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The rates of the hydrolysis of p-nitrotrifluoroacetanilide (pNFA) catalyzed by α- and β-cyclodextrins (α-, β-CD) were measured at pressures up to 2 kbar at 25 °C and at pH 6.9 in a 0.05 M Tris buffer solution. The substrate binding constants, K, and the rate constants of the acylation process, kacyl, increased monotonically up to 2 kbar. From the pressure dependence of K, the volume changes (ΔV) accompanying the formation of the inclusion complexes at 1 bar were −3±2 cm3/mol for α-CD–pNFA and −2±2 cm3/mol for β-CD–pNFA. The activation volumes (ΔV) for the cleavage of the anilide molecule in the acylation process were −25±2 cm3/mol for α-CD–pNFA and −18±2 cm3/mol for β-CD–pNFA. The reaction mechanisms of the cleavage of the anilide substrte by CDs were discussed on the basis of the volume parameters (ΔV and ΔV*).

The conformations and electronic structures of dibenzoyl peroxide (BPO) and the benzoyloxyl radical (PhCOO) were elucidated by means of closed-shell and restricted open-shell SCF MINDO/3 calculations. The dihedral angle of BPO between the two PhCOO planes was predicted to be 115°, and the barrier to the trans form of BPO was estimated to be very small. The ground state of the PhCOO radical was predicted to be of the ∑-type. The non-planar conformation of PhCOO was more stable (2 kcal/mol) than the planar one. The variation in the radical-pair property of the lowest state of acetyl peroxide during the homolytic dissociation process was estimated by the analysis of the two-configuration wavefunctions. The substituent effect on the rate of the homolytic dissociation of BPO was discussed in terms of the electronic structures of substituted BPO.

The photochemical electrocyclic reaction paths of s-cis-acrylaldehyde to oxetene were examined on the basis of the potential surfaces obtained by the MINDO/3 CI calculation, and compared with those of the corresponding conjugated hydrocarbon system. The strong S0-S2 interaction, which appears in the disrotatory mode of the cyclization of butadiene, was not observed in the acrylaldehyde–oxetene system. There appears to be a step-by-step path, in which the π→π* induced rotation of the methylene group is followed by the ring-closing step. The zwitterion in which the positive charge is localized on the terminal carbon atom is involved in this step. Since the σ lone-pair electrons of the oxygen atom play a key role in the ring-closing step, this path is characteristic of the hetero-atom conjugated system and cannot be deduced by analogy or by a simple extension of the concepts established for the photoreactions of all-hydrocarbon conjugated systems. The possible decay paths from acrylaldehyde in the excited st...

The near-UV absorption spectra of phenol-dioxane in n-hexane were observed under hydrostatic pressures up to 1480 atm and at 30 °C. With an increase in the pressure, the spectra shift toward the longer wavelength side and the amount of the hydrogen-bonded phenol increases. The equilibrium constant for (Remark: Graphics omitted.) was obtained, and the volume change accompanying the hydrogen-bond formation was estimated to be −3.0–−3.4 cm3/mol.

Absorption spectra of intramolecular CT bands of nitrobenzene, p-nitrophenol, p-nitroaniline, acetophenone, p-hydroxyacetophenone, and p-aminoacetophenone are observed in several nonpolar solvents at 1 bar, and in heptane up to 4400 bar. The fact that all solvent shifts are linearly red for the function of refractive index (n) of solvents, (n2−1)/(2n2+1), consists with the solvent shift theory. On the other hand, the pressure shifts are not straight but convex upward for (n2−1)/(2n2+1) and the red shifts by pressure exceeds the solvent shifts. The similar convex pressure shifts are found in 1Lb bands of several aromatic compounds by plotting the high pressure data of Robertson et al. in spite of the straight solvent shifts in these 1Lb bands measured by us. Therefore the convex pressure shift may be regarded as a general tendency of the electronic spectrum, being ascribed to decrease in the distance between a solute and the surrounding solvents by compression. From comparison with the pressure shift of th...

