Search

Carotenoids tend to form supramolecular aggregates via non‐covalent interactions where the chirality of individual molecules is amplified to the macroscopic level. We show that this can also be achieved for non‐chiral carotenoid monomers interacting with polysaccharides. The chirality induction in canthaxanthin (CAX), caused by heparin (HP) and hyaluronic acid (HA), was monitored by chiroptical spectroscopy. Electronic circular dichroism (ECD) and Raman optical activity (ROA) spectra indicated the presence of multiple carotenoid formations, such as H‐ and J‐type aggregates. This is consistent with molecular dynamics (MD) and density functional theory (DFT) simulations of the supramolecular structures and their spectroscopic response. [ABSTRACT FROM AUTHOR]

Although the potential of Raman Optical Activity (ROA) spectroscopy in the field of organic and inorganic materials research has been well demonstrated, its practical application is still limited. This work shows historical background, current state of the art and challenges of ROA spectroscopy facing scientists today. Expectations and development prospects for the coming years are also discussed. Efforts have already been made to improve but also to properly interpret the ROA signal when the ROA technique is combined with other spectroscopies (i.e., ROA/Electronic Circular Dichroism and ROA/Circularly Polarized Luminescence). The paper shows how to intensify the ROA effect to shorten the spectrum accumulation time, control possible artefacts and support the analysis of ROA spectra with actual and new theoretical approaches. However, the challenge is to increase the interest in this technique among the academic community, develop reliable protocols and adapt them for practical use. National and international research networks can significantly contribute to the growth of methodologies and standardization in areas in which the ROA has so far been little used. This paper presents a perspective vision for the future progress of ROA alongside other chiroptical methods. [ABSTRACT FROM AUTHOR]

Experimental vibrational Raman and Raman optical activity (ROA) spectra for diacetyl L‐tartaric acid (DAT), two of its esters, namely, monomethyl and lauryl esters (T1OH and T12OH), and corresponding sodium salts (DATNa, T1ONa, and T12ONa), are measured. T12OH and T12ONa represent the first chiral surfactants investigated using ROA spectroscopy. The quantum chemical (QC) predictions using B3LYP functional and 6‐311++G(2d,2p) basis set are used to interpret the ROA spectra for DAT, DATNa, T1OH, and T1ONa. It is found that the use of implicit solvation, as represented in polarizable continuum model (PCM), for predicting the experimental ROA spectra in aqueous solutions is inadequate for DAT and T1OH. However, the same PCM predicts the experimental ROA spectra satisfactorily for the DATNa and T1ONa. This favorable observation for the latter is attributed to the absence of intra‐ and inter‐molecular hydrogen bonding interactions for sodium salts in aqueous solutions. The overwhelming number of conformations resulting from 12‐carbon alkyl chain, in T12OH and T12ONa, makes it impractical to undertake QC predictions for them. Nevertheless, it is found that the predictions made for shorter alkyl chain analogs, namely, T1OH and T1ONa, may be used to explain the experimental ROA spectra of T12OH and T12ONa. The current work highlights the importance of converting carboxylic acids to corresponding sodium salts and of QC predictions for shorter achiral alkyl chain analogs to interpret the ROA spectra of chiral surfactants that contain long achiral alkyl chains. [ABSTRACT FROM AUTHOR]

In this study, we found that a recently discovered ECD-Raman effect dominated over the natural Raman optical activity in a series of atropisomeric naphthalenediimides, and we investigated the kind of information about the molecular structure that could be obtained from the spectra. The ECD-Raman effect is polarised Raman scattering modulated by electronic circular dichroism. We showed that the spectra significantly depended on the substitution of the solute and/or the change of the solvent. Moreover, the spectra could be well-predicted by the theory, thus providing an interesting tool to monitor the chirality of the binaphthyl compounds. [ABSTRACT FROM AUTHOR]

Resonance Raman optical activity (RROA) possesses all aspects of a sensitive tool for molecular detection, but its measurement remains challenging. We demonstrate that reliable recording of RROA of chiral colorful compounds is possible, but only after considering the effect of the electronic circular dichroism (ECD) on the ROA spectra induced by the dissolved chiral compound. We show RROA for a number of model vitamin B12 derivatives that are chemically similar but exhibit distinctively different spectroscopic behavior. The ECD/ROA effect is proportional to the concentration and dependent on the optical pathlength of the light propagating through the sample. It can severely alter relative band intensities and signs in the natural RROA spectra. The spectra analyses are supported by computational modeling based on density functional theory. Neglecting the ECD effect during ROA measurement can lead to misinterpretation of the recorded spectra and erroneous conclusions about the molecular structure. [ABSTRACT FROM AUTHOR]

