טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentZiserman Lior
SubjectNanoconstructs and Self-Assembly of Lipoamino-Acid
Amphiphiles
DepartmentDepartment of Biotechnology and Food Engineering
Supervisors Professor Dganit Danino
Professor Amram Mor
Full Thesis textFull thesis text - English Version


Abstract

Controlled formation of nanometric scale architectures stands in the heart of nanotechnology and nanomaterials science. In the present work, we have built a library of stable organic nanostructures by using tailor-made cationic, lysine based, lipoamino-acids, and by manipulating the physico-chemical conditions.

Comprehensive nanostructural analysis was performed involving several advanced microscopy techniques: cryogenic-transmission electron microscopy (cryo-TEM), negative-stain (NS)-TEM and high resolution scanning electron microscopy (HR-SEM). This was supported by spectroscopic measurements such as light scattering, Fourier transform infra red spectroscopy (FTIR), and calorimetric methods. However, cryo-TEM served as the main research instrument; it is the only method which enables direct visualization of soluble nanocomplexes while preserving their native state.

We discovered that in neutral pH aqueous solutions and at room temperature a simple lipoamino-acid named Nα-lauryl-lysyl-aminolauryl-lysyl-amide (C12K-α12) spontaneously forms nanofibers immediately after solution preparation. Within several hours they widen up into twisted-ribbons (with Gaussian curvature). Afterwards, the widening process continues slowly followed by twisted- to coiled-ribbon (with cylindrical curvature) morphological transformation. Finally, after a few months of incubation, the coiled-ribbons close the gap between their pitches forming hollow nanotubes with an average diameter of 70-120 nm. This transformation process, known as ‘chiral self-assembly’, originates from the molecules' amphiphilic character, chirality, and the ability to form intra- and inter-molecular hydrogen bonds. Such a twisted-to-coiled ribbon transformation course was suggested theoretically only recently; we provide the first experimental evidence.

By applying different molecular designs we expanded the library of nanoconstructions that may be formed by C12K-α12 related substances. For example, by altering lysines chirality, we constructed flat ribbons using racemic solutions or alternatively, fixed the system at the helical ribbon stage using racemic (meso) C12K-α12 molecules.

pH control enabled systematical formation of wide, flat, membranes at basic environment, or narrow long fibers using an acidic environment. Furthermore, by neutralizing basic (pH = 12) C12K-α12 solutions the nanotubes formation time was shortened from months to minutes.

We studied the C12K-α12 organizational behavior in physiological solutions: saline and phosphate buffered saline (PBS). The results revealed C12K-α12 sensitivity to the presence of anions. In both cases, coagulation occurred. However, the PBS effect was more pronounced.

By screening the organizational behavior of different C12K-α12 related lipoamino-acids, we elucidated the relationship between molecular architecture and the non-covalent forces in controlling the self-assembly process.

Finally, two initial attempts to utilize C12K-α12 nanostructures as templates for potentially applicative inorganic depositions were performed: gold nanoparticles and ceramic (silica) coatings.