Kinetics of the conformational transition of poly(methacrylic acid) after a pH jump, 2. Studies of nonradiative energy transfer

Abstract

75Kinetics of the conformational transition of poly(methacry1ic acid) after a pH jump, 2 a ) Studies of nonradiative energy transferDedicated to Prof. Paul Rempp on the occasion of his 60th birthday SUMMARY:Doubly labeled poly(methacry1ic acid) (PMA) samples with two different concentrations of carbazole and anthracene labels were prepared, and one sample was divided into two fractioiis of different molecular weight. Emission spectra were recorded in solutions without added salt, at ionic strengths 0,05 and 0,40 and in a 2: 1 water-methanol mixture, as a function of pH. Tfie nonradiative energy transfer (NET) from carbazole donor to anthracene acceptor decayed i t s the PMA coils expanded. On mixing solutions of the labeled PMA with buffer solutions of varying ionic strength in water or aqueous methanol in a stopped-flow apparatus, the expansic n of the PMA was monitored by the decrease in anthracene emission intensity when the soluticn was irradiated in the carbazole absorption band. Only part of the process could be followed, since the initial expansion occurred in a sub-millisecond time. Some studies were also carried out on the kinetics of chain contraction when partially neutralized PMA solutions wei'e acidified. The changing NET with the conformational transition of PMA was correlated with the change in the intrinsic viscosity of the polymer. The kinetic data obtained were generally in excellent agreement with those of an earlier study in which conformational changes of PM.\ were monitored by the changing emission of a dansyl label. In particular, the surprisirg slowness of the final approach to equilibrium was substantiated. a) Part I : cf.'). b, On leave of absence from the Institute

On the versatility of fluorescence techniques in polymer research

“…23 Alternatively, the polymer could be doubly labeled with a donor and an acceptor fluorophore, and the chain expansion could be followed by the decreasing efficiency of the nonradiative energy transfer. 24 The two approaches yielded similar results. A small part of the expansion was too fast to be followed by stopped-flow kinetics; most of the expansion took place within a second, but the final approach to equilibrium was surprisingly slow.…”

Investigation of pH-induced conformational change and hydration of poly(methacrylic acid) by analytical ultracentrifugation

“…PMAA chain expands rather sharply at pH 4-6 when a critical charge density is attained, where the degree of ionization is about 0.3, whereas poly(acrylic acid) (PAA) chain expands smoothly with increasing pH. [12][13][14][15] The pH-induced conformational change of PMAA has been studied by different techniques such as viscometry, 14,16,17 fluorescence spectroscopy, [18][19][20][21][22][23][24][25][26][27] small angle X-ray scattering (SAXS), [28][29][30] Raman spectroscopy, 31,32 infrared spectroscopy, 13 laser light scattering 33,34 and analytical ultracentrifugation. 35 However, it is hard to investigate the conformational changes of individual PMAA chains that occur in response to changes in pH because most of the measurements were conducted at a relatively high concentration.…”

Effect of the Molecular Weight on the Dynamics of the Conformational Transition of Poly(methacrylic acid)

“…[17][18][19] However, just a few data have been published on the kinetics of the pH-induced conformational transition of synthetic polyelectrolytes. 9,14,15,[20][21][22] The kinetics of the conformational transition of an alternating maleic acid-styrene copolymer was studied by Ohno et al, and the transition was observed to occur in approximately 500 ms. 14,15 Different fluorescent probes have been used to study the expansion of PMA following a pH jump, where the fluorescence intensity change is assumed to monitor the rate of polymer coil expansion. 9,21,22 Part of the process could not be followed because it was faster than 1 ms, but most of the transition occurs in the range 600-1000 ms.…”