Molar mass determination by end group analysis - amino group determination in aliphatic and partially aromatic polyamides with 1-fluoro-2,4-dinitrobenzene in benzyl alcohol

End group analysis is the most important absolute method of obtaining number-average molar mass values for polymers of the step-growth polymerization type. A great number of methods are available which primarily differ in the detection of the end group concerned. Special chemical methods based on the formation of covalent derivatives of the end groups (e.g. introduction of UV/VIS chromophores) are important if there is a need to demonstrate, with the aid of gel permeation chromatography, that damage to the polymer (e.g. onset of cross-linking) has occurred. In the case of fibre-forming polycondensation products, the applicability of end group analysis is often restricted by the lack of suitable reagents and solvents. This is also true of the determination of amino end groups in polyamides by means of 1-fluoro-2,4-dinitrobenzene, as is already contained in the German Standards specification (DIN 54 274) - albeit only for polyamide 6 and 6,6. This contribution describes a modified version of the 1-fluoro-2,4-dinitrobenzene method. The analytical principle and practical procedure correspond to those of DIN 54 274, but the solvent used for the reaction with the reagent is benzyl alcohol, and that for the photometric evaluation is 1,1,1,3,3,3-hexafluoro-2-propanol. The scope of the method is thus increased. Examples of applications for this method are commercial products based on aliphatic polyamides (6; 11; 12; 6,6; 6, 12), partially aromatic polyamides (2,4,4-trimethylhexamethylenediamine, terephthalic acid; copolyamides with bis-(4-aminocyclohexyl)propane(2), isophthalic acid, ω-aminododecanoic acid) and multicomponent systems with the abovementioned polyamides (bicomponent fibres, blends). It is shown that large differences may arise between the value determined by titration and the actual amino end group content. In addition, the presence of secondary amino groups can be demonstrated in polyamides of the Trogamid T type.     

Studies on triazine dye-enzyme interaction by means of affinity partitioning

Affinity partitioning in aqueous two-phase systems composed of dextran and polyethylene glycol the latter being partially replaced by dye-substituted polymer was evaluated for the study of enzyme-dye interaction. The method was found excellently suited for the recognition of any interaction between a certain enzyme and triazine dyes by determining the actual partition coefficient, K. Two enzymes, intestinal alkaline phosphatase and yeast phosphofructokinase, were studied. Alkaline phosphatase binds more or less specifically to various triazine dyes. A number of substrates but also inorganic phosphate, NAD⁺ and selected chromophores are competing agents in enzyme-dye interaction whereas hydrophobic and uncompetitive inhibitors fail to compete with the dye. Thus, information on the chemical nature of the dye-enzyme interaction was obtained. Affinity partitioning turned out also appropriate to study the structural dynamics of enzymes. This was exemplified on the specific interaction of phosphofructokinase with a number of triazine dyes. A change of the allosteric properties of the enzyme in respect to ATP-inhibition and its reversibility was indicated by a corresponding alteration of the partition coefficient. The results are discussed in terms of a conformational change of the enzyme.