A Blob Model To Study Chain Folding by Fluorescence

Abstract

Monodisperse polystyrenes (M w/M n < 1.15) with molecular weights of 6K, 40K, and 110K and one polydisperse polystyrene (M w/M n = 1.5) with a molecular weight of 110K were synthesized. The chromophore pyrene was randomly and covalently attached onto the polymers. The dynamics of the chains were investigated quantitatively by monitoring the fluorescence of the pyrene monomer. The polymer coil was divided into several blobs among which pyrene is randomly distributed according to a Poisson distribution. The kinetics of the pyrene groups are monitored by only three parameters: k diff, the rate at which one excited pyrene encounters one ground state (GS) pyrene inside a blob; k e[blob], the product characterizing the exchange of GS pyrene between blobs (k e is the rate of exchange and [blob] is the blob concentration inside the polymer coil); and 〈 n〉, the average number of GS pyrene per blob. We show that the parameters retrieved by this analysis are internally consistent within the theoretical framework of the blob model. A critical polymer chain length is found above which polymer chain dynamics behave in a similar manner, regardless of the size of the polymer. Below the critical polymer chain length, chain dynamics are chain length-dependent.

Internal Dynamics of Dendritic Molecules Probed by Pyrene Excimer Formation

“…The resulting dimers D* constituted of poorly stacked pyrenes emit with a lifetime τ D that is different from τ E0 . Whereas τ E0 takes values between 40 and 70 ns in organic solvents [139], lifetimes τ D have been obtained that were as short as 2-4 ns [108,126] or as long as 100-150 ns [103,[112][113][114]116].…”

Long Range Polymer Chain Dynamics Studied by Fluorescence Quenching

“…The fluorescence blob model (FBM) was introduced in 1999 to fill this theoretical gap. 35 The FBM defined the blob as the volume within the polymer coil probed by an excited dye. The blob could then be viewed as a unit Fluo.…”

“…To date, the FBM has been applied to the analysis of the monomer and excimer decays acquired with several polymers randomly labeled with pyrene. 35,37,67,68,[72][73][74][75] Table 2. Chemical structure of the polystyrenes and poly(N-isopropylacrylamide) randomly labeled with pyrene.…”

“…As it turns out, the same quantitative information about polymer chain dynamics can be obtained by conducting time-resolved fluorescence experiments on actual polymers that are randomly labeled and whose fluorescence decays are analyzed with the Fluorescence Blob Model (FBM). 35 Third, this Perspective proposes that the product <kblob×Nblob> obtained from the FBM analysis of decays acquired with randomly labeled polymers provides a measure of the Long Range Polymer Chain Dynamics (LRPCD) in solution that might be as robust as the glass transition temperature (Tg) is to describe LRPCD in the solid state. Since…”

Contraction and Collapsing Kinetics of Single Synthetic Polymer Chains at Small Quench Depths

“…(1) In protein folding kinetic studies, the exponential fitting of time-dependent fluorescence (intrinsic fluorescence of tryptophan residues, added ANS probes, FRET) changes has been typically employed, and the results generally agree with the time-dependence size changes. [92] (2) In a series of reports by Martinho et al [19,21,81,82] and Duhamel et al, [86,87,93] a blob model was proposed for the investigation of polymer chain folding by the fluorescence technique and successfully correlated the temperature dependence of I e /I m of pyrene-labeled chains with their size shrinkage during collapse. (3) It would be excellent to directly follow the time dependence of coil sizes during collapsing.…”