bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vibrational analysis of the chorismate rearrangement: relaxed force constants, isotope effects and activation entropies calculated for reaction in vacuum, water and the active site of chorismate mutase
Authors: Ruggiero Giuseppe D. , Guy Sara J. , Martí Sergio , Moliner Vicent , Williams Ian H. 
Published: May 2004

AbstractWe present results derived from vibrational Hessians calculated for the reactant complex, transition structure and product complex of the rearrangement of chorismate to prephenate under different conditions. The AM1 semiempirical MO and B3LYP/6–31G* density functional methods were employed for calculations in vacuum, whereas a hybrid QM/MM method AM1/CHARMM/TIP3P was used for calculations in water and within the active site of B. subtilis chorismate mutase. Kinetic and equilibrium isotope effects and entropies of activation and reaction were investigated as a function of the increasing size of the Hessian, as the system is expanded to include not only the atoms of chorismate/prephenate itself but also an increasing number of surrounding water molecules (up to 99) or active‐site residues (up to 225 atoms). Primary 13C and 18O isotope effects are not sensitive to the size of the Hessian, but secondary 3H–C5 and 3H2–C9 effects require the inclusion of at least those atoms directly involved in hydrogen bonds to the substrate or, better, a complete first solvation shell or cage of active‐site amino acid residues. Pauling bond orders for the breaking CO and making CC bonds are remarkably similar for the transition structures in all three media. Relaxed force constants for stretching of these bonds (which allow meaningful comparisons to be made along a reaction path) give a significantly different picture of the bonding changes in the transition structures. The ratio of logarithms of kinetic and equilibrium isotope effects does not agree with measures of transition‐state structure derived from Pauling bond orders or from relaxed force constants. There is no simple relationship between kinetic isotope effects and transition‐state structure for this Claisen rearrangement. The calculated vibrational entropy of activation for the enzymic reaction agrees well with an experimental value for E. coli chorismate mutase. Vibrational entropy reduces the free energy barrier for the catalysed reaction by about 1 kJ mol−1 at 333 K. Copyright © 2004 John Wiley & Sons, Ltd.
Correlating biological activity with calculated geometric motifs in cyclolinopeptide A analogs
Authors: Zubrzak P. , Leplawy M. T. , Kowalski M. L. , Szkudlińska B. , Paneth P. , Silberring J. , Suder P. , Zabrocki J. 
Published: May 2004

AbstractThree linear and three cyclic analogs of cyclolinopeptide A, with phenylalanine residues in position 8 and/or 9 replaced by N‐benzylglycine, were synthesized using the SPPS method and cyclization with TBTU reagent. The peptides were examined for their immunosuppressive activity in a lymphocyte proliferation test. In order to test the importance of the edge‐to‐face interactions between Phe8–Phe9 aromatic rings, molecular modeling studies were carried out. The results support its importance of the edge‐to‐face interactions for the biological activity of these compounds and indicate that the distance between the two rings also plays an essential role. Copyright © 2004 John Wiley & Sons, Ltd.
Hydrolysis of 2‐(p‐nitrophenoxy)tetrahydropyran: solvent and α‐deuterium secondary kinetic isotope effects and relationships with the solvolysis of simple secondary alkyl arenesulfonates and the enzyme‐catalyzed hydrolysis of glycosides
Authors: Ahmad Imran A. , Birkby Sara L. , Bullen Claire A. , Groves Patrick D. , Lankau Timm , Lee Won Heui , Maskill Howard , Miatt Peter C. , Menneer Iain D. , Shaw Katherine 
Published: May 2004

