ASTROBIOLOGYVolume 7, Number 5, 2007© Mary Ann Liebert, Inc.DOI: 10.1089/ast.2006.0076

Special Paper

TD-1HNMR Measurements Show EnantioselectiveDissociation of Ribose and Glucose in the

Presence of H217O

ROMULUS ION SCOREI,1 VILY MARIUS CIMPOIASU,1 and RADU POPA2

ABSTRACT

We used Time Domain 1H Nuclear Magnetic Resonance (NMR) to characterize changes inproton exchange between water and sugar enantiomers at different concentrations of H2

17O(�15–450 mM) and found that dissociation of the (�)-enantiomers of glucose and ribose oc-curs at significantly higher rates at higher concentrations of H2

17O. The mechanism behindthis enantioselective effect is unclear. The hypothesis we propose is that the large magneticfield (Bo �0.6T) applied during NMR measurements induces electric moments opposite insign for the D and L-isomers. Because 17O has a nuclear electric quadrupole moment � 0, asym-metrically hydrated complexes may form between the Bo-polarized enantiomers and H2

17O.Either H2

17O is more often hydrating the (�)- than the (�)-enantiomers—and consequentlypK differences between H2

16O and H217O lead to differences in proton exchange between

enantiomers and water—or the orientation of H217O relative to the Bo-polarized enantiomers

is different, in total or in part, which leads to hydrated complexes with different spatial geome-tries and different proton exchange properties. This effect is significant for Magneto-ChiralStereo-Chemistry (MCSC) and astrobiology, and it may help us better understand specific in-stances of mass independent isotopic fractionation and aid in the development of new tech-nologies for chiral and isotopic separation. Key Words: NMR—Proton exchange—Ribose—Glucose—H2

17O—Enantioselective—Chirality. Astrobiology 7, 733–744.

733

INTRODUCTION

THE ORIGIN OF life’s high enantiomeric excess(e.e.) and homochirality is unclear because

enantiomers have very similar physical andchemical properties. Thus, enantioselective reac-tions are few and inefficient. Theoretical ap-proaches used to explain prebiotic handednessinclude Parity-Violation in Electroweak Differ-

ences (PVED), interactions with Circularly Polar-ized Light (CPL), and interactions with variouschiral structures. Sizable stereo-preference was re-ported only in a very limited number of chiral-chi-ral interactions (Fujiwara and Nishimoto, 1990,1998, 2005; Soai, 2002); PVED is too weak to resultin large differences in reactivity between enan-tiomers (Mason and Tranter, 1983; Kondepudi andNelson, 1985; Salam, 1991); stereophotolysis with

1University of Craiova, Craiova, Romania.2Portland State University, Portland, Oregon.

CPL has low chiral specificity and results in sig-nificant e.e. only if sizable photolysis of bothenantiomers has occurred (Kagan et al., 1974).

In previous Nuclear Magnetic Resonance(NMR) measurements, we observed small, yetconsistent, differences in proton exchange be-tween sugar enantiomers (Cimpoiasu and Scorei,2003; Scorei and Cimpoiasu, 2004). Hypothesesby which we hoped to explain these results in-volved the presence of chemical impurities, in-ternal gradients, or the large magnetic field (Bo�0.6T) applied during NMR measurements. Re-luctance to accept that the large magnetic fieldwas of significance is understandable since vari-ous futile attempts were made in the last 100years to use magnetic fields alone to induce chi-rality in chemical processes (Avalos et al., 1998;Feringa and Van Delden, 1999; Barron, 2000). Yetcombinations of two or more external factors (e.g.,electric fields, magnetic fields, gravitation, androtation) can have chiral effects (Thiemann andTeutsch, 1990) via adding extra interactive di-mensions. Hence, we asked whether the enantio-differences we found were due to a combinationbetween the applied Bo and a local electricallyasymmetric component present throughout ourmeasurements.

