Tryptophan complexes

First, the pH-dependence of the enantioselectivity of the reaction between 3.8c and 3.9 catalysed by the copper(L-tryptophan) complex has been studied. Above pH 5 the enantioselectivity reaches a plateau value (Figure 3.3). The diminished enantioselectivities observed at lower pH most likely... 

Figure 3.5. Gibbs energies of complexation of 3.8a-g to the copper(II)(Lr tryptophan) complex versus those for complexation to copper aquo ion.

An equilibrium constant for binding of 3.8c to the nickel(II)(L-tryptophan) complex of 805 M has been obtained, compared to 530 M in the presence of glycine... 

Batyaev I, Fogileva R. Thermodynamics of tryptophan complexation with rare earth elements. Zh Neorg Khim 1976 21 1199-1201. 

The trp operon controls the production of tryptophan biosynthetic enzymes at two levels, depending on the intracellular concentrations of tryptophan. When tryptophan levels are high, Trp repressor-tryptophan complexes are formed and Trp repressor binding to the trp operon inhibits transcription. A second level of control is called attenuation and it involves the premature termination of transcription when TRP-tRNATrp is abundant and a termination structure is formed, resulting in the disengagement of RNA polymerase from the DNA. 

Fig. 14.21. a Tryptophan environment in ternary complex of tryptophan, the tryptophan repressor, and a fragment of DNA, showing hydrogen bonds between tryptophan and both macromolecules, b Attempts to model interaction between the observed indole propionate/tryptophan complex and DNA suggest that the indole propionate antagonist interferes with DNA interaction... 

Roller, N.C. Oomens, J. Dunbar, R.C. IRMRD spectroscopy of metal-ion/tryptophan complexes. Phys. Chem. Chem.Phys. 2006, 8, 2744—2751. 

Verkerk UH, Zhao JP, Saminathan IS, Lau JKC, Oomens J, Hopkinstm AC, Sin KWM (2012) Infrared multiple-photon dissociation spectroscopy of tiipositive ions lanthanum-tryptophan complexes. Inorg Chem 51 4707-4710... 

Sensitivity levels more typical of kinetic studies are of the order of lO molecules cm . A schematic diagram of an apparatus for kinetic LIF measurements is shown in figure C3.I.8. A limitation of this approach is that only relative concentrations are easily measured, in contrast to absorjDtion measurements, which yield absolute concentrations. Another important limitation is that not all molecules have measurable fluorescence, as radiationless transitions can be the dominant decay route for electronic excitation in polyatomic molecules. However, the latter situation can also be an advantage in complex molecules, such as proteins, where a lack of background fluorescence allow s the selective introduction of fluorescent chromophores as probes for kinetic studies. (Tryptophan is the only strongly fluorescent amino acid naturally present in proteins, for instance.)... 

Crystal stmctures of complexes of copper(II) with aromatic amine ligands and -amino acids " " and dipeptides" have been published. The stmctures of mixed ligand-copper complexes of L-tryptophan in combination with 1,10-phenanthroline and 2,2 -bipyridine and L-tyrosine in combination with 2,2 -bipyridine are shown in Figure 3.2. Note the subtle difference between the orientation of the indole ring in the two 1,10-phenanthroline complexes. The distance between the two... 

Hyde, C.C., et al. Three-dimensional structure of the tryptophan synthase az pz multienzyme complex from Salmonella typhimurium. J. Biol. Chem. 263 17857-17871, 1988. 

A method that has been the standard of choice for many years is the Lowry procedure. This method uses Cn ions along with Folin-Ciocalteau reagent, a combination of phosphomolybdic and phosphotnngstic acid complexes that react with Cn. Cn is generated from Cn by readily oxidizable protein components, such as cysteine or the phenols and indoles of tyrosine and tryptophan. Although the precise chemistry of the Lowry method remains uncertain, the Cn reaction with the Folin reagent gives intensely colored products measurable spectrophotometrically. 

The structure of the complex of (S)-tryptophan-derived oxazaborolidine 4 and methacrolein has been investigated in detail by use of H, B and NMR [6b. The proximity of the coordinated aldehyde and indole subunit in the complex is suggested by the appearance of a bright orange color at 210 K, caused by formation of a charge-transfer complex between the 7t-donor indole ring and the acceptor aldehyde. The intermediate is thought to be as shown in Fig. 1.2, in which the s-cis conformer is the reactive one. 

---