bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of C3‐Symmetric Nano‐Sized Polyaromatic Compounds by Trimerization and Suzuki−Miyaura Cross‐Coupling Reactions
Authors: Kotha Sambasivarao , Kashinath Dhurke , Lahiri Kakali , Sunoj Raghavan B. 
Published: September 2004

AbstractVarious C3‐symmetric molecules were prepared by trimerization of acetyl aromatic compounds and subsequently coupled with various boronic acids under Pd0 catalysis conditions to generate oligoaryl/‐heteroaryl C3‐symmetric molecules. Several furan‐ and thiophene‐containing star‐shaped molecules were prepared by the use of Suzuki−Miyaura cross‐coupling as a key step. Structural and conformational details were explored by semi‐empirical molecular orbital theory using the AM1 method. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of Glycosyl Phosphonates by Michael‐Type Addition to 2‐Nitroglycals
Authors: Pachamuthu Kandasamy , Figueroa‐Perez Ignacio , Ali Ibrahim A. I. , Schmidt Richard R. 
Published: September 2004

AbstractA new synthetic strategy, which allows to synthesize both α‐ and β‐anomers of 2‐acetylaminoglycosyl phosphonate or exclusively β‐anomer is described. The present strategy is a successful Michael‐type addition of dimethyl hydrogen phosphonate to 2‐nitroglycals. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Superacidic Activation of α,β‐Unsaturated Amides and Their Electrophilic Reactions
Authors: Koltunov Konstantin Yu. , Walspurger Stéphane , Sommer Jean 
Published: September 2004

AbstractThe electrophilic reactivity of α,β‐unsaturated amides towards weak nucleophiles such as arenes and cyclohexane, initiated either with triflic acid (CF3SO3H) or with excess AlCl3, has been studied. The amides generally condense readily with aromatics in the presence of AlCl3 to give 3‐arylpropionamides and related compounds in excellent yields, while some amides also undergo selective ionic hydrogenation with cyclohexane to give saturated amides. The proposed mechanism of these reactions involves dicationic intermediates (superelectrophiles). The direct observation of a dicationic species (by low‐temperature NMR) is reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
On the Role of Water in Amide Hydrolysis
Authors: Zahn Dirk 
Published: September 2004

AbstractThe mechanism of the water‐assisted amide hydrolysis of N‐methylacetamide has been elucidated by Car‐Parrinello simulation and related to prior investigations of the acid‐ and the base‐catalyzed pathways. Each process was investigated in aqueous solution, and the water molecules were found to play a crucial role in the amide hydrolysis, with several reaction steps involving proton‐transfer events in which the water molecules serve as donors or acceptors. This calls for a quantum treatment of all electronic degrees of freedom, including those of the solvent molecules. A detailed analysis of the mechanisms of the amide hydrolysis pathways obtained from our simulations is given. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Theoretical Studies on Cycloaddition Reactions between 1‐Aza‐2‐azoniaallene Cations and Isocyanates
Authors: Wei Mei‐Ju , Fang De‐Cai , Liu Ruo‐Zhuang 
Published: September 2004

AbstractThe mechanisms of the title reactions between 1‐aza‐2‐azoniaallene cations and isocyanic acid or isocyanates have been theoretically explored at the B3LYP/6‐31++G** level. It was found that all of these reactions proceed in asynchronous but concerted pathways. The substituent effects are also obvious; e.g., the presence either of an electron‐withdrawing chlorine substituent on the 1‐aza‐2‐azoniaallene cation or of an electron‐releasing methyl substituent on the isocyanate both favor the cycloaddition reactions. For the [1,2]‐shift reactions, all the substituents lower their activation barrier, especially Cl substituents on the 1‐aza‐2‐azoniaallene cation, but when Cl substituents are present on the 1‐aza‐2‐azoniaallene cation the rearrangement product is not as stable as others. In addition, solvent effects with the PCM model are also reported, and a model reaction has been investigated at the MP2/6‐31+G* and QCISD/6‐31+G* levels as well as by DFT. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Diethyl Cyclopropylidenemalonate: Facile Preparation, Generation in situ, and Various Transformations
Authors: de Meijere Armin , Kostikov Rafael R. , Savchenko Andrei I. , Kozhushkov Sergei I. 
Published: September 2004

