Hideaki Kasai

Surface morphology influences how multiple adsorbed species interact on metal surfaces. This study investigates the coadsorption of hydrazine (N2H4) and hydroxyl (OH) on vicinal Ni(533) surface using density functional theory (DFT) calculations. We identify stable N2H4–OH coadsorption configurations and characterize them by their respective relative energies and structural properties. The most energetically favorable configuration features cis-N2H4 and OH respectively adsorbed on terrace and step-edge sites. In contrast to vicinal surfaces with narrower terrace, such as Ni(211), the wider terrace on Ni(533) limits the formation of extended hydrogen-bonded arrangements. This results in a different energetic ordering and increases the energy separation between the coadsorption configurations. These findings demonstrate how the terrace width can be utilized to control the conformational preference of N2H4 in N2H4-OH coadsorption system.

Targeted Alpha Therapy (TAT) using ²¹¹ At–AuNP is a new and growing field of multidisciplinary research that would ultimately provide the medical community with another way to treat cancer.

We have performed first principles calculation study based on density functional theory on the adsorption of iodine and astatine on Au(111) and Au(211), including spin-orbit coupling (SOC) effects in some calculations. These surfaces are the dominant surface termination to represent a face-centered cubic nanoparticle. We found that both iodine and astatine adsorb stronger on the edge-bridge site of the Au(211) surface than on the flat Au(111) surface by about 0.2 eV. This result also makes the adsorbate less likely to diffuse after adsorption on the (211) surface as compared to the (111) surface. Additionally, we found that SOC effects, usually a necessity when considering heavy elements, are not significant in these cases, as can be seen by the energy and geometric data. Finally, we found the difference in adsorption energy between iodine and astatine on gold surface can be expected due to the presence of 4f electrons in astatine, which is not present in iodine. The 4f electrons offer less shielding of the nucleus, making the valence electrons of astatine closer to the nucleus, and therefore a smaller atomic radius. This information is useful both for experimental verification and future developments of gold nanoparticles for radiotherapy.

Gold nanoparticles (AuNPs) are used in many applications including in cancer therapy. One way to improve the quality of treatment is to design AuNPs to provide optimum adsorption to the radionuclides being employed. Therefore, we have to first understand the mechanism and quantify the strength of such adsorption process. This study looks at the adsorption characteristics of iodine and astatine on gold nanoparticles, specifically the (111) surface to learn more about adsorption of such heavy elements on Au surfaces. Both iodine and astatine are found to be able to bond with Au(111) via covalent bonding most stably on the face-centered cubic (fcc) site. We also found that the adsorption strength of iodine and astatine on gold are comparable, and that spin orbit coupling correction does not significantly affect the adsorption energies.

Radioactive iodine (e.g. I-125, I-131) have been used for decades in the medical community for cancer treatment and imaging. Using gold nanoparticles as a carrier for iodine opens possibilities of new treatments for cancer and also for tracking cancerous cells. To design an optimized version of gold nanoparticle for such purpose, we need to understand the bonding mechanism and gauge the strength of such bonding. To this end we performed theoretical calculations on the adsorption state of iodine on gold (111) surface. The results show good adsorption of iodine to gold, most stably on the hollow sites. The bonding mechanism is via the hybridization of the 5p orbital of the iodine with the 6s and 5d orbitals of the neighboring gold atoms. These results act as a first step to designing an optimized gold nanoparticle that can be used in future radiotherapy treatments

Astatine-211 (²¹¹At or simply At) used as an α particle emitter is currently gaining as treatment method for cancer cells. It must however be attached to a carrier to facilitate the treatment process. Gold nanoparticle is a good candidate that has been used in several tests. Knowing the physics behind the adsorption of astatine on gold nanoparticles would be advantageous in designing a more optimal method for such applications. We therefore performed density functional theory calculation on astatine adsorption on gold (111) surface to understand both the mechanism of astatine bonding with gold and the strength of the bonding. We found the mechanism of adsorption to be the hybridization between the 6p orbital of astatine and the 5d and 6s orbitals of the gold. We also found the adsorption strength of astatine on gold to be -1.43 eV at the fcc hollow site. Both results provide us with a good starting point towards our goal of designing an optimized gold nanoparticle for radiotherapy.

Two types of melanin pigments, brown to black eumelanin and yellow to reddish brown pheomelanin, are biosynthesized through a branched reaction, which is associated with the key intermediate dopaquinone (DQ). In the presence of l-cysteine, DQ immediately binds to the –SH group, resulting in the formation of cysteinyldopa necessary for the pheomelanin production. l-Cysteine prefers to bond with aromatic carbons adjacent to the carbonyl groups, namely C5 and C2. Surprisingly, this Michael addition takes place at 1,6-position of the C5 (and to some extent at C2) rather than usually expected 1,4-position. Such an anomaly on the reactivity necessitates an atomic-scale understanding of the binding mechanism. Using density functional theory-based calculations, we investigated the binding of l-cysteine thiolate (Cys–S⁻) to DQ. Interestingly, the C2–S bonded intermediate was less energetically stable than the C6–S bonded case. Furthermore, the most preferred Cys–S⁻-attacked intermediate is at the carbon-carbon bridge between the two carbonyls (C3–C4 bridge site) but not on the C5 site. This structure allows the Cys–S⁻ to migrate onto the adjacent C5 or C2 with small activation energies. Further simulation demonstrated a possible conversion pathway of the C5–S (and C2–S) intermediate into 5-S-cysteinyldopa (and 2-S-cysteinyldopa), which is the experimentally identified major (and minor) product. Based on the results, we propose that the binding of Cys–S⁻ to DQ proceeds via the following path: (i) coordination of Cys–S⁻ to C3–C4 bridge, (ii) migration of Cys–S⁻ to C5 (C2), (iii) proton rearrangement from cysteinyl –NH₃⁺ to O4 (O3), and (iv) proton rearrangement from C5 (C2) to O3 (O4).