bluuebunny/crossref_metadata_2025_split huggingface dataset:
Are delayed‐start design trials to show neuroprotection in Parkinson's disease fundamentally flawed?
Authors: Clarke Carl E. 
Published: January 2008

AbstractConsiderable effort has gone into preclinical neuroprotection research in Parkinson's disease (PD) and several large clinical trials have been mounted, but no agent has been conclusively shown to be protective. The latest innovation in PD neuroprotection trial design is the delayed‐start design trial. If patients with early PD do better after 12 to 18 months of immediate drug therapy compared to those in whom it is delayed for 6 to 9 months, this is attributed to a neuroprotective effect. However, delayed‐start design trials may be fundamentally flawed. It has been suggested that physiological mechanisms compensating for the loss of dopaminergic neurones in early PD may be deleterious and that immediate treatment may prevent such mechanisms and thereby be neuroprotective. If this hypothesis is correct, any drug with a symptomatic effect will be neuroprotective in early PD and delayed‐start design trials will show this generic effect, not a neuroprotective effect specific to the drug. Delayed‐start design trials require patients to potentially stay untreated for 6 to 9 months. This may lead to the selection of slowly progressive types of PD, such as that in younger patients and those with tremor‐dominant disease, so the results may not be generalizable to the majority of patients. Delayed‐start design trials are powered to find small differences in total UPDRS score which may not be clinically significant; larger and longer placebo‐controlled trials are required to confirm the clinical significance of their findings. These arguments add to the growing tide of opinion for a fundamental rethink of our policy toward neuroprotection research in PD. © 2008 Movement Disorder Society
Estimating the extent of reporting to FDA: a case study of statin‐associated rhabdomyolysis
Authors: McAdams Mara , Staffa Judy , Dal Pan Gerald 
Published: January 2008

AbstractPurposeTo estimate the extent of reporting to FDA through statin‐associated rhabdomyolysis data.MethodsData included incidence rates (IRs) of hospitalized rhabdomyolysis among statin users from a population‐based study, and comparable reported AERS cases and national estimates of statin use from an AERS analysis. Using IRs, national estimates of statin use and average days supply per prescription, we estimated the number of US statin‐associated cases of hospitalized rhabdomyolysis. We compared this estimate to the observed number of cases reported to FDA to evaluate the extent of reporting. We repeated this method for atorvastatin, cerivastatin, pravastatin, and simvastatin and statin combinations. We performed sensitivity analyses to check for biases such as misclassification of statin use and cohort selection bias. We evaluated potential time‐dependent cerivastatin reporting by a “Dear Health Care Provider (DHCP)” letter.ResultsThe estimated extent of reporting to FDA varied by statin (atorvastatin, 5.0%; cerivastatin, 31.2%; simvastatin, 14.2%; all four combined, 17.7%; and non‐cerivastatin statins combined, 9.9%). No pravastatin‐associated cohort cases occurred. Across a reasonable value range, sensitivity analyses did not significantly alter the results; overall the cohort was similar to national statin‐users. There was a large increase in AERS reports after the cerivastatin DHCP letter and the estimated extent of reporting increased from 14.8 to 35.0%.ConclusionsThe extent of reporting of adverse events to FDA varied by statin and may be influenced by publicity. For statins‐associated rhabdomyolysis, the estimated extent of reporting appears to range from 5 to 30% but in the absence of stimulated reporting appears to be 5–15%. Copyright © 2008 John Wiley & Sons, Ltd.
Prediction of protein structure from ideal forms
Authors: Taylor William R. , Bartlett Gail J. , Chelliah Vijayalakshmi , Klose Daniel , Lin Kuang , Sheldon Tom , Jonassen Inge 
Published: January 2008

AbstractFor many years it has been accepted that the sequence of a protein can specify its three‐dimensional structure. However, there has been limited progress in explaining how the sequence dictates its fold and no attempt to do this computationally without the use of specific structural data has ever succeeded for any protein larger than 100 residues. We describe a method that can predict complex folds up to almost 200 residues using only basic principles that do not include any elements of sequence homology. The method does not simulate the folding chain but generates many thousands of models based on an idealized representation of structure. Each rough model is scored and the best are refined. On a set of five proteins, the correct fold score well and when tested on a set of larger proteins, the correct fold was ranked highest for some proteins more than 150 residues, with others being close topological variants. All other methods that approach this level of success rely on the use of templates or fragments of known structures. Our method is unique in using a database of ideal models based on general packing rules that, in spirit, is closer to an ab initio approach. Proteins 2008. © 2008 Wiley‐Liss, Inc.
Multilevel Analysis of a Measure of Community Prevention Collaboration
Authors: Brown Eric C. , Hawkins J. David , Arthur Michael W. , Abbott Robert D. , Van Horn M. Lee 
Published: January 2008

