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mass-independent enrichment and Isotope Anomalies ifi anomalo(5) in _]S of 33A = 2.0 per rail. The Meteorite Sulfonic Acids value of iPSA is zero within measurement uncertainty; however, the 33A values of George W. Cooper,* Mark H. Thiemens, Teresa L. Jackson, ESA and nPSA, although small, are anom- Sherwood Chang alous (Table 1). Present measurements of 36S have _eater uncertainty than those of Intramolecular , hydrogen, and sulfur isotoperatios were measured on a homol- other S isotopes (Table 1) because of its low ogous series of organic sulfonic acids discovered in the Murchison meteorite. Mass- natural abundance (0.02%) coupled with independent sulfur isotope fractionafions were observed along with high / the small (micromolar) sample sizes. Corre- hydrogen ratios. The deuterium enrichments indicate formation of the hydrocarbon sponding 36A values are of course also less portion of these compounds In a low-temperature environment that is consistent with certain. In MSA, the largest sample, 836S, is that of interstellar clouds. Sulfur-33 enrichments observed in methanesulfonic acid could about the value expected for a mass-depen- have resulted from gas-phase ultraviolet irradiation of a precursor, . The dent process, 836S = 2834S (5). source of the sulfonic acid precursors may have been the reactive interstellar The 8_3C values of the sulfonics decrease carbon monosulfide. with increasing carbon number, as observed with homologous series of carbo_lic acids and hydrocarbons from Murchison (12). In relation to the known 8_3C values of Previous isotopic measurements of organic along with unusual ratios of H and C iso- Murchison organic compounds, the 8'_C compounds from the Murchison meteorite, topes in both classes of compounds, may values of the sulfonic acids span the range a carbonaceous chondrite, have shown that demonstrate that at least some meteorite from those of the amino acids to those of the -soluble polar organic compounds organic compounds containing S and P are carboxylic acids (_40 to -5) (1). generally have high 2H/H (D/H), 13C/11C, traceable to origins in interstellar clouds or As with the results obtained on and lSN/_4N ratios relative to Earth and the proto-solar nebula. Murchison amino acids (13), the D/H ra- solar system ratios (I). The origins of such In systems involving only two stable tios of the sulfonics substantially exceed isotopic enrichments have been attributed isotopes, such as C, H, and N, it is difficult terrestrial ratios, indicating formation of to precursor formed in low-tem- to discriminate between ordinary mass- the C-H bonds in a region that allows perature (_ 10 to 200 K) interstellar clouds dependent isotopic fractionation (for ex- such D enrichment, that is, a low-temper- by grain surface and gas-phase ion-molecule ample, evaporation or other kinetic iso- ature environment like that in interstellar reactions (2). After incorporation into the tope effects) and mass-independent process- clouds (2). In comparison with the D/H proto-solar system and meteorite parent es such as nucleosynthesis or symmetry- ratios of other Murchison organic com- bodies at about 4.5 billion years ago, the dependent chemical mechanisms. Studying pounds, the sulfonics fall in the range of interstellar precursors reacted during a peri- an element with four stable isotopes, such as the polar hydrocarbons and insoluble C od of aqueous alteration to form some of the S, removes this limitation by allowing one (SD _ 500 to 1000) (I). Because the observed meteoritic compounds (3). to observe graphically the deviation of an phosphonics are present in small amounts, The finding of homologous series of or- isotope from mass-dependent behavior (5, their isotope ratios are not corrected and ganic alkyl sulfonic acids (Scheme 1A) and 6). Recently, some bulk ureilite meteorites are minimum values. Their D/H ratios are phosphonic acids (Scheme 1B) (R = have been shown to have small _3S excesses also above terrestrial ratios (Table 1). C.H2.