bluuebunny/crossref_metadata_2025 huggingface dataset:
A Double-Blinded, Randomized Controlled Trial of Oxytocin at the Beginning versus the End of the Third Stage of Labor for Prevention of Postpartum Hemorrhage
Authors: Huh Warner K. , Chelmow David , Malone Fergal D.
Published: April 2004

Objective: The objective of this study was to compare the administration of oxytocin at the beginning and end of the third stage of labor for the prevention of postpartum hemorrhage. Methods: Patients with documented singleton pregnancies were randomly assigned to two groups. The first received 10 units of oxytocin intramuscularly at delivery of the anterior shoulder of the fetus and an identical appearing placebo injection following delivery of the placenta. The second received the opposite medication sequence. The study was double blinded. Blood loss was measured by weighing all fluids collected, visual estimation, and serial blood counts. Results: 27 women received oxytocin at the delivery of the fetal shoulder and 24 after the placenta. Oxytocin given after placenta delivery resulted in lower blood loss (345 vs. 400 ml, p = 0.28), lower collection bag weight (763 vs. 833 g, p = 0.55), lower change in HgB (–1.26 vs. –1.32 g, p = 0.86), lower ΔHCT (–3.43 vs. –3.64%, p = 0.85), and a shorter third stage of labor duration (8.6 vs. 9.2 min, p = 0.75). The incidence of postpartum hemorrhage, defined as estimated blood loss >500 ml (0 vs. 14.8%) was significantly lowered with oxytocin following placental delivery (p = 0.049). Conclusions: In our study, postpartum hemorrhage was less frequent when oxytocin administration was delayed until after placenta delivery.
Fluorescence Detection of Redox‐Sensitive Metals in Neuronal Culture: Focus on Iron and Zinc
Authors: REYNOLDS IAN J.
Published: April 2004

Abstract: Detection of neurotoxic metals in the intracellular milieu has made an important contribution to the understanding of the mechanism of metal‐induced neuronal injury. Fluorescent, metal‐sensitive dyes have proven to be valuable in the measurement of a variety of neurotoxic cations in neurons, and these dyes have provided a number of insights into the relationships between elevations in the cytosolic free‐metal concentrations and neuronal death. However, the dyes also have important limitations that can make the interpretation of dye signals difficult. In this review, the characteristics of dyes that can be used to detect both iron and zinc inside neurons, and the methods necessary to distinguish these ions from other intracellular signals, are reviewed. Also provided are examples of the use of the dyes for the redox‐sensitive detection of iron and zinc. Finally, the challenges facing the use of these dyes for quantitative determination of changes in intracellular free‐ion concentrations are discussed.
Severity of Neurodegeneration Correlates with Compromise of Iron Metabolism in Mice with Iron Regulatory Protein Deficiencies
Authors: SMITH SOPHIA R. , COOPERMAN SHARON , LAVAUTE TIM , TRESSER NANCY , GHOSH MANIK , MEYRON‐HOLTZ ESTHER , LAND WILLIAM , OLLIVIERRE HAYDEN , JORTNER BERNARD , SWITZER ROBERT , MESSING ALBEE , ROUAULT TRACEY A.
Published: April 2004

Abstract: In mammals, iron regulatory proteins 1 and 2 (IRP1 and IRP2) posttranscriptionally regulate expression of several iron metabolism proteins including ferritin and transferrin receptor. Genetically engineered mice that lack IRP2, but have the normal complement of IRP1, develop adult‐onset neurodegenerative disease associated with inappropriately high expression of ferritin in degenerating neurons. Here, we report that mice that are homozygous for a targeted deletion of IRP2 and heterozygous for a targeted deletion of IRP1 (IRP1+/− IRP2−/−) develop a much more severe form of neurodegeneration, characterized by widespread axonopathy and eventually by subtle vacuolization in several areas, particularly in the substantia nigra. Axonopathy develops in white matter tracts in which marked increases in ferric iron and ferritin expression are detected. Axonal degeneration is significant and widespread before evidence for abnormalities or loss of neuronal cell bodies can be detected. Ultimately, neuronal cell bodies degenerate in the substantia nigra and some other vulnerable areas, microglia are activated, and vacuoles appear. Mice manifest gait and motor impairment at stages when axonopathy is pronounced, but neuronal cell body loss is minimal. These observations suggest that therapeutic strategies that aim to revitalize neurons by treatment with neurotrophic factors may be of value in IRP2−/− and IRP1+/− IRP2−/− mouse models of neurodegeneration.
Selective Cu2+/Ascorbate‐Dependent Oxidation of Alzheimer's Disease β‐Amyloid Peptides
Authors: SCHöNEICH CHRISTIAN
Published: April 2004

Abstract: This review summarizes tandem mass spectrometric investigations on the selectivity of metal‐catalyzed oxidation of β‐amyloid peptide (βAP) and related sequences. A remarkable feature of the Cu2+/ascorbate‐dependent oxidation of these peptides is the switch from predominantly His oxidation in the neurotoxic peptide βAP1‐40 to predominantly Tyr oxidation in the nonneurotoxic reverse sequence βAP40‐1. Within βAP1‐40, His13 and His14 of the high‐affinity Cu2+‐binding site are most sensitive to oxidation. Eventually, the oxidation of one or both of these His residues could result in a less redox‐active βAP‐Cu2+ complex, lowering the incidence of βAP‐Cu2+‐dependent Fenton‐type reactions for the benefit of surrounding biological tissue.
Redox Metals in Alzheimer's Disease
Authors: TODORICH BOZHO M. , CONNOR JAMES R.
Published: April 2004

