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1.
Gas‐phase ion–molecule reactions for the identification of the sulfone functionality in protonated analytes in a linear quadrupole ion trap mass spectrometer 下载免费PDF全文
2.
Raghavendhar R. Kotha Ravikiran Yerabolu Duanchen Ding Lucas Szalwinski Xin Ma Ashley Wittrig John Kong John J. Nash Hilkka I. Kenttämaa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(17):4472-4477
The reactivity of a carbon-centered σ,σ,σ,σ-type singlet-ground-state tetraradical containing two meta-benzyne moieties was examined in the gas phase. Surprisingly, the tetraradical showed higher reactivity than its individual meta-benzyne counterparts. The reactivity of meta-benzynes is controlled by their (calculated) distortion energy ΔE2.3, singlet–triplet spitting ΔES–T, and electron affinity (EA2.3) of the meta-benzyne moiety at the transition state geometry for hydrogen-atom abstraction reactions. The addition of a second meta-benzyne moiety to a meta-benzyne does not significantly change EA2.3. However, ΔE2.3 is substantially decreased for both meta-benzyne moieties in the tetraradical, and this explains their higher reactivities. The decrease in ΔE2.3 for each meta-benzyne moiety in the tetraradical is rationalized by stabilizing spin–spin coupling between one radical site in each meta-benzyne moiety. Therefore, spin–spin coupling between the meta-benzyne moieties in this tetraradical increases its reactivity, whereas spin–spin coupling within each meta-benzyne moiety decreases its reactivity. 相似文献
3.
Raghupathi Mutyala Venkatram R. Reddy Ravikiran Donthi V.S. Ramakrishna Kallaganti Rajesh Chandra 《Tetrahedron letters》2019,60(10):703-706
The enantioselective synthesis of the tetrahydropyranopyrazole scaffold has been achieved. The quinidine catalyzed reaction of allenoates with arylidenepyrazolones proceeded with high enantio- and diastereoselectivity while the reactions of alkylidenepyrazolones were less efficient. Allene ketones also afforded tetrahydropyranopyrazole derivatives in high yields, however, with only moderate enantioselectivity. The primary adduct undergoes further functional group transformations without effecting the initially formed chiral centre. 相似文献
4.
Displacement field based on higher order shear deformation theory is implemented to study the static behavior of functionally graded metal–ceramic (FGM) beams under ambient temperature. FGM beams with variation of volume fraction of metal or ceramic based on power law exponent are considered. Using the principle of stationary potential energy, the finite element form of static equilibrium equation for FGM beam is presented. Two stiffness matrices are thus derived so that one among them will reflect the influence of rotation of the normal and the other shear rotation. Numerical results on the transverse deflection, axial and shear stresses in a moderately thick FGM beam under uniform distributed load for clamped–clamped and simply supported boundary conditions are discussed in depth. The effect of power law exponent for various combination of metal–ceramic FGM beam on the deflection and stresses are also commented. The studies reveal that, depending on whether the loading is on the ceramic rich face or metal rich face of the beam, the static deflection and the static stresses in the beam do not remain the same. 相似文献
5.
Shailendra K. Saxena Rupnayan Borah Vivek Kumar Hari Mohan Rai Ravikiran Late V.G. Sathe Ashisha Kumar Pankaj R. Sagdeo Rajesh Kumar 《Journal of Raman spectroscopy : JRS》2016,47(3):283-288
A combined effect of doping (type and species) and size on Raman scattering from silicon (Si) nanowires (NWs) has been presented here to study interplay between quantum confinement and Fano effects. The SiNWs prepared from low doping Si wafers show only confinement effect, as evident from the asymmetry in the Raman line‐shape, irrespective of the doping type. On the other hand SiNWs prepared from wafer with high doping shows the presence of electron–phonon interaction in addition to the phonon confinement effect as revealed from the presence of asymmetry and antiresonence in the corresponding Raman spectra. This combined effect induces an extra asymmetry in the lower energy side of Raman peak for n‐type SiNWs whereas the asymmetry flips from lower energy side to the higher energy side of the Raman peak in p‐type SiNWs. Such an interplay can be represented by considering a general Fano‐Raman line‐shape equation to take care of the combined effect in SiNWs. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
6.
Structural Chemistry - Manganese (Mn) is an important metal that is crucial in biological cell mechanism and function. However, its binding mechanism is poorly characterized. In the present study,... 相似文献
7.
An Antibacterial β‐Lactone Kills Mycobacterium tuberculosis by Disrupting Mycolic Acid Biosynthesis 下载免费PDF全文
Dr. Johannes Lehmann Dr. Tan‐Yun Cheng Dr. Anup Aggarwal Dr. Annie S. Park Dr. Evelyn Zeiler Dr. Ravikiran M. Raju Dr. Tatos Akopian Dr. Olga Kandror Prof. Dr. James C. Sacchettini Prof. Dr. D. Branch Moody Prof. Dr. Eric J. Rubin Prof. Dr. Stephan A. Sieber 《Angewandte Chemie (International ed. in English)》2018,57(1):348-353
The spread of antibiotic resistance is a major challenge for the treatment of Mycobacterium tuberculosis infections. In addition, the efficacy of drugs is often limited by the restricted permeability of the mycomembrane. Frontline antibiotics inhibit mycomembrane biosynthesis, leading to rapid cell death. Inspired by this mechanism, we exploited β‐lactones as putative mycolic acid mimics to block serine hydrolases involved in their biosynthesis. Among a collection of β‐lactones, we found one hit with potent anti‐mycobacterial and bactericidal activity. Chemical proteomics using an alkynylated probe identified Pks13 and Ag85 serine hydrolases as major targets. Validation through enzyme assays and customized 13C metabolite profiling showed that both targets are functionally impaired by the β‐lactone. Co‐administration with front‐line antibiotics enhanced the potency against M. tuberculosis by more than 100‐fold, thus demonstrating the therapeutic potential of targeting mycomembrane biosynthesis serine hydrolases. 相似文献
8.
Mass spectrometric identification of the N‐monosubstituted N‐hydroxylamino functionality in protonated analytes via ion/molecule reactions in tandem mass spectrometry 下载免费PDF全文
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Ravikiran Donthi Venkatram R. Reddy Sivakumar N. Reddy Rajesh Chandra 《Tetrahedron letters》2019,60(1):1-4
The base catalysed Tamura cycloaddition reaction of vinylidene indanediones afforded the corresponding spiro[indane-1,3-dione-1-tetralone] structures as single diastereomers in excellent yields. Chiral bifunctional hydrogen bonding thiourea catalysts rendered the reaction enantioselective. However, the selectivity observed was moderate with Soós catalyst providing an enantiomeric ratio of 82.5:17.5. 相似文献
10.
The polarimetric calibration of synthetic aperture radar (SAR) imagery requires the equalization of a multiple-input, multiple-output (MIMO) distortion system. For wide-band, wide-angle SAR systems, the distortion is frequency and angle dependent and can be accurately modelled as a two-dimensional finite impulse response (FIR) filter bank. This paper presents a design algorithm, using a Gröbner basis, to compute a FIR filter bank that exactly inverts the multi-channel distortion. The results presented for polynomial inversion of MIMO FIR systems hold for sampled data signals of arbitrary dimension. 相似文献