bluuebunny/crossref_metadata_2025 huggingface dataset:
Modification of phenol–formaldehyde resol resins by lignin, starch, and urea
Authors: Turunen Marko , Alvila Leila , Pakkanen Tuula T. , Rainio Jouni
Published: February 2003

Lignin‐based chemicals, starch, and urea were used as modifiers for phenol–formaldehyde resol resins. The effects of the addition stage of the modifiers used in the synthesis of the resins and the type of modification reagent on the structures of the resins and their molar masses and reactivities were investigated. The modifications with corn starch and lignin promoted condensation; this was verified by increased molar masses and high ratios of methylene bridges to the sum of free ortho and para aromatic groups with respect to the corresponding reference resin without a modification reagent. The later the modifier was added to the resin condensation mixture, the more methylene bridges were formed with respect to the amounts of free ortho and para aromatic groups. In addition, when urea or wheat starch was added in the later condensation stage, the final condensation also reached high stages. The modifications with lignosulfonate and starch, as well as the early addition of urea, enhanced p–p′ bridge structures. The lowest condensation stage and, therefore, the highest reactivity were found when wheat starch was added with the starting reagents. The curing heat of the wheat‐starch‐modified resins decreased according to the deferred addition point of starch. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 582–588, 2003
Effect of stress state and polymer morphology on environmental stress cracking in polycarbonate
Authors: Raman Arun , Farris Richard J. , Lesser Alan J.
Published: February 2003

Environmental stress crazing or cracking (ESC), a long studied phenomenon, is the brittle failure of glassy thermoplastics, which are normally ductile, under the synergistic action of stress and certain surface active agents. This work involves a study of a polycarbonate—oleic acid system under two novel in‐depth conditions: multiaxial stress states and changes in the polymer morphology. Initial uniaxial creep tests showed that the formation of cracks rather than crazes is observed. Multiaxial testing is done using blister tests where the polycarbonate film is stressed using a pressurizing medium to form a blister that is in a biaxial state of stress. Changes in the polymer morphology are induced by orientation of the polymer film. On samples exposed to stress and surface active agents, the stress component that is perpendicular to the direction in which the crazes/cracks form appears to influence the crack patterns. The polymer orientation has a significant influence. The orientation not only induces crack formation in a direction parallel to the orientation (regardless of the direction of the major principal stress), but it also reduces the stress required for crack formation for all stress states. Any attempt at modeling the phenomenon of environmental stress cracking therefore needs to take these effects into account. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 550–564, 2003
Polyelectrolyte complex formation between alginate and chitosan as a function of pH
Authors: Simsek‐Ege Fatma A. , Bond Gillian M. , Stringer John
Published: February 2003

Chitosan and alginate are two polyelectrolytes that can be used as thickening agents in the food industry, in drug‐release systems in pharmaceutical applications as biomaterials in wound healing, and cell culture applications, or as ion exchange material for the removal of heavy metal ions from industrial wastewaters. These two polysaccharides can also be used together to form a polyelectrolyte complex, especially to encapsulate proteins, cells, and enzymes. Although there are many applications of these polyions, few publications explain the interaction between their functional groups. This is mostly because of the difficulty of following ionic interaction in an interface of macromolecules, especially since they alter much with the reaction conditions such as pH. The present study reveals the interaction between chitosan and alginate at different pH values by means of a particular method for Fourier transform infrared (FTIR) studies. A previously reported disagreement between the yield of the complexes in weight and density of the interacting functional groups is explained through this method. The obtained results are supported with the morphological studies of the polyelectrolyte beads prepared at different pH values. Freeze‐dried beads of both alginate and chitosan‐coated alginate beads could be viewed after hexamethyl disilazane (HMDS) treatment. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 346–351, 2003
Complexation of uranyl ions by polypyrrole doped by sulfonated and phosphonated polyethyleneimine
Authors: Leroy D. , Martinot L. , Mignonsin P. , Strivay D. , Weber G. , Jérôme C. , Jérôme R.
Published: February 2003

Branched polyethyleneimine (PEI) was sulfonated by reaction with chloropropanesulfonylchloride and phosphonated by reaction with phosphorous acid and formaldehyde. The accordingly formed polyanions were used as doping agents for polypyrrole (PPy). The amount of doping polyanions into thin films of PPy was measured by Rutherford back‐scattering. These films were tested for their capacity to extract uranyl ions from liquid wastes of low level activity. The uranium content was determined by neutron activation analysis, autoradiography, and gravimetry of uranium oxide after calcination. The resistance against static and dynamic leachings was also estimated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 352–359, 2003
Autoantibodies against B23, a nucleolar phosphoprotein, occur in scleroderma and are associated with pulmonary hypertension
Authors: Ulanet Danielle B. , Wigley Fredrick M. , Gelber Allan C. , Rosen Antony
Published: February 2003

Objective

To determine whether the abundant nucleolar phosphoprotein B23 is a target of autoantibodies in scleroderma, and to examine the clinical phenotype associated with these antibodies.

Methods

Ninety‐two randomly selected scleroderma sera were screened by enzyme‐linked immunosorbent assay against recombinant human B23. Demographic, clinical, and serologic parameters associated with B23 autoantibody status were examined.

Results

We demonstrated that autoantibodies against B23 occur in ∼11% of sera obtained from patients with scleroderma. B23 seropositivity was related to pulmonary hypertension, antifibrillarin antibody, anti‐RNP antibody, and decreased lung capacity. In multivariate analysis, B23 autoantibodies remained strongly associated with moderate‐to‐severe pulmonary hypertension and antifibrillarin antibodies.