AbstractThe effect of solvent composition in aqueous ethanol, trifluoroethanol and hexafluoropropan‐2‐ol on the rate constant and activation parameters for the uncatalysed hydrolysis of 2‐(p‐nitrophenoxy)tetrahydropyran (1) was investigated, and the m(YOTs) value is 0.60. This appreciable but less than maximal value is in accordance with an SN1 mechanism with rate‐limiting ionization. The α‐deuterium secondary kinetic isotope effect (α‐kie) for the uncatalysed hydrolysis of 1 is 1.17 in water (46°C), 1.15 in aqueous trifluoroethanol (50% mole fraction, 70.6°C) and 1.13 in aqueous ethanol (50% mole fraction, 70.6°C). These values correspond to about 1.19 at 25°C, which is characteristic of rate‐limiting ionization in an SN1 reaction and appreciably higher than values for enzyme‐catalysed glycolysis. The α‐kie is smaller under aqueous acidic conditions (1.07, 0.1 mol dm−3 hydrochloric acid, 20.2°C) when 1 hydrolyses with acid catalysis. The previously reported α‐kie for the hydrolysis of 1 in buffered aqueous dioxan (1.063, 25°C) is now seen to correspond to acid‐catalysed hydrolysis. These new results for 1 indicate that transition structures in enzyme‐catalysed glycolyses with α‐kie values of less than about 1.15 at 25°C involve a lower degree of carbenium ion character than has hitherto been assumed. Copyright © 2004 John Wiley & Sons, Ltd.
Dual temperature‐ and pH‐sensitive hydrogels from interpenetrating networks and copolymerization of N‐isopropylacrylamide and sodium acrylate
Authors: Chen Hong , Hsieh You‐Lo 
Published: May 2004

AbstractHydrogels responsive to both temperature and pH have been synthesized in the forms of sequential interpenetrating networks (IPNs) of N‐isopropylacrylamide (NIPAAm) and sodium acrylate (SA) and compared with the crosslinked random copolymers of N‐isopropylacrylamide and SA. Whereas the stimuli‐sensitive behaviors of copolymer hydrogels were strongly dependent on the ionic SA contents, the IPN hydrogels exhibited independent swelling and thermal behaviors of each network component. The sequences and media in the synthesis of IPNs influenced the swelling capacities of the IPNs, but not the temperature or pH ranges at which the swelling changes occurred. In IPNs, a more expanded primary gel network during the synthesis of the secondary network contributed to the better swelling of the final IPNs. Both the swelling and thermal behaviors of the IPNs suggest that poly(N‐isopropylacrylamide) and poly(sodium acrylate) are phase separated regardless of their synthesis conditions. The presence of the poly(sodium acrylate) network did not influence the temperature or the extent of phase transition of the poly(N‐isopropylacrylamide) network in the IPNs, but did improve the thermal stability of the IPNs. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3293–3301, 2004
Two‐Phase Flow Characterization by Automated Digital Image Analysis. Part 2: Application of PDIA for Sizing Sprays
Authors: Kashdan Julian T. , Shrimpton John S. , Whybrew Adam 
Published: May 2004

AbstractA series of experiments were conducted in order to assess the robustness and accuracy of a recently developed digital image analysis technique (PDIA). This paper investigates the application of the PDIA technique to the sizing of relatively small fuel droplets of diameters in the range 5 to 30 μm produced by a pressure‐swirl atomizer. The measurement performance of the PDIA system has been assessed in terms of individual object diameters and also number and volume probability density functions of diameter in comparison to phase Doppler anemometry (PDA) data obtained under identical conditions. PDIA measurements revealed good agreement with spray data obtained by PDA at a measurement location 36 diameters downstream from the nozzle orifice with differences in the arithmetic mean diameter, D10 and volume mean diameter, D30 of approximately 5 and 3% respectively. The PDIA technique was shown to detect the presence of very large, predominantly non‐spherical droplets whose diameters were in excess of 100 μm. These droplets, although few in number constitute a significant proportion of the total spray volume and would have otherwise been either erroneously measured or have passed through the probe volume undetected using PDA due to non‐sphericity. Smaller objects may also be measured correctly by both methods although sensitivity to signal‐to‐noise ratio, for both methods can generate spurious and contradictory errors.
Thermal effects in stretching of Go‐like models of titin and secondary structures
Authors: Cieplak Marek , Hoang Trinh Xuan , Robbins Mark O. 
Published: May 2004

AbstractThe effect of temperature on mechanical unfolding of proteins is studied using a Go‐like model with a realistic contact map and Lennard–Jones contact interactions. The behavior of the I27 domain of titin and its serial repeats is contrasted to that of simple secondary structures. In all cases, thermal fluctuations accelerate the unraveling process, decreasing the unfolding force nearly linearly at low temperatures. However, differences in bonding geometry lead to different sensitivity to temperature and different changes in the unfolding pattern. Due to its special native‐state geometry, titin is much more thermally and elastically stable than the secondary structures. At low temperatures, serial repeats of titin show a parallel unfolding of all domains to an intermediate state, followed by serial unfolding of the domains. At high temperatures, all domains unfold simultaneously, and the unfolding distance decreases monotonically with the contact order, that is, the sequence distance between the amino acids that form the native contact. Proteins 2004. © 2004 Wiley‐Liss, Inc.
Absence of kinetic thermal stabilization in a hyperthermophile rubredoxin indicated by 40 microsecond folding in the presence of irreversible denaturation
Authors: LeMaster David M. , Tang Jianzhong , Hernández Griselda 
Published: May 2004

