bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and properties of segmented main‐chain liquid‐crystalline polyurethanes with a high aspect ratio mesogenic diol as a chain extender
Authors: Padmavathy T. , Srinivasan K. S. V.
Published: August 2002

Main‐chain liquid‐crystalline polyurethanes were synthesized based on a high aspect ratio mesogenic diol (4‐{[4‐(6‐hydroxyhexyloxy)‐phenylimino]‐methyl}‐benzoic acid 4‐{[4‐(6‐hydroxyhexyloxy)‐phenylimino]‐methyl}‐phenyl ester) as a chain extender; polycaprolactone (PCL) diol soft segments of different number‐average molecular weights (530, 1250, or 2000); and different diisocyanates, including 1,4‐hexamethylene diisocyanate (HMDI), 4,4′‐methylene bis(cyclohexyl isocyanate) (H12MDI), and 4,4′‐methylene bis(phenyl isocyanate) (MDI). The structure of the polymers was confirmed with Fourier transform infrared spectroscopy, and differential scanning calorimetry and polarizing microscopy measurements were carried out to examine the liquid‐crystalline and thermal properties of the polyurethanes, respectively. The mesogenic diol was partially replaced with 20–50 mol % PCL. A 20 mol % mesogen content was sufficient to impart a liquid crystalline property to all the polymers. The partial replacement of the mesogenic diol with PCL of various molecular weights, as well as the various diisocyanates, influenced the phase transitions and the occurrence of mesophase textures. Characteristic liquid‐crystalline textures were observed when a sufficient content of the mesogenic diol was present. Depending on the flexible spacer length and the mesogenic content, grained and threadlike textures were obtained for the HMDI and H12MDI series polymers, whereas the polyurethanes prepared from MDI showed only grained textures for all the compositions. The polymers formed brittle films and could not be subjected to tensile tests. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1527–1538, 2002
Synthesis and structure of wholly aromatic liquid–crystalline polyesters containing meta‐ and ortholinkages
Authors: He Chaobin , Lu Zhihua , Zhao Lun , Chung Tai‐Shung
Published: August 2002

Wholly aromatic main‐chain rigid‐chain polymers containing meta‐ and orthokink linkages were synthesized. The thermal property, liquid crystallinity, and crystalline structure were studied using DSC, polarized light microscopy, and wide‐angle X‐ray scattering. These polymers exhibited liquid crystallinity up to 50 mol % of meta‐ and orthokink linkages. The existence of liquid crystallinity in these polymers may be attributed to the adoption of cis conformation in kink units in these polymers because the energy penalty for doing so can be compensated by the formation of the liquid–crystalline phase. The crystallinity of the polymers was low, and the crystal structure was quite similar to that of the pure polymers (without kink units). This can be explained by that fact that the crystal region mainly consists of the nonkink units, and the kink units disrupt the crystallization of the polymers and form defects. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1242–1248, 2001
Ferrocene‐based organophosphorus liquid–crystalline polymers: Synthesis and characterization
Authors: Senthil S. , Kannan P.
Published: August 2002

Ferrocene‐containing polyphosphate and phosphonate esters were synthesized by the solution polycondensation method. The structure of the polymers was confirmed using various spectroscopic techniques. The formation of two types of chain blocks was confirmed by 31P NMR spectroscopy. Hot stage optical polarized microscope (HOPM) analysis revealed that all the polymers have a liquid–crystalline property. The char yields of the synthesized similar polymers were much higher than those of nonphosphorus polymers already reported in the literature. DSC analysis confirmed our predictions over the liquid–crystalline property, glass‐transition temperature, isotropization temperature, and thermal stability of the polymers. The effects of substitution on the side chain, structure of the liquid‐–crystalline phase, and thermal stability of the polymers have also been discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2396–2403, 2001
Atom transfer radical polymerization through N‐chlorosulfonamides
Authors: Filiz Şenkal B. , Hizal Gürkan , Biçak Niyazi
Published: August 2002

Controlled polymerizations of vinyl monomers such as methyl methacrylate and styrene are achieved using N‐chloro,N‐propyl‐p‐toluenesulfonamide (NCPT) together with a cuprous bromide/hexahexyl triethylenetetramine (CuBr/H‐TETA) complex. Although N‐halosulfonamides are known to decompose radically to give free chlorine, NCPT alone (without a cuprous complex) does not initiate any polymerization even in prolonged reaction times. Instead these add to the double bonds to give 2‐chloroethylsulfonamides. In the present polymerization system a good chlorine donator (NCPT) is combined with an organic soluble complex (CuBr/H‐TETA) to perform atom transfer radical polymerizations (ATRPs) in homogenous conditions. The linear proportionality of the molecular weights to the conversions and straight lines observed in ln(M0/M) (where M0 and M are the monomer contents at the beginning and at any time, respectively) versus time plots indicate typical controlled polymerization characteristics. The use of freshly prepared NCPT is advisable due to its slow and spontaneous decomposition when standing at room temperatures. Because of their easy preparation, N‐chlorosulfonamides can be used and are preferred instead of special halogen compounds commonly used in copper mediated ATRP. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2691–2695, 2001
Synthesis and properties of fluorene‐based fluorinated polymers
Authors: Kameshima Hisamitsu , Nemoto Nobukatsu , Endo Takeshi
Published: August 2002