Conclusion

These data unite B23 with the group of nucleolar autoantigens targeted in scleroderma and thus focus attention on changes in the nucleolus that render its components immunogenic in this disease. The demonstration that antibodies to B23 are associated with an increased prevalence of pulmonary hypertension points to anti‐B23 antibodies as a possible marker of a specific phenotype in scleroderma.
Treatment of polyarteritis nodosa and microscopic polyangiitis with poor prognosis factors: A prospective trial comparing glucocorticoids and six or twelve cyclophosphamide pulses in sixty‐five patients
Authors: Guillevin Loïc , Cohen Pascal , Mahr Alfred , Arène Jean‐Pierre , Mouthon Luc , Puéchal Xavier , Pertuiset Edouard , Gilson Brigitte , Hamidou Mohamed , Lanoux Patricia , Bruet Alain , Ruivard Marc , Vanhille Philippe , Cordier Jean‐François
Published: February 2003

Objective

Because the optimal cyclophosphamide (CY) treatment duration for severe polyarteritis nodosa (PAN) without virus infection and microscopic polyangiitis (MPA) has not been established, we conducted a trial to compare the effectiveness of 6 versus 12 CY pulses given in combination with corticosteroids (CS).

Methods

Sixty‐five (18 PAN, 47 MPA) previously untreated patients were randomized to receive 12 (n = 34) or 6 (n = 31) CY pulses combined with CS. PAN and MPA were histologically proven or met ACR criteria. All patients presented ≥1 factor of severity according to the five factor score (FFS). CY pulses were administered every 2 weeks for 1 month, then every 4 weeks. The end point of the study was the number of events (relapses and/or deaths) occurring in each group, analyzed according to an intention‐to‐treat strategy. The outcome was evaluated by Cox proportional hazards analysis.

Results

The baseline characteristics were similar for both groups. The mean (± SD) followup was 32 ± 21 months. Survival analysis showed a significantly lower relapse probability (P = 0.02; hazards ratio [HR] = 0.34) and higher event‐free survival (P = 0.02, HR = 0.44) for the 12 CY‐pulse group while the mortality rates were not significantly different (P = 0.47).

Conclusion

These results suggest that 6 CY pulses are less effective than 12 CY pulses to treat severe PAN and MPA, particularly with respect to the risk of relapses.
Use of the trust in physician scale in patients with rheumatic disease: Psychometric properties and correlates of trust in the rheumatologist
Authors: Freburger Janet K. , Callahan Leigh F. , Currey Shannon S. , Anderson Lynda A.
Published: February 2003

Objectives

To assess the psychometric properties of the Trust in Physician Scale and to identify variables associated with patients' trust in their rheumatologist.

Methods

Analyses of self reported data from 713 patients with rheumatoid arthritis, osteoarthritis, or fibromyalgia. Study variables included the Trust in Physician Scale, a decision‐making question, a medical skepticism measure, and demographic and health‐related measures. Internal consistency and construct validity were assessed using correlational analyses and factor analysis. A regression analysis was conducted to identify factors associated with trust in the rheumatologist.

Results

Internal consistency of the scale was high (Cronbach's alpha = 0.87). Scale items also loaded on a single factor. Construct validity was supported by inverse correlations between higher trust scores and both skepticism and independent decision making. Decreased trust was associated with older age, minority status, higher education, diagnosis of fibromyalgia or osteoarthritis, and poorer health.

Conclusion

The Trust in Physician Scale is appropriate for patients with rheumatic disease. Several patient characteristics appear to be associated with lower trust in the rheumatologist.
Evidence for aerobic insufficiency in women with systemic lupus erythematosus
Authors: Keyser Randall E. , Rus Violeta , Cade William Todd , Kalappa Neeta , Flores Raymond H. , Handwerger Barry S.
Published: February 2003

Objective

To determine if fatigue is associated with diminished aerobic capacity in women with systemic lupus erythematosus (SLE).

Methods

Eighteen women (age 35 ± 9 years) with mild SLE (Systemic Lupus Activity Measure = 3.1 ± 2.1) and 16 healthy but sedentary controls (age 38 ± 8 years) completed peak treadmill exercise tests to determine aerobic capacity and Fatigue Severity Scales to quantify the severity of fatigue. Measures of oxygen consumption (VO2) were recorded during the treadmill tests.

Results

Peak VO2 was lower in patients with SLE (19.2 ± 4.4 ml/kg/minute) as compared with controls (27.4 ± 4.7 ml/kg/minute) and expected values (30.7 ± 3.1 ml/kg/minute; P < 0.0006 versus controls and P < 0.0001 versus expected). Functional aerobic impairment was observed in 14 of the 18 patients with SLE. In patients with SLE, ventilatory threshold, a marker for the onset of lactic acidemia, was observed at the lowest energy requirement for instrumental activities of daily living. Peak VO2 in the patients with SLE was similar to the highest energy requirements for instrumental activities of daily living, leaving little or no reserve for more intense occupational and recreational activities. Peak VO2 was significantly higher (P < 0.0001) than the activity of daily living requirements in controls, providing a substantial energy reserve. Fatigue severity score (FSS) was 5.0 ± 1.4 in patients with SLE, with 14 of the 18 patients having scores above 4.0, a score indicating that fatigue severity limited physical activity. Of the 14, 12 had functional aerobic impairment. An FSS of greater than 4.0 was not observed in controls (mean = 2.5 ± 0.7).

