Showing papers in "Journal of The Serbian Chemical Society in 2005"

Topology and stability of conjugated hydrocarbons: The dependence of total π-electron energy on molecular topology

Abstract: In spite of the fact that research on the mathematical properties of the total π-electron energy E (as computed by means of the Huckel molecular orbital approximation) started already in the 1940s, many results in this area have been obtained also in the newest times. In 1978 this author published in this journal a review on E. The present article is another review on E, summarizing the progress in the theory of E, achieved since then.

Synthesis and antibacterial activity of some Schiff bases derived from 4-aminobenzoic acid

Abstract: The following Schiff bases have been synthesized: (1) 4-(2-chlorobenzylidene)amino benzoic acid JP1, (2) 4 (furan-2-ylmethylene)amino benzoic acid JP2, (3) 4-[(3-phenylallylidene)amino]benzoic acid JP3, (4) 4 (2-hydroxybenzylidene)amino benzoic acid JP4, (5) 4 (4-hydroxy-3-methoxybenzylidene)amino benzoic acid JP5 and (6) 4 (3-nitrobenzylidene)amino benzoic acid JP6. They were screened as potential antibacterial agents against a number of medically important bacterial strains. The antibacterial activity was studied against A. faecalis ATCC 8750, E. aerogenes ATCC 13048, E. coli ATCC 25922, K. pneumoniae NCIM 2719 S. aureus ATCC 25923, P. vulgaris NCIM 8313, P. aeruginosa ATCC 27853 and S. typhimurium ATCC 23564. The antibacterial activity was evaluated using the Agar Ditch method. The solvents used were 1,4-dioxane and dimethyl sulfoxide. Different effects of the compounds were found in the bacterial strains in vestigated and the solvents used, suggesting, once again, that the antibacterial activity is dependent on the molecular structure of the compound, the solvent used and the bacterial strain under consideration. In the present work, 1,4-dioxane proved to be a good solvent in inhibiting the above stated bacterial strains.

RP-HPLC determination of vitamins, folic acid and B12 in multivitamin tablets

Abstract: A simple and sensitive reversed-phase, ion-pair HPLC method was developed and validated for the simultaneous determination of B-group vitamins, thiamine chloride hydro- chloride (B1), nicotinamide (B3), pyridoxine hydrochloride (B6) and folic acid in Pentovit ® coated tablets The cyanocobalamine (B12) was determined separately, because of its low concentration in the investigated multivitamin preparation RP-HPLC analysis was per- formed with a LKB 2150 HPLC system, equipped with a UV/VIS Waters M 484 detector The procedures for the determination of B1 ,B 2 ,B 6 and folic acid were carried out on a Supelcosil ABZ + (15 cm 46 mm; 5 m) column with methanol-5mM heptanesulphonic acid sodium salt 01 % triethylamine TEA (25:75 V/V); pH 28 as the mobile phase For the determination of B12 a Suplex pKb-100 (15 cm 46 mm; 5 m) column and methanol-wa- ter (22:78 V/V) as the mobile phase were used The column effluents were monitored at 290 nm for B1 ,B 3 ,B 6 and folic acid, and at 550 nm for B12 The obtained results and statistical parameters for all the investigated vitamins of the B-group in Pentovit ® coated tablets were satisfactory and ranged from 904 % to 1085 % (RSD from 05 % to 41 %) The parame- ters for the validation of the methods are given

Voltammetric determination of imidacloprid and thiamethoxam

Abstract: A simple voltammetric method using a glassy carbon working electrode was developed for the determination of two members from the neonicotinoid group of insecticides: imidacloprid and thiamethoxam. The experiments showed that the voltammetric response depends on the mode of electrode surface pretreatment and the polarization mode. The response appeared to be linear in the range from 0.028 to 0.50 mg/cm 3 for both analytes. The limit of detection was 0.0077 mg/cm 3 for imidacloprid and 0.0085 mg/cm 3 for thiamethoxam, the limit of quantitation was 0.026 mg/cm 3 and 0.028 mg/cm 3 , respectively. The developed method was applied for the determination of these insecticides in potato samples sprayed with Confidor 200-SL or Actara 25-WG as well as commercial formulations of imidacloprid and thiamethoxam. A recovery trial was performed to assess the accuracy of the results, the recovery values being between 95 102 % for both of neonicotinoids.