Abstract: Redox metals in the brain play many important roles in maintenance of cellular function. The maintenance of their homeostasis is of paramount importance to a number of diseases such as Alzheimer's disease and multiple sclerosis. Iron, copper, and zinc are metals of special interest in the pathogenesis of these disorders. This review will focus primarily on iron.
Magnetic Iron Compounds in Neurological Disorders
Authors: DOBSON JON
Published: April 2004

Abstract: Although iron plays an important role in many aspects of human neurophysiology, it also can be toxic under certain circumstances. Anomalous amounts of iron are known to be associated with most types of neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases. To date, little is known about the specific iron compounds present in this tissue and there is recent evidence to suggest that some forms are magnetic. This raises important questions with regard to the role of magnetic iron compounds in disease initiation and progression and, indeed, the origin of these compounds. This paper reviews recent work on the identification and analysis of magnetic iron compounds associated with neurological disorders.
The Relevance of Iron in the Pathogenesis of Parkinson's Disease
Authors: GÖTZ MARIO E. , DOUBLE KAY , GERLACH MANFRED , YOUDIM MOUSSA B. H. , RIEDERERE PETER
Published: April 2004

Abstract: Investigations that revealed increased levels of iron in postmortem brains from patients with Parkinson's disease (PD) as compared to those from individuals not suffering from neurological disorders are reported. The chemical natures in which iron predominates in the brain and the relevance of neuromelanin for neuronal iron binding are discussed. Major findings have been that iron levels increase with the severity of neuropathological changes in PD, presumably due to increased transport through the blood‐brain barrier in late stages of parkinsonism. Glial iron is mainly stored as ferric iron in ferritin, while neuronal iron is predominantly bound to neuromelanin. Iron overload may induce progressive degeneration of nigrostriatal neurons by facilitating the formation of reactive biological intermediates, including reactive oxygen species, and the formation of cytotoxic protein aggregates. There are indications that iron‐mediated neuronal death in PD proceeds retrogradely. These results are also discussed with respect to their relevance for disease progression in relation to cytotoxic α‐synuclein protofibril formation.
Manganese‐Induced Parkinsonism and Parkinson's Disease
Authors: Olanow C W.
Published: April 2004

Abstract: It has long been appreciated that manganese exposure can cause neurotoxicity and a neurologic syndrome that resembles Parkinson's disease (PD). Current evidence indicates that manganese‐induced parkinsonism can be differentiated from PD because of its predilection to accumulate in and damage the pallidum and striatum rather than the SNc. The clinical syndrome, response to levodopa, imaging studies with MRI and PET, and pathologic features all help to distinguish these two conditions and permit the correct diagnosis to be established. This is of particular relevance in differentiating patients with parkinsonism due to manganese intoxication from patients with idiopathic PD who have incidental manganese exposure.
Mitochondrial Localization of Human PANK2 and Hypotheses of Secondary Iron Accumulation in Pantothenate Kinase‐Associated Neurodegeneration
Authors: JOHNSON MONIQUE A. , KUO YIEN MING , WESTAWAY SHAWN K. , PARKER SUSAN M. , CHING KATHERINE H. L. , GITSCHIER JANE , HAYFLICK SUSAN J.
Published: April 2004

Abstract: Mutations in the pantothenate kinase 2 gene (PANK2) lead to pantothenate kinase‐associated neurodegeneration (PKAN, formerly Hallervorden‐Spatz syndrome). This neurodegenerative disorder is characterized by iron accumulation in the basal ganglia. Pantothenate kinase is the first enzyme in the biosynthesis of coenzyme A from pantothenate (vitamin B5). PANK2, one of four human pantothenate kinase genes, is uniquely predicted to be targeted to mitochondria. We demonstrate mitochondrial localization of PANK2 and speculate on mechanisms of secondary iron accumulation in PKAN. Furthermore, PANK2 uses an unconventional translational start codon, CUG, which is polymorphic in the general population. The variant sequence, CAG (allele frequency: 0.05), leads to skipping of the mitochondrial targeting signal and cytosolic localization of PANK2. This common variant may cause mitochondrial dysfunction and impart susceptibility to late‐onset neurodegenerative disorders with brain iron accumulation, including Parkinson's disease.
Novel Chelators for Central Nervous System Disorders That Involve Alterations in the Metabolism of Iron and Other Metal Ions
Authors: RICHARDSON DES R.
Published: April 2004

Abstract: Recent evidence suggests that iron (Fe) and other metals play a role in a number of neurodegenerative diseases including Friedreich's ataxia, Alzheimer's disease, Huntington's disease, and Parkinson's disease. In this review, the role of Fe and other metals in the pathology of these conditions is assessed and the potential of Fe chelators for treatment is discussed. Lipophilic chelators have been designed that may be capable of crossing the blood‐brain barrier, a property lacking in desferrioxamine (DFO), a chelator in widespread clinical use. A far less commonly used chelator, clioquinol, has already shown activity in vivo in animal models and also in Alzheimer's disease patients. Considering that there is no effective treatment for many neurological diseases, the therapeutic use of lipophilic Fe chelators remains a potential strategy that requires investigation. In particular, we discuss the development of several series of aroylhydrazone chelators that could have high potential in the treatment of these diseases.
Navigation and seasonal migratory orientation in juvenile sea turtles
Authors: Avens Larisa , Lohmann Kenneth J.
Published: April 2004