Conclusion

In women with SLE, aerobic capacity was diminished to levels that were insufficient for engaging in activities of daily living and below those expected to result from physiologic deconditioning. This functional aerobic impairment was strongly correlated with the perception of severe, activity‐limiting fatigue.
Breaking non‐native hydrophobic clusters is the rate‐limiting step in the folding of an alanine‐based peptide
Authors: Chowdhury Shibasish , Zhang Wei , Wu Chun , Xiong Guoming , Duan Yong
Published: February 2003

The formation mechanism of an alanine‐based peptide has been studied by all‐atom molecular dynamics simulations with a recently developed all‐atom point‐charge force field and the Generalize Born continuum solvent model at an effective salt concentration of 0.2M. Thirty‐two simulations were conducted. Each simulation was performed for 100 ns. A surprisingly complex folding process was observed. The development of the helical content can be divided into three phases with time constants of 0.06–0.08, 1.4–2.3, and 12–13 ns, respectively. Helices initiate extreme rapidly in the first phase similar to that estimated from explicit solvent simulations. Hydrophobic collapse also takes place in this phase. A folding intermediate state develops in the second phase and is unfolded to allow the peptide to reach the transition state in the third phase. The folding intermediate states are characterized by the two‐turn short helices and the transition states are helix–turn–helix motifs—both of which are stabilized by hydrophobic clusters. The equilibrium helical content, calculated by both the main‐chain Φ–Ψ torsion angles and the main‐chain hydrogen bonds, is 64–66%, which is in remarkable agreement with experiments. After corrected for the solvent viscosity effect, an extrapolated folding time of 16–20 ns is obtained that is in qualitative agreement with experiments. Contrary to the prevailing opinion, neither initiation nor growth of the helix is the rate‐limiting step. Instead, the rate‐limiting step for this peptide is breaking the non‐native hydrophobic clusters in order to reach the transition state. The implication to the folding mechanisms of proteins is also discussed. © 2002 Wiley Periodicals, Inc. Biopolymers 68: 63–75, 2003
Modeling HIV‐1 integrase complexes based on their hydrodynamic properties
Authors: Podtelezhnikov Alexei A. , Gao Kui , Bushman Frederic D. , McCammon J. Andrew
Published: February 2003

We present a model structure of a candidate tetramer for HIV‐1 integrase. The model was built in three steps using data from fluorescence anisotropy, structures of the individual integrase domains, cross‐linking data, and other biochemical data. First, the structure of the full‐length integrase monomer was modeled using the individual domain structures and the hydrodynamic properties of the full‐length protein that were recently measured by fluorescence depolarization. We calculated the rotational correlation times for different arrangements of three integrase domains, revealing that only structures with close proximity among the domains satisfied the experimental data. The orientations of the domains were constrained by iterative tests against the data on cross‐linking and footprinting in integrase–DNA complexes. Second, the structure of an integrase dimer was obtained by joining the model monomers in accordance with the available dimeric crystal structures of the catalytic core. The hydrodynamic properties of the dimer were in agreement with the experimental values. Third, the active sites of the two model dimers were placed in agreement with the spacing between the sites of integration on target DNA as well as the integrase–DNA cross‐linking data, resulting in twofold symmetry of a tetrameric complex. The model is consistent with the experimental data indicating that the F185K substitution, which is found in the model at a tetramerization interface, selectively disrupts correct complex formation in vitro and HIV replication in vivo. Our model of the integrase tetramer bound to DNA may help to design anti‐integrase inhibitors. © 2002 Wiley Periodicals, Inc. Biopolymers 68: 110–120, 2003
Free energy calculations for theophylline binding to an RNA aptamer: Comparison of MM‐PBSA and thermodynamic integration methods
Authors: Gouda Hiroaki , Kuntz Irwin D. , Case David A. , Kollman Peter A.
Published: February 2003

We have applied the molecular mechanics Poisson–Boltzmann surface area (MM‐PBSA) method (J. Srinivasan, T. E. Cheatham, P. Cieplak, P. A. Kollman, and D. A. Case, Journal of the American Chemical Society, 1998, Vol. 120, pp. 9401–9409) to study the interaction of an RNA aptamer with theophylline and its analogs. The MM‐PBSA free energy analysis provides a reasonable absolute binding free energy for the RNA aptamer–theophylline complex formation. Energetic analysis reveals that the van der Waals interaction and the nonpolar contribution to solvation provide the basis for the favorable absolute free energy of complex. This trend is similar to other protein–ligand interactions studied previously. The MM‐PBSA method also ranks the relative binding energies of five theophylline analogs approximately correctly, but not as well as the more conventional thermodynamic integration calculations, which were carried out to convert theophylline into its analogs. The comparison of MM‐PBSA with TI suggests that the MM‐PBSA method has some difficulties with the first‐solvation‐shell energetics. © 2002 Wiley Periodicals, Inc. Biopolymers 68: 16–34, 2003
Simulation of the different biological activities of diethylstilbestrol (DES) on estrogen receptor α and estrogen‐related receptor γ
Authors: Nam Kiyean , Marshall Paul , M. Wolf Romain , Cornell Wendy
Published: February 2003

