Molecular Dynamics Simulations of Rhodamine B Zwitterion Diffusion in Polyelectrolyte Solutions

Abstract

Polyelectrolytes continue to find wide interest and application in science and engineering, including areas such as water purification, drug delivery, and multilayer thin films. We have been interested in the dynamics of small molecules in a variety of polyelectrolyte (PE) environments; in this paper, we report simulations and analysis of the small dye molecule rhodamine B (RB) in several very simple polyelectrolyte solutions. Translational diffusion of the RB zwitterion has been measured in fully atomistic, 2 μs long molecular dynamics simulations in four different polyelectrolyte solutions. Two solutions contain the common polyanion sodium poly(styrene sulfonate) (PSS), one with a 30mer chain and the other with 10 trimers. The other two solutions contain the common polycation poly(allyldimethylammonium) chloride (PDDA), one with two 15-mers and the other with 10 trimers. RB diffusion was also simulated in several polymer-free solutions to verify its known experimental value for the translational diffusion coefficient, D RB , of 4.7 × 10 −6 cm 2 /s at 300 K. RB diffusion was slowed in all four simulated PE solutions, but to varying degrees. D RB values of 3.07 × 10 −6 and 3.22 × 10 −6 cm 2 /s were found in PSS 30-mer and PSS trimer solutions, respectively, whereas PDDA 15-mer and trimer solutions yielded values of 2.19 × 10 −6 and 3.34 × 10 −6 cm 2 /s. Significant associations between RB and the PEs were analyzed and interpreted via a two-state diffusion model (bound and free diffusion) that describes the data well. Crowder size effects and anomalous diffusion were also analyzed. Finally, RB translation along the polyelectrolytes during association was characterized.

Unusual Aspects of Charge Regulation in Flexible Weak Polyelectrolytes

“…For instance, Fluorescence Correlation Spectroscopy (FCS) and Fluorescence Recovery After Photobleaching (FRAP) experiments both in vivo [ 243 ] and in vitro [ 244 ], track the diffusion coefficient of tracer proteins in crowded media, suggesting a reduction in the diffusion coefficient of the tracer protein by up to two orders of magnitude due to the presence of MCr. These observations have been confirmed by computer simulations [ 245 , 246 , 247 , 248 , 249 , 250 , 251 ], which also predict anomalous diffusion regimes [ 252 , 253 , 254 , 255 , 256 ]. The shape and softness of the involved particles can also play a role in diffusion under MCr conditions [ 257 , 258 , 259 ].…”

Rhodamine B as an efficient multifunctional passivator for the improvement of perovskite solar cell performance

“…42 Due to the low viscosity and limited solubility of PCBM solution, its film-forming performance is usually poor, 43 and the smoother surface is beneficial for the formation of high-quality interfacial contact between MAPbI 3 and PCBM. Because RhB contains the positively charged diethyl ammonium and negatively charged Cl − anion and its dipole is 5.5 D, 44 which may produce an interface dipole on the MAPbI 3 film, triggering the formation of an extra electric field. To prove this hypothesis, the contact potential differences (CPD) of MAPbI 3 films before and after passivation were measured by KPFM (Fig.…”

“…This interfacial dipole will generally induce an extra electric field, which is favorable to the charge extraction and transportation at the cathode interface, enhancing the device performance. 44–46…”

“…This interfacial dipole will generally induce an extra electric field, which is favorable to the charge extraction and transportation at the cathode interface, enhancing the device performance. [44][45][46] To investigate the effect of RhB on the crystallinity of the MAPbI 3 , XRD patterns of MAPbI 3 films were determined (Fig. 2e).…”

Characterizing Counterion-Dependent Aggregation of Rhodamine B by Classical Molecular Dynamics Simulations

“…However, appropriate FFs need to be developed, possibly validating them with experimental evidence. While MD simulations have been used to simulate the RB absorption on clay minerals [ 12 ], graphene [ 13 ], and membranes [ 14 ] and to reproduce the diffusion in polyelectrolyte solutions [ 15 ], to the best of our knowledge they have not been used to describe the interaction of RB with bulky hydrophobic counterions in a solution. Thus, the characterization of the key molecular interactions responsible for the formation of dye networks suitable for LH purposes remains unexplored.…”