bluuebunny/crossref_metadata_2025_split huggingface dataset:
Antiamoebin I in Methanol Solution: Rapid Exchange between Right‐Handed and Left‐Handed 310‐Helical Conformations
Authors: Shenkarev Zakhar O. , Paramonov Alexander S. , Nadezhdin Kirill D. , Bocharov Eduard V. , Kudelina Irina A. , Skladnev Dmitry A. , Tagaev Andrey A. , Yakimenko Zoya A. , Ovchinnikova Tatiana V. , Arseniev Alexander S. 
Published: June 2007

AbstractAntiamoebin I (Aam‐I) is a membrane‐active peptaibol antibiotic isolated from fungal species belonging to the genera Cephalosporium, Emericellopsis, Gliocladium, and Stilbella. Antiamoebin I has the amino acid sequence: Ac‐Phe1‐Aib‐Aib‐Aib‐Iva‐Gly‐Leu‐Aib8‐Aib‐Hyp‐Gln‐Iva‐Hyp‐Aib‐Pro‐Phl16. By using the uniformly 13C,15N‐labeled sample of Aam‐I, the set of conformationally dependent J couplings and 3hJNC couplings through H‐bonds were measured. Analysis of these data along with the data on magnetic nonequivalence of the 13Cβ nuclei (Δδ(13Cβ)) in Aib and Iva residues allowed us to draw the univocal conclusion that the N‐terminal part (Phe1–Gly6) of Aam‐I in MeOH solution is in fast exchange between the right‐handed and left‐handed 310‐helical conformations, with an approximately equal population of both states. An additional conformational exchange process was found at the Aib8 residue. The 15N‐NMR‐relaxation and CD‐spectroscopy measurements confirmed these findings. Molecular modeling and Monte Carlo simulations revealed that both exchange processes are correlated and coupled with significant hinge‐bending motions around the Aib8 residue. Our results explain relatively low activity of Aam‐I with respect to other 15‐amino acid residue peptaibols (for example, zervamicin) in functional and biological tests. The high dynamic ‘propensity’ possibly prevents both initial binding of the antiamoebin to the membrane and subsequent formation of stable ionic channels according to the barrel‐stave mechanism.
Solvent Effects on the Secondary Structure of the Membrane‐Active Zervamicin Determined by PELDOR Spectroscopy
Authors: Milov Alexander D. , Tsvetkov Yuri D. , Gorbunova Elena Y. , Mustaeva Leyla G. , Ovchinnikova Tatiana V. , Handgraaf Jan‐Willem , Raap Jan 
Published: June 2007

AbstractZervamicin is a voltage‐gated ion‐channel‐forming peptide. Channels are generally considered to be formed by first insertion of amphipathic molecules into the phospholipid bilayer, followed by self‐assembly of a variable number of transmembrane helices. We have studied the length of the peptide structure to address the question whether this peptide is long enough to span the phospholipid bilayer. The pulsed electron‐electron double resonance (PELDOR) spectroscopic technique was used to determine the length of the helical molecule in membrane‐mimicking solvents. This was achieved from the distance‐related dipole–dipole interaction between spin labels, which were located at both ends of the linear peptide chain. The data were obtained by using samples of frozen glassy solutions of MeOH, MeOH/toluene, and MeOH/CHCl3. Contributions of inter‐ and intramolecular interactions of spin labels were separated to analyze the intramolecular interaction and the distance distribution function between the labels. It is shown that the main maximum of the distribution functions is located at a distance of ca. 3.3 nm, and this distance appears to be only slightly dependent on the solvent composition. The distribution function was observed to narrow after addition of either CHCl3 or toluene to MeOH. This effect is rationalized in terms of a decreased mobility of the terminal amino acid residues. By molecular‐dynamics simulations, it was shown that the conformation, corresponding with the predominant distance found by PELDOR, agrees well with the mixed α/310‐helical that was previously determined by NMR. However, in the case toluene was added to the MeOH solution to further increase the hydrophobicity of the environment of the membrane‐active peptide, the distribution function gives rise to a minor fraction (7–8%) with a distance of 4.2 nm. This distance corresponds most likely to the more extended 27‐helix structure.
Alamethicin Interaction with Lipid Membranes: A Spectroscopic Study on Synthetic Analogues
Authors: Stella Lorenzo , Burattini Marcello , Mazzuca Claudia , Palleschi Antonio , Venanzi Mariano , Coin Irene , Peggion Cristina , Toniolo Claudio , Pispisa Basilio 
Published: June 2007