Fluorene‐based polymers containing various fluorinated benzene (fluorobenzene, p‐difluorobenzene, and tetrafluorobenzene) moieties were synthesized. In addition, perfluorooctylation of poly‐[(9,9‐dioctylfluorene‐2,7‐diyl)‐co‐(fluorene‐2,7‐diyl)] was carried out to afford fluorene‐based polymers with perfluorooctyl moiety at the 9‐position on the fluorene ring. To evaluate the effect of fluorine moiety, polymers containing nonfluorinated benzene moieties and nonfluorinated octyl groups were synthesized. The photoluminescence measurements indicated that all these polymers exhibited blue emission in solution, but a polymer containing a perfluorooctyl group did not emit in the film state. Polymers containing various fluorinated benzene moieties showed higher fluorescence quantum yields and thermal stability than those containing nonfluorinated benzene. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3143–3150, 2001
Self‐initiating performance of maleic anhydride on surface photografting polymerization
Authors: Deng Jian‐Ping , Yang Wan‐Tai
Published: August 2002

Maleic anhydride (MAH) was photografted onto low‐density polyethylene (LDPE) films with a grafting efficiency of about 70% in the absence of a photoinitiator. The self‐initiating performance was attributed to a mechanism of abstracting hydrogen atoms from LDPE chains by excited MAH dimers. The supporting experimental results were as follows: (1) the far‐UV radiation (200–300 nm) was indispensable for the graft polymerization and 2) the crosslinking reaction of LDPE inevitably accompanied the grafting of MAH. In addition, the initiation performance of MAH was further confirmed by surface photografting of acrylic acid in the presence of MAH, where MAH was used as the photoinitiator. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3246–3249, 2001
Synthesis and luminescence of polyphosphazenes with carbazolyl side chains
Authors: Li Zhen , Qin Jingui , Deng Xianyu , Cao Yong
Published: August 2002

Two new blue‐light‐emitting polyphosphazenes (1 and 2) containing carbazolyl groups as side chains were synthesized from a highly reactive macromolecular intermediate by a nucleophilic substitution reaction. Molecular structural characterization for the polymers was presented by 1H NMR, IR, and ultraviolet–visible spectra, gel permeation chromatography, and differential scanning calorimetry. The polymers exhibited excellent solubility in common organic solvents and were thermally stable. A fluorescence analysis of the two materials in tetrahydrofuran showed a strong blue light emitting. The quantum yields of the polyphosphazenes were 0.55 for 1 and 0.64 for 2, relative to quinoline (in 0.1 N H2SO4). An electroluminescent diode was fabricated, and a bright blue light was observed; the maximum external quantum efficiency was about 0.026% at an applied forward voltage of 23 V. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3428–3433, 2001
Theoretical consideration of the molecular mass distribution of starlike polymers formed by attachment of linear polymers to dendritic cores
Authors: Liu Hewen , Wilén Carl‐Eric
Published: August 2002

Star‐shaped polymers can be synthesized by condensation of linear polymers to dendritic cores. The distribution of molecular masses of such hybrid star polymers and the factors influencing it have been investigated by calculations based on population balance equations and Laplace transformations. Moreover, the expressions for numerical calculations of molecular mass distributions have been derived for both Poisson and Schultz–Zimm types of initial molecular mass distributions. According to the calculation results, the molecular mass distribution of the star polymers is strongly dependent on the distribution of the length of linear polymers. Beyond this, the molecular mass development is affected by several parameters that describe the reaction degree of dendritic cores, thus, by the fraction of all functional groups of dendritic cores involved in grafting, denoted by p; the average branching degree of one starlike molecule, represented by ρ; or the fraction of dendritic molecules becoming the cores of star polymers, expressed by p/ρ, provided the star molecule contains only one core. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2751–2758, 2001
Inelastic neutron scattering from isotactic polypropylene
Authors: Annis B. K. , Kim Man‐Ho , Alamo R. , Pyda M.
Published: August 2002

We used inelastic neutron scattering to probe the low‐energy excitations in semicrystalline isotactic polypropylenes with different degrees of crystallinity. The contributions from the amorphous and crystalline regions to the total scattering intensity were extracted under the assumption of a weighted linear contribution of the two regions in a simplified two‐phase system. The resulting intensity from the amorphous region showed a peak at 1.2 meV that was in good agreement with the previously determined boson peak characteristic of atactic polypropylene. The possibility of a contribution to the boson peak region by longitudinal acoustic mode modes that are characteristic of semicrystalline polymers and appear in the same low‐frequency region is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2852–2859, 2001
Interface development in polycarbonate/poly(methyl methacrylate) bilayer films
Authors: Hutchings L. R. , Richards R. W. , Thompson R. L. , Clough A. S. , Langridge S.
Published: August 2002

