Crystal structures of three sterically congested disilanes.

In the three sterically congested silanes, C24H38Si2 (1) (1,1,2,2-tetra-isopropyl-1,2-di-phenyl-disilane), C24H34Br4Si2 (2) [1,1,2,2-tetra-kis-(2-bromo-propan-2-yl)-1,2-di-phenyl-disilane] and C32H38Si2 (3) (1,2-di-tert-butyl-1,1,2,2-tetra-phenyl-disilane), the Si-Si bond length is shortest in (1) and longest in (2), with (3) having an inter-mediate value, which parallels the increasing steric congestion. A comparison of the two isopropyl derivatives, (1 and 2), shows a significant increase in the Si-C(ipso) distance with the introduction of bromine. Also, in the brominated compound 2, attractive inter-molecular Br⋯Br inter-actions exist with Br⋯Br separations ca 0.52 Šshorter than the sum of the van der Waals radii. In compound 2, one of the bromo-isopropyl groups is rotationally disordered in an 0.8812 (9):0.1188 (9) ratio. Compound 3 exhibits 'whole mol-ecule' disorder in a 0.9645 (7):0.0355 (7) ratio with the Si-Si bonds in the two components making an angle of ca 66°.

Functionalized silicon nanoparticles from reactive cavitation erosion of silicon wafers.

A new sonochemical process for the top-down production of silicon nanoparticles (<1 nm) with surface functional groups is described. The procedure involves a combination of acoustic cavitation erosion of a single-crystalline silicon surface coupled with simultaneous reaction with a reactive organic compound such as 1-hexyne. The sonochemical formation of the photoluminescent silicon nanoparticles by reactive cavitation erosion can be easily up-scaled.

Mild two-step method to construct DNA-conjugated silicon nanoparticles: scaffolds for the detection of microRNA-21.

We describe a novel two-step method, starting from bulk silicon wafers, to construct DNA conjugated silicon nanoparticles (SiNPs). This method first utilizes reactive high-energy ball milling (RHEBM) to obtain alkene grafted SiNPs. The alkene moieties are subsequently reacted with commercially available thiol-functionalized DNA via thiol-ene click chemistry to produce SiNP DNA conjugates wherein the DNA is attached through a covalent thioether bond. Further, to show the utility of this synthetic strategy, we illustrate how these SiNP ODN conjugates can detect cancer-associated miR-21 via a fluorescence ON strategy. Given that an array of biological molecules can be prepared with thiol termini and that SiNPs are biocompatible and biodegradable, we envision that this synthetic protocol will find utility in salient SiNP systems for potential therapeutic and diagnostic applications.

Cytotoxicity of surface-functionalized silicon and germanium nanoparticles: the dominant role of surface charges.

Although it is frequently hypothesized that surface (like surface charge) and physical characteristics (like particle size) play important roles in cellular interactions of nanoparticles (NPs), a systematic study probing this issue is missing. Hence, a comparative cytotoxicity study, quantifying nine different cellular endpoints, was performed with a broad series of monodisperse, well characterized silicon (Si) and germanium (Ge) NPs with various surface functionalizations. Human colonic adenocarcinoma Caco-2 and rat alveolar macrophage NR8383 cells were used to clarify the toxicity of this series of NPs. The surface coatings on the NPs appeared to dominate the cytotoxicity: the cationic NPs exhibited cytotoxicity, whereas the carboxylic acid-terminated and hydrophilic PEG- or dextran-terminated NPs did not. Within the cationic Si NPs, smaller Si NPs were more toxic than bigger ones. Manganese-doped (1% Mn) Si NPs did not show any added toxicity, which favors their further development for bioimaging. Iron-doped (1% Fe) Si NPs showed some added toxicity, which may be due to the leaching of Fe(3+) ions from the core. A silica coating seemed to impart toxicity, in line with the reported toxicity of silica. Intracellular mitochondria seem to be the target for the toxic NPs since a dose-, surface charge- and size-dependent imbalance of the mitochondrial membrane potential was observed. Such an imbalance led to a series of other cellular events for cationic NPs, like decreased mitochondrial membrane potential (ΔΨm) and ATP production, induction of ROS generation, increased cytoplasmic Ca(2+) content, production of TNF-α and enhanced caspase-3 activity. Taken together, the results explain the toxicity of Si NPs/Ge NPs largely by their surface characteristics, provide insight into the mode of action underlying the observed cytotoxicity, and give directions on synthesizing biocompatible Si and Ge NPs, as this is crucial for bioimaging and other applications in for example the field of medicine.

Wetting properties of silicon films from alkyl-passivated particles produced by mechanochemical synthesis.

A facile and efficient method using high energy ball milling (HEBM) to produce surfaces with a static and advancing contact angle in the superhydrophobic regime consisting of alkyl-passivated crystalline silicon particles is described. Deposition of the functionalized silicon material forms stable films on a variety of surfaces due to strong hydrophobic interactions between the individual particles. The process offers the ability to control the particle size from a micro-scale to a nano-scale region and thus to tune the surface roughness. Because of changing surface morphology and the decreasing surface roughness of the films due to the increasing milling times the static and dynamic contact angles follow a polynomial function with a maximum dynamic advancing contact angle of 171 degrees. This trend is correlated to the commonly used Wenzel and Cassie-Baxter models.