It has been proposed that large Bo can havesmall asymmetric effects on enantiomers at thelevel of charge distribution around chiral centers,induced magnetic moments, and energy differ-ences (Gilat, 1999; Buckingam, 2004; Buckinghamand Fischer, 2006; Harris and Jameson, 2006). Itwas also proposed that measurements of NMRchirality be made of this effect in conjunction withlarge external electric fields (�1 kv/cm). The factthat no significant electric fields were to be ap-plied in our experiments prompted us to askwhether the effects observed would involveasymmetric interactions between the Bo-exposedenantiomers and other molecular structures, suchas molecules that carry isotopes with electricquadrupole moments (Q) other than zero. Be-cause we were working with pure solutions ofenantiomers in dH2O, we focused our attentionon H2

17O, which reaches natural concentrationsof �19 mM. (17O has a (�)-nuclear quadrupolemoment Q � �0.02578 to �0.26 barns, these val-ues assuming constructive and destructive inter-ference, respectively; Stone, 2001). We measuredthe effect of different concentrations of H2

17O onproton exchange in pure aqueous solutions ofenantiomers and report results regarding the fre-

quency spread of the exchangeable protons, theexchange rate, and pK and �G differences.

Until the mechanism is sufficiently understood(and due to the fact that these experiments wereperformed in the dark), we will use the acronymMCSC (Magneto-Chiral Stereo-Chemistry) toavoid confusion with Magneto-Chiral Dichroism(MCD) or Magneto-Chiral Anisotropy (MChA),both of which involve photochemical reactions(Wagnière and Meyer, 1982; Barron and Vrban-cich, 1984; Rikken and Raupach, 1997, 2000;Rikken et al., 2002). We also want to avoid con-fusion between our approach and NMR chiralityproposals (Buckingam, 2004; Buckingham andFischer, 2006; Harris and Jameson, 2006). In ourstudy, we measured differences in reactivity be-tween different solutions of pure enantiomers,while NMR chirality is intended to measure e.ewith both L and D present.

MATERIALS AND METHODS

L(�)-ribose, D(�)-ribose, L(�)-glucose, andD(�)-glucose were purchased from Sigma anddissolved in ddH2O (MilliQ) at 0.58 M, 1.17 M,and 2.02 M for ribose, and at 0.276 M, 0.528 M,0.973 M, and 1.681 M for glucose. The H2

17O-en-riched water was purchased from Spectra StableIsotopes and used at concentrations between 14.9mM and 450 mM. Because high values of NMRtransverse relaxation time (R2) for H2

17O-en-riched water were previously observed in the 6–7pH range (Yeung and Lent, 1987), we carried outour experiments at pH 6.3 (adjusted by titrationwith 1 M HCl). The pH was also measured at theend of the experiments, and the values were usedto correct Kexchange.

Time Domain 1H Nuclear Magnetic Resonance(TD-1HNMR) relaxation curves were carried outwith a 25 MHz spectrometer (Aremi 78 TD-LRP)equipped with an audio filter bandwidth of 1MHz, at Bo � 0.589 T with a quadrature phase-sensitive detector. The temperature was con-trolled at 298 � 0.2 K. The transverse relaxationrates (R2) were acquired using a Carr-Purcell-Meiboom-Gill (CPMG) sequence: 90°x-(��-180°y;-�-measurement-)n-RD, for a range of inter-pulse delay (�) values of 0.4–20 ms (Scorei andCimpoiasu, 2006). The R2 values can be deter-mined by way of CPMG-NMR with 1–2% accu-racy (Steinbrecher et al., 2000). The number ofechoes varied from 640 to 20,480. All measure-

SCOREI ET AL.734

ments were made after a mutarotation process ofsugars in solution (6 h at 298 K) without de-gassing, as dissolved O2 does not modify the re-lationship between R2 and �. We used low-reso-lution NMR because the measurement of thecontribution of the proton exchange betweenH2

17O and H216O to the NMR measurement be-

comes important at low fields (Khallouk et al.,2005).

Using H217O-enriched water allows accurate

measurements of the pH and the proton chemi-cal exchange (Yeung and Lent, 1987; Steinbrecheret al., 2000). It is expected that, in the case of mod-erately rapid chemical exchange and low con-centrations of H2

17O, the proton line-widths arelargely determined by scalar relaxation with 17O.Because the 17O mole fraction (P) and the 2nd or-der magnetic moment (M2) are linearly correlatedin the 0–1% 17O range, we used a 0–1% 17O atomicratio range for our measurements.

