Photoinduced heterolysis of the carbon-oxygen bond in bichromophoric 1-arylmethyloxy-2-pyridones

Irradiation of the title compound having a 9-anthryl (1a) or a 1-pyrenyl group (1b) in methanol was found to give the heterolytic C---O bond cleavage products: 1-hydroxy-2-pyridone and arylmethyl methyl ether, (which predominate for the reaction of 1a), along with 2-pyridone, aryl-substituted methanol and aryl aldehyde derived from the homolysis of the N---O bond (that mainly occurs in the photolysis of 1b). Spectroscopic analysis of the ground-state and excited singlet-state behavior of 1 revealed that a non-emissive intramolecular exciplex (whose formation rate is much faster in 1a than in 1b) plays a key role in inducing the C---O bond heterolysis.     

Extraction-spectrophotometric determination of vanadium with N-m-tolyl-N-phenylhydroxylamine and its application to coal and coal fly-ash

N-m-Tolyl-N-phenylhydroxylamine is proposed for the spectrophotometric determination of small amounts of vanadium. The reddish-violet complex formed with the reagent in 3-6M hydrochloric acid after extraction with chloroform shows an absorption maximum at 530 nm, and obeys Beer's law for 0-76.5 mug of vanadium in 10 ml of chloroform. The proposed method has been successfully applied to the determination of vanadium in coal and coal fly-ash.     

An Ideal One-Dimensional Antiferromagnetic Spin System Observed in Hydrogen-Bonded Naphth[2,3-d]imidazol-2-yl Nitronyl Nitroxide Crystal: The Role of the Hydrogen Bond

A novel stable organic radical, 2-(naphth[2,3-d]imidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide (4), has been designed, synthesized, and structurally characterized to examine the effects of ring extension on 2-(benzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide (2). 4 forms four-centered intramolecular and intermolecular hydrogen bonds, and the hydrogen bonds are repeated along the c-axis to form a one-dimensional chain structure. This hydrogen-bonding motif contrasts that of 2, which forms three-centered intramolecular and intermolecular hydrogen bonds. The magnetic susceptibility measurement of 4 reveals that an antiferromagnetic interaction is dominant between spins, and the magnetic behavior is reproduced by the Bonner-Fisher model with J = -14 cm-1. Because each hydrogen-bonded chain is well isolated, a magnetic interaction pathway was thought to exist along the chain direction. Two interaction pathways have been assumed: (i) through-space interaction between the O atoms of the nitroxide and (ii) through the NH...ON intermolecular hydrogen bond. We have concluded that pathway (i) is predominant, by considering the identical magnetic data between the NH nondeuterated and deuterated samples. The hydrogen bond mainly has a role in crystal scaffolding.     

Exciton Coupling and Complexation Behaviour of β-Cyclodextrin Naphthoate

The host–guest complexation behaviour of-cyclodextrin 6-O-mono-2-naphthoate(1) and 6-[(N-2-naphthoyl-2-aminoethyl) amino]-6-deoxy--cyclodextrin (2) have been studied by the circular dichroism method. The exciton coupling band of 1 suggests that two naphthoyl moieties are partly included in one -CD cavity. Host 1 could form a dimer in a more polar solvent and the dimer could be dissociated in a less polar solvent or by adding a guest. Solvent-induced, concentrationinduced, and guest-induced circular dichroism variations were examined. No exciton coupling was observed for host 2.     

Elimination-addition mechanism for nucleophilic substitution reaction of cyclohexenyl iodonium salts and regioselectivity of nucleophilic addition to the cyclohexyne intermediate

