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131.
Andreas Manz Elisabeth Verpoorte Carlo S. Effenhauser Norbert Burggraf Daniel E. Raymond D. Jed Harrison H. Michael Widmer 《Journal of separation science》1993,16(7):433-436
Miniaturization of separation columns implies equally reduced vol- umes of injectors, detectors, and the connecting channels. Planar chip technology provides a powerful means for the fabrication of micron-sized structures such as channels. This is demonstrated by two examples. An optical absorbance detector chip exhibits the expected behavior of a 1 mm optical path length cell despite its volume of 1 nL. A capillary electrophoresis device allows integrated injections of 100 pL samples, efficiencies of 70,000 to 160,000 theoretical plates in 10 to 20 seconds, and external laser-induced fluorescence detection at any capillary length of choice between 5 and 50 mm. 相似文献
132.
Reaction of the triolide 1 from (R)-3-hydroxybutanoic acid with Lawesson's reagent 5 leads to the mono-, di-, and trithio derivatives 6–8 which can be isolated in pure form (20–40% yields), and which have crystal structures very similar to the parent triolide 1 (Fig. 1). Similarly, pentolide 3 is converted to mixtures of various thio derivatives, three of which are separated ( 10–12 ) by HPLC and fully characterized. The X-ray structures of the mono- and of one of the dithiopentolides ( 10, 12 ) differ remarkably from each other (Fig. 3). Reduction of the thiotriolides 6–8 (NaBH4, R3SnH, Cl3SiH, Raney-Ni) gives 12-membered rings containing up to three ether groups (chiral crown ethers, 15, 17–19 ) in poor yields. The thiotriolides react spontaneously and in yields of up to 96% with ammonia, certain primary amines, and hydroxylamine to give imine and oxime derivatives with intact 12-membered-ring backbones ( 20, 22–24, 30 , see crystal structures in Figs. 4–7). The rigid structure of all the derivatives of triolide 1 puts the C?O, C?S, and C?NR O-, S-, and N-atoms in juxtaposition (a feature reminiscent of the side chains in the iron-binder enterobactin, Fig. 6). Imines containing PPh2 groups are prepared ( 30, 33, 35 ) from the thiotriolides and tested as chiral ligands for PdII-catalyzed 1,3-diphenyallylations (→ 37 , enantiomer ratio up to 77:23). The reactions described demonstrate that multiple reactions of the triolide 1 from (R)-3-hydroxybutanoic acid which proceed through tetrahedral intermediates are possible without ring opening – the skeleton is remarkably stable, and this might be exploited as a template for bringing up to three pendent substituents into close proximity to allow a study of their interactions and cooperative properties. Also, the di- and trithio derivatives 7 and 8 could be used for cross-linking in molecules containing primary NH2 groups. 相似文献
133.
Ranganathan Bharadwaj Andreas Windemuth S. Sridharan Barry Honig Anthony Nicholls 《Journal of computational chemistry》1995,16(7):898-913
We propose a fast implementation of the boundary element method for solving the Poisson equation, which approximately determines the electrostatic field around solvated molecules of arbitrary shape. The method presented uses computational resources of order O(N) only, where N is the number of elements representing the dielectric boundary at the molecular surface. The method is based on the Fast Multipole Algorithm by Rokhlin and Greengard, which is used to calculate the Coulombic interaction between surface elements in linear time. We calculate the solvation energies of a sphere, a small polar molecule, and a moderately sized protein. The values obtained by the boundary element method agree well with results from finite difference calculations and show a higher degree of consistency due to the absence of grid dependencies. The boundary element method can be taken to a much higher accuracy than is possible with finite difference methods and can therefore be used to verify their validity. © 1995 by John Wiley & Sons, Inc. 相似文献
134.
The protonation and deprotonation rates of the coordinated amide groups in the Cu2+-complexes of 1,8-diamino-3,6-diaza-2,7-octanedione (DED = L) have been studied by stopped-flow techniques. Starting at low pH from Cu2+ and DED the dimeric Cu2L24+-complex, fully formed within the mixing time of the stopped-flow instrument, reacts in two consecutive steps to yield the final product CuLH?2. The rate constants of the forward and backward reactions have been determined and are given in Table 1. The intermediate was identified as Cu2L2H?22+ by measuring its VIS.-absorption spectrum. The rate constants for the interconversion of the amide groups from the O- to the N-coordinated form in the Cu2+-complexes of DED, 2,10-dioxo-1, 4, 8, 11 tetraazaundecane (DANA) and triglycine (TRIGLY) are compared with each other. It is shown that these rate constants are similar, no matter whether the amide group is terminal or internal as long as the rotation is easily possible as is the case in the dimeric species Cu2L24+ and Cu2L2H?22+. However, for CuLH?2 the inter-conversion only takes place after opening of one of the chelate rings in a rapid protonation preequilibrium. 相似文献
135.
The azido tetrazolo valence isomerism of twenty 9-methyl-s-triazolo[4,3-c]tetrazolo[1,5-a]pyrimidines with different substituents at position 5 has been studied by means of 1H NMR spectroscopy. All the compounds have been found to be tetrazoles in the solid state and in (CD3)2SO solution; in CF3COOH azido and tetrazolo isomers are in equilibrium. From equilibrium constants K and thermodynamic data determined it is concluded that in this series K depends on both electronic effects and steric requirements of the 5-substituents. A linear relation between K and σ was found for 5-arylderivatives because ΔS° keeps approximately constant and the substituent mainly operates on ΔH°. 相似文献
136.
