Cluster Shell Research Articles

Novel multifunctional nanospheres of Zn1/3Fe8/3O4@Ag: synthesis, properties and application for multi-modality tumor imaging.

New multifunctional nanospheres have been designed and synthesized through a green and facile strategy, which could be readily used in multi-modality tumor imaging through near-infrared fluorescence (NIRF) imaging, magnetic resonance imaging (MRI) and computed tomography (CT) imaging. Such nanospheres are made of porous superparamagnetic Zn1/3Fe8/3O4 nanosphere cores covered by a thin layer shell of Ag clusters. While the shell of Ag clusters provides efficient NIRF imaging, the Zn1/3Fe8/3O4 nanosphere cores allow external magnetic manipulation and readily facilitates their utilization for MRI and CT imaging.

High-Nuclearity Silver Thiolate Clusters Constructed with Phosphonates

The n-butylphosphonate ligand has been employed to construct three new silver(I) thiolate compounds. Single-crystal X-ray analysis revealed that complexes 1 and 2 are Ag48 and Ag51 coordination chain polymers, while 3 contains a discrete Ag48 cluster, in which three different kinds of silver(I) thiolate cluster shells enclose three different phosphonate-functionalized silver(I) cluster cores, respectively. The structures of clusters in 1–3 feature three three-shell arrangements, S@Ag12@(nBuPO3)9@Ag36S23, S@Ag11@(nBuPO3)7(MoO4)2 @Ag40S27 and MoO4@Ag12@(nBuPO3)8S6 @Ag36S24, respectively.

High-Nuclearity Silver Thiolate Clusters Constructed with Phosphonates.

The n-butylphosphonate ligand has been employed to construct three new silver(I) thiolate compounds. Single-crystal X-ray analysis revealed that complexes 1 and 2 are Ag48 and Ag51 coordination chain polymers, while 3 contains a discrete Ag48 cluster, in which three different kinds of silver(I) thiolate cluster shells enclose three different phosphonate-functionalized silver(I) cluster cores, respectively. The structures of clusters in 1-3 feature three three-shell arrangements, S@Ag12 @(nBuPO3 )9 @Ag36 S23 , S@Ag11 @(nBuPO3 )7 (MoO4 )2 @Ag40 S27 and MoO4 @Ag12 @(nBuPO3 )8 S6 @Ag36 S24 , respectively.

A study on mechanical properties of cement paste using magnetite-silica nano-composites

Micro- and nano-siliceous particles have been employed as one of major components of Portland cement composites because of their filling effect and pozzolanic reaction. Enhancing the mechanical properties of Portland cement composites using nano-particles without workability reduction and dispersion difficulties is one of the challenges in the cement field of research. In order to overcome disadvantages of nano-particles in cement, a new method was investigated in this study. Magnetite-silica core-shell nano-composites (MS), which have been widely used in biological fields, were employed here as fillers and reinforcements in cement pastes. These nano-composite particles consist of nano-magnetite (NM) cluster and nano-amorphous silica shell. Different types of analysis such as X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer were conducted on these particles to investigate their properties. MS particles were synthesised by coating nano-magnetite particles with tetraethyl orthosilicate (TEOS) as a source of silica. MS particles were used as an additive material in cement paste mixes with cement replacement ratios of 0·05, 0·1 and 0·2%. Additional samples were also made with the same cement replacement ratio of NM and nano-silica (NS). Experimental results indicated that the compressive strength of cement paste can be increased up to 14%. This is mainly attributable to the pozzolanic effect of silica shell in combination with the filler and nuclei effect of these particles. It was also found that the MS does not change the workability of mixes considerably. Additionally, the microstructure of cement pastes was characterised using scanning electron microscopy to evaluate the effect of NM, NS and MS particles on the microstructure of cement pastes.

A study on mechanical properties of cement paste using magnetite-silica nano-composites

