Coordination asymmetry in μ-oxido divanadium complexes: Development of synthetic protocols

This brief review deals with the development of a general protocol for the synthesis of μ-oxido divanadium(V) compounds [LOV^V-(μ-O)-V^VO(Salen)] (L = L¹–L⁵) (1–5) incorporating coordination asymmetry. One of the vanadium centers in these compounds has an octahedral environment, completed by tetradentate Salen ligand, while the other center has a square pyramidal geometry, made up of tridentate biprotic Schiff-base ligands (H₂L^1–5) with ONO (1–3) and ONS (4, 5) type donor combinations. Single crystal X-ray diffraction, ESI-MS, and multi-nuclear NMR (¹H and ⁵¹V) spectroscopy have been used extensively for the characterization of these compounds. The V₂O₃ core in these compounds, save 3, has a rare type of twist-angular structure. The V(1)?V(2) separations (3.7921(7)–3.3084(6) Å) are by far the largest in these compounds compared to their peers containing a V₂O₃ core. The molecules retain their unsymmetrical binuclear structures also in solution as established by NMR spectroscopy. The mixed-oxidation compound (ImH)[L⁴OV^IV-(μ-O)-V^VOL⁵] 7 containing two dissimilar ligands has a V₂O₃ core with a syn-angular structure and exhibits crystallographically imposed mirror symmetry due to static disorder. In solution of donor solvents, this angular core structure changes into a linear one (anti-linear) by accepting solvents in to the vacant coordination site of the metal centers. Finally, the protocol for the synthesis of heterobimetallic compounds with vanadium(V) and Re(VII) combination flanked by a single μ-oxido bridge has been developed in which the precursor complexes [V^IVOL^6,7] (H₂L^6,7 are Salen type of ligands) are allowed to oxidize aerially in the presence of added perrhenate anion. The oxidized [V^VOL^6,7]⁺ species hold the ReO₄^? anion in the vacant coordination site of the metal ion, trans to the terminal oxido group, thus generating the V^V–O–Re^VII moiety in the heterobimetallic compounds (9 and 10). Both X-ray crystallography and ¹H NMR spectroscopy have been used to establish the identities of these compounds. In compound 9, the Re(1)–O(11)–V(1) bridge angle is barely linear (170.2(3)°) with a Re?V separation of 3.9647(9) Å. The redox behavior of 9 and 10 are quite interesting, each undergoing two reductions both in the positive potential range at E_1/2 = 0.59 and 0.16 V vs. Ag/AgCl reference and have single-electron stoichiometry, confirmed by constant potential coulometry.     

Interaction of [VIVO(acac)2] with Human Serum Transferrin and Albumin

[VO(acac)₂] is a remarkable vanadium compound and has potential as a therapeutic drug. It is important to clarify how it is transported in blood, but the reports addressing its binding to serum proteins have been contradictory. We use several spectroscopic and mass spectrometric techniques (ESI and MALDI‐TOF), small‐angle X‐ray scattering and size exclusion chromatography (SEC) to characterize solutions containing [VO(acac)₂] and either human serum apotransferrin (apoHTF) or albumin (HSA). DFT and modeling protein calculations are carried out to disclose the type of binding to apoHTF. The measured circular dichroism spectra, SEC and MALDI‐TOF data clearly prove that at least two VO–acac moieties may bind to apoHTF, most probably forming [V^IVO(acac)(apoHTF)] complexes with residues of the HTF binding sites. No indication of binding of [VO(acac)₂] to HSA is obtained. We conclude that V^IVO–acac species may be transported in blood by transferrin. At very low complex concentrations speciation calculations suggest that [(VO)(apoHTF)] species form.     

