bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of the Effect of the Phosphane Bridging Chain Nature on the Structural and Photophysical Properties of a Series of Gold(I) Ethynylpyridine Complexes
Authors: Ferrer Montserrat , Gutiérrez Albert , Rodríguez Laura , Rossell Oriol , Lima João C. , Font‐Bardia Mercè , Solans Xavier
Published: May 2008

Alkynyl AuI complexes of the type [Au(C≡CC5H4N)(PPh3)] (1) [Au2(C≡CC5H4N)2 (diphosphane)] [diphosphane = bis(diphenylphosphanyl)methane (2), bis(diphenylphosphanyl)isopropane] (3), bis(diphenylphosphanyl)acetylene (4), 1,2‐bis(diphenylphosphanyl)ethane (5), 1,3‐bis(diphenylphosphanyl)propane (6), 1,4‐bis(diphenylphosphanyl)butane (7), 1,1′‐bis(diphenylphosphanyl)ferrocene (8) and [Au3(C≡CC5H4N)3(triphos)] [triphos = 1,1,1‐tris(diphenylphosphanylmethyl)ethane] (9) were prepared by reaction of [Au(C≡CC5H4N)]n with the suitable phosphane. Determination of the X‐ray crystal structures of several compounds bearing different carbon backbones between the phosphorus atoms reveals the influence of the nature of the phosphane spacer on the establishment of intra and/or intermolecular gold–gold interactions. The absorption and emission properties of the complexes were analysed by taking into account the presence or absence of intermetallic interactions. Although UV/Vis spectra show differences for compounds with intramolecular Au–Au contacts, a conclusive trend was not observed in the emission behaviour. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Square‐Planar (Pentafluorophenyl)nickel(II) Complexes by Derivatization of a C–F Activation Product
Authors: Schaub Thomas , Backes Marc , Radius Udo
Published: May 2008

The NHC‐stabilized C–F activation product [Ni(iPr2Im)2(F)(C6F5)] (1) was isolated from the reaction of [Ni(cod)2] with 1,3‐diisopropylimidazol‐2‐ylidene (iPr2Im) and hexafluorobenzene. Square‐planar (pentafluorophenyl)nickel complexes of the type [Ni(iPr2Im)2(X)(C6F5)] were obtained by a systematic derivatization of 1. The reaction of 1 with silylated compounds and organyllithium compounds led smoothly to replacement of the fluorido ligand in 1 by halogenido, trifluoromethanesulfonato, cyanido, organyl, selenolato, thiolato, and hydrido ligands. According to these procedures, the NHC‐stabilized (pentafluorophenyl)nickel complexes [Ni(iPr2Im)2(X)(C6F5)] (X = Cl 2, I 3, CF3SO3 4, CN 5), [Ni(iPr2Im)2(R)(C6F5)] (R = Me 6, Ph 7, C2Ph 8, η1‐Cp 9), [Ni(iPr2Im)2(SR)(C6F5)] (R = Ph 10, nPr 11), [Ni(iPr2Im)2(SeR)(C6F5)] (R = Ph 12, iPr 13), and [Ni(iPr2Im)2(H)(C6F5)] (14) were prepared. The complexes 4, 6. 9, 11, 13 and 14 were structurally characterized.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
quart‐Feproline: Synthesis of a Very Rigid [3]Ferrocenophane‐Derived Artificial Amino Acid
Authors: Tebben Ludger , Kehr Gerald , Fröhlich Roland , Erker Gerhard
Published: May 2008

Starting from the α‐(dimethylamino)[3]ferrocenophane derivative 1, a short reaction sequence was developed to form a doubly anellated dihydropyrrole derivative 6 containing the ferrocenophane framework. Intermediate 6 was used for the synthesis of the (R,S,pS)‐enantiomer of the rigid artificial amino acid “quart‐Feproline”. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Star‐ and Banana‐Shaped Oligomers with a Pyrimidine Core: Synthesis and Light‐Emitting Properties
Authors: Achelle Sylvain , Ramondenc Yvan , Marsais Francis , Plé Nelly
Published: May 2008

By using Suzuki–Miyaura cross‐coupling reactions we have synthesised a series of star‐ and banana‐shaped oligomers with a pyrimidine unit as the central core and π‐conjugated arms consisting of aromatics bearing electron‐donor substituents. The position of the arms as well as the nature of their substituents were investigated with a view to accessing compounds that exhibit interesting light‐emitting properties. The best fluorescence quantum yields were obtained withbanana‐shaped pyrimidines substituted with p‐(dimethylamino)phenyl or 2‐furyl groups. Comparison of the optical properties of oligomers with benzene, pyrimidine or s‐triazine as the central unit revealed that the pyrimidinic compounds gave the best results. Some of the oligomers synthesised exhibit solvatochromic properties and pH sensibility, which could allow their use as polarity or pH sensors.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Chirality Transfer from Epoxide to Carbanion: Base‐Induced Alkylation of O‐Carbamoyl Cyanohydrins of β‐Silyl‐α,β‐epoxy Aldehyde
Authors: Sasaki Michiko , Kawanishi Eiji , Shirakawa Yuri , Kawahata Masatoshi , Masu Hyuma , Yamaguchi Kentaro , Takeda Kei
Published: May 2008

