The Experts below are selected from a list of 246 Experts worldwide ranked by ideXlab platform
Prasad L Polavarapu - One of the best experts on this subject based on the ideXlab platform.
-
absolute configuration and conformation of r t butylphenylphosphinoamidate Chiroptical Spectroscopy and x ray analysis
Journal of Organic Chemistry, 2020Co-Authors: Ana G Petrovic, Prasad L Polavarapu, Andrzej łopusinski, D Krasowska, Wanda Wieczorek, Malgorzata Szyrej, Jaroslaw Blaszczyk, J DrabowiczAbstract:The absolute configuration and conformations of (-)-tert-butylphenylphosphinoamidate have been determined using three different Chiroptical spectroscopic methods, namely, vibrational circular dichr...
-
absolute configurations of naturally occurring 5 and 3 ladderanoic acids isolation Chiroptical Spectroscopy and crystallography
Journal of Natural Products, 2018Co-Authors: Vijay Raghavan, Prasad L Polavarapu, Jordan L Johnson, Donald F Stec, Bongkeun Song, Grzegorz Zajac, Malgorzata Baranska, Constance M Harris, Nathan D Schley, Thomas M HarrisAbstract:We have isolated mixtures of [5]- and [3]-ladderanoic acids 1a and 2a from the biomass of an anammox bioreactor and have separated the acids and their phenacyl esters for the first time by HPLC. The absolute configurations of the naturally occurring acids and their phenacyl esters are assigned as R at the site of side-chain attachment by comparison of experimental specific rotations with corresponding values predicted using quantum chemical (QC) methods. The absolute configurations for 1a and 2a were independently verified by comparison of experimental Raman optical activity spectra with corresponding spectra predicted using QC methods. The configurational assignments of 1a and 2a and of the phenacyl ester of 1a were also confirmed by X-ray crystallography.
-
determination of the absolute configurations of chiral drugs using Chiroptical Spectroscopy
Molecules, 2016Co-Authors: Prasad L PolavarapuAbstract:Chiroptical Spectroscopy has emerged as a promising tool for the determination of absolute configurations and predominant conformations of chiral molecules in academic laboratories. This promise has led to the adaption of Chiroptical spectroscopic methods as valuable tools in chiral drug discovery research programs of the pharmaceutical industry. Most major pharmaceutical companies have invested in in-house Chiroptical Spectroscopy applications and reported successful outcomes. In the context of continuously increasing applications of Chiroptical Spectroscopy for chiral molecular structure determination, a review of recent developments and applications for chiral drugs is presented in this manuscript.
-
structural analysis using Chiroptical Spectroscopy insights and cautions
Chirality, 2016Co-Authors: Prasad L PolavarapuAbstract:Chiroptical Spectroscopy has evolved into a promising tool for chiral molecular structural determination in the last four decades. Determination of the absolute configurations (ACs) of bromochlorofluoromethane and [(2) H1 ,(2) H2 ,(2) H3 ]-neopentane demonstrated the enviable advantages of Chiroptical Spectroscopy. Furthermore, uncovering the errors in the ACs reported in the literature established a glimpse of what can be accomplished with the modern Chiroptical spectroscopic methods. Despite these triumphs, it is important to exercise caution in the practice of Chiroptical spectroscopic methods, because certain widely practiced approaches can lead to erroneous conclusions. Selected major accomplishments and special precautions needed for future applications are emphasized. Chirality 28:445-452, 2016. © 2016 Wiley Periodicals, Inc.
-
molecular structure determination using Chiroptical Spectroscopy where we may go wrong
Chirality, 2012Co-Authors: Prasad L PolavarapuAbstract:Chiroptical Spectroscopy is being widely used for determining the three-dimensional molecular structures (i.e., absolute configurations and conformations) of chiral molecules. The general procedure used with any of the Chiroptical spectroscopic methods is to analyze the experimental data using corresponding quantum chemical predictions. Such analysis involves multiple steps, including consideration of conformations, solvent effects, electronic transitions, stereoisomers, and experimental artifacts, each of which possesses certain limitations. These limitations, when not recognized or properly taken into account, may lead to incorrect conclusions. This review emphasizes on selected examples that illustrate the potential limitations in utilizing the Chiroptical spectroscopic methods. The examples used include hibiscus acid dimethylester, hibiscus acid disodium salt, 3,3′-diphenyl-[2,2′-binaphthalene]-1,1′-diol, tartaric acid esters, and 6,6′-dibromo-[1,1′-binaphthalene]-2,2′-diol. Chirality 24:909–920, 2012. © 2012 Wiley Periodicals, Inc.
