Comment on a sum rule for vibrational raman optical activity

We present an analytical time-dependent Hartree-Fock algorithm for the calculation of the derivatives of the electric dipole-magnetic dipole polarizability with respect to atomic Cartesian coordinates. Combined with analogous procedures to determine the derivatives of the electric dipole-electric dipole and electric dipole-electric quadrupole polarizabilities, it enables a fully analytical evaluation of the three frequency-dependent vibrational Raman optical activity (VROA) invariants within the harmonic approximation. The procedure employs traditional non-London atomic orbitals, and the gauge-origin dependence of the VROA intensities has, therefore, been assessed for the commonly used aug-cc-pVDZ and rDPS:3-21G basis sets.

Raman and vibrational Raman optical activity (ROA) spectra have been calculated for three molecules: H2O2, CHDTF and CHDTOH. The effects of electron correlation on the ROA parameters of these relatively small systems have been investigated by means of the multiconfigurational self-consistent field (SCF) approach. A range of correlation-consistent basis sets has been used in the calculations. The basis set convergence of the calculated ROA parameters is fairly well achieved when sets of at least d-aug-cc-pVTZ quality are used. On the other hand, the aug-cc-pVDZ set seems to be sufficient for a qualitative analysis. Diffuse functions, possibly a double set, are essential to ensure a good quality of the calculated ROA spectrum. In most cases the sign and approximate magnitude of the ROA are correctly predicted at the SCF level, and the corresponding ROA spectra should be considered qualitatively accurate.

Vibrational Spectra:Principles and Applications with emphasis on optical activity

Natural resonance electronic Raman optical activity (ROA) is observed for the first time. Coincidently, the first example of vibrational ROA enhanced by low‐lying electronic transition is reported. These new phenomena were measured using the rare‐earth complex Eu(tfc)3 (+)‐tris[3‐trifluoroacetyl‐D‐camphorato]europium(III), where electronic resonance occurs between the 532‐nm laser excitation and the 7F1 → 5D1 transition of the Eu3+ metal center. Electronic Raman spectra involve the Raman transitions terminating on the low‐lying electronic states of Eu(tfc)3. The observed vibrational ROA spectra are enhanced relative to typical ROA spectra by the proximity of vibrational states of Eu(tfc)3 to its low‐lying electronic states with significant magnetic‐dipole character, whereas the parent vibrational Raman spectra do not appear to be resonance‐enhanced since the 532‐nm vibrational Raman spectrum has similar relative intensities to the corresponding Raman spectrum measured with 1064‐nm laser excitation. Copyright © 2010 John Wiley & Sons, Ltd.

Infrared vibrational circular dichroism (VCD) and vibrational Raman optical activity (ROA) have been measured and compared quantitatively over the frequency range from 835 to 1345 cm−1 for trans-pinane, cis-pinane, α-pinene, and β-pinene. For these molecules in this region of spectral overlap between VCD and ROA, the average ratio of VCD or ROA to its parent vibrational intensity favors ROA by a factor of two to three. Several vibrational modes in each molecule yield both large VCD and large ROA, while several other modes show little propensity toward significant VCD or ROA intensity. Beyond this general property of a few strongly chiral and strongly achiral vibrational modes, little additional correlation between VCD and ROA intensity is found. This quantitative compilation of VCD, infrared, ROA, and Raman intensities provides an experimental basis for computational intensity studies of VCD, ROA, and their theoretical comparison.

