Photochemically induced coupling reaction of triarylstibines with olefins

Photoreaction of triarylstibines with styrenes resulted in the formation of 2-aryl-1-phenylethanols accompanied by air oxidation. Formation of the products has been explained by the valence expansion of the oxygen-antimony-styrene complex to a five-valent intermediate, followed by reductive coupling.     

Photochemically induced cholesteric-nematic transition in liquid crystals

By doping a nematic liquid crystal with dissymmetric chiral compounds it has been shown that the twist of the resulting cholesteric structure is proportional to the solute concentration. Using as doping agent a photolabile chiral compound a cholesteric-nematic transition has been obtained under UV irradiation.     

Photochemically catalyzed reaction of ochratoxin A with D- and L-cysteine

The photolysis (>300 nm) of ochratoxin A (OTA, N-[[(3R)-5-chloro-8-hydroxy-3-methyl-1-oxo-7-isochromanyl]carbonyl]-3-phenyl-L-alanine, 1) in the presence of excess (2 and 12 molar equiv) cysteine (CySH) has been investigated and found to yield sulfur adducts 5 and 6 that are characterized by liquid chromatography-mass spectrometry and 1H-NMR spectroscopy. The adduct 5 was ascribed to the Michael addition conjugate resulting from covalent attachment of CySH to the ochratoxin quinone (4) generated by photooxidation of OTA. This species was also formed by photolysis of a synthetic sample of the hydroquinone of OTA (ochratoxin hydroquinone, 3) in the presence of 12 equiv L-CySH. The conjugate 5 derived from photolysis of 3 with L-CySH was used for 1H-NMR analysis. The sulfur adduct 6 was the major species detected from covalent attachment of CySH to photoactivated OTA, and it resulted from direct displacement of the OTA Cl atom by CySH. The implications of the cysteinyl adducts to the in vivo toxicity of OTA are discussed, with particular emphasis given to conjugate 5, as products from the photooxidative pathway may be of relevance to the nephrotoxic properties of OTA.     

Photochemically induced oxidative surface modification of polyimide films

Polyimide membranes that contain both the phthalimide chromophore and abstractable hydrogens undergo photochemically-induced oxidative surface modification when they are irradiated with ultraviolet (UV) light for 0.5–30 min in air. The reaction requires 200–300 nm light and the presence of oxygen, and the surface-modified membranes show much higher oxygen/nitrogen selectivities than the untreated films. A mechanism for the photochemical reaction that is based on the photochemistry of structurally-similar monomeric phthalimides is proposed. The observed selectivity increases can also be explained by this mechanism. © 1993 John Wiley & Sons, Inc.     

Photochemically induced fluorimetric determination of the antimalarial mefloquine

Mefloquine (MQ) was determined quantitatively in pharmaceutical tablets by irradiating the MQ solution for 2–7 min with a high-pressure UV lamp, measuring simultaneously the increase in fluorescence signal at room temperature (298 K) and comparing the signal with that of a standard. The effects of several solvents (acetone, dioxane, ethanol, methanol, propan-2-ol, tetrahydrofuran, water) and “pH” on the fluorescence properties of MQ and its photochemical decomposition product were studied. The limit of detection of MQ was 50 ng ml^?1. The mean overall recovery from pharmaceutical tablets was 102.3 ± 4%.     

Photochemically induced reactions of decacarbonyldimanganese(0)