AbstractAlamethicin (Alm) is one of the most extensively studied membrane‐active antibiotic peptides, but several aspects of its mechanism of action are still under debate. In this study, synthetic analogues of natural Alm F50/5 (Alm‐N), labeled with a 9H‐fluoren‐9‐yl group at the N‐ (F‐Alm) or C‐terminus (Alm‐F), were employed to investigate the position and orientation of this peptide in the membrane environment. Depth‐dependent fluorescence quenching and polarized ATR‐FT‐IR experiments demonstrated that, in the absence of a transmembrane potential, Alm inserts its N‐terminus into the membrane, while the C‐terminus is exposed to the outer aqueous phase. We also found that the peptaibol populates different orientations with respect to the membrane normal. Furthermore, fluorescence resonance‐energy transfer (FRET) indicated that no peptide translocation to the inner leaflet of lipid bilayers occurs. The mechanism of action of Alm is discussed on the basis of these findings.Two other Alm analogues, Alm‐P and Alm‐S, were exploited to investigate the role of specific Alm residues in terms of membrane‐perturbing activity. Substitution of two or three Gln (E) residues (the only polar amino acids in the alamethicin sequence) by γ‐methyl glutamate (Glu(OMe)) residues induced marked variations in the aggregation and partition behaviors of the peptaibols, which, in turn, modulate their membrane activity. In particular, substitution of Gln18 and Gln19 caused a six‐fold increase in membrane‐perturbing activity, thus demonstrating that these residues are not essential for the stabilization of Alm pores.
Channel‐Forming Activity of Alamethicin: Effects of Covalent Tethering
Authors: Woolley G. Andrew 
Published: June 2007

AbstractIn this short review article, the effects of covalent tethering of alamethicin molecules on channel‐forming behavior are described. Broadly speaking, these chemical modifications have provided insight into all three aspects of channel behavior: the structure of the conducting state, the ion‐selectivity and ion‐permeation properties, and the voltage dependence. Each of these aspects are discussed in turn.
Membrane Permeabilization of a Mammalian Neuroendocrine Cell Type (PC12) by the Channel‐Forming Peptides Zervamicin, Alamethicin, and Gramicidin
Authors: Weidema Adam F. , Kropacheva Tatyana N. , Raap Jan , Ypey Dirk L. 
Published: June 2007

