Voltammetric study of the interaction of pentoxifylline (PTX) with Zn(II) in the presence and absence of cysteine

The interaction of pentoxifylline (PTX) with Zn(II) in the presence and absence of cysteine at physiological pH (7.40) was investigated for the first time by square-wave and cyclic voltammetry techniques. The Zn(II)–PTX complex was found to be an electroinactive inert complex, the composition of the formed complex is 1?:?1 (metal?:?ligand), and the logarithm of its stability constant (log β_1?:?1) was determined as 3.46 by direct monitoring of the current of free zinc(II). The logarithm of the stability constant (log β_1?:?2) and stoichiometry of the complexation of Zn(II) with cysteine were determined to be 9.94 and 1?:?2, respectively. The stability constants were in agreement with those calculated from electronic spectral data. In the presence of cysteine, Zn(II)–PTX dissociated and an irreversible peak for Zn(II)–cysteine appeared at ?1.342?V. Cysteine prevents complex formation of Zn(II) with PTX.     

Stabilization of the Cellulase Enzyme Complex as Enzyme Nanoparticle

The native Celluclast BG cellulase enzyme complex consists of different enzymes which can also degrade great substrate molecules as native celluloses. This enzyme complex has been covered by a very thin, a few nanometers thick, polymer layer, in order to improve its stability. It has been proved that the polymer layer around the enzyme molecules does not hinder the digestion as great substrates as crystalline cellulose polymer. The stability of the prepared enzyme nanoparticles (PE) could significantly be increased comparing to that of the native one what was proved by results of the total cellulose activity measured. The pretreated enzyme complex holds its activity often a few magnitudes of orders longer in time than that of the native enzyme complex (enzyme without pretreatment). It retains its activity at least ten times longer than that of the native one, at a temperature range between 20 and 37?°C. The pretreated enzyme complex can have about 50?% of its original activity during 12?h of incubation at even 80?°C, while the native cellulase one totally lost it during 6?h incubation time. The activity of PE has not been significantly reduced even at extreme pH values, namely in the pH range of 1.5 to 12.     

Determination and comparison of stability constants of tungsten(VI) and molybdenum(VI) with nitrilotriacetic acid and glutamic acid at different ionic strengths

The formation constants of species formed in the systems H⁺?+?W(VI)?+?nitrilotriacetic acid (NTA) and H⁺?+?NTA have been determined in aqueous solution for pH?=?4–9 at 25°C and different ionic strengths ranging from 0.1 to 1.0?mol?dm^?3 NaClO₄, using potentiometric and spectrophotometric techniques. It was shown that tungsten(VI) forms a mononuclear 1?:?1 complex with NTA of the type WO₃L^3? at pH?=?7.5. The composition of the complex was determined by the continuous variations method. The complexation of molybdenum(VI) with glutamic acid was investigated in aqueous solution ranging in pH from 4 to 9, using polarimetric, potentiometric and spectrophotometric techniques. The composition of the complex was determined by the continuous variations method. It was shown that molybdenum(VI) forms a mononuclear 1?:?1 complex with glutamic acid of the type MoO₃L^2? at pH?=?6.0. The dissociation constants of glutamic acid and the stability constants of the complex were determined at 25°C and at ionic strengths ranging from 0.1 to 1.0?mol?dm^?3 sodium perchlorate. In both complex formation reactions the dependence of the dissociation and stability constants on ionic strength is described by a Debye-Huckel type equation. Finally, a comparison has been made between the patterns of ionic strength dependence for the two complexes and the results have been compared with data previously reported.     

