Chiral luminescence quenching

Trigonal ML3 metal complexes exist as optically active pairs. The complexes can show enantiomeric selective binding to DNA and in excited state quenching.<34) One of the optically active enantiomers of RuLj complexes binds more strongly to chiral DNA than does the other enantiomer. In luminescence quenching of racemic mixtures of rare earth complexes, resolved ML3 complexes stereoselectively quench one of the rare earth species over the other. 35-39 Such chiral recognition promises to be a useful fundamental and practical tool in spectroscopy and biochemistry. 

Such chiral luminescent dendrimers, whose fluorescence is quenched significantly more strongly by one enantiomer of a chiral guest molecule than by its mirror-image counterpart, would be of interest for rapid determination of the... 

The stereoselective luminescence quenching of the MLCT excited A- [Ru(bpy)3] was also carried out in water (I = 0.01 mol dm ) with the different chiral viologen derivatives by Tsukahara and collaborators [22]. In chiral viologens, l,r-bis(l-phenylethylcarbamoylmethyl)-4,4 -bipyridinium (OAV ), l,l -bis(l-naphthylethylcarbamoylmethyl)-4,4 -bipyridinium (POAV " ), and 1-(1 -phenylethyl-carbamoy Imethyl)-1 -( 1 -naphthylethylcarbamoylmethyl)-4,4 -bipyridinium (NPOAV " ), the optically active groups, are introduced to the 1,1 -positions through the amido group, as shown in Scheme 6. 

A study has been made of the emission of some related Tb and Eu macrocylic complexes, immobilized in a sol-gel glass, which is made pH-dependent either by perturbing the energy of the aryl singlet or triplet state, or by modulating the degree of quenching of the lanthanide excited state. The effect of bicarbonate chelation on the polarized luminescence from chiral... 

A particularly interesting paper deals with chiral discrimination in electronic energy transfer processes between dissymmetric metal complexes in solution . Time resolved luminescence measurements show that enantioselective excited state quenching occurs. 

There is an impressive battery of spectroscopic techniques available for probing interactions between metal complexes and DNA. The oldest of these, UV/vis spectroscopy, is still one of the most sensitive ways to analyze dye-DNA interactions. For chiral metal complexes, circular dichroism is an invaluable tool. Fluorescence spectroscopy has in particular made great strides in recent years with respect to these applications, and aside from the measurement of simple emission from an excited metal complex, one can utilize emission polarization, luminescence lifetimes, and differential fluorescence quenching to obtain still more information about the environment about a metal complex. The application of ruthenium complexes, in particular, to developing probes for DNA, has been initiated in our laboratory and we focus here on some of its applications. 

Meskers SCJ, Dekkers HPJM (2001) Enantioselective quenching of luminescence molecular recognition of chiral lanthanide complexes by biomolecules in solution. J Phys Chem A... 

For the simple model enantiopure systems described above, it was concluded that the time dependence of the CPL and total luminescence were identical, and, therefore, the dissymmetry ratio contained no dynamic molecular information. This, of course, would not be the case if intramolecular geometry changes, that would effect the chirality of the molecular transitions, were occurring on the same time scale as emission. However, no such examples of this type of study have yet appeared. Time-resolved CPL measurements have been useful in the study of racemic mixtures of lanthanide complexes in which racemi-zation or excited state quenching is occurring on the same time scale as emission. 

Meskers SCJ, Dekkers HPJM. Enantioselective Quenching of Luminescence Molecular Recognition of Chiral Lanthanide Complexes by Biomolecules in Solution. J Phys Chem A 2001 105 4589 599. 

Metal-centered circularly polarized luminescence (CPL) can also be observed for rare earth complex. Since the luminescence from a chiral rare earth complex is circularly polarized, the chirality of the excited states can be determined. Most reported CPL studies have dealt with luminescent Eu " " and Tb + complexes. Racemic Tb " " complex 16 generates non-racemic excited states upon interaction with chiral species. Its CPL signals are enantioselectively quenched by biological vitamin B12 derivatives (Meskers and Dekkers, 2001), cytochrome c... 

---