Quantitative structure-activity and structureproperty relationship (QSAR/QSPR) studies are unquestionably of great importance in modern chemistry and biochemistry. The concept of QSAR/QSPR is to transform searches for compounds with desired properties using chemical intuition and experience into a mathematically quantified and computerized form. Once a correlation between structure and activity/property is found, any number of compounds, including those not yet synthesized, can be readily screened on the computer in order to select structures with the properties desired. It is then possible to select the most promising compounds to synthesize and test in the laboratory. Thus, the QSAR/QSPR approach conserves resources and accelerates the process of development of new molecules for use as drugs, materials, additives, or for any other purpose. While it is not easy to find successful structureactivity/property correlations, the recent exponential growth in the number of papers dealing with QSAR/ QSPR studies clearly demonstrates the rapid progress in this area. To obtain a significant correlation, it is crucial that appropriate descriptors be employed, whether they are theoretical, empirical, or derived from readily available experimental characteristics of the structures. Many descriptors reflect simple molecular properties and thus can provide insight into the physicochemical nature of the activity/ property under consideration. Recent progress in computational hardware and the development of efficient algorithms has assisted the routine development of molecular quantummechanical calculations. New semiempirical methods supply realistic quantum-chemical molecular quantities in a relatively short computational time frame. Quantum chemical calculations are thus an attractive source of new molecular descriptors, which can, in principle, express all of the electronic and geometric properties of molecules and their interactions. Indeed, many recent QSAR/QSPR studies have employed quantum chemical descriptors alone or in combination with conventional descriptors. Quantum chemistry provides a more accurate and detailed description of electronic effects than empirical methods.1 Quantum chemical methods can be applied to quantitative structure-activity relationships by direct derivation of electronic descriptors from the molecular wave function. In many cases it has been established that errors due to the approximate nature of quantum-chemical methods and the neglect of the solvation effects are largely transferable within structurally related series; thus, relative values of calculated descriptors can be meaningful even though their absolute values are not directly applicable.2 Moreover, electronic descriptors derived from the molecular wave function can be also partitioned on the basis of atoms or groups, allowing the description of various molecular regions separately. Most work employing quantum chemical descriptors has been carried out in the field of QSAR rather than QSPR, i.e. the descriptors have been correlated with biological activities such as enzyme inhibition activity, hallucinogenic activity, etc.3-6 In part this has been because, historically, the search for quantitative relationships with chemical structure started with the development of theoretical drug design methods. Quantum-chemical descriptors have also been reported to correlate the reactivity of organic compounds, octanol/water partition coefficients, chromatographic retention indices, and various physical properties of molecules.7-11 The present article reviews applications of quantum chemical descriptors in the development of QSAR/QSPR dealing with the chemical, physical, biochemical, and pharmacological properties of compounds.

http://depa.fquim.unam.mx/amyd//archivero/TrabajoFINAL2013-1_21514.pdf

Quantum-Chemical Descriptors in QSAR/QSPR Studies

High-efficiency fluorescent organic light-emitting diodes have been realized by employing custom-designed molecules that make it possible to convert non-radiative triplet states into radiative singlet states.

Organic light-emitting diodes employing efficient reverse intersystem crossing for triplet-to-singlet state conversion

Electrostatic Basis for Enzyme Catalysis

Helicenes: synthesis and applications.

Nucleic acids are electroactive species producing well developed voltammetric peaks on the mercury electrode sensitively reflecting small damages to the double-helical DNA. Nucleic acid-modified electrodes can easily be prepared by immersing the electrode into a 5 μL drop of the DNA and/or RNA solution. Such nucleic acid-modified electrodes strongly decrease the quantities of DNA and RNA required for analysis. They offer a number of other advantages which may be of use in biochemical and molecular biological research. Past, present and future aspects of nucleic acid voltammetric analysis are reviewed.

From polarography of DNA to microanalysis with nucleic acid-modified electrodes

1,3,3,5-Tetraarylpentane-1,5-diones 2 and 5 react with tetraphosphodecasulfide in xylene at elevated temperature to give the corresponding 2,4,4,6-tetraaryl-4H-thiopyrans 4 and 7. The mechanism of this transformation involves a fast initial step of dehydration of 2 and 5 to 2,4,4,6-tetraaryl-4H-pyrans 3, followed by a slower transformation to the 4H-thiopyran analogues 4. Using 2D NMR techniques, a complete assignment of the 1H and 13C NMR spectra of the 1-oxide and 1,1-dioxide analogues of 4(1, X = SO and SO2) as well as of compounds 3c, j, I, m, 4a–m, 6(the pyran analogue of 7) and 7 has been carried out. Compounds 4 and 7 undergo a reversible photochemical colour change after UV illumination. The maxima of the new absorption bands are situated at 540–660 nm. The non-exponential time dependence of the photodecolouration of 4a in the solid state is analysed in terms of dispersive first-order reaction kinetics. Dioxygen accelerates the decolouration process; the half-life at 299 K lies between 6600 s in air and several days in a vacuum (10–3 Pa). The trapping of photoproducts 10a, 10e and 11a enables us to postulate the whole photolysis sequence.

Novel preparation and photochromic properties of 2,4,4,6-tetraaryl-4H-thiopyrans

Theoretical substituent effects upon the acidity of the title compounds were investigated using STO-3G basis sets augmented by diffuse functions for all oxygen atomic centers of the probe groups. The results are discussed in connection with the available gas-phase data within a novel conception of attractive and repulsive substituent effects.

An ab initioLCAO‐MO study of the substituent effect in benzenoid systems: Meta‐ and para‐substituted benzoic acids

Electrochemical oxidation of 3,5-difunctional 1,4-dihydropyridine derivatives

Results of a study on the photochromic behaviour of various 2,4,4,6-tetraphenyl-4 H -pyrans ( 1 ), 2,4,4,6-tetraphenyl-1,4-dihydropyridines ( 2 and 3 ) and 1,2,4,4,6-pentaphenyl-1,4-dihydropyridines ( 4 ) are reported. Most investigated materials undergo a photochromic change in the solid state after illumination with UV light. The maxima of the new absorption bands are located in the range 545–630 nm, depending on the chemical structure of the substituents. The non-exponential time dependence of photochromic decolouration of the model compound, 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropyridine ( 3a ), is analysed in terms of a dispersive first-order reaction, i.e. is described by the formula exp(− t α ), where α is the dispersion parameter.

Josef Kuthan

Papers

Novel preparation and photochromic properties of 2,4,4,6-tetraaryl-4H-thiopyrans

An ab initioLCAO‐MO study of the substituent effect in benzenoid systems: Meta‐ and para‐substituted benzoic acids

Electrochemical oxidation of 3,5-difunctional 1,4-dihydropyridine derivatives

Solid state photochromism of 2,4,4,6-tetraphenyl-4H-pyran and 1,4-dihydropyridine derivatives

Contribution to the study of cyclocondensations of cyanoacetic acid derivatives with benzylideneacetophenone