AbstractThe striking kinetic stability of many proteins derived from hyperthermophilic organisms has led to the proposal that such stability may result from a heightened activation barrier for unfolding independent of a corresponding increase in the thermodynamic stability. This in turn implies a corresponding retardation of the folding reaction. A commonly cited model for kinetic thermal stabilization is the rubredoxin fromPyrococcus furiosus(Pf), which exhibits an irreversible denaturation lifetime at 100°C of nearly a week. Utilizing protein resonances shifted well outside of the random coil chemical shift envelope, nuclear magnetic resonance (NMR) chemical exchange measurements onPfrubredoxin as well as on the mesophileClostridium pasteurianum(Cp) rubredoxin demonstrate reversible thermal transition temperatures of 144°C (137°C for the N‐terminal modified A2K variant) and 104°C, respectively, with similar (un)folding rates of ≈25,000 s−1, only modestly slower than the diffusion controlled rate. The absence of a substantial activation barrier to rubredoxin folding as well as the similar folding kinetics of the mesophile protein indicate that kinetic stabilization has not been utilized by the hyperthermophile rubredoxin in achieving its extreme thermal stability. The two‐state folding kinetics observed forPfrubredoxin contradict a previous assertion of multiphasic folding based on hydrogen exchange data extrapolated to an estimated midpoint of transition temperature (Tm) of nearly 200°C. This discrepancy is resolved by the observation that the base‐catalyzed hydrogen exchange of the model dipeptide (N‐acetyl‐L‐cysteine‐N‐methylamide)4‐Cd2+is 23‐fold slower than that of the free cysteine model dipeptide used to normalize thePfrubredoxin hydrogen exchange data. Proteins 2004. © 2004 Wiley‐Liss, Inc.
The protective effect of film metallization against oxidative deterioration and discoloration of sensitive foods
Authors: Piergiovanni L. , Limbo S. 
Published: May 2004

AbstractThe importance of the optical properties of packaging materials is often underestimated and little attention is generally given to the shelf‐life of light‐sensitive food products. In this paper, the effects of the light barrier of different metallized films in delaying chemical degradative reactions, which occur in dry lasagna made with eggs and spinach, were investigated. The array of films evaluated in the experiment accounted for a large distribution of optical properties. Pouches prepared from the different films were filled with dry lasagna and stored at room temperature for about 4 months under a fluorescent light source. Sensory evaluations, CIE‐L*, a*, b* colour measurements and hexanal formation were evaluated during storage. The shelf‐life of lasagna packed in metallized films was 2.5 times greater than the same product packed in non‐metallized films. A correlation between transmittance values of the packaging films and shelf‐life reduction was obtained. Because of the fat and the pigments of lasagna and also its shape (large surface area), lasagna seems to be a good model system when studying the protective performance of packaging materials against degradative reactions that involve oxygen and are very sensitive to light exposure. Copyright © 2004 John Wiley & Sons, Ltd.
The evolution of methods for female sterilization
Authors: Wilson E.W. 
Published: May 2004

AbstractMethods for the sterilization of women by occlusion of the Fallopian tubes have evolved by changes in the approaches to the tubes and trials of various methods for occluding the tubal lumen. Approaches to the tube have included: the anterior abdominal wall routes by laparotomy, minilaparotomy and laparoscopy; a vaginal approach through the posterior vaginal fornix; and transcervical approaches, either blind, or via the hysteroscope. Methods for obtaining tubal occlusion have included: excision and suture techniques; electrocautery; clips and rings; intratubal occlusive devices and chemicals introduced into the tubal lumen. The development of each of the approaches to the tube and of the methods for obtaining tubal occlusion are discussed.
Specifications for new technologies for female sterilization for use in developing countries
Authors: Dusitsin N. 
Published: May 2004

