Thermal–electrical–structural performances of hot heat exchanger with different internal fins of thermoelectric generator for low power generation application

Journal of Thermal Analysis and Calorimetry - In this study, an electro-thermo-structural coupled numerical analysis is conducted to evaluate the thermal, electrical, and structural performances of...     

Rapid densitometric method for simultaneous analysis of umbelliferone, psoralen, and eugenol in herbal raw materials using HPTLC

The term 'phenolics' refers to a vast array of biologically active compounds ubiquitous in plants, many of which have been used in traditional medicine for thousands of years. Umbelliferone, psoralen, and eugenol are widely occurring phenolic compounds of plant origin, for which many biological activities against chronic diseases have been reported. A simple HPTLC method has been developed for the simultaneous quantification of umbelliferone, psoralen, and eugenol. These three compounds were quantified in the dried fruit pulp of Aegle marmelos and in the fruit of Trachyspermum ammi and Foeniculam vulgare. The technique enables rapid and sensitive simultaneous analysis in different samples. The method was validated for precision, repeatability, and accuracy in accordance with ICH guidelines. The accuracy of the method was checked by a recovery study conducted at three different levels and the average percentage recovery was found to be 98.88% for umbelliferone, 100.104% for psoralen, and 99.33% for eugenol. The proposed HPTLC method for the simultaneous quantification of umbelliferone, psoralen, and eugenol was found to be simple, precise, specific, sensitive, and accurate. It can be used for routine quality control of herbal raw materials as well as formulations containing any or all of these compounds.     

Amine-templated open-framework zinc arsenates of varying dimensionalities: synthesis, structure, polymorphism, and transformation reactions

Eight new open-framework zinc arsenates, encompassing the entire hierarchy of open-framework structures, have been prepared hydrothermally. The structures include zero-dimensional, one-dimensional chains, two-dimensional layers, and three-dimensional structures formed through the transformation of the molecular zinc arsenates. The structure of [C6N4H21][Zn(HAsO4)2(H2AsO4)], I, is composed of ZnO4 and H2AsO4 units connected through the vertices forming four-membered rings with HAsO4 units hanging from the Zn center. The four-membered rings are connected through the corners forming the one-dimensional chain structures in [C4N2H12][Zn(HAsO4)2] x H2O, II, and [C5N2H14][Zn(HAsO4)2] x H2O, III. ZnO4 and AsO4 units form a fully four-connected two-dimensional structure in [C4N2H12][Zn(AsO4)]2, IV. One-dimensional zigzag ladders are connected through HAsO4 units forming two-dimensional layers in [C4N2H12]1.5[Zn2(AsO4)(HAsO4)2] x H2O, V, while the similar building units form a layer with hanging HAsO4 units in the layered arsenate [C6N4H21]6[Zn12(HAsO4)21], VI. Hanging HAsO4 units are also observed in the polymorphic structures of [C6N3H20][Zn2(AsO4)(HAsO4)2] x 2H2O, VII and VIII. Formation of zero-dimensional monomer, I, a fully four-connected layer, IV, and the polymorphic structures, VII and VIII, are important and noteworthy. The transformation reactions of I indicate that the monomer is reactive and gives rise to structures of higher dimensionalities, indicating a possible Aufbau-type building-up process in these structures.     

Development and validation of a TLC-densitometric method for the simultaneous quantitation of strychnine and brucine from Strychnos spp. and its formulations

A simple, sensitive, and specific thin-layer chromatography densitometric method has been developed for the simultaneous quantitation of strychnine and brucine. These two marker compounds are quantitated in the seeds of Strychnos nux-vomica, Strychnos ignatii, and its formulations. The method involves densitometric evaluation of strychnine and brucine after resolving it by high-performance TLC on silica gel plate with toluene-ethyl acetate-diethyl amine-methanol (7:2:1:0.3 v/v) as the mobile phase. The method is validated for precision (interday and intraday), repeatability, and accuracy. The relationship between the concentration of standard solutions and the peak response is linear within the concentration range of 160 to 480 ng/spot for strychnine and 80 to 480 ng/spot for brucine. Instrumental precision is found to be 0.54 and 0.78 (% CV), and repeatability of the method is 1.01 and 1.06 (% CV) for strychnine and brucine, respectively. Accuracy of the method is checked by recovery study conducted at three different levels and the average percentage recovery is found to be 99.13% for strychnine and 100.16% for brucine. The proposed HPTLC method for the simultaneous quantitation of strychnine and brucine is found to be simple, precise, specific, sensitive, and accurate, and it can be used for routine quality control of raw material of Strychnos spp. It also can be applied in quantitating any of these marker compounds in other formulations.     