We describe the application of the molecular dynamics (MD) and molecular mechanics–generalized Born/surface area (MM‐GB/SA) approaches to the simulation of the different biological activity of diethylstilbestrol (DES) on two highly homologous nuclear receptors—estrogen receptor α (ER‐α) and estrogen‐related receptor γ (ERR‐γ). DES exerts an agonistic effect against ER‐α and an antagonistic effect against ERR‐γ. Using the x‐ray crystal structures of ER‐α in the canonical agonist bound form (PDB code: 3ERD) and antagonist bound form (PDB code: 3ERT), ERR‐γ homology models have been constructed for the receptor in two different conformations. MM‐GB/SA binding free energy calculations of DES in the ER‐α and ERR‐γ structures suggest that DES exhibits a greater free energy of binding in the agonist bound conformation of ER‐α, while the antagonist bound conformation is preferred for ERR‐γ. Further dissection of the free energy contributions coupled with calculation of the ligand binding pocket volume suggests that the van der Waals interactions for DES within the smaller binding pocket volume of ERR‐γ are less favorable and this is the main factor for DES antagonism in ERR‐γ. This approach has potential general applicability to the prediction of the biological activity of nuclear receptor ligands. © 2002 Wiley Periodicals, Inc. Biopolymers 68: 130–138, 2003
Parvalbumin, calbindin, or calretinin in cortically projecting and GABAergic, cholinergic, or glutamatergic basal forebrain neurons of the rat
Authors: Gritti Ivana , Manns Ian D. , Mainville Lynda , Jones Barbara E.
Published: February 2003

The basal forebrain (BF) plays an important role in modulating cortical activity and facilitating processes of attention, learning, and memory. This role is subserved by cholinergic neurons but also requires the participation of other noncholinergic neurons. Noncholinergic neurons include γ‐amino butyric acidergic (GABAergic) neurons, some of which project in parallel with the cholinergic cells to the cerebral cortex, others of which project caudally or locally. With the original aim of distinguishing different subgroups of GABAergic neurons, we examined immunostaining for the calcium binding proteins (CBPs) parvalbumin (Parv), calbindin (Calb), and calretinin (Calret) in the rat. Although the CBP+ cell groups were distributed in a coextensive manner with the GABAergic cells, they were collectively more numerous. Of cells retrogradely labeled with cholera toxin (CT) from the prefrontal or parietal cortex, Parv+ and Calb+ cells, but not Calret+ cells, represented substantial proportions (∼35–45% each) that collectively were greater than that of GABAergic projection neurons. From dual immunostaining for the CBPs and glutamic acid decarboxylase (GAD), it appeared that the vast majority (>90%) of the Parv+ group was GAD+, whereas only a small minority (<10%) of the Calb+ or Calret+ group was GAD+. Significant proportions of Calb+ (>40%) and Calret+ (>80%) neurons were immunopositive for phosphate‐activated glutaminase, the synthetic enzyme for transmitter glutamate. The results suggested that, whereas Calret+ cells predominantly comprise caudally or locally projecting, possibly glutamatergic BF neurons, Parv+ cells likely comprise the cortically projecting GABAergic BF neurons and Calb+ cells the cortically projecting, possibly glutamatergic BF neurons that would collectively participate with the cholinergic cells in the modulation of cortical activity. J. Comp. Neurol. 458:11–31, 2003. © 2003 Wiley‐Liss, Inc.
Distribution of dopamine D2 receptor mRNAs in the brain and the pituitary of female rainbow trout: An in situ hybridization study
Authors: Vacher Coralie , Pellegrini Elisabeth , Anglade Isabelle , Ferriére François , Saligaut Christian , Kah Olivier
Published: February 2003

The distribution of D2R (dopamine D2 receptor) mRNAs was studied in the forebrain of maturing female rainbow trout by means of in situ hybridization using a 35S‐labeled riboprobe (810 bp) spanning the third intracytoplasmic loop. A hybridization signal was consistently obtained in the olfactory epithelium, the internal cell layer of the olfactory bulbs, the ventral and dorsal subdivisions of the ventral telencephalon, and most preoptic subdivisions, with the notable exception of the magnocellular preoptic nucleus, and the periventricular regions of the mediobasal hypothalamus, including the posterior tuberculum. In the pituitary, the signal was higher in the pars intermedia than in the proximal and the rostral pars distalis, but no obvious correspondence with a given cell type could be assigned. Labeled cells were also located in the thalamic region, some pretectal nuclei, the optic tectum, and the torus semicircularis. These results provide a morphologic basis for a better understanding on the functions and evolution of the dopaminergic systems in lower vertebrates. J. Comp. Neurol. 458:32–45, 2003. © 2003 Wiley‐Liss, Inc.
Morphologic and cytochemical criteria for the identification and delineation of individual subnuclei within the lateral habenular complex of the rat
Authors: Geisler Stefanie , Andres Karl Hermann , Veh Rüdiger W.
Published: February 2003