AbstractReductive cyclopropanation of triethyl methanetricarboxylate (4a) with ethylmagnesium bromide in the presence of titanium tetraisopropoxide furnished diethyl 2‐(1′‐hydroxycyclopropyl)malonate (5a) in 50% yield. Dehydromesylation of the mesylate of cyclopropanol 5a, generated in situ, by treatment with an excess of triethylamine gave diethyl cyclopropylidenemalonate 3‐Et as a highly reactive, unstable compound, which could be isolated as an oil in 39% yield, but more favorably could also be generated in situ from the mesylate or the acetate 11 (prepared from 5a in 90% yield) and trapped without isolation with various N‐, O‐, S‐, and C‐nucleophiles. Thus, ammonia, dimethylamine, isopropylamine, diethylamine, dibenzylamine, morpholine, N‐methylpiperazine, piperazine, aniline, p‐cresol, 1‐thionaphthol, and cyanide anion easily add to the double bond of the diester 3‐Et generated in situ at ambient temperature, forming 1′‐substituted cyclopropylmalonates 10a−i in 18−95% yields. The α,β‐unsaturated diester 3‐Et also easily enters into 1,3‐dipolar and Diels−Alder cycloadditions with nitrones, ethyl diazoacetate, azide anion, and dienes to give the corresponding cycloadducts in 12−83% yields. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Cover Picture: Synthesis and Biological Evaluation of Macrosphelide Cores (Eur. J. Org. Chem. 19/2004)
Authors: Ishihara Kentaro , Kawaguchi Takanori , Matsuya Yuji , Sakurai Hiroaki , Saiki Ikuo , Nemoto Hideo 
Published: September 2004

AbstractThe cover picture shows the structures of the bioactive natural macrolide, macrosphelide A (third structure from left) and its artificial analogues. The other structures exhibit different oxidation states at the allylic positions on the common 16‐membered ring skeleton. The antitumor activity increases from left to right. This image reflects the importance of the oxygen functionalities for the bioactivity of naturally occurring macrosphelides, as discussed in the article by H. Nemoto et al. on p. 3973 ff.
Field assessments on the accuracy of spherical gauges in rainfall measurements
Authors: Chang Mingteh , Harrison Lee 
Published: September 2004

AbstractIn an effort to reduce wind effect on rainfall catch to a minimum level, Chang and Flannery (2001. Hydrological Processes 15: 643–654) designed two spherical orifices to modify the standard gauge and other gauges in use today. Because of the spherical shape, the two orifices will catch rain with an effective diameter always equal to the actual diameter, regardless of wind speed and direction. This report covers the testing of spherical gauges at two different locations, one at the City Landfill, Nacogdoches, TX, and the other at the NWS Forecast Office, Shreveport, LA. Based on 131 storms at Nacogdoches and 94 storms at Shreveport, observed between May 1998 and February 2001, the results showed: (1) spherical gauges recorded an average 6–9% greater than standard gauge and 3–4% less than pit gauge, only 1–2% less than reported in the original study; (2) the catch of spherical gauges was not significantly affected by three gauge heights at 0·91, 1·83, and 2·74 m above the ground, but catch by the standard gauge decreased with increasing gauge height; (3) improvements of the spherical gauges were most significant for larger storms and for winds at higher speeds; (4) the spherical gauge with cylinders recorded 1–2% more rainfall than the spherical gauge with vanes; and (5) correlation coefficients between catch deficiencies and wind speed were low and weak because of the distance and height of the existing wind sensor.Owing to greater surface wetting and evaporation loss, the spherical gauges may underestimate rainfall catch by standard gauge for small storms (generally less than 5·0 mm), especially on hot summer afternoons and for smaller storms. However, the underestimates do not overshadow the merits of spherical gauges, because the differences are too small to be of hydrologic significance. Using polyethylene or other synthesized materials to construct spherical orifices may improve the catch for small storms. The results of the study agreed with the previous claims that spherical gauges are effective in reducing wind effects on rainfall measurements. The spherical gauges could greatly improve the accuracy of hydrologic simulations and the efficiency on the designs and management of water resources. They are suitable for large‐scale applications. Copyright © 2004 John Wiley & Sons, Ltd.
Effects of suspended sediment characteristics and bed sediment transport on streambed clogging
Authors: Rehg Kristin J. , Packman Aaron I. , Ren Jianhong 
Published: September 2004

