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排序方式: 共有398条查询结果,搜索用时 203 毫秒
101.
Ramaswamy Murugavel Prof. Subramaniam Kuppuswamy Nayanmoni Gogoi Ramamoorthy Boomishankar Dr. Alexander Steiner Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(3):994-1009
In contrast to the well‐known reaction of phosphonic acids RP(O)(OH)2 with divalent transition‐metal ions that yields layered metal phosphonates [RPO3M(H2O)]n, the 2,6‐diisopropylphenyl ester of phosphoric acid, dippH2, reacts with zinc acetate in methanol under ambient conditions to afford tetrameric zinc phosphate [(ArO)PO3Zn(MeOH)]4 ( 1 ). The coordinated methanol in 1 can be readily exchanged by stronger Lewis basic ligands at room temperature. This strategy opens up a new avenue for building double‐four‐ring (D4R) cubane‐based supramolecular assemblies through strong intercubane hydrogen‐bonding interactions. Seventeen pyridinic ligands have been used to synthesize as many D4R cubanes [(ArO)PO3Zn(L)]4 ( 2 – 18 ) from 1 . The ligands have been chosen in such a way that the majority of them contain an additional functional group that could be used for noncovalent synthesis of extended structures. When the ligand does not contain any other hydrogen‐bonding donor–acceptor sites (e.g., 2,4,6‐trimethylpyridine (collidine)), zero‐dimensional D4R cubanes have been obtained. The use of pyridine, lutidine, 2‐aminopyridine, and 2,6‐diaminopyridine, however, results in the formation of linear or zigzag one‐dimensional assemblies of D4R cubanes through strong intermolecular C? H???O or N? H???O interactions. Construction of two‐dimensional assemblies of zinc phosphates has been achieved by employing 2‐hydroxypyridine or 2‐methylimidazole as the exo‐cubane ligand on zinc centers. The introduction of an alcohol side chain on the pyridinic ligand in such a way that the ? CH2OH group cannot participate in intracubane hydrogen bonding (e.g., pyridine‐3‐methanol, pyridine‐4‐methanol, and 3,5‐dimethylpyrazole‐N‐ethanol) leads to the facile noncovalent synthesis of three‐dimensional framework structures. Apart from being useful as building blocks for noncovalent synthesis of zeolite‐like materials, compounds 1 – 18 can also be thermolyzed at approximately 500 °C to yield high‐purity zinc pyrophosphate (Zn2P2O7) ceramic material. 相似文献
102.
Cairncross RA Becker JG Ramaswamy S O'Connor R 《Applied biochemistry and biotechnology》2006,131(1-3):774-785
Management of moisture penetration and hydrolytic degradation of polylactide (PLA) is extremely important during the manufacturing, shipping, storage, and end-use of PLA products. Moisture transport, crystallization, and degradation, in PLA have been measured through a variety of experimental techniques including size-exclusion chromatography, differential scanning calorimetry, and X-ray diffraction. Quartz crystal microbalance and dynamic vapor sorption experiments have also been used to measure moisture sorption isotherms in PLA films with varying crystallinity. A surprising result is that, within the accuracy of the experiments, crystalline and amorphous PLA films exhibit identical sorption isotherms. 相似文献
103.
Copper(II) perchlorate and (PhCONH)P(O)(OH)2 (H2bpa) react in methanol to yield [Cu(Hbpa)2]n, a novel layered solid that displays several interesting features. Unlike the previously reported copper phosphonates, a rare hexacoordination around the metal is observed in the title compound because of the amide C=O coordination to Cu in addition to the phosphoramidate P-O coordination. The six-membered chelate rings present in the title compound are made up of five different elements (Cu, P, C, N, and O). 相似文献
104.
R. P. Tripathi H. C. Verma S. Chandrasekhar S. Ramaswamy 《Hyperfine Interactions》2008,186(1-3):153-160
The paper describes part of the study carried out on the iron bearing phases of china clays collected from different china clay reserves of the country. Chemical assays of the clays as well as the “panned” impurities were determined by standard methods and the rational mineral data was calculated from the composition. XRD and thermal analysis also were carried out to get the mineralogy of the samples. Mössbauer spectral studies were conducted on the iron rich phases separated from the clays by “panning” to get information on the different iron minerals present in these clays. It was observed that Mössbauer spectra of the impurities from the low iron containing clays were qualitatively much different from those of the impurities from the high iron containing clays. 相似文献
105.
