Ordered Mesoporous Silica as Supports in the Heterogeneous Asymmetric Catalysis

Enantioselective synthesis of organic compounds has been studied by homogeneous catalysts for several years. However, these catalysts have yet to make a significant impact on industrial scales for fine chemical synthesis. A primary reason is the designing of a homogeneous asymmetric catalyst, which requires relatively bulky ligands and catalyst recovery and recycling often causes problems. One of the convincing ways to overcome this problem is to immobilise the asymmetric catalyst onto a solid support and the resulting heterogeneous asymmetric catalyst system can, in principle, be readily re-used. A large number of supports such as inorganic oxides including zeolites, alumina, zirconia, silica and organic polymers have been employed as supports in heterogeneous asymmetric catalysis. Therefore, in this review article we have summarized the work done by us in our laboratory on the immobilization of chiral transition metal complexes such as Ru, Ir, Mn and Ti onto ordered mesoporous silica and its asymmetric catalysis. All these immobilized catalysts were well characterized by different physicochemical techniques to confirm the structural retention of the support as well as the active metal complex after immobilization. This report includes our asymmetric catalytic investigations in enantioselective reactions such as hydrogenation of ketones, olefins, oxidation of sulfides and oxidative kinetic resolution of alcohols and sulfoxides through immobilized heterogeneous catalyst systems.     

Development and Validation of RP-UHPLC Method for Quantification of Gliclazide in Bulk and Pharmaceutical Dosage Form Using Quality-by-Design (QbD) Approach: A Shifting Paradigm

The current research endeavours quality-by-design (QbD)-aided chromatographic techniques for the quantification of gliclazide (GLZ) in bulk and pharmaceutical dosage forms. Analytical QbD was initiated by assigning both an analytical target profile (ATP) and critical analytical attributes (CAAs). Furthermore, risk evaluation studies, along with factor screening studies, helped identify critical method parameters (CMPs). Optimisation was carried out using a 3² full factorial design by utilising the identified CMP, that is, flow rate (X1) and pH of buffer (X2) at three different levels along with evaluation of the selected CAA, that is, the retention time (Y1) and the peak area (Y2). In addition, the influence of sole and interactive CMPs on CAAs was checked using the data obtained statistically and with response surface plots. The confirmation of significance (P?<?0.05) of the method parameters was determined using analysis of variance (ANOVA). Chromatographic separation was achieved using a stainless-steel C8 column (25 cm?×?4 mm) in isocratic elution mode using phosphate buffer (pH 3.4) and HPLC-grade acetonitrile (50:50 v/v) as the eluent. The flow rate was adjusted to 1 mL min^?1 and the eluent was detected at 230 nm. The validated method, alongside subsequent stress degradation studies conducted according to the ICH guidelines, further favours it as a highly efficient method for the analysis of regular drugs as well as their degraded products. The method proposed above provided a successful demonstration of the QbD-based approach in developing an extremely sensitive and dependable technique for estimating the GLZ for routine analysis and pre-clinical applications.

     

Green chemical synthesis of Pd nanoparticles for use as efficient catalyst in Suzuki‐Miyaura cross‐coupling reaction

Herein, we report the synthesis of tiny spherical Pd nanoparticles (NPs) by green chemical method under ambient conditions using flower extract of Lantana camara plant. The size of the Pd NPs is tunable from 4.7 to 6.3 nm by systematically controlling the concentration of either metal ions or plant extract. The synthesized Pd NPs were well characterized by different spectroscopic, microscopic and diffractometric techniques. The Pd NPs offered good size‐dependent catalytic activity in the Suzuki‐Miyaura C‐C coupling reaction under mild reaction conditions in (1: 1) water‐ethanol mixture. The catalyst is stable and exhibited excellent reusability up to three cycles of coupling reaction after which the catalytic activity decreases.     

Montmorillonite K-10 as a Reusable Catalyst for Fischer Type of Glycosylation under Microwave Irradiation

Montmorillonite K10 catalyzed Fischer type glycosylation was studied for various monosacharides with different alcohols under microwave irradiation. The method was found to be efficient, economic, simple and time saving and the catalyst montmorillonite K-10 was reused three times without loss of catalytic activity and anomeric selectivity. With glycerol, the method gave products glycosylated at primary alcohols only.     