AbstractZervamicin IIB (ZER) is a 16‐mer peptaibol that produces voltage‐dependent conductances in artificial membranes, a property considered responsible for its antimicrobial activity to mainly Gram‐positive microorganisms. In addition, ZER appears to inhibit the locomotor activity of the mouse (see elsewhere in this Issue), probably by affecting the brain. To examine whether the electrophysiological properties of the neuronal cells of the central neural system might be possibly influenced by the pore forming ZER, the present study was undertaken as a first attempt to unravel the molecular mechanism of this biological activity. To this end, membrane permeabilization of the neuron‐like rat pheochromocytoma cell (PC12) by the channel‐forming ZER was studied with the whole‐cell patch‐clamp technique, and compared with the permeabilizations of the well‐known voltage‐gated peptaibol alamethicin F50/5 (ALA) and the cation channel‐forming peptide‐antibiotic gramicidin D (GRAM). While 1 μM GRAM addition to PC12 cells kept at a membrane potential Vm=0 mV causes an undelayed gradual increase of a leak conductance with a negative reversal potential of ca. −24 mV, ZER and ALA are ineffective at that concentration and potential. However, if ZER and ALA are added in 5–10 μM concentrations while Vm is kept at −60 mV, they cause a sudden and strong permeabilization of the PC12 cell membrane after a delay of 1–2 min, usually leading to disintegrating morphology changes of the patched cell but not of the surrounding cells of the culture at that time scale. The zero reversal potential of the established conductance is consistent with the known aselectivity of the channels formed. This sudden permeabilization does not occur within 10–20 min at Vm=0 mV, in accordance with the known voltage dependency of ZER and ALA channel formation in artificial lipid membranes. The permeabilizing action of these peptaibols on the culture as a whole is further supported by K+‐release measurements from a PC12 suspension with a K+‐selective electrode. Further analysis suggested that the permeabilizing action is associated with extra‐ or intracellular calcium effects, because barium inhibited the permeabilizing effects of ZER and ALA. We conclude, for the membrane of the mammalian neuron‐like PC12 cell, that the permeabilizing effects of the peptides ZER and ALA are different from those of GRAM, consistent with earlier studies of these peptides in other (artificial) membrane systems. They are increased by cis‐positive membrane potentials in the physiological range and may include calcium entry into the PC12 cell.
The Peptaibol Alamethicin Induces an rRNA‐Cleavage‐Associated Death in Arabidopsis thaliana
Authors: Rippa Sonia , Adenier Hervé , Derbaly Michel , Béven Laure 
Published: June 2007

AbstractThe plant‐metabolic response to amphipathic peptides produced by the soil fungi of the genus Trichoderma remains largely unknown. The present investigation was undertaken to examine the death process in alamethicin‐treated Arabidopsis thaliana plantlets. The rapid death triggered by alamethicin (at 50 μM) was shown to be associated with protein‐synthesis arrest and with specific cleavage of 18S and 25S ribosomal RNA. The use of an inhibitor of nitric oxide (NO) synthases and of an NO scavenger suggested that rRNA cleavage was suppressed by NO. Experiments conducted with a synthetic alamethicin analogue, in which all α‐aminoisobutyric acid (Aib) residues have been replaced by leucine moieties, showed that the non‐coded residues are essential for the ability of the peptaibol to induce rRNA cleavage in Arabidopsis. Our data indicate that further investigations on the mode of action of alamethicin in planta could be of great interest to study the death‐signaling pathway associated with rRNA degradation in plants.
Neuroleptic Properties of the Ion‐Channel‐Forming Peptaibol Zervamicin: Locomotor Activity and Behavioral Effects
Authors: Ovchinnikova Tatiana V. , Levitskaya Natalia G. , Voskresenskaya Olga G. , Yakimenko Zoya A. , Tagaev Andrey A. , Ovchinnikova Anastasia Y. , Murashev Arkadiy N. , Kamenskii Andrey A. 
Published: June 2007

AbstractZervamicins IIA and IIB are members of the peptaibol family of peptide antibiotics. They are produced by the fungus Emericellopsis salmosynnemata. Peptaibols are known to be of potential usefulness for chemotherapeutic applications, as are other secondary fungal metabolites. Previously, we have found zervamicins to decrease spontaneous locomotor activity in mice, suggesting their neurotropic properties on an equal footing with antimicrobial activity. The current study deals with behavioral effects of zervamicins IIA and IIB in mice. According to our results, both zervamicins induce a reliable decrease in locomotion and exploratory activity measured in the hole‐board test. The behavioral effects of zervamicin IIA become apparent at lower dosages (0.05–2.0 mg/kg) as compared with zervamicin IIB (0.5–12.0 mg/kg). The experiments on behavioral effects in the elevated plus maze test showed that both zervamicins caused a reliable decrease in the number of head‐dippings, open‐arm entries, and rearings. The observed behavioral effects may be rather associated with a decrease in the exploratory activity than with anxiety‐related responses in mice. Zervamicins induced depression‐like behavior of experimental animals in the forced‐swim test. Both peptaibols reduce physical endurance and change motor coordination of experimental animals in the bar‐holding test. Taken together, the data obtained clearly indicate that both zervamicins possess neuroleptic activity.
Gadofullerenes as nanoscale magnetic labels for cellular MRI
Authors: Sitharaman Balaji , Tran Lesa A. , Pham Quynh P. , Bolskar Robert D. , Muthupillai Raja , Flamm Scott D. , Mikos Antonios G. , Wilson Lon J. 
Published: June 2007