+I) in Murchison is of interest be- (_0.1 per mil) (7), and excess 3_S (_0.16 Any proposed mechanism for sulfonic cause, in meteorites, the sulfonic acids are per rail) was found in an oldhamite (CaS) acid formation must account for the follow- the first well-characterized series of o_anic separate from the Norton County enstatite ing observations: (i) the magnitudes of the S compounds, and the phosphonic acids are meteorite (8). 8C, 8S, and _3A values of MSA and the the only identified organic P compounds We examined the methyl (MSA), ethyl lower corresponding values of the other sul- (4). In addition to D/H and _3C/t2C mea- (ESA), isopropyl (iPSA), and n-propyl fonics; (ii) the similarity in structure cou- surements, our objective was to determine if (nPSA) sulfonic acids. The extraction from pled with a decline in abundance of the Murchison and the separation of sulfonic sulfonics with increasing carbon number acids (sulfonics) and phosphonic acids (4), as with other homologous series of me- A B O o (phosphonics) from other fractions of teoritic organic compounds (I); and (iii) II I! Murchison compounds were done as de- the similar D/H ratios among homologs. The second observation would seem to in- HO-- S --R HO-- P--R scribed in (9). We achieved baseline chro- matographic separation of individual sul- dicate formation of the sulfonics by the II I fonics (I0). The phosphonics are present in same or closely related processes. The rela- o OH very small amounts in Murchison (4); tively constant D/H ratios of the sulfonics Scheme 1 therefore, only bulk isotopic measurements could imply that unsaturated precursors were attempted (Table 1). (C.S_) to the sulfonics were formed first, the sulfonic acids had unusual S isotope In Murchison MSA, 33S, _4S, and 368 roll'owed by hydrogenation and D enrich- ratios. Such anomalies in the sulfonic acids, (Table 1) are enriched relative to their ment in a pool of nearly uniform H. The G.W.Cooper,SET]InstituteandNASAAmesResearch abundances in various organic and inorgan- D/H values of the sulfonics as a group are Center,MS239-4,MoffettReid,CA94035,USA. ic phases from several meteorites (6-8, I I ). nearly identical to those of Murchison polar S. Chang,NASAAmesResearchCenter,MS 239-4, The corresponding BS values of the other hydrocarbons and insoluble carbonaceous MoffettReid,CA94035,USA. material (1), which raises the possibility M. H. Thiemensand T. L. Jackson,Departmentof sulfonics fall within a range previously ob- Chemistryand Biochemistry,Universityof C_.,a_omia,served for organic phases in Murchison and that C-H bonds of the precursors to the SanDiego,LaJolla,CA92093-0356,USA. other carbonaceous chondrites (I 1). The S three groups were formed in the same pool *Towhomcorrespondenceshouldbeaddressed. isotopic distribution of MSA also shows an of H.

1072 SCIENCE • VOL. 277 • 22 AUGUST 1997 • www.sciencemag.org Table 1. Results of intramolecular measurements of stable isotopes of S, C, and H, from Murchison sulfonic acids. Uncorrected B_ac values (in per mil) from a previous experiment with comparable amounts of sample are as follows: MSA, 25.4; ESA, 4.8; nPSA, 1.8; iPSA, - 11.2. These are left uncorrected because of uncertainties in blank CO2 amounts. The corresponding 33&value of MSA was 1.24 per mil (29). In a preliminary experiment, 8_3C values were also lower (30); however, because of refined procedures, the present sutfonics are purer isolates. The errors in measurement of samples are those of the corresponding procedural standard. Although the amount of sulfur in the procedural blank was so small that the resulting silver sulfide [see procedures in (6)] could not be weighed, a small amount was seen (as SO,) on the ion chromatograrn, a maximum of _0.3 I, mol. 8_aC values are blank corrected. The standards used for B;3C and BD measurements were Pee Dee beiemnite and standard mean ocean water, respectively. All isotope values are given in per mil.

