Properties of lysine-containing zinc amino acid mixed complexes and evaluation of their zinc supplying ability

Zinc deficiency is one of the serious problems of trace element nutrition in the world, which causes a series of pathologic effects. Based on the principles of bioinorganic chemistry, the ternary complexes of Zn-lysiue-histidine were studied as a substitution of zinc sulfate for zinc supplementation. It has also been proved by animal trail.     

Chiral zinc homoenolate of methyl isobutyrate. A new building block for the synthesis of chiral α-methylesters

Chiral homoenolate of methyl isobutyrate prepared in a few steps from optically active methyl β-hydroxy isobutyrate reacts with carbon electrophiles to give chiral α-methyl esters.     

Catalytic activity of a ζ-class zinc and cadmium containing carbonic anhydrase. Compared work mechanisms

The carbonic anhydrase is the enzyme that catalyzes the reversible hydration of carbon dioxide and represents one of the most ancient proteins to which a plethora of works was devoted. The three main classes rely on zinc ion for activity. Most recently a new class of CA was discovered in marine diatoms to use naturally a cadmium ion as catalytic metal. In the present investigation we focused our attention on a carbonic anhydrase cambialistic enzyme (CDCA1) belonging to this new class. The study was inspired by the discovery that the replacement of zinc ion with cadmium does not entail significant differences in the catalytic performance of the enzyme. Our aim was to give further insight of the enzymatic work mechanism. Different possible reaction paths were considered for both metallic forms of the enzyme and comparison with previous studies concerning other carbonic anhydrases was made. The effects of the solvent on the energetics of the catalytic process, was also taken into account by means of a polarizable continuum model. The results obtained from density functional calculations, using a well consolidated mixing of exchange-correlation potential and basis set, and performed with a model of the active site designed on the basis of the X-ray crystal structure, proposed for both metal ions similar reaction pathways consisting in the nucleophilic attack by the metal bound hydroxide to the carbon dioxide with bicarbonate formation, in a next internal rotation of this last fragment, and then in the formation of a species ready for the product removal. Similar activation barriers were found in the rate determining steps that confirm the experimental indication concerning the comparable efficiency of the enzyme in the presence of a zinc or cadmium metal ion.     

Structure and energetics of β-diketonates. XVI. Molecular structure and vibrational spectrum of zinc acetylacetonate according to gas-phase electron diffraction and quantum-chemical calculations

The molecular structure of zinc acetylacetonate was studied in a simultaneous electron diffraction and mass spectrometric experiment at 376(7) K and by quantum-chemical calculations. The Zn(acac)₂ molecule has a structure of D _2d symmetry with the chelate rings lying in mutually perpendicular planes. The main geometrical parameters of the molecule are r _h1(Zn-O) = 1.942(4) Å, r _h1(C-O) = 1.279(3) Å, r _h1(C-C_r) = 1.398(3) Å, r _h1(C-C _m ) = 1.504(5) Å, ∠(O-Zn-O) = 93.2(7)°, ∠(Zn-O-C) = 125.9(7)°, ∠(C-C_r-C) = 125.8(14)°, ∠(O-C-C _m ) = 115.2(9)°. The effective rotation angle of methyl groups is close to 30°, which is indicative of the free rotation of these groups. The vibration frequencies were obtained by quantumchemical calculations, and the IR spectrum of the Zn(acac)₂ molecule was interpreted.     

Vibrational spectra of carboxylato complexes—I. Infrared and Raman spectra of beryllium(II) acetate and formate and of zinc(II) acetate and zinc(II) acetate dihydrate

The spectra of the title compounds have been recorded and interpreted. On this basis, the structures of the anhydrous compounds Be(OOCH)₂, Be(OOCMe)₂, Zn(OOCMe)₂ are predicted to have tetrahedral coordination with the carboxylate ions acting as bidentate ligands.     

Progress and prospect of the zinc–iodine battery

The zinc–iodine battery has the advantages of high energy density and low cost owing to the flexible multivalence changes of iodine and natural abundance of zinc resources. Compared with the flow battery, it has simpler components and more convenient installation, yet it still faces challenges in practical applications. How to select suitable materials as the cathode and electrolyte to control the process of energy storage reaction and inhibit the self-transformation of by-products, together with the corrosion resistance of metallic zinc are crucial factors. Herein, the principles of the zinc–iodine flow battery and zinc–iodine battery are described, and the unprecedented progresses are highlighted. This mini review is anticipated to provide valuable guidance for the further development of the zinc–iodine battery.     

