Micellar solubilization: structural and conformational changes investigated by 1H and 13C liquid-state NMR

A combination of (1)H self-diffusion measurements and (13)C chemical shift analysis has been used for the study of the solubilization of amphiphilic additives C(n)H(2n+1)X (n=4, 6; X=OH, NH(2)) in cetyltrimethylammonium bromide (CTAB) micelles. This approach, which could be extended to other mixed systems, allows complementary data on structures of micelles and conformations of alkyl chains to be obtained. Previous results on these systems are confirmed and new features emerge. All the additives studied behave as cosurfactants. Their degree of solubilization is determined solely by their alkyl chain length. In the case of cosurfactants with n=6, polar head group differences have been shown to modify micellar structures. This effect has been linked to differences in cosurfactant penetration into micelles. In parallel, the area of CTAB head groups and the length of cetyl chains gradually decrease on average when solubilizing more cosurfactants. Cetyl chain compression is strong in the case of cosurfactants with n=4, whereas it is slightly compensated by an extension below the micellar surface in the case of longer cosurfactants. These conformational changes are related respectively to the formation of smaller spherical micelles and of anisotropic or swollen micelles.     

高效液相色谱二氮杂冠醚键合相的合成及性能研究

本文报道在硅胶表面进行固－液相反应，合成硅胶键合二氮杂冠醚高效液相色谱固定相。采用有机元素分析、热分析、红外光谱、金属离子的络合容量测定等对键合材料进行鉴定和表征，并对其色谱性能进行了研究。     

Size, volume fraction, and nucleation of Stober silica nanoparticles

29Si NMR, small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS) are used to monitor the synthesis of silica nanoparticles from the base-catalyzed hydrolysis of TEOS in methanol and ethanol. The reactions are conducted at a [TEOS] =0.5 M, low concentrations of ammonia ([NH(3)] =0.01-0.1 M), and [H(2)O] =1.1-4.4 M to resolve the initial size of the first nuclei and to follow their structural evolution. It is found that after an induction period where there is a buildup of singly hydrolyzed monomer, the first nuclei are fractal and open in structure. Interestingly, the nuclei are twice as large in ethanol (R(g) approximately 8 nm) as those in methanol (R(g) approximately 4 nm). The data suggest that the difference in primary particle size is possibly caused by a higher supersaturation ratio of the singly hydrolyzed monomer in methanol than in ethanol if it is assumed that the surface energy of the first nuclei is the same in methanol and ethanol. The particle number concentration and the volume fraction of the silica particles are calculated independently from the SAXS, DLS, and 29Si NMR results. Finally, the rate of nucleation is obtained from the particle number concentrations.     

Diels-Alder polymers. III. Polymers containing phenylated phenylene units

The Diels-Alder reaction of biscyclopentadieneones with diacetylenes produces colorless, soluble, phenylated polyphenylenes of high molecular weight (M?_n ? 40,000) in nearly quantitative conversions. The polymers are noncrystalline, form clear films, and are stable in air to 550°C. Under nitrogen, the polymers lost approximately half the phenyl groups attached to the phenylene main chain to give brown-black insoluble polyphenylenes of very low crystallinity.     

Is use of the hydrophobic moment a sound basis for predicting the structure-function relationships of membrane interactive alpha-helices?

Amphiphilic alpha-helices play a fundamental role in protein membrane association and show a segregation of polar and apolar amino acid residues. Based on correlations between amphiphilic properties and biological function, a number of theoretical approaches have been developed, which quantify alpha-helix amphiphilicity and then attempt to assign function. The most commonly used measure of amphiphilicity is the hydrophobic moment, < microH >, which, when used in conjunction with an alpha-helix's mean hydrophobicity, < H >, has been used to classify membrane interactive amphiphilic alpha-helices as either surface active or transmembrane. Here, the predictive efficacy of plot methodology is reviewed by examining published data, which compare the function of known membrane interactive amphiphilic alpha-helices to that assigned by this methodology. The results of this review are discussed in relation to the reliability of < microH > as a quantifier of alpha-helical amphiphilicity, and the ability of < microH > and < H > to describe alpha-helical structure / function relationships. It is concluded that hydrophobic moment plot methodology is not a generally reliable predictor of alpha-helical structure / function relationships. It appears that the inefficacy of plot methodology is primarily due to the inability of the plot diagram to accommodate the heterogeneity of the alpha-helical classes it attempts to define. However, the predictive efficacy of the methodology appears to be improved if other alpha-helical parameters are also considered when assigning alpha-helical function. It is suggested that the conventional methodology should be seen only as an indicator for the assignation of structure / function relationships, providing a guide to future experimental investigations.     

