Exploring Water Radiolysis in Proton Cancer Therapy: Time-Dependent, Non-Adiabatic Simulations of H\u3csup\u3e+\u3c/sup\u3e + (H2O)1-6

© 2017 Privett et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. To elucidate microscopic details of proton cancer therapy (PCT), we apply the simplest-level electron nuclear dynamics (SLEND) method to H+ + (H2O)1-6 at ELab = 100 keV. These systems are computationally tractable prototypes to simulate water radiolysis reactions - i.e. the PCT processes that generate the DNA-damaging species against cancerous cells. To capture incipient bulk-water effects, ten (H2O)1-6 isomers are considered, ranging from quasi-planar/ multiplanar (H2O)1-6 to smallest-drop prism and cage (H2O)6 structures. SLEND is a time-dependent, variational, non-adiabatic and direct method that adopts a nuclear classicalmechanics description and an electronic single-determinantal wavefunction in the Thouless representation. Short-time SLEND/6-31G∗ (n = 1-6) and /6-31G∗ ∗ (n = 1-5) simulations render cluster-to-projectile 1-electron-transfer (1-ET) total integral cross sections (ICSs) and 1- ET probabilities. In absolute quantitative terms, SLEND/6-31G∗ 1-ET ICS compares satisfactorily with alternative experimental and theoretical results only available for n = 1 and exhibits almost the same accuracy of the best alternative theoretical result. SLEND/6-31G∗ ∗ overestimates 1-ET ICS for n = 1, but a comparable overestimation is also observed with another theoretical method. An investigation on H+ + H indicates that electron direct ionization (DI) becomes significant with the large virtual-space quasi-continuum in large basis sets; thus, SLEND/6-31G∗ 1-ET ICS is overestimated by DI contributions. The solution to this problem is discussed. In relative quantitative terms, both SLEND/6-31∗ and /6-31G∗ ∗ 1-ET ICSs precisely fit into physically justified scaling formulae as a function of the cluster size; this indicates SLEND\u27s suitability for predicting properties of water clusters with varying size. Longtime SLEND/6-31G∗ (n = 1-4) simulations predict the formation of the DNA-damaging radicals H, OH, O and H3O. While smallest-drop isomers are included, no early manifestations of bulk water PCT properties are observed and simulations with larger water clusters will be needed to capture those effects. This study is the largest SLEND investigation on water radiolysis to date

Design of Nickel Supported on Water-Tolerant Nb2O5 Catalysts for the Hydrotreating of Lignin Streams Obtained from Lignin-First Biorefining

R.R. acknowledges the financial support provided by the ERC Consolidator Grant LIGNINFIRST (Project Number: 725762). R.R. and A.A.S.C. thank FAPESP for the support provided (Process Number: 2016/50423-3). The authors are grateful to LNLS/CNPEM for the infrastructure (XPD beamline and chemistry laboratory), LNNano for the STEM infrastructure, the GPMMM laboratory (IQ-UNICAMP) for the quantitative FTIR of adsorbed pyridine analysis, CNPq for the PhD scholarship (Process Number: 165106/2014-0), and CAPES for the PDSE scholarship (Process Number: 88881.132245/2016-01). This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. Finally, the authors are thankful to CBMM for the ammonium niobium oxalate hydrate samples.Peer reviewedPublisher PD

Exploring water radiolysis in proton cancer therapy: Time-dependent, non-adiabatic simulations of H+ + (H2O)1-6.

To elucidate microscopic details of proton cancer therapy (PCT), we apply the simplest-level electron nuclear dynamics (SLEND) method to H+ + (H2O)1-6 at ELab = 100 keV. These systems are computationally tractable prototypes to simulate water radiolysis reactions-i.e. the PCT processes that generate the DNA-damaging species against cancerous cells. To capture incipient bulk-water effects, ten (H2O)1-6 isomers are considered, ranging from quasi-planar/multiplanar (H2O)1-6 to "smallest-drop" prism and cage (H2O)6 structures. SLEND is a time-dependent, variational, non-adiabatic and direct method that adopts a nuclear classical-mechanics description and an electronic single-determinantal wavefunction in the Thouless representation. Short-time SLEND/6-31G* (n = 1-6) and /6-31G** (n = 1-5) simulations render cluster-to-projectile 1-electron-transfer (1-ET) total integral cross sections (ICSs) and 1-ET probabilities. In absolute quantitative terms, SLEND/6-31G* 1-ET ICS compares satisfactorily with alternative experimental and theoretical results only available for n = 1 and exhibits almost the same accuracy of the best alternative theoretical result. SLEND/6-31G** overestimates 1-ET ICS for n = 1, but a comparable overestimation is also observed with another theoretical method. An investigation on H+ + H indicates that electron direct ionization (DI) becomes significant with the large virtual-space quasi-continuum in large basis sets; thus, SLEND/6-31G** 1-ET ICS is overestimated by DI contributions. The solution to this problem is discussed. In relative quantitative terms, both SLEND/6-31* and /6-31G** 1-ET ICSs precisely fit into physically justified scaling formulae as a function of the cluster size; this indicates SLEND's suitability for predicting properties of water clusters with varying size. Long-time SLEND/6-31G* (n = 1-4) simulations predict the formation of the DNA-damaging radicals H, OH, O and H3O. While "smallest-drop" isomers are included, no early manifestations of bulk water PCT properties are observed and simulations with larger water clusters will be needed to capture those effects. This study is the largest SLEND investigation on water radiolysis to date