Lipase immobilized by different techniques on various support materials applied in oil hydrolysis

Abstract: Batch hydrolysis of olive oil was performed by Candida rugosa lipase immobilized on Amberlite IRC-50 and Al 2 O 3 These two supports were selected out of 16 carriers: inorganic materials (sand, silica gel, infusorial earth, Al 2 O 3 ), inorganic salts (CaCO 3 , CaSO 4 ), ion-exchange resins (Amberlite IRC-50 and IR-4B, Dowex 2X8), a natural resin (colophony), a natural biopolymer (sodium alginate), synthetic polymers (polypropylene, polyethylene) and zeolites Lipase immobilization was carried out by simple adsorption, adsorption followed by cross-linking, adsorption on ion-exchange resins, combined adsorption and precipitation, pure precipitation and gel entrapment The suitability of the supports and techniques for the immobilization of lipase was evaluated by estimating the enzyme activity, protein loading, immobilization efficiency and reusability of the immobilizates Most of the immobilizates exhibited either a low enzyme activity or difficulties during the hydrolytic reaction Only those prepared by ionic adsorption on Amberlite IRC-50 and by combined adsorption and precipitation on Al 2 O 3 showed better activity, 2000 and 430 U/g support, respectively, and demonstrated satisfactory behavior when used repeatedly The hydrolysis was studied as a function of several parameters: surfactant concentration, enzyme concentration, pH and temperature The immobilized preparation with Amberlite IRC-50 was stable and active in the whole range of pH (4 to 9) and temperature (20 to 50 °C), demonstrating a 99 % degree of hydrolysis In repeated usage, it was stable and active having a half-life of 16 batches, which corresponds to an operation time of 384 h Its storage stability was remarkable too, since after 9 months it had lost only 25 % of the initial activity The immobilizate with Al 2 O 3 was less stable and less active At optimal environmental conditions, the degree of hydrolysis did not exceed 79 % In repeated usage, after the fourth batch, the degree of hydrolysis was reduced to 535 %

Influence of Mie scattering on nanoparticles with different particle sizes and shapes: Photometry and analytical ultracentrifugation with absorption optics

Abstract: Nanoparticles are used in large quantities for very different applications. A precise determination of the diameter and the particle size distribution which is responsible for the application properties is therefore essential. Reliable methods for measuring the above mentioned quantities are photometric measurements and analytical ultracentrifugation with an UV optics detector. Both methods are ruled by the Mie effect, that is scattering and absorption of the particles as function of the diameter, the wavelength, and the shape of the particles. The extinction coefficients e=τ/c for spheres, rods, and core shell particles have been calculated and plotted over a wide range of the size parameter πd/λ. Two examples for multimodal latex particles and core shell particles have been given and demonstrate the applicability of the method.

Reactions of carbon radicals generated by 1,5-transposition of reactive centers

Abstract: Radical intermediates can undergo specific reactions, such as intramolecular rearrangements, i.e., the transpositions of radical centers, which are not known in classical ionic organic reactions. 1,5-Transposition of a radical center to a non-activated carbon atom are of great synthetic importance. It can be successfully applied for the introduction of different functional groups (oxygen, nitrogen, sulfur, halogens) onto a carbon atom remote from the present functional group. In addition to functionalization of a remote non-activated carbon atom, the formation of new C-C bonds on the δ-carbon atom have also been achieved. 1,5-Transposition of the radical centers takes place from alkoxyl, aminyl and carbon radicals to a remote carbon atom. Relocation of the radical centers preferentially involves 1,5-transfer of a hydrogen atom, although migrations of some other groups are known. The reactions of the carbon radical generated by 1,5-relocation of the radical center are presented and their synthetic applications are reviewed.