Calaminici P Jug K Köster AM Arbez-Gindre C Screttas CG 《Journal of computational chemistry》2002,23(2):291-297
This paper presents calculations of dipole moments (mu), static polarizabilities (alpha), and first hyperpolarizabilities (beta) of phosphonic acid stilbene derivatives calculated in the framework of density functional theory. These calculations were performed using a finite field approach implemented in the density functional program ALLCHEM and were of an all-electron type using local exchange-correlation functional and specially designed basis sets. The molecular structures have been fully optimized using the semiempirical program MSINDO. Some of the investigated stilbenes have been synthesized very recently while others are described for the first time. Donor and acceptor groups of these analogues have been modified and the influence of these changes on the first hyperpolarizabilities has been investigated. This work demonstrates that the nonlinear optical response beta of these compounds increases dramatically when the acceptor moiety is displaced by analogues containing alkali metal groups. A general mechanism for the design of novel nonlinear optical materials with large first hyperpolarizabilities is described. 相似文献
137.
Andreas Mandelis 《Chemical physics letters》1984,108(4):388-392
A new, powerful, and experimentally very convenient spectroscopic technique is described. The technique uses pyroelectric polyvinylidene difluoride (PVDF) thin film detectors in contact with solid or liquid samples. The instrumental and spectral characteristics of photopyroelectric spectroscopy (PPES) are presented, and its advantages over conventional photoacoustic spectroscopy (PAS) are discussed. 相似文献
138.
The prospects of performing DNA hybridisation assays in a novel sequential scheme are explored in this article. It is based on recording the kinetics of hybridisation on a microfluidic device measuring only 10 by 5 mm. It contains a split channel system for fast mixing and a subsequent meandering channel to observe the evolution of the mixture by optical means. The problems of diffusion limitations in the laminar flow regime are overcome by reducing the average diffusion distance to a few micrometers only. DNA oligomers (20-mers) of different sequences were injected on the chip for mixing. The detection of hybridisation was based on the fluorescence of DNA-intercalating dyes. Two modes of operation were investigated. First, the samples were injected into the micromixing device at a high flow rate of 40 microl min(-1). When the sample passed through the actual micromixing unit, the flow rate was reduced to allow for measurement of fluorescence levels at various steady-state reaction times in the range of 2-15 s, as defined by the channel geometry. Using this continuous flow approach, photobleaching of fluorophores could be avoided. In a buffer containing 0.2 M NaCl, 2 base-pair mismatches could routinely be detected within 5-20 s. Single base-pair mismatches were successfully identified under low salt conditions. In the second mode, the flow was completely stopped and the evolution of the total fluorescence signal influenced by the hybridisation of oligomers and photobleaching was observed. Whereas the sequence-dependent effects remained unchanged, the assay times between the mixing of two oligomers and clear identification of their hybridisation properties could be reduced down to a maximum of 5-7 s, in some cases even below 1 s. 相似文献
139.
Jolanta Olkowska‐Oetzel Dieter Fenske Petra Scheer Andreas Eichhfer 《无机化学与普通化学杂志》2003,629(3):415-420
Syntheses and Thermal Properties of Cluster Molecules, formed from Groups 11‐13‐16 Elements In the presence of PPh3, CuX (X = Cl, CH3COO) or AgOC(O)C6H5 and GaCl3 react in THF with S(SiMe3)2 or Se(SiMe3)2 to yield [Cu6Ga8Cl4S13(PPh3)6] ( 1 ), [Cu6Ga8Cl4Se13(PPh3)6] ( 2 ), [Ag6Ga8Cl4S13(PPh3)6] ( 4 ) and [Ag6Ga8Cl4Se13(PPh3)6] ( 5 ). The use of PnPr2Ph instead of PPh3 and subsequent layering with n‐hexane leads to the formation of the cluster [Cu6Ga8Cl4Se13(PnPr2Ph)12] ( 3a , 3b ). Reaction of CuCl, GaCl3 and PnPr3 with Se(SiMe3)2 in THF results in the crystallisation of the ionic cluster (HPnPr3)2[Cu2Ga4Cl4Se6(PnPr3)4] ( 6 ). The structures of 1 — 6 were determined by X‐ray single crystal structure analysis. Thermogravimetric measurements of the cluster molecules and powder diffraction patterns of the remaining powders reveal the potential use of them as single source precursor compounds for the synthesis of the related ternary solid state materials. 相似文献
140.
Thoma G Streiff MB Katopodis AG Duthaler RO Voelcker NH Ehrhardt C Masson C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(1):99-117
Polyvalent carbohydrate-protein interactions occur frequently in biology, particularly in recognition events on cellular membranes. Collectively, they can be much stronger than corresponding monovalent interactions, rendering it difficult to control them with individual small molecules. Artificial macromolecules have been used as polyvalent ligands to inhibit polyvalent processes; however, both reproducible synthesis and appropriate characterization of such complex entities is demanding. Herein, we present an alternative concept avoiding conventional macromolecules. Small glycodendrimers which fulfill single molecule entity criteria self-assemble to form non-covalent nanoparticles. These particles-not the individual molecules-function as polyvalent ligands, efficiently inhibiting polyvalent processes both in vitro and in vivo. The synthesis and characterization of these glycodendrimers is described in detail. Furthermore, we report on the characterization of the non-covalent nanoparticles formed and on their biological evaluation. 相似文献