Micro- and nano-siliceous particles have been employed as one of major components of Portland cement composites because of their filling effect and pozzolanic reaction. Enhancing the mechanical properties of Portland cement composites using nano-particles without workability reduction and dispersion difficulties is one of the challenges in the cement field of research. In order to overcome disadvantages of nano-particles in cement, a new method was investigated in this study. Magnetite-silica core-shell nano-composites (MS), which have been widely used in biological fields, were employed here as fillers and reinforcements in cement pastes. These nano-composite particles consist of nano-magnetite (NM) cluster and nano-amorphous silica shell. Different types of analysis such as X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer were conducted on these particles to investigate their properties. MS particles were synthesised by coating nano-magnetite particles with tetraethyl orthosilicate (TEOS) as a source of silica. MS particles were used as an additive material in cement paste mixes with cement replacement ratios of 0·05, 0·1 and 0·2%. Additional samples were also made with the same cement replacement ratio of NM and nano-silica (NS). Experimental results indicated that the compressive strength of cement paste can be increased up to 14%. This is mainly attributable to the pozzolanic effect of silica shell in combination with the filler and nuclei effect of these particles. It was also found that the MS does not change the workability of mixes considerably. Additionally, the microstructure of cement pastes was characterised using scanning electron microscopy to evaluate the effect of NM, NS and MS particles on the microstructure of cement pastes.

Changes in cluster magnetism and suppression of local superconductivity in amorphous FeCrB alloy irradiated by Ar+ ions

We show that сluster magnetism in ferromagnetic amorphous Fe67Cr18B15 alloy is related to the presence of large, D=150–250Å, α-(Fe Cr) clusters responsible for basic changes in cluster magnetism, small, D=30–100Å, α-(Fe, Cr) and Fe3B clusters and subcluster atomic α-(Fe, Cr, B) groupings, D=10–20Å, in disordered intercluster medium. For initial sample and irradiated one (Φ=1.5×1018ions/cm2) superconductivity exists in the cluster shells of metallic α-(Fe, Cr) phase where ferromagnetism of iron is counterbalanced by antiferromagnetism of chromium. At Φ=3×1018ions/cm2, the internal stresses intensify and the process of iron and chromium phase separation, favorable for mesoscopic superconductivity, changes for inverse one promoting more homogeneous distribution of iron and chromium in the clusters as well as gigantic (twice as much) increase in density of the samples. As a result, in the cluster shells ferromagnetism is restored leading to the increase in magnetization of the sample and suppression of local superconductivity. For initial samples, the temperature dependence of resistivity ρ(T)~T2 is determined by the electron scattering on quantum defects. In strongly inhomogeneous samples, after irradiation by fluence Φ=1.5×1018ions/cm2, the transition to a dependence ρ(T)~T1/2 is caused by the effects of weak localization. In more homogeneous samples, at Φ=3×1018ions/cm2, a return to the dependence ρ(T)~T2 is observed.

Hydrated Ions: From Individual Ions to Ion Pairs to Ion Clusters.

The structure of hydrated ions plays a central role in chemical and biological sciences. In the present paper, five ions, namely, Na(+), K(+), Mg(2+), Ca(2+) and Cl(-), are examined using molecular dynamics simulations. In addition to hydrated individual ions and ion pairs identified previously, hydrated ion clusters containing 3, 4, 5, or more ions are identified in the present paper. The dependence of hydration numbers and mole fractions of individual ions, ion pairs, and larger ion clusters on the electrolyte concentration is determined. As the electrolyte concentration increases, the mole fraction of hydrated individual ions decreases, and the mole fraction of hydrated larger ion clusters increases. The results also reveal that the hydrogen bonding numbers of the H2O molecules of the first hydration shells of individual ions, ion pairs, and larger ion clusters are insensitive to the electrolyte concentration, but sensitive to the nature and conformation of ions.

First direct evidence of ammonoid ovoviviparity

Ammonoids had high evolutionary rates and diversity throughout their entire history and played an important role in the high-resolution sub-division of the Mesozoic, but much of their palaeobiology remains unclear, including the brooding habitat. We present our study of the first recorded ammonite embryonic shell clusters preserved with calcified embryonic aptychi in situ within the body chambers of mature macroconch shells of the Early Aptian (Early Cretaceous) ammonite Sinzovia sazonovae. The following support the idea that the clusters are egg masses, which developed inside ammonite body chambers: the absence of post-embryonic shells and any other fossils in these clusters, the presence of the aptychi in all embryonic shell apertures and peculiarities of adult shells preservation. These facts confirm earlier speculations that at least some ammonoids could have been ovoviviparous and that, like many modern cephalopods, they could have reproduced in mass spawning events. The aptychi of ammonite embryonic shells are observed here for the first time, indicating that they were already formed and calcified before hatching. Our results are fully congruent with the peculiar modes of ammonoid evolution: quick recovery after extinctions, distinct evolutionary rates, pronounced sexual dimorphism and the nearly constant size of embryonic shells through ammonoid history. We assume that adaptation to ovoviviparity may be the reason for the presence of these features in all post-Middle Devonian ammonoids.