Photolysis at ca. 350 nm of Mn₂(CO)₁₀ in the presence of each of I₂, CH₃I, SnI₄, CuCl₂ - 2 H₂O, HgX₂ (X  Cl, Br or I), C₆H₅HgI, η⁵-C₅H₅Cr(NO)₂Cl, (η⁵-C₅H₅)₂Cr₂(NO)₄ and [Co₂(CNCH₃)₁₀](BF₄)₄, generally under N₂ or CO in several organic solvents (mainly cyclohexane and THF), was investigated. The observed photoreactions are best rationalized in terms of initial homolytic cleavage of the MnMn bond. In the presence of a halogen (X)-containing compound, the resultant Mn(CO)₅· radical abstracts X to yield Mn(CO)₅X. These reactions are characterized by high quantum efficiencies (generally, _φ-Mn2(CO)10?0.36). Following the abstraction, the remaining metal-containing species (usually a radical), SnCl₃·, CuCl, HgX·, C₆H₅Hg· or η⁵-C₅H₅Cr(NO)₂·, undergoes further abstraction of halogen by Mn(CO)₅·, coupling with the Mn(CO)₅· or ligand substitution. Isolated metal-containing products include SnI₂, Cu, Mn(CO)₅HgX, Hg, [Mn(CO)₅]₂Hg and η⁵-C₅H₅Cr(CO)₂NO. Photolysis of Mn₂(CO)₁₀ in the presence of each of the metal-metal bonded compounds, (η⁵-C₅H₅)₂Cr₂(NO)₄ and [Co₂(CNCH₃)₁₀](BF₄)₄, does not give the respective heterodinuclear combinations, (η⁵-C₅H₅)(NO)₂CrMn(CO)₅ and [(CH₃NC)₅CoMn(CO)₅]²⁺, as detectable or isolable species; instead, η⁵-C₅H₅Cr(CO)₂NO, Mn(CO)₄NO, Mn₂(CO)₉CNCH₃, and [Mn(CO)(CNCH₃)₅]₊ are among the isolated products. The photoreaction between Mn₂(CO)₁₀ and CH₃I provides a convenient synthesis of Mn(CO)₅I.     

Quadrupole type mass spectrometric study of the abstraction reaction between hydrogen atoms and ethane

The reactions of photochemically generated deuterium atoms of selected initial translational energy with ethane have been investigated. At each initial energy the relative probability of the atoms undergoing reaction or energy loss on collision with ethane was investigated, and the phenomenological threshold energy was measured as 30+/-5kJmol(-1) for the abstraction from the secondary C-H bonds. The ratio of relative yields per bond, secondary:primary was approximately 3 at the higher energies studied. The correlation of threshold energies with bond dissociation energies, heats of reaction and activation energies is discussed for abstraction reactions with several hydrocarbons.     

Photochemically induced electron transfer from [3]ferrocenophanylbutanoate anions

The anions of 4-([3]ferrocenophanyl)butanoic acids (Id and IId), when excited by light of around 240 nm wavelength in aqueous solution in the presence of N₂O, undergo photo-oxidation to zwitterions (III and IV respectively) in a manner completely analogous to the reaction of 4-ferrocenylbutanoate anion. The differences in the kinetic parameters of the reactions are thought to be attributable in part to slight tilting of the cyclopentadienyl rings caused by the connecting trimethylene bridge.     

Photochemically induced disturbance of the alkyl chain packing in vesicular membranes

In previous reports, we presented the synthesis and properties of double-tailed azobenzene-substituted phosphate amphiphiles (Kuiper et al. Synthesis 2003, 695 and Kuiper et al. Langmuir 2004, 20, 1152). We also reported that an ion channel can be regulated by trans-cis isomerization of these amphiphiles, which were incorporated in the membrane (Folgering et al. Langmuir 2004, 20, 6985). In the present study, the effect of trans-cis isomerization of both single- and double-tailed azobenzene-substituted amphiphiles on the aggregation and packing behavior has been studied. The phase transition temperature of a membrane and the thermal half-life times of the cis azobenzene-substituted amphiphiles in membranes have been measured. Furthermore, the synthesis and properties of single-tailed azobenzene-substituted phosphate amphiphiles are described and compared with those of the double-tailed analogues. The single-tailed azobenzene-substituted phosphates have a low solubility in water and form micelles, sheets, and crystals. In all cases the trans-cis isomerization leads to a disturbance of the chain packing. Both single- and double-tailed cis azobenzene-substituted phosphates lowered the main phase transition temperature of bilayer membranes. The effect increased when the azobenzene moiety was situated closer to the head group. Accordingly, the half-life times of the cis azobenzene group was shorter when the azobenzene group was positioned closer to the head group for both the single- and double-tailed amphiphiles. Interestingly, the thermal cis-trans isomerization of the single-tailed azobenzene-substituted phosphates was faster in a DOPC membrane than that for the free monomer in aqueous solution.     

