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1.
Summary The method for estimation of iodide formulated in the earlier publications of the series bas been modified by the use of sodium fluoride as the complexing agent in the place of oxalate or phosphoric acid. The results obtained are in excellent agreement with the calculated ones and the method has been successfully applied for the estimation of iodide in iodized salt. 相似文献
2.
Chandrashekar Ramarao Ramadevi Nandipati Rajasekhar Navakoti Ramanjaneyulu Kottamasu 《Tetrahedron letters》2012,53(6):637-640
1,2-Dihydroxy benzenes have been protected as cyclic diacetals using 2,3-butane dione. These diacetals are extremely robust and can be further chemically diversified and resolved with chirality embedded in the 1,4-dioxane ring attached to the aromatic back bone as a result of the anomeric effect. These systems can serve as ligands, auxiliaries or organocatalysts for asymmetric synthesis. 相似文献
3.
Ramanjaneyulu GS Darshan DV Mahendar K Kantam ML Prabhakar S 《European journal of mass spectrometry (Chichester, England)》2011,17(3):265-275
A set of diastereomeric α-sulfanyl-β-amino acid derivatives, which are important building blocks for pharmaceuticals with potent biological activity, are studied by electrospray ionization tandem mass spectrometry. The collision induced dissociation (CID) spectra of [M+H](+), [M+NH(4)](+), [M+Na](+) and [M+Li](+) of the diastereomers were studied, among them the CID of [M+Na](+) and [M+Li](+) showed consistent differences in the relative abundance of characteristic ions that enabled distinction of the anti isomers from syn isomers. The decomposition pathways for the diagnostic ions were arrived at based on high-resolution mass spectrometry data, multiple mass spectrometry data, deuterium labeling experiments and the mass shift in accordance with the substituents located at different places. Loss of (R(1)-C(6)H(4)-CH=NH) and (Cat-NH-SO(2)R(2)) from [M+Cat](+), where Cat=Na and Li, and the product ions as a results of McLafferty rearrangement involving either >S=O or >C=O group were found to be diagnostic. The McLafferty rearrangement product ions involving >S=O group were more abundant in syn isomers while those involving >C=O group were more abundant in anti isomer. The selectivity observed in the decomposition of [M+Li](+) ions was found to be similar to that of [M+Na](+) ions, but in few cases the differences are marginal in the decomposition [M+Li](+) ions. 相似文献
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5.
Ramanjaneyulu GS Sudhakar N Rao BV Prabhakar S 《Rapid communications in mass spectrometry : RCM》2008,22(14):2241-2247
Febrifugine is an alkaloid with potent antimalarial activity isolated from Dichroa febrifuga and Hydrangea umbellate, and it exists naturally with its diastereomeric component, isofebrifugine. Here we report the differentiation of diastereomeric synthetic precursors of isofebrifugine (1, cis) and febrifugine (2, trans) and a structurally similar model diastereomeric pair without a halogen substituent (3 and 4) by electrospray ionization (ESI) tandem mass spectrometry. Compounds 1-4 contain a tert-butoxycarbonyl (BOC) substituent, and the collision-induced dissociation (CID) spectra of the [M+H](+), [M+Na](+) and [M+Li](+) ions of 1-4 include the expected product ions corresponding to the loss of C(4)H(8) (isobutene) and of C(5)H(8)O(2) (BOC-H). Loss of C(5)H(8)O(2) is dominant in cis isomers (1 and 3) and/or loss of C(4)H(8) ions is dominant in trans isomers (2 and 4). The decomposition of [M+H](+) ions shows stereoselectivity in the formation of the [M+H-(BOC-H)-C(3)H(5)OBr](+) and [M+H-(BOC-H)-C(6)H(5)CH(2)OH](+) ions. The [M+Cat](+) ions (where Cat = Na or Li) additionally show loss of NaBr and HBr from [M+Cat-(BOC-H)](+), and these product ions are constantly more abundant in cis isomers than in trans isomers. The stereoselectivity for the product ion corresponding to the loss of [(BOC-H)+C(3)H(5)OBr] from [M+H](+) ions differs from that from [M+Cat](+) ions. 相似文献
6.
Summary The reaction between hydrogen peroxide and hydriodic acid has been used in the iodimetric estimation of peroxide by catalysing the reaction with 3 drops of 20% solution of sodium tungstate. The presence of preservatives, such as salicylic acid, boric acid and glycerol, does not interfere in the method. Sodium vanadate, ferric and ferrous iron also have a pronounced catalytic action on this reaction.The authors wish to thank Dr. Mata Prasad, D. Sc., F. R. I. C., F. N. I., for his encouragement and interest in this work. 相似文献
7.
Summary The conditions of decomposition of ferric phosphate complex under varying concentrations of iodide, acid and the complexing agent have been studied and made use of in the formulation of a method for the estimation of iodide, using chromic aeid-hydriodic acid reaction, phosphoric acid being substituted for the oxalate for binding the ferric iron in the method described in an earlier paper. 相似文献
8.
A short asymmetric approach for the synthesis of bis-tetrahydrofuran units of various annonaceous acetogenins is described. The key steps of the synthesis are self-cross metathesis and Sharpless asymmetric dihydroxylation. 相似文献
9.
P. S. Ramanjaneyulu K. L. Ramakumar Y. S. Sayi 《Accreditation and quality assurance》2010,15(12):665-671
Boron doped zirconium–niobium alloy is employed for neutron reactivity control in advanced nuclear reactors. An accurate knowledge
of the boron content and uncertainty associated with the measurement result is essential for reactivity calculations. In view
of the refractory nature of the alloy, boron determination in these matrices is a challenging task for analytical chemists.
Also due to non-availability of matrix-matched reference materials, direct solid analysis cannot be resorted to. With this
in view, a simple and sensitive method based on potentiometric determination of boron as tetrafluoroborate with tetrafluoroborate
ion selective electrode has been developed. After dissolving the sample, boron was quantitatively converted to BF4
− with the addition of HF. Potential response was measured with Orion 9305 BN BF4
− ion selective electrode. The response of the ion selective electrode was Nernstian in the range of 0.1–100.0 μg/g of boron
in the solution. The method has been validated by two independent methods namely spectrophotometry and inductively coupled
plasma-atomic emission spectrometry (ICP-AES). All identifiable sources of uncertainties in the methodology have been individually
assessed. The combined uncertainty is calculated employing uncertainty propagation law. The expanded relative uncertainty
in the measurement (coverage factor 2) is 6.50%. 相似文献
10.
NL Asfandiarov AI Fokin VG Lukin EP Nafikova GS Lomakin VS Fal'ko YV Chizhov 《Rapid communications in mass spectrometry : RCM》1999,13(12):1116-1123
A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd. 相似文献