Novel method for efficient aerobic oxidation of silyl ethers to carbonyl compounds catalyzed with N-hydroxyphthalimide (NHPI) and lipophilic Co(II) complexes

In this work, a new method for highly efficient and selective oxidative deprotection of a variety of structurally diverse trimethylsilyl (TMS) and tert-butyldimethylsilyl (TBS) ethers using molecular oxygen in the presence of N-hydroxyphthalimide (NHPI) and various types of Co(II) complexes is reported. As a result of the relatively neutral reaction medium, acid-sensitive functional groups such as phenolic TBS ethers survived intact under the presented reaction conditions.     

A chiroptical approach for the absolute stereochemical determination of P-stereogenic centers

A simple chiroptical solution for the absolute stereochemical determination for asymmetric phosphorus V stereocenters is presented. Strong coordination of the phosphorus oxide with the Zn-metallo center of the racemic host Zn-MAPOL 2 leads to an induced axial chirality of the host, yielding a strong ECCD signal. A mnemonic is proposed to correlate the asymmetry of the guest molecule with the observed ECCD signal.

A simple chiroptical solution for the absolute stereochemical determination for asymmetric phosphorus V stereocenters is presented.     

Kinetics of the Initial Stage of Gelation in Chitosan Solutions Containing Glutaric Aldehyde: Viscometric Study

The effects of glutaric aldehyde concentration C _GA(in the range from 0.07 to 0.2 wt %) and temperature T(from 20 to 65°C) on the kinetics of an increase in the effective viscosity _effof aqueous solutions of chitosans (C _CH= 2.4 wt %, pH 3.6, and ionic strength I= 0.05) with molecular masses equal to 33 × 10⁴and 55 × 10⁴and the degrees of substitution at N-acetyl and amino groups of 0.08 and 0.90, respectively were studied. The kinetic curves _eff(t) exhibited the induction periods of a relatively slight increase in the viscosity of chitosan–glutaric aldehyde mixed solutions with time followed by the periods of a drastic increase in the viscosity. The former periods correspond to the formation of gel clusters; the latter periods, to the gelation over the whole volume of a solution. Optimal ranges of the parameters C _GAand Twere determined for the preparation of spherical gel particles of slightly cross-linked chitosan, which are used for the sorption of heavy metals from low-concentrated solutions.     

Alkylated chitosans of low molecular weight as non-viral transfection vectors for gene therapy

Low molecular weight chitosans (5 kDa) hydrophobically modified with 3, 10, and 18 mol % of tetradecenoyl (TDC) groups have been synthesized. Their good solubility at neutral pH, their surface activity and micelle-forming properties as well as their ability to interact with negatively charged phospholipid vesicles mimicking the internal layer of cell plasma membranes, allow us to consider them as potential non-viral transfection vectors for gene therapy.     

Limits on gravitational-wave emission from selected pulsars using LIGO data

We place direct upper limits on the amplitude of gravitational waves from 28 isolated radio pulsars by a coherent multidetector analysis of the data collected during the second science run of the LIGO interferometric detectors. These are the first direct upper limits for 26 of the 28 pulsars. We use coordinated radio observations for the first time to build radio-guided phase templates for the expected gravitational-wave signals. The unprecedented sensitivity of the detectors allows us to set strain upper limits as low as a few times 10(-24). These strain limits translate into limits on the equatorial ellipticities of the pulsars, which are smaller than 10(-5) for the four closest pulsars.     

Selective oxidation of sulfides to sulfoxides using 30% hydrogen peroxide catalyzed with a recoverable silica-based tungstate interphase catalyst

Various types of aromatic and aliphatic sulfides are selectively oxidized to sulfoxides and sulfones in good to excellent yields using 30% H2O2 in the presence of catalytic amounts of a novel recoverable silica-based tungstate interphase catalyst at room temperature. The catalyst can be recovered and reused for at least eight reaction cycles under the described reaction conditions without considerable loss of reactivity. [reaction: see text]     

Hydrophobically Associating Alginate Derivatives: Surface Tension Properties of Their Mixed Aqueous Solutions with Oppositely Charged Surfactants

The comparative study of the interfacial properties of an anionic polysaccharide, sodium alginate (Alg), and its hydrophobically modified derivative (Alg-C(12)), covalently substituted by dodecyl chains (12% mol/mol saccharide unit), was carried out in the absence or in the presence of an oppositely charged surfactant, dodecyltrimethylammonium bromide (DTAB). The drastically different behaviors which were observed are interpreted in terms of the arrangement and mobility of the hydrophobic long alkyl chains, depending on the nature of their fixation, covalent or ionic, on the polysaccharide backbone. Copyright 2000 Academic Press.     

Laser‐micromachined cellulose acetate adhesive tape as a low‐cost smart material

An off‐the‐shelf, moisture‐responsive, acetate‐backed adhesive tape is investigated as a commercially available smart material for fabricating low‐cost, multifunctional, humidity‐responsive millimeter‐scale structures. Laser ablation is used for cutting and thinning‐down the tape to enhance its response. Water‐submerged cantilevers show a radius of curvature of 3 mm or lower (for laser‐thinned cantilevers). Additionally, their humidity response is a function of the angle between the longitudinal axis of the cantilever and polymer orientation. A cut angled at 80° with respect to this orientation results in a tip rotation of up to 25°, enabling the formation of bending cantilevers with twisting behavior. The tape cantilevers are further functionalized with magnetic nanoparticles and used to create four‐finger grippers that close underwater within minutes and can sample 100 µL of liquid. A cyclic humidity monitor is also fabricated using a tape strip that walks unidirectionally on a ratchet‐shaped surface upon exposure to humidity variations. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1263–1267     

A novel and simple method for the preparation of (R)- and (S)-pyrrolidine-2-phosphonic acids: phosphonic acid analogues of proline

A simple and convenient method has been developed for the preparation of (R)- and (S)-pyrrolidine-2-phosphonic acids. The thermal reaction of proline with diethyl phosphite in the presence of benzaldehyde gave an N-benzyl derivative of diethyl pyrrolidine-2-phosphonate, which was transformed into two diastereomeric amides by sequential debenzylation and acylation with (+)-dibenzoyl-l-tartaric anhydride. The two diastereomeric amides were separated by column chromatography and the structure of one of them was determined by X-ray crystallographic analysis. Hydrolysis of the amides in the usual manner afforded (R)- and (S)-pyrrolidine-2-phosphonic acids. The advantages of the present method are that it is easy, rapid, and prepares both enantiomers of pyrrolidine-2-phosphonic acids.