Amount 8_aC 8D* _33S _34S _36S 3'3_1, Compound (p.rnof)

R (in R-SOa) CH3 (MSA) 3.8 29.8 483 7.63 11.27 22.5 2.00 CHaCH 2 (ESA) 1.7 9.1 787 0.33 1.13 0.8 -0.24 CHaCHaCHa(nPSA ) 0.9 -0.4 536f 0.20 1.20 2.1 -0.40 (CHa)2CH (iPSA) 0.7 -0.9 852 0.32 0.68 2.9 -0.02 Bulk R-SOft: - 6 600 .... Phosphonics (uncorrected) - - 20 219 .... Blank - -21.6 -55 .... Standard MSA - -39.1 - 100 0.45 0.80 2.7 0.03 Standard 1§ - -42.2 _+0.3 -107 -+ 4 .... Standard 2l] .... 0.25 -- 0.05 -0.51 = 0.1 -1.9 _ 1.0 0.00 _-+0.05 NBS-22 standard¶ - - 29.8 - 122 .... •The 8D values are corrected for blank and exchangeablehydrogen. In contrast to C and S, less than quantitative yields of H were obtained for MSA and nPSA. However, measurementsof a standard (NBS-22) with the same vacuum and combustion procedure indicated no D/H or _ac/_ac fractionation, and procedural standards consistingof differentamounts of MSAshowed close agreemant, 4-4,of 8D values(above). 1"Thisvalue is obtained after correctingfor exchangeablehydrogenonly. ;_Frorna different sample of Murchison.The matching bulk sample was lost. §Proceduralstandards,MSA: 1, 1.4, and 7 F.mol. HProceduralstandards, MSA: 1 and 7 laJ-nol. ¶8_3C= -29.7, 8D = -118.

REFERENCES AND NOTES The difference in S isotope composition (20). The C/S ratio of the solid usually between MSA and the other sulfonics likely ranges from 1/1 to 5/1 (18). The require- 1. J. R. Croninand S. Chang, in Chemistry of 's arises from the differential fractionation fac- ments of a surface and low temperatures for Origins,J. M. Greenberg,V. Pirroneno,C. Mendoza- Gomez, Eds. (Kluwer, Dordrecht, Netherlands, tors associated with the formation of the CS polymerization are met by interstellar 1993), pp. 209-258. individual molecules. A potential source of grains. In addition, CS will self-polymerize 2. E. F. Van Dishoeck, G. A. Blake, B. T. Dralne,J. I. the 33S enrichment in MSA (33A = 2.0 per or is stable in the presence of some po- Lunine, in Protostarsand Planets III, E. H. Levy and J. 1.Lunine, Eds. (Univ. of Arizona, Tucson, AZ. mil) could be gas-phase ultraviolet (UV) tentially interfering interstellar compounds. 1993), pp. 16.3-241. irradiation of a precursor molecule such as For example, CS is stable in the presence 3. T. E. Bunch and S. Chang, Geochim. Cosmochirn. CSa. In the laboratory, mass-independent of solid (21) and (22) Acta 44, 1543 (1980). isotope effects have been produced by the and polymerizes in the presence of liquid 4. G. W. Cooper, W. M. Onwo, J. R. Cronin, Ibid. 56, 4109 (1992). gas-phase UV irradiation of symmetric mol- methanol (21). In the photolysis of CS 2 5. Also see(6).Thestableisotopes of S havemassesof ecules such as CS z (14), CO z, and O 3 (15). (which produces CS), formation of a solid 32 (95.02%), 33 (0.78%), 34 (4.21%), and 36 The isotope effects may derive from molec- phase was not prevented by the addition of (0.02%)atomic mess units (ainu). The deviation of the ratioof Sisotopesin a samplefrom the standard excess hydrogen and other molecules (23). ular symmetry factors (16). In the irradia- (S in the CanyonDiablo iron meteorite} is given in tion (313-nm wavelength) of CS z (14), a The CS reaction products or interstellar parts per thousand or per rail, which is defined as 3_S excess of 5.3 per mil was observed in the molecules of relevance to the present study _'S = [[(xs/32S)sarnl>_/(xS/32S)standar_] - 1) x 1000, wherex = 33, 34, or 36. If plotted on a three- resulting solid phase, which was character- are CS z (SCS), CzS (CC.S), C2S z (SCCS), Isotope graph, normal mass-de_endant fraction- ized as (CSz) =. In that experiment, a large C3S (CCCS), and C3S z (SCCCS) (24). ationsshouldlie on the line @3S = 0.5 83_S,be- 3eS deficit was also observed, which is not These compounds are potential precursors to causethe differencebetween _S