Metal complexes with Schiff-base ligands pyridoxal and semicarbazide-based derivatives

Abstract: The most important results of extensive studies (syntheses, spectral, magnetic, voltammetric and structural characteristics and biological activity) of metal complexes with pyridoxal semi-, thiosemi- and isothiosemicarbazones are reviewed.

Platinum monolayer electrocatalysts for oxygen reduction: Effect of substrates, and long-term stability

Abstract: We describe a novel concept for a Pt monolayer electrocatalyst and present the results of our electrochemical, X-ray absorption spectroscopy, and scanning tunneling microscopy studies. The electrocatalysts were prepared by a new method for depositing Pt monolayers involving the galvanic displacement by Pt of an underpotentially depos- ited Cu monolayer on substrates of Au (111), Ir(111), Pd(111), Rh(111) and Ru(0001) single crylstals, and Pd nanoparticles. The kinetics of O2 reduction showed significant enhancement with Pt monolayers on Pd(111) and Pd nanoparticle surfaces in compari- son with the reaction on Pt(111) and Pt nanoparticles, respectively. This increase in cata- lytic activity is attributed partly to the decreased formation of PtOH, as shown by in situ X-ray absorption spectroscopy. The results illustrate that placing a Pt monolayer on a suitable substrate of metal nanoparticles is an attractive way of designing better O 2 re- duction electrocatalysts with very low Pt contents.

Cardiac Tissue Engineering

Abstract: We hypothesized that clinically sized (1-5 mm thick),compact cardiac constructs containing physiologically high density of viable cells (10 8 cells/cm 3 ) can be engineered in vitro by using biomimetic culture systems capable of providing oxygen transport and electrical stimulation, designed to mimic those in native heart. This hypothesis was tested by culturing rat heart cells on polymer scaffolds, either with perfusion of culture medium (physiologic interstitial velocity, supplementation of perfluorocarbons), or with electrical stimulation (continuous application of biphasic pulses, 2 ms, 5 V, 1 Hz). Tissue constructs cultured without perfusion or electrical stimulation served as controls. Medium perfusion and addition of perfluorocarbons resulted in compact, thick constructs containing physiologic density of viable, electromechanically coupled cells, in contrast to control constructs which had only a 100 μm thick peripheral region with functionally connected cells. Electrical stimulation of cultured constructs resulted in markedly improved contractile properties, increased amounts of cardiac proteins, and remarkably well developed ultrastructure (similar to that of native heart) as compared to non-stimulated controls. We discuss here the state of the art of cardiac tissue engineering, in light of the biomimetic approach that reproduces in vitro some of the conditions present during normal tissue development.

Anomalous dissolution of metals and chemical corrosion

Abstract: An overview is given of the anomalous behavior of some metals, in particular Fe and Cr, in acidic aqueous solutions during anodic dissolution. The anomaly is recog- nizable by the fact that during anodic dissolution more material dissolves than would be expected from the Faraday law with the use of the expected valence of the formed ions. Mechanical disintegration, gas bubble blocking, hydrogen embrittlement, passive layer cracking and other possible reasons for such behavior have been discussed. It was shown, as suggested by Kolotyrkin and coworkers, that the reason can be, also, the chemical reaction in which H2O molecules with the metal form metal ions and gaseous H2 in a potential independent process. It occurs simultaneously with the electrochemical corrosion process, but the electrochemical process controls the corrosion potential. On the example of Cr in acid solution it was shown that the reason for the anomalous behav- ior is dominantly chemical dissolution, which is considerably faster than the electro- chemical corrosion, and that the increasing temperature favors chemical reaction, while the other possible reasons for the anomalous behavior are of negligible effect. This ef- fect is much smaller in the case of Fe, but exists. The possible role of the chemical disso- lution reacton and hydrogen evolution during pitting of steels and Al and stress corro- sion cracking or corrosion fatigue are discussed.