Evaluation of the binding of oxovanadium(IV) to human serum albumin

The understanding of the biotransformations of insulin mimetic vanadium complexes in human blood and its transport to target cells is an essential issue in the development of more effective drugs. We present the study of the interaction of oxovanadium(iv) with human serum albumin (HSA) by electron paramagnetic resonance (EPR), circular dichroism (CD) and visible absorption spectroscopy. Metal competition studies were done using Cu(II) and Zn(II) as metal probes. The results show that V(IV)O occupies two types of binding sites in albumin, which compete not only with each other, but also with hydrolysis of the metal ion. In one of the sites the resulting V(IV)O-HSA complex has a weak visible CD signal and its X-band EPR spectrum may be easily measured. This was assigned to amino acid side chains of the ATCUN site. The other binding site shows stronger signals in the CD in the visible range, but has a hardly measurable EPR signal; it is assigned to the multi metal binding site (MBS) of HSA. Studies with fatted and defatted albumin show the complexity of the system since conformational changes, induced by the binding of fatty acids, decrease the ability of V(IV)O to bind albumin. The possibility and importance of ternary complex formation between V(IV)O, HSA and several drug candidates - maltol (mal), picolinic acid (pic), 2-hydroxypyridine-N-oxide (hpno) and 1,2-dimethyl-3-hydroxy-4(1H)-pyridinone (dhp) was also evaluated. In the presence of maltol the CD and EPR spectra significantly change, indicating the formation of ternary VO-HSA-maltol complexes. Modeling studies with amino acids and peptides were used to propose binding modes. Based on quantitative RT EPR measurements and CD data, it was concluded that in the systems with mal, pic, hpno, and dhp (V(IV)OL(2))(n)(HSA) species form, where the maximum value for n is at least 6 (mal, pic). The degree of formation of the ternary species, corresponding to the reaction V(IV)OL(2) + HSA -->/<-- V(IV)OL(2)(HSA) is hpno > pic ≥ mal > dhp. (V(IV)OL)(n)(HSA) type complexes are detected exclusively with pic. Based on the spectroscopic studies we propose that in the (V(IV)OL(2))(n)(HSA) species the protein bounds to vanadium through the histidine side chains.     

Studies on Cu(II) ternary complexes involving an aminopenicillin drug and imidazole containing ligands

Equilibrium studies on the ternary complex systems involving ampicillin (amp) as ligand (A) and imidazole containing ligands viz., imidazole (Him), benzimidazole (Hbim), histamine (Hist) and histidine (His) as ligands (B) at 37 °C and I = 0.15 mol dm^?3 (NaClO₄) show the presence of CuABH, CuAB and CuAB₂. The proton in the CuABH species is attached to ligand A. In the ternary complexes the ligand, amp(A) binds the metal ion via amino nitrogen and carbonyl oxygen atom. The CuAB (B = Hist/His)/CuAB₂ (B = Him/Hbim) species have also been isolated and the analytical data confirmed its formation. Non-electrolytic behavior and monomeric type of chelates have been assessed from their low conductance and magnetic susceptibility values. The electronic and vibrational spectral results were interpreted to find the mode of binding of ligands to metal and geometry of the complexes. This is also supported by the g tensor values calculated from ESR spectra. The thermal behaviour of complexes were studied by TGA/DTA. The redox behavior of the complexes has been studied by cyclic voltammetry. The antimicrobial activity and CT DNA cleavage study of the complexes show higher activity for ternary complexes.     

The n.m.r. of paramagnetic complexes of vanadyl acetylacetonate with organic phosphites and hydroperoxides

The vanadium IV ion in vanadyl acetylacetonate (V^IV) forms labile paramagnetic complexes with organic phosphites in the first coordination sphere. The enthalpy of complex formation between V^IV and triphenyl phosphite was 2.6 kcal mol^?1. Complex formation enthalpies ΔH and the activation energies E of ligand (hydroperoxide) escape from the metal ion sphere were determined from the temperature dependence of paramagnetic broadening of the n.m.r. lines of hydroperoxides in the presence of vanadyl acetylacetonate. At low temperatures the phosphite sharply weakens the bond between the metal ion and hydroperoxide in the second coordination sphere (ΔH decreases fivefold). Taken in excess, phosphite displaces the hydroperoxide molecules from the coordination sphere of the V^IV ion and thus blocks it. The observed n.m.r. characteristics of the paramagnetic complexes explain, on the model level, the kinetic regularities of the reaction of hydroperoxides with phosphite catalysed by transient metal ions.     

