Thermally induced solid-state transformation of cimetidine. A multi-spectroscopic/chemometrics determination of the kinetics of the process and structural elucidation of one of the products as a stable N3-enamino tautomer

Exposure of cimetidine (CIM) to dry heat (160–180 °C) afforded, upon cooling, a glassy solid containing new and hitherto unknown products. The kinetics of this process was studied by a second order chemometrics-assisted multi-spectroscopic approach. Proton and carbon-13 nuclear magnetic resonance (NMR), as well as ultraviolet and infrared spectroscopic data were jointly used, whereas multivariate curve resolution with alternating least squares (MCR-ALS) was employed as the chemometrics method to extract process information. It was established that drug degradation follows a first order kinetics.     

A short and efficient synthesis of grisan

A three-step synthesis of grisan (spiro[benzofuran-2(3H)-1′-cyclohexane]), using methoxymethoxybenzene and 1-chloromethylcyclohexene as starting materials, is described.     

Macroscopic mass and energy balance of a pilot plant anaerobic bioreactor operated under thermophilic conditions

Intensive poultry production generates over 100,000 t of litter annually in West Virginia and 9×10⁶ t nationwide. Current available technological alternatives based on thermophilic anaerobic digestion for residuals treatment are diverse. A modification of the typical continuous stirred tank reactor is a promising process being relatively stable and owing to its capability to manage considerable amounts of residuals at low operational cost. A 40-m³ pilot plant digester was used for performance evaluation considering energy input and methane production. Results suggest some changes to the pilot plant configuration are necessary to reduce power consumption although maximizing biodigester performance.     

On the theory of radiative transitions in centrosymmetric complexes

The theory of radiative transitions, in centrosymmetric complexes, is examined in great detail, within the framework of the crystal field method.In connection with radiative transitions, the current method of calculations, with and without invoking closure approximation, are considered from a purely theoretical point of view, by taking advantage of the irreducible tensor method put forward by Griffith.Explicit equations are derived throughout the course of this work to account for the vibronic electric dipole moments, associated with d-d and f-f type of excitations.At high Academy of Pedagogic Sciences, Santiago, Chile.     

Application of a chemometric method for simultaneous determination of acetaminophen and diclofenac in content-uniformity and drug-dissolution studies

A new, repeatable, and rapid method has been developed for resolution of binary mixtures of acetaminophen and diclofenac with minimum sample pretreatment and without separation of the analytes. The method, based on the PLS1 processing of absorbance data in the UV region, was successfully used for quantification of the drug content of three tablet preparations. The results obtained were in good agreement with HPLC recovery data. The method also enabled determination of drug-dissolution profiles of these commercial tablets, by simultaneous determination of both analytes during the dissolution test.     

Dynamics of water adsorption on TiO2 monitored by work function spectroscopy

Water adsorption dynamics on two TiO₂ (1 1 0) rutile surfaces at room temperature has been investigated using the work function (WF) change as a function of time. The first surface was prepared in a standard way using sputtering/annealing cycles, whereas the second one was long term annealed at 620 K in moderate vacuum conditions (the residual gas pressure of about 1 × 10⁻⁷ mbar) and cleaned afterwards. The WF change show striking difference as compared to those obtained for highly reduced TiO₂ (1 1 0) rutile or the (2 × 1) reconstructed surfaces. For the first kind of surface we show that the observed adsorption dynamics can be qualitatively explained by the present understanding of the water adsorption on non-reconstructed TiO₂ (1 1 0) rutile surface according to which the bridging oxygen vacancies and Ti rows are the main adsorption sites. Although generally similar to the former results, water adsorption dynamics on the second kind of the surface has an additional feature that can be only explained by a new adsorption site, which we suggest to be due to (2 × 1) reconstructed regions coexisting with the non-reconstructed TiO₂ (1 1 0) surface.     

Predicting retrosynthetic pathways using transformer-based models and a hyper-graph exploration strategy

We present an extension of our Molecular Transformer model combined with a hyper-graph exploration strategy for automatic retrosynthesis route planning without human intervention. The single-step retrosynthetic model sets a new state of the art for predicting reactants as well as reagents, solvents and catalysts for each retrosynthetic step. We introduce four metrics (coverage, class diversity, round-trip accuracy and Jensen–Shannon divergence) to evaluate the single-step retrosynthetic models, using the forward prediction and a reaction classification model always based on the transformer architecture. The hypergraph is constructed on the fly, and the nodes are filtered and further expanded based on a Bayesian-like probability. We critically assessed the end-to-end framework with several retrosynthesis examples from literature and academic exams. Overall, the frameworks have an excellent performance with few weaknesses related to the training data. The use of the introduced metrics opens up the possibility to optimize entire retrosynthetic frameworks by focusing on the performance of the single-step model only.

We present an extension of our Molecular Transformer model combined with a hyper-graph exploration strategy for automatic retrosynthesis route planning without human intervention.     

Facile,efficient and eco-friendly synthesis of 5-sulfenyl tetrazole derivatives of indoles and pyrroles

A concise, two-step eco-friendly approach towards the synthesis of 5-sulfenyl tetrazole derivatives of indoles and pyrroles, is reported. The synthesis comprises the oxone-mediated thiocyanation of the starting heterocycles towards intermediate 3-thiocyanato indoles and 2-thiocyanato pyrroles, and their subsequent treatment with sodium azide in 2-propanol/water under zinc bromide promotion.