skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.


Title: Range and sensitivity of 17O nuclear spin-lattice relaxation as a probe of aqueous electrolyte dynamics
The study of electrolytic solutions is of relevance in many research fields, ranging from biophysics, materials, and colloid science to catalysis and electrochemistry. The dependence of solution dynamics on the nature of electrolytes and their concentrations has been the subject of many experimental and computational studies, yet it remains challenging to obtain a full understanding of the factors that govern solution behavior. Here, we provide additional insights into the behavior of aqueous solutions of alkali chlorides by combining 17O relaxation data with diffusion and viscosity data and contrast their behavior with 1H nuclear magnetic resonance relaxation data. The main findings are that 17O relaxation correlates well with viscosity data but not with diffusion data, while 1H relaxation correlates with neither. Certain ionic trends match known ion-specific series behavior, especially at high concentrations. Notably, we also examine the ranges of the interactions and conclude that the majority of the effects are tied to local water reorientation dynamics.  more » « less
Award ID(s):
2108205
PAR ID:
10513087
Author(s) / Creator(s):
;
Publisher / Repository:
American Institute of Physics
Date Published:
Journal Name:
The Journal of Chemical Physics
Volume:
160
Issue:
15
ISSN:
0021-9606
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Liétor-Santos, J-J (Ed.)
    The effect of branches on the linear rheology of entangled wormlike micelle solutions is modeled by tracking the diffusion of micellar material through branch points. The model is equivalent to a Kirchhoff circuit model with the sliding of an entangled branch along an entanglement tube due to the constrained diffusion of micellar material analogous to the flux of current in the Kirchhoff circuit model. When combined with our previous mesoscopic pointer algorithm for linear micelles that can both break and fuse, the model adds a branch sprouting process and therefore enables simulation of the dynamics of structural change and stress relaxation in ensembles of micelle clusters of different topologies. Applying this new model to study the relationships between fluid rheology and microstructure of micelles, our results show that branches change the scaling law exponents for viscosity versus micelle strand length. This contrasts with the long-standing hypothesis that branches affect viscosity and relaxation in the same way that micelle ends do. The model also suggests a process for inferring branching density from salt-dependent linear rheology. This is exemplified by mixed surfactant solutions over a range of salt concentrations with flow properties measured using both mechanical rheometry and diffusing wave spectroscopy (DWS). By elucidating the connection between the branching characteristics, such as strand length and branching density, with the nonmonotonic variation of solution viscosity, the above model provides a powerful new tool to help extract branching information from rheology. 
    more » « less
  2. The hierarchical structure and dynamics of polymer solutions control the transport of nanoparticles (NPs) through them. Here, we perform multi-particle collision dynamics simulations of solutions of semiflexible polymer chains with tunable persistence length l p to investigate the effect of chain stiffness on NP transport. The NPs exhibit two distinct dynamical regimes – subdiffusion on short time scales and diffusion on long time scales. The long-time NP diffusivities are compared with predictions from the Stokes–Einstein relation (SER), mode-coupling theory (MCT), and a recent polymer coupling theory (PCT). Increasing deviations from the SER as the polymer chains become more rigid ( i.e. as l p increases) indicate that the NP motions become decoupled from the bulk viscosity of the polymer solution. Likewise, polymer stiffness leads to deviations from PCT, which was developed for fully flexible chains. Independent of l p , however, the long-time diffusion behavior is well-described by MCT, particularly at high polymer concentration. We also observed that the short-time subdiffusive dynamics are strongly dependent on polymer flexibility. As l p is increased, the NP dynamics become more subdiffusive and decouple from the dynamics of the polymer chain center-of-mass. We posit that these effects are due to differences in the segmental mobility of the semiflexible chains. 
