Spectroscopic and Calorimetric Studies of Molecular Recognitions in a Dendrimer–Surfactant Complex

Abstract

Molecular recognitions, causing supramolecular complex formation between a hyperbranched polymer molecule (polyamidoamine (PAMAM) dendrimer generation 3) with oppositely charged surfactant sodium dodecyl sulfate (SDS) in aqueous solution, were studied by using various spectroscopic techniques and calorimetric titration of heat change measurements. Spectroscopic measurements were performed using dynamic Stokes shift (DSS), rotational anisotropy decay, and translational diffusion of a fluorescent probe molecule coumarin 153 (C153) noncovalently attached to the dendrimer-surfactant complex. All these studies unanimously confirm that the critical aggregation concentration (CAC) of SDS falls to ∼0.8 mM (from its critical micelle concentration (CMC) ∼ 8 mM) in the presence of ∼0.2 mM dendrimer. Further studies of isothermal titration calorimetry (ITC) measurement show that the CAC of SDS in the presence of dendrimer remains invariant to the dendrimer concentration. Complexation reaction between SDS and dendrimer is highly exothermic in nature. A maximum heat release (ΔH∼ -6.6 kJ/mol of SDS binding) was observed at a SDS-to-dendrimer mole ratio of ∼3-5; where up to 3 to 5 SDS molecules were encapsulated by one dendrimer molecule to form dendrimer-SDS encapsulation complex. When negatively charged SDS was replaced with a positively charged surfactant dodecyl-trimethylammonium-bromide (DTAB), we found that the DTAB hardly interacted with positively charged dendrimer due to the charge-charge repulsions.

Model‐Free Estimation of Energy‐Transfer Timescales in a Closely Emitting CdSe/ZnS Quantum Dot and Rhodamine 6G FRET Couple

“…Timescales associated with the kinetics are obtained from TRES analysis. Construction of TRES was performed by following a procedure reported by the groups of Fleming and Maroncelli, more details of which can be found in the Supporting Information and previous reports in the literature . TRES without area normalization are not very useful for FRET analysis because the intensity of TRES gradually decreases with time, owing to the natural excited‐state decay process, and this phenomenon can mix easily with other processes of interest, which also cause intensity changes (e.g., FRET, PET).…”

Ribbon Phase of Dendrimer–Surfactant Complexes

“…The present study investigates the complexes of a cationic PAMAM G4 dendrimer with a common anionic surfactant, sodium dodecyl sulfate (SDS), where the dendrimer was prior charged by full protonation. In contrast to the complexes with DBSA, the complexation in the present system is driven by the entropic gain from the release of the counterions originally condensed on dendrimer and SDS micelle upon the electrostatic binding between the two constituents . We will demonstrate that the electrostatic complexation led to the fusion of SDS spherical micelles into cylinders organized to form the so-called “ribbon phase”.…”

“…In contrast to the complexes with DBSA, the complexation in the present system is driven by the entropic gain from the release of the counterions originally condensed on dendrimer and SDS micelle upon the electrostatic binding between the two constituents. 28 We will demonstrate that the electrostatic complexation led to the fusion of SDS spherical micelles into cylinders organized to form the so-called "ribbon phase". Often formed in surfactant systems, ribbon phase is a class of columnar mesophase composed of the cylinders with noncircular cross section packed in the crystallographic lattices with oblique, primitive rectangular, centered rectangular or hexagonal symmetry.…”

Probing of Reorganization Dynamics within the Different Phases of Themotropic Liquid Crystals

“…A more detail of TRES construction procedure and theoretical approaches can be found in several literatures. [58][59][60][61][62][63][64] We plotted the time evolution of solvent correlation function [C(t)] using emission energies at different times. C(t)[= (n t -n 1 )/(n 0 -n 1 )] is a function of 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 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 energies of complete unsolvated state (n 0 , t= 0), partially solvated state (n t , t= t) and complete solvated state (n 1 , t= 1), of the excited C153 dipole.…”

“…A detail of measurement techniques, fittings and instrumental part for rotational anisotropy measurement can be found elsewhere. [59][60][61][62][63] In 1926, Perrin correlated the anisotropy with rotational diffusion process responsible for depolarization of the emitting light using the following equation. [67] r ¼ r 0 =ð1 þ t=qÞ ð 1Þ…”