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91.
Asymmetric acyl-transfer promoted by readily assembled chiral 4-N,N-dialkylaminopyridine derivatives
Dálaigh CO Hynes SJ O'Brien JE McCabe T Maher DJ Watson GW Connon SJ 《Organic & biomolecular chemistry》2006,4(14):2785-2793
The development of a new class of chiral 4-N,N-dialkylaminopyridine acyl-transfer catalysts capable of exploiting both van der Waals (pi) and H-bonding interactions to allow remote chiral information to stereochemically control the kinetic resolution of sec-alcohols with moderate to excellent selectivity (s = 6-30). Catalysts derived from (S)-alpha,alpha-diarylprolinol are considerably superior to analogues devoid of a tertiary hydroxyl moiety and possess high activity and selectivity across a broad range of substrates. 相似文献
92.
Maher RC Cohen LF Gallop JC Le Ru EC Etchegoin PG 《The journal of physical chemistry. B》2006,110(13):6797-6803
We make systematic measurements of Raman anti-Stokes/Stokes (aS/S) ratios using two different laser excitations (514 and 633 nm) of rhodamine 6G (RH6G) on dried Ag colloids over a wide range of temperatures (100 to 350 K). We show that a temperature scan allows the separation of the contributions to the aS/S ratios from resonance effects and heating/pumping, thus decoupling the two main aspects of the problem. The temperature rise is found to be larger when employing the 633 nm laser. In addition, we find evidence for mode specific vibrational pumping at higher laser power densities. We analyze our results in the framework of ongoing discussion on laser heating/pumping under surface-enhanced Raman scattering (SERS) conditions. 相似文献
93.
Maher RC Cohen LF Le Ru EC Etchegoin PG 《The journal of physical chemistry. B》2006,110(39):19469-19478
We present an in-depth analysis of the experimental estimation of cross-sections in surface enhanced raman scattering (SERS) by vibrational pumping. The paper highlights the advantages and disadvantages of the technique, pinpoints the main aspects and limitations, and provides the underlying physical concepts to interpret the experimental results. Examples for several commonly used SERS probes are given, and a discussion on future possible developments is also presented. Obtaining good estimates of SERS cross-sections is, in general, an extremely hard problem and has been a longstanding ambition of the SERS community for reasons that go from the purely applied (quantification of signals) to the more fundamental (comparisons of theoretical electromagnetic enhancement factors with experiment). Any method that can produce a standard protocol for the estimation of cross-sections is, accordingly, of great interest and an effort to understand its principles and limitations is required. 相似文献
94.
95.
Mohammed A. Al-Nuri Mohammed A. Hannoun Nidal A. Zatar Maher A. Abu-Eid Waheed J. Al-Jondi Ahmad I. Hussein 《光谱学快报》2013,46(4):409-416
A new method for isolation and spectrophotometric determination of plumbagin is presented. Plumbagin was isolated by thin layer chromatography (TLC) and column chromatography (CC) techniques, as an orange tinged yellow long crystalline substances. Plumbagin exhibits two absrop-tion maxima at 410 and 510 nm. Stability of the color, pKa value, and the effect of pH were studied. Beer's law is obeyed over the range 0.9-45 ppm. The method is applied to the determination of plumbagin in roots, stems, and leaves of Plumbago europaea L. plant. 相似文献
96.
P Rodrigues Hoyne L M Benson T D Veenstra L J Maher S Naylor 《Rapid communications in mass spectrometry : RCM》2001,15(17):1539-1547
Electrospray ionization mass spectrometry is playing an increasing role in the study of noncovalent interactions involving biomolecules. RNA-RNA complexes are important in many areas of biology, including RNA catalysis, RNA splicing, ribosome function, and gene regulation. Here, microelectrospray mass spectrometry (microESI-MS) is used to study noncovalent base-pairing interactions between RNA oligonucleotides, an area not previously explored by this technique. Using a set of complementary RNA oligonucleotides, we demonstrate the formation of the expected double-helical RNA complexes composed of three distinct oligonucleotides. The ability to study specific RNA noncovalent interactions by microESI-MS has the potential to provide a unique method by which to analyze and assign precise molecular masses to RNA-RNA complexes. 相似文献
97.
Sheila Mawaziny Salah Arafa Magdy F. Iskandar Maher Z. El-Subee 《Journal of polymer science. Part A, Polymer chemistry》1976,14(3):671-675
Electron spin resonance (ESR) spectra were observed at ?160°C and at room temperature for γ-irradiated poly-α-methylstyrene. The spectrum observed at room temperature has been attributed to the radical species while that at ?160°C results from the same radical and superposition of the spectrum due to the radical ?H2-C(CH3)(C6H5)-. The radicals which are stable at room temperature could be used to graft vinyl acetate. 相似文献
98.
Azilah Abdul-Rahman Angelo A. Amoroso Timothy N. Branston Amitava Das John P. Maher Jon A. McCleverty Michael D. Ward Andrzej Wlodarczyk 《Polyhedron》1997,16(24):1182-4362
The new diphenolato complexes [{Mo(NO){HB(dmpz)3}Cl}2Q] where dmpz = 3,5-dimethylpyrazolyl and Q = OC6H4(C6H4O (n = 1 or 2), OC6H4CR=CRC6H4O (R = H or Et), and OC6H4CH=CHC6H4CH=CHC6H4O have been prepared and their electrochemical properties (cyclic and differential pulse voltammetry) compared with previously reported analogues where Q = OC6H4O, OC6H4EC6H4O (E = SO2, CO and S), OC6H4 (CO)C6H4 C6H4(CO)C6H4O and 1,5- and 2,7-O2C10H6. The electrochemical interaction between the redox centres in the new complexes is very weak, in contrast to that in the 1,4-benzenediolato and naphthalendiolato species. The EPR spectra of the reduced mixed-valence species [{Mo(NO){HB(dmpz)3}Cl}2Q]− where Q = 1,3- and 1,4-OC6H4O and OC6H4SC6H4O shows that they are valence-trapped at room temperature, whereas those of the dianions [{Mo(NO){HB(dmpz)3}Cl}2Q]2− where Q = 1,4-OC6H4O, OC6H4EC6H4O (E = CO or S) and OC6H4CH=CHC6H4CH=CHC6H4O shows that the unpaired spins on each molybdenum centre are strongly correlated (J, the spin exchange integral AMo, the metal-hyperfine coupling constant). The electrochemical properties and the comproportionation constants for the reaction [{Mo(NO){HB(dmpz)3} Cl}2Q] + [{Mo(NO){HB(dmpz)3}Cl}O]2]2−2[{Mo(NO) {HB(dmpz)3}Cl}2Q]− where Q = diphenolato bridge, are compared with related compounds containing benzenediamido and dianilido bridges. 相似文献
99.
In this paper we give a necessary and sufficient condition in terms of the Jacobi–Dunkl transform in order that a Jacobi–Dunkl
convolution of distributions is hypoelliptic. 相似文献
100.
We report the development of a new class of readily prepared chiral 4-(pyrrolidino)-pyridine catalysts capable of exploiting both van der Waals (pi) and H-bonding interactions, thus allowing remote chiral information to stereochemically control the kinetic resolution of sec-alcohols. 相似文献