and 32Sis1 ainu and thedifferencebetween _S and a2Sis 2 ainu, the case for Murchison MSA. Recent exper- the observed meteoritic sulfonic acids of the which gives0.5 as theslope. Similarly,83eS= 1.97 iments (I 7), however, have shown the pro- same carbon number. A high-resolution 8_S. Therefore, any mass-independent isotopic cess to be wavelength dependent, and the mass spectrometry study of organic matter in anomalyinmS and 3eSis given by (inper mil)aaA= B_3S- 0.5 @aS and as& = 8a_S _ 1.97 8a4S, sign of the fractionations may be reversed. the Murray carbonaceous meteorite identi- respectively.All known terrestrial S lies on normal At present, it may only be concluded that a fied species of elemental compositions CS z, mass-dependentfracticnation lines. The calculation process capable of producing a 33S excess CzS, C_S, C_S z, and C3SO, in addition to of 5 valuesfor C and H is similarto that of S, that is, exists in an astrophysical environment. many others (25). CSz is commonly seen in BH = {[(H/7..)_,_m_e/(H/L)standaj--1}X 1000, where H and L arethe heaw and light isotopes, respective- carbonaceous meteorites (25, 26). In addi- At the low temperatures of interstellar ly, of eachelement. space, chemical reactions of the molecule tion, in the present study, the unsaturated 6. X. Gaoand M. H. Thiemens,Geochim. Cosmochlm. CS are capable of producing compounds analog of ESA, vinyl sulfonic acid Acta 55, 2671 (1991). 7. M. H. Thiemensand T. Jackson, Lunar Planet.Sci. that could serve as sulfonic acid precursors (HzC=C(H)SO3-), was identified in an ex- XXVI, 1405(1995). and have mass-independent isotope anom- tract of a Murchison sample. These observa- 8. M. H. Thiemenset al., Meteoritics 29, 540 (t 994). alies resulting from gas-phase UV irradia- tions reinforce the possibility that the sulfon- 9. G. W. Cooper and J. R. Cronin, Geochim. Cosmo- tion. CS is reactive and relatively abundant ics and perhaps other interstellar carbon- chim. Acta59, 1003 (1995). 10. The fractioncontainingthe sulfonicsand phosphon- chain compounds arose from unsaturated in interstellar space (2). In the laboratory, ics(9) was then injected into a Dionex (Sunnyvale, CS forms several molecules and an insolu- precursors, resulting from CS chemistry. CA) ion chromatograph (1(3)equipped with two 9 ble solid phase on surfaces when it is con- Compounds of the type C_S z, if definitely mm by 250 mm DionexAS4-A columns and eluted with a carbonatebuffer, 1.8 mM Na.aCOa + 1.7 mM densed at low temperatures (18, 19). Mol- identified in meteorites, comets, or interstel- Nal-ICOa (4 mgmin),to collect sulfonics and phos- ecule formation in the solid phase has been lar clouds, may be more indicative of a reac- phonicsasseparategroups. At this step, nPSAsep- reported at temperatures as low as 33 K tive S-rich starting material like CS. aratessufficientlyfrom the other sulfonicsfor collec-

www.sciencemag.org • SCIENCE • VOL. 277 * 22 AUGUST 1997 1073 " tion. To collect the remaining sulfonics individually, same structure as the CS condensation products 30. G. W. Cooper and S. C.,heng, Lunar Plenet. Sc/. we then reinjected the sulfonics into the IC, which (and the identified interstellar molecules), they XXV1, 281 (19953. was edUil_bed with a 10 m by 100 mm Phenomenex would seem to require a special carder in the me- 31. We thank C. Moore {Arizona State University, Center (Torrance, CA) star-ion anion exchange column, and teorite matrix, perhaps a carbon phase such as one for Meteorite Studies) for the sample of the Murchi- eluted them with a 5.4 mM Na2CO 3 + 5,1 mM produced from polymerization of CS or other reac- son meteorite; A. Tharpe for _ isotope mea- NaHCO 3 iouffer. We separated ESA from a small tive molecules (or both). surements; K. K]abunde and S. Charnley for helpful amount of co-eluting sulfate by rainjecting the two 26. M. H. Studier, R. Hayatsu, E. Armlets, _id. 36, 189 conve_sa_on; and V. Morris, N. Lemer, D. Des Ma- compounds and e_uting them with a 3.2 mM (1972). rais, K. Zahnle, and L. Allamendola for comments on N_CO 3 -F 3.1 NaHCO 3 mM buffer. Baseline sepa- 27. M L. Coleman and M. P. Moore, Anal Chem. 50, the menuscdpt. Supported by NASA grant NAGW ration between MSA end ESA/sulfate was -2 rain; 1594 (1978). 