Heat capacities of copper(II) formate tetrahydrate and tetradeuterate: A comparative study of phase transitions in layer hydrate crystals

The heat capacities of copper(II) formate tetrahydrate and tetradeuterate have been measured from 12 to 300 K with an adiabatic calorimeter. They have sigmoidal temperature dependence except near the antiferroelectric-paraelectric transition temperatures, 235.78 ± 0.05 K and 245.64 ± 0.05 K, respectively. The corresponding enthalpy changes are 836.0 ± 1.0 J mol^?1 and 936.9 ± 0.5 J mor^?1. The entropy changes are 3.546 ± 0.005 JK^?1mol^?1 and 3.814 ± 0.002 JK^?1 mol^?1. The heat capacities are larger in the high temperature phase than in the low temperature phase, the difference amounting to 5.74 JK^?1 mol^?1 and 7.15 JK^?1 mol^?1 for the hydrate and the deuterate, respectively. The heat capacity anomaly is compared with those in tin(II) chloride dihydrate and potassium hexacyanoferrate trihydrate and discussed in relation to the structure of the hydrogen bond networks in these substances. The discussion is extended to include possible properties of the hydrogen bond frameworks in ices I_h and II.     

Reaction profiles and substituent effects for the reduction of carbonyl compounds with monomer and dimer simple metal hydride reagents

Reaction profiles and energetics for the reactions of substituted benzaldehydes with a series of different simple metal hydrides (BH(3), BMeH(2), BMe(2)H, AlH(3), and AlMe(2)H) are examined computationally. B3LYP/6-31G optimizations and MP2/6-311G single point energy calculations revealed that the Al reagents are more reactive than B reagents. Replacement of H with Me on BH(3) or AlH(3) makes the reduction transition state (TS) less stable. Accordingly the overall reactivity is in the order AlH(3) > AlMe(2)H > BH(3) > BMe(2)H. The Hammett rho value for substituted benzaldehydes (BAs) is negative for the initial complex formation and positive for the hydride-transfer step. The size and the sign of the apparent rho value depend on the relative stabilities of the separated reactants and the complex. The TS structures vary according to the Hammond postulate for substituted BAs and the variation is reflected in carbonyl-carbon and aldehyde-deuterium isotope effects. Comparison of the reaction profiles of the monomer and dimer reagents reveals that the real reacting species is the monomer in the gas phase for BH(3) but the dimer for BMe(2)H.     

Ruthenium-complex-catalyzed regio- and stereoselective linear codimerization of 2-norbornenes with acrylic compounds

A linear codimerization of 2-norbornenes with acrylic compounds such as acrylates and an acrylamide proceeded efficiently by ruthenium catalyst systems, RuCl3(tpy)/Zn (tpy = 2,2':6',2' '-terpyridine) or [RuCl2(C6H6)]2/Zn in a primary or secondary alcoholic solvent, to afford the corresponding exo-trans-2-norbornylacrylates as major products regio- and stereoselectively along with a small amount of cis isomers. The reaction of 2,5-norbornadiene with methyl acrylate also gave the linear exo-trans codimer, which was effectively catalyzed by the addition of triarylphosphines to the RuCl3(tpy)/Zn catalyst system.     

Feeding attractants for the muricid gastropod Drupella cornus, a coral predator

The muricid gastropods genus Drupella are known to be voracious coral predator. Outbreaks of them have accelerated significant destruction on coral reefs, but its precise mechanism is poorly understood. Here, we describe the identification of montiporic acids C (1) and A (2) isolated from sea water extracts of the coral Montipora sp., which showed potent feeding-attractant activity toward D. cornus.     

Direct measurement of the counterion distribution within swollen polyelectrolyte films

The depth profile of the counterion concentration within thin polyelectrolyte films was measured in situ using contrast variant specular neutron reflectivity to characterize the initial swelling stage of the film dissolution. We find substantial counterion depletion near the substrate and enrichment near the periphery of the film extending into the solution. These observations challenge our understanding of the charge distribution in polyelectrolyte films and are important for understanding film dissolution in medical and technological applications.     

