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11.
Köse ME Crutchley RJ Derosa MC Ananthakrishnan N Reynolds JR Schanze KS 《Langmuir : the ACS journal of surfaces and colloids》2005,21(18):8255-8262
Polymer films consisting of a linear poly(dimethylsiloxane) end-functionalized with a luminescent Ir(III) complex (Ir-PDMS), blended with polystyrene (PS), function as optical oxygen sensors. The sensor response arises by quenching of the luminescence from the Ir(III) chromophore by oxygen that permeates into the polymer film. The morphology and luminescence oxygen sensor properties of blend films consisting of Ir-PDMS and PS have been characterized by fluorescence microscopy, atomic force microscopy, and scanning electron microscopy. The investigations demonstrate that microscale phase segregation occurs in the films. In blends that contain a relatively small amount of Ir-PDMS in PS (ca. 10 wt %), the Ir-PDMS exists as circular domains, with diameters ranging from 2 to 5 mum, surrounded by the majority PS phase. For larger weight fractions of Ir-PDMS in the blends, the film morphology becomes bicontinuous. A novel epifluorescence microscopy method is applied that allows the construction of Stern-Volmer quenching images that quantify the oxygen sensor response of the blend films with micrometer spatial resolution. These images provide a map of the oxygen permeability of the polymer blend films with a spatial resolution of ca. 1 mum. The results of this investigation show that the micrometer-sized Ir-PMDS domains display a 2-3-fold higher oxygen sensor response compared to the surrounding PS matrix. This result is consistent with the fact that PDMS is considerably more gas permeable compared to PS. The relationship of the microscale morphology of the blends to their performance as macroscale optical oxygen sensors is discussed. 相似文献
12.
Aboelella NW Lewis EA Reynolds AM Brennessel WW Cramer CJ Tolman WB 《Journal of the American Chemical Society》2002,124(36):10660-10661
The X-ray structure of a 1:1 Cu/O(2) adduct revealed side-on (eta(2)) O(2) coordination. Density functional calculations corroborated the structure, indicated a significant contribution of a Cu(III)-(O(2)(2-)) resonance form, and provided insights into the key bonding interactions. Reaction of a 1:1 adduct supported by a slightly different beta-diketiminate ligand with Cu(I) reagents resulted in the formation of novel asymmetric bis(mu-oxo) complexes that were identified by EPR, UV-vis, and Raman spectroscopy, as well as by an X-ray structure in one instance. 相似文献
13.
Jacob G. Reynolds 《Silicon Chemistry》2007,3(5):267-269
The Partial Charge Model was developed to predict the hydroxylation, polymerization, and precipitation of ions. The purpose
of this study is to evaluate the Partial Charge Model for describing the polymerization of silica in aqueous solutions. The
Partial Charge Model predicts the stability of ions and complexes based on the assumption that the stable species will have
the same electronegativity as the mean electronegativity of the solution. The silica system was chosen for model validation
because of the rare availability of self-consistent thermodynamic data on many dissolved but polymerized silicate anions,
including both linear and cyclical species. The electronegativity of each species was calculated using the Partial Charge
Model and the results were plotted against the stability constants for the ions. The silicate anions segregated into groups
on the plot based on the number of charges per silicon atom in the polymer. Plots of the log of the stability constant versus
the change in electronegativity produced a linear relationship for the silica polymers containing one negative charge per
silicon atom, which resulted in an r
2 of 0.9978. Thus, the Partial Charge Model successfully describes the thermodynamics of silica polymerization in aqueous solution
for species that are sufficiently alike, but was not accurate for all silica species. 相似文献
14.
RU Chang Bi Zbigniew Dauter Eleanor Dodson Guy Dodson Federico Gordiano Rod Hubbard Colin Reynolds 《Journal of Chemical Sciences》1983,92(4-5):473-483
Insulin modified by the removal of its 5 B chain C terminal residues is monomeric but remains substantially potent. The crystal
structures of the beef and insulin (dpi) with two molecules in the asymmetric unit has been determined by x-ray analysis. The 3-dimensional structure ofdpi proves to be generally similar to that of native molecule in 2Zn insulin. More detailed comparison reveals that the slight
differences in the two independent molecules of beefdpi are distributed uniformly throughout the structure in contrast to insulin in 2Zn insulin, where the structural changes are
concentrated in specific regions.
The loss of symmetry in thedpi crystal appears to be the inability of the A9 serine to pack effectively in the C2 cell. The efficient packing of the sheepdpi molecule whose crystal structure has also been determined and where A9 is glycine supports this conclusion. 相似文献
15.
J. A. Van Allan G. A. Reynolds J. F. Stenberg 《Journal of heterocyclic chemistry》1979,16(8):1661-1662
A general method for the preparations of pyranthiones is particularly useful for preparing substituted xanthiones which are unavailable by established procedures. Reaction of a xanthone with p-tosyl isocyanate or with trichloroacetyl isocyanate produces the corresponding imino derivatives, which upon treatment with n-butylamine followed by hydrogen sulfide gives the desired xanthione in good yield. 相似文献
16.
