Application of encapsulated hollow Gold nanocluster targets for high-quality and quasi-monoenergetic ions generation

With persistent progress in ultra-intense laser pulses, Coulomb explosion (CE) of spherical nanoclusters can in principle produce high-quality-quasi-monoenergetic ions. Focusing on using CE framework, in this paper, we have proposed a target scheme to accelerate light/heavy ions’ beam. The scheme relies on encapsulating a hollow Gold nanocluster inside a hollow proton-Carbon (HC) nanosphere. The ability of this suggestion has been simulated by the two-dimensional particle-in-cell code (EPOCH). Simulation results exhibit that a hollow Gold cluster can positively increase the electrons’ extraction. This condition may improve the acceleration of low-divergence H+, C6+, and Au67+ ions. Our simulation shows that at the end of the interaction, for a Gold cluster with an optimal hollow radius of 91.3 nm, the cut-off energy of H+, C6+, and Au67+ are about 54.9 MeV/u, 51.5 MeV/u, and 54.9 MeV/u, respectively. In this case, an increase of about 52% for H+ and 61% for C6+ is obtained, contrast to bare HC hollow nanosphere (i.e., a hollow nanosphere with no cluster), while the relative divergence decreases to 1.38 and 1.86, respectively for H+ and C6+ ions. We have also compared our simulation results with another proposed target structure composed of a void area with an optimum diameter of 70.4 nm between the fully- Gold nanocluster and HC nanosphere. We have exhibited that the results are improved, contrast to bare nanosphere. However, the cut-off energy suppression and angular divergence increase are shown compared with encapsulated hollow Gold nanocluster structure.

A multifunctional AIE gold cluster-based theranostic system: tumor-targeted imaging and Fenton reaction-assisted enhanced radiotherapy

Background As cancer is one of the main leading causes of mortality, a series of monotherapies such as chemotherapy, gene therapy and radiotherapy have been developed to overcome this thorny problem. However, a single treatment approach could not achieve satisfactory effect in many experimental explorations. Results In this study, we report the fabrication of cyclic RGD peptide (cRGD) modified Au4-iron oxide nanoparticle (Au4-IO NP-cRGD) based on aggregation-induced emission (AIE) as a multifunctional theranostic system. Besides Au4 cluster-based fluorescence imaging and enhanced radiotherapy, iron oxide (IO) nanocluster could realize magnetic resonance (MR) imaging and Fenton reaction-based chemotherapy. Abundant toxic reactive oxygen species generated from X-ray irradiation and in situ tumor-specific Fenton reaction under acidic microenvironment leads to the apoptotic and necrotic death of cancer cells. In vivo studies demonstrated good biocompatibility of Au4-IO NP-cRGD and a high tumor suppression rate of 81.1% in the synergistic therapy group. Conclusions The successful dual-modal imaging and combined tumor therapy demonstrated AIE as a promising strategy for constructing multifunctional cancer theranostic platform. Graphical Abstract

From the Superatom to a Large Variety of Supermaterials: A Theoretical Study

<p>Metal clusters have been a subject of interdisciplinary research for many years as they act as a bridge between atoms and solid-state materials. In particular, clusters that show distinct thermodynamic stability and unusual atom like behavior, with an electronic shell structure that exhibits a superatomic nature, have attracted considerable attention. The concept of clusters behaving as individual atoms and furthermore mimicking the chemistry of specific elements directly leads to the idea of using those nanoparticles as building blocks for new functional materials. Furthermore, it is interesting that one can change the properties of cluster assembled materials by solely changing the properties of the individual clusters involved. In this work, various factors affecting superatomic assemblies are identified and critically analyzed within the means of first-principles computations. The icosahedral gold cluster Au₁₃[RS(AuSR)₂]₆ has been chosen as a model system to study the tunability of the electronic structure using single atomic impurities. In this context the doped clusters were found to be tunable such, that they reveal atomic properties, e.g. electron affinities similar to individual halogen atoms. In addition, the choice of ligands protecting the clusters is evaluated regarding the stability of the whole cluster and the involvement of the ligands in creating the superatomic structure. The latter was found to be important when thinking of orbital overlap in superatomic assemblies. In a next step the knowledge gained is used to investigate cluster-cluster interactions and detect pairs of clusters that are good candidates to create new superatomic materials. Furthermore basic principles regarding cluster assemblies are established and partially tested in an experimental collaboration studing the structure of an Au₉(PPh₃)₈-C₆₀ assembly. Beyond the investigation of individual gold clusters and gold cluster materials, the electronic structure of binary solid state materials consisting of ligand protected transition metal-chalcogen clusters and fullerenes, as synthesized by Roy et al., is presented. This study shows an intermediate case of non-tunable clusters and furthermore displays the partial loss of the superatomic character of the transition metal chalcogen clusters due to charge transfer. An experimental collaboration conducted in cooperation with the research group of Prof. Beate Paulus in Berlin proceeds even further and investigates the absorption of water on non-superatomic aluminumoxo fluoride clusters.</p>

