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The paper proposes a new stochastic multiobjective technoeconomic model for integrating photovoltaic (PV) and wind energy resources in electricity price (EP)‐driven distribution systems. The primary goal of this paper is to determine the optimal location and capacity for renewable energy‐based distributed generation, specifically PV and wind resources, while considering weather and system uncertainties. These uncertainties include stochastic variations in PV illumination intensity, wind speed, EP, and load fluctuations. To address these uncertainties, the paper employs scenario modeling techniques named as Latin hypercube sampling with Cholesky decomposition. This technique generates multiple correlated scenarios that represent uncertain variables. Subsequently, a scenario reduction technique is applied to identify the scenario with the highest probability. Later, a mathematical model is developed to minimize an objective function that encompasses various factors like system losses, node voltage deviations, the cost of purchasing power from the grid; and simultaneously maximize the total annual energy savings. The objective is to find optimal solutions that strike a balance between different objectives. To obtain an efficient optimum solution, this paper employs an effective meta‐heuristic technique named as JAYA algorithm. The results obtained by the JAYA algorithm are juxtaposed with those obtained using particle swarm optimization and genetic algorithm techniques. The proposed method is evaluated using Institute of Electrical and Electronics Engineers (IEEE) 33‐node and IEEE 69‐node test feeders to validate its feasibility and effectiveness. However, the effectiveness of the proposed method is not limited to any size of test systems. [ABSTRACT FROM AUTHOR]

The heat transfer from the low latitudes to high latitudes is responsible for maintaining the earth's climate dynamics. Thus, deciphering the possible mechanism driving the variability of the Indian summer monsoon (ISM) during the Holocene Epoch has been critical to understand the hydroclimatic changes of the low latitudes. Despite several efforts, the teleconnection of ISM with the global climate dynamics remains under-represented and poorly understood. The present study aims to delineate the ISM variability and its possible forcing mechanism from western India (Gujarat). In this study, a sediment core (~65 cm long) was raised from the Jaffrabad mudflat (MIT) in western Gujarat. The sediment samples were subjected to geochemical analysis to investigate paleomonsoon, paleo-sediment source and paleoweathering changes. The results show that, with the addition of intermediate sources, the sediments were principally derived from the hinterland's Deccan basalts. Further, the study suggested a warm and wet climate due to strong ISM during 10,650−5500 cal yr BP associated with the solar as well as orbital forcings. The weak monsoon during 5500−2700 cal yr BP has been linked with southward migration of the Intertropical Convergence Zone (ITCZ) along with the increased El Niño-like conditions. Further, the wavelet analysis revealed that a combined influence of solar, orbital and North Atlantic forcings led to monsoon variability along western India, during the Holocene Epoch. By reconciling the geochemical proxies, the present study has implications in the reconstruction of paleomonsoon and establishing the possible teleconnection with the global climate system. [ABSTRACT FROM AUTHOR]

Worldwide thin layer chromatography (TLC) is still in very much use in various different application fields (e.g. natural products chemistry, monitoring the organic/enantioselective synthesis, and routine analysis in analytical laboratories). Herein is presented an account of the efficient resolution/enantioseparation of racemic and non-racemic mixtures of several different types of active pharmaceutical ingredients, and biologically important compounds by TLC using a direct approach along with quantitative determination and isolation of native forms via non-covalent diastereomer formation. Different approaches and mechanisms of direct enantioseparation using different chiral reagents are discussed. It provides a route for a wide range of chiral stationary phases (CSPs) which can be in-home thought out, produced, assessed, and customized. The achievements and new challenges in the field are presented. Besides, it presents a very useful coverage for the non-specialists to the subject who want to understand where this study fits into the existing literature in this general area. [ABSTRACT FROM AUTHOR]

Enantiorecognition and resolution are of essential importance in many diverse areas of science. Whenever there arises a need to analyze/investigate enantiomers in different situations chromatography stands up in our minds immediately. Nevertheless, chemoselective and enantioselective recognition/discrimination (without going for separation) constitutes a different perception and requirement. The techniques using chiroptical sensing cause detection based on molecular interactions induced in different manners. Enantioselective sensing of monosaccharides in γ‐cyclodextrin assembly and by diboronic acid based fluorescent sensors, application of bi‐naphthol and H8BINOL based sensors and dendrimers, metal‐to‐ligand charge transfer transitions in CD, exciton‐coupled circular dichroism, surface enhanced Raman spectroscopy, and enantioselective indicator displacement sensor arrays for enantioselective recognition/detection of chiral organic compounds, such as amines, amino acids/alcohols, and hydroxycarboxylic acids have been discussed in progressive manner with mechanistic explanations, wherever available. Besides, the chiroptical vs LC approach has been discussed. The present paper is focused on certain different non‐chromatographic optical techniques and aims to extend an understanding and a view to consider such techniques which have been successful in selective detection, and determination of absolute configuration and enantiomeric excess, (without resorting to separation vis‐à‐vis LC) and that have potential use in high‐throughput chiral assay and combinatorial search for asymmetric catalysts and reagents. [ABSTRACT FROM AUTHOR]

Beryllium-10 (10Be) has proven to be an essential tool for building chronology and understanding millennial-scale surface processes. Measurements in both the water column and authigenic fractions from various archives (such as surface sediments and Fe-Mn crusts) have provided valuable information on processes regulating Be isotopic distribution in the global oceans. Unlike the Pacific and the Atlantic Oceans, Be isotopic measurements in the Indian Ocean are sparse. Here, based on Be isotopic measurements on surface sediments from the central and northern Indian Ocean, an attempt is made to understand the processes controlling spatial Be isotopic distribution. Our data from the northern Indian Ocean suggests that terrestrial input is one of the primary contributors of 9Be. Owing to higher terrestrial flux, the sediment samples from the Bay of Bengal show higher 9Be concentrations and lower 10Be/9Be ratios. Our study suggests that scavenging by sediment particles plays a vital role in the distribution of Be isotopes in well-mixed open ocean water. Between carbonates and clay particles, carbonates are less efficient in scavenging Be from the water column. [ABSTRACT FROM AUTHOR]

