bluuebunny/crossref_metadata_2025_split huggingface dataset:
Unusual contributions of molecular architecture to rheology and flow birefringence in hyperbranched polystyrene melts
Authors: Kharchenko Semen B. , Kannan Rangaramanujam M. , Cernohous Jeff J. , Venkataramani Shivshankar , Babu Gaddam N. 
Published: September 2002

AbstractWith the increase in sophisticated synthesis methods, it appears that polymer architecture may be a tunable property. Therefore, the role of architecture in rheological and processing properties has received renewed attention, mainly because of dendrimer synthesis and metallocene‐catalyst technology. Linear polymers and hyperbranched polymers represent two ends of branching complexity. Some previous studies have suggested that hyperbranched polymers may behave like unentangled polymers, whereas others have proposed that they exhibit the properties of soft colloids. In an effort to compare the responses of linear and hyperbranched polymers, we synthesized starlike hyperbranched polystyrenes (HBPSs) of various branch lengths and numbers of branches. The HBPSs used in this study were unentangled or weakly entangled, allowing us to study the effect of branch density more readily. Two linear polystyrene (L‐PS) melts and two HBPSs were studied. Using a custom‐built rheooptical apparatus, we characterized the rheology and flow birefringence of these materials. To our knowledge, these are the first flow birefringence measurements on highly branched polymer melts. Our results suggest that the flow behavior of HBPS is significantly different from that of L‐PS: (1) HBPS shows nonterminal behavior in the low‐frequency rheological response; (2) when the stress‐optical rule (SOR) holds, the stress‐optical coefficient of HBPS is much lower than those of analogous linear polymers; and (3) when the branch density is high and the branch length is sufficiently low, the SOR fails for these homopolymer melts. A significant increase in the birefringence for a given amount of stress in the low‐frequency region suggests that there may be a soft core in these materials due to the strong preferential radial orientation of chain segments near the center of a molecule versus those near the periphery. The predominantly elastic response of the soft structures may be responsible for the enhanced form birefringence. Our preliminary results indicate that these materials may exhibit both polymeric and soft‐colloid natures. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2562–2571, 2001
Nanocomposites of poly(ethylene terephthalate‐co‐ethylene naphthalate) with organoclay
Authors: Chang Jin‐Hae , Park Dae‐Keun 
Published: September 2002

AbstractPoly(ethylene terephthalate‐co‐ethylene naphthalate) (PETN)/organoclay was synthesized with the solution intercalation method. Hexadecylamine was used as an organophilic alkylamine in organoclay. Our aim was to clarify the intercalation of PETN chains to hexadecylamine–montmorillonite (C16–MMT) and to improve both the thermal stability and tensile property. We found that the addition of only a small amount of organoclay was enough to improve the thermal stabilities and mechanical properties of PETN/C16–MMT hybrid films. Maximum enhancement in both the ultimate tensile strength and initial modulus for the hybrids was observed in blends containing 4 wt % C16–MMT. Below a 4 wt % clay loading, the clay particles could be highly dispersed in the polymer matrix without a large agglomeration of particles. However, an agglomerated structure did form in the polymer matrix at a 6 wt % clay content. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2581–2588, 2001
Ionic poly(p‐phenylene terephthalamide)s: Preparation and characterization
Authors: Chen W. C. , Sauer J. A. , Hara M. 
Published: September 2002

AbstractThe preparation and characterization of two types of ionic poly(p‐phenylene terephthalamide) (PPTA) is described. A sufficient number of ionic groups were added to render modified PPTA soluble in dimethylsulfoxide (DMSO). In one type, a hydrogen atom of the amide group was replaced by an ionic propanesulfonate group. In the other type, one of the hydrogen atoms on the phenylene ring was replaced by an ionic sulfonate group. The ionic PPTAs in DMSO showed an upturn in viscosity at very low concentrations that was characteristic of the polyelectrolyte behavior. Fourier transform infrared spectra of these samples were also studied. When the ionic group was attached at the end of the short propane side chain, the intensity of both the free and hydrogen‐bonded NH stretching mode was reduced compared with that of PPTA. Depending on the location of the ionic group, there were some changes in the intensity and wave number of the asymmetric and symmetric vibrations of the ionic SO group and the stretching mode of the carbonyl group. In both ionic PPTAs, there was an upward shift in the frequency of the symmetric vibrations of the sulfonate ion when the counterion, having been monovalent, became divalent. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2653–2663, 2001
Structured disorder and conformational selection
Authors: Tsai Chung‐Jung , Ma Buyong , Sham Yuk Yin , Kumar Sandeep , Nussinov Ruth 
Published: September 2002

