Nonhydrolytic Conditions Research Articles

Sol–Gel Derived Epitaxial MgTiO3 Thin Films

MgTiO3 thin flms have been successfully grown on a sapphire crystal by the sol–gel process. Epitaxial growth of MgTiO3 thin films was obtained using magnesium acetylacetonate and titanium isopropoxide in the sol–gel process. In nonhydrolytic conditions, the c-axis oriented ilmenite structure of MgTiO3 thin films developed at the crystallization temperatures 650–800°C with a 3-fold axis symmetry in the c-plane. These epitaxial MgTiO3 thin films had extremely fine features in morphology, i.e., a fine grain size of 10–20 nm and a very smooth surface of 0.9 nm rms roughness. The epitaxial MgTiO3 thin films exhibited a UV absorption edge at 280 nm and were transparent in the wavelength range of 400–1100 nm. The ordinary refractive index of the epitaxially grown MgTiO3 thin films was 2.305, very close to the value of single-crystal MgTiO3. This suggests that the epitaxially grown MgTiO3 thin films are well crystallized and sufficiently strain-relaxed due to the small lattice mismatch with Al2O3 substrate.

Nonhydrolytic sol-gel routes to layered metal(IV) and silicon phosphonates

Three nonhydrolytic routes to methyl and phenylphosphonates have been developed involving the systems: (i) MCl4-RPO(OR)2 or M(OR)4-RPOCl2 (M=Si, Ti); (ii) MCl4-RPOCl2-ether (M=Sn, Ti, Zr); (iii) MCl4-RPOCl2-alcohol (M=Sn, Ti, Zr). It is noteworthy that use of nonhydrolytic conditions opens a route to water-sensitive silicon phosphonates. In most cases the phosphonates were obtained as gels. The poorly crystalline materials obtained after drying were characterised by solid-state NMR spectroscopy and their layered structure could be shown by powder X-ray diffraction. However a higher degree of crystallinity could be obtained under solvothermal conditions, either by the direct alcoholysis of chloride precursors with tert-butanol (2-methylpropan-2-ol), or by a simple postsynthesis treatment in tert-butanol.

Nickel-catalysed electrochemical reductive deprotection of allyl ethers

The selective deprotection of a series of functionalized alkyl and aryl allyl ethers to the parent alcohols or phenols, under non-hydrolytic conditions, is effected by the combination of electrochemistry and catalysis by NiII–bipyridine complexes.

Reductive deprotection of aryl allyl ethers with Pd(Ph 3) 4/NaBH 4

Treatment of aryl allyl ethers with catalytic amounts of Pd(PPh 3) 4 and NaBH 4 at room temperature afforded the parent phenol in high yield under non-hydrolytic conditions.

Protecting Group for Carboxyl Function: Mild and Facile Cleavage of 2-Cyanoethyl Ester under Non-hydrolytic Conditions.

The use of the 2-cyanoethyl group for carboxyl-protection is described. This group was readily introduced by esterification using ethylene cyanohydrin and the deprotection was carried out under mild conditions using tetrabutylammonium fluoride in dimethylformamide-tetrahydrofuran.

Facile Derivatizations of Heptamethine Cyanine Dyes

Abstract Treatment of dye 3 with sodium methoxide, morpholine, or diphenylphosphine gives the respective substituted derivatives 4, 5 and 6 in high yields. The reaction of 3 with sodium acetate followed by workup affords ketone 7 which is also obtained by demethylation of a methoxy derivative 4 under non-hydrolytic conditions.

Site-specific epsilon-NH2 monoacylation of pancreatic phospholipase A2. 2. Transformation of soluble phospholipase A2 into a highly penetrating "membrane-bound" form.

Long-chain lecithins present in bilayer structures like vesicles or membranes are only very poor substrates for pancreatic phospholipases A2. This is probably due to the fact that pancreatic phospholipases A2 cannot penetrate into the densely packed bilayer structures. To improve the weak penetrating properties of pancreatic phospholipases A2, we prepared and characterized a number of pancreatic phospholipase A2 mutants that have various long acyl chains linked covalently to Lys116 in porcine and to Lys10 in bovine phospholipase A2 [Van der Wiele, F.C., Atsma, W., Dijkman, R., Schreurs, A.M.M., Slotboom, A.J., & De Haas, G.H. (1988) Biochemistry (preceding paper in this issue)]. When monomolecular surface layers of L- and D-didecanoyllecithin were used, it was found that the introduction of caprinic, lauric, palmitic, and oleic acid at Lys116 in the porcine enzyme increases its penetrating power from 13 to about 17, 20, 32, and 22 dyn/cm, respectively, before long lag periods were obtained. Incorporation of a palmitoyl moiety at Lys10 in the bovine enzyme shifted the penetrating power from 11 to about 25 dyn/cm. Only the best penetrating mutant, viz., porcine phospholipase A2 having a palmitoyl moiety at Lys116, was able to cause complete leakage of 6-carboxyfluorescein entrapped in small unilamellar vesicles of egg lecithin under nonhydrolytic conditions. Similarly, only this latter palmitoylphospholipase A2 completely hydrolyzed all lecithin in the outer monolayer of the human erythrocyte at a rate much faster than Naja naja phospholipase A2, the most powerful penetrating snake venom enzyme presently known.

Properties of the high-affinity single-stranded DNA binding state of the Escherichia coli recA protein.