AbstractFine sediment deposition in streambeds can reduce pore water fluxes and the overall rate of hyporheic exchange, producing deleterious effects on benthic and hyporheic ecological communities. To increase understanding of the factors that control the reduction of hyporheic exchange by fine sediment deposition, we conducted experiments in a laboratory flume to observe changes in the rates of solute exchange and kaolinite clay deposition as substantial amounts of kaolinite accumulated in the streambed. Two long‐term experiments were conducted, with durations of 14 days and 29 days. Use of a laboratory flume system allowed steady stream flow conditions to be maintained throughout both experiments, and alternating injections of known quantities of kaolinite and a sodium chloride tracer were used to assess the effect of clay accumulation on hyporheic exchange directly. In the first experiment, there was no bed sediment transport and kaolinite deposition formed a highly clogged near‐surface layer that greatly reduced hyporheic exchange. Application of a fundamental model for advective hyporheic exchange indicated that the effective permeability and porosity of the streambed decreased substantially during the course of the experiment. In the second experiment, the kaolinite was prepared with different surface properties to be more mobile, and the experiment was conducted with a small degree of bed sediment transport. As a result, no distinct clogged layer developed, and the rate of hyporheic exchange was found to remain approximately constant throughout the experiment (29 days). These results indicate that increasing fine sediment loads, e.g. those that occur from changes in land use, can have substantially different impacts on hyporheic exchange and associated ecological processes depending on the stream flow conditions, the rate and frequency of bed sediment transport, and the extent of interaction of the introduced fines with bed sediments. Copyright © 2004 John Wiley & Sons, Ltd.
Dynamics in land cover and its effect on stream flow in the Chemoga watershed, Blue Nile basin, Ethiopia
Authors: Bewket Woldeamlak , Sterk Geert 
Published: September 2004

AbstractThe objective of this study was to analyse changes in stream flow patterns with reference to dynamics in land cover/use in a typical watershed, the Chemoga, in northwestern highland Ethiopia. The results show that, between 1960 and 1999, total annual stream flow decreased at a rate of 1 · 7 mm year−1, whereas the annual rainfall decreased only at a rate of 0 · 29 mm year−1. The decrease in the stream flow was more pronounced during the dry season (October to May), for which a statistically significant decline (0 · 6 mm year−1) was observed while the corresponding rainfall showed no discernible trend. The wet season (June to September) rainfall and stream flow did not show any trends. Extreme low flows analysed at monthly and daily time steps reconfirmed that low flows declined with time, the changes being highly significant statistically. Between 1960 and 1999, the monthly rainfall and stream flow amounts of February (month of lowest long‐term mean flow) declined by 55% and 94% respectively. Similarly, minimum daily flows recorded during the three driest months (December to February) showed statistically highly significant declines over the same period. It declined from 0 · 6 m3 s−1 to 0 · 2 m3 s−1 in December, from 0 · 4 m3 s−1 to 0 · 1 m3 s−1 in January and from 0 · 4 m3 s−1 to 0 · 02 m3 s−1 in February (1 · 0 m3 s−1 = 0 · 24 mm day−1 in the Chemoga watershed). In contrast, extreme high flows analysed at monthly (for August) and daily (July to September) time steps did not reveal discernible trends. The observed adverse changes in the stream flow have partly resulted from changes in land cover/use and/or degradation of the watershed that involved destruction of natural vegetative covers, expansion of croplands, overgrazing and increased area under eucalypt plantations. The other contributory factor has been the increased dry‐season water abstraction to be expected from the increased human and livestock populations in the area. Given the significance of the stream flow as the only source of water to the local people, a set of measures aimed at reducing magnitudes of surface runoff generation and increasing groundwater recharge are required to sustain the water resource and maintain a balanced dry‐season flow in the watershed. Generally, an integrated watershed management approach, whereby the whole of the watershed can be holistically viewed and managed, would be desirable. Copyright © 2004 John Wiley & Sons, Ltd.
Statistical probability distribution of snow depth at the model sub‐grid cell spatial scale
Authors: Marchand Wolf‐Dietrich , Killingtveit Ånund 
Published: September 2004

