The edta complex of platinum(IV): a titrimetric and spectrophotometric study

Platinum in the form of hexachloroplatinate(IV) reacts slowly with EDTA in a 1:1 mole ratio. At the concentration level used (a few mg per 50–75 ml), favorable conditions were solution of pH 3–4.5, and 3–8-fold molar excess of EDTA. Complete reaction required heating at 100° for 1.5–2 h. The reaction rate was retarded by acetate ion, but not by nitrate or sulfate. Titrimetric determination of platinum was accomplished by addition of excess standard EDTA, buffering to pH 3–4.5, heating the mixture at 100° for 1.5 h, buffering to pH 5.3 with acetic acid-acetate, and back-titrating with zinc acetate to a xylenol orange end-point. Blank corrections were necessary to compensate for trace metal impurities in the water and/or reagents. Determinations of 0.4–3 mg of platinum per 50 ml were accurate to ± 1.3% standard deviation. Both titrimetric and spectrophotometric evidence ruled out the possibility of reduction of platinum(IV) by EDTA. Titrimetric methods showed the complex to be PtCl₄HY^3-, where Y is the deprotonated EDTA.     

Development of the crystallinity and rigid amorphous fraction in cold‐crystallized isotactic polystyrene

The phase structure of crystalline isotactic polystyrene (iPS) has been investigated with temperature‐modulated differential scanning calorimetry (TMDSC), wide‐angle X‐ray scattering (WAXS), and Fourier transform infrared (FTIR) spectroscopy. Quenched amorphous samples have been cold‐crystallized at 140 or 170 °C for various crystallization times. The degree of crystallinity obtained from WAXS, with the ratio of the crystal peak intensity to the total peak intensity, shows excellent agreement with the crystallinity determined from TMDSC total heat flow endotherms. For the first time, FTIR results show that the absorbance peak ratio (I/I) has a linear correlation with the crystalline mass fraction (χ_c) for cold‐crystallized iPS according to the following relation: I/I = 0.54χ_c + 0.16. This relationship allows the crystallinity of iPS to be determined from infrared spectroscopy analyses in cases in which it is difficult to perform thermal or X‐ray measurements. On the basis of the measurements of the heat capacity increment at the glass transition, we find that a significant amount of the rigid amorphous fraction (RAF) coexists with the crystalline and mobile amorphous phases in cold‐crystallized iPS. The RAF increases systematically with the crystallization time, and a greater amount is formed at a lower crystallization temperature. A three‐phase model (crystalline phase, mobile amorphous phase, and rigid amorphous phase) is, therefore, appropriate for the interpretation of the structure of cold‐crystallized iPS. The origin of the low‐temperature endothermic peak (annealing peak) has been investigated with TMDSC and FTIR spectroscopy and has been shown to be due to irreversible relaxation of the RAF. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3026–3036, 2003     

Aqueous surfactant solutions which exhibit ultra-low tensions at the oil-water interface

Ultra-low values of the tension at an oil-aqueous electrolyte solution interface can be developed by the addition of water-soluble surfactants of the petroleum sulfonate type. Interfacial tensions in the range of 10⁻³ dyne/cm or lower are readily achieved with surfactant concentrations of the order of 0.1 wt%. For a given oil and aqueous solution, the minimum interfacial tension resulting from the addition of a petroleum sulfonate depends markedly on the average equivalent weight of the sulfonate. Sulfonates having average equivalent weights higher and lower than a previously determined optimum weight, when mixed so as to yield this particular average weight, will also produce ultra-low interfacial tensions. For a given oil, additional control of this unusual type of interfacial activity is accomplished by adjustment of the electrolyte concentration of the aqueous phase.     

Thermal expansion of the crystal lattice of novel thermoplastic polyimides

Measurements of the coefficient of thermal expansion (CTE) of the crystalline lattice of two semicrystalline thermoplastic polyimides are reported. NEW-TPI and LARC-CPI polyimides were studied using elevated temperature wide-angle x-ray scattering (WAXS) from 25°C. To 325°C. To examine possible shifts in the c-axis, a novel approach developed in our lab was used to create highly oriented samples. Films were treated in 1-methyl-2-pyrrolidinone (NMP) at the reflux temperature, washed and then dried under constraint. The films treated in this manner were highly oriented, with c-axes preferentially aligned along the film normal. The advantage of this orientation is that it allows numerous reflections of type (00l) to be examined for temperature shifts of the c-axis using reflection mode WAXS. No systematic shift of the c-axis lattice parameter as a function of temperature was observed in either NEW-TPI or LARC-CPI. The c-axis thermal expansion is concluded to be smaller than 8 x 10^?6/°C for LARC-CPI, and for NEW-TPI may be weakly negative. From WAXS of unoriented films, systematic shifts in the a and b lattice parameters were deduced as a function of temperature. The linear CTEs relating these unit cell parameters at temperature T to their values at 0°C are: ©1995 John Wiley & Sons, Inc.     

Enantioselective Synthesis of L- and D-Carboranylalanine

The enantioselective synthesis of L- and D-carboranylalanine is reported. Imides 13 and 14 are treated with titanium tetrachloride, DIEA, and NBS to introduce a bromo functionality in 98:2 ratio at the alpha-center. Azide displacement with TMGA, displacement of the oxazolidinone template with titanium tetrabenzyloxide, and subsequent hydrogenolysis permits L- or D-carboranylalanine to be isolated in high stereoselectivity and 35-40% yields overall.     

Phonetic identification in quiet and in noise by listeners with cochlear implants

This study examined the effect of noise on the identification of four synthetic speech continua (/ra/-/la/, /wa/-/ja/, /i/-/u/, and say-stay) by adults with cochlea implants (CIs) and adults with normal-hearing (NH) sensitivity in quiet and noise. Significant group-by-SNR interactions were found for endpoint identification accuracy for all continua except /i/-/u/. The CI listeners showed the least NH-like identification functions for the /ra/-/la/ and /wa/-/ja/ continua. In a second experiment, NH adults identified four- and eight-band cochlear implant stimulations of the four continua, to examine whether group differences in frequency selectivity could account for the group differences in the first experiment. Number of bands and SNR interacted significantly for /ra/-/la/, /wa/-/ja/, and say-stay endpoint identification; strongest effects were found for the /ra/-/la/ and say-stay continua. Results suggest that the speech features that are most vulnerable to misperception in noise by listeners with CIs are those whose acoustic cues are rapidly changing spectral patterns, like the formant transitions in the /wa/-/ja/ and /ra/-/la/ continua. However, the group differences in the first experiment cannot be wholly attributable to frequency selectivity differences, as the number of bands in the second experiment affected performance differently than suggested by group differences in the first experiment.     

Astrotricoumarin, an antiproliferative 4'-hydroxy-2',3'-dihydroprenylated methylcoumarin from an Astrotrichilia sp. from the Madagascar dry forest

Bioassay guided fractionation of the ethanol extract of a new endemic species of the genus Astrotrichilia led to the isolation of the new antiproliferative 3-(4'-hydroxy-2',3'-dihydroprenyl)-4,6-dimethoxy-5-methylcoumarin, named astrotricoumarin (8) with an IC50 value of 6.8 microM against the A2780 cell line. The structure of compound 8 was elucidated on the basis of its physical and spectroscopic data, including extensive 1D- and 2D-NMR analysis.