New azo-dye-doped polymer systems as dynamic holographic recording media

Polymer materials show their impact on optical storage technology for developing high information density and fast access-type memories with a high read-out efficiency. New azo-dye-doped polymer materials have been developed and used for recording dynamic holograms. Dynamic holograms with reasonably high diffraction efficiency have been recorded at 468 nm, and the efficiency of the Write, Read and Erase (WRE) cycle in these azo-dye-doped polymer materials was determined. Significant observations in these materials are: (i) there is no need to change the polarization of the writing beam to erase the recorded holograms, (ii) the whole WRE cycle is very fast (3–6 s) and (iii) recording of more than 250 WRE cycles without any fatigue of the recording materials is possible.     

The molecular structure and conformation of gaseous bis(chloromethyl)dimethyl silane as determined by electron diffraction

The molecular structure of bis(chloromethyl) dimethyl silane has been investigated in the gas phase at a nozzle temperature of 60° C. The molecules exist mainly in the GG form with the presence of 30% (+10%, ?20%) AG form. The values of the principal distances (r_a) and angles with estimated error limits of 2σ are r(C-H) = 1.093 (0.009) Å, r(C-Cl) = 1.801 (0.019) Å, r(Si-C) (the average Si-C bond) = 1.875 (0.009) Å, ∠(CSiC) = 109.5°, ∠(SiCCl) = 110.5° (0.4), ∠(CCH) = 112.5° (1.8) and φ (the gauche torsion angle relative to 0° for the anti form) = 117.4° (3.8).     

A new dimeric carbazole alkaloid from Glycosmis stenocarpa roots

A new dimeric pyranocarbazole alkaloid, bisisomahanine (1), was isolated from the roots of Glycosmis stenocarpa (DRAKE) TAN., along with two known monomeric carbazole alkaloids, murrayafoline-A (2) and murrayanine (3). The planar structure of bisisomahanine was determined to be 9,9'-dihydroxy-3,3',8,8'-tetramethyl-3,3'-bis-(4-methyl-3-pentenyl)-3,3',11,11'-tetrahydro-10,10'-(bipyrano[3,2-a]carbazole) from the combination of spectroscopic and chemical evidence. Bisisomahanine is the first dimeric prenylated pyranocarbazole alkaloid with a 1,1' type of linkage; the NMR and CD spectroscopic data indicated it to be a mixture of diastereomers having a dominant configuration at the axis of chirality. (1)H- and (13)C-NMR assignments of murrayafoline-A were made on the basis of 2D-experiments.     

Identifying guanosine self assembly at natural isotopic abundance by high-resolution 1H and 13C solid-state NMR spectroscopy

By means of the (1)H chemical shifts and the proton-proton proximities as identified in (1)H double-quantum (DQ) combined rotation and multiple-pulse spectroscopy (CRAMPS) solid-state NMR correlation spectra, ribbon-like and quartet-like self-assembly can be identified for guanosine derivatives without isotopic labeling for which it was not possible to obtain single crystals suitable for diffraction. Specifically, characteristic spectral fingerprints are observed for dG(C10)(2) and dG(C3)(2) derivatives, for which quartet-like and ribbon-like self-assembly has been unambiguously identified by (15)N refocused INADEQUATE spectra in a previous study of (15)N-labeled derivatives (Pham, T. N.; et al. J. Am. Chem. Soc.2005, 127, 16018). The NH (1)H chemical shift is observed to be higher (13-15 ppm) for ribbon-like self-assembly as compared to 10-11 ppm for a quartet-like arrangement, corresponding to a change from NH···N to NH···O intermolecular hydrogen bonding. The order of the two NH(2)(1)H chemical shifts is also inverted, with the NH(2) proton closest in space to the NH proton having a higher or lower (1)H chemical shift than that of the other NH(2) proton for ribbon-like as opposed to quartet-like self-assembly. For the dG(C3)(2) derivative for which a single-crystal diffraction structure is available, the distinct resonances and DQ peaks are assigned by means of gauge-including projector-augmented wave (GIPAW) chemical shift calculations. In addition, (14)N-(1)H correlation spectra obtained at 850 MHz under fast (60 kHz) magic-angle spinning (MAS) confirm the assignment of the NH and NH(2) chemical shifts for the dG(C3)(2) derivative and allow longer range through-space N···H proximities to be identified, notably to the N7 nitrogens on the opposite hydrogen-bonding face.     

