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91.
Dipeptides (DP), namely valyl–glycine (Val–Gly), alanyl–proline (Ala–Pro), and valyl–proline (Val–Pro) were synthesized by classical solution phase methods and characterized. The kinetics of oxidation of amino acids (AA) and DP by N‐bromosuccinimide (NBS) was studied in the presence of perchlorate ions in acidic medium at 28°C. The reaction was followed spectrophotometrically at λmax = 240 nm. The reactions follow identical kinetics, being first order each in [NBS], [AA], and [DP]. No effect on [H+], reduction product [succinimide], and ionic strength was observed. Effects of varying dielectric constant of the medium and addition of anions such as chloride and perchlorate were studied. Activation parameters have been computed. The oxidation products of the reaction were isolated and characterized. The proposed mechanism is consistent with the experimental results. An apparent correlation was noted between the rate of oxidation of AA and DP. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 376–385, 2006 相似文献
92.
Four tetrapeptide analogues of elastin sequences, glycyl‐glycyl‐alanyl‐proline (GGAP), glycyl‐glycyl‐valyl‐proline (GGVP), glycyl‐glycyl‐isoleucyl‐proline (GGIP), and glycyl‐glycyl‐phenylalanyl‐proline (GGFP) were synthesized, based on their increasing order of hydrophobicity, by a classical solution phase method and were characterized. These tetrapeptides (TETPs) were oxidized using Mn(OAc)3 in 25% acetic acid at 298 K, and the kinetics of the reaction was monitored spectrophotometrically at λmax = 400 nm. A first‐order dependence of rate on each of [Mn(OAc)3], [OAc?], and substrate [TETP], an inverse order dependence on [H+], has been observed. The rate is independent of [Mn(II)]. However, an inverse order dependence on varying the dielectric constant using various percentages (v/v) of acetic acid has also been observed, and but addition of anions such as Cl? and ClO4? has insignificant effect on the rate. Activation parameters have been evaluated using the Arrhenius and Erying plots. The oxidation products were isolated and characterized. Based on the results obtained, a plausible mechanism involving [Mn(OAc)4]? has been proposed. An apparent correlation was noted between the rate of oxidation of these TETPs by Mn(III) in the presence of sulfate ions in sulfuric acid medium and Mn(OAc)3 in the acetic acid medium. The rate of oxidation with Mn(OAc)3 was observed to be slower than with the former. The rate of oxidation of GGFP was found to be higher than GGIP, GGVP, and GGAP. This may be due to the presence of an aromatic side chain and/or because of the increased hydrophobicity. The overall order of rate of oxidation of TETPs is GGFP > GGIP > GGVP > GGAP, which also represents an increasing order of their hydrophobicity. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 115–123, 2006 相似文献
93.
K.P. Gopinathan Nair Channe Gowda J.Shylaja Kumari S.J. Anasuya T.K. Umesh Ramakrishna Gowda 《Radiation Physics and Chemistry》1994,43(6):581-584
Total attenuation cross sections for several amino acids have been measured for Ba133 photons in a narrow beam good geometry setup, using a hyper pure germanium detector. These values are compared with the values calculated using the mixture rule based on the data of Hubbell for the individual elements and found to be in good agreement. 相似文献
94.
The present study deals with the static pressure and mean velocity fields generated due to the mixing of two plane turbulent
jets in a confined passage. Four different impingement angles, viz., 15, 30, 45 and 60 degrees, have been investigated. It
is found that the inlet angle is the most important parameter governing the extent of the central recirculation zone, the
wall recirculation zones, the position of the confluence point and the distance required for complete mixing. The rate of
decay of the maximum velocity is very rapid for inlet angles exceeding 45 degrees. 相似文献
95.
The real and imaginary parts,f’(E) and”(E) of the dispersion corrections to the forward Rayleigh scattering amplitude (also called anomalous scattering factors) for
the elements La, Ce, Pr, Nd, Sm, Gd, Dy, Ho and Er, have been determined by a numerical evaluation of the dispersion integral
that relates them through the optical theorem to the photoeffect cross-sections. The photoeffect cross-sections are derived
from the total attenuation cross-section data set experimentally determined using high resolution high purity germanium detector
in a narrow beam good geometry set-up for these elements in the photon energy range 5 to 1332 keV and reported earlier by
the authors. Below 5 keV, Scofield’s photoeffect cross-sections compiled in XCOM program have been interpolated and used.
Simple formulae forf” in terms of atomic number and energy have also been obtained. The data cover the energy region from 6 to 85 keV and atomic
numberZ from 57–68. The results obtained are found to agree fairly well with the other available data. 相似文献
96.
P.Z.?Saheb S.?Asokan Email author K.A.?Gowda 《Applied Physics A: Materials Science & Processing》2003,77(5):665-668
Samples of bulk Ge20Te80-xPbx(2x8) glasses have been prepared by melt quenching and their electrical switching behavior has been investigated as a function of lead content and sample thickness. The samples are found to exhibit a threshold type of switching. The switching voltages are found to decrease with increase in lead content and they show an anomaly at the composition x=5 and a minimum at the composition x=7.5 respectively. The samples are found to withstand about 28 switching cycles, before latching permanently to the ON state. PACS 61.43.Dq; 61.43.Fs; 72.20.Ht; 72.80.Ng; 73.61.Jc;
84.32.Dd; 85.30.Fg 相似文献
97.
Netkal M. Made Gowda Norman M. Trieff Dandinasivara S. Mahadevappa V.M.Sadagopa Ramanujam Robert S. Trieff 《Microchemical Journal》1982,27(1):87-96
The status of sodium N-chloro-p-nitrobenzenesulfonamide (chloramine-N) as a new redox titrant is examined. Analytical applications of CAN as a potential titrimetric reagent in the direct determination of diverse reducing agents such as glutathione, thioglycolic acid, thiourea, ascorbic acid, methionine, sulfite, and arsenite have been described. CAN has been synthesized and its structure elucidated from the spectral data and elemental analyses. The ultraviolet and infrared spectra and Fourier transform 1H and 13C nuclear magnetic resonance spectral data have been presented. 相似文献
98.
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100.