Dimensionality of hypercube clusters

We investigate clusters of hypercubes in d-dimensional space as a function of the number of vertices, N, and number of cluster shells, L. The number of links, vertices, and exterior vertices exhibit ‘magic number’ characteristics versus L, as the dimension of the space changes. Starting with only the spatial coordinates, we create an adjacency and distance matrix that facilitates the calculation of topological indices, including the Wiener, hyper-Wiener, reverse Wiener, Szeged, Balaban, and Kirchhoff indices. Some known topological formulas for hypercubes when L = 1 are experimentally verified. The asymptotic limits with N of the topological indices are shown to exhibit power law behavior whose exponent changes with d and type of topological index. The asymptotic graph energy is linear with N, whose slope changes with d, and in 2D agrees numerically with previous calculations. Also, the thermodynamic properties such as entropy, free energy, and enthalpy of these lattices show logarithmic behavior with increasing N. The hypercubic clusters are projected onto 3D space when the dimensionality $$d>3$$ .

Catalytic activity of TM@Cu12 core–shell nanoclusters for water gas shift reaction

The mechanism of water gas shift reaction (WGSR; CO + H2O → CO2 + H2) catalyzed by nanosized single-atom core–shell clusters have been studied using density-functional theory (DFT) calculations. To investigate single atom effects on catalytic activation, Cu12-based nanoclusters with nine different transition-metal (TM) elements have been designed into core−shell TM@Cu12 (TM = Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au) bimetallic nanoclusters. Three WGSR mechanisms including the redox, carboxyl, and formate mechanisms, which are equal to CO* + O* → CO2 (g), CO* + OH* → COOH* → CO2(g) + H*, and CO* + H* + O* → CHO* + O* → HCOO** → CO2(g) + H*, respectively, have been investigated. And the WGSR prefer to follow the carboxyl mechanism on the entire TM@Cu12 surfaces. Free energy profiles are calculated in order to find the turnover-determining transition state (TDTS) and the turnover-determining intermediate (TDI) that govern turnover frequency (TOF) and selectivity. The TOF of the group 9 (Co, Rh, and Ir) are all higher than group 10 and 11. They are thus the promising candidates for improved WGSR catalysts. Our results will be important for predicting the energetic trends of other catalytic reactions and for designing a better catalyst for the industrially important reaction.

Controlled reactivity tuning of metal-functionalized vanadium oxide clusters.

Controlling the assembly and functionalization of molecular metal oxides [Mx Oy ](n-) (M=Mo, W, V) allows the targeted design of functional molecular materials. While general methods exist that enable the predetermined functionalization of tungstates and molybdates, no such routes are available for molecular vanadium oxides. Controlled design of polyoxovanadates, however, would provide highly active materials for energy conversion, (photo-) catalysis, molecular magnetism, and materials science. To this end, a new approach has been developed that allows the reactivity tuning of vanadium oxide clusters by selective metal functionalization. Organic, hydrogen-bonding cations, for example, dimethylammonium are used as molecular placeholders to block metal binding sites within vanadate cluster shells. Stepwise replacement of the placeholder cations with reactive metal cations gives mono- and difunctionalized clusters. Initial reactivity studies illustrate the tunability of the magnetic, redox, and catalytic activity.

Energy landscape exploration of sub-nanometre copper-silver clusters.

The energy landscapes of sub-nanometre bimetallic coinage metal clusters are explored with the Threshold Algorithm coupled with the Birmingham Cluster Genetic Algorithm. Global and energetically low-lying minima along with their permutational isomers are located for the Cu(4)Ag(4) cluster with the Gupta potential and density functional theory (DFT). Statistical tools are employed to map the connectivity of the energy landscape and the growth of structural basins, while the thermodynamics of interconversion are probed, based on probability flows between minima. Asymmetric statistical weights are found for pathways across dividing states between stable geometries, while basin volumes are observed to grow independently of the depth of the minimum. The DFT landscape is found to exhibit significantly more frustration than that of the Gupta potential, including several open, pseudo-planar geometries which are energetically competitive with the global minimum. The differences in local minima and their transition barriers between the two levels of theory indicate the importance of explicit electronic structure for even simple, closed shell clusters.

Core-shell clusters of human haemoglobin A and human serum albumin: artificial O2-carriers having various O2-affinities.