The instrument was calibrated by measuringthe scalar coupling constant between 1H and 17O(1J17O-1H) during the titration of H2

16O with H217O

(Eq. 1); we used the well-established relationshipbetween the relaxation rate and the scalar cou-pling constant (Lankhorst et al., 1983).

R2(�) � �

� �1 � tanh(Kexchange �)�Eq. 1

where R2 � NMR transverse relaxation time;1/T2 � the transverse relaxation rate; � � theinterpulse delay of the acquisition sequence

� in the limit � � � (Wang et al.,

2003); M2 � P�3152�(2�1J17O-1H) is the 2nd order mag-

netic moment (Gottwald et al., 2005); P � the 17Omole fraction; 1J17O-1H � the scalar coupling con-stant between 1H and 17O.

From the slope between M2 and P, we extractedthe value for 1J17O-1H. The obtained value (93.14 �8 Hz) is in agreement with previous reports (Ye-ung and Lent, 1987; Ronen et al., 1998).

The decrease of the transverse magnetizationwas fitted to a monoexponential equation. We ap-plied the NMR results, i.e., the transverse relax-ation rate (1/T2) versus interpulse delay (�) to Eq.2 (Gottwald et al., 2005; Scorei and Cimpoiasu,

1�T2(�)

1�T2(0)

M2��Kexchange�

1��Kexchange�

1�T2(0)

1�T2(�)

2006; Grucker et al., 1986), to extract the frequencyspread (��) and the equilibrium exchange con-stant (Kexchange).

R2(�) � �

� �1 � tanh(Kexchange�)�Eq. 2

where Kexchange � the equilibrium exchange con-stant, representing the proton exchange rate be-tween sites A and B; where site A is the H2

16Oand site B is the sugar or the H2

17O; �� � the fre-quency spread of exchangeable protons, definedby Gottwald et al. (2005), i.e., the frequency dif-ference between site A and site B, a measure ofthe chemical shift relative to H2

16O; pB � protonfraction in site B (i.e., the ratio between the num-ber of exchangeable protons in site B and the to-tal number of exchangeable protons).

The proton transfer process in water was ex-tracted from Kexchange (Eq. 3) (Zhang et al., 1995).

Kexchange � KH10�pH � KOH10pH�pKw � KW Eq. 3

where KH and KOH are the rate constants of acid-and base-catalyzed exchange; KH � 8.2 109 s�1

(Glasel, 1972; Cerdán et al., 1993); KOH � 4.0 109

s�1 (Glasel, 1972; Cerdán et al., 1993); KW � wa-ter-catalyzed exchange.

We obtained an average calibration value forthe H2

16O-H217O Kexchange of 1600 � 289 s�1 and

a pH of 6.25 � 0.1, which is in agreement withthe electrode-based pH measurements. In Eq. 2,the Kexchange term represents the proton exchangerate between different molecules (Lankhorst et al.,1983). The �K parameter is the difference be-tween the Kexchange of the solutions of enan-tiomers (Eq. 4).

�K � Kexchange of the (�)-enantiomer� Kexchange of the (�)-enantiomer Eq. 4

The pK differences (�pK) between the solvatedenantiomers were calculated from Eq. 5 (Zhanget al., 1995):

Kexchange � Kd Eq. 5

where Kd � diffusion-controlled collision rate;pK � �log(Ka); Ka � acidity constant.

10pH�pK��1 � 10pKw�pK

pB��2��

Kexchange�

1��Kexchange�

1�T2(0)

1�T2(�)

ENANTIOSELECTIVE DISSOCIATION OF RIBOSE AND GLUCOSE WITH H217O BY NMR 735

RESULTS

The dependence of �� on the concentration of H2

17O

We identified the presence of proton exchangebetween sugars (ribose and glucose) and waterand interpreted this exchange using Eqs. 1 and 2.In the absence of free H2

17O (i.e., no proton ex-change between H2

16O and H217O), �� is derived

from Eq. 2, represents the proton exchange be-tween the sugar and H2

16O, and thus is connecteddirectly with the chemical shift. In the presenceof free H2