• Associations of common genetic risk variants with GDM risk in the north Indian population were investigated. • Relative risk, population penetrance and attributable risk for risk allele variants was higher in GDM mother. • Four variants FTO, PPARG2, SLC30A8, and TCF7L2 were significantly associated with BMI, HbA1c and insulin. • Four variants FTO, PPARG2, SLC30A8, and TCF7L2 were significantly associated with GDM in North Indian population. The current study sought to investigate the associations of common genetic risk variants with gestational diabetes mellitus (GDM) risk in the north Indian population and to evaluate their utility in identifying GDM cases. A case-control study, including 300 pregnant women, was included, and clinical and pathological information was collected. The amplification-refractory mutation system (ARMS) was used for genotyping four single nucleotide polymorphisms (SNPs), namely FTO (rs9939609), PPARG2 (rs1801282), SLC30A8 (rs13266634), and TCF7L2 (rs12255372). The odds ratio and confidence interval were determined for each SNP in different genetic models. Further, attributable risk, population penetrance, and relative risk were also calculated. The risk allele A of FTO (rs9939609) poses a two times higher risk of GDM (p = 0.02, OR = 2.5). The CG and GG genotypes of PPARG2 (rs1801282) have half a lower risk of GDM. In SLC30A8 (rs13266634), the recessive model analysis showed a two times higher risk of having GDM, while the recessive model (TT vs. GG + GT) analysis in TCF7L2 (rs12255372) indicates a lower risk of GDM. Finally, the relative risk, population penetrance, and attributable risk for risk allele in all four variants was higher in GDM mothers. All four polymorphisms were found to be significantly associated with BMI, HbA1c, and insulin. Our study first time confirmed a significant association with GDM for four variants, FTO, PPARG2, SLC30A8, and TCF7L2, in the North Indian population. [ABSTRACT FROM AUTHOR]

Twenty nail dystrophy refers to the condition of trachyonychia affecting all the twenty nails. The term trachyonychia is used to describe thin brittle nails with excessive longitudinal ridging. Treatment of twenty nail dystrophy is difficult due to poor bioavailability of drugs in nails. Tofacitinib is novel JAK-STAT inhibitor that has been used successfully for the treatment of nail dystrophy with alopecia areata suggests the possibility of the drug being used for twenty nail dystrophy. [ABSTRACT FROM AUTHOR]

Chronic acral hyperkeratotic dermatosis includes several conditions such as lichen simplex chronicus (LSC), hypertrophic lichen planus (HLP), psoriasis vulgaris (Ps), acral acanthosis nigricans, acquired zinc deficiency, and necrolytic acral erythema (NAE). LSC, Ps, and HLP respond to conventional treatments such as topical corticosteroids, immuno-modulators such as tacrolimus, and oral methotrexate. Zinc-responsive acral hyperkeratosis is a novel entity that resembles the above mentioned diagnoses clinically but fails to respond to the above treatment options. NAE is a rare condition, commonly associated with hepatitis C virus infection and manifest similar clinical features of zinc-responsive acral hyperkeratosis, but differs histopathologically. Both conditions show a good response to oral zinc supplementation. As there is a paucity of literature on zinc-responsive acral hyperkeratosis, we are highlighting the case. [ABSTRACT FROM AUTHOR]

The role of messenger RNA (mRNA) in biological systems is extremely versatile. However, it’s extremely short half-life poses a fundamental restriction on its application. Moreover, the translation efficiency of mRNA is also limited. On the contrary, circular RNAs, also known as circRNAs, are a common and stable form of RNA found in eukaryotic cells. These molecules are synthesized via back-splicing. Both synthetic circRNAs and certain endogenous circRNAs have the potential to encode proteins, hence suggesting the potential of circRNA as a gene expression machinery. Herein, we aim to summarize all engineering aspects that allow exogenous circular RNA (circRNA) to prolong the time that proteins are expressed from full-length RNA signals. This review presents a systematic engineering approach that have been devised to efficiently assemble circRNAs and evaluate several aspects that have an impact on protein production derived from. We have also reviewed how optimization of the key components of circRNAs, including the topology of vector, 5′ and 3′ untranslated sections, entrance site of the internal ribosome, and engineered aptamers could be efficiently impacting the translation machinery for molecular and metabolic reprogramming. Collectively, molecular and metabolic reprogramming present a novel way of regulating distinctive cellular features, for instance growth traits to neoplastic cells, and offer new possibilities for therapeutic inventions. [ABSTRACT FROM AUTHOR]

The climate variability over western India has been significantly influenced by the perturbations in the Indian summer monsoon (ISM) and thus, provides a crucial platform to investigate the paleomonsoon variations, weathering intensity, and sediment source. The mudflats of southern Saurashtra, western India are deprived of perennial rivers, but the region receives terrestrial contribution exclusively due to activation of seasonal rivers during the monsoon. In the present study, an attempt has been made to investigate the paleomonsoon and palaeoweathering using various geochemical proxies (detrital, productivity, redox, and weathering) on the mudflat sediment core of southern Saurashtra, western Gujarat. The core is chronologically constrained by 14C, 210Pb, and 137Cs dating techniques. The study suggests ISM strengthening during 2000–1800 cal yr BP with intermittent marginal ISM weakening during 1950–1970 cal yr BP and 1930–1890 cal yr BP associated with the reduced solar irradiance. Further, ISM weakening has been invoked during Dark Age Cold period (1800–1300 cal yr BP) and Little Ice Age (800–200 cal yr BP) interrupted by a marginal ISM strengthening during Medieval Warm period and the last two centuries witness climate warming. Based on historical rainfall data and Al2O3, an intermittent strengthening of ISM during 90–30 cal yr BP has been suggested while a gradual increase in the weathering intensity synchronous to the rise in sea surface temperature (SST) during the last 200 cal yr BP revealed the role of temperature on the intensity of chemical weathering in the study area. In spite of changes in the geochemical proxies as a function of ISM fluctuations, the palaeoweathering intensities has remained nearly consistent wherein the chemical weathering was less operative and accompanied by the deposition of texturally immature sediments. The sediments of Diu mudflat indicate mafic signatures thereby underscoring a major contribution of the Deccan basalts along with other variable sources. [ABSTRACT FROM AUTHOR]

Summary: In this paper, an optimal linear quadratic regulator (LQR)‐based integral controller (i.e., linear quadratic integral [LQI]) has been designed with an innovative approach for the tracking problems of a wind‐driven doubly‐fed induction generator (DFIG) system. The main objective of this controller is to reject the deviations that occurred in the DFIG powers together with the DC‐link voltage due to the perturbations in the stator voltage. The purpose of the inclusion of integral action with the well‐known modern optimal controller LQR is to guarantee zero steady‐state error for disturbance rejection/set‐point tracking. Further, the genetic algorithm (GA) technique is included for the optimal design of the LQI weighting matrices, which rapidly, as well as effectively rejects the disturbances from the system by regulating the augmented state variables. Therefore, to overcome these issues we have chosen the appropriate control model, which controls as a whole, that is, a multi‐input‐multi‐output (MIMO) system. The DFIG system is a MIMO system, which has been modeled in a state‐space approach in the d‐q axes rotating frame of reference. To examine the effectiveness and robustness of the suggested control strategy, small‐signal stability has been done by eigen values and participation factors method on digital simulations in the MATLAB/Simulink environment. Furthermore, the optimal control solutions have been tested under the various larger perturbations in the stator voltage and the mechanical torque. The comparative simulation results among the different controllers show that the proposed controller greatly enhances the dynamic performances and the robustness of the DFIG‐based wind energy systems (WES). [ABSTRACT FROM AUTHOR]

