Spectroscopic investigation on structure and pH dependent Cocrystal formation between gamma-aminobutyric acid and benzoic acid

A review on advancement of cocrystallization approach and a brief on screening, formulation and characterization of the same

The objective of this review is, to discuss recent advancements in screening methods for co-formers, evaluation cum confirmation methods and co-crystallization with examples. Co-crystals are considered as a new form of an old drug entity. Co-crystals improve the stability, hygroscopicity, solubility, dissolution, and physicochemical properties of pure drugs without altering chemical and pharmacological properties. Advancement in co-crystal formulation methods like electrospray and laser-irradiation methods are showing potential for solvent-free co-crystallization and tends to give better yield and lesser loss of materials. Screening methods are also transformed from trial and error to in-silico methods, which facilitate the selection process by reducing the time of screening and increasing the number of co-formers to be screened. Advanced evaluation methods like Raman and solid-state NMR spectroscopy provide a better understanding of crystal lattice by pinpointing the interaction between drug/co-former molecules. The same evaluation methods can also differentiate between the formation of salt and co-crystals. Co-crystals are helping open a new door in pharmaceutical industries in the field of formulation for the improvement of physicochemical properties in existing old molecules and several new molecules. With a motto of "making a good drug better", co-crystals show scope for vast research and give researchers an ocean of opportunities to make the impossible, possible.

Raman and Terahertz Spectroscopic Characterization of Solid-state Cocrystal Formation within Specific Active Pharmaceutical Ingredients

Cocrystallization of specific active pharmaceutical ingredients (APIs) in the solid-state phase is becoming a feasible way to improve their corresponding physicochemical properties and ultimate bioavailability without making and breaking any covalent bonds within them. Many recent reports deal with the characterization and analysis topics of pharmaceutical APIs-based cocrystals. In this mini-review, we will focus on the recent steady-state and time-dependent spectroscopic investigation into the cocrystallization of specific APIs based on both Raman and emerging terahertz spectroscopy in pharmaceutical fields. Distinctive spectral, structural and also kinetic information of pharmaceutical APIs-based cocrystals are obtained and discussed, which would highlight the potential of vibrational spectroscopy as an attractive technique for various drug research and development during cocrystallization of specific APIs.

Rapid in situ analysis of l-histidine and α-lactose in dietary supplements by fingerprint peaks using terahertz frequency-domain spectroscopy

A simple, green and nondestructive method based on terahertz fingerprint peaks has been developed for rapid in situ analysis of l-histidine and α-lactose in dietary supplements. Fingerprint absorption peaks of l-histidine and α-lactose located at 0.77 and 0.53 THz could be directly used for identification and quantitation of these analytes in commercial dietary supplements. Compared with the partial least squares regression model (PLSR), the linear least squares regression (LLSR) method based on peak areas presented better performance, with the linear correlation coefficients of 0.9899 and 0.9910 for l-histidine and α-lactose, respectively. Furthermore, analysis time per sample can be shortened to less than 1 min due to the narrower spectral acquisition region. The accuracies were 94.8-110% and 98.9-110%, comparable to those of ion chromatography for l-histidine and high-performance liquid chromatography for α-lactose. The results presented great potential of the developed method for rapid in situ analysis of nutrients in dietary supplements.

Structural insights into anhydrous and monohydrated forms of 2,4,6-trihydroxybenzoic acid based on Raman and terahertz spectroscopic characterization