AbstractComprehensive snow depth data, collected using georadar and hand probing, were used for statistical analyses of snow depths inside 1 km grid cells. The sub‐grid cell spatial scale was 100 m. Statistical distribution functions were found to have varying parameters, and an attempt was made to connect these statistical parameters to different terrain variables. The results showed that the two parameters mean and standard deviation of snow depth were significantly related to the sub‐grid terrain characteristics. Linear regression models could explain up to 50% of the variation for both of the snowcover parameters mentioned. Copyright © 2004 John Wiley & Sons, Ltd.
Observations of urban snow properties in Calgary, Canada
Authors: Ho C. L. I. , Valeo C. 
Published: September 2004

AbstractUrban winter hydrology has garnered very little attention owing to the general notion that high‐intensity rainfalls are the major flood‐generating events in urban areas. As a result, few efforts have been made to research urban snow and its melt characteristics. This study investigates the characteristics of urban snow that differentiate it from rural snow, and makes recommendations for incorporating these characteristics into an urban snowmelt model. A field study was conducted from the fall of 2001 to the spring of 2002 in the city of Calgary, Canada. Snow depths and densities, soil moisture, soil temperature, snow albedo, net radiation, snow evaporation, and surface temperature were measured at several locations throughout the winter period. The combination of urban snow removal practices and the physical elements that exist in urban areas were found to influence the energy balance of the snowpack profoundly. Shortwave radiation was found to be the main source of energy for urban snow; as a consequence, the albedo of urban snow is a very important factor in urban snowmelt modelling. General observations lead to the classification of snow as one of four types: snow piles, snow on road shoulders, snow on sidewalk edges, and snow in open areas. This resulted in the development of four separate functions for the changing snow albedo values. A study of the frozen ground conditions revealed that antecedent soil moisture conditions had very little impact on frozen ground, and thus frozen ground very nearly always acts as a near impervious area. Improved flood forecasting for urban catchments in cold regions can only be achieved with accurate modelling of urban winter runoff that involves the energy balance method, incorporating snow redistribution and urban snow‐cover characteristics, and using small time steps. Copyright © 2004 John Wiley & Sons, Ltd.
Estimation of source water to cedar elm in a central Texas riparian ecosystem
Authors: Muttiah Ranjan S. , White Joseph D. , Duke Jacquelyn R. , Allen Peter M. 
Published: September 2004

AbstractA riparian ecosystem downstream of a small dam in central Texas was instrumented for sap flow, soil moisture content, and stream level from 2001. Stable isotopes in water (D and 18O) were analysed from rainfall, stream, lake, and cored sapwood cellulose from cedar elm (Ulmus crassifolia). The isotope signature of water source to cedar elm was identified by back calculation starting with the water isotopes in cellulose, and accounting for leaf‐water evaporation and biological fractionation during cellulose synthesis. The estimated mean isotope of the source water to cedar elm was enriched above rainfall in similarity to stream water during 2002. Flow paths that may have contributed to estimated variability from regional base flow and recharge water were identified using the variably saturated HYDRUS‐2D model. Copyright © 2004 John Wiley & Sons, Ltd.
Analysis of agricultural drought in Iiuni, Eastern Kenya: application of a Markov model
Authors: Biamah E. K. , Sterk G. , Sharma T. C. 
Published: September 2004

