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Pranita Bora Dr. Basanta Saikia Dr. Bipul Sarma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(3):699-710
Nucleation events and crystal growth can be guided by molecular recognition at interfaces through intermolecular interactions. The short-acting antimicrobial sulfa drug sulfathiazole is known for its concomitant crystallization, which has five known polymorphs, due to conformational flexibility and hydrogen-bond synthon variation. In its development stage of a drug the issue of concomitant crystallization needs to be addressed with respect to patent litigation, including legal actions to protect patents against infringement. A functional self-assembled monolayer (SAM) of organic thiol on a gold surface has been employed as an efficient approach to control concomitant nucleation of such flexible drugs. The crystallization on a SAM surface is mostly kinetically driven and often leads to the nucleation of novel metastable forms. Spectroscopic, thermal analysis and X-ray diffraction studies reveal that a previously unknown, sixth form of the drug nucleates on the designed SAM surface. 相似文献
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Reversed‐phase liquid chromatography with electrospray mass detection and 1H and 13C NMR characterization of new process‐related impurities,including forced degradants of Efavirenz: Related substances correlated to the synthetic pathway 下载免费PDF全文
In this study, a stability‐indicating reversed‐phase liquid chromatographic electrospray mass spectrometric method was developed and validated for the determination of process‐related impurities and forced degradants of Efavirenz in bulk drugs. Efavirenz was subjected to acid, alkaline hydrolysis, H2O2 oxidation, photolysis, and thermal stress. Significant degradation was observed during alkaline hydrolysis, and the degradants were isolated on a mass‐based purification system and characterized by high‐resolution mass spectrometry, positive electrospray ionization tandem mass spectrometry, and 1H and 13C NMR spectroscopy. Accurate mass measurement and NMR spectroscopy revealed the possible structure of process‐related impurities and degradant under stress conditions. The acceptable separation was accomplished on Waters bondapak C18 column (250 mm × 4.6 mm; 5 μm), using 5 mM ammonium acetate and acetonitrile as a mobile phase in a gradient elution mode at a flow rate of 1.0 mL/min. The eluents were monitored by diode array detector at 247 nm and quantitation limits were obtained in the range of 0.1–2.5 μg/mL for Efavirenz, degradants, and process‐related impurities. The liquid chromatography method was validated with respect to accuracy, precision, linearity, robustness, and limits of detection and quantification as per International Conference on Harmonization guidelines. 相似文献
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Papu Kalita Biman Medhi Haobam Kisan Singh Himangshu Pratim Bhattacharyya Nikhil Gupt Dr. Manabendra Sarma 《Chemphyschem》2023,24(3):e202200727
The conical intersection (CI) governs the ultra-fast relaxation of excited states in a radiationless manner and are observed mainly in photochemical processes. In the current work, we investigated the effects of substituents on the reaction dynamics for the conversion of gauche-1,3-butadiene to bicyclobutane via photochemical electrocyclization. We incorporated both electron withdrawing (−F) and donating (−CH3) groups in the conjugated system. In our study, we optimized the minimum energy conical intersection (MECI) geometries using the multi-configurational state-averaged CASSCF approach, whereas, to study the ground state reaction pathways for the substituted derivatives, dispersion corrected, B3LYP-D3 functional was used. The non-adiabatic surface hopping molecular dynamics simulations were performed to observe the behaviour of electronic states involved throughout the photoconversion process. The results obtained from the multi-reference second-order perturbation correction of energy at the XMS-CASPT2 level of theory, topography analysis, and non-adiabatic dynamics suggest that the −CH3 substituted derivatives can undergo faster thermal conversion to the product in the ground state with a smaller activation energy barrier compared to −F substituted derivative. Our study also reveals that the GBUT to BIBUT conversion follows both conrotatory and disrotatory pathways, whereas, on substitution with −F or −CH3, the conversion proceeds via the conrotatory pathway. 相似文献
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The turbulent film boiling from a vertical non-isothermal surface is formulated with due consideration to thermal radiation from its lateral face. It is observed that the application of Reynolds analogy together with thermal conduction in the test surface has yielded a conjugate solution from which the case of an isothermal condition can be generated as a special case. The analysis has further paved the way in establishing a functional relation between the Nusselt numberNu, radiation parameterN R , fin parameterM, temperature ratio termT s /(T w,0?T s ), and a product of characteristic modified Grashof, Prandtl and superheating parameter defined as (Gr 2 Pr S). In a fully developed turbulent film boiling i.e., modified Grashof number being greater than 1010, the temperature ratio term accounts for the non-linearities arising due to the inclusion of radiation from the lateral face of the fin. The results are in good agreement with experimental data over a wide range of system conditions. 相似文献