Interplay between near-field properties and au nanorod cluster structure: extending hot spots for surface-enhanced raman scattering

Materials science has observed a continuous increase in the use of metal nanoparticles in a wide range of studies, from fundamental physics to technological applications such as photocatalysis and optical communication devices. This broad scope has the same fundamental origin, the localized surface plasmons, whose excitation leads to strong light confinement, especially in the vicinity of closely spaced nanoparticles, the hot spots. The field amplification may be used to amplify the Raman scattering of adsorbed molecules, which is known as surface-enhanced Raman scattering (SERS). A crucial and limiting characteristic of SERS hot spots is their very localized nature. that influences the SERS intensity reproducibility as well as the probabilities of observation of single-molecule SERS signals. In this paper we discuss the correlation between SERS performance and gold nanorod cluster structures using transmission electron microscopy, SERS spectra and numerical simulations. The experimental data showed interesting behavior for the combination of end-to-end and side-by-side interactions, revealing the possibility of creating strong hot spots with a more extended spatial distribution. The results give insights into the development of high-performance SERS substrates301226242633CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP302792/2015-5; 408985/2016-0sem informação2011/17923-9; 2016/21070-

Grids for the projectile impact parameter <i>b</i> for the SLEND simulations.

<p>[<i>b</i>]₁ = grids for short-time simulations to calculate 1-electron-transfer total integral cross sections; [<i>b</i>]₂ = grids for long-time simulations to predict fragmentation processes. Grid data are given as [<i>b</i>_Min, <i>b</i>_Max, Δ<i>b</i>] ⇒ <i>b</i> = <i>b</i>_Min, <i>b</i>_Min + Δ<i>b</i>, <i>b</i>_Min + 2Δ<i>b</i> … <i>b</i>_Max. All units are in a.u.</p

SLEND/6-31G* and /6-31G** target-to-proton total 1-ET ICSs <i>σ</i>_{1−<i>ET</i>} for H⁺ + (H₂O)_1-6 vs. the water cluster size <i>n</i>.

<p>Current data are in comparison with available experimental and theoretical <i>σ</i>_{1−<i>ET</i>} for <i>n</i> = 1 [Exp.: A [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174456#pone.0174456.ref070" target="_blank">70</a>], B [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174456#pone.0174456.ref071" target="_blank">71</a>], C [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174456#pone.0174456.ref072" target="_blank">72</a>] and D [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174456#pone.0174456.ref073" target="_blank">73</a>], Theory A: basis generator method (BGM) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174456#pone.0174456.ref023" target="_blank">23</a>], Theory B: continuum distorted wave-eikonal initial state (CDW-EIS) approximation [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174456#pone.0174456.ref022" target="_blank">22</a>]]. SLEND values are fit to the scaling formula <i>σ</i>_{1−<i>ET</i>} (<i>x</i>) = <i>cn</i>^2/3. The error of the SLEND ICSs is ± 0.005 Ä. The errors from the Theory A and B results compared herein were not reported.</p

H⁺ + (H₂O)_1-6 initial conditions.

<p>A given water cluster (not depicted for clarity’s sake) is placed at rest with its center of mass at the origin of the coordinate axes and with its major (pseudo-)plane of symmetry with maximum coincidence with the x-y plane. The H⁺ projectile is initially prepared with position and momentum and and with impact parameter <i>b</i> (Panel I). Different projectile-target relative orientations Ω = (<i>α</i>, <i>β</i>, <i>γ</i>) are generated by rotating and through the <i>extrinsic</i> Euler angles <i>γ</i> (Panel I), <i>β</i> (Panel II), and <i>α</i> (Panel III) around the <i>space-fixed</i> z, y, and z axes, respectively. The definite initial conditions of the H⁺ projectile to start the simulations, and , are shown in Panel IV (cf. text for more details).</p

Orientation-averaged impact-parameter-weighted target-to-proton 1-ET probabilities at the SLEND/6-31G* (left panel) and /6-31G** (right panel) levels vs. <i>b</i> for the investigated (H₂O)_1-6.

<p>Water cluster isomers are denoted with the number code in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174456#pone.0174456.g001" target="_blank">Fig 1</a> (1, 2 … 6b, 6c).</p

SLEND cluster-to-proton 1-electron-transfer integral cross sections <i>σ</i>_{1−<i>ET</i>} for H⁺ + (H₂O)_<i>n</i>, <i>n</i> = 2–6, at <i>E</i>_<i>Lab</i> = 100 keV.

<p>Cf. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174456#pone.0174456.g001" target="_blank">Fig 1</a> for the structures of the water cluster isomers. The error of the SLEND integral cross sections is ± 0.005 Ä.</p