Avvaru Praveen Kumar

Recent Development on Spectroscopic Methods for Chiral Analysis of Enantiomeric Compounds

Abstract Chirality has become a central theme in scientific research and is an important task in the field of analytical chemistry. In the past few decades, demand for chiral recognition and separation has increased due to the importance of chirality in many fields such as pharmaceutics, chemical industry, agriculture, and biological and clinical analysis. A survey of the literature suggests that different spectroscopic methods are applied to achieve the analysis of chiral enantiomeric compounds. This article is intended to focus on chiral analysis and affords a brief overview on chiral analysis of enantiomeric compounds using different spectroscopic methods, such as fluorescence spectroscopy, mass spectrometry, and nuclear magnetic resonance spectroscopy. In this review, primarily the intensive studies of how chiral recognition is achieved and an updated view of the different strategies used up to recognize the chirality of enantiomeric compounds are discussed.

Determination of enantiomeric compositions of DOPA by tandem mass spectrometry using the kinetic method with fixed ligands

A fixed ligand (FL) version of the kinetic method was applied to rapid, simple, and accurate chiral analysis of DOPA, which is an important drug used for treatment of Parkinsons disease. Singly charged clusters containing the transition metal ion Cu(II), pyridyl ligands which serve as a fixed ligand, some amino acid as a reference, and the analyte DOPA were generated by electrospray ionization. The cluster ion of interest was mass-selected, and the kinetics of its competitive unimolecular dissociations was investigated in an ion trap mass spectrometer. The chiral selectivity (R(chiral)), the ratio of the two fragment ion abundances when the cluster contains one pure enantiomer of the analyte expressed relative to that for the other enantiomer, varies with fixed ligands, references, and transition metals. Chiral discrimination was optimized in 1,10-phenanthroline as a FL, L-Phe and L-Pro as a reference, and Cu(II) as a central metal ion. Quantitative determinations of the enantiomeric composition of DOPA were achieved using two-point calibration curves. The linear relationship between the logarithm of the fragment ion abundance ratio (ln R) and enantiomeric compositions (ee%) of the DOPA allows the determination of the chiral purity of enantiomeric mixtures.

Chiral zirconia magnetic microspheres as a new recyclable selector for the discrimination of racemic drugs

Separation of enantiomers of a chiral compound is one of the most interesting and challenging tasks because of their identical physical and chemical properties. Magnetic materials possessing chiral functionality on their surface can not only exhibit magnetic properties but also recognize chirality. Fe3O4@ZrO2 core-shell nano-materials have not been reported previously for chiral separation of racemates. Zirconia has been shown to be the most stable oxide mechanically, thermally and chemically, and shows better physical and chemical properties among inorganic metal oxides. The present work explores core-shell microspheres consisting of a Fe3O4 magnetic core covered by a zirconia shell (Fe3O4@ZrO2) which are immobilized with cellulose tris(3,5-dimethylphenylcarbamate) to get chiral zirconia magnetic microspheres (CZMMs). As-synthesized CZMMs have been applied for the separation of racemic chiral drugs and the results indicate the CZMMs are potential chiral nanomaterials for enantioseparations. Most importantly the synthesized CZMMs have shown an excellent recyclability and can be used for further chiral separations of different kinds of racemates.

Novel dithiols as capping ligands for CdSe quantum dots: optical properties and solar cell applications