Isolation and synthesis of anthraquinones and related compounds of Rubia cordifolia

Abstract: Anthraquinones and their glycosides, along with other compounds, have been isolated and characterized from the acetone:water (1:1) percolation of dried roots of Rubia cordifolia. Selected anthraquinones were synthesized using montmorillonite clays under solventless condition in 75 to 85 % yield.

Sterol composition of the Adriatic Sea algae Ulva lactuca, Codium dichotomum, Cystoseira adriatica and Fucus virsoides

Abstract: The sterol composition of two green algae and two brown algae from the South Adriatic was determined. In the green alga Ulva lactuca, the principal sterols were cholesterol and isofucosterol. In the brown alga Cystoseira adriatica, the main sterols were cholesterol and stigmast-5-en-3s-ol, while the characteristic sterol of the brown algae, fucosterol, was found only in low concentration. The sterol frac- tions of the green alga Codium dichotomum and the brown alga Fucus virsoides con- tained practically only one sterol each, comprising more than 90 % of the total ster- ols (clerosterol in the former and fucosterol in the latter).

Study of gold-platinum and platinum-gold surface modification and its influence on hydrogen evolution and oxygen reduction

Abstract: Surface modification of the electrodes was conducted from sulfuric acid solutions containing the corresponding metal-chloride complexes using cyclic voltam- metry. Comparing the charges of the hydrogen underpotential deposition region, and the corresponding oxide reduction regions, it is concluded that a platinum overlayer on gold forms 3D islands, while gold on platinum forms 2D islands. Foreign metals present in an amount of up to one monolayer exert an influence on the change in re- action rate with respect to both hydrogen evolution (HER) and oxygen reduction (ORR) reactions. A platinum overlayer on a gold substrate increases the activity for HER and for ORR, compared with pure gold. These results can be understood in terms of a simple model, in which the change in the H and OH binding energies are directly proportional to the shift of the d-bond center of the overlayer. On the con- trary, a gold layer on platinum slightly decreases the activity for both reactions compared with pure platinum.

Open-framework aluminophosphates: synthesis, characterization and transition metal modifications

Abstract: This review is a brief summary of open-framework aluminophosphates and their transition metal-substituted modifictions. The materials exhibit structural and compositional diversity, as well as a wide range of pore openings, which are crystallographically ordered and can be tuned by an appropriate choice of synthesis conditions. The diameters of the apertures, cages and channels fall in the range of 0.4 to about 1.5 nm, which recommends aluminophosphates for a novel area of application nanocatalysis. Isomorphous substitution of the framework elements by transition metal ions which possess redox ability creates active sites inside the aluminophosphate lattice and opens routes towards shape selective bi-functional ca- talysis. In order to obtain an insight into the location of the transition metal ions, dif- ferent characterization techniques have to be used.

Characterization of carbon cryogels synthesized by sol-gel polycondensation

Abstract: Resorcinol-formaldehyde (RF) cryogels were synthesized by the sol-gel polycondensation of resorcinol (R) with formaldehyde (F) and freeze-drying was carried out with t-butanol. Carbon cryogels were obtained by pyrolyzing RF cryogels in an inert atmosphere. Characterization by nitrogen adsorption showed that the carbon cryogels were micro and mesoporous materials with high specific surface areas (SBET ≈ 550 m2/g). Cyclic voltammeter experiments at various scan rates (2 to 200 mV s-1) were performed to study the electrical double-layer charging of carbon cryogel electrodes in 0.5 mol dm-3 HClO4 solution. It has been demonstrated that it is possible to sub-divide the total specific capacitance into the mesoporous and the microporous specific capacitance by analyzing the linear dependence of the charge (q) on the reciprocal of the square root of the potential scan rate (υ-1/2), and the linear dependence of the reciprocal charge (1/q) on the square root of the potential scan rate (υ-1/2). The specific capacitance was found to be constant over a wide range of sample weight (12.5 to 50.0 _g) and a very promising specific capacitance value of 150 F/g, was found for this material operating in an acidic 0.5 mol dm-3 HClO4 solution at room temperature.