Petr Bouř - One of the best experts on this subject based on the ideXlab platform.
-
recent trends in Chiroptical Spectroscopy theory and applications of vibrational circular dichroism and raman optical activity
ChemPlusChem, 2020Co-Authors: Monika Krupova, Jiři Kessler, Petr BouřAbstract:Chiroptical Spectroscopy exploring the interaction of matter with polarized light provides many tools for molecular structure and interaction studies. Here, some recent discoveries are reviewed, primarily in the field of vibrational optical activity. Technological advances results in the development of more sensitive vibrational circular dichroism (VCD), Raman optical activity (ROA) or circular polarized luminescence (CPL) spectrometers. Significant contributions to the field also come from the light scattering and electronic structure theories, and their implementation in computer systems. Finally, new Chiroptical phenomena have been observed, such as enhanced circular dichroism of biopolymers (protein fibrils, nucleic acids), plasmonic and resonance chirality-transfer ROA experiments. Some of them are not yet understood or attributed to instrumental artifacts so far. Nevertheless, these unknown territories also indicate the vast potential of the Chiroptical Spectroscopy, and their investigation is even more challenging.
-
chiral sensing of amino acids and proteins chelating with euiii complexes by raman optical activity Spectroscopy
Physical Chemistry Chemical Physics, 2016Co-Authors: Jiři Kessler, Petr BouřAbstract:Chiroptical Spectroscopy of lanthanides sensitively reflects their environment and finds various applications including probing protein structures. However, the measurement is often hampered by instrumental detection limits. In the present study circularly polarized luminescence (CPL) of a europium complex induced by amino acids is monitored by Raman optical activity (ROA) Spectroscopy, which enables us to detect weak CPL bands invisible to conventional CPL spectrometers. In detail, the spectroscopic response to the protonation state could be studied, e.g. histidine at pH = 2 showed an opposite sign of the strongest CPL band in contrast to that at pH = 7. The spectra were interpreted qualitatively on the basis of the ligand-field theory and related to CPL induced by an external magnetic field. Free energy profiles obtained by molecular dynamic simulations for differently charged alanine and histidine forms are in qualitative agreement with the spectroscopic data. The sensitivity and specificity of the detection promise future applications in probing peptide and protein side chains, chemical imaging and medical diagnosis. This potential is observed for human milk and hen egg-white lysozymes; these proteins have a similar structure, but very different induced CPL spectra.
-
determining the absolute configuration of two marine compounds using vibrational Chiroptical Spectroscopy
Journal of Organic Chemistry, 2012Co-Authors: Kathrin H Hopmann, Petr Bouř, Jaroslav Sebestik, Jana Novotna, Wenche Stensen, Marie Urbanova, Johan Svenson, John S Svendsen, Kenneth RuudAbstract:Chiroptical techniques are increasingly employed for assigning the absolute configuration of chiral molecules through comparison of experimental spectra with theoretical predictions. For assignment of natural products, electronic Chiroptical spectroscopies such as electronic circular dichroism (ECD) are routinely applied. However, the sensitivity of electronic spectral parameters to experimental conditions and the theoretical methods employed can lead to incorrect assignments. Vibrational Chiroptical methods (vibrational circular dichroism, VCD, and Raman optical activity, ROA) provide more reliable assignments, although they, in particular ROA, have been little explored for assignments of natural products. In this study, the ECD, VCD, and ROA Chiroptical spectroscopies are evaluated for the assignment of the absolute configuration of a highly flexible natural compound with two stereocenters and an asymmetrically substituted double bond, the marine antibiotic Synoxazolidinone A (SynOxA), recently isolated...
Minhaeng Cho - One of the best experts on this subject based on the ideXlab platform.