Recently, organic ligands have been shown to play a significant role in optical and electronic properties of CdSe quantum dots and also in solar cell applications. We report organic dithiols as novel capping ligands for CdSe quantum dots (QDs). The organic dithiol compounds were designed in such a way that the two thiol groups of a dithiol (acts as a bidentate ligand) can bond directly to an inorganic CdSe QD surface which passivate effectively to show high optical efficiency by promoting interfacial charge transfer. This work would offer a direct and effective pathway to synthesize CdSe QDs that attaches dithiol ligands with aromatic functionality while maintaining the size and shape control of the CdSe QDs. The structure, crystallinity, and optical properties of the dithiol-capped CdSe QDs were analyzed by XRD, TEM, and photoluminescence. The covalent immobilization of dithiols onto CdSe QDs was confirmed by XPS, FT-IR, TGA, XRD and TEM characterizations. Further, the influence of dithiol-type capping ligands on the optical properties of highly luminescent CdSe QDs was investigated. It has been found that the growth rate and the photoluminescence intensity of CdSe QDs were strongly dependent on the type of dithiol ligands. We also experimentally investigated the use of dithiol-capped CdSe QDs in solar cells. The dithiol shell allows for the electron transport from the surface of the QDs, evidenced by better performance as CdSe QDs sensitized solar cells. The power conversion efficiency (η) of CdSe QDs reached up to 0.65%.

Isomeric Discrimination and Quantification of Thyroid Hormones, T3 and rT3, by the Single Ratio Kinetic Method Using Electrospray Ionization Mass Spectrometry

The single ratio kinetic method is applied to the discrimination and quantification of the thyroid hormone isomers, 3,5,3′-triiodothyronine and 3,3′,5′-triiodothyronine, in the gas phase, based on the kinetics of the competitive unimolecular dissociations of singly charged transition-metal ion-bound trimeric complexes [MII(A)(ref*)2-H]+ (MII = divalent transition-metal ion; A=T3 or rT3; ref* = reference ligand). The trimeric complex ions are generated using electrospray ionization mass spectrometry and the ions undergo collisional activation to realize isomeric discrimination from the branching ratio of the two fragment pathways that form the dimeric complexes [MII(A)(ref*)-H]+ and [MII(ref*)2-H]+. The ratio of the individual branching ratios for the two isomers Riso is found strongly dependent on the references and the metal ions. Various sets are tried by choosing the reference from amino acids, substituted amino acids, and dipeptides in combination with the central metal ion chosen from five transition-metal ions (CoII, CuII, MnII, NiII, and ZnII) for the complexes in this experiment. The results are compared in terms of the isomeric discrimination for the T3/rT3 pair. Calibration curves are constructed by relating the ratio of the branching ratios against the isomeric composition of their mixture to allow rapid quantitative isomer analysis of the sample pair. Furthermore, the instrument-dependence of this method is investigated by comparing the two sets of results, one obtained from a quadrupole ion trap mass spectrometer and the other from a quadrupole time-of-flight mass spectrometer.

High field conduction in glassy Se90Sb8Ag2 alloy: Applicability of Meyer-Neldel rule

The present paper reports the measurements of high field conduction in glassy Se90Sb8Ag2 alloy. For this purpose, I-V characteristics have been taken at certain fixed temperatures. The results indicate that super - ohmic behaviour is observed at high electric fields. The results fit well with the theory of space charge limited conduction for the uniform distribution of traps. From the temperature dependence of conductivity, activation energy is obtained at different electric fields, which is found to be field dependent. Pre-exponential factor is found to depend on the activation energy and obeys Meyer-Neldel rule.The present paper reports the measurements of high field conduction in glassy Se90Sb8Ag2 alloy. For this purpose, I-V characteristics have been taken at certain fixed temperatures. The results indicate that super - ohmic behaviour is observed at high electric fields. The results fit well with the theory of space charge limited conduction for the uniform distribution of traps. From the temperature dependence of conductivity, activation energy is obtained at different electric fields, which is found to be field dependent. Pre-exponential factor is found to depend on the activation energy and obeys Meyer-Neldel rule.

Role of Ag additives on light-induced metastable defects in a Se–In glassy system

Abstract The paper reports the role of Ag additives on light induced metastable defects in Se–In glassy alloys using a well-known thermally stimulated current (TSC) technique. Amorphous thin films of Se90In10−xAgx (x = 0, 2, 4, 8) were prepared by thermal evaporation. Measurements were made in the given thin films prior to and after exposing amorphous thin films to white light for different exposure times (0–1.5 hrs). The density of light induced metastable defects increases with exposure time, and the fractional increase in light induced metastable defect density decreases as Ag concentration increases.