Heterocyclic systems containing S/N regioselective nucleophilic competition: Facile synthesis, antitubercular and antimicrobial activity of thiohydantoins and iminothiazolidinones containing the benzo

Abstract: The required compounds N-aryl-N'-(3-chloro-2-benzo(b)thenoyl)-thiou- reas 1a-k were prepared by condensing 3-chloro-2-benzo(b)thenoyl chloride with different arylamines using ammonium thiocyanate, which in turn when treated with chloroacetic acid, yielded 1-aryl-3-(3-chloro-2-benzo(b)thenoyl)thiohydantoins 2a-k, while in the presence of sodium acetate treated with chloroacetic acid, yielded 2-arylimino-3-(3-chloro-2-benzo(b)thenoyl)-4-thiazolidinones 3a-k. All the synthe- sized compounds were screened for their antitubercular and antimicrobial activities. Some selected compounds were selected for their further antitubercular screening.

Inorganic analysis of herbal drugs. Part I. Metal determination in herbal drugs originating from medicinal plants of the family Lamiacae

Abstract: Elemental profiles of the total analyte content of major, minor and trace el- ements (Cu, Zn, Mn, Fe, K, Ca, Mg, Al, Ba and B) in 8 herbal drugs, originating from medicinal plants of the family Lamiacae, were determined. Flame atomic ab- sorption/emission spectroscopy (FAAS/FAES), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and energy dispersive X-ray fluorescence (EDXRF) were applied, and the advantages and limitations of these techniques are also dis- cussed. The whole procedure, from sample preparation via dissolution to the actual measurements, was validated by using CRM (NIST 1573a - Tomato leaves). The re- covery values obtained were in the range 90.64 - 101.58 %. A high degree of simi- larity in their elemental profiles was noticed from the results of qualitative analysis, while quantitative analysis shows significant diversity due to the variety of the influ- encing sources. The medicinal plants investigated in this work contained Cu (5.92- 14.79 mg kg -1 ), Zn (15.0 - 43.0 mg kg -1 ), Mn (25 - 111 mg kg -1 ), Fe (74 - 546 mg kg -1 ), K (1.80 - 6.24 %), Ca (0.90 - 1.43 %), Mg (0.17 - 0.67 %), Al (49 - 378 mg kg -1 ), Ba (15.53 - 69.84 mg kg -1 ) and B (34.7 - 56.5 mg kg -1 ).

Electrodeposition and characterization of Fe-Mo alloys as cathodes for hydrogen evolution in the process of chlorate production

Abstract: Fe-Mo alloys were electrodeposited from a pyrophosphate bath using a single diode rectified AC current. Their composition and morphology were investigated by SEM, optical microscopy and EDS, in order to determine the influence of the deposition conditions on the morphology and composition of these alloys. It was shown that the electrodeposition parameters, such as: chemical bath composition and current density, influenced both the composition of the Fe-Mo alloys and the current efficiency for their deposition, while the micro and macro- morphology did not change significantly with changing conditions of alloy electrodeposition. It was found that the electrodeposited Fe-Mo alloys possessed a 0.15 V to 0.30 V lower overvoltage than mild steel for hydrogen evolution in an electrolyte commonly used in commercial chlorate production, depending on the alloy composition, i.e., the conditions of alloy electrodeposition.

Comparative study of the active sites in zeolites by different probe molecules

Abstract: This review summarizes some of the recently published results concerning the acid sites in the zeolites ZSM-5 and Y studied by temperature-programmed desorption (TPD) and adsorption calorimetry using different probe molecules NH 3 CO, N 2 O and n-hexane. For the first time it has been shown that the acid sites in hydrated zeolites are accessible for n-hexane adsorption.

