Sept., 1957
THEINTERACTION OF CARRAGEENIN WITH COUNTERIONS
FOPTi [O&3si(C,H6)&, the spectra of samples of the opaque crystals and the colorless plates crystallized from ether were identical. Neither the peaks belonging to butyl alcohol nor the peaks of tetrabutoxytitanium were detected in either sample. Three strong peaks at 739, 717 and 696 ern.-’ correspond in intensity and position to three peaks attributed by Young to diphenyl substitution in octaphenylcyclotetrasiloxane. Hexaphenylcyclotrisiloxane can be differentiated from octaphenylcyclotetrasiloxane by the intensity pattern of these three peaks. In addition, octaphenylcyclotetrasiloxane has a strong absorption a t 1079 cm.-’, but the siloxane trimer absorbs at 1013 cm.-’. These peaks
1177
are due to the Si-O-Si stretch vibrations. They are distinctive features of the two cyclosiloxanes. The spectrum of Ti [O&3si(C,H,)s]zhas a strong absorption doublet at 1093 and 1066 cm.-’, but no absorption in the vicinity of 1013 cm.-’. This doublet corresponds to the 1079 cm.-l peak of octaphenylcyclotetrasiloxane. On the basis of this additional evidence, the colorless plates are believed to consist of molecules which contain two rings of four diphenylsiloxy groups, with each ring bonded through oxygen to the central titanium atom. We wish to acknowledge gratefully the financial assistance of the Office of Naval Research, during this investigation.
THE INTERACTION OF CARRAGEENIN WITH COUNTERIONS BY R. E. SCHACHAT AND H. MORAWETZ Contribution from the Central Laboratories, General Foods Company, Hoboken, N.J., and the Polymer Research Institute, Polytechnic Institute of Brooklyn, Brooklyn 1, Neu York Received April $8, 1067
The dialysis equilibrium of carrageenin solutions containing large concentrations of potassium, ammonium, calcium, magnesium or ethylenediammonium was investigated. The polymer solutions gave no evidence of a selective affinity for potassium over sodium. Magnesium was held in the olymer phase more strongly than calcium; the data for ammonium and ethylenediammonium are inconclusive. The resuLs indicate that counterion binding to isolated carrageenin molecules does not correlate with the ability to induce gel formation.
Introduction Carrageenin, an acidic polysaccharide with halfester sulfate groups, is a constituent of the alga Chondrus crispus and has long been known to be precipitable by potassium salts, while it remains in solution in the presence of similar concentrations of sodium.’ Smith and Cook2 have demonstrated that precipitation by potassium ion may be utilized to separate the natural product into two fractions, the potassium sensitive fraction (“K-fraction”) constituting about 40 weight % of carrageenin. More recently, Smith, O’Neill and Perlin have reported an interesting chemical difference between the two carrageenin fractions.8 They found that the K-fraction contains 24% of 3,6-anhydrogalactose units, which were almost completely absent in the portion of carrageenin which remains in solution in the presence of potassium ion. The difference in the behavior of the K-fraction toward sodium and potassium ion is in striking contrast to the stronger tendency of Na+ to participate in complex ion formation4-6 The clarification of the physico-chemical basis of the “potassium sensitivity” of carrageenin is particularly interesting in view of the many instances in which selectivity in the response to Na+ and K+ is a factor governing biological phenomena. The present
study was undertaken to show whether selective complex formation of potassium with carrageenin solutions may be demonstrated by dialysis equilibrium. The precipitation or gelation of carrageenin in the presence of divalent cations is less surprising, since many natural or synthetic polymeric acids behave in an analogous fashion. However, even here dialysis equilibrium data were expected to illuminate the nature of the ion-polyelectrolyte interaction.
Experimental
Carrageenin .-The carrageenin was Viscarin (Algin Co., Rockland, Me.). Its moisture content was determined by drying to constaiit weight a t 70” at a pressure of 100 mm. The intrinsic viscosity in 0.2 N NaCl a t 25” was 0.2 dl./g. The potassium sensitive fraction (K-fraction) was determined by precipitating three times a sample of 4 g. (on a dry basis) dissolved in 2 liters of water, once with 700 ml. and twice with 400 ml. of 1 N KCI. The salt solution was run in with stirring and the stirring was continued for 30 minutes before separating the precipitate by centrifugation. The last supernatant gave no precipitate on mixing with a double volume of isopropyl alcohol, indicating the absence of carrageenin. The slurry of potassium carrageenate was washed repeatedly with isopropyl alcohol until the su ernatant was free of chloride. The slurry was then filteref onto a tared fritted glass funnel, dehydrated with isopropyl alcohol and vacuum dried at 70’ for 7 hours. The yield was 59.47& The fraction of carrageenin not pre(1) L. Stoloff, in “Natural Plant Hydrocolloids.” American Chemicipitated by potassium chloride was precipitated from the cal Society, 1954, p. 92. combined supernatants by mixing with two volumes of isopropyl alcohol. It constituted 36% of the original (2) D. B. Smith and W. H. Cook, Arch. Biochsm. Biophye., 48, 232 Sam le. (1953). (3) E?. B. Smith, A. N. O’Neill and A. 8. Perlin, Can. J . Chem., 33, Tge original Viscarin contained considerable amounts of 1352 (1955). potassium and alkaline earths and it was purified by 9 batchwise treatments with the cation exchanger IR-120 (Rohm (4) G. Schwarsenbach, E. Kampitach and R. Steiner, Helv. Chim. A d o , 29, 364 (1946). and Haas) in the sodium form. The final sample contain+, on !dry ba$s, 6.6% Na, 0.018% K and lO.l% S. (6) G. Sahwaraenbsch and H. Ackermann, ibid., 80, 1788 (1947). The intrinsic viscosity was 7.2 dl./g. This purified Vis(6) W. C. Fernelius and L. G. VanUitert, Acta Chsm. Scand., I, 1726 carin (sodium carrageenate) was used in all the experiments. (1954).
