Synchrotron Radiation-induced X-ray Photoelectron Spectroscopy Research Articles

Copper-Based Complexes with Adamantane Ring-Conjugated bis(3,5-Dimethyl-pyrazol-1-yl)acetate Ligand as Promising Agents for the Treatment of Glioblastoma.

The new ligand L2Ad, obtained by conjugating the bifunctional species bis(3,5-dimethylpyrazol-1-yl)-acetate and the drug amantadine, was used as a chelator for the synthesis of new Cu complexes 1-5. Their structures were investigated by synchrotron radiation-induced X-ray photoelectron spectroscopy (SR-XPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and by combining X-ray absorption fine structure (XAFS) spectroscopy techniques and DFT modeling. The structure of complex 3 was determined by single-crystal X-ray diffraction analysis. Tested on U87, T98, and U251 glioma cells, Cu(II) complex 3 and Cu(I) complex 5 decreased cell viability with IC50 values significantly lower than cisplatin, affecting cell growth, proliferation, and death. Their effects were prevented by treatment with the Cu chelator tetrathiomolybdate, suggesting the involvement of copper in their cytotoxic activity. Both complexes were able to increase ROS production, leading to DNA damage and death. Interestingly, nontoxic doses of 3 or 5 enhanced the chemosensitivity to Temozolomide.

Binuclear organometallic Pt(II) complexes as stabilizing ligands for gold and silver metal nanoparticles

The bifunctional hybrid thioester ligands containing square planar Pt(II) centers 2,7-bis[2-(trans-acetylthio-bis-(tributylphosphine)platinumII)ethynyl]-9,9-didodecyl-9H-fluorene (1) and trans-4,4′-bis[2-(trans-acetylthio-bis-(tributylphosphine)platinumII)ethynyl]stilbene (2) have been prepared in a four-step procedure and used as stabilizing and interconnecting ligands for gold and silver nanoparticles (MNPs), formed in-situ upon deacylation of the MeCOS-Pt(II)-terminal groups. The metallic surface is linked to the Pt(II) centers of the ligands via M-S-Pt(II) bridges. The size of the AuNPs and AgNPs which aggregate into a bi-dimensional network through hybrid metal-organic bridges was controlled by careful choice of synthetic parameters. The morpho-structural features of the nanoparticles, investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and synchrotron radiation induced X-ray photoelectron spectroscopy (SR-XPS), highlighted the linkage between the nanoparticles, featuring diameters below 10 nm.

Direct Conjugation of Resveratrol on Hydrophilic Gold Nanoparticles: Structural and Cytotoxic Studies for Biomedical Applications.

Strongly hydrophilic gold nanoparticles (AuNPs), functionalized with citrate and L-cysteine, were synthetized and used as Resveratrol (RSV) vehicle to improve its bioavailability. Two different conjugation procedures were investigated: the first by adding RSV during AuNPs synthesis (1) and the second by adding RSV after AuNPs synthesis (2). The two different conjugated systems, namely AuNPs@RSV1 and AuNPs@RSV2 respectively, showed good loading efficiency (η%): η1 = 80 ± 5% for AuNPs@RSV1 and η2 = 20 ± 3% for AuNPs@RSV2. Both conjugated systems were investigated by means of Dynamic Light Scattering (DLS), confirming hydrophilic behavior and nanodimension (<2RH> 1 = 45 ± 12 nm and <2RH> 2 = 170 ± 30 nm). Fourier Transform Infrared Spectroscopy (FT-IR), Synchrotron Radiation induced X-Ray Photoelectron Spectroscopy (SR-XPS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) techniques were applied to deeply understand the hooking mode of RSV on AuNPs surface in the two differently conjugated systems. Moreover, the biocompatibility of AuNPs and AuNPs@RSV1 was evaluated in the concentration range 1.0–45.5 µg/mL by assessing their effect on breast cancer cell vitality. The obtained data confirmed that, at the concentration used, AuNPs do not induce cell death, whereas AuNPs@RSV1 maintains the same anticancer effects as the unconjugated RSV.

Cysteine-Modified Self-Assembling Peptides on Gold: The Role of the Head and Tail.

