Proton Order–Disorder Phenomena in a Hydrogen‐Bonded Rhodium–η5‐Semiquinone Complex: A Possible Dielectric Response Mechanism

A newly synthesized one‐dimensional (1D) hydrogen‐bonded (H‐bonded) rhodium(II)–η⁵‐semiquinone complex, [Cp*Rh(η⁵‐p‐HSQ‐Me₄)]PF₆ ([ 1 ]PF₆; Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl; HSQ=semiquinone) exhibits a paraelectric–antiferroelectric second‐order phase transition at 237.1 K. Neutron and X‐ray crystal structure analyses reveal that the H‐bonded proton is disordered over two sites in the room‐temperature (RT) phase. The phase transition would arise from this proton disorder together with rotation or libration of the Cp* ring and PF₆^? ion. The relative permittivity ε_b′ along the H‐bonded chains reaches relatively high values (ca., 130) in the RT phase. The temperature dependence of ¹³C CP/MAS NMR spectra demonstrates that the proton is dynamically disordered in the RT phase and that the proton exchange has already occurred in the low‐temperature (LT) phase. Rate constants for the proton exchange are estimated to be 10^?4–10^?6 s in the temperature range of 240–270 K. DFT calculations predict that the protonation/deprotonation of [ 1 ]⁺ leads to interesting hapticity changes of the semiquinone ligand accompanied by reduction/oxidation by the π‐bonded rhodium fragment, producing the stable η⁶‐hydroquinone complex, [Cp*Rh³⁺(η⁶‐p‐H₂Q‐Me₄)]²⁺ ([ 2 ]²⁺), and η⁴‐benzoquinone complex, [Cp*Rh⁺(η⁴‐p‐BQ‐Me₄)] ([ 3 ]), respectively. Possible mechanisms leading to the dielectric response are discussed on the basis of the migration of the protonic solitons comprising of [ 2 ]²⁺ and [ 3 ], which would be generated in the H‐bonded chain.     

Bénard–Marangoni convection in a small circular container: influence of the Biot and Prandtl numbers on pattern dynamics and free surface deformation

We studied, experimentally, the pattern dynamics and free surface deformation in Bénard–Marangoni convection, in a circular container (aspect ratio = 6). The free surface deformation fields were visualized by interferometry and temperature fields by infrared thermography. We considered the influence of the Marangoni (up to 2,623), Biot and Prandtl numbers. More dynamics are induced by increasing the Biot number and transition to a time-dependent flow has been observed. Conversely, increasing the Prandtl number reduces the dynamics. The deformation increases as a function of the Marangoni number until it reaches asymptotic values, which are functions of the Biot and Prandtl numbers.     

Effect of Solvent on the Radical Copolymerizability of Styrene with Acrylonitrile

Radical copolymerization of styrene (St, M₁) with acrylonitrile (AN, M₂) has been carried out using azobisisobutylonitrile as an initiator in benzene, dimethylsulfoxide, acetonitrile, and ethanol at 60 and 80°C. Good linear correlationships were obtained by plotting the values of log r₁, log r₂, Q₂, and e₂ against those of vC[dbnd]N and vC[dbnd]C determined in the solvents: the increase in the interaction between AN and the solvent was found to decrease the values of log r₁ and e₂ but to increase those of log r₂ and Q₂. The results are discussed in terms of the solvation both in the ground state and in the transition state.     

Enzyme and Nonenzyme Hydrolyses of End Ester Group in Polyethylene Glycol Esters

The enzyme and nonenzyme hydrolyses of the end ester group in polyethylene glycol (PEG) esters were studied. The end monoester in PEG ester is known to be easily hydrolyzed by alkaline or acidic solution. 2-Methyl-ω-benzoyloxypoly(oxy-1,2-ethanediyl)(Bz-PEG) and 2-methyl-ω-4-nitrobenzoyloxypoly(oxy-1,2-ethanediyl) were found to be hydrolyzed by lipase and esterase in Tris buffer solution (pH 7.7) but 2-methyl-ω-acetoxypoly(oxy-1,2-ethanediyl) was not. The parameters of enzyme reaction in the hydrolysis of ester bonds in Bz-PEG by esterase were estimated to be as follows: V_max = 6.09 × 10^?7 mol/dm^3.s, K_m = 7.63 × 10^?4 mol/dm³.     

Epoxidation of Allylic Alcohols with Hydrogen Peroxide Catalyzed by [PMO12O40]3-[C5H5N+(CH2)15CH3]3

Applicatims a Mo- and W-based heteropoly acids (HPA) as a catalyst in the oxidation of olefins have extensively been investigated¹. However, a patent work is only attempted concerning the evoxidatim of olefins with H₂0₂ by HPA²⁾ since the oxirane ring is cleaved because of a strong acidity of HPA itself. Herein, an effective epoxidatim of some allylic alcohols with H₂0₂ by a new Mo-species (MPCP), which was prepared from 12-molybdatophosphoric acid (H₃PMo₁₂0₄₀) and cetylpyridinium chloride (C₅H₅N (CH₂), ₁₅CH₃- C1^-) under two-phase conditions using chloroform as an organic solvent, is described.     

Molecular chaperone-like properties of sodium caseinate to suppress the pressure-induced aggregation of β-lactoglobulin

ABSTRACT

The objective of this study was to determine whether sodium caseinate can inhibit the aggregation of whey protein induced by pressure treatment. Solutions of β-lactoglobulin (β-Lg, 0.2%, w/v) and mixtures containing 0.2% (w/v) β-Lg and 0–0.5% (w/v) sodium caseinate (NaCas) were pressurized at 400–800?MPa. NaCas suppressed the aggregation of β-Lg induced by pressure treatment, and this function was dependent on the concentration of NaCas. Furthermore, NaCas altered the aggregation process of β-Lg by suppressing the transition of the aggregate from the soluble phase to the insoluble phase and, as a result, the fraction of insoluble aggregates was decreased. During this process, NaCas formed stable complexes with the denatured β-Lg, and the formation of complexes prevented further aggregation of β-Lg. These results indicate that NaCas exhibits a chaperone-like activity under high pressure.     

Radical Copolymerization of Vinylidene Chloride with 3(2-Methyl)-6-methylpyridazinone in Several Solvents

The radical copolymerization of vinylidene chloride (Vc, M₁) with 3(2-methyl)-6-methylpyridazinone (I, M₂) was carried out in benzene, ethanol, phenol, and acetic acid at 60 and 80°C. The monomer reactivity ratios were found to vary with the reaction conditions. The linear correlationships were obtained by plotting the values of log r₁ against those of ^V C[dbnd]O and ^V C[dbnd]C of monomers determined in the solvents.     

Efficient Light-Harvesting Antennae Resulting from the Dense Organization of Dyes into DNA Junctions through d-Threoninol

Herein we report the construction of efficient light-harvesting antennae by hybridization of DNA oligonucleotides containing high densities of fluorophores into DNA junctions through d -threoninol. Six pyrene donors could be incorporated into each arm without self-quenching. A perylene acceptor was located at the center of the junction. Antenna effects of a duplex and three- to eight-way junctions were systematically compared. Six- and eight-way junctions had the highest antenna effects, and their effective absorption coefficients were 8.5 times higher than that of perylene. Interestingly, even-numbered junctions had higher efficiencies than odd-numbered junctions. Nondenaturing gel analyses and fluorescence lifetime measurements demonstrated that the strong odd–even effects were derived from differences in the stability of junctions. The results presented will guide the design of efficient artificial photosynthetic systems.