Inverted porphyrins and expanded porphyrins: An overview

Porphyrins and metallopophyrins have attracted the attention of chemists for the past 100 years or more owing to their widespread involvement in biology. More recently, synthetic porphyrins and porphyrin-like macrocycles have attracted the attention of researchers due to their diverse applications as sensitizers for photodynamic therapy, MRI contrasting agents, and complexing agents for larger metal ions and also for their anion binding abilities. The number of π-electrons in the porphyrin ring can be increased either by increasing the numberof conjugated double bonds between the pyrrole rings or by increasing the number of heterocyclic rings. Thus, 22π sapphyrins, 26π rubyrins, 30π heptaphyrins, 34π octaphyrins and higher cyclic polypyrrole analogues containing 40π, 48π, 64π, 80π and 96π systems have recently been reported in the literature. These macrocycles show rich structural diversity where normal and different kinds of inverted structures have been identified. In this review, an attempt has been made to collect the literature of the inverted porphyrins and expanded porphyrins reported until December 2001. Since themeso aryl expanded porphyrins have tendency to form both inverted and non-inverted structures more emphasis has been given tomeso aryl expanded porphyrins.     

Conformational flexibility of longifolene

The flexibility of the bicyclo[2.2.1]heptane-based tricyclic bridged system in longifolene is analysed based on x-ray structural data. In this context, the molecular structure of three differently substituted longifolenes has been analysed. The highly substituentdependent conformation provides scope for the synthesis of a variety of commercially oriented products. NCL Communication Number 3459     

Kinetics and mechanism of sulphurous acid oxidation by hexachloroiridate(IV) in hydrochloric acid

Summary The reaction between sulphurous acid and hexachloroiridate(IV) appears to take place through the formation of an intermediate complex followed by decomposition to give oxidation products. The rate is retarded as the hydrogen ion concentration increases. Thermodynamic parameters associated with the equilibrium step as well as with the slowest step have been calculated. The probable mechanism of the reaction is discussed.     

The method of successive updated iterated defect correction and its application to second kind volterra integral equations

We present a new method for the numerical solution of Volterra integral equations of the second kind. This method is based on the technique of Iterated Defect Correction. Numerical examples are given to demonstrate the power of our method.Based on his research at Indian Institute of Technology, Kanpur, India.     

Ligand effect in epoxidatidns by hydroperoxides using molybdenum catalyst: epox idation of 3-carene

Epoxidation of (+)-3-carene with pinane hydroperoxide in presence of various transition metal catalysts, has been evaluated as a preparative method for (+)-3α,4α-epoxycarane. Catalysts based on Mo(VI) were found to be most suitable. A distinct ligand effect was noted for this oxidation and a plausible rationale is put forward.     

Barriers and dispersal surfaces in minimum-time interception

Dispersal points and points on the barrier are located for a class of pursuit-evasion and interception problems. These points are determined by constructing cross sections of the isochrones, and hence by obtaining the barrier, dispersal, and control-level surfaces. The method is illustrated through examples from minimum-time interception of a target moving in a straight line in a horizontal plane.The authors are indebted to F. Neuman, M. Sidar, J. Shinar, H. Erzberger, and G. Leitmann for their comments. The first author wishes to acknowledge the financial support of the National Research Council.     

XANES and EXAFS of copper compounds: Studies of copper carboxylates with metal-metal bonds and of the complex formed by Pseudomonas aeruginosa

X-ray absorpion near edge structure (xanes) of copper compounds with copper in 1⁺, 2⁺ and 3⁺ states has been studied. Extended x-ray absorption fine structure (exafs) has been employed to determine bond distances and coordination numbers in several model copper compounds. Employing bothxanes andexafs, the structure of the copper complex formed by the micro-organismPseudomonas aeruginosa has been shown to be square-planar with the Cu-O distance close to that in cupric glucuronates and cupric acetylacetonate.exafs has been shown to be useful for studying metal-metal bonds in copper carboxylates. Communication No. 228 from the Solid State and Structural Chemistry Unit