bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calculating NMR paramagnetic relaxation enhancements without adjustable parameters: the spin‐3/2 complex Cr(III)(AcAc)3
Authors: Miller Jeremy , Schaefle Nathaniel , Sharp Robert 
Published: January 2005

AbstractNMR paramagnetic relaxation enhancement (NMR‐PRE) produced by the electron spin S = 3/2 complex Cr(III)(acac)3 (acac = acetylacetonato) has been simulated by spin dynamic (SD) simulation methods in order to test current theory of NMR‐PRE. This system provides a particularly demanding test of theory, since the Zeeman and zero field splitting (zfs) contributions to the electron spin Hamiltonian are of comparable magnitude in the range of magnetic field variation of the data, and Brownian reorientation of both the zfs tensor and the interspin vector play important roles in the relaxation mechanism. For Cr(III)(acac)3, all of the sensitive parameters of theory were known from independent experiments, so that a calculation was possible without variation of parameters. The R1 field dispersion profile (fdp), reported by Wang et al. (J. Magn. Reson. 1987; 73: 277), exhibit a single pronounced dispersive feature between 0.23 and 2.1 T. SD simulations showed that this feature results physically from the change in spatial quantization of the electron spin motion that occurs in the intermediate regime of field strengths where the Zeeman and zfs energies are comparable. Thus, the observed R1 dispersion for Cr(III)(acac)3 has a qualitatively different physical origin than the dispersions of Solomon–Bloembergen–Morgan theory, where R1 dispersions result from Zeeman breaking of level degeneracies. The shape of the experimental fdp suggests that the point‐dipole approximation is invalid for Cr(III)(acac)3 due to delocalization of electron spin density onto the π‐system of the acac ligand. After accounting for the altered geometry, good agreement with experiment was obtained. Copyright © 2003 John Wiley & Sons, Ltd.
Direct measurement of the transverse and longitudinal 15N chemical shift anisotropy–dipolar cross‐correlation rate constants using 1H‐coupled HSQC spectra
Authors: Hall Jennifer B. , Fushman David 
Published: January 2005

AbstractWe describe direct methods for the measurement of the transverse and longitudinal 15N chemical shift anisotropy–dipolar cross‐correlation rates based on comparison of the 15N doublet components observed in 1H‐coupled 1H–15N HSQC‐type spectra. This allows the determination of the cross‐correlation rates with no need for correction factors associated with other methods. The signal overlap problem of coupled HSQC spectra is addressed by using the IPAP scheme (Ottiger M, Delaglio F, Bax A. J. Magn. Reson. 1998; 131: 373). The methods proposed here use a conventional t1 evolution period, which allows one to minimize the truncation artifacts observed in a constant‐time‐type experiment (Hall JB, Dayie K, Fushman D. J. Biomol. NMR 2003; 26: 181). Applications of these measurements to the B3 domain of protein G are discussed. Copyright © 2003 John Wiley & Sons, Ltd.
Reorientational dynamics of glycerol derived from temperature‐dependent multi‐nuclear magnetic resonance relaxation data
Authors: Friedrich Anke , Dölle Andreas , Zeidler Manfred D. 
Published: January 2005

AbstractLongitudinal1H,2H and13C relaxation rates of [1H8]glycerol and [2H8]glycerol have been recorded at 250.13 MHz, 38.27 MHz and 62.89 MHz respectively, over the temperature range 260 to 350 K. In addition, the nuclear Overhauser enhancement factors of13C nuclei were recorded, since they depend only on the reorientational dynamics. It proved possible to fit all experimental data to a Cole–Davidson model extended by the Vogel–Fulcher–Tammann temperature dependence and the Lipari–Szabo libration parameter. Separate parameters were obtained for the inner CH and the outer CH2groups. The overall picture of glycerol is one of a hydrogen‐bonded liquid, where the outer CH2groups perform fast librational motions whereas the inner CH group is rigidly fixed. Copyright © 2003 John Wiley & Sons, Ltd.
Methyl TROSY: explanation and experimental verification
Authors: Ollerenshaw Jason E. , Tugarinov Vitali , Kay Lewis E. 
Published: January 2005