The lateral habenular complex is part of the habenular nuclei, a distinct structure in the dorsal diencephalon of all vertebrates. In contrast to the bewildering diversity of behaviors, in which the lateral habenular complex is thought to be involved, there is an astonishing lack of information concerning its cellular organization, its neuronal circuits, and the neurophysiological mechanisms, which may provide the physiological and molecular basis for its diverse biological functions. This problem may be due to an unexpected heterogeneity of the lateral habenular complex. Recently, a detailed subnuclear organization has been described (Andres et al. [1999] J Comp Neurol 407:130–150), which provides the base for a subsequent physiological and behavioral analysis of this area. Available criteria, however, can be applied to semithin sections only. To facilitate further investigations, the present work aimed to elaborate novel morphologic and immunocytochemical criteria that can be applied to conventional cryostat or Vibratome sections to allow identification and delineation of subnuclei of the lateral habenular complex. Consequently, the regional, cellular, and subcellular localization of approximately 30 different neuroactive molecules was investigated. Of these candidate molecules, γ‐aminobutyric acid‐B receptor protein, Kir3.2 potassium channel protein, tyrosine hydroxylase, and neurofilament heavy chain proved to be suitable markers. Our observation suggests that the habenular subnuclei express distinct immunocytochemical characteristics. These features may be used to identify and delineate the subnuclei on conventional cryostat or Vibratome sections. From our results, it is expected that the further functional analysis of the lateral habenular complex will be facilitated considerably. J. Comp. Neurol. 458:78–97, 2003. © 2003 Wiley‐Liss, Inc.
Nanoelectrospray‐based detection and sequencing of substoichiometric amounts of phosphopeptides in complex mixtures
Authors: Köcher Thomas , Allmaier Günter , Wilm Matthias
Published: February 2003

A novel immobilized metal affinity chromatography (IMAC)‐based protocol was successfully used for sample preparation prior to nanoelectrospray‐based sequencing of phosphopeptides. In a first step, phosphorylated peptides are detected in an unseparated peptide mixture using precursor ion scanning in the negative ion mode on a triple‐quadrupole mass spectrometer. Then the phosphorylated peptides are enriched by passing the sample over an IMAC column and sequenced in the positive ion mode. The IMAC‐based enrichment allows the sequencing of phosphorylated peptides even if other, much more abundant, peptides are present at the same m/z value in the original mixture. Using this two‐step approach, we are able to combine the simplicity, sensitivity and specificity of precursor ion scanning‐based detection of phosphopeptides using the nanoelectrospray ion source with the ability to sequence phosphorylated peptides even if they are present in substoichiometric amounts. Copyright © 2003 John Wiley & Sons, Ltd.
Electrospray mass spectra of group 6 (Fischer) carbenes in the presence of electron‐donor compounds
Authors: Sierra M. A. , Gómez‐Gallego M. , Mancheño M. J. , Martínez‐Alvarez R. , Ramírez‐López P. , Kayali N. , González A.
Published: February 2003

Fischer carbene complexes 1–7 are not ionized under standard electrospray ionization (ESI) conditions. We report here that unsaturated chromium and tungsten (Fischer) carbene complexes can be ionized in an electrospray ion source in the presence of electron‐donor compounds such as hydroquinone (HQ) or tetrathiafulvalene (TTF). The addition of these compounds, which seem to act as electron transfer agents, permits the recording and study of their ESI mass spectra in the negative mode of detection. Both chromium and tungsten(0) carbene complexes undergo in the first fragmentation stage a double simultaneous decarbonylation process. Copyright © 2003 John Wiley & Sons, Ltd.
Fragmentation reactions of protonated peptides containing glutamine or glutamic acid
Authors: Harrison Alex. G.
Published: February 2003

A variety of protonated dipeptides and tripeptides containing glutamic acid or glutamine were prepared by electrospray ionization or by fast atom bombardment ionization and their fragmentation pathways elucidated using metastable ion studies, energy‐resolved mass spectrometry and triple‐stage mass spectrometry (MS3) experiments. Additional mechanistic information was obtained by exchanging the labile hydrogens for deuterium. Protonated H—Gln—Gly—OH fragments by loss of NH3 and loss of H2O in metastable ion fragmentation; under collision‐induced dissociation (CID) conditions loss of H—Gly—OH + CO from the [MH − NH3]+ ion forms the base peak C4H6NO+ (m/z 84). Protonated dipeptides with an α‐linkage, H—Glu—Xxx—OH, are characterized by elimination of H2O and by elimination of H—Xxx—OH plus CO to form the glutamic acid immonium ion of m/z 102. By contrast, protonated dipeptides with a γ‐linkage, H—Glu(Xxx—OH)—OH, do not show elimination of H2O or formation of m/z 102 but rather show elimination of NH3, particularly in metastable ion fragmentation, and elimination of H—Xxx—OH to form m/z 130. Both the α‐ and γ‐dipeptides show formation of [H—Xxx—OH]H+, with this reaction channel increasing in importance as the proton affinity (PA) of H—Xxx—OH increases. The characteristic loss of H2O and formation of m/z 102 are observed for the protonated α‐tripeptide H—Glu—Gly—Phe—OH whereas the protonated γ‐tripeptide H—Glu(Gly—Gly—OH)—OH shows loss of NH3 and formation of m/z 130 as observed for dipeptides with the γ‐linkage. Both tripeptides show abundant formation of the y2″ ion under CID conditions, presumably because a stable anhydride neutral structure can be formed. Under metastable ion conditions protonated dipeptides of structure H—Xxx—Glu—OH show abundant elimination of H2O whereas those of structure H—Xxx—Gln—OH show abundant elimination of NH3. The importance of these reaction channels is much reduced under CID conditions, the major fragmentation mode being cleavage of the amide bond to form either the a1 ion or the y1″ ion. Particularly when Xxx = Gly, under CID conditions the initial loss of NH3 from the glutamine containing dipeptide is followed by elimination of a second NH3 while the initial loss of H2O from the glutamic acid dipeptide is followed by elimination of NH3. Isotopic labelling shows that predominantly labile hydrogens are lost in both steps. Although both [H—Gly—Glu—Gly—OH]H+ and [H—Gly—Gln—Gly—OH]H+ fragment mainly to form b2 and a2 ions, the latter also shows elimination of NH3 plus a glycine residue and formation of protonated glycinamide. Isotopic labelling shows extensive mixing of labile and carbon‐bonded hydrogens in the formation of protonated glycinamide. Copyright © 2003 John Wiley & Sons, Ltd.
Accurate mass measurements by Fourier transform mass spectrometry in the study of advanced glycation end products/peptides
Authors: Marotta Ester , Lapolla Annunziata , Fedele Domenico , Senesi Antonella , Reitano Rachele , Witt Matthias , Seraglia Roberta , Traldi Pietro
Published: February 2003

