Gold Nanoparticle Formation via X-ray Radiolysis Investigated with Time-Resolved X-ray Liquidography.

We report the generation of gold nanoparticles (AuNPs) from the aqueous solution of chloro(2,2',2″-terpyridine)gold(III) ion ([Au(tpy)Cl]2+) through X-ray radiolysis and optical excitation at a synchrotron. The original purpose of the experiment was to investigate the photoinduced structural changes of [Au(tpy)Cl]2+ upon 400 nm excitation using time-resolved X-ray liquidography (TRXL). Initially, the TRXL data did not show any signal that would suggest structural changes of the solute molecule, but after an induction time, the TRXL data started to show sharp peaks and valleys. In the early phase, AuNPs with two types of morphology, dendrites, and spheres, were formed by the reducing action of hydrated electrons generated by the X-ray radiolysis of water, thereby allowing the detection of TRXL data due to the laser-induced lattice expansion and relaxation of AuNPs. Along with the lattice expansion, the dendritic and spherical AuNPs were transformed into smaller, raspberry-shaped AuNPs of a relatively uniform size via ablation by the optical femtosecond laser pulse used for the TRXL experiment. Density functional theory calculations confirm that the reduction potential of the metal complex relative to the hydration potential of X-ray-generated electrons determines the facile AuNP formation observed for [Au(tpy)Cl]2+.

Proton Transfer Accompanied by the Oxidation of Adenosine.

Despite numerous experimental and theoretical studies, the proton transfer accompanying the oxidation of 2'-deoxyadenosine 5'-monophosphate 2'-deoxyadenosine 5'-monophosphate (5'-dAMP, A) is still under debate. To address this issue, we have investigated the oxidation of A in acidic and neutral solutions by using transient absorption (TA) and time-resolved resonance Raman (TR3 ) spectroscopic methods in combination with pulse radiolysis. The steady-state Raman signal of A was significantly affected by the solution pH, but not by the concentration of adenosine (2-50 mm). More specifically, the A in acidic and neutral solutions exists in its protonated (AH+ (N1+H+ )) and neutral (A) forms, respectively. On the one hand, the TA spectral changes observed at neutral pH revealed that the radical cation (A.+ ) generated by pulse radiolysis is rapidly converted into A. (N6-H) through the loss of an imino proton from N6. In contrast, at acidic pH (<4), AH.2+ (N1+H+ ) generated by pulse radiolysis of AH+ (N1+H+ ) does not undergo the deprotonation process owing to the pKa value of AH.2+ (N1+H+ ), which is higher than the solution pH. Furthermore, the results presented in this study have demonstrated that A, AH+ (N1+H+ ), and their radical species exist as monomers in the concentration range of 2-50 mm. Compared with the Raman bands of AH+ (N1+H+ ), the TR3 bands of AH.2+ (N1+H+ ) are significantly down-shifted, indicating a decrease in the bond order of the pyrimidine and imidazole rings due to the resonance structure of AH.2+ (N1+H+ ). Meanwhile, A. (N6-H) does not show a Raman band corresponding to the pyrimidine+NH2 scissoring vibration due to diprotonation at the N6 position. These results support the final products generated by the oxidation of adenosine in acidic and neutral solutions being AH.2+ (N1+H+ ) and A. (N6-H), respectively.

Clustering dynamics of the metal-benzene sandwich complex: the role of microscopic structure of the solute in the bis(eta6-benzene)chromium .Arn Clusters (n = 1-15).

Ar clustering dynamics around the metal-benzene sandwich complex, bis(eta (6)-benzene)chromium: Cr(Bz) 2, is found to occur in two distinct regimes. The shift of the ionization potential (IP) upon the addition of Ar is measured to be 151 cm (-1), and it is constant until the number of Ar solvents ( n) becomes 6. The IP shift per Ar is found to be suddenly decreased to 82 cm (-1) for the clusters of n = 7-12. The cluster distribution indicates that the n = 6 cluster is most populated in the molecular beam. These experimental findings with the aid of ab initio calculation indicate that the first six Ar solvent molecules are attached to top and bottom of Cr(Bz) 2 to give the robust structure for the Cr(Bz) 2-Ar 6 cluster whereas the next six Ar molecules are gathered on the side of the solute core to give the highly symmetric structure of the Cr(Bz) 2-Ar 12 cluster.