Heats of solution of 1∶1 electrolytes in 1-propanol,and derived enthalpies of transfer from water

Heats of solution of 13 11 electrolytes in 1-propanol have been determined calorimetrically at various electrolyte concentrations, and extrapolated to zero concentration to give H _s ^o values for these electrolytes. Together with literature data on three additional 11 electrolytes, these measurements yield a self-consistent set of single-ion enthalpies of transfer from water to 1-propanol. Values are tabulated for 10 univalent cations and five univalent anions. It is shown that the H _t ^o (Ph ₄ As⁺)=H _t ^o (Ph ₄ B^–) assumption yields chemically reasonable single-ion values. Using this assumption, it may be deduced that all the univalent ions studied have about the same enthalpy in 1-propanol as in methanol.     

La luminescence différée du styrène en solution vitreuse dans le méthylcyclohexane

The trapping of electrons and styrene cations and anions has been studied in a methylcyclohexane glass by the techniques of deferred luminescence. Radiothermoluminescence curves consist of two peaks, at 90 and 95°K, in this matrix. The second peak increases linearly with styrene concentration up to 2 × 10^?2M when it reaches a constant value, whereas the first peak increases from 10^?4 to 10^?3M and then decreases at higher concentrations and is not discernible at concentrations above 10^?2M. We propose two mechanisms which are qualitatively consistent with this behavior and are based essentially on the recombination of styrene cations with thermally detrapped electrons in the first peak and with anions in the second peak. Photothermoluminescence (i.e., thermoluminescence after photoionization with ultraviolet light) similarly consists of the 90 and 95°K peaks for a 10^?3M solution and of the 95° peak alone for a 10^?d M solution. Radiophotoluminescence excitation spectra at 77°K, corresponding to absorption spectra of trapped electrons and styrene anions, show that anions are the predominant negative species in 10^?2 molar solution, and trapped electrons in 10^?3 molar solution. Spectral analysis of radiothermoluminescenece shows the presence of two emission bands, one of which is identical with styrene fluorescence excited by the 254 Nm mercury line (λ_max = 292, 302, 307, and 317 Nm). The other band has three fairly poorly resolved maxima at 474, 486 and 496 nm and seems to correspond to the fluorescence of C₆H₅?H-CH₃ radicals formed during radiolysis.     

Developments on carbon dioxide reduction: Their promise,achievements, and challenges

CO₂ reduction processes continue to be developed for electrosynthesis, energy storage applications, and environmental remediation. A number of promising materials have shown high activity and selectivity to target reduction products. However, the progress has been mainly at a small laboratory scale, and the technical challenges of large scale CO₂ reduction have not been considered adequately. This review covers recent advancements in catalyst materials and cell designs. The leading materials for CO₂ reduction to a number of useful products are presented with their corresponding cell and reactor designs. The latest efforts to progress to industrially relevant scales are discussed, along with the challenges that must be met for carbon dioxide reduction to be a viable route for mass scale production.     

Post-source decay in the analysis of polystyrene by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Various secondary series are observed in matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectra of polystyrene. The number and positions of the series depend on the choice of matrix and added cation. For a given treatment, series observed in linear mode are not necessarily observed in reflectron mode, and vice versa. Post-source decay analysis was used to determine that the secondary series arise at least in part from formation and decay of adducts of polystyrene with matrix species. There is some treatment-to-treatment variation, but adduct formation and decay were observed for all tested treatments. The multiplicity of secondary series makes it unclear whether post-source decay occurs for the main series (polystyrene + cation)⁺ ions under the conditions normally used for polystyrene analysis. Such ions do undergo post-source decay at laser fluences greater than normally used. Although only polystyrene was investigated in this work, other polymers may also produce adduct and decay series in MALDI analysis. Their presence can mask the presence of minor components in a sample, but at least as observed here, do not have a strong influence on molecular mass determinations.     

Photodynamic effectiveness and vasoconstriction in hairless mouse skin after topical 5-aminolevulinic acid and single- or two-fold illumination

Several options were investigated to increase the efficacy of photodynamic therapy (PDT) using protoporphyrin IX (PpIX) induced by topically applied 5-aminolevulinic acid (ALA). Hairless mice with normal skin or UVB-light-induced skin changes were used as a model. In the first part of the study animals were illuminated immediately (t = 4) or 6 h (t = 10, PpIX fluorescence maximum) after the end of a 4 h ALA application. A total incident light fluence of 100 J/cm2 (514.5 nm) was delivered at a fluence rate of 100 or 50 mW/cm2. The PDT-induced damage to normal skin was more severe after treatment at t = 10 than at t = 4. Illumination at 50 mW/cm2 caused significantly more visible damage than the same light fluence given at 100 mW/cm2. For UVB-illuminated skin, different intervals or fluence rates made no significant difference in the severity of damage, although some qualitative differences occurred. In situ fluence rate measurements during PDT indicated vasoconstriction almost immediately after the start of the illumination. A fluorescein exclusion assay after PDT demonstrated vasoconstriction that was more pronounced in UVB-treated skin than in normal skin. The second part of the study examined the effect of two illuminations. The first illumination bleaches the PpIX fluorescence. At the start of the second illumination, new PpIX had been formed. Light of 514.5 nm was delivered at 100 mW/cm2 to a total incident light fluence of 200 J/cm2 at t = 4 (single illumination) or 100 J/cm2 at t = 4 plus 100 J/cm2 at t = 10. There was no visual difference in skin damage between 100 and 200 J/cm2 single illumination. Two-fold illumination (100 + 100 J/cm2) caused significantly more skin damage, indicating a potentially successful option for increasing the efficacy of topical ALA-PDT.     