Molecular self-assembly consists of the spontaneous aggregation of molecules into a well-defined structure guided by noncovalent bonds. The self-assembly strategy is ubiquitous in nature and recently has been proposed as a nature-mimetic strategy in polymer science and biomaterial engineering. In this context, we aim at designing and testing innovative but simple chemical strategies to efficiently modify surfaces by exploiting minor modifications in the bioactive molecule functionalities, for example, introducing cysteine (Cys) as a terminal residue in self-assembling peptides (SAPs). In this work, we report the attenuated total reflection-Fourier transform infrared spectroscopy, synchrotron radiation-induced X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and time-of-flight secondary ion mass spectrometry investigation of self-assembled layers of oligopeptides anchored onto gold surfaces through cysteine residues, opportunely inserted in an SAP (EAK16-II) main chain in three different positions: at the amine end group, at the carboxyl end group, and at both terminal groups (i.e., a bidentate SAP). This study, which allowed us to individuate in the bidentate SAP the best candidate for the controlled production of ordered SAP layers on the gold substrate surface, is envisaged to open wide perspectives for efficient chemical modification of surfaces with biomolecules, leading to obtaining innovative bioactive materials for applications in the field of tissue engineering.

Gallium- and Iron-Pyoverdine Coordination Compounds Investigated by X-ray Photoelectron Spectroscopy and X-ray Absorption Spectroscopy.

Iron is an essential nutrient for nearly all forms of life, although scarcely available due to its poor solubility in nature and complex formation in higher eukaryotes. Microorganisms have evolved a vast array of strategies to acquire iron, the most common being the production of high-affinity iron chelators, termed siderophores. The opportunistic bacterial pathogen Pseudomonas aeruginosa synthesizes and secretes two siderophores, pyoverdine (PVD) and pyochelin (PCH), characterized by very different structural and functional properties. Due to its chemical similarity with Fe(III), Ga(III) interferes with several iron-dependent biological pathways. Both PVD and PCH bind Fe(III) and Ga(III). However, while the Ga-PCH complex is more effective than Ga(III) in inhibiting P. aeruginosa growth, PVD acts as a Ga(III) scavenger and protects bacteria from Ga(III) toxicity. To gain more insight into the different outcomes of the biological paths observed for the Fe(III) and Ga(III)-siderophore complexes, better knowledge is needed of their coordination geometries that directly influence the metal complexes chemical stability. The valence state and coordination geometry of the Ga-PCH and Fe-PCH complexes has recently been investigated in detail; as for PVD complexes, several NMR structural studies of Ga(III)-PVD are reported in the literature, using Ga(III) as a diamagnetic isosteric substitute for Fe(III). In this work, we applied up-to-date spectroscopic techniques as synchrotron-radiation-induced X-ray photoelectron spectroscopy (SR-XPS) and X-ray absorption fine structure (XAFS) spectroscopy coupled with molecular modeling to describe the electronic structure and coordination chemistry of Fe and Ga coordinative sites in PVD metal complexes. These techniques allowed us to unambiguously determine the oxidation state of the coordinative ions and to gather interesting information about the similarities and differences between the two coordination compounds as induced by the different metal.

Comparison between silver and gold nanoparticles stabilized with negatively charged hydrophilic thiols: SR-XPS and SERS as probes for structural differences and similarities

The electronic and molecular structure, as well as the chemical nature of noble metal (silver, gold) nanoparticles (AgNPs, AuNPs) stabilized by the negatively charged hydrophilic organic thiol Sodium 3-mercapto-1-propanesulfonate (3-MPS) has been probed combining Synchrotron Radiation-induced X-ray Photoelectron Spectroscopy (SR-XPS) and Surface Enhanced Raman Spectroscopy (SERS). Complementary information about the electronic, chemical and molecular structure is obtained combining SERS and XPS data, allowing to evidence structural similarities and differences related to the noble metal choice. These results coherently suggest the effective 3-MPS chemical absorption onto the nanoparticle surface, which allows to obtain a stable and biocompatible system, suitable for ad hoc further functionalization as required for several applications in biotechnology. It was observed that the NPs molecular overlayer is made up by covalent bonds between thiols and metallic surface atoms, without degradation of the molecule. The metals SR-XPS spectra analysis collected on the silver and gold nanoparticles points out a small surface to volume atomic percent ratio, as a consequence of the NPs size (≥5nm). Surface-enhanced Raman Scattering (SERS) spectroscopy was employed for the investigation of the NP molecular conjugation. SERS spectra acquired on the capped Ag and AuNPs are in very good agreement and suggest that the same organic layer is covering the NPs. The conjugation with 3-MPS is confirmed by comparing SERS data with the conventional Raman signature of the ligand. The reproducibility of SERS measurements overall points out the high purity and homogeneity of the system and the good integrity of the organic capping layer.

