Time-resolved optical studies, heat dissipation and melting of Ag and Au nanoparticle systems and arrays

Transient absorption spectroscopy has been extensively used in recent years to examine the temporal response of isolated nanoparticles (NPs) to the absorption of light [1]. These studies are largely based on the use of the surface plasmon resonance (SPR) to monitor characteristics of the NP such as electronic and lattice temperature, shape and morphology as a function of time. In the case of extended Au/Ag NP structures the plasmon resonance is strongly distorted due to the inter-particle coupling effects. For example, we have observed this effect in Rhodamine dye functionalized Au nanoparticles which undergo self-assembly to form nanostructures due to the interactions between the dye molecules attached to the surfaces of the nanoparticles. Indeed the SPR splits into two with one resonance remaining in the vicinity of that of the isolated AuNPs and is generally called the transverse SPR while a second resonance due to an extended excitation spanning across multiple particles appears to the lower energies. The precise spectral energy and shape of the extended plasmon resonance depends on the inter-particle distance, the particle disposition and the number of particles involved. When the plasmon band or interband spectral region of the NP is excited by an intense pulse the photon energy absorbed by the electrons is transferred to the lattice of the NP as heat through electron-phonon coupling. Depending on the intensity of the light pulse and thus the initial electron temperature a number of outcomes are possible. The first aim of this work is to use low intensity pump pulses to study the wavelength dependence of the sub 10 ps dynamics which reflects the electron-photon scattering within the nanoparticle structure. On the other hand, the interaction of more intense light with the NPs can modify the morphology of NP systems, for example by reshaping gold nanorods into nanospheres or, in general, mediate the synthesis of metallic nanostructures. At medium intensities the initial temperature is sufficient to induce melting of the NPs which can lead to morphological changes of the NP structure. Higher intensities can cause other effects such as photofragmentation of the NPs, release of stabiliser molecules from the surface of the NPs or even Coulomb explosion due to multiple ionisation events. The second aim of this work is to concentrate on the effects of medium intensity laser excitation of a self-assembled Au/Ag NP systems. The NP system is excited by a femtosecond laser pulse of different wavelengths allowing selective deposition of energy and the subsequent heat dissipation through phonon-phonon coupling and morphological changes are monitored in time by recording transient absorption spectra in the visible range. This wavelength range makes it possible to follow the phonon-phonon coupling effects on the recovery of the bleaching of both the transverse and extended plasmon resonances of the NP system. As the intensity of the pump pulse is increased it can be seen that the NPs are no longer able to dissipate all of the heat before arrival of subsequent laser pulses thus leading to melting of the NP structure and strong changes in the plasmon response of the system. The overall aim of this study is to fully understand the delocalized electron-phonon coupling in the extended plasmon region of the NP structures and to use this knowledge to control the melting in nanostructures. The methods developed can be useful for plasmon mediated nano-engineerin

Gas Phase Oxidation of Carbon Monoxide by Sulfur Dioxide Radical Cation: Reaction Dynamics and Kinetic Trend With the Temperature

Gas phase ion chemistry has fundamental and applicative purposes since it allows the study of the chemical processes in a solvent free environment and represents models for reactions occurring in the space at low and high temperatures. In this work the ion-molecule reaction of sulfur dioxide ion SO2.+ with carbon monoxide CO is investigated in a joint experimental and theoretical study. The reaction is a fast and exothermic chemical oxidation of CO into more stable CO2 by a metal free species, as SO2.+, excited into ro-vibrational levels of the electronic ground state by synchrotron radiation. The results show that the reaction is hampered by the enhancement of internal energy of sulfur dioxide ion and the only ionic product is SO.+. The theoretical approach of variational transition state theory (VTST) based on density functional electronic structure calculations, shows an interesting and peculiar reaction dynamics of the interacting system along the reaction path. Two energy minima corresponding to [SO2–CO].+ and [OS–OCO].+ complexes are identified. These minima are separated by an intersystem crossing barrier which couples the bent 3B2 state of CO2 with C2v symmetry and the 1A1 state with linear D∞h symmetry. The spin and charge reorganization along the minimum energy path (MEP) are analyzed and eventually the charge and spin remain allocated to the SO.+ moiety and the stable CO2 molecule is easily produced. There is no bottleneck that slows down the reaction and the values of the rate coefficient k at different temperatures are calculated with capture theory. A value of 2.95 × 10−10 cm3s−1molecule−1 is obtained at 300 K in agreement with the literature experimental measurement of 3.00 × 10−10 ± 20% cm3s−1molecule−1, and a negative trend with temperature is predicted consistently with the experimental observations

Radiation Damage Mechanisms of Chemotherapeutically Active Nitroimidazole Derived Compounds

Photoionization mass spectrometry, photoelectron-photoion coincidence spectroscopic technique, and computational methods have been combined to investigate the fragmentation of two nitroimidazole derived compounds: the metronidazole and misonidazole. These molecules are used in radiotherapy thanks to their capability to sensitize hypoxic tumor cells to radiation by “mimicking” the effects of the presence of oxygen as a damaging agent. Previous investigations of the fragmentation patterns of the nitroimidazole isomers (Bolognesi et al., 2016; Cartoni et al., 2018) have shown their capacity to produce reactive molecular species such as nitric oxide, carbon monoxide or hydrogen cyanide, and their potential impact on the biological system. The results of the present work suggest that different mechanisms are active for the more complex metronidazole and misonidazole molecules. The release of nitric oxide is hampered by the efficient formation of nitrous acid or nitrogen dioxide. Although both metronidazole and misonidazole contain imidazole ring in the backbone, the side branches of these molecules lead to very different bonding mechanisms and properties

