Condensation dynamics of the L-Pro-L-Phe and L-Hyp-L-Phe binary mixtures in solution

Impact of D2O on the peptidization of L-alanine

This is our fifth consecutive study carried out in an order to collect experimental evidence on the impact of heavy water (D2O) on the spontaneous peptidization of proteinogenic α-amino acids and this time its subject matter is L-alanine (L-Ala). Our four earlier studies have been focused on the two sulfur-containing α-amino acids (i.e., L-cysteine (L-Cys) and L-methionine (L-Met)), and on two structurally related α-amino acids (i.e., L-proline (L-Pro) and L-hydroxyproline (L-Hyp)). It seemed interesting to assess the effect exerted by D2O on L-Ala, the simplest chiral (endogenous and proteinogenic) α-amino acid with as low molar weight, as 89.09 g mol−1 only. As analytical techniques, we used high-performance liquid chromatography with the diode array detection (HPLC–DAD), mass spectrometry (MS), and scanning electron microscopy (SEM). The obtained results make it clear that the impact of heavy water on the dynamics of the spontaneous peptidization of L-Ala is even stronger than with the four other α-amino acids discussed earlier (although in all five cases, heavy water significantly hampers spontaneous oscillatory peptidization). Unlike in the four previous cases, though, the solubility of L-Ala in pure D2O is quite low and it takes twice as much time to dissolve it in D2O than in MeOH + X, 70:30 (v/v). Consequently, the peptidization of L-Ala in heavy water is even more obstructed than it was the case with the other investigated α-amino acids and it results in considerable yields of the L-Ala crystals (most probably at least partially deuterated) at the expense of the L-Ala-derived peptides. Perhaps it might be interesting to add that out of five α-amino acids investigated so far, which can be divided into two groups of endogenous and exogenous species, two endogenous species (L-Cys and L-Pro) undergo spontaneous oscillatory peptidization in an aqueous-organic solvent (i.e., in the absence of D2O) following the circadian rhythm, whereas two exogenous ones (i.e., L-Met and L-Hyp) do not. The third endogenous species (L-Ala) first undergoes two initials oscillations which are damped (not periodic) and the oscillatory changes are on a scale of ca. 10 h (as estimated with use of the Fourier transform approach) and after that, the system reaches a steady state.

Spontaneous Pulsation of Peptide Microstructures in an Abiotic Liquid System

We report observations of pulsating peptide formation and depeptidization in 70% aqueous acetonitrile solutions of l-Pro-l-Phe and l-Cys, resulting in the oscillatory appearance and disappearance of solid masses of microfibers and microspheres, respectively. We monitor the concentration changes of the monomeric amino acids by high-performance liquid chromatography. The concentration of all amino acid solutions used is 1.0 mg mL(-1), due to solubility limitations in 70% aqueous acetonitrile. The nonlinear concentration changes of l-Pro, l-Phe and l-Cys, and the amounts of the main peptidization products observed within our monitoring periods (for l-Pro-l-Phe, 250 h, and for l-Cys, 70 h) are typically from several to 20% of the original monomer concentrations. We follow the formation and decay of the insoluble peptides by turbidimetry. We also investigate the materials formed using scanning electron microscopy and mass spectrometry. We carry out numerical simulations on a simple model that reflects the main features of spontaneous pulsation of peptide fiber or sphere formation in this abiotic liquid system.

Dynamics of Spontaneous Peptidization of l-, d- and dl-Serine in an Abiotic Solution as Investigated with Use of TLC-Densitometry and the Auxiliary Chromatographic Techniques

From our earlier investigations, it comes out that proteinogenic amino acids can undergo spontaneous oscillatory reactions of chiral inversion and peptidization. l-Serine (l-Ser) is an important proteinogenic amino acid with many vital functions in human and mammalian organisms, e.g., it is responsible for good condition of the nervous cell membranes. It undergoes spontaneous oscillatory processes of chiral inversion and peptidization, and the goal of this study was to compare the dynamics of its peptidization with that of d-Ser and dl-Ser (racemate). The main analytical technique used in our experiment was TLC-densitometry, and the auxiliary chromatographic techniques were HPLC-evaporative light scattering detector and LC-MS. The results obtained witness to the differences in peptidization dynamics of the two Ser enantiomers (l and d) and of the racemic mixture thereof (dl). It was shown that dl-Ser characterizes with the higher, and l- and d-Ser with the lower peptidization yields.