An austempering study of ductile iron alloyed with copper

Abstract: Austempered ductile iron (ADI) has proved to be an excellent material as it possesses attractive properties: high strength, ductility and toughness are combined with good wear resistance and machinability. These properties can be achieved upon adequate heat treatment which yields the optimum microstructure for a given chemical composition. In this paper the results of an investigation the austempering of ADI alloyed with 0.45 % Cu for a range of times and temperatures are reported. The microstructure and fracture mode developed throughout these treatments have been identified by means of light and scanning electron microscopy and X-ray diffraction analysis. It was shown that the strength, elongation and impact energy strongly depend on the amounts ofbainitic ferrite and retained austenite. Based on these results, and optimal processing window was established.

Viscosities of binary mixtures of toluene with butan-1-ol and 2-methylpropan-2-ol

Abstract: The viscosities of binary liquid mixtures of toluene with butan-1-ol and 2-methylpropan-2-ol have been determined at 298.15, 303.15, 308.15, 313.15 and 318.15 K over the whole concentration range. The Hind, Grunberg-Nissan, Wijk, Auslander and McAllister models were used to calculate the viscosity coefficients and these were compared with the experimental data for the mixtures. Excess vis- cosities were also calculated and fitted to the Redlich-Kister equation. Various ther- modynamic properties of viscous flow activation were determined and their varia- tions with composition are discussed.

The effects of yttrium on the hydrogenation performance and surface properties of a ruthenium-supported catalyst

Abstract: The effects of yttrium on the hydrogenation performance and surface properties of a Ru/sepiolite catalyst were studied. With CO2 methanation and CS2 poisoning as the testing reactons, TPR, TPD, XRD and CO chemisorption as the characterizations, the results showed that the presence of yttrium can increase the hydrogenation activity and anti-poisoning capacity of the Ru/sepiolite catalyst, which is due to a change of surface properties of the Ru/sepiolite. In the process of the catalytic reaction, the adjusting behavior of yttrium for the Ru/sepiolite catalyst aids in increasing the catalytic activity and anti-poisoning capacity of the catalyst.

Purification of natural zeolite-clinoptilolite for medical application-Extraction of lead

Abstract: A series of experiments of the leaching of lead and other cations from three samples of natural zeolite-clinoptilolite, (Sample 1-deposit Zlatokop, Vranjska Banja, Serbia and Montenegro; Sample 2-deposit Bala Mare, Romania; Sample 3-Igros near Brus, Serbia and Montenegro) using EDTA was conducted. The results of the experi- ments showed that the extraction efficiencies from the examined samples were differ- ent. If a suficiently large amount of EDTA was applied, most of the lead was extracted only from Sample 1-deposit Zlatokop. Similar effects were obtained for the leaching of iron. The differences in the extraction efficiencies may be due to the difference of the of lead and iron species present in the zeolite crystals. The effects of EDTA concentration and solid/liquid ratio on the extraction of lead, iron and aluminum were studied.

Oxidative dehydrogenation of isobutane over titanium pyrophosphate catalyst

Abstract: The catalytic properties of titanium pyrophosphate in the oxidative dehydrogenation of isobutane to isobutylene were investigated in the 400 – 550 oC temperature range. Asignificant change of the product distribution and of the apparent activation energy of the reaction was observed at about 490 oC. This phenomenon, already observed in the oxidative dehydrogenation of n-butane, has been interpreted by the existence of two reaction mechanisms depending upon the reaction temperature. Comparison with the n-butane reaction allowed different activation pathways for the activation of alkanes to be proposed. The catalytic properties of TiP2O7 in the oxidative dehydrogenation of isobutane was also compared to those obtained previously with several other pyrophosphates and TiP2O7 was found to be less active and selective for this reaction.