AbstractThe difficulties in providing readily accessible sterilization services for women in rural settings in developing countries are described; they include: problems with personnel; problems with training; anesthesia difficulties; and cost. For a new method of sterilization to be useful in such situations several criteria concerned with overcoming the perceived problems must be met. Any new procedure should be simple, easily learned, capable of being completed with a single visit, and should require only local anesthesia.
Postmenopausal hormone therapy into the 21st century
Authors: Speroff L. 
Published: May 2004

AbstractAt the time of the menopause, a review of the major health issues can be especially rewarding. Besides the general issues of good health, particular attention is now being focused on prevention of cardiovascular disease and osteoporosis because of the potentially beneficial effects of postmenopausal hormone therapy. Hormone therapy should be offered to most women as they consider their paths for successful aging. However, as for any pharmacological intervention, the benefits of treatment must outweigh the risk. The available data would appear to indicate that, for most women, this is in fact the case with current research into future hormonal therapies aimed at further improving the benefit:risk ratio.
HRT and the risk of deep vein thrombosis
Authors: Barlow D.H. 
Published: May 2004

AbstractVenous thromboembolism (VTE) has long been recognized as a risk of oral contraceptive use in women, but until recently hormone replacement therapy (HRT) was not thought to be associated with a similar risk; the epidemiological literature having been reassuring. The recent publication of four independent epidemiological studies has changed our perspective on VTE risk on HRT. These studies suggest that the risk of VTE may be increased by up to three‐fold during HRT. However, the absolute risk remains low at approximately one occurrence in 5000 woman‐years and appears greatest in the early years of HRT use. However, given that mortality from VTE is low, it seems unlikely that these new findings will substantially change the overall balance of benefits and risks associated with long‐term HRT.
Juvenile Sandhoff disease—Nine new cases and a review of the literature
Authors: Hendriksz C. J. , Corry P. C. , Wraith J. E. , Besley G. T. N. , Cooper A. , Ferrie C. D. 
Published: May 2004

AbstractSummary: Juvenile Sandhoff disease (McKusick 268800) is a rare lysosomal storage disorder with only 12 cases recorded in the literature. This condition is also referred to as the subacute form of hexosaminidase deficiency. We describe 9 new cases of Pakistani origin and compare these with the other published cases. Ataxia and speech abnormalities were the commonest presentation. Constipation and urinary incontinence were frequent and may be due to autonomic neuropathy. Cherry‐red spot was not noted in any of our cases. Increased lower limb reflexes were the commonest physical finding. Significant delay in diagnosis may be due to the nonspecific presentation of this condition. Diagnosis was on the basis of hexosaminidase deficiency. Residual enzyme activity did not correlate with the clinical picture. Emerging therapies make early diagnosis of this disorder important.
Low‐protein diet and progression of retinal degeneration in gyrate atrophy of the choroid and retina: A twenty‐six‐year follow‐up
Authors: Santinelli R. , Costagliola C. , Tolone C. , D'Aloia A. , D'Avanzo A. , Prisco F. , Perrone L. , del Giudice E. Miraglia 
Published: May 2004

AbstractSummary: Gyrate atrophy of the choroid and retina is an autosomal recessive chorioretinal dystrophy which leads to a slowly progressive loss of vision. The primary defect is due to a deficiency of the enzyme ornithine δ‐aminotransferase, which is responsible for markedly elevated levels of ornithine in plasma and other body fluids. Although several therapeutic regimens have been proposed, the reduction in ornithine accumulation obtained by reducing the intake of its precursor arginine (semisynthetic low‐arginine diet) is the one most practised. In this clinical and molecular study we report a patient with hyperornithinaemia and gyrate atrophy of the choroid and retina who had been diagnosed when she was 3 years 9 months old. She also presented mild mental retardation, delayed language development and speech defects. The patient has recently been found to be homozygous for the new Gly91Arg amino acid substitution of the enzyme ornithine δ‐aminotransferase. This mutation lies in a region of the mature protein that is considered crucial for the mitochondrial targeting activity. In this patient, a 28‐year treatment with a completely natural low‐protein diet (0.8 g/kg per day of natural protein) has been able to significantly reduce ornithine plasma levels, and to greatly delay the natural progression of the chorioretinal changes. This study suggests that, in the long‐term treatment of gyrate atrophy, the efficacy in slowing the progression of chorioretinal changes and the palatability of a completely natural low‐protein diet make this treatment a potentially viable alternative in patients refusing the semisynthetic diet.
Discordant PKU phenotype in one family due to disparate genotypes and a novel mutation
Authors: Johnston J. J. , Lichter‐Konecki U. , Wilson E. , Cobb B. R. , Evans B. M. , Schnur R. E. , Wong L ‐J. C. 
Published: May 2004

