Necrodols: Anti-insectan terpenes from defensive secretion of carrion beetle (Necrodes surinamensis)

Two compounds recently isolated from the defensive gland ofNecrodes surinamensis, -and -necrodol, first representatives of a new category of monoterpenes (the necrodanes), are shown to be repellent to ants and other insects and irritating to cockroaches and flies. The compounds doubtless play a defensive role inNecrodes. The possible long-range applied significance of research on insect repellents is discussed.Paper No. 80 of the seriesDefense Mechanisms of Arthropods. Paper No. 79 is T. Eisner et al., Experientia 42:204–207 (1986).     

Mn(II), Co(II) and Ni(II) complexes of 4-(2-thiazolylazo)resorcinol: Syntheses, characterization, catalase-like activity, thermal and electrochemical behaviour

Manganese(II), cobalt(II) and nickel(II) acetates react with the ligand, 4-(2-thiazolylazo)resorcinol, to form complexes of general formula [ML₂] for MCo(II), Ni(II) and [ML₂]·2H₂O for MMn(II). Each of the azo complexes was characterized using elemental analysis, electrolytic conductance, UV–visible spectroscopy and magnetic susceptibility. An octahedral structure is proposed for all complexes prepared, which molar conductance data revealed to be non-electrolytes. IR spectra reveal that the ligand is coordinated to the metal ions in a tridentate manner via the resorcinol OH, azo N and thiazole N groups as donor sites. The electrochemical behaviour of the ligand and its complexes were obtained by cyclic voltammetry. Thermal decomposition studies were undertaken to secure additional information on the structure of the investigated compounds. The manganese(II) complex catalysed the disproportionation of hydrogen peroxide in the presence of imidazole.     

Determination of kinetic parameters for isothermal decomposition of azo initiators of polymerization by differential scanning calorimetry

Summary A new method for the determination of kinetic parameters for thermal decomposition of initiators of polymerisation by isothermal Differential Scanning Calorymetry (DSC) is described. This method is mainly applied to the azo initiators which exhibit a phase transition in their decomposition range. First the procedure for AIBN, taken as model, is described. Then this method is applied to two synthesized initiators: a ,-dihydroxy azo and an ,-azo disubstitued by fluorinated groups.     

Second-order nonlinear optical property of polyphosphazenes containing charge-transporting agents and indole-based chromophore

A new post functional strategy was developed to prepare polyphosphazenes with a high density of the indole based chromophore (nitro-indole or sulfonyl-indole chromophores) and carbazolyl side groups. Thus polyphosphazene (P1) with carbazolyl and indole groups was first prepared by direct nucleophilic substitution reaction with poly(dichlorophosphazene). Then, polyphosphazenes (P2-P4) containing charge-transporting agent (carbazolyl groups) and indole azo chromophores were synthesized via a post azo coupling reaction between P1 and p-nitrobezenediazonium fluoroborate or p-ethylsulfurylbenzenediazonium fluoroborate in N-methylpyrrolindone (NMP). The structures of P1-P4 were characterized, and the poled film of P2-4 revealed a resonant d₃₃ values in the range of 7-26 pm/V by second harmonic generation (SHG) measurements.     

The preparation and performance of lignin-based activated carbon fiber adsorbents for treating gaseous streams

Two types of lignin-based carbon fibers were prepared by electrospinning method. The first was activated with Fe₃O₄ (LCF-Fe), and the second was not activated with Fe₃O₄ (LCF). Gas phase adsorption isotherms for toluene on LCF-Fe and LCF were studied. The gas phase adsorption isotherm for 0% RH showed LCF-Fe have about 439 mg/g adsorption capacity which was close to that of commercially available activated carbon (500 mg/g). The Dubinin-Radushkevich equation described the isotherm data very well. Competitive adsorption isotherms between water vapor and toluene were measured for their RH from 0 to 80%. The effect of humidity on toluene gas-phase adsorption was predicted by using the Okazaki et al. model. In addition, a constant pattern homogeneous surface diffusion model (CPHSDM) was used to predict the toluene breakthrough curve of continuous flow-packed columns containing LCF-Fe, and its capacity was 412 mg/g. Our study, which included material characterization, adsorption isotherms, kinetics, the impact of humidity and fixed bed performance modeling, demonstrated the suitability of lignin-based carbon fiber for volatile organic compound removal from gas streams.