The Maillard reaction occurring between sugars and amino groups is important in living systems. When amino groups belonging to protein chains are involved, the Maillard reaction has been invoked as responsible for protein cross‐linking and the production of ‘toxic’ compounds. The reaction leads to the production of a heterogeneous group of substances, usually called advanced glycation end products (AGEs). Classical analytical approaches, such as spectroscopic (ultraviolet, fluorescence) and mass spectrometric (matrix‐assisted laser desorption/ionization, liquid chromatography/electrospray ionization mass spectrometry) methods, have shown that the digestion mixture is highly complex. However, there are clear differences between the digestion mixtures of glycated and unglycated human serum albumin (HSA). In the former case, possible glycated peptides belonging to the AGE peptide class may be identified. Tandem mass spectrometric experiments on selected species seemed to be promising as regards structural information, but it was thought of interest to undertake the present investigation, based on liquid chromatography/electrospray ionization Fourier transform mass spectrometry, in order to obtain definitive results on their elemental composition. Using this approach, about 20 glycated peptides were detected and their possible structures were postulated by examining the known sequence of HSA. Copyright © 2003 John Wiley & Sons, Ltd.
Saturation transfer in human red blood cells with normal and unstable hemoglobin
Authors: Sogami Masaru , Uyesaka Nobuhiro , Era Seiichi , Kato Kazuo
Published: February 2003

Saturation transfer phenomena from irradiated protein protons to observed water protons in packed human red blood cells (RBCs) with normal or unstable hemoglobin (Hb), i.e. Hb Yokohama and Hb Koeln, were studied using intermolecular cross‐relaxation rates [CR; 1/TIS(H2O)], action spectra {[1 −(I∞/I0)] vs f2 (ppm), where I0 and I∞ are the longitudinal magnetization of observed water protons before and after long‐time f2‐irradiation, respectively}, CR spectra [CR vs f2 (ppm)] and CR ratio vs f2 (ppm) with f2‐irradiation from −100 to 100 ppm at γH2/2π of 69 or 250 Hz. RBCs (Hb Yokohama) exhibited many large Heinz bodies and strongly impaired filterability, while RBCs (Hb Koeln) showed few microscopically typical Heinz bodies and virtually normal filterability. However, increases in CR values for RBCs (Hb Koeln) and RBCs (Hb Yokohama), monitored by f2‐irradiation below ∼−6 and above ∼14 ppm, clearly indicated marked increases in association or aggregation of unstable Hb in RBCs compared with those in normal RBCs. CR values, monitored between ∼0 and ∼10 ppm, were related to not only association or aggregation of unstable Hb but also amounts of water in RBCs. Aggregation or association of unstable Hb exhibited greater effects on CR values compared with those of methemoglobin formation. Copyright © 2003 John Wiley & Sons, Ltd.
In vivo monitoring of rat brain metabolites during vigabatrin treatment using localized 2D‐COSY
Authors: Welch John W. R. , Bhakoo Kishore , Dixon Ruth M. , Styles Peter , Sibson Nicola R. , Blamire Andrew M.
Published: February 2003

A two‐dimensional COSY‐based localization sequence was designed to allow the in vivo monitoring of proton metabolites in rat brain [particularly γ‐aminobutyric acid (GABA), glutamine, taurine and myo‐inositol]. The sequence incorporated OSIRIS signal localization, B1‐insensitive water suppression and phase‐sensitive COSY acquisition. The method was used to study the effects of the GABA‐transaminase inhibitor vigabatrin on rat brain metabolite concentrations. Wistar rats were treated daily for 3 days with an oral dose of vigabatrin (200 mg/kg, n = 4). Localized COSY spectra were obtained during a 120 min acquisition from a 270 µl central brain voxel and compared with nine untreated control animals. Significant elevations were observed in GABA (267% of control, p < 0.005, Mann–Witney test), glutamine (130% of control, p < 0.005) and taurine (113% of control, p < 0.05). Changes in GABA and taurine were consistent with previous data on the action of Vigabatrin, and support a previously hypothesized link between these compounds. The increase in glutamine was more surprising and may reflect the balance between the level and/or site of GABA‐transaminase inhibition and downregulation of GABA synthesis. Copyright © 2003 John Wiley & Sons, Ltd.
Validity of Big Five personality judgments in childhood: a 9 year longitudinal study
Authors: Asendorpf Jens B. , Van Aken Marcel A. G.
Published: February 2003

