Calcium Complex (calcium + complex)

Distribution by Scientific Domains


Selected Abstracts


Chiral Calcium Complexes as Broensted Base Catalysts for Asymmetric Addition of ,-Amino Acid Derivatives to ,,,-Unsaturated Carbonyl Compounds.

CHEMINFORM, Issue 37 2007
Susumu Saito
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


Coordination complexes of functionalized pyrazines with metal ions: reagents for the controlled release of flavourant molecules at elevated temperatures

FLAVOUR AND FRAGRANCE JOURNAL, Issue 2 2006
Colin Baillie
Abstract The potential for stabilization of volatile flavourant molecules such as functionalized pyrazines by coordination to metal ions, and the application of the resultant coordination complexes as controlled release agents at elevated temperatures were explored. New complexes containing the flavourant molecules 2,3,5-trimethylpyrazine (TMP), 2-ethyl-3-methylpyrazine (EMP) and 2-acetylpyrazine (ACP) with copper(II) and copper(I) salts were prepared and structurally characterized. Representative examples of known copper(II) and calcium(II) complexes containing pyrazine carboxylic acids were also prepared. The complexes were examined by thermal analysis techniques and demonstrated, by a combination of thermogravimetric (TGA) and pyrolysis GC,MS analyses, to act as convenient reagents for the release of the parent pyrazine at elevated temperatures. Thus, pyrolysis GC,MS revealed that the complex [Cu3Cl3(EMP)2]n cleanly releases EMP in 96.5% selectivity at 200 °C. Of particular significance is that the calcium complex [Ca(3-aminopyrazine-2-carboxylate)2·H2O], under ramped pyrolysis conditions, was shown to undergo decarboxylation prior to the release of 2-aminopyrazine (AMP), as essentially the only volatile component, in the temperature range 600,800 °C. This finding provides a precedent for the application of complexes of pyrazinecarboxylate salts with metal ions (of which an almost infinite number of combinations is potentially available) as controlled release agents of the parent pyrazine molecule at elevated temperatures, suitable for exploitation by the foodstuffs, flavour and fragrance industries. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Effect of the combination of a benzophenone-type ultraviolet absorber with thermal stabilizers on the photodegradation of poly(vinyl chloride)

JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 1 2010
Xiuqin Xiang
The effect of the combination of a UV absorber (Chimassorb 81) with different types of thermal stabilizers, including an organic calcium complex and an organotin mercaptide, on the photodegradation of poly(vinyl chloride) (PVC) was investigated by color difference measurements, UV,Vis spectroscopy, Fourier-transform infrared spectroscopy, thermogravimetric (TG) analysis, and viscosity-average molecular weight determination. Films of PVC containing 0.5 phr of Chimassorb 81, with and without 2 phr of a thermal stabilizer, were prepared by solution casting. Then the accelerated UV weathering of the films was carried out under xenon light with an irradiance of 0.51 W/(m2 · nm) at 65°C. The results showed that both Chimassorb 81 and the mixture of Chimassorb 81 with the organic calcium complex showed good behavior in inhibiting the photodehydrochlorination and photooxidation of PVC. In contrast, the combination of Chimassorb 81 and methyltin mercaptide significantly accelerated initial color development during the final 200 h of exposure because of the UV sensitivity of the organotin. Moreover, when Chimassorb 81 and the methyltin mercaptide were used together to stabilize PVC films, the expected antioxidant effect of the mixture was not observed, in contrast to the behavior found with other stabilized systems, perhaps because the Chimassorb 81 had been depleted by the methyltin mercaptide during the UV irradiation. The TG analysis revealed that ultraviolet irradiation had caused severe destruction of the PVC chains. However, addition of Chimassorb 81 or the combination of Chimassorb 81 with the organic calcium complex effectively prevented the destruction, as was demonstrated by changes in the activation energies for thermal degradation. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers [source]


The Mechanism of Water Oxidation: From Electrolysis via Homogeneous to Biological Catalysis