AbstractIn this study, anionic gadofullerene {Gd@C60[C(COOH)2]10} was used as an in vitro cellular magnetic resonance imaging label. The cellular uptake characteristics of this gadofullerene were significant and nonspecific, and excellent labeling efficiency (98–100%) was achieved without a transfecting agent. The average uptake was up to 133.6 ± 5.5 pg Gd per cell or 1011 Gd3+ ions per cell. The difference in the longitudinal relaxation time T1 between labeled and unlabeled cells generated good contrast between labeled and unlabeled cells. A clinical magnetic resonance imaging imager at 1.5 T showed that signal intensity on the T1 weighted magnetic resonance images was 250% greater in labeled cells. Thus, the anionic gadofullerene {Gd@C60[C(COOH)2]10} is an attractive candidate for ex vivo labeling and noninvasive in vivo tracking of any mammalian cell via magnetic resonance imaging. Copyright © 2007 John Wiley & Sons, Ltd.
Thermal properties of a Nd:LuVO4 crystal
Authors: Ran Donggang , Xia Hairui , Sun Shangqian , Liu Fengqin , Ling Zongcheng , Ge Wenwei , Zhang Huaijin , Wang Jiyang 
Published: June 2007

AbstractA Nd‐doped lutetium orthovanadate Nd:LuVO4 crystal has been grown using a modified Czochralski method. The thermal properties of this crystal have been studied by measuring the thermal expansion, specific heat and thermal diffusivity. The thermal expansion coefficients are α11 = 1.7 × 10‐6, α22 = 1.5 × 10‐6 and α33 = 9.1 × 10‐6/K in the temperature range of 298–573 K along the three respective crystallographic axes. The specific heat is almost linear and increases from 0.442 to 0.498 Jg‐1K‐1 in the measured temperature range. The thermal diffusivity is anisotropic and decreases with increasing temperature from 295 to 548 K. At room temperature the calculated thermal conductivities κ11 and κ33 are 7.96 and 9.77 Wm‐1K‐1, respectively. These thermal parameters of Nd:LuVO4 crystal have indicated that it is an excellent candidate laser material. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural, optical and photoluminescence properties of ZnS: Cu nanoparticle thin films as a function of dopant concentration and quantum confinement effect
Authors: Jayanthi K. , Chawla S. , Chander H. , Haranath D. 
Published: June 2007

