An application of the reaction field theory to hydrated metal cations in the framework of the MNDO,AM1, and PM3 methods

A reaction field theory, combined with the MNDO, AM1, and PM3 molecular orbital methods, was applied to hydration phenomena of metal cationic species. The first hydration shell was treated explicitly by using a supermolecular model, [M(H₂O)_n]^m+, and its surrounding medium was described with a continuum dielectric. Hydration free energies were evaluated as a sum of the contributions from the electrostatic interaction with the bulk medium, the hydrated cluster formation, the cavity formation, and the vaporization of water molecules forming the cluster. As a whole, calculated hydration energies were in good agreement with the corresponding experimental data over various kinds of metal cationic species. © 1995 by John Wiley & Sons, Inc.     

Reaction of poly(vinyl chloride) with superoxide anion

Reaction of poly(vinyl chloride) (PVC) with superoxide anion was carried out in tetrahydrofuran (THF) at 40°C in a nitrogen atmosphere. Remarkable changes in infrared (IR) spectra of the samples treated with superoxide anion were observed in the following regions: ca. 3300, 1680, 1620, and 765 cm^?1, which suggested the formation of hydroxyl groups, α,β-unsaturated ketone groups, and ethylenic structures. Ultraviolet–visible spectra also showed the formation of polyene structures. The content of chlorine in the polymer decreased and that of oxygen increased with reaction time. The reaction mechanism was discussed on the basis of these results.     

Mechanisms of pharmacokinetic interaction between propranolol and quinidine in rats.

In order to study the mechanism of propranolol-quinidine interaction, the effects of quinidine on propranolol pharmacokinetics were examined in male Wistar rats. The concurrent oral administration of quinidine (10 mg/kg) markedly increased the plasma concentration of propranolol (2.5 mg/kg), and the area under the propranolol concentration-time curve increased about 3.6-fold. These results are consistent with previous observations in man and indicate the possible usefulness of the male Wistar rat as an animal model for investigating the mechanisms of the drug interaction. When propranolol was given intravenously, a concurrent administration of quinidine increased the apparent distribution volume of propranolol, mainly by decreasing its plasma protein binding. However, the systemic clearance of propranolol was not significantly altered by quinidine. Thus, quinidine increased the availability of oral propranolol from 13.8 +/- 2.2 to 44.2 +/- 4.6% (p less than 0.01). Furthermore, quinidine delayed the elimination of propranolol from the isolated perfused rat liver. These results indicate that quinidine reduces the presystemic elimination of propranolol in the liver, thereby increasing its systemic availability after oral administration.     

Effects of pressure and solvents on the infrared absorption intensity of the O-H stretching mode of phenol in solutions

Effects of pressure and solvents on the infrared spectrum of phenol in solutions have been investigated using a hydrostatic high-pressure cell with synthetic diamond windows. For the first time, we performed a quantitative investigation of the effect of pressure on the absolute intensity of O-H stretching mode up to 150 MPa (in CCl4) and 200 MPa (in CS2). For comparison, we measured the effect of solvents on the absorption intensity. The Polo-Wilson theory, which is the most traditional theory for medium effects on the intensity, was tested for present results. The pressure dependence was in sufficient agreement with their formula, while the solvent dependence is unsatisfactory. This suggests that the traditional intensity correction by Polo-Wilson's formula is practically valid for pressure-tuning infrared experiments.     

Stereospecific synthesis of urea-tethered neoglycoconjugates starting from glucopyranosyl carbamates

Silyl-assisted elimination reaction of glucopyranosyl carbamates has been established for the synthesis of α- and β-d-glucopyranosyl isocyanates and ureas. This method proved to be useful for the synthesis of urea-tethered neoglycoconjugates.     

Vinyl polymerization. Part 268. Polymerization of acrylonitrile initiated by the system of tetramethyl tetrazene and bromoacetic acid

The polymerization of acrylonitrile (AN) initiated by the system of tetramethyl tetrazene (TMT) and bromoacetic acid (BA) in dimethylformamide (DMF) was studied. The TMT–BA system could initiate the polymerization of AN more easily than TMT alone. The polymerization was confirmed to proceed through a radical mechanism. The initial rate of polymerization R_p was expressed by the equation: R_p = [TMT]^0.62-[BA]^0.5[AN]^1.5. The overall activation energy for the polymerization was estimated as 9.4 kcal/mole. In the absence of monomer, the reaction of TMT with BA in DMF was also studied kinetically by measuring the evolution of nitrogen gas. The reaction was first-order in TMT and first-order in BA; the rate data at 49°C were k₂ = 9.1 × 10^?2l./mole-sec., ΔH? = 17.0 kcal/mole, and ΔS? = ? 6.6 eu. In addition, the treatment of TMT with BA in benzene led to the formation of tetramethylhydrazine radical cation, which was identified by its ESR spectrum. On the other hand, the relatively strong interaction between TMT and DMF was observed by absorption spectrophotometry.     