This report describes the synthesis, structure, and O2-binding properties of core-shell clusters composed of human haemoglobin A (HbA) in the centre and human serum albumin (HSA) at the periphery (HbA-HSAm) as potential O2-carriers designed as red blood cell (RBC) substitutes. Protein clusters were prepared by covalent linkages between HbA lysins and HSA cysteine-34 using a heterobifunctional cross-linker, succinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate. Major products (m = 2, 3, 4) were isolated using gel filtration chromatography. The low isoelectric points (pI = 5.0-5.2) of the clusters were almost identical to that of HSA, proving the wrapping of HbA by negatively charged HSA. The 3D reconstruction of HbA-HSA3 based on transmission electron microscopy images revealed a complete triangular structure. The proposed geometries enabled us to assign a possible spatial arrangement of the HbA centre and HSA periphery. The HbA-HSAm clusters showed higher O2-affinities (P50 = 8-9 Torr) than the native HbA. The clusters prepared under N2 atmosphere showed a low O2-affinity (P50 = 26 Torr) resembling those of human RBC. Moreover, the cluster containing an αα-cross-linked HbA with bis(3,5-dibromosalicyl)fumarate showed a markedly low O2-affinity (P50 = 35 Torr). These HbA-HSAm clusters with various O2-affinities can support a new generation of RBC substitutes, which can be better tuned to play a role in O2 transport.

Energetics of hydrogen desorption from highly reactive clusters based on the sodium and magnesium alanates and boranates

The structure and electronic properties of sodium and magnesium aluminohydrides (alanates) and borohydrides (boranates) are systematically investigated in first-principles calculations using density functional theory. A study of the result of successive attachments of AlH4 and BH4 complexes to Na and Mg reveals superhalogen behavior for the clusters Na(AlH4)2, Na(BH4)2, Mg(AlH4)3 and Mg(BH4)3, whose electron affinities are 4.93 eV, 5.07 eV, 5.20 eV and 5.13 eV, respectively, which far exceed that of chlorine (3.6 eV). The energetics of the H-removal from these clusters is also investigated and the results show that the hydrogen release is substantially less energy demanding for the superhalogen moieties. The energy cost for H-removal decreases from 3.72 eV in Na(AlH4) to 0.49 eV in Na(AlH4)2, and from 4.63 eV in Mg(BH4)2 to 0.37 eV in Mg(BH4)3. For the closed shell clusters, the alanates have superior performance with respect to the release of hydrogen as compared with the boranates. For the superhalogens, the energy cost for H-removal from Na(AlH4)2 is half of that one for the Na(BH4)2 cluster, whereas for the Mg clusters Mg(AlH4)3 and Mg(BH4)3 it is nearly equivalent (0.41 eV and 0.37 eV, respectively). This arises from the formation of an insurgent dimerized unit where the H atoms exhibit considerable loss of bonding charge.

Hidden charge states in soft-x-ray laser-produced nanoplasmas revealed by fluorescence spectroscopy.

Highly charged ions are formed in the center of composite clusters by strong free-electron laser pulses and they emit fluorescence on a femtosecond time scale before competing recombination leads to neutralization of the nanoplasma core. In contrast to mass spectrometry that detects remnants of the interaction, fluorescence in the extreme ultraviolet spectral range provides fingerprints of transient states of high energy density matter. Spectra from clusters consisting of a xenon core and a surrounding argon shell show that a small fraction of the fluorescence signal comes from multiply charged xenon ions in the cluster core. Initially, these ions are as highly charged as the ions in the outer shells of pure xenon clusters with charge states up to at least 11+.

Structural, Dynamic, and Transport Properties of Concentrated Aqueous Sodium Chloride Solutions under an External Static Electric Field

In the absence of an external electric field, it has already been known that ion clusters are formed instantaneously in moderately concentrated ionic solutions. In this work, we use molecular dynamics (MD) simulations to investigate the changes of structural, dynamic, and transport properties in a sodium chloride solution under an external electric field from the ion cluster perspective. Our MD simulation results indicate that, with a strong external electric field E (≥0.1 V/nm) applied, ion clusters become smaller and less net charged, and the structures and dynamics as well as transport properties of the ion solution become anisotropic. The influence of the cluster structure and shell structure to transport properties was analyzed and the Einstein relation was found invalid in this system.

