Conformational Transitions of Polymer Chains in Solutions Characterized by Fluorescence Resonance Energy Transfer

Abstract

The critical overlap concentration C* is an important concept in polymer solutions and is defined as the boundary between dilute and semidilute regimes. In this study, the chain conformational changes of polystyrene (PS) with both high (Mn = 200,000 Da) and low (Mn = 13,000 Da) molecular weights in cis-decalin were compared by intrachain fluorescence resonance energy transfer (FRET). The random labeling of donor and acceptor chromophores strategy was employed for long PS chains, whereas chain-end labeling was used for short PS chains. By monitoring the spectroscopic intensity ratio between acceptor and donor, the concentration dependence on chain conformation from dilute to semidilute solutions was determined. Both long and short chains exhibit a conformational transition concentration, above which the polymer chains begin to collapse with concentration significantly. Interestingly, for randomly labeled polymer long chains, such concentration is consistent with C* determined from the viscosity result, below which only slight conformational change of polymer chain takes place. However, for the chain-end labeled short chain, the conformational transition concentration takes place earlier than C*, below which no significant polymer conformation change is observed.

Diffusion-Enhanced Förster Resonance Energy Transfer in Flexible Peptides: From the Haas-Steinberg Partial Differential Equation to a Closed Analytical Expression

“…DFRET is just one method in a whole range of optical methods for studying the structure and dynamics of polymers [ 10 , 11 , 12 , 13 , 14 , 17 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 ]. When we go into detail, we realize that any progress in DFRET can synergistically promote progress in this entire field [ 13 ].…”

“…When we go into detail, we realize that any progress in DFRET can synergistically promote progress in this entire field [ 13 ]. The structure and dynamics of polymers are so important that numerous methods based on two optical molecular labels have been developed [ 2 , 3 , 5 , 6 , 10 , 11 , 13 , 15 , 17 , 22 , 23 , 24 , 25 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 47 , 48 , 49 , 57 , 58 , 59 , 63 , 64 , 65 , 66 , 67 , 68 ]. These labels are either synthetically conjugated to the chain or naturally present, as, for instance, Trp or Tyr in a peptide or protein.…”

Fluorescence Resonance Energy Transfer Measurements in Polymer Science: A Review

“…Qin et al [ 202 ] performed a very similar study to find c * of both high (200, 000 g mol −1 ) and low (13, 000 g mol −1 ) MW PS, which were labeled with anthracene and carbazole via ATRP and click chemistry. For both MWs, there was a conformational transition where the chains began to collapse as the concentration went into the semi‐dilute region.…”

“…[187][188][189][190][191][192] FRET can directly measure intramolecular distances within the range of ≈1-10 nm in real-space and realtime, which can be used determine chain dimensions such as the polymer end-to-end distances. [47,[193][194][195][196][197][198][199][200][201][202] This fluorescence technique can also be employed to study intermolecular structural information in polymer melts, such as through trapping experiments. [203] As polymer chain dimensions are highly dependent on the surrounding environments, short exposure times, and real-space measurements using FRET techniques provide advantages for investigating polymer chain conformations in response to stimuli such as shear and solvent quality, which can be difficult to investigate using other methods.…”

Low Dielectric Constant and Anisotropic Mechanical Properties of Dispenser‐Printed Polyetherimide Films Using Two‐Step Thermal Treatment

“…Based on the scaling theory of polymer solutions, three different regions exist: dilute, semi‐dilute, and concentrated solutions. [ 22–24 ] When a solvent is eliminated and a solution becomes concentrated, the distance between the polymer chains decreases, resulting in a conformational transition, where the polymer chains contact and overlap with each other. Therefore, once the dissolved polymer material is solidified by heat treatment, it may exhibit a conformational structure different from its original state.…”