Enantioselective C–C bond formation at an α‐position of a nitrile group with an external electrophile can be realized, although in modest ee, with the aid of both the concerted process of an epoxysilane rearrangement and a carbamoyl group. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Rejection of trace organic pollutants with high pressure membranes (NF/RO)
Authors: Verliefde A.R.D. , Heijman S.G.J. , Cornelissen E.R. , Amy G.L. , Van der Bruggen B. , van Dijk J.C.
Published: May 2008

This article presents a modeling approach for the rejection of trace organic pollutants in high‐pressure membranes. The rejection values of uncharged organic solutes with a wide range of solute size and hydrophobicity are determined. Sigmoidal rejection curves are constructed and modeled for solutes of different hydrophobicity. The model is based on a log‐normal pore size distribution model. A model is also presented to model the rejection of charged organic solutes, based on the rejection of uncharged solutes and the concept of a “charge concentration polarization.” Moreover, scale‐up issues arising when translating results from bench‐scale units to full‐scale plants are addressed, by assessing the viability of a full‐scale rejection model. The full‐scale model is based on a convection‐diffusion model for the transport of organic solutes through the high‐pressure membranes and the use of mass balances in the system. © 2008 American Institute of Chemical Engineers Environ Prog, 2008
A prevalence‐based association test for case‐control studies
Authors: Ryckman Kelli K. , Jiang Lan , Li Chun , Bartlett Jacquelaine , Haines Jonathan L. , Williams Scott M.
Published: May 2008

Genetic association is often determined in case‐control studies by the differential distribution of alleles or genotypes. Recent work has demonstrated that association can also be assessed by deviations from the expected distributions of alleles or genotypes. Specifically, multiple methods motivated by the principles of Hardy‐Weinberg equilibrium (HWE) have been developed. However, these methods do not take into account many of the assumptions of HWE. Therefore, we have developed a prevalence‐based association test (PRAT) as an alternative method for detecting association in case‐control studies. This method, also motivated by the principles of HWE, uses an estimated population allele frequency to generate expected genotype frequencies instead of using the case and control frequencies separately. Our method often has greater power, under a wide variety of genetic models, to detect association than genotypic, allelic or Cochran‐Armitage trend association tests. Therefore, we propose PRAT as a powerful alternative method of testing for association. Genet. Epidemiol. 2008. © 2008 Wiley‐Liss, Inc.
Mapping the signal‐to‐noise‐ratios of cortical sources in magnetoencephalography and electroencephalography
Authors: Goldenholz Daniel M. , Ahlfors Seppo P. , Hämäläinen Matti S. , Sharon Dahlia , Ishitobi Mamiko , Vaina Lucia M. , Stufflebeam Steven M.
Published: May 2008

Although magnetoencephalography (MEG) and electroencephalography (EEG) have been available for decades, their relative merits are still debated. We examined regional differences in signal‐to‐noise‐ratios (SNRs) of cortical sources in MEG and EEG. Data from four subjects were used to simulate focal and extended sources located on the cortical surface reconstructed from high‐resolution magnetic resonance images. The SNR maps for MEG and EEG were found to be complementary. The SNR of deep sources was larger in EEG than in MEG, whereas the opposite was typically the case for superficial sources. Overall, the SNR maps were more uniform for EEG than for MEG. When using a noise model based on uniformly distributed random sources on the cortex, the SNR in MEG was found to be underestimated, compared with the maps obtained with noise estimated from actual recorded MEG and EEG data. With extended sources, the total area of cortex in which the SNR was higher in EEG than in MEG was larger than with focal sources. Clinically, SNR maps in a patient explained differential sensitivity of MEG and EEG in detecting epileptic activity. Our results emphasize the benefits of recording MEG and EEG simultaneously. Hum Brain Mapp 2009. © 2008 Wiley‐Liss, Inc.
Effects of aging on cerebral blood flow, oxygen metabolism, and blood oxygenation level dependent responses to visual stimulation
Authors: Ances Beau M. , Liang Christine L. , Leontiev Oleg , Perthen Joanna E. , Fleisher Adam S. , Lansing Amy E. , Buxton Richard B.
Published: May 2008

Calibrated functional magnetic resonance imaging (fMRI) provides a noninvasive technique to assess functional metabolic changes associated with normal aging. We simultaneously measured both the magnitude of the blood oxygenation level dependent (BOLD) and cerebral blood flow (CBF) responses in the visual cortex for separate conditions of mild hypercapnia (5% CO2) and a simple checkerboard stimulus in healthy younger (n = 10, mean: 28‐years‐old) and older (n = 10, mean: 53‐years‐old) adults. From these data we derived baseline CBF, the BOLD scaling parameter M, the fractional change in the cerebral metabolic rate of oxygen consumption (CMRO2) with activation, and the coupling ratio n of the fractional changes in CBF and CMRO2. For the functional activation paradigm, the magnitude of the BOLD response was significantly lower for the older group (0.57 ± 0.07%) compared to the younger group (0.95 ± 0.14%), despite the finding that the fractional CBF and CMRO2 changes were similar for both groups. The weaker BOLD response for the older group was due to a reduction in the parameter M, which was significantly lower for older (4.6 ± 0.4%) than younger subjects (6.5 ± 0.8%), most likely reflecting a reduction in baseline CBF for older (41.7 ± 4.8 mL/100 mL/min) compared to younger (59.6 ± 9.1 mL/100 mL/min) subjects. In addition to these primary responses, for both groups the BOLD response exhibited a post‐stimulus undershoot with no significant difference in this magnitude. However, the post‐undershoot period of the CBF response was significantly greater for older compared to younger subjects. We conclude that when comparing two populations, the BOLD response can provide misleading reflections of underlying physiological changes. A calibrated approach provides a more quantitative reflection of underlying metabolic changes than the BOLD response alone. Hum Brain Mapp 2009. © 2008 Wiley‐Liss, Inc.
White matter hyperintensities in the forties: Their prevalence and topography in an epidemiological sample aged 44–48
Authors: Wen Wei , Sachdev Perminder S. , Li Jason J. , Chen Xiaohua , Anstey Kaarin J.
Published: May 2008

