PH-induced conformational transition

A. Cesaro, A. Ciana, T. Delben, G. Manzini and S. Paoletti, Physicochemical Properties of Pectic Acid. I. Thermodynamic Evidence of a pH-Induced Conformational Transition in Aqueous Solution. Biopolymers Biopolymers, 21 (1982) 431. 

Particular interest in poly(methacrylic acid), (PMA), has arisen because it represents the first clear example of a S5mthetic vinyl poly-electrol57te whose chain can undergo in aqueous solution a pH-induced conformational transition of distinctly cooperative character. Furthermore, to the author s knowledge, PMA is the only vinyl polyelectrol5de available in samples with a different degree and t5q)e of stereoregularity. Such samples have been prepared and examined in detail. 

Cesaro, A., Ciana, A., Delben, F., Manzini, G. and Paoletti, 1982. Thermodynamic evidence of a pH-induced conformational transition in aqueous solution, Biopolymers, 21 431449. 

Water soluble synthetic polyelectrolytes have attracted increasing attention in recent years, mainly because of their wide utility in industrial applications, and also because of their resemblance to biopolymers. PolyCmethacrylic acid), PMA, a wea)c polyelectrolyte, exhibits a mar)ced pH induced conformational transition. A wide variety of techniques have been employed to gain more information on the nature of the conformational transition of PMA, these techniques include viscometry, potential titrimetry,(1-5) Raman spectrometry,(6) calorimetry,(7-9) electrical conductometry,(10) dilatometry,(11) H NMR linewidth,(12) viscoelastic studies,(13) )cinetics of chemical reactions, (14) small-angle neutron scattering,(15) pH jump,(16,17) and fluorescent probing.(18-27)... 

Langella E, Improta R, Barone V (2004) Checking the pH-induced conformational transition of prion protein by molecular dynamics simulations effect of protonation of histidine residues. Biophys J 87 3623... 

Nar H, Messerschmidt A, Huber R, Vandekamp M, Canters GW (1991) Crystal-structure analysis of oxidized pseudomonas aeruginosa azurin at pH 5.5 and oH 9.0 - a pH-induced conformational transition involves a peptide-bond flip. J Mol Biol 221 765-772... 

The effect on the conformational-aggrega-tlonal properties of pectate in aqueous solution brought by the addition of specific ions (H+, Ca +. Cu +) was studied by osmometric, microcalorimetric, dilato-metric, and rheological methods. Evidence is provided for the intramolecular nature of the pH induced conformational transition. The addition of divalent ions brings about at the same time a conformational change of the chain of pectate and chain-chain association. 

The modified titration curves of the fractionated (MA-St)n aqueous NaCl at various ionic strengths from 0.009 to 0.27 resembled the potentiometric behaviors of the maleic acid copolymer with n-butyl vinyl ether and poly(methacrylic acid) in aqueous salts. There was no precipitation or turbidity in the deionized polymer solution, except in aqueous NaCl of 0.27 M. The conformational transition from the compact to extended coil form was seen in diagp ams of the intrinsic viscosity vs. qp and the reduced viscosity in the range 0.1 < aj < 0.4 was independent of polymer concentration. Both the potentiometric and viscometric titration data showed that the pH-induced conformational transition of (MA-St)n in aqueous NaCl is due to intramolecular interaction. The unperturbed molecular dimensions were calculated from the viscosity data and the acid compact form of this copolymer was found to be not so compact as the conformations of globular proteins. Dilatometry did also indicate existence of the transition,and the transition was observed in aqueous solutions of various salts chlorides, bromides, perchlorates and thiocyanates of Na" ", K" ", Rb" ", Cs" " and... 

In summary, (MA-St) and (MA-MSO are in the compact forms being stabilized by the intramolecular hydrophobic interactions between the phenyl groups at low Op and the pH-induced conformational transitions accompany exposure of the phenyl groups on the molecular surfaces. 

In view of the increasing interest concerning the existence of non electrostatic interactions and their influence on the conformation of polyelectrolyte chains, we have extensively investigated in our laboratory some synthetic polyelectrolytes showing a pH-induced conformational transition. 

The results reported above of various measuring methods used with different kinds of polyelectrolytes undergoing a pH-induced conformational transition may be combined to form a consistent picture on the main cause for stabilization of compact structure of polyions in water. 

Fig. 10.9. Schematic representation of pH-induced conformation transitions in IPEC(HPE/ enzyme-GPE) system [28]...

Poly (methacrylic acid). pH-induced conformational transition thermodynamic data. Summary of microcalorimetric and potentiometric data for the conformational transition of poly (methacrylic acid) in aqueous solution... 

Maleic acid - bulit vinyl ether copolymer pH-induced conformational transition ... 

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