AbstractTraditionally, molecular disorder has been viewed as local or global instability. Molecules or regions displaying disorder have been considered inherently unstructured. The term has been routinely applied to cases for which no atomic coordinates can be derived from crystallized molecules. Yet, even when it appears that the molecules are disordered, prevailing conformations exist, with population times higher than those of all alternate conformations. Disordered molecules are the outcome of rugged energy landscapes away from the native state around the bottom of the funnel. Ruggedness has a biological function, creating a distribution of structured conformers that bind via conformational selection, driving association and multimolecular complex formation, whether chain‐linked in folding or unlinked in binding. We classify disordered molecules into two types. The first type possesses a hydrophobic core. Here, even if the native conformation is unstable, it still has a large enough population time, enabling its experimental detection. In the second type, no such hydrophobic core exists. Hence, the native conformations of molecules belonging to this category have shorter population times, hindering their experimental detection. Although there is a continuum of distribution of hydrophobic cores in proteins, an empirical, statistically based hydrophobicity function may be used as a guideline for distinguishing the two disordered molecule types. Furthermore, the two types relate to steps in the protein folding reaction. With respect to protein design, this leads us to propose that engineering‐optimized specific electrostatic interactions to avoid electrostatic repulsion would reduce the type I disordered state, driving the molten globule (MG) → native (N) state. In contrast, for overcoming the type II disordered state, in addition to specific interactions, a stronger hydrophobic core is also indicated, leading to the denatured → MG → N state. Proteins 2001;44:418–427. © 2001 Wiley‐Liss, Inc.
Computational study of lipid‐destabilizing protein fragments: Towards a comprehensive view of tilted peptides
Authors: Lins L. , Charloteaux B. , Thomas A. , Brasseur R. 
Published: September 2002

AbstractTilted peptides are short sequence fragments (10–20 residues long) that possess an asymmetric hydrophobicity gradient along their sequence when they are helical. Due to this gradient, they adopt a tilted orientation towards a single lipid/water interface and destabilize the lipids. We have detected those peptides in many different proteins with various functions. While being all tilted‐oriented at a single lipid/water interface, no consensus sequence can be evidenced. In order to better understand the relationships between their lipid‐destabilizing activity and their properties, we used IMPALA to classify the tilted peptides. This method allows the study of interactions between a peptide and a modeled lipid bilayer using simple restraint functions designed to mimic some of the membrane properties. We predict that tilted peptides have access to a wide conformational space in membranes, in contrast to transmembrane and amphipathic helices. In agreement with previous studies, we suggest that those metastable configurations could lead to the perturbation of the acyl chains organization and could be a general mechanism for lipid destabilization. Our results further suggest that tilted peptides fall into two classes: those from proteins acting on membrane behave differently than destabilizing fragments from interfacial proteins. While the former have equal access to the two layers of the membrane, the latter are confined within a single lipid layer. This could be in relation with the organization of lipid substrate on which the peptides physiologically act. Proteins 2001;44:435–447. © 2001 Wiley‐Liss, Inc.
A conserved helix‐unfolding motif in the naturally unfolded proteins
Authors: Zetina Carlos R. 
Published: September 2002

AbstractAmong the naturally unfolded proteins there are many polypeptides that retain an extended conformation in the absence of any apparent signal. Using sequence alignment and secondary structure prediction tools, a conserved (LS/SL)(D/E)(D/E)(D/E)X(E/D) motif is uncovered in the vicinity of the N‐terminus of their unfolded helices. A comparison of these data with published observations allows one to propose that the (LS/SL)(D/E)(D/E)(D/E)X(E/D) motif is a helix‐unfolding signal. Furthermore, the strong similarity between this motif and the STXXDE casein kinase II phosphorylation site suggests a regulatory mechanism for the naturally unfolded proteins within the cell. Proteins 2001;44:479–483. © 2001 Wiley‐Liss, Inc.
The effect of the herbicide diuron on soil microbial activity
Authors: Prado Alexandre G S , Airoldi Claudio 
Published: September 2002