In order to characterize molecular structures of 2,4,6-trihydroxybenzoic acid (PCA) by means of vibrational spectroscopic techniques, we report investigation of PCA monohydrated form and its anhydrous polymorphic one by using terahertz and Raman spectral characterization. The experimental THz spectra show that the monohydrated PCA only has two absorption bands at 0.69 and 1.65 THz respectively in the frequency region from 0.2 to 1.8 THz, meanwhile the anhydrous form has a few significantly different absorption bands at 0.75, 1.01, 1.46 and 1.64 THz, respectively. Furthermore, Raman spectra characterized such differences of vibrational modes shown within 200-1800 cm^-1 region about the monohydrated and anhydrous forms of PCA. In view of various possible theoretical structural forms that may exist in anhydrous PCA and its monohydrated one, density functional theory calculations were performed to simulate optimized structures and vibrational mode of above two PCA polymorphic forms. Theoretical results and experimental THz/Raman spectra of anhydrous PCA show that the dimer synthon via the carboxylic group ••• carboxyl group and its ortho-phenolic hydroxyl group inter-molecular hydrogen bonding interaction establishing the theoretical form I (AH-I) is more consistent with experimental observation than other theoretical forms (AH-II and AH-III). Meanwhile, the theoretical monohydrated form I (MH-I), which is formed by the linkage of carboxyl group and its ortho-phenolic hydroxyl group with water molecule, is also much more agreement with experimental spectral observations of PCA monohydrate than other monohydrated forms (MH-II and MH-III). Our study demonstrates effectively qualitative analysis of both micro-molecular structures and dehydrated transitions between anhydrous and hydrated polymorphic forms of PCA, thus providing rich information on the corresponding structural changes of anhydrous and hydrated PCAs due to various inter-molecular and intra-molecular interactions based on their finger-print vibrational spectra combined with theoretical simulations.

The supramolecular self-assembly of 5-fluorouracil and caffeic acid through cocrystallization strategy opens up a new way for the development of synergistic antitumor pharmaceutical cocrystal

Cocrystallizing with caffeic acid (CF) provides a new strategy for effectually optimizing in vivo/vitro properties of anticancer drug 5-fluorouracil (FL).

Vibrational (FT-IR, Raman) analysis of tea catechins based on both theoretical calculations and experiments

Structural investigations, based on density functional theory (DFT) calculations, are performed on tea catechins, including 4-aminobutyric acid (GABA), L-theanine (Thea), caffeine (CAF), theobromine (TB), theophylline (TP), catechin (C), epicatechin (EC), gallocatechin (GC), epigallocatechin (EGC), catechin gallate (CG), epicatechin gallate (ECG), gallocatechin gallate (GCG) and epigallocatechin gallate (EGCG). With an identified lowest energy conformer of investigated molecules, FTIR and FT-Raman spectra have been assigned according to DFT calculations in the way of B3LYP/6-31 + G (d, p). Normal spectra of these catechin powders are also measured by Raman spectrometers. There is a kind of everlasting correlation between experimental results and theoretical data. And our research has also obtained a clear evidence for reliable assignments of vibrational bands, bringing great feasibility to the rapid tea catechin detection.

Broadband terahertz recognizing conformational characteristics of a significant neurotransmitter γ-aminobutyric acid

γ-Aminobutyric acid (GABA) is the chief inhibitory neurotransmitter in the central nervous system, its conformational behavior is critical for selective biological functions and the process of signal transmission. Although this neuroactive molecule has been extensively studied, its vibrational properties related to the conformation and intermolecular interactions in the terahertz (THz) band have not been identified experimentally yet. In this study, we applied a broadband THz time-domain spectroscopy (THz-TDS) system from 0.5 to 18 THz to characterize a unique THz fingerprint of GABA. The density functional theory calculation results agree well with the THz experimental spectrum. The study shows that the vibrational modes of GABA at 1.15 and 1.39 THz originate from distinct collective vibrations. The absorptions at the higher THz frequencies also carry part of collective vibrations, but more reflect the specific and local vibrational information, including the skeleton deformation and the rocking of the functional groups, which are closely associated with the conformation and flexibility of GABA. This study may help to understand the conformational transitions of neurotransmitter molecules and the resonant response to THz waves.

γ-Aminobutyric acid (GABA) is the chief inhibitory neurotransmitter in the central nervous system, its conformational behavior is critical for selective biological functions and the process of signal transmission.