104 research outputs found
Oxidation of benzoin catalyzed by oxovanadium (IV) schiff base complexes
BACKGROUND: The oxidative transformation of benzoin to benzil has been accomplished by the use of a wide
variety of reagents or catalysts and different reaction procedures. The conventional oxidizing agents yielded mainly
benzaldehyde or/and benzoic acid and only a trace amount of benzil. The limits of practical utilization of these
reagents involves the use of stoichiometric amounts of corrosive acids or toxic metallic reagents, which in turn
produce undesirable waste materials and required high reaction temperatures.
In recent years, vanadium complexes have attracted much attention for their potential utility as catalysts for various
types of reactions.
RESULTS: Active and selective catalytic systems of new unsymmetrical oxovanadium(IV) Schiff base complexes for
the oxidation of benzoin is reported. The Schiff base ligands are derived between 2-aminoethanol and 2-hydroxy-1-
naphthaldehyde (H2L1) or 3-ethoxy salicylaldehyde (H2L3); and 2-aminophenol and 3-ethoxysalicylaldehyde (H2L2) or
2-hydroxy-1-naphthaldehyde (H2L4). The unsymmetrical Schiff bases behave as tridentate dibasic ONO donor
ligands. Reaction of these Schiff base ligands with oxovanadyl sulphate afforded the mononuclear oxovanadium(IV)
complexes (VIVOLx.H2O), which are characterized by various physico-chemical techniques.
The catalytic oxidation activities of these complexes for benzoin were evaluated using H2O2 as an oxidant. The best
reaction conditions are obtained by considering the effect of solvent, reaction time and temperature. Under the
optimized reaction conditions, VOL4 catalyst showed high conversion (>99%) with excellent selectivity to benzil
(~100%) in a shorter reaction time compared to the other catalysts considered.
CONCLUSION: Four tridentate ONO type Schiff base ligands were synthesized. Complexation of these ligands with
vanadyl(IV) sulphate leads to the formation of new oxovanadium(IV) complexes of type VIVOL.H2O.
Elemental analyses and spectral data of the free ligands and their oxovanadium(IV) complexes were found to be in
good agreement with their structures, indicating high purity of all the compounds.
Oxovanadium complexes were screened for the oxidation of benzoin to benzil using H2O2 as oxidant. The effect of
time, solvent and temperature were optimized to obtain maximum yield. The catalytic activity results demonstrate
that these catalytic systems are both highly active and selective for the oxidation of benzoin under mild reaction
conditions.Web of Scienc
Species-Specific Expansion and Molecular Evolution of the 3-hydroxy-3-methylglutaryl Coenzyme A Reductase (HMGR) Gene Family in Plants
Kazakh dandelion (Taraxacum kok-saghyz, Tk) is a rubber-producing plant currently being investigated as a source of natural rubber for industrial applications. Like many other isoprenoids, rubber is a downstream product of the mevalonate pathway. The 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) enzyme catalyzes the conversion of 3-hydroxy-3-methylglutaryl-CoA to mevalonic acid, a key regulatory step in the MVA pathway. Such regulated steps provide targets for increases in isoprenoid and rubber contents via genetic engineering to increase enzyme activities. In this study, we identify a TkHMGR1 gene that is highly expressed in the roots of Kazakh dandelion, the main tissue where rubber is synthesized and stored. This finding paves the way for further molecular and genetic studies of the TkHMGR1 gene, and its role in rubber biosynthesis in Tk and other rubber-producing plants
X-Ray Phase-Contrast Tomography of Renal Ischemia-Reperfusion Damage
Purpose: The aim of the study was to investigate microstructural changes occurring in unilateral renal ischemia-reperfusion injury in a murine animal model using synchrotron radiation. Material and Methods: The effects of renal ischemia-reperfusion were investigated in a murine animal model of unilateral ischemia. Kidney samples were harvested on day 18. Grating-Based Phase-Contrast Imaging (GB-PCI) of the paraffin-embedded kidney samples was performed at a Synchrotron Radiation Facility (beam energy of 19 keV). To obtain phase information, a two-grating Talbot interferometer was used applying the phase stepping technique. The imaging system provided an effective pixel size of 7.5 mu m. The resulting attenuation and differential phase projections were tomographically reconstructed using filtered back-projection. Semi-automated segmentation and volumetry and correlation to histopathology were performed. Results: GB-PCI provided good discrimination of the cortex, outer and inner medulla in non-ischemic control kidneys. Post-ischemic kidneys showed a reduced compartmental differentiation, particularly of the outer stripe of the outer medulla, which could not be differentiated from the inner stripe. Compared to the contralateral kidney, after ischemia a volume loss was detected, while the inner medulla mainly retained its volume (ratio 0.94). Post-ischemic kidneys exhibited severe tissue damage as evidenced by tubular atrophy and dilatation, moderate inflammatory infiltration, loss of brush borders and tubular protein cylinders. Conclusion: In conclusion GB-PCI with synchrotron radiation allows for non-destructive microstructural assessment of parenchymal kidney disease and vessel architecture. If translation to lab-based approaches generates sufficient density resolution, and with a time-optimized image analysis protocol, GB-PCI may ultimately serve as a non-invasive, non-enhanced alternative for imaging of pathological changes of the kidney
Consumer willingness to pay for organic and locally grown produce on Dominica: insights into the potential for an “Organic Island”
Composição química de nozes e sementes comestíveis e sua relação com a nutrição e saúde
The genetic heterogeneity of colorectal cancer predisposition - guidelines for gene discovery
Evaluation of Cubic-Like Advanced ZnMn2O4 Electrode for High-Performance Supercapacitor Applications
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