Oscillating repulsive force between macroscopic surfaces as a consequence of the fluctuation of the density in the gap region

We try to explain the short-range repulsive force between surfaces as a consequence of a decrease in the configurational entropy of liquid molecules in the gap region as the width of the gap decreases. A simple model shows that the density has an oscillating variation when the surfaces are pushed towards each other. As a consequence, an oscillating repulsive force appears between the macroscopic surfaces, which is the result of a loss of configurational freedom of the liquid molecules because of their orientation in the gap. Received: 14 August 2000 Accepted: 30 January 2001     

Improved straightforward chemical synthesis of dihydroxyacetone phosphate through enzymatic desymmetrization of 2,2-dimethoxypropane-1,3-diol

Dihydroxyacetone phosphate (DHAP) was synthesized in high purity and yield in four steps starting from dihydroxyacetone dimer (DHA) (47% overall yield). DHA was converted into 2,2-dimethoxypropane-1,3-diol, which was desymmetrized by acetylation with lipase AK. The alcohol function was phosphorylated to give dibenzyl phosphate ester 4. From 4, two routes were investigated for large-scale synthesis of DHAP. First, acetate hydrolysis was performed prior to hydrogenolysis of the phosphate protective groups. The acetal hydrolysis was finally catalyzed by the phosphate group itself. Second, acetate and acetal hydrolysis were performed in one single step after hydrogenolysis.     

Mechanical and physico-chemical characterization of cyclodextrin finished polyamide fibers

We present the study of the cyclodextrin (CDs) finishing of polyamide fibers (PA) by means of citric acid (CTR) as crosslinking agent. We observed that the mode of grafting happened by the formation of a crosslinked polymer formed between CTR and CDs. This polymer physically adhered to the fibers network and was resistant to hot water washings. Modified fibers were characterized by evaluating the contact angle with a polar liquid and by studying the hysteresis of damping of PA fibers (Cahn balance) with various grafting rates and by studying the absorptivity of grafted fabrics via the technique of the posed drop (Digidrop^® instrument). Then a mechanical characterization of the PA fabrics grafted with various proportions of CDs was accomplished, by traction and tear tests by using a tensile-test bench Lohmergy. Finally a topographic study of PA grafted surfaces was approached by atomic force microscopy (AFM and LFM; contact and non-contact mode) which permitted to evaluate the roughness and the chemical heterogeneity of the grafted surfaces.     

Zirconium(IV)-porphyrins as novel ionophores for fluoride-selective polymeric membrane electrodes

The feasibility of using Zr(IV)-porphyrins as novel ionophores for preparing anion-selective polymeric membrane electrodes is examined. Electrodes constructed using o-nitrophenyl octyl ether plasticized poly(vinyl chloride) membranes containing Zr(IV)-octaethylporphyrin (OEP) dichloride (Zr(IV)[OEP]Cl₂) or Zr(IV)-tetraphenylporphyrin (TPP) dichloride (Zr(IV)[TPP]Cl₂) were found to exhibit enhanced potentiometric selectivity toward fluoride compared to electrodes based on a typical anion-exchanger (e.g. tridodecylmethylammonium chloride). At pH 5.5, the electrodes displayed the following selectivity sequences: ClO₄⁻ > SCN⁻ > I⁻ > F⁻ > NO₃⁻ > Br⁻ > NO₂⁻ > Cl⁻ and F⁻ > ClO₄⁻ > SCN⁻ > I⁻ > NO₂⁻ > NO₃⁻ > Br⁻ > Cl⁻ for membranes doped with Zr(IV)[OEP]Cl₂) and Zr(IV)[TPP]Cl₂, respectively. Both ionophores are shown to operate via a charged carrier mechanism, with 10 mol% of lipophilic tetraphenylborate derivative in the membrane phase required to achieve optimal selectivity. Electrodes prepared with both metalloporphyrin species display super-Nernstian response toward fluoride with slopes typically greater than −100 mV per decade. It is shown, via UV-VIS spectroscopy of the membrane phase, that this behavior occurs due to spontaneous formation of hydroxide ion bridged porphyrin dimers in the membrane in the presence of the lipophilic anionic additive. The dimers are easily converted to monomeric species upon increasing the concentration of fluoride in the sample solution. Decreasing the pH of sample buffer background solution (from pH 5.5 to pH 3) decreases the lower detection limit (DL) of the electrode response toward fluoride (by two-order of magnitude) and improves the electrodes’ selectivity.     

