1,721,136 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Molecular recognition: A thermodynamic study of non bonded interactions in aqueous solutions of iminoacids. Effects of steric and geometric isomerism
No full textEnthalpies of dilution of binary and ternary aqueous solutions containing L- and D-proline, cis-L- and cis-D-4-hydroxy proline, trans-L-4-hydroxy proline, have been determined by flow calorimetry at 25°C. Pairwise self- and cross-interaction coefficients of the virial expansion of the excess enthalpies were evaluated. They are positive for solutions of unsubstituted prolines. On the contrary, upon the introduction of a hydroxy group, they become negative, reaching the largest value for the cis-L-/cis-D-4-hydroxy proline system. The results are interpreted in terms of preferential configurations, stabilized by interactions between the hydrophilic groups
Prediction of excess enthalpies for ternary aqueous solutions of nonelectrolytes
No full textThe excess enthalpies HxyE of ternary aqueous solutions of nonelectrolytes are used to test the possibility of making predictions for ternary solutions from the properties of the binary solutions only. Two methods are proposed: one is based on the empirical rule (hxx ·hyy )1/2=hxy . Another leads to the numerical prediction of the overall HxyE . Both are successful for most of the pairs of solutes for which HxE, HyE >0. © 1980 Plenum Publishing Corporation
A model for the interactions involving hydrophilic structure maker solutes: A thermodynamic study of ternary aqueous solutions of glucose and hydroxylated substances
No full textEnthalpies of dilution of ternary aqueous solutions containing glucose and alkan-1-ols, alkan-1,2-diols and alkan-m,n-diols were determined at 298.15 K by flow microcalorimetry. The pair-wise cross interaction coefficients of the virial expansion of the excess enthalpies were evaluated: they are positive and depend in a complex manner on the length of the alkyl chain of the alkanols. The behaviour of these systems is interpreted in terms of preferential interactions between the hydrophilic groups of the alkanols and the destructured domain present on glucose. © 1996 Akadémiai Kiadó
The hydrophobic effect in aqueous solutions of positional isomers of alkan-n-ols. A calorimetric study at 298.15 K
No full textEnthalpies of dilution were measured for binary aqueous solutions of positional isomers of pentanol and hexanol, and for some ternary solutions containing two of the following alcohols: methanol, ethanol, propan-1-ol, butan-1-ol, and pentan-1-ol. The enthalpic interaction coefficients found depend greatly on the alkyl chain length and on the position of the hydroxyl functional groups. A refinement of the model of overlapping hydration cospheres is proposed. Two hydrated molecules should interact through a preferential, "side on", orientation, stabilized by the contemporaneous juxtaposition of the hydroxyl groups and the alkyl chains. The effects which cause the hxx values of positional isomers to differ are discussed. © 1991
Chiral recognition in aqueous solutions. Preferential configurations of α-aminoacids bearing substituted alkyl chains at 25°C
No full textCalorimetric measurements were carried out at 25°C on binary and ternary aqueous solutions containing L and D forms fo the following α-aminoacids: tryptophan, cysteine, methionine, phenylalanine, histidine, threonine, and citrulline, which contain both hydrophilic and hydrophobic domains. Differences were found between the values of the homochiral and heterochiral pairwise enthalpic interaction coefficients for tryptophan, cysteine, and methionine. To the contrary, chiral recognition was not detected for phenylalanine, histidine, citrulline, and threonine. The data were interpreted in terms of a "preferential configuration" model. Chiral recognition is detected only when the interactions of the side chains in the homo- and heterochiral configurations are different. Chiral recognition disappears when a competition exists between zwitterion-zwitterion interactions and side chain-side chain interactions. In some cases, such as for citrulline, compensation effects can occur due to thermal contributions from different domains which mask chiral recognition. © 1995 Plenum Publishing Corporation
Preferential configurations in solution: Calorimetric study of ternary aqueous systems containing a destructuring agent and derivatives of α-amino acids at 298 K
No full textEnthalpies of dilution of ternary aqueous solutions containing α-amino acids or their N-acetyl or N-acetylamide derivatives and urea, glycine, N-acetylglycine and N-acetylglycinamide have been determined by flow microcalorimetry at 298.15 K. Pairwise cross-interaction coefficients of the virial expansion of the excess enthalpies were evaluated. The behaviour of these systems seems to be determined by a balance between favourable hydrophilic-hydrophilic and repulsive hydrophilic-hydrophobic interactions. A common behaviour was shown by every studied series of substances, independently of the nature of the destructuring agent. The pairwise cross-interaction coefficients increase with increasing length of the alkyl side chains until a plateau is attained. This seems to be a general rule when homologous series of solutes having hydrophobic domains interact with a structure-breaker solute
A model for the interaction between hydrophilic and hydrophobic solutes. A calorimetric study of the aqueous solutions containing alkylureas and urea at 298.15 K.
No full textThe heats of dilution of ternary aqueous solutions of urea and alkylureas and of ternary aqueous solution of mono, di and tetra alkylureas have been determined calorimetrically at 298.15 K. Pairwise cross interaction coefficients of the virial expansion of the excess enthalpies were determined. The behaviour of these systems was interpreted in terms of preferential interactions between hydrophilic domains and of repulsive interactions between hydrophobic and hydrophilic domains
Dependence of the cooperativity of hydrophobic interactions on the nature of functional groups. A microcalorimetric study of binary aqueous solutions of α,ω-difunctional compounds at 298.15 K
No full textEnthalpies of dilution of binary aqueous solutions containing α,ω-amino acids, α,ω-dicarboxylic acids, α,ω-diamines and α,ω-diols have been determined at 298.15 K by flow microcalorimetry. The pairwise enthalpic coefficients of the virial expansion of the excess enthalpies were evaluated. These coefficients show that the investigated substances differ greatly in the cooperativity of their hydrophobic interactions, depending on the nature of the functional group. The diamines show the highest cooperativity among the solutes studied to date. The coefficients were interpreted using the 'preferential configuration' model and compared with the results obtained from a statistical approach
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