PRC2 is a transcriptional repressive complex and its inhibitors have been found to have a potential role in cancer therapeutics. In this study, SUZ12 - a subunit of PRC2 complex was studied with the help of protein-ligand docking for various naturally occurring plant steroids and flavonoids. The structure of SUZ12 was modeled by homology modeling tool and validated with the help of various computational tools. The best model was selected based on the percentage of residues that are present in either of favored, allowed or disallowed regions using the Ramachandran Plot. This was further followed by docking studies with plant-based flavonoids and phytosterols (Tangeritin, Apigenin, Diosgenin, Luteolin, and Guggulsterone) using Patchdock and YASARA docking software. Luteolin and Guggultserone were observed to have the highest binding energies towards SUZ12 and Tageratin scored the lowest. Luteolin, Guggulsterone, and apigenin showed binding at the zinc finger domain. Thus, this virtual screening for binding of various compounds identified that luteolin and apigenin might disrupt the secondary structure of SUZ12 protein and thus hamper the functioning of PRC2. This analysis can be further used for the designing of potent drugs against diseases caused by hyperactivation of the PRC2 complex, thereby aiding knowledge in the field of research. [ABSTRACT FROM AUTHOR]

For the last few decades, there has been rising concern across the globe about depletion of conventional energy sources and the consequent energy crisis. Simultaneously, search for other energy sources, such as wind energy and solar energy, has been gaining momentum as well. Particularly, wind energy has become a viable alternative source of energy. As the wind power penetration continually increases, stability of the grid‐connected doubly fed induction generator (DFIG)‐based wind turbine system has become essential for wind power generation. This study presents the influence of a grid‐side converter current dynamics on the small‐signal stability by using the eigenvalue and participation factor technique which provides five distinct system modes, namely mechanical (M), stator electrical, converter electrical, electro‐mechanical and non‐oscillatory mode. In addition, flexible alternating current transmission system device has been incorporated to examine its effect on the system stability at different compensation levels. Furthermore, the sensitivity of a grid‐connected DFIG system concerning system parameter variations and its impact on stability of the system modes has been investigated. Simulations have been carried out in the MATLAB/Simulink environment. [ABSTRACT FROM AUTHOR]

The limited extent of instrumental records going back in time and control of various climatic variables on Indian Summer Monsoon (ISM) has reinvigorated the unprecedented effort in documenting climate changes for the last two millennia. Although extensive studies on late Holocene ISM reconstruction are available, comprehensive understanding on the influence of natural forcing factors on ISM and their plausible signatures is not arrived at till date. In view of this, the present study attempts to address the ISM variations during the last two millennia with special emphasis on natural forcing factors (solar and volcanic) and climate variables (ocean-atmospheric processes). The Saurashtra peninsula of Gujarat in western India receives majority of rainfall during ISM and hence it provides an ideal test-bed to study the ISM variability. A multiproxy approach has been adopted on a sediment core retrieved from the active mudflat of Southern Saurashtra which was chronologically supported by 210Pb, 137Cs and 14C. The present study demonstrates vacillating climate with strengthened ISM during Roman Warm Period and Medieval Warm Period (2000−950 cal yr BP) as a result of increased solar irradiance interrupted by reduced ISM during Dark Ages of Cold Period (∼1500 cal yr BP). The plausible occurrence of volcanic eruption before the onset of Little Ice Age (500−200 cal yr BP) caused the southward migration of Intertropical Convergence Zone (ITCZ) leading to enhanced western disturbances in the study area thereby resulting in cool and wet climate in the region. The study also emphasizes the increased El Nino events with gradual decline in the ISM since Little Ice Age. Further, the study underscores a climate warming during the last two centuries that corroborates well with the instrumental records. Thus, the present study has implication towards understanding the significant role of volcanic activity and solar variability in controlling the millennia scale climate oscillations with additional feedback mechanisms. [ABSTRACT FROM AUTHOR]

Abstract A 1 MV Accelerator Mass Spectrometer (AMS) has been installed at Physical Research Laboratory (PRL), Ahmedabad, India which is tuned for measurement of 14C, 10Be and 26Al and is fully operational. The facility is acronymed as PRL-AURiS (PRL-Accelerator Unit for Radioisotope Studies). Measurements on various reference materials, have demonstrated its ability to achieve precision for 14C, 10Be and 26Al to 2.2, 4.8 and 5.3‰ levels, with background values of 3.9 × 10−16, 5.8 × 10−16 and 1.6 × 10−14 respectively. [ABSTRACT FROM AUTHOR]

A successful attempt was made to fabricate a thin foil of natural Mo target on a thick Au backing with Indium in between to improve adhesion between the foils. Rolling at elevated temperature was considered to fabricate Mo foil while gold foil was fabricated employing conventional rolling technique. The heating of Mo foil under natural environment lead to the oxidation or carbonization on foil surface which was confirmed through Energy Dispersive X-ray Spectroscopy (EDS) measurements. Indium of thickness ∼ 86 μ g /cm2 was evaporated on Mo foil to improve adhesion between Mo and Au foils. The characterization of fabricated thin Mo foil was done using the Energy Dispersive X-ray Spectroscopy (EDS) and the Scanning Electron microscope (SEM) techniques. Thickness measurement of the target (Mo-Au) was done using Energy Dispersive X-ray Fluorescence (EDXRF) technique, in the measurements the thickness of the Mo foil and of gold backing are found out to be 1.3 mg/cm2 and 9 mg/cm2 respectively. • Cold Rolling method for rolling of gold foil. • Hot rolling method for rolling of hard material Molybdenum. • Use of very thin layer of Indium to improve adhesion. • EDX and SEM measurements for quality testing of target prepared. • Use of EDXRF technique for accurate thickness measurement of different layers of target. • Composite target for nuclear physics experiment. [ABSTRACT FROM AUTHOR]

Direct enantiomeric resolution of commonly used five racemic β-adrenolytics, namely, bisoprolol, atenolol, propranolol, salbutamol and carvedilol has been achieved by thin layer chromatography using bovine serum albumin (BSA) as chiral additive in stationary phase. Successful resolution of the enantiomers of all racemic β-adrenolytics was achieved by use of different composition of simple organic solvents having no buffer or inorganic ions. The effect of variation in pH, temperature, amount of BSA as the additive, and composition of mobile phase on resolution was systematically studied. Spots were visualized in iodine vapors. Native enantiomers for each of the five analytes were isolated and identified and their elution order was determined. The limit of detection was found to be 0.7, 1.2, 0.84, 1.6 and 0.9 μg (per spot) for each enantiomer of bisoprolol, atenolol, propranolol, salbutamol and carvedilol, respectively. [ABSTRACT FROM AUTHOR]

