Volker Buss - Academia.edu (original) (raw)

Papers by Volker Buss

Open Journal of Physical Chemistry, 2012

Different structures are proposed for the complexes formed from the interaction between the catio... more Different structures are proposed for the complexes formed from the interaction between the cationic cyanine dye 1, 1'-diethyl-2, 2'-carbocyanine chloride (Pinacyanol chloride) and the anionic surfactant sodium bis (2-ethylhexyl) sulfosuccinate (Aerosol-OT) in ethanol-water solutions. UV/vis and electronic circular dichroism (CD) spectra provide tools to study the concentration and solvent dependence of this interaction. The aggregation spectra of the dye are dominated by a strongly blue-shifted, sharp and single visible band, which appears at concentrations much below the critical micelle concentration (cmc) of Aerosol-OT. Above the cmc, the spectra in pure aqueous solution indicate dissociation into monomer and dimer species, and the system becomes completely empty of chirality. Two different CD spectra with a distinct isosbestic point are observed for complexes with different surfactant to dye ratios. Both the addition of ethanol (more than 7.5%) and increasing the temperature retards the metachromatic process between the dye and Aerosol-OT. By using the peakFit program, the two overlapping excitonic absorption bands together with the optically inactive absorption band for one spectrum (the most optimal one) at a specific Aerosol-OT concentration were separated.

Encyclopedia of Spectroscopy and Spectrometry, 1999

Introduction Rhodopsin is a membrane protein, which is responsible for black and white vision in ... more Introduction Rhodopsin is a membrane protein, which is responsible for black and white vision in the vertebrate eye. 1) It consists mainly of seven so-called transmembrane helices which form a pocket. It was established that the visual pigment rhodopsin contains as chromophore 11-cis-retinal protonated Schi# base 2) and the visual process is initiated by the photochemical isomerization of 11-cis to all-trans. The isomerization eventually leads to the chemical signal of a nerve impulse sent to the brain which enables us to see. Of all double bonds in the molecule which can theoretically undergo cis-trans isomerization, only the C11-C12 double bond is a#ected by the action of light: When rhodopsin absorbs light of # 500 nm the chromophore makes a Franck-Condon transition into the first excited singlet state where it isomerizes to the all-trans isomer bathorhodopsin, a process which is complete within 200 fs. On the other hand, the dark-isomerization of the chromophore occurs in t

We report ab initio calculations of the ground and several excited states of protonated 11-cis-an... more We report ab initio calculations of the ground and several excited states of protonated 11-cis-and all-trans-retinal Schiff base, the chromophores of the visual pigment rhodopsin and its photoproduct, bathorhodopsin, respectively. A supramolecule in which a formate anion and water have been attached to the Schiff base is described as a first attempt to model part of the complex environment of the chromophore. For highly coiled geometries of the retinals CD spectral data have been calculated. The comparison with experimental data suggests that a revision of the presently accepted structures may be necessary.

Introduction Dye molecules are of particular interest, since they are a subject of intense inter-... more Introduction Dye molecules are of particular interest, since they are a subject of intense inter-disciplinary research involving all branches of chemistry, in particular physical and theoretical chemistry, and also physics and biology. The fundamental problem is the interaction of dye molecules with light and the subsequent change of conformation and its impact on the surrounding, which is usually protein-like. In this short note we investigate whether conformational changes of the dye molecules will be altered due to the presence of the surface of an ionic crystal. In this case conformational changes are caused by the Figure 1. Conformation of trimethin. Figure 2. Conformation of monomethin. repulsive methyl groups in the case of monomethin and not by the absorption of light leading to a cis-trans transformation. We have used the Vienna ab initio simulation package (VASP) which is a program designed for molecular-dynamics (MD) simulations based on Density Functional Theory. It use

Density functional theory (DFT) calculations based on the self-consistent-charge tight-binding ap... more Density functional theory (DFT) calculations based on the self-consistent-charge tight-binding approximation have been performed to study the influence of the protein pocket on the 3dimensional structure of the 11-cis-retinal Schiff base (SB) chromophore. Starting with an effectively planar chromophore embedded in a protein pocket consisting of the 27 nextnearest amino acids the relaxed chromophore geometry resulting from energy optimization and molecular dynamics (MD) simulations has yielded novel insights with respect to the following questions: (i) The conformation of the #-ionone ring. The protein pocket tolerates both conformations, 6-s-cis and 6-s-trans, with a total energy difference of 0.7 kcal/mol in favour of the former. Of the two possible 6-s-cis conformations, the one with a negative twist angle (optimized value: -35 ) is strongly favoured, by 3.6 kcal/mole, relative to the one in which the dihedral is positive. (ii) Out-of-plane twist of the chromophore. The environmen...

Recently the structure of rhodopsin was determined from the X-ray diffraction data extending to t... more Recently the structure of rhodopsin was determined from the X-ray diffraction data extending to the reso- lution of 2.8 ûA. We have studied the effects of amino acids and of water using A density functional based tight-binding code. A model retinal binding pocket was employed containing 27 residues within 4.5 ûA distance from the retinal molecule and water molecules. Our re- sults show that one water molecule hydrogen bonded to Glu113 plays an important role in stabilizing the proto- nated state of the Schiff base. We also discuss the struc- ture of 11-cis-retinal PSB, which is highly twisted in the protein pocket. The C11-C12 and C12-C13 bonds are twisted in negative and positive directions respectively, which is confirmed by circular dichroism experiments.