CHEMCATCHEM, Issue 7 2010
Holger Dau Prof.
Abstract Striving for new solar fuels, the water oxidation reaction currently is considered to be a bottleneck, hampering progress in the development of applicable technologies for the conversion of light into storable fuels. This review compares and unifies viewpoints on water oxidation from various fields of catalysis research. The first part deals with the thermodynamic efficiency and mechanisms of electrochemical water splitting by metal oxides on electrode surfaces, explaining the recent concept of the potential-determining step. Subsequently, novel cobalt oxide-based catalysts for heterogeneous (electro)catalysis are discussed. These may share structural and functional properties with surface oxides, multinuclear molecular catalysts and the catalytic manganese,calcium complex of photosynthetic water oxidation. Recent developments in homogeneous water-oxidation catalysis are outlined with a focus on the discovery of mononuclear ruthenium (and non-ruthenium) complexes that efficiently mediate O2 evolution from water. Water oxidation in photosynthesis is the subject of a concise presentation of structure and function of the natural paragon,the manganese,calcium complex in photosystem,II,for which ideas concerning redox-potential leveling, proton removal, and OO bond formation mechanisms are discussed. The last part highlights common themes and unifying concepts. [source]


{Bis(3,5-Di- tert -butyl-2-oxidobenzyl)[2-(N,N -dimethyl­amino)ethyl]amine-,4N,N,,O,O,}zinc(II) and {bis­(3- tert -butyl-5-methyl-2-oxidobenzyl)[2-(N,N -dimethyl­amino)ethyl]amine-,4N,N,,O,O,}(tetra­hdyrofuran)zinc(II)

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2006
Ruth H. Howard
The title zinc(II) complexes, [Zn(C34H54N2O2)], (II), and [Zn(C28H42N2O2)(C4H8O)], (III), were obtained as monomeric 1:1 complexes, in contrast with the calcium complexes supported by the same ligand class. Complex (II) crystallizes with two independent mol­ecules in the asymmetric unit, which have similar geometric parameters. The donor atoms in (II) form a distorted trigonal,pyramidal arrangement around the zinc centre. Complex (III) contains a coordinated tetra­hydro­furan mol­ecule, resulting in a five-coordinate trigonal,bipyramidal arrangement around the Zn atom. The electron density provided by the coordination of this tetra­hydro­furan mol­ecule elongates the Zn,O and Zn,N bonds by approximately 0.07 and 0.10,Å, respectively, in comparison with (II). Neither (II) nor (III) is active as an ,-caprolactone polymerization catalyst. The data presented here demonstrate that Zn may bind both an ONNO ligand and an additional oxygen-based ligand. The lack of activity is thus not due to steric hinderance at the metal atom. [source]


Hydrocarbon-Soluble Calcium Hydride: A "Worker-Bee" in Calcium Chemistry

CHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2007
Jan Spielmann
Abstract The reactivity of the hydrocarbon-soluble calcium hydride complex [{CaH(dipp-nacnac)(thf)}2] (1; dipp-nacnac=CH{(CMe)(2,6- iPr2C6H3N)}2) with a large variety of substrates has been investigated. Addition of 1 to CO and CN functionalities gave easy access to calcium alkoxide and amide complexes. Similarly, reduction of the CN bond in a cyanide or an isocyanide resulted in the first calcium aldimide complexes [Ca{NC(H)R}(dipp-nacnac)] and [Ca{C(H)NR}(dipp-nacnac)], respectively. Complexation of 1 with borane or alane Lewis acids gave the borates and alanates as contact ion pairs. In reaction with epoxides, nucleophilic ring-opening is observed as the major reaction. The high reactivity of hydrocarbon-soluble 1 with most functional groups contrasts strongly with that of insoluble CaH2, which is essentially inert and is used as a common drying agent. Crystal structures of the following products are presented: [{Ca{OC(H)Ph2}(dipp-nacnac)}2], [{Ca{NC(H)Ph}(dipp-nacnac)}2], [{Ca{C(H)NC(Me)2CH2C(Me)3}(dipp-nacnac)}2], [{Ca{C(H)NCy}(dipp-nacnac)}2], [Ca(dipp-nacnac)(thf)]+[H2BC8H14], and [{Ca(OCy)(dipp-nacnac)}2]. The generally smooth and clean conversions of 1 with a variety of substrates and the stability of most intermediates against ligand exchange make 1 a valuable key precursor in the syntheses of a wide variety of ,-diketiminate calcium complexes. [source]