Synthesis,characterization and visible-light photocatalytic activity of TiO2–SiO2 composite modified with zinc porphyrins

Three types of silica gel supported titanium dioxide particles immobilizing Zn(II) carboxylphenyl porphyrins appending p-CH₃, p-H and p-Cl phenyl substituents (designated as ZnMP–TiO₂–SiO₂, ZnPP–TiO₂–SiO₂ and ZnCP–TiO₂–SiO₂, respectively) have been synthesized and characterized using SEM, XRD, IR, AFS, DRS, UV–Vis, XPS and TG. The photodegradation of α-terpinene in aqueous suspension was used to determine the photocatalytic activity of TiO₂–SiO₂ samples which had been impregnated with Zn(II) porphyrins, as sensitizers. The experimental results confirmed that the photocatalytic activitys of these composites are much higher than those of the nonmodified TiO₂–SiO₂ under visible light irradiation and follow the order of ZnMP–TiO₂–SiO₂ > ZnPP–TiO₂–SiO₂ > ZnCP–TiO₂–SiO₂.     

Two-fragment α-adrenolytics. 4. Synthesis of phosphorylated derivatives of 2-aryloxyethylamines and N-phenylpiperazine

The reactions of 3-chloropropylphosphonates, 3-chloropropylthiophosphonates, or 3-chloropropylphosphinates with 2-aryloxyethylamines or N-phenylpiperazine afford the corresponding 3-(2-aryloxyethylamino)propylphosphonates and -phosphinates or 3-(4-phenylpiperazin-1-yl)propylphosphonates and -phosphinates. The compounds obtained exhibit -adrenolytic and hypotensive activities, the latter being found to depend on the substituents at the P atom.     

Passivation layer–dependent catalysis of zinc oxide nanostructures

Electrochemical and photoelectrochemical catalysis of surface-passivated zinc oxide (ZnO) nanostructures with three different metal oxides were investigated. Initially, vertically aligned ZnO nanorods structures were developed over conductive substrates by a two-step approach and then passivated with an ultrathin zinc hydroxide, that is, Zn(OH)₂, cobalt oxide, that is, CoO, and Zn(OH)₂/CoO as bilayer, by electrochemical deposition. Compared with the pristine ZnO structures, the surface-passivated nanostructures possess slightly rough surfaces, whereas their crystal structure remains unchanged. From electrochemical catalysis studies under dark and illumination, it is noticed that vertically aligned ZnO nanostructures passivated with narrow band-gap CoO layers have a predominant water oxidation performance than that of the structures passivated with other oxide materials. It is mainly attributed to the eradication of surface states present on ZnO nanorods. Interestingly, the structures passivated with bilayers, that is, Zn(OH)₂/CoO, showed significant stability and durability (～103% retention in current density@60^th min) with a continuous oxygen evolution reaction process for long durations.     

2-Oxooxazolopyridines. 2. Synthesis of N′-alkyl-N-(2-oxo-3-pyridyl)ureas

In reactions with amines 2-oxo-7-trifluoromethyl-5-phenyl-(1H)-oxazolo[5,4-b]pyridines and alkyl N-(2-oxo-3-pyridyl)carbamates are converted into N-alkyl- and N,N-dialkyl-N-(2-oxo-3-pyridyl)ureas respectively.For Communication 1, see [1].Riga Technical University, Riga LV-1048, Latvia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 385–391, March, 1998.     

Reaction of aminoquinolines with unsaturated carboxylic acids. 2. Cyclization of N-quinolyl-β-alanines

The cyclization of N-(3-quinolyl)- and N-(6-quinolyl)--alanines was carried out to give uncondensed hexahydropyrimidine derivatives, while the cyclization of N-(5-quinolyl)- and N-(8-quinolyl)--alanines gave tetrahydrophenanthrolinone derivatives.Communication 1, see ref. [1].Kaunas Technological University, 3028 Kaunas, Lithuania, Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 653–657, May, 2000.     

Synthesis and properties of thiazole halohydrazones. 2. Interaction of 2-α-chlorobenzylidenehydrazino-4-ethoxy-carbonylthiazole with nucleophiles

In the interaction of 2--clzlorobenzylidenehydrazino-4-ethoxycarbonylthiazole with nucleophiles, two competing reactions take place. 1) nucleophilic replacement of the chlorine atom to form the corresponding substitution product; 2) elimination of a hydrogen chloride molecule, concluding in cyclization of the intermediate nitrilimine to form 3 phenyl-5-ethoxycarbonylthiazolo(2, 3-c]-1, 2, 4-triazole. The direction taken by the interaction depends on the nature of the nucleophile and is determined primarily by the ratio of basicity and nucleophilicity of the agent.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, 256–259, February, 1994. Original article submitted December 30, 1993.     

Effect of zinc oxide on microhardness and sintering behavior of MgO–Al2O3–SiO2 glass–ceramic system

Glass–ceramic in the MgO–Al₂O₃–SiO₂ system with crystallization ability of gahnite (ZnO·Al₂O₃) and mullite were synthesized. It was found that the glass–ceramic containing gahnite phase had desirable mechanical behavior and reached to an acceptable hardness and density. The compositions were designed based on magnesium oxide replacement (from MgO–Al₂O₃–SiO₂ glass–ceramic system) with zinc oxide. Glass–ceramics were characterized by DTA, X-ray diffraction and scanning electron microscopy. Heat treatment at 1100 °C cause form gahnite crystals in glass–ceramic. Microhardness increased with increasing gahnite crystals. To achieve good mechanical properties, the initially formed high gahnite phase must transform.     

