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71.
J. P. Shukla S. A. Pai M. S. Subramanian 《Journal of Radioanalytical and Nuclear Chemistry》1976,34(2):241-248
The co-ordination of plutonyl ions with 2-thenoyltrifluoroacetone (HTTA) has been investigated by distribution studies of239Pu between benzene and aqueous perchlorate medium at 25°C in order to understand the nature of the extracted species and their
stability. The formation constants of the first and second complexes have been evaluated by Rydberg's graphical method as
well as by least squares analysis of the distribution data using a computer programme. The overall formation constant (β2) for Pu(VI)-HTTA system has been found to be of the order of 1012. 相似文献
72.
Maverick AW Laxman RK Hawkins MA Martone DP Fronczek FR 《Dalton transactions (Cambridge, England : 2003)》2005,(1):200-206
The tetradentate Schiff-base ligand SIXH2 (alpha,alpha-bis(salicylimino)-m-xylene), prepared from salicylaldehyde and m-xylylenediamine, forms cofacial binuclear complexes with Pd and Cu. Of the two isomers possible (trans-syn and trans-anti) for M2(SIX)2, these complexes crystallize exclusively as the trans-anti isomer. In ansolvous Pd2(SIX)2, the metal-containing planes are approximately parallel, with PdPd 4.416(1) A. Pd2(SIX)2 also forms a crystalline solvate, in which the molecules adopt a more open conformation with longer metal-metal distances (5.109(1) and 5.112(1) A). The M...M distance is significantly longer in Cu2(SIX)2 (6.653(1) A), because of conformational changes in the m-xylylene moieties and substantial tetrahedral distortion about Cu. 相似文献
73.
A new type of inorganic biosensor is introduced. The sensor comprises glucose oxidase enzymes encapsulated in a sol-gel-derived
Prussian blue-silicate hybrid network. Glucose is detected by the biocatalytic reduction of oxygen followed by catalytic reduction
of hydrogen peroxide by the Prusian blue catalyst. The sol-gel silicate entails a rigid encapsulating matrix, the Prussian
blue provides chemical catalysis and charge mediation from the reduction site to the supporting electrode, and the enzyme
is responsible for the biocatalysis. The feasibility of a dual optical/electrochemical mode of analysis is also demonstrated. 相似文献
74.
The thermodynamics of the complexing between hexavalent U and 1-phenyl-3-methyl-4-benzoylpyrazolone-5 (PMBP) have been studied in 70 vol% aqueous—dioxane medium at 25 and 35±0.1°C following the Bjerrum—Calvin pH titration technique, as applied by Van Uitert and Haas. The ligand is mono-protonic. The refinement of results of formation constants has been accomplished by the method of least squares treatment after an algebraic transformation. The formation of 1:1, 1:2 and 1:3 complexes has been observed, the order of stability being log K1 > log K2 > log K3. The stability invariably increases with an increase in temperature both in aqueous as well as aqueous dioxane media. The changes in ΔG0, ΔH0 and ΔS0 at 25 and 35°C for the overall equilibrium constants have also been evaluated. Uranyl complexes of PMBP are entropy stabilized, the values of enthalpy changes being positive. Other factors which affect chelate stability are briefly discussed. 相似文献
75.
76.
Thasan Raju Sankar Manivasagan Balachandran Revathy Kumarasamy Kulangiappar Arunachalam Muthukumaran 《Tetrahedron letters》2007,48(21):3681-3684
Electrochemical oxidation of benzylic and substituted benzylic alcohols by two-phase electrolysis yields the corresponding aldehydes as products. The reaction was carried out in a single compartment cell with platinum electrodes at room temperature in chloroform using an aqueous sodium bromide solution (25%) containing a catalytic amount of HBr. The two-phase electrolysis resulted in high yields (74-96%) of benzaldehyde from primary alcohols and secondary alcohols were oxidized to the corresponding ketone but only in low yields under these conditions. 相似文献
77.
M. D. Naresh V. Subramanian V. Arumugam R. Sanjeevi 《Colloid and polymer science》1991,269(6):590-594
The mechanical behavior of keratin is studied, focusing on the mechanism of failure. For this purpose, a new procedure has
been suggested to differentiate the time-dependent and time-independent losses of energy at different strain levels. The matrix
of keratin fibers was found to play an important role in the mechanism of failure. 相似文献
78.
Chattaraj PK Roy DR Elango M Subramanian V 《The journal of physical chemistry. A》2005,109(42):9590-9597
It is demonstrated that among various possible isomers of all-metal aromatic compounds such as Al(4)(2-) and their complexes the most stable isomer with the minimum energy is the hardest and the least polarizable. A similar situation is observed for different isomers of all-metal antiaromatic compounds such as Al(4)(4-) and their complexes. It is shown that linear Al(4)(4-) is energetically more stable than its cyclic isomer. The reaction energies associated with the complexation processes highlight the stability of those complexes. The difference in energy, hardness, and polarizability between a cyclic molecule and its linear counterpart convincingly shows that an aromatic molecule exhibits negative changes in energy and polarizability but positive changes in hardness as expected from the principles of minimum energy, minimum polarizability, and maximum hardness. Although the aromaticity of Al(4)(2-) is unequivocally established through this study, the antiaromaticity picture in the case of Al(4)(4-) is shown to be poorly understood;however, the present analysis sheds light on this controversy. 相似文献
79.