Volumetric study of (2-methoxyethanol + tetrahydrofuran + cyclohexane) at T=298.15 K

The excess molar volumes V_m^E at T=298.15 have been determined in the whole composition domain for (2-methoxyethanol + tetrahydrofuran + cyclohexane) and for the parent binary mixtures. Data on V_m^E are also reported for (2-ethoxyethanol + cyclohexane). All binaries showed positive V_m^E values, small for (methoxyethanol + tetrahydrofuran) and large for the other ones. The ternary V_m^E surface is always positive and exhibits a smooth trend with a maximum corresponding to the binary (2-methoxyethanol + cyclohexane). The capabilities of various models of either predicting or reproducing the ternary data have been compared. The behaviour of V_m^E and of the excess apparent molar volume of the components is discussed in both binary and ternary mixtures. The results suggest that hydrogen bonding decreases with alcohol dilution and increases with the tetrahydrofuran content in the ternary solutions.     

Supramolecular hybrid composites of metalloporphyrins and fullerene encapsulated in the ordered nano-channels of FSM-16 as oxygen carriers,and photo-catalysis for selective propene oxidation towards acetone

The planar oxomolybdenum(IV) and Fe(II) tetraphenylporphyrins (tpp) and fullerene C₆₀ are encapsulated by monolayer dispersion technique in the mesoporous ordered channels(2.7, 4.7 nm diameter) of FSM-16. They exhibit a stoichiometric adsorption of O₂ at 300 K and 50–250 Torr forming a 1:1 dioxygen complexes(ν(O–O)=928 and 1025 cm^-1) with Mo^IVO(tpp) and Fe^II(tpp) entrapped in FSM-16, although the Mo(=O) and Fe porphyrins are inactive for O₂ uptake in crystal and solution. The mesoporous cylindrical channels of FSM-16 act as the confined hydrophobic circumstances to accommodate isolated Mo and Fe porphyrins and prevent the irreversible formation of a paramagnetic μ-oxo dimer, similar to the picket-fenced porphyrin complexes such as Mo^IVO(tmp)=5,10,15,20-tetramesitylporphyrin). The reversible removal of O₂ bound with the Mo and Fe porphyrins proceeds at 300 K by high-pressure Hg photoirradiation. The isotopic labeling tracer studies reveal that they are catalytically active for oxygen transfer via fullerene C₆₀ in the selective photo-oxidation of propene towards acetone at 303–393 K.     

The investigation of the interactions between CdSe quantum dots and human serum albumin by resonance Rayleigh scattering and second-order scattering spectra

Human serum albumin (HSA) was the most abundant protein in human plasma and has significant physiological function. In Tris–HCl buffer solution (pH 7.4), water-soluble semiconductor CdSe quantum dots (QDs) reacted with HSA and the products resulted in a great enhancement of the intensity of resonance Rayleigh scattering (RRS) and second-order scattering (SOS). Based on this, a new method was developed to investigate the interactions between QDs and HSA. The parameters with regard to determination were optimized, and the reaction mechanism was discussed. Under optimal conditions, the increments of scattering intensity (ΔI) were directly proportional to the concentrations of HSA in the range of 0.4–48.0 μmol L^?1. The detection limits were 0.10 μmol L^?1 for RRS method and 0.25 μmol L^?1 for SOS method. The proposed method was sensitive, simple and rapid. It has been successfully applied to the determination of HSA in human urine samples. Analytical results obtained with this novel assay were satisfactory.     