Immobilization of a copper-Schiff base complex in a Y-zeolite matrix: Preparation,chromogenic behavior and catalytic oxidation

A new zeolite-immobilized hybrid catalyst Cu(MeO-salen)-NaY has been prepared by encapsulating [Cu(MeO-salen)(H₂O)] (1) [where MeO-salenH₂ = N,N′-(ethylene)-bis-(3-methoxysalicylaldimine)] in a NaY zeolite matrix. The hybrid material has been characterized by UV–Vis, IR and EPR spectrometry and by X-ray powder diffraction analysis. The pristine complex [Cu(MeO-salen)(H₂O)] (1) has also been synthesized and characterized by all the spectrometric methods mentioned above as well as by single crystal X-ray diffraction analysis. A brilliant color change (green to red) has been observed when the complex [Cu(MeO-salen)(H₂O)] (1) is immobilized in the zeolitic matrix. X-ray powder diffraction analysis of Cu(MeO-salen)-NaY reveals that the structural integrity of the mother zeolite in the hybrid material remains intact upon immobilization of the complex. The coordination geometry around the Cu^II ion in [Cu(MeO-salen)(H₂O)] is found to be square pyramidal. Spectroscopic studies indicate that coordination geometry of the complex undergoes a significant distortion when it is entrapped in the zeolite cavity. While Cu(MeO-salen)-NaY shows excellent catalytic activity and product selectivity in the hydroxylation of phenol and 1-naphthol, [Cu(MeO-salen)(H₂O)] (1) remains virtually catalytically inactive in these reactions.     

Effect of Donor-Acceptor Chromophores on Photophysical Properties of Newly Synthesized Pyrazolo-Pyrrolo-Pyrimidines (PPP)

Novel pyrazolo-pyrrolo-pyrimidine (PPP) derivatives having remarkable photophysical properties are designed with the help of theoretical semiempirical calculations. These compounds then synthesized successfully and studied effect of substituents on its photophysical properties.

Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> alloy nanoparticles embedded SiO<Subscript>2</Subscript> films: synthesis and structure

Cu–Ni fcc alloy nanoparticles (NPs) of tunable atomic ratios were generated in SiO₂ films. The films were prepared using the Cu(NO₃)₂ and Ni(NO₃)₂ co-doped inorganic–organic hybrid silica sols by single dipping. Transparent, crack-free, glassy SiO₂ films of 310 ± 10 nm in thickness embedded with high mol percent of Cu–Ni alloy NPs were yielded after annealing at 750 °C in 10% H₂-90% Ar atmosphere. Nominal compositions of the films were 20 mol% (Cu–Ni)-80 mol% SiO₂. Optical spectral study of the heat-treated films showed disappearance of Cu plasmon bands due to Cu–Ni alloy formation. Grazing incidence X-ray diffraction (GIXRD) studies revealed the formation of Cu–Ni alloy (2:1, 1:1 and 1:2) NPs inside the SiO₂ film. GIXRD showed a systematic shifting of the diffraction peaks with respect to the fcc Cu–Ni alloy composition, maintaining the nominal ratios. Transmission electron microscopy (TEM) studies of the representative Cu_0.5Ni_0.5-doped film showed existence of homogeneously dispersed Cu–Ni alloy NPs of average size 6.35 nm inside the SiO₂ matrix. The energy dispersive X-ray scattering (EDX) analysis of the individual NPs using the nano-probe (scanning TEM mode) confirmed the presence of both the Cu and Ni with the desired atomic ratio.     

A facile synthesis and crystallographic analysis of N-protected β-amino alcohols and short peptaibols

A facile, efficient and racemization-free method for the synthesis of N-protected β-amino alcohols and peptaibols using N-hydroxysuccinimide active esters is described. Using this method, dipeptide, tripeptide and pentapeptide alcohols were isolated in high yields. The conformations in crystals of β-amino alcohol, dipeptide and tripeptide alcohols were analysed, with a well-defined type III β-turn being observed in the tripeptide alcohol crystals. This method is found to be compatible with Fmoc-, Boc- and other side-chain protecting groups.     

Tube-like natural halloysite/fluoroelastomer nanocomposites with simultaneous enhanced mechanical, dynamic mechanical and thermal properties

A novel kind of fluoroelastomer nanocomposites based on tube-like halloysite clay mineral were successfully prepared using a bis-phenol curing system, which resulted in prominent improvements in mechanical and dynamic mechanical properties and in the elevation as high as 30 K of the thermal decomposition temperature. Wide-angle X-ray scattering and transmission electron microscopy techniques were employed to assess the morphology developed in the nanocomposites, while stress strain diagrams were used to evaluate the mechanical properties. These nanocomposites were further characterized by moving die rheometer, dynamic mechanical properties and thermo-gravimetric analysis. Structure-properties relationship and the improvement of the mechanical, dynamic mechanical and thermal properties of fluoroelastomers are reported in the present study. Increasing amount of the filler reduced the curing efficiency of the bis-phenol curing system, which was evident from the rheometric and physical properties of the resulting composites. A sort of filler–filler interaction was perceived during the strain sweep analysis of the composites. The polymer–filler interaction was reflected in the improved mechanical and thermal properties which were the consequence of proper dispersion of the nanotubes in the polymer matrix; whereas the intercalation of macromolecular chains into the nanotubes was not reflected in the X-ray diffraction analysis.