Communication: Towards catalytic nitric oxide reduction via oligomerization on boron doped graphene

We use density functional theory to describe a novel way for metal free catalytic reduction of nitric oxide NO utilizing boron doped graphene. The present study is based on the observation that boron doped graphene and O-N=N-O- act as Lewis acid-base pair allowing the graphene surface to act as a catalyst. The process implies electron assisted N=N bond formation prior to N-O dissociation. Two N-2 + O-2 product channels, one of which favoring N2O formation, are envisaged as outcome of the catalytic process. Besides, we show also that the N-2 + O-2 formation pathways are contrasted by a side reaction that brings to N3O3- formation and decomposition into N2O + NO2-

Enhanced Manifold of States Achieved in Heterostructures of Iron Selenide and Boron-Doped Graphene

Enhanced superconductivity is sought by employing heterostructures composed of boron-doped graphene and iron selenide. Build-up of a composite manifold of near-degenerate noninteracting states formed by coupling top-of-valence-band states of FeSe to bottom-of-conduction-band states of boron-doped graphene is demonstrated. Intra- and intersubsystem excitons are explored by means of density functional theory in order to articulate a normal state from which superconductivity may emerge. The results are discussed in the context of electron correlation in general and multi-band superconductivity in particular

Simulations of Nonadiabatic Dynamics in Complex Systems: Application to Self Assembled Monolayers

Nowadays the Theoretical and Computational Chemistry is called to face problems related to Material Science or Biology and involving large and complex system that are difficult to treat with ``standard'' computational techniques. The work done during my PhD goes in this direction and I have tried to deal with different complex systems with the appropriate techniques. The work presented in the chapters of this thesis deals with two different topics: the first one is the computational study of Self Assembled Monolayers of azo-compounds through QM/MM dynamics, while the second is the set up of a new method to perform excited state dynamics by means of force-fields and of a rate model for the nonadiabatic transitions

The photo-orientation of azobenzene in viscous solutions, simulated by a stochastic model

We report a computational study of the photo-orientation kinetics in a viscous solution of azobenzene in ethylene glycol, under irradiation with linearly polarized light. The development of anisotropy and its interplay with photoisomerization are simulated by a stochastic model. A distinctive feature of the model is that it takes into account the photo-orientation angular distributions, specific for each isomer, obtained by nonadiabatic dynamics simulations at the molecular level. We find that the anisotropy, as measured by optical absorption dichroism, does not necessarily increase monotonously with time. As expected, the photo-orientation turns out to be strongly coupled with photoisomerization, but the latter is not a mandatory ingredient of this phenomenon: we predict that any chromophore undergoing large amplitude geometry relaxation during its excited state dynamics can develop anisotropy under suitable conditions

Evidence for electron transfer between graphene and non‐covalently bound π‐systems

Hybridizing graphene and molecules possess a high potential for developing materials for new applications. However, new methods to characterize such hybrids must be developed. Herein, the wet‐chemical non‐covalent functionalization of graphene with cationic π‐systems is presented and the interaction between graphene and the molecules is characterized in detail. A series of tricationic benzimidazolium salts with various steric demand and counterions was synthesized, characterized and used for the fabrication of graphene hybrids. Subsequently, the doping effects were studied. The molecules are adsorbed onto graphene and studied by Raman spectroscopy, XPS as well as ToF‐SIMS. The charged π‐systems show a p‐doping effect on the underlying graphene. Consequently, the tricationic molecules are reduced through a partial electron transfer process from graphene, a process which is accompanied by the loss of counterions. DFT calculations support this hypothesis and the strong p‐doping could be confirmed in fabricated monolayer graphene/hybrid FET devices. The results are the basis to develop sensor applications, which are based on analyte/molecule interactions and effects on doping

Bonding between π-Conjugated Polycations and Monolayer Graphene: Decisive Role of Anions

Functionalization and precise modulation of the electronic properties of graphene are key processes in the development of new applications of this promising material. This study examines the potential of using organic polycations as p-dopants and/or anchoring motifs for non-covalent functionalization. A library of hybrid materials was prepared through wet-chemical non-covalent functionalization. Both chemical vapor deposition graphene and reduced graphene oxide were functionalized with a series of neutral and polycationic benzimidazole-based systems. We report on how both the number of anions and the size, shape, and magnitude of the positive charge of the benzimidazole-based systems cooperatively affect the redox properties as well as the affinity for and the nature of bonding to graphene. The redox properties of the benzimidazole-based systems were studied by cyclic voltammetry. The functionalized graphene materials were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. Density functional theory calculations were performed to make contact between the experimental results obtained for molecular samples and hybrid materials. No universal dependence of the binding affinity on a single parameter, such as the amount of positive charge or the size of the system, was found. Instead, the cooperative effect of the three-dimensional structure of the benzimidazole-based systems and the number of anions was found to play a pivotal role. Together, these parameters determine the degree of partial electron sharing and magnitude of dispersion forces involved in the binding of members of this family of benzimidazole-based systems to graphene