Effects of the environment on the uracil molecule ionization induced by 12C4+ ion beam

In this study the fragmentation of isolated uracil molecules, uracil clusters and hydrated uracil clusters induced by 12 C 4+ ions at 36 keV energy has been investigated. The mass spectra obtained by a TOF mass spectrometer are analyzed and compared to each other in order to see how the environment affects the fragmentation dynamics. The main differences between the mass spectra are highlighted and possible fragmentation pathways are proposed

Photo-biomodulation as a prevention modality of oral mucositis in patients undergoing allogeneic hematopoietic stem cell transplantation

The aim of the study was to observe the eectiveness of a photo-biomodulation (PBM) protocol for the prevention of oral mucositis (OM) in patients undergoing allogeneic hematopoietic stem cell transplantation (aHSCT). A case-control study was conducted on 40 patients undergoing aHSCT. The patients were divided into two groups; the preventive group (PG) included 20 patients (7 females and 13 males) who were subjected to intra-oral PBM for five sessions a week, starting one day before the conditioning regimen and continuing until the 10th day after transplantation (D+10). In each session, ten points on the at-risk mucosal surfaces were irradiated using a double diode laser that emits two wavelengths simultaneously at 650 nm and at 904–910 nm with the following parameters at each point: energy of 4 J, and power of 88.9 mW. The control group (CG) included 20 patients (10 females and 10 males) who were not subjected to laser therapy and were selected retrospectively to compare the obtained results. For all patients, OM was assessed by the World Health Organization (WHO) grading scale. Eight patients in the PG did not experience OM during their hospitalization period (with grade 0). Severe OM was observed in 40% of the patients in the PG, while in the CG, severe OM was shown in 85% of the patients. The mean duration of OM in the PG was significantly lower than that of CG (4.7 days in the PG and 15 days in the CG) (p < 0.001). The study demonstrated that the preventive PBM protocol reduced the severity and duration of OM in patients undergoing aHSCT

Il progetto Lab2Go per la diffusione della pratica laboratoriale nelle Scuole Secondarie di II grado

Even if laboratory practice is essential for all scientific branches of knowledge, it is often neglected at High School, due to lack of time and/or resources. To establish a closer contact between school and experimental sciences, Sapienza Università di Roma and the Istituto Nazionale di Fisica Nucleare (INFN) launched the Lab2Go project, with the goal of spreading laboratory practice among students and teachers in high schools

Ion/neutral complexes generated during unimolecular fragmentation: Intra-complex hydride abstraction by tert-butyl cations from electron-rich and electron-poor 1,3-diphenylpropanes

Matthias C, Cartoni A, Kuck D. Ion/neutral complexes generated during unimolecular fragmentation: Intra-complex hydride abstraction by tert-butyl cations from electron-rich and electron-poor 1,3-diphenylpropanes. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY. 2006;255-256:195-212.The hydride transfer and proton transfer occurring between the constituents of ion/neutral complexes of tert-butyl cations and electron-rich and electron-poor 1,3-diphenylpropanes, [(CH3)(3)C+ C6H5CH2CH2CH2C6H4X] were investigated by use of CI/MIKE spectrometry of nine 1-(tert-butylphenyl)-3-arylpropanes and 16 site-specific deuterium-labeled isotopomers. The competition between H- abstraction by the (CH3)(3)C+ ion from the neutral arene and H+ transfer to it was found to be strongly affected by the electron-donating substituents, in particular by X = OCH3, on the one hand, and X = F and CF3, on the other, suggesting that the 1,3-diphenylpropane molecule within the I/N complex acts and reacts as a bidentate solvating partner to the carbocation. The effect of the substituents X on the regioselectivity of the intra-complex hydride abstraction from the two benzylic CH2 groups, k(gamma-H)/k(alpha-H), and their influence on the kinetic isotope effect (k(H)/k(D))(gamma), operating during the abstraction from the substituted benzylic moiety, were determined in a semi-quantitative approach by assuming (k(H)/k(D))(alpha) = 1.60, the generally observed value for the unsubstituted benzylic moiety. The regioselectivity range was found to span almost three orders of magnitude, from k(gamma-H)/k(alpha-H) >= 11.2 for the complex [(CH3)(3)C+ (C6H5CH2CH2CH2C6H4)-H-alpha-H-gamma(p-OCH3)] to k(gamma-H)/k(alpha-H) <= 0.04 for the complex [(CH3)(3)C+ (C6H5CH2CH2CH2C6H4)-H-alpha-H-gamma(p-CF3)]. (C) 2006 Elsevier B.V. All rights reserved

Gas-Phase Fluorination of Acetylene by XeF+: Formation, Structure and Reactivity of C2H2F+ Isomeric Ions

The gas phase reactivity of XeF+ towards acetylene was investigated by triple quadrupole mass spectrometry. XeF+ promotes both F+ and Xe+ transfer to acetylene, yielding C2H2F+ and C2H2Xe+, respectively. The C2H2F+ ions formed were probed by low-energy collisionaly activated dissociation mass spectrometry and characterized as CH2=CF+, namely the isomer identified as the most stable by previous theoretical studies. The 1-fluorovinyl cation reacts in the gas phase with typical nucleophiles (CH3COCH3, CH3CN, CH3OH, C2H4) as bronsted acid and/or as a fluorinating agent, depending on the thermochemistry of the processes involved