The functional layered organosilica materials prepared with anion surfactant templates

A novel strategy for the synthesis of layered organosilica is demonstrated. The ionic interaction between the anionic group of a surfactant (sodium dodecyl sulfate) and the cationic organic group of an organosilane (3-aminopropyltrimethoxysilane, ATMS) under acidic conditions was utilized to create a layered organosilica at room temperature. The inorganic part of the organosilica layer was an Si-O hexagonal sheet, and organofunctional groups were alternately arranged on both sides of the sheet. The layered structure of the ATMS organosilica was retained after the removal of the surfactant with chloride anion. The properties of the layered ATMS organosilica were investigated. The layered ATMS-Cl organosilica is stable and possesses a definite layer structure in water or ethanol. Various kinds of anions can be intercalated in the interlayer space of the layered ATMS organosilicas and the layer was expanded dependent on the intercalated anions. The structure of the layered ATMS organosilica was well retained during the intercalation processes.     

Photochemistry of 2-(1-naphthyl)-2H-azirines in matrixes and in solutions: wavelength-dependent C-C and C-N bond cleavage of the azirine ring

The photochemistry of 3-methyl-2-(1-naphthyl)-2H-azirine (1a) was investigated by the direct observation of reactive intermediates in matrixes at 10 K and by the characterization of reaction products in solutions. As already reported, the photolysis of the azirine 1a with the short-wavelength light (>300 nm) caused the C-C bond cleavage of the 2H-azirine ring to produce the nitrile ylide 2. However, the products derived from the C-N bond cleavage were exclusively obtained in the irradiation of 1a with the long-wavelength light (366 nm) both in matrixes and in solutions. When 1a was irradiated in the presence of O(2) with the long-wavelength light, acetonitrile oxide (6) was produced through the capture of the biradical 4 generated by the C-N bond cleavage of 1a with O(2). An introduction of a nitro group into the naphthyl ring of 1a resulted in an acceleration of the decomposition in the long-wavelength irradiation and an extension of the wavelength region where the products derived from the C-N bond cleavage were selectively obtained. On the basis of molecular orbital calculations with the INDO/S method, the reason for the wavelength-dependent selective C-C and C-N bond cleavage of the azirine ring of 1a is discussed.     

Direct observation of cellulose dissolution in subcritical and supercritical water over a wide range of water densities (550–1000 kg/m<Superscript>3</Superscript>)

Direct observations of the heating of microcrystalline cellulose (230 DP) in water at temperatures up to 410 °C and at pressures up to 700 MPa were made with a batch-type microreactor. Cellulose particles were found to dissolve with water over temperatures ranging from 315 to 355 °C at high pressures. Dissolution temperatures depended on water density and decreased from about 350 °C at a water density of 560 kg/m³ to a minimum of around 320 °C at a water density of 850 kg/m³. At densities greater than 850 kg/m³, the dissolution temperatures increased and reached a value of about 347 °C at 980 kg/m³. The cellulose dissolution temperatures were independent of heating rates for values ranging from 10 to 17 °C/s. The low dependence of dissolution temperatures on the heating rates is strong evidence for simultaneous dissolution and reaction of the cellulose. Different phenomena occurred depending on water density. At low densities, particles turned transparent and seemed to dissolve into the aqueous phase from the surface. From 670 to 850 kg/m³, the cellulose particles visibly swelled just before completely collapsing and dissolving into the aqueous phase. The swelling probably increased water accessibility and particle surface area and thus lead to the lower dissolution temperatures observed. From 850 to 1000 kg/m³, the particles required longer times to dissolve and many fine brown-like particles were generated as the particles dissolved. FT-IR spectra of the residues were analyzed. Residues formed from heating cellulose at high densities still retained some cellulose character whereas those as low densities had little cellulose character, especially in the O–H stretching vibration region.