Volume 76, Issue 10

Charge-transfer-to-solvent (CTTS) reactions represent the simplest possible electron-transfer reaction. One of the reasons that such reactions have become the subject of recent interest is that transfer of a CTTS electron from an atomic anion to the solvent involves only electronic degrees of freedom, so that all the dynamics involved in the reaction are those of the solvent. Thus, CTTS reactions provide an outstanding spectroscopic window on the dynamics of the solvent during electron transfer. In this paper, we will review our recent work studying the CTTS reaction of the sodium anion, (Na − or sodide) in a series of ether solvents. By comparing the results of ultrafast spectroscopic pump/probe experiments and mixed quantum/classical molecular dynamics simulations, we work to build a molecular-level picture of how solvent motions control the dynamics of CTTS, including the distance to which the electron is ejected and the rates of both the forward and back electron-transfer reactions.

The macrocyclic cyclodextrins (enzymic conversion products of starch) were discovered in 1891, and the structures were elucidated in the mid-1930s. Their industrial significance become obvious in the 1970s, and by now thousand of tons of the three cyclodextrins (alpha-, beta-, and gamma-CD) and of their chemical derivatives and inclusion complexes are produced industrially. The outer surface of these doughnut-shaped molecules is hydrophilic, but they possess an axial open cavity, which is of hydrophobic character and capable of including other apolar molecules (or their moiety) in case of geometric compatibility. This is the essence of molecular encapsulation by inclusion complex formation.

The combination of metallosupramolecular modules (MEMOs) as functional and amphiphiles as structural components is presented in detail to illustrate our current understanding of encapsulation using surfactants, lipids, and dendrimers. The simplicity of fabrication and the availability of the starting components allow this technique as an attractive tool to create new nanoscale molecular materials. The interaction of amphiphiles and MEMOs occurs spontaneously and is driven by the release of counterions as well as electrostatic and hydrophobic interactions.

The macro acidity constants valid for aqueous solutions of several adenine, guanine,and hypoxanthine derivatives are summarized. It is shown how the application of the corresponding constants, e.g., for 7,9-dimethyladenine, allows a quantification of the intrinsic acidic properties of the (N1)H 0/+ and (N7)H + sites via micro acidity constants, and how to use this information for the calculation of the tautomeric ratios regarding the monoprotonated species, that is, N7-N1*H versus H*N7-N1, meaning that in one isomer H + is at the N1 site and in the other at N7. It is further shown that different metal ions coordinated to a given site, e.g., N7, lead to a different extent of acidification, e.g., at (N1)H; the effect decreases in the series Cu 2+ >Ni 2+ >Pt 2+ ~Pd 2+ . Moreover, the application of micro acidity constants proves that the acidifications are reciprocal and identical. This means, Pt 2+ coordinated to (N1) –/0 sites in guanine, hypoxanthine, or adenine residues acidifies the (N7)H + unit to the same extent as (N7)-coordinated Pt 2+ acidifies the (N1)H 0/+ site. In other words, an apparently increased basicity of N7 upon Pt 2+ coordination at (N1) –/0 sites disappears if the micro acidity constants of the appropriate isocharged tautomers of the ligand are properly taken into account. There is also evidence that proton–proton interactions are more pronounced than divalent metal ion–proton interactions, and that these in turn are possibly larger than divalent metal ion–metal ion interactions. The indicated quantifications of the acid-base properties are meaningful for nucleic acids including the formation of certain nucleobase tautomers in low concentrations, which could give rise to mutations.

The concept of a macroscopic device can be extended to the molecular level by designing and synthesizing (supra)molecular species capable of performing specific functions. Molecular devices need energy to operate and signals to communicate with the operator. The energy needed to make a device work can be supplied as chemical energy, electrical energy, or light. Luminescence is one of the most useful techniques to monitor the operation of molecular-level devices. The extension of the concept of a device to the molecular level is of interest, not only for basic research, but also for the growth of nanoscience and the development of nanotechnology. In this article, some of the most recent experiments performed in our laboratory will be reviewed.

Solutions of the zwitterionic betaine dye 4-(2,4,6-triphenylpyridinium-1-yl)-2,6-di- phenylphenolate are solvatochromic, thermochromic, piezochromic, and halochromic. That means the position of its longest-wavelength intramolecular charge-transfer absorption band depends on solvent polarity, solution temperature, external pressure, and the nature and concentration of added salts. The extraordinarily large negative solvatochromism of this standard betaine dye has been used to establish UV/vis spectroscopically an empirical scale of solvent polarity, called E T (30), respectively E T N scale, meanwhile known for many organic solvents and solvent mixtures. In this review, the solvatochromic properties of some new hydrophilic and lipophilic betaine dyes with better solubility in water (respectively, nonpolar solvents), as well as some recent applications of these betaine dyes in various fields of interest [e.g., microheterogeneous (micellar) and polymer solutions, chemical sensors, as well as surface polarity of silicas, aluminas, and cellulose derivatives] are described.

This report describes the principles underlying a comprehensive electronic database that contains data essential for calculation of analytical results from neutron-activation analysis (NAA) and that is available through IUPAC. The method used is a comparator method called the k 0 method, where k 0 is a dimensionless factor which is experimentally measured with high accuracy for more than 130 isotopes and which makes use of the gamma spectroscopic line for an analyte isotope relative to a gold comparator. The database contains recommended values for k 0 and other relevant nuclear data.

This workshop has been organized to cover various quantitative structure-activity relationship (QSAR) and computer aided procedures currently carried out for the prediction of the endocrine activity of unknown compounds. Each of the procedures has own scope as well as limitations. It seems inappropriate to consider that a single quantitative prediction model derived from each of these procedures could solve the entire issue. Because the model building is highly dependent on the data/knowledge about endocrine activity of a large number of existing compounds accumulated to date and the data/knowledge are growing constantly, the model has a destiny to be amended “forever ”as the structure-activity data of newly synthesized compounds are accumulated. The skepticism about in silico and QSAR procedures put forward in the past is likely to be cleared at least to some extent if not entirely by participating in this workshop.