We report the effect of annealing over a range of temperatures and times on the mixing, stability, and interfacial width in thin bilayer films of bisphenol A–polycarbonate (PC) on deuterated poly(methyl methacrylate) (dPMMA). These bilayer films were highly stable when annealed at temperatures of up to 438 K, the temperature at which the degradation of the blends of these materials was first detectable by thermogravimetric analysis. At higher temperatures, dewetting of the PC upper layer of the film occurred at an increasing rate. Nuclear reaction analysis showed that the PC and dPMMA layers remained segregated. Neutron reflectometry data showed that the interfacial width between the two polymer layers grew rapidly from 0.5 nm for an unannealed sample to approximately 4.0 nm, the latter value being in good agreement with the predicted value for the interfacial width in the absence of any reaction. Extended annealing at 438 K and lower temperatures had no effect on the interfacial width, whereas at higher temperatures, the interfacial width increased to approximately 5.5 nm before the films became unstable. The broadening of the interface found at higher annealing temperatures was attributed to an increase in the miscibility of the polymers induced by the monomer from the unzipping of the dPMMA chains. There was no evidence of a thermally induced chemical reaction between the two polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2351–2362, 2001
Investigation at the chain segmental level of the miscibility of poly(vinyl chloride)/atactic poly(methyl methacrylate) blends
Authors: Lau Cheryl , Mi Yongli
Published: August 2002

We employed high‐resolution 13C cross‐polarization/magic‐angle‐spinning/dipolar‐decoupling NMR spectroscopy to investigate the miscibility and phase behavior of poly(vinyl chloride) (PVC)/poly(methyl methacrylate) (PMMA) blends. The spin–lattice relaxation times of protons in both the laboratory and rotating frames [T1(H) and T1ρ(H), respectively] were indirectly measured through 13C resonances. The T1(H) results indicate that the blends are homogeneous, at least on a scale of 200–300 Å, confirming the miscibility of the system from a differential scanning calorimetry study in terms of the replacement of the glass‐transition‐temperature feature. The single decay and composition‐dependent T1ρ(H) values for each blend further demonstrate that the spin diffusion among all protons in the blends averages out the whole relaxation process; therefore, the blends are homogeneous on a scale of 18–20 Å. The microcrystallinity of PVC disappears upon blending with PMMA, indicating intimate mixing of the two polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2390–2396, 2001
Structural and functional properties of hemocyanin from Cyanagraea praedator, a deep‐sea hydrothermal vent crab
Authors: Chausson Fabienne , Bridges Christopher R. , Sarradin Pierre‐Marie , Green Brian N. , Riso Ricardo , Caprais Jean‐Claude , Lallier François H.
Published: August 2002

Cyanagraea praedator (Crustacea: Decapoda: Brachyura) is an endemic species of the East Pacific Rise hydrothermal vents, living in the upper part of black smoker chimneys. Because we were seeking species that have made respiratory adaptations to the hydrothermal environment, we looked at Cyanograea hemocyanin (Hc) and determined its quaternary structure and the oxygen‐binding properties in relation to temperature, pH, and lactate. C. praedator Hc is composed of dodecamers and hexamers, with dodecamers formed by the perpendicular association of two hexamers. The composition of these polymers was determined by electrophoresis and, for the first time, by electrospray mass spectrometry. Dodecamers and hexamers are composed of six subunits common to the two forms, with molecular mass ranging from 75,008 Da to 75,534 Da. In addition, we found two dodecamer‐specific subunits, at 75,419 Da and 75,629 Da. The native hemocyanin possesses a high oxygen affinity (P50 varies between 4 and 10 Torr at pH 7.5, 15°C) and a large Bohr coefficient (Δ log P50/ΔpH ∼ −1.8). Oxygen affinity is not affected by lactate or, surprisingly, temperature between 5°C and 35°C (ΔH = 1.16 kJ/mol1 5–35°C). Dialysis of native hemolymph elicited a significant increase in Hc‐O2 affinity (ΔP50 = 2.5 Torr at pH 7.5), an effect opposite the usual trend observed for crustacean hemocyanins. In this article these functional properties are interpreted in relation to characteristics of the environment. Proteins 2001;45:351–359. © 2001 Wiley‐Liss, Inc.
Design and initial characterization of a circular permuted variant of the potent HIV‐inactivating protein cyanovirin‐N
Authors: Barrientos Laura G. , Louis John M. , Hung Jason , Smith Trent H. , O'Keefe Barry R. , Gardella Roberta S. , Mori Toshiyuki , Boyd Michael R. , Gronenborn Angela M.
Published: August 2002

A circular permuted variant of the potent human immunodeficiency virus (HIV)‐inactivating protein cyanovirin‐N (CV‐N) was constructed. New N‐ and C‐termini were introduced into an exposed helical loop, and the original termini were linked using residues of the original loop. Since the three‐dimensional structure of wild‐type cyanovirin‐N is a pseudodimer, the mutant essentially exhibits a swap between the two pseudo‐symmetrically related halves. The expressed protein, which accumulates in the insoluble fraction, was purified, and conditions for in vitro refolding were established. During refolding, a transient dimeric species is also formed that converts to a monomer. Similar to the wild‐type CV‐N, the monomeric circular permuted protein exhibits reversible thermal unfolding and urea denaturation. The mutant is moderately less stable than the wild‐type protein, but it displays significantly reduced anti‐HIV activity. Using nuclear magnetic resonance spectroscopy, we demonstrate that this circular permuted monomeric molecule adopts the same fold as the wild‐type protein. Characterization of these two architecturally very similar molecules allows us to embark, for the first time, on a structure guided focused mutational study, aimed at delineating crucial features for the extraordinary difference in the activity of these molecules. Proteins 2002;46:153–160. © 2001 Wiley‐Liss, Inc.
Interhelical hydrogen bonds and spatial motifs in membrane proteins: Polar clamps and serine zippers
Authors: Adamian Larisa , Liang Jie
Published: August 2002

