Molecular Insight into Dye–Surfactant Interaction at Premicellar Concentrations: A Combined Two-Photon Absorption and Molecular Dynamics Simulation Study

Abstract

Both electrostatic and hydrophobic interactions play pivotal roles in ligand−surfactant binding interaction, especially for ionic surfactants. While much studies have been reported in the micellar region, less attention has been paid on such interactions at a low (premicellar) surfactant concentration. We here study the interaction between the cationic dye rhodamine 6G (R6G) with surfactants of different charge types: anionic SDS, cationic CTAB, and nonionic Tx 100 using absorption and emission spectroscopy. We identify that R6G forms dimeric aggregates at a premicellar concentration of SDS. Formation of aggregates is also confirmed from classical simulation measurements. CTAB and Tx 100 do not form any such aggregate, presumably owing to unfavorable electrostatic interactions. For a molecular-level understanding, we perform two-photon absorption (TPA) spectroscopy for the same systems. TPA allows us to calculate the two-photon absorption cross section and subsequently the change in the dipole moment (Δμ) between ground and excited states of the dye. We calculate the Δμ and observe that it passes through a maximum at a surfactant concentration half of the critical micelle concentration of SDS. This observation imparts support to earlier quantum mechanical calculation, which infers deviation from the parallel orientation of the dye during surfactant-induced aggregation. We extended our measurements and varied the carbon chain length of the anionic surfactant, and we found that all of them exhibit a maximum in Δμ, while their relative magnitude is dependent on the surfactant carbon chain length.

Fluorescent Nanoassembly of Tetrazole-Based Dyes with Amphoteric Surfactants: Investigation of Cyanide Sensing and Antitubercular Activity

“…However, upon comparison, it was noticed that the extent of cyanide-mediated fluorescence quenching was more prominent with P2 compared to P1 both in the presence of S1 and S2 surfactants (Figure c). This might be due to the larger hydrophobic residue for P2 , which forces the molecules of P2 to be buried in the relatively hydrophobic region . Further, the sensitivity toward CN – ions was compared between S1 and S2 surfactants for both P1 and P2 .…”

“…This might be due to the larger hydrophobic residue for P2, which forces the molecules of P2 to be buried in the relatively hydrophobic region. 42 Further, the sensitivity toward CN − ions was compared between S1 and S2 surfactants for both P1 and P2. For both P1 and P2 compounds, it was observed that the degree of fluorescence quenching was larger in the case of surfactant S2.…”

Role of Alkyl Chain Length in Surfactant-Induced Precipitation of Reactive Brilliant Blue KN-R

“…MD simulation is a classic method to gain a better understanding of the dye-surfactant interaction [42]. Thus, we used this method to analyze the interactions of RBB KN-R with DTAB, TTAB, and CTAB.…”

Insights into the Adsorption Properties of Mixed Matrix Membranes (Pebax 1657-g-Chitosan-PVDF-Bovine Serum Albumin@ZIF-CO3-1) for the Antiviral COVID-19 Treatment Drugs Remdesivir and Nirmatrelvir: An In Silico Study

“…By identifying the most promising adsorbents or drug candidates through simulations, researchers can reduce the number of experiments that need to be carried out experimentally, saving time and resources. The importance of in silico studies for designing and optimizing adsorbent materials for practical applications cannot be overstated, as several studies have shown that they provide a comprehensive understanding of the sorption behavior of the system. ,− …”