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71.
V S Ramamurthy D P Mahapatra R T Yadav G V Ravi Prasad Arjun Gopalakrishna 《Pramana》1992,39(5):L583-L587
A conventional tandem Van de Graaff accelerator is used to produce charged carbon cluster beams. The unique capability of
the method for studying highly charged clusters unaccessible to other methods of producing cluster beams is demonstrated. 相似文献
72.
Ramamurthy Prabhakaran 《Experimental Mechanics》1980,20(9):320-321
Widely different techniques have been employed in the fabrication of transparent, birefringent, anisotropic model materials. Some of the techniques reported in the technical literature are briefly reviewed. A simple method of fabricating large plates of arbitrary layup is described. 相似文献
73.
Nicholas J. Turro Jeffrey McVey V. Ramamurthy Peter Lechtken 《Angewandte Chemie (International ed. in English)》1979,18(8):572-586
An adiabatic photoreaction is a chemical process that occurs entirely on a single excited electronic energy surface. As a rule, most photoreactions of organic molecules start on an excited electronic surface but “jump” to a lower surface somewhere along the reaction coordinate. There are, however, exceptions to this general rule. For example, photoreactions involving small structural changes and minor alterations in covalent bonding (e.g., proton transfer and complex formation) are commonly found to occur adiabatically. The purpose of this review is to survey examples of more complicated adiabatic photoreactions such as fragmentation, electrocyclic rearrangements, and geometrical isomerizations. The concepts employed are presented in an introductory discussion. 相似文献
74.
Sekar P Greyson EC Barton JE Odom TW 《Journal of the American Chemical Society》2005,127(7):2054-2055
This communication describes a new synthetic approach to one- (1D) and two-dimensional (2D) NbSe2 nanoscale materials using soft chemical methods. Our one-pot synthesis provides a direct route to control the morphology of nanostructures that can exhibit complex electronic properties, and can produce layered, nanocrystalline materials in high yield. 相似文献
75.
76.
Abstract Solid-state irradiation of cyclodextrin complexes of α,α-dimethyldeoxybenzoin results in the formation of a significant amount of rearrangement product, 4-isopropylbenzophenone, in addition to cage products. This behavior is not observed in the photolysis in solution or in micellar media. 相似文献
77.
R. Kumaran T. Varalakshmi E. J. Padma Malar P. Ramamurthy 《Journal of fluorescence》2010,20(5):993-1002
Photophysical studies of photoinduced electron transfer (PET) and non-PET based acridinedione dyes with guanidine hydrochloride
(GuHCl) were carried out in water and methanol. Addition of GuHCl to photoinduced electron transfer (PET) based acridinedione
dye (ADR 1) results in a fluorescence enhancement, whereas a non-PET based dye (ADR 2) shows no significant change in the
fluorescence intensity and lifetime. Addition of GuHCl to ADR 1 dye in methanol results in single exponential decay behaviour,
on the contrary a biexponential decay pattern was observed on the addition of GuHCl in water. Absorption and emission spectral
studies of ADR 1 dye interaction with GuHCl reveals that the dye molecule is not in the protonated form in aqueous GuHCl solution,
and the dye is confined to two distinguishable microenvironment in the aqueous phase. A large variation in the microenvironment
around the dye molecule is created on the addition of GuHCl and this was ascertained by time-resolved area normalized emission
spectroscopy (TRANES) and time-resolved emission spectroscopy (TRES). The dye molecule prefers to reside in the hydrophobic
microenvironment, rather in the hydrophilic aqueous phase is well emphasized by time-resolved fluorescence lifetime studies.
The mechanism of fluorescence enhancement of ADR 1 dye by GuHCl is attributed to the suppression of the PET process occuring
through space. 相似文献
78.
Shailaja J Kaanumalle LS Sivasubramanian K Natarajan A Ponchot KJ Pradhan A Ramamurthy V 《Organic & biomolecular chemistry》2006,4(8):1561-1571
Photochemistry of 17 aryl alkyl ketones included within cation exchanged zeolites has been examined. In solution five of the 17 ketones undergo intramolecular hydrogen abstraction reaction even in the presence of a chiral amine and the rest are photoreduced to the corresponding alcohol. Within zeolites all 17 ketones yielded in presence of a chiral amine, the corresponding alcohol as the major product. When a chiral amine was used as the coadsorbent within alkali ion exchanged zeolites, enantiomerically enriched alcohol was formed in all cases. The best chiral induction was obtained with phenyl cyclohexyl ketone (enantiomeric excess: 68%). 1H-13C Cross Polarization Magic Angle Spinning (CP-MAS) experiments, with a model ketone (perdeuterated acetophenone) and chiral amine (pseudoephedrine) included within MY zeolites, suggested that the cation brings the reactant and the chiral amine closer. The role of the cation in such a process is also revealed by the computation results. The results presented here highlight the importance of a supramolecular structure in forcing a closer interaction between a reactant and a chiral inductor that could be used to achieve asymmetric induction in photoproducts. 相似文献
79.
The photochemistry of 31 alpha-oxoamides capable of undergoing gamma-hydrogen transfer has been examined within zeolites. These molecules, upon excitation, yield two products--a beta-lactam and oxazolidinone--in solution, both resulting from gamma-hydrogen transfer. While in benzene the major product is oxazolidinone, within an MY zeolite, the main product is a beta-lactam. In this investigation, we have focused our attention on asymmetric induction in the formation of the beta-lactam product. Two approaches--using a chiral inductor and chiral auxiliary--have been employed. While in solution, in the presence of chiral inductors, achiral alpha-oxoamides yield beta-lactams with zero enantioselectivity; within zeolites, an ee of up to 44% has been achieved. Alpha-oxoamides appended with a chiral auxiliary gave beta-lactams with less than 5% diastereoselectivity in solution while within zeolites, the same alpha-oxoamides gave the products with de's of up to 83%. Such a remarkable influence of zeolites is attributed to an alkali ion interaction with the reactant alpha-oxoamides and to the confined environment of the zeolite interior. At this stage, we have not been able to provide a model with predictive power and further work is needed to understand this valuable asymmetric induction strategy. 相似文献
80.
The critical scaling behavior of K-doped Nd-Mn-O based double-exchange ferromagnetic compounds was studied by measuring isothermal magnetization of Nd0.84K0.16MnO3 and Nd0.77K0.23MnO3 samples. The critical exponents β, γ and δ corresponding to the spontaneous magnetization, initial susceptibility and isothermal magnetization, respectively, were determined by analyzing the magnetization data in terms of the modified Arrott plot method. The critical exponent values of both samples are found to be comparable to values predicted by a mean field model. The role of ferromagnetic clusters on the scaling behavior is discussed. The critical exponent values are found to be consistent with the Widom scaling relation and the universal scaling hypothesis. 相似文献