Synthesis, spectral and electrochemical properties of cyclotriphosphazene appended with six metalloporphyrins

The metal derivatives (Co^II, Ni^II, Cu^II, Zn^II and Sn^IV) of hexaporphyrinato cyclotriphosphazene systems were prepared by treating the hexaporphyrin assembly on cyclotriphosphazene ring with the appropriate metal salt under standard metallation conditions. The complete metallation of all six porphyrin units in hexaporphyrin assembly required 10-12 h reflux as judged by the absorption spectroscopy. The metal derivatives were confirmed by molecular ion peak in mass spectra for all compounds. ³¹P and ¹H NMR spectra for Ni(II), Zn(II) and Sn(IV) derivatives and ESR spectra for Cu(II) derivative also confirmed the complete metallation of all six porphyrin units. The hexametalloporphyrin assemblies are freely soluble in common organic solvents. The spectral, electrochemical and fluorescence studies indicate that the six porphyrin units in assemblies interact very weakly and retain their individual characteristic features in the ground and excited states.     

Antioxidant and electrochemical properties of dihydroquercetin monosuccinate,the novel water-soluble bioflavonoid derivative

Dihydroquercetin monosuccinate is a synthetic derivative of native antioxidant dihydroquercetin, which has a wide spectrum of pharmacological properties. Being more soluble in water than its precursor, the novel synthetic derivative of the bioflavonoid maintains a high antioxidant activity, which is confirmed by the TEAC method and the voltammetry data. The redox transformations of dihydriquercetin monosuccinate on a graphite electrode are more complicated as compared to the parent flavonoid.     

Purification and properties of human liver monoamine oxidase

Human liver monoamine oxidase [monoamine: O₂ oxidoreductase (deaminating), E. C. 1.4.3.4] was purified by a method which does not depend on the isolation of mitochondria, and in which vacuum dialysis, during which the enzyme separates out as a yellow precipitate, is an important step in purification. By this method a final specific activity of 550 and fold purification of 40 was attained. A single peak was obtained with the analytical ultracentrifuge, and a sedimentation constant of 6.78S noted. A single active band was observed by polyacrylamide gel electrophoresis. The enzyme exhibits optimum activity at pH 8.7, with no activity below pH 5.5 or above pH 11.8. Using benzylamine hydrobromide as the substrate, in 0.05 m phosphate buffer (pH 7.4) at 27 °C, the Michaelis constant was found to be 1.7 × 10^?3m. The enzyme, which is quite stable, is a flavo-protein, as shown by absorption and fluorescence spectra. The C-terminal group is glycine. The molecular weight, as determined by SDS polyacrylamide-gel electrophoresis, is 64,000. Repeated attempts to determine the N-terminal group were unsuccessful.     

Crystal structure of Schizosaccharomyces pombe riboflavin kinase reveals a novel ATP and riboflavin-binding fold

The essential redox cofactors riboflavin monophosphate (FMN) and flavin adenine dinucleotide (FAD) are synthesised from their precursor, riboflavin, in sequential reactions by the metal-dependent riboflavin kinase and FAD synthetase. Here, we describe the 1.6A crystal structure of the Schizosaccharomyces pombe riboflavin kinase. The enzyme represents a novel family of phosphoryl transferring enzymes. It is a monomer comprising a central beta-barrel clasped on one side by two C-terminal helices that display an L-like shape. The opposite side of the beta-barrel serves as a platform for substrate binding as demonstrated by complexes with ADP and FMN. Formation of the ATP-binding site requires significant rearrangements in a short alpha-helix as compared to the substrate free form. The diphosphate moiety of ADP is covered by the glycine-rich flap I formed from parts of this alpha-helix. In contrast, no significant changes are observed upon binding of riboflavin. The ribityl side-chain might be covered by a rather flexible flap II. The unusual metal-binding site involves, in addition to the ADP phosphates, only the strictly conserved Thr45. This may explain the preference for zinc observed in vitro.     

Analysis of the domain properties of the novel cytochrome P450 RhF

The properties of the heme, flavin mononucleotide (FMN) and FeS domains of P450 RhF, from Rhodococcus sp. NCIMB 9784, expressed separately and in combination are analysed. The nucleotide preference, imidazole binding and reduction potentials of the heme and FMN domains are unaltered by their separation. The intact enzyme is monomeric and the flavin is confirmed to be FMN. The two one-electron reduction potentials of the FMN are -240 and -270 mV. The spectroscopic and thermodynamic properties of the FeS domain, masked in the intact enzyme, are revealed for the first time, confirming it as a 2Fe-2S ferredoxin with a reduction potential of -214 mV.     

