Formation of Supramolecular Assemblies by Modulating Self-Assembling Properties of Diacetylenic Phosphocholines
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Formation of Supramolecular Assemblies by Modulating Self-Assembling Properties of Diacetylenic Phosphocholines
Alok Singh, Eva M. Wong, Mark S. Spector and Joel M. Schnur Center for Bio/Molecular Science & Engineering, Naval Research Laboratory, Washington, DC 20375 USA ABSTRACT
Diacetylenic phospholipid dispersions in water produce tubules (500 nm diameter) and helices from their initial vesicular morphology as a function of temperature and concentration. A binary mixture consisting of diacetylenic phospholipid, 1,2 bis (tricosa-10, 12-diynoyl)-sn-glycero-3-phosphocholine and a short chain phospholipid, 1,2-dinonanoyl –sn-glycero-3-phosphocholine was studied to explore the morphological transformation of lipids into tubules to develop an approach to control and produce tubules of different diameters. Circular dichroic spectra not only indicated the chiral nature of these tubules, but also provided distinct spectral signatures differentiating micro- and nanotubules. The effects of temperature and lipid concentration on the formation and stability of tubules were also explored. An equimolar lipid mixture provided structures with uniform morphology, which were stable for several hours up to 36 °C. The thermal stability of nanotubules makes them an attractive candidate for many practical applications including controlled release technology.
INTRODUCTION
Phospholipids by virtue of their unique self-assembling properties belong to an important class of biomaterials. Their pivotal role in biological membranes to facilitate multiple, complex functions inside, within and on the membranes makes them technologically attractive. In non-biological environments, phospholipids typically form multi-lamellar vesicles upon dispersion in water. The formation of tubular structures from diacetylenic lipids is an important example of synthetic material derived from natural precursor, which permits extension of self-assembly for making technologically relevant novel structures [1,2]. Tubules, helices and ribbons have been the subject of numerous scientific studies due to their potential applications in the areas of chemistry, biology and material science [3-5]. Initial reports on diacetylenic phospholipids described the formation of microtubules with a fixed internal diameter of 500 nm [6]. Subsequent studies reported the formation of other forms of self-assembling structures, such as helices, ribbons and tubules [7] and the means to produce tubules with variable diameters [8,9]. The overall goal of the current research is to construct tubules with diameters ranging from nano to micrometers. The system must be reproducible, and tolerant to minor fluctuations in temperature and pH of the dispersion medium. We have focused on HH3.36.1
inserting a short chain lipid whose chain length was equal to the number of methylene groups present between diacetylene and ester group on glycerol molecule, particularly 1,2 tricosadiyn-10,12-oyl)-sn-glycer-3-phosphocholine (DC8,9PC) and 1,2 dinonanoyl-snglycero-3-phosphocholine (DNPC) [10-11]. The m
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