Oxidovanadium (IV) and iron (III) complexes with O2N2 donor linkage as plausible antidiabetic candidates: Synthesis,structural characterizations,glucose uptake and model biological media studies

With the upsurging cases of type II diabetic patients, the demand for safe and effective oral antidiabetic drugs is also increasing. Coordination complexes have proven their mettle as efficient oral drug candidates, which thereby motivated us in this work to design new transition metal complexes as plausible candidates for the treatment of diabetes. A reduced salen ligand, {H₂(hpdbal)₂-an} ( 1 ) derived vanadium (IV) and iron (III) complexes, namely, [V^IVO{(hpdbal)₂-an}] ( 2 ) and [{Fe^III (OH₂)((hpdbal)₂-an)}₂ μ₂-SO₄] ( 3 ) were synthesized in this study. The newly obtained ligand and complexes were characterized using usual analytical and spectroscopic techniques. The potential of these compounds in inducing increased glucose uptake by diabetic cells were studied by using insulin resistant HepG2 cells as model diabetic cells and 2-NBDG molecule as a D-glucose analogue and fluorescent tracker. The cells added with the vanadium (IV) complex 3 induced significant NBDG uptake of 95.4% which was higher than that induced by metformin, the standard antidiabetic drug. To elucidate the behavior of the complexes in biological media, model solution studies were conducted with a wide range of pH conditions and protein bovine serum albumin (BSA). The complexes demonstrated effective binding with BSA which was concluded through spectroscopic titration studies and were also found to be sufficiently stable over physiological pH conditions. The study can thus prove to be beneficial in the quest for new antidiabetic drugs.     

Studies on some ternary complexes of copper(II) involving an amino penicillin drug

Multiple equilibrium studies by pH-metric measurements in the ternary copper(II) complexes with ampicillin(amp) as ligand A and glycine(gly), dl-2-aminobutanoic acid(2aba), dl-3-aminobutanoic acid(3aba), 1,2-diaminopropane(dp), 1,3-diaminopropane(tp), dl-2,3-diaminopropanoic acid(dapa), dl-2,4-diaminobutanoic acid(daba) & dl-2,5-diaminopentanoic acid(ornithine)(orn) as ligands B show the presence of CuABH, CuAB or CuAH?1 B ternary complex species. In the CuAB species the binding of the ligands A and B is similar to their binding in their respective binary complexes. In CuABH_?1 species the deprotonation occurs with amp(A) ligand. The Δlog K values indicate higher stabilities for the ternary complexes than the binary species. The CuAB species with B = gly, 2aba, dapa & orn have been isolated and characterized. The conductivity measurements indicate that the complexes are non-electrolytes. Magnetic susceptibility and electronic spectral data suggest a square pyramidal geometry for CuAB with B = gly/2aba complexes and distorted octahedral geometry for CuAB with B = dapa/orn. The vibrational spectra are interpreted to find the mode of binding of ligand to metal. The TG/DTA studies reveal that the complexes decompose in three steps, indicating non-involvement of hydrated or coordinated water molecules in the complex. The cyclic voltammograms indicate a quasi reversible Cu²⁺/Cu⁺ couple. The antimicrobial activity and CT-DNA cleavage ability of the complexes show higher activity for ternary complexes.     

Understanding the nature of vanadium species supported on activated carbon and its catalytic properties in the aerobic oxidation of aromatic alcohols

Vanadium oxide catalysts supported on activated carbon (V/AC) with V loadings ranging from 1 to 20 wt.% were prepared by a wet-impregnation method. Various physicochemical characterization techniques, including nitrogen physisorption, X-ray diffraction (XRD), Raman spectroscopy, X-ray absorption (XANES and EXAFS), X-ray photoelectron spectroscopy (XPS), and electron spin resonance (ESR), were employed to understand the nature of vanadium species on activated carbon. The results revealed that vanadium oxide mainly existed in a highly dispersed state for 10 wt.% or less vanadium loadings; a large amount of vanadium resulted in aggregated microcrystalline phase. Vanadium species on activated carbon surface showed a similar local coordination structure to that of NH₄VO₃ with a distorted tetrahedral symmetry at low vanadium loadings, whereas octahedral coordination was dominant at high vanadium loadings (>10 wt.%). All V/AC samples showed V⁵⁺ as the major oxidation state. Nevertheless, V⁴⁺ centered in a distorted tetrahedral symmetry could be detected at a vanadium loading greater than 4 wt.%. The catalytic activity for the benzyl alcohol oxidation largely depended on the dispersion, oxidation state, and local coordination of vanadium oxides on activated carbon. Highly dispersed vanadium (5+) species with a distorted tetrahedral coordination were postulated to account for the excellent catalytic performances of V/AC catalysts (TOF = 39.1 h^?1).     

