Steric and Electronic Effects, Enantiospecificity, and Reactive Orientation in DNA Binding/Cleaving by Substituted Derivatives of [SalenMn(III)](+)

Twenty-six derivatives of [SalenMn(III)](+) (1) bearing halogen, nitro, amino, ether, alkyl, or aryl substituents on the aromatic rings and/or at the imine positions or containing 1,3-propylene-, 1,2-phenylene-, 1,2-cyclohexane-, or 1,2-diphenylethylenediamine in place of ethylenediamine as the bridging moiety have been synthesized. The DNA binding/cleaving properties of these complexes in the presence of terminal oxidants have been examined using DNA affinity cleaving techniques. Active derivatives produced DNA cleavage from the minor groove at sites containing multiple contiguous A:T base pairs. For aryl-substituted derivatives, DNA cleavage efficiency was found to vary with both the identity and position of attachment of substituents. The precise patterns of cleavage at A:T target sites varied with the position of attachment of substituents, but not with the identity of the substituents. The results suggest that substituents alter specificity through both steric and electronic effects. The 3,3'-difluoro and -dichloro derivatives produced cleavage patterns that match those of the parent complex, suggesting that the activated form of 1 produces cleavage from an orientation in which the concave edge of the complex faces away from the floor of the DNA minor groove. Bridge modifications yield complexes with reduced DNA cleaving activity relative to 1. DNA cleaving efficiency was found to vary with both the structure and stereochemistry of the bridge. Cleavage efficiency for the complex derived from (R,R)-cyclohexanediamine was 5 times greater than that for the (S,S) enantiomer. Cleavage patterns produced by the enantiomeric complexes at A:T rich target sites were different, demonstrating enantiospecific recognition and cleavage of right-handed double-helical DNA.     

Y-branch - the key component for crosstalk reduced optical switches: modelling analysis

A novel design method for switching devices is demonstrated based on waveguide structures with Y-branches and abrupt waveguide changes as key elements. A combination of BPM calculation and eigenmode analysis is shown to be a promising tool to obtain deep insight into the physical mode behaviour. Based on the analysis, a mode converter to match the eigenmodes in amplitudes and phase can be developed and introduced as a correcting device. This method is demonstrated for the crosstalk compensation of a digital switch (DOS) and a Δβ-reversal switch. A crosstalk of about −20 dB can be reduced to −40 dB by this method. This revised version was published online in November 2006 with corrections to the Cover Date.     

SYNGRAT,an electrooptically controlled tunable filter with a synthesized grating structure

A new design for a single-stage filter, calledsyn thesizedgrat ing structure (SYNGRAT), is presented and investigated theoretically. It is shown that, even for weak electrooptical effects, the tuning range can be as high as 450 channels for a channel separation of 1 nm. The electrooptically synthesized grating structure gives full control of the filter characteristics in terms of channel separation, side-lobe suppression and coupling efficiency over a very large tuning range. Efficient side-lobe suppression can be used to reduce the crosstalk. This concept gives new freedom of functionality and flexibility.