Conformation of poly(γ‐glutamic acid) in aqueous solution

Abstract

Local conformation and overall conformation of poly(γ-DL-glutamic acid) (PγDLGA) and poly(γ-L-glutamic acid) (PγLGA) in aqueous solution was studied as a function of degree of ionization ε by (1) H-NMR, circular dichroism, and potentiometric titration. It was clarified that their local conformation is represented by random coil over an entire ε range and their overall conformation is represented by expanded random-coil in a range of ε > ε(*) , where ε(*) is about 0.3, 0.35, 0.45, and 0.5 for added-salt concentration of 0.02M, 0.05M, 0.1M, and 0.2M, respectively. In a range of ε < ε(*) , however, ε dependence of their overall conformation is significantly differentiated from each other. PγDLGA tends to aggregate intramolecularly and/or intermolecularly with decreasing ε, but PγLGA still behaves as expanded random-coil. It is speculated that spatial arrangement of adjacent carboxyl groups along the backbone chain essentially affects the overall conformation of PγGA in acidic media.

Conformational Analysis of Carboxymethylamylose by Potentiometric Titration and SAXS

“…Similar α dependence of p K a is observed in data (5) and (6) in 0.06 m KI/I 2 aqueous solution, where α 3,min < α < α 3 * (= ca.0.75) and α > α 3 * correspond to Region I and II, respectively. As was shown in the study of Wada and in our previous paper, α dependence of p K a for PLGA forms a curve initially having negative slope and then horizontal slope in Region C and positive slope in Region D. Thus, the features in the titration curves of PLGA in Region C and D well resemble those of CMA in Region I and II, respectively. It is well established that Region C of PLGA reflects a mixture of helical chain and completely coiled molecule and Region D reflects a completely coiled molecule and so it is speculated that the conformation of CMA would be gradually changed from a helical‐chain or a compact‐coiled chain to an extended‐coiled chain as α increases in Region I and then it would take an extended‐coiled chain in Region II.…”

“…It is well known that α dependence of pH + log{(1‐α)/α}} (p K a ) is applied to analyze local conformation of polypeptides and polyelectrolytes . Some examples of its applicability are found in our studies of poly(α‐ L ‐glutamic acid) (PLGA), poly(γ‐ L ‐glutamic acid) and carboxymethylcellulose …”

Polyaminoacids in Biomimetic Collagen Mineralization: Roles of Isomerization and Disorder in Polyaspartic and Polyglutamic Acids

“…However, other analysis has demonstrated strong similarities between the CD spectra of polyaspartate and polyglutamate, both resembling the polyproline II helix. , This apparent discrepancy is explained by the work of Saudek et al, who showed that the α-helix-forming ability of poly- l -aspartic acid is disrupted by an increasing proportion of β-bonds, , likely by increasing the conformational freedom of the polymer and disrupting hydrogen bonding, and that fully ionized poly-α- l -aspartate exhibits a polyproline II-like CD spectrum . A similar trend is evident in CD spectroscopy of poly-α- l -glutamic acid, which also adopts a polyproline II-like structure in its fully ionized form, with a loss of negative peak intensity for poly-γ-glutamic acid . Thus, the large proportion of β structural isomers in our commercial sample of pAsp100 is consistent with the lack of an ordered secondary structure.…”

Titrations without the Additions: The Efficient Determination of pKa Values Using NMR Imaging Techniques

“…The chemical shifts of moieties participating in chemical phenomena such as protonation/deprotonation, − host–guest complexation, − or supramolecular assembly − are often observed to vary with pH. Valuable information including p K a values, ,− conformations, ,, and assembly states , can thus be obtained by analysis of chemical shift data. In the conventional procedure, a series of NMR spectra are recorded separately, the pH of the sample being adjusted manually between successive NMR measurements.…”