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• W3176206432 abstract "The aim of this PhD thesis was to study possible ways of interaction between goldnanoparticles (AuNPs) and biological molecules. I have approached this problem in twoways: a) by addressing the interaction of non-functionalized nanoparticles with a moleculethrough the Au-N “bond” formation; b) by functionalizing AuNPs with proper ligands ableto “covalently capture” a target protein.In spite of the fact that most protein interact with “naked” AuNPs through the aminogroups present on their surface, very little is known about the nature of this interaction. TheAu-N interaction is much weaker than the most popular Au-S one. Because of this, I haveset up experiments aimed at addressing i) how the Au-N interaction correlates with theproperties of an amino group (its pKa, level of substitution); ii) the possible mode ofbindings of amino groups to the nanoparticles and its dependence on the AuNPs size; iii)the kinetics of these processes. I have used ethanol as the solvent throughout most of myexperiments because, being a less competitive solvent than water, it allowed me to moreprecisely tune the strength of the Au-N interaction. Of course, this choice will require, at alater stage, to check the transferability of the information acquired to the natural biologicalsolvent. The results showed that there is a very good correlation between amine pKa andits affinity to the AuNPs surface and that there are at least three different modes of bindingof the amines. They are characterized by quite different kinetics and percentages of aminesbound to the gold nanoparticle surface. The Bronsted plots of the logarithm of the apparentaffinity constants of the amines for the AuNPs surface vs their pKa were linear with slopesin the -0.4 - -0.6 interval indicating that the same properties that control the interaction ofan amine with a proton control also that with the surface Au atoms.The ability of amines to interact with the AuNPs surface has prompted me to study theinteraction of peptides presenting free amines at their termini. Thus, I have discovered thatpeptide sequences functionalized with primary amines at the N- and C-terminus are able toinduce the aggregation of AuNPs in ethanol following their folding into a helicalconformation. Random coil peptides are unable to induce such an aggregation process. Ihave observed that the aggregation can be monitored spectrophotometrically by followingthe shift of the surface plasmon resonance (SPR) band of the nanoparticles and confirmeddenaturation of the peptides results in diminished crosslinking ability. I then examined howthe helicity parameter 222/208 correlates with the shift of the SPR band to longerwavelength and I found a reasonably good linear correlation. All the date I have obtainedsupport the existence of a relationship between the amount of helical content of a peptidesequence and its ability to induce aggregation of the AuNPs. I also have tried to find mild passivating agents, soluble in an aqueous solution, thatcould be easily replaced by more stable ones in a controlled way. The most obvious choicewas to rely on the Au-N bond in view of the expertise I had acquired on the matter. Byusing glucosamine phosphate (GAP) as a natural and inexpensive passivating agent, quiteserendipitously, I discovered that this compound was leading to the formation ofnanowires. Indeed, in an aqueous solution devoid of any surfactant, I was able to obtain,under aerobic conditions and substoichiometric nanoparticle passivation (i. e. theconcentration of passivating agent is lower than the concentration of surface Au atoms),Au-nanowires of controlled length and reasonably narrow dimensional distribution startingfrom AuNPs. Since the challenge of obtaining plasmonic nanosystems absorbing light inthe near infrared is always open because of the interest that such systems pose inapplications such as nanotherapy or nanodiagnostics, I explored more in detail the initialresults I had obtained. I discovered that oxygen was required to induce the process and thatglucosamine phosphate was oxidized to glucosaminic acid phosphate and H2O2 was alsoproduced. I could establish that the process leading to the nanosystems comprisesnanoparticles growth, their aggregation into necklace-like aggregates, and the final fusioninto nanowires. Control experiments in an anaerobic environment confirmed that the fusionrequires the consumption of H2O2. I could passivate the nanowires with an organic thiol,lyophilize and resuspend them in water without losing their dimensional and opticalproperties. By adjusting the length of the nanowires, I could also tune the position of theirbroad surface plasmon band in the range 630 to >1350 nm. Finally, I have started investigating the way to functionalize AuNPs with a suitabletargeting agent to obtain the “covalent capture” of an enzyme. The strategy requires thepreparation of a thiolated molecule featuring an irreversible inhibitor of the target protein.I have selected as my target Urokinase, also called urinary plasminogen activator (uPA oru-PA), a serine protease. Elevated expression levels of urokinase have been found to becorrelated with tumor malignancy. This makes urokinase an attractive drug target, and, so,inhibitors have been sought to be used as anticancer agents. Based on published results,concerning the structure of the irreversible inhibitor, The chemical structure of Ligand 2 can be divided into four parts: 1) the hydrophilicoligo(ethylene glycol) moiety (blue) bearing thiol, as a water soluble linker to be anchoredon the nanoparticles surface; 2) general linker (orange), which acts as a building block forcoupling the capture unit; 3) inhibitor unit, which ensures high selectively for the targetprotein; 4) capture unit that leads to phosphorylation of serine. I have also used Ligand 1assuming that it should be able, when used to co-passivate the AuNPs to tune theirsolubility in water and prevent, in a biological fluid, unspecific interactions with plasmaproteins." @default.
• W3176206432 created "2021-07-05" @default.
• W3176206432 creator A5069433267 @default.
• W3176206432 date "2019-12-02" @default.
• W3176206432 modified "2023-09-27" @default.
• W3176206432 title "The interaction of biomolecules with gold nanoparticles: from amine-driven binding to covalent capture" @default.
• W3176206432 hasPublicationYear "2019" @default.
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