bqp)2]2+ (bqp = 2,6-bis(8'-quinolinyl)pyridine) has been prepared, which has a coordination geometry much closer to a perfect octahedron than the typical Ru(terpyridine)2-type complex. Thus, the complex displays a 3.0 mus lifetime of the lowest excited metal-to-ligand charge transfer (3MLCT) state at room temperature. This is, to the best of our knowledge, the longest MLCT state lifetime reported for a RuII-polypyridyl complex at room temperature. The structure allows for the future construction of rod-like, isomer-free molecular arrays by substitution of donor and acceptor moieties on the central pyridine units. This makes it a promising photosensitizer for applications in molecular devices for artificial photosynthesis and molecular electronics.
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| 10. |
- Abrahamsson, Maria, et al.
(författare)
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Bistridentate Ruthenium(II)polypyridyl-Type Complexes with Microsecond 3MLCT State Lifetimes : Sensitizers for Rod-Like Molecular Arrays
- 2008
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Ingår i: Journal of the American Chemical Society. - : ACS. - 0002-7863 .- 1520-5126. ; 130:46, s. 15533-15542
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Tidskriftsartikel (refereegranskat)abstract
- A series of bistridentate ruthenium(II) polypyridyl-type complexes based on the novel 2,6-di(quinolin-8-yl)pyridine (dqp) ligand have been synthesized and their photophysical properties have been studied. The complexes are amenable to substitution in the 4-position of the central pyridine with conserved quasi-C2v symmetry, which allows for extension to isomer-free, rod-like molecular arrays for vectorial control of electron and energy transfer. DFT calculations performed on the parent [Ru(dqp) 2](2+) complex (1) predicted a more octahedral structure than in the typical bistridentate complex [Ru(tpy)2](2+) (tpy is 2,2':6',2"-terpyridine) thanks to the larger ligand bite angle, which was confirmed by X-ray crystallography. A strong visible absorption band, with a maximum at 491 nm was assigned to a metal-to-ligand charge transfer (MLCT) transition, based on time-dependent DFT calculations. 1 shows room temperature emission (Phi = 0.02) from its lowest excited ((3)MLCT) state that has a very long lifetime (tau = 3 micros). The long lifetime is due to a stronger ligand field, because of the more octahedral structure, which makes the often dominant activated decay via short-lived metal-centered states insignificant also at elevated temperatures. A series of complexes based on dqp with electron donating and/or accepting substituents in the 4-position of the pyridine was prepared and the properties were compared to those of 1. An unprecedented (3)MLCT state lifetime of 5.5 micros was demonstrated for the homoleptic complex based on dqpCO2Et. The favorable photosensitizer properties of 1, such as a high extinction coefficient, high excited-state energy and long lifetime, and tunable redox potentials, are maintained upon substitution. In addition, the parent complex 1 is shown to be remarkably photostable and displays a high reactivity in light-induced electron and energy transfer reactions with typical energy and electron acceptors and donors: methylviologen, tetrathiofulvalene, and 9,10-diphenylanthracene. This new class of complexes constitutes a promising starting point for the construction of linear, rod-like molecular arrays for photosensitized reactions and applications in artificial photosynthesis and molecular electronics.
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