White matter hyperintensities (WMHs) are a frequent finding on T2‐weighted MRI of the brain in elderly individuals, but their prevalence and severity in younger asymptomatic populations is less well studied. We report the topography of WMHs on T2‐weighted fluid inversion recovery (FLAIR) MRI in 428 individuals aged 44‐48 years recruited randomly from a healthy community sample. WMHs were delineated from FLAIR and T1‐weighted scans by using a computer algorithm, further verified and then classified using k‐nearest neighbor (kNN) algorithm into deep WMH (DWMH), and periventricular WMH (PVWMH), which included extended periventricular “rims” and frontal and occipital “caps”. Small caps and pencil‐thin rims were not taken as WMHs for this analysis. The new computer algorithm was validated and compared with the scores of visual rating, and the correspondence between the two methods was high. We found that 218 (50.9%) subjects had WMHs. 146 of the 218 (34.1% of whole sample population of 428) subjects had deep white matter hyperintensities (DWMHs). The average number of WMH clusters (occurrences) per brain was 1.37 (0.94 for DWMH and 0.43 for pathological PVWMH) and the mean WMH tissue volume was 0.278 ml. There was no significant sex difference in the severity and distribution of WMHs. The study suggests that small punctate or focal WMHs are common in the brains of individuals in their 40s, and may represent an early stage of development of these lesions. Hum Brain Mapp 2009. © 2008 Wiley‐Liss, Inc.
A voxel‐based morphometry study of frontal gray matter correlates of impulsivity
Authors: Matsuo Koji , Nicoletti Mark , Nemoto Kiyotaka , Hatch John P. , Peluso Marco A.M. , Nery Fabiano G. , Soares Jair C.
Published: May 2008

Impulsivity is a personality trait exhibited by healthy individuals, but excessive impulsivity is associated with some mental disorders. Lesion and functional neuroimaging studies indicate that the ventromedial prefrontal region (VMPFC), including the orbitofrontal cortex (OFC), anterior cingulate cortex (ACC) and medial prefrontal cortex, and the amygdala may modulate impulsivity and aggression. However, no morphometric study has examined the association between VMPFC and impulsivity. We hypothesized that healthy subjects with high impulsivity would have smaller volumes in these brain regions compared with those with low impulsivity. Sixty‐two healthy subjects were studied (age 35.4 ± 12.1 years) using a 1.5‐T MRI system. The Barratt impulsiveness scale (BIS) was used to assess impulsivity. Images were processed using an optimized voxel‐based morphometry (VBM) protocol. We calculated the correlations between BIS scale scores and the gray matter (GM) and white matter (WM) volumes of VMPFC and amygdala. GM volumes of the left and right OFC were inversely correlated with the BIS total score (P = 0.04 and 0.02, respectively). Left ACC GM volumes had a tendency to be inversely correlated with the BIS total score (P = 0.05). Right OFC GM volumes were inversely correlated with BIS nonplanning impulsivity, and left OFC GM volumes were inversely correlated with motor impulsivity. There were no significant WM volume correlations with impulsivity. The results of this morphometry study indicate that small OFC volume relate to high impulsivity and extend the prior finding that the VMPFC is involved in the circuit modulating impulsivity. Hum Brain Mapp 2009. © 2008 Wiley‐Liss, Inc.
Endogenous brain oscillations and related networks detected by surface EEG‐combined fMRI
Authors: Laufs Helmut
Published: May 2008

It is difficult to study the brain “at rest” with an approach generally pursued in science when external manipulation (independent variable) is used to obtain informative measurements (dependent variable) about the object of interest. External manipulation in its classic sense may suspend the resting state, and hence the object of interest will evade. Naturally, unless in a final and irreversible state, biological rest will always be an endogenously dynamic process. Combining two modalities, electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), to simultaneously measure the brain's activity from two angles, one can be chosen to be interpreted as the independent variable and the other as the dependent variable, and without external manipulation the brain's spontaneous dynamics can be studied. The EEG, for example, observes endogenous modulations of vigilance and detects spontaneous events such as sleep spindles or epileptic discharges and can be used as the independent variable, i.e., to form a regressor to interrogate the fMRI data (dependent variable). The opposite is possible as well, and data fusion attempts try using all data both as dependent and independent variables at the same time. This review limits itself to an exemplary discussion of simultaneous EEG/fMRI studies in humans, and among a variety of proposed resting state networks only discusses a few, especially those for which non‐resting state literature has proposed a functional meaning: the “default mode” network and an attentional network. It will be shown that one EEG feature can correlate with different fMRI activation maps and that a single resting state network may be associated with a variety of EEG patterns giving insight into the function of different resting states and the relationship between the two modalities in themselves. Hum Brain Mapp 2008. © 2008 Wiley‐Liss, Inc.
Consciousness and cerebral baseline activity fluctuations
Authors: Boly Melanie , Phillips Christophe , Balteau Evelyne , Schnakers Caroline , Degueldre Christian , Moonen Gustave , Luxen Andre , Peigneux Philippe , Faymonville Marie‐Elisabeth , Maquet Pierre , Laureys Steven
Published: May 2008

