Characterization of the citrate precursor, used for synthesis of nanosized Mg-Zn ferrites

The citrate precursor has been used to synthesize nanocrystalline Mg-Zn-ferrites. The nature of the prepared precursor is characterized and compared with those of the precursors studied earlier, prepared by the same process. The study has been performed by inorganic and organic elemental analyses, Fourier Transformed Infrared Spectroscopy (FTIR), Mössbauer spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Electron Paramagnetic Resonance (EPR), Electronic absorption spectrometry in the UV-VIS region, Differential Thermal analysis/ Thermogravimetry (DTA-TG) analyses, and X-ray diffraction (XRD) analysis. The collected results determined the precursor as a coordination polymer with monomer unit (NH₄)₄{M [Fe(C₆H₅O₇)₂]₂}, where M=Zn or Mg.      

Homo- and heteropolynuclear platinum complexes stabilized by dimethylpyrazolato and alkynyl bridging ligands: synthesis, structures, and luminescence

This work describes the synthesis of cis-[Pt(C[triple bond]CPh)2(Hdmpz)2] (1) and its use as a precursor for the preparation of homo- and heteropolynuclear complexes. Double deprotonation of compound 1 with readily available M(I) (M = Cu, Ag, Au) or M(II) (M = Pd, Pt) species affords the discrete hexanuclear clusters [{PtM2(mu-C[triple bond]CPh)2(mu-dmpz)(2)}(2)] [M = Cu (2), Ag (3), Au (4)], in which both "Pt(C[triple bond]CPh)2(dmpz)(2)" fragments are connected by four d(10) metal centers, and are stabilized by alkynyl and dimethylpyrazolate bridging ligands, or the trinuclear complexes [Pt(mu-C[triple bond]CPh)2(mu-dmpz)(2){M(C/\P)}2] (M = Pd (5), Pt (6); C/\P = CH(2)-C(6)H(4)-P(o-tolyl)2-kappaC,P), respectively. The X-ray structures of complexes 1-4 and 6 are reported. The X-ray structure of the platinum-copper derivative 2 shows that all copper centers exhibit similar local geometry being linearly coordinated to a nitrogen atom and eta(2) to one alkynyl fragment. However in the related platinum-silver (3) and platinum-gold (4) derivatives the silver and gold atoms present three different coordination environments. The complexes have been studied by absorption and emission spectroscopy. The hexanuclear complexes exhibit bright luminescence in the solid state and in fluid solution (except 4 in the solid state at 298 K). Dual long-lived emission is observed, being clearly resolved in low-temperature rigid media. The low-energy emission is ascribed to MLM'CT Pt(d)/pi(C[triple bond]CPh)-->Pt(p(z))/M'(sp)/pi*(C[triple bond]CPh) modified by metal-metal interactions whereas the high-energy emission is tentatively attributed to an emissive state derived from dimethylpyrazolate-to-metal (d(10)) LM'CT transitions pi(dmpz)-->M'(d(10)).     

Cholinesterase inhibition based determination of pancuronium bromide in biological samples

Pancuronium bromide (PCBr) inhibition effect on enzyme cholinesterase from pooled human serum (Che, EC 3.1.1.8 acylcholine acylhydrolase) was used for development of a spectrophotometric kinetic method for PCBr determination in human serum and urine. Optimal conditions for the basic and inhibitor reactions were established: pH=7.7 and substrate concentration c(benzoylcholine chloride)=1.33 mmol/L. Kinetic parameters were also determined: Michaelis-Menten’s constant K_M=0.40 mmol/L, maximal reaction rate V_max=52.2 μmol/L min, inhibition constant K_i=0,56 μmol/L and IC₅₀=1.31 μmol/L. Linear dependence between the reaction rate and inhibitor concentration exists in PCBr concentration range 8.20–68.25 nmol/L, which corresponds to the real sample concentrations from 0.328 to 2.730 μmol/L. The method detection and quantification limits were 2.01 nmol/L and 6.67 nmol/L, respectively. Precision of the method was tested for three pancuronium concentrations (10.70, 29.35 and 51.25 nmol/L). Relative standard deviation (RSD) was in the range 0.15–7.45%. Accuracy was examined by standard addition method. Influence of the substances usually present in serum and urine on the reaction rate was tested. The developed method was applied for PCBr content determination in serum model samples, urine model samples and in urine taken during surgery. The method has good sensitivity, accuracy, precision and it is suitable for clinical practice.      

Newton additive and multiplicative Schwarz iterative methods

Daniel B. Szyld^¶ Department of Mathematics, Temple University, Philadelphia, PA 19122, USA ^{Convergence properties are presented for Newton additive andmultiplicative Schwarz (AS and MS) iterative methods for thesolution of nonlinear systems in several variables. These methodsconsist of approximate solutions of the linear Newton step usingeither AS or MS iterations, where overlap between subdomainscan be used. Restricted versions of these methods are also considered.These Schwarz methods can also be used to precondition a Krylovsubspace method for the solution of the linear Newton steps.Numerical experiments on parallel computers are presented, indicatingthe effectiveness of these methods.}     

