The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

Unique electronic and chemical properties of metal nanoparticles have drawn the attention of chemists, physicists, biologists, and engineers who wish to use them for the development of new generation nanodevices. Metal nanoparticles such as gold and silver show noticeable photoactivity under UV−visible irradiation as is evident from the photoinduced fusion and fragmentation processes. Binding a photoactive molecule (e.g., pyrene) to metal nanoparticle enhances the photochemical activity and renders the organic−inorganic hybrid nanoassemblies suitable for light-harvesting and optoelectronic applications. The nature of charge-transfer interaction of fluorophore with gold surface dictates the pathways with which the excited-state deactivates. Obtaining insight into energy and electron-transfer processes is important to improve the charge separation efficiencies in metal−fluorophore nanoassemblies and photocatalytic activity of metal−semiconductor composites.

https://pubs.acs.org/doi/pdf/10.1021/jp0209289

Photophysical, photochemical and photocatalytic aspects of metal nanoparticles

This critical review covers the advances made using the 4-bora-3a,4a-diaza-s-indacene (BODIPY) scaffold as a fluorophore in the design, synthesis and application of fluorescent indicators for pH, metal ions, anions, biomolecules, reactive oxygen species, reactive nitrogen species, redox potential, chemical reactions and various physical phenomena. The sections of the review describing the criteria for rational design of fluorescent indicators and the mathematical expressions for analyzing spectrophotometric and fluorometric titrations are applicable to all fluorescent probes (206 references).

Fluorescent indicators based on BODIPY

Molecular orbital theory for organic chemists

The most common approach for quantifying interactions in supramolecular chemistry is a titration of the guest to solution of the host, noting the changes in some physical property through NMR, UV-Vis, fluorescence or other techniques. Despite the apparent simplicity of this approach, there are several issues that need to be carefully addressed to ensure that the final results are reliable. This includes the use of non-linear rather than linear regression methods, careful choice of stoichiometric binding model, the choice of method (e.g., NMRvs.UV-Vis) and concentration of host, the application of advanced data analysis methods such as global analysis and finally the estimation of uncertainties and confidence intervals for the results obtained. This tutorial review will give a systematic overview of all these issues—highlighting some of the key messages herein with simulated data analysis examples.

Determining association constants from titration experiments in supramolecular chemistry

Introduction The various colors of iodine in different solvents have attracted the attention of investigators for over half a century. Beckmann’ showed that the differences are not due to any change in the molecular weight of iodine and suggested solvation as the cause of brown color. Lachman2 supported this explanation, pointing out that the solvents which give a violet color are saturated, those which give brown colors are unsaturated. He stated that small additions of alcohol to a solution of iodine in chloroform suffice to shift the color stepwise from violet to brown. Hildebrand and Glascock3 found that when iodine and an alcohol were both added to a “violet” solvent, bromoform or ethylene bromide, the molal lowering of the freezing point was considerably less than additive, indicating combination of iodine with alcohol. Furthermore, they investigated colorimetrically the equilibria of iodine with ethyl alcohol, ethyl acetate and nitrobenzene dissolved together in a “violet” solvent such as carbon tetrachloride, chloroform or carbon disulfide, and found in each case an equilibrium constant corresponding to a 1 : 1 compound. They calculated the heat of combination in one case. There followed a long series of investigations of the general problem, well summarized by Gmelin4 and in a recent review by Kleinberg and Davidson.6 But the original division of iodine solutions into two or more distinct color classes became untenable with the work of Waentig, Groh’ and \\X7alkers which showed that the position of the absorption bands of iodine solutions in the visible region moved gradually from violet to brown, the shift being only small in the case of benzene in which the color of iodine is a red-violet. We have long been curious about the chemical basis for iodine solvates. It is not a question of dipole moment, as Walkers concluded, for we have recently shown rather conclusively that the iodine solubility, which would be altered by solvation effects, bears little or no relation to the dipole moment of the solvent mole~ule .~ The alcohols are extraordinary dipoles, and their effect is readily understandable, but the case of benzene seemed

A Spectrophotometric Investigation of the Interaction of Iodine with Aromatic Hydrocarbons

Ultraviolet absorption bands of iodine in aromatic hydrocarbons

Solubility of Perfluoro-n-heptane with Benzene, Carbon Tetrachloride, Chloroform, n-Heptane and 2,2,4-Trimethylpentane

A RECENT communication by Bayliss1, commenting upon the spectroscopic evidence for specific, 'chemical' interaction between iodine and benzene obtained by us2, quite properly includes the remark that such spectroscopic evidence should be "interpreted with caution", and he advanced a formula for the shift of the ultra-violet absorption band of iodine toward the red in terms of its polarizability, dipole-strength, and the refractive index of the solvent. We ourselves, at the outset of our investigation, were prepared to find the influence of the solvent to be general or physical rather than specific; but the evidence we obtained later3 has all been in favour of a definite 1 : 1 molecular complex. Excellent constancy was obtained for the constant of the equilibrium, I2 + A⇄I2.A in a 'violet' (neutral) solvent, where A denotes an aromatic hydrocarbon. Moreover, the interaction is stronger in the case of the more basic mesitylene than in benzene, whereas, according to the formula of Bayliss, it should be weaker.

/pdf/interaction-of-iodine-with-aromatic-hydrocarbons-36pk4a6a4r.pdf

H. A. Benesi

Papers

A Spectrophotometric Investigation of the Interaction of Iodine with Aromatic Hydrocarbons

Ultraviolet absorption bands of iodine in aromatic hydrocarbons

Solubility of Perfluoro-n-heptane with Benzene, Carbon Tetrachloride, Chloroform, n-Heptane and 2,2,4-Trimethylpentane

Interaction of Iodine with Aromatic Hydrocarbons

Solubility of Iodine in Ethyl Alcohol, Ethyl Ether, Mesitylene, p-Xylene, 2,2-Dimethylbutane, Cyclohexane and Perfluoro-n-heptane