AbstractThis study assesses a measure of community‐wide collaboration on prevention‐specific activities (i.e., prevention collaboration) in context of the theory of community change used in the Communities That Care prevention system. Using data from a sample of 599 community leaders across 41 communities, we examined the measure with regard to its factor structure, associations with other concurrent community‐level measures, and prediction by individual‐ and community‐level characteristics. Results of multilevel confirmatory factor analysis provide evidence for the construct validity of the measure and indicate significant (p < .05) associations with concurrent validity criteria. Female community leaders reported significantly higher levels of prevention collaboration and community leaders sampled from religious organizations reported lower levels of prevention collaboration than did their respective counterparts. Although no community‐level characteristics were associated significantly with prevention collaboration, community clustering accounted for 20–28% of the total variation in the measure. Findings support the use of this measure in assessing the importance of collaboration in community‐based prevention initiatives.
Synthesis, Surface‐Active Properties, and Antimicrobial Activities of New Neutral and Cationic Trimeric Surfactants
Authors: Murguía Marcelo C. , Cristaldi Mariano D. , Porto Ayelén , di Conza José , Grau Ricardo J. 
Published: January 2008

AbstractNeutral and cationic series of new trimeric β‐hydroxy amino or ammonium surfactants were synthesized via a two‐step process involving the Williamson etherification and regioselective oxirane ring opening with primary and tertiary amines, which afforded good to excellent yields. The synthesized compounds were obtained in high purity by a simple purification procedure on column chromatography. The critical micelle concentration (CMC), effectiveness of surface tension reduction (γCMC), surface excess concentration (Γ), and area per molecule at the interface (A) were determined and values indicate that the cationic series is characterized by good surface‐active and self‐aggregation properties. The antimicrobial activities are reported for the first time against representative bacteria and fungi for trimeric compounds. The antimicrobial potency was found to be dependent on the target microorganism (Gram‐positive bacteria > fungi > Gram‐negative bacteria), as well as both the neutral or ionic nature (cationic > neutral) and alkyl chain length (tri‐C12 > tri‐C18 > tri‐C8) of the compounds. The tri‐C8 and tri‐C18 compounds were found to be almost inactive and the tri‐C12 compounds, the most potent antimicrobial surface‐active agents from the synthesized series. The trimeric C12 cationic compound was found to be comparable to benzalkonium chloride against Gram‐positive bacteria and fungi, in vitro. The antimicrobial effectiveness of this new compound and the facile two‐step procedure for synthesizing it with an excellent overall yield (92%) provide a cost effective trimeric gemini surfactant.
Kinetic Parameters of a Homogeneous Transmethylation of Soybean Oil
Authors: Doell Ryan , Konar Samir K. , Boocock David G. B. 
Published: January 2008

AbstractThe kinetic parameters of a truly homogeneous base‐catalyzed transmethylation of soybean oil at four temperatures from 23 to 50 °C have been determined for the first time. The addition of oxolane, as well as a high methanol/oil molar ratio (27:1), was used to achieve and maintain a monophasic system throughout the reactions. Second order rate constants were determined in terms of the concentrations of the mechanistic reactants, which were the glycerides and methoxide ions (and not methanol). Doubling the methoxide concentration increased the reaction rate twofold. At 23 °C the rate constants for the conversion of triglycerides to diglycerides, diglycerides to monoglycerides, and monoglycerides to glycerol were 6.3, 15.3 and 13.0 L mol−1 min−1, respectively. These increased to 54.2, 136 and 139 L mol−1 min−1 at 50°C. These latter values (adjusted to 60 °C) were 65, 770 and 190 times larger, respectively, than values cited previously (and adjusted to the methoxide basis) for a transmethylation of Pongamia oil, which was also claimed to be homogeneous. Activation energies for all three steps were the same (63 kJ mol−1). Pre‐exponential factors showed that in diglycerides and triglycerides the second and third ester chains sterically hindered the attack of methoxide ions on the ester carbonyl groups.
Effects of seasonality, litter removal and dry-season irrigation on litterfall quantity and quality in eastern Amazonian forest regrowth, Brazil
Authors: Vasconcelos Steel Silva , Zarin Daniel Jacob , Araújo Maristela Machado , Rangel-Vasconcelos Lívia Gabrig Turbay , de Carvalho Cláudio José Reis , Staudhammer Christina Lynn , Oliveira Francisco de Assis 
Published: January 2008