17O, the NMR line broadening due toH2

17O covers the NMR lines, which represent thechemical shift. In this case, �� is only measurablein the �6–8 pH range (Meiboom, 1961; Lankhorstet al., 1983), and it is derived from J (Eq. 1). The�� values for the exchange between ribose andglucose enantiomers and H2

16O versus H217O (re-

ported via P17O, representing the ratio betweenthe number of exchangeable protons from H2

17Oand the total number of exchangeable protons insolution) are presented in Fig. 1. At low H2

17Oconcentrations, no proton exchange was ob-served, this being below detection limits. At anaverage concentration range of H2

17O (Fig. 1), sig-nificant differences were seen between enan-tiomers, with inhibited exchange signal in thepresence of (�)-ribose and (�)-glucose relative to(�)-ribose and (�)-glucose, respectively. Athigher concentrations of H2

17O, the behavior ofthe enantiomers appeared similar, though the up-per threshold varied between ribose and glucose.

Because �� is sensitive to hydration, it can beused to interpret the hydration behavior of theenantiomers (Gottwald et al., 2005). We proposethat at large Bo the affinity of the enantiomers forH2

17O is asymmetric with the (�)-enantiomershaving greater affinity for H2

17O than the (�)-enantiomers. At large molar ratios between (�)-sugars and H2

17O, the sugars will remove H217O

more efficiently from solution. This eliminates theH2

16O-H217O exchange signal, which in turn al-

lows for observation of the signal of the protonexchange between sugars and H2

16O. Hence, thesugar:H2

17O ratios can be estimated from thetransitions in the graphs, where the behavior ofthe (�)-enantiomers becomes similar with the be-havior of the (�)-enantiomers. These ratios wereestimated to be �5:1 for (�)-ribose and �15:1 for(�)-glucose. When the concentration of H2

17O

was very large, i.e., beyond the capacity of thesugars to “chelate” the H2

17O, a significant por-tion of the H2

17O molecules remained free and,consequently, the H2

16O-H217O proton exchange

signal dominated the NMR readings, masking thesugar-H2

16O proton exchange signal.

The dependence of Kexchange on the concentrationof H2

17O

Physical-chemical differences between watermolecules with different isotopic signatures (e.g.,H2

16O, 2H216O, H2

18O) include those having to dowith freezing points (Horita and Cole, 2004) andaffinity for protons (Kudish et al., 1973; Krezeland Ball, 2004). Hence, hydration of the enan-tiomers with water molecules with different iso-topic signatures should also influence the disso-ciation properties of the enantiomers. Thedependence of Kexchange on the concentration ofH2

17O for the different enantiomers of ribose andglucose is presented in Fig. 2. We found that theproton exchange between sugars and water is lessfrequent in the presence of H2

17O. There are atleast two ways to interpret this result:

1) Adding H217O to H2

16O destructures the or-ganization of the bulk solvent and increases theexchange rate with the dissolved sugar, similarto the effects of H2

18O on H216O (Krezel and Ball,

2004);2) In the presence of H2

17O, differences in theaffinity of H2

16O versus H217O for L- versus D-enan-

tiomers, coupled with differences in the tenden-cies of H2

16O versus H217O to exchange protons,

make the proton exchange rate enantioselective.Our results of Kexchange on (�)-ribose (Fig. 2A)

indicate that the addition of H217O disorganizes

the bulk fluid, which increases the sugar:H216O

exchange rate. Less variation was observed with(�)-ribose, probably because the higher affinitybetween (�)-ribose and H2

17O, coupled with thelower tendency of H2

17O to exchange protons, in-hibits exchange. Hence, both mechanisms pro-posed above may contribute to our results. Wepredict that further increase in the concentrationof H2

17O (i.e., overwhelming the sugars’ capacityto chelate H2

17O) or lower concentrations of sug-ars (i.e., leaving most of the H2

17O free in solu-tion) should increase the Kexchange of (�)-riboseas well. The trend from Fig. 2B indicates that (�)-glucose is more easily saturated with H2

17O than(�)-ribose. Changes in �K during the titration of

SCOREI ET AL.736

ENANTIOSELECTIVE DISSOCIATION OF RIBOSE AND GLUCOSE WITH H217O BY NMR 737

FIG. 1. Frequency spread (��) values showing evidence of proton exchange during titration with H217O in wa-

ter solutions that contain enantiomers of ribose (A) and glucose (B). The values plotted in the graphs representchanges in �� by titration with H2

17O. The proton fraction (P17O) is the ratio between the number of exchangeableprotons from H2

17O and the total number of exchangeable protons in the solution. Results for all concentrations ofribose and glucose were used in these graphs because the sugar molecules were in excess of H2

17O and because thevalue of the chemical shift is independent of sugar concentration.