AbstractIn TROSY experiments, relaxation interference effects are exploited to produce spectra with improved resolution and signal‐to‐noise. Such experiments cannot be explained using the standard product operator formalism, but must instead be analyzed at the level of individual density matrix elements. Herein we illustrate this point using an example from our recent work on a TROSY 1H–13C correlation experiment for methyl groups in large proteins. Methyl groups are useful spectroscopic probes of protein structure and dynamics because they are found throughout the critical core region of a folded protein and their resonances are intense and well dispersed. Additionally, it is relatively easy to produce highly deuterated protein samples that are 1H,13C labeled at selected methyl positions, facilitating studies of high molecular weight systems. Methyl groups are relaxed by a network of 1H–1H and 1H–13C dipolar interactions, and in the macromolecular limit the destructive interference of these interactions leads to unusually slow relaxation for certain density matrix elements. It is this slow relaxation that forms the basis for TROSY experiments. We present a detailed analysis of evolution and relaxation during HSQC and HMQC pulse schemes for the case of a 13C1H3 spin system attached to a macromolecule. We show that the HMQC sequence is already optimal with respect to the TROSY effect, offering a significant sensitivity enhancement over HSQC at any spectrometer field strength. The gain in sensitivity is established experimentally using samples of two large proteins, malate synthase G (81.4 kDa) and ClpP protease (305 kDa), both highly deuterated and selectively 1H,13C‐labeled at isoleucine δ methyl positions. Copyright © 2003 John Wiley & Sons, Ltd.
8S paramagnetic centres in molecular assemblies: possible effect of their proximity on the water proton relaxivity
Authors: Nicolle Gaëlle M. , Helm Lothar , Merbach André E. 
Published: January 2005

AbstractEPR spectra of gadolinium chelates were recorded showing electron spin relaxation enhancement due to intramolecular Gd(III)–Gd(III) interaction. This enhancement was separated from other relaxation processes by replacing successively Gd(III) by the very similar Y(III). X‐band EPR line widths of the binuclear complex Gd2(OHEC)2− increase by a factor of 1.2 to 1.8 with respect to YGd(OHEC)2−. Electron spin relaxation of Gd(III) bound on the surface of micelles formed by gadofluorine 8 increases linearly with the mole fraction of Gd(III) versus Y(III). It has been shown that the increase in electron spin relaxation due to Gd–Gd interactions decreases 1H relaxivity measured on surrounding water protons. In the case of gadolinium‐based magnetic resonance imaging contrast agents this effect can limit maximum relaxivity achieved by optimizing rotational tumbling and water exchange process. Copyright © 2003 John Wiley & Sons, Ltd.
Solution‐phase chemical shift anisotropy as a promising tool to probe intermolecular interactions and peptide bond geometry: a case study on 15N‐labeled Nα‐t‐Boc‐L‐valine
Authors: Kövér Katalin E. , Batta Gyula , Hruby Victor J. 
Published: January 2005

AbstractGeometry‐dependent chemical shift anisotropy (CSAg) values of 1H and 15N nuclei have been determined in solution for 15N‐labeled, Nα‐t‐Boc‐L‐valine by measurements of CSA/dipole–dipole cross‐correlated relaxation rates using longitudinal variants of the recently proposed one‐dimensional cross‐correlation experiments. We demonstrate that solvent dependence of the CSAg is an invaluable tool for monitoring intermolecular H‐bonding interactions. In addition, enhanced temperature dependence was observed for CSAg, which indicates that the anisotropy of chemical shift is more sensitive to subtle changes in the electronic environment of the nucleus than the motionally averaged isotropic chemical shift.15N CSAg values have been determined in cyclosporin A at natural isotope abundance using the proposed 1H‐detected pulse schemes. A remarkable correlation was observed between the measured 15N CSAg and the peptide ω angle, taken from the X‐ray structure of cyclosporin A. Copyright © 2003 John Wiley & Sons, Ltd.
Simulation of radio‐frequency field inhomogeneity effects: application to pulse trains aimed at the determination of CSA–dipolar interference terms
Authors: Leclerc Sébastien , Bouguet‐Bonnet Sabine , Mutzenhardt Pierre , Brondeau Jean , Canet Daniel 
Published: January 2005