On the Mixed Crystals Formation in the Fe(Zn) (HCOO)2–Cd(HCOO)2–H2O System

The solubility in the Fe(HCOO)₂–Cd(HCOO)₂–H₂O and Zn(HCOO)₂–Cd(HCOO)₂–H₂O systems have been studied by the method of physico-chemical analysis at 25 °C and mixed crystals of the type Fe_1-xCd_x(HCOO)₂.2 H₂O and Zn_1-xCd_x (HCOO)₂. 2 H₂O have been obtained. The lattice parameters of the mixed crystals have been calculated. It has been established that the isostructural Fe(HCOO)₂. 2 H₂O and Cd(HCOO)₂. 2 H₂O form isomorphous mixed crystals, whereas the isostructural Zn(HCOO)₂. 2 H₂O and Cd(HCOO)₂. 2 H₂O yield isodimorphous mixed crystals. The difference in the behaviour of the two pairs of formate salts has been attributed to the difference in the Me–O_m, bond lengths in the coordination octahedra, forming the crystal structures.     

Polymer-Modified Single-Walled Carbon Nanotubes Affect Photosystem II Photochemistry,Intersystem Electron Transport Carriers and Photosystem I End Acceptors in Pea Plants

Single-walled carbon nanotubes (SWCNT) have recently been attracting the attention of plant biologists as a prospective tool for modulation of photosynthesis in higher plants. However, the exact mode of action of SWCNT on the photosynthetic electron transport chain remains unknown. In this work, we examined the effect of foliar application of polymer-grafted SWCNT on the donor side of photosystem II, the intersystem electron transfer chain and the acceptor side of photosystem I. Analysis of the induction curves of chlorophyll fluorescence via JIP test and construction of differential curves revealed that SWCNT concentrations up to 100 mg/L did not affect the photosynthetic electron transport chain. SWCNT concentration of 300 mg/L had no effect on the photosystem II donor side but provoked inactivation of photosystem II reaction centres and slowed down the reduction of the plastoquinone pool and the photosystem I end acceptors. Changes in the modulated reflection at 820 nm, too, indicated slower re-reduction of photosystem I reaction centres in SWCNT-treated leaves. We conclude that SWCNT are likely to be able to divert electrons from the photosynthetic electron transport chain at the level of photosystem I end acceptors and plastoquinone pool in vivo. Further research is needed to unequivocally prove if the observed effects are due to specific interaction between SWCNT and the photosynthetic apparatus.     

Transition metal complexes with thiosemicarbazide-based ligand – Part LV: Synthesis and X-ray structural study of novel Ni(II) complexes with pyridoxal semicarbazone and pyridoxal thiosemicarbazone

Reaction of aqueous solutions of Ni(NO₃)₂ and pyridoxal semicarbazone (PLSC) in the presence of NaN₃ afforded two complexes, viz. green, paramagnetic binuclear octahedral [Ni₂(PLSC)₂(μ_1,1-N₃)₂(N₃)₂] · 2H₂O (1) and, as admixture, red, octahedral [Ni(PLSC–H)₂] · 2H₂O (2) complex. Under the same reaction conditions, pyridoxal thiosemicarbazone (PLTSC) gave only one diamagnetic square-planar, red complex [Ni(PLTSC–H)N₃] · H₂O (3). In the absence of NaN₃, the reaction of PLTSC and Ni(NO₃)₂ yielded brown paramagnetic octahedral complex [Ni(PLTSC)₂](NO₃)₂ · H₂O (4).     

Antimicrobial Triterpenoids and Ingol Diterpenes from Propolis of Semi-Arid Region of Morocco

The chemical composition and antimicrobial activity of propolis from a semi-arid region of Morocco were investigated. Fifteen compounds, including triterpenoids (1, 2, 7–12), macrocyclic diterpenes of ingol type (3–6) and aromatic derivatives (13–15), were isolated by various chromatographic methods. Their structures were elucidated by a combination of spectroscopic and chiroptical methods. Compounds 1 and 3 are new natural compounds, and 2, 4–6, and 9–11 are newly isolated from propolis. Moreover, the full nuclear magnetic resonance (NMR) assignments of three of the known compounds (2, 4 and 5) were reported for the first time. Most of the compounds tested, especially the diterpenes 3, 4, and 6, exhibited very good activity against different strains of bacteria and fungi. Compound 3 showed the strongest activity with minimum inhibitory concentrations (MICs) in the range of 4–64 µg/mL. The combination of isolated triterpenoids and ingol diterpenes was found to be characteristic for Euphorbia spp., and Euphorbia officinarum subsp. echinus could be suggested as a probable and new plant source of propolis.     

Special manifolds and shape fibrator properties

Our main interest in this paper is further investigation of the concept of (PL) fibrators (introduced by Daverman [R.J. Daverman, PL maps with manifold fibers, J. London Math. Soc. (2) 45 (1992) 180-192]), in a slightly different PL setting. Namely, we are interested in manifolds that can detect approximate fibrations in the new setting. The main results state that every orientable, special (a new class of manifolds that we introduce) PL n-manifold with non-trivial first homology group is a fibrator in the new category, if it is a codimension-2 fibrator (Theorem 8.2) or has a non-cyclic fundamental group (Theorem 8.4). We show that all closed, orientable surface S with χ(S)<0 are fibrators in the new category.