Two Tetra-CdII-Substituted Vanadogermanate Frameworks

Two new tetra-Cd(II)-substituted vanadogermanate frameworks {(CdX)4Ge8V(IV)10O46(H2O)[V(III)(H2O)2]4(GeO2)4}·8H2O (X = ethylenediamine (en, 1) and 1,2-diaminopropane (dap, 2)) were hydrothermally prepared and characterized by IR spectra, elemental analysis, powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and X-ray single-crystal diffraction. Both are isomorphic, and their 3-D frameworks are made up of tetra-Cd(II)-substituted {(CdX)4Ge8V(IV)10O46(H2O)}(12-) fundamental building units interconnected through planar tetra-V(III) [V(III)4O2(H2O)8](8-) clusters and tetrahedral GeO4 bridges. In the unique {(CdX)4Ge8V(IV)10O46(H2O)}(12-) cage, four [Ge2O7] dimers and four CdO4N2 trigonal prisms are alternately concatenated by μ3-O bridges to create a round {Ge8Cd4O28(X)4}(16-) fragment, five VO5 groups are linked by sharing edges to generate a pentanuclear [V5O17] subunit, and then the {Ge8Cd4O28(X)4}(16-) fragment is sandwiched by two V5O17 subunits via sharing O-atoms producing a D4h-symmetric {(CdX)4Ge8V(IV)10O46(H2O)}(12-) cage with a free water molecule located at the center. As we know, both display unprecedented 3-D organic-inorganic hybrid frameworks built up from the largest number of transition-metal-substituted vanadogermanate {(CdX)4Ge8V(IV)10O46}(12-) cluster shells linked by both GeO4 tetrahedra and rare [V(III)4O2(H2O)8](8-) clusters. Magnetic measurements reveal the antiferromagnetic couplings within the magnetic vanadium centers.

Shell and alpha cluster structures in 8Be with tensor-optimized shell model

We study the shell and alpha cluster structures in the ground and excited states of 8Be in terms of the tensor-optimized shell model (TOSM). In TOSM, the tensor correlation is optimized in the full space of 2p2h configurations involving high-momentum components. The short-range correlation is treated with the unitary correlation operator method (UCOM). We use the effective interaction based on the bare nucleon-nucleon interaction AV8$^\prime$. The 8Be states consist of two groups of ground band states and highly excited states with the isospin T=0 and T=1. It is found that the tensor contributions of the ground band states are stronger than the highly excited states and that the kinetic energies and the central contributions of the ground band states are almost twice the 4He values. These features suggest two-alpha clustering for the ground band states in 8Be. We also estimate the correlation energy of the $\alpha$ clustering using the alpha cluster model. In the highly excited states, the calculated spectrum in TOSM reproduces the experimental level order and the relative energies of each level. This agreement suggests that those states can be interpreted as shell-like states. The level order is found to be sensitive to the presence of the tensor force in comparison with the results using the Minnesota effective interaction without the tensor force. It is also found that the tensor contributions in the T=0 states are stronger than the T=1 states, which is consistent with the state dependence of the tensor force.

More of the “Fullercages”

AbstractAll complex intermetallic phases have been searched for their structural building principles, in particular for the occurrence of fullercages, i.e., fullerene‐like cluster shells. The diversity of inter‐metallics featuring compounds of this kind is discussed as well as the geometrical building principles characteristic for their endohedral constituting clusters. Typically, the core cluster corresponds to a polyhedron of the Frank‐Kasper (FK) type, which is surrounded by a fullerene‐like shell dual to it. The next cluster shell is again a FK polyhedron followed by a fullerene‐like shell, and this can be repeated. The chemical composition of these complex intermetallics (CIMs) is quite diverse, mostly combining electropositive elements from groups 1–4 with electronegative elements of groups 7–14, for instance Li‐Ga or RE‐Cd (RE = rare earth element). However, also less‐common combinations from elements of groups 1 and 2, such as Li‐Ba, or from groups 11 and 12, such as Cu‐Cd, are known.

Cold State-Selected Molecular Collisions and Reactions

Over the past decade, and particularly the past five years, a quiet revolution has been building at the border between atomic physics and experimental quantum chemistry. The rapid development of techniques for producing cold and even ultracold molecules without a perturbing rare-gas cluster shell is now enabling the study of chemical reactions and scattering at the quantum scattering limit with only a few partial waves contributing to the incident channel. Moreover, the ability to perform these experiments with nonthermal distributions comprising one or a few specific states enables the observation and even full control of state-to-state collision rates in this computation-friendly regime: This is perhaps the most elementary study possible of scattering and reaction dynamics.