ChemInform

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The influence of protein induced chromophore deformations on reaction timescale and quantum yield... more The influence of protein induced chromophore deformations on reaction timescale and quantum yield is investigated using ab initio molecular dynamics in vacuo on four and five double bond models of the retinal chromophore. The opposite twist of the C11 = C12 and the C12-C13 bonds appears to be the prerequisite for the highly stereoselective and efficient cis-trans photodynamics of the

Journal of Molecular Structure: THEOCHEM, 1996

Ab initio calculations have been performed on all-trans-retinal, 1, 11-cis-12-s-c&-retinal, 2, an... more Ab initio calculations have been performed on all-trans-retinal, 1, 11-cis-12-s-c&-retinal, 2, and ll-cis-12-s-trans-retinal, 3, as well as their corresponding N-methyl Schiff bases and protonated N-methyl Schiff base derivatives. Geometries preoptimized at the RHF/3-21G level were fully optimized with the RHF/6-31G** basis set. The stabilities in order of increasing energy are 1,2 and 3 for the aldehydes and Schiff bases, but 1,3 and 2 for the protonated species. Geometries are in excellent agreement with available X-ray results. Minute details are reproduced with surprising accuracy, except for the large dihedral angles at the C6-C7 bond (and the C12-Cl3 bond for the 11-cis isomers) where packing effects may play an important role. Geometry changes from the aldehydes to the corresponding Schiff bases are negligible, while protonation is accompanied by the loss of double bond fixation and an increased tendency towards planarization. The geometry about the C6-C7 bond is distorted 6-s-& in the aldehydes and the Schiff bases, while in the protonated Schiff bases an additional almost planar 6-s-trans conformation is found. Tbe out-of-plane deformation about the C12-Cl3 bond is 49' in 2,5" in 3 and 0" in the protonated Schiff base of 3.

Journal of Biophysical Chemistry, 2011

Under certain conditions algal alginates bind pinacyanol chloride in the form of dimers-this is t... more Under certain conditions algal alginates bind pinacyanol chloride in the form of dimers-this is the conclusion drawn from a uv/vis and circular dichroism (CD) spectroscopic study of aqueous solutions of the dye in a 10-fold molar excess of the polysaccharide from different sources. With its easily detected features the dimer holds promise as a diagnostic tool for alginate conformational analysis. Binding of the strongly blue-shifted (maximum wavelength = 485 nm) dimer is probably mediated by the charged groups and involves guluronate units only. By using the peak-Fit program, the two overlapping excitonic absorption bands together with the optically inactive band resulted from the interaction of pinacyanol with a specific alginate concentration were separated. The standard Gibbs energy of the interaction was calculated as -27.02 kJ·mol -1 . The dimers are sensitive against acid and divalent cations.

The results of structure optimization and molecular dynamics simulation of host-guest γ -cyclodex... more The results of structure optimization and molecular dynamics simulation of host-guest γ -cyclodextrin-pinacyanol dye inclusion complexes are obtained by applying a density functional based tight-binding code. The results attempt to correlate UV/Vis and circular dichroism spectral data with calculated aggregate structures of the sandwich dimer, with the monomers twisted slightly against each other. The sense of twist is predetermined by the chirality of the complexing host. The UV/Visspectral are interpreted using the exciton model. Within this model, each excited state of the monomer generates two excitonic states in the dimer. The interaction between the two monomers results then in a Davydov splitting of the two dimer states. The opposite signs of the two dimer states can be attributed to the twist of the monomers when they interact.

Journal of the Chemical Society, Perkin Transactions 1, 1995

The title compound has been synthesised in racemic form by a biomimetic reaction sequence. The tw... more The title compound has been synthesised in racemic form by a biomimetic reaction sequence. The two enantiomers were resolved by column chromatography of one of the synthetic intermediates. On the basis of CD results a tentative absolute configuration for ...

Journal of the Chemical Society-Dalton Transactions, 2001

... 31 P NMR (δ, J /Hz) (s, µ-P) a 1 H NMR ( δ, J /Hz) (s, CH 3, camphanate) a IR ν as (CO 2)b / ... more ... 31 P NMR (δ, J /Hz) (s, µ-P) a 1 H NMR ( δ, J /Hz) (s, CH 3, camphanate) a IR ν as (CO 2)b / cm 1 CD λ (∆ ε)/nm (L mol 1 cm 1 )c UV-VIS λ max (ε)/nm (L mol 1 cm 1 )c 5a 100 114.4 0.90, 0.91, 0.98 1608 207 ( 7.0), 229 ( 43.2), 247 (14.8), 269 ( 10.7), 288 ( 11.6), 321 (27.3), ...

We present results of ab initio total energy calculations and molecular-dynamics simulations of d... more We present results of ab initio total energy calculations and molecular-dynamics simulations of dye molecules on the NaCl(100) surface. The investigations concentrate on the flat dye molecules trimethin, [C19H17N2O2]+, which form sandwich-like structures if closely packed, and the cyanine molecule monomethin, [C21H23N2]+, which shows a typical stereochemical deformation due to two repulsive methyl groups. The molecular-dynamics simulations are able to reproduce the experimentally observed configurations of the charged dye molecules on surfaces.

Cheminform, 2010

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.