The reaction of 4-substituted cyclohex-1-enyl(phenyl)iodonium tetrafluoroborate with tetrabutylammonium acetate gives both the ipso and cine acetate-substitution products in aprotic solvents. The isomeric 5-substituted iodonium salt also gives the same mixture of the isomeric acetate products. The reaction is best explained by an elimination-addition mechanism with 4-substituted cyclohexyne as a common intermediate. The cyclohexyne formation was confirmed by deuterium labeling and trapping to lead to [4 + 2] cycloadducts and a platinum-cyclohexyne complex. Cyclohexyne can also be generated in the presence of some other mild bases such as fluoride ion, alkoxides, and amines, though amines are less effective bases for the elimination. Kinetic deuterium isotope effects show that the anionic bases induce the E2 elimination (k(H)/k(D) > 2), while the amines allow formation of a cyclohexenyl cation in chloroform to lead to E1 as well as S(N)1 reactions (k(H)/k(D) approximately 1). Bases are much less effective in methanol, and methoxide was the only base to efficiently afford the cyclohexyne intermediate. Nucleophiles react with the cyclohexyne to give regioisomeric products in the ratio dependent on the ring substituent. The observed regioselectivity of nucleophilic addition to substituted cyclohexynes is rationalized from calculated LUMO populations, which are governed by the bond angles at the acetylenic carbons: The less deformed carbon has a higher LUMO population and is preferentially attacked by the nucleophile.     

Synthesis of N-substituted C-normorphinans and their pharmacological properties.

Several N-substituted C-normorphinans (VIII and IX) were synthesized and tested for their analgetic and narcotic antagonist activities and physical dependence capacity. Treatment of N-formyl- octahydro-2-pyrindine (IIIc) with polyphosphoric acid readily gave N-formyl-C-normorphinan (IV). The N-nor bases (V and VII) obtained from IV were converted to VIII and IX. The N-methyl derivative (I), which was previously reported to be inactive by Haffner's method, exhibited potent analgetic activity by the hot plate method and the AcOH-induced writhing test. Compounds VIII and IX showed pharmacological properties similar to those of N-substituted morphinans and exhibited agonist (analgetic) and/or narcotic antagonist activities. The C-nor analogue (IXa) of cyclorphan (IIc) exhibited potent analgetic and antagonist activities with no physical dependence capacity in the single-dose suppression tests both in rats and monkeys.     

Supramolecular Photochirogenesis. 3. Enantiodifferentiating Photoisomerization of Cyclooctene Included and Sensitized by 6-O-Mono(o-methoxybenzoyl)–cyclodextrin

Supramolecular enantiodifferentiating photoisomerization of (Z)-cyclooctene (1Z) to chiral (E)-isomer (1E) through inclusion and sensitization by 6-O-mono(o-methoxybenzoyl)--cyclodextrin (2) was investigated in water and in aqueous methanol solutions at various temperatures. A dramatic inversion of the product chirality was observed to occur by simply changing the solvent from water to methanol. Thus, the supramolecular photosensitization in aqueous solution gave (R)-(–)-1E in 15% enantiomeric excess (ee), whereas in methanol the antipodal (S)-(+)-1E was obtained in 5% ee. The temperature and solvent dependencies of the product ee are discussed.     

Porphyrin-sensitized nanoparticulate TiO2 as the photoanode of a hybrid photoelectrochemical biofuel cell

Porphyrin-sensitized nanoparticulate TiO(2) on conducting glass has been investigated as a photoanode material for a new cell that converts light energy into electricity. The cell is a hybrid of a dye-sensitized nanoparticulate semiconductor photoelectrochemical solar cell, and a biofuel cell that oxidizes glucose. Porphyrin molecules excited by light inject electrons into the photoanode, from where they enter the external circuit. The resulting porphyrin radical cations are reduced by NADH in aqueous buffer, ultimately regenerating the photoanode and producing NAD(+). Glucose dehydrogenase oxidizes glucose, and in the process recycles NAD(+) back to NADH. The photoanode is coupled with a suitable cathode to make a functioning cell (Hg/Hg(2)SO(4) was employed for evaluation purposes). The cell produces 1.1 V at open circuit and has a fill factor of 0.61. These values are both significantly higher than those for a previously reported cell of a similar type based on an SnO(2) electrode.     