SCOREI ET AL.738

FIG. 2. The dependence of the proton exchange rate (Kexchange) in solutions of enantiomers of ribose (A) and glu-cose (B) on the concentration of H2

17O. The highest rates were obtained with (�)-ribose and (�)-glucose.

ENANTIOSELECTIVE DISSOCIATION OF RIBOSE AND GLUCOSE WITH H217O BY NMR 739

FIG. 3. Differences between the exchange rate (�K(s�1)) of solutions of enantiomers of ribose (A) and glucose(B) at different concentrations of H2

17O. All concentrations of sugars used were included.

SCOREI ET AL.740

ribose and glucose enantiomers with H217O are

presented in Fig. 3. Here, increase in �K is seenat increased concentrations of H2

17O (�100 mMfor glucose and �350 mM for ribose). This alsosuggests that the H2

17O-binding capacity is largerfor (�)-ribose than for (�)-glucose.

The dependence of �pK and �Go on theconcentration of H2

17O

Earlier results (Kudish et al., 1973; Krezel andBall, 2004) showed that deuterated water andH2

18O have larger pKs than H216O. Changes in pK

in the presence of H217O may be due to two fac-

tors: (1) the pK being a combination of the pKs ofdifferent solvents (H2

16O and H217O) mixed in

different proportions, and (2) destructuring ef-fects of H2

17O on the organization of H216O,

which should decrease the pK. Though compli-cations arise when trying to calculate solutions ofenantiomers with different affinities in mixturesof water with different isotopic signatures, it canbe predicted that adding an H2

17O-removershould decrease proton concentration, i.e., in-crease in the overall pK. Not knowing the ab-solute value of Kd (see Eq. 5), one cannot calcu-late the pK but can calculate the �pK. Moleculeswhose enantiomers show the largest differencesin their affinities for H2

17O should display thelargest �pK as well. The relationship between theconcentration of H2

17O and the �pK of differentsugar solutions is presented in Fig. 4. The calcu-lated �pKs were 1.16 � 0.3 for ribose and 0.44 �0.20 for glucose. The ratio between these �pKs isconsistent with the sugar:H2

17O molar bindingratios calculated from �� (i.e., �5:1 for ribose and�15:1 for glucose). Using ��Go � 2.303RT�pKa,we found that the differences in ionization ener-gies between the enantiomers are �1.58kcal/mole for ribose and �0.59 kcal/mole forglucose. Hence, under our experimental condi-tions (i.e., Bo �0.6 T and 14.9 mM H2

17O), (�)-ribose and (�)-glucose should also be more reac-tive than their enantiomers.

DISCUSSION

Based on ��, we found differences betweenenantiomers of glucose and ribose in their affin-ity for H2

16O versus H217O, but only within a

certain range of H217O concentrations (P17O

�0.002–0.009 for ribose and P17O �0.0005–0.0025

for glucose). At low concentrations of H217O (14.9

mM) and high concentrations of sugars (the low-est concentrations we used were 580 mM for ri-bose and 276 mM for glucose), Low ResolutionTD-1HNMR cannot distinguish differences be-tween enantiomers. At high concentrations ofH2

17O, beyond the capacity of the sugars to re-move the H2

17O from the solution, chiral differ-ences may still exist, but the free H2

17O in thebulk water obscures the sugar-dependent proton-exchange NMR signal. The affinity of the enan-tiomers for H2

17O was larger for L(�)-ribose thanfor D(�)-ribose and larger for D(�)-glucose thanfor L(�)-glucose. The sugar:H2

17O binding ratioswere �5:1 for (�)-ribose and �15:1 for (�)-glu-cose. We believe that the carbon involved in thisaffinity is the �-anomeric C1, because when boricacid forms an ester with glucose (in which casethe OH group from the �-anomeric carbon is in-volved), the effect from Fig. 1 disappears (un-published results). Results on Kexchange showedthat the proton exchange between sugar enan-tiomers and water is more frequent with H2

16Othan with H2

17O. This rate was influenced by boththe sugar:H2

17O binding ratio and the abundanceof free H2

17O. Increased concentrations of H217O

in the vicinity of the anomeric carbon resulted insignificant increase in pK, i.e., lower ionization re-activity.