Nano-crystalline Mn0.3Ni0.3Zn0.4Fe2O4 obtained by novel fumarato-hydrazinate precursor method

Carboxylate hydrazinate complex involving mixed metals have been synthesized and used as precursor for preparing the nanocrystalline Mn?CNi?CZn ferrite. Chemical composition of complex was fixed from chemical analysis results, infrared studies, thermogravimetric and differential scanning calorimetric analysis and isothermal weight loss studies. Nano-crystalline Mn?CNi?CZn ferrite particles obtained by thermal autocatalytic decomposition were characterized using X-ray diffraction studies, infrared spectral studies and TEM measurement. Two peaks in the region of 340?C420 and 550?C660?cm^?1 observed in the infrared spectrum of ??as synthesized?? oxide are characteristics of spinel ferrites. Average particle size of ??as synthesized?? Mn?CNi?CZn ferrite was found to be 10?nm. ??As synthesized?? Mn?CNi?CZn ferrite showed Curie point at 313?°C. Saturation magnetization (44.7?emu/g) observed for ??as synthesized?? Mn?CNi?CZn ferrite is lower than bulk material which is indicative of its nano-crystalline nature. Seebeck coefficient measurement has shown that the material exhibits n-type semiconducting behavior.     

Acid Catalyzed Dissociation of 4‐Aminopyridine Complex of Pentacyanoferrate (II)

Fe(CN)₅ampy^3? (ampy = 4‐aminopyridine) complex was unstable at pH ≤ 4 with respect to the dissociation due to the protonations of the complex. The first protonation on the 4‐aminopyridine ligand at pK_a = 3.2 resulted in a ? 150‐fold in crease in rate of dissociation as compared to that of the complex in the neutral solution. However, further protonation of the complex on the cyanide ligand at pK_a = 1.5 in creased the rate only slightly. The large in crease in the rate constant of dissociation for Fe(CN)₅ampyH^2? complex suggests that in the transition state the proton is likely shifted from the amino group and becomes coordinated to a pair of dπ electrons directed at the face of the coordinated octahedron.     

Host–guest interactions between dapsone and β-cyclodextrin (Part II): thermal analysis, spectroscopic characterization, and solubility studies

The complex of dapsone with β-cyclodextrin was prepared by the co-precipitation/freeze–drying method. The physical–chemical characteristics of the complex were investigated by different methods and compared with those of the physical mixture and of the isolated compounds. The methods used were infrared spectroscopy, X-ray diffractometry and differential scanning calorimetry. The stability constant was calculated from phase solubility diagram (Higuchi–Connors) and fluorescence spectroscopy. The stoichiometry of the complex was confirmed by Job’s plot. Fluorescence measurements at different temperatures provided the thermodynamic parameters of the complexation. The infrared spectrum showed the disappearance of the SO₂ asymmetric stretching band of the drug at 1275?cm^?1 after complexation. The amorphization of the samples, as revealed by the X-ray diffraction patterns, was an indirect proof of the inclusion complex. The thermal analysis showed that the curves of the physical mixture are combination of the curves of both constituents (dapsone and β-cyclodextrin) while the absence of the melting peak of the drug in the DSC curve of the complex suggests the inclusion of the drug molecule in the host cavity as a 1:1 complex as indicated by Job’s plot. There was a linear increase in its solubility with the increase of the cyclodextrin concentration and the complex was classified as an A_L-type. The value of the stability constant was 3,998?L?mol^?1 calculated by the Higuchi–Connors diagram and around 18,100?L?mol^?1 from the fluorescence method indicating a strong interaction between the host and the guest. Complex formation was a spontaneous and enthalpy directed process.     

Admittance measurements of adsorption properties of 2,2′-bipyridine complexes: Part I. Cobalt(II) and nickel(II) complexes in aqueous solutions

The complex [Co bipy₃]²⁺ in aqueous perchlorate solution yields on the d.c. polarogramthree adsorption type pre-waves and a main reduction wave at ?1.2 V (SCE) corresponding to the reduction to monovalent complex. From admittance measurements and other results it can be concluded that two most positive pre-waves at ?0.2 V and ?0.5 V (SCE) are of non-faradaic nature being related to the adsorption of the complex with specifically adsorbed anions of the supporting electrolyte with the formation of a compact adsorbed layer of much lower interfacial capacity. The most negative pre-wave at ?0.9 V just preceding the main wave corresponds to the reduction of the adsorbed complex. The main wave at ?1.2 V is distorted by the adsorption of reaction products. Very similar and also strong adsorption-coupled interaction was found with divalent nickel trisbipyridine complex.     

