Martin Willeke

High-Resolution Spectroscopic Studies and Theory of Parity Violation in Chiral Molecules

We review the high-resolution spectroscopic approach toward the study of intramolecular dynamics, emphasizing molecular parity violation. Theoretical work in the past decade has shown that parity-violating potentials in chiral molecules are much larger (typically one to two orders of magnitude) than anticipated on the basis of older theories. This makes experimental approaches toward small molecular parity-violating effects promising. The concepts and results of intramolecular dynamics derived from spectroscopy are analyzed as a sequence of symmetry breakings. We summarize the concepts of symmetry breakings (de facto and de lege) in view of parity violation in chiral molecules. The experimental schemes and the current status of spectroscopic experiments on molecular parity violation are established. We discuss the promises of detecting and accurately measuring parity-violating energy differences Delta(pv) E on the order of 10(11) J mol(1) (approximately 100 aeV) in enantiomers of chiral molecules with regard to their contribution to fundamental physics in the framework of the standard model of particle physics and more speculative future fundamental symmetry tests such as for the combined charge conjugation, parity, and time-reversal (CPT) symmetry violation.

Parity Violation Dominates the Dynamics of Chirality in Dichlorodisulfane

Meaninglessly small would be the effects from parity violation according to the traditional point of view on the structure and dynamics of chiral molecules; enantiomers would thus exist as symmetry-related structures, which are de facto stable because of very long tunneling times. With ClSSCl as the first example, electroweak and tunneling dynamics calculations demonstrate that the de lege asymmetry arising from the parity-violating energy difference ΔEpv between the two enantiomers ((P)- and (M)-ClSSCl, the figure shows the torsional potentials) dominates by far over the tunneling splitting in the symmetrical case. These results are of fundamental interest for our concept of molecular chirality.

Vesicles as Soft Templates for the Enzymatic Polymerization of Aniline

The feasibility of using surfactant vesicles as soft templates for the peroxidase-triggered polymerization of aniline was investigated. It was found that mixed anionic vesicles (diameter approximately 80 nm) composed of sodium dodecylbenzenesulfonate (SDBS) and decanoic acid (1:1, molar ratio) are promising templates. In the presence of the vesicles and horseradish peroxidase/hydrogen peroxide (H2O2) as initiator system, aniline polymerizes under optimized conditions at pH=4.3 to the desired conductive emeraldine form of polyaniline (PANI). The optimal polymerization conditions were elaborated, and some of the chemical and physicochemical aspects of the reaction system were investigated. After addition of aniline and peroxidase to the vesicles, aniline is only loosely associated with the vesicles, as shown by NOESY-NMR and zeta potential measurements. In contrast, the peroxidase strongly binds to the vesicle surface, as shown by fluorescence measurements using TNS (2-(p-toluidino)naphthalene-6-sulfonate) as vesicle membrane probe. This binding of the enzyme to the vesicle surface indicates that the polymerization reaction is initiated predominantly on the surface of the vesicles. Cryo-transmission electron microscopy indicates that the polymerization product remains associated with the vesicles on their surface. For short reaction times (30 s<t<60 s), it is shown that oligoanilines containing an excess of oxidized units are obtained, as shown by VIS/NIR spectroscopy and MALDI-TOF mass spectrometry. For longer reaction times (1 min<t<30 min), the relative amount of over oxidized units in PANI decreases until polymers are obtained which have a VIS/NIR spectrum that is typical for the emeraldine salt form of PANI (lambdamax approximately 1000 nm). The appearance of stable unpaired electrons during the reaction was demonstrated by EPR measurements, in full support of the in situ formation of the conductive emeraldine salt form of PANI. At the end of the reaction (after 1 h), the PANI formed remains homogenously dispersed in the aqueous solution thanks to the presence of the vesicles. No precipitation occurs on a time scale of at least several weeks. FTIR and 13C NMR measurements of the product isolated from the reaction mixture confirm the formation of the emeraldine form of PANI. If the polymerization reaction is carried out in the absence of vesicles but under otherwise identical reaction conditions, the outcome of the reaction is very different, i.e., no indication at all for the formation of the conductive form of PANI.