Mathematical simulation of the oxygen–ethane reaction

Previous experimentation on the initial stages of the oxygen-ethane reaction at temperatures near 600°C demonstrated the existence of a significant induction period under homogeneous conditions. Below 0.13% conversion, the rate with oxygen is less than the rate of ethane pyrolysis in the absence of oxygen. Experiments were conducted with mixtures of ～1% ethane and ～0.4% oxygen in nitrogen using the “wall-less” technique. Mathematical simulations of the oxidative and simple pyrolyses of ethane were established by a numerical analysis. The experimentally observed induction period and the mechanisms previously proposed are supported by these computations. Steady-state conditions are much more slowly attained in the presence of oxygen than in its absence.     

Photochemically induced reactions of selected ketones with 4-cyanopyridine in neutral and acidic medium

The presence of the 4-cyanopyridine, in neutral or acidic medium, interferes with the normal behavior of the biradicals obtained by direct excitation of selected ketones, and results in formation of pyridinic derivatives.     

Photochemically induced reaction of 1, N4-dimethylcytosinewith isopropanol

Photoexcited 1, $\text{N}$⁴-dimethylcytosine (I) adds isopropanol to form 5,6-dihydro-1, $\text{N}$⁴-dimethyl-6-(2-hydroxy-2-propyl)cytosine (II) as the major product; a small amount of 5,6-dihydro-1-methyluracil (III) is formed as well.     

Cation radical induced cycloaddition reaction between aryl imines and ethyl diazoacetate

The reaction of ethyl diazoacetate with aryl imines can be initiated by persistent cation radical salt tris(4-bromophenyl)aminium hexachloroantimonate, giving exclusively cis-aziridine carboxylates.     

Photochemically induced phase transitions in the system cetyltrimethyl-ammonium bromide-water containing N-methyl-N,N-diphenylamine

Phase transition temperatures from lyotropic liquid crystals to the isotropic micellar solution of the system cetyltrimethylammonium bromide-water (CTAB-H₂O) were measured in the presence of 0.1-0.9 weight % of N-methyl-N,N-diphenylamine (MPA). They were determined by optical and viscometric methods and were found to increase as a function of MPA concentration in solutions containing 21 and 23 weight % of CTAB. This effect was reversed when MPA was in situ photochemically converted to N-methylcarbazole, allowing photochemically induced phase transitions.     

Analysis of the collision induced far infrared spectrum of ethane

Analysis of observed far i.r. collision-induced absorption in ethane and ethane—rare gas mixtures indicates that only a small fraction is due to the canonical multipole-induced and overlap-induced dipole moments. Nevertheless, multipole-induced dipole spectra calculated with no adjustable parameters are shown to fit the low-frequency wing ( < 60 cm⁻¹) of the observed ethane collision-induced spectrum to within 10%. More than half of the observed intensity in the ethane and ethane—rare gas far i.r. spectra has been shown to be due to rotational and vibrational modulation of dipoles induced by electric fields which do not reflect the full symmetry of the inducing molecule but depend strongly on local symmetry of the inducing charge distribution. The ethane CC stretch, ν₃ at 993 cm⁻¹, has been observed to have a collision-induced absorption which is also assigned to effects of local symmetry. In addition to the non-resonant effects due to overlap and frame distortion, we present a new theoretical analysis of a resonant intermolecular effect, also due to frame distortion, at the frequency of the torsional mode, ν₄.     

Study of the ethane oxidation reaction by the kinetic tracer method

The kinetics of ethane oxidation was studied at 320, 340, 353 and 380°C, mixture composition 2 C₂H₆ + 1 O₂, and total pressure 609 torr. It was found that at 320°C CH₂O and CH₃CHO were branching agents. A series of experiments was conducted on 2C₂H₆ + O₂ oxidation in the presence of 0.7% ¹⁴C-labeled ethylene. The ethylene oxide was found to form only from C₂H₄, formaldehyde formed from C₂H₄ and C₂H₆; and CH₃CHO, C₂H₅OH, and CH₃OH formed only from ethane. The formation rates of C₂H₄, C₂H₄O, and CH₂O were calculated by the kinetic tracer method. At 320°C the fraction of oxygen-containing products formed from C₂H₄ was 16–18%, and at 353 and 380°C it was 30–40%.