A role for Thr 252 in cytochrome P450cam oxygen activation

Molecular dynamics simulations of the ferrous dioxygen bound form of wild type cytochrome P450cam were performed and the results analyzed to reveal the time-dependent interactions of T252 with surrounding residues as well as with bound oxygen. The results indicate a time-dependent bimodal interaction of T252 with both G248 and the terminal oxygen of the bound dioxygen. The hydrogen bonding interaction of T252 with these two moieties is "anticorrelated" in the sense that the breaking of the T252-G248 hydrogen bond is concurrent with formation of the T252-dioxygen interaction. These simulations support the probability of a role of T252 in stabilization of the initial dioxygen bound complex and promotion of subsequent formation of compound I previously indicated by several experimental studies.     

Synthesis and antioxidant activity of 3-substituted guaiazulene derivatives

A series of 3-substituted guaiazulene derivatives has been synthesized and their antioxidant properties were evaluated by monitoring their capacity for scavenging the stable free-radical DPPH. 3-Vinylguaiazulene was the most potent, possessing antioxidant activity superior than alpha-tocopherol. These derivatives were also moderate inhibitors of the proliferation of human promyelocytic leukemia cells.     

Studies of polyester fiber as carrier for microbes in a quantitative test method for disinfectants

Tests were conducted by a Task Force on Disinfectant Test Methods that was appointed to investigate controversies regarding the accuracy of AOAC test methods for disinfectants as presented in AOAC's Official Methods of Analysis, Chapter 6. The general principles for new and improved AOAC tests are discussed, and a disinfectant test using microbes labeled onto a polyester fiber surface is described. The quantitative test measures the survival of test microbes as a function of exposure time as well as the exposure conditions required to kill 6 log10 of the test microbes. The time required was similar to that for the kinetics of the kill of Bacillus subtilis-labeled cylinders as tested by methods of the AOAC Sporicidal Test 966.04.     

NOVEL POLYMER WIDE VIEWING ANGLE COMPENSATION FILMS FOR LIQUID CRYSTAL DISPLAYS(LCDS)

We report on generating uniaxial negative birefringent compensation films, made of specifically designedpolyimides. These polymers were synthesized via a polycondensation of dianhydride [such as 2, 2' -bis(3, 4-dicarboxyphenyl)hexafluoropropane dianhydride] and 2, 2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl. The uniaxial negative birefringent (n_x =n_y > n_z) polyimide substrates are achieved using a solution-casting method in conventional solvents, which exhibit thedesirable optical phase retardation [(n_x - n_z)×d] values from 50 to 400 nm varying with the film thickness. In thesepolyimide films, the long chain rigid molecules adopt intrinsic planar orientaion. In detail, the majority of phenylene-imiderings and phenylenes preferentially adopt nearly planar conformations parallel to the film substrae. In addition, these filmsalso possess high transparency (or transmittance) and little color shift. The unique color dispersion curve indicates that thistype of materials is very suitable for the applications in LCDs due to an excellent mimic for the retardation color dispersioncurve with respect to LC molecules. Significantly low in-plane retardation (< 1 nm) allows this new technology based film toachieve sufficiently high contrast ratio while highly negative retardation dramatically suppresses the gray scale inversion toimprove the viewing angle performance in a variety of new mode LCDs.     

Fourier representation method for electronic structures of linear polymers

The Fourier representation method described in the previous paper of this series is used to make electronic structure calculations for a linear chain of equally spaced hydrogen atoms. The electronic wavefunction is assumed to be a determinant of doubly-occupied crystal orbitals of modulated-plane-wave type, built from one 1s Slater-type orbital of screening parameter ζ centered on each atom. The energy is calculated from the electrostatic zero-order Hamiltonian with exact evaluation of all Coulomb and exchange contributions, and is optimized with respect to the lattice spacing and ζ value. Good agreement with work by others is noted, indicating a near-equivalence of modulated-plane-wave and tight-binding wavefunctions for this half-filled-valence-band system. The linear chain is calculated to be far more stable than cubic three-dimensional hydrogen crystals. This fact sheds light on the unusually large calculated nearest-neighbor distances in the cubic crystals, and is related to a suggestion that under certain conditions the most stable structure for solid atomic hydrogen may be of lower symmetry than cubic. The previous paper of this series: Harris, F. E.: J. Chem. Phys.56, 4422 (1972) [1]. Chargé de Recherches du F.N.R.S. (Fonds National Belge de la Recherche Scientifique).