The origin of within‐subject variability in perceptual experiments is poorly understood. We here review evidence that baseline brain activity in the areas involved in sensory perception predict subsequent variations in sensory awareness. We place these findings in light of recent findings on the architecture of spontaneous BOLD fluctuations in the awake human brain, and discuss the possible origins of the observed baseline brain activity fluctuations. Hum Brain Mapp 2008. © 2008 Wiley‐Liss, Inc.
Adversities of acculturation? Prevalence of obesity among immigrants
Authors: Kaushal Neeraj
Published: May 2008

I study factors associated with prevalence of obesity among immigrants as the length of their stay in the US becomes longer. Using the National Health Interview Surveys for 1990–2004, I create ‘synthetic cohorts’ of immigrants that allow controlling for two important determinants of obesity: age at arrival and period of arrival in the US. I find that immigrants with a BA degree did not experience any change in obesity as their stay in the US advanced. Obesity among those without a BA degree, however, increased with duration of stay. Similarly, while some ethnic groups experienced increase in obesity with duration, others did not. For those who experienced increase in obesity with duration, the rise was higher during the first five years of residence than later and greater for those who arrived at a relatively young age. Copyright © 2008 John Wiley & Sons, Ltd.
Evaluation of three evaporation estimation methods in a Canadian prairie landscape
Authors: Armstrong Robert N. , Pomeroy John W. , Martz Lawrence W.
Published: May 2008

Three approaches to estimating actual evaporation (evaporation from water, soil, and transpiration from plants) are evaluated against eddy covariance observations taken during the summer period of 2006 over an upland mixed‐grass site in the St Denis National Wildlife Area, central Saskatchewan. The Penman–Monteith (P–M) combination approach explicitly takes into consideration the influence of surface resistance and available energy in order to calculate evaporation from non‐saturated surfaces. The Granger and Gray (G–D) expression is an extension of the Penman equation to the case of non‐saturated surfaces using a complimentary approach that considers the relative evaporation G, or the ratio of actual to potential evaporation as an inverse function of the relative drying power of the air, D. D is a function of the humidity deficit and available energy. The Dalton‐type bulk transfer (BT) approach typically applied in land surface schemes considers turbulent transfer along the humidity gradient between the surface and atmosphere as diagnosed from the land surface temperature. In this case, surface temperature was observed radiometrically rather than modelled. The models were evaluated for several temporal scales from 15 min to seasonal, and compared with measured evaporation data obtained by an eddy covariance system. Results suggest that all three approaches have ‘reasonable’ applicability for estimating evaporation at point‐scales for periods longer than daily, but none of the methods provide consistently reliable daily or sub‐daily estimates of evaporation. Copyright © 2008 John Wiley & Sons, Ltd.
Haplotype‐specific expression of the human PDGFRA gene correlates with the risk of glioblastomas
Authors: Toepoel Mascha , Joosten Paul H.L.J. , Knobbe Christiane B. , Afink Gijs B. , Zotz Rainer B. , Steegers‐Theunissen Regine P.M. , Reifenberger Guido , van Zoelen Everardus J.J.
Published: May 2008

Aberrant expression of the platelet‐derived growth factor α‐receptor (PDGFRA) gene has been associated with various diseases, including neural tube defects and gliomas. We have previously identified 5 distinct haplotypes for the PDGFRA promoter region, designated H1, H2α, H2β, H2γ and H2δ. Of these haplotypes H1 and H2α are the most common, whereby H1 drives low and H2α high transcriptional activity in transient transfection assays. Here we have investigated the role of these PDGFRA promoter haplotypes in gliomagenesis at both the genetic and cellular level. In a case–control study on 71 glioblastoma patients, we observed a clear underrepresentation of H1 alleles, with pH1 = 0.141 in patients and pH1 = 0.211 in a combined Western European control group (n = 998, p < 0.05). Furthermore, in 3 out of 4 available H1/H2α heterozygous human glioblastoma cell lines, H1‐derived mRNA levels were more than 10‐fold lower than from H2α, resulting at least in part from haplotype‐specific epigenetic differences such as DNA methylation and histone acetylation. Together, these results indicate that PDGFRA promoter haplotypes may predispose to gliomas. We propose a model in which PDGFRA is upregulated in a haplotype‐specific manner during neural stem cell differentiation, which affects the pool size of cells that can later undergo gliomagenesis. © 2008 Wiley‐Liss, Inc.
Low CAIX expression and absence of VHL gene mutation are associated with tumor aggressiveness and poor survival of clear cell renal cell carcinoma
Authors: Patard Jean‐Jacques , Fergelot Patricia , Karakiewicz Pierre I. , Klatte Tobias , Trinh Quoc‐Dien , Rioux‐Leclercq Nathalie , Said Jonathan W. , Belldegrun Arie S. , Pantuck Allan J.
Published: May 2008

