7Li-NMR and FTIR studies of lithium, potassium, rubidium, and cesium complexes with ionophore lasalocid in solution.

Lasalocid metal salts were combined with 1 : 1 lithium and 2:2 potassium, rubidium, and cesium to form complexes. The nature of the lasolocid salt complexes was studied in a solid and chloroform by FTIR spectroscopy in the middle and far IR regions. The process of the complexation of lithium was also studied by (7)Li-NMR. In chloroform a 1 : 1 complex of lasalocid and Li(+) ions was formed. Continuous absorption was observed in the far FTIR spectrum of this complex. It indicated large Li(+) polarizability, which was due to fast fluctuations of the Li(+) ions in the multiminima potentials, in the monomeric structure. In the lasalocid salt with the other monovalent cations (K(+), Rb(+), Cs(+)) 2:2 complexes were formed in which the cations showed cation polarizability, which strongly depended on the mass and the radius of the cations.

A study of the possible and preferred site of protonation in 7-methyl-1,5,7-triazabicyclo[4,4,0]dec-5-ene by vibrational spectroscopic methods.

The normal co-ordinate analysis have been carried out for 7-methyl-1,5,7-triazabicyclo[4,4,0]dec-5-ene (MTBD) and its three possible protonated tautomeric forms. The calculations and measured infrared (IR) spectra are consistent with a tautomeric species in which the proton is attached to an imine nitrogen atom.

Model molecules for the active centre of alcoholdehydrogenases--an FT-IR study.

We synthesized a triamide of Kemp's acid with two cysteine groups and one histidine group (compound 1), and a triamide of 1,3,5-pentane tricarboxylic acid with tyrosine, histidine, and arginine molecules (compound 2). From compound 1 we obtained the hydrated Zn2+ complex, compound 3. The FT-IR spectra of various complexes of compounds 1-3 with NAD+ show no IR continua and hence, no hydrogen-bonded chains with proton polarizability are present. In the case of the complex (compounds 2 and 3 and NAD+) an intense continuum demonstrates that a hydrogen-bonded chain is formed with large proton polarizability due to collective proton motion. This proton pathway is discussed. The O atom of the nicotinamide group of NAD+ is a strong hydrogen bond acceptor. This result is discussed with regard to the catalytic mechanism.

Aspartic proteinases: Fourier transform infrared spectroscopic studies of a model of the active side.

We synthesized and studied by Fourier transform infrared spectroscopy nine monosalts of diamides as models for the active side of aspartic proteinases. One compound, the monosalt of meta-aminobenzoic acid diamide of fumaric acid (m-FUM), shows the same biological activity as pepsin with regard to the splitting of peptide bonds of the Pro-Thi-Glu-Phe-Phe(4-NO2)-Arg-Leu heptapeptide. The monosalt of m-FUM forms with oxindole a complex in which the carboxylic acid group of the monosalt of m-FUM is strongly hydrogen bonded with the O atom of the peptide bond of oxindole. When one water molecule is added to this complex, the strong field of the carboxylate group destabilizes an O-H bond of the water molecule. The distorted water molecule attacks the carbon atom of the peptide group, and the water proton transfers to the peptide N atom. Simultaneously, the C-N bond of the amide group is broken. Hence it is demonstrated that the catalytic mechanism of aspartic acid proteinases is a base catalysis. The results show that for this catalytic mechanism there are sufficient carboxylic and carboxylate groups, as well as a water molecule in the correct arrangement. It was also demonstrated with other monosalts of dicarboxylic acids that well-defined steric conditions of the carboxylic acid and the carboxylate group must be fulfilled to show hydrolytic activity with regard to oxindole molecules.

A model molecule of the hydrogen-bonded chain in the active site of bacteriorhodopsin.

We synthesized a 2-N-methylaminoethyl-tetramethylquanidine amide of Kemp's triacid (CP2). Furthermore, we added to CP2 tetrabutylammonium 4-tert-butylphenolate. The pKa value of 4-tert-butylphenol is comparable to that of tyrosine. We studied by FT-IR spectroscopy CP2 and the complex of CP2 with 4-tert-butylphenolate. This complex is a model for the hydrogen-bonded chain in the active centre of the bacteriorhodopsin molecule. An intense continuum in the FT-IR spectra demonstrates that this hydrogen-bonded chain shows large proton polarizability due to collective proton motion. As earlier demonstrated also Schiff base carboxylic acid bonds show large proton polarizability. Thus, in all these hydrogen bonds protons can easily be shifted by collective proton motion due to changes of the local electrical fields and by changes of specific interactions arising from conformational changes.

Aspartic proteinases--Fourier transform IR studies of the aspartic carboxylic groups in the active site of pepsin.

Fourier transform (FTIR) difference spectra of pepsin minus diazoacetylnorleucine methyl ester (DAN) or minus diazoacetyl-L-phenylalanine methyl ester (DAP) modified pepsin, respectively, demonstrated that Asp-215 is not deprotonated in pepsin. The FTIR difference spectrum of pepsin minus 1,2-epoxyparanitrophenoxypropane (EPNP) modified pepsin demonstrates that Asp-32 is present in pepsin as CO2- anion. The position of the v(C = O) vibration demonstrates that no (O...H...O)- hydrogen bond between Asp-215 and Asp-32 is formed. Furthermore, no H3O+ is present in the active center. Studies of the complex of pepsin with the inhibitor pepstatin prove that the inhibitor removes the water from the active site and Asp-32 becomes protonated.

Formation of disulphide bonds in the reaction of SH group-containing amino acids with trimethylamine N-oxide. A regulatory mechanism in proteins.

Two amino acids containing SH group (cysteine and homocysteine)+trimethylamine N-oxide systems were studied by FTIR and 1H NMR spectroscopy. This study demonstrates that cysteine and homocysteine ethylesters react with trimethylamine N-oxide. Immediately after mixing, SH...ON<==>S-...H+ ON hydrogen bonds with large proton polarizability are are formed. Then a reaction proceeds resulting in the formation of corresponding disulphides. Trimethylamine N-oxide is present in biological systems. Thus, our results suggest that trimethylamine N-oxide may play a regulatory role in S-S bond formation in enzymes and other proteins.