Promotion effect of metal oxides on C-O bond dissociation in CO hydrogenation over Rh/SiO2 Catalyst — possible role of partially reduced state cations

In CO hydrogenation over Rh/SiO₂ catalysts, the effect of additive metal oxides on C-O bond dissociation was studied by using pulse surface reaction rate analysis (PSRA). The addition of oxides of Al, Ti, Cr, V, and Mn resulted in an increase in the rate constant for the dissociation according to this sequence, while the oxides of Cu, Zn, and Ag added decreased the rate constant to almost the same extent. In contrast to these metal oxides, MoO₃ and WO₃ did not change the dissociation activity. CO adsorption measurement indicated that all of the added metal oxides covered a considerable portion of the Rh metal surface, although the efficiency of covering was different from one metal oxide to another. Covering the Rh metal surface with an added metal oxide should decrease the rate constant of C-O bond dissociation, because ensemble sites, consisting of a group of surface Rh atoms and considered necessary for the dissociation, were destroyed. The suppression effect resulted from the destruction of the ensemble sites by adding the oxides of Cu, Zn, and Ag. For other metal oxides, temperature-programmed reduction (TPR) or O₂ uptake measurement revealed that the added oxides, especially those existing on the Rh metal surface, were in a partially reduced state under reaction conditions. Owing to its high affinity for an oxygen atom, the cation in a partially reduced state participated in the reaction in such a way that the oxygen end of adsorbed CO species was bound to the cation so as to dissociate the C-O bond, which resulted in promotion of the dissociation. The observed promotion was explained in terms of the enhancement owing to the high affinity sufficient to overcome the suppression caused by destroying ensemble sites. Lack of the promotion effect of MoO₃ and WO₃ might result from a balance between promotion due to the high affinity of the partially reduced Mo or W and suppression caused by destroying ensemble sites. Excellent correlation was observed between the intrinsic activity increase, from which the suppression effect was excluded, and the heat of formation of metal oxide including MoO₃ and WO₃. Since the heat of formation of metal oxide is considered to be a measure of the affinity, this correlation supports the idea that the high affinity of additive cations for an oxygen atom is of primary importance in the promotion of C-O bond dissociation in CO hydrogenation.     

Determination of arsenite, arsenate, and monomethylarsonic acid in seawater by ion-exclusion chromatography combined with inductively coupled plasma mass spectrometry using reaction cell and hydride generation techniques

This paper describes a robust and sensitive method for the determination of arsenic species in seawater by ion-exclusion liquid chromatography (LC) combined with inductively coupled plasma mass spectrometry (ICP-MS) using reaction cell and hydride generation (HG) techniques. A good separation of arsenite, arsenate, and monomethylarsonic acid was achieved using an ion-exclusion column packed with a sulfonated polystyrene resin and a dilute nitric acid at pH 2.0 as the eluent, even when a large volume, i.e. 200 mul, of seawater samples containing a large amount of matrix was repeatedly injected. Separations of the chloride ion due to the matrix and arsenic species were partially performed; however, the extensive peak of ArCl due to high content of Cl(-) in a sample overlapped peaks of the three arsenic species on (75)As measurement by ICP-MS. This ArCl polyatomic interference was efficiently eliminated by collision of ArCl molecules with helium in an octopole reaction cell which was introduced prior to a mass spectrometer. Detection limits of the three arsenic species in a sample containing 2% Cl(-), the concentration of which is comparable to that in a seawater sample, by LC-ICP-MS with the octopole reaction system (ORS), ranged from 21 to 25 pg As ml(-1); these values were three-six times lower than those by LC-ICP-MS without ORS. As another technique for ArCl interference elimination, HG prior to ICP-MS was also successfully used not only to reduce the interference but also to improve the detection limits to 3.4-4.5 pg As ml(-1). The developed LC-ICP-ORS-MS and LC-HG-ICP-MS were validated by analyzing a certified reference material (CRM) of seawater. In addition, no serious decrease in analytical performance of present methods was observed in the experimental periods of half a year for LC-ICP-ORS-MS and 1 year for LC-HG-ICP-MS, respectively. The latter method was successfully applied to characterize seasonal variations of three arsenic species in deep seawater and surface seawater.