Reflectance and ellipsometric study of anodic film on platinum electrode

The anodic films on platinum electrode in 0.05 M sulfuric acid solution were examined by means of ellipsometry. By measuring the relative phase retardation (Δ), relative amplitude reduction (tanψ) and also the intensity of the reflected polarized light, the optical constants of the films (n, k) and thickness (τ) at various potentials were obtained. The results showed that the optical properties of the film remain nearly constant (n = 2.8, k = 1.7) while the thickness increases from 2 Å to 5 Å with anodic potential. From this evidence, it is concluded that the film is made of an oxide of platinum forming a definite phase.     

Lignans from the Bark of Magnolia kobus

The Et₂O‐soluble fraction from the bark of Magnolia kobus led to the isolation of two new lignans, (+)‐(7α,7′α,8α,8′α)‐3′,4,4′,5,5′‐pentamethoxy‐7,9′: 7′,9‐diepoxylignan‐3‐ol ( 1 ) and (+)‐(7α,7′α,8α,8′α)‐4,5‐dimethoxy‐3′,4′‐(methylenedioxy)‐7,9′: 7′,9‐diepoxylignan‐3‐ol ( 2 ), along with five known lignans 3 – 7 . Their structures were established on the basis of various spectroscopic analyses including 1D‐ (¹H, ¹³C, and DEPT) and 2D‐NMR (COSY, NOESY, HMQC, and HMBC) and by comparison of their spectral data with those of related compounds.     

Surface organization, light-driven surface changes, and stability of semifluorinated azobenzene polymers

A series of polymers with 4-perfluoroalkyl-modified azobenzene side groups was investigated for its light-induced changes in surface properties. The ultraviolet (UV) light activated trans to cis isomerization of the azobenzene group, and the influence of molecular order and orientation on this process were studied using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and water contact angle measurements. Light-induced molecular reorganization in the near-surface region was studied by NEXAFS using in situ UV irradiation of polymer thin films. Differential scanning calorimetry and wide-angle X-ray scattering studies showed that sufficiently long fluoroalkyl groups formed well-ordered smectic mesophases in the bulk, as well as on the surface, which was evidenced by NEXAFS. The disruption of mesogen packing by photoisomerization was found to be influenced by the fluoroalkyl segment length. Surfaces with perfluorohexyl and perfluorooctyl groups that showed high orientational order were also highly resistant to light-induced changes. In such cases, the trans-cis isomerization resulted in greater lowering of the azobenzene phenyl ring order parameters than the perfluoroalkyl order parameters. UV exposure caused reorientation of the phenyl rings of the azobenzene group, but the terminal perfluoroalkyl segments remained more or less ordered.     

Sodium chains as core nanowires for gelation of organic solvents from a functionalized nicotinic acid and its sodium salt

A new metallo-organic gelator formed from an admixture of a substituted nicotinic acid and its sodium salt is described. The nicotinic acid is substituted in the 6-position by an acetal functionality. The crystal structure of the 1:1 mixture revealed that the sodium atoms are aligned in infinite chains with the two organic units hydrogen bonded together to create potentially trinucleating ligands that encase the metal core, which leads to tube-like structures. These one-dimensional crystals were found to spontaneously gelify dichloromethane and provide pyridine gels with high thermal resistance. Gel formation was investigated by several analytical techniques, which included differential scanning calorimetry, TEM, freeze fracture electron microscopy (FFEM), IR spectroscopy and X-ray diffraction, and was found to be induced by the swelling of the one-dimensional material. FFEM and powder X-ray diffraction have revealed that the sodium chains are associated in a highly compacted state into a layered structure inside the gel. Doping these robust gels with dyes by diffusion, such as xylene cyanol, methyl yellow and bromo thymol blue, is feasible without destruction of the gels.     

Tyrosine nitration site specificity identified by LC/MS in nitrite-modified collagen type IV

Non-enzymatic nitrite induced collagen cross-linking results in changes reminiscent of age-related damage and parallels the well-known model system, non-enzymatic glycation. We have recently observed that nitrite modification of basement membrane proteins can induce deleterious effects on overlying retinal pigment epithelial cells in studies relevant to age-related macular degeneration. The present work was undertaken in order to confirm 3-nitro-tyrosine (3-NT) as a product of the reaction and to identify the site specificity of nitration in collagen IV, a major component of basement membranes. Human collagen type IV was modified via incubation with 200 mM NaNO(2) (pH=7.38) for one week at 37(o)C. The modified protein was prepared in 2 different ways, including acid hydrolysis and trypsin digestion for site specificity determination. The samples were analyzed by LC/MS using a C(12) RP column. Site specificity was determined from tandem MS/MS data utilizing TurboSEQUEST software and the Swiss-Prot sequence database. 3-NT was detected in protein digests and acid hydrolysates of nitrite modified collagen IV. Positive identification with standard 3-NT was confirmed by identical R(t), lambda(max)=279 nm and 355 nm, and m/z=227. Analyses of tryptic digests identified four sites of tyrosine nitration, alpha1(IV)Y348, alpha1(IV)Y534, alpha2(IV)Y327, and alpha2(IV)Y1081. These sites are located in the triple-helical region of the protein and provide clues regarding potential sites for nitrite modification in collagen type IV.     

Selective CO2 adsorption in a flexible non-interpenetrated metal-organic framework

We have prepared a flexible metal-organic framework and demonstrated that when activated by supercritical CO(2) it has greater gas sorption capacities than that activated by the heat-evacuation method, and it selectively adsorbs CO(2) over N(2) at room temperature.     

Chiral separation of N-methyl-dl-aspartic acid in rat brain tissue as N-ethoxycarbonylated (S)-(+)-2-octyl ester derivatives by GC-MS

A selective and sensitive analytical method was developed for enantiomeric separation and determination of N‐methyl‐DL‐aspartic acid (NMA). The method involved the conversion of each enantiomer into N‐ethoxycarbonylated (S)‐(+)‐2‐octyl ester derivative for the direct separation by gas chromatography–mass spectrometry (GC‐MS). The diastereomeric derivatives showed characteristic mass spectral properties for analysis by selected ion monitoring mode (SIM) and enabling enantioseparation on an achiral capillary column. Two enantiomers were baseline separated, and the detection limits for N‐methyl‐L‐aspartic acid (NMLA) and N‐methyl‐D‐aspartic acid (NMDA) were 0.07 and 0.03 ng/g, respectively. When applied to rat brain tissues for absolute configuration of NMA, only NMDA was determined, while NMLA was monitored as lower than the limit of detection. Copyright © 2012 John Wiley & Sons, Ltd.