Herein, enantioseparation of two anti-inflammatory drugs, namely, (RS)-ketorolac and (RS)-etodolac, commonly marketed and administered as racemates, was achieved by RP-HPLC. This method provided very low limit of detection values (3.69 and 3.02 ng mL−1 for diastereomeric derivatives of (R)- and (S)-Ket, respectively) as compared to those reported in literature. (S)-Naproxen benzotriazole ester, which was used as a chiral reagent, was synthesized and characterized by UV, IR, and 1H NMR spectroscopies, elemental analysis, and polarimetry. The diastereomeric derivatives were synthesized via microwave irradiation, separated on an analytical scale by RP-HPLC, and then isolated by preparative HPLC. The use of a mobile phase containing methanol and aqueous triethylamine phosphate (TEAP) in the isocratic mode was found to be successful for the separation of diastereomeric derivatives, and the separation conditions with respect to pH, flow rate, and buffer concentration were optimized. The diastereomeric derivatives were characterized, and their absolute configuration was established. Hydrolysis of the derivatives provided native enantiomers under mild reaction conditions. This study describes the successful enantioseparation of the above mentioned two analytes by semi-preparative HPLC with easy recovery of the native enantiomers without racemization and with the establishment of molecular asymmetry. [ABSTRACT FROM AUTHOR]

This paper deals with a genetic algorithm (GA)-based linear quadratic regulator (LQR) controller to improve the dynamic response, stability, and robustness of the doubly fed induction generator (DFIG) system at various stator voltage disturbances. The complete model has been represented by a state-space model. This helps to optimally control all the states through the full-state feedback LQR controller. GA is employed in the LQR algorithm for optimal tuning of the Q and R matrices. For finding out the effectiveness of the proposed controller, its dynamic response has been compared with proportional integral (PI) and LQR controllers. The simulation results indicate that the proposed controller has better performance in comparison to the PI and LQR controllers in terms of peak value, settling time, rise time, and steady-state values of the DFIG outputs. The stability and robustness of the study system have also been investigated by the eigenvalue and participation factor analyses. [ABSTRACT FROM AUTHOR]

Quaternary paleoclimatic and paleomagnetic reconstructions using marine sediment cores require appropriate dating techniques in order to build the chronology. Due to the widespread use of the radiocarbon dating method, the majority of studies focusing on paleo reconstructions are restricted to the last 50 ka. There are very few methods those can be used to obtain chronology beyond the radiocarbon dating limit. Marine sediment cores as old as 10–12 Ma can be dated using 10Be because of its comparatively long half-life of 1.39 Ma. However, there are various intricacies which restrict this method to date young marine sediment cores (<1 Ma). In this study, we provide the findings of measurements obtained for beryllium isotopes (10Be and 9Be) in a sediment core from the central Indian Ocean. It was observed that the changes associated with the decay of 10Be are much smaller than the Be isotopic fluctuations related to variations in geomagnetic field intensity. While ignoring the points showing high anomalous 10Be/9Be ratios, a continuous decrease in the 10Be/9Be ratio with depth was observed as a function of the decay of 10Be. Based on the decay of 10Be, the sediment core was dated to be ∼350 ka (at 570 cm depth) with an average sedimentation rate of 1.6 cm/ka. Radiocarbon dating in conjunction with beryllium isotope data were employed to decipher the past 10Be production changes due to variations in geomagnetic field intensity over the last 45 ka. A drastic increase in the 10Be/9Be ratio at 41.4 ka was attributed to the Laschamp geomagnetic excursion event. About 40% increase in the 10Be/9Be ratio (hence, 10Be production) was observed during this event. Another anomalous increase in the 10Be/9Be ratio was observed at ∼300 cm depth, possibly representing the Iceland Basin event. This study highlights the importance of 10Be as a chronological tool and the limitations associated due to various anomalous excursions associated with 10Be production and/or environmental modulations. • A sediment core from the central Indian Ocean was investigated for 10Be dating. • 10Be depositional flux ages are younger than the 10Be decay ages. • The 5.8 m long sediment core is dated to be ∼350 ka based on the decay of 10Be. • The signature of the Laschamp event was observed at ∼41.4 ka. [ABSTRACT FROM AUTHOR]

Enantioseparation of four commonly used β-adrenolytics (bisoprolol, salbutamol, and carvedilol, marketed as racemic mixtures) has been achieved by both TLC and RPHPLC via an indirect approach. A new chiral reagent, ( S )-naproxen benzotriazole ester, was synthesized and it was characterized by UV, IR, 1 HNMR, elemental analysis and polarimetry. It was used to synthesize diastereomeric derivatives of the three β-adrenolytics under microwave irradiation. TLC separation of diastereomeric derivatives was achieved which were then isolated by preparative approach; these were characterized and were used as standard reference for determining absolute configuration of diastereomeric derivatives and for establishing validated HPLC method for enantioseparation and sensitive detection of the three β-adrenolytics in human plasma. Mobile phase in gradient mode containing methanol and aqueous triethylaminephosphate (TEAP) was successful for HPLC separation; conditions with respect to pH, flow rate, and buffer concentration were optimized. The method is capable to accurately quantitate β-adrenolytics in human plasma with minimal sample clean-up and rapid separation by TLC and RPHPLC. The limit of detection values were 0.97 and 0.87 ng/mL for diastereomeric derivatives of ( S )- and ( R )-bisoprolol, respectively, which are very low in comparison to literature reports. [ABSTRACT FROM AUTHOR]

Micellar liquid chromatographic method has been developed for enantioseparation of four β-adrenolytics, namely, (RS)-salbutamol, (RS)-carvedilol, (RS)-bisoprolol, and (RS)-betaxolol. Both sodium docyl sulfate and Brij-35 were used as the surfactants in water as the mobile phase. Advantages for using both the surfactants in combination were investigated. Two (S)-ketoprofen-based activated esters were synthesized by activating its carboxylic group with N-hydroxybenzotriazole and N-hydroxysuccinimide, respectively. The esters were characterized by UV, IR, 1H-NMR, HRMS, and elemental analyses. These reagents were used for the synthesis of diastereomeric derivatives of the chosen β-adrenolytics. These diastereomeric derivatives were enantioseparated on C18 column by high-performance liquid chromatography. Chromatographic conditions were optimized by varying concentration of surfactant and buffer, and pH. The method was validated according to International Conference of Harmonization guideline and the retention factor (k), selectivity factor (α), resolution factor (RS), and limit of detection and limit of quantification were calculated. [ABSTRACT FROM AUTHOR]

For the last few decades, there has been rising concern across the globe about depletion of conventional energy sources and the consequent energy crisis. Simultaneously, search for other energy sources, such as wind energy and solar energy, has been gaining momentum as well. Particularly, wind energy has become a viable alternative source of energy. As the wind power penetration continually increases, stability of the grid-connected doubly fed induction generator (DFIG)-based wind turbine system has become essential for wind power generation. This study presents the influence of a grid-side converter current dynamics on the small-signal stability by using the eigenvalue and participation factor technique which provides five distinct system modes, namely mechanical (M), stator electrical, converter electrical, electro-mechanical and non-oscillatory mode. In addition, flexible alternating current transmission system device has been incorporated to examine its effect on the system stability at different compensation levels. Furthermore, the sensitivity of a grid-connected DFIG system concerning system parameter variations and its impact on stability of the system modes has been investigated. Simulations have been carried out in the MATLAB/Simulink environment. [ABSTRACT FROM AUTHOR]