AbstractThin films of ZnS: Cu nanoparticles were deposited in chemical bath by a pH controlled solution synthesis technique. The copper concentration was varied from 0 to 0.1M%. XRD and SEM indicated variations in diffracted intensity and morphology with Cu concentration. The PL spectrum of the undoped ZnS nanoparticles showed emission peaks at 393 and 432nm that could be attributed to the intrinsic defect states of ZnS nanoparticles. For ZnS: Cu samples three peaks in the range of 390nm, 480nm and 525nm were observed. With increase in Cu concentration from 0.001 to 0.1M%, the peak position of 480nm and 525nm did not change, whereas 390nm peak red shifted to longer wavelength region to 422nm. In addition, it was found that the overall photoluminescence intensity reached maximum at 0.01M% and quenched with further increase in Cu concentration. Enhancement of blue and green light emission by seven and twenty fivefold respectively compared to undoped ZnS was observed in ZnS: Cu with optimal dopant concentration. Time resolved decay of photoluminescence showed faster decay for 390 – 420nm purple/ blue emission compared to green (525nm) Cu related emission which is in the microsecond time scale. Optical absorption measurements indicate enhancement of band gap (3.89eV) for undoped ZnS suggesting the quantum confinement effect in the developed nanoparticles of size below the Bohr diameter. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cover Picture: Expansion and activation of CD4+CD25+ regulatory T cells in Heligmosomoides polygyrus infection – Eur. J. Immunol. 7/2007
Authors: Finney Constance A. M. , Taylor Matthew D. , Wilson Mark S. , Maizels Rick M. 
Published: June 2007

AbstractThe cover shows a photograph of an individual adult Heligmosomoides polygyrus, a gastrointestinal nematode parasite and was provided by Finney et al. (pp. 1874–1886). In this study authors analyse in detail the development and phenotype (CTLA‐4, GITR, CD103) of cells responsible for the suppression of the early Th2 responses during murine H. polygyrus infection. Both CD25+Foxp3+ and CD25+Foxp3‐ subsets are increased during infection but, interestingly, only the latter display significant increases in TGF‐β levels.
Synthesis and Characterization of CuII Complexes with Amino Acid Substituted Di(2‐pyridyl)amine Ligands
Authors: Kirin Srećko I. , Yennawar Hemant P. , Williams Mary Elizabeth 
Published: June 2007

AbstractThe two‐step syntheses of the substituted di(2‐pyridyl)amine ligands (dpa), dpa‐CH2CO2H (1) and dpa‐PhCO2H (2), are described. Ligands 1 and 2 are successfully coupled to the amino acid phenylalanine, yielding the derivatives 4 and 6, respectively. Four CuII(dpa)2 complexes, [Cu(dpa‐CH2CO2tBu)2(NO3)2] (3Cu), [Cu(dpa‐CH2CO‐PheOMe)2(H2O)2](NO3)2·2MeOH (4Cu), [Cu(dpa‐PhCO2Me)2 (MeOH)2](ClO4)2 (5Cu) and [Cu(dpa‐PhCO‐PheOMe)2(ClO4)2] (6Cu) have been prepared and characterized, including their single crystal X‐ray structures. Fluorescence emission at UV (for 3 and 4) or blue (for 5 and 6) wavelengths of the free ligands is preserved in the corresponding Cu complexes, although with lower intensity. X‐band EPR spectra of 4Cu and 6Cu both revealed one axial CuII signal with hyperfine and superhyperfine splittings. Complexes 4Cu and 6Cu are chiral inorganic complexes with amino acid bioconjugates that may serve as nucleoside analogs in modified peptide nucleic acids (PNA). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Classification of feeding fats by FT‐IR spectroscopy
Authors: Gasperini Gianmaria , Fusari Elena , Della Bella Laura , Bondioli Paolo 
Published: June 2007

AbstractIn this paper, a technique useful for the classification of different food oil co‐ and by‐products of potential use for feed preparation is shown. The proposal is based upon a Fourier transform infrared evaluation of different classes of compounds, and its elaboration was carried out starting from the knowledge of the chemical composition of each feedstock category. Using this technique, a sure classification of fatty acid calcium soaps, fully hydrogenated fatty acids, lecithins, acid oils from chemical refining, acid oils from physical refining and fish oils can be easily done. The remaining categories of animal fats, fried oils and oils recovered from exhausted bleaching earth can be differentiated by using one or two additional chemical tests. The scope of this paper is to provide a quick, easy and non‐expensive tool for a correct classification of feedstock, in order to allow the choice of correct and applicable analytical tests for the evaluation of the quality and of the composition of each sample.
Inhibition of butter oxidation by some phenolics
Authors: Soulti Kalliopi , Roussis Ioannis G. 
Published: June 2007

