Fourier Transform Infrared Spectroscopy and Vibrational Circular Dichroism Assisted Elucidation of the Solution-State Supramolecular Speciation in Racemic and Enantiopure Ketoprofen

The molecular structure and solution-state molecular interactions in the popular non-steroidal anti-inflammatory drug, ketoprofen, are extensively studied with the aim of gaining a better understanding of the chemical behavior of its solution state and its connection to its nucleation pathway and crystallization outcome. Using as reference solid-state X-ray structures of enantiomeric and racemic forms of ketoprofen, a set of self-assembly models underpinned by density functional theory calculations has been considered for the analysis of spectroscopic data, infrared (IR) and vibrational circular dichroism (VCD), obtained for solutions of the samples as a function of composition and solvent. From our results it can be concluded that, contrary to the general belief for generic carboxylic acids, there are no cyclic dimeric structures of ketoprofen present in solution, but rather linear arrays made up of two (in high polar or diluted media) or more units (in low polar or low dilution media). This observation is in line with the idea that the weak contacts (other than H-bonding) would hold the key to molecular self-assembly, in agreement with recent studies on other aromatic carboxylic acids.

LC-HRMS Studies on Ruxolitinib Degradation: A Comprehensive Approach during Drug Development

Ruxolitinib a kinases inhibitor, was subjected to stress studies as described in ICH Q1A(R2) guideline. Solution state hydrolytic and solid state oxidative and thermal stress studies were carried out to...

J-driven Dynamic Nuclear Polarization for sensitizing high field solution state NMR

Dynamic nuclear polarization (DNP) is widely used to enhance solid state nuclear magnetic resonance (NMR) sensitivity. Its efficiency as a generic signal-enhancing approach for liquid state NMR, however, decays rapidly...

Understanding Solution State Conformation and Aggregate Structure of Conjugated Polymers via Small Angle X-ray Scattering

Donor-acceptor (D-A) conjugated polymers are high-performance organic electronic materials that exhibit complex aggregation behavior. Understanding the solution state conformation and aggregation of conjugated polymers is crucial for controlling morphology during thin-film deposition and the subsequent electronic performance. However, a precise multiscale structure of solution state aggregates is lacking. Here, we present an in-depth small angle X-ray scattering (SAXS) analysis of the solution state structure of an isoindigo-bithiophene based D-A polymer (PII-2T) as our primary system. Modeling the system as a combination of hierarchical fibrillar aggregates mixed with dispersed polymers, we extract information about conformation and multiscale aggregation and also clarify the physical origin of features often observed but unaddressed or misinterpreted in small-angle scattering patterns of conjugated polymers. The persistence length of the D-A polymer extracted from SAXS agrees well with a theoretical model based on the dihedral potentials. Additionally, we show that the broad high q structure factor peak seen in scattering profiles can be attributed to lamellar stacking occurring within the fibril aggregates and that the low q aggregate scattering is strongly influenced by the polymer molecular weight. Overall, the SAXS profiles of D-A polymers in general exhibit a sensitive dependence on the co-existence of fibrillar aggregate and dispersed polymer chain populations. We corroborate our findings from SAXS with electron microscopy of freeze-dried samples for direct imaging of fibrillar aggregates. Finally, we demonstrate the generality of our approach by fitting the scattering profiles of a variety of D-A polymers. The results presented here establish a picture of the D-A polymer solution state structure and provide a general method of interpreting and analyzing their scattering profiles.

Stability and Degradation Kinetic study of Bilastine in Solution State by RP-HPLC Method

Aim: The current study dealt with the degradation behavior of Bilastine and degradation kinetics of a drug in solution state. Background: Very limited information on the effect of pH on maximum stability has been published. In order to understand the degradation kinetics of bilastine, aqueous stability studies were carried out, because such studies on bilastine have not been reported in the literature, further no methods have reported about shelf-life determination of bilastine. The study design involves selection of stability indicating RP-HPLC method for estimation of drug then evaluation of degradation kinetics, shelf-life determination and validation of proposed method. Results: The Shimadzu HPLC series 1100 was used for stress degradation analysis of bilastine in tablet dosage form. The analysis was performed using Agilent ZORBAX SB-C8 (4.6×150×5µm) column and Phosphate Buffer: Acetonitrile (pH-5.0) in the ratio of 60:40 as mobile phase; wavelength selected for analysis was 254nm with the flow rate of 1mL/min at which drug showed sharp peak. The analysis was performed on the isocratic pump mode with the injection volume of 20µl. The mobile phase is used as diluent. The proposed method was found to be linear over the range 10 to 50 µg/mL. The analysis was performed by placing standard and samples with 7 different pH buffer, oxidative and neutral hydrolytic solutions in oven at 40ºC, 60⁰C and room temperature for an interval of 30, 60, 90, 120, 150, 180 mints for standard and samples. The results indicated that the pH, temperature, ionic strength and oxidation greatly influence the stability of Bilastine and the degradation behavior of Bilastine followed pseudo-first-order kinetics. Bilastine was most stable in neutral, alkaline, lower temperature conditions and lower ionic strength. Conclusion: The proposed method was found to be specific, selective and robust and successfully applied for its assay, degradation (stress testing) of drug and degradation kinetics in solution state. Keywords: Degradation, Stability, Bilastine, RP-HPLC, Kinetics