Abstract |
This dissertation focuses on a class of materials that have been designed to exhibit a
response to external stimuli such as light, pH, and metals. Commonly referred “as
"smart materials," these substances present promising opportunities in a myriad of
applications, from bioimaging to antimicrobial and anticancer therapies.
Chapter I presents a general introduction about the peptides, one prime example of
such materials. Due to the complex process of protein self-assembly, peptides play a
pivotal role in research, serving as foundational components in the development of
these novel materials. Biologically, peptides inherently self-assemble into a diverse
array of organized structures using a bottom-up approach. Their inherent
biocompatibility, biodegradability, and bio-functionality make them prime candidates
for such investigations.
This thesis is organized into three primary chapters, each centered on the specific
stimulus to which these materials are responsive.
Chapter 2 provides a deep dive into the ability of the dipeptide Fmoc-FF to be used as
a light-responsive delivery vehicle. This peptide sequence possesses the inherent
capacity to assemble into a three-dimensional hydrogel under physiological
conditions. By encapsulating a chromophore molecule, this hydrogel gains the ability
to respond to light and form antimicrobial structures. Our research specifically
revolved around the investigation of such antimicrobial properties for hydrogels
encapsulating porphyrins. In particular, we focused on the cationic porphyrins
H2T(MePy)P(I4), Zn-T(MePy)P(I4), and Zn-T(MePy)P(Cl4), chosen for their distinct
structural properties. Field-emission scanning electron microscopy (FESEM) was
employed to analyze the morphology of both the scaffold and the embedded structures,
which appeared as fibrillar. Additionally, we conducted mechanical tests to assess
how the association with porphyrins affected their structural rigidity, revealing that
the encapsulation of H2T(MePy)P(I4) produced the least rigid structure. Finally, the
antimicrobial efficacy was assessed against both Gram-positive and Gram-negative
bacterial strains.
In Chapter 3, we present our work related to the development of fluorescent
molecules for bioimaging. The broader target was to design trackers which could
enter a cancer cell and hence allow its visual detection. In particular, we adopted peptide sequences containing histidine, which have the potential to coordinate with
porphyrin-modified nitrilotriacetic acid (NTA) (chromophores) through metal
chelation. This constituted our fluorescent probes tailored for bioimaging applications
within cancer cells. Two peptides, namely RDSGAΙTIGH and the protected dipeptide
Fmoc-FH, were at the center of our investigations. Both peptides inherently contain
histidine residues in their structures. We confirmed the successful formation of the
hybrids via FESEM imaging, and observed the peptide-porphyrin coordination
generated structures which were morphologically different from those of the peptides
or porphyrins alone. Moreover, this was complemented with UV-Vis spectroscopy
measurements, which confirmed the successful coordination. Finally, the coordinated
systems were studied for their ability to penetrate HeLa cancer cells.
Finally, Chapter 4 reports our endeavor of assembling biocompatible nanoparticles
carrying metal ions, which could be used for antibacterial or anticancer applications.
In particular, we studied a cyclic-HF peptide as a coordinating agent for copper and
zinc ions. FESEM imaging combined with EDX showed that the fibrillar structure
formed by the peptide alone were modified into flower-like in the presence of copper
ions indicating that CuO nanoparticles (NPs) were formed, and into spherical ones in
the presence of zinc ions indicating that ZnO NPs were formed, which proved the
successful coordination. Testing against Gram-positive and Gram-negative bacterial
strains provided indication that the CuO NPs are slightly more efficient than ZnO NPs
in terms of antimicrobial effect. Moreover, tests performed in tumoral environments
showed an increased antitumor efficiency of both NPs, due to the low pH which
favors the release of the metal ions.
Synthesis of all porphyrin molecules was carried out by the members of Prof.
Coutsolelos group, namely Georgios Charalambidis, Georgios Landrou, Vasilis
Nikolaou, Manos Nikoloudakis, Eleni Glymenaki and Maria Kandyli, in the
framework of a long term-collaboration of the two groups and part of the research
was co-financed by the European Union and Greek national funds through the
Operational Program Competitiveness, Entrepreneurship, and Innovation, under the
call RESEARCH – CREATE – INNOVATE (project Acronym : EPHESIAN, project
code: T1EDK-01504).
|