Juvenile loggerhead and green turtles that inhabit inshore waters of North Carolina, USA undertake long seasonal migrations, after which they often return to specific feeding areas. In addition, juvenile turtles are capable of homing to specific sites after being displaced. As a first step towards investigating the navigational mechanisms that underlie these movements,juvenile turtles were captured in coastal waters of North Carolina and displaced 30–167 km along circuitous routes while deprived of visual cues. At the testing location, turtles were tethered in a circular arena and permitted to swim while their orientation was monitored. Between May and September, when juvenile loggerhead and green turtles inhabit feeding areas along the North Carolina coast, turtles oriented in directions that corresponded closely with the most direct route back to their capture locations. During October and November, however, both loggerhead and green turtles oriented southward, a direction consistent with the migratory paths of turtles beginning their autumn migration. The results demonstrate for the first time that both homing and migratory orientation can be elicited in juvenile turtles under laboratory conditions in which orientation cues can be readily manipulated. In addition, the results provide evidence that juvenile loggerheads can assess their position relative to a goal using local cues available at the test site and are therefore capable of map-based navigation.
A computational study of the aerodynamic forces and power requirements of dragonfly (Aeschna juncea) hovering
Authors: Sun Mao , Lan Shi Long
Published: April 2004

Aerodynamic force generation and mechanical power requirements of a dragonfly (Aeschna juncea) in hovering flight are studied. The method of numerically solving the Navier–Stokes equations in moving overset grids is used.

When the midstroke angles of attack in the downstroke and the upstroke are set to 52° and 8°, respectively (these values are close to those observed), the mean vertical force equals the insect weight, and the mean thrust is approximately zero. There are two large vertical force peaks in one flapping cycle. One is in the first half of the cycle, which is mainly due to the hindwings in their downstroke; the other is in the second half of the cycle, which is mainly due to the forewings in their downstroke. Hovering with a large stroke plane angle (52°), the dragonfly uses drag as a major source for its weight-supporting force (approximately 65% of the total vertical force is contributed by the drag and 35% by the lift of the wings).

The vertical force coefficient of a wing is twice as large as the quasi-steady value. The interaction between the fore- and hindwings is not very strong and is detrimental to the vertical force generation. Compared with the case of a single wing in the same motion, the interaction effect reduces the vertical forces on the fore- and hindwings by 14% and 16%, respectively,of that of the corresponding single wing. The large vertical force is due to the unsteady flow effects. The mechanism of the unsteady force is that in each downstroke of the hindwing or the forewing, a new vortex ring containing downward momentum is generated, giving an upward force.

The body-mass-specific power is 37 W kg-1, which is mainly contributed by the aerodynamic power.
The use of power spectral analysis to determine cardiorespiratory control in the short-horned sculpinMyoxocephalus scorpius
Authors: Campbell H. A. , Taylor E. W. , Egginton S.
Published: April 2004

Anaesthesia and minor surgery to place electrocardiogram recording electrodes in the short-horned sculpin caused a decrease in mean normal beat(R–R) interval and heart rate variability (HRV), measured as the standard deviation in the R–R interval (SDRR). Mean R–R interval increased to a steady state value (1.9±2.9 s) 72 h post-surgery, but SDRR took 120 h to stabilise (0.56±0.09 s). Power spectral analysis applied to recordings of instantaneous heart rate showed no spectral peaks immediately after surgery, with the development of twin peaks (at 0.02 and 0.05 Hz) that also became stable 120 h post surgery. Bilateral cardiac vagotomy abolished the variability in beat-to-beat interval, and both the high and low frequency peaks, suggesting that much of the regulation of heart rate and HRV in sculpin was under parasympathetic, cholinergic control that was withdrawn as a result of surgical and handling stress. Rate of oxygen consumption \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(({\dot{M}}_{\mathrm{O}_{2}})\) \end{document} and heart rate (fH) were monitored simultaneously and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\dot{M}}_{\mathrm{O}_{2}}\) \end{document} showed a good correlation with both mean R–R interval(r2=–0.89) and SDRR (r2=0.93),although a more significant (ANCOVA, P=0.02) covariance existed between the post-surgical decrease in \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\dot{M}}_{\mathrm{O}_{2}}\) \end{document} and increase in SDRR. These data suggest that sculpin use fHas a way of moderating oxygen consumption, fine-tuned on a beat-to-beat basis by cholinergic control. We conclude that power spectral analysis is a useful method of determining HRV in fish, and that HRV is a more sensitive measure of recovery from disturbance than fH alone.
Hydrodynamic stimulation of dinoflagellate bioluminescence: a computational and experimental study
Authors: Latz Michael I. , Juhl Andrew R. , Ahmed Abdel M. , Elghobashi Said E. , Rohr Jim
Published: April 2004