Synthesis and luminescence properties of a novel blue emitting phosphor NaMgPO4:Eu2+

A novel blue‐emitting phosphor of Eu²⁺‐activated NaMgPO₄ was prepared by combustion‐assisted synthesis. Sodium dihydrogen phosphate and magnesium nitrate were used as the source of Na, P and Mg, respectively. The ratios of magnesium and phosphorus components that were dissolved into the combustion solution were changed from 1:1 to 1:1.3. Their effect on the crystallinities and photoluminescence spectra of the phosphor particles were investigated. The post‐heated phosphor particles had a broad excitation wavelength that ranged from 240 to 410 nm. The phosphor particles prepared from the combustion solution with a 1:1.2 ratio of magnesium to phosphorus had maximum emission intensity under ultraviolet excitation. The effect of doped Eu²⁺ concentration on the emission intensity of NaMgPO₄:Eu²⁺ was also investigated.     

Synthesis and luminescence properties of two novel lanthanide (III) complexes of acetophenonylcarboxymethyl sulphoxide

A novel ligand containing multiple coordinating groups (sulfinyl, carboxyl and carbonyl groups), acetophenonylcarboxymethyl sulphoxide, was synthesized. Its corresponding two lanthanide (III) binary complexes were synthesized and characterized by element analysis, molar conductivity, FT‐IR, TG‐DTA and UV spectroscopy. Results showed that the composition of these complexes was REL₃L^‐ (ClO₄)₂·3H₂O (RE = Eu (III), Tb (III); L = C₆H₅COCH₂SOCH₂COOH; L^‐ = C₆H₅COCH₂SOCH₂COO^‐). FT‐IR results indicated that acetophenonylcarboxymethyl sulphoxide was bonded with an RE (III) ion by an oxygen atom of the sulfinyl and carboxyl groups and not by an oxygen atom of the carbonyl group due to high steric hinderance. Fluorescent spectra showed that the Tb (III) complex had excellent luminescence as a result of a transfer of energy from the ligand to the excitation state energy level (⁵D₄) of Tb (III). The Eu (III) complex displayed weak luminescence, attributed to low energy transfer efficiency between the triplet state energy level of its ligand and the excited state (⁵D₀) of Eu (III). As a result, the Tb (III) complex displayed a good antenna effect for luminescence. The fluorescence decay curves of Eu (III) and Tb (III) complexes were also measured. Copyright © 2012 John Wiley & Sons, Ltd.     

Ruthenium mediated C-H activation of benzaldehyde thiosemicarbazones: Synthesis, structure and, spectral and electrochemical properties of the resulting complexes

Reaction of five 4R-benzaldehyde thiosemicarbazones (R = OCH₃, CH₃, H, Cl and NO₂) with [Ru(PPh₃)₃(CO)(H)Cl] in refluxing methanol in the presence of a base (NEt₃) affords complexes of two different types, viz. 1-R and 2-R. In the 1-R complexes the thiosemicarbazone is coordinated to ruthenium as a dianionic tridentate C,N,S-donor via C-H bond activation. Two triphenylphosphines and a carbonyl are also coordinated to ruthenium. The tricoordinated thiosemicarbazone ligand is sharing the same equatorial plane with ruthenium and the carbonyl, and the PPh₃ ligands are mutually trans. In the 2-R complexes the thiosemicarbazone ligand is coordinated to ruthenium as a monoanionic bidentate N,S-donor forming a four-membered chelate ring with a bite angle of 63.91(11)°. Two triphenylphosphines, a carbonyl and a hydride are also coordinated to ruthenium. The coordinated thiosemicarbazone ligand, carbonyl and hydride constitute one equatorial plane with the metal at the center, where the carbonyl is trans to the coordinated nitrogen of the thiosemicarbazone and the hydride is trans to the sulfur. The two triphenylphosphines are trans. Structures of the 1-CH₃ and 2-CH₃ complexes have been determined by X-ray crystallography. All the complexes show intense transitions in the visible region, which are assigned, based on DFT calculations, to transitions within orbitals of the thiosemicarbazone ligand. Cyclic voltammetry on the complexes shows two oxidations of the coordinated thiosemicarbazone on the positive side of SCE and a reduction of the same ligand on the negative side.     

