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111.
112.
Xiao Lian Zhang Joseph T. Hupp Gerald D. Danzer 《Journal of Electroanalytical Chemistry》1995,380(1-2)
The comparative interfacial oxidation kinetics of the approximate structural isomers trans-(O)2ReV(py)+4 and cis-(O)2ReV(bpy)(py)+2 (py, pyridine; bpy, 2,2′-bipyridine) have been assessed in aqueous solution via conventional cyclic voltammetry at a highly ordered pyrolytic graphite (HOPG) electrode. HOPG was employed because of its known propensity to diminish interfacial electron transfer (ET) rates (by ca. three to four orders of magnitude) and because of a probable lack of importance of kinetic work terms (diffuse double-layer corrections). Measured rates for the trans complex exceed those for the cis by about a factor of 3. Expressed as an effective activation Gibbs energy difference ΔG*, this corresponds to a cis-trans difference of ca. 3 kJ mol−1. The actual vibrational barriers to ET have determined from a combination of published X-ray structural results (trans complex) and new resonance Raman results (cis complex). The values are 0.6 kJ mol −1 for the trans oxidation and 4.4 kJ mol−1 for the cis oxidation (i.e. close to the barrier difference inferred from rate measurements). Further analysis shows that most of the barrier difference is associated with displacement of a (predominantly) Re-N(bpy) stretching mode found only in the cis system. Differences in metal-oxo displacements (cis > trans) are also implicated. 相似文献
113.
Noeen Malik Xian Lin Dirk Löffler Bin Shen Christoph Solbach Gerald Reischl Wolfgang Voelter Hans-Jürgen Machulla 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(3):1025-1033
For detection of hypoxic tumor tissue, all radiotracers synthesized until now, are based on the concept that cellular uptake
is being controlled by diffusion. As a new approach, we chose the concept to have the tracer hypothetically transported into
the cells by well known carrier systems like the amino acid transporters. For this purpose, radiosynthesis of O-[2-[18F]fluoro-3-(2-nitro-1H-imidazole-1yl)propyl]tyrosine ([18F]FNT]) was carried out from methyl 2-(benzyloxycarbonyl)-3-(4-3-(2-nitro-1H-imidazol-1-yl)-2-(tosyloxy)propoxy) phenyl)propanoate via no-carrier-added nucleophilic aliphatic substitution. After labelling,
81 ± 0.9% of labelled intermediate i.e. methyl 2-(benzyloxycarbonyl)-3-(4-(2-[18F]fluoro-3-(2-nitro-1H-imidazole-1-yl)propoxy) phenyl)propanoate was obtained at 140 °C. At the end of radiosynthesis, [18F]FNT was obtained in an overall radiochemical yield of 40 ± 0.9% (not decay corrected) within 90 min in a radiochemical purity
of >98% in a formulation ready for application in the clinical studies for PET imaging of hypoxia. 相似文献
114.
Jakubczyk D Barth C Kubas A Anastassacos F Koelsch P Fink K Schepers U Brenner-Weiß G Bräse S 《Analytical and bioanalytical chemistry》2012,403(2):473-482
N-Acyl-l-homoserine lactones (AHLs) are synthesized by Gram-negative bacteria. These quorum-sensing molecules play an important role
in the context of bacterial infection and biofilm formation. They also allow communication between microorganisms and eukaryotic
cells (inter-kingdom signalling). However, very little is known about the entire mechanism of those interactions. Precise
structural studies are required to analyse the different AHL isomers as only one form is biologically most active. Theoretical
studies combined with experimental infrared and Raman spectroscopic data are therefore undertaken to characterise the obtained
compounds. To mimic interactions between AHL and cell membranes, we studied the insertion of AHL in supported lipid bilayers,
using vibrational sum-frequency-generation spectroscopy. Deuterium-labelled AHLs were thus synthesized. Starting from readily
available deuterated fatty acids, a two-step procedure towards deuterated N-acyl-l-homoserine lactones with varying chain lengths is described. This included the acylation of Meldrum’s acid followed by amidation.
Additionally, the detailed analytical evaluation of the products is presented herein. 相似文献
115.
Gerald G. Miller Kevin Brown Ronald B. Moore Malcolm S. McPhee Zhenjun J. Diwu Jixiang Liu Liren Huang J. William Lown David A. Begg Vera Chlumecky John Tulip 《Photochemistry and photobiology》1995,61(6):632-638
Hypocrellins are naturally occurring compounds with photosensitizing properties in biological systems. We have prepared synthetic derivatives of hypocrellin B, which have promise as photosensitizers in the clinical application of photodynamic therapy. The intracellular localization and uptake kinetics of hypocrellin B and several selected hypocrellin congeners were determined semiquantitatively by fluorescence confocal microscopy in monolayer cultures of EMT6/Ed murine tumor cells. Each compound had unique uptake kinetics. Although no compound tested to date has demonstrated nuclear labeling, most could be detected in lysosomes, Golgi, endoplasmic reticulum and, to a minor extent, in cellular membranes. No two compounds gave identical labeling distributions. The differences are assumed to originate in physicochemical properties characteristic of each compound, which may ultimately impact upon the primary modality of phototoxicity. 相似文献
116.