Study on phenol oxidation with H2O2

Abstract: Two new ligands, 1-hydroxy-5- 4-(2-hydroxybenzylideneamino)pheno - xy -3-oxapentane (HL1) and 1-methoxy-5- 4-(2-hydroxybenzylideneamino)pheno - xy -3-oxapentane (HL2), and their Mn(III) complexes were synthesized and characterized. The two new Schiff base Mn(III) complexes were used to mimic peroxidase in the oxidation of phenol by hydrogen peroxide. The effect of the mole ratio of H2O2 to the complex, pH and temperature on the reaction rate was investigated. The mechanism of the catalytic oxidation is discussed. A kinetic mathematic model for the oxidation of phenol catalyzed by Schiff base Mn(III) complexes has been constructed.

The effects of alkyd/melamine resin ratio and curing temperature on the properties of the coatings

Abstract: Synthetic resins are used as binders in protective coatings. An alkyd/melamine resin mixture is the usual composition for the preparation of a coating called "baking enamel" cured through functional groups of resins. The effects of the alkyd/butylated melamine resin ratio (from 85/15 to 70/30) and curing temperature (from 100 °C to 160 °C) on the crosslinking and properties of the coating are presented in this paper. The degree of curing was determined by differential scanning calorimetry. These data were used for the estimation of the degree of crosslinking. The hardness, elasticity impact resistance, degree of adherence and gloss were also determined. Optimal coating properties could be achieved with an alkyd/melamine resin ratio of 75/25, a curing temperature of 130 °C and a curing time of 30 min.

Catalytic growth of carbon nanotubes with large inner diameters

Abstract: Carbon nanotubes (2.4 g/g catalyst), with large inner diameters were successfully synthesized through pyrolysis of methane on a Ni-Cu-Al catalyst by adding sodium carbonate into the carbon nanotubes growth system. The inner diameter of the carbon nanotubes prepared by this method is about 20-60 nm, while their outer diameter is about 40-80 nm. Transmission electron microscopy and X-ray diffraction were employed to investigate the morphology and microstructures of the carbon nanotubes. The analyses showed that these carbon nanotubes have large inner diameters and good graphitization. The addition of sodium carbonate into the reaction system brings about a slight decrease in the methane conversion and the yield of carbon. The experimental results showed that sodium carbonate is a mildly toxic material which influenced the catalytic activity of the Ni-Cu-Al catalyst and resulted in the formation of carbon nanotubes with large inner diameters. The growth mechanism of the carbon nanotubes with large inner diameters is discussed in this paper.

A primer on electrocatalysis

Abstract: A short review of the development and achievement of electrocatalysis in the last 50 years is given. The need for the knowledge of the reaction mechanism and position of the rate determining step for rational choice of catalyst is particularly stressed. Fundamental aspects of electrocatalysis are elaborated in more detail on the examples of electrochemically important reactions of hydrogen evolution and oxygen reduction, as well on the reaction of electrochemical oxidation of organic fuels (e.g., methanol).

Structure-activity relationship study of steroidal 1,2,4,5-tetraoxane animalarials using computational procedures

Abstract: A three-dimensional QSAR pharmacophore model for antimalarial activ- ity of steroidal 1,2,4,5-tetraoxanes was developed from a set of 17 substituted antimalarial derivatives out of 27 analogues that exhibited remarkable in vitro activity (below 100 ng/mL) against sensitive and multidrug-resistant Plasmodium falciparum malaria. The pharmacophore, which contains two hydrogen bond accep- tors (lipid) and one hydrophobic (aliphatic) feature, was found to map well onto the potent analogues and many other well-known antimalarial trioxane drugs including artemisinin, arteether, artesunic acid, and tetraoxanes. The presence of at least one hydrogen bond acceptor in the trioxane or the tetraoxane moiety appears to be neces- sary for potent activity of this class of compounds. Docking calculations of some of these compounds with heme are consistent with the above observation as the prox- imity of the heme iron to the oxygen atom of the trioxane or the tetraoxane moiety favors potent activity of the compounds. Electron transfer from the oxygen of trioxane or the tetraoxane appears to be crucial for mechanism of action of the com- pounds. This information together with the pharmacophore should enable search for new peroxide containing antimalarial candidates from databases and custom de- signed synthesis of more efficacious and safer analogues.