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131.
Combinatorial development of new catalysts with phosphodiesterase and esterase activities requires specific fluorescent probes for rapid visual detection of hydrolytic activity. Such fluorescent probes have been synthesized with special attention to solubility in water and stability towards spontaneous hydrolysis at a given pH. The probes reported here include compound 5 based on a fluorescein fluorophore, compound 12 for FRET-detection of phosphodiester hydrolysis and compound 25 based on a quinolinium fluorophore. 相似文献
132.
The title compound is a crucial intermediate in the biomimetic conversion of vincadifformine 1 into vincamine 7. Its configuration at C-16 is established by a combination of chemical and spectroscopic evidence. Iodine oxidation converts 14 into the bridged lactam 18, thus proving a β configuration for the hydroxy group at C-16. The same reaction applied to vindoline 19 gives 21 identical with one of the compounds obtained by microbiological transformation of 19. The 13C NMR spectra of derivatives 3 and 8 (obtained by oxidation of vincadifformine) show that oxidation proceeds with introduction of the substituent at C-16, with a β-configuration. The alcohol 3 however, posesses a different conformation due to strong hydrogen bonding with N-4. 相似文献
133.
J. P. Dodelet J. Le Brech C. Chapados R. M. Leblanc 《Photochemistry and photobiology》1980,31(2):143-155
Abstract— Alcohol vapors affect the photovoltaic properties of anhydrous chlorophyll a (Chi a). At 23°C, a photovoltaic cell of the type Allanhydrous Chi a|Ag has been successively submitted to non saturating vapors of methanol, ethanol, 1-propanol, 2-propanol, cyclopropyl carbinol, cyclopentanol, methyl cyclopropyl carbinol, 1-butanol, 1-pentanol and chloroethanol. The action spectrum of anhydrous Chi a has a maximum in the red at 672 nm. This maximum is shifted towards 700 nm under the influence of alcohol vapors. The most important changes occur for ethanol, 1-propanol and 2-propanol. In the same way, the conversion efficiencies of light energy into electrical energy, measured at the maximum in the red are, for the same alcohols, higher than the initial value 1.7 times 10-2 % obtained on the average for anhydrous Chi a. A maximum value of 6.3 times 10-2 % has been obtained after rehydration of Chi a solvated with 2-propanol. The influence of alcohol vapors has been interpreted in terms of microcapillarity of anhydrous Chi a and a mean microcavity radius of 11 ± 6 Å has been deduced from the photocurrent variation with the amount of alcohol vapor present in the measuring area. Furthermore, the action spectrum shift towards 700 nm has been interpreted by the formation, at 23°C, of Chi a special aggregates whose action spectrum has been obtained by difference. Infrared spectroscopy demonstrated that anhydrous Chi a obtained from electrodeposition is an assembly of Chi a dimers and that alcohol vapors, producing the special aggregates formation at 23°C, induce a decrease of the free C=O ketone band and an increase of the associated C=O ketone. The C=O esters band is not affected by the Chi a reorganization. 相似文献
134.
A novel, sensitive method for detecting protease inhibitors by using fluorescent protease substrates in gels is described. The protease inhibitors were separated on sodium dodecyl sulfate (SDS)-polyacrylamide gels containing a copolymerized peptide substrate, namely 4-methyl-coumaryl-7-amide (MCA). As the incorporated substrates in the gel, Boc-Phe Ser-Arg-MCA was used for trypsin, Suc-Ala-Ala-Pro-Phe-MCA for alpha-chymotrypsin, and Z-Phe-Arg-MCA for papain. After electrophoresis, washing and incubating the gel with the target protease solutions allowed the substrate to be cleaved by the protease, and the release of the fluorescent 7 amino-4 methyl-coumarin (AMC), which was detected under a UV transilluminator. The uncleaved peptide-MCA substrate remained where the inhibitors were present, and was visualized as dark blue bands on the light-green fluorescent background gel. This new method offers several advantages over other previous methods including: (i) greatly increased sensitivity can be achieved in a shorter period of time, which may be useful for discovering new protease inhibitors in small amounts of crude material; (ii) the procedure is quite simple and quick since the incubation period is very short and no time is needed for staining and destaining steps; (iii) since these probes using substrate specificity/target proteases, they are excellent tools for detection and discrimination of unknown protease inhibitors for various target proteases. 相似文献
135.
Zwitterionic amphiphiles of the general formula H(CH2)y
+ N(CH3)2(CH2)n PO2C6H
5
–
, where the number of intercharge methylenesn is varied, were studied in dilute aqueous solution. Their critical micellar concentrations show a peculiar variation withn, first increasing asn varies from 1 to 4 and then slowly decreasing as methylenes are added up to 10. This behavior is interpreted as being the consequence of two opposite contributions. The first is the classical CMC lowering due to the increase of hydrophobic character with the total number of methylene groups in the surfactant molecule. The second contribution is the increase in the dipole moment of the zwitterionic headgroup withn, leading to stronger dipole-dipole repulsions between headgroups at the micellar surface. Experimental results suggest that the dipole moment does not increase linearly withn because of the polymethylene chain flexibility. This is supported by13C NMR relaxation experiments. 相似文献
136.