Dinoflagellate bioluminescence provides a near-instantaneous reporter of cell response to flow. Although both fluid shear stress and acceleration are thought to be stimulatory, previous studies have used flow fields dominated by shear. In the present study, computational and experimental approaches were used to assess the relative contributions to bioluminescence stimulation of shear stress and acceleration in a laminar converging nozzle. This flow field is characterized by separate regions of pronounced acceleration away from the walls, and shear along the wall. Bioluminescence of the dinoflagellates Lingulodinium polyedrum and Ceratocorys horrida, chosen because of their previously characterized different flow sensitivities, was imaged with a low-light video system. Numerical simulations were used to calculate the position of stimulated cells and the levels of acceleration and shear stress at these positions. Cells were stimulated at the nozzle throat within the wall boundary layer where, for that downstream position, shear stress was relatively high and acceleration relatively low. Cells of C. horrida were always stimulated significantly higher in the flow field than cells of L. polyedrum and at lower flow rates, consistent with their greater flow sensitivity. For both species, shear stress levels at the position of stimulated cells were similar to but slightly greater than previously determined response thresholds using independent flow fields. L. polyedrum did not respond in conditions where acceleration was as high as 20 g. These results indicate that shear stress, rather than acceleration, was the stimulatory component of flow. Thus, even in conditions of high acceleration, dinoflagellate bioluminescence is an effective marker of shear stress.
Force development, energy state and ATP production of cardiac muscle from turtles and trout during normoxia and severe hypoxia
Authors: Overgaard Johannes , Gesser Hans
Published: April 2004

The effects of hypoxia on energy economy of cardiac muscle were compared between the hypoxia-tolerant freshwater turtle at 20°C and the hypoxia-sensitive rainbow trout at 15°C. Isolated ventricular preparations were left either at rest or stimulated at 30 min-1 to develop isometric twitch force. Under oxygenated conditions, twitch force and oxygen consumption were similar for the two species. Overall metabolism was reduced during severe hypoxia in both resting and stimulated preparations and under these conditions most of the ATP production was derived from anaerobic metabolism. During hypoxia, a metabolic depression of approximately 2/3 occurred for non-contractile processes in both turtle and trout preparations. During hypoxia, lactate production and residual oxygen consumption were similar in turtle and trout. Cellular energy state and phosphorylation potential decreased during severe hypoxia in both species and this reduction was more severe in preparations stimulated to contraction. However, in turtle ventricular preparations the energy state and phosphorylation potential stabilised at higher levels than in trout, and turtle preparations also maintained a higher twitch force throughout the hypoxic period. Moreover,twitch force relative to total ATP hydrolysis was markedly increased during hypoxia in turtle while this ratio was unchanged for trout. The main findings of this study are: (1) cellular energy liberation and the energy demand of non-contractile processes decreased to similar levels in hypoxic turtle and trout myocardium; (2) turtle myocardium maintained a substantially higher cellular energy state and twitch force development than trout myocardium during hypoxia and (3) the ratio of twitch force to ATP hydrolysis increased during hypoxia in turtle but was unchanged in trout. It is possible that this superior economy of the contracting turtle myocardium contributes to the remarkable hypoxia tolerance of freshwater turtles.
Swimming gaits, passive drag and buoyancy of diving sperm whalesPhyseter macrocephalus
Authors: Miller Patrick J. O. , Johnson Mark P. , Tyack Peter L. , Terray Eugene A.
Published: April 2004

Drag and buoyancy are two primary external forces acting on diving marine mammals. The strength of these forces modulates the energetic cost of movement and may influence swimming style (gait). Here we use a high-resolution digital tag to record depth, 3-D orientation, and sounds heard and produced by 23 deep-diving sperm whales in the Ligurian Sea and Gulf of Mexico. Periods of active thrusting versus gliding were identified through analysis of oscillations measured by a 3-axis accelerometer. Accelerations during 382 ascent glides of five whales (which made two or more steep ascents and for which we obtained a measurement of length) were strongly affected by depth and speed at Reynold's numbers of 1.4–2.8×107. The accelerations fit a model of drag, air buoyancy and tissue buoyancy forces with an r2 of 99.1–99.8% for each whale. The model provided estimates (mean ± s.d.) of the drag coefficient(0.00306±0.00015), air carried from the surface (26.4±3.9 l kg-3 mass), and tissue density (1030±0.8 kg m-3)of these five animals. The model predicts strong positive buoyancy forces in the top 100 m of the water column, decreasing to near neutral buoyancy at 250–850 m. Mean descent speeds (1.45±0.19 m s-1) were slower than ascent speeds (1.63±0.22 m s-1), even though sperm whales stroked steadily (glides 5.3±6.3%) throughout descents and employed predominantly stroke-and-glide swimming (glides 37.7±16.4%)during ascents. Whales glided more during portions of dives when buoyancy aided their movement, and whales that glided more during ascent glided less during descent (and vice versa), supporting the hypothesis that buoyancy influences behavioural swimming decisions. One whale rested at∼10 m depth for more than 10 min without fluking, regulating its buoyancy by releasing air bubbles.
Dynamics of pectoral fin rowing in a fish with an extreme rowing stroke:the threespine stickleback (Gasterosteus aculeatus)
Authors: Walker Jeffrey A.
Published: April 2004

The dynamics of pectoral fin rowing in the threespine stickleback are investigated by measuring the instantaneous force balance on freely swimming fish throughout the stroke cycle and comparing the measured forces with fin motions and an unsteady, blade-element model of pectoral fin propulsion. Both measured and modeled forces suggest that attached vortex and circulatory forces and not inertial (added mass) forces dominate the force balance. Peak forces occur at midstrokes. There is no evidence for large force peaks at the stroke transitions due to either rapid fin rotation (supination) or rapid fin closure against the body. The energetics of pectoral fin rowing are estimated using the unsteady blade-element model and an indirect method based on the center of mass dynamics. The results indicate that the mechanical efficiency of pectoral fin rowing is low (0.1–0.3) relative to a flapping mechanism and possibly relative to axial undulation at comparable speeds.
Quantitative structure–activity relationships (QSARs) as a tool for predicting the sorption of organic chemicals in soils
Authors: Gerstl Zev
Published: April 2004

The use of quantitative structure‐activity relationships (QSARs) based on linear free‐energy relationships (LFERs), molecular connectivity (MC) indices, and on more sophisticated quantum mechanical approaches, for predicting soil sorption coefficients is reviewed. The nature and energetics of sorption of organic chemicals by soils are also briefly reviewed.

