TD-¹HNMR Measurements Show Enantioselective Dissociation of Ribose and Glucose in the Presence of H₂¹⁷O

Abstract

We used Time Domain (1)H Nuclear Magnetic Resonance (NMR) to characterize changes in proton exchange between water and sugar enantiomers at different concentrations of H(2)(17)O (approximately 15-450 mM) and found that dissociation of the (-)-enantiomers of glucose and ribose occurs at significantly higher rates at higher concentrations of H(2)(17)O. The mechanism behind this enantioselective effect is unclear. The hypothesis we propose is that the large magnetic field (B(o) approximately 0.6T) applied during NMR measurements induces electric moments opposite in sign for the D and L-isomers. Because (17)O has a nuclear electric quadrupole moment not = 0, asymmetrically hydrated complexes may form between the B(o)-polarized enantiomers and H(2)(17)O. Either H(2)(17)O is more often hydrating the (+) than the (-)-enantiomers--and consequently pK differences between H(2)(16)O and H(2)(17)O lead to differences in proton exchange between enantiomers and water--or the orientation of H(2)(17)O relative to the B(o)-polarized enantiomers is different, in total or in part, which leads to hydrated complexes with different spatial geometries and different proton exchange properties. This effect is significant for Magneto-Chiral Stereo-Chemistry (MCSC) and astrobiology, and it may help us better understand specific instances of mass independent isotopic fractionation and aid in the development of new technologies for chiral and isotopic separation.

Rooting Prebiotic Chirality in Spinomeric Chemistry?

“…Enantio-differences in proton exchange behavior were reported earlier in ribose and glucose and were shown to be controlled by the concentration of H 17 (Scorei et al, 2007). We found that such enantio-differences are also present in amino acids (Asn and Ala), where they are (apart from H 17 2 O) also controlled by pH (Cimpoiaş u et al, submitted).…”

“…Time domain 1 H nuclear magnetic resonance (TD-1 HNMR) relaxation parameters were obtained at 298 AE 0.2 K on a 25 MHz spectrometer (Aremi78 TD-LRP, audio filter bandwidth of 1 MHz, B o ¼ 0.589 T with quadrature phase sensitive detector) as reported earlier (Scorei et al, 2007). This approach allows for measurement of a set of key proton exchange parameters, such as R 2 (0); K exchange ; DpK, and M 2 , with 1-2% accuracy (Yeung and Lent, 1987;Steinbrecher et al, 2000;Scorei and Cimpoiaş u, 2006).…”

“…K exchange can be used to calculate differences in ionization between enantiomers (DDpK),(Scorei et al, 2007). Changes in…”

Nickel Complexes of Alanine Having a Preference for One Chiral Form over Another upon Crystallization

“…Unexpected differences between D and L enantiomers of amino acids, peptides and sugars have recently been investigated. [2][3][4][5][6][7] The differential rates of D-and L-tyrosine crystallization was also reported. 8 Nickel and iron are the most abundant transition metals in the earth's crust.…”

Comments in a Discussion: Differential Rates of d- and l-tyrosine Crystallization

“…Nemoto et al (2005) investigated the behavior of D and L-alanine in simulated hydrothermal conditions, and determined that L-alanine was more resistant to racemization, so that it consistently produced an enantiomeric excess. Scorei et al (2007) investigated aqueous solutions of Dand L-ribose and glucose, using nuclear magnetic resonance methods to monitor proton exchange between the enantiomers in solution and H 2 17 O that was added as a probe for this purpose. Proton exchange was significantly faster for the (−) enantiomers of both ribose and glucose.…”