AbstractThe inhibitory effect of the herbicide diuron [3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea] on microbial activity in red Latosol soil was followed using microcalorimetry. The activity of the micro‐organisms in 1.50 g of soil sample was stimulated by addition of 6.0 mg of glucose and 6.0 mg of ammonium sulfate under 35% controlled humidity at 298.15 (± 0.02) K. This activity was determined by power–time curves that were recorded for increasing amounts of diuron, varying from zero to 333.33 µg g−1 soil. An increase in the amount of diuron in soil caused a decrease of the original thermal effect, to reach a null value above 333.33 µg g−1 of herbicide. The power–time curve showed that the lag‐phase period and peak time increased with added herbicide. The decrease of the thermal effect evolved by micro‐organisms and the increase of the lag‐phase period are associated with the death of microbial populations caused by diuron, which strongly affects soil microbial communities.© 2001 Society of Chemical Industry
The molecular interactions of pyrethroid insecticides with insect and mammalian sodium channels
Authors: Vais Horia , Williamson Martin S , Devonshire Alan L , Usherwood Peter N R 
Published: September 2002

AbstractRecent progress in the cloning of α (para) and β (TipE) Na channel sub‐units fromDrosophila melanogaster(fruit fly) andMusca domestica(housefly) have facilitated functional expression studies of insect Na channels inXenopus laevisoocytes, assayed by voltage clamp techniques. The effects of Type I and Type II pyrethroids on the biophysical properties of these channels are critically reviewed. Pyrethroid resistance mutations (termedkdrandsuper‐kdr) that reduce the sensitivity of the insect Na channel to pyrethroids have been identified in a range of insect species. Some of these mutations (eg L1014F, M918T and T929I) have been incorporated into theparaNa channel ofDrosophila, either individually or in combination, to investigate their effects on the sensitivity of this channel to pyrethroids. Thekdrmutation (L1014F) shifts the voltage dependence of both activation and steady‐state inactivation by ∼5 mV towards more positive potentials and facilitates Na channel inactivation. Incorporation of thesuper‐kdrmutation (M918T) into theDrosophilaNa channel also increases channel inactivation and causes a >100‐fold reduction in deltamethrin sensitivity. These effects are shared by T929I, an alternative mutation that conferssuper‐kdr‐like resistance. Parallel studies have been undertaken using the rat IIA Na channel to investigate the molecular basis for the low sensitivity of mammalian brain Na channels to pyrethroids. Rat IIA channels containing the mutation L1014F exhibit a shift in their mid‐point potential for Na activation, but their overall sensitivity to permethrin remains similar to that of the wild‐type rat channel (ie both are 1000‐fold less sensitive than the wild‐type insect channel). Mammalian neuronal Na channels have an isoleucine rather than a methionine at the position (874) corresponding to thesuper‐kdr(M918) residue of the insect channel. Replacement of the isoleucine of the wild‐type rat IIA Na channel with a methionine (I874M) increases deltamethrin sensitivity 100‐fold. In this way, studies of wild‐type and mutant Na channels of insects and mammals are providing a molecular understanding ofkdrandsuper‐kdrresistance in insects, and of the low pyrethroid sensitivity of most mammalian Na channels. They are also giving valuable insights into the binding sites for pyrethroids on these channels.© 2001 Society of Chemical Industry
Selecting the right compounds for screening: use of surface‐area parameters
Authors: Tice Colin M 
Published: September 2002

AbstractPolar surface area, total surface area and percentage surface area have been calculated from three‐dimensional structures of 88 post‐emergence herbicides, 93 pre‐emergence herbicides and 237 insecticides. Preferred ranges of values of these parameters were identified. Since the compounds in the training sets are used on a wide variety of species and target sites with various application modes, the parameter ranges are necessarily broad. The utility of the surface‐area parameter ranges in selection of compounds for agrochemical screening was compared with the use of ranges of the Lipinski Rule of 5 parameters: molecular mass, calculated log P, number of hydrogen‐bond donors and number of hydrogen‐bond acceptors. The more computationally intensive surface‐area parameters did not offer any obvious advantage over the Lipinski Rule of 5 parameters.© 2002 Society of Chemical Industry
A protocol for evaluation of the role of disinfectants in limiting pathogens and weed moulds in commercial mushroom production
Authors: Abosriwil Salem O , Clancy Kevin J 
Published: September 2002

