Theoretical study on the mechanisms of formation of primal carbon clusters and nanoparticles in space

We present a theoretical study of assembling clusters and nanoparticles in space from primordial aggregations of unbound carbon atoms. Geometry optimization and SCC-DFTB dynamics methods are employed to predict carbon clusters, their time evolution and stability. The initial density of the aggregates is found to be of primary importance for the structure of the clusters. Aggregates with low initial density yield clusters with an approximately equal prevalence of sp and sp2 hybridization with almost missing sp3. Higher initial density results in sp2-dominant molecules, resembling the carbon skeleton of polycyclic aromatic hydrocarbons (PAHs). Larger initial aggregations result in sp2-dominant polymers. Such materials are highly porous and possess a similarity to laterally bound nanotubes. Some clusters resemble fullerene building blocks. We employed metadynamics to model the inter-fragment coupling of such structures and predict the formation of spheroid nanoparticles, closely resembling fullerenes. One such structure has the lowest binding energy per atom among the studied molecules. All zero-dimensional forms, obtained by the simulations, conform to the experimentally detected types of molecules in space. The theoretical IR spectrum of the nanoparticles closely resembles that of fullerene C70 and therefore such imperfect structures may be mistaken for known fullerenes in experimental infrared (IR) telescope studies.

Molecular structure and interactions of water intercalated in nickel hydroxide

The structure and properties of α-Ni(OH)2 containing water and nitrate have been investigated computationally. The adsorption of water molecules on the Ni(OH)2 surface is also investigated to provide insight into the nature of the water-Ni(OH)2 interactions. The spectroscopic and dynamical behaviour of the intercalated species has been characterized and used to explain experimental findings reported for this material. The results presented here indicate that the water molecules interact non-covalently with Ni(OH)2, with a binding energy that is comparable in magnitude with that of the water dimer hydrogen bond. The presence of the intercalated species increases the distance between the Ni(OH)2 layers such that the interlayer interactions are negligible. The weakening of the interlayer interactions facilitates the horizontal displacement of the layers relative to one another, providing a possible origin for stacking faults observed in α-Ni(OH)2. Comparison of the vibrational frequencies calculated here with the experimental spectra confirms that α-Ni(OH)2 containing only water molecules can be synthesized. The structures of the water molecules intercalated in α-Ni(OH)2 were found to be analogous to those absorbed in γ-NiOOH, while the water-layer interactions are stronger in γ-NiOOH. The results presented here characterize the structure and interactions of water intercalated in nickel hydroxides and also provide insights into the effects of intercalated water on the properties of layered metal hydroxides.

Carbonate and carbonate anion radicals in aqueous solutions exist as CO3(H2O)62− and CO3(H2O)6˙− respectively: the crucial role of the inner hydration sphere of anions in explaining their properties

An effort to reproduce the physical properties of CO₃²⁻ and CO₃˙⁻ in water proves that one has to include an inner hydration sphere of six water molecules for both anions.

Molecular dynamics simulations of zinc oxide solubility: From bulk down to nanoparticles

The solubility of metal oxides is one of the key descriptors for the evaluation of their potential toxic effects, both in the bulk form and in nanoparticulated aggregates. Current work presents a new methodology for the in silico assessment of the solubility of metal oxides, which is demonstrated using a well-studied system, ZnO. The calculation of the solubility is based on statistical thermodynamics tools combined with Density Functional Tight Binding theory for the evaluation of the free energy exchange during the dissolution process. Models of small ZnO clusters are used for describing the final dissolved material, since the complete ionic dissolution of ZnO is hindered by the formation of O^2- anions in solution, which are highly unstable. Results show very good agreement between the computed solubility values and experimental data for ZnO bulk, up to 0.5 mg L^-1 and equivalents of 50 μg L^-1 for the free Zn²⁺ cation in solution. However, the reference model for solid nanoparticles formed by free space nanoparticles can only give a limited quantitative solubility evaluation for ZnO nanoparticles.

Keto-polymethines: a versatile class of dyes with outstanding spectroscopic properties for in cellulo and in vivo two-photon microscopy imaging

The synthesis of keto-heptamethine derivatives has been expanded to various new symmetrical and asymmetrical structures, including an unprecedented di-anionic keto-polymethine. The spectroscopic behavior of these new dyes has been systematically and thoroughly investigated, revealing that the formation of hydrogen bond interactions with protic solvents is responsible for a dramatic enhancement of the fluorescence quantum yield in the far-red spectral region. The existence of these strong hydrogen-bond interactions was further confirmed by molecular dynamics simulations. These bis-dipolar polymethines exhibit large two-photon absorption (TPA) cross-sections (σ² in GM) in the near-infrared, making them ideal candidates for NIR-to-NIR two-photon microscopy imaging applications. We demonstrate that the molecular engineering of the hydrophilic/hydrophobic balance enables targeting of different cellular components, such as cytoplasm or cell membranes. Addition of appropriate substituents provides the molecule with high-water-solubility, affording efficient two-photon probes for angiography.

Nanostructured water and carbon dioxide inside collapsing carbon nanotubes at high pressure

We present simulations of the collapse under hydrostatic pressure of carbon nanotubes containing either water or carbon dioxide.