Chiral probe experiment

Chrominm(III) and Cobalt(III) Nucleotide Complexes. Coordination isomers of Cr(III)- and Co(III)-nucleotides can be separated and used to test for specificity. Since Cr(III) is diamagnetic, EPR and NMR experiments can supplement the chirality probes . ... 

Cyclizable, chiral and dehalogenation probe compounds have been successfully used to detect the occurrence of ET during the addition reactions of Grignard and other reagents. However, no such probe experiment has been examined for lithium reagents. 

P, Si, some metals) can be prepared in chiral form and do invite the use of standard techniques.( ) However, many important displacement reactions take place at mono- or divalent reaction centers, where there is no possibility of using a chiral probe of mechanism. In this paper, we report the results of experiments designed to probe the preferred geometry and mechanism of radical displacements at divalent sulfur, a reaction center characterized by a plane of symmetry. Further, the technique is general and can presumably be used to study the geometries of other displacement reactions at centers which are inherently achiral or cannot be easily prepared in chiral form.(2)... 

McGown and co-workers have recently described a new instrumental approach for FDCD measurements that is capable of individually resolving multiple chiral fluorophores in complex mixtures [31-33]. As has been pointed out [31], CD measurements, and consequently FDCD measurements provide information about the average chiral characteristics of the sample under study. By introducing lifetime resolution into the FDCD experiment, identical fluorophores residing in different chemical environments can be resolved by measuring the differences in their excited state lifetimes. As has been demonstrated, lifetime analysis is a very powerful tool for probing complex systems and the chemical characteristics which one can differentiate by such an approach can be extremely subtle. 

FDCD measurements, and a basic theoretical formalism for this technique, were first reported by Turner, Tinoco and Maestre in 1974 [5]. In this experiment one uses the selectivity and sensitivity of luminescence measurements to probe the local chiral environment of fluorescent chromophores. The ultimate goal in many applications of FDCD is to relate the observed differential fluorescence signal to the conventional CD measurement. In certain multi-component absorbing systems this procedure may be difficult. This technique is sometimes applied to systems for which CD measurements are impossible or very difficult. FDCD, like CPL and other polarization sensitive techniques, is not immune to troublesome background and noise problems, and these will be discussed in Section 3. The only detailed discussion of the applicability of FDCD measurements, and other characteristics of the technique has been presented by Turner in 1978 [6]. In this chapter we will also list some of the more recent applications of FDCD. 

Rather than presenting a review of all the possible applications of CPL spectroscopy as a selective probe of chiral structure, we will focus our discussion in this section on three specific experiments that, we believe, illustrate the kinds of unique information that may be obtained from this technique. These three studies will all be concerned with CPL from optically active lanthanide complexes of approximate D3 symmetry. Almost all of these particular CPL measurements have... 

The chiral samples of malonyl-CoA were then used to probe the steric course of fatty acid biosynthesis. Again, the experiment was complicated by tritium exchange during the incubation, both before and after the Claisen condensation step, resulting in 51% tritium retention from the S isomer and 23% tritium retention from the R isomer. Fatty acid biosynthesis involves Claisen condensation of malonyl-CoA with an acyl-CoA ester of 2 n carbon chain length to... 

In order to obtain independent evidence for the involvement of the cyclodextrin cavity, fluorescence measurements were carried out for copper(II) ternary complexes with L- or D-tryptophan. In fact, the fluorescence spectrum of tryptophan has already been shown to be sensitive to the polarity of the microenvironment in which it is located and has been used in many studies as a probe for the conformation of proteins and peptides [53]. As for many fluorophores, the indole fluorescence of Trp is quenched by the copper(II) ion this effect has been used as a measure of the stability constants of copper(II) complexes [54, 55]. In a recent work, it has been shown that the fluorescence of dansyl derivatives of amino acids undergo enantioselective fluorescence quenching by chiral copper(n) complexes and that fluorescence measurements can be used for the study of enatioselectivity in the formation of ternary complexes in solution [56]. Bearing this in mind, we performed the same type of experiments by adding increasing amounts of the [Cu(CDhm)] + complex to a solution of D- or L-tryptophan [36]. The fluorescence titration curve shows that the artificial receptor inhibits the indole... 

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