Radical-induced decomposition reactions of diacyl peroxides were investigated on the basis of the electronic structure of the peroxide-radical systems which were calculated using an approximate restricted open-shell SCF MO method in the MINDO/3 approximation, and on the basis of configuration analysis of the transition state of the reaction. For the transition state, (1) the change in peroxy O–O bond length is expected to be small, (2) the odd-electron density on the leaving group of the SH2 displacement is expected to be very small, although appreciable odd-electron delocalization from the radical to the peroxide was observed, (3) the charge-transfer (CT) interactions which correspond to electron transfer from the radical to the peroxide was found to be important in the transition state. The trends observed in the orbital energies of the LUMO of substituted dibenzoyl peroxides and in the CT character of the transition state, which involves the singly-occupied MO of the radical and the 2pσ* MO of the pero...

The photochemical electrocyclic reaction mechanism of methyleneamine N-oxide to form oxaziridine was explored on the basis of the potential energy surfaces obtained by the MINDO/3 CI calculation. The strong interaction between the ground state and the doubly-excited state, which appears in the disrotatory cyclization process of the corresponding hydrocarbon system, was not observed. Instead, a deep potential well, which can be a leakage channel from the excited state to the ground state, was found in the S1 surface. The predicted reaction path is characteristic of hetero-atom conjugated systems, and an important participation of the oxygen σ lone-pair electrons is expected in this reaction path.

The pre-steady-state of the hydrolysis of p-nitrophenyl pivalate (pNPT) catalyzed by α-chymotrypsin (α-CHT) in Tris buffer solutions was measured up to 2.4 k bar at 25 °C. The reaction was initiated by substrate binding, and followed by acylation and deacylation processes. From the pressure dependence on the dissociation constants (Ks), the volume change ΔVKs was −14±1 cm3 mol−1. From the pressure dependence on the rate constants (kacyl and kdeacyl) of the acylation and deacylation processes, the activation volumes ΔVacyl\eweq and ΔVdeacyl\eweq were −24±1 and −2±1 cm3 mol−1, respectively. The reaction mechanisms of α-CHT are discussed in terms of the reaction and activation volumes.

The rates of the hydrolysis of 2-valeryloxy(C5)- and 2-heptanoyloxy(C7)-benzoic acids catalyzed by α-chymotrypsin (α-CHT) were measured at pressures up to 2000 bar at 30 °C and pH 7.8 in a 0.05 M Tris buffer solution. The apparent Michaelis constant, Kmapp, was estimated to vary from 5.9 to 9.9 mM, and kcat from 11×10−3 to 52×10−3 s−1, for the C5 ester, and Kmapp, from 4.7 to 10 mM, and kcat from 37×10−3 to 200×10−3 s−1, for the C7 ester, between 1 and 2000 bar. From the pressure dependences of Kmapp and kcat, the volume changes accompanying the dissociation of the enzyme–substrate complex and the activation volume for the process of the product formation were calculated to be −6.3±2 and −20±2 cm3/mol for the C5 ester and −9.5±2 and −21±2 cm3/mol for the C7 ester. The effects of the pressure on the hydrolysis of p-nitrophenyl acetate (PNPA) catalyzed by α-CHT have also been measured up to 3000 bar at pH 7.8 in a 0.05 M Tris buffer solution and at 25 °C and 35 °C. The activation volumes were −3 cm3/mol at ...

Absorption spectra of the CT band of I2 complexes were observed in several nonpolar solvents at 1 bar, and in heptane up to 4400 bar. All solvent shifts were red with an increase in (n2−1)/(2n2+1), the refractive index (n) function of solvents, consistent with the solvent shift theory. On the other hand pressure caused a variety of shifts, that is, red shifts in benzene–, toluene–, and mesitylene–I2 complexes, an inversion shift from red to blue in HMB–I2 complex, and blue shifts in Et3N–, n-Pr3N–, and n-Bu3N-I2 complexes, though increase in pressure invariably raises the (n2−1)(2n2+1) value of solvent. The pressure shifts of I2 complexes seem to be interpreted by a sum of two effects. One is the increased polarity of the solvent, which causes a red shift. The other is the decrease in the bond distance between a donor and an acceptor, which contributes to a blue shift in a strong CT complex and to a red shift in a week one. The pressure and solvent shifts of I2 complexes were compared with those of π-dono...