Polar and ionizable amino acid residues are frequently found in the transmembrane (TM) regions of membrane proteins. In this study, we show that they help to form extensive hydrogen bond connections between TM helices. We find that almost all TM helices have interhelical hydrogen bonding. In addition, we find that a pair of contacting TM helices is packed tighter when there are interhelical hydrogen bonds between them. We further describe several spatial motifs in the TM regions, including “Polar Clamp” and “Serine Zipper,” where conserved Ser residues coincide with tightly packed locations in the TM region. With the examples of halorhodopsin, calcium‐transporting ATPase, and bovine cytochrome c oxidase, we discuss the roles of hydrogen bonds in stabilizing helical bundles in polytopic membrane proteins and in protein functions. Proteins 2002;47:209–218. © 2002 Wiley‐Liss, Inc.
Elucidation of the mode of substrate binding to hydroxynitrile lyase from Hevea brasiliensis
Authors: Gruber Karl
Published: August 2002

The hydroxynitrile lyase from Hevea brasiliensis (Hb‐HNL) is used as a catalyst in enantiospecific syntheses of α‐hydroxynitriles from aldehydes and methyl‐ketones. The catalyzed reaction represents one of the few industrially relevant examples of enzyme mediated CC coupling reactions. In this work, we modeled Hb‐HNL substrate complexes that have as yet proven inaccessible to experimental structure determination and were able to identify two binding modes for the natural substrate acetone cyanohydrin in docking simulations. Discrimination of the two alternatives was achieved by modeling complexes with two different chiral cyanohydrins followed by an analysis of the respective relative binding energies from molecular mechanics and thermodynamic integration. Only for one of the alternative binding modes the experimentally established S‐selectivity of the enzyme was correctly predicted. Our results yielded further support for an enzymatic mechanism involving the catalytic triad Ser80, His235, and Asp207 as a general acid/base. A pivotal role was ascribed to Lys236, which seems to be crucial for enzymatic activity at low pH values. In addition, the modeling calculations provided possible explanations for the observed substrate and enantioselectivity of the enzyme that rationalize available mutational data and will be the basis for future protein engineering efforts. Proteins 2001;44:26–31. © 2001 Wiley‐Liss, Inc.
Cryptic epitopes in N‐terminally truncated prion protein are exposed in the full‐length molecule: Dependence of conformation on pH
Authors: Matsunaga Yoichi , Peretz David , Williamson Anthony , Burton Dennis , Mehlhorn Ingrid , Groth Darlene , Cohen Fred E. , Prusiner Stanley B. , Baldwin Michael A.
Published: August 2002

Prion diseases are diseases of protein conformation. Structure‐dependent antibodies have been sought to probe conformations of the prion protein (PrP) resulting from environmental changes, such as differences in pH. Despite the absence of such antibodies for full‐length PrP, a recombinant Fab (D13) and a Fab derived from mAb 3F4 showed pH‐dependent reactivity toward epitopes within the N‐terminus of N‐terminally truncated PrP(90–231). Refolding and maintaining this protein at pH ≥5.2 before immobilization on an ELISA plate inhibited reactivity relative to protein exposed to pH ≤4.7. The reactivity was not affected by pH changes after immobilization, showing retention of conformation after binding to the plate surface, although guanidine hydrochloride at 1.5–2 M was able to expose the cryptic epitopes after immobilization at pH ≥5.2. The α‐helical CD spectrum of PrP(90–231) refolded at pH 5.5 was reduced somewhat by these pH changes, with a minor shift toward β‐sheet at pH 4 and then toward coil at pH 2. No covalent changes were caused by the pH differences. This pH dependence suggests titration of an acidic region that might inhibit the N‐terminal epitopes. A similar pH dependence for a monoclonal antibody reactive to the central region identified an acidic region incorporating Glu152 as a significant participant. Proteins 2001;44:110–118. © 2001 Wiley‐Liss, Inc.
Adsorption and degradation of thiazopyr in compost‐amended and non‐amended soils
Authors: Fernández María D , Sánchez‐Brunete Consuelo , Rodríguez Alvaro J , Tadeo José L
Published: August 2002

Adsorption and degradation of thiazopyr on two unamended soils and a soil amended annually during 8 years with compost were studied under laboratory conditions and compared with the results obtained on soils amended with fresh sewage sludge compost. The adsorption isotherms fitted the Freundlich equation well and a marked sorption increase was found in amended soils. Degradation data followed first‐order kinetics and thiazopyr had a half‐life of about 75 days at 25 °C and 60% water‐holding capacity of soil. The addition of fresh compost markedly decreased the rate of thiazopyr degradation, whereas the compost mineralised in the field after annual additions had only a small influence. Incubation studies with sterile soils showed a very significant decrease of the degradation rate, indicating that degradation by micro‐organisms was the main pathway of thiazopyr degradation in the soils studied.

