Presence Of Complexes Research Articles

Proton-coupled electron transfer from a luminescent excited state

A luminescent cationic iridium complex with a 2,2'-biimidazole ligand forms hydrogen-bonded 1 : 1 adducts with benzoate anions; photoexcitation of the metal complex in presence of 3,5-dinitrobenzoate triggers a proton-coupled electron transfer.

LÉVY HIERARCHY IN WEAK SET THEORIES

We investigate the interactions of formula complexity in weak set theories with the axioms available there. In particular, we show that swapping bounded and unbounded quantification preserves formula complexity in presence of the axiom of foundation weakened to an arbitrary set base, while it does not if the axiom of foundation is further weakened to a proper class base. More attention is being paid to the necessary axioms employed in the positive results, than to the combinatorial strength of the positive results themselves.

Thermodynamic analysis of conformational transitions in oligonucleotide complexes in presence of Na+and Mg2+ions, using “Staggering Zipper” model

Curves of transitions in double (2-->1 transition) and triple (3-->2 transition) complexes of oligonucleotides dA(N1)with dT(N2) in solutions with Na(+) and Mg(2+) are calculated for the case of oligomer lengths from 10 to 500 nucleotides in the wide range of ion concentrations. The calculated curves of transitions and their differential analogs reflect rather exactly the position and form of experimental curves and describe dependences of transition temperatures on the length of molecules, their concentration, and ionic conditions. Values of the nucleation parameter beta for the systems studied are determined by comparison of the calculated and experimental data obtained in a number of works. The average beta value equal to 10(-3) l/mole is in an agreement with values reported for similar systems earlier. It is shown that disordering of duplex and triplex ends ("end fraying") has an essential influence on the form of melting curves, their asymmetry and the increase of the transition interval.

Palladium–NHC complexes do catalyse the diboration of alkenes: mechanistic insights

Novel catalytic activation of the B-B bond by palladium(II)-NHC complexes in presence of a mild base (NaOAc) and an excess of diboron reagent enables chemoselective 1,2-diboration of alkenes, suggesting the heterolytic cleavage of diboron rather than oxidative addition of a B-B bond to the metal.

Photochemistry of the [Fe III(edta)(H 2O)] − and [Fe III(edta)(OH)] 2− complexes in presence of environmentally relevant species

The study shows that the *[Fe II(edta )(H 2O] − or *[Fe II(edta )(OH)] 2− LMCT excited state can undergo self-quenching generating the [(H 2O)(edta )Fe II(μ-OH x )Fe III(edta)] x−4 millisecond intermediate, the fate of which depends on the availability of molecular oxygen. In the presence of O 2 or another external electron acceptor the excited state undergoes oxidative quenching, whereas the presence of an external electron donor leads to its reductive quenching. In the former case, the EDTA undergoes oxidation by the external electron acceptor in reaction catalysed by the excited Fe(III) complex, which changes its coordination sphere to [Fe III(ed3a)]. Thus, with reference to the Fe(III) complex the process can be classified as photosubstitution, whereas with reference to the oxidized electron donors it can be identified as oxidation photocatalysed by the Fe(III) complex. The reductive quenching results in reduction of Fe(III) in the excited complex accompanied by oxidation of EDTA and/or external electron acceptor; thus the process can be identified as photoreduction of the Fe(III) complex. Numerical analysis of the [Fe(edta)(H 2O] − and [Fe(edta)(OH)] 2− absorption spectra leads to conclusion that there are two different LMCT excited states, which differ in location of the unpaired electron (on N or O atom). Reactive decay of these excited states leads, however, to generation of analogous products, although with different quantum yields. The Fe(III) photocatalytic cycle can be driven by sunlight and in the aerated media plays a crucial role in abatement of the pollutants, which have either electron donor or electron acceptor character. Among others, the photocatalytic cycle contributes to abate one of the most noxious pollutants, i.e. chromate(VI).

Effect on the Solubility, Wettability, and Dispersibility of the β‐CD‐Deltamethrin Inclusion Complex in Presence of Mixed Surfactant (C14MEA/AOS) Blend

An inclusion complex formation using β‐cyclodextrin (β‐CD) as the host molecule and deltamethrin as guest molecule was a first step towards improvement in conventional insecticide formulations. β‐CD‐deltamethrin inclusion complex formation in the absence and presence of the nonionic myrisitic acid monoethanolamide (C14MEA)/anionic α‐olefin sulfonate C12‐C14 (AOS) mixed surfactant system was comparatively studied. The co‐evaporation method was used for complex formation, which was subsequently characterized by analytical methods such as FTIR and XRD techniques. Important physical properties such as solubility, dispersion stability, and wettability were also studied.