AbstractIn vitro and in vivo evaluations of the effects of three commercial disinfectants on isolates of Trichoderma harzianum Rifai and Cladobotryum dendroides (Bull) W Gams & Hoozemans were combined in the development of methodologies for realistic assessment of disinfectant performance. ‘Environ’ and ‘Purogene’ incorporated into agar media at 50 mg AI litre−1 were effective in totally preventing the mycelial growth of T harzianum and C dendroides isolates, whereas with ‘Sudol’ a concentration of 500 mg AI litre−1 was required. Evaluation of a model in vivo system was combined with observations on the fungicidal effects of disinfectants. Spore suspensions of T harzianum (Th1), T harzianum (Th2) and C dendroides prepared from culture washings with sterilised distilled water were used as contaminating inoculum. Environ, Sudol and Purogene in aqueous solutions at 1000 mg AI litre−1 were sprayed onto these building structure surfaces before or after artificial contamination with spore suspensions. Re‐isolation from surfaces was carried out using agar swabs, which were prepared in visking tubing, applied to treated surfaces and incubated at 25 °C for 24, 48, 72 or 96 h. Environ and Purogene were more effective than Sudol in limiting the recovery of Trichoderma spp and C dendroides. All three disinfectants applied 12 h after artificial contamination onto wood, concrete or glazed surfaces were able to reduce the recovery of these isolates more effectively than when they were applied 12 h before artificial contamination. Greater persistence of contamination was noted on the rougher surfaces (wood and concrete) than on the smoother glazed surface. It was concluded in this in vivo evaluation that, in many cases, the protection achieved by the physical nature of the smooth glazed tile surfaces was equivalent to that available from the application of disinfectants, thus highlighting the attention needed to the nature of building surfaces in the structures used in the mushroom industry. The artificial contamination and re‐isolation techniques allowed significant comparison between disinfectant materials, timings and surface types. In the in vivo experiments using a single standardised test concentration, the relative fungicidal effects of the disinfectants, which varied in the complexity of their active ingredients, were better discriminated than the effects observed in vitro, although the general trend was similar.© 2002 Society of Chemical Industry
Bioassay and field‐simulator studies of the efficacy of pymetrozine against peach‐potato aphids, Myzus persicae (Hemiptera: Aphididae), possessing different mechanisms of insecticide resistance
Authors: Foster Stephen P , Denholm Ian , Thompson Robin 
Published: September 2002

AbstractTwenty‐one clones of the peach‐potato aphid, Myzus persicae (Sulzer), carrying various combinations of known mechanisms of insecticide resistance were assessed for their response to the new pyridine azomethine compound, pymetrozine, in leaf‐dip bioassays. Pymetrozine was also applied as a foliar spray to populations of four different UK M persicae clones on potato plants in field‐simulator chambers. Neither study showed any evidence of cross‐resistance to this compound. Pymetrozine, used in conjunction with other effective aphicides, such as pirimicarb and imidacloprid, can therefore play an important role in insecticide resistance‐management strategies for M persicae.© 2002 Society of Chemical Industry
Broad‐spectrum insecticide resistance in obliquebanded leafroller Choristoneura rosaceana (Lepidoptera: Tortricidae) from Michigan
Authors: Ahmad Mushtaq , Hollingworth Robert M , Wise John C 
Published: September 2002

AbstractNineteen insecticides, belonging to nine chemical classes, were bioassayed by dietary exposure against two strains of obliquebanded leafroller, Choristoneura rosaceana, collected from Michigan apple orchards. Berrien is a putatively organophosphate‐resistant strain from a commercial orchard with a history of insecticide use, and Kalamazoo a susceptible strain from an isolated and unsprayed orchard. The Berrien strain was moderately resistant (about 25‐fold) to organophosphates such as azinphos‐methyl and chlorpyrifos. Very low resistance (<10‐fold) was also observed to pyrethroids such as cypermethrin, zeta‐cypermethrin, bifenthrin, deltamethrin and esfenvalerate, to the ecdysone agonists tebufenozide and methoxyfenozide, and to the chlorinated pyrrole chlorfenapyr. Endosulfan and carbamates such as thiodicarb, methomyl and carbaryl had low intrinsic toxicities against both strains, with little difference in sensitivity between them. There was no resistance to spinosad. Emamectin benzoate was found to be the most toxic insecticide against C rosaceana, with slightly higher lethal doses required for the Berrien strain. Unexpectedly, Berrien exhibited a very high level of resistance (>700‐fold) to indoxacarb, which has never been used in Michigan to control this insect pest. The active metabolite of indoxacarb, DCJW, was considerably more toxic than the parent compound, but the resistance against DCJW was comparable to that seen with indoxacarb. This indicates that a failure to activate indoxacarb was not the mechanism of resistance in Berrien. The low level of resistance to several chemistries recorded in Michigan C rosaceana can be managed at this stage by adopting a rotation of chemistries having different modes of action.© 2002 Society of Chemical Industry
Antagonists of oxytocin featuring replacement with modified β‐mercaptopropionic acids at position 1
Authors: Flouret George , Majewski Tadeusz , Balaspiri Lajos , Brieher William , Mahan Kevin , Chaloin Olivier , Wilson Laird , Slaninová Jirina 
Published: September 2002

