Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Comparison between Free and Immobilized Ion Effects on Hydrophobic
  Interactions: A Molecular Dynamics Study   Fundamental studies of the effect of specific ions on hydrophobic
interactions are driven by the need to understand phenomena such as
hydrophobically driven self-assembly or protein folding. Using
beta-peptide-inspired nano-rods, we investigate the effects of both free ions
(dissolved salts) and proximally immobilized ions on hydrophobic interactions.
We find that the free ion effect is correlated with the water density
fluctuation near a non-polar molecular surface, showing that such fluctuation
can be an indicator of hydrophobic interactions in the case of solution
additives. In the case of immobilized ion, our results demonstrate that
hydrophobic interactions can be switched on and off by choosing different
spatial arrangements of proximal ions on a nano-rod. For globally amphiphilic
nano-rods, we find that the magnitude of the interaction can be further tuned
using proximal ions with varying ionic sizes. In general, univalent proximal
anions are found to weaken hydrophobic interactions. This is in contrast to the
effect of free ions, which according to our simulations strengthen hydrophobic
interactions. In addition, immobilized anions of increasing ionic size do not
follow the same ordering (Hofmeister-like ranking) as free ions when it comes
to their impact on hydrophobic interactions. The immobilized ion effect is not
simply correlated with the water density fluctuation near the non-polar side of
the amphiphilic nano-rod. We propose a molecular picture that explains the
contrasting effects of immobilized versus free ions.

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The categories of this paper are: cs
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
26
The categories of this paper are: bayes-an
22
The categories of this paper are: chao-dyn
30
The categories of this paper are: q-alg
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
6
The categories of this paper are: astro-ph
0
The categories of this paper are: hep-ph
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
21
The categories of this paper are: adap-org
34
The categories of this paper are: chem-ph
14
The categories of this paper are: math-ph