Abstract:Litterfall quantity and quality may respond to alterations in resource availability expected with ongoing land-use and climate changes. Here, we quantify the effects of altered resource availability on non-woody litterfall quantity and quality (nitrogen and phosphorus concentrations) in eastern Amazonian forest regrowth (Brazil) through two multi-year experimental manipulations: (1) daily irrigation (5 mm d−1) during the dry season; and (2) fortnightly litter removal. Consistent with other tropical forest data litterfall exhibited seasonal patterns, increasing with the onset of the dry season and declining with the onset of the rainy season. Irrigation did not affect litterfall mass and had little impact on nitrogen (N) or phosphorus (P) concentrations and return, except for decreasing litter P concentration at the end of two irrigation periods. Litter removal did not alter litterfall mass or P concentration, but progressively reduced litterfall N during the course of the experiment. Overall, these results suggest significant resistance to altered resource availability within the bounds of our experimental treatments; our findings may help to constrain carbon and nutrient cycling predictions for tropical forests in response to land-use and climate changes.
Repeated disturbances and canopy disturbance regime in a tropical semi-deciduous forest
Authors: de Lima Renato A. Ferreira , Martini Adriana M. Zanforlin , Gandolfi Sérgius , Rodrigues Ricardo Ribeiro 
Published: January 2008

Abstract:The canopy disturbance regime and the influence of gap methods on the interpretation of forest structure and dynamics were evaluated in a tropical semi-deciduous forest in south-eastern Brazil. We encountered a gap density of 11.2 gaps ha−1and an average size which varied from 121 to 333 m2depending on the gap delimitation method considered (minimum gap size was 10 m2). Although average size was slightly higher, the median value obtained (78 m2) was comparable to other tropical forest sites and the gap size-class distribution found supported the pattern described for such forest sites. Among 297 gap makers, snapping and uprooting were the most common modes of disturbance. The number and basal area of gap makers were good predictors of gap size. Almost 25% of all gaps suffered from repeated disturbance events that brought about larger gap sizes. Such processes, along with delimitation methods, strongly influenced the estimation of turnover rate and therefore the interpretation of forest dynamics. These results demonstrated the importance of further studies on repeated disturbances, which is often neglected in forest studies.
δ13C inPentaclethra macrolobatrees growing at forest edges in north-eastern Costa Rica
Authors: Schedlbauer Jessica L. , Kavanagh Kathleen L. 
Published: January 2008

AbstractFragmented forest landscapes with large proportions of edge area are common in the tropics, though little is known about functional responses of trees to edge effects. Foliar δ13C can increase our understanding of tree function, as these values reflect changes in ci/caas trees respond to environmental gradients. We expected that foliar δ13C would be enriched, indicating a decline in ci/ca, inPentaclethra macrolobatrees growing at forest edges in north-eastern Costa Rica. We also anticipated this isotopic shift in δ13C values of soil carbon and soil respired CO2. Three transects perpendicular to forest edges were established at three study sites, and six plots per transect were located 0–300 m from edges. Within plots, foliage, soil and soil respired CO2were collected for isotopic analyses. Foliar δ13C, thus ci/ca, and soil carbon δ13C did not vary along the edge to interior gradient. δ13C for canopy and understorey foliage averaged −29.7‰ and −32.5‰, respectively, while soil carbon δ13C averaged −28.0‰. Soil respired CO2δ13C ranged from −29.2‰ to −28.6‰ and was significantly depleted within 50 m of edges. The predominant lack of functional responses at forest edges indicates thatP. macrolobatrees are robust and these forests are minimally influenced by edge effects.
PHOTOCHEMISTRY OF 4‐AMINOPYRIMIDINES 2,6‐DIMETHYL‐4‐AMINOPYRIMIDINE
Authors: Wierzchowski K. L. , Shugar D. 
Published: January 2008