Gold Nanoparticles Stabilized with Aromatic Thiols: Interaction at the Molecule–Metal Interface and Ligand Arrangement in the Molecular Shell Investigated by SR-XPS and NEXAFS

Small gold nanoparticles capped with 4-trimethylsilylethynyl-1-acetylthiobenzene (SEB) were prepared with spherical shape and different mean sizes (5–8 nm). The functionalized gold nanoparticles (AuNPs-SEB) were deposited onto TiO2 substrates, and the interaction at the molecule–gold interface, the molecular layer thickness, and the ligand organization on the surface of Au nanospheres were investigated by means of synchrotron radiation induced X-ray photoelectron spectroscopy (SR-XPS) and angular dependent near edge X-ray absorption spectroscopy (NEXAFS) at the C K-edge. In order to obtain better insight into the molecular shell features, the same measurements were also carried out on a self-assembling monolayer (SAM) of SEB anchored on a “flat” gold surface (Au/Si(111) wafer). The comparison between angular dependent NEXAFS spectra collected on the self-assembling monolayer and AuNPs-SEB allowed for successfully probing the molecular arrangement of SEB molecules on the gold nanospheres surface. Furthermo...

Thiol–ene Mediated Neoglycosylation of Collagen Patches: A Preliminary Study

Despite the relevance of carbohydrates as cues in eliciting specific biological responses, the covalent surface modification of collagen-based matrices with small carbohydrate epitopes has been scarcely investigated. We report thereby the development of an efficient procedure for the chemoselective neoglycosylation of collagen matrices (patches) via a thiol-ene approach, between alkene-derived monosaccharides and the thiol-functionalized material surface. Synchrotron radiation-induced X-ray photoelectron spectroscopy (SR-XPS), Fourier transform-infrared (FT-IR), and enzyme-linked lectin assay (ELLA) confirmed the effectiveness of the collagen neoglycosylation. Preliminary biological evaluation in osteoarthritic models is reported. The proposed methodology can be extended to any thiolated surface for the development of smart biomaterials for innovative approaches in regenerative medicine.

Two-Dimensional Networks of Ag Nanoparticles Bridged by Organometallic Ligand

Silver nanoparticles stabilized with organometallic bifunctional thiol-containing Pt(II) centers have been prepared giving rise to 2D networks that have been characterized through high-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), synchrotron radiation-induced X-ray photoelectron spectroscopy (SR-XPS), and energy-dispersive X-ray diffraction (EDXD) analysis. This study of 2D self-assembly of Ag nanoparticles opens new perspectives for manipulation and stabilization of nanoparticles assemblies, suitable for applications in optoelectronic devices.

Self assembling monolayers of dialkynyl bridged Pd(II) thiols obtained by thermally induced multilayer desorption: Thermal and chemical stability investigated by SR-XPS

Self assembling monolayers (SAMs) of organometallic thiols trans-[HS–Pd(PBu3)2–SH], trans-[HS–Pd(PBu3)2(–CC–C6H5)] and trans,trans-[HS–Pd(PBu3)2(–CC–C6H4–C6H4–CC–Pd(PBu3)2–SH] on gold were obtained from the corresponding multilayers through thermally induced desorption. Temperature-dependent synchrotron radiation-induced X-ray photoelectron spectroscopy (SR-XPS) measurements were carried out on the heated multilayers during the annealing process, in order to investigate the thermal and chemical stability of the systems. SAMs of the same organometallic thiols were also obtained by rinsing the thick films with appropriate solvents. SR-XPS was used to ascertain that the molecular and electronic structure of the two series of SAMs are not influenced by the rinsing or thermal desorption process, i.e. both strategies allow for obtaining well ordered monolayers of organometallic thiols.

Gold Nanoparticle Dyads Stabilized with Binuclear Pt(II) Dithiol Bridges

The synthesis and characterization of gold nanoparticles (AuNPs-1) stabilized by a novel bifunctional thiolate organometallic complex containing Pt(II) centers, that is, trans,trans-[(CH3COS)(PBu3)2Pt–C≡C–C6H4–C6H4–C≡C–Pt(PBu3)2(SCOCH3)] (complex 1), has been carried out. As a comparison, gold nanoparticles stabilized with an organic thiol, allylmercaptane, that is, AuNPs-2, and self-assembled monolayers (SAMs) of both thiols were also prepared and investigated. The AuNPs-1 show a direct link between Pt(II) and Au nanoparticles through a single S bridge and are candidates for the achievement of 2D or 3D networks. The size control of the Au nanoparticles was achieved by careful control of synthesis parameters, and the hybrids were characterized by means of high-resolution transmission electron microscopy (HR-TEM) and synchrotron radiation induced X-ray photoelectron spectroscopy (SR-XPS). SR-XPS measurements allowed the assessment of the anchoring of the organic or organometallic thiols onto gold substrate...