3551 and the Exobiologyand Pro- between ESA/sulfate and iPSA, it was _9 rain, and 28. R. Steudel, 7_Naturforsch. Te_7B. 218, 1106 (1966). grams of NASA. " between ESA and sulfate, it was -1 min. After re- 29. G. W. Cooper, M, H. Thiemens, T. L. Jackson, S. moval of the buffer with HCI, each com- Chang, Meteori_cs 30, 500 (1995). 7 April 1997; accepted 8 JL_y 1997 pound was then placed in a quartz tube and dded by rotary eval_3ration (maximum temperature _ 50°C). Copper oxide was then placed in each tube, and high vacuum, with mild warming (<100°C), was Discrete Intensity Jumps and Intramolecular used for complete drying. The samples were then sealed and combusted to sulfate, CO_, end H_O at Electronic Energy Transfer in the 800°C, The CO_ end H=O were collected with a _ocedure similar to that of Epstein et al. (13). The of Single Conjugated Molecules H20 was converted to H by the method of Coleman end Moore (27) with a zinc catalyze from J. M. Hayes of Indiana University. The CO 2 and H were then an- David A. Vanden Bout, Wai-Tak Yip, Dehong Hu, Dian-Kui Fu, alyzed w_th 6-60-Nuclide and 3-60-HD-Nuclide mass spectrometers. The sulfate was extracted from Timothy M. Swager, Paul F. Barbara* each tube with hydrochloric acid and prepared for S isotopic analysis as in (_. 11. X. Gao end M. H. Thiemens, Geochim. Cosmochim. Single-molecule fluorescence spectroscopy of a multichromophoric conjugated polymer Acta 57, 3159 (1993). (molecular weight _20,000) revealed surprising single-step photobleaching kinetics and 12. G, Yuen, N. Blair, D. J. Des Marais, S. Chang, Nature acute jumps in fluorescence intensity. These jumps were shown not to result from 307, 252 (1984). 13. S. Epstein, R. V, Krishnamurthy, J. R. Cronin, S. spectral diffusion and were attributed to fluctuations in the quantum yield of emission Pizzaretlo, G. U. Yuen, ibid. 326, 477 (1987}. for the molecules. The data indicate efficient intramolecular electronic energy transfer 14. J, J. Colman, X. Xu, M, H. Thiemens, W. C. Trogler, along the polymer chain to a localized fluorescence-quenching polymer defect. The Science 273,774 (19953. defects are created by reversible photochemistry of the polymer. These findings have 15, K. Maue_sberger, J, Morton, B. Scueler, J. Stehr, Geophys. Res. Lett. 20, 1031 (1993). implications for the use of conjugated in light-emitting diode displays and 16. J. Heidenreich end M. H. Thiemens, J. Chem. Phys. sensors. 84, 2129 (1986). 17. X. Xu end M. H. Thiemens, unpublished data, 18. E. Moltzen, K. J. K]abunde, A. Senning, Chem. Rev. 88, 391 (1988). In most of the literature, this solid phase is referred to as a "CS polymer," and we will Recent developments in fluorescence mi- timate impact of the energy migration on use the terms i:x_yrner end polymerization for con- photochemistry is of intense fundamental venlence. In the laboratory, this polymerization is croscopy have allowed for the detection, highly exothermic. The heat of formation (&H_) values imaging, and spectroscopy of single mole- and practical interest. Conjugated polymers in the range of -50 kca[/mol of CS have bean esti- cules at room temperature (1-12). As a such as poly(p-phenylene vinylene) (PPV) mated for the formation of CS polymers. and poly(p-pyridylene vinylene) (PPyV) 19. K. J. Klabunde, E. Moltzen, K. Voska, Phosphorus consequence, single-molecule spectroscopy Sulfur Silica Relat. E/ern. 43, 47 (1989). (SMS) has moved from studies at cryogenic have shown great promise for light-emitting 20. R. B. Bohn, Y. Hennachi, L. Andrews, J. Am. Chem. temperatures (13) to a broader range of device applications (16, 17). We studied a Soc. 114, 6452 (1992). environmental conditions. In many cases, derivatized PPV-PPyV copolymer com- 21. C. M. Wl_ite, thesis, University of North Dakota, direct information about the molecular dis- pound with a molecular weight of _20,000 Grand Forks (1974). 