Is Br2 hydration hydrophobic?

Abstract

The spectroscopic properties of bromine in aqueous systems suggest it can behave as either hydrophilic or hydrophobic solute. In small water clusters, the halogen bond and the hydrogen-halogen interaction are responsible for its specific way of binding. In water hydrates, it is efficiently hosted by two different cages forming the crystal structure and it has been frequently assumed that there is little or no interaction between the guest and the host. Bromine in liquid solution poses a challenging question due to its non-negligible solubility and the large blue shift measured in its absorption spectra. Using a refined semi-empirical force field, PM3-PIF, we performed a Born-Oppenheimer molecular dynamics study of bromine in liquid water. Here we present a detailed study in which we retrieved the most representative hydration structures in terms of the most frequent positions around bromine and the most common water orientations. Albeit being an approximate description of the total hydration phenomenon, it captures the contribution of the leading molecular interactions in form of the recurrent structures. Our findings confirm that the spectroscopic signature is mainly caused by the closest neighbors. The dynamics of the whole first hydration shell strongly suggests that the external molecules in that structure effectively isolate the bulk from the presence of bromine. The solvation structure fluctuates from a hydrophilic to a hydrophobic-like environment along the studied trajectory.

Halogen Bonds in Clathrate Cages: A Real Space Perspective

“…The initial interpretation of the observed electronic shifts in ultraviolet and visible spectra of bromine clathrate assumed that halogen bonding could not be responsible since all the water lone‐pairs are involved in hydrogen bonding of the water lattice and thus not available for halogen bonding . In contrast the much larger blue‐shifts observed in bromine aqueous solutions were consistent with the formation of halogen bonding interactions . However evidence of halogen bonding in clathrate cages was strongly suggested in ab initio local correlation calculations through an energy partitioning analysis and calculation of the electronic shifts at selected geometries .…”

Design, Synthesis, In vitro and In silico Alpha Glucosidase and Lipoxygenase Inhibition Studies of Copper(II) Oxamide Complexes

“…An increment in inhibitory activity was noticed in O10 , by substituting the phenyl ring at para position with methoxy (IC 50 =95.7±0.51 μM). Further increase in activity was observed in O4 where substitution is done by bromo, at para position (IC 50 =92.3±0.14 μM) as reported that bromo substituted compounds may possess better inhibitory activity as compared to others [42] which may happen due to hydrophobic nature of bromine and bromine being more polarizable than hydrogen which could influence the electron density distribution within the molecule, affecting its interactions with the active site residues of the enzyme [43] . Similar behavior was observed when in O3 , the moiety was substituted at para position by chloro group, (IC 50 =88.8±0.14 μM) as shown in Figure 3.…”

Density Functional Study on the Fundamental and Valence Excited States of Dibromine in T, P, and H Clathrate Cages

“…Halogen molecules like Br 2 or Cl 2 are excellent probes of their surrounding environment. The beautiful spectroscopic experiments by Janda and Apkarian’s groups showed that the maximum absorption peak in UV–vis absorption experiments shifts in different amounts in aqueous systems. − The observed blue-shift is due to the intermolecular interactions present, from the “classical” halogen bond (XB) to some variants. − The latest diffraction experiments by Udachin et al confirmed that Cl 2 is hosted in a cage almost too small to fit in, and so it also is for Br 2 . , This result evidenced that the guest–host interactions should go beyond the weak van der Waals regime since the free diameter of the 5 12 cages is estimated at ∼5.0 Å, and the van der Waals size of dichlorine is 5.5 Å. Recently, our group showed that the stabilization of Cl 2 @5 12 , Cl 2 @5 12 6 2 , and Br 2 @5 12 6 2 is the result of a subtle balance of forces.…”