Synthesis and investigation of spectral and electrochemical properties of alkyl-substituted planar binuclear phthalocyanine complexes sharing a common naphthalene ring

Hexa-tert-butyl and dodeca-n-butyl-substituted planar binuclear phthalocyanines sharing a common naphthalene ring with Mg as a central metal were synthesized with high yields and characterized by UV/Vis spectra, luminescence spectra, NMR, electrochemical, and spectroelectrochemical measurements. On the base of these complexes, the metal-free phthalocyanine ligands and the series of binuclear phthalocyanine complexes of rare earth elements (REE) were synthesized.All compounds obtained revealed an intensive near IR-absorption reaching 855 nm for trinuclear phthalocyanine. A crucial increase in NMR spectra resolution was achieved by the addition of ethylene glycol as a disaggregating agent. Spectroelectrochemical measurements during oxidation showed reversible changes of absorbance at 709 and 800 nm.     

Synthesis and luminescence properties of Ca3(BO3)2:Eu3+ via two‐step method

Novel Ca₂B₂O₅·H₂O:Eu³⁺ nanotubes, constructed with nanobelts, were prepared using a hydrothermal method. The Ca₃(BO₃)₂:Eu³⁺ nanobelts with a thickness of about 100 nm were made for the first time using a two‐step hydrothermal process with Ca₂B₂O₅·H₂O:Eu³⁺ as the precursor. The samples were characterized by energy dispersive X‐ray spectroscopy, X‐ray diffraction, Fourier transform infra‐red spectroscopy, thermogravimetry differential thermal analysis and scanning electron microscopy. The relationship between Ca₃(BO₃)₂:Eu³⁺ and Ca₂B₂O₅·H₂O:Eu³⁺ was also studied. Possible reaction and growth mechanisms for Ca₂B₂O₅·H₂O:Eu³⁺ and Ca₃(BO₃)₂:Eu³⁺ were proposed. Ca₃(BO₃)₂:Eu³⁺ preserved the basic microstructure unit of Ca₂B₂O₅·H₂O:Eu³⁺. Both Ca₂B₂O₅·H₂O:Eu³⁺ and Ca₃(BO₃)₂:Eu³⁺ exhibited red emissions centred at 614 nm, but the maximum excitation peaks for Ca₂B₂O₅·H₂O:Eu³⁺ and Ca₃(BO₃)₂:Eu³⁺ differed. Ca₃(BO₃)₂:Eu³⁺ exhibited higher photoluminescence intensity but a lower R/O value than Ca₂B₂O₅·H₂O:Eu³⁺.     

Synthesis and luminescence properties of novel 8‐hydroxyquinoline derivatives and their Eu(III) complexes

Six novel 8‐hydroxyquinoline derivatives were synthesized using 2‐methyl‐8‐hydroxyquinoline and para‐substituted phenol as the main starting materials, and were characterized by ¹H nuclear magnetic resonance (NMR), mass spectrometry (MS), ultraviolet (UV) light analysis and infra‐red (IR) light analysis. Their complexes with Eu(III) were also prepared and characterized by elemental analysis, molar conductivity, UV light analysis, IR light analysis, and thermogravimetric–differential thermal analysis (TG–DTA). The results showed that the ligand coordinated well with Eu(III) ions and had excellent thermal stability. The structure of the target complex was EuY^1–6(NO₃)₃.2H₂O. The luminescence properties of the target complexes were investigated, the results indicated that all target complexes had favorable luminescence properties and that the introduction of an electron‐donating group could enhance the luminescence intensity of the corresponding complexes, but the addition of an electron‐withdrawing group had the opposite effect. Among all the target complexes, the methoxy‐substituted complex (–OCH₃) had the highest fluorescence intensity and the nitro‐substituted complex (–NO₂) had the weakest fluorescence intensity. The results showed that 8‐hydroxyquinoline derivatives had good energy transfer efficiency for the Eu(III) ion. All the target complexes had a relatively high fluorescence quantum yield. The fluorescence quantum yield of the complex EuY³(NO₃)₃.2H₂O was highest among all target complexes and was up to 0.628. Because of excellent luminescence properties and thermal stabilities of the Eu(III) complexes, they could be used as promising candidate luminescent materials.     