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Spectrophotometric investigations and computational calculations of prototropic tautomerism and acid-base properties of some new azo dyes

The prototropic tautomerism in four novel azo compounds derived from pyrazolo[1,5-a]pyrimidin-7(4H)-one was intensively examined. Tautomeric structures which result from annular and azo-hydrazone tautomerism were exposed to semiempirical and density functional theory (DFT) calculations, allowing the recording of structural parameters, physicochemical properties and equilibrium constants to be recorded. The values of the equilibrium constants determined among the most stable forms clearly showed that compounds 1 and 2 co-exist in the NH and hydrazone forms. However, NH tautomers were strongly preferred to other forms in compounds 3 and 4. The observed electronic absorption bands were assigned and compared with the predicted transitions using a time-dependent DFT method (TDDFT). In all solvents employed, except for DMF and acetonitrile, compounds 1 and 2 exhibited azo-hydrazone tautomerism. However, the ionized species were predominant in highly polar solvents for compounds 3 and 4. In DMF, all the investigated dyes exist either in acid-base equilibrium or in the ionized form depending on the molecular structure. Hence, the values of the ionization constant (K_ion) and Gibbs free energy (ΔG) of the equilibrium existing in solution were calculated. In addition, the pK_a values of the investigated dyes were determined spectrophotometrically.     

Role of dissolution of Mn(iii) species in discharge and recharge of chemically-modified MnO2 battery cathode materials

Various experimental techniques, including cyclic-voltammetry, constant current discharge and recharge, with a detecting electrode for determination of soluble Mn(iii) intermediate species, were used to study the reaction mechanism involved in the reduction of a chemical modified form of MnO₂ that is multiply rechargeable. The results show how dissolution of Mn(iii) species plays an important role in the overall path of the reduction reaction and also in the rechargeability of the material. Mainly an heterogeneous reduction mechanism is involved; substantial loss of capacity can arise if diffusion of the soluble Mn(iii) species into the bulk electrolyte solution is allowed to take place. In practical cells, this effect must be minimized using cells with starved electrolyte, i.e. with only a small free volume-fraction of KOH electrolyte in the MnO₂-carbon electrode structure. Soluble Mn(iii) species were detected in in situ experiments by means of (a) a spectro-electrochemical procedure, (b) a collector electrode system at which dissolved Mn(iii) was reoxidized to MnO₂, and (c) a rotating ring-disc electrode.     

Comparisons between azo dyes and Schiff bases having the same benzothiazole/phenol skeleton: Syntheses, crystal structures and spectroscopic properties

Three pairs of heterocyclic azo dyes and their corresponding Schiff bases were prepared by diazotization and Schiff-base condensation reactions between substituted 2-aminobenzothiazoles and either 3-(diethylamino)phenol or 3,5-dichloro-2-hydroxybenzaldehyde in order to obtain some high performance Disperse Red dyes and compare the structural and spectral differences between the azo dyes and Schiff bases. All azo dyes and Schiff bases in this work have the same benzothiazole/phenol skeleton but different substituent group in the phenyl ring. X-ray single-crystal diffraction analyses of selected compounds reveal that they have a similar planar conformation between the benzothiazole and phenol units but dissimilar dimeric crystal packing. Electronic spectra of the dyes demonstrate that the presence of NN and CN double bond chromophore units as well as substituent effects of different auxochrome groups in the benzothiazole backbone leads to significant alterations of bathochromic and hypsochromic shifts despite only slight differences in their molecular structures.     

Variation of total phenolic content and individual low-molecular-weight phenolics in foliage of mountain birch trees (Betula pubescens ssp.tortuosa)

We studied seasonal and between-tree variation in the composition and content of total and individual low-molecular-weight phenolics (LMWP) in leaves of mountain birch trees (Betula pubescens ssp.tortuosa). The major phenolic compounds were chlorogenic acid, quercetin-3-O--D-glucuronopyranoside, myricetin-3-O-(5-acetyl)-L-rhamnopyranoside, and 1-O-galloyl--D-(2-O-acetyl)-glucopyranose. The content of total phenolics, as well as the sum of individual LMWP, varied only slightly among trees while variation in contents of individual LMWP was large. Concentrations of almost all phenolics decreased during the growing season but pairwise correlations between individual phenolics remained similar over the whole season indicating tree-specific LMWP profiles over the season. Among flavonoids, the between-tree component of variation was 2.6 times as large as the seasonal component, while for variation of nonflavonoids the between-tree component was larger than the seasonal one. To explain the significant correlations within both flavonoid and nonflavonoid compounds, we discuss the biogenesis of LMWP in birch leaves, as well as their ecological role.     