Photomagnetism of a sym-cis-dithiocyanato iron(II) complex with a tetradentate N,N'-bis(2-pyridylmethyl)1,2-ethanediamine ligand

A comprehensive study of the magnetic and photomagnetic behaviors of cis-[Fe(picen)(NCS)(2) ] (picen = N,N'-bis(2-pyridylmethyl)1,2-ethanediamine) was carried out. The spin-equilibration was extremely slow in the vicinity of the thermal spin-transition. When the cooling speed was slower than 0.1?K min(-1), this complex was characterized by an abrupt thermal spin-transition at about 70?K. Measurement of the kinetics in the range 60-70?K was performed to approach the quasi-static hysteresis loop. At low temperatures, the metastable HS state was quenched by a rapid freezing process and the critical T(TIESST) temperature, which was associated with the thermally induced excited spin-state-trapping (TIESST) effect, was measured. At 10?K, this complex also exhibited the well-known light-induced excited spin-state-trapping (LIESST) effect and the T(LIESST) temperature was determined. The kinetics of the metastable HS states, which were generated from the freezing effect and from the light-induced excitation, was studied. Single-crystal X-ray diffraction as a function of speed-cooling and light conditions at 30?K revealed the mechanism of the spin-crossover in this complex as well as some direct relationships between its structural properties and its spin state. This spin-crossover (SCO) material represents a fascinating example in which the metastability of the HS state is in close vicinity to the thermal spin-transition region. Moreover, it is a beautiful example of a complex in which the metastable HS states can be generated, and then compared, either by the freezing effect or by the LIESST effect.     

聚乙烯亚胺-钴络合物对氧还原电流的影响

研究了聚乙烯亚胺 钴络合物 (PEI Co)在电解质溶液中的氧可逆结合特性及对氧还原电流的影响 .PEI Co络合物溶解于电解质的水溶液中 ,在氧气气氛中络合物与氧结合 ,UV Vis光谱在 310nm处出现了新的吸收峰 ,并在 2 80nm处观察到等吸光点 .PEI Co络合物与氧结合平衡曲线服从Langmuir行为 ,络合物与氧结合的亲和力 (p50 )为 0 6 6 7kPa .氧与PEI Co加成物的解离反应表观速率常数为 1 1× 10 5s- 1 ,表明络合物具有快速、可逆的氧结合特性 .在PEI Co络合物存在下 ,氧电极的还原电流显著增加 ,并且随PEI Co络合物的浓度以及气氛中氧浓度的增加而增加 .[PEI链节 ] [Co]=5 1时 ,氧还原电流达到极大值 ,说明PEI Co络合物与氧形成了结构为 [N5CoⅢ O2 CoⅢ N5]的加成物 .     

Field determination of fluoride in drinking water using a polymeric aluminium complex of 5-(2-carboxyphenylazo)-8-hydroxyquinoline impregnated paper

A simple field method which allows the determination of fluoride in drinking water with a small handheld instrument called Arsenator was developed. Arsenator is a commercially available instrument which was used successfully for reliable determination of arsenic. In the proposed method the functionality of the Arsenator which is based on a photometric measurement of a spot on the reagent paper is expanded to analyse fluoride. A polymeric aluminium complex of 5-(2-carboxyphenylazo)-8-hydroxyquinoline (LH₂) has been prepared as a new specific reagent for fluoride. Job's method of continuous variation was adopted for the determination of the composition of the coloured complex, which was further characterized by UV-VIS spectroscopic studies. The molar absorptivity of the complex formation is 8.48?×?10³?L?mol^?1?cm^?1 at 410?nm. The coloured complex reacts with fluoride on an impregnated paper where its colour changes are dependent on the concentration of fluoride in water samples. The change in the colour was measured using the Arsenator. The method allows a reliable determination of fluoride in the range 0.3 to 2.0?mg?L^?1. Further spectophotometric determinations of fluoride in drinking water were also studied. The determination is based on the reaction of aluminium complex with fluoride in the examined samples. Beer's law is obeyed in the range 0.3 to 2.0?mg?L^?1 of fluoride at 495?nm. Sensitivity, detection limit and quantitation limit of the method were found to be 0.251?±?0.007?µg^?1?mL, 0.1?mg?L^?1 and 0.3?mg?L^?1, respectively. The optimum reaction conditions and other analytical conditions were evaluated. The effect of interfering ions on the determination is described. There is no interference by nitrate or chloride. Sulphate interfered only at high concentrations which are not expected in drinking water.     

