This study demonstrates the Fourier transform infrared (FTIR) spectroscopic characterization of natural kaolinite from north-eastern India. The compositional and structural studies were carried out at room temperature by using X-ray fluorescence (XRF), electron microprobe (EPMA) analyses and Fourier transform infrared (FTIR) spectroscopic techniques. The main peaks in the infrared spectra reflected Al-OH, Al-O and Si-O functional groups in the high frequency stretching and low frequency bending modes. Few peaks of infrared spectra inferred to the interference peaks for quartz as associated minerals. The present study demonstrates usefulness of the spectroscopic techniques in determining quality and crystalline nature of kaolinite from the Assam and Meghalaya, northeastern India

We present here optical properties and crystallinity index of quartz (SiO 2 ) in natural rocks samples from the Mikir and Khasi hills, Assam, India. Infrared spectroscopy has been used to study the structure of quartz in rock samples and estimate the mining quality of quartz mineral, which is substantiated by calculating the crystallinity index. Systematic investigations of structure have been carried out in between 10 µm (1000 cm -1 ) and 20 µm (500 cm -1 ) bands of silicates. Investigation is based on the assignment of infrared bands to certain structural groups of SiO 4 tetrahedra. The crystallinity of samples has been ascertained by comparing the ratio of intensity of the characteristic peak at 778 and 695 cm -1 with the corresponding ratio for a standard sample. The crystallinity parameter is calculated by using a standard procedure which can be used to estimate the distribution of quartz in various rocks for mining purpose. The infrared spectroscopic investigation is found to be an ideal tool for structure elucidation and for estimating quartz crystallinity of the natural samples.

The bronchodilator drug, theophylline (THP), though a BCS class-I drug is considered as a representative compound to prepare variable stoichiometry cocrystals with isomeric aminobenzoic acids (o-ABA, m-ABA & p-ABA) as coformers. Cocrystals are synthesized using crystal engineering principles through liquid assisted mechanochemical grinding. Four different stoichiometry cocrystals of THP are isolated with o-ABA. Coformer m-ABA and p-ABA afforded only 1:1 cocrystals irrespective of crystallization media and different starting materials ratios. All cocrystal materials are subjected for aqueous solubility and diffusion/membrane permeability to examine drug biopharmaceutic properties to predict the in vivo performance of the drug. They exhibited different but improved solubility and modulated diffusion/membrane permeability when compared with pure THP. The interplay of drug solubility and membrane permeability that predicts the overall bioavailability is emphasized based on hydrogen bond synthons and solute···solvent interactions. Hirshfeld surface analysis is carried out in all cases to determine whether a correlation exists between permeability and drug-coformer interactions.

In the preparation of theophylline cocrystals, phenol coformers facilitate water assimilation due to their weaker O–H⋯N(imidazole) synthon. The presence of –COOH prevents water incorporation and provides added physical stability at high humidity. This study shows the feasibility of cocrystal design of an API to tune physical properties based on hydrogen bond synthons.

The noncovalent interactions arising from solute•••solute (i.e., drug•••drug, drug•••neutraceutical, or drug•••coformer) and solute•••solvent play a significant role in predicting desired properties of an active compound. We demonstrated here the role of π•••π interactions in the presence of hydrogen bonding, the two important cohesive and adhesive forces in the crystallization of small molecules to regulate certain physiochemical properties in their multicomponent crystals. Acridine was employed as a representative cocrystal partner with isomeric dihydroxybenzoic acids. The choice was intentional as with a single hydrogen bond acceptor acridine provides increased surface area to favor the stacking of πframeworks at van der Waals separation (∼3.5 Å) and herringbone C−H•••π interactions, and isomeric dihydroxybenzoic acids easily form COOH•••N acridine and O−H•••N acridine hydrogen bonds in competition. Structure elucidation of several cocrystals/salts underlines the influence of continuous and discrete π•••π stacking and C−H•••π interactions supported by other hydrogen bonds on their physiochemical properties such as solubility, cell membrane permeation, and release behavior in vitro. Experiments were performed in various pH ranges (pH = 1.2 SAL and 7.4 PBS) in order to imitate human physiological conditions. Molecular packing and interaction energies suggest a significant contribution of π•••π interactions in the modulation of property. In fact coformers' conformational energy, lipophilicity, and Log P values were found to be valued contributors. Therefore, the present study anticipates the contribution towards understanding of the impact of π•••π and C−H•••π interactions supported by hydrogen bonds on modulating physiochemical properties, essentially improving efficacy of a drug.

Drug release behavior of few ethenzamide cocrystals was investigated at different pH buffers. Change in lipophilic behavior and conformational adjustment of drug along with supramolecular synthons were probed for their improved drug efficacy.

Rare example of carboxamide linked 2D COF has been synthesized and applied as robust organic catalyst for selective oxidation reactions with no metal add-ons. The reaction undergoes free radical mechanism aided by the conjugated π-cloud and amide functionality present in the COF.

We report here for the first time the spectroscopic characterization of natural fulgurites of Garuamukh. On April 22, 2005 at 04 : 00 local time, large amounts of black-brown colour of colloidal solution came out from below the earth's surface at Garuamukh near Nagaon town (latitude 26°20′39″N, longitude 92°41′39″E, Assam, India) with fire and smoke. This colloidal solution got transformed into fulgurites, glassy material, within a few hours. We present here the characterization of the fulgurites by Fourier transform infrared (FTIR) absorption, X-ray diffraction and X-ray fluorescence methods. The amorphous nature of the substance has been confirmed by Fourier transform infrared spectra of the fulgurites, which exhibit prominent absorption band in the region 400-1200 cm -1 , the basic component of amorphous silica. The present study might have significant implications in understanding the thermodynamic properties of naturally occurring glasses, which are formed by shock metamorphism.