Assessing alkyl-, silyl-, and halo-substituent effects on the electron affinities of silyl radicals

Neutral anion energy differences for a large class of alpha-substituted silyl radicals have been computed to determine the effect of alkyl, silyl, and halo substituents on their electron affinities. In particular, we report theoretical predictions of the adiabatic electron affinities (AEAs), vertical electron affinities (VEAs), and vertical detachment energies (VDEs) for a series of methyl-, silyl-, and halo-substituted silyl radical compounds. This work utilizes the carefully calibrated DZP++ basis set, in conjunction with the pure BLYP and OLYP functionals, as well as with the hybrid B3LYP, BHLYP, PBE1PBE, MPW1K, and O3LYP functionals. Bromine has the largest effect in stabilizing the anions, and the BLYP/DZP++ AEA for SiBr(3) is 3.29 eV. The other predicted electron affinities are for SiH(3) (1.37 eV), SiH(2)CH(3) (1.09 eV), SiH(2)F (1.54 eV), SiH(2)Cl (1.94 eV), SiH(2)Br (2.05 eV), SiH(2)(SiH(3)) (1.77 eV), SiH(CH(3))(2) (0.92 eV), SiHF(2) (1.86 eV), SiHCl(2) (2.53 eV), SiHBr(2) (2.67 eV), Si(CH(3))(3) (0.86 eV), SiF(3) (2.66 eV), SiCl(3) (3.21 eV), Si(SiH(3))(3) (2.25 eV), and SiFClBr (3.13 eV). For the five silyl radicals where experimental data are available, the BLYP functional gives the most accurate determination of AEAs; the average absolute error is 0.04(1) eV, whereas the corresponding errors for the O3LYP, MPW1K, PBE1PBE, B3LYP, OLYP, and BHLYP functionals are 0.05(8), 0.06(0), 0.06(3), 0.08(5), 0.11(5), and 0.15(3) eV, respectively.     

A two-color-change, nanoparticle-based method for DNA detection

Herein, we describe the detailed synthesis of Ag/Au core-shell nanoparticles, the surface-functionalization of these particles with thiolated oligonucleotides, and their subsequent use as probes for DNA detection. The Ag/Au core-shell nanoparticles retain the optical properties of the silver core and are easily functionalized with thiolated oligonucleotides due to the presence of the gold shell. As such, the Ag/Au core-shell nanoparticles have optical properties different from their pure gold counterparts and provide another “color” option for target DNA-directed colorimetric detection. Size-matched Ag/Au core-shell and pure gold nanoparticles perform nearly identically in DNA detection and melting experiments, but with distinct optical signatures. Based on this observation, we report the development of a two-color-change method for the detection and simultaneous validation of single-nucleotide polymorphisms in a DNA target using Ag/Au core-shell and pure gold nanoparticle probes.     

Tetrahydropyridoazepines and tetrahydropyridoazepinones from the corresponding dihydroquinolones

The p-toluenesulfonate of 7,8-dihydro-5(6H)quinoloneoxime( 3 ) was subjected of a Beckmann rearràngement. The resulting 2,3,4,5-tetrahydro-1H-pyrido[3,2-b]azepin-2-one ( 4 ) was reduced with lithium aluminum hydride affording 2,3,4,5-tetrahydro-1H-pyrido[3,2-b] azepine ( 5 ). 5,6-l)ihydro-8(7H)quinolone ( 7 ), obtained by oxidation of 5,6,7,8-tetrahydro-8-quinolinol ( 6 ), was converted into the p-toluenesulfonate of 5,6-dihydro-8(7H)quinolone oxitne ( 9 ). Similarly the latter compound could be rearranged into 2,3,4,5-letrahydro-1H-pyrido [2,3-b] azepin-2-one ( 10 ) which on reduction produced 2,3,4,5-tetrahydro-1H-pyrido [2,3-b] azepine ( 11 ).     

Chemical ionization mass spectrometry of bifunctional cyclopentanes and cyclohexanes. A correlation between stereochemistry and chemical ionization spectra

A correlation has been fround between the stereochemistry of 3-methoxyeyclopentyl and 3-methoxyccyelohexyl acetic acid esters and their methane or isobutane themical ionizaion spectra: only the cis compounds yield quasimolecular ions and the [MH? CH₃OH]⁺ ions are more abundant for the trans isomers. A similar situation occurs in the iow temperature methane chemical ionization spectra of the coresponding trimethylsilylethers.