The polarographic determination of indium in zinc-base alloys : The determination of indium in zinc and in “lead-free” zinc alloys

The use of a potassium iodide base electrolyte for the separation of the polarographic steps due to indium and cadmium is discussed and theoretical data relating to the interference of the step due to lead with that due to indium are presented. An experimental study is given together with details of the attempted removal of lead interference. A method is presented for the polarographic determination of indium in zinc alloys, applicable when the lead concentration is small compared with that of indium.     

2-Benzopyrylium salts. 41. Intramolecular transformations of 4-1′-dimers of α-unsubstituted 2-benzopyrylium salts

Recyclization reactions of 4-1-dimers of 2-benzopyrylium salts leading to naphthalene derivatives are described. A new variant of the intramolecular Cannizzaro rearrangement has been discovered.For communication 40, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 175–180, February, 1991.     

Intramolecular [2 + 2] photocycloaddition. 2. Mechanism of intramolecular photocyclization of α,ω-bis(p-vinylphenyl)alkanes

From the photophysical measurements of the title reaction, the formation of cyclophanes is concluded to be facilitated by high microscopic concentration of styrene moieties and depressed by strain loaded at the transition state.     

Sol–gel derived nano zinc oxide for the reduction of zinc oxide level in natural rubber compounds

Zinc oxide (ZnO) nanoparticles are synthesized by polymeric sol–gel method and characterized by X-ray diffraction, field-emission scanning electron microscopy. The cure characteristics, mechanical properties and thermal behaviour of natural rubber (NR) systems containing nano ZnO are investigated and compared to those of NR with micro-sized (conventional) ZnO. The NR vulcanizate with 0.5 phr (parts per hundred parts of rubber) sol–gel derived nano ZnO shows improvement in the curing and mechanical properties in comparison to the NR vulcanizate with 5 phr conventional ZnO. Thermogravimetric analysis reveals that nano ZnO impose better thermal stability than conventional ZnO in the NR vulcanizates. Thus, nano ZnO not only acts as a curing activator but also nano filler to improve the resulting properties of the NR vulcanizates. More essentially nano ZnO leads to the reduction of ZnO level in the NR compounds. Therefore, sol–gel derived nano ZnO diminishes the pollution of aquatic environment due to higher amount of conventional ZnO in rubber compounds.     

Coordination behaviour of 2,2′-bipyridine towards the dichloroacetates of zinc and cadmium

The coordiantion compounds [Zn(C₁₀H₈N₂)(Cl₂HCCOO)(H₂O)₃]⁻·[Zn(C₁₀H₈N₂)(Cl₂HCCOO)₃]⁺ and [Cd(C₁₀H₈N₂)₂(Cl₂CHCOO)₂] were synthesised and characterised by elemental and thermal analysis, IR and UV–VIS spectroscopy, and X-ray crystallography. The complexes are air stable and well-soluble in water. The zinc atoms are five and six coordinated and the cadmium atom is six coordinated. The coordination polyhedra of central atoms can be described as trapezoidal pyramid and octahedron in zinc compound and as rectangular bipyramid strongly distorted towards skew trapezoidal bipyramid in cadmium compound. In both compounds all dichloroacetate groups are monodentate. The bond valences considerations show that all 2,2′-bipyridine molecules are bonded almost 2 times stronger than carboxylate groups. In the structure of zinc compound exist O–H···O hydrogen bonds and in both structures can be found weak C–H···O hydrogen bonds. Additionally, both compounds are pile-stacked by π···π interactions. The IR spectra show typical vibrations for chelating 2,2′-bipyridine molecules and terminal monodentate carboxylate groups. The thermal decomposition studies show zinc compound decomposes in 4 steps and cadmium compound decomposes in 5 steps with formation of oxides as a final products. The ligands decompose gradually, first dichloroacetates and next 2,2′-bipyridine.     

Comparative characterisation of zinc oxide thin films prepared from zinc acetate with or without water of hydration via the sol–gel method

Zinc oxide thin films were prepared using either zinc acetate dihydrate or anhydrous zinc acetate via the sol–gel method. Comparative characterisation of the crystallographical, morphological, optical/spectroscopical and electrical properties of the so-obtained films was performed. The idea of one- (in the case of the anhydrous precursor), and two- (in the other case) stage hydrolysis/condensation was postulated, which was supported by the characterisation results. The film prepared using the anhydrous precursor had a more pronounced c-axis crystal orientation preference, with a larger average crystallite size and more porous morphology. The transparency of this film was significantly lower over the UV/visible region due to its more porous morphology, which also resulted in lower intensity of the ‘near band edge emission’, and higher electrical resistivity. The overall results also suggested that anhydrous zinc acetate could be employed as a precursor for the sol–gel synthesis of zinc oxide thin films, which might have potential advantages in microelectronic and optoelectronic applications.