AbstractThe ability of some phenolic compounds to inhibit butter oxidation was evaluated. Peroxide values and thiobarbituric acid reactive substances were monitored during storage of butter at 50 °C and at 110 °C. Gallic acid, caffeic acid and catechin, each at 80 mg/L, inhibited butter oxidation at 50 °C to a degree equal to that of butylated hydroxyanisole (BHA) at 200 mg/L. Gallic acid, at 80 mg/L, was more effective than BHA, at 200 mg/L, in inhibiting butter oxidation at 110 °C. Present results indicate that some phenolics, and especially gallic acid, may be taken into account as antioxidants in butter.
Reductive Coupling of Aromatic Aldehydes Promoted by an Aqueous TiCl3/tBuOOH System in Alcoholic Cosolvents
Authors: Clerici Angelo , Greco Cosimina , Panzeri Walter , Pastori Nadia , Punta Carlo , Porta Ombretta 
Published: June 2007

AbstractThe tert‐butoxyl radical, generated by the aqueous TiIII/TBHP system, abstracts an H atom from alcoholic cosolvents (EtOH, iPrOH), leading to α‐hydroxyalkyl radicals thatreduce aromatic aldehydes to the corresponding 1,2‐diols. The reactivities observed are explained by resonance stabilization of the α‐hydroxybenzyl radicals formed in the electron‐transfer (ET) process. Good Hammett‐type correlations are obtained. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Cover Picture: Progress in Supramolecular Chemistry of Gases (Eur. J. Org. Chem. 20/2007)
Authors: Rudkevich Dmitry M. 
Published: June 2007

AbstractThe cover picture shows a star field filled with molecules of environmentally important gases. Gases are very interesting for molecular recognition. Supramolecular complexes with gases have been obtained by utilizing dynamic, reversible forces. On this basis, supramolecular, optical sensors for the detection of gases have been introduced. Studies on molecules and molecular materials for gas entrapment, separation, storage and release that involve synthetic containers, self‐assembling capsules and even nanotubes and fullerenes have been well in progress. Moreover, supramolecular fixation of gases has yielded stable and selective chemical reagents for preparative organic chemistry. Gases have also been used as building blocks for supramolecular nanostructures. Dynamic, switchable polymers that can be used as storing and separating materials have been constructed from gases. The current progress in supramolecular chemistry and molecular recognition of gases is presented in the Microreview by D. M. Rudkevich on p. 3255 ff. The star field picture is a courtesy of Joe Eakin, Director, The Planetarium at The University of Texas at Arlington.
The uniform estimation of the M/G/1 processor sharing response time distribution
Authors: Hartmann Harro L. 
Published: June 2007

AbstractThis contribution avoids frequently used transform and inversion problems by a decomposition of the transition state model in the original domain. First, the relevant differential‐recurrence backward equation system valid for the M/M/1 processor sharing (PS) is converted to a sum of a service component and an arrival–departure component. The first one yields a pure differential equation system, which can be solved exactly and proves to be uniformly valid for M/G/1 PS systems. The second component vanishes for small and large processor utilisations but contributes to shorter response times otherwise. Thus, the PS service component defines an estimate of the true response time distribution. Second, the higher order moments of the estimates form simple upper bounds of their true much more complicated counterparts where the first moments agree. Partly simulative case studies subject to M, D, H2, heavy‐tailed service time distributions, and PS with permanent customers confirm the new estimation. Third, reference values of the arrival–departure component provide an approximate solution of the differential‐recurrence equation system. This significantly improves the accuracy of the estimates for moderate utilisations. Finally it is shown that the remaining inaccuracies of the estimates are far below expectable forecast errors for high economic loads and otherwise the approximation significantly supports PS system engineering for moderate loads too. Copyright © 2007 John Wiley & Sons, Ltd.