The p-methoxystyrene monomer has been synthesized from anisole through p-methoxyacetophenone and p-methoxyphenyl methyl carbinol. Then copolymers of p-methoxystyrene and styrene have been prepared. The dielectric properties of the copolymers in a benzene solution have been measured, and it has been found that the value of the dipole moment, μ, of the p-methoxystyrene monomer unit in the copolymers increases with an increase in the styrene content, e. g., from 1.21 D (for poly-p-methoxystyrene) to 1.32 D (for the copolymer in which the mole fraction of p-methoxystyrene is 0.175) at 20°C. The variation in the value of μ has been discussed in view of the detailed arrangement of polar monomer units. The theory concenring the relation between the dielectric polarization and the detailed structure of the copolymer molecule developed in the preceding paper, Part I, has been applied to the experimental results. In addition, a similar analysis has been made for the dielectric polarizations of the p-chlorostyrene-s...

Diketopiperazine (DKP) was used as a model compound to investigate hydrogen bond interactions between the peptide bond and water under high pressure. The solubility of DKP in water was measured as a function of pressure up to about 6000 atm at 15,25 and 35°C. It was observed that the solubility decreases with increasing pressure up to about 4500 atm, and then increases above this pressure. The solubility follows a simple exponential dependence upon pressure at least below 4500 atm. The volume change ΔV accompanying the dissolution of DKP in water is obtained from this pressure dependence of the solubility. The values of ΔV are 5.2 and 5.9 ml/mol at 25° and 35°C, respectively. These values coincide well with those obtained from dilatometric measurements at 1 atm. The reason why the solubility is inverted at the pressure above and below 4500 atm is ascribed to the change of water structure brought about by the compression. The effect of pressure on proteins reported in the previous paper is discussed in rel...

The dipole moments of six lower members of the polyethylene glycol diethyl ethers have been measured, and their configurations have been studied. As the configurations of these compounds the two models have been considered; one is a mixture of the various rotational isomers, and the other a model in which the positions of the internal rotations of two C–O bonds around the C–C bond approximately take the gauche positions with regard to each other, and the positions of the C–O bond and the C–C bond around the C–O bond take positions similar to those mentioned above with regard to each other.

The Monte Carlo method is employed on a high-speed digital computer in order to generate non-intersecting random chains simulating polymer molecules. For this purpose the GT-model of polyethylene is used. Suitable potential functions are used to calculate the energy and the probability of each chain conformation thus generated. The nonbonded-interaction energy is calculated by the Lennard-Jones “6–12” potential function. The average dimensions are then calculated by using this energy. It is suggested that the hydrogen atoms contribute largely to the statistical properties of the ethylene polymers.

The solution behavior of poly-p-methoxystyrene in toluene and butanone was measured by light-scattering and viscosity methods, and the results were compared with those of polystyrene and poly-p-chlorostyrene in order to discuss the mutual interactions between the solvent and the substituent on the phenyl group. The results show that toluene is a good solvent and butanone a poor one for poly-p-methoxystyrene; these relationships between poly-p-methoxystyrene and solvents are inverse to those for poly-p-chlorostyrene and similar to those for polystyrene, although the extensions of poly-p-chlorostyrene and poly-p-methoxystyrene are much larger than that of polystyrene at the same degree of polymerization because of the strong mutual interaction between, the solvent and the substituent on the phenyl group. It is clear, from the application of Kurata-Stockmayer theory to the experimental results obtained for poly-p-methoxystyrene, that the unperturbed dimension of poly-p-methoxystyrene is larger than that of p...

The effect of pressure on the association of rhodamine B (RB) and methylene blue (MB) in water has been investigated on the basis of their absorption spectra under hydrostatic pressures up to 4500 atm at room temperatures. Pressure increases the association of these dyes. The volume changes accompanying the 2 monomer\ightleftarrowsdimer process are calculated. The values are −10.4 cc/mol and −10.6 cc/mol in RB and MB respectively. These negative values are inconsistent with the suggestions by Rohatgi and Singhal and by Mukerjee and Ghosh that hydrophobic bonds are responsible for the associations of RB and MB. It is more plausible to assume that the hydrogen bond is the main binding force in the dye associations. London’s dispersion force and the increase in the dielectric constant of water with the increase in the pressure may also assist the dye associations.