Starting from the eight B3LYP/6-31G* optimized N-acetyl-l-alanine N'-methylamide (AAMA) structures recently reported by Jalkanen and Suhai,1 we studied the effect of hydration on the AAMA geometries, relative energies, and vibrational properties by applying the solvent continuum model, by adding four explicit water molecules to each of the conformers, and finally by combining the two approaches. For the four lowest energy AAMA+4H2O complexes, we have calculated the B3LYP/6-31G* Hessians and atomic polar tensors (APT), RHF/6-31G* atomic axial tensors (AAT), RHF/6-311+G** electric dipole−electric dipole polarizability derivatives (EDEDPD), RHF/6-31G* electric dipole−magnetic dipole polarizability derivatives (EDMDPD), and RHF/6-31G* electric dipole−electric quadrupole polarizability derivatives (EDEQPD), which gave us the required quantities to simulate the vibrational absorption (VA), Raman, vibrational circular dichroism (VCD), and Raman optical activity (ROA) spectra. The explicit water model reveals the H-bonding between the AAMA and the water molecules. The water stabilizes two AAMA structures (PII and αR), which are not stable in the isolated state. The influence of the explicit water molecules on the AAMA vibrational spectra was also discussed. The solvent continuum model applied to the AAMA+4H2O complexes further modified the orientations of the water molecules and influenced the vibrational modes and intensities. By comparing the calculated and the observed Raman, VCD, and ROA spectra, we suggest that the PII structure of AAMA (φ ∼ −93°, ψ ∼ 128°) is the dominant one in aqueous solutions.

The theory of magneto-chiral birefringence and dichroism is extended to systems composed of diamagnetic molecules acted on by an optical field. For molecules with the point group symmetries 3, 4, 6, ∞, 32, 422, and 622 expressions are derived for the magneto-chiral birefringence and dichroism in the presence of weak as well as very strong optical molecular reorientation caused by a linearly polarized, circularly polarized, or unpolarized laser beam. Measurements of magneto-chiral birefringence and dichroism at optical saturation provide direct information on the respective magnetic dipole and electric quadrupole polarizability tensor components.

A vibrational Raman optical activity (ROA) study of a range of different structural types of virus exemplified by filamentous bacteriophage fd, tobacco mosaic virus, satellite tobacco mosaic virus, bacteriophage MS2 and cowpea mosaic virus has revealed that, on account of its sensitivity to chirality, ROA is an incisive probe of their aqueous solution structures at the molecular level. Protein ROA bands are especially prominent from which, as we have shown by comparison with the ROA spectra of proteins with known structures and by using a pattern recognition program, the folds of the major coat protein subunits may be deduced. Information about amino acid side-chain conformations, exemplified here by the determination of the sign and magnitude of the torsion angle chi(2,1) for tryptophan in fd, may also sometimes be obtained. By subtracting the ROA spectrum of the empty protein capsid (top component) of cowpea mosaic virus from those of the intact middle and bottom-upper components separated by means of a caesium chloride density gradient, the ROA spectrum of the viral RNA was obtained, which revealed that the RNA takes up an A-type single-stranded helical conformation and that the RNA conformations in the middle and bottom-upper components are very similar. This information is not available from the X-ray crystal structure of cowpea mosaic virus since no nucleic acid is visible.

Vibrational Raman optical activity (ROA) is measured in our laboratory as a small intensity difference in Raman scattered light from chiral molecules in right and left circularly polarized incident light.[l, 2] Recently, a series of instrumental advances [3] has opened up the realm of biopolymers, including proteins, polysaccharides and now nucleic acids, to this novel chiroptical technique. For proteins and polysaccharides it has already been demonstrated that ROA can probe key structural elements more incisively than conventional Raman spectroscopy because it can cut through the complexity of the conventional spectra by probing directly the crucial chiral elements of biomolecular structure. In this contribution we focus on some of our recent results on polynucleotides and as an example present the Raman and ROA spectra of poly(rG)•poly(rC) in H2O between 650 and 1750 cm −1 in Figure 1.