Ab initio calculations of mode selective tunneling dynamics in 12CH3OH and 13CH3OH

A simplified formulation of the harmonic reaction path Hamiltonian (RPH) approach is used to calculate mode specific tunneling splittings and stereomutation times in (CH3OH)-C-12 and (CH3OH)-C-13. The experimental torsional spectrum is very well reproduced, as well as the few known isotope shifts. The mode specific changes in tunneling splitting are investigated for the excitation of fundamentals and OH stretching overtones. Good agreement between experiment and the RPH model is obtained, except for excitations of modes which are perturbed by anharmonic resonances. The inverted tunneling splittings (E level below A) experimentally observed for the fundamental transitions of the CH-stretching modes nu(2) and nu(9) and of the CH-rocking mode nu(11) are shown to result from a pure symmetry effect and not from a breakdown of vibrational adiabaticity. Introducing a proper geometrical phase factor but retaining the adiabatic separation of the torsional dynamics yields calculated values of Delta(ν) over tilde (2)=-3.6 cm(-1), Delta(ν) over tilde (9)=-3.2 cm(-1), and Delta(ν) over tilde (11)=-8.2 cm(-1) that are in satisfactory agreement with experimental data. Negative tunneling splittings are also predicted for the asymmetric CH-bending modes nu(4) and nu(10) and the CH3-rocking mode nu(7). A smooth decrease of the tunneling splitting is calculated for increasing OH stretching excitation [Delta(ν) over tilde(nu(1))=6.2 cm(-1),...,Delta(ν) over tilde (6nu(1))=1.5 cm(-1)] in quantitative agreement with experiment [Delta(ν) over tilde(nu(1))=6.3 cm(-1),...,Delta(ν) over tilde (6nu(1))=1.6 cm(-1)]. The effect is shown to result in about equal parts from the increase of the effective torsional barrier and the effective lengthening of the OH bond

Ab initio calculations for the anharmonic vibrational resonance dynamics in the overtone spectra of the coupled OH and CH chromophores in CD2H–OH

We report high level ab initio calculations (treating correlation by second order Moller–Plesset perturbation theory, MP2) of a five-dimensional normal coordinate subspace of the potential and electric dipole hypersurfaces of the Cs conformer of dideuteromethanol, CD2HOH. Accurate vibrational variational calculations are carried out using a discrete variable representation (DVR) for the five anharmonically coupled modes (three coupled CH stretching and bending modes and the OH stretching and high frequency OH bending mode). The overtone spectra of the OH chromophore are calculated and analyzed in detail with respect to their anharmonic resonance dynamics leading to short time intramolecular vibrational redistribution (IVR) via the close resonance coupling of 5νOH (5ν1) with 4νOH+νCH(4ν1+ν2), as previously observed and assigned experimentally. While the assignment of the resonance is confirmed by the ab initio calculation, a sequence of calculations including various subspaces (two-dimensional to five-dime...

Ab initio calculation and spectroscopic analysis of the intramolecular vibrational redistribution in 1,1,1,2-tetrafluoroiodoethane CF3CHFI

We report a new mechanism for intramolecular vibrational redistribution (IVR) in CF3CHFI which couples the CH chromophore vibrations through a strong Fermi resonance to the formal CF stretching normal mode (a heavy atom frame mode) involving the trans F-atom across the CC bond. The analysis is made possible by comparing spectroscopic results with extensive ab initio calculations of the vibrational fundamental and overtone spectra in the range extending to 12 000 cm−1. Potential energy and electric dipole moment hypersurfaces are calculated ab initio by second order Moller–Plesset perturbation theory (MP2) on a grid involving the CH stretching, two CH bending modes and one high frequency CF stretching normal mode. The potentials are scaled to obtain agreement between the experimental spectrum and the theoretical spectrum calculated by a discrete variable representation technique on this grid. Both spectra are then analyzed in terms of three-dimensional (3D) and four-dimensional (4D) effective vibrational H...