© 2001 Society of Chemical Industry
Designing herbicide formulation characteristics to maximize efficacy and minimize rice injury in paddy environments
Authors: Cryer Steven A , Mann Richard K , Erhardt‐Zabik Susan , Keeney F Nelson , Handy Paul R
Published: August 2002

Mathematical descriptors, coupled with experimental observations, are used to quantify differential uptake of an experimental herbicide in Japonica and Indica rice (Oryza sativa, non‐target) and barnyardgrass (Echinochloa crus‐galli, target). Partitioning, degradation, plant uptake and metabolism are described using mass‐balance conservation equations in the form of kinetic approximations. Estimated environmental concentrations, governed by the pesticide formulation, are described using superimposed analytical solutions for the one‐dimensional diffusion equation in spherical coordinates and by a finite difference representation of the two‐dimensional diffusion equation in Cartesian coordinates. Formulation attributes from granules include active ingredient release rates, particle sizes, pesticide loading, and granule spacing. The diffusion model for pesticide transport is coupled with the compartment model to follow the fate and transport of a pesticide from its initial application location to various environmental matrices of interest. Formulation effects, partitioning and degradation in the various environmental matrices, differential plant uptake and metabolism, and dose‐response information for plants are accounted for. This novel model provides a mechanism for selecting formulation delivery systems that optimize specific attributes (such as weed control or the therapeutic index) for risk‐assessment procedures. In this report we describe how this methodology was used to explore the factors affecting herbicide efficacy and to define an optimal release rate for a granule formulation.

© 2001 Society of Chemical Industry
METI‐acaricide resistance in Tetranychus urticae does not confer resistance to the naphthoquinones
Authors: Devine Gregor J , Khambay Bhupinder P S
Published: August 2002

The naphthoquinones and the METI group of compounds act on sites associated with mitochondrial respiration, but METI‐resistant strains of two‐spotted spider mite from Japan and the UK exhibited no cross‐resistance to the naphthoquinones. The potential for developing commercial naphthoquinones therefore remains high.

© 2001 Society of Chemical Industry
Insecticidal arylalkylbenzhydrolpiperidines: novel inhibitors of voltage‐sensitive sodium and calcium channels in mammalian brain
Authors: Leong Darrell , Bloomquist Jeffrey R , Bempong Jeffrey , Dybas Jane A , Kinne Lyle P , Lyga John W , Marek Francis L , Nicholson Russell A
Published: August 2002

Using preparations derived from whole mouse brain, we have demonstrated that insecticidal arylalkylbenzhydrolpiperidines inhibit the depolarization of synaptoneurosomes as measured by rhodamine 6G fluorescence and block 22Na+ uptake into synaptosomes, when veratridine is used as the activator. These insecticides also have the ability to potently displace the binding of [3H]batrachotoxinin A 20‐α‐benzoate ([3H]BTX‐B) to neuronal sodium channels in a concentration‐dependent manner. The study compounds can be classified as competitive inhibitors of radioligand binding, since they decrease the affinity of [3H]BTX‐B for site 2 without affecting the concentration of sites labelled by this radioligand. Our kinetic analyses revealed that at its IC50, the 4‐carbomethoxyaminobenzylpiperidine analogue reduces the rate of association of [3H]BTX‐B with site 2, whereas higher concentrations were required to accelerate dissociation of the [3H]BTX‐B:sodium channel complex. These results indicate an ability to interact with both non‐activated and persistently activated states of the voltage‐sensitive sodium channel, but higher affinity for the former. Such a profile also implies that inhibition of [3H]BTX‐B binding to site 2 occurs via an allosteric mechanism. In addition, arylalkylbenzhydrolpiperidines interact with presynaptic voltage‐sensitive calcium channels, since we demonstrate that they inhibit increases in [free Ca++] and 45Ca++ uptake when evoked by high KCl concentration in mouse brain synaptosomal preparations. Such effects generally occur at concentrations that are higher than those required to inhibit sodium channels. Blockade of sodium and calcium channels may therefore contribute to the in vivo neurological effects observed in rodents exposed to these insecticides.

© 2001 Society of Chemical Industry
PCR‐based detection of sterol demethylation inhibitor‐resistant strains of Penicillium digitatum
Authors: Hamamoto Hiroshi , Hasegawa Koji , Nakaune Ryoji , Lee Young Jin , Akutsu Katsumi , Hibi Tadaaki
Published: August 2002

A simple method for detecting sterol demethylation inhibitor (DMI)‐resistant strains of the citrus green mould pathogen, Penicillium digitatum, has been developed. The method involves detection of a tandem repeat of a transcriptional enhancer in the promoter region of PdCYP51, which encodes the target enzyme of DMIs, by PCR, using conidia as template. The presence of the tandem repeat leads to overexpression of this gene and confers DMI resistance to the fungus. We examined the relationship between the presence of the tandem repeat and DMI resistance in 39 strains of P digitatum. The results suggested that the DMI resistance mechanism based on the tandem repeat is common in this fungus. Using this method, the presence of DMI resistance of this fungus can be detected within 5–6 h.