C-O bond cleavage of benzophenone substituted by 4-CH2OR (R = C6H5 and CH3) with stepwise two-photon excitation

The C-O bond cleavage from benzophenone substituted with 4-CH2OR (p-BPCH2OR, 1-3), such as p-phenoxymethylbenzophenone (1, R= C6H5) and p-methoxymethylbenzophenone (2, R= CH3), occurred by a stepwise two-photon excitation during two-color, two-laser flash photolysis. On the other hand, no C-O bond cleavage occurred from p-hydroxymethylbenzophenone (3, R = H). The first 355-nm laser excitation of 1-3 generates p-BPCH2OR in the lowest triplet excited state (T1) which has an absorption at 532 nm. When p-BPCH2OR(T1) is excited with the second 532-nm laser to p-BPCH2OR in the higher triplet excited state (T(n)), the C-O bond cleavage occurred within the laser flash duration of 5 ns. The quantum yields of the C-O bond cleavage during the second 532-nm laser irradiation were found to be 0.015 +/- 0.007 and 0.007 +/- 0.003 for 1 and 2, respectively. Although these values are low, the diminishing 1(T1) or 2(T1) was found to convert, in almost 100% yield, to phenoxyl (C6H5O*) and p-benzoylbenzyl (BPCH2*) radicals or methoxyl (CH3O*) and BPCH2* radicals, respectively. The T(n) excitation energy, the energy barrier along the potential surface between the T(n) states and product radicals, and delocalization of the T(n) state molecular orbital including BP and CH2OR (R = C6H5, CH3, H) moieties are important factors for the occurrence of the C-O bond cleavage. It is found that the C-O bond cleavage and production of free radicals, such as BPCH2*, C6H5O*, and CH3O*, can be performed by a stepwise two-photon excitation. The present study is an example in which the chemical reactions can be selectively initiated from the T(n) state but not from the S1 and T1 states.     

Synthesis of 1,3,4-thiadiazol-2-ylacetic acid derivatives

1,3,4-Thiadiazol-2-ylacetic acids 4 were prepared by lithiation of 2-methyl-1,3,4-thiadiazoles 1 , followed by treatment with carbon dioxide. Diethyl 1,3,4-thiadiazol-2-ylmalonates 6 were prepared by nucleophilic displacement reaction of the corresponding bromides 5 with diethyl malonate. Introduction of the amino group at the a-position of 4 or 6 was carried out via oximation or bromination to give the amino ester 9 or 4 . Attempts to prepare DL-α-amino-1,3,4-thiadiazol-2-ylacetic acids from 9 or 4 were unsuccessful because the amino acids were decarboxylated too rapidly to be isolated in the free form.     

Highly regioselective diels-alder reactions of 2-trimethylsilylmethyl- 1,3-butadiene catalyzed by a lewis acid and applications to syntheses of terpenes

2-Trimethylsilylmethyl-1,3-butadiene undergoes highly regioselective Diels-Alder reactions with dienophiles such as acrolein and methyl vinyl ketone catalyzed by aluminum chloride in which the “para” isomers are obtained almost exclusively. The adducts are converted readily to a variety of naturally occurring mono and sesquiterpenes.     

Poly(Vinyl 2-furylacrylate), a new photosensitive polymer

Poly(vinyl 2-furylacrylate), a new photosensitive polymer, was prepared, and its photosensitivity was investigated. The polymer cannot be synthesized by the usual procedure, condensation of poly(vinyl alcohol) and 2-furylacrylyl chloride in hot pyridine, but is easily prepared by the aqueous alkaline process, regardless of the degree of polymerization. Poly(vinyl 2-furylacrylate) is remarkably highly photosensitive and is spectrally sensitized by aromatic nitro compounds and aromatic carbonyl compounds. The mechanism of photochemical reaction is considered to involve the dimerization of the furylacrylyl group, and the quantum yield appears to be constant.