An electronic circular dichroism spectroscopy method for the quantification of L- and D-amino acids in enantiomeric mixtures.
Ontology highlight
ABSTRACT:
SUBMITTER: Ding R
PROVIDER: S-EPMC8074886 | biostudies-literature |
REPOSITORIES: biostudies-literature
Similar Datasets
Project description:Ketone handedness was discriminated using circular dichroism (CD) spectroscopy by monitoring the metal-to-ligand charge transfer (MLCT) bands of complexes between [Cu(I)((S)-1)(CH(3)CN)(2)]PF(6) and derivatized α-chiral cyclohexanones (4). This method was able to quantify the enantiomeric excess of unknown samples using a calibration curve, giving an absolute error of ±7%. The analysis was fast, allowing potential application of this assay in high-throughput screening (HTS).
| S-EPMC3097997 | biostudies-literature
Project description:Over 300 chiral drug substances lack official United States Pharmacopeia (USP) methods for the enantiomeric purity determination. Because enantiomeric analysis typically requires specialized methods for each drug compound, developing protocols for each of these 300+ substances would be an expensive and laborious endeavor. Alternatively, if a detector capable of determining the enantiomeric composition without chiral separation could be used with certain drug compounds, this could be implemented relatively rapidly into official testing monographs. Circular dichroism (CD) detection following HPLC (HPLC-CD) has been proposed for this purpose but studies performed thus far have not prioritized its compatibility with validated regulatory methods. In this study, HPLC-CD was evaluated for enantiomeric purity determinations of 13 drug substances using HPLC methods consistent with assay protocols described in United States Pharmacopeia (USP) monographs. Of these selected substances, three (sitagliptin, timolol, and levalbuterol) showed no CD activity and one other (levofloxacin) could not be analyzed due to incompatibility of the mobile phase with the CD detector. For the remaining 9 substances, method validation was performed to determine the linearity, accuracy, precision and limits of quantitation of enantiomer impurities, which was compared to limits established by USP. It was found that enantiomeric impurities for four substances (pramipexole, levocetirizine, (S)-citalopram, and tolterodine) could be quantitatively determined at levels suitable to USP specifications. This analysis demonstrated that HPLC-CD does provide an effective enantiomeric characterization strategy for compatible chiral compounds, and can be implemented quickly and economically compared to traditional column-dependent chiral separation or derivatization methods.
| S-EPMC6033541 | biostudies-literature
Project description:Asymmetric reactions often need to be evaluated during the synthesis of chiral compounds. However, traditional evaluation methods require the isolation of the individual enantiomer, which is tedious and time-consuming. Thus, it is desirable to develop simple, practical online detection methods. We developed a method based on high-performance liquid chromatography-electronic circular dichroism (HPLC-ECD) that simultaneously analyzes the material conversion ratio and absolute optical purity of each enantiomer. In particular, only a reverse-phase C18 column instead of a chiral column is required in our method because the ECD measurement provides a g-factor that describes the ratio of each enantiomer in the mixtures. We used our method to analyze the asymmetric hydrosilylation of β-enamino esters, and we discussed the advantage, feasibility, and effectiveness of this new methodology.
| S-EPMC5333115 | biostudies-literature
Project description:Intrinsically disordered proteins (IDPs) are comprised of significant numbers of residues that form neither helix, sheet, nor any other canonical type of secondary structure. They play important roles in a broad range of biological processes, such as molecular recognition and signalling, largely due to their chameleon-like ability to change structure from unordered when free in solution to ordered when bound to partner molecules. Circular dichroism (CD) spectroscopy is a widely-used method for characterising protein secondary structures, but analyses of IDPs using CD spectroscopy have suffered because the methods and reference datasets used for the empirical determination of secondary structures do not contain adequate representations of unordered structures. This work describes the creation, validation and testing of a standalone Windows-based application, DichroIDP, and a new reference dataset, IDP175, which is suitable for analyses of proteins containing significant amounts of disordered structure. DichroIDP enables secondary structure determinations of IDPs and proteins containing intrinsically disordered regions.
| S-EPMC10409736 | biostudies-literature
Project description:A method for discriminating between α-chiral primary amine enantiomers is reported. The method utilizes circular dichroism (CD) spectroscopy and a sensing ensemble composed of 2-formyl-3-hydroxypyridine (4) and Fe(II)(TfO)(2). Aldehyde 4 reacts rapidly with chiral amines to form chiral imines, which complex Fe(II) to form a series of diastereomeric octahedral complexes that are CD-active in both the UV and visible regions of the spectrum. NMR studies showed that for enantiomerically pure imine complexes, the Δ-fac isomer is preferred. A statistical analysis of the distribution of stereoisomers accurately modeled the calibration curves for enantiomeric excess (ee). CD signals appearing in the UV region were bisignate, and the nulls of the CD signals were coincident with maxima in the UV spectrum, consistent with exciton coupling. Time-dependent density functional theory and semiempirical calculations confirmed that the CD signals in the UV region arise from coupling of the π-π* transitions in the imine chromophores and that they can be used to describe the signs and magnitudes of the curves accurately. The CD signals in the visible region arise from metal-to-ligand charge-transfer bands, and these signals can be used to determine the ee values of chiral amines with an average absolute error of ±5%. Overall, the strategy presented herein represents a facile in situ assembly process that uses commercially available simple reagents to create large optical signals indicative of ee values.