The properties of the high-affinity single-stranded DNA (ssDNA) binding state of Escherichia coli recA protein have been studied. We find that all of the nucleoside triphosphates that are hydrolyzed by recA protein induce a high-affinity ssDNA binding state. The effect of ATP binding to recA protein was partially separated from the ATP hydrolytic event by substituting calcium chloride for magnesium chloride in the binding buffer. Under these conditions, the rate of ATP hydrolysis is greatly inhibited. ATP increases the affinity of recA protein for ssDNA in a concentration-dependent manner in the presence of both calcium and magnesium chloride with apparent Kd values of 375 and 500 microM ATP, respectively. Under nonhydrolytic conditions, the molar ratio of ATP to ADP has an effect on the recA protein ssDNA binding affinity. Over an ATP/ADP molar ratio of 2-3, the affinity of recA protein for ssDNA shifts cooperatively from a low-to a high-affinity state.

Synthesis of Nitriles and Symmetrical Organic Sulphides from Biprotic Carbothioamides and an α-Halogenated Ketone, Ester or Nitrile

Abstract Thioacetamide has been used as an elegant sulphur transfer reagent for C-S-C coupling of reactive halides.1–4 Sulphur extrusion of biprotic carbothioamides to form corresponding nitriles has been reported with the help of (i) dichlorocarbene;5 (ii) triphenylphosphine, carbon tetrachloride, triethylamine;6 (iii) diethyl azocarboxylate, triphenylphosphine;7 and (iv) soft metal ions.8 Here, we report that under non-hydrolytic conditions viz. DMF/OEt, EtOH/OEt and DMF/Et3N, biprotic carbothioamides (1, R=CH3, C6H5, CH2C6H5) react with bromoacetophenone (2, Z=COC6H5), ethyl bromoacetate (2, Z=COOEt).

Maleimide polymers. I. A polymeric color reaction

AbstractCertain copolymers of maleimide and N‐substituted maleimides yield brilliant colors when treated with sufficiently strong basic reagents under nonhydrolytic conditions. For color generation, the copolymer must be capable of HX elimination. The chromophores which account for color probably result from the ionization of acidic protons in structures involving one or more double bonds conjugated with imide carbonyl. The analogy to the color reactions of aconitylanil is pointed out. Spectra covering the range of 330–700 mμ are presented for a number of copolymer–amine color‐generating systems. The colors produced in base with radical‐initiated polymaleimide and imidazole‐initiated poly‐N‐alkylmaleimides as well as the absence of color with anionic polymaleimide and radical poly‐N‐alkylmaleimides are discussed in light of what is known about their polymerization kinetics and mechanisms. Corresponding maleic anhydride copolymer systems are mentioned.

Fractionation and characterization of glycoproteins containing hydroxyproline from the leaves of Vicia faba.

A survey was conducted of the distribution, solubility, chemical and some physical properties of the constituents of the leaves of Vicia faba containing hydroxyproline. With aqueous trichloroacetic acid about 30% of the total leaf hydroxyproline could be brought into solution. The rest remained insoluble in aqueous or non-aqueous solvents tested under non-hydrolytic conditions. The material soluble in trichloroacetic acid was resolved by phenol-aqueous (pH 8) partitioning into (a) predominantly polysaccharide-type materials with small amounts of firmly bound proteins containing hydroxyproline; (b) into some insoluble material and (c) into glycoproteins and glycolipids containing hydroxyproline soluble in the phenol-rich phase. These last were separated into at least four cationic, one anionic and one stationary components on continuous high voltage electrophoresis in phenol–acetic acid–water. The four cationic glycoprotein fractions were resolved further on the basis of their size on a Bio Gel P 100 column operated in phenol–acetic acid–water. The stationary component was composed of a mixture of glycolipids and contained strongly bound amino acids including hydroxyproline. Analytical results for the major components obtained in this work clearly indicated the presence in the leaves of Vicia faba of a number of glycoproteins, polysaccharide-protein complexes and glycolipids containing hydroxyproline each with characteristic and different composition, molecular size and solubility. Previous work on cell-wall protein (extensin) was discussed in the light of these results.

Pectic Substance in Cotton and Its Relation to the Properties of the Fibre

Pectic substance has long been known to be present in naturally-occurring cotton fibres. There exist, how ever, at least two divergent viewpoints regarding the lo cation of this substance in the fibre. The difference in these viewpoints has led to very different conclusions re garding the influence of pectic substance on such important properties of cotton as tensile strength, moisture and dye absorption, and viscosity in cuprammonium hydroxide solu tions. The chief difficulty, heretofore encountered in attempts to evaluate more precisely the role of the pectic substance, has been the lack of a reliable method for its quantitative estimation in the presence of other carbohydrate material. Recently, however, a new method, which permits the accu rate determination of small amounts of uronic acids in the presence of large proportions of cellulose, was developed in this laboratory. This development has made possible the present investigation, which concerns itself with the state of the pectic szcbstance in native cotton fibres, its ease of removal by various reagents, its behavior in cuprammonium hydroxide solutions and its influence on the tensile strength and on the viscosity of cuprammonium dispersions of the cotton. The results indicate that a pectin-cellulose complex does not exist in cotton fibres and that the pectic sub stance is present as an insoluble salt. The replacement of these ions, under non-hydrolytic conditions, by the mono valent cations, sodium or ammonium, renders the pectic substance soluble. Cotton freed of pectic substance with alkali showed no change in tensile strength or in viscosity, whereas treatment of the fibre with acids, which removed only a small proportion of the pectic substance, produced an appreciable lowering of these two properties. When dewaxed fibres were dispersed in cuprammonium solutions, it was found that a small portion remained in soluble and was readily removed in a centrifuge. Analysis of the material showed it to consist practically entirely of pectic substance. Similar results were obtained on fibres which had been pretreated with concentrated hydro chloric acid. Consideration of these results led to the con clusion that the pectic substance does not contribute to the viscosity of cuprammonium dispersions of cotton. Deter minations of the viscosities of cuprammonium solutions to which had been added several samples of pectic material from different sources substantiate this conclusion.