AbstractTwenty analogues were synthesized of [Pmp1, D‐Trp2, Arg8]oxytocin, PA, (Pmp = β,β‐pentamethylene‐β‐mercaptopropionic acid), a potent antagonist of the uterotonic effect of oxytocin in the rat (uterotonic test in vitro, pA2 = 7.77) and in the baboon. Systematic substitution of Pmp1 was made with β‐mercaptopropionic acids featuring replacement of the 4‐methylene group of the cyclohexyl ring of Pmp with isosteric O, S, NH or with C=O. Since the more hydrophilic NH and C=O substitutions showed a sharply decreased antagonistic potency (rat uterotonic test in vitro), additional modifications were made to reduce their hydrophilicity. Acylation of the NH group with various acyl groups, and ketalization or thioketalization of C=O with more or less bulky substituents led to a partial restoration of potency, the N‐carbamyl‐ and the 2‐mercapto‐2‐adamantaneacetyl analogues being equipotent with PA. Internal cyclization by amidation of the NH‐group with Gly‐9, resulted in a bicyclic analogue, (cyclo 1–9)[(HN)Pmp1, Gly9]PA which was equipotent with PA. When Pen‐6 was introduced into the bicyclic derivative instead of Cys‐6, to reduce the flexibility of the rings, the resulting (cyclo 1–9)[(HN)Pmp1, Pen6, Gly9]PA had somewhat better potency (pA2 = 8.17) in the uterotonic test and no detectable activity in the antidiuretic assay. In the case of substitution of PA with β,β‐(3‐thiapentamethylene)‐β‐mercaptopropionic acid, (S)Pmp, there was also an increase in inhibitory potency in the uterotonic test (pA2 = 8.08); the analogue had extremely weak antidiuretic activity. To establish the importance of the steric effects of the Pen‐6 substitution, analogues [Pen6]PA and [(S)Pmp1, Pen6]PA were made and found to be very potent, with a pA2 of 8.72 and 8.86, respectively. The high potency of the latter analogue and its extremely weak action in the diuretic assay makes it an attractive candidate for studies on the inhibition of the biological effects of oxytocin and for the prevention of preterm labour. Copyright © 2002 European Peptide Society and John Wiley & Sons, Ltd.
CCK8 peptide derivatized with diphenylphosphine for rhenium labelling: synthesis and molecular mechanics calculations
Authors: Morelli Giancarlo , De Luca Stefania , Tesauro Diego , Saviano Michele , Pedone Carlo , Dolmella Alessandro , Visentin Roberta , Mazzi Ulderico 
Published: September 2002

AbstractA novel CCK8 derivative bearing a chelating agent at its N‐ end and its oxo‐rhenium(V) complex have been synthesized and characterized. The chelating agent N‐{N‐[3‐(diphenylphosphino)propionyl]glycyl} cysteine (PN2S) ligand, the coordination set of which is made by the phosphorus atom of phosphine, the nitrogen atoms of the two amido groups and the sulphur atom of cysteine, has been used due to its high affinity towards the oxo‐rhenium(V) moiety. Molecular modelling studies indicate that the CCK8 peptide adopts the right conformation for cholecystokinin receptor binding, and that modifications on the N‐terminal side of CCK8 obtained by introducing chelating agents and its metal complexes should not affect the interaction with CCKA receptor. Copyright © 2002 European Peptide Society and John Wiley & Sons, Ltd.