Evaluation of lithium separation by dispersive liquid–liquid microextraction using benzo-15-crown-5

In this article a dispersive liquid?Cliquid microextraction method was applied for evaluation of lithium separation from aqueous solution. Benzo-15-crown-5 (B15C5) was used as a chelating agent prior to extraction. An appropriate mixture of disperser solvent and extraction solvent were added rapidly into the aqueous sample containing lithium ion; as a result, a cloudy solution was formed which consisted of fine droplets of extraction solvent dispersed entirely into aqueous phase. The mixture was centrifuged and the lithium complex with B15C5 was sedimented at the bottom of the conical sample holder. Then, 2.0?mL of enriched phase containing lithium complex was used for determination of lithium ion by flame atomic absorption spectrometry. The conditions for the microextraction performance were investigated. Under the best optimized conditions, the accepted recovery factors for the lithium obtained, ranged from 37.24 to 99.63?%. Furthermore, high preconcentration factors (7.46?C19.93) were also achieved. The relative standard deviation for three replicate measurements of 0.127?mg?L^?1 of lithium was 2.83?%.     

Trace determination of zirconium by adsorptive anodic stripping voltammetry of its complex with alizarin violet using a glassy carbon electrode modified with acetylene black-dihexadecyl hydrogen phosphate composite film

We report on a novel electrochemical method for the sensitive determination of trace zirconium (Zr) at a glassy carbon electrode modified with a film of acetylene black containing dihexadecyl hydrogen phosphate and in the presence of alizarin violet (AV). The method is based on the preconcentration of the Zr(IV)-AV complex at a potential of ?200?mV (vs. SCE). The adsorbed complex is then oxidized, producing a response with a peak potential of 526?mV. Compared to the poor electrochemical signal at the unmodified GCE, the electrochemical response of Zr(IV)-AV complex is greatly improved, as confirmed by the significant increase in peak current. The effects of experimental conditions on the oxidation current were studied and a calibration plot established. The oxidation current is linearly related to the Zr(IV) concentration in the 8.0?pM to 10?nM concentration range (c_AV?=?0.2???M) and 10?nM ~0.6???M (c_AV?=?2.0???M), and the detection limit (S/N?=?3) is as low as 4.0?pM for a 3-min accumulation time. The method was successfully employed to the determination of zirconium in standard ore samples.

Long-lived room-temperature near-IR phosphorescence of BODIPY in a visible-light-harvesting N^C^N Pt(II)-acetylide complex with a directly metalated BODIPY chromophore

Room-temperature long-lived near-IR phosphorescence of boron-dipyrromethene (BODIPY) was observed (λ(em) = 770?nm, Φ(P) = 3.5?%, τ(P) = 128.4?μs). Our molecular-design strategy is to attach Pt(II) coordination centers directly onto the BODIPY π-core using acetylide bonds, rather than on the periphery of the BODIPY core, thus maximizing the heavy-atom effect of Pt(II). In this case, the intersystem crossing (ISC) is facilitated and the radiative decay of the T(1) excited state of BODIPY is observed, that is, the phosphorescence of BODIPY. The complex shows strong absorption in the visible range (ε = 53,800 M(-1) cm(-1) at 574?nm), which is rare for Pt(II)-acetylide complexes. The complex is dual emissive with (3)MLCT emission at 660?nm and the (3)IL emission at 770?nm. The T(1) excited state of the complex is mainly localized on the BODIPY moiety (i.e. (3)IL state, as determined by steady-state and time-resolved spectroscopy, 77?K emission spectra, and spin-density analysis). The strong visible-light-harvesting ability and long-lived T(1) excite state of the complex were used for triplet-triplet annihilation based upconversion and an upconversion quantum yield of 5.2?% was observed. The overall upconversion capability (η = ε×Φ(UC)) of this complex is remarkable considering its strong absorption. The model complex, without the BODIPY moiety, gives no upconversion under the same experimental conditions. Our work paves the way for access to transition-metal complexes that show strong absorption of visible light and long-lived (3)IL excited states, which are important for applications in photovoltaics, photocatalysis, and upconversions, etc.     