On the basis of the data presented we may conclude that from the large body of physicochemical parameters, the n‐octanol/water partition coefficient (Kow) has been most successful in modeling sorption data of organic chemicals. From the large set of nonempirical parameters that are defined in terms of a compound's 2‐ or 3‐dimensional structure and can be derived for any chemical without experimental efforts, the MC indices have proven the most reliable and easily available.
Diffusion Parameters of the Extracellular Space
Authors: Syková Eva
Published: April 2004

Extrasynaptic communication between neurons or neurons and glia is mediated by the diffusion of neuroactive substances in the extracellular space (ECS). Diffusion in the central nervous system (CNS) is inhomogeneous and often anisotropic. Changes in ECS volume and geometry accompany physiological neuronal activity, development, lactation, stimulation, and aging, as well as pathological states, e.g., anoxia/ischemia, seizures, injury, demyelination, and tumors. Ionic changes and amino acid release result in cellular swelling, compensated for by ECS shrinkage and a decrease in the apparent diffusion coefficients of neuroactive substances or water (ADCW) as determined by diffusion analysis using the real‐time iontophoretic tetramethylammonium (TMA+) method or diffusion‐weighted NMR. The diffusion parameters of the CNS in adult mammals (including humans), ECS volume fraction α (α = ECS volume/total tissue volume) 0.20–0.25 and tortuosity 1.5‐1.6, hinder the diffusion of neuroactive substances and water. A significant decrease in ECS volume (to 0.16) and an increase in diffusion barriers (tortuosity), accompanied by learning deficits, occur in aging CNS, accompanied by astrogliosis, rearrangement of astrocytic processes, and a loss of extracellular matrix. Decreases in ADCTMA and ADCW due to astrogliosis and increased proteoglycan expression were found after brain injury and in grafts of embryonic tissue. Tenascin‐R‐deficient mice also revealed significant changes in ADCTMA and ADCW. Plastic changes in ECS volume, tortuosity, and anisotropy significantly affect neuron–glia communication, the spatial relation of glial processes towards synapses, glutamate or GABA “spillover”, and synaptic cross‐talk. The various changes occur during pathological states and, as such, can be important for diagnosis, drug delivery, and treatment.
Some “Reflections” on the Effects of Finite Gradient Pulse Lengths in PGSE NMR Experiments in Restricted Systems
Authors: Price William S. , Söderman Olle
Published: April 2004

It is generally difficult to analytically derive models describing the echo attenuation in pulsed gradient spin‐echo (PGSE) experiments for even the simplest porous systems that are commonly studied—especially when the gradient pulse (δ) is of finite length compared to the timescale of the diffusion measurement (Δ). Consequently, various levels of approximation are used to evaluate PGSE experiments. In the present paper, a conceptual view ofq‐space is given and two of the most common approximations, the short gradient pulse (SGP) and Gaussian phase distribution (GPD) approximations, are compared in detail with a recent matrix method, which provides “analytically” exact results giving a visual representation of the limitations of these approximations. The simulations are performed for diffusion between a pair of reflecting planes separated by a distancea.A modification that is sometimes applied to the short gradient pulse approximation in attempting to extend it to finite gradient pulses is also compared. The simulations reveal that, except when the experimental conditions closely match the requirements of the SGP and GPD simulations, the matrix method must be used in order to correctly interpret the data.
Effect of oxic state on nonpolar organic contaminant distribution, mobility, and bioavailability in estuarine sediments
Authors: Pedersen Joel A. , Schweitzer Linda E. , Lin Chen‐Hung Michael , Suffet I.H.(Mel)
Published: April 2004

Dissolved and particle‐associated natural organic matter plays an important role in nonpolar organic chemical distribution, mobility, and bio‐availability in sediment environments. We investigated the influence of oxic state on the association of a model hydrophobic organic chemical (HOC), 2,2',4,4'‐tetrachlorobiphenyl (TeCB), with dissolved and particle‐associated organic matter in estuarine sediments. Site‐specific distribution data were used to model the effect of oxic state on diffusive flux of TeCB across the sediment‐water interface. Additional experiments examined the role of oxic state in TeCB bioavailability to a deposit‐feeding epibenthic echinoderm.

Aeration of estuarine sediment pore waters induced a negligible change to greater than an order of magnitude decrease in the dissolved organic carbon (DOC)–water distribution coefficient, Kpwdoc, in all but one system examined. Correspondingly, oxidation of sediment solids effected a negligible to 0.5 log unit decrease in the particle associated organic carbon‐water distribution coefficient, Koc. These results indicate that aeration of anoxic estuarine sediments induced by dredging, bioturbation, or storm events may result in release of HOCs from particle‐associated and dissolved organic matter, increasing the concentration of the truly dissolved compound.

