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81.
We present results from a computational study of 4-[4-(dimethylamino)-phenylazo] benzene boronic acid (DABBA) (the 4'-boronic acid isomer of the aminoazobenzene dye N,N-dimethylaminoazobenzene) and its associated anion, as well as, several cyclic esters formed from these azoborates and various conformers of D-glucose. Azo dyes that also contain one or more boronic acid functional groups are of practical importance in the development of chemical sensors for saccharide recognition because of their ability to induce a visible color change upon binding. The lowest-energy DABBA:D-glucose esters found in this investigation consistently involved at least one of the exocyclic hydroxymethyl groups on the D-glucose moiety rather than vicinal cis or trans diol arrangements of hydroxyl groups on the ring. 相似文献
82.
Aromatic primary amines are determined by injection into dilute hydrochloric acid carrier which merges sequentially with 4-N-methylaminophenol and dichromate. The purple-red color formed by oxidative coupling of amines with 4-N-methylaminophenol is measured at 530 nm. In contrast to the manual procedure, the flow-injection procedure avoided errors arising from the instability of the coupling intermediate, oxidation of the amine, and too great an excess of the oxidant. The method improves the selectivity for certain amines in the presence of those which are sterically hindered or have an electron-deficient aromatic nucleus. Nitrite is determined by diazotization of sulfanilamide and quantifying the residual sulfanilamide by oxidative coupling. The sample thourghout for the assay of amines (0.05–20 μg ml?1 NH2-N) and nitrite (1–10 μg ml?1 NO2--N) was 120 h?1. A system for the consecutive determination of aromatic primary amines and nitrite is decribed. 相似文献
83.
Tushar K. Chakraborty B.Krishna MohanS.Kiran Kumar Ajit C. Kunwar 《Tetrahedron letters》2003,44(3):471-473
Synthesis and conformational studies of two short peptides containing pyrrole amino acids (1, Paa), Boc-Paa-Paa-d-Pro-Gly-Xaa-Paa-Paa-OMe (2: Xaa=Ala; 3: Xaa=Val), were carried out in which it was established that replacement of Ala in 2 with a Val residue helps peptide 3 to adopt a well-defined β-hairpin conformation in a nonpolar solvent, like CDCl3. 相似文献
84.
Alex. G. Harrison R. Krishna Mohan Rao Kallury 《Journal of mass spectrometry : JMS》1980,15(5):249-256
A study of the electron impact and chemical ionization (H2, CH4, and iso-C4H10) mass spectra of stereoisomeric benzoin oximes and phenylhydrazones indicates that while the former can be distinguished only by their chemical ionization mass spectra the latter are readily distinguishable by both their electron impact and chemical ionization mass spectra. The electron impact mass spectra of the isomeric oximes are practically identical; however, the chemical ionization spectra show that the E isomer forms more stable [MH]+ and [MH? H2O]+ ions than the Z isomer for which both the [MH]+ and [MH? H2O]+ ions are relatively unstable. In electron impact the Z-phenylhydrazone shows a lower [M]+˙ ion abundance and more facile loss of H2O than does the E isomer. This more facile H2O loss also is observed for the [MH]+ ion of the Z isomer under chemical ionization conditions. 相似文献
85.
Herein we report the synthetic strategy towards the pyran core of macrolactin 3 via Sharpless epoxidation, titanium(IV) mediated regioselective ring-opening reaction of epoxyallyl alcohol/epoxy alcohol and oxa-Michael addition as the key steps. 相似文献
86.
3,4-Diaroylfuroxans 1 react with various dipolarophiles 3 under microwave activation to afford the cycloadduct 4 instead of the expected isoxazole 5 in good yields in the absence of solvent. 相似文献
87.
S. Krishna Prasad Yoji Maeda Corresponding author D. S. Shankar Rao S. Anitha Nagamani Uma S. Hiremath C. V. Yelamaggad 《Liquid crystals》2013,40(11):1277-1283
The phase behaviour of two achiral bent core banana-shaped compounds, the hexyloxy (compound I) and decyloxy (compound II) members of the 1,3-phenylene bis[N-(2-hydroxy-4-n-alkoxybenzylidene)-4′-aminobenzoate] series was investigated under hydrostatic pressures up to 300?MPa using high pressure differential thermal analysis and light transmission methods. The reversible transition sequence crystal (Cr1)–B1 phase–isotropic liquid (I), observed at room pressure for compound I, remains in the pressure region up to c 70?MPa. At higher pressures a pressure-induced crystalline phase (Cri) appears between the Cr1 and B1 phases, its temperature region becoming wider with increasing pressure. The temperature vs. pressure phase diagram shows a triple point of 72.9?MPa and 160.3°C for the Cr1, Cri and B1 phases, indicating the lower limit of pressure for the Cri phase. In compound II the reversible transition sequence crystal (Cr1)–B2 phase–I is seen over the whole pressure region, and the temperature range of the B2 phase remains unaltered. It is concluded that both the B1 and B2 banana phases are stable over the whole pressure region studied. 相似文献
88.
89.
Vijaya Bhargavi M. Shashikala P. Sumakanth M. Krishna C. 《Russian Journal of General Chemistry》2018,88(4):804-811
Russian Journal of General Chemistry - In the present study novel 1,2,4-oxadiazolo sulfonamides 3a–3o are synthesized by an efficient method based on the reaction of 1,2,4-oxadiazole amines... 相似文献
90.
S. Krishna Prasad R. Shashidhar B. R. Ratna B. K. Sadashiva G. Heppke S. Pfeiffer 《Liquid crystals》2013,40(1):111-116
Abstract We present here precise measurements of the layer spacing for two compounds, viz. 4-n-heptyloxyphenyl-4′-(4″-cyanobenzoyloxy)benzoate and 4-n-undecyloxyphenyl-4′-(4″-cyanobenzyloxy)benzoate. Contrary to earlier reports our data do not show any jump in the layer spacing at the expected Ad-A2 transition temperature, showing thereby that for both compounds A2 evolves continuously from the Ad phase. 相似文献