The mid-late Holocene period is seldom known for any drastic climatic perturbations, but witnessed significant anthropogenic growth and thus has been a subject of scientific importance. In this study, sediment core raised from an active mudflat of Diu Island, Southern Saurashtra coast, Gujarat with a climatic history for the last 4100 yr BP has been investigated based on geochemical proxies (productivity, weathering and detrital). Results indicate warm and humid conditions during Holocene Climate Optimum (HCO) between 4105 and 2640 cal yr BP as a result of monsoon intensification followed by an arid conditions between 2640 and 1930 cal yr BP. Later during 1930−355 cal yr BP, the region regained warm and humid conditions. The mudflat responded in accordance with the global climatic perturbations during last 2000 yr witnessing signatures of Roman Warm Period and Medieval Warm Period. Additionally, cool and humid climatic conditions persisted during Little Ice Age followed by Modern Warming Period witnessed during last 300 yr. [ABSTRACT FROM AUTHOR]

Since the very first resolution of racemic tartaric acid by Pasteur, the importance of resolution and methodology has been on a path of continuous understanding and expansion. The science and chemistry of achieving such targets has changed a lot. The advent of chromatography changed the direction by involving synthetic, semisynthetic, or naturally occurring chiral materials for a direct approach to resolution, where rapid and reversible association occurs to form diastereomers with different stabilities and partition coefficients responsible for overall enantioseparation. It has now reached a stage where the separation of excess enantiomers from nonracemic mixtures has been achieved in a totally achiral environment, which does not appear to be in line with the prevalent concepts of basic stereochemistry. Caution should be exercised when enantiomerically enriched mixtures - obtained by enantioselective synthesis - are chromatographed for purification in preparative organic synthesis. [ABSTRACT FROM AUTHOR]

The article presents a study which suggests the change in sedimentation in the northern Andaman Sea that depicts a function of changing monsoonal activity and the detrital influence. The development of high-resolution chronology of northern Andaman marine sediment core through the use of radiocarbon dating on selected foraminiferal species is explored. The determination of sedimentation rate using a linear interpolation age-depth model of the clam software with Monte Carlo method is tackled.

Corals provide high-resolution radiocarbon record of the surface ocean. These high-resolution records can provide understanding of the surface ocean conditions and processes regulating these conditions. A Porites coral from the Andaman Sea was investigated for its high-resolution radiocarbon record between 2007 and 2014. The radiocarbon measurement of the coral shows a post-bomb period decline trend (2.7‰ yr−1) along with seasonal variations. A positive correlation is observed between the seasonal radiocarbon changes and the stable oxygen isotope values of the coral. The coral registers the seasonal changes in mixed layer depth and sea surface temperature between the monsoon and non-monsoon periods. Recent radiocarbon values of the Andaman Sea surface water have been found to be higher compared to the contemporary atmospheric radiocarbon values. • Sub-annual variations in coral Δ14C record from the Andaman Sea is reported. • Seasonal Δ14C variations are overlaid on long term declining trend of 2.7‰ yr−1. • Positive correlation between seasonal Δ14C changes and δ18O changes in the coral. • Andaman coral δ18O and Δ14C values capture the SST and MLD changes respectively. [ABSTRACT FROM AUTHOR]

Element geochemistry and Sr–Nd isotopes have been used to characterise the palaeoflood sediments at a tributary junction in lower Narmada Valley archiving the Little Ice Age (LIA) and to determine the present day sources for the mainstem and the tributary sediments. The major and trace element concentrations show minor variations in values post 360 Cal yr BP. The 87 Sr/ 86 Sr and ε Nd values of palaeoflood sediments range from 0.7122 to 0.7191 and − 2.89 to + 6.28 respectively. The bed sediments from the mainstem river (Narmada) and its tributary (Karjan) yield 87 Sr/ 86 Sr values of 0.72394 and 0.7113 and ε Nd values of − 7.18 and + 6.09 respectively. Potential sources of palaeoflood sediments have been investigated from Sr and Nd isotope compositions and mixing of the mainstem as well as the tributary sediments is suggested. Pronounced contribution from the Deccan Basalt during the early part of the Little Ice Age is inferred. The more radiogenic Nd values indicate a contribution from the weathering of younger Deccan basalts, especially the Poladpur formations. The control of weathering intensity and mineral sorting is observed in ‘higher than the source rock’ 87 Sr/ 86 Sr ratios of the sediments. The major and trace element variations during the last 700 years are not conclusive although, isotopic signatures of the flood sediments help in constraining the flux from the tributaries. Sr and Nd isotopic composition of the palaeoflood sediments can be used to track the monsoon intensity and pattern but their concentrations in a fluvial system remain primarily controlled by mineral sorting processes and mixing of sources. [ABSTRACT FROM AUTHOR]

In the northwestern Himalaya (Ladakh and Karakoram), the spatial and temporal changes in the late Quaternary glaciation were modulated by a combination of two contrasting moisture sources (viz., the Indian Summer Monsoon and the mid-latitude westerlies). The inferences about their relative contribution to glacier expansion are based on the ages obtained on moraines. Since the moraines suffer from poor preservation and chronological uncertainty, the present study, therefore, resorted to a near-continuous relict proglacial lake succession in order to reconstruct the continuous pattern of glacier fluctuations during Marine Isotopic Stage-2 (MIS-2). Since the AMS radiocarbon ages (both organic and inorganic matter) suffered from various complexities such as dead carbon contribution and hard water effect, the paleohydrological inferences in this study were drawn primarily based on optical ages (along with sedimentological and geochemical analysis). The proglacial lake sedimentation was modulated by the temporal changes in meltwater discharge. This is attributed to the waning and waxing of proximal valley glaciers. Evidence accrued from the lake sediment supported by the published moraine chronology suggests that valley glaciers expanded during the onset of MIS-2 and persisted until around the Last Glacial Maximum (LGM). The beginning of MIS-2 is marked by the onset of cooling (~ 30 ka), which led to a marginal advance in the glaciers. Additionally, early MIS-2 was characterised by millennial-scale climatic fluctuations. For example, a short-lived increase in humidity was observed between 30.2 ka and 29.3 ka, followed by a reversal towards a drier climate between 29.3 ka and 28.1 ka. During the early part of MIS-2, glaciers were driven by the decrease in temperature, whereas the enhanced moisture contribution during mid MIS-2 was responsible for extensive glacier growth. We hypothesise that the enhanced moisture was contributed by the mid-latitude westerlies, with subordinate contribution from the Indian Summer Monsoon (ISM). This we attribute to the southward positioning of the Intertropical Convergence Zone (ITCZ) during MIS-2. • A relict proglacial lake deposit was used to understand glacial boundary conditions. • The OSL method provided more robust chronology than the 14C method. • Evidence of MIS-2 glaciation was observed in the lacustrine sedimentation. • Increase in wetness observed during mid MIS 2 was due to enhanced westerlies. [ABSTRACT FROM AUTHOR]

