LITERATURE CITED
(1) Aronson, A. L., Hammond, P. B., Nucleonics 22, 90 (1964). (2) Bagnall, K. W., Freeman, J. H.,
Robertson, D. S., Robinson, P. S., Stewart, M. A. A., AERE-CIR-2566
(1958). (3) Black, S. C., Health Phys. 7,87 (1961). (4) Figgins, P. E., “The Radiochemistry of Polonium,” NAS-NS-3037 (1961): ( 5 ) Fink, R. M., “Biological Studies with
Polonium, Radium, and Plutonium,” pp. 18-27, McGraw-Hill, New York, 1950.
(6) Gorsuch, T. T., Analyst 84,135 (1959).
( 7 ) Groos, V. E., Sattler, E. L., Stahlhofen, W., Atomkernenergie 8,32 (1963). (8) Harrison, A. D. R., Lindsey, A. J., Phillips, R., Anal. Chem. Acta 13, 459 (1955).
(9) Hill, C. R., Health Phys. 8,17 (1962). (10) Hill, C. R., Ibid., 9, 952 (1963). (11) Hill, C. R., Nature 187, 211 (1960). (12) Holtzman, R. B., Health Phys. 9,385 (1963). (13) Ibld., 10, 763 (1964). (14) Jaworoeski, Z., Nukleonika 8, 333 (1963). (15) Korkisch, J., Feik, F., ANAL.CHEM. 36, 1793 (1964). (16) Latimer, W. M., “The Oxidation Studies of the Elements and Their Potentials in Aqueous Solutions,” PrenticeHall, Englewood Cliffs, N. J., 1959. (17) Milland, H. T., ANAL. CHEM.35, 1017 (1963). (18) Osborne, R. V., Nature, 199, 295 (1963).
(19) Radford, E. P., Hunt, V. R., Science 143, 247 (1964). (20) Robbins, M. C., “The Determination of Polonium in Urine,” LA-1904 (1955’1. (21) Saltzer, M., Hursh, J. B., Arch. Ind. Hyg. Occ. Med. 9,89 (1954). (22) Stahlhofen, W., “Der Naturliche
Gehalt Des Menschlichen Korpers An Alphastrahlenden Nukliden,” Doctoral Dissertation, Johann-Wolfgang-Goethe Universitv. Frankfurt. Germanv. 1964. (23) Turne;,’R. C., Radley, J. MY,’ Mayneord, W. V., Brit. J . Radwl. 31, 397 (1958).
RECEIVEDfor review October 15, 1965. Accepted November 29, 1965. Mention of commercial products does not imply endorsement by the Public Health Service.
Proton Nuclear Magnetic Resonance Studies of Several Polyalcohols, Hydroxy Acids, and Derivatives of D-Gluconic Acid DONALD T. SAWYER and JAMES R. BRANNAN Department of Chemistry, University of California, Riverside, Calif. Proton NMR spectra have been recorded and interpreted for ethyleneglycol, glycerol, erythritol, sorbitol, glycolic acid, D-glyceric acid, tartronic acid, tartaric acid, acetic acid, malonic acid, succinic acid, ascorbic acid, Dgluconic acid, D-saccharic acid, Dglucono-&lactone, D-glucono-y-lactone, D-saccharodilactone, and D-glucurane. The effects of solution pH also have been studied to aid in the interpretation of the spectra for these compounds. A number of spin-spin interactions due to protons attached to asymmetric centers are observed for several of the compounds; these have been interpreted to a limited extent and give some insight into the structure of the compounds.