Measurements of the rates of hydrolysis of methyl, ethyl, propyl, and butyl acetates have been made to 2 kbar in water catalyzed by dodecyl hydrogensulfate (DSA) micelle at 40 °C. The rate of hydrolysis decreases with compression up to approximately 1 kbar and then increases above 1 kbar; methyl acetate differs in these respects. The inversion phenomenon under pressure has been explained by the incorporation of both the H3O+ ion and ester molecules into the micellar phase. The observed value of the over all activation volume at 1 atm ΔV* is −5.3±1 cm3/mol for methyl, 0.40±1 cm3/mol for ethyl, 9.7±1 cm3/mol for propyl, and 20±1 cm3/mol for butyl acetate, respectively. From the activation volumes of HCl and DSA micellar catalysts, the volume change accompanying the incorporation of the esters into the micellar phase ΔΔVmicelle, has been estimated to be 4.0±1 cm3/mol for methyl, 9.8±1 cm3/mol for ethyl, 18.7±1 cm3/mol for propyl, and 27.9±1 cm3/mol for butyl acetate, respectively. The values above have been ...

The electrical conductivity of ZnSO4 in water was measured at high pressures up to 3000 kg/cm2 and at 25 °C. The dissociation constant of the ion pair (Km) increased with an increase in the pressure. The volume change (ΔV°) accompanying the dissociation was −8.0±0.5 ml/mol at 25 °C. The distance of the closest approach (a) of the ion pair, calculated using the observed Km value and the theoretical equation of Bjerrum, increased with an increase in the pressure. In view of these ΔV° and a values, the ion pair of ZnSO4 was assumed to be of the solvent-separated type. It was also concluded that the number of water molecules separating the ions constituting an ion pair increases with an increase in the pressure.

Absorption spectra of the visible I2 band of I2 complexes with Et2O, Et2S, and Et2Se in heptane have been measured up to 3300 bar at 25 °C. The equilibrium constants and volume changes accompanying complex formation, the molar extinction coefficients and the absorption maxima have been estimated. The volume changes were found comparable with those estimated from the X-ray data of the I2 complexes in the crystalline state. The enhancement of the molar extinction coefficient and the blue shift of the visible I2 band with increasing pressure have been established. The results suggest a decrease in the bond distance between an n-donor and I2, compared with the spectroscopic properties of the I2 complex at 1 bar. The decrease has been estimated as 0.008 nm with increasing pressure up to 3300 bar.

The effect of pressure on the gelation of macromolecules, such as gelatin, polyvinyl alcohol, and methyl cellulose, was investigated in order to clarify which binding forces contribute to their gel formations. The values for ΔH and ΔV accompanying the gel formation were calculated from the Eldrige-Ferry’s plot and the Clausius-Clapeyron equation respectively. The values for ΔH and ΔV in the gel fromations of gelatin and polyvinyl alcohol are both negative, while those in methyl cellulose are both positive. From the thermodynamical considerations, it has been found that the formation of hydrogen bonds results in negative values of ΔV Fand ΔH, while that of hydrophobic bonds results in positive values of ΔV and ΔH. Therefore, it may be assumed that the main binding forces in the gelations of gelatin and polyvinyl alcohol may be attributed to hydrogen bonds, and that those in methyl cellulose may be attributed to hydrophobic bonds, at least up to 6000 atm.

A semi-empirical NDDO MO method was applied to formyloxyl(HCOO) and acetoxyl(CH3COO) radicals in order to determine whether the ground-state electronic structure of the acyloxyl radical is of σ- or π-type. A σ-type state was found to be more stable than a π-type state over the entire range of values of the OCO angles of these radicals. This appears to be in agreement with the experimental facts which have been derived from the ESR spectra of several acyloxyl radicals.

Restricted open-shell SCF MINDO/3 calculation gives the Σ state for the electronic ground state of the succinimido radical.

Semiempirical MC-LCAO-MO calculations have been made on the ground-state coronene. The inclusion of the off-diagonal terms in the MC bond-order formula is, in this case, essential to improve the bond orders and the bond lengths over the usual single configuration calculation.

The acid-catalyzed hydration of simple olefins was studied on the basis of a semi-empirical SCF NDDO method. The substituent effect on the activation energy agreed well with experimental result.