    more » « less
  3. Many  biological  macromolecules  rely  on  metal  ions  to  maintain  structural  integrity  and  control  their  regulatory  function. In biological fluids, detection and identification of metal ions requires sensitive analytical tools with clear readouts.  In  this  work,  we  sought  to  investigate  the  potential  of  solution  Nuclear  Magnetic  Resonance  (NMR)  spectroscopy to analyze metal ion solutions and mixtures. To enable 1H NMR detection, we prepared the complexes of  eight  metal  ions  with  the  chelating  agent,  1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic  acid  (BAPTA).  The 1H NMR spectra were collected for BAPTA samples as a function of metal ion concentrations. The analysis of NMR data revealed that all metal ions with a notable exception of Mg2+ bind BAPTA with high affinities and form complexes with 1:1 metal-to-chelator stoichiometry. Both methylene and aromatic regions of the BAPTA 1H NMR spectra  experience  significant  changes  upon  the  metal  ion  complex  formation.  We  identified  the  spectroscopic  signatures  of  trivalent  and  paramagnetic  ions  and  demonstrated  that  the  binary  Zn2+/Pb2+  metal  ion  mixture  can  be  successfully analyzed by NMR. We conclude that complexation with BAPTA followed by the 1H NMR analysis is a sensitive method to detect and identify both nutritive and xenobiotic metal ions. 
    more » « less
  4. The diffusion of proteins is significantly affected by macromolecular crowding. Molecular simulations accounting for protein interactions at atomic resolution are useful for characterizing the diffusion patterns in crowded environments. We present a comprehensive analysis of protein diffusion under different crowding conditions based on our recent docking-based approach simulating an intracellular crowded environment by sampling the intermolecular energy landscape using the Markov Chain Monte Carlo protocol. The procedure was extensively benchmarked, and the results are in very good agreement with the available experimental and theoretical data. The translational and rotational diffusion rates were determined for different types of proteins under crowding conditions in a broad range of concentrations. A protein system representing most abundant protein types in the E. coli cytoplasm was simulated, as well as large systems of other proteins of varying sizes in heterogeneous and self-crowding solutions. Dynamics of individual proteins was analyzed as a function of concentration and different diffusion rates in homogeneous and heterogeneous crowding. Smaller proteins diffused faster in heterogeneous crowding of larger molecules, compared to their diffusion in the self-crowded solution. Larger proteins displayed the opposite behavior, diffusing faster in the self-crowded solution. The results show the predictive power of our structure-based simulation approach for long timescales of cell-size systems at atomic resolution. 
    more » « less
  5. Polymer solution processability in extensional-flow dominated operations is strongly influenced by polymer conformation and solution phase behavior. Cosolvent addition can be used to tailor polymer conformation and solution phase behavior to yield formulations that are amenable to processes such as spraying and atomization, coating, and fiber spinning. The addition of N,N-dimethylformamide (DMF) to aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions induces unique phase behavior and microstructure formation, yet the effects on solution processability have remained unexplored. In this work, the effect of DMF cosolvent content on the rheology (both shear and extensional) and microstructure of PNIPAM solutions is investigated. While all examined PNIPAM solutions exhibit nearly Newtonian steady shear behavior regardless of DMF content, the same solutions exhibit varying degrees of extensibility. Surprisingly, the extensional relaxation time increases by more than twenty-fold with increasing DMF content in the water-rich regime. In the DMF-rich regime, however, solution extensibility dramatically decreases. Interestingly, this unique variation in extensional flow behavior does not scale as expected based on changes in the measured intrinsic viscosity and radius of gyration. Instead, a mechanism is proposed that relates the extensional flow behavior to the solution microstructure, which is found to vary with DMF content in light scattering measurements. In the water-rich regime, DMF molecules are proposed to bridge PNIPAM chains via hydrogen bonding and hydrophobic interactions, resulting in physically crosslinked aggregates. In extensional flows, these aggregates behave like a polymer with higher apparent molecular weight, increasing the extensional relaxation time. In the DMF-rich regime, non-bridging DMF molecules increasingly solvate individual PNIPAM chains; consequently, more individual chains are stretched in extensional flows, leading to a reduction in the extensional relaxation time. These findings demonstrate that interactions between components in these ternary systems have unexpected but significant implications in solution extensional flow behavior. Additionally, in the case of PNIPAM/DMF/water, the processability of polymer-containing formulations can be modulated for spraying or for fiber spinning applications just by varying cosolvent (DMF) content. 
    more » « less