Synthesis of metal−organic complex arrays

The Merrifield solid-phase peptide synthesis technique has been adapted to the synthesis of homo- and heterometallic metal?organic complex arrays (MOCAs). A terpyridine-appended and Fmoc-protected L-tyrosine derivative was metalated with Pt(II), Rh(III), or Ru(II) ions in solution and sequentially coupled at the surface of functionalized polymeric resin to give a metal complex triad (Rh?Pt?Ru), tetrad (Ru?Rh?Pt?Pt), pentad (Rh?Pt?Ru?Pt?Rh), and hexad (Rh?Pt?Ru?Pt?Rh?Pt) with specific metal sequence arrangements. These were cleaved from the resin, and their character was confirmed by mass spectrometry.     

杯芳烃钕/二正丁基镁/六甲基磷酰胺催化4-乙烯基吡啶的均聚及其与苯乙烯的共聚

聚4-乙烯基吡啶[P（4-VP）]是一种功能高分子,由于在吡啶环上有一个碱性的氮原子,它能进一步与酸反应生成各种盐,与卤代烃生成季铵盐以及与金属离子生成配合物,可用作高分子电解质,高分子试剂,高分子功能材料等,因此有不少文献对它的合成进行了报道,合成聚4-乙烯基吡啶及其与苯乙烯（St）的共聚物,除了用丁基锂作引发剂外,过渡金属的Ziegler-Natta催化剂,以及烷基铝和烷基锌等也常被用作催化剂,但用这些催化剂催化所得的聚4-乙烯基吡啶及其与苯乙烯的共聚物产率低,分子量小。     

Characterization of the interaction between a platinum(II) complex and human serum albumin: spectroscopic analysis and molecular docking

In this study, the interaction between (2,2?-bipyridine)(pyrrolidinedithiocarbamato) platinum(II) nitrate, [Pt(bpy)(pyr-dtc]NO₃, and human serum albumin (HSA) was investigated by various spectroscopic methods (UV–vis, fluorescence, CD and FT-IR) and molecular docking technique at three temperatures. UV–vis absorption spectroscopy showed that Pt(II) complex can denature the protein at moderate concentrations. The results of emission quenching at two temperatures has revealed that the quenching mechanism of Pt(II) complex with HSA was static quenching mechanism. Binding constants (K), binding site number (n) and corresponding thermodynamic parameters ?G?, ?H? and ?S? were calculated and revealed that hydrophobic forces played a major role when Pt(II) complex interacted with HSA. The binding distance (r) between above complex and HSA based on Förster?s theory of non-radiation energy transfer was calculated as 3.22 nm. Alterations of HSA secondary structure induced by complex were confirmed by FT-IR and CD measurements. Also, a molecular docking study was performed for identification of key structural features of binding of the Pt complex into the receptor and predicting bioactive conformers. Our results may provide valuable information to understand the mechanistic pathway of drug delivery and to pharmacological behavior of drug.     

Quaternary ammonium oxidative demethylation: X-ray crystallographic, resonance Raman, and UV-visible spectroscopic analysis of a Rieske-type demethylase