We attempted to describe, in a series of clear cell renal cell carcinoma (RCC), the relationship between CAIX expression, VHL gene mutations, tumor characteristics and outcome. Radical nephrectomy was performed in 100 patients. Genomic DNA was extracted from frozen tumor samples. Four amplimers covering the whole coding sequence of the VHL gene were synthesized by PCR and sequenced. The monoclonal antibody M75 was used to evaluate CAIX protein expression immunohistochemically. VHL mutations were identified in 58 patients (58%) and high CAIX expression (>85%) was observed in 78 (78%). Tumors with VHL mutation showed higher CAIX expression than those without (p = 0.02). Low CAIX expression and absence of VHL mutation were associated with a more advanced tumors e.g., higher T stages and presence of metastases. VHL mutation and high CAIX expression predicted longer progression‐free survival (p = 0.037) and disease‐specific survival (p = 0.001), respectively. In combination, they defined three prognostic groups (p = 0.002): (i) good prognosis, defined as VHL mutation and high CAIX (2‐year survival: 86%), (ii) intermediate prognosis with either VHL mutation or high CAIX (69%), and (iii) poor prognosis with no VHL mutation and low CAIX (45%, median survival 18 months). CAIX expression, but not VHL mutational status, was an independent prognostic factor in multivariate analysis. Taken together, CAIX expression and VHL mutational status are able to stratify patients with clear cell RCC into distinct groups with regards to clinicopathological variables and prognosis, with low CAIX expression and absence of VHL mutation being associated with a poor clinicopathological phenotype and diminished survival. © 2008 Wiley‐Liss, Inc.
Electron crystallography of aquaporins
Authors: Andrews Simeon , Reichow Steve L. , Gonen Tamir
Published: May 2008

Aquaporins are a family of ubiquitous membrane proteins that form a pore for the permeation of water. Both electron and X‐ray crystallography played major roles in determining the atomic structures of a number of aquaporins. This review focuses on electron crystallography, and its contribution to the field of aquaporin biology. We briefly discuss electron crystallography and the two‐dimensional crystallization process. We describe features of aquaporins common to both electron and X‐ray crystallographic structures; as well as some structural insights unique to electron crystallography, including aquaporin junction formation and lipid‐protein interactions. © 2008 IUBMB IUBMB Life, 60(7): 430–436, 2008
Molecular mechanisms of oxidative stress‐induced carcinogenesis: From epidemiology to oxygenomics
Authors: Toyokuni Shinya
Published: May 2008

Oxidative stress is associated with inflammation, radiation, reperfusion, and iron overload. Epidemiological observations have shown that oxidative stress is one of the major sources of carcinogenesis, the top‐ranked cause of human mortality worldwide. In situations of oxidative stress, reactive oxygen and nitrogen species contribute to the alteration of genome information, presumably followed by selection of the adapted proliferating cells in a given environment. Recent data suggest that common molecular mechanisms exist in oxidative stress‐induced carcinogenesis, including p16INK4A inactivation. Thus far, oxidative DNA damage in the genome as a cause of mutation has been recognized to be randomly distributed based on in vitro experiments, while localization of oxidative DNA damage in vivo has not been pursued. However, using a novel technique based on DNA immunoprecipitation in combination with genome information, we now know that the localization of oxidative DNA damage is not random in vivo. We propose to call this rather novel research area “oxygenomics.” Many signaling pathways start from the recognition of DNA damage. Thus, possible underlying principles should be elucidated in association with each cell type, the genomic location of the damage with its transcriptional activity as well as the chromatin status determining the epigenetic effect. © 2008 IUBMB IUBMB Life, 60(7): 441–447, 2008
Chemically modified light‐curable chitosans with enhanced potential for bone tissue repair
Authors: Qiu Yongzhi , Zhang Ning , Kang Qian , An Yuehuei , Wen Xuejun
Published: May 2008

Light curable polymers are showing great potential in overcoming some of the current obstacles in bone repair. With stereolithography, they can be fabricated into scaffolds with desired topography for repairing bone defects in irregular shapes. In this study, we developed a series of light curable chitosans, which have photocurability and good solubility in organic solvent. Through adjusting the feeding ratio of the raw components, the content of photocurable groups in the backbone of chitosan can be controlled. The light curable chitosans were characterized through FTIR–ATR and 1H NMR, which also confirmed their controllable photocurability. NIH 3T3 fibroblasts were co‐cultured with the photocured samples for 7 days and the results indicated that these photocured chitosans are cyto‐compatible. Scaffolds with interconnected pores, fabricated using salt leaching and photocuring and seeded with fetal bovine osteoblasts, were implanted subcutaneously in the backs of athymic rat. Histological study on the implants at 6 weeks showed that the photocured chitosans have good osteoconductivity. The results indicated the light curable chitosans have good biocompatibility and osteoconductivity. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009
Biomimetic organic–inorganic nanocomposite coatings for titanium implants
Authors: Sikirić Maja Dutour , Gergely Csilla , Elkaim Rene , Wachtel Ellen , Cuisinier Frederic J. G. , Füredi‐Milhofer Helga
Published: May 2008