P. Duane Walker Paul G. Mezey Gerald M. Maggiora Mark A. Johnson James D. Petke 《Journal of computational chemistry》1995,16(12):1474-1482
The shape group method (SGM) and the associated (a,b)-parameter maps provide a detailed shape characterization of molecular charge distributions. This method is applied to the study of the variations of shape and conjugation of conformers of 2-phenyl pyrimidine in their electronic ground state. Within the SGM framework, the method of (a,b)-parameter maps provides a concise, nonvisual, algorithmic technique for shape characterization of molecules with fixed nuclear geometries. Moreover, shape codes derived from the (a,b)-parameter maps afford a practical means for efficiently storing the shape properties of molecules in an electronic database. The shape codes of two or more charge distributions can be compared directly, and numerical measures of molecular shape similarity can be computed using a technique that is simple, fast, and inexpensive, especially in relation to direct, pairwise comparisons of electronic charge densities. The quantitative and automated nature of the method suggests applications in the field of computer-aided molecular design. In this study, the method is used for the first time to determine detailed numerical shape codes and shape similarity measures for a nontrivial conformational problem involving changes in energy and in conjugation. Numerical shape similarity measures of eight conformers of 2-phenyl pyrimidine are determined and correlated with variations in conformational energy and conjugation. The competing effects of steric repulsion and conjugation lead to important correlations between conformational energy and shape. © 1995 John Wiley & Sons, Inc. 相似文献
117.
Zapata-Torres G Fierro A Miranda-Rojas S Guajardo C Saez-Briones P Salgado JC Celis-Barros C 《Journal of chemical information and modeling》2012,52(5):1213-1221
Although substrate conversion mediated by human monoaminooxidase (hMAO) has been associated with the deprotonated state of their amine moiety, data regarding the influence of protonation on substrate binding at the active site are scarce. Thus, in order to assess protonation influence, steered molecular dynamics (SMD) runs were carried out. These simulations revealed that the protonated form of the substrate serotonin (5-HT) exhibited stronger interactions at the protein surface compared to the neutral form. The latter displayed stronger interactions in the active site cavity. These observations support the possible role of the deprotonated form in substrate conversion. Multigrid docking studies carried out to rationalize the role of 5-HT protonation in other sites besides the active site indicated two energetically favored docking sites for the protonated form of 5-HT on the enzyme surface. These sites seem to be interconnected with the substrate/inhibitor cavity, as revealed by the tunnels observed by means of CAVER program. pK(a) calculations in the surface loci pointed to Glu32?, Asp32?, His???, and Asp132 as candidates for a possible in situ deprotonation step. Docking analysis of a group of inhibitors (structurally related to substrates) showed further interactions with the same two docking access sites. Interestingly, the protonated/deprotonated amine moiety of almost all compounds attained different docking poses in the active site, none of them oriented to the flavin moiety, thus producing a more variable and less productive orientations to act as substrates. Our results highlight the role of deprotonation in facilitating substrate conversion and also might reflect the necessity of inhibitor molecules to adopt specific orientations to achieve enzyme inhibition. 相似文献
118.
119.
Chhavi Bhardwaj Jerry F. Moore Yang Cui Gerald L. Gasper Hans C. Bernstein Ross P. Carlson Luke Hanley 《Analytical and bioanalytical chemistry》2013,405(22):6969-6977
Laser desorption postionization mass spectrometry (LDPI-MS) imaging is demonstrated with a 10.5 eV photon energy source for analysis and imaging of small endogenous molecules within intact biofilms. Biofilm consortia comprised of a synthetic Escherichia coli K12 coculture engineered for syntrophic metabolite exchange are grown on membranes and then used to test LDPI-MS analysis and imaging. Both E. coli strains displayed many similar peaks in LDPI-MS up to m/z 650, although some observed differences in peak intensities were consistent with the appearance of byproducts preferentially expressed by one strain. The relatively low mass resolution and accuracy of this specific LDPI-MS instrument prevented definitive assignment of species to peaks, but strategies are discussed to overcome this shortcoming. The results are also discussed in terms of desorption and ionization issues related to the use of 10.5 eV single-photon ionization, with control experiments providing additional mechanistic information. Finally, 10.5 eV LDPI-MS was able to collect ion images from intact, electrically insulating biofilms at ~100 μm spatial resolution. Spatial resolution of ~20 μm was possible, although a relatively long acquisition time resulted from the 10 Hz repetition rate of the single-photon ionization source. Figure
Neutral species laser desorbed from cocultured biofilms undergo single photon ionization by VUV radiation and resultant ions are detected by time-of-flight mass spectrometry 相似文献
120.
Dr. David Martin Dr. Nicolas Lassauque Florian Steinmann Gerald Manuel Prof. Guy Bertrand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(44):14895-14901
Experimental and computational investigations of anti‐Bredt amidinium salts are presented. Calculations show that the pyramidalization of an amino group can significantly destabilize the formal carbocation center of amidiniums, due to the decreased π donation. In some cases, the unfavorable ‐I effect of nitrogen surpasses its beneficial +M effect, and amidiniums become less stable than iminiums. It is shown that although 1‐aza‐3‐azonia[3.3.1]bicyclo‐non‐2‐enes can be isolated, they feature a nonclassical reactivity, which is more typical for iminium than amidinium salts, such as pronounced electrophilicity and azomethineylide instead of carbene formation. 相似文献