AbstractSummary: Classical phenylketonuria (PKU) and mild hyperphenylalaninaemia (MHP) are two ends of the broad diagnostic spectrum in phenylalanine hydroxylase (PAH) deficiency. We have analysed a family in which classical PKU, MHP and a normal phenotype occurred in family members with different mutations. Sequence analysis revealed three mutations segregating in the family. The individual with classical PKU had two previously reported deleterious mutations. A third novel mutation was identified in the other two individuals. This report demonstrates that when discordant phenotypes occur in a family, without protein loading or phenylalanine tolerance test, complete analysis of the PAH gene may be performed in order to support the diagnosis and assist in accurate genetic counselling and patient management.
Association of ABCA2 expression with determinants of Alzheimer's disease
Authors: Chen Zhijian J. , Vulevic Bojana , Ile Kristina E. , Soulika Athena , Davis Warren , Reiner Peter B. , Connop Bruce P. , Nathwan Parimal , Trojanowski John Q. , Tew Kenneth D. 
Published: May 2004

ABSTRACTWith the use of a novel method for detecting differential gene expression, alterations in functional gene clusters related to transport or oxidative stress response and β‐amyloid (Aβ) peptide metabolism were identified in a HEK293 cell line engineered to overexpress the human ATP binding cassette transporter ABCA2. These included fatty acid binding protein, phospholipid binding protein, phospholipid synthesis protein, transporter cofactors, seladin‐1, Aβ precursor protein (APP), vimentin, and low‐density lipoprotein receptor‐related protein. ABCA2 was highly expressed in neuroblastoma cells and colocalized with Aβ and APP. Additionally, increased APP protein levels were detected within ABCA2/APP double‐transfected cells, and increased Aβ was detected in the media of ABCA2‐transfected cells relative to controls. The transporter was abundant in the temporal and frontal regions of both normal and Alzheimer's disease (AD) brain but was detected at lower concentrations in the parietal, occipital, and cerebellar regions. The ABCA2 transfected cell line expressed resistance to a free radical initiator, confirming involvement in protection against reactive oxygen species and suggesting a further possible link to AD.
Prolonged Visual Disturbance Secondary to Isolated Sphenoid Sinus Disease
Authors: Lee Li‐Ang , Huang Chi‐Che , Lee Ta‐Jen 
Published: May 2004

AbstractObjectives/Hypothesis: The objective was to evaluate the efficacy of endoscopic sinus surgery in patients with isolated sphenoid sinus disease with visual disturbances of more than 72 hours' duration.Study Design: Retrospective review.Methods: A sequential series of patients with isolated sphenoid sinus disease with visual disturbances who underwent endoscopic surgery performed by the same surgeon between 1995 and 2002 were reviewed. Patients with malignant tumors were excluded from the study. Patients were evaluated preoperatively and postoperatively to record the effects of this approach on visual acuity and diplopia.Results: The study population included six women and seven men with a mean age of 56.2 years (age range, 31–75 y). Eight eyes had vision loss attributable to compressive optic neuropathy (27%) and optic neuritis (27%); seven eyes with diplopia had abducens palsy (40%) and oculomotor nerve palsy (7%). Sphenoid sinus lesions included sinusitis (38%), mucocele (31%), and aspergillosis (31%). The mean interval between the onset of visual disturbances and surgery was 6.6 months (range, 3 d–3.5 y). Visual disturbances improved in 60% of the patients (P < .01). There was better improvement in diplopia than in vision loss (P < .01). The results of endoscopic sinus surgery for patients with abducens palsy and aspergillosis were excellent (83% and 80%, respectively). Optic neuritis and visual disturbances lasting for more than 6 months were regarded as poor prognostic factors.Conclusion: The study supports the treatment of visual disturbances resulting from isolated sphenoid sinus disease by endoscopic sinus surgery. A timely operation may prevent permanent sequelae.