From the Superatom to a Large Variety of Supermaterials: A Theoretical Study

<p>Metal clusters have been a subject of interdisciplinary research for many years as they act as a bridge between atoms and solid-state materials. In particular, clusters that show distinct thermodynamic stability and unusual atom like behavior, with an electronic shell structure that exhibits a superatomic nature, have attracted considerable attention. The concept of clusters behaving as individual atoms and furthermore mimicking the chemistry of specific elements directly leads to the idea of using those nanoparticles as building blocks for new functional materials. Furthermore, it is interesting that one can change the properties of cluster assembled materials by solely changing the properties of the individual clusters involved. In this work, various factors affecting superatomic assemblies are identified and critically analyzed within the means of first-principles computations. The icosahedral gold cluster Au₁₃[RS(AuSR)₂]₆ has been chosen as a model system to study the tunability of the electronic structure using single atomic impurities. In this context the doped clusters were found to be tunable such, that they reveal atomic properties, e.g. electron affinities similar to individual halogen atoms. In addition, the choice of ligands protecting the clusters is evaluated regarding the stability of the whole cluster and the involvement of the ligands in creating the superatomic structure. The latter was found to be important when thinking of orbital overlap in superatomic assemblies. In a next step the knowledge gained is used to investigate cluster-cluster interactions and detect pairs of clusters that are good candidates to create new superatomic materials. Furthermore basic principles regarding cluster assemblies are established and partially tested in an experimental collaboration studing the structure of an Au₉(PPh₃)₈-C₆₀ assembly. Beyond the investigation of individual gold clusters and gold cluster materials, the electronic structure of binary solid state materials consisting of ligand protected transition metal-chalcogen clusters and fullerenes, as synthesized by Roy et al., is presented. This study shows an intermediate case of non-tunable clusters and furthermore displays the partial loss of the superatomic character of the transition metal chalcogen clusters due to charge transfer. An experimental collaboration conducted in cooperation with the research group of Prof. Beate Paulus in Berlin proceeds even further and investigates the absorption of water on non-superatomic aluminumoxo fluoride clusters.</p>

Superatomic Au25(SC2H5)18 Nanocluster under Pressure

The last decade has witnessed significant advances in the synthesis and structure determination of atomically precise metal nanoclusters. However, little is known about the condensed matter properties of these nanosized metal nanoclusters packed in a crystal lattice under high pressure. Here using density function theory calculations, we simulate the crystal of a representative superatomic gold cluster, [Au25(SR)18]0 (R = C2H5), under various pressures. At ambient conditions, [Au25(SC2H5)18]0 clusters are packed in a crystal via dispersion interactions; being a 7e superatom, each cluster carries a magnetic moment of 1μB or one unpaired electron. Upon increasing compression (from 10 to 110 GPa), we observe the formation of inter-cluster Au-Au, Au-S, and S-S covalent bonds between staple motifs, thereby linking the clusters into a network. The pressure-induced structural change is accompanied by the vanishment of the magnetic moment and the semiconductor-to-metal transition. Our work shows that subjecting crystals of atomically precise metal nanoclusters to high pressures could lead to new crystalline states and physical properties.

