Vanadyl compounds

Similar complexes are formed between poly(viayl alcohol) and titanium lactate (96,101), titanyl sulfate (102), or vanadyl compounds (103). 

The same group showed (Baumeister et al., 1997) that addition of vanadyl compounds as cocatalysts solved a recurring problem in hydrogenations the build-up of arylhydroxylamine intermediates, which can lead to runaway reaction conditions. Vanadyl complexes catalyse the disproportionation of aiylhydroxylamines and, hence, prevent their build-up during... 

Vanadyl compounds hydrolyze much more easily than any other metal chelates of the first transition series, and in some conditions the vanadyl 1 1 chelates prefer combination with hydroxyl to a second ligand molecule.385 Unless otherwise stated formation constants fixyz presented in this review correspond to the reaction shown in equation (15). 

The Crystal Spectrum of V0S04-5H20 and Spectral Properties of other Vanadyl Compounds.—The electronic absorption spectra of a single crystal of VOSO4-5H2O have been determined for light polarized both parallel and perpendicular to the molecular V-O axis. These spectra are shown in Big. 5. It is important to note that the positions of the absorption maxima... 

Magnetic Properties of Vanadyl Compounds.— The paramagnetic resonance of V02+ has been investigated for a number of complexes and < g > values are all very nearly 2.7 14 15 24-29 A survey of g values for different complexes is given in Table V. In the molecular orbital description of VO(HiO)J, the formulas for the g values become... 

Fish and Komlenic (1984) and Fish et al. (1984) have demonstrated that the vanadyl compounds associated with apparently high molecular weight fractions (2000+) observed by SEC-HPLC can, to a certain extent, be extracted as low-molecular-weight compounds with an aqueous pyridine solution. Nearly all of these extracted vanadyl compounds from either the... 

Percent Vanadium in Each Molecular Weight Category of Vanadyl Compounds in the Four Heavy Crude Petroleums and Their Asphaltenes, Maltenes, Asphaltene Polar Extracts, and Extracted Asphaltenes by 50/100/1000 A SEC-HPLC-GFAA Analysis"- ... 

Shioda, N., Ishigami, T., Han, F., Moriguchi, S., Shibuya, M., Iwabuchi, Y., and Fukunaga, K. (2007). Activation of phosphatidylinositol 3-kinase/protein kinase B pathway by a vanadyl compound mediates its neuroprotective effect in mouse brain ischemia. Neuroscience 148, 221-229. 

In vanadyl compounds the characteristic coordination group of is a very distorted octahedron. The metal atom is displaced from the centre towards the 0 atom and the sixth ligand is very weakly bonded, (a), or in some cases not within bonding distance (b). The coordination is therefore more realistically described as tetragonal pyamidSl see also the structures of oxy-compounds of V (p. 467). 

Examples of vanadyl compounds in crude oil. Left porphinogenic (vanadyldesoxiphyllerythrin) middle and right, non-porhinogenic. 

Extraction.3 — The method used in extracting vanadium from its ores varies widely with the nature and richness of the ore and the value of the by-products. The difficulties encountered are mainly in connection with the purification of vanadium from uranium, aluminium, iron, and silica. It is probable that no two mills use exactly the same process. In general the methods 4 use (1) an acid method, producing soluble vanadyl compounds or (2) an alkali method, producing soluble alkali vamwlates. The following outline methods illustrate the general principles employed —... 

VO " bonds most effectively to electronegative atoms, e.g. F, Cl, O and N, and bonds to S and P are also known. Fluoro and oxygen complexes are specially stable. Complexes with oxygen donors follow the expanded Irving-Williams series VO >Cu >Ni >Co > > Mn. The presence of one or two nitrogen donors places VO " lower in the series. Vanadyl compounds hydrolyze much more easily than any other metal chelates of the first transition series, and in some conditions the vanadyl 1 1 chelates prefer combination with hydroxyl to a second ligand molecule. Unless otherwise stated formation constants presented in this review correspond to the reaction shown in equation (15). 

Macrocycle deformations are observed between 640 and 120 cm in NPcVO and in the range 510-350 cm in Pc VO the highest frequencies correspond to the ring deformations of benzene and pyrrole, while the lowest are macrocycle ring deformations. Bands at 570 and 457cm in PcVO and the band at 537 cm of NPcVO are characteristic of each macrocycle. Bands at 372, 308 and 235 cm observed only in the vanadyl compounds correspond to VO-N vibrations. Other bands in this region are mainly due to macrocycle ring out of plane deformations. 

A microporous structure of one-dimensional hydrophobic channels lined by methylene groups is formed by CozCOj-GHj-POa) H O [120], but the vanadyl compound [V0]2[03p-CH2-P03l 4H2O has a layer structure. Phosphonates form various types of cavity structures [121,122],... 

Fish, R.H., Komlenic, J.J., (1984), Molecular characterization and profile identification of vanadyl compounds in heavy crude petroleums by liquid chromatography/graphite furnace atomic absorption spectrometry. Anal. Chem. 56, 510-517. 

The vanadyl compounds (VO ) produce EPR signals less intense (Fig. 3c), with anisotropic g-factor and hf splitting. For the vanadium in the presence of an external magnetic field, the interaction of electron spin (5 = 1/2) with the nucleus W (/ = 7/2) has 16 possible states distributed between the two values S M = + j and = - )/as shown in diagram (Fig. 9). 

Fig. 9. Schematic diagram of the hf splitting for unpaired electron interaction with a nucleus of nuclear spin 1=7/2 and allowed transitions to vanadyl compounds (VO2+).

Transport of small, neutral V(IV) complexes is thought to take place via a passive diffusion process. Crans and coworkers used a combination of ICP-AES and EPR to track and quantify the membrane transport of VO(acac)2 and VO(ma)2, and observe the redox chemistry and interactions with the erythrocyte membrane of these compounds [82]. The intensity of the central signal of the room-temperature EPR spectra of VO(acac)2 and VO(ma)2 was used to quantify the amount of V(IV) species during stability tests or membrane transport experiments. For experiments with erythrocytes, transport of the vanadyl compounds into the cytoplasm yielded a highly anisotropic spectrum due to binding of the vanadyl species with cellular components. ICP-AES was used to quantify the total cytosolic vanadium. 

The first application of higher-resolution pulsed EPR techniques was reported by Fukui et al. in 1995, who reported insights into the in-vivo coordination structure of vanadyl ions in rat kidney and liver, taken from animals administered a chronic i.v. dose of VOSO4 [69]. ESEEM spectroscopy (2-pulse) was used to detect and quantify small superhyperfine coupling constants of vanadyl compounds in these organs. 

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