Determination of albumins by its quenching effect on the fluorescence of Tb 3+-oxolinic acid complex in presence of sodium dodecyl sulphate

It is found that the fluorescence intensity of Tb 3+-oxolinic acid (OA) complex can be greatly quenched by albumins in sodium dodecyl sulphate (SLS). Under optimum conditions, the quenched fluorescence intensity is in proportion to the concentration of proteins in the range of 5.0×10 −8–1.0×10 −5 g ml −1 for bovine serum albumin (BSA), 1.0×10 −7–1.0×10 −5 g ml −1 for human serum albumin (HSA) and 4.0×10 −7–1.0×10 −5 g ml −1 for egg albumin (EA). Their detection limits ( S/ N=3) are 2.1×10 −8, 2.5×10 −8 and 5.0×10 −8 g ml −1, respectively. In addition, the interaction mechanism is also investigated.

De-epoxidation of Violaxanthin in the Minor Antenna Proteins of Photosystem II, LHCB4, LHCB5, and LHCB6

The conversion of violaxanthin to zeaxanthin is essentially required for the pH-regulated dissipation of excess light energy in the antenna of photosystem II. Violaxanthin is bound to each of the antenna proteins of both photosystems. Former studies with recombinant Lhcb1 and different Lhca proteins implied that each antenna protein contributes specifically to violaxanthin conversion related to protein-specific affinities of the different violaxanthin binding sites. We investigated the violaxanthin de-epoxidation in the minor antenna proteins of photosystem II, Lhcb4-6. Recombinant proteins were reconstituted with different xanthophyll mixtures to study the conversion of violaxanthin at different xanthophyll binding sites in these proteins. The extent and kinetics of violaxanthin de-epoxidation were found to be dependent on the respective protein and, for each protein, also on the binding site of violaxanthin. In particular, violaxanthin bound to Lhcb4 was nearly inconvertible for de-epoxidation, whereas violaxanthin bound to Lhcb5 was fully convertible but with slow kinetics. Lhcb6 exhibited heterogeneous violaxanthin conversion characteristics, which could be assigned to different populations of reconstituted Lhcb6 complexes with respect to violaxanthin binding sites. The results support the proposed different binding affinities of violaxanthin to the three putative violaxanthin binding sites (V1, N1, and L2) in antenna proteins. Under consideration of former studies with Lhcb1 and Lhca proteins, the data imply that violaxanthin bound to the V1 and N1 binding site of antenna proteins is easily accessible for de-epoxidation in all antenna proteins, whereas violaxanthin bound to L2 is either only slowly or not convertible to zeaxanthin, depending on the respective protein.

Calculation of electric dipole intensity parameters of 4f–4f transitions of Pr(III) and glutathione reduced (GSH) complex in presence and absence of Zn(II)

Comparative absorption and spectral analysis of 4f–4f transitions of Pr(III) and glutathione reduced (GSH) complex in presence and absence of Zn(II) is carried out in different aquated organic solvents of CH 3OH, CH 3CN, DMF and dioxane and their equimolar mixtures at different pH (3.0, 4.0, 5.0 and 6.0). The values of experimentally calculated oscillator strengths ( P) and computed values of Judd–Ofelt electric dipole intensity parameters, T λ ( λ = 2, 4, 6) are discussed for different 4f–4f transitions in different experimental conditions. The changes in the values of oscillator strengths ( P) and T λ parameters suggest the specific correlation between relative intensities, ligand structures and nature of interaction of Pr(III) with GSH in the presence and absence of Zn(II).

Studies on “sugar-reactivity” of agars extracted from some Indian agarophytes

Sugar reactivity was observed within the sugar–agar complexes in presence of sucrose and glucose with agars of Indian agarophytes viz. Gelidiella acerosa, Gracilaria edulis, Gracilaria crassa and Gelidium pusillum. The sugar reactivity was more pronounced in presence of sucrose than glucose. Oxoid agar was used as the reference material. Control agar gel contained 1.12% agar (w/w) in water. Sucrose–agar and glucose–agar gels in water consisted of 50% (w/w) sucrose and 50% (w/w) glucose, respectively along with 1.12% (w/w) agars of the four seaweeds mentioned above. Addition of sucrose resulted in increase (ca. 25–45%) in gel strength; increase (2–3 °C) in gelling and melting temperatures was observed in the gels prepared with agars from all the agarophytes and Oxoid agar. On the other hand, addition of glucose resulted in increase (19–34%) in the gel strength and gelling and melting temperatures of the agar gels of Oxoid as well as of all other agars decrease (2–3 °C). Maximum sugar reactivity was observed with the 50% level of sucrose and glucose in agar gels. Rheological and thermogravimetric characteristics of these gel samples were studied. The latter showed two patterns e.g. control agar gel of Oxoid agar was thermally less stable than the four control agar samples studied; in sugar–agar gel samples it followed a reverse pattern. To our knowledge, this is the first report of “sugar reactivity” of agar of Indian agarophytes. Sugar reactivity of agar in presence of glucose is also reported for the first time. The results of this study will be useful in bioprospecting as well as in exploring new applications.

