Non-invasive in situ monitoring of catalyzed chemical reactions can show and probe the stability of the catalyst and ensure a high yield of the desired chemical processes. Infrared in situ measurement techniques in attenuated total reflection (ATR) and transmission mode were used to assess the feasibility of these methods and ultimately compare their ability to monitor and detect active or degrading catalyst species. Four different process configurations were used, namely (i) a stirred tank reactor equipped with ATR-IR; (ii) a continuously operated miniplant with ATR-IR; (iii) a continuously operated miniplant with transmission-IR; (iv) a stirred tank reactor equipped with transmission-IR. The established hydroformylation of a long-chain olefin catalyzed by a rhodium-phosphite catalyst was taken as a representative reaction. The potential for process monitoring in molecular catalysis was evaluated. Advanced chemometric analyses by Band Target Entropy Minimization (BTEM) were performed following spectral monitoring to obtain pure component spectra estimates as well as relative time-dependent concentration profiles. In general, this study showed that infrared measurements in transmission mode are able to detect active catalytic species and can follow deactivation phenomena in batch reactions and continuously operated miniplants. Apart from the substrates and products, a number of catalytic intermediates appear to be in equilibrium exchange at reaction conditions and hence the deconvolution of multispecies spectra exhibits superimpositions of these species. Quantum chemical calculations support the structural identification of measured vibrational spectra. This comparative study of ATR versus transmission and batch experiment versus continuously operated miniplant shows that transmission IR is capable of getting in-depth spectroscopic data that can be deconvoluted by BTEM. A distinct dosing strategy is important to get meaningful data on the molecular catalyst under process conditions. This study gives a unique perspective on in situ spectroscopic infrared investigations in molecular catalysis and future process control.
Pharmaceutical cocrystals have rapidly emerged as a new class of API solids with great promise and advantages. Much work has been focused on exploring the crystal engineering and design strategies that facilitate formation of cocrystals of APIs and ligands/cocrystal formers. However, fewer attempts have been made to understand the equilibrium phase behavior and phase transition kinetics of the cocrystallizing solutions. This limited knowledge on the solution physical chemistry often leads to difficulty in screening for potential molecular pairs of API and ligand that form cocrystals effectively. In this study, the long-time self-diffusivities measured using pulsed gradient spin-echo nuclear magnetic resonance (PGSE NMR) are used to characterize the particle interactions in solutions for pharmaceutical cocrystallizing systems. For the pairs of API and ligand that produce cocrystals, the heteromeric attractions between API and ligand are found to be stronger than the homomeric attractions between API molecules and between ligand molecules, suggesting that an energetically favorable condition is induced for the formation of cocrystals. To the best of our knowledge, this is the first report of using the pair contribution of the self-diffusivity as a screening tool for cocrystal formation.
Crystal structure determination is the key to a detailed understanding of crystalline materials and their properties. This requires either single crystals or high‐quality single‐phase powder X‐ray diffraction data. The present contribution demonstrates a novel method to reconstruct single‐phase powder diffraction data from diffraction patterns of mixtures of several components and subsequently to determine the individual crystal structures. The new method does not require recourse to any database of known materials but relies purely on numerical separation of the mixture data into individual component diffractograms. The resulting diffractograms can subsequently be treated like single‐phase powder diffraction data, i.e. indexing, structure solution and Rietveld refinement. This development opens up a host of new opportunities in materials science and related areas. For example, crystal structures can now be determined at much earlier stages when only impure samples or polymorphic mixtures are available.
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