-
terahertz Chiroptical Spectroscopy of an α helical polypeptide a molecular dynamics simulation study
Journal of Physical Chemistry B, 2014Co-Authors: Jun Ho Choi, Minhaeng ChoAbstract:Vibrational Spectroscopy has provided incisive information on the structure of biological molecules. Here, using a molecular dynamics simulation method, infrared vibrational circular dichroism and vibrational optical rotatory dispersion spectra of a right-handed α-helix in the terahertz (THz) frequency range are calculated. Both the autocorrelation function of an electric dipole moment and the cross-correlation function of electric and magnetic dipole moments of the α-helix are calculated and Fourier-transformed to obtain THz absorption and optical activity spectra, which reveal characteristic features of the helical polypeptide structure. The anharmonicity and delocalized nature of the low-frequency modes in the THz frequency domain are taken into account to obtain statistically convergent results on the THz optical activity spectra. In addition, the magnitude of the THz vibrational optical activity signal of the α-helix is directly compared with those of typical, previously studied mid- and near-infrare...
-
terahertz Chiroptical Spectroscopy of an α helical polypeptide a molecular dynamics simulation study b
The Journal of Physical Chemistry, 2014Co-Authors: Jun Ho Choi, Minhaeng ChoAbstract:Vibrational Spectroscopy has provided incisive information on the structure of biological molecules. Here, using a molecular dynamics simulation method, infrared vibrational circular dichroism and vibrational optical rotatory dispersion spectra of a right-handed α-helix in the terahertz (THz) frequency range are calculated. Both the autocorrelation function of an electric dipole moment and the cross-correlation function of electric and magnetic dipole moments of the α-helix are calculated and Fourier-transformed to obtain THz absorption and optical activity spectra, which reveal characteristic features of the helical polypeptide structure. The anharmonicity and delocalized nature of the low-frequency modes in the THz frequency domain are taken into account to obtain statistically convergent results on the THz optical activity spectra. In addition, the magnitude of the THz vibrational optical activity signal of the α-helix is directly compared with those of typical, previously studied mid- and near-infrared chiral molecules. We anticipate that THz Chiroptical Spectroscopy that has not yet been demonstrated experimentally would provide highly important and complementary information on protein structure and dynamics.
-
amplifications in Chiroptical Spectroscopy optical enantioselectivity and weak value measurement
ChemInform, 2013Co-Authors: Hanju Rhee, Joseph S Choi, David J Starling, John C Howell, Minhaeng ChoAbstract:Chiroptical Spectroscopy utilizing left- and right-handed electromagnetic fields has been used to obtain stereochemical information on chiral molecules in condensed phases. However, due to weak signals (10−6 to 10−2 of absorption), not only are accurate measurements of Chiroptical signals difficult but also preferential excitation of one type of handed molecule over the other using chiral fields (i.e., optical enantioselectivity) is limited. Recently, methods have been developed to enhance Chiroptical signals and optical enantioselectivity by properly controlling polarization states, designing detection schemes, and modifying spatial properties of chiral fields. In the physics community, similar enhancements have been introduced using a quantum mechanical theory called “weak value measurement.” Here we provide examples of these techniques, corresponding enhancement mechanisms, and more importantly connections between them.
-
ultrafast Chiroptical Spectroscopy monitoring optical activity in quick time
Journal of Analytical Science and Technology, 2011Co-Authors: Hanju Rhee, Intae Eom, Minhaeng ChoAbstract:Optical activity Spectroscopy provides rich structural information of biologically important molecules in condensed phases. However, a few intrinsic problems of conventional method based on electric field intensity measurement scheme prohibited its extension to time domain technique. We have recently developed new types of optical activity spectroscopic methods capable of measuring Chiroptical signals with femtosecond pulses. It is believed that these novel approaches will be applied to a variety of ultrafast Chiroptical studies.
Ewoud De Gussem - One of the best experts on this subject based on the ideXlab platform.