Unveiling VIVO2+ Binding Modes to Human Serum Albumins by an Integrated Spectroscopic–Computational Approach

Human serum albumin (HSA) is involved in the transport of metal ions and potential metallodrugs. Depending on the metal, several sites are available, among which are N-terminal (NTS) and multi-metal binding sites (MBS). Despite the large number of X-ray determinations for albumins, only one structure with Zn²⁺ is available. In this work, the binding to HSA of the V^IVO²⁺ ion was studied by an integrated approach based on spectroscopic and computational methods, which allowed the systems to be characterized even in the absence of X-ray analysis. The behavior depends on the type of albumin, defatted (HSA^d) or fatted (HSA^f). With HSA^d ‘primary’ and ‘secondary’ sites were revealed, NTS with (His3, His9, Asp13, Asp255) and MBS with (His67, His247, Asp249, Asn99 or H₂O); with increasing the ratio V^IVO²⁺/HSA^d, ‘tertiary’ sites, with one His-N and other donors (Asp/Glu-O or carbonyl-O) are populated. With HSA^f, fatty acids (FAs) cause a rotation of the subdomains IA and IIA, which results in the formation of a dinuclear ferromagnetic adduct (V^IVO)₂^D(HSA^f) with a μ_1,1-Asp249 and the binding of His247, Glu100, Glu252, and His67 or Asn99. FAs hinder also the binding of V^IVO²⁺ to the MBS.     

Probing the binding of fluoxetine hydrochloride to human serum albumin by multispectroscopic techniques

The interaction between human serum albumin (HSA) and fluoxetine hydrochloride (FLX) have been studied by using different spectroscopic techniques viz., fluorescence, UV–vis absorption, circular dichroism and FTIR under simulated physiological conditions. Fluorescence results revealed the presence of static type of quenching mechanism in the binding of FLX to HSA. The values of binding constant, K of FLX-HSA were evaluated at 289, 300 and 310 K and were found to be 1.90 × 10³, 1.68 × 10³ and 1.45 × 10³ M^?1, respectively. The number of binding sites, n was noticed to be almost equal to unity thereby indicating the presence of a single class of binding site for FLX on HSA. Based on the thermodynamic parameters, ΔH⁰ and ΔS⁰ nature of binding forces operating between HSA and FLX were proposed. Spectral results revealed the conformational changes in protein upon interaction. Displacement studies indicated the site I as the main binding site for FLX on HSA. The effect of common ions on the binding of FLX to HSA was also investigated.     

Identification of pyrazosulfuron-ethyl binding affinity and binding site subdomain IIA in human serum albumin by spectroscopic methods

Pyrazosulfuron-ethyl (PY) is a sulfonylurea herbicide developed by DuPont which has been widely used for weed control in cereals. The determination of PY binding affinity and binding site in human serum albumin (HSA) by spectroscopic methods is the subject of this work. From the fluorescence emission, circular dichroism and three-dimensional fluorescence results, the interaction of PY with HSA caused secondary structure changes in the protein. Fluorescence data demonstrated that the quenching of HSA fluorescence by PY was the result of the formation of HSA–PY complex at 1:1 molar ratio, a static mechanism was confirmed to lead to the fluorescence quenching. Hydrophobic probe 8-anilino-1-naphthalenesulfonic acid (ANS) displacement results show that hydrophobic patches are the major sites for PY binding on HSA. The thermodynamic parameters ΔH° and ΔS° were calculated to be ?36.32 kJ mol^?1 and ?35.91 J mol^?1 K^?1, which illustrated van der Waals forces and hydrogen bonds interactions were the dominant intermolecular force in stabilizing the complex. Also, site marker competitive experiments showed that the binding of PY to HSA took place primarily in subdomain IIA (Sudlow's site I). What presented in this paper binding research enriches our knowledge of the interaction between sulfonylurea herbicides and the physiologically important protein HSA.     