AbstractThe cross‐correlation relaxation rate constant between dipolar interaction and chemical shift anisotropy (interference term) is of considerable interest for structural and dynamical determinations. The present study focuses on methods related to its impact on longitudinal nuclear relaxation, and especially to a procedure based on the applications of a train of π pulses applied to both nuclei involved in such a process (Levitt MH, Di Bari L. Bull. Magn. Reson. 1994; 16: 94–114). The resulting steady state leads, in principle, to a straightforward determination of the relevant interference term. Simulations taking into account inhomogeneity of the radio‐frequency (RF) field show that artifacts are responsible for instabilities which in practice preclude such a determination. An alternative method making use of a very limited number of RF pulses, combined with an appropriate filter, proves to be rather robust in view of achieving a proper measurement of the required interference term. Copyright © 2003 John Wiley & Sons, Ltd.
Nuclear spin relaxation study of the solution reorientation of 3,5‐dichlorophenyl‐ and phenylethynyl‐mercury cyanide molecules and shielding tensors of nuclei forming the –HgCN and –CCHgCN groups: estimation of the heavy atom effect of mercury
Authors: Molchanov Sergey , Gryff‐Keller Adam 
Published: January 2005

Abstract3,5‐Dichlorophenylmercury cyanide (1) and phenylethynylmercury cyanide (2) dissolved in DMSO‐d6 have been investigated using 13C, 15N and 199Hg NMR and density functional theory (DFT) calculations. The longitudinal relaxation times of 13C and 199Hg nuclei of compounds 1 and 2 and of the 15N nucleus of 1 have been measured at two magnetic fields. On the basis of these data the rotational diffusion constants describing the reorientation rates of the investigated molecules in solution and the shielding anisotropy parameters for nuclei of atoms forming the –HgCN group have been determined. The available NMR characteristics of several other cyanomercury compounds and those containing the ethynylmercury fragment have also been collected. The experimental values of carbon and nitrogen shielding parameters for the cyanomercury and ethynylmercury groups have been compared with those calculated theoretically using the DFT GIAO method. This comparison has allowed an estimation of the size of the deshielding heavy atom effect experienced by the sp‐hybridized mercury‐bonded carbons atoms. Copyright © 2003 John Wiley & Sons, Ltd.
Shuttling device for high‐resolution measurements of relaxation and related phenomena in solution at low field, using a shared commercial 500 MHz NMR instrument
Authors: Redfield Alfred G. 
Published: January 2005

AbstractAn apparatus is described that can pneumatically move an aqueous liquid NMR sample sealed in a 5 or 8 mm standard tube, from the center of a standard Varian 500 MHz spectrometer and probe out to any position in its fringe field, and back, under computer control. Applications to low‐field relaxation and other measurements are discussed briefly, particularly using 31P, and 15N and 13C with proton detection, utilizing the full power of the commercial system for preparation before, and detection after, a relaxation or mixing interval at low field. Transverse relaxation, polarization transfer, and other transverse manipulations are virtually impossible with this apparatus while the sample is at the low (fringe) field, because of the tremendous inhomogeneity of that field. The spectrometer and probe are unmodified commercial products and the apparatus is expected to be usable in any other system or field without much modification. The apparatus is wheeled to the instrument and installed, and later removed without trace, in less than 1 h each way, including a probe change. A pneumatic glass shuttle tube, 22 mm inside diameter, held in an aluminum support tube, is temporarily inserted in place of the upper tube that is supplied by the manufacturer to be inserted into the top of the magnet. A standard thin‐walled NMR tube is connected to a plastic piston shuttle that is moved up or down inside the shuttle tube, by low vacuum or pressure applied from the top. The low value of magnetic field, where the relaxation process measured occurs, is determined by a movable mechanical stop whose position is changed manually between runs. The downward path is initiated by a short higher pressure pulse, followed by a long lower pressure interval. The round trip time limit is about 0.2 s, suitable for relaxation rate measurements in the range up to about 10 s−1. Variable‐temperature operation uses the regulator of the host instrument. After an overview, a detailed description of all aspects of construction and use is provided. The shuttling apparatus itself is relatively straightforward, but development of a simple sample confinement method was difficult, as expected. Problems of bubble formation and of denaturation of a protein are partly solved, and sample loading and sealing is easy. Pulse programs for this apparatus are easily generated from otherwise standard pulse sequences by addition of a few simple instructions. Operation does not require any special knowledge, nor much extra training. A major result of our program is to show that the sensitivity using such a shuttle can be that of the host instrument, not affected by such possible problems as vibration, and only reduced by the predictable losses due to relaxation during the 200–300 ms round trip shuttle time, and the inability to utilize solvent flipback methods. Copyright © 2003 John Wiley & Sons, Ltd.
β‐Cyclodextrin adducts of Gd(III) chelates: useful models for investigating the structural and dynamic determinants of the relaxivity of gadolinium‐based systems
Authors: Aime Silvio , Gianolio Eliana , Terreno Enzo , Menegotto Ivan , Bracco Chiara , Milone Luciano , Cravotto Giancarlo 
Published: January 2005