A new class of organic–inorganic nanocomposites, to be used as coatings for surface enhancement of metal implants for bone replacement and repair, has been prepared by a biomimetic three‐step procedure: (1) embedding amorphous calcium phosphate (ACP) particles between organic polyelectrolyte multilayers (PE MLs), (2)in situtransformation of ACP to octacalcium phospate (OCP) and/or poorly crystalline apatite nanocrystals by immersion of the material into a metastable calcifying solution (MCS) and (3) deposition of a final PE ML. The organic polyelectrolytes used were poly‐L‐glutamic acid and poly‐L‐lysine. The nanocomposites obtained by each successive step were characterized by scanning electron microscopy, energy dispersive X‐ray analysis (EDS), and XRD, and their suitability as coatings for metal implants was examined by mechanical andin vitrobiological tests. Coatings obtained by the first deposition step are mechanically unstable and therefore not suitable. During the second step, upon immersion into MCS, ACP particles were transformed into crystalline calcium phosphate, with large platelike OCP crystals as the top layer. After phase transformation, the nanocomposite was strongly attached to the titanium, but the top layer did not promote cell proliferation. However, when the coating was topped with an additional PE ML (step 3), smoother surfaces were obtained, which facilitated cell adhesion and proliferation as shown byin vitrobiological tests using primary human osteoblasts (HO) directly seeded onto the nanocomposites. In fact, cell proliferation on nanocomposites with top PE MLs was far superior than on any of the individual components and was equivalent to proliferation on the golden standard (plastic). © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009
Fibrin scaffold promotes adenoviral gene transfer and controlled vector delivery
Authors: Breen Ailish , Dockery Peter , O'Brien Timothy , Pandit Abhay
Published: May 2008

Gene therapy using adenoviral vectors in tissue regeneration is hindered by a short duration of transgene expression. It is hypothesized that a fibrin scaffold will enhance delivery of the adenovirus to a wound site, precluding the need for high repeated doses. It was aimed to analyze whether fibrin could deliver a low single dose of viral vector to a wound site, without compromising transfection efficiency. Fibrin scaffold containing adenovirus encoding β‐galactosidase, fibrin alone, adenovirus alone, and no treatment groups were applied to a rabbit ear ulcer model. β‐Galactosidase transgene expression was measured at 7 and 14 days. Transgene expression was enhanced in the fibrin containing adenovirus group at 7 days. By 14 days, there was low expression and no difference between groups. Stereological methods assessing wound healing aimed to determine whether the adenovirus capsid elicited an unfavorable inflammatory response and whether fibrin's beneficial properties were altered by addition of adenovirus. The fibrin adenovirus group showed a wound‐healing response similar to fibrin alone, showing maximum cellularity and angiogenesis at 7 days. By 14 days, cellularity and angiogenesis subsided, and this effect was not inhibited by the presence of adenovirus. Adenovirus alone did not cause an unfavorable inflammatory response. It is concluded the fibrin aids in the delivery of a low‐dose viral vector, thereby avoiding a chronic inflammatory response, and allowing superior transfection than viral vector alone. This has wide‐ranging implications on the use of viral vectors in tissue engineering. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009
Synthesis and characterization of thermosensitive and pH‐sensitive poly (N‐isopropylacrylamide‐acrylamide‐vinylpyrrolidone) for use in controlled release of naltrexone
Authors: Salehi R. , Arsalani N. , Davaran S. , Entezami A. A.
Published: May 2008

In this article N‐isopropylacrylamide (NIPAAm)‐acrylamide (AAm)‐vinyl pyrrolidone (VP) terpolymers were prepared using free radical copolymerization method by varying feed ratios of monomers. The composition ratio and structure of polymer were determined by NMR and FTIR. The glass transition temperature was examined by DSC. The thermo‐responsive behaviors of polymeric solutions were investigated by turbidimetry using UV‐Visible spectroscopy. The sol–gel transition of the polymer solutions occurred reversibly within 1 min in response to the temperature. By alternating the monomer feed ratio, the synthesized terpolymers had their own distinctive lower critical solution temperature (LCST). In addition to the thermosensitivity, the terpolymers also showed a response to pH changes. The increase in ionic strength of the buffer solution with addition of salt lowered the LCST of the polymers. The ability to shift the phase transition temperature of the terpolymers provided excellent flexibility in tailoring transitions for specific uses. Swelling experiments were performed on the terpolymer disks in buffer solutions with different pH and ionic strength at varying temperature. We investigated naltrexone release as a model drug in phosphate buffer. Drug loading efficiency was varying from 8.75 to 55%. Gel composition, pH, and ionic concentration affected the drug loading. Finally in vitro drug release studies at 36–37°C indicating 35–70% naltrexone release from terpolymers at the end of 30 days. In addition, these gels sustained naltrexone release for 30 days. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009
Bond‐based 3D‐chiral linear indices: Theory and QSAR applications to central chirality codification
Authors: Castillo‐Garit Juan A. , Marrero‐Ponce Yovani , Torrens Francisco , García‐Domenech Ramón , Romero‐Zaldivar Vicente
Published: May 2008