Gibbs functions for transfer of divalent metal cations from water to water + methanol mixtures using potentiometry, polarography and solubility measurements

Gibbs functions for transfer from water to methanol and to a full range of water + methanol mixtures were obtained for Cu²⁺, Cd²⁺, Pb²⁺, Hg²⁺, Zn²⁺, Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ using potentiometric or polarographic measurements in these solvents. In addition, data were obtained from the solubility products of the alkaline-earth iodates. From values obtained by the different methods and literature data, a table of selected values is given.     

Novel species in the electrochemical reduction of a metalmetal bond bridged by a bidentate fluorophosphine

The purple bridged bimetallic complex [CH₃N(PF₂)₂]₃Co₂(CO)₂ undergoes successive chemically and electrochemically reversible one-electron reductions to the corresponding green radical anion and pale-yellow dianion. The radical anion is relatively unreactive towards oxygen and methyl iodide. The dianion is not only reactive towards oxygen and methyl iodide but also captures small positively charged species (e.g. Li⁺ and H⁺) with significant alteration of its chemical properties.     

The use of Omega Chrome Fast Blue 2G in the microdetermination of some metals

Summary Omega Chrome Fast Blue 2G has been found to be a suitable indicator for the detection of the equivalence point of calcium, magnesium and manganese in the presence of cadmium, nickel, and aluminium, when they are masked by the addition of cyanide or triethanolamine. It is also a suitable indicator for the back titration of aluminium using calcium or magnesium as a back titrant.This dye has also been found to be a suitable reagent for the colorimetric determination of calcium, magnesium, manganese and thorium.     

Synthesis of Some Novel 2‐Anilinothiophene, 2,3′‐Bithienyl and Thienylthiopyridine Derivatives Resistance to Penicillium Digitatum Effect the Fruit

Reaction of benzotriazol‐1‐yl acetone 1 with phenyl isothiocyanate followed with α‐chloroacetone or ethyl‐α‐chloroacetate afforded 2‐anilinothiophenes 3 or 4 , respectively. Treatment of 3 with malononitrile at different reaction conditions afforded 6 or 7 . Reaction of 1 with CS₂ in DMF and phenacylbromide afforded S‐alkylated thiophene 10 . Reactions of the latter compound with different active methylene nitriles afforded thienylthiopyridine derivatives 14 and 15 . Condensation of 10 with hydrazine hydrate afforded hydrazon derivative 16 . Reaction of thiophene 17 with formamide in DMF afforded 19 which converted to N‐thienylpyrimidine 20 when treated with malononitrile. The structure of the newly synthesized compounds has been established on the basis of their analytical and spectral data. The compounds were also investigated for antibacterial and antifungal activities.     

Unsteady incompressible flow of magnetized aluminium oxide and titanium oxide nanoparticles with blood base fluid

In this investigation, a mixed convective nanoparticles fluid flow over an inclined plate is deliberated. The effects of slip boundary wall and magnetic field are also considered. The dimensionless governing system for the considered problem is attained by implementing recent definitions of fractional derivatives (FD). The generalized solution is obtained through the Laplace Transformation Scheme (LTS) for the momentum and thermal expressions. To improve the novelty and to demonstrate some more physical perception of the stated research work, some remarkable special cases of velocity distribution through CF and AB-fractional derivative concept are addressed, whose daily life implication is well known in the existing literature. Moreover, to evaluate the physical interest of the stated problem, the outcomes of the obtained system graphical illustrations are made by utilizing MATHEMATICA. As a result, we concluded that the aluminium oxide $A{l}_2{O}_3$ nanoparticles show more decaying behavior as compared to titanium oxide $Ti{O}_2$ nanoparticles for temperature and velocity profile. Furthermore, both fields i.e., momentum and thermal distributions are increased with the help of rising estimations parameter. Current results report novel applications in enhancement of heat transfer, thermal engineering, chemical processes, engineering and electronics devices, solar systems, extrusion processes, fission reactions etc.     

Temperature-sensitive polypeptide brushes-coated mesoporous silica nanoparticles for dual-responsive drug release

A multifunctional nanohybrid based on mesoporous silica nanoparticle and biocompatible polypeptide was fabricated for targeted and dual-responsive therapy of tumor cells.