Ligand substitution reaction at a binuclear organoplatinum(II) complex

The ligand substitution reactions of the N-donor ligand in the binuclear dimethylplatinum(II) complex of formula cis,cis-[Me₂Pt(μ-NN)(μ-dppm)PtMe₂], 1, in which dppm = bis(diphenylphosphino)methane and NN = phthalazine, by different nucleophilic phosphorous-donors L, L = P(O-ⁱPr)₃ or PPh₃ and L₂ = dppm, to form the dinuclear complexes 2, cis,cis-[Me₂LPt(μ-dppm)PtLMe₂] and cis,cis-[Me₂Pt(μ-dppm)₂PtMe₂], respectively, are studied. Complex 1 has a MLCT band in the visible region which was used to easily follow the kinetics of its ligand substitution reactions. These reactions which involve diplatinum(II) complex 1 containing cis Pt-C bonds, proceeded by the normal associative mechanism. In associative reactions of the present work, as expected, the rate of the reactions was depended on the concentration and the nature of the entering group. The nucleophilicity of PPh₃ is stronger than P(O-ⁱPr)₃ on the basis of its stronger σ-donor ability and its lower solvation and is responsible for the observed 3-fold increase of its rate as compared to that of P(O-ⁱPr)₃. Also, the solvation energy involved is suggested to be responsible for the observation of higher rates in benzene than in acetone. The ΔH^‡/ΔS^‡ compensation plot gives a straight line which suggests the operation of the same mechanism for all entering nucleophiles.     

Dispersive liquid-liquid microextraction combined with graphite furnace atomic absorption spectrometry: ultra trace determination of cadmium in water samples

Dispersive liquid-liquid microextraction (DLLME) technique was successfully used as a sample preparation method for graphite furnace atomic absorption spectrometry (GF AAS). In this extraction method, 500 μL methanol (disperser solvent) containing 34 μL carbon tetrachloride (extraction solvent) and 0.00010 g ammonium pyrrolidine dithiocarbamate (chelating agent) was rapidly injected by syringe into the water sample containing cadmium ions (interest analyte). Thereby, a cloudy solution formed. The cloudy state resulted from the formation of fine droplets of carbon tetrachloride, which have been dispersed, in bulk aqueous sample. At this stage, cadmium reacts with ammonium pyrrolidine dithiocarbamate, and therefore, hydrophobic complex forms which is extracted into the fine droplets of carbon tetrachloride. After centrifugation (2 min at 5000 rpm), these droplets were sedimented at the bottom of the conical test tube (25 ± 1 μL). Then a 20 μL of sedimented phase containing enriched analyte was determined by GF AAS.Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of the chelating agent have been optimized. Under the optimum conditions, the enrichment factor 125 was obtained from only 5.00 mL of water sample. The calibration graph was linear in the rage of 2-20 ng L⁻¹ with detection limit of 0.6 ng L⁻¹. The relative standard deviation (R.S.D.s) for ten replicate measurements of 20 ng L⁻¹ of cadmium was 3.5%. The relative recoveries of cadmium in tap, sea and rivers water samples at spiking level of 5 and 10 ng L⁻¹ are 108, 95, 87 and 98%, respectively. The characteristics of the proposed method have been compared with cloud point extraction (CPE), on-line liquid-liquid extraction, single drop microextraction (SDME), on-line solid phase extraction (SPE) and co-precipitation based on bibliographic data. Therefore, DLLME combined with GF AAS is a very simple, rapid and sensitive method, which requires low volume of sample (5.00 mL).     

Catalyst‐Free and Green Synthesis of Some Novel Benzamide Derivatives

In the present work, a simple, green, rapid, and catalyst‐free procedure for the synthesis of benzamide derivatives by ring opening of azlactones with diamines such as ethylene diamine and 1,3‐propylenediamine is described. The present method offers several advantages such as short reaction times, easy work‐up, and mild reaction conditions in the absence of catalyst and any toxic solvent and material. In addition, the structure obtained by X‐ray crystallography was compared with the theoretical results obtained by density functional theory using the B3LYP functional and cc‐pVDZ basis sets.     

Antireflection properties of germanium–carbon coating on zinc supplied substrate

In this research, germanium–carbon coatings were deposited on ZnS and glass substrates by a RF plasma enhanced chemical vapor deposition method using GeH₄ and CH₄ as precursors. ZnS/Ge_1?xC_x double-layer antireflection coating with optical thickness of one quarter wavelength was designed. The samples were characterized by fourier transform infrared spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy and nanoindentation. The coatings exhibited a structure free of pores with a very good adhesion to substrate. Based on the XRD patterns, no diffraction peak was found, so all the coatings mainly had an amorphous structure. The infrared (IR) transmittance spectrum show that the maximum IR transmittance in the band of 1030–1330 cm^?1 was about 84.6%, which is higher than ZnS substrate by 10%. In addition, the reflection of ZnS substrate is about 25%. This system has reduced the reflection from the substrate by 15%.     

Determination of Toxic Elements in Muscle Tissues of Five Fish Species Using Ultrasound‐Assisted Pseudodigestion by Electrothermal Atomic Absorption Spectrophotometry: Optimization Study

A simple and rapid method is described for the determination of As, Cd, and Pb in muscle tissue of five freshwater fish species by ultrasound‐assisted pseudodigestion (USD). A Plackett‐Burman experimental design was used as a multivariate strategy for the evaluation of the effects of varying several variables at once. The variables such as sonication time (ST), sample mass of muscle tissues (SM), temperature of ultrasonic bath (T), nitric acid (A1), and mixture of acid and oxidant (A2) have been studied. From these studies, some variables showed significant effect on % recovery, and they were further optimized by a 2³+star central composite design, which involved 16 experiments. Optimum values of the variables were selected for the development of USD to determine the contents of As, Cd, and Pb in muscle tissue of five fish species, used as bioindicators for Lake Manchar (Sindh, Pakistan) to know whether consumption of these fishes threatens human health. The determination of three toxic elements under study was carried out by electrothermal atomic absorption spectrometry (ETAAS). The accuracy of the optimized procedure was evaluated by analysis of certified reference materials DORM‐2 (Dogfish Muscle Certified Reference Material for Trace Elements) and by comparison with conventional wet acid digestion methodology. No significant differences were observed for p=0.05 when comparing the values obtained by the proposed USD method and conventional digestion method (CDM) (paired t‐test). The average relative standard deviation of the USD method varied between 4.05%, 7.53%, and 4.55% for As, Cd, and Pb, respectively (n=10).     

Application of Polytyramine Nanoparticles to the Corrosion Protection of Copper

Electrochemical polymerization of tyramine was achieved on copper electrode surface from tyramine in 0.3 M oxalic acid (pH=1.2) solution by using cyclic voltammetry technique. The formation of polytyramine nanoparicles (PTN) were characterized by cyclic voltammetry (CV), fourier transform infrared‐attenuated total reflectance (FTIR‐ATR) spectroscopy and scanning electron microscopy (SEM). The corrosion behavior of PTN coated copper was investigated by means of the change of open circuit potential with exposure time (E_ocp t), electrochemical impedance spectroscopy (EIS) and anodic polarization curves in 3.5 % NaCl solutions at room temperature. The obtained results showed the shift of corrosion potential toward positive values for electropolymerized copper and a significant decrease in corrosion current and corrosion rate in comparison with bare copper, so that the PTNs coating could be used as an important protection against corrosion of copper.