Limits of the validity of the mass ratio independence of the Stokes—Einstein relation: molecular dynamics calculations and comparison with the Enskog theory

Detailed molecular dynamics simulations have been carried out to investigate the mass ratio dependence of the tracer self-diffusion coefficient D 2 in binary, atomic Lennard-Jones mixtures as a function of density n and length diameter ratio σ22/σ11. For a compact representation of our results an exponential approach is employed. The results are compared with the Stokes-Einstein relation, which predicts no mass ratio dependence, and the Enskog theory. The validity ranges regarding the mass ratio dependence for Enskog and Stokes-Einstein like behaviour are given as well as the mass ratio dependence in the crossover regions between these two cases. For length parameter ratios σ22/11 <1, the Stokes-Einstein prediction is not valid for mass ratios 1/16≤m2/m1 ≤50. For length parameter ratios σ22/σ11>2 and for mass ratios m2/m1 < 1, the Stokes-Einstein regime (regarding the mass ratio dependence) is reached for smaller densities than for the same system but m2/m1 >1.

The use of Trametes versicolor laccase for the polymerization of aniline in the presence of vesicles as templates

The enzymatic polymerization of aniline to polyaniline (PANI) with Trametes versicolor laccase (TvL) as catalyst and dioxygen (O₂) as oxidant was investigated in an aqueous medium containing unilamellar vesicles with an average diameter of about 80 nm formed from AOT (=sodium bis(2-ethylhexyl) sulfosuccinate). Compared to the same reaction carried out with horseradish peroxidase isoenzyme C (HRPC) as catalyst and hydrogen peroxide (H₂O₂) as oxidant, notable differences were found in the kinetics of the reaction, as well as in the characteristics of the PANI obtained. Under comparable optimal conditions, which are pH 3.5 for TvL/O₂ and pH 4.3 for HRPC/H₂O₂, the reaction with TvL/O₂ was much slower than with HRPC/H₂O₂, i.e. ≈27 days vs. 1 day reaction time to reach equilibrium with >90% yield at 25 °C. Although in both cases, aniline monomer coupling occurred mainly via the carbon atom in para position of aniline, UV-vis-NIR absorption and EPR measurements indicate that the reaction with TvL/O₂ yielded mainly overoxidized products (with λ(max)=730 nm). These products had a lower amount of unpaired electrons if compared with the products obtained with HRPC/H₂O₂ (with λ(max)≈1000 nm, which is characteristic for the polaron state of PANI-ES, the emeraldine salt form of PANI). Similarly to previous findings with HRPC/H₂O₂, enzyme inactivation occurred during the polymerization also in the case of TvL/O₂. Since the aqueous PANI-vesicle suspensions obtained are of high colloidal stability, they can be used directly as ink in a conventional thermal inkjet printer for printing on paper or on surface treated polyimide films. Printed PANI-ES patterns on paper changed colour from green (emeraldine salt) to blue (emeraldine base) upon exposure to ammonia gas, demonstrating the expected ammonia sensing properties.

Rovibrational analysis of the ν 4,2ν 6 Fermi resonance band of CH35ClF2 by means of a polyad Hamiltonian involving the vibrational levels ν 4, 2ν 6,ν 6+ν 9 and 2ν 9, and comparison with ab initio calculations