Valérie Bernat Catherine Ringard-Lefebvre Geneviève Le Bas Sylviane Lesieur 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):113-119
Interactions of α-cyclodextrin (α-CD) with dimyristoylphosphatidylcholine (DMPC) and Egg phosphatidylcholine (Egg-PC) were studied (i) by analyzing surface
pressure-area isotherms and surface tension of phospholipid monolayers formed at the interface between air and α-CD aqueous solutions and (ii) by X-ray diffraction performed on fully hydrated α-CD/phospholipid binary mixtures. The cyclodextrin molecules strongly interact with the two-dimension phospholipid assembly.
Their addition into the aqueous sub-phase leads to the removal of part of the phospholipids from the air-water interface:
the higher the α-CD concentration, the higher the phospholipid depletion. This should preferentially involve interactions between cyclodextrin
and the phosphatidylcholine head group as α-CD is water-soluble and not surface-active. At the three-dimension level, the bilayer packing of the phospholipid lamellar
phase appears not affected by the presence of cyclodextrin as shown by X-ray scattering at small angles whereas wide-angle
diffraction patterns reveal the formation of a crystalline phase organized in a pseudo-hexagonal lattice usually characteristic
of α-CD dimers. These results point out that α-CD should interact with bilayer-forming phospholipid molecules but likely according to a process that would preserve intact
at least a part of the multilamellar assembly. 相似文献
137.
Getahun Z Huang CY Wang T De León B DeGrado WF Gai F 《Journal of the American Chemical Society》2003,125(2):405-411
It is well-known that the C=N stretching vibration in acetonitrile is sensitive to solvent. Therefore, we proposed in this contribution to use this vibrational mode to report local environment of a particular amino acid in proteins or local environmental changes upon binding or folding. We have studied the solvent-induced frequency shift of two nitrile-derivatized amino acids, which are, AlaCN and PheCN, in H(2)O and tetrahydrofuran (THF), respectively. Here, THF was used to approximate a protein's hydrophobic interior because of its low dielectric constant. As expected, the C=N stretching vibrations of both AlaCN and PheCN shift as much as approximately 10 cm(-1) toward higher frequency when THF was replaced with H2O, indicative of the sensitivity of this vibration to solvation. To further test the utility of nitrile-derivatized amino acids as probes of the environment within a peptide, we have studied the binding between calmodulin (CaM) and a peptide from the CaM binding domain of skeletal muscle myosin light chain kinase (MLCK(579-595)), which contains a single PheCN. MLCK(579-595) binds to CaM in a helical conformation. When the PheCN was substituted on the polar side of the helix, which was partially exposed to water, the C=N stretching vibration is similar to that of PheCN in water. In constrast, when PheCN is introduced at a site that becomes buried in the interior of the protein, the C=N stretch is similar to that of PheCN in THF. Together, these results suggest that the C=N stretching vibration of nitrile-derivatized amino acids can indeed be used as local internal environmental markers, especially for protein conformational studies. 相似文献
138.
Ponce De León CA Montes Bayón M Caruso JA 《Analytical and bioanalytical chemistry》2002,374(2):230-234
Vitamin E supplements are either isolated from plants sources or prepared synthetically. Isolation from plants includes eight different tocopherol structures. Vitamin E synthesis includes seven different stereoisomers, which involves the use of several catalysts that may lead to trace element contamination in the vitamin. The use of ICP-MS is an ideal technique for detecting these trace elements. However, the oily nature of the samples requires the development of a sample preparation methodology. This study was done upon the request of synthetic vitamin E manufacturers to test the trace metal purity of their samples. In this work, the comparison of an acid microwave digestion and emulsion preparation is discussed. Cromium, nickel, tin and lead were found in the synthetic vitamin E analyzed and 200, 60, 9 and 45 ppb were the concentrations found respectively for these elements.Digesting the samples gives slightly lower detection limits compared to the emulsion preparation. 相似文献
139.
The problem of successive transverse plane reconstruction in single photon emission computerized tomography (SPECT) is modeled in its more general form, which implies the definition of emission tomographic operators (ETO's) for which an analytical solution can be derived. The properties of the attenuated tomographic operator (ATO) are described and discussed, including the attenuation which is distributed on the reconstruction domain. For this particular operator, a regularizing method (RIM) is proposed, for which it is demonstrated and tested with simulation studies that a filtered, accurate solution can be extracted for the tomographic images as obtained using a single photon emission tomograph based on a rotating gamma camera in clinical use. 相似文献
140.
Taylor MJ Hunter K Hunter KB Lindsay D Le Bouhellec S 《Journal of chromatography. A》2002,982(2):225-236
A LC-MS-MS method capable of the quantitative determination of a range of pesticide residues present in crude extracts from a variety of fruit and vegetables has been developed. Isocratic LC conditions have been used in conjunction with electrospray ionisation tandem mass spectrometry to detect and identify up to 38 pesticides presented as various mixtures in different matrices. The utility of the method is demonstrated by the analysis of crude extracts, with no sample clean up, from grape, kiwi fruit, strawberry, spinach, lemon, peach and nectarine. Mean recoveries ranging from 63 to 96% with relative standard deviations < 20% were obtained for 30 of the 38 pesticides following analysis of organic produce fortified at concentrations between 0.01 and 0.8 mg/kg. Detected residues were quantified from interpolation against calibration data generated using matrix-matched standards that covered analyte concentration ranges between 0.005 and 0.8 microg/ml. Conditions suitable for the qualitative and quantitative confirmation of residues detected in samples are specified. 相似文献