Bejoy Francis Sabu Thomas R. Sadhana Nicole Thuaud R. Ramaswamy Seno Jose V. Lakshmana Rao 《Journal of Polymer Science.Polymer Physics》2007,45(17):2481-2496
Bisphenol‐A‐based difunctional epoxy resin was modified with poly(ether ether ketone) with pendent tert‐butyl groups (PEEKT). PEEKT was synthesized by the nucleophilic substitution reaction of 4,4′‐difluoro benzophenone with tert‐butyl hydroquinone in N‐methyl‐2‐pyrrolidone. Blends with various amounts of PEEKT were prepared by melt‐mixing. All the blends were homogeneous in the uncured state. The glass transition temperature of the binary epoxy/PEEKT blends was predicted using several equations. Reaction‐induced phase separation was found to occur upon curing with a diamine 4,4′‐diaminodiphenyl sulfone. The phase morphology of the blends was studied using scanning electron microscopy. From the micrographs, it was found that PEEKT‐rich phase was dispersed in a continuous epoxy matrix. The domain size increased with the amount of PEEKT in the blends. The increase in domain size was due to the coalescence of the domains after phase separation. Dynamic mechanical analysis of the blends gave two peaks corresponding to epoxy‐rich phase and thermoplastic‐rich phase. The tensile strength and modulus of the blends remained close to that of the unmodified resin, while the flexural properties decreased with the addition of PEEKT to epoxy resin. The fracture toughness of the epoxy resin increased with the addition of PEEKT. Investigation of the fracture surfaces revealed evidences for local plastic deformation of the matrix, crack pinning, crack path deflection, and ductile tearing of PEEKT‐rich phase. Thermogravimetric analysis revealed that the initial decomposition temperature of the blends were close to that of the unmodified resin. Finally, the properties of the blends were compared with other modified PEEK/epoxy blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2481–2496, 2007 相似文献
106.
107.
108.
A. Ousegui S. Zhu H. S. Ramaswamy A. Le Bail 《Journal of Thermal Analysis and Calorimetry》2006,86(1):243-248
The evaluation of the latent heat and enthalpy of fusion of food systems
in the case of high pressure–low temperature processing is important
for modelling purposes as well as for technical applications. A high pressure
calorimeter has been designed for this purpose. The high pressure calorimeter
was used to evaluate the latent heat during a pressure scan at constant temperature.
It permits to measure the heat of phase transitions and to obtain the relationship
between the initial freezing temperature T
ifp
and the average pressure while the phase transition is going on.
This
work presents a modelling of results obtained from an experimental approach
using a high pressure calorimeter and from a mathematical model developed
from existing data on the phase change of pure water.
The modelling
work consisted in evaluating the latent heat measured in previous tests from
computations taking into account the dependence of the latent heat of fusion
of water on pressure. Models predicting the amount of frozen water in a food
matrix under atmospheric conditions were used to determine the initial amount
of frozen water in the sample. Then a stepwise procedure was operated in a
program to reproduce the pressure rise occurring during a high pressure calorimeter
test. The amount of melted ice at each pressure step was calculated using
conventional ice fraction models, which were adapted to pressure dependence
of the initial freezing temperature and the dependence of the latent heat
pressure. The comparison was satisfactory, especially at low temperatures. 相似文献
109.
Ramaswamy Ravichandran Soundar Divakar 《Journal of inclusion phenomena and macrocyclic chemistry》1993,16(3):201-208
Studies on the effect of-cyclodextrin (BCD) and its derivatives on the selectivity in hydroxymethylation of guaiacol by formaldehyde was carried out. Fairly high selectivity with respect to isovanillyl alcohol formation was achieved. Significantly, the selectivity-enhancing effects of 2,6-di-O-methyl-BCD was much larger, giving rise to 22% more of isovanillyl alcohol formation than BCD and its polymer. UV, fluorescence,1H-NMR spectroscopic and potentiometric studies were also carried out to determine the orientation of guaiacol inside the BCD cavity. 相似文献
110.
Ultraviolet-A induced changes in photosystem II of thylakoids: effects of senescence and high growth temperature 总被引:3,自引:0,他引:3
Nayak L Biswal B Ramaswamy NK Iyer RK Nair JS Biswal UC 《Journal of photochemistry and photobiology. B, Biology》2003,70(2):59-65
Ultraviolet-A (UV-A) radiation induced changes in photosystem II (PS II) of senescing leaves of wheat seedlings were investigated. UV-A radiation did not show any significant effect on the level of photosynthetic pigments. However, the decline in F(v)/F(m) and oxygen evolution rate indicated the damaging effect of the radiation on primary photochemistry of PS II. Modification at the Q(B)-binding site was inferred from the observed downshift of peak temperature of thermoluminescence (TL) B-bands. The UV-A induced changes in PS II of chloroplasts from senescing leaves were found to be synergistically accelerated by high growth temperature. 相似文献