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51.
Kiran Kumar Morishetti Betty De Suan Huang Jessica Marney Yates Jianhua Ren 《Journal of the American Society for Mass Spectrometry》2010,21(4):603-614
The sequence and conformational effects on the gas-phase acidities of peptides have been studied by using two pairs of isomeric
cysteine-polyglycine peptides, CysGly3,4NH2 and Gly3,4CysNH2. The extended Cooks kinetic method was employed to determine the gas-phase acidities using a triple quadrupole mass spectrometer
with an electrospray ionization source. The ion activation was achieved via collision-induced dissociation experiments. The
deprotonation enthalpies (Δacid
H) were determined to be 323.9 ± 2.5 kcal/mol (CysGly3NH2), 319.2 ± 2.3 kcal/mol (CysGly4NH2), 333.8 ± 2.1 kcal/mol (Gly3CysNH2), and 321.9 ± 2.8 kcal/mol (Gly4CysNH2), respectively. The corresponding deprotonation entropies (Δacid
S) of the peptides were estimated. The gas-phase acidities (Δacid
G) were derived to be 318.4 ± 2.5 kcal/mol (CysGly3NH2), 314.9 ± 2.3 kcal/mol (CysGly4NH2), 327.5 ± 2.1 kcal/mol (Gly3CysNH2), and 317.4 ± 2.8 kcal/mol (Gly4CysNH2), respectively. Conformations and energetic information of the neutral and anionic peptides were calculated through simulated
annealing (Tripos), geometry optimization (AM1), and single point energy calculations (B3LYP/6-31+G(d)), respectively. Both
neutral and deprotonated peptides adopt many possible conformations of similar energies. All neutral peptides are mainly random
coils. The two C-cysteine anionic peptides, Gly3,4(Cys-H)−NH2, are also random coils. The two N-cysteine anionic peptides, (Cys-H)−Gly3,4NH2, may exist in both random coils and stretched helices. The two N-cysteine peptides, CysGly3NH2 and CysGly4NH2, are significantly more acidic than the corresponding C-terminal cysteine ones, Gly3CysNH2 and Gly4CysNH2. The stronger acidities of the former may come from the greater stability of the thiolate anion resulting from the interaction
with the helix-macrodipole, in addition to the hydrogen bonding interactions. 相似文献
52.
Kiran F. Shelke Suryakant B. Sapkal Kirti S. Niralwad Bapurao B. Shingate Murlidhar S. Shingare 《Central European Journal of Chemistry》2010,8(1):12-18
A green, mild and efficient method for Knoevenagel condensation of 3-formylchromone/2-chlroquinoline-3-carbaldehyde with active
methylene compounds such as Meldrum’s acid/ethyl cyanoacetate using biosupported cellulose sulphuric acid (CSA) in the solid-state
by grinding under solvent-free condition has been developed. This method provides several advantages including environmental
friendliness, shor t reaction times, high yields and a simple work-up procedure. Moreover, the CSA was successfully reused
for four cycles without significant loss of activity. 相似文献
53.
M.S.R.N. Kiran M. Ghanashyam Krishna K.A. Padmanabhan 《Solid State Communications》2011,151(7):561-563
Titanium nitride films of a thickness of ∼1.5 μm were deposited on amorphous and crystalline substrates by DC reactive magnetron sputtering at ambient temperature with 100% nitrogen in the sputter gas. The growth of nanostructured, i.e. crystalline nano-grain sized, films at ambient temperature is demonstrated. The microstructure of the films grown on crystalline substrates reveals a larger grain size/crystallite size than that of the films deposited on amorphous substrates. Specular reflectance measurements on films deposited on different substrates indicate that the position of the Ti-N 2s band at 2.33 eV is substrate-dependent, indicating substrate-mediated stoichiometry. This clearly demonstrates that not only structure and microstructure, but also chemical composition of the films is substrate-influenced. The films deposited on amorphous substrates display lower hardness and modulus values than the films deposited on crystalline substrates, with the highest value of hardness being 19 GPa on a lanthanum aluminate substrate. 相似文献
54.
The ferroelectric ceramics Ba5RTi3V7O30 (R=Ho, Gd, La) have been synthesized by solid-state reaction technique. Preliminary X-ray structural analysis confirmed a single-phase formation of the compound in orthorhombic structure. Surface morphology of the compounds was studied by scanning electron microscopy (SEM). Detailed studies of electrical properties (i.e., dielectric constant, loss tangent, ac conductivity) as a function of temperature (RT-773 K) and at four different frequencies (1 kHz, 10 kHz, 100 kHz and 1 MHz) show ferroelectric–paraelectric phase transition of the compounds of diffuse-type. The activation energy has been evaluated from ac conductivity following Arrhenius equation. The conductivity pattern shows that it is strongly frequency dependent and obeys Jonscher's power relation. 相似文献
55.