T. Sudhakar Rao Ganapathi R. Revankar Ravi S. Vinayak Roland K. Robins 《Journal of heterocyclic chemistry》1991,28(7):1779-1788
Several disubstituted pyrazolo[3,4-d]pyrimidine, pyrazolo[1,5-a]pyrimidine and thiazolo[4,5-d]pyrimidine ribonucleosides have been prepared as congeners of uridine and cytidine. Glycosylation of the trimethylsilyl (TMS) derivative of pyrazolo[3,4-d]pyrimidine-4,6(1H,5H,7H)-dione ( 4 ) with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose ( 5 ) in the presence of TMS triflate afforded 7-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)pyrazolo-[3,4-d]pyrimidine-4,6(1H,5H)-dione ( 6 ). Debenzoylation of 6 gave the uridine analog 7-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidine-4,6(1H,5H)-dione ( 3 ), identical with 7-ribofuranosyloxoallopurinol reported earlier. Thiation of 6 gave 7 , which on debenzoylation afforded 7-β-D-ribofuranosyl-6-oxopyrazolo[3,4-d]pyrimidine-4(1H,5H)-thione ( 8 ). Ammonolysis of 7 at elevated temperature gave a low yield of the cytidine analog 4-amino-7-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidin-6(1H)-one ( 11 ). Chlorination of 6 , followed by ammonolysis, furnished an alternate route to 11 . A similar glycosylation of TMS-4 with 2,3,5-tri-O-benzyl-α-D-arabinofuranosyl chloride ( 12 ) gave mainly the N7-glycosylated product 13 , which on debenzylation provided 7-β-D-arabinofuranosylpyrazolo[3,4-d]pyrimidine-4,6(1H,5H)-dione ( 14 ). 4-Amino-7-β-D-arabinofuranosyl-pyrazolo[3,4-d]pyrimidin-6(1H)-one ( 19 ) was prepared from 13 via the C4-pyridinium chloride intermediate 17 . Condensation of the TMS derivatives of 7-hydroxy- ( 20 ) or 7-aminopyrazolo[1,5-a]pyrimidin-5(4H)-one ( 23 ) with 5 in the presence of TMS triflate gave the corresponding blocked nucleosides 21 and 24 , respectively, which on deprotection afforded 7-hydroxy- 22 and 7-amino-4-β-D-ribofuranosylpyrazolo[1,5-a]pyrimidin-5-one ( 25 ), respectively. Similarly, starting either from 2-chloro ( 26 ) or 2-aminothiazolo[4,5-d]pyrimidine-5,7-(4H,6H)-dione ( 29 ), 2-amino-4-β-D-ribofuranosylthiazolo[4,5-d]pyrimidine-5,7(6H)-dione ( 28 ) has been prepared. The structure of 25 was confirmed by single crystal X-ray diffraction studies. 相似文献
80.
Mareque-Rivas JC Prabaharan R Parsons S 《Dalton transactions (Cambridge, England : 2003)》2004,(10):1648-1655
Ligands derived from the tripodal N4 ligand tris(pyridylmethyl)amine ((pyCH2)3N, tpa) of general formula (6-RNHpyCH2)nN(CH2py)(3-n)(R = H, n= 1-3 L(1-3); R = neopentyl, n= 1-3 L'(1-3)) were used to elucidate and quantify the magnitude of the effects exerted by hydrogen bonding and hydrophobic environments in the zinc-water acidity of their complexes. The pKa of the zinc-bound water molecule of [(L(1-3))Zn(OH2)]2+ and [(L'(1-3))Zn(OH2)]2+ 1'-3' was determined by potentiometric pH titrations in water (1-3) or water-ethanol (1:1) (1'-3'). The zinc(II) water acidity gradually increases as the number of -NH2 hydrogen bonding groups adjacent to the water molecule increases. Thus, the zinc-bound water of [(L3)Zn(OH2)]2+ and [(tpa)Zn(OH2)]2+ deprotonate with pKa values of 6.0 and 8.0, respectively. The pKa of the water molecule, however, is only raised from 8.0 in [(tpa)Zn(OH2)]2+ to 9.1 in [(bpg)Zn(OH2)]+ (bpa =(pyCH2)2N(CH2COO-)). Moreover, the acidity of the zinc-bound water of several of the five-coordinate zinc(II) complexes with the hydrogen bonding groups is greater than that of four-coordinate [((12)aneN3)Zn(OH2)]2+ (pKa = 7.0). This result shows that the magnitude of the effect exerted by the hydrogen bonding groups can be larger than that induced by changing one neutral by one anionic ligand, and/or even by changing the coordination number of the zinc(II) centre. The X-ray structure of [(L'2)Zn(OH)]ClO4 2' and [(L'3)Zn(OH)]ClO4.CH3CN 3'.CH3CN is reported, and show the neopentylamino groups forming N-H...O hydrogen bonds with the zinc-bound hydroxide. Although, which have hydrogen bonding and hydrophobic groups, have a zinc-bound water more acidic than [(tpa)Zn(OH2)]2+, their pKa is not always lower than that of 1-3. This result suggests that a hydrogen bonding microenvironment may be more effective than a hydrophobic one to increase the zinc-water acidity. 相似文献