Abstract— Ultraviolet irradiation (2537 Å) of 2,6‐dimethyl‐4‐aminopyrimidine (I) results in an intramolecular rearrangement with the formation, either in aqueous or anyhdrous medium, of only one photoproduct, 2‐amino‐3‐cyanopent‐2‐enemine (II), in quantitative yield. The quantum yield for this reaction is 0.043 einsteins/mole.Deamination of II gives, quantitatively, 2‐amino‐3‐cyanopent‐2‐en‐4‐one (III) and this, in turn, may be deaminated to give, quantitatively, 3‐cyanopent‐2‐en‐2‐01‐4‐0ne (cyanoacetyl‐acetone, IV). Identification of II was achieved initially through isolation of III and IV. Some of the chemical and physico‐chemical properties of these compounds are reported, as well as methods for obtaining all of them on a preparative scale.The mono‐protonated form of I also gives II on irradiation, but in lower quantum yield, 7.3times108 einsteins/mole. Irradiation of the doubly protonated form of I in strongly acid medium leads directly to the formation of a mixture of II, III and IV, with approxi mately the same quantum yield.The possible mechanisms for the foregoing photochemical reactions are discussed and their significance related to the photochemistry of 4‐aminopyrimidines in general and to those of nucleic acid derivatives in particular.
SOME EFFECTS OF LIGHT ON LEAF GROWTH IN PISUM SATIVUM AND TROPAEOLUM MAJUS
Authors: Sale P. J. M. , Vince D. 
Published: January 2008

Abstract— The effect of wave‐length of light on leaf expansion in Tropaeolum majus‘Double Orange Gleam’ and Pisurn sativum‘Meteor’ has been studied. In both species leaf growth is strongly promoted by light.Increasing the daily duration of exposure to light increased leaf expansion in Tropueolum in both blue and red wave‐bands over a range of light intensities. In Pisum a similar effect of ail increase in duration of irradiation was found over the whole range of intensities used for blue light but only at the highest intensity for red light: at the two lower intensities in red an increase in duration of the light treatment beyond 1 hr did not increase leaf expansion.In both species a period of 4 hr of blue followed by 4 hr of red promoted leaf growth more than 4 hr of red followed by 4 hr of blue. The effect of a 4 hr period of red light was largely prevented when it was followed by far‐red; the effect of 4 hr of blue light, on the other hand, was not affected by subsequent exposure to far‐red.It is concluded that leaf growth in Pisum and Tropaeolum is dependent not only on the ‘low‐energy’ red/far‐red reversible reaction but also on one or more ‘high‐enerFy’ photo‐reactions.
DIFFERENTlAL REACTIVITY OF EXCITED SINGLETS AND TRIPLETS*
Authors: Rosenberg J. L. 
Published: January 2008

Summary Experimental data from the oxygen quenching of excited states, from the acidities of excited states, and from the kinetics of photosynthesis indicate that the lowest excited singlet and the lowest triplet states of aromatic molecules may not have the same reactivity.The reasons for these differences may be connected with the energy deficit of triplets, with spin conservation rules, with differences in the nuclear geometry, or with differences in the electronic configuration or polarizability. With improved theoretical representations of excited states, the observed differences in reactivity may serve to increase our understanding of the nature of primary photochemical events.
PHOTOINHIBITION OF CHLOROPLAST REACTIONS
Authors: Kok Bessel , Gassner Edward S. , Rurainski Hans J. 
Published: January 2008

Abstract— An attemlpt was made to localize the site of photoinhibition of photosynthesis by measuring the decay of various chloroplast reactions after exposure to very strong light. A11 substrate reductions coupled to oxygen evolution as well as photophosphorylation mediated by PMS, proved equally sensitive to photoinhibition. Reactions involving only the long wave photosystem, such as TPN reduction with ascorbate as electron donor and photooxidation of cytochromec by detergent‐treated chloroplasts were sensitive to a lower degree.Photoinhibition irreversibly annihilated the ‘variable’ fraction of fluorescence emission —it decreased the steady state yield 2‐3 fold and abolished the slow rise of the emission at the onset of illurnination.It is concluded that the primary site of light inactivation is in, or close to, the trapping centers of the oxygen evolving step of photosynthesis. Pre‐illumination leaves these traps in a state capable of draining light from sensitizing pigments but unable to perform useful photochemistry.
ACTION DE LA QUANTITÉ JOURNALIÈRE DE LUMIÈRE SUR LA FLORAISON, LE POIDS SEC ET LA TENEUR EN EAU DE QUELQUES PLANTES DE JOURS COURTS ET DE JOURS LONGS
Authors: Bouillenne R. 
Published: January 2008

