Substituted (RS,SR)-1-phenylethyl phenyl sulfoxides (threo) (XC6H4S(O)CH(CH3)C6H4Y) and some substituted (RR,SS)-sulfoxides (erythro) were prepared and kinetic investigation for the thermal decomposition was carried out at 80.0, 90.0, and 100.0 °C in dioxane. Hammett plots for threo-XC6H4S(O)CH(CH3)C6H5 gave positive ρ-values (ρX=0.60–0.64 at three temperatures), while those for threo- and erythro-C6H5S(O)CH(CH3)C6H4Y snowed V-shape lines with bottoms at the m-OCH3 substituent though the effects of the substituents are small. Meanwhile, large kinetic isotope effects for threo- and erythro-C6H5S(O)CH(CD3)C6H4Y (Y=H, p-OMe, m-Cl) (kH⁄kD=4–6) were observed at all temperatures. The activation energies were in the range of 104–121 kJ mol−1 for all sulfoxides, while the activation entropies were relatively large (7–37 J K−1 mol−1) and were correlated with Hammett σ-values to give small negative trend. Reactions of all erythro-isomers examined were 2–3 times faster than those of the corresponding threo-isomers. From these results, it is suggested that the pyrolysis of 1-arylethyl aryl sulfoxides proceeds via a concerted mechanism in which the transition state is variable from an El-like to a conjugated one. In the latter transition state, conjugation of the phenyl group bearing the electron-withdrawing substituent with the developing π-bond electron acidifies the β-proton.

To develop a simple method to determine the degree of substitution (dS) for starch ester, we prepared starch acetate with various dS values (0—3) and examined the mode of starch-iodine complex formation for the starch acetate by monitoring the ultraviolet-visible (UV-vis) spectra and their Fourier-transform infrared (FT-IR) spectral changes. The effect of acetylation on the formation of the starch-iodine complex was investigated by monitoring the decrease in absorbance at 680 nm (blue value). The blue value decreased by increasing the standard dS value determined by NMR for starch acetate, but two different correlations between the blue values and the dS values were observed for the low- and highly-substituted starch acetate. The FT-IR spectra for starch acetate particles were measured using a diffuse reflection method. The peak areas and absorbances of the bands assigned to the acetyl group showed a poor correlation with standard dS values from the NMR. On the other hand, the FT-IR peaks assigned to sodium acetate produced by saponification of the starch acetate could be detected using the ATR (attenuated total reflection) method; they showed a good correlation with the standard dS values from the NMR. From these results, it was concluded that the ATR method should be available for the dS determination of starch acetate.

The hydrolysis of alkoxy(aryl)(phenyl)-λ6-sulfanenitriles in several buffer solutions was found to follow a good pseudo-first-order kinetic equation, giving the corresponding sulfoximides and alcohols (for the case of the hydrolysis of neopentyloxy-λ6-sulfanenitrile, giving a rearranged product, 2-methyl-2-butanol). The dependence of the rate of hydrolysis on the structure of the alkyl group showed the opposite trend to the usual SN2 character, i.e. Me < Pr < Bu ≈ Et < i–Pr, except for neopentyl. The pH-rate profiles indicated that the rate of hydrolysis is also first order in [H+] at pH more than 6.08, and trends to saturate at low pH. According to these kinetic results, a two-step reaction mechanism was proposed which involves a pre-equilibrium protonation on the nitrogen atom of the alkoxy-λ6-sulfanenitriles, followed by a rate-determining C-O bond cleavage via an SN2 or SN1 mechanism on the alkyl carbon atom depending on the structure of the alkyl group. From a double-reciprocal plot of 1/kobs vs. 1/[H+], the pKa value and the rate constant of the second reaction of neopentyloxy(diphenyl)-λ6-sulfanenitrile were estimated to be 5.02 and 7.02×10-3 s-1, respectively. The substituent effects on the phenyl group of neopentyloxy(diphenyl)-λ6-sulfanenitrile afforded a large negative ρ-value (-1.88) for pKa and positive one (+1.66) for the second reaction at 25.2 °C. The small negative ρ-values observed at pH 6.27 for diphenyl(propoxy)-λ6-sulfanenitrile (-0.42) and neopentyloxy(diphenyl)-λ6-sulfanenitrile (-0.26) were found to be the results of a cancellation of those for the opposite trend of the reactions of the pre-equilibrium and the second step. The activation parameters for both the pre-equilibrium and the subsequent reactions were also estimated based on the parameters for the hydrolysis of neopentyloxy(diphenyl)-λ6-sulfanenitrile at pH 6.22 and 2.99. The buffer effect is due to a nucleophilic attack of the buffer base to the alkyl carbon atom of the protonated alkoxy-λ6-sulfanenitriles. The sulfoximide moiety in the protonated λ6-sulfanenitrile is revealed to be a very good leaving group.

Temperature-responsive changes in catalytic properties of enzymes modified with a temperature-responsive polymer, poly(N-isopropylacrylamide) (PIPA), were examined. PIPA with a carboxyl group at its end was prepared using 2,2'-azoisobutyronitrile as initiator in the presence of 3-mercaptopropionic acid as a chain transfer reagent. After being activated by the coupling with N-hydroxysuccinimide, PIPA was directly bound to enzymes such as acid phosphatase and trypsin. The catalytic activities of the modified enzymes showed a bending point in their Arrhenius plots at about 33 "C due to a coil-globule transition of PIPA chains. The ratio of amidase-and esterase-activities of trypsin modified with PIPA chains was largely affected by the changes in temperature. As for the semi-enzymatic synthesis of N-benzoyl-L-arginylglycinamide, secondary hydrolysis of the peptide product observed with free trypsin was effectively suppressed in modified trypsin at 45 "C (above the transition temperature), and the peptide was obtained with higher conversion.

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