AbstractGadolinium‐chelates bearing hydrophobic substituents on their surfaces form inclusion complexes with β‐cyclodextrin. When the chelate contains more than one substituent, the observed relaxation enhancement has to be analysed on the basis of the contributions arising from the actual speciation of the resulting inclusion complexes. This analysis allows the assessment of the binding constants for the individual inclusion complexes, as well as their specific relaxation enhancements. The relaxivities obtained of the supramolecular adducts display a good linearity with their molecular weights to outline that, in these systems, the main determinant of the relaxation enhancement is represented by the overall molecular reorientational time. Copyright © 2003 John Wiley & Sons, Ltd.
Reorientational dynamics of two isomers of thiacalix[4]arene
Authors: Lang Jan , Tošner Zdeněk , Lhoták Pavel , Kowalewski Jozef 
Published: January 2005

AbstractMolecular reorientation and local mobility of two isomers of 25,26,27,28‐tetrapropoxy‐2,8,14,20‐tetrathiacalix[4]arene, cone and 1,3‐alternate, were studied by means of NMR relaxation. The chemical shift anisotropy of 13C nuclei was determined in the solid state. Nuclear relaxation due to dipole–dipole interaction and chemical shift anisotropy was analysed in the framework of the Lipari–Szabo approach. The aromatic core of both isomers was found rigid on the subnanosecond time scale. The amplitude of the local motion of the lower rim propoxy substituents increases towards the methyl ends. The methylene groups of the propoxy residues of the cone isomer possess more motional freedom than in the 1,3‐alternate, where they are sterically hindered by the adjacent aromatic rings. Global reorientation of the cone is slower than the motion of the 1,3‐alternate, which rotates partly anisotropically. Copyright © 2003 John Wiley & Sons, Ltd.
Trajectory of development in adolescents and adults with autism
Authors: Seltzer Marsha Mailick , Shattuck Paul , Abbeduto Leonard , Greenberg Jan S. 
Published: January 2005

AbstractThis article seeks to elucidate the trajectory of development in adolescents and adults with autism. Prospective, retrospective, and cross‐sectional studies are reviewed to reveal the manifestation of and changes in the core symptoms of autism in adolescence and adulthood. Comparing children with adolescents and adults, modest degrees of symptom abatement and improvement in skills have been documented in multiple studies, as are increases in verbal and decreases in performance IQ. Nevertheless, most individuals do not attain normative outcomes in adulthood and continue to manifest significant degrees of symptomatology and dependency. However, a small sub‐group (about 15%) has more favorable adult outcomes. © 2004 Wiley‐Liss, Inc. MRDD Research Reviews 2004;10:234–247.
Designing mouse behavioral tasks relevant to autistic‐like behaviors
Authors: Crawley Jacqueline N. 
Published: January 2005

AbstractThe importance of genetic factors in autism has prompted the development of mutant mouse models to advance our understanding of biological mechanisms underlying autistic behaviors. Mouse models of human neuropsychiatric diseases are designed to optimize (1) face validity, i.e., resemblance to the human symptoms; (2) construct validity, i.e., similarity to the underlying causes of the disease; and (3) predictive validity, i.e., expected responses to treatments that are effective in the human disease. There is a growing need for mouse behavioral tasks with all three types of validity for modeling the symptoms of autism. We are in the process of designing a set of tasks with face validity for the defining features of autism: deficits in appropriate reciprocal social interactions, deficits in verbal social communication, and high levels of ritualistic repetitive behaviors. Social approach is tested in an automated three‐chambered apparatus that offers the subject a choice between a familiar environment, a novel environment, and a novel environment containing a stranger mouse. Preference for social novelty is tested in the same apparatus, with a choice between the start chamber, the chamber containing a familiar mouse, and the chamber containing a stranger mouse. Social communication is evaluated by measuring the ultrasonic distress vocalizations emitted by infant mouse pups and the parental response of retrieving the pup to the nest. Resistance to change in ritualistic repetitive behaviors is modeled by forcing a change in habit, including reversal of the spatial location of a reinforcer in a T‐maze task and in the Morris water maze. Mouse behavioral tasks that may model additional features of autism are discussed, including tasks relevant to anxiety, seizures, sleep disturbances, and sensory hypersensitivity. Applications of these tests include (1) behavioral phenotyping of transgenic and knockout mice with mutations in genes relevant to autism, (2) characterization of mutant mice derived from random chemical mutagenesis, (3) DNA microarray analyses of genes in inbred strains of mice that differ in social interaction, social communication and resistance to change in habit, and (4) evaluation of proposed therapeutics for the treatment of autism. Published 2004 Wiley‐Liss, Inc. MRDD Research Reviews 2004;10:248–258.
Neuroanatomical substrates of social cognition dysfunction in autism
Authors: Pelphrey Kevin , Adolphs Ralph , Morris James P. 
Published: January 2005