The mechanism behind this chiral disruptionremains unclear. Identifying it requires exploringthe various sources of asymmetry that may bepresent during measurements and carrying outmore experiments. However, a couple of mecha-nisms can be explored and hypotheses formu-lated in an atttempt to explain these results. Thecontribution of PVED has to be considered,though the MCSC effect observed appears quitelarge (��G � 1.58 kcal/mole for ribose and �0.59kcal/mole for glucose) to be due to PVED alone.Magneto-photochemical reactions are not rele-vant here because our experiments occurred inthe dark. Hence, we cannot use MagnetoChiralDichroism or MagnetoChiral Anisotropy (Wag-nière and Meyer, 1982; Barron and Vrbancich,1984; Rikken and Raupach, 1997, 2000; Rikken etal., 2002) as a basis for a hypothesis. An amplifi-cation of the chiral disruption via an iterativechemical transformation (e.g., a chemical cycle)also seems unlikely because ours is a simplechemical system, without the sizable internal en-ergy flux that can be used to justify changes inentropy based on energy dissipation.

ENANTIOSELECTIVE DISSOCIATION OF RIBOSE AND GLUCOSE WITH H217O BY NMR 741

Our results show that, when the concentrationof H2

17O becomes very low, both �� and Kexchangeare identical, which is an indication that impuri-ties have non-significant levels. It is the intro-

duction of H217O that results in significant enan-

tio-differences. Hence, a chiral impurity seemsunlikely. Large external electrical fields were pro-posed to influence the activity of Bo-exposed

FIG. 4. The pK differences (�pK) between enantiomers of ribose and glucose at different concentrations of H217O.

FIG. 5. Proposed mechanism for the MagnetoChiral Chemical effect. The figure shows ribose only. The presenceof a large Bo leads to an induced electric moment in the x-direction of opposite sign between enantiomers: i.e., Q 0for L(�)-ribose and D(�)-glucose (A) and Q � 0 for D(�)-ribose and L(�)-glucose (B). Because 17O has a nuclear elec-tric quadrupole moment (Q � 0), the interaction between sugars and H2

17O is attractive, as shown in (A) and repul-sive in (B). In (C) the complex between L(�)-ribose and H2

17O, coupled with pK differences between H217O and H2

16O(i.e., a lower tendency of H2

17O to exchange protons relative to H216O), decreases the proton exchange rate between

enantiomers and solution relative to proposed mechanism shown in (D).

enantiomers, but such fields were not applied inour experiments, nor were large electrical fieldspresent in the vicinity of the NMR instrument.Asymmetric effects due to interactions with sur-faces are possible, though not dominant, becausethe NMR tubes do not have a large scale asym-metry, their surface:volume ratio is very smallwith most sugar molecules freely rotating in so-lution, and also because the asymmetry increaseswith the addition of H2

17O.The one variable that was unquestionably cor-

related with chiral differences was H217O, and

thus at least one hypothesis has to be consideredwith regard to its role. Because the 17O atom isdifferent from 16O with respect to its nuclear elec-tric quadrupole and because H2

17O is expected toshow different pK from H2

16O, such a hypothesisshould take into account differences in the hy-dration of enantiomers with H2

17O. Our resultsshowed that the 1J17O-1H coupling constant dis-appeared at certain H217O:(�)-enantiomer ratios.To neutralize the exchange between 17O and 1H,spin pairing has to occur between the nuclearmagnetic spin of the 17O and the nuclear mag-netic spins of the surrounding ortho 1H nuclei.Such configuration may be present if the hydra-tion of the enantiomers with H2