© 2001 Society of Chemical Industry
Influence of topsoil tilth and soil moisture status on losses of pesticide to drains from a heavy clay soil
Authors: Brown Colin D , Fryer Chris J , Walker Allan
Published: August 2002

Twelve lysimeters with a surface area of 0.5 m2 and a length of 60 cm were taken over mole drains from a Denchworth heavy clay soil and divided into two groups with either a standard agricultural tilth or a finer topsoil tilth. The influence of topsoil tilth on leaching of the herbicide isoproturon and a bromide tracer was evaluated over a winter season. The effect of variations in soil moisture status in the immediate topsoil on leaching of isoproturon, chlorotoluron and linuron was investigated in the following winter season. Here, water inputs were controlled such that lysimeters received 50 mm at a maximum intensity of 2 mm h−1 over a 4‐week period with herbicides applied on day 15. Three treatments received the water either all prior to application, all after application, or evenly spread over the 4‐week period. Leaching losses of the three herbicides were monitored for a subsequent drainage event. Analysis of covariance showed a significant effect of topsoil tilth and total flow on both the maximum concentrations (P  = 0.034) and total losses (P  = 0.012) of isoproturon in drainflow. Both concentrations and losses were c 35% smaller from lysimeters with the finer tilth. However, generation of the fine tilth in the field was restricted by a wet autumn and this is not considered a reliable management option for reducing pesticide losses from heavy clay soils. In the second experiment, variation in soil moisture content prior to and after application did not have any significant effect (P < 0.05) upon subsequent losses of the three herbicides to drains.

© 2001 Society of Chemical Industry
Evidence for oil‐induced oxidative stress to larvae of the lightbrown apple moth, Epiphyas postvittana Walker (Lepidoptera: Tortricidae)
Authors: Taverner Peter D , Bailey Peter T , Roush Richard T
Published: August 2002

For the purpose of understanding better the mode of action of alkanes on insects, the relationship between mortality, weight loss in oxygen enriched atmospheres and dietary antioxidants was examined using an alkane, C15 Ampol CPD and a spray oil, C23 DC‐Tron NR, on lightbrown apple moth, Epiphyas postvittana Walker, (LBAM). The results showed that the surfactant blend used in CPD was an insignificant contributor to the overall toxicity of dilute oil/water emulsions. Higher weight loss occurred in CPD‐dipped larvae than C23 DC‐Tron NR‐dipped larvae, which suggests that alkanes disrupt tracheal waxes and render insects more prone to desiccation. High levels of oxygen increased the toxicity of CPD to LBAM larvae. In addition, dietary supplements of anti‐oxidant, α‐tocopherol, fed to LBAM larvae were successful in reducing the toxicity of CPD. These results suggest that the alkane may contribute to oxidative injury. The potential role of oil‐induced oxidative stress in acute and chronic toxicity in insects is discussed.

© 2002 Society of Chemical Industry
A type‐II β‐turn, proline‐containing, cyclic pentapeptide as a building block for the construction of models of the cleavage site of pro‐oxytocin
Authors: Dettin Monica , Falcigno Lucia , Campanile Tiziano , Scarinci Claudia , D'Auria Gabriella , Cusin Marina , Paolillo Livio , Di Bello Carlo
Published: August 2002

Previous studies have indicated that proteolytic activation of pro‐hormones and pro‐proteins occurs most frequently at the level of basic amino acids arranged in doublets and that the dibasic sites are situated in or next to β‐turns. Investigations utilizing synthetic peptides reproducing the N‐terminal processing domain of pro‐oxytocin‐neurophysin have suggested a close relationship between the secondary structure of the cleavage locus and enzyme recognition, the minimal recognized sequence being the ‐Pro‐Leu‐Gly‐Gly‐Lys‐Arg‐Ala‐Val‐Leu‐ segment of the native precursor. NMR investigations and energy minimization studies have demonstrated that this sequence is organized in two type‐II β‐turns involving the ‐Pro‐Leu‐Gly‐Gly‐ and ‐Lys‐Arg‐Ala‐Val‐ sequences. To further strengthen the above reported hypothesis and to study the role of turn subtypes, a new proline containing cyclic substrate of the processing enzyme, in which the N‐terminal side that comes before the Lys‐Arg pair is constrained to adopt a type‐II β‐turn, has been synthesized. The presence of a type‐II β‐turn structure in this cyclic peptide model has been demonstrated by a combined NMR, CD and FT‐IR absorption investigation. A preliminary study shows that PC1 is able to recognize and process our constrained substrate. Copyright © 2001 European Peptide Society and John Wiley & Sons, Ltd.
Representative values of thermal actions for concrete bridges
Authors: Soukhov Dmitri
Published: August 2002

The pre‐standard ENV 1991‐2‐5 Thermal Actions was concluded in 1996 and deals with the thermal actions induced in the structures due to climatic effects (air temperature, solar radiation). These climatic conditions cause a non‐linear temperature profile through the depth of the bridge deck. This profile can be subdivided into three parts which are called ‘thermal actions’: bridge effective temperature, linear temperature difference, non‐linear part. For concrete bridges the first two parts play the most important role. According to pre‐ standards ENV 1991‐1 Basis of Design thermal actions are defined as variable actions and following representative values have to be determined: –characteristic value, with return period of 50 years; –infrequent value, with return period of one year; –frequent value, with return period of two weeks; –quasi‐permanent value Three groups of bridge cross sections are investigated: box girders, T‐girders, slabs.

The climatic data were obtained from the meteorological station Giessen (Hessen, Germany). This station located in the centre of Germany and Europe and can be considered as a representative place for middle Europe. The record period is from 1981 to 1990.

To exclude the problem of autocorrelation the three‐day maximum of climatic effects and extreme value distribution type III are used for statistical analysis. Then the representative values of climatic effects are calculated.