Abstract— Experiments were carried on in the Liège Phytotron for two years to discover what reactions could be obtained when both short‐day and long‐day plants were placed in the same light energy per day (light intensity × daily light duration in various combinations) and receiving respectively 8 or 16 hr light per day. It was observed that both types of plants give parallel dry weight curves in both long‐day and short‐day, but this happens only during the vegetative state following germination.Differences occur in those dry weight curves in short‐day plants and also in long‐day plants when cultivated under inductive photoperiodic light and induced to flower.In these suitable light conditions, their dry weight increased compared with that of plants left in a non‐inductive photoperiodic fight.The evolution of tissue water content (stems, leaves, flowers), expressed as water % of the dry weight, is also interesting to observe in the same experimental environments. This evolution plays an important physiological part in flower formation, as has been shown before by R. Bouillenne.Both types of plants cultivated in their respective non‐inductive light point out a very simple curve of water content. First a rapid increase of water into the tissues during the first 10 days after germination; then from this maximum, the curve goes down regularly and slowly till a constant low level.However, in inductive light exposure, water content percentage curves are really different for both types of species. Considering the same daily value of light energy given in each case, it is possible to conclude that the induction of flower does not depend on the daily light quantity but on something else which is connected with the photoperiodism.These fluctuations of the water content will be investigated.
EFFECT OF U.V.‐IRRADIATION ON SEDIMENTATION BEHAVIOR OF VARIOUS PROTEINS
Authors: Dose Klaus , Sena Luigi 
Published: January 2008

Abstract— Moderate u.v.‐doses (2537 Å) sufficient to reduce enzymatic activities of native enzymes up to about 90 per cent, in general do not produce measurable amounts of smaller dialyzable fragments.The disappearance of the original boundary in sedimentation diagrams is mostly due to the formation of rapidly sedimenting polydispersed material. Generally the sedimentation constants of the native proteins are not significantly changed. The boundaries, however, often loose their symmetry. The quantum yields for the disappearance of the original boundaries are roughly inversely proportional to the molecular weights. The number of molecules disappearing from the main peak is smaller than the number of molecules inactivated by a given dose. The data indicate that ultracentrifugation provides no satisfactory method for separation of native molecules from the damaged and inactivated. Proteins with labile quaternary structures (e.g. thyroglobulin or hemocyanine) which tend to dissociate under very mild conditions show an enhanced dissociation after u. v.‐irradiation.
INTERSYSTEM CROSSING AND DIMERIZATION IN AQUEOUS SOLUTIONS OF URACIL AND OROTIC ACID
Authors: JOHNS H. E. 
Published: January 2008

ResumenUn analisis cinético de la fotoquímica en el u.v. de uracilo y ácido orótico muestra que el hidrato se forma a partir del estado singulete, mientras que el dímero lo hace a partir del estado triplete. El rendimiento cuantico de la formación del hidrato es independiente de la longitud de onda de irradiación, mientras que el rendimiento cuántico de la formación de triplete aumenta a longitudes de onda menores. Se presenta además una explicación para el aumento de “intersystem crossing” a altos niveles de excitación basada en la presen‐cia de tautomeros.
EVIDENCE OF REACTIVE INTERMEDIATES IN SECO/CYCLO ISOMERIZATIONS BY LOW‐TEMPERATURE TECHNIQUES
Authors: QUINKERT G. 
Published: January 2008

Abstract— Matrix isolation methods at low temperatures have been used to trap seco‐isomeric intermediates in photochemical electrocyclic transformations of cyclo isomers. The stereochemical behavior is found to be consistent with the Woodward‐Hoffman rules.RESUMENSe han usado soluciones a bajas temperaturas para atrapar intermediaries seco‐isoméricos en transformacíones fotoquímicas electrocíclicas de cicloisómeros. Se ha encontrado que el comportamiento estereoquímico es consistente con las reglas de Woodward y Hoffmann.