Mass spectrometric study of the dissociation of Group XI metal complexes with fatty acids and glycerolipids: Ag2H+ and Cu2H+ ion formation in the presence of a double bond

Results of mass spectrometric studies are reported for the collisional dissociation of Group XI (Cu, Ag, Au) metal ion complexes with fatty acids (palmitic, oleic, linoleic and α-linolenic) and glycerolipids. Remarkably, the formation of M₂H⁺ ions (M = Cu, Ag) is observed as a dissociation product of the ion complexes containing more than one metal cation and only if the lipid in the complex contains a double bond. Ag₂H⁺ is formed as the main dissociation channel for all three of the fatty acids containing double bonds that were investigated while Cu₂H⁺ is formed with one of the fatty acids and, although abundant, is not the dominant dissociation channel. Also, Cu(I) and Ag(I) ion complexes were observed with glycerolipids (including triacylglycerols and glycerophospholipids) containing either saturated or unsaturated fatty acid substituents. Interestingly, Ag₂H⁺ ion is formed in a major fragmentation channel with the lipids that are able to form the complex with two metal cations (triacylglycerols and glycerophosphoglycerols), while lipids containing a fixed positive charge (glycerophospocholines) complex only with a single metal cation. The formation of Ag₂H⁺ ion is a significant dissociation channel from the complex ion [Ag₂(L–H)]⁺ where L = Glycerophospholipid (GP) (18:1/18:1). Cu(I) also forms complexes of two metal cations with glycerophospholipids but these do not produce Cu₂H⁺ upon dissociation. Rather organic fragments, not containing Cu(I), are formed, perhaps due to different interactions of these metal cations with lipids resulting from the much smaller ionic radius of Cu(I) compared to Ag(I).     

Studies on the interaction between imidacloprid and human serum albumin: Spectroscopic approach

The interaction between imidacloprid (IMI) and human serum albumin (HSA) was investigated using fluorescence and UV/vis absorption spectroscopy. The experimental results showed that the fluorescence quenching of HSA by IMI was a result of the formation of IMI–HSA complex; static quenching was confirmed to result in the fluorescence quenching. The apparent binding constant K_A between IMI and HSA at three differences were obtained to be 1.51 × 10⁴, 1.58 × 10⁴, and 2.19 × 10⁴ L mol^?1, respectively. The thermodynamic parameters, ΔH° and ΔS° were estimated to be 28.44 kJ mol^?1, 174.76 J mol^?1 K^?1 according to the van’t Hoff equation. Hydrophobic interactions played a major role in stabilizing the complex. The distance r between donor (HSA) and acceptor (IMI) was obtained according to fluorescence resonance energy transfer. The effect of IMI on the conformation of HSA was analyzed using synchronous fluorescence spectroscopy CD and three-dimensional fluorescence spectra, the environment around Trp and Tyr residues were altered.     

Ultrasensitive determination of serum albumin using resonance light scattering based on ZnS-polyacrylic acid nanoparticles

ZnS-polyacrylic acid (ZnS-PAA) was prepared by an in situ polymerization method using nano-ZnS as core in the presence of acrylic acid (AA), and ZnS-PAA nanoparticles was characterized by ultraviolet spectrometry (UV) and transmission electron microscopy (TEM). Based on the significant increase of the resonance light scattering (RLS) intensity with the interaction between nanoparticles and serum albumin, RLS method was developed for the sensitive determination of serum albumin (BSA and HSA). Under optimum conditions, the change of the intensity (ΔI) of the RLS spectra at λ = 392 nm was linearly proportional to the concentration of BSA and HSA. The linear range was 1–100 ng mL^?1 for HSA and 1–120 ng mL^?1 for BSA, and the limit of detection (LOD) was 0.4 ng mL^?1 for HSA and 0.5 ng mL^?1 for BSA. This method proved to be very sensitive, rapid, simple and tolerant of most interfering substances.     