In a 9 year longitudinal study over childhood, the Big Five personality traits were assessed at ages 4–6 by teacher Q‐sorts, at age 10 by parental Q‐sorts, and at age 12 by parental and friend ratings on bipolar adjective scales. The Big Five Q‐sort indices were based on definitions proposed by John, Caspi, Robins, Moffitt, and Stouthamer‐Loeber (1994) for adolescent boys. They were related to judgments and behavioural observations of inhibition and aggressiveness, and to antecedents and consequences of school achievement such as IQ and cognitive self‐esteem. Neuroticism and low extraversion correlated with social inhibition, low agreeableness and low conscientiousness with aggressiveness, and conscientiousness and/or culture/intellect/openness with antecedents and outcomes of school achievement. These correlations were consistently found throughout childhood. Copyright © 2002 John Wiley & Sons, Ltd.
Helix propensities of short peptides: Molecular dynamics versus bioinformatics
Authors: Bystroff Christopher , Garde Shekhar
Published: February 2003

Knowledge‐based potential functions for protein structure prediction assume that the frequency of occurrence of a given structure or a contact in the protein database is a measure of its free energy. Here, we put this assumption to test by comparing the results obtained from sequence‐structure cluster analysis with those obtained from long all‐atom molecular dynamics simulations. Sixty‐four eight‐residue peptide sequences with varying degrees of similarity to the canonical sequence pattern for amphipathic helix were drawn from known protein structures, regardless of whether they were helical in the protein. Each was simulated using AMBER6.0 for at least 10 ns using explicit waters. The total simulation time was 1176 ns. The resulting trajectories were tested for reproducibility, and the helical content was measured. Natural peptides whose sequences matched the amphipathic helix motif with greater than 50% confidence were significantly more likely to form helix during the course of the simulation than peptides with lower confidence scores. The sequence pattern derived from the simulation data closely resembles the motif pattern derived from the database cluster analysis. The difficulties encountered in sampling conformational space and sequence space simultaneously are discussed. Key words: Proteins 2003;50:552–562. © 2003 Wiley‐Liss, Inc.
Crystal structures of a psychrophilic metalloprotease reveal new insights into catalysis by cold‐adapted proteases
Authors: Aghajari Nushin , Van Petegem Filip , Villeret Vincent , Chessa Jean‐Pierre , Gerday Charles , Haser Richard , Van Beeumen Jozef
Published: February 2003

Enzymes from psychrophilic organisms differ from their mesophilic counterparts in having a lower thermostability and a higher specific activity at low and moderate temperatures. It is in general accepted that psychrophilic enzymes are more flexible to allow easy accommodation and transformation of the substrates at low energy costs. Here, we report the structures of two crystal forms of the alkaline protease from an Antarctic Pseudomonas species (PAP), solved to 2.1‐ and 1.96‐Å resolution, respectively. Comparative studies of PAP structures with mesophilic counterparts show that the overall structures are similar but that the conformation of the substrate‐free active site in PAP resembles that of the substrate‐bound region of the mesophilic homolog, with both an active‐site tyrosine and a substrate‐binding loop displaying a conformation as in the substrate‐bound form of the mesophilic proteases. Further, a region in the catalytic domain of PAP undergoes a conformational change with a loop movement as large as 13 Å, induced by the binding of an extra calcium ion. Finally, the active site is more accessible due to deletions occurring in surrounding loop regions. Proteins 2003;50:636–647. © 2003 Wiley‐Liss, Inc.
Physics and materials challenges for lead-free solders
Authors: Tu K. N. , Gusak A. M. , Li M.
Published: February 2003

At present, the electronic industry is actively searching for Pb-free solders due to environmental concerns over Pb-containing solders. Solder joints are widely used to bond chips to their substrates for electrical connection and packaging. Lacking reliability data, many electronic companies will be reluctant to adopt Pb-free solders in the advanced products. Hence, it is timely to review our understanding of structure-property relationship and potential reliability issues of Pb-free solders. A brief history of solder joint processes in electronic manufacturing is presented to serve as a background for the review. It emphasizes the unique phenomenon of spalling of interfacial intermetallic compound in solder reactions. Challenges for Pb-free solders from the point of view of physics and materials are given since the reliability issues of solder joints will remain with us when advanced Cu/low k dielectric interconnect technology is introduced into microelectronic devices.
Quantum path minimization: An efficient method for global optimization
Authors: Liu Pu , Berne B. J.
Published: February 2003

A new unbiased global optimization approach is proposed, based on quantum staging path integral Monte Carlo sampling and local minimization of individual imaginary time slices. This algorithm uses the quantum tunneling effect to speed up the crossing of energy barriers. This method differs in important ways from previous work on quantum annealing and is able to find all the global minima of Lennard-Jones clusters of size up to N=100, except for N=76, 77, and 98. The comparison between this new algorithm and several other classes of algorithms is presented.
Influence of radiative transfer on optical cooling in the condensed phase
Authors: Heeg Bauke , Rumbles Garry
Published: February 2003

The effect of fluorescence reabsorption on the optical cooling in the condensed phase was calculated using a stochastic model, based on spectral data of Rhodamine 101 in ethanol. The redshift in measured fluorescence for increasing Rhodamine 101 concentrations is reproduced for concentrations up to 10−4 M, suggesting that radiative transfer can be simulated accurately using a relatively simple random walk model. This also ensures a degree of accuracy in calculating the effect of radiative transfer processes on the optical cooling of a sample of given geometry. The stochastic method, using only the absorbance and molecular fluorescence (i.e., fluorescence unaffected by reabsorption) spectra as the input values, allows one to estimate the chromophore concentration for which maximum cooling efficiency occurs, given a cell geometry and quantum yield and vice versa. The method predicts a cooling efficiency that is an order of magnitude lower than has been reported previously [J. L. Clark and G. Rumbles, Phys. Rev. Lett. 76, 2037 (1996); J. L. Clark, P. F. Miller, and G. Rumbles, J. Phys. Chem. A 102, 4428 (1998)]. The difference is attributed to an overestimate of the experimental data that is in part due to the measurement of a local cooling effect rather than a macroscopic, bulk cooling.
Features of diffuse phase transition in lead barium niobate ferroelectric ceramics
Authors: Santos Ivair A. , Garcia Ducinei , Eiras José A. , Arantes Vera L.
Published: February 2003