Investigating the properties of Bacillus thuringiensis Cry proteins with novel loop replacements created using combinatorial molecular biology

Cry proteins are a large family of crystalline toxins produced by Bacillus thuringiensis. Individually, the family members are highly specific, but collectively, they target a diverse range of insects and nematodes. Domain II of the toxins is important for target specificity, and three loops at its apex have been studied extensively. There is considerable interest in determining whether modifications in this region may lead to toxins with novel specificity or potency. In this work, we studied the effect of loop substitution on toxin stability and specificity. For this purpose, sequences derived from antibody complementarity-determining regions (CDR) were used to replace native domain II apical loops to create "Crybodies." Each apical loop was substituted either individually or in combination with a library of third heavy-chain CDR (CDR-H3) sequences to create seven distinct Crybody types. An analysis of variants from each library indicated that the Cry1Aa framework can tolerate considerable sequence diversity at all loop positions but that some sequence combinations negatively affect structural stability and protease sensitivity. CDR-H3 substitution showed that loop position was an important determinant of insect toxicity: loop 2 was essential for activity, whereas the effects of substitutions at loop 1 and loop 3 were sequence dependent. Unexpectedly, differences in toxicity did not correlate with binding to cadherins--a major class of toxin receptors--since all Crybodies retained binding specificity. Collectively, these results serve to better define the role of the domain II apical loops as determinants of specificity and establish guidelines for their modification.     

Synthesis and transfection properties of novel non-toxic monocationic lipids. Variation of lipid anchor, spacer and head group structure

This report describes the synthesis and the transfection properties of novel monocationic non-toxic lipids. We have carried out structural variations in all three units of the transfection lipid, the lipid anchor, the spacer moiety and the positively charged head group. Our results lead to the conclusion that systematic modification of structural subunits is a promising way to enhance the transfection efficiency.     

A novel nanohybrid of daunomycin and single-walled carbon nanotubes: photophysical properties and enhanced electrochemical activity

A nanohybrid adduct of the widely used, functional dye, daunomycin (DM), with single-walled carbon nanotubes (SWNTs) was prepared. Ultraviolet-visible-near infrared and fluorescence spectroscopy and electrochemistry of DM-functionalized SWNTs reveal that DM interacts with SWNTs through strong π–π stacking and there is a significant photo-induced charge-transfer interaction between the two components. Importantly, the novel adduct modified the glassy carbon (GC) electrode to give a much enhanced electrochemical activity than those of DM adsorbed onto not only the bare GC electrode but also the SWNTs-modified GC electrode.     

The globule diameter and some electron and conformational properties of the flavoprotein fragment of mitochondrial NADH dehydrogenase studied by fluorescence spectroscopy

The globule dimensions and some electron and conformational properties of the flavoprotein (peripheral) fragment of the mitochondrial NADH dehydrogenase were determined by the time-resolved, phase-modulating, and polarization fluorescence spectroscopies, as well as correlated confocal microscopy. The rotational and the diffusion (translocation) diameters of the protein fragment were shown to be no less than 44 and ∼72 ?, respectively. The diameter of protomitochondrial particles from the bovine heart, which were used for the isolation of the fraction of peripheral fragments, was no less than 2300 ?. The fluorescence from tryptophan and flavin fluorophores in the fragment is strongly quenched by iron of the iron-sulfur clusters, which suggests that a strong electron-vibrational interaction of iron with Trp residues and flavin takes place. An overlapping of the electron clouds of iron-sulfur clusters, Trp residues, and flavin is likely to facilitate the electron transfer through the protein. The heat inactivation of the enzyme was accompanied by neither its substantial conformational changes, nor a considerable release of iron ions from the clusters located near the Trp residues.     