Model simulations indicated that oxygenation of anoxic sediments would result in a 34–100% increase in TeCB diffusive flux. Pore water dissolved organic matter (DOM)facilitated TeCB transport across the sediment‐water interface and increased diffusive flux by up to a factor of 1.7. A sensitivity analysis indicated that facilitation of diffusive transport by DOM would be significant in the systems under investigation when log Kpwdoc exceeded approximately 5.7. Therefore, disturbing anoxic sediments can mobilize HOCs. In bioaccumulation assays using sea urchins, TeCB bioavailability temporarily increased after anoxic sediments were disturbed and aerated, but long‐term bioavailability remained unaltered when sediment reduction potential returned to the level of the unaerated control.
Microprobe laser mass spectrometry studies of polycyclic aromatic hydrocarbon distributions on harbor sediments and coals
Authors: Seb Gillette J. , Ghosh Upal , Mahajan Tania B. , Zare Richard N. , Luthy Richard G.
Published: April 2004

Microprobe two‐step laser mass spectrometry (μL2MS) was used to assess the distribution and origin of polycyclic aromatic hydrocarbons (PAHs) on sediment particles dredged from the harbor of Milwaukee, Wisconsin. PAH concentrations are largely associated with coal‐derived particles and other carbonaceous environments. PAH distributions on these coal‐derived particles and carbonaceous environments, which are thought to have separate origins, were found to be quite similar. μL2MS data of coal and thermally‐processed coal showed profound differences from μL2MS data obtained from the coal‐derived particles in the sediment. The results of these experiments indicate that the coal‐derived particles are not the source of PAHs in the sediment but are scavengers of PAH contaminants in the Milwaukee Harbor sediments.
Targeting of phosphonoacetate to the liver: Synthesis of a phosphonoacetate—trilactoside conjugate
Authors: Bhat Shridhar , Vaino Andrew R. , Szarek Walter A.
Published: April 2004

As part of continuing studies on drug delivery to the human liver, a phosphonoacetate—trilactoside conjugate (12) has been synthesized in an overall yield of 23%. The shortness of the synthesis of this conjugate hinges upon a successful Michaelis—Arbuzov reaction of bromoacetamide 8 with tris‐(trimethylsilyl) phosphite.
Design and preparation of polyphenyl distance markers for solid‐state 19F NMR
Authors: Monde Kenji , Tomita York , Gilchrist M. Lane , McDermott Ann E. , Nakanishi Koji
Published: April 2004

With 13C‐labeled samples, it is possible to measure internuclear distances up to 7 Å by solid‐state NMR, thus providing a powerful tool for probing ligand—receptor interactions. However, limitations in measurable distances and appreciable natural abundant 13C background signals present problems in solid‐state 13C NMR. In order to overcome these disadvantages, a set of reference compounds with known F—F distances, namely, quinolinol, p‐biphenyl, and p‐terphenyl‐bearing trifluoromethyl and trifluoromethylthio groups, have been synthesized. The preparation of these reference compounds and means for diluting these references in solid‐state NMR are described.
Quantum simulations of vibrational dephasing of molecules in a cryogenic environment: HArF in an argon cluster
Authors: Jungwirth Pavel , Gerber R. Benny , Ratner Mark A.
Published: April 2004

The Classical Separable Potential (CSP) method, which is a meanfield approximation to multidimensional quantum dynamics, is applied to the dephasing process of a vibrationally excited HArF molecule in an argon cluster at low temperatures. Dephasing timescales of the order of 1 ps are estimated for dynamics following fundamental excitation of either the H–Ar or the Ar–F stretching mode of HArF. The CSP approach is valid over such timescales, and it is thus a viable approach to quantum simulations of dephasing at low temperatures. Vibrational relaxation is much slower: Quasi‐classical molecular dynamics simulations yield a relaxation time around 100 ps for the initial v = 1 Ar–F stretching excitation. Such timescales are beyond the validity range of CSP; therefore, this or similar separable methods are inapplicable for vibrational energy decay.
NMR Studies of Diffusion‐Coherence Phenomena in Red Cell Suspensions: Current Status
Authors: Regan David G. , Kuchel Philip W.
Published: April 2004

Pulsed field‐gradient spin‐echo (PGSE) nuclear magnetic resonance (NMR) diffusion experiments conducted on some heterogeneous systems have been observed to show periodicities in the data. These “coherence patterns” are manifest in the normalized PGSE signal intensities as a function of the spatial wave vector q in so‐called q‐space plots. The sample that to our knowledge best reveals these coherence patterns is suspensions of red blood cells (RBC). The origin of these patterns and their mathematical and physical underpinnings are now well established. We have used computer simulations of molecular diffusion in lattices of RBC and other cells to aid in the interpretation and analysis of the corresponding experimental data. The aim of this review is to present the current status of NMR q‐space studies of RBC suspensions that show the diffusion‐coherence effect.
Cadmium (zinc) manganese sulfide nanocrystalline (Cd1‐xMnxS and Zn1‐xMnxS) dilute magnetic semiconductors. synthesis, annealing, and effects of surface oxidation on magnetic properties
Authors: Dang Qianyu , Wen Genwang , Sorensen Christopher M. , Klabunde Kenneth J.
Published: April 2004

