Degradation of polymers and morphology: Photo-oxidative degradation of isotactic polystyrene in presence of sulfur dioxide as function of polymer crystallinity

The photo-oxidative chain scission of isotactic polystyrene films has been studied as a function of the degree of crystallinity, SO₂, and NO₂ pressures, and temperature. The rate of chain scission increases in the presence of SO₂ with extent of crystallinity. It is assumed to be faster due to strain in and near the folds in the crystalline areas than in the amorphous regions. In the presence of NO₂, chain scission increases up to about 8% crystallinity but subsequently becomes constant with further increase in crystallinity. It is suggested that the diffusion rates of oxygen and nitrogen dioxide into the films decrease with increasing crystallinity. These two processes compensate each other.     

Charged polypeptide vesicles with controllable diameter

We report the preparation and characterization of charged, amphiphilic block copolypeptides that form stable vesicles and micelles in aqueous solution. Specifically, we prepared and studied the aqueous self-assembly of a series of poly(L-lysine)-b-poly(L-leucine) block copolypeptides, KxLy, where x ranged from 20 to 80 and y ranged from 10 to 30 residues, as well as the poly(L-glutamatic acid)-b-poly(L-leucine) block copolypeptide, E60L20. Furthermore, the vesicular assemblies show dynamic properties, indicating a high degree of membrane fluidity. This characteristic provides stimuli-responsive properties to the vesicles and allows fine adjustment of vesicle size using liposome-based extrusion techniques. Vesicle extrusion also provides a straightforward means to trap solutes, making the vesicles promising biomimetic encapsulants.     

An addition to the oxoacid family: H2B12(OH)12

The acid H(2)B(12)(OH)(12) can be isolated as a crystalline solid by protonation of the hydroxylated borane anion, B(12)(OH)(12)(2)(-). This acidic compound has low solubility in water, conducts protons in the solid state, and has thermal stability to a temperature of 400 degrees C. The conductivity mechanism is a Grotthuss mechanism with a low activation enthalpy (9-13 kcal/mol). This new acid represents an addition to the class of oxoacids, of which sulfuric and phosphoric acid are the most prominent examples.     

The weakly bound He-HCCCN complex: high-resolution microwave spectra and intermolecular potential-energy surface

Rotational spectra of the weakly bound He-HCCCN and He-DCCCN van der Waals complexes were observed using a pulsed-nozzle Fourier-transform microwave spectrometer in the 7-26-GHz frequency region. Nuclear quadrupole hyperfine structures due to the 14N and D nuclei (both with nuclear-spin quantum number I = 1) were resolved and assigned. Both strong a and weaker b-type transitions were observed and the assigned transitions were used to fit the parameters of a distortable asymmetric rotor model. The dimers are floppy, near T-shaped complexes. Three intermolecular potential-energy surfaces were calculated using the coupled-cluster method with single and double excitations and noniterative inclusion of triple excitations. Bound-state rotational energy levels supported by these surfaces were determined. The quality of the potential-energy surfaces was assessed by comparing the experimental and calculated transition frequencies and also the corresponding spectroscopic parameters. Simple scaling of the surfaces improved both the transition frequencies and spectroscopic constants. Five other recently reported surfaces [O. Akin-Ojo, R. Bukowski, and K. Szalewicz, J. Chem. Phys. 119, 8379 (2003)], calculated using a variety of methods, and their agreement with spectroscopic properties of He-HCCCN are discussed.     

Thermodynamic functions of β-halonapthalenes from 0.25 to 16 atmospheres

Real gas thermodynamic functions, C_p, S, (H  H_o)/T, and ? (F  H_o)/T, have been calculated for β-halonaphthalenes (β  C₁₀H₇X, where X  F, Cl, Br, I) from 0.25 to 16 atm within the temperature range of 273.15 K to 1200 K, correcting the thermodynamic property ideal gas values by means of the Berthelot equation of state.     

Le vibrateur ch2, un auxiliaire approprié à l''étude structurale d''alcanes substttues par des groupements polaires : II. Polyhalogéno-propanes

The vibrational spectra of some polyhalogeno-propanes (1,3-dibromopropane. 1,2,3- trichloropropane, 1,2,3-tribromopropane, 1,2,2,3-tetrachloropropane) are investigated in the region 1400–1500 cm⁻¹. The results demonstrate that the bending mode frequency δ(CH₂) of a CH₂X group depends on the nature of the halogen X and on the direction in space of C-X' bonds located in the or position (CH₂X-CX'-). The application of these rules enables the conformation of 1,3-difluoropropane and 1,2,2,3-tetrabromopropane to be studied for the first time.     

Determination of thiols by titrimetric and chromatographic procedures based on reactions with aromatic thiosulfonates

Semimicro titrimetric procedures and micro high-performance liquid chromatographic procedures are described for the determination of aliphatic and aromatic thiols, based on the highly selective reaction with aromatic thiosulfonates. The reaction products, a sulfinic acid and a mixed disulfide, contain an aromatic moiety, permitting the use of an u.v. detector. The chromatographic procedure offers the advantages of application to mixtures, coupled with cross-checking of the determination by material balance from simultaneous measurement of the two reaction products.     

Aldehydes from alkyllithiums with 2-carbon homologation

1-Phenylthio-trimethylsilylalkanes, uhich are readily converted to aldehydes, are prepared by the addition of alkyllithiums to phenylthioethene, trimethylsilylethene and 1-phenylthio-1-trimethylallylethene.     

Direct determination of lead in polluted sea water by carbon-furnace atomic absorption spectrometry

A simple and rapid method is described for the direct determination of lead in polluted sea water by carbon furnace atomic absorption spectrometry. Filtered sea water is diluted (1+1) with'deionised distilled water and ammonium nitrate is added to act as a matrix modifier. Aliquots of this mixture are injected into a tantalum-coated graphite tube in a HGA-2200 furnace atomiser operated under gas-stop conditions. With the standard addi- tion method, a detection limit (20) of 1 μg Pb 1^-1 is achieved. Good agreement between the proposed method and results obtained by anodic stripping voltammetry was achieved for samples taken from the Firth of Forth.     

Determination of heptacaine hydrochloride in solution using nuclear analytical methods

The applicability of two nuclear analytical methods for the determination of hepatacaine hydrochloride in solution was studied, i. e. radionuclide X-ray fluorescence analysis and radiometric titrations based on precipitate formations. Methods used were evaluated on the basis of obtained sensitivity values.