Hetero-Polar Sextuple Bond: A Relativistic Quantum Chemical Study**

Number of bonds formed by sharing an electron pair between two atoms is not restricted to one, it can go beyond four and six is the maximum. While homopolar sextuple bond in Mo₂ and W₂ has been reported, such a high bond order in heteropolar diatomics has remained elusive. In the pursuit of the sextuple bond in polar diatomics, the present study depicts the existence of such multiple bonds in Rhodium-Scandium hetero-diatom based on relativistic quantum chemical calculations. The bonding comprises of three normal electron sharing covalent bonds and three dative covalent bonds.     

Synthesis of 3‐aminomethylidenechroman‐2‐carboxamides by a Sequential One‐pot Three Component Reaction and by Post‐Passerini Condensation Modification

3‐Arylaminomethylidenechroman‐2‐carboxamide has been synthesized by a one‐pot three component reaction among 3‐formylchromone, aromatic amine, and cyclohexyl isocyanide. 3‐(N‐alkylsubstitued/unsubstituted)aminomethylidenechroman‐2‐carboxamides were synthesized by heating Passerini products derived from chromone‐3‐carbaldehyde with different aliphatic primary amines. The products obtained from the reactions of aliphatic primary amines readily form chromeno[2,3‐c]pyrrole when heated in acetic acid. Bischromanones have also been synthesized using this methodology.     

On the Mechanism of Copper(I)‐Catalyzed Azide–Alkyne Cycloaddition

The copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) reaction regiospecifically produces 1,4‐disubstituted‐1,2,3‐triazole molecules. This heterocycle formation chemistry has high tolerance to reaction conditions and substrate structures. Therefore, it has been practiced not only within, but also far beyond the area of heterocyclic chemistry. Herein, the mechanistic understanding of CuAAC is summarized, with a particular emphasis on the significance of copper/azide interactions. Our analysis concludes that the formation of the azide/copper(I) acetylide complex in the early stage of the reaction dictates the reaction rate. The subsequent triazole ring‐formation step is fast and consequently possibly kinetically invisible. Therefore, structures of substrates and copper catalysts, as well as other reaction variables that are conducive to the formation of the copper/alkyne/azide ternary complex predisposed for cycloaddition would result in highly efficient CuAAC reactions. Specifically, terminal alkynes with relatively low pK_a values and an inclination to engage in π‐backbonding with copper(I), azides with ancillary copper‐binding ligands (aka chelating azides), and copper catalysts that resist aggregation, balance redox activity with Lewis acidity, and allow for dinuclear cooperative catalysis are favored in CuAAC reactions. Brief discussions on the mechanistic aspects of internal alkyne‐involved CuAAC reactions are also included, based on the relatively limited data that are available at this point.     

Chemical data mining of the NCI human tumor cell line database

The NCI Developmental Therapeutics Program Human Tumor cell line data set is a publicly available database that contains cellular assay screening data for over 40 000 compounds tested in 60 human tumor cell lines. The database also contains microarray assay gene expression data for the cell lines, and so it provides an excellent information resource particularly for testing data mining methods that bridge chemical, biological, and genomic information. In this paper we describe a formal knowledge discovery approach to characterizing and data mining this set and report the results of some of our initial experiments in mining the set from a chemoinformatics perspective.     

Web service infrastructure for chemoinformatics

The vast increase of pertinent information available to drug discovery scientists means that there is a strong demand for tools and techniques for organizing and intelligently mining this information for manageable human consumption. At Indiana University, we have developed an infrastructure of chemoinformatics Web services that simplifies the access to this information and the computational techniques that can be applied to it. In this paper, we describe this infrastructure, give some examples of its use, and then discuss our plans to use it as a platform for chemoinformatics application development in the future.     

Euler–Poincaré Flows on <Emphasis Type="Italic">sl</Emphasis><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> Opers and Integrability

We consider the action of vector field Vect(S ¹) on the space of an sl _n - opers on S ¹, i.e., a space of nth order differential operator . This action takes the sections of Ω ^–(n–1)/2 to those of Ω ^(n+1)/2, where Ω is the cotangent bundle on S ¹. In this paper we study Euler–Poincaré (EP) flows on the space of sl _n opers, in particular, we demonstrate explicitly EP flows on the space of third and fourth order differential operators (or sl ₃ and sl ₄ opers) and its relation to Drienfeld–Sokolov, Hirota–Satsuma and other coupled KdV type systems. We also discuss the Boussinesq equation associated with the third order operator. The solutions of the sl _n oper defines an immersion in homogeneous coordinates. We derive the Schwarzian KdV equation as an evolution of the solution curve associated to Δ ⁽ⁿ⁾, we study the factorization of higher order operators and its compatibility with the action of Vect(S ¹). We obtain the generalized Miura transformation and its connection to the modified Boussinesq equation for sl ₃ oper. We also study the eigenvalue problem associated to sl ₄ oper. We discuss flows on the special higher order differential operators for all u _i = f(u,u _x ,u _xx ⋯) and its connection to KdV equation. Finally we explore a relation between projective vector field equation and generalized Riccati equations.      

Kinetic and redox characteristics of phenoxyl radicals of eugenol and isoeugenol: A pulse radiolysis study

The phenoxyl radicals of eugenol (EgOH) and isoeugenol (iEgOH) were generated by the specific one‐electron oxidant N₃^· using pulse radiolysis technique, and were characterized by their absorption spectra, decay and formation kinetics, and one‐electron reduction potential (E₇¹) values. Reactivities of eugenol phenoxyl radical with the biologically important molecule, trolox C (analogue of vitamin E, α‐tocopheral), were determined. Reactions of OH with these phenols were studied at different pHs and suitable mechanisms for these reactions were suggested. Scavenging abilities of the phenols toward highly damaging Br^·, NO₂^·, and CCl₃O₂^· radicals were evaluated. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 17–23, 2000     

pH‐Dependent Nitrotyrosine Formation in Ribonuclease A is Enhanced in the Presence of Polyethylene Glycol (PEG)

Protein nitration can occur as a result of peroxynitrite‐mediated oxidative stress. Excess production of peroxynitrite (PN) within the cellular medium can cause oxidative damage to biomolecules. The in vitro nitration of Ribonuclease A (RNase A) results in nitrotyrosine (NT) formation with a strong dependence on the pH of the medium. In order to mimic the cellular environment in this study, PN‐mediated RNase A nitration has been carried out in a crowded medium. The degree of nitration is higher at pH 7.4 (physiological pH) compared to pH 6.0 (tumor cell pH). The extent of nitration increases significantly when PN is added to RNase A in the presence of crowding agents PEG 400 and PEG 6000. PEG has been found to stabilize PN over a prolonged period, thereby increasing the degree of nitration. NT formation in RNase A also results in a significant loss in enzymatic activity.