For calculation of temperature profile the one‐dimensional heat flow model through concrete bridge deck is used. This model runs off for four different representative values of climatic effects. Afterwards four representative values for uniform temperature component and for linear temperature differences are obtained. The reduction coefficients Ψ are also calculated. The characteristic values of thermal actions are included in the document ENV 1991‐2‐5 Thermal Actions and the Ψ coefficients are included in the document ENV 1991‐3 Traffic Loads on Bridges.
Recent European research advances in snow loading and their possible implementation in the Eurocodes
Authors: Del Corso R , Formichi P , Stiefel U
Published: August 2002

The main results of a prenormative research programme on snow loads, sponsored in 1996 by the European Commission, are presented. The research work, to which eight European scientific institutions took part, addressed the determination of ground and roof snow loads for ultimate and serviceability limit states verifications.

European regulations regarding snow loads are currently in the process of being updated, as Eurocode 1 is being converted from ENV 1991‐2‐3 to EN 1991‐1‐3. Many of the research results have been considered during the conversion process, but their direct introduction into the new code has raised some problems, since such results are not yet well established. The use of the research results for normative purposes is discussed and some open problems are presented.
Obtaining confidence intervals for Cpk using percentiles of the distribution of Ĉp
Authors: Hoffman Lorrie L.
Published: August 2002

Ĉpk is used as an estimate of process capability and can reflect performance degradation due to both shifts in the process mean and variability. Exact upper and lower confidence limits for the actual parameter value are elusive. Objections to existing estimators focus on two areas: the difficulty of executing the needed computations and the excessive widths of those confidence bounds. The CPE estimator (so called since it relies on Ĉp ) which we derive in this paper is formed by simply multiplying Ĉpk by a value from the inverse chi‐square distribution. A PASCAL computer program is supplied which generates those percentiles. Our CPE is compared via simulation to other estimators and is shown to be the preferred selection in most cases by providing the requisite probability coverage and narrow interval widths. Copyright © 2001 John Wiley & Sons, Ltd.
Identification and fine tuning of closed‐loop processes under discrete EWMA and PI adjustments
Authors: Pan Rong , del Castillo Enrique
Published: August 2002

Conventional process identification techniques of a open‐loop process use the cross‐correlation function between historical values of the process input and of the process output. If the process is operated under a linear feedback controller, however, the cross‐correlation function has no information on the process transfer function because of the linear dependency of the process input on the output. In this paper, several circumstances where a closed‐loop system can be identified by the autocorrelation function of the output are discussed. It is assumed that a proportional integral controller with known parameters is acting on the process while the output data were collected. The disturbance is assumed to be a member of a simple yet useful family of stochastic models, which is able to represent drift. It is shown that, with these general assumptions, it is possible to identify some dynamic process models commonly encountered in manufacturing. After identification, our approach suggests to tune the controller to a near‐optimal setting according to a well‐known performance criterion. Copyright © 2001 John Wiley & Sons, Ltd.
Theoretical study of metal ligand aromatic cation–π interactions of [Co(NH3)6]3+ with benzene
Authors: Žmirić Aleksandra , Milčić Miloš , Zarić Snežana D.
Published: August 2002

In this work, density functional theory calculations on geometries and energies of all possible conformers of the [Co(NH3)6]3+–C6H6 cation–π complex are described. The calculations show that stationary points are several η2 and the η3 structures. The most stable η3 structure has bonding energy, after basis set superposition error correction, of 32.18 kcal/mol. The energies of η3 structures are similar; also, the energies of η2 structures are similar while the difference in energy between η3 and the η2 structures is about 2 kcal/mol. This indicates a possibility for various orientations of the benzene ring with respect to interacting ligands in the case of metal ligand aromatic cation–π (MLACπ) interactions and a possibility for the existence of these interactions in different molecular systems. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Semiempirical INDO/S calculations on the absorption spectrum of mono‐ and trinuclear vanadium(II) complexes
Authors: Niedwieski Antonio Carlos , Soares Jaísa Fernandes , Jeffery Leigh George , Nunes Fábio Souza , Da Motta Neto Joaquim Delphino
Published: August 2002

This work is concerned with prospective starting materials for the synthesis of larger molecules used as functional models of the substrate binding and reducing site of the vanadium nitrogenase. It is well known that the mononuclear adduct of vanadium(II) chloride with N,N,N′,N′‐tetramethylethylenediamine, henceforth referred to as [VCl2(tmeda)2], is a good starting material for the synthesis of trinuclear vanadium complexes. We now report the results of semiempirical calculations on the spectroscopy of [VCl2(tmeda)2] using the intermediate neglect of differential overlap (INDO) method. For the mononuclear complex, the ground state was calculated to be a quartet, about 45 kcal/mol below the doublet. For the positively charged trinuclear vanadium complex, [V3(μ‐Cl)3(μ3‐Cl)2(tmeda)3]+, the ground state was calculated to be a decatet, about 47 kcal/mol below the octet. For both complexes the frontier orbitals are dominated by the vanadium 3d manifold, and accordingly the electronic spectra are dominated by d‐d* excitations within this manifold. The INDO/S‐calculated spectra are in good agreement with the observed UV‐visible spectra in both cases. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 245–251, 2002
Exploiting the interdependence of maximum entropy parameters in eigenvalue problems
Authors: Bandyopadhyay K. , Bhattacharyya K. , Bhattacharya A. K.
Published: August 2002