Chemical composition analysis of germanate glass by alkalimetric titration of germanate mannitol complex

A titrimetric method has been developed for the determination of germanium in glass. Germanium anion in aqueous solution combine with two molecules of mannitol to form a germanate mannitol complex in presence of sufficient mannitol. The complex is moderately strong acid and germanium can be determined by alkalimetric titration. The proposed method is simple, rapid and selective and the method is successfully applied for the determination of germanium in glass.

Environment Friendly Protocol for Enantioselective Epoxidation of Non-Functionalized Alkenes Catalyzed by Recyclable Homochiral Dimeric Mn(III) Salen Complexes with Hydrogen Peroxide and UHP Adduct as Oxidants

Environment friendly oxidants e.g. H2O2 and anhydrous urea hydrogen peroxide adduct (UHP) epoxidize non-functionalized alkenes (epoxide yield 40–99%) with high enantioselectivity (up to 94% ee) in 4–15 h using two recyclable homochiral dimeric Mn(III) salen complexes in presence of PyN-oxide with the catalysts reusability several times when UHP was used as an oxidant.

Lattice location and thermal evolution of small B complexes in crystalline Si

The lattice location of B in Si has been investigated by channelling analyses using nuclear reactions (650keV proton beam, B11(p,α)Be8). The formation at room temperature of a specific, small B complex in presence of an excess of point defects has been inferred. In particular, B implanted in Si or B substitutional dissolved in Si and irradiated with proton beam form a unique B complex with B atoms not randomly located. The angular scans along the ⟨100⟩ and ⟨110⟩ axes are compatible with B–B pairs aligned along the ⟨100⟩ axis. The thermal annealing in the 200–950°C range of the B complexes, analyzed by lattice location and carrier concentration measurements, depends on the residual defect density in the lattice. The B complexes dissolve at low temperature if no excess of Si self-interstitials (Is) exists or they evolve into large B clusters and then dissolve at high temperature if Is supersaturation holds.

Effects of Tris and Hepes buffers on the interaction of palladium–diaminopropane complexes with DNA

The Pd(II) complexes, [PdCl 2(1,2-pn)] and [PdCl 2(1,3-pn)] (pn is diaminopropane), were synthesized and characterized by analytical and spectroscopic (FT-IR, 1H NMR and 13C NMR) techniques. UV difference spectral study performed on Pd-pn/DNA systems, indicate a pronounced interaction of palladium complexes with DNA in cell-free media; comparison of λ max, Abs max and % H values observed for the two compounds might be attributed to structural differences of the chelated ligand rings. Results obtained from electrophoretic analysis of Pd complexes in presence of pBR322 plasmid DNA show a clear decreasing of the supercoiled (SC) DNA form mobility, that could be attributed to unwinding of the double helix; a parallel increasing of the open-circular (OC) DNA form mobility is also noted, this fact implying that the binding of complexes either shortens or condenses the DNA helix. Interaction studies of Pd complexes with plasmid DNA in different buffer systems indicate that DNA binding efficiency capable of modifying the tertiary structure of pBR322 decreased from NaClO 4 to Hepes 2, Hepes 1 [Hepes = 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid], and Tris [(hydroxymethyl)aminomethane] buffers, in this order. Moreover, the level of DNA modifications produced by palladium complexes in 10 mM NaClO 4 remains unchanged after transferring the samples into the medium required for subsequent biophysical or biochemical analyses.

Proton transfer reaction in 2-hydroxy-3-formyl benzoic acid at room temperature and 77 K and some study on AM1 potential surfaces

Proton transfer processes in 2-hydroxy-3-formyl benzoic acid (2HFBA) have been studied by means of absorption and emission spectroscopy in some non-polar and weakly polar solvents at room temperature and 77 K in relation to 4-hydroxy-3-formyl benzoic acid (4HFBA). The excited state intramolecular proton transfer (ESIPT) is evidenced by a large Stokes shifted emission (10,500 cm −1) due to the formation of enol tautomer of 2HFBA in non-polar solvents. In 1,4-dioxane and tetrahydrofuran, 2HFBA forms hydrogen bonded complex while both tautomer and hydrogen bonded complex have been detected in benzene. Unlike 4HFBA, 2HFBA forms hydrogen bonded complex in presence of a base, like triethyl amine in non-polar solvents due to the rupture of intramolecular bond. Moreover, 2HFBA shows phosphorescence even in absence of base on lowering the temperature to 77 K. The energetics of the ground and excited state proton transfer in 2HFBA have been studied at the AM1 level of approximation. The ground singlet is predicted to have a large activation barrier on the proton transfer path while the barrier height is much lower on the corresponding excited singlet surface.