| S-EPMC3329375 | biostudies-literature
Project description:Circular dichroism (CD) spectropolarimeters typically employ one photoelastic modulator. However, spectropolarimeters employing two or even four modulators are more versatile and can be used to subvert common measurement errors arising from imperfectly isotropic samples or sample holders. Small linear anisotropies that can cause large errors in CD measurement can be associated with multi-well sample holders. Thus, high-throughput CD analyses in multi-well plates have not yet been demonstrated. One such application is the determination of enantiomeric excess of a library of reaction products. Herein, a spectropolarimeter employing four photoelastic modulators and a translation stage was used to determine the enantiomeric excess of a family of chiral amine complexes much more rapidly than could be achieved with a robotic fluid injection system. These experiments are proof of concept for high-throughput CD analysis. In practice, commercially available glass bottomed well plates are sufficiently strain free such that a simple instrument with just one photoelastic modulator and a vertical optical train should be able to deliver the CD without special considerations given herein. On the other hand, polystyrene well plates cannot be used in this way.
| S-EPMC4224325 | biostudies-literature
Project description:Primary methods play an important role in metrology. They can be used for the value assignment of certified reference materials, enabling the accuracy and comparability of the measurement. A novel potential primary method for enantiomer quantitation based on high-performance liquid chromatography-circular dichroism is described using L-phenylalanine as an example. The optimal quantitation range of L-Phe was from 0.1?mg/g to 1.2?mg/g, where both the relative bias and method variance were lower than 1%. The LOD and LOQ were 4??g/g and 30??g/g, respectively. The proposed method was also applied to the determination of the mass fraction of pure porcine insulin in solid. The average mass fraction obtained was 0.922?g/g with a RSD of 1.5%, and the associated relative uncertainty is 3.8% (k?=?2), which agreed well with that obtained from the traditional isotope dilution mass spectrometry method. The LOD and LOQ for insulin quantitation were found to be 0.12?mg/g and 0.44?mg/g, respectively. The proposed method can be entirely described and understood by equations and a complete uncertainty statement can be defined in SI units.Therefore, it may be a potential primary method useful for the quantification of chiral compounds and proteins, and a supplementary method to the traditional isotope dilution mass spectrometry approach.
| S-EPMC5943587 | biostudies-literature
Project description:A curated library of circular dichroism spectra of 23 G-quadruplexes of known structure was built and analyzed. The goal of this study was to use this reference library to develop an algorithm to derive quantitative estimates of the secondary structure content of quadruplexes from their experimental CD spectra. Principal component analysis and singular value decomposition were used to characterize the reference spectral library. CD spectra were successfully fit to obtain estimates of the amounts of base steps in anti-anti, syn-anti or anti-syn conformations, in diagonal or lateral loops, or in other conformations. The results show that CD spectra of nucleic acids can be analyzed to obtain quantitative structural information about secondary structure content in an analogous way to methods used to analyze protein CD spectra.
| S-EPMC5920796 | biostudies-literature
Project description:Intrinsically disordered proteins lack a stable tertiary structure and form dynamic conformational ensembles due to their characteristic physicochemical properties and amino acid composition. They are abundant in nature and responsible for a large variety of cellular functions. While numerous bioinformatics tools have been developed for in silico disorder prediction in the last decades, there is a need for experimental methods to verify the disordered state. CD spectroscopy is widely used for protein secondary structure analysis. It is usable in a wide concentration range under various buffer conditions. Even without providing high-resolution information, it is especially useful when NMR, X-ray, or other techniques are problematic or one simply needs a fast technique to verify the structure of proteins. Here, we propose an automatized binary disorder-order classification method by analyzing far-UV CD spectroscopy data. The method needs CD data at only three wavelength points, making high-throughput data collection possible. The mathematical analysis applies the k-nearest neighbor algorithm with cosine distance function, which is independent of the spectral amplitude and thus free of concentration determination errors. Moreover, the method can be used even for strong absorbing samples, such as the case of crowded environmental conditions, if the spectrum can be recorded down to the wavelength of 212 nm. We believe the classification method will be useful in identifying disorder and will also facilitate the growth of experimental data in IDP databases. The method is implemented on a webserver and freely available for academic users.
| S-EPMC9110821 | biostudies-literature
Project description:Ultraviolet (UV) synchrotron radiation circular dichroism (SRCD) spectroscopy has made an important contribution to the determination and understanding of the structure of bio-molecules. In this paper, we report an innovative approach that we term time-resolved SRCD (tr-SRCD), which overcomes the limitations of current broadband UV SRCD setups. This technique allows accessing ultrafast time scales (down to nanoseconds), previously measurable only by other methods, such as infrared (IR), nuclear magnetic resonance (NMR), fluorescence and absorbance spectroscopies, and small angle X-ray scattering (SAXS). The tr-SRCD setup takes advantage of the natural polarization of the synchrotron radiation emitted by a bending magnet to record broadband UV CD faster than any current SRCD setup, improving the acquisition speed from 10 mHz to 130?Hz and the accessible temporal resolution by several orders of magnitude. We illustrate the new approach by following the isomer concentration changes of an azopeptide after a photoisomerization. This breakthrough in SRCD spectroscopy opens up a wide range of potential applications to the detailed characterization of biological processes, such as protein folding and protein-ligand binding.
| S-EPMC6823104 | biostudies-literature