Poly potentiometry

In a related application, polyelectrolyte microgels based on crosslinked cationic poly(allyl amine) and anionic polyfmethacrylic acid-co-epoxypropyl methacrylate) were studied by potentiometry, conductometry and turbidimetry [349]. In their neutralized (salt) form, the microgels fully complexed with linear polyelectrolytes (poly(acrylic acid), poly(acrylic acid-co-acrylamide), and polystyrene sulfonate)) as if the gels were themselves linear. However, if an acid/base reaction occurs between the linear polymers and the gels, it appears that only the surfaces of the gels form complexes. Previous work has addressed the fundamental characteristics of these complexes [350, 351] and has shown preferential complexation of cationic polyelectrolytes with crosslinked car-boxymethyl cellulose versus linear CMC [350], The departure from the 1 1 stoichiometry with the non-neutralized microgels may be due to the collapsed nature of these networks which prevents penetration of water soluble polyelectrolyte. 

Complex formation of poly(amino acid)s and poly(amine)s with several metal ions has been studied by means of potentiometry, colorimetry, and spectrometry in aqueous solutions. In most cases, conformational change of the polymeric ligand is induced as the result of complex formation, leading to changes in reactivity. 

The poly(methacrylic acid)-polyvinylpyrrolidone system have been studied in detail in the series of the homopolymer complexes investigated by the authors (Table 2). The possibility of complex formation in this system has been shown by potentiometry, conductometry and viscometry and also by IR spectroscopic and thermogravimetric investigations of PMAA-PVP complexes in the solid state27,57). 

The exchange reactions between salts of polymer adds (bases) and weak polybases (polyadds) in aqueous solutions are accompanied by considerable pH changes and also by the appearance of turbidity, particularly if the components are mixed in equivalent quantities. The copredpitation of polymeric adds and polybases was described first by Fuoss and Sadek This behavior of the mixture of two oppositely charged polyelectrolytes can be explained by the formation of a polyelectrolyte complex, this reaction being accompanied by elimination of a low-molecular weight acid or base. Thus, the exchange reaction between poly(acrylic add) and pdly(4-vinyl-ethylpyridinium bromide) was shown by potentiometry and turbidimetry to result in the precipitation of an insoluble macromolecular product, i.e. the ionic comj ex, and... 

FIG. 5 Simultaneous titration of H+ cellulose sulfate with a branched poly (eth-yleneimine) by conductometry, potentiometry, and turbidimetry. (From Ref. 32.)... 

Direct Potentiometry Detemdnatiou of Hydrogen Chlonde Gas. A system has been described for the continuous monitoring of the HCl levels in gases or aerosols using a chloride-ion-selective electrode [IS]. This arose from a study on the loss of volatile decomposition products from poly(vinyl chloride) (PVQ and other chlorocarbon polymers in simulated fires. The method works well because of the excellent solubility of HQ in water, and the fact that the chloride electrode senses only free Q ion. Thus, other volatile chloride compounds will not be sensed. 

Peptides are known to show some specificity toward metal binding, as was shown by titration experiments nsing H-NMR [7,8], potentiometry [9], luminescence measnrements [10], infrared (IR), circular dichroism (CD), and ultraviolet (UV spectroscopies [11]. Poly-L-aspartic acid binds to metals such as Eu, Ce, La +, Cu ", and Pb ", and acts as a corrosion inhibitor for steel and iron. This property has been ascribed to the carboxylate side chain of aspartic acid [12,13]. 

On the basis of CD data one can safely exclude the righthanded a-helix from the possible ordered forms. Myer and Barnard [10] interpreted the CD spectra of the poly (His) ordered conformations in terms of a j -structure, this assignment however being complicated by the influence of side-chain chromophores [11]. In our study we have collected more evidences in favour of Myer and Bernard s proposal and investigated the thermodynamics of the P coil conformational transition [5]. Among the different types of data and informations derived from this study, I shall here collect and illustrate to you a few results more directly connected with the energetics of the transition of poly (His) and which, in my opinion, afford a further example of the useful joint applications microcalorimetry and potentiometry may find in the field of our concern. 

For example, the enthalpy values for the jS coil transition of poly-L-lysine reported by Pederson et al. [13] (potentiometry) and by Chou and Scheraga [14] (calorimetry) differ by nearly 2 kcal mole ... 

---