AbstractIn this review article, we summarize recent progress toward understanding the neural structures and circuitry underlying dysfunctional social cognition in autism. We review selected studies from the growing literature that has used the functional neuroimaging techniques of cognitive neuroscience to map out the neuroanatomical substrates of social cognition in autism. We also draw upon functional neuroimaging studies with neurologically normal individuals and individuals with brain lesions to highlight the insights these studies offer that may help elucidate the search for the neural basis of social cognition deficits in autism. We organize this review around key brain structures that have been implicated in the social cognition deficits in autism: (1) the amygdala, (2) the superior temporal sulcus region, and (3) the fusiform gyrus. We review some of what is known about the contribution of each structure to social cognition and then review autism studies that implicate that particular structure. We conclude with a discussion of several potential future directions in the cognitive neuroscience of social deficits in autism. © 2004 Wiley‐Liss, Inc. MRDD Research Reviews 2004;10:259–271.
Autism and 15q11‐q13 disorders: Behavioral, genetic, and pathophysiological issues
Authors: Dykens Elisabeth M. , Sutcliffe James S. , Levitt Pat 
Published: January 2005

AbstractNew insights into biological factors that underlie autism may be gained by comparing autism to other neurodevelopmental disorders that have autistic features and relatively well‐delineated genetic etiologies or neurobiological findings. This review moves beyond global diagnoses of autism and instead uses an endophenotypic approach to compare specific clusters of autistic symptomatology to features of chromosome 15q11‐q13 disorders. Paternally or maternally derived deficiencies of 15q11‐q13 result in Prader‐Willi or Angelman syndromes, and we first use a global approach to review potential autism susceptibility genes in the 15q11‐q13 region. We then use a more trait‐based approach to suggest possible ties between specific phenotypic characteristics of autism and Prader‐Willi syndrome, namely savant‐like skills. We conclude with insights from pathophysiological studies that implicate altered development of specific neuron types and circuits in the cerebral cortex as part of the pathophysiological processes associated with autism and mental retardation. © 2004 Wiley‐Liss, Inc. MRDD Research Reviews 2004;10:284–291.
Toward a developmental neurobiology of autism
Authors: Polleux Franck , Lauder Jean M. 
Published: January 2005

AbstractAutism is a complex, behaviorally defined, developmental brain disorder with an estimated prevalence of 1 in 1,000. It is now clear that autism is not a disease, but a syndrome with a strong genetic component. The etiology of autism is poorly defined both at the cellular and the molecular levels. Based on the fact that seizure activity is frequently associated with autism and that abnormal evoked potentials have been observed in autistic individuals in response to tasks that require attention, several investigators have recently proposed that autism might be caused by an imbalance between excitation and inhibition in key neural systems including the cortex. Despite considerable ongoing effort toward the identification of chromosome regions affected in autism and the characterization of many potential gene candidates, only a few genes have been reproducibly shown to display specific mutations that segregate with autism, likely because of the complex polygenic nature of this syndrome. Among those, several candidate genes have been shown to control the early patterning and/or the late synaptic maturation of specific neuronal subpopulations controlling the balance between excitation and inhibition in the developing cortex and cerebellum. In the present article, we review our current understanding of the developmental mechanisms patterning the balance between excitation and inhibition in the context of the neurobiology of autism. © 2004 Wiley‐Liss, Inc. MRDD Research Reviews 2004;10:303–317.