| Enthalpy changes upon dilution and ionization of poly(L-glutamic acid) in aqueous solutions. | |
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MedLine Citation:
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PMID: 16852668 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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The enthalpy changes accompanying the dilution and ionization of poly(L-glutamic acid) in water have been measured at 25 degrees C for two degrees of polymerization (DP = 115 and DP = 480) at various degrees of ionization, alpha, for a concentration range from about 0.2 to 0.002 monomol/L. The heat of dilution displays an unusual dependence on the degree of ionization, which is in sharp contrast to the behavior of other weak carboxylic polyelectrolytes, such as poly(acrylic acid). The exothermic heat effects observed at low values of alpha become endothermic for the region where the helix-coil transition is most pronounced, and for high degrees of ionization, they are exothermic again. Evidently, an endothermic heat effect, produced by an additional conformational transition in the dilution process, is superimposed on the exothermic enthalpy of dilution, and it overweighs the latter in the region of alpha where the conformational transition is prevailing. The calorimetric titration curve, which gives the dependence of the heat of ionization, deltaH(i), on alpha, has a maximum and is typical for poly(carboxylic acids) which undergo pH-induced conformational transition, such as poly(methacrylic acid). The values of deltaH(i) obtained at two polymer concentrations indicate that the enthalpy of ionization depends on the polypeptide concentration. |
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Authors:
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Andrej Godec; Joze Skerjanc |
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Publication Detail:
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Type: Journal Article |
Journal Detail:
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Title: The journal of physical chemistry. B Volume: 109 ISSN: 1520-6106 ISO Abbreviation: J Phys Chem B Publication Date: 2005 Jul |
Date Detail:
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Created Date: 2006-07-20 Completed Date: 2007-06-26 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 101157530 Medline TA: J Phys Chem B Country: United States |
Other Details:
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Languages: eng Pagination: 13363-7 Citation Subset: IM |
Affiliation:
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Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5, 1000 Ljubljana, Slovenia. |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Acrylic Resins
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chemistry Electrolytes / chemistry* Hydrogen-Ion Concentration Ions Polyglutamic Acid / chemistry* Protein Conformation Thermodynamics Water / chemistry* |
| Chemical | |
Reg. No./Substance:
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0/Acrylic Resins; 0/Electrolytes; 0/Ions; 25513-46-6/Polyglutamic Acid; 7732-18-5/Water; 9003-01-4/carbopol 940 |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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