-
synthesis of the natural product building block 5 3 bromophenyl 4 hydroxy 5 methylhexan 2 one and its chiral characterization by using Chiroptical Spectroscopy
ChemPhysChem, 2013Co-Authors: Wouter A Herrebout, Ewoud De Gussem, Jelle Cornelus, Sam Pieters, Dries Van Den Bossche, Johan Van Der Eycken, Patrick BultinckAbstract:The absolute configuration of 5-(3-bromophenyl)-4-hydroxy-5-methylhexan-2-one, an intermediate in the synthesis of various natural products, is assigned by using vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and optical rotatory dispersion (ORD). Experimental spectra were compared to density functional theory (DFT) calculations of the molecule with known configuration. These three techniques independently confirm that the absolute configuration is (S)-5-(3-bromophenyl)-4-hydroxy-5-methylhexan-2-one, thus enabling us to assign the absolute configuration with high reliability. The reliability of the VCD analysis was assessed quantitatively by using the CompareVOA program. We found that, in cases in which the agreement between theory and experiment was very good, a value of 10 cm(-1) for the triangular weighting function gave a more-realistic discriminative power between enantiomers than the default value of 20 cm(-1).
-
on the determination of the stereochemistry of semisynthetic natural product analogues using Chiroptical Spectroscopy desulfurization of epidithiodioxopiperazine fungal metabolites
Chemistry: A European Journal, 2011Co-Authors: Fanny L Cherblanc, Patrick Bultinck, Wouter A Herrebout, Ewoud De Gussem, Laura Alcazarfuoli, Elaine Bignell, Nadine Chapmanrothe, Robert S Brown, Henry S RzepaAbstract:Isolation and semisynthetic modification of the fungal metabolite chaetocin gave access to a desulfurized analogue of this natural product. Detailed Chiroptical studies, comparing experimentally obtained optical rotation values, electronic circular dichroism spectra, and vibrational circular dichroism spectra to computationally simulated ones, reveal the desulfurization of chaetocin to unambiguously proceed with retention of configuration. Consideration of the plausible mechanisms for this process highlighted inconsistencies in the stereochemical assignment of related molecules in the literature. This in turn allowed the stereochemical reassignment of the natural product analogue dethiodehydrogliotoxin.
Ewan W. Blanch - One of the best experts on this subject based on the ideXlab platform.
-
surface enhanced raman optical activity seroa
Chemical Society Reviews, 2008Co-Authors: Salim Abdali, Ewan W. BlanchAbstract:Raman optical activity (ROA) directly monitors the stereochemistry of chiral molecules and is now an incisive probe of biomolecular structure. ROA spectra contain a wealth of information on tertiary folding, secondary structure and even the orientation of individual residues in proteins and nucleic acids. Extension of ROA to an even wider range of samples could be facilitated by coupling its structural sensitivity to the low-concentration sensitivity provided by plasmon resonance enhancement. This leads to the new technique of surface enhanced ROA, or SEROA, which is complementary to both SERS and ROA. In this tutorial review, we present a survey of theoretical and experimental work undertaken to develop SEROA and discuss these efforts in the context of the ROA technique, and, based on the authors’ work, outline possible future directions of research for this novel Chiroptical Spectroscopy.
-
unfolded proteins studied by raman optical activity
Advances in Protein Chemistry, 2002Co-Authors: Laurence D. Barron, Ewan W. Blanch, Lutz HechtAbstract:Publisher Summary To understand the behavior of unfolded proteins it is necessary to employ experimental techniques able to discriminate between the dynamic true random coil state and more static types of disorder, including situations in which some ordered secondary structure might be present. One such technique is a novel Chiroptical Spectroscopy called Raman optical activity (ROA). This chapter reviews the application of ROA to studies of unfolded proteins. Because many discrete structure-sensitive bands are present in protein ROA spectra, the technique provides a fresh perspective on the structure and behavior of unfolded proteins and of unfolded sequences in proteins such as A-gliadin and prions that contain distinct structured and unstructured domains. It also provides new insight into the complexity of order in molten globule and reduced protein states and of the more mobile sequences in fully folded proteins such as β-lactoglobulin. The power of ROA in this area derives from the fact that, like the complementary technique of vibrational circular dichroism (VCD), it is a form of vibrational optical activity and so is sensitive to chirality associated with all the 3N−6 fundamental molecular vibrational transitions, where N is the number of atoms.