A real space approach to study the effect of off-diagonal disorder on superconductivity

We present an efficient numerical methodology to study the effect of off-diagonal randomness on superconductivity. This is a real space approach using Bogoliubov-de-Gennes (BdG) method coupled with augmented space vector recursion (ASVR) technique for disorder averaging. We find in the presence of off-diagonal randomness s-wave superconductivity is favoured by greater hopping integral strength between similar species as compared to that between dissimilar ones and d-wave superconductivity is suppressed by off-diagonal randomness much like diagonal randomness. Combined diagonal and off-diagonal randomness leads to asymmetry in both the normal as well as the superconducting densities of states.     

Cover Feature: Rare Spin Avoided σ-σ Diradical Planar Tetracoordinate Boron Cluster: A Proto-Star for Planar Pentacoordination (ChemPhysChem 18/2023)

We report a global planar star-like cluster B₃Li₃ featuring three planar tetracoordinate boron centres with a rare spin avoided σ-σ diradical character. The cluster was found to be stable towards dissociation into different fragments. The spin density was found to be localized solely on the three boron atoms in the molecular plane. This spin avoided σ-σ diradical character leads to the extension of the coordination number to yield a neutral B₃Li₃H₃ and a cationic B₃Li₃H₃⁺ cluster with three planar pentacoordinate boron centres in their global minimum structures. The planar geometry of the aninonic B₃Li₃H₃⁻ cluster is slightly higher in energy. The planar global clusters were found to maintain planarity in their ligand protected benzene bound complexes, B₃Li₃(Bz)₃, B₃Li₃H₃(Bz)₃ and B₃Li₃H₃(Bz)₃⁺ with high ligand dissociation energies offering candidature for experimental detection.     

Reduced graphene oxide/iron oxide hybrid composite material as an efficient magnetically separable heterogeneous catalyst for transfer hydrogenation of ketones

Reduced graphene oxide was synthesized and functionalized with FeSO₄⋅7H₂O to form a reduced graphene oxide/iron oxide hybrid composite. The hybrid composite was extensively characterized using various techniques. Its application for transfer hydrogenation of various ketones was studied. The investigation showed that it serves as a good catalyst for transfer hydrogenation of aromatic and some aliphatic ketones resulting in excellent isolated yields (97–99%) of products. It is magnetically separable showing good reusability. The products were characterized and compared with authentic ones.     

Organotin-oxometalate coordination polymer catalyzed oxyfunctionalization of monoterpenes

The organotin-oxometalate coordination polymers [(nBu₃Sn)₂MO₄]·nH₂O (where, M = Mo or W) were prepared by the interaction of nBu₃SnCl with sodium salts of molybdate or tungstate and tested in oxyfunctionalization of monoterpenes with urea hydroperoxide (UHP) as an oxidizing agent. The oxyfunctionalization of monoterpenes gave commercially important products such as epoxides, ketones and hydroxyl derivatives. Among the two catalyst, organotin-oxomolybdate [(nBu₃Sn)₂MoO₄] showed higher activities and epoxide selectivities under selected liquid phase oxyfunctionalization conditions with most of the monoterpenes such as limonene, -pinene, β-pinene, carene, camphene, gerniol and linalool. The integrity of the organotin-oxometalates polymers were confirmed by X-ray diffraction BET surface area, FT-IR, FT-Raman, SEM, TG/DTA and MAS NMR (¹³C, ¹¹⁹Sn) analysis. The effects of reaction parameters on limonene conversions and product selectivities have been studied in detail using [(nBu₃Sn)₂MoO₄] catalyst. There was no leaching of the active catalyst into the reaction medium and catalyst was recyclable without loss in its activity in the oxidation reaction.     

Mass enhancement factor for Pd and Pt

We report calculations of the mass enhancement factors for Pd and Pt by comparing the physical quantities using the interpolation scheme band structure, with the corresponding experimental data. Our results are compared with other theoretical calculations.