22. M.A.P. Hogg and J. E. Spice, J. Chem. Soc. 158, tribution of physical quantities, rather than (Fig. 1A). 4196 (1958). just the ensemble-averaged values obtained Spectroscopic studies on bulk polymer 23. M. De Sorgo, A. J. Yarwcod, O. P. Strausz, H. E. materials suggest that conjugated polymer Gunning, Can, J. Chem. 43, 1886 (1965). by bulk measurements, can now be ob- 24. Some reported CS reaction products are CS_, C2S, tained. Most room-temperature SMS stud- emission is often dominated by energy C2S_, CaS, CaS 2, CO, CO 2, OCS, S, S_, SO, and ies have involved aromatic dye molecules migration to local minima in their op- SO_. On the basis of infrared observations of low- tical band structure (18). For example, temperature (solid phase) CS reactions, Steudel (28) that correspond to a single chromophore in suggested a reaction sequence where molecules of a fluctuating environment and have re- -derivatized poly(p-phenylene- increasing carbon number are formed, leading to a vealed direct information on chemical and ethynylene)s in solution have been shown polymer: xCS -* CS2, CCS, C3S2, CvSz --_ polymer. spectroscopic heterogeneity of single mole- to selectively emit from states associated Of the above molecules, C_S2and S2 ('#searched for) have not been reported to occur in the interstellar cules (4, 14), as well as on the dynamics of with the anthracene end groups (19). Al- medium, In addition to CS2 (see text), OCS and S, these inhomogeneities (I0, 15). though excitation diffusion along the are also observed in carbonaceous metecrites (25, Here, we used SMS to study molecules chains in conjugated polymers is efficient, 26). 25. J. M. Hayes and K, Biemann, Geochim. Cosmo- that each comprise many similar chro- the actual optical excitation (exciton) may chim. Acta 32, 239 (1968]. In the expedments, core mophores, such as conjugated fluorescent be localized and may have a coherence samples of the meteorites were placed directly in polymers. Intramolecular migration of ener- length of only a few monomer units (20). the inlet of the mass spectrometer. For the identi- Thus, spectroscopic evidence of conjugated fication of ions C2S, CaS, end C3SO, a sample was gy among these chromophores and the ul- heated only between 25 ° end 100°C for a total of 5 polymers suggests that their broad absorp- rain. The authors give reasons as to why this tem- D. A. Vanden Bout, W.-T, Y_p, D. Hu, P. F. Barbara, tion spectra are the result of overlapping perature and time range is not severe enough to Department of Chemistry, University of Minnesota, Min- produce S compounds by decomposition of S and absorption bands from different segments neapolis, MN 55455, USA. along the polymer chain, and that their organics, In the case ofCaS 2, heating was between D.-K. Fu and T. M. Swager, Department of Chemistry, 160 = end 200°C for 5 min. No theory of how such Massachusetts Institute of Technology, Cambridge, MA emission is strongly affected by energy mi- reactive compounds could have survived in the 02139, USA. grations, often to sites remote from the meteorite for billions of years was offered. Howev- er, if the compounds were indigenous end of the 'To whom correspondence should be addressed. absorption (18). This hypothesis can be

1074 SCIENCE • VOL. 277 • 22 AUGUST 1997 • www.sciencemag.org