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1.
The use of open-access mass spectrometry to monitor synthetic chemistry reactions, and also the integrity and purity of new chemical entities, has been a part of the medicinal chemist's tool-box for more than 5 years. Originally in our group at Wyeth Research there were two open-access methods available to the chemists, flow injection analysis (FIA) and liquid chromatography/mass spectrometry (LC/MS). The FIA method was approximately 3 min long, while the LC/MS method was approximately 20 min long (including an 8 min gradient). Within the first 2 years, the total number of open-access analyses increased by approximately 125%. It is interesting, however, that the number of LC/MS analyses increased by more than 285%. This is attributed to the fact that the chemists began using the LC/MS data to monitor reactions and also to check final product integrity and purity. In addition, the number of chemists performing parallel synthesis reactions has increased; thus, individual chemists can produce sample sets of up to 100 vials. This paper describes the implementation of new methodology, which accommodates the need for much faster run times and also the ability to acquire alternating positive and negative ion spectra within the same run. In addition, the instrument has been configured to e-mail the resulting processed data report to the submitting chemist. Several methods have been developed, including structure elucidation using in-source collision-induced dissociation (CID) and night-time analysis. The LC/MS methods for this system are described herein and are applicable to both industrial and academic synthetic chemistry optimization efforts. 相似文献
2.
A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed. 相似文献
3.
Amita Gupta Alexei Yu Ganin Parmanand Sharma Vikrant Agnihotri LM Belova KV Rao Mikhail E Kozlov AA Zakhidov RH Baughman 《Pramana》2002,58(5-6):1051-1059
We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show
a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are
found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there
exists no report in literature on any BiNi compound which is magnetic. 相似文献
4.
In an attempt to identify and characterize the intermediates involved in multi-step palladium catalyzed coupling reactions, under fast atom bombardment (FAB) conditions, the selection of a matrix to enhance ion formation without degrading the palladium complex is critical. In general, it is observed that the analysis of tetrakis(triphenylphosphine)palladiurn(0) using glycerol, m-nitrobenzyl alcohol or o-nitrophenyl octyl ether as the FAB matrix compound produces several ions which correspond to complexes of the type PdxLyOz+ (L = PPh3; x = 1-4; y = 1-4; z = 0-2), in addition to clusters containing one or more matrix molecules. FAB mass spectra generated using triethanolamine- or tetramethylene sulfone (sulfolane) are observed to contain ions related to the palladium(0) complex with little or no interference from ions related to the oxidation or reduction processes. 相似文献
5.
Diane J. Lamb Hui M. Wang Larry M. Mallis Robert J. Linhardt 《Journal of the American Society for Mass Spectrometry》1992,3(8):797-803
Negative ion fast-atom bombardment tandem mass spectrometry has been used in the analysis of monosulfated disaccharides. These commercially obtained disaccharides have been enzymatically prepared from glycosaminoglycans using polysaccharide lyases. Three disaccharides from chondroitin sulfate and dermatan sulfate and two disaccharides from heparan sulfate and chemically derivatized heparin were analyzed. All five disaccharides were isomeric, with differences in sulfate position and linkage position. The full-scan mass spectra are useful in differentiating isomers when the sulfate group resides on different saccharide units. This structural information was obtained from fragment ions produced through cleavage at the glycosidic linkage. the full-scan mass spectra of each monosulfated disaccharide also produced intense molecular anions having long lifetimes. Collisional activation of these resulted in tandem mass spectra rich in significant product ions. Some of these fragment ions were formed through ring cleavage and were useful in the determination of both sulfate and linkage position. 相似文献
6.
A simple nonlinear buckling analysis is applied to a one-degree-of-freedom arch under impact loading in which viscous damping may also be included. Such a loading consists of a falling body striking centrally the joint mass of the arch in such a way that a completely plastic impact can be postulated. When there is no damping the exact dynamic buckling load for such a kind of loading-associated with an unbounded motion can be established by using a static criterion (approach). More specifically, it was shown that the dynamic buckling load corresponds to that unstable equilibrium state where the total potential energy of the system is zero. Furthermore, it was proved that the second variation of the total potential energy at the foregoing unstable equilibrium state is negative definite. This implies that the curve loading versus displacement resulting by the vanishing of the total potential energy has always a maximum on the afore mentioned unstable state. It was also found that the system may become sensitive to initial conditions. If damping is included the foregoing static criterion yields lower bound buckling estimates. These findings were verified by employing a highly efficient approximate technique as well as the numerical scheme of Runge-Kutta for solving any nonlinear initial-value problem. 相似文献
7.
A gas chromatograph/time-of-flight (GCT) mass spectrometer, with high mass measurement accuracy to within 5 ppm, has been used for the automated accurate mass analysis of multicomponent mixtures and drug discovery compounds. A multicomponent mixture was analyzed several times over the course of a week to assess the reproducibility and ruggedness of the automated method while operating the GCT in electron ionization mode. For example, the data for 31 radical cations generated via electron ionization was processed using automated software (i.e. OpenLynx) to provide for mass accuracies less than 5 ppm for nearly 100% of the ions from multiple injection data. Mass accuracies of the radical anions of polyaromatic hydrocarbons generated via negative chemical ionization, and protonated pyridines and quinolines generated via methane chemical ionization, were mainly less than 5 ppm from multiple injection data. In addition, the automated method has been used for the accurate mass analysis of drug discovery compounds. 相似文献
8.
A.N. Kounadis J. Mallis A. Sbarounis 《Archive of Applied Mechanics (Ingenieur Archiv)》2006,75(6-7):395-404
The postbuckling response of perfect and geometrically imperfect elastic columns resting on an elastic Winkler type foundation
is thoroughly discussed. This is established by employing an approximate analytic technique leading to very reliable results
in the vicinity of the critical state. It was found that the critical state of perfect columns is a stable symmetric bifurcation
point and consequently there is no sensitivity to initial geometrical imperfections. Moreover, a simple but readily analyzed
mechanical model is proposed to simulate the salient features of buckling mechanism of the column on elastic foundation with
those of the model. The simplicity, reliability and efficiency of the proposed analysis as well as the successful modeling
of the buckling mechanism of the column by that of a single mode mechanical model are illustrated with the aid of numerical
examples. 相似文献
9.
Kerns EH Di L Bourassa J Gross J Huang N Liu H Kleintop T Nogle L Mallis L Petucci C Petusky S Tischler M Sabus C Sarkahian A Young M Zhang MY Huryn D McConnell O Carter G 《Combinatorial chemistry & high throughput screening》2005,8(6):459-466
Integrity profiling of HTS hits is valuable for verification of the hit identity and purity. This provides early discovery researchers with more confident SAR theories. Methodology for integrity profiling of HTS hits must be high throughput, consume little material, and selectively provide structure-based data. Analytical techniques that can be utilized for integrity profiling methods are reviewed for their appropriateness in sample preparation, component separation, detection, purity quantitation, identity confirmation, and follow-up. 相似文献
10.