The importance of the electric‐dipole—electric‐quadrupole polarizability contribution to the vibrational Raman optical activity (VROA) and dimensionless circular intensity difference spectra of (1S)‐camphor is examined. The spectra are simulated with and without this tensor contribution using density functional theory calculations, and similarity is evaluated for each against the experimental spectra. Careful examination of the comparison between experimental and calculated spectra reveals multiple vibrational bands, in the ~1,130–950 cm−1 region, originating from −C–H bending vibrations that are dominated by the electric‐dipole—electric‐quadrupole polarizability contributions. The similarity overlap analysis also reveals that the similarity overlap between experimental and predicted spectra in the measured spectral range increases, by up to 12%, when electric‐dipole—electric‐quadrupole polarizability contributions are included. The negative VROA band at 1,125 cm−1 in the experimental spectrum of (1S)‐(‐)‐camphor can only be reproduced in the predicted spectra when electric‐dipole—electric‐quadrupole polarizability contribution is included. Investigations on additional molecules indicated that (a) two experimental VROA bands of (1S,4R)‐(+)‐fenchone at ~1,740 and 220 cm−1 originate from dominating electric‐dipole—electric‐quadrupole polarizability contribution and (b) the symmetric and antisymmetric ring deformation modes of dimethyloxirane have dominating electric‐dipole—electric‐quadrupole polarizability contribution. These observations establish the importance of electric‐dipole—electric‐quadrupole polarizability contribution to VROA for the first time. [ABSTRACT FROM AUTHOR]

Carotenoid microcrystals, extracted from cells of carrot roots and consisting of 95 % of achiral β‐carotene, exhibit a very intense chiroptical (ECD and ROA) signal. The preferential chirality of crystalline aggregates that consist mostly of achiral building blocks is a newly observed phenomenon in nature, and may be related to asymmetric information transfer from the chiral seeds (small amount of α‐carotene or lutein) present in carrot cells. To confirm this hypothesis, we synthesized several model aggregates from various achiral and chiral carotenoids. Because of the sergeant‐and‐soldier behavior, a small number of chiral sergeants (α‐carotene or astaxanthin) force the achiral soldier molecules (β‐ or 11,11′‐[D2]‐β‐carotene) to jointly form supramolecular assemblies of induced chirality. The chiral amplification observed in these model systems confirmed that chiral microcrystals appearing in nature might consist predominantly of achiral building blocks and their supramolecular chirality might result from the co‐crystallization of chiral and achiral analogues. [ABSTRACT FROM AUTHOR]

Experimental vibrational Raman, vibrational Raman optical activity (VROA), and dimensionless circular intensity difference (CID) spectra are analyzed with quantum chemical (QC) predictions of the corresponding spectra using the B3LYP functional and the aug-cc-pVDZ basis set, for five bicyclic terpenes as test cases. The experimentally measured vibrational Raman and VROA spectra have arbitrary y-axis intensities, because of their dependence on instrumental parameters. As a result, the absolute magnitudes of intensities in experimental and calculated vibrational Raman or vibrational ROA spectra are not normally analyzed. However, the experimental dimensionless CID spectrum is independent of the instrumental parameters and can be evaluated quantitatively with corresponding QC predicted CID spectrum. The similarity overlaps between experimental and quantum chemical predictions of vibrational Raman, VROA, and dimensionless CID spectra are evaluated. The quantum chemical predictions of dimensionless CID spectral magnitudes at B3LYP/aug-ccpVDZ level match well with the corresponding experimental magnitudes. The individual anisotropic contributions to VROA and CID spectra are also presented. The anisotropic contribution involving electric dipole-electric quadrupole polarizability derivative tensor is relatively smaller than that involving electric dipole-magnetic dipole polarizability derivative tensor. A new format, which contains all of the information needed for the spectral analysis, has been advanced for presenting the vibrational Raman, VROA, and CID spectra and their similarity analysis with corresponding QC-predicted spectra. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Raman optical activity (ROA) spectra were calculated for a set of conformers of astaxanthin, which is a non-rigid molecule exhibiting strong resonance enhancement in the visible range. Single electronic state theory of the Resonance ROA (RROA) predicts the spectrum to be monosigned. For astaxanthin, it appeared that some of the conformers exhibit different sign of the bands than the other conformers. As a result, the conformer population averaged spectrum of astaxanthin can exhibit both signs of the bands, or be monosigned depending on which conformers are dominating, that reflects a departure from the single electronic state approximation. Moreover, use of different basis sets and/or density functional theory (DFT) functionals results in different conformer populations, thus yielding again either monosigned ROA spectrum or with bands of both signs. Consequences of these two findings for the astaxanthin RROA spectrum are discussed. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