Copolymerisation radicalaire du méthacrylate de méthyle et du chlorure de vinylidène avec ou sans dérive de composition

Two sets of methylmethacrylate-vinylidene chloride copolymers were prepared via radical copolymerization in dimethylformamide. The first set is carried out in batches. Gas-chromatographic analysis of samples allows a kinetic study from which the reactivity ratios r_M - 2.73 and r_C - 0.24 are derived. For the second set a new apparatus, briefly described, has been used. It permits to keep constant the composition of the monomer mixture, through addition of methyl methacrylate, monitored by a chromatographic analysis. The two sets of copolymers are analyzed using nuclear magnetic resonance (60 MHz) leading to the triad distribution, from which the reactivity ratios are derived. Owing to the composition drift, the method cannot be applied to the first set of copolymers; but in that case, it is possible to calculate the triad distribution, the knowledge of the reactivity ratios, and the calculation fits quite well the experimental results.     

Nanometric layers for direct, signal-on, selective, and sensitive electrochemical detection of oligonucleotides hybridization

We report a signal-on, reagentless electrochemical DNA biosensor, based on an electroactive self-assembled naphthoquinone derivative (JUG(thio)) monolayer. This system achieves highly sensitive (approximately 300 pM) and selective signal-on detection. Before hybridization, the single strand can interact with JUG(thio) and slow down the redox reaction. When the complementary target is added, the formation of the double helix eliminates the single strand/JUG(thio) interactions and the JUG(thio) redox rate, and hence the current increase.     

Inhalable Thioflavin S for the Detection of Amyloid Beta Deposits in the Retina

We present an integrated delivery technology herein employing the aerosolized method to repurpose thioflavin S for imaging amyloid beta (Abeta) deposits in the retina as a surrogate of Abeta in the brain for early detection of Alzheimer’s disease. The data showed that wild type (WT) mice also have Abeta deposits in the retinae, albeit much less than 5XFAD mice. Further, only in 5XFAD mice, significant Abeta deposits were found associated with retinal ganglion cells (RGCs) in whole-mount and cross-section data. Furthermore, the fluorescent signal depicted from thioflavin S corroborates with Abeta immunohistochemistry staining information. Overall, this probe delivery via inhalation method is also applicable to other Abeta-binding molecules, such as Congo red, curcumin, and thioflavin T. The advantage of imaging retinal amyloid deposits compared to the brain counterparts is that the eye is easily accessible by in vivo imaging and it reduces the effort to design a probe that must cross the formidable blood-brain barrier.     

Screening and evaluation of α-glucosidase inhibitors from indigenous medicinal plants in Dak Lak Province,Vietnam

α-Glucosidase inhibitors have received much attention due to their important use in treating diabetes mellitus. Although some synthetic α-glucosidase inhibitors have been available for a long time, they often cause various unexpected side effects. Thus, the present study was aimed at finding a safe, natural source of α-glucosidase inhibitors. Twenty-six samples of 22 medicinal plants were collected in the Dak Lak province of Vietnam and evaluated for α-glucosidase inhibitory activity. Trunk bark extract from Euonymus laxiflorus Champ (ELC extract) was selected as the best α-glucosidase inhibitor with the smallest IC₅₀ = 0.36 mg/mL against rat-derived α-glucosidase. This extract had a stronger inhibitory activity against α-glucosidase from Saccharomyces cerevisiae (IC₅₀ = 1.32 µg/mL) and Bacillus stearothermophilus (IC₅₀ = 5.15 µg/mL). The potential inhibition against some other enzymes were tested, and the results showed that the ELC extract did not inhibit fungal cellulase but strongly inhibited porcine α-amylase (IC₅₀ = 6.7 µg/mL). The ELC extract also inhibited the proteases papain and bromelain, with IC₅₀ = 339 µg/mL and IC₅₀ = 226 µg/mL, respectively. The thermal and pH stabilities of the ELC extract were also investigated.     

Explanation for Malischewsky's approximate expression for the Rayleigh wave velocity

An approach for obtaining approximations of the Rayleigh wave velocity created by the principle of least squares is introduced. In view of this approach, Malischewsky's approximation of the Rayleigh wave velocity for Poisson ratios v in the set of [-1, 0.5] proposed quite recently is explained. It is shown that Malischewsky's approximation obtained by trial and error is (almost) identical with the one established by this approach.     

Role of pore curvature on the thermal stability of gold nanoparticles in mesoporous silica

Pores arranged in a two-dimensional hexagonal structure inside spherical mesoporous silica particles help to prevent the thermal sintering of gold nanoparticles compared to straight pores in MCM-41.