Equilibrium Ultracentrifugation and Light Scattering of Sodium Lauryl Sulfate and Dodecyltrimethylammonium Bromide Solutions¹

Abstract

Chemist1 u Division, Oak Hidoe National Lahoratoru. Oak R i d g e , l'ennessce. and D e p a r t m n l o/ Chemislrjl. Montana State C'olleg6, 13oteman, Montana (Received Jzdu 106Y) hIiccllar weights of' sodium lauryl sulfate in 0.1 arid 0.4 AI SaCl measured by cqiiilibrium iilt,racciit,rifugation and in 0.4 AT NaC1 by light, scattcriiig are in good agrccment with each other and with values in the literaturc. The micc.llcs are predominantly monodisperse in 0.4 Ji' NaCl, but appcar to bc polydisperse in 0.5 , I ! SaCI. Degrees of aggregation appear to be less in 0.4 M LiCI than in 0.4 ; I ! SaCI. .4 method of estimation of critical micelle concentration by ultracentrifugation is illustrated. Although t,hc partial spccific volume of dodecylt~rimet,hylammonium bromidc (I)T.213) is too near unity for good estimates of molecular 13 eight by equilibrium ultracentrifugation, the tochriiquc dons indicate a monodispcrse distribution in 0.1 M NaHr and polydispcrsit,y in 2.0 AT SaRr. 1,ight scattering values of TITAR dcgrcc of aggregation are presented and compared with literature values. SOF e anomalous observations in the sodimcntatioii of soaps at low centrifugal fields arc prcsont!cd.A number of different, cxpcrimcntd mcthods havc been used in the past to secure information coriceriiiiig the dogrw of aggregation of surfactants in solution. In t,hc case of sodium lauryl Fiulfatt, NaTIS, for cxnmplc, these include light scattering, -I(' self-difrusiori, I sedimentation vclocity,*2 sodirncntatjion velocity combincd wit,h diffiision, I 2 -l 5 centrifugation a t solut,ion boundaries'? (Archibald method), conductivity, 16,17 osmotic prcssiire,18 and X-ray diffraction.1° Sincc different procedures havc led to substantial variations in estimates of aggregation in some cases, it seemed worthwhilo to athcmpt, a study of such systems by equilibrium ultracentrifugation, a method hitherto not applied, to our knowledge.Alt,hough thcrc arc disadvantages to cquilihrium ultracentrifugation, they are in many instances, at least, different from those of other methods. Dust, for example, is a trivial interference hcrc, in contrast to light scattering; the presence of otfher impurities would also be expected to be less important, In X-ray scattering, l9 solutions considerably more concentrated than those in question are involved. Xo assumptions concerning particle shape, which are required in the interpretation of self-diffusion and conductivity, need be made hcrc. Sedimentation velocity requires auxiliary deterniination of diffusiori oocfficicritjs, the mcasurcmcrit, of which is cnmplic,zt,ed by the morinIn(>r-micellar equilit)ria. l 2 Iri the Archibald ~iiotliod, i i i (1) This doc:urrierit is based in part on work performed for the 11. S.Atorriir~ Erirrgy Corrinrissiorl at thc Ouk ltidge Sational 1,ahoratory, operxted by lTnioir C d ) i d e Corporation. Work prcscutcd at, the 141st S s t i o n x l Meetii~g of the Arricricurl Chemical Society. ~'asliirigton. n. ('., Mardl 20-29, 1982.

Self-assembled aggregates in the gravitational field: Growth and nematic order

“…So, even the earth gravitational field can influence the equilibrium properties of such heavy objects as microtubules. Note, that one can reach 10 4 − 10 5 times larger gravitational acceleration in an ultracentrifuge, 9 which sometimes is used in the process of preparation of microtubules, 8 or in the pelleting experiments. 10,11 To this end, the gravitational field can serve as a driving force for the assembly and, eventually, to the nematic ordering of growing aggregates.…”

Light-scattering from detergent-complexed biological macromolecules

“…The aggregation numbers (n) for SDS micelles as a function of ionic strength have been measured by numerous groups and compared by Anacker et al (1964). At an ionic strength of 0.21 a reasonable range for n is 100+ 10.…”

Studies of the denaturation and partial renaturation of ovalbumin

“…For solutions containing protein the total refractive increment was first measured, relative to buffer. The contribution of protein to this quantity was calculated from the protein concentration determined from an extinction measurement; subtraction then gave the contribution of sodium dodecyl sulphate, which was converted into the concentration by use of the value R = 1.21 x 10-4 litre/g for the specific refractive increment of sodium dodecyl sulphate (Anacker et al, 1964).…”

“…The value v = 0.865ml/g was used for the partial specific volume of sodium dodecyl sulphate (Anacker et al, 1964). In the presence of guanidinium chloride as a third component the quantity (1 -vp) necessary for the evaluation of molecular weights from sedimentationequilibrium experiments was replaced by (1-/'p0), where qb' is the apparent specific volume and p0 the solvent density (Casassa & Eisenberg, 1964).…”

“…In the absence of protein the concentration of sodium dodecyl sulphate inside the dialysis sac rose rapidly (2h) to 1.1mg/ml, but increased thereafter only very slowly (1.5mg/ml after 40h). The critical micelle concentration of sodium dodecyl sulphate in 0.10M-NaCl is about 0.5mg/ml at 25°C (Anacker et al, 1964;Emerson & Holtzer, 1967); it is recognized that transfer of detergent across a dialysis membrane does occur above the critical micelle concentration (Harrap & O'Donnell, 1954;Mysels et al, 1963), but that this is a slow process in the presence of excess of salt. Thus the value 1.1mg/ml may include a proportion due to micelles, although no micellar component could be detected by sedimentation-velocity analysis.…”