Interfacial Behavior of N-Nitrosodiethylamine/Bovine Serum Albumin Complexes at the Air-Water and the Chloroform-Water Interfaces by Axisymmetric Drop Tensiometry

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• 作者：J. Juá ; rez ; J. G. Galaz ; L. Machi ; M. Burboa ; L. E. Guti&eacute ; rrez-Millá ; n ; F. M. Goycoolea ; M. A. Valdez
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：March 15, 2007
• 年：2007
• 卷：111
• 期：10
• 页码：2727 - 2735
• 全文大小：125K
• 年卷期：v.111,no.10(March 15, 2007)
• ISSN：1520-5207

文摘

Interfacial properties of N-nitrosodiethylamine/bovine serum albumin (NDA/BSA) complexes were investigatedat the air-water interface. The interfacial behavior at the chloroform-water interface of the interaction productof phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), dissolved in the chloroform phase,and NDA/BSA complex, in the aqueous phase, were also analyzed by using a drop tensiometer. The secondarystructure changes of BSA with different NDA concentrations were monitored by circular dichroism spectroscopyat different pH and the NDA/BSA interaction was probed by fluorescence spectroscopy. Different NDA/BSA mixtures were prepared from 0, 7.5 × 10^-5, 2.2 × 10^-4, 3.7 × 10^-4, 5 × 10^-4, 1.6 × 10^-3, and 3.1 ×10^-3 M NDA solutions in order to afford 0, 300/1, 900/1, 1 500/1, 2 000/1, 6 000/1, and 12 500/1 NDA/BSAmolar ratios, respectively, in the aqueous solutions. Increments of BSA mages/gifchars/alpha.gif" BORDER=0>-helix contents were obtained up tothe 2 000/1 NDA/BSA molar ratio, but at ratios beyond this value, the mages/gifchars/alpha.gif" BORDER=0>-helix content practically disappeared.These BSA structure changes produced an increment of the surface pressure at the air-water interface, as themages/gifchars/alpha.gif" BORDER=0>-helix content increased with the concentration of NDA. On the contrary, when mages/gifchars/alpha.gif" BORDER=0>-helix content decreased,the surface pressure also appeared lower than the one obtained with pure BSA solutions. The interaction ofDPPC with NDA/BSA molecules at the chloroform-water interface produced also a small, but measurable,pressure increment with the addition of NDA molecules. Dynamic light scattering measurements of themolecular sizes of NDA/BSA complex at pH 4.6, 7.1, and 8.4 indicated that the size of extended BSA moleculesat pH 4.6 increased in a greater proportion with the increment in NDA concentration than at the other studiedpH values. Diffusion coefficients calculated from dynamic surface tension values, using a short-term solutionof the general adsorption model of Ward and Tordai, also showed differences with pH and the NDAconcentration. Both, the storage and loss dilatational elastic modulus were obtained at the air-water and atthe chloroform-water interfaces. The interaction of NDA/BSA with DPPC at the chloroform-water produceda less rigid monolayer than the one obtained with pure DPPC (1 × 10^-5 M), indicating a significant penetrationof NDA/BSA molecules at the interface. At short times and pH 4.6, the values of the storage elastic moduluswere larger and more sensible to the NDA addition than the ones at pH 7.1 and 8.4, probably due to agel-like network formation at the air-water interface.