A density functional study on iodine dioxide–water complexes

Evolutionary roots of iodine and thyroid hormones in cell-cell signaling

In vertebrates, thyroid hormones (THs, thyroxine, and triiodothyronine) are critical cell signaling molecules. THs regulate and coordinate physiology within and between cells, tissues, and whole organisms, in addition to controlling embryonic growth and development, via dose-dependent regulatory effects on essential genes. While invertebrates and plants do not have thyroid glands, many utilize THs for development, while others store iodine as TH derivatives or TH precursor molecules (iodotyrosines)-or produce similar hormones that act in analogous ways. Such common developmental roles for iodotyrosines across kingdoms suggest that a common endocrine signaling mechanism may account for coordinated evolutionary change in all multi-cellular organisms. Here, I expand my earlier hypothesis for the role of THs in vertebrate evolution by proposing a critical evolutionary role for iodine, the essential ingredient in all iodotyrosines and THs. Iodine is known to be crucial for life in many unicellular organisms (including evolutionarily ancient cyanobacteria), in part, because it acts as a powerful antioxidant. I propose that during the last 3-4 billion years, the ease with which various iodine species become volatile, react with simple organic compounds, and catalyze biochemical reactions explains why iodine became an essential constituent of life and the Earth's atmosphere-and a potential marker for the origins of life. From an initial role as membrane antioxidant and biochemical catalyst, spontaneous coupling of iodine with tyrosine appears to have created a versatile, highly reactive and mobile molecule, which over time became integrated into the machinery of energy production, gene function, and DNA replication in mitochondria. Iodotyrosines later coupled together to form THs, the ubiquitous cell-signaling molecules used by all vertebrates. Thus, due to their evolutionary history, THs, and their derivative and precursors molecules not only became essential for communicating within and between cells, tissues and organs, and for coordinating development and whole-body physiology in vertebrates, but they can also be shared between organisms from different kingdoms.

Experimental and theoretical study of substituent effects of iodonitrobenzenes

The electronic structures and substituent effects of o-, m-, and p-iodonitrobenzene have been studied by ultraviolet photoelectron spectroscopy (UPS). The observed bands were interpreted on the basis of empirical arguments and theoretical calculations. The analysis of electronic effects of the donor/acceptor substituent groups is essential for the reliable assignment of the observed photoelectron spectra. The investigation of pi- and n-orbital ionization potentials enabled us to describe the correlation between substituent effects and the relative reactivities of the iodonitrobenzenes. It was found that the energy order of the pi(2) and n(II) parallel orbitals is reversed as a result of the combined influence of the electron-withdrawing nitro group and the electron-donating iodine atom. Distinct changes of the pi and n bands occur in o-iodonitrobenzene. This characteristic depends on the conjugation between the pi orbitals of the benzene ring and the nitro group and the interaction of in-plane lone pairs of iodine and one of the oxygen atoms of the nitro group in the adjacent position. This might contribute to the high reactivity of o-iodonitrobenzene in a number of reactions.