Sept., 1957
STRAINELECTROMETRY AND CORROSION
the polymer contained anionic groups with a similar spacing so as to allow close fitting of opposite charges. There is no clear indication of ethylenediamine binding in the results obtained at the higher concentration and the data for the lower concentration are subject to the same uncertainty as discussed above for the ammonium ion. The results of the present investigation show clearly that there is no correlation between the ability of individual carrageenin molecules t o bind counterions and the effectiveness of these counterions to produce, under favorable conditions, the precipitation or gelation of the hydrocolloid. Stoloffl gives the order of effectiveness of cations in the gelation of carrageenin as K + > Ca++ > Mg++ > Na+ while the dialysis equilibrium data show no difference in the Dolvmer interaction with K + and Na+ and the rev&se”order of affinity with
1179
the alkaline earths. It must be concluded that gel formation involves the counterions in a different manner than interaction with the isolated macromolecules. This interaction could be either in the nature of “salt bridges” or the formation of microcrystallites which might be able to accommodate only cations of a certain given size. A similar interpretation of the selectivity of carrageenin between sodium and potassium was proposed by Bayleyi3 on the basis of X-ray diffraction data. Acknowledgment.-The authors wish to express their thanks to E. Borker and A. Stefanucci of the General Foods Research Laboratories who carried out all the analyses required for this study and to J. Olsen and M. Glicksman for valuable technical assistance. (13) s. T.Bayley, Biochim. Biophys. Acta, 17, 194 (1955).
STRAIN ELECTROMETRY AND CORROSION. 11. CHEMICAL EFFECTS WITH COPPER ELECTRODES BY ALBERTG. FUNK,J. CALVIN GIDDINGS, CARLJ. CHRISTENSEN AND HENRY EYRING Department of Ch.emistry, Univer.sity of Utah, Salt Lake City, Utah Received ApriE 87, 3867
The potent.ia1 transient induced in a copper electrode through mechanical strain is studied as it depends upon the concentration of various solutions. Thc transients are of about one Recond duration, and the potential chmge is ordinarily about 0.1 volt. The results have been interpreted in terms of the film-rupture model, previously presented by the authors.’ Other possible mechanisms of potential change have been presented, and in certain cases these additional reactions appear to be important.
Introduction A metal electrode in aqueous solution acquires a potential as a result of chemical reactions near the metal-solution interface. When the electrode is plastically strained, a change of the interface chemistry leads to a change in the measured potential of the electrode. This potential change is generally negative (anodic), and is short-lived; a time of about one second is required for its decay. The decay time, as well as the maximum voltage change, depend upon the nature of the electrode and the content of the solution. We have measured these electrode strain transients with several metal electrodes (most extensively with copper), and in many different solutions. The data have been used to study the importance of the several chemical processes contributing t o the voltage change. Preliminary results have been published e1sewhere.l Considerable effort has been directed at understanding the change of electrode potential due to strain, but fewer people have considered the potential transient immediately following strain. However, the work of Dudley, Elliott, McFadden and Shemilt,2like our own, is concerned primarily with the electrode strain transients of copper in various solutions. They record transient voltages as high as 30 mv. in cupric sulfate solutions. Results were (1) A. G. Funk, J. C. Giddings, C. J. Christensen and H. Eyring. Proc. Natl. Acad. Sci., May (1957). (2) R. 8. Dudley, R. Elliott, W. H. McFadden and L. W. Shemilt, J. Chsm. Phys., 28, 585 (1955).
also obtained for solutions of cupric chloride, magnesium sulfate and potassium nitrate. Nikitin3 measured electrode strain transients for copper, as well as for silver and iron. He observed larger potential transients in the case of work-hardened copper than for a soft-drawn electrode. Zaretskii4 used copper, magnesium and aluminum in a series of similar experiments. Gautam and Jha5 found potential transients for copper, but these were of opposite sign to those of references 2 and 3, as well as those reported here. The external resistance in their circuit was so low as to preclude transients of more than a few millivolts. Experimental Procedure The apparatus used to study the effects of deformation and stress on changes in the electrode potentials of metals includes a shielded, constant-temperature cell containing two wire electrodes and the solution. The wire electrodes are inserted through holes in the bottom of the cell and connected to an insulated frame. They are then connected into the amplifier with shielded cables to avoid pick-up of stray electrical fields. One wire is left undisturbed whilc the other is attached to an insulated weight holder. Tension is ap lied by adding designated weights to the weight, holder. $he changes in length are read by a pivoted pointer on a meter stick.
Theory and Results An example of the potential-time behavior of (3) L. V. Nikitin, J . Gen. Chem. ( U . S . S . R . ) , 11, 146 (1941). ( 4 ) E. M. Zaretskii, ZhuT. Priklad. Khdm., 24, 614 (1851). ( 5 ) L. R. Gautam and J. B. Jha, Proc. Ind. Acad. Sci., M A , 350
(1953).
