Photophysical investigations of coumarin-7 (C7) dye in different solvents using absorption, steady-state fluorescence and time-resolved fluorescence measurements reveal the behavioral changes of the dye in nonpolar and other solvents. In moderate to higher polarity solvents, the experimental parameters such as fluorescence quantum yield (Phif), fluorescence lifetime (tauf), radiative rate constant (k(f)), nonradiative rate constant (k(nr)) and Stokes' shift (Deltav) follow almost linear correlations with the Lippert-Mataga solvent polarity parameter Deltaf but show unusual deviations in nonpolar solvents. From the observed results, it is inferred that the dye exists in a planar intramolecular charge transfer structure in moderate to higher polarity solvents, but in nonpolar solvents, the dye exists in a nonplanar structure with its 7-NEt2 group adopting a pyramidal type of configuration. Unlike some of the other coumarin dyes, namely coumarin-120 (C120) (4-CH3-7-NH2-1,2-benzopyrone) and coumarin-151 (C151) 4-CF3-7-NH2-1,2-benzopyrone), which also show similar structural changes in nonpolar and other solvents, the C7 dye does not show any activation-controlled deexcitation process in nonpolar solvents. This is attributed to the very slow flip-flop motion of the 7-NEt2 group of the C7 dye in comparison with the very fast flip-flop motion of the 7-NH2 group in the C120 and C151 dyes. Qualitative potential energy diagrams are presented to rationalize the observed results of C7 dye and to compare these with those of the other dyes such as C120 and C151. A support for the observed results and interpretation has also been obtained from quantum chemical calculations on the structures of the C7 dye. 相似文献
Three new manganese oxy-bis(benzoate) compounds, synthesized by increasing the reaction temperature, with increasing dimensionality and decreasing Mn-Mn distances, indicate a possible pathway through an entropy driven dehydration route. 相似文献
An international project team (including members from US, Canada and UK) was formed from a number of interested biopharmaceutical companies and regulatory authorities to conduct a cross-organisation collaboration exercise. The results of the first comparison with eight different organisations that used instruments of the same equipment model, the same reagents, and the same methodology has been reported previously [1]. This report represents the addition of other instruments using a different run buffer. The relative migration times were different, as expected, prohibiting a direct comparison between companies. The within-organisation variability was low for both relative migration time (<0.34% RSD% for all companies save one) and the peak area (<5% RSD% for all companies save one) when measuring the purity of a representative IgG sample. The apparent molecular weight of bovine serum albumin was measured with good precision (less than 10% RSD% across all companies) to the theoretical value when all data is utilized (67.5 kDa compared to 66.4 kDa). For a representative IgG sample, the three main components, IgG Light Chain, IgG Non-glycosylated Heavy Chain, and IgG Heavy Chain, could not be separated, specifically the IgG Non-glycosylated Heavy Chain and IgG Heavy Chain. When the IgG Non-glycosylated Heavy Chain and IgG Heavy Chain were combined for all organisations, the fractional peak area for the IgG Light Chain and IgG Non-glycosylated Heavy Chain + IgG Heavy Chain peak also showed excellent agreement, with less than 7.5 and 3.5% RSD%, respectively. The value of this exercise is in demonstrating the reliability of CE for the determination of apparent size of biopharmaceutical proteins. This underpins the appropriate use of such CE data in support of regulatory submissions.
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. 相似文献
We report the design and characterization of a microfluidic hydrogen fuel cell with a flowing sulfuric acid solution instead of a Nafion membrane as the electrolyte. We studied the effect of cell resistance, hydrogen and oxygen flow rates, and electrolyte flow rate on fuel cell performance to obtain a maximum power density of 191 mW/cm2. This flowing electrolyte design avoids water management issues, including cathode flooding and anode dry out. Placing a reference electrode in the outlet stream allows for independent analysis of the polarization losses on the anode and the cathode, thereby creating an elegant catalyst characterization and optimization tool. 相似文献
Size- and charge-selective ion transfer across the zeolite-Y-modified interface between two immiscible electrolyte solutions (ZM-ITIES) is described. The zeolite-Y membrane is prepared from pressed disks by healing with tetraethyl orthosilicate (TEOS). Size- and charge-selective transfer of the tetraethylammonium cation, size-selective exclusion of tetrabutylammonium cation, and charge-selective exclusion of the tetrafluoroborate and perchlorate anions are demonstrated at the ZM-ITIES. The exclusion studies suggest that the membrane is coherent and contains a low density of pinholes, after healing with TEOS. Various factors affecting the ion transfer such as analyte concentration, supporting electrolyte concentration, and scan rate are investigated. The diffusion coefficient of tetraethylammonium ions within the zeolite-Y pores is found to be on the order of 10(-8) cm2 s(-1). 相似文献
Rubber materials have wide range of commercial applications such as, infant diapers, famine hygiene products, drug delivery devices and incontinency products such as rubber tubes, tyres, etc. In the present work, studies on mechanical properties of some selected rubber materials viz., natural rubber (NR), styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR) and ethylene propylene diene monomer (EPDM) have been carried out in three states viz., raw, vulcanized and reinforced. To enhance the quality of rubber elastomers, an attempt is made to prepare new elastomers called polyblends. In the present study an attempt is made to blend NR with NBR and with EPDM. We here report, a novel approach for the evaluation of various physico-mechanical properties such as mechanical strength, tensile strength, elongation and hardness. The method is simple, direct and fast and involves infrared spectral measurements for the evaluation of these properties. With the applications of modern infrared spectroscopy, the mechanical strength of these rubber materials have been analyzed by calculating the internal standards among the methyl and methylene group vibrational frequencies obtained from FTIR spectroscopy. Also the tensile strength measurements carried out by universal testing machine. The results pertaining physico-mechanical properties of the rubber derivatives undertaken in the present study obtained by IR-based method are in good agreement with data resulted from the standard methods. 相似文献