Enantioseparation of amino acid analogues racemic β-amino alcohols has hitherto been thought impossible without prior derivatization. Method developers of chromatographic enantioseparation often face detection challenge due to low ultraviolet (UV) absorbance of these molecules. A new chiral derivatizing reagent, benzimidazole-(S)-naproxen amide, was synthesized to provide UV detectable chiral moiety for detection of respective diastereomers of eight β-amino alcohols (DL-alaninol, DL-leucinol, DL-prolinol, DL-phenylalaninol, DLphenylglycinol, DL-valinol, DL-homophenylalaninol and DL-methioninol). An HPLC method has been developed and validated and both the diastereomers were separated within 31 min runtime. Excellent resolution to a pmol detection limit level was achieved. The developed HPLC method for enantioseparation of b-amino alcohols is the firstever report of its own kind having such a high detection sensitivity. [ABSTRACT FROM AUTHOR]

The present work reports preparative enantioseparation of ( RS)-baclofen using thin-layer chromatography (TLC) and high-performance (HPLC). Diastereomers were synthesized using a new monochloro-s-triazine-based chiral derivatizing reagent (CDR), namely, N-(4-chloro-6-piperidinyl-[1,3,5]-triazine-2-yl)-L-phenylalanine, under . Acetonitrile-0.1% aq. triflouroacetic acid in gradient elution mode and CH3OH-CH2Cl2 (4:5; v/v) were successful as mobile phase in HPLC and TLC, respectively. The two diastereomers were isolated by preparative TLC. Molecular dissymmetry was established by developing the lowest energy optimized structures of the diastereomers based on Density Functional Theory and with the help of 1H NMR showing anisotropic effect associated with aromatic ring of s-triazine (in the CDR). The configuration of diastereomers was established as [L-Phe-( R)-Bac] and [L-Phe-( S)-Bac], where the first notation refers to the configuration of chiral auxiliary (of the CDR) and the second to that of the analyte Bac. were found to be 0.056 and 0.061 ng mL−1, respectively, for the two diastereomers. Determination of absolute configuration of the two diastereomers lent support to the elution order and separation mechanism. Chirality 27:299-305, 2015. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

An efficient and concise approach for recognizing chirality and determining the absolute configuration of the diastereomers of ( RS )-Betaxolol, [( RS )-Bet] is described, which in turn is a measure of the enantiomeric purity of Bet since the diastereomers were separated and isolated using preparative TLC. A reverse phase HPLC method was developed and validated for the enantioseparation of ( RS )-Betaxolol. Diastereomers were synthesized, using a naproxen based chiral derivatizing reagent, under microwave irradiation. The absolute configuration of both diastereomers was established with the help of 1 H NMR spectroscopy and by developing the lowest energy optimized structures of the diastereomers based on density functional theory. The configuration of the diastereomers was established as [( S )-Nap-( R )-Bet] and [( S )-Nap-( S )-Bet]. The determination of the absolute configuration of the two diastereomers lent support to elution order and separation mechanism. The limits of quantitation were found to be 0.80 ng mL −1 for the diastereomers. [ABSTRACT FROM AUTHOR]

Five d -amino acids have been used for the first time to synthesize chiral derivatizing reagents (as variants of Marfey's reagent) by nucleophilic displacement of one of the fluorine atoms in 1,5-difluoro-2,4-dinitrobenzene as against the literature reports on application of only l -amino acids or their amides as chiral auxiliaries in dinitrobenzene (DNB) moiety. Five other DNB based reagents were also prepared by nucleophilic substitution of fluorine atom with the set of the same amino acids in l -configuration, as chiral auxiliaries. These reagents were characterized and used for synthesis of diastereomers of ( RS )-Mexiletine spiked in human plasma. Diastereomers were synthesized employing microwave irradiation and were separated on reversed-phase C 18 column. Performance of the two types of chiral derivatizing reagents was compared. The reagents containing d -amino acids provided enhanced separation of diastereomers than those containing l -amino acids. The best resolution was obtained using mobile phase consisting of acetonitrile and 0.1% trifluoroacetic acid in gradient mode. The detection was carried out at 340 nm. The method so developed was validated for linearity, accuracy and precision. The limit of quantitation was found to be approximately 25.2 ng mL −1 in human plasma. [ABSTRACT FROM AUTHOR]

Lazarine leprosy is an unusual expression of usually borderline tuberculoid (BT) form characterized by spontaneous ulceration of skin lesions. This is presumably the result of an exaggerated type 1 reaction. It commonly occurs in the BT, borderline lepromatous forms and rarely in the lepromatous forms of leprosy. We report two cases of lazarine leprosy in the BT and BT downgrading to borderline lepromatous spectrum in healthy and immunocompetent males. [ABSTRACT FROM AUTHOR]

Enantioseparation of (RS)-Bupropion was achieved as its diastereomers which were prepared with chiral derivatizing reagents (CDRs) synthesized from cyanuric chloride. Five new CDRs were prepared by nucleophilic substitution of Cl atom in 6‐butoxy derivative of cyanuric chloride with amino acids (namely, L‐Leu, L‐Val, L‐Phe, D‐Phg and L‐Ala) as chiral auxiliaries to give monochloro-s-triazine reagents and other five dichloro-s-triazine reagents were prepared by monosubstitution with the above-mentioned amino acids. The diastereomers were synthesized under microwave irradiation and by conventional method. Separation efficiencies of the two sets of CDRs, among themselves and among the two groups, have been compared on the basis of resolution (RS) and difference between the retention times of resolved diastereomers. The method was validated for detection limit, linearity, accuracy and precision. [ABSTRACT FROM AUTHOR]

The adsorption potential of a nonliving algaNostoc comminutumfor the removal of hazardous dyes from aqueous solutions was assessed. The algal biomass in its native form exhibited the highest dye removal efficiency at a pH of 1 and at a contact time of 50 min. The effect of various chemical pretreatments was studied in order to assess the role of surface chemistry and the underlying mechanism. Combined with Fourier transform infrared (FTIR) studies, it was concluded that the carboxylic and amine groups played a dominant role in the dye binding process. pH studies further revealed that besides the electrostatic mechanism, other physical interactions might be operative, which is also revealed from the Dubinin-Radushkevich (D-R) isotherm model. Kinetic studies indicated that the adsorption process followed the second-order kinetics and particle diffusion mechanisms were operative. Thermodynamic studies revealed that the adsorption of two dyes onto the algal biomass was feasible, spontaneous, and exothermic under the studied conditions. Microwave irradiation was proposed as a green method for the regeneration and reuse of the biomass. A 16% loss in the regeneration efficiency of the biosorbent was observed, which reveals its stability and reuse potential. Column experiments with real textile wastewater established the practicality of the developed system. Finally, a comparative study revealed the efficacy of the biosorbent with other previously reported biosorbents for dye removal. [ABSTRACT FROM AUTHOR]

