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1.
Schug KA Joshi MD Frycák P Maier NM Lindner W 《Journal of the American Society for Mass Spectrometry》2008,19(11):1629-1642
In this work is described the investigation of bivalent versus monovalent enantioselective molecular recognition in the context
of enantioselective separations. Electrospray ionization-mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS) are
used for evaluating enantioselective systems through the measurement of (1) relative solution-phase binding constants via
titration and (2) relative gas-phase binding via collision threshold dissociation. In HPLC, a cinchonane-type chiral stationary
phase (CSP) based on tert.-butylcarbamoylquinine provides vastly increased retention and enantioselectivity for separation of bivalent versus monovalent
alkoxy-benzoyl-N-blocked leucine enantiomers. The bivalent enantiomers are able to span and simultaneously interact with multiple
interaction sites on the CSP surface, leading to enhanced separation. ESI-MS titration measurements also show an increased
avidity for binding between bivalent selector and bivalent selectand, compared with the monovalent system. However, enhanced
enantioselectivities measured in HPLC for the bivalent system cannot be reproduced by MS due to inherent mechanistic differences.
Assumed discrepancies in relative response factors also give rise to systematic errors which are discussed. The results of
MS/MS gas-phase experiments show that enantioselectivity is essentially lost in the absence of solvation, but that dissociation
thresholds can provide a measure of relative dissociation energy in the bivalent interaction system compared to the monovalent
counterpart. Such measurements may prove useful and efficient in better understanding multivalent interactions, in line with
current theoretical considerations of effective concentrations and ion trap effects. This is the first application of mass
spectrometric methods for assessing increased avidity of binding in multivalent enantioselective molecular recognition. 相似文献
2.
Joshi MD Chalumot G Kim YW Anderson JL 《Chemical communications (Cambridge, England)》2012,48(10):1410-1412
A novel class of ionic liquids (ILs), exhibiting high selectivity towards boron species as well as the ability to phase separate from water, were synthesized from N-methyl-D-glucamine. The complexation of boric acid/borate with the ILs was confirmed using (11)B NMR. 相似文献
3.
In the present investigation, we describe some novel calixarene based heterocyclic compounds (5a-5i) in which 1,3,4-oxadiazole and 1,3,4-thiadiazole derivatives have been coupled with 5,11,17,23-tetra-tert-butyl-25,27-bis(chlorocarbonyl-methoxy)-26,28-dihydroxy calix[4]arene. All the newly synthesized calixarene based heterocyclic compounds have been characterized by elemental analysis and various spectroscopic methods like FTIR, (1)H NMR, (13)C NMR, and FAB-MS. All the final scaffolds have been subjected to antioxidant activity, in vitro antimicrobial screening against two gram (+ve) bacteria (S. aureus, S. pyogenes), two gram (-ve) bacteria (E. coli, P. aeruginosa) and two fungal strains (C. albicans, A. clavatus) and also have been screened for their antitubercular activity against Mycobacterium tuberculosis H(37)Rv. 相似文献
4.
Metal-ceramic composites produced by melt infiltration of the ceramic preform were studied. The ceramic preform of these materials is manufactured through freeze-casting process and the microstructure can be presented as distribution of the lamellar domains. Micromechanical models were used for the calculation of the effective elastic properties of the domains. The minimum compliance problem was solved for sample subjected to the four-point bending test. The optimal orientation and volume fracture of the micro constituents were identified using different models. The difference between the initial and optimized design was analyzed. The convergence of the provided optimization procedure was very rapid. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
K. B. Modi T. K. Pathak N. H. Vasoya V. K. Lakhani G. J. Baldha P. K. Jha 《Indian Journal of Physics》2011,85(3):411-420
The X-ray Debye temperatures, θ
M
, of spinel ferrite composition Ni0.5Zn0.5Fe2O4, mechanically milled upto 9 hrs, were determined from integrated intensities of selected Bragg reflections. The θ
M
was found to increase with milling time. The results are explained in the light of milling induced grain orientation and
surface effect. The values of θ
M
were found to be lower as compared to the Debye temperatures obtained from infrared spectral data analysis. The difference
can be explained on the basis of increase in an excess free volume in the form of vacancies and vacancy clusters associated
with grain boundaries. 相似文献
6.
Glucaminium-based ionic liquids are a new class of solvents capable of extracting boron-species from water with high efficiency. The complexation behavior of these ILs with borate was thoroughly studied using 11B NMR. Two different complexes, namely, monochelate complex and bischelate complex, were observed. 11B NMR was used extensively to determine the formation constants for monochelate and bischelate complexes. The IL concentration was observed to have a significant effect on the IL–borate complexes. Using an in situ dispersive liquid–liquid microextraction (in situ DLLME) method, the extraction efficiency for boron species was increased dramatically when lithium bis[(trifluoromethyl)sulfonyl]imide (LiNTf2) was used as the metathesis salt in an aqueous solution containing 0.1 M sodium chloride. IL regeneration after extraction was achieved using 0.1 M hydrochloric acid. The extraction efficiency of boron species was consistent when the IL was employed after three regeneration cycles. The selectivity of the IL for boron species in synthetic seawater samples was similar to performing the same extraction from Milli-Q water samples. 相似文献
7.
Systematic Structural Characterization of Chitooligosaccharides Enabled by Automated Glycan Assembly
8.
We found that the PVC membrane, containing azo calix[4]arene is a suitable ionophore, exhibited a Nernstian response for neodymium (Nd3+) ions (with slope of 19.8 ± 0.2 mV decade−1 for the triply charged ion) over a wide linear range of 4.0 × 10−8 to 1.0 × 10−1 mol L−1 with a detection limit 1.0 × 10−8 mol L−1, a relatively fast response time, in the whole concentration range (<10 s), and a considerable life time at least for four months in the pH range of 4.0-8.0. Furthermore, the electrode revealed high selectivity with respect to all the common alkali, alkaline earth, transition and heavy metal ions, including the members of the lanthanide family other than Nd3+. Concerning its applications, it was effectively employed for the determination of neodymium ions in industrial waste water as well as in lake water. 相似文献
9.
First Total Synthesis of Trehalose‐Containing Branched Oligosaccharide OSE‐1 of Mycobacterium gordonae (Strain 990)
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Manishkumar A. Chaube Prof. Dr. Suvarn S. Kulkarni 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(39):13544-13548
The first total synthesis of the branched oligosaccharide OSE‐1 of Mycobacterium gordonae (strain 990) is reported. An intramolecular aglycon delivery approach was used for constructing the desymmetrized 1,1′‐α,α‐linked trehalose moiety. A [3+2] glycosylation of the trisaccharide donor and trehalose acceptor furnished the right hand side pentasaccharide. Regioselective O3 glycosylation of L ‐rhamnosyl 2,3‐diol allowed expedient synthesis of the left hand side tetrasaccharide. The nonasaccharide was assembled in a highly convergent fashion through a [4+5] glycosylation. 相似文献
10.
Cu(I) and Ni(II) coordination polymers with 4,4′-bipyridine and 2,2′-bipyridine, respectively, that have been synthesized from an ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate) gave different coordination environment and supramolecular networks than the corresponding synthesis from the other solvents. The resultant complexes were characterized by single crystal x-ray diffraction methods. 相似文献