Herein, the structure resulting from in situ turnover in a chemically challenging quaternary ammonium oxidative demethylation reaction was captured via crystallographic analysis and analyzed via single-crystal spectroscopy. Crystal structures were determined for the Rieske-type monooxygenase, stachydrine demethylase, in the unliganded state (at 1.6 ? resolution) and in the product complex (at 2.2 ? resolution). The ligand complex was obtained from enzyme aerobically cocrystallized with the substrate stachydrine (N,N-dimethylproline). The ligand electron density in the complex was interpreted as proline, generated within the active site at 100 K by the absorption of X-ray photon energy and two consecutive demethylation cycles. The oxidation state of the Rieske iron-sulfur cluster was characterized by UV-visible spectroscopy throughout X-ray data collection in conjunction with resonance Raman spectra collected before and after diffraction data. Shifts in the absorption band wavelength and intensity as a function of absorbed X-ray dose demonstrated that the Rieske center was reduced by solvated electrons generated by X-ray photons; the kinetics of the reduction process differed dramatically for the liganded complex compared to unliganded demethylase, which may correspond to the observed turnover in the crystal.     

Solution-processable high-efficiency bis(trifluoromethyl)phenyl functionalized phosphorescent neutral iridium(III) complex for greenish yellow electroluminescence

A novel and highly efficient bis(trifluoromethyl)phenyl functionalized iridium(III) complex is designed and synthesized. The complex shows intensive greenish yellow phosphorescence (525?nm with 563?nm as shoulder), high photoluminescence efficiency (0.90) and moderate full width at half maximum (72?nm). The bulky bis(trifluoromethyl)phenyl moiety introduced into the complex provides the excellent solubility and effective steric hindrance for solution-processed organic light-emitting diodes. The maximum power efficiency and current efficiency of electroluminescence are 4.13?lm/W and 9.54?cd/A, respectively.     

Synthesis of a New Chiral Source, (1R,2S)‐1‐Phenylphospholane‐2‐carboxylic Acid,via a Key Intermediate α‐Phenylphospholanyllithium Borane Complex: Configurational Stability and X‐ray Crystal Structure of an α‐Monophosphinoalkyllithium Borane Complex

A synthetic route to enantiomerically pure (1R,2S)‐1‐phenylphospholane‐2‐carboxylic acid ( 1 ), which is a phosphorus analogue of proline, has been established. A key step is the deprotonation–carboxylation of the 1‐phenylphospholane borane complex 3 by using sBuLi/1,2‐dipiperidinoethane (DPE). Configurational stability of the key intermediate, the amine‐coordinated α‐phosphinoalkyllithium borane complex 4 , was investigated by employing lithiodestannylation–carboxylation of both diastereomers of the 1‐phenyl‐2‐trimethylstannylphospholane borane complex 7 in the presence of several kinds of amines, and as a result, 4 was found to be configurationally labile even at ?100 °C. The key intermediate, the DPE‐coordinated trans‐1‐phenyl‐2‐phospholanyllithium borane complex 9 , was isolated, and the structure was identified by X‐ray crystal structure analysis. This is the first X‐ray crystal structure determined for an α‐monophosphinoalkyllithium borane complex. Remarkably, the alkyllithium complex is monomeric and tricoordinate at the lithium center with a slightly pyramidalized environment, and the existence of a Li? C bond (2.170 Å) has been confirmed. Moreover, ¹H–⁷Li HOESY and ⁶Li NMR analyses suggested the structure of 9 in solution as well as the existence of an equilibrium between 9 , its cis isomer, and the ion pair 8 at room temperature, which was extremely biased towards 9 at ?100 °C. Finally, 1 was used as a chiral ligand in a palladium‐catalyzed allylic substitution, and the desired product was obtained in high yield with good enantioselectivity.     

Electrochemical study of indapamide and its complexation with ��-cyclodextrin

Electrochemical oxidation of indapamide has been investigated at glassy carbon electrode using cyclic and differential pulse voltammetry (DPV). Indapamide exhibited two well resolved signals which attributed to the oxidation of indoline ring and benzamide moiety in phosphate buffers in the pH range of 2.7?C10.1. The oxidation processes have been shown to be irreversible and diffusion controlled. The formation of an inclusion complex of indapamide with ??-cyclodextrin (??-CD) has been investigated by cyclic, differential pulse voltammetry as well as UV?CVis spectrophotometry. The stability constant of the complex was determined to be 6199 and 2717 M^?1 using differential pulse voltammetry and UV?CVis spectrophotometry, respectively.