56.
Mauji Ram Salim Khan Prabhakar Jha Mather A. Khan Usha Kiran Saleem Javed Malik Z. Abdin 《Chromatographia》2008,68(1-2):129-133
A simple, rapid, specific and sensitive thin layer chromatographic (TLC) method has been developed for the quantitative estimation of mevalonic acid (MVA) in leaves of medicinal plants; Artemisia annua, Psorelia corylifolia, Vinca rosea, Withania somnifera and Barleria proinites. The assay procedure involved conversion of MVA to its lactone, mevalonolactone (MVAL). Mevalonic acid was extracted from the leaf tissues of plants. Separation of MVAL was carried out on silica gel 60 F254 TLC plates using benzene:acetone (3:2) as the mobile phase. The densitometric determination of MVAL was performed at 600 nm after derivatization with anisaldehyde reagent in absorption–reflectance mode. The method was validated over the linearity range of 100–500 ng spot?1 and correlation coefficient for the calibration curve was >0.99. The average recovery of MVAL, used as internal standard, was higher than 98%. The lower limit of detection was found to be 50 ng spot?1. 相似文献
57.
Jian-Jun Qin Maung Htun Oo Kiran A. Kekre Boris Liberman 《Journal of membrane science》2010,346(1):8-14
The objective of the study was to further develop a novel cleaning technique for reverse osmosis in reclamation of municipal secondary effluent. This technique is a new backwash method via direct osmosis (DO) by intermittent injection of the high salinity (HS) solution without stopping of high pressure pump and it is environment and membrane friendly technique. In the study, DO-HS trials were carried out with a UF-RO pilot system which was operated on site with the secondary treated effluent as the raw feed. Different operating conditions for DO-HS treatment in the actual process were investigated. It was found that the operation for implementation of the DO-HS cleaning technique developed was easy. For the first time, the actual profiles of HS concentration, DO backwash flow rate, brine flow rate and permeate pressure during DO-HS treatment have been demonstrated. It was observed that turbidity of the brine stream during DO-HS treatment at 3 NTU was 5 times higher than that before DO-HS treatment. The results from this study have confirmed the previous hypothesis with DO-HS treatment that there would be a strong driving force for DO backwash to lift and sweep the foulants from the membrane surface which would be carried over to the brine. The optimal plant operating conditions in terms of RO feed flow rate, HS concentration and HS injection time are ready for the DO-HS method to be adopted and validated in a long-term continuous plant operation. 相似文献
58.
Kiran Matcha 《Tetrahedron letters》2010,51(20):2754-6476
A concise synthesis of a highly functionalized tricyclic ring system representing the CDE core of nortriterpenoid schintrilactones A and B is described using a tandem ROM-RCM of a norbornene derivative. 相似文献
59.
A simple and efficient total synthesis of ellipticine was developed via the Suzuki-Miyaura coupling of sterically sensitive 2-hydroxybenzeneboronic acid with a multifunctional aryl halide using Pd(OAc)2 as a catalyst and Cu(OAc)2·H2O as an additive in DMSO/H2O as a key step followed by double N-arylation and cyclization. 相似文献
60.
Hosakere D Revanasiddappa Telangusadhushetty N Kiran Kumar 《Analytical sciences》2002,18(10):1131-1135
A simple, sensitive and rapid spectrophotometric method was developed for the determination of thallium(III) using trifluoperazine hydrochloride (TFPH). The method is based on the oxidation of TFPH by thallium(III) in a phosphoric acid medium to form a red-colored radical cation with an absorption maximum at 505 nm. Beer's law is valid over the concentration range of 0.5 - 6.5 microg ml(-1) of thallium(III). The molar absorptivity and Sandell's sensitivity of the color system are 2.14 x 10(4) l mol(-1) cm(-1) and 0.0095 microg cm(-2), respectively. The optimum reaction conditions and other analytical parameters were evaluated. The tolerance limit of the method towards various ions usually associated with thallium has been studied. The proposed method has been successfully applied to the analysis of thallium in alloys, minerals, standard reference material, water, and urine samples. 相似文献