We exploit the interrelation among the parameters embedded in the maximum entropy ansatz to develop a scheme for obtaining accurate estimates of the ground‐state energy and wave function of systems for which the potential is represented by a rational function. Our scheme reduces an N‐parameter optimization problem to a two‐parameter one, leading to considerable simplification of the prevalent strategy. An indirect route for the study of excited states is also sketched. Test calculations on hydrogenic systems subject to strong or superstrong radial magnetic fields with and without electric field reveal the advantages of our approach. Additional studies on 1‐D anharmonic oscillators affirm its workability and generality. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Theoretical studies on the structures and isomerization of methylene lithium‐chlorosilylenoid H2CSiLiCl
Authors: Feng Shengyu , Feng Dacheng , Li Meijiang , Zhou Yufang
Published: August 2002

The methylene lithium‐chlorosilylenoid H2CSiLiCl was studied with ab initio calculations at the G2(MP2) level. Its four equilibrium structures, p‐complex, three‐membered ring, σ complex and silene, and three isomerization transition states were located. The calculations show that the nonplanar p‐complex structure is the lowest in energy among four equilibrium structures of H2CSiLiCl and should be experimentally detectable. The silene and σ complex structures with high energies are unstable and easy to isomerize to the most stable p‐complex structure via three‐membered ring one. Also, the geometric characteristics and bonding properties of various structures were analyzed and discussed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Features of the fluorine‐substituted acetaldehydes dynamics in the low‐lying electronic states: Quantum mechanical study of the CHF2CHO molecule lowest excited singlet state
Authors: Bataev Vadim A. , Dolgov Eugeniy K. , Abramenkov Alexandr V. , Pupyshev Vladimir I. , Godunov Igor A.
Published: August 2002

The potential energy surface (PES) for the CHF2CHO molecule in the excited S1 state is calculated by the CASSCF method. The features of the 1‐ and 2‐D cross‐sections of PES are considered in comparison with those of the relative molecules. The vibrational frequencies are calculated in harmonic approximation and the vibrational energy levels for the inversion motion of the carbonyl fragment CCHaO and for the torsion motion of the CHF2‐top are calculated in anharmonic approximation by the 1‐ and 2‐D variational methods. The calculated data are compared with the experimental ones. The problems of the experimental data interpretation are considered. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Modeling the internal mobility of the molecule of DNA
Authors: Yakushevich Ludmila V.
Published: August 2002

Recent investigations of the DNA molecule showed that it has a rather moveable structure and that internal DNA mobility plays an important role in biologic activity of the molecule. We describe here one possible way of modeling the internal DNA mobility based on the Hamiltonian formalism and analytic methods of finding solutions of corresponding dynamic equations. The approach developed in this article permits us to model internal motions of both small and large amplitudes. To illustrate the algorithm, we consider in details modeling internal DNA motions associated with the process of unwinding of the DNA double helix. We discuss merits and demerits of the model obtained. Different ways to improve the model and approach by applying computer methods, databanks, and methods of visualizations are also discussed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
On equilibrium intensive thermodynamic properties of composed p‐particles in many‐body systems
Authors: Bochicchio Roberto C. , Alcoba Diego R.
Published: August 2002

Equilibrium intensive thermodynamic properties of p‐particles (p‐ons), i.e., composed particles formed by few particles of the same nature such as fermion or boson pairs (p=2), trios (p=3), etc., are investigated. The relation of the p‐particle correlation functions to its p‐hole counterparts and an existing covariant structure in the hierarchy of the p‐particle correlation functions allow these generalized intensive properties to be properly defined and characterized. The connection between these generalized properties of the composed objects and those of the components is also derived. An explicit derivation of the chemical potential for pairs and its generalization to p‐particles is performed. Such results are further extended to any intensive property. Finally, the present development allows some previous results to be clearly interpreted thus yielding an important support for our theory. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 85: 63–71, 2001
Convergence of the orbital expansion in a correlated system: A test study on positronium
Authors: Bendazzoli Gian Luigi , Evangelisti Stefano , Leininger Thierry
Published: August 2002

Positronium, the bound state of an electron and a positron, is an exactly soluble quantum system, similar to a light isotope of hydrogen. It can be studied using the finite basis quantum chemistry codes developed for atoms and molecules. In fact, positronium can be mimicked by two electrons with opposite spins, in the absence of any nucleus and having the sign of the Coulomb interaction reversed. The exact wave function has a cusp in the points of coalescence of the two particles (a “Coulomb peak”), and this fact makes the convergence of the total energy, as a function of the basis set size, extremely slow. For this reason, positronium can be used to test the convergence properties of the quantum chemistry methods used to describe the dynamic correlation. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
An ab initio post‐Hartree–Fock study of vibrational infrared spectra of 5‐azacytosine and cytosine*
Authors: Yevgeniy Podolyan  , Yury V. Rubin  , Leszczyński Jerzy
Published: August 2002

Post‐Hartree–Fock ab initio studies were performed to predict the infrared (IR) vibrational spectra of the two most stable tautomers of 5‐azacytosine and cytosine. All geometries were optimized without symmetry restrictions by the gradient procedure at the MP2 level of theory using the standard 6‐31G(d,p) basis set. IR spectra have been calculated at the MP2/6‐31G(d,p) approximation. We found similar patterns in the sequence of the modes of the harmonic frequencies for both cytosine and 5‐azacytosine in the 3400–900 cm−1 region and distinctive differences in the high‐frequency region. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 83: 203–212, 2001