Using a direct position-space renormalization-group approach we study percolation clusters in the limits , wheres is the number of occupied elements in a cluster. We do this by assigning a fugacityK per cluster element; asK approaches a critical valueK
c
, the conjugate variables . All exponents along the path (K–K
c
) 0 are then related to a corresponding exponent along the paths . We calculate the exponent , which describes how the radius of ans-site cluster grows withs at the percolation threshold, in dimensionsd=2, 3. Ind=2 our numerical estimate of =0.52±0.02, obtained from extrapolation and from cell-to-cell transformation procedures, is in agreement with the best known estimates. We combine this result with previous PSRG calculations for the connectedness-length exponent , to make an indirect test of cluster-radius scaling by calculating the scaling function exponent using the relation =/. Our result for is in agreement with direct Monte-Carlo calculations of , and thus supports the cluster-radius scaling assumption. We also calculate ind=3 for both site and bond percolation, using a cell of linear sizeb=2 on the simple-cubic lattice. Although the result of such small-cell calculations are at best only approximate, they nevertheless are consistent with the most recent numerical estimates.Supported in part by grants from ARO and ONR 相似文献
17.
Simultaneous analysis of methionine- and leucine-enkephalin from rat brain: quantification by liquid chromatography-electrochemistry 总被引:1,自引:0,他引:1
This study focuses on the application of liquid chromatography with electrochemical detection (LC-ED) for the analysis of methionine-enkephalin (ME) and leucine-enkephalin (LE) extracted from rat brain regions. The high applied potentials necessary for enkephalin detection required the development of an efficient sample processing protocol. Brain extracts were processed using chromatographic mode sequencing (CMS). The decrease in electroactive interfering substances by CMS improved the chromatographic resolution of ME and LE and the electrode performance. Other qualitative and analytical methods were used to evaluate the enkephalin data obtained by LC-ED for rat brain regions. This study demonstrates that LC-ED provides both the sensitivity and specificity necessary for the analysis of enkephalins from rat brain regions. 相似文献
18.
A study of the dynamical molecular structure of a dilute polar fluid is reported, in which 13C spin-lattice relaxation times of decanol in deuterated cyclohexane are presented for the individual carbon atoms, and the results are discussed in the context of viscosity data of decanol in alkane systems. The two techniques provide complementary information about the mobility of the alcohol chains and the onset of multimer formation, which is also pertinent to the dynamics of electron solvation in the same systems. 相似文献
19.
Kryatov SV Chavez FA Reynolds AM Rybak-Akimova EV Que L Tolman WB 《Inorganic chemistry》2004,43(6):2141-2150
Dioxygen activation by enzymes such as methane monooxygenase, ribonucleotide reductase, and fatty acid desaturases occurs at a nonheme diiron active site supported by two histidines and four carboxylates, typically involving a (peroxo)diiron(III,III) intermediate in an early step of the catalytic cycle. Biomimetic tetracarboxylatodiiron(II,II) complexes with the familiar "paddlewheel" topology comprising sterically bulky o-dixylylbenzoate ligands with pyridine, 1-methylimidazole, or THF at apical sites readily react with O(2) to afford thermally labile peroxo intermediates that can be trapped and characterized spectroscopically at low temperatures (193 K). Cryogenic stopped-flow kinetic analysis of O(2) adduct formation carried out for the three complexes reveals that dioxygen binds to the diiron(II,II) center with concentration dependences and activation parameters indicative of a direct associative pathway. The pyridine and 1-methylimidazole intermediates decay by self-decomposition. However, the THF intermediate decays much faster by oxygen transfer to added PPh(3), the kinetics of which has been studied with double mixing experiments in a cryogenic stopped-flow apparatus. The results show that the decay of the THF intermediate is kinetically controlled by the dissociation of a THF ligand, a conclusion supported by the observation of saturation kinetic behavior with respect to PPh(3), inhibition by added THF, and invariant saturation rate constants for the oxidation of various phosphines. It is proposed that the proximity of the reducing substrate to the peroxide ligand on the diiron coordination sphere facilitates the oxygen-atom transfer. This unique investigation of the reaction of an O(2) adduct of a biomimetic tetracarboxylatodiiron(II,II) complex provides a synthetic precedent for understanding the electrophilic reactivity of like adducts in the active sties of nonheme diiron enzymes. 相似文献
20.
James C. Thompson A.P.Gerald Wright William F. Reynolds 《Journal of fluorine chemistry》1981,17(6):509-529
Consideration of 19F-19F and 29Si-19F coupling constants in a series of organosilicon derivatives containing SiF2 and Si2F4 units reveals a number of trends which are useful for structural and stereochemical assignments. For example the vicinal 19F-19F coupling constants in a number of CSiF2SiF2C- derivatives (including straight chain compounds, disilacyclobutanes and disilacyclohexanes) show an apparent linear dependence on dihedral angle, varying in magnitude from near zero for small values of φ up to ca. 19 Hz for φ ~ 180°. This is particularly useful for stereochemical assignments [1,2]. In addition 29Si-19F coupling constants appear to fall in quite distinct ranges (1JSiF > 300 Hz, 29 Hz < 2JSiF < 55 Hz, 3JSiF < 10 Hz). This is quite useful for structural assignments [1,6]. Reaction of SiF2 with 1,3-cyclohexadiene gives two new silicon fluorine compounds: a disilabicyclo[2,2,2]octene and an HSi2F5-substituted cyclohexadiene. 相似文献