The recently introduced non‐stochastic and stochastic bond‐based linear indices are been generalized to codify chemical structure information for chiral drugs, making use of a trigonometric 3D‐chirality correction factor. These improved modified descriptors are applied to several well‐known data sets to validate each one of them. Particularly, Cramer's steroid data set has become a benchmark for the assessment of novel quantitative structure activity relationship methods. This data set has been used by several researchers using 3D‐QSAR approaches such as Comparative Molecular Field Analysis, Molecular Quantum Similarity Measures, Comparative Molecular Moment Analysis, E‐state, Mapping Property Distributions of Molecular Surfaces, and so on. For that reason, it is selected by us for the sake of comparability. In addition, to evaluate the effectiveness of this novel approach in drug design we model the angiotensin‐converting enzyme inhibitory activity of perindoprilate's σ‐stereoisomers combinatorial library, as well as codify information related to a pharmacological property highly dependent on the molecular symmetry of a set of seven pairs of chiral N‐alkylated 3‐(3‐hydroxyphenyl)‐piperidines that bind σ‐receptors. The validation of this method is achieved by comparison with earlier publications applied to the same data sets. The non‐stochastic and stochastic bond‐based 3D‐chiral linear indices appear to provide a very interesting alternative to other more common 3D‐QSAR descriptors. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008
An optimized initialization algorithm to ensure accuracy in quantum Monte Carlo calculations
Authors: Fisher Daniel R. , Kent David R. , Feldmann Michael T. , Goddard William A.
Published: May 2008

Quantum Monte Carlo (QMC) calculations require the generation of random electronic configurations with respect to a desired probability density, usually the square of the magnitude of the wavefunction. In most cases, the Metropolis algorithm is used to generate a sequence of configurations in a Markov chain. This method has an inherent equilibration phase, during which the configurations are not representative of the desired density and must be discarded. If statistics are gathered before the walkers have equilibrated, contamination by nonequilibrated configurations can greatly reduce the accuracy of the results. Because separate Markov chains must be equilibrated for the walkers on each processor, the use of a long equilibration phase has a profoundly detrimental effect on the efficiency of large parallel calculations. The stratified atomic walker initialization (STRAW) shortens the equilibration phase of QMC calculations by generating statistically independent electronic configurations in regions of high probability density. This ensures the accuracy of calculations by avoiding contamination by nonequilibrated configurations. Shortening the length of the equilibration phase also results in significant improvements in the efficiency of parallel calculations, which reduces the total computational run time. For example, using STRAW rather than a standard initialization method in 512 processor calculations reduces the amount of time needed to calculate the energy expectation value of a trial function for a molecule of the energetic material RDX to within 0.01 au by 33%. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008
Structure and dynamics of phosphate ion in aqueous solution: An ab initio QMCF MD study
Authors: Pribil Andreas B. , Hofer Thomas S. , Randolf Bernhard R. , Rode Bernd M.
Published: May 2008

A simulation of phosphate in aqueous solution was carried out employing the new QMCF MD approach which offers the possibility to investigate composite systems with the accuracy of a QMMM method but without the time consuming creation of solute–solvent potential functions. The data of the simulations give a clear picture of the hydration shells of the phosphate anion. The first shell consists of 13 water molecules and each oxygen of the phosphate forms in average three hydrogens bonds to different solvent molecules. Several structural parameters such as radial distribution functions and coordination number distributions allow to fully characterize the embedding of the highly charged phosphate ion in the solvent water. The dynamics of the hydration structure of phosphate are described by mean residence times of the solvent molecules in the first hydration shell and the water exchange rate. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008
Influence of intrinsic defects on the properties of zinc oxide
Authors: Jug Karl , Tikhomirov Viatcheslav A.
Published: May 2008

The effects of oxygen vacancies and zinc interstitials on the structure and energy of zinc oxide were studied with the semiempirical MO method MSINDO. Cyclic clusters were chosen as model systems. Single and multiple removal of oxygen atoms and zinc interstitials in zinc oxide served to determine the defect formation energy and the band gap. The interaction between two and three oxygen vacancies was investigated. The vacancies cause a decrease of the band gap, which originates from an occupied defect level. This is also found for zinc interstitials under zinc rich conditions. The defect formation energy of such zinc interstitials is found to be lower than that of oxygen vacancies at 0 K but decreases for oxygen vacancies and increases for zinc interstitials with increasing temperature. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008
Mechanistic studies on the formation of glycosidase‐substrate and glycosidase‐inhibitor covalent intermediates
Authors: Brás Natércia F. , Moura‐Tamames Sara A. , Fernandes Pedro A. , Ramos Maria J.
Published: May 2008

Glycoside hydrolases catalyze the breaking of the glycosidic bond. This type of bond fashioned between two monosaccharides is very stable, and the polymers created are involved in multiple cellular processes, being crucial to life. In this article, computational methods were used to study the first step of the mechanism of reaction of retaining glycoside hydrolases in atomic detail. The systems modeled included a simplified reaction center and a small substrate/inhibitor. Using DFT calculations we were able to corroborate and provide molecular‐level detail to the dissociative mechanism proposed in the literature. The role of the hydrogen bridge between the nucleophile and the C2OH group of the ring was also investigated. Therefore, we concluded that this bridge is responsible for lowering the activation barrier by 5.1 kcal mol−1 with functional BB1K/6‐311+G(2d,2p), and the absence of the bridge explains, at least in part, the inhibitory effect of fluoro‐substituted glycosides in the −2 position. The hydrogen bridge could also be involved in favoring the ring distortion verified in the transition state, and the dissociative character of the reaction mechanism. Using the NBO method, point atomic charges were calculated. In the transition state, the positive charge generated in the sugar ring is distributed nearly equally between the anomeric carbon and the ring oxygen, through a partial double bond involving the two atoms. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008
Nutritional endoderm: a way to breach the holoblastic–meroblastic barrier in tetrapods
Authors: Elinson Richard P.
Published: May 2008

