1. and Hydroxy Acids in Aqueous Ethanol
Experimental Evidence of a Spontaneous Condensation of Profens, Amino Acids
and Hydroxy Acids in Aqueous Ethanol
M. Sajewicz, M. Matlengiewicz, D. Kronenbach, M. Gontarska, A. Noworzyn, A. Ostrowska, T. Kowalska
Institute of Chemistry, Silesian University, 9 Szkolna Street, Katowice, Poland
INTRODUCTION
It is generally believed that condensation of amino acids and hydroxy acids (resulting in peptides and poly(hydroxy acids), respectively), and also of profens is rather difficult because energetically unfavourable, as it needs a considerable energetic input in order to split one water molecule from each pair of binding compounds [1]. This conviction affects many present-day presumptions regarding, e.g., prebiotic condensation of amino acids resulting in formation of peptides coupled through peptide bonds (NH-C=O). Hence, the experiments are still devised which involve ion irradiation of amino acid solutions to imitate the presumable prebiotic conditions of peptide formation [2]. Moreover, computational simulations are carried out to prove that energetically, polycondensation of amino acids (and hydroxy acids) would be more favourable, if carbon, oxygen, and/or nitrogen atoms in amino acid and hydroxy acid molecules were replaced by their respective analogues, i.e., silicon, sulphur, and phosphorus atoms [3].
AIM
In this study, an experimental evidence is provided to prove that condensation with certain low-molecular-weight profens, amino acids and hydroxy acids carried out at ambient temperature can be effortless, if it is carried out in aqueous ethanol (with predominant proportion of alcohol), or in the course of chromatographic procedure on microporous surface of silica gel, evidently due to dehydrating properties of both, ethanol and silica gel. Further it seems that energetically effortless condensation of profens, amino acids and hydroxy acids is inseparably linked with an ability of these acids to undergo a spontaneous oscillatory chiral conversion, first described in papers [4-6].
TLC
Demonstration of the phenylglycine ageing product immobile on the starting point of the chromatogram, suggesting a considerable molecular weight change
Again, TLC proves to be a simple yet invaluable analytical technique which can provide a decisive experimental evidence to demonstrate that the aged samples of the investigated profens, -amino acids, and - and -hydroxy acids not only undergo chiral conversion:
(+)-enantiomer  enol  (-)-enantiomer
but some other more profound structural changes as well.
BIURET TEST
Experimental evidence of peptization of phenylglycine in 70% aq. EtOH
Fig. 1. Densitograms showing concentration profiles of R-phenylglycine, S-phenylglycine, and racemic R,S-phenylglycine, depending on storage period with the respective amino acid solutions in 70% aqueous ethanol.
Fig. 2. 3D densitogram of R-phenylglycine, S-phenylglycine, and the racemic and scalemic phenylglycine mixtures. Lanes 1 and 2: R-phenylglycine; lanes 3 and 4: racemic R,S-phenylglycine; lanes 5 and 6: scalemic phenylglycine (R:S, 0.75:0.25); lanes 7 and 8: scalemic phenylglycine (R:S, 0.25:0.75); lanes 9 and 10: S-phenylglycine.
(a)
(b)
(c)
Fig. 3. Test tubes showing the colour outcome of the biuret test with 70% ethanol solutions of (a) R-phenylglycine, (b) S-phenylglycine, and (c) racemic R,S-phenylglycine after storage for three days.
13C NMR spectroscopy
Experimental evidence of condensation of selected carboxylic acids in solutions
Ketoprofen
monomer condensate
(a)
Fig MHz 13C NMR spectrum of L-(+)-lactic acid first dissolved and stored for ten days in pure ethanol, and then recorded in CDCl3 at 25 ºC.
Fig MHz 13C NMR spectrum of S-(+)-mandelic acid first stored for ten days in pure ethanol, and then recorded in CDCl3 at 25 ºC.
Schematic presentation of the combined process, involving chiral conversion cum condensation of profens
(b)
Profens
(two parallel reaction steps)
Fig. 6. Aliphatic range of the 13C NMR spectra for (a) ketoprofen condensate and (b) ketoprofen monomer. Methyl line at ppm in (b) is accompanied by two additional lines at and ppm in (a). These new lines originate from the methyl groups in the repeating units of the condensate. The signal of methine carbon at ppm in pure ketoprofen (b) is flanked by a new small line at in (a) coming from the end groups. The new lines at and ppm in (a) originate from new quaternary carbons formed in the main chain of the polymer.
(a)
α-Amino acids
(three parallel reaction steps)
α- and β-Hydroxy acids
(three parallel reaction steps)
(a)
(b)
(b)
Fig. 7. Aromatic range of the 13C NMR spectra for (a) ketoprofen condensate and (b) ketoprofen monomer. In spectrum (a) two small new peaks appear at and ppm, respectively, which can be attributed to C-2’ and C-6’, respectively, in the new molecular environment of ketoprofen condensate (as compared with pure ketoprofen, spectrum (b)).
Chiral conversion cum condensation involving enol formation
Chiral conversion cum condensation involving enol formation
Condensation of two amino acid molecules through peptide bonds (enol form not involved)
Condensation of two mandelic acid molecules (enol form not involved)
REFERENCES
[1] A.B. Meggy, J. Chem. Soc., 1444–1454 (1956)
[2] J.M. Chiaramello et al., Int. J. Astrobiol., 4, (2005)
[3] W. Wang, H. Yuan, X. Wang, Z. Yu, Adv. Space Res., 40, (2007)
[4] M. Sajewicz, R. Piętka, A. Pieniak, T. Kowalska, Acta Chromatogr., 15, (2005)
[5] M. Sajewicz et al., J. Liq. Chromatogr. Relat. Technol., 31, (2008)
[6] M. Sajewicz, M. Gontarska, D. Kronenbach, T. Kowalska, Acta Chromatogr., 20, (2008)
CONCLUSION
We provide an inventive experimental evidence on condensation of selected profens, amino acids and hydroxy acids obtained, e.g., by means of thin-layer chromatography, 13C NMR spectroscopy, and biuret test.