Cd1‐xMnxS and Zn1‐xMnxS dilute magnetic semiconductor nanocrystals were prepared in aqueous and non‐aqueous solutions by simple precipitation methods with x values ranging from 0.1 to 0.5. X‐ray powder diffraction showed the asprepared sample crystal sizes were about 2–3 nm with zinc blende cubic structure. After thermal annealing, the crystals converted to the hexagonal wurzite structure as the crystallite size reached 100–120 nm. The manganese ions on the surface were very easily oxidized in the air and were the cause of an antiferromagnetic transition at near 37 K.
Family of thiomercuric derivatives of sugars: Synthesis, fungicidal/herbicidal activity, and application to the X‐ray structure determination of the corresponding enzymes
Authors: Belakhov Valery , Dor Evgenia , Hershenhorn Joseph , Botoshansky Mark , Bravman Tsafrir , Kolog Mirit , Shoham Yuval , Shoham Gil , Baasov Timor
Published: April 2004

A series of thiomercuric derivatives of mono‐ and disaccharides 1–7, in which methylmercury or phenylmercury is covalently attached to anomeric thioglycosides, were synthesized for structure—function studies of glycosidases. Thiomethylmercuryl xylobiosides 5 and 6 were found to inhibit intracellular xylanase‐T6 in a competitive manner, with Ki values of 0.35 mM and 0.01 mM, respectively. These inhibitors have been co‐crystallized with the enzyme and are being used for X‐ray analysis. 1‐(Thiomethylmercuric)‐ß‐D‐xyloside (3) affords crystals belonging to the orthorhombic space group P212121 and at 293(2) K: a = 6.7510(2), b = 9.7140(2), c = 29.4770(9) Å, V = 1933.08(9) Å, Z = 8, R(F2) = 0.0329, and Rw(F2) = 0.0626. There are two molecules (A and B) in the asymmetric unit, and each one shows an almost linear S–Hg–C arrangement. Biological tests on 1–7 indicated that they exhibit potent fungicidal and herbicidal activities.
Description and importance of interchain excited states in conjugated polymer photophysics
Authors: Jakubiak Rachel , Yan Ming , Wan Wai Chou , Hsieh Bing R. , Rothberg Lewis J.
Published: April 2004

We compare the photoluminescence (PL) of poly‐p‐phenyl‐enevinylene (PPV) to that of one of its soluble derivatives, poly (2‐methoxy, 5‐(21‐ethylhexoxy)‐p‐phenylenevinylene) (MEH‐PPV). We show that excimers due to π‐orbital overlap of adjacent polymer backbones are formed in MEH‐PPV in high quantum yield. They do not emit light at room temperature, potentially explaining the reduction of PL yield in MEH‐PPV films relative to solution. The herringbone packing of polymer chains in PPV prevents π‐π stacking, but low PL yields are observed anyway. We conclude that polymer design to inhibit interchain registration is a questionable strategy to increase luminescence yields. The low PL yield in PPV is ascribed to bound polaron pair formation and preliminary data suggest that these may also form upon photoexcitation of MEH‐PPV films.
Sonochemical synthesis of crystalline nanoporous zinc oxide spheres and their application in dye‐sensitized solar cells
Authors: Chen Siguang , Kumar Rangari Vijaya , Gedanken Aharon , Zaban Arie
Published: April 2004

A composite material made of zinc oxide and polyvinyl alcohol was prepared by a sonochemical method. Annealing of the composite under air removed the polymer, leaving porous spheres of ZnO. This change was accompanied by a change of the surface area from 2 m2/g to 34 m2/g. The porous ZnO particles were used as the electrode material for dye‐sensitized solar cells (DSSCs). It was tested by forming a film of the doped porous ZnO on a conductive glass support. The performance of the solar cell is reported.
Application of time‐dependent density‐functional theory to electron—ion coupling in ethylene
Authors: Bertsch George F. , Giansiracusa Jeffrey , Yabana Kazuhiro
Published: April 2004

To examine the applicability of the time‐dependent density‐functional theory (TDDFT) for treating the electron–nucleus coupling in excited states, we calculate the strength distribution associated with the π–π* transition in ethylene. The observed optical transition strength in the 7–8.5 eV region shows a complex structure arising from coupling to C–C stretch motion, to torsional motion, and to Rydberg excitations. The mean energy of the observed peak is reproduced to about 0.2 eV accuracy by the TDDFT in the local density approximation (LDA). The reflection approximation is used to calculate the peak broadening. Roughly half of the broadening can be attributed to the fluctuation in the C–C coordinate. The asymmetry in the line shape is also qualitatively reproduced by the C–C coordinate fluctuation. We find, in agreement with other theoretical studies, that the torsional motion is responsible for the progression of weak transition strength extending from the peak down to about 6 eV. The LDA reproduces the strength in this region to a factor of about 3. We conclude that the TDDFT is rather promising for calculating the electron–nucleus coupling at short times.
Synthesis and structural studies of “branched” 2‐linked trisaccharides related to h‐type 2 blood group determinants
Authors: Duus Jens Ø. , Nifant'ev Nikolay E. , Shashkov Alexander S. , Khatuntseva Elena A. , Bock Klaus
Published: April 2004

A series of fucosylated trisaccharides l‐Fuc‐(1→2)‐ß‐d‐Gal‐(1→4)‐ß‐X‐OMe (1‐6, X = d‐GlcNAc, d‐Qui (6‐deoxy‐Glc), d‐Xyl) related to H type 2 blood group determinant have been synthesized both as their α‐ and ß‐ L‐Fuc anomers together with the component disaccharide starting compounds (7‐11). The conformational properties of the trisaccharides together with their parent disaccharides have been investigated by NMR spectroscopy (proton and carbon chemical shifts and proton NOEs) in combination with computer modeling using the Monte Carlo approach and the HSEA force field using the GEGOP program with the main focus on the α‐linked fucose series.