Constant drift velocity of carriers in organic compounds

Summary It has been found in some organic compounds that the drift mobility of carriers decreases with the increasing electric field (HANSEL et al. 1978, HALADYJ et al. 1980, KANIA 1980, KONDRASIUK and SZYMANSKI 1972, MYCIELSKI and LIPINSKI 1978). All these experimental results can be interpreted on the assumption that the time of flight of carriers across a sample is controlled by one difficult jump. For such a system the Einstein equation is not valid and the drift velocity of carriers is independent of the electric field.     

Structure and properties of styrene-divinylbenzene copolymers

The effects of the solvating power of pure diluents on the porous structure and swelling properties of styrene-divinylbenzene (Sty-DVB) copolymers were investigated. The Hildebrand solubility parameter () and the three-dimensional solubility parameter (t) were used to predict the diluent-polymer affinity. In a general way, t was a better predictor than . It was found that the accessibility of polymer surfaces depends not only on the fixed pore volume but also on the elasticity of internuclear chains.     

On the electrochemistry of 2,4,6-triphenylnitrobenzene and related compounds

Cyclic voltammetry at a glassy carbon electrode of 2,4,6-triphenylnitrobenzene (1) in DMF shows two reversible one-electron reductions. Preparative reduction of 1 yields 2,4,6-triphenylaniline under both acidic and alkaline conditions and in DMF in the presence of acetic anhydride. On reduction in dry DMF is formed a stable, violet radical anion with a broad maximum at 682 nm; in acetonitrile 1 is reported to yield an unstable bluish radical which is transformed to a yellow-purple radical with a maximum at 520 nm. Solid-state ¹³C NMR confirmed the existence of two stereoisomers in the crystals found by X-ray structure determination, whereas ¹³C NMR in chloroform at ambient temperature indicated one isomer in solution. 2,4,6-Triphenylaniline shows in CV in acetonitrile a reversible oxidation; in acetonitrile containing pyridine it is oxidized to azo(2,4,6-triphenylbenzene). This compound is in acidic aqueous DMF reduced to 2,4,6-triphenylaniline. The three phenyl groups act as electron donating groups during reductions akin to p-hydroxy or p-amino groups.     

(1S,2R,4S,5S)-angelicoidenol-2-o-β-d-glucopyranoside—A moose deterrent compound in Scots pine (Pinus sylvestris L.)

Hydrophilic extracts of Scots pine (Pinus sylvestris L.) twigs have been investigated for palatability to moose in feeding experiments. The predominant repellent effect was observed from the 2-O--d-glucopyranoside of the monoterpene (1S,2R,4S,5S)-angelicoidenol. Of other isolated and tested substances, only taxifolin-3-O--d-glucopyranoside had a deterring effect. One fraction-containing mainly aliphatic compounds-also had a strong effect, but the effect was lost after further fractionation. Tannin-containing fractions had no effect. Angelicoidenol glucoside has not previously been reported fromP. sylvestris. The results are discussed in view of phenols as defense compounds.     

Poly(p-substituted phenylacetylene) with perfluoroalkyloxydimethylsilyl side groups for oxygen and ethanol permselective membrane

Summary p-(1H,1H,2H,2H-perfluorodecyloxydimethylsilyl)phenylacetylene(ACf8) and p-(1H,1H,2H,2H-Perfluorohexyloxydimethylsilyl)phenylacetylene(ACf4) were synthesized and copolymerized with p-trimethylsilylphenylacetylene(ASi). The resulting copolymers, copoly(ACf8/ASi) and copoly(ACf4/ASi), were fabricated to tough membranes showing high oxygen permeabilities(Po ₂) of 10^-8 cc(STP)·cm/cm²·s·cmHg and high oxygen permselectivities(=Po ₂/Pn ₂) of more than 2.7. In particular, a copoly(ACf4/ASi) containing 15.1 mol% of ACf4 unit showed the best result: Po ₂=3.51x10^-8 cc(STP)·cm/cm²·s·cmHg and =3.04. The values were in a top level and very close to those of upper bound line in an -Po ₂ plot of data in the literature. In addition, copoly(ACfn/ASi) membranes were ethanol permselective owing to water repellency of the perfluoroalkyl groups. Copoly(ACf4/ASi) membranes showed better oxygen and ethanol permselectivity than copoly(ACf8/ASi) membranes.     