The syntheses of optically active compounds (whether of pharmaceutical or synthetic importance, or as promising candidates as chiral ligands and auxiliaries in asymmetric syntheses) result in the formation of a mixture of products with one enantiomer predominating. Usually, the practice is to use standard open-column chromatography for the first purification step in an enantioselective synthesis; the workup of the reaction product by crystallization or achiral chromatography would mask the real efficiency of the enantioselective methodology, since enantiomeric ratio (er) of the product may change by any of these methods. Most of the synthetic organic chemists are aware of the influence of crystallization on the er value. Majority of synthetic organic chemists are, however, not aware, while employing standard chromatography, that there may be an increase or decrease of er value. In other words, an undesired change in er goes unnoticed when such a mixture of enantiomers is isolated by chromatography on an achiral-phase because of the prevalent concept of basic stereochemistry. Such unnoticed errors in enantioselective reactions may lead to misinterpretations of the enantioselective outcome of the synthesis. The scientific issue is, what is the difference between a racemic and nonracemic mixture in achiral environment ( e.g., achiral-phase chromatography) that leads to enantiomeric enrichment, amounting to separation of one particular enantiomer? There are sporadic reports on enantiomer separation of nonracemic mixtures in an achiral environment particularly from the scientists working in analytical chemistry. To cover/discuss all these reports is out of the scope of this article. The aim of the present report is to draw attention to the following points: i) How should the synthetic organic chemists and analytical chemists take care of the unexpected separation of enantiomers from nonracemic mixtures in a totally achiral environment? ii) What are the technical terms used in recent literature? iii) The requirement of revisiting definitions/terms (introduced in recent years, in particular) to describe such separations of enantiomers in light of prevalent scientific/chemical terminology used in the ' language of chemistry', the text book concept, and IUPAC background. iv) To propose logical scientific terminology or phrases for explaining the possible mechanism of separation under these conditions. v) To discuss briefly the concept/possibile phenomenon responsible for these enantioselective effects. It is also attempted to explain the effect of change of physical parameters influencing the separation from nonracemic mixture in achiral-phase chromatography. [ABSTRACT FROM AUTHOR]

Diastereomers of threeβ-blockers (orciprenaline, betaxolol, and propranolol) were synthesized using three new chiral derivatizing reagents that were prepared by substituting one fluorine atom in 1,5-difluoro-2,4-dinitrobenzene with two chirally pure amines and one L-amino acid. The reagents were characterized using ultraviolet-visible spectroscopy, infrared spectroscopy, elemental analysis, and proton nuclear magnetic resonance. Diastereomers were synthesized under microwave irradiation at 50 s at 80% of 800 W and also by stirring for 50 min at 45°C. The diastereomers were separated by reversed-phase high-performance liquid chromatography on a C18column with detection at 340 nm using acetonitrile and aqueous trifluoroacetic acid as the mobile phase components. The conditions of derivatization and chromatographic separation were optimized. The method was validated for accuracy, precision, limit of detection, and limit of quantification. [ABSTRACT FROM AUTHOR]

• First radiocarbon ventilation age estimates for glacial deep Central Indian Ocean. • Extreme isolation of glacial Central Indian Basin during HS-1 & HS-2. • Radiocarbon ventilation age decreased up to mid Holocene since HS-1. • North Atlantic control on deep Central Indian Ocean hydrography. • Important role of Central Indian Ocean in glacial carbon sequestration. The Indian Ocean accounts for over 20% of the global ocean volume, nearly at par with the Atlantic, and possesses a unique hydrography characterized by turn-over entirely through exchange with the Southern Ocean, Pacific and Atlantic. Despite its volumetric and hydrographic importance, the role of the Indian Ocean in glacial-interglacial carbon cycle dynamics remains poorly constrained. Radiocarbon dates on foraminifera from two marine sediment cores have been used to decipher past changes in the 'radiocarbon ventilation age' of deep waters from the Central Indian Ocean (CIO) basin. Time-series spanning the last 37 ka show coherent variations in both sediment cores, and indicate greatly enhanced ocean-atmosphere radiocarbon disequilibrium in the region during the last glaciation, with peak ocean-atmosphere radiocarbon age offsets occurring during Heinrich Stadial-1 (HS-1) and Heinrich Stadial-2 (HS-2). Uniquely, as compared to the bulk of existing radiocarbon data for the last deglaciation, CIO radiocarbon ventilation ages only approach modern values during the Holocene, with Benthic-Atmosphere (B-Atm) offsets remaining >3000 14C yrs during the Bølling–Allerød period ∼ 15 ka BP. The more gradual rejuvenation of the CIO is supported by parallel oxygenation indicators, as well as existing stable isotope data and Nd isotope trends. Together, the data suggest that the CIO was isolated from well-ventilated North Atlantic sourced deep waters during the last glacial, and particularly during Heinrich stadials 2 and 1. These findings underline the important role played by the Indian Ocean in deglacial carbon cycle change, particularly in the latter half of the last deglaciation. [ABSTRACT FROM AUTHOR]

Corals growing in shallow oceanic regions record the radiocarbon variations in ocean surface waters. Tracing bomb radiocarbon in various carbon reservoirs, can help understand the pathways and rates of carbon exchange between the different reservoirs. The northern Indian Ocean comprising two adjoining basins the Arabian Sea and the Bay of Bengal demonstrates contrasting behaviour both in its hydrological condition and CO 2 sequestration. In this study, coral based bomb radiocarbon records from the Lakshadweep Islands and the Andaman Islands in the northern Indian Ocean have been analysed. The estimates of air-sea CO 2 exchange rate based on bomb radiocarbon for the Lakshadweep is 13.4 ± 2.1 mol m−2 yr−1 and for the northern Andaman is 8.8 ± 1.3 mol m−2 yr−1. The bomb radiocarbon based air-sea CO 2 exchange over the Indian Ocean follow the trend of empirical relationship with wind speed. Using the air-sea CO 2 exchange rates, the net regional CO 2 fluxes over the Lakshadweep and the northern Andaman region has been determined. • Post bomb radiocarbon in the northern Andaman region show relatively enriched values compared to the Lakshadweep region. • Estimated air-sea CO 2 exchange rate over Lakshadweep region is 13.4 ± 2.1 mol m−2 yr−1 and over northern Andaman region is 8.8 ± 1.3 mol m−2 yr−1. • The Lakshadweep and the northern Andaman region show net CO 2 flux of 2.5 and −0.3 Tg C yr−1 respectively. [ABSTRACT FROM AUTHOR]