The series of compounds allow for the investigation of interaction between the sugar units in the—in principle—linear structures, which in practice behave as branched trisaccharides.

The interaction between the terminal fucose unit and the unit at the reducing end has been probed by substitution of the bulky CH2OH group with CH3 and H substituents, respectively. Compounds with severe steric interactions can be identified by the non‐additivity of their carbon chemical shifts and subsequently confirmed by the detailed conformational assessment by NOEs and computer modeling. The most severe contacts arise in the GlcNAc and Qui trisaccharide series, whereas the Xyl‐containing trisaccharide derivatives only exhibit weak steric interaction as probed by the NMR parameters.
Synthesis of Chain‐end Functionalized Polyolefins and Polyolefin Diblock Copolymers via the Combination of Metallocene Catalysts and Reactive Chain Transfer Agents
Authors: Chung T.C. (Mike)
Published: April 2004

This paper discusses a facile route to prepare chain‐end functionalized polyolefins containing a terminal functional group (OH, COOH, NH2, etc.), and polyolefin diblock copolymers containing a polyolefin block and a functional polymer block. The chemistry is centered at an in situ chain transfer reaction during metallocene‐mediated α‐olefin polymerization using two reactive chain transfer (CT) agents, including dialkylborane (R2B‐H) and styrenic molecule/H2, to form polyolefin containing a reactive alkylborane and styrenic terminal group, respectively. With the appropriate choice of metallocene catalyst, the polymer formed shows narrow molecular weight distribution (Mw/Mn∼2), and the polymer molecular weight is inversely proportional to the molar ratio of [CT agent]/[α‐olefin]. In turn, the terminal borane group is very versatile in interconversion to various polar groups. More importantly, it can be quantitatively transformed to a living radical initiator for chain extension reaction with functional monomers. On the other hand, the terminal styrenic group was then selectively metallated and transformed to a stable polymeric anion for living anionic polymerization. The overall diblock co‐polymer process resembles a transformation reaction from metallocene‐mediated α‐olefin polymerization to a living free radical or a living anionic polymerization of functional monomers.
Mutations of phenylalanine‐193 in the putative substrate access channel alter the substrate specificity of cytochrome P450cam
Authors: Stevenson Julie‐Anne , Jones Jonathan P. , Wong Luet‐Lok
Published: April 2004

The Phe‐193 residue on the surface of cytochrome P450cam is part of a cluster of residues proposed to undergo dynamic fluctuations to permit the entry of substrates into the active site pocket. The role of this residue in the activity of P450cam has been investigated. The F193A, F193V, F193I, and F193L mutations were introduced into the Y96F mutant, which had been shown to oxidize a wider range of molecules at faster rates than the wild‐type enzyme. The F193L mutation had very little effect, while the F193A and F193I mutations reduced the camphor oxidation rate and almost abolished the styrene and naphthalene oxidation activity of the Y96F mutant. In contrast, the high activity of the Y96F mutant for the oxidation of adamantane, hexane, and 3‐methylpentane was largely retained, although the product distributions were significantly altered. This dramatic difference between the F193L and F193I mutations warrants further investigation. The turnover rates of the Y96F–F193I with all the substrates showed the same dependence on the Pd:P450cam concentration ratio as for the Y96F mutant, clearly indicating that if the F193 mutations had affected substrate access, substrate entry was still fast compared to the first electron transfer, which remained the rate‐limiting step for the overall reaction. We concluded that the F193A and F193I mutations shifted the substrate specificity of P450cam by causing structural changes that were relayed from their surface position down to the vicinity of the heme. The altered substrate binding resulted in differential electron transfer kinetics between classes of compounds.
A mechanistic study: Nucleophile dependence in glucosylations with glucosyl bromides
Authors: Bowden Tim , Garegg Per J. , Maloisel Jean‐Luc , Konradsson Peter
Published: April 2004

Glycosylations using glucosyl bromides and various promoters (Et4NBr, HgBr2, or AgOTf) were investigated, competitively and kinetically. The reactions were found to be dependent in both glucosyl bromide and nucleophilic concentration, indicating a SN2‐type rate, determining step. For the AgOTf promoted reaction an ion pair mechanism involving glucosyl triflates is suggested.
High field conduction in poly(p‐phenylene vinylene)
Authors: Conwell Esther M. , Rakhmanova Svetlana V.
Published: April 2004

We have shown that in polyacetylene, for electric fields above 106 V/cm polarons are dissociated because the electron or hole can move much faster than the lattice distortion. Similar results should hold for poly(p‐phenylene vinylene), PPV. To determine whether the free carriers thus created can be heated by the field sufficiently to allow impact ionization, we investigated free‐carrier scattering in PPV. The important scatterers are longitudinal acoustic modes, molecular vibrations, and librational torsional modes. The coupling constants and important frequencies are known approximately for the first two of these processes in PPV. Using these values, some reasonable values for librons, and the calculated band structure of PPV, we conclude that at least some of the carriers could be heated to 2 eV at a field of ∼106 V/cm, and that they could acquire energy required for impact ionization at not much higher fields.