AbstractIn semi‐arid Kenya, episodes of agricultural droughts of varying severity and duration occur. The occurrence of these agricultural droughts is associated with seasonal rainfall variability and can be reflected by seasonal soil moisture deficits that significantly affect crop performance and yield. The objective of this study was to stochastically simulate the behaviour of dry and wet spells and rainfall amounts in Iiuni watershed, Kenya. The stochastic behaviour of the longest dry and wet spells (runs) and largest rainfall amounts were simulated using a Markov (order 1) model. There were eight raingauge stations within the watershed. The entire analysis was carried out using probability parameters, i.e. mean, variance, simple and conditional probabilities of dry and rain days. An analysis of variance test (ANOVA) was used to establish significant differences in rainfall characteristics between the eight stations. An analysis of the number of rain days and rainfall amount per rain day was done on a monthly basis to establish the distribution and reliability of seasonal rainfall. The graphic comparison of simulated cumulative distribution functions (Cdfs) of the longest spells and largest rainfall amounts showed Markovian dependence or persistence. The longest dry spells could extend to 24 days in the long rainy season and 12 in the short rainy season. At 50% (median) probability level, the largest rainfall amounts were 91 mm for the long rainy season and 136 mm for the short rainy season. The short rains were more reliable for crop production than the long rains. The Markov model performed well and gave adequate simulations of the spells and rainfall amounts under semi‐arid conditions. Copyright © 2004 John Wiley & Sons, Ltd.
Peptide‐modified alginate surfaces as a growth permissive substrate for neurite outgrowth
Authors: Dhoot Nikhil O. , Tobias Chris A. , Fischer Itzhak , Wheatley Margaret A. 
Published: September 2004

AbstractDifferent strategies are being investigated for treatment of spinal cord injuries, one of the most promising being application of neurotrophic factors, which have been shown to prevent neuronal death and stimulate regeneration of injured axons. Ex vivo gene therapy has emerged as the leading delivery method at the site of the injury, and we have shown previously that encapsulating genetically engineered fibroblasts in an immunoprotective alginate capsule can permit implantation of the factor‐secreting cells without need for immunosuppression. This strategy could be greatly enhanced by providing the sprouting neurons with a permissive substrate upon which to attach and grow. We report here studies on the modification of an alginate gel surface by either coating it with laminin or by covalent attachment of YIGSR peptide. Using NB2a neuroblastoma cells, we found that native alginate elicited minimal cell attachment (∼1.5%); however, YIGSR‐alginate conjugate elicited a fivefold increase in numbers of cells attached using peptide ratios of 0.5 and 1 mg/g alginate, ranging from 9.5% of the cells at the lower ratio, to about 44% at the higher. Only a further 19% increase was obtained at an increased peptide density of 2 mg/g alginate (∼63% over control). Laminin‐coated gels showed ∼60% cell attachment. However, laminin coating did not stimulate differentiation and neurite growth, whereas both numbers and lengths of outgrowths increased with increasing peptide density on peptide‐modified alginate. We demonstrate here the ability of the peptide‐modified alginate gels to allow adhesion of NB2a neuroblastoma cells and to promote neurite outgrowth from these cells when attached to the peptide‐modified alginate surface. Also, we show that the adhesion of NB2a neuroblastoma cells and neurite outgrowth from the attached cells is a function of the peptide density on the gel surface. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 71A: 191–200, 2004
Site‐specific delivery of acidic fibroblast growth factor stimulates angiogenic and osteogenic responses in vivo
Authors: Kelpke S. S. , Zinn K. R. , Rue L. W. , Thompson J. A. 
Published: September 2004

AbstractA major clinical problem in orthopedics is the healing of nonunion fractures. Limitations of this bone repair process include insufficient angiogenesis and mineralization. Integrating appropriate biomaterials with site‐specific neovascularization and osteogenesis at the wound site has been the focus of several clinically relevant therapeutic strategies. As an extracellular protein, acidic fibroblast growth factor (FGF‐1) induces, coordinates, and sustains site‐specific molecular responses associated with angiogenesis and osteogenesis. To establish the ability of this growth factor to coordinate bone regenerative process in vivo, site‐specific delivery of FGF‐1, entrapped in a fibrin/hydroxyapatite composite, was evaluated. Kinetic analysis in vivo revealed the biocomposite was capable of delivering biologically active FGF‐1. Release kinetics revealed an initial delivery of 87.5 ng/h of active FGF‐1 in the first 20 h, followed by a reduced delivery of 28 ng/h during the next 20 h. In situ immunohistological analyses demonstrated that FGF‐1–containing implants induced increased angiogenesis and infiltration of cells expressing osteogenic related markers (i.e., osteopontin, osteocalcin). Collectively, these efforts support that site‐specific delivery of active FGF‐1 in a fibrin/hydroxyapatite composite is competent to induce not only angiogenesis but also osteogenic cellular responses. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 71A: 316–325, 2004