Pt accelerated coarsening of A15 precipitates in Cr-Si alloys

The effect of alloying Cr-rich Cr-Si alloys with Pt was investigated by a combination of complementary experimental methods and atomic scale modelling. The investigated Cr-Si and Cr-Si-Pt (Cr ⩾86 at.%) alloys developed a two-phase microstructure consisting of Cr solid solution (Crss) matrix and strengthened by A15 precipitates during annealing at 1200\ub0C. It was found that additions of 2 at.% Pt increase the coarsening rate by almost five times considering annealing times up to 522 h. Pt was found to change the precipitate matrix orientation relationship, despite its low influence on the Crss matrix/A15 precipitate misfit. Through this experimental and modelling approach new insight has been gained into mechanisms of enhanced coarsening by Pt addition. The increased coarsening is principally attributed to a change in interface composition and structure resulting in different thermodynamic stabilities: Pt-containing A15 phase was found to have a broader compositional range if both elements, Pt and Si, are present compared to only Si. Additionally, the Crss phase was found to have a higher solubility of Pt and Si over just Si. Both factors additionally facilitated Ostwald ripening

Racial differences in systemic sclerosis disease presentation: a European Scleroderma Trials and Research group study

Objectives. Racial factors play a significant role in SSc. We evaluated differences in SSc presentations between white patients (WP), Asian patients (AP) and black patients (BP) and analysed the effects of geographical locations.Methods. SSc characteristics of patients from the EUSTAR cohort were cross-sectionally compared across racial groups using survival and multiple logistic regression analyses.Results. The study included 9162 WP, 341 AP and 181 BP. AP developed the first non-RP feature faster than WP but slower than BP. AP were less frequently anti-centromere (ACA; odds ratio (OR) = 0.4, P < 0.001) and more frequently anti-topoisomerase-I autoantibodies (ATA) positive (OR = 1.2, P = 0.068), while BP were less likely to be ACA and ATA positive than were WP [OR(ACA) = 0.3, P < 0.001; OR(ATA) = 0.5, P = 0.020]. AP had less often (OR = 0.7, P = 0.06) and BP more often (OR = 2.7, P < 0.001) diffuse skin involvement than had WP.AP and BP were more likely to have pulmonary hypertension [OR(AP) = 2.6, P < 0.001; OR(BP) = 2.7, P = 0.03 vs WP] and a reduced forced vital capacity [OR(AP) = 2.5, P < 0.001; OR(BP) = 2.4, P < 0.004] than were WP. AP more often had an impaired diffusing capacity of the lung than had BP and WP [OR(AP vs BP) = 1.9, P = 0.038; OR(AP vs WP) = 2.4, P < 0.001]. After RP onset, AP and BP had a higher hazard to die than had WP [hazard ratio (HR) (AP) = 1.6, P = 0.011; HR(BP) = 2.1, P < 0.001].Conclusion. Compared with WP, and mostly independent of geographical location, AP have a faster and earlier disease onset with high prevalences of ATA, pulmonary hypertension and forced vital capacity impairment and higher mortality. BP had the fastest disease onset, a high prevalence of diffuse skin involvement and nominally the highest mortality

Un modello per il fenomeno della foto-orientazione, con applicazione alla fotoisomerizzazione dell'azobenzene

Lo scopo generale del mio lavoro di tesi è investigare computazionalmente il processo di orientazione che subisce un campione di molecole di azobenzene non interagenti tra loro, poste in un solvente viscoso ed eccitate con luce polarizzata linearmente. Si tratta quindi di studiare la cinetica ed il meccanismo della foto­orientazione nel caso più semplice. Le simulazioni della cinetica utilizzano i risultati di simulazioni più dettagliate, a livello di singola molecola, che si concentrano sui processi di eccitazione, decadimento non radiativo e rilassamento geometrico. Si tratta di simulazioni di dinamica molecolare che forniscono dati sulla distribuzione di orientazioni ottenuta dopo il ritorno allo stato fondamentale e l'eventuale isomerizzazione. Per simulare la cinetica della foto­orientazione con il gruppo di ricerca abbiamo elaborato un modello stocastico, che rappresenta il comportamento di un gran numero di molecole mediante scelte casuali riguardanti ogni singola molecola. Questo modello consente quindi di passare dai tempi e dimensioni molecolari a quelli mesoscopici (milioni di molecole), cioè di risolvere un tipico problema “multiscala”, sia pure ad un livello piuttosto semplice. In particolare ho studiato la foto­orientazione di azobenzene dovuta ad eccitazione nella banda π → π* , dove si ha l'assorbimento più intenso e rapporti di coefficienti d'estinzione ε_trans/ε_cis variabili a piacimento scegliendo la lunghezza d'onda. Ho preventivamente realizzato simulazioni di dinamica molecolare per l'azobenzene nella banda π → π* , in tre ambienti diversi a scopo di confronto: nel vuoto, in metanolo ed in glicol etilenico. Lo studio della cinetica di foto­orientazione è basato sui risultati della dinamica di una singola molecola di azobenzene in glicol etilenico. Tutto questo è stato fatto per determinare le condizioni sperimentali adatte per osservare il fenomeno di foto­orientazione in un solvente moderatamente viscoso come il glicol etilenico a temperatura ambiente. Inoltre, è stata verificata l'importanza della reazione di fotoisomerizzazione nel rendere più efficace il processo di orientazione, e sono stati distinti i contributi dei due isomeri all'anisotropia misurabile otticamente