Photoresponsive diblock copolymers bearing strong push–pull azo chromophores and cholesteryl groups

A series of diblock copolymers bearing strong push–pull azo chromophores and cholesteryl groups on the respective blocks was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. The liquid crystal phase structure, microphase-separated morphology, and photoresponsive properties of the block copolymers were investigated by using DSC, POM, AFM, XRD and laser irradiation. The results show that the cholesteryl block (PChEMA) forms smectic-A mesophase and the morphology depends on the length of the azo block (PAzoCN). When the azo block is short, such as PChEMA₅₀-b-PAzoCN₇, no microphase separation can be identified. For PChEMA₅₀-b-PAzoCN₂₈, PAzoCN appears as the hexagonal-packed nanocylinders embedded in the PChEMA matrix. When the azo block length further increases, the block copolymer PChEMA₅₀-b-PAzoCN₇₃ forms microphase-separated lamellae. The microphase separation shows no obvious restraint on the photoinduced orientation of the azo chromophores, but micron-scale mass transport of the photoresponsive PAzoCN block is inhibited by the phase confinement.     

Electrosynthesis of a manganese(iii) aminopolycarboxylate complex in alkaline media

Mn(iii)CyDTA [(trans-cyclohexane-1,2-diamine-N,N,N,N-tetraacetato) manganate(iii)] was generated electrochemically from Mn(ii)CyDTA (6–54 mm) in 0.1 m NaHCO₃ at pH 9.0 and 10.5, respectively, 25 °C, for two CyDTA/Mn molar ratios (1/1 and 2/1). A divided batch electrochemical reactor was employed with anode current densities from 2.6 to 102 A m^–2. Separate cyclic voltammetry experiments of Mn(iii)CyDTA in alkaline media showed a prepeak behaviour, indicating the adsorption of Mn(ii) species. The visible anodic deposit, formed during the electrosynthesis of Mn(iii)CyDTA at pH 10.5 and 1/1 CyDTA/Mn molar ratio on stainless steel and PbO₂/Pb, reduces the current efficiency for Mn(iii). For a Mn(ii) concentration of 18 mm and at 13 A m^–2, the graphite and platinized titanium anodes gave a current efficiency for Mn(iii) of 78% and 66%, respectively, without a visible deposit. A 2/1 CyDTA/Mn molar ratio, avoided a visible anodic deposit formation, but gave lower current efficiencies for Mn(iii) than in the case of a 1/1 ligand to metal ratio. The electrosynthesis of Mn(iii)CyDTA is recommended for routine preparation of the complex and is also suitable for in situ electrochemically mediated oxidations in alkaline media (up to pH 11).     

Electroconductive membrane ‘Celec’ for application in zinc/air alkaline batteries: An impedance study of oxygen reduction at the interface Pt/Celec

Oxygen reduction was studied at a platinum electrode on a new ceramic membrane named Celec in 6m KOH with a view to application of this ceramic material in Zn/air batteries. Cyclic voltammetry and impedance measurements were carried out on the oxygen electrode to investigate the oxygen reduction mechanism in the presence of the Celec ceramic. The impedance diagrams recorded at low and high overpotentials show different characteristics, which are well interpreted by the proposed mechanisms.     

Diffraction by difference holograms in electrooptic crystals

We propose a new method to read erasable volume phase holograms in electrooptic crystals nondestructively. We describe the basic ideas of diffraction by difference holograms and present first experimental results for LiNbO₃: Fe crystals.     

Advanced oxidant regeneration of granular activated carbon for controlling air‐phase VOCs

The Pennsylvania State University is researching an advanced oxidation (AO) system for controlling volatile organic compounds (VOCs) (Cannon et al. 1994). The system includes an air‐phase photolytic chamber, an air/water stripping tower, and granular activated carbon (GAC) beds, and the work herein describes he evaluation of the GAC beds. Field GACs have been evaluated, which had previously been loaded with VOCs and regenerated with AO for several years at several full scale installations. Full scale response then was simulated in laboratory‐scale experiments.

Results revealed that following 500 to 1000 daily loading and regeneration cycles, one field GAC lost 35% of its micropore volume, and 17–35% of its capacity to adsorb several VOCs. Under another condition, for a furniture coating GAC, 80% of the micropore volume was lost after several years of loading and reactivation cycles, and 23 to 63% of the VOC adsorption capacity was lost.

Laboratory results revealed that prolonged AO regeneration destroyed or desorbed most of the MIBK within the first inch of a GAC bed. AO regeneration also removed a fourth of the MIBK in the next five inches of the packed GAC bed. Several byproducts were created by the MIBK destruction, which generally contained one‐to‐three fewer carbon atoms than does MIBK, and also contained more oxygen functional groups.

Concurrent with these experiments, thermogravimetric analysis (TGA) tests were performed to evaluate the rate and extent of MIBK adsorption onto virgin GAC, and revealed that the MIBK adsorption capacity was fairly insensitive to the ranges of concentration and temperature that were employed. A modeling analysis of the diffusion characteristics onto virgin GAC revealed that during the time frame of three to five hours, the mass transfer rate appeared to be governed by restricted diffusion.