Chirality plays a crucial role in drug discovery and development. As a result, a significant number of commercially available drugs are structurally dissymmetric and enantiomerically pure. The determination of the exact 3D structure of drug candidates is, consequently, of paramount importance for the pharmaceutical industry in different stages of the discovery pipeline. Traditionally the assignment of the absolute configuration of druggable molecules has been carried out by means of X-ray crystallography. Nevertheless, not all molecules are suitable for single-crystal growing. Additionally, valuable information about the conformational dynamics of drug candidates is lost in the solid state. As an alternative, vibrational optical activity (VOA) methods have emerged as powerful tools to assess the stereochemistry of drug molecules directly in solution. These methods include vibrational circular dichroism (VCD) and Raman optical activity (ROA). Despite their potential, VCD and ROA are still unheard of to many organic and medicinal chemists. Therefore, the present review aims at highlighting the recent use of VOA methods for the assignment of the absolute configuration of chiral small-molecule drugs, as well as for the structural analysis of biologics of pharmaceutical interest. A brief introduction on VCD and ROA theory and the best experimental practices for using these methods will be provided along with selected representative examples over the last five years. As VCD and ROA are commonly used in combination with quantum calculations, some guidelines will also be presented for the reliable simulation of chiroptical spectra. Special attention will be paid to the complementarity of VCD and ROA to unambiguously assess the stereochemical properties of pharmaceuticals.

Experimental and ab initio theoretical vibrational Raman optical activity of alanine

Simultaneous haemo-filtration and haemo dialysis

Determination of the absolute handedness, known as absolute configuration (AC), of chiral molecules is an important step in any field related to chirality, especially in the pharmaceutical industry. Vibrational optical activity (VOA) has become a powerful tool for the determination of the AC of chiral molecules in the solution state after nearly forty years of evolution. VOA offers a novel alternative, or supplement, to X-ray crystallography, permitting AC determinations on neat liquid, oil, and solution samples without the need to grow single crystals of the pure chiral sample molecules as required for X-ray analysis. By comparing the sign and intensity of the measured VOA spectrum with the corresponding ab initio density functional theory (DFT) calculated VOA spectrum of a chosen configuration, one can unambiguously assign the AC of a chiral molecule. Comparing measured VOA spectra with calculated VOA spectra of all the conformers can also provide solution-state conformational populations. VOA consists of infrared vibrational circular dichroism (VCD) and vibrational Raman optical activity (ROA). Currently, VCD is used routinely by researchers in a variety of backgrounds, including molecular chirality, asymmetric synthesis, chiral catalysis, drug screening, pharmacology, and natural products. Although the application of ROA in AC determination lags behind that of VCD, with the recent implementation of ROA subroutines in commercial quantum chemistry software, ROA will in the future complement VCD for AC determination. In this review, the basic principles of the application of VCD to the determination of absolute configuration in chiral molecules are described. The steps required for VCD spectral measurement and calculation are outlined, followed by brief descriptions of recently published papers reporting the determination of AC in small organic, pharmaceutical, and natural product molecules.

In the recent work [A.~Yamaguchi et. al, Phys. Rev. Lett. {\bf 123}, 113201 (2019)] Cd has been identified as an excellent candidate for a lattice clock. Here, we carried out computations needed for further clock development and made an assessment of the higher-order corrections to the light shift of the $5s^2\, ^1\!S_0$--$5s5p\, ^3\!P_0^o$ clock transition. We carried out calculations of the magnetic dipole and electric quadrupole polarizabilities and linear and circular hyperpolarizabilities of the $5s^2\, ^1\!S_0$ and $5s5p\, ^3\!P_0^o$ clock states at the magic wavelength and estimated uncertainties of these quantities. We also evaluated the second-order Zeeman clock transition frequency shift.

Casimir interactions are not pair-wise additive. This property leads to collective effects that we study for a pair of objects near a conducting wall. We employ a scattering approach to compute the interaction in terms of fluctuating multipoles. The wall can lead to a non-monotonic force between the objects. For two atoms with anisotropic electric and magnetic dipole polarizabilities we demonstrate that this non-monotonic effect results from a competition between two- and three body interactions. By including higher order multipoles we obtain the force between two macroscopic metallic spheres for a wide range of sphere separations and distances to the wall.