Synthesis, structures, spectral and electrochemical properties of copper(II) complexes of sterically hindered Schiff base ligands

The Schiff base ligands 2-(2,6-diisopropylphenyliminomethyl)phenol H(L1), 5-diethylamino-2-(2,6-diisopropylphenyliminomethyl)phenol H(L2), 2,4-di-tert-butyl-6-(2,6-diisopropylphenyliminomethyl)phenol H(L3), 3-(2,6-diisopropylphenyliminomethyl)naphthalen-2-ol H(L4) and 4-(2,6-diisopropylphenyliminomethyl)-5-hydroxymethyl-2-methylpyridin-3-ol H(L5) have been synthesized by the condensation, respectively, of salicylaldehyde, 4-(diethylamino)salicylaldehyde, 3,5-di-tert-butylsalicylaldehyde, 2-hydroxy-1-napthaldehyde and pyridoxal with 2,6-diisopropylaniline. The copper(II) bis-ligand complexes [Cu(L1)₂] 1, [Cu(L2)₂] 2, [Cu(L3)₂] 3, [Cu(L4)₂] 4 and [Cu(L5)₂] · CH₃OH 5 of these ligands have been isolated and characterized. The X-ray crystal structures of two of the complexes [Cu(L1)₂] 1 and [Cu(L5)₂] · CH₃OH 5 have been successfully determined, and the centrosymmetric complexes possess a CuN₂O₂ chromophore with square planar coordination geometry. The frozen solution EPR spectra of the complexes reveal a square-based CuN₂O₂ chromophore, and the values of g_‖ and g_‖/A_‖ index reveal enhanced electron delocalization by incorporating the strongly electron-releasing -NEt₂ group (2) and fusing a benzene ring on sal-ring (4). The Cu(II)/Cu(I) redox potentials of the Cu(II) complexes reveal that the incorporation of electron-releasing -NEt₂ group and fusion of a benzene ring lead to enhanced stabilization of Cu(II) oxidation state supporting the EPR spectral results. The hydrogen bonding interactions between the two molecules present in the unit cell of 5a generate an interesting two-dimensional hydrogen-bonded network topology.     

A study of the spectral and luminescence manifestations of the aggregation of thymine chromophores in polythymidylic acid aqueous solutions at room temperature in the context of photochemical information recording using thymine

The luminescence and excitation spectra of polythymidylic acid aqueous solutions at room temperature were studied. In addition to the previously described band at 338 nm, two new bands at 320 and 350 nm were recorded at various excitation wavelengths. An examination of the excitation spectra that had not been studied previously, as well as their comparison with the differential absorption spectra previously recorded during photodimerization, allowed us to interpret the band at 320 nm as the band of noninteracting chromophores; the band at 338 nm as the band of the most photochemically active, densely packed stacking dimmers (exciton splitting of absorption band of ～4000 cm^?1); and the band at 350 nm as the band of photochemically inactive large stacking aggregates (n ≥ 10, exciton splitting of ～8000 cm^?1). The changes in the optical density of the polythymidylic acid aqueous solution at γ = 270 nm after successive irradiation of the solution with light at 279 + 302 and 248 nm were studied. The reasons for their incomplete reversibility are discussed.     

Covalent attachment of flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) to enzymes: the current state of affairs.

The first identified covalent flavoprotein, a component of mammalian succinate dehydrogenase, was reported 42 years ago. Since that time, more than 20 covalent flavoenzymes have been described, each possessing one of five modes of FAD or FMN linkage to protein. Despite the early identification of covalent flavoproteins, the mechanisms of covalent bond formation and the roles of the covalent links are only recently being appreciated. The main focus of this review is, therefore, one of mechanism and function, in addition to surveying the types of linkage observed and the methods employed for their identification. Case studies are presented for a variety of covalent flavoenzymes, from which general findings are beginning to emerge.     

Role of a novel dual flavin reductase (NR1) and an associated histidine triad protein (DCS-1) in menadione-induced cytotoxicity

Microsomal cytochrome P450 reductase catalyzes the one-electron transfer from NADPH via FAD and FMN to various electron acceptors, such as cytochrome P450s or to some anti-cancer quinone drugs. This results in generation of free radicals and toxic oxygen metabolites, which can contribute to the cytotoxicity of these compounds. Recently, a cytosolic NADPH-dependent flavin reductase, NR1, has been described which is highly homologous to the microsomal cytochrome P450 reductase. In this study, we show that over-expression of NR1 in human embryonic kidney cells enhances the cytotoxic action of the model quinone, menadione. Furthermore, we show that a novel human histidine triad protein DCS-1, which is expressed together with NR1 in many tissues, can significantly reduce menadione-induced cytotoxicity in these cells. We also show that DCS-1 binds NF1 and directly modulates its activity. These results suggest that NR1 may play a role in carcinogenicity and cell death associated with one-electron reductions.