P
ROTON NUCLEAR MAGNETIC ONANCE SPECTROSCOPY has
RES-
been shown to be an effective means for studying the bonding and structure of a number of complexing agents and metal chelates in aqueous solution (1, 4, 6). Because of a continuing interest in metal-gluconate complexes and because of the general lack of understanding of the structures of such systems (9), an NMR study of this group of chelates has been initiated. However, the spectra for these systems are sufficiently complicated that an extensive NMR study of gluconic acid, its salts, and its lactones has been necessary before the spectra for the metal gluconate systems 192
ANALYTICAL CHEMISTRY
could be interpreted. Interpretation of the gluconate spectra has been based on studies of a number of compounds related to the gluconic acid molecule. The present discussion summarizes a study of the proton NMR spectra for gluconic acid and these related compounds. The approach has been similar to that for previous studies of the metalEDTA chelate systems (6) ; that is, the NMR spectra have been recorded as a function of solution pH. This has permitted the effect of protonation of the carboxylate group upon the chemical shift of neighboring protons to be observed and has been especially useful for interpreting the spectra. A number of the compounds have not been studied by NMR previously and for a number of others the spectra which have been observed have not been assigned. By studying a large group of related polyhydroxy compounds generalized assignments and spectra interpretations have been possible. A recent review by Hall discusses the use of NMR for the study of carbohydrates (3). EXPERIMENTAL
The NMR spectra were recorded with a Varian A-60 high-resolution spectrometer equipped with a 60 Mc. oscillator and a variable temperature probe. The 100 Mc. spectra were recorded using the facilities at Varian Associates, Palo Alto, Calif. Spin decoupling experiments were made on a Varian HR-60 spectrometer equipped
with R.F. irradiation accessories a t the University of California, Los Angeles. Chemical shifts were measured by using tetramethylammonium chloride (TMA) as an internal reference. The resonance for this material is 3.177 p.p.m. downfield from 3-(trimethyl sily1)-1-propane sulfonic acid, sodium salt (TMS), and the reported resonances can be converted to this reference by adding the difference. The TMA reference has the advantage of having a constant chemical shift, independent of solution pH and composition, which is close to the chemical shifts for C-H protons of the materials studied. This permitted smaller and more sensitive sweep widths than would have been possible by using TMS. The p H of the sample solutions was measured with a Leeds and Northrup line-operated pH meter equipped with high-range glass electrode. The meter was standardized with National Bureau of Standards buffers and the p H values were determined a t 25’ C. All sample solutions were prepared with deuterium oxide (DzO) because of the close proximity of the alcoholic C-H protons to the resonance for HzO. For this reason the indicated pH values should be corrected by the expression (6) pD = “meter reading” 0.40 This has not been done for the data presented because the NMR sample probe was operated at 40’ unless indicated otherwise. Thus the reported p H values are approximate, but are meaningful in a relative sense. The solutions were prepared from reagent grade chemicals which were
+
A
B
D
B
06
a4
6, ppm, vs TMA
O?
Figure 1. NMR spectra a t 60 Mc. of (A) ethyleneglycol, (B) glycerol, (C) erythritol, and (D) sorbitol in DzO solutions
usually used without further purification. I n some cases the sample materials were recrystallized one or two times. The delta lactone of D-gluconic acid was used for the preparation of the sample solutions of gluconic acid and gluconate ion. The gamma lactone of D-gluconic acid was supplied by Dr. H . S. Isbell, Division of Physical Chemistry National Bureau of Standards. The sample concentrations were made approximately 1F and the solution acidity was adjusted with concentrated HNOl or with KOH pellets. RESULTS AND INTERPRETATIONS
The general approach for interpretation of the NMR spectra has been t o deduce assignments for simplified analogs of the more complex hydro,xy and sugar acids. This then permits the more complex spectra of the latter compounds to be interpreted. I n some cases spin decoupling has been useful
in simplifying spectra to the extent that assignments are made possible. Polyalcohols. The simplest members of the polyhydroxy group of compounds that have been studied are the polyalcohols. These provide a reference base from which the effect of various substituents upon the chemical shifts for the alcoholic C-H protons can be determined. Also, the polyalcohols, because of symmetry and their monofunctional character, have the simplest and easiest KXR spectra to interpret and therefore provide a route to the interpretation of the much more complex spectra of the sugar acids. A composite of the S M R spectra for ethylene glycol, glycerol, erythritol, and sorbitol (2-, 3-, 4-, and 6-carbon polyalcohols, respectively) is shown in Figure 1. Ethylene glycol has a single resonance a t 0.472 p.p.m. downfield from ThIA, but the other polyalcohols are more complex with a main central peak a t 0.450 p.p.m., 0.522 p.p.m., and 0.537 p.p.m. for glycerol, erythritol, and sorbitol, respectively. Thus, the major resonance occurs between 0.45 and 0.55 p.p.m. for this class of compounds and i s due t o the protons of the -CH20H and >CHOH groups. This serves as a guide for the assignment of resonances to similar groups in the sugar acids when substituent effects are absent. Aliphatic and Hydroxy Acids. An additional group of compounds that serve as simplified analogs to the sugar acids are several aliphatic and hydroxy acids. The chemical shifts under both acidic and basic conditions have been measured for acetic, malonic, and succinic acids as well as for their hydroxy analogs and are tabulated in Table I. A11 of these compounds give simple one-line spectra. The difference in chemical shift, A, between the acid form and the salt form of the species also is summarized. The difference is dependent on the number of C-H protons per carboxylate group and as seen from Table I the values of A are about 0.19, 0.29, 0.40, and 0.59 p.p.m. for ratios of protons to carboxylates of 3:1, 2:1, 1:1, and 1:2, respectively . D-Glyceric Acid. I n contrast t o the acids summarized in Table I, Dglyceric acid has a complex spectrum indicating extensive spin-spin interaction between nonequivalent protons, Its spectra a t both 60 Me. and a t 100 Me. are shown in Figure 2. The upper curves are for the acid form and the bottom curves are for a pH 13.5 solution, Additional spectra have been recorded at 60 Me. over the entire p H range; the chemical shifts of the resonance lines as a function of pH are shown in Figure 3. Figures 2 and 3 as well as the areas of the peaks establish that the dorvnfield resonances are due to the pro-
~
100Mc
1 14
I
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-.”-t