16O relative toH2

17O is asymmetric. Because hydration itselfcannot violate symmetry rules, we propose thatenantiomers are asymmetrically electrically po-larized prior to their interaction with H2

17O, dueto the presence of the large Bo (�0.6 T). In at leastone theoretical model (Gilat, 1999), it was pro-posed that the electrical configuration around theasymmetric carbons becomes biased in the pres-ence of large Bo. In Buckingam’s interpretation(2004), a magnetic field Bz

(o) induces in a free-tumbling molecule a circulation of electrons inthe xy-plane, which causes an oscillating electricfield Ey to induce an out-of-phase dipole momentin the x-direction proportional to the asymmetricpolarizability. Buckingam (2004) proposed thatthis oscillating movement of electrons in the x-di-rection causes an induced electric moment in thex-direction, which is of opposite sign betweenenantiomers. We speculate that in the presence ofBo differences in polarization between L and D

lead to asymmetric hydration with H217O, which

caries a nuclear electric quadrupole � 0. This enan-tioselection may take two forms: enantio-differ-ences in hydration affinity with H2

17O and enan-tio-differences in the spatial orientation of H2

17Orelative to the sugar. In an external Bo, which or-

ders the orientation of the electrical moments of thefree-tumbling molecules, a competition may occurbetween the quadrupolar repulsion (Uq �1/R5)and the van der Waals attraction (UvdW �1/R6)(Dzyaloshinskii et al., 1998). Because both the Bo-polarized enantiomers and the H2

17O have non-zero electric moments, this may help explain theasymmetry of the sugar:H2

17O interactions (Fig. 5);in this case, pK differences between H2

16O andH2

17O cause differences in proton exchange. If theorientation of the H2

17O relative to the polarizedenantiomers varies, this may also be used to ex-plain differences in proton exchange.

CONCLUSIONS

During TD-1H NMR measurements, we founddifferences in the dissociation of ribose and glu-cose correlated with the concentration of H2

17O(at 14 mM). The L(�)-ribose and D(�)-glucosehad higher affinity for H2

17O than their enan-tiomers, the (�)-enantiomers had higher affinityfor H2

17O than for H216O, and L(�)-ribose was a

better “scavenger” of H217O than D(�)-glucose.

One hypothesis we propose is that enantiose-lective interactions may occur between enan-tiomers asymmetrically polarized under high Bo(�0.6 T) and H2

17O (based on the nuclear elec-tric quadrupole moment of 17O). If these MCSCeffects are due to Bo and H2

17O, then bringingeither one of these variables close to zero shouldcancel the effect. The role of the magnitude ofBo, temperature, pH, and concentrations ofH2

17O at �14 mM were not investigated, yetthey are important in deciphering the mecha-nism(s) behind this effect.

We predict that, under the experimental con-ditions presented here, the (�)-enantiomers ofribose and glucose should also be more reactivethan their enantiomers, and a similar effectshould be observed with other molecules of bio-chemical importance. These results have impor-tant consequences in astrobiology and MCSC. Inthe future, theoretical and experimental appli-cations should be pursued to explore prebioticchiral chemistry on the surface of magnetic min-erals. MCSC effects may also shed light on mech-anisms that cause mass-independent isotopicfractionation. Last but not least, the presence ofboth large Bo and molecules that have isotopeswith Q � 0 may also be studied for consequenceson the physiology of living cells.

SCOREI ET AL.742

ACKNOWLEDGMENTS

Thanks to Dr. Ing. Constantin Doru Stanescu,Professor Dr. Dana Iordachescu, Dr. RobertHazen, Dr. David Deamer, and Dr. G.L.J.A.Rikken for support and insightful discussions.

ABBREVIATIONS

CPL, Circularly Polarized Light; CPMG, Carr-Purcell-Meiboom-Gill; e.e., enantiomeric excess;MCSC, Magneto-Chiral Stereo-Chemistry; NMR,Nuclear Magnetic Resonance; PVED, Parity-Vio-lation in Electroweak Differences; Q, electricquadrupole moments; R2, transverse relaxationtime; TD-1HNMR, Time Domain 1H NuclearMagnetic Resonance.

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