The deceptively simple evolutionary transition from complete, holoblastic cleavage of the zygote to incomplete, meroblastic cleavage occurred only once in tetrapods, with the evolution of the amniote egg. By examining the development of a frog with large eggs, we identified a new tissue called the nutritional endoderm, which provides a possible intermediate step to breach the holoblastic–meroblastic barrier. Nutritional endoderm is divided into cells, but the cells disappear and do not contribute to tissues of the frog after the yolk is depleted. The complete loss of this yolk‐rich tissue raises the question as to what feature of early development requires cellularization of this endoderm. J. Exp. Zool. Mol. Dev. Evol. 312B:526–532, 2009. © 2008 Wiley‐Liss, Inc.
Climatology of wind patterns in the northeast of the Iberian Peninsula
Authors: Jiménez Pedro A. , González‐Rouco J. Fidel , Montávez Juan P. , García‐Bustamante Elena , Navarro Jorge
Published: May 2008

A classification of daily surface wind fields over the Comunidad Foral de Navarra (CFN) region (northeastern Iberian Peninsula (IP)) into wind pattern (WP) types is performed. Daily wind data measured at 41 meteorological stations are employed to represent the surface wind field. Two methodologies are used to develop the classification, one based on the spatial and the other on the temporal similarity. Both methodologies produce comparable results yielding six robust wind patterns. The detected wind field types are season dependent, thereby revealing an annual cycle evolution. The patterns with northwestern circulations are dominant (60.9%) followed by the southeastern ones (30.5%), showing the strong influence of the orography over surface circulations, since valleys in the region are directed mainly along the NW–SE direction.

A sea level pressure (SLP) map pattern classification is also performed to evaluate the connections between the synoptic circulations and the surface flows. Eight pressure patterns (PPs) were identified and related to the surface WPs already formed. The associations found were clear enough to understand the forcing mechanism of the different WPs. The ageostrophic balance and the pressure gradient along the valleys seem to successfully describe the general characteristics of the surface circulations over the study region.

The behaviour of some atmospheric parameters such as temperature, relative humidity, global radiation and precipitation, which help to describe the atmospheric state associated with each surface circulation type, is also described. They show different advective regimes, and in particular the cold and dry northwestern strong wind locally known as Cierzo and the warm and moist southeastern wind known as Bochorno are recognized. A WP responsible for precipitation episodes of high intensity in the northern region of the CFN is also recognized. Copyright © 2008 Royal Meteorological Society
Pyrazole formation: Examination of kinetics, substituent effects, and mechanistic pathways
Authors: Sloop Joseph C. , Lechner Brent , Washington Gary , Bumgardner Carl L. , Loehle W. David , Creasy William
Published: May 2008

Reaction kinetics for the condensation of 1,3‐diketones 1a–o with selected arylhydrazines (aryl = Ph, 4‐NO2Ph, 4‐CH3OPh, and 2,4‐diNO2Ph) was studied using 19F NMR spectroscopy. Product regioselectivity is modulated by reactant ratios, substituents, and acidity. Reaction rates were found to be influenced by substituents on the diketones and on phenylhydrazines as well as by acidity of the reaction medium with rates varying as much as 1000‐fold. Hammett ρ values for these cyclizations were determined. The reaction was found to be first order in both the diketone and arylhydrazine. The rate‐determining step for pyrazole formation shifts as a function of pH. Mechanistic details and reaction pathways supporting these findings are proposed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 370–383, 2008
Consumers' product‐locating behavior: Exploring the application of signal detection theory
Authors: Liu Sandra S. , Chen Jie , Melara Robert D. , Massara Francesco
Published: May 2008

This study explores the application of signal detection theory to the analysis of consumers' product‐locating behavior. Two research questions are addressed: (1) whether characteristics of the shopping environment, including external memory aids and store layout, affect signal‐detection statistics and (2) whether the signal‐detection statistics can be predicted from subjective measures of shopping motivation and product familiarity. The experiments are conducted in a virtual store. The results show that (1) the signal‐detection statistics of sensitivity and response bias can be used to measure product‐locating behavior; (2) external memory aids significantly affect sensitivity; and (3) signal‐detection statistics are significantly associated with shopping motivation. © 2008 Wiley Periodicals, Inc.
Residues of deoxynivalenol (DON) in pig tissue after feeding mash or pellet diets containing low concentrations
Authors: Döll Susanne , Dänicke Sven , Valenta Hana
Published: May 2008

Residues of deoxynivalenol (DON) and its metabolite de‐epoxy‐DON (DOM) were analyzed in specimens of pigs fed diets containing 0, 25, and 50% contaminated wheat (2.5 mg DON/kg) fed as mash or pellets over the final growing period of 11 wk. Median DON concentrations decreased from bile > kidney > serum > liver = muscle, while DOM was only detected in bile and kidney. Maximum carry over rates were 0.0319 for kidney, 0.0064 for liver, and 0.0043 for muscle, demonstrating that the contribution of animal derived food to the consumers' exposure is very low. The high interindividual variation of DON concentrations in all analyzed specimen of pigs fed diets containing similar concentrations of DON does not allow a diagnostic differentiation of animals fed diets containing DON concentrations of approximately 61% of the guidance level of 0.9 mg DON/kg, and those fed diets containing 137% of this concentration. The different feed forms did not affect residue concentrations in any of the investigated specimens.