The Indian monsoon significantly influences the sea surface conditions in the northern Indian Ocean. Corals growing in shallow waters record such monsoon-induced surface water changes. The record of monsoon signatures in the stable isotopic composition of the Porites coral skeleton from the Lakshadweep Islands, off the coast of Southwestern India, has been investigated. Corals record enhanced rainfall periods on the interannual scale along with seasonal changes in the sea surface temperature (SST) in their stable oxygen isotopic composition (δ 18O). Inter-colony variability observed in the δ 18O of the Lakshadweep corals was studied to decipher the δ 18O-SST relation of the region. The carbon isotopic (δ13C) values for the coral show change during the monsoon period. The observed variations in the coral δ13C values are modulated by other processes, along with its photosynthetic activity. The stable isotopic variation from the Lakshadweep coral demonstrated seasonal and interannual scales variability induced by monsoon activity. Thus, past monsoonal variations can be deciphered from long-term coral records from the Lakshadweep region. • Lakshadweep corals show inter-colony variability in mean δ 18O values. • Coral derived δ 18O sw values from Lakshadweep record enhanced rainfall period. • Lakshadweep coral record SST minima more robustly as compared to SST maxima. • Seasonal δ 13C changes in Lakshadweep corals are not simply a function of light availability. [ABSTRACT FROM AUTHOR]

Six dichloro- s-triazine (DCT) reagents having l-Leu, d-Phg, l-Val, l-Met, l-Ala and l-Met-NH as chiral auxiliaries in cyanuric chloride were introduced for enantioseparation of 13 proteinogenic amino acids. Four other DCTs and six monochloro- s-triazine (MCT) reagents having amino acid amides as chiral auxiliaries were also synthesized. These 16 chiral derivatizing reagents (CDRs) were used for synthesis of diastereomers of all the 13 analytes using microwave irradiation, which were resolved by reversed-phase high-performance liquid chromatography (RP-HPLC) using C18 column and gradient eluting mixture of aqueous TFA and acetonitrile with UV detection at 230 nm. It required only 60-90 s for derivatization using microwave irradiation. Better resolution and lower retention times were observed for the diastereomers prepared with CDRs having amino acids as chiral auxiliaries as compared to counterparts prepared with reagents having amino acid amides as chiral auxiliaries. As the best resolution of all the 13 analytes was observed for their diastereomers prepared using the DCT reagent having l-Leu as chiral auxiliary, this CDR was further employed for derivatization of Lys, Tyr, His and Arg followed by RP-HPLC analysis of resulting diastereomers. The results are discussed in light of acid and amide groups of chiral auxiliaries constituting CDRs, electronegativities of the atoms of achiral moieties constituting CDRs and hydrophobicities of side chains of amino acids constituting CDRs and analytes. [ABSTRACT FROM AUTHOR]

l-Ala-NH, l-Val-NH, l-Leu-NH, and d-Phg-NH were used as chiral auxiliaries to synthesize four chiral derivatizing reagents (CDRs) of each of the three categories, viz., difluoro dinitro benzene (DFDNB) based chiral variants, and cyanuric chloride (CC) based monochloro-s-triazine reagents (MCTs) and dichloro-s-triazine reagents (DCTs). DFDNB based chiral variants were synthesized by substituting one of the fluorine atoms of DFDNB with respective amino acid amides. The MCTs and DCTs were synthesized by substituting chlorine atom with aforesaid amino acid amide moieties in 6-methoxy dichloro-s-triazine and in CC, respectively. In total, 12 CDRs were characterized and used for microwave-assisted synthesis (45 s at 80% of 800 W using DFDNB-based chiral variants, 80 s at 90% of 800 W power using MCTs, and 50 s at 80% of 800 W power using DCTs) of diastereomers of (A) SeMet, and (B) mixture of (1) SeMet and Met, and (2) SeMet, Met, and Cys. The diastereomers were enantioseparated by reversed-phase high-performance liquid chromatography using gradient elution with mobile phases containing aq. TFA (0.1%)-MeCN in different compositions. The method was validated for accuracy, precision, and limit of detection. [ABSTRACT FROM AUTHOR]

Abstract: (S)-Naproxen-benzotriazole was synthesized by the reaction of (S)-naproxen with 1H-benzotriazole using coupling reagent dicyclohexyl carbodiimide and 4-dimethylamino pyridine (DCC/DMAP). It was used as chiral derivatizing reagent for microwave irradiated synthesis of diastereomers of penicillamine, cysteine and homocysteine. The diastereomers were separated by reversed phase high performance liquid chromatography using gradient elution of triethylammonium phosphate (pH 3.5)–acetonitrile (30–65% within 30min). The method was validated for accuracy, precision, and limit of detection. [Copyright &y& Elsevier]

Two new chiral monochloro- s-triazines (MCT) were synthesized [viz N-(4-chloro-6-piperidinyl-[1,3,5]-triazine-2-yl)- l-leucine amide and N-(4-chloro-6-piperidinyl-[1,3,5]-triazine-2-yl)- l-leucine) (CDR 1 and 2, respectively)] by the nucleophilic displacement of chlorine atoms in s-triazine moiety. One of the Cl atoms was replaced with piperidine, and the second Cl atom in the 6-piperidinyl derivative was replaced with amino acid amide (viz l-Leu-NH) and amino acid ( l-Leu). These reagents were characterized and used as CDRs for chiral separation of protein and non-protein amino acids, and were separated on a reversed-phase C column. The reaction conditions were optimized for the synthesis of diastereomers using one MCT reagent. The separation method was validated for limit of detection, linearity, accuracy, precision, and recovery. [ABSTRACT FROM AUTHOR]

Abstract: A new series of chiral derivatizing reagents (CDRs) consisting of four dichloro-s-triazine reagents was synthesized by nucleophilic substitution of one chlorine atom in trichloro-s-triazine with amino acids, namely l-Leu, d-Phg, l-Val and l-Ala as chiral auxiliaries. Two other sets of CDRs consisting of four dichloro-s-triazine (DCT) and six monochloro-s-triazine (MCT) reagents were also prepared by nucleophilic substitution of chlorine atom(s) with different amino acid amides as chiral auxiliaries in trichloro-s-triazine and its 6-methoxy derivative, respectively. These 14 CDRs were used for the synthesis of diastereomers of (R,S)-mexiletine under microwave irradiation (i.e. 60s and 90s at 85% power (of 800W) using DCT and MCT reagents, respectively), which were resolved by reversed-phase high-performance liquid chromatography using C18 column and gradient eluting mixtures of methanol with aqueous trifluoroacetic acid (TFA) with UV detection at 230nm. The resolution (R s), difference between retention times of resolved diastereomers (Δt) and retention factors (k) obtained for the three sets of diastereomers were compared among themselves and among the three groups. Explanations have been offered for longer retention times and better resolution of diastereomers prepared with DCT reagents in comparison of their MCT counterparts and, for the influence of hydrophobicity of the side chain R of the amino acid in the CDRs on retention times and resolution. The newly synthesized CDRs were observed to be superior as compared to their amide counterparts in terms of providing better resolution and cost effectiveness. The method was validated for limit of detection, linearity, accuracy and precision. [ABSTRACT FROM AUTHOR]