High resolution FTIR spectra of the ν4/2ν6 band system in the region 750–850 cm−1 were measured with our Bruker IFS 125 HR Zürich prototype (ZP2001) spectrometer using an instrumental resolution of better than 0.001 cm−1 (FWHM, unapodized or 1/MOPD =0.001 cm−1 with the maximum optical path difference MOPD). The spectra were analysed by means of a polyad Hamiltonian built up from the ν4/2ν6 Fermi dyad and the 2ν6,ν6+ν9,2ν9 Coriolis triad which share the level 2ν6. The levels ν6+ν9 and 2ν9 are not directly observed but are included as dark states. Spectroscopic parameters for ν6+ν9 and 2ν9 as well as the Coriolis coupling constants for the Coriolis triad were transferred from the Coriolis dyad ν6,ν9 using previously reported values. The analysis included both isotopomers CH35ClF2, and CH37ClF2. The deperturbed band centres of ν4 and 2ν6 obtained from the fit are cm−1 and cm−1 for CH35ClF2, and cm−1 and cm−1 for CH37ClF2. The Fermi resonance coupling matrix element obtained for CH35ClF2 is F = −7.6839 cm−1. In the corresponding analysis of the isotopomer CH37ClF2, we employed also this value without further adjustment. A comparison with results obtained in the framework of simpler models shows that the inclusion of the full Coriolis triad is essential. We also report ab initio calculations on the MP2 level of theory with aug-cc-pVDZ and aug-cc-pVTZ basis sets pertaining to (q4 ), (q 6) and (q 4 , q 6 ) subspaces. These results agree well with the empirical findings and allow us to assign a sign to certain coupling constants which cannot be obtained from the analysis of the experimental spectra.

Doppler-limited FTIR spectrum of the v 3(a′)/v 8 (a″) Coriolis resonance dyad of CHC1F2: analysis and comparison with ab initio calculations

Abstract The Doppler-limited FTIR spectrum of the band system in the region 1070–1170 cm−1 (Doppler width ≈ 0.0015 cm−1, FWHM) was measured with our new Bruker IFS 120 HR Zürich prototype (ZP2001) spectrometer. This instrument allows for an unapodized resolution of 0.0007 cm−1 (FWHM). This is the highest resolution realized so far by a commercial FTIR spectrometer system. It allows high-resolution analysis of the room temperature spectra of the strongly coupled modes v 3(a′) and v 8 (a″), corresponding to the symmetric and antisymmetric CF-stretching vibrations, including also further couplings not analysed previously. The present analysis is based on effective rotational Hamiltonians for the v 3=1 and v 8=1 states, including all terms up to sextic, and involves the full first-order Coriolis interaction operator Consideration of both the and first-order Coriolis terms proved essential in order to obtain good line-by-line agreement between observed and calculated rovibrational structures over the full band system. In addition, the analysis of two local resonances allowed us to determine the vibrational wavenumbers of the 3v 9 and v 6+2v 9) levels with good accuracy. We describe possible approaches to the analysis. The final analysis involves both chlorine isotopomers and includes all hybrid components which are allowed by symmetry. It results in the band centres cm−1, cm−1, cm−1 and (v 6+2v 9)0=1144.32 cm−1, where the last digit is rounded, relating to the first digits differing in two types of analyses and data sets from our work. The main Coriolis interaction parameters are cm−1 and cm−1. In addition, smaller interactions could also be determined quantitatively. Our results are in essential agreement with the original analysis of Luckhaus and Quack (1989, Molec. Phys., 68, 745), which was, however, much less complete and precise. We discuss the comparison of different types of analyses and further recent results on this band system. We report ab initio calculations for this molecule on the MP2 level of theory with an aug-cc-pVDZ or an aug-cc-pVTZ basis set. Various subspaces of the potential energy and electric dipole moment hypersurface have been calculated in reduced normal coordinates including up to three dimensions. With these hypersurfaces we determined the corresponding vibrational absorption spectra, comprising transition wave- numbers and intensities. An analysis of the vibrational levels with an effective Hamiltonian was used to derive anharmonic constants. We also derived Coriolis coupling constants and integrated absorption intensities ab initio, which are compared with the present and previous experimental and theoretical results. The complete set of data as analysed is tabulated in Appendix A of this publication [61].