MOLECULAR SWITCH BASED ON BITHIOPHENE-AZOBENZENE: HOW TO CONTROL CONDUCTANCE THROUGH THE MONOLAYER USING LIGHT

Молекулярные переключатели на основе азобензола (азо) являются светочувствительными молекулами, которые могут переключаться между двумя конфигурационными состояниями под действием света. Светочувствительные азо -монослои можно использовать для модуляции работы выхода, то есть они влияют на свойства электродов. В данной работе мы отвечаем на вопрос, что происходит со структурами, электронными свойствами и перераспределением заряда в монослоях азобитиофена (азо-бт) в зависимости от светового стимула, используя теорию функционала плотности. Моделируются два типа переключателей, различающихся расположением азо и бт от группы пришивки молекулы к поверхности: азо-бт и бт-азо . Один из них (бт-азо) описан в литературе, другой же является продуктом молекулярного дизайна. Мы описываем транс- и цис-изомеры для каждого переключателя, находящегося в контакте с кластером золота. Наше моделирование объясняет гигантское соотношение в проводимости ON/OFF-состояний при воздействии УФ-излучения на монослой улучшенной электронной связью между цис-изомерами (состояние ON) и кластером золота. Транс-изомеры же (OFF состояние) моделируемых переключателей играют роль изоляторов. Кроме того, мы показываем, какие именно свойства улучшаются после молекулярного дизайна. Данное исследование открывает новые возможности в разработке инновационных модификаций поверхности электродов. Molecular switches based on azobenzene (azo) are defined as light-responsive molecules which can change between two configurational states under light stimuli. Responsive azo monolayers can be used to modulate the work function, i.e. they tune the properties of the interfaces at the electrodes. In this work, we investigate what happens to the structures, electronic properties, and the charge redistribution within azo-bithiophene (azo-bt) monolayers depending on the light stimulus using density functional theory. Two types of switches differing in the order of azo and bt counting from the anchor group are modelled: azo-bt and bt-azo . One of them (bt-azo) is known from the literature, the remaining one is a product of rational design. We describe trans- and cis-isomers for each switch being in a contact with a gold cluster. Our simulations explain a giant ON/OFF conductance ratio upon UV light stimulus by improved electronic coupling between the cis-isomers (ON-state) and the gold cluster. The trans-isomers (OFF-state) of the simulated switches play the role of the insulators. Moreover, we show which molecular properties are enchanced by molecular design. This study opens up new avenues to the development of the innovative design of electrode surface modifications.

Adsorption/Desorption Behaviors and SERS Chemical Enhancement of 6-Mercaptopurine on a Nanostructured Gold Surface: The Au20 Cluster Model

Computational approaches are employed to elucidate the binding mechanism and the SERS phenomenon of 6-mercaptopurine (6MP) adsorbed on the tetrahedral Au20 cluster as a simple model for a nanostructured gold surface. Computations are carried out in both vacuum and aqueous environments using a continuum model. In the gaseous phase and neutral conditions, interaction of 6MP with the gold cluster is mostly dominated by a covalent Au−S bond and partially stabilized by the Au⋅⋅⋅H−N coupling. However, in acidic solution, the nonconventional Au⋅⋅⋅H−S hydrogen-bond becomes the most favorable binding mode. The 6MP affinity for gold clusters decreases in the order of vacuum > neutral solution > acidic medium. During the adsorption, the energy gap of Au20 substantially declines, leading to an increase in its electrical conductivity, which can be converted to an electrical noise. Moreover, such interaction is likely a reversible process and triggered by either the low pH in sick tissues or the presence of cysteine residues in protein matrices. While N−H bending and stretching vibrations play major roles in the SERS phenomenon of 6MP on gold surfaces in neutral solution, the strongest enhancement in acidic environment is mostly due to an Au⋅⋅⋅H−S coupling, rather than an aromatic ring-gold surface π overlap as previously proposed.

Gold Clusters: From the Dispute on a Gold Chair to the Golden Future of Nanostructures

The present work opens with an acknowledgement to the research activity performed by Luciana Naldini while affiliated at the Università degli Studi di Sassari (Italy), in particular towards gold complexes and clusters, as a tribute to her outstanding figure in a time and a society where being a woman in science was rather difficult, hoping her achievements could be of inspiration to young female chemists in pursuing their careers against the many hurdles they may encounter. Naldini’s findings will be a key to introduce the most recent results in this field, showing how the chemistry of gold compounds has changed throughout the years, to reach levels of complexity and elegance that were once unimagined. The study of gold complexes and clusters with various phosphine ligands was Naldini’s main field of research because of the potential application of these species in diverse research areas including electronics, catalysis, and medicine. As the conclusion of a vital period of study, here we report Naldini’s last results on a hexanuclear cationic gold cluster, [(PPh3)6Au6(OH)2]2+, having a chair conformation, and on the assumption, supported by experimental data, that it comprises two hydroxyl groups. This contribution, within the fascinating field of inorganic chemistry, provides the intuition of how a simple electron counting may lead to predictable species of yet unknown molecular architectures and formulation, nowadays suggesting interesting opportunities to tune the electronic structures of similar and higher nuclearity species thanks to new spectroscopic and analytical approaches and software facilities. After several decades since Naldini’s exceptional work, the chemistry of the gold cluster has reached a considerable degree of complexity, dealing with new, single-atom precise, materials possessing interesting physico-chemical properties, such as luminescence, chirality, or paramagnetic behavior. Here we will describe some of the most significant contributions.