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The problem of heat transfer to non-Newtonian laminar falling liquid films on horizontal tubes is investigated theoretically for constant heat flux and isothermal conditions imposed at the inner periphery of the tube. The local and average heat transfer coefficients are obtained as function of the system parameters by conjugating the convective transport of heat to the liquid film to the thermal conduction in the material of the tube in the peripheral direction. The results indicate that the average heat transfer coefficient can be described successfully by three dimensionless groups characterizing the dynamic flow characteristics of the film, modified Prandtl number and the index of the power law variation of the rate of angular shear deformation of the fluid with respect to the shear stress.Das Problem des Wärmeübergangs an laminar ablaufende Fallfilme nicht-Newtonscher Flüssigkeiten an horizontalen Rohren wird unter Voraussetzungen konstanter Temperatur bzw. konstanten Wärmeflusses bezüglich des Rohrinnenumfangs theoretisch untersucht. Die örtlichen und gemittelten Wärmeübergangskoeffizienten erhält man als Funktion der Systemparameter unter gleichzeitiger Berücksichtigung des konvektiven Wärmetransportes an dem Flüssigkeitsfilm und der Wärmeleitung im Rohrmaterial in Umfangsrichtung. Die Ergebnisse zeigen, daß sich der gemittelte Wärmeübergangskoeffizient zufriedenstellend in Abhängigkeit von drei dimensionslosen Kenngrößen darstellen läßt. Diese charakterisieren das dynamische Fließverhalten des Films bzw. entsprechen einer modifizierten Prandtl-Zahl und dem Exponenten des Potenzgesetzes, welches die Abhängigkeit der Scherdeformation der Flüssigkeit von der Schubspannung wiedergibt. 相似文献
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The heat transfer rates from a horizontal cylindrical surface of an internally heated tube under constant heat flux conditions are evaluated with the aid of integral analysis giving due consideration to both natural convection and thermal radiation to ambient medium of air. It is observed that non-isothermal conditions around the periphery of the tube arise due to the conjugate effects of the three modes of energy transmission viz., conduction, convection and radiation. The theoretical analysis is further validated with the experimental results and the coincidence is found to be very satisfactory.Die Wärmeübertragungsraten einer horizontalen zylindrischen Oberfläche eines innen erwärmten Rohres mit konstantem Wärmestrom sind mit Hilfe von Integralrechnungen berechnet worden, die sich auf die freie Konvektion und thermische Strahlung mit Luft als Umgebungsmedium beziehen. Es ist beobachtet worden, daß nicht-isotherme Bedingungen am Umfang des Rohres aus den drei Energieübertragungsarten Leitung, Konvektion und Strahlung entstehen. Die theoretische Berechnung wurde mit experimentellen Ergebnissen bestätigt und die Koinzidenz stellte sich als sehr zufriedenstellend heraus. 相似文献
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Metal-acteylacetonates are important sublimable metal-organic precursors for metal-oxide thin film formation over solid preforms by MOCVD (Metal Organic Chemical Vapour Deposition) technique. Mixed-metal-acetylacetonates (MMAA) are suitable starting materials for mixed metal nano-oxidic thin film formation through such facile routes. Layered Double Hydroxides (LDH) of suitable metal ion combination can perform as appropriate starting base for neutralisation by enol form of 2,4-pentanedione or acteylacetonate tautomer ligands to obtain such MMAA. In this paper synthesis of composite crystals of Cu(II)/Cr(III) acetylacetonates (CCAA) is reported by the reaction of Cu–Cr-LDH with acetylacetone. The products were characterized by various different techniques. The surface area and pore volume analysis of the crystals showed the formation of nanopores in the compound. TEM analysis confirmed that the inner core of the nanoporous crystals of Cu(acac)2 was covered by coating of poorly crystallised Cr(acac)3 and they together form the composite crystals, and they together form the composite crystals. Due to eutectic mixture formation the melting point of CCAA lies in between the melting points of individual components Cu(acac)2 and Cr(acac)3 and shows sublimability, a property important for the formation of MOCVD films. The composite was used for CuCr2O4 spinel mixed oxide films formation over solid ceramic honeycomb monolithic substrates. Application prospects of the route in the field of catalysis is high as it can directly combine the benefits of mixed metal oxide catalysis and structured supports without the involvement of a third component. In this work the performance of such a catalytic device has been tested for low temperature decomposition of high Global Warming Potential (GWP) gas N2O to N2 and O2. 相似文献
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