[Display omitted] • ROA and CPL were used in the spectral recognition of GSH peptide and its model post-translational modifications (PTMs). • The effect of pH and chirality induction of Eu(III) probes on the spectral recognition of studied peptides was discussed. • Eu(III) probes proved to be sensitive to the structural modifications of model PTMs. Raman Optical Activity combined with Circularly Polarized Luminescence (ROA-CPL) was used in the spectral recognition of glutathione peptide (GSH) and its model post-translational modifications (PTMs). We demonstrate the potential of ROA spectroscopy and CPL probes (EuCl 3 , Na 3 [Eu(DPA) 3 ], NaEuEDTA) in the study of unmodified peptide, i.e. GSH, and its derivatives, i.e. glutathione oxidized (GSSG), S-acetylglutathione (GSAc) and S-nitrosoglutathione (GSNO). ROA spectral features of GSH, GSSG, and GSAc were determined along with thier changes upon the different pH conditions. Apart from the ROA, induced CPL signals of Eu(III) probes also proved to be sensitive to the structural modifications of GSH-based model PTMs, enabling their spectral recognition, especially by the NaEuEDTA probe. [ABSTRACT FROM AUTHOR]

This work demonstrates resonance Raman optical activity (RROA) spectra of three truncated vitamin B12 derivatives modified within the nucleotide loop. Since truncated cobalamins possess sufficiently high rotational strength in the range of ROA excitation (532 nm), it was possible to record their spectra in the resonance condition. They showed several distinct spectral features allowing for the distinguishing of studied compounds, in contrast to other methods, i.e., UV-Vis absorption, electronic circular dichroism, and resonance Raman spectroscopy. The improved capacity of the RROA method is based here on the excitation of molecules via more than two electronic states, giving rise to the bisignate RROA spectrum, significantly distinct from a parent Raman spectrum. This observation is an important step in the dissemination of using RROA spectroscopy in studying the complex structure of corrinoids which may prove crucial for a better understanding of their biological role. [ABSTRACT FROM AUTHOR]

Abstract This comprehensive study on selected 14 carbohydrates in water solution is an extension of previously published one focused only on solid state analysis. Here, Raman spectroscopy was used as a dedicated method for analysis of carbohydrates in solution, both using a normal effect (RS) and its chiral analogue: Raman Optical Activity spectroscopy (ROA). The compounds were selected as biologically important and representative of all groups: monosaccharides, disaccharides, trisaccharides, cyclodextrines and polysaccharides. RS and ROA spectra are presented together with an expanded discussion on various structures and conformations of studied carbohydrates in the solution taking into account particular regions, i.e. (1) low wavenumber region (250–600 cm−1), (2) anomeric region (600–950 cm−1), (3) fingerprint region (950–1200 cm−1) and (4) CH 2 and COH deformations region (1200–1500 cm−1). So, the following information can be obtained about: (1) the absolute configuration of the anomeric centre; (2) the configuration of the anomeric centre and the orientation of the anomeric hydroxyl group; (3) the ring structures and the relative orientation of substituents and (4) the conformation of the exocyclic CH 2 OH (4), respectively. Raman spectroscopy and Raman Optical Activity were shown as unique tools to study complex structures of carbohydrates. Graphical Abstract Unlabelled Image Highlights • Raman and Raman Optical Activity (ROA) spectra of 14 carbohydrates in aqueous solution were analyzed in detail. • Studied carbohydrates were selected as biologically representative from among mono-, di-, tri- and polysaccharides. • An expanded discussion on various structures and conformations of studied carbohydrates in the solution is described. • Raman and ROA spectroscopy are shown as unique tools to study complex structures of carbohydrates. [ABSTRACT FROM AUTHOR]

Raman optical activity (ROA) spectroscopy is hampered by low sensitivity, with limited possibilities for enhancing the signal. In the present study, we report a new mechanism whereby chirality is enhanced using the resonance resulting from supramolecular aggregation. We have named this mechanism aggregation-induced resonance Raman optical activity (AIRROA). As an example, we study J-aggregates of astaxanthin (AXT), which show strong absorption of circularly polarized light in the range of ROA excitation. The implications of aggregation-induced signal enhancement for chiroptical spectroscopy are discussed. [ABSTRACT FROM AUTHOR]