Conformational and stereoelectronic investigation of chloromethyl methyl sulfide and its sulfinyl and sulfonyl analogs

Three compounds based on polyoxometalate building blocks, [Cu(en)₂]{[Cu(en)₂]₂[Mo^VI₅Mo^V₃V^IV₈O₄₀(PO₄)]} · 4H₂O (1), [Co(en)₂]{[Co(en)₂]₂[HMo^VI₄Mo^V₄V^IV₈O₄₀(PO₄)]} · 5H₂O (2) and [Ni(en)₂]{[Ni(en)₂]₂[Mo^VI₅Mo^V₃V^IV₈O₄₀(VO₄)]} · 2H₂O (3) (en = ethylenediamine), have been synthesized and characterized by elemental analysis, IR, XPS, XRD, TGA and single-crystal X-ray diffraction analysis. The result of structure determination shows that isomorphic compounds 1, 2 and 3 feature a one-dimensional chain built from the reduced tetra-capped pseudo-Keggin polyoxoanion, which is further interconnected by [M(en)₂]²⁺ (M = Cu, Co and Ni) groups via the terminal oxygen atoms of polyoxoanions. The crystal data for these compounds are the following: 1, monoclinic, space group C2/c, a = 26.702(3) Å, b = 13.4539(14) Å, c = 19.5987(19) Å, β = 108.650(2)°, V = 6671.0(12) Å³, Z = 4; 2, monoclinic, space group C2/c, a = 26.244(3) Å, b = 13.5070(17) Å, c = 19.581(3) Å, β = 106.881(2)°, V = 6641.8(15) Å³, Z = 4; 3, monoclinic, space group C2/c, a = 26.2789(15) Å, b = 13.5408(6) Å, c = 19.6312(9) Å, β = 106.2590(10)°, V = 6706.1(6) Å³, Z = 4. Variable-temperature magnetic susceptibility measurements of compounds 1 and 3 reveal the feature of antiferromagnetic exchange in these compounds.     

Kinetics and mechanism of the chromic oxidation of 3-O-methyl-d-glucopyranose

The oxidation of 3-O-methyl-d-glucopyranose (Glc3Me) by Cr^VI in acid medium yields Cr^III, formic acid and 2-O-methyl-d-arabinose as final products when a 50-times or higher excess of Glc3Me over Cr^VI is used. The redox reaction takes place through the combination of Cr^VI → Cr^IV → Cr^II and Cr^VI → Cr^IV → Cr^III pathways. Intermediacy of free radicals and Cr^II in the reaction was demonstrated by the observation of induced polymerization of acrylamide and detection of CrO₂²⁺ formed by reaction of Cr^II with O₂. Intermediate oxo-Cr^V–Glc3Me species were detected by EPR spectroscopy. In 0.3–0.5 mol/L HClO₄, intermediate Cr^V rapidly decompose to the reaction products, while, at pH 5.5–7.5, where the redox processes are very slow, five-coordinate Cr^V bis-chelates of the pyranose and furanose forms of Glc3Me remain more than 15 h in solution. The C1–C2 bond cleavage of Glc3Me upon reaction with Cr^VI distinguishes this derivative from glucose, which is oxidized to gluconic acid.     

Crystallisation of some mixed Na/V and K/V fluorides by solvothermal methods

Single crystals of several phases in the Na–V–(O)F and K–V–(O)F systems have been grown using a mild solvothermal route in water/ethylene glycol. At a temperature of 100 °C the V⁴⁺-containing oxyfluoride phases Na₄V₂O₂F₈ and K₂VOF₄ are prepared, exhibiting dimeric and chain-like vanadium oxyfluoride units, respectively. On raising the reaction temperature to 220 °C reduction to V³⁺ occurs, and three different two-dimensional sheet structures are crystallised, NaVF₄, KVF₄ and K₅V₃F₁₄. Precise crystal structures are reported for the latter two, which represent members of the Dion–Jacobson and Chiolite families, respectively.