Tetrakis(mu-triisopropylsilanethiolato)-1:2kappa4S:S;2:3kappa4S:S-bis(triisopropylsilanethiolato)-1kappaS,3kappaS-trizinc(II).

The title compound, [Zn(3)(C(9)H(21)SiS)(6)] or [((i)Pr(3)SiS)Zn(mu-SSi(i)Pr(3))(2)Zn(mu-SSi(i)Pr(3))(2)Zn(SSi(i)Pr(3))], is the first structurally characterized homoleptic silanethiolate complex of zinc. A near-linear arrangement of three Zn(II) ions is observed, the metals at the ends being three-coordinate with one terminally bound silanethiolate ligand. The central Zn(II) ion is four-coordinate and tetrahedral, with two bridging silanethiolate ligands joining it to each of the two peripheral Zn(II) ions. The nonbonding intermetallic distances are 3.1344 (11) and 3.2288 (12) A, while the Zn...Zn...Zn angle is 172.34 (2) degrees. A trimetallic silanethiolate species of this type has not been previously identified by X-ray crystallography for any element.

Monoclinic form of 1,2,4,5-tetra-cyclo-hexyl-benzene.

The mol-ecule of the title compound, C(30)H(46), has a crystallographically imposed inversion center and the cyclo-hexyl groups are oriented with their methine H atoms pointing towards one another (H⋯H = 1.99 Å). The cyclohexyl groups adopt chair conformations. A significant C-H⋯π inter-action assembles mol-ecules into layers parallel to (100).

Triclinic form of 1,2,4,5-tetra-cyclo-hexyl-benzene.

The mol-ecule of the title compound, C(30)H(46), has a crystallographically imposed inversion center and the cyclo-hexyl groups are oriented with their methine H atoms pointing towards one another (H⋯H = 2.04 Å).

1-Bromo-2,4,6-tricyclo-hexyl-benzene.

The title compound, C(24)H(25)Br, packs efficiently in the crystal structure with no solvent-accessible voids and several inter-molecular H⋯H contacts approximating the sum of the van der Waals radii. The mol-ecule is quite crowded, with intra-molecular Br⋯H and C⋯H contacts ca 0.38 and 0.30 Å, respectively, less than the sum of the corresponding van der Waals radii. All cyclo-hexyl rings adopt chair conformations with the 'seat' of the chair inclined at approximately 57-81° to the mean plane of the benzene ring, while those ortho to bromine have their centroids displaced in opposite directions from this plane.

Dicoordinate copper(I) silanechalcogenolates.

The copper silanechalcogenolates tBu3PCuESiPh3 (1, E = O; 2, E = S; 3, E = Se) were prepared from the reaction of [tBu3PCu(CH3CN)3]BF4 with [Ph3SiELi(THF)2]2 in acetonitrile. The compounds were obtained as colorless, crystalline, but thermally labile solids. X-ray crystallography shows that complexes 1-3 are monomeric in the solid state with no Cu...Cu interactions. The Cu atoms have either a linear or a near-linear coordination geometry in all three complexes. Interestingly, the O atom in complex 1 is also linear, which is in contrast to the highly bent S (2) and Se analogues (3). Density functional theory calculations suggest that both the linear geometry of 1 and an associated extremely short Cu-O distance [1.769(4) A] are not the result of pi delocalization but are the result of a fine balance of electrostatic interaction and Pauli repulsion.

Dynamic processes in silyl palladium complexes: evidence for intermediate Si-H and Si-Si sigma-complexes.

The silyl palladium complexes (dcpe)PdH(SiHtBu2) and (dcpe)Pd(SiHMe2)2 display NMR spectra that vary with temperature. The dynamic NMR behavior is consistent with long-lived sigma-complexes as intermediates. In the case of (dcpe)PdH(SiHtBu2), the intermediate is believed to be a symmetric complex with doubly bridged hydrogen atoms between the silicon and palladium. Dynamic interchange of the two silicon atoms in (dcpe)Pd(SiHMe2)2 is consistent with an intermediate Si-Si sigma-complex.

A dicoordinate palladium(0) complex with an unusual intramolecular eta(1)-arene coordination.

The reaction of (tmeda)PdMe2 with dcpBiph gives (dcpBiph)2Pd in high yield. The solid-state structure of (dcpBiph)2Pd reveals a bent P-Pd-P framework and an unusual eta1-arene interaction between the palladium and the distal ring of one of the biphenyl substituents. In solution, an additional conformer exists which does not show a pi-interaction with a biphenyl ring. The low-coordinate complex, (dcpBiph)2Pd, undergoes C-X oxidative addition reactions with PhX (X = I, Br, Cl). A minor product resulting from metalation of the biphenyl ring is also observed.

The first stable mononuclear silyl palladium hydrides.

The reaction of tertiary silanes with the low valent palladium complex [(mu-dcpe)Pd]2 affords equilibrium mixtures with mononuclear silyl palladium hydrides. These complexes have been characterized by NMR spectroscopy and, in one case, by X-ray crystallography. The silyl palladium hydride complexes rapidly interchange silicon and hydride coordination environments in solution which give rise to extraordinary temperature-dependent kinetic isotope effects for the fluxional process. An intermediate 2eta-Si-H complex is proposed for the interchange.