Synthesis, characterization and photoluminescence properties of Gd2O3:Eu3+ nanophosphors prepared by solution combustion method

Gd2O3:Eu3+ (0.5-8.0 mol%) nanophosphors have been prepared by low temperature solution combustion method using metal nitrates as oxidizers and oxalyl dihydrazide (ODH) as a fuel. The phosphors are well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and photoluminescence (PL) techniques. PXRD patterns of as-formed and calcined (800 degrees C, 3 h) Gd2O3 powders exhibit monoclinic phase with mean crystallite sizes ranging from 20 to 50 nm. Eu3+ doping changes the structure from monoclinic to mixed phase of monoclinic and cubic. SEM micrographs shows the products are foamy, agglomerated and fluffy in nature due to the large amount of gases liberated during combustion reaction. Upon 254 nm excitation the photoluminescence of the Gd2O3:Eu3+ particles show red emission at 611 nm corresponding to D-5(0)-> F-7(2) transition. It is observed that PL intensity increases with calcination temperature. This might be attributed to better crystallization and eliminates the defects, which serve as centers of non-radiative relaxation for nanomaterials. It is observed that the optical energy gap (E-g) is widened with increase Eu3+ content. (C) 2010 Elsevier B.V. All rights reserved.

Total synthesis of the fungal metabolite (+/-)-acremine G: acceleration of a biomimetic Diels-Alder reaction on silica gel

A total synthesis of the bioactive tetracyclic natural product acremine G has been achieved in which a regio- and stereoselective biomimetic Diels-Alder reaction between two readily assembled building blocks, accelerated on a solid support (silica gel), forms the key step. (c) 2010 Elsevier Ltd. All rights reserved.

Synthesis Based On Cyclohexadienes .6. A New Total Synthesis Of (+/-)-Methyl Acorate And (+/-)-Methyl Epi-Acorate

A new method of construction of carbon-carbon bond is described. Thus the dianions generated from the metal-ammonia reduction of substituted benzoic acids readily undergo Michael addition with methyl crotonate resulting in synthetically useful products having a quaternary carbon. Based on this strategy, new syntheses of (+/-)-methyl acorate (14b) and (+/-)-methyl epi-corate (15) are reported.

Mechanism of gel-to-crystallite conversion process in the synthesis of nanocrystalline multinary oxides

Description of gel-to-crystallite conversion process is made towards the synthesis of nanocrystalline titanates and aluminates. Thermodynamic and kinetic factors governing the conversion of a gel to meta-stable and stable nanocrystalline products(s) are discussed. Correlations between these factors and the preparative conditions employed for the syntheses of titanates and aluminates are arrived at.

Synthesis of Reduced Metabolites of Isoflavonoids, and their Enantiomeric Forms

Isoflavonoids are naturally occurring plant derived biochemicals, which act as phytoalexins. Isoflavonoids are of interest due to their estrogenic and other potential physiological properties, particularly in mammals that typically consume isoflavonoid rich nutrients such as soy and red clover. The literature review of this thesis mainly focuses on the reduced metabolites of hydroxy and/or methoxy substituted isoflavones with four groups: isoflavan-4-ols, isoflav-3-enes, isoflavans and α-methyldeoxybenzoins (1,2-diarylpropan-1-ones), which are all reduced metabolites of food derived isoflavones in mammals. Related isoflavan-4-ones are briefly discussed. Results of an extensive survey of the literature concerning the synthesis of polyhydroxy- or methoxysubstituted isoflavonoids and especially asymmetric approaches are discussed. The experimental section describes new synthetic methods to prepare polyphenolic reduced isoflavonoid structures such as isoflav-3-enes, isoflavan-4-ones, cis- and trans-isoflavan-4-ols, 1,2-diarylpropan-1-ones and isoflavans by various hydride reagents and hydrogenations. The specific reactivity differences of various hydride reagents toward isoflavonoids are discussed. The first enantioselective synthesis of natural (S)-(-)-equol and the opposite enantiomer (R)-(+)-equol is also described by the asymmetric iridium PHOX catalysed hydrogenation of isoflav-3-enes. Both of these equol enantiomers are found to possess biological activity in mammals due to estrogen receptor binding activity. The natural enantiomer prefers estrogen receptor β and the R-enantiomer prefers the estrogen receptor α. Also the precursor, isoflav-3-ene, is found to possess positive biological effects on mammals. In connection with the synthetic work, the (S)-(-)-equol was discovered from serum of ewes after isoflavone rich red clover feeding. The chiral HPLC method was developed to identify natural equol enantiomer for the first time in this species. The first synthesis of natural isoflavonoid (R)-(-)-angolensin and its enantiomer (S)-(+)-angolensin is desribed by the use of recyclable chiral auxiliaries (chiral pseudoephedrines). The method offers a general approach also to other natural polyphenolic 1,2-diarylpropan-1-ones and to further study isoflavonoid metabolism in human and other mammals. The absolute configurations of these new chiral isoflavonoid metabolites were determined by X-ray spectroscopy. Also thorough NMR and MS analysis of synthesised structures are presented.