Features of the diffuse phase transition in lead barium niobate (PbxBa1−xNb2O6–PBN) ferroelectric ceramics are presented and discussed. Ceramics were prepared near to the morphotropic phase boundary (x∼0.63) and the dielectric properties were investigated. The character of the ferroelectric phase transition was carefully analyzed, indicating that the diffuseness coefficient decreases as the lead concentration increases. This effect is attributed to the increase of the unit-cell polarization with the morphotropic phase boundary proximity. The polarization enhancement induces the formation and interaction between the polar microregions in PBN samples at temperatures higher than Tm. The appearance of dilatation centers, which act as strong oscillating random-field sources and are naturally created due to the peculiar A-site vacancy distribution in PBN structure, increases the maximum dielectric permittivity by the polarization mobility enhancement. On the other hand, the temperature of maximum dielectric permittivity is decreased due to the action of the random fields.
Influence of surface states on the two-dimensional electron gas in AlGaN/GaN heterojunction field-effect transistors
Authors: Jogai B.
Published: February 2003

The electron transfer into the two-dimensional electron gas (2DEG) of AlGaN/GaN heterojunction field-effect transistors (HFETs) is examined theoretically using a charge-control model. The model is based on a self-consistent solution of the Poisson, Schrödinger, and charge balance equations, together with the k⋅p Hamiltonian for the valence band states. Realistic surface boundary conditions are imposed, and surface states are included using Fermi–Dirac statistics. Based on the assumption that surface donors are the underlying cause of the 2DEG, a wide range of published data on the 2DEG can be explained. For instance, the variation of the 2DEG density with the AlGaN layer thickness and mole fraction can be accounted for, along with other experimental results, such as the reduction of the 2DEG density when the HFET is capped with a GaN layer, the saturation of the 2DEG density for thick GaN caps, and the increase in the 2DEG density when the surface is passivated.
Multiphoton intrapulse interference. II. Control of two- and three-photon laser induced fluorescence with shaped pulses
Authors: Lozovoy Vadim V. , Pastirk Igor , Walowicz Katherine A. , Dantus Marcos
Published: February 2003

Nonlinear optical processes are controlled by modulating the phase of ultrafast laser pulses taking advantage of multiphoton intrapulse interference. Experimental results show orders of magnitude control over two- and three-photon excitation of large organic molecules in solution using specific phase functions. We show simulations on the effect of phase modulation on the second- and third-order amplitude of the electric field spectrum, and demonstrate that the observed control is not caused by simple changes in peak intensity.
Effect of Pt buffer layer on structural and magnetic properties of FePt thin films
Authors: Chen J. S. , Xu Yingfan , Wang J. P.
Published: February 2003

Ordered FePt thin films with face-centered-tetragonal (fct)-(001) preferred orientation have been prepared by magnetron sputtering a FePt layer onto a Cr91Ru9 underlayer. The effects of a Pt buffer layer between the CrRu underlayer and FePt layer on the structural and magnetic properties of the FePt films were investigated. The long range ordering parameter increases as the thickness of the Pt buffer layer increases from 0 to 4 nm. Further increase in the Pt buffer layer thickness (6 nm) causes the decrease of the ordering parameter. The out-of-plane coercivity of the films increases linearly with the increase of the thickness of the Pt buffer layer. Upon introduction of a 4 nm Pt buffer layer the number of defects in the FePt films are decreased drastically. The changes in the structural and magnetic properties of FePt films are related to the suppression of the Cr diffusion by the Pt buffer layer.
Properties of La-silicate high-K dielectric films formed by oxidation of La on silicon
Authors: Gougousi Theodosia , Kelly M. Jason , Terry David B. , Parsons Gregory N.
Published: February 2003

In this article, we present data on the properties of La-based high-k dielectric films prepared by oxidation of La deposited by physical vapor deposition on silicon. Films are characterized by x-ray photoelectron spectroscopy, infrared absorption, and capacitance versus voltage analysis. We find that when we oxidize La metal sputter deposited on Si substrates, it reacts with the silicon substrate to form La silicate. La films as thick as 300 Å will react completely with Si under moderate oxidation conditions (900 °C for 10 min) suggesting a very rapid silicidation reaction between La and Si. Under some processing conditions the as-deposited films contain a small La2O3 component that reduces to La silicate upon anneal at high temperatures. La-silicate films do not phase separate into La2O3 and SiO2 upon annealing at 1050 °C, and their resistance to H2O incorporation depends critically on the oxidation temperature. Electrical measurements show a high concentration of positive fixed charge.
Mechanism of electrical degradation and breakdown of insulating polymers
Authors: Zakrevskii V. A. , Sudar N. T. , Zaopo A. , Dubitsky Yu. A.
Published: February 2003

The electrical breakdown of polymers with saturated bonds is considered as a consequence of formation of low-density regions in the bulk of the polymers. These regions form due to the dissociation of chemical bonds initiated by the ionization of macromolecules in a high electric field. It was shown that the electrical lifetime of a polymer can be estimated based on this approach.