Microspectrophotometric determination of thorium(IV) and uranium(VI) with methylthymol blue

Attempts have been made to improve the sensitivity of complexation reactions of Th I V and U V I with methylthymol blue (MTB) in presence of cationic surfactant cetyldimethylethylammonium bromide (CDEAB). The marked bathochromic shift in λ m a x , considerable increase in sensitivity and extreme stability of these ternary complexes in presence of CDEAB were found to be useful in microdetermination of metal ions under study. The composition and values of conditional formation constants have been evaluated in presence of CDEAB and various analytical parameters, viz. conformity to Beer's law, photometric ranges, Sandell's sensitivity and molar absorptivity have been studied.

Synthesis, Characterization, and Catalytic Activity of Polymer Anchored Amino Acid Mn(II) Complexes

Chloromethylated styrene‐divinylbenzene copolymer beads with 6% and 8% crosslink were chemically modified by reaction with L‐valine leading to the incorporation of nitrogen and oxygen as ligating sites on the surface of the polymer. These polymeric ligands on treatment with a solution of manganese(II) acetate gave the corresponding metal complex. The polymer supported Mn(II) complexes were characterized by elemental analyses, FT‐IR, diffuse reflectance, ESR, scanning electron micrographs (SEM), and thermal analysis. Catalytic epoxidation of various olefins such as styrene, cis‐cyclooctene, norbornylene, and cyclohexene were investigated using the supported metal complexes in presence of tert‐butyl hydroperoxide as the terminal oxidant. The influence of various reaction parameters such as catalyst concentration, nature of substrate, temperature, type of oxidant, solvent etc. on conversion and selectivity was studied. Kinetic data indicate that the catalysts could be recycled without significant degradation of polymer matrix. The possible mechanistic pathways are discussed.

Kinetic and stability studies on the chloroperoxidase complexes in presence of tert-butyl hydroperoxide

The inactivation of native chloroperoxidase (CPO) from Caldariomyces fumago in the presence of tert-butyl hydroperoxide ( tert-BuOOH) was investigated. A kinetic analysis was made and the inactivation constants ( V 3 and K 3) were evaluated. In prolonged times, uni-exponential equation describes the enzyme time course inactivation. A method based on the rate of inactivation of the enzyme in the presence of the inactivating molecule tert-BuOOH was also performed. A second group of inactivation constants ( j 3 and K) was obtained, which is sufficiently close to the first two, thus verifying that the decreasing of enzyme absorbance corresponds to the decay of activity.

Effect of pH and temperature on the formation of hydroxyapatite at low temperatures by decomposition of a Ca–EDTA complex

Hydroxyapatite (HAp) was synthesized through the decomposition of a Ca(EDTA) complex in presence of phosphate ions. Ion concentrations are much higher than previously reported. This route allows the formation of HAp at temperatures below 140 °C and at different pH values. Phase identification, crystallinity and morphology of the obtained products were studied via FTIR, SEM, XRD and EDS.

Catalytic asymmetric epoxidation of non-functionalised alkenes using polymeric Mn(III) Salen as catalysts and NaOCl as oxidant

Enantioselective epoxidation of non-functionalised alkenes using polymeric Mn(III) Salen complex in presence of PyN–O using NaOCl gave excellent (>99%) epoxide yield with high chiral induction in case of nitro and cyano chromene and the catalyst could be reused up to five cycles. Polymeric chiral Mn(III) Salen complexes 1a , 1b were synthesised by the interaction of 1 S ,2 S -(+)-l,2-diaminocyclohexane, 1 R ,2 R -(+)-l,2-diphenyl ethylenediamine with 5,5′-methylene-di-3- tert -butylsalicylaldehyde. Number of repetitive units and molecular weight of the polymeric ligands were found to be between 10 and 12 and M n = ∼5200 and ∼5400, respectively by VPO. Enantioselective epoxidation of chromenes, indene and styrene mediated by complexes 1a and 1b (2 mol%) as catalyst using NaOCl as an oxidant gave >99% epoxide yields except for cyclochromene where the yield is in the range of 50–61% in 2.5–12 h. The enantiomeric excess (ee) for the product epoxide was found to be in the range of 75 to >99%, except for styrene (ee, 32–56%). The catalysts were easily recovered by precipitation and were re-used up to five times with some loss of activity while there was no loss of enantioselectivity in the product epoxide. The effect of axial bases, oxidants and phase transfer reagents on activity and enantioselectivity of the catalytic system was also studied.