Mark J. Fink

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.

Synthetic, structural, and dynamic NMR studies of (bisphosphine)palladium(0) complexes of dibenzylideneacetone

Abstract Two complexes of the type (R2PCH2CH2PR2)Pd(dba) have been prepared by the reaction of Pd2(dba)3·CHCl3 with R2PCH2CH2PR2 (R=iPr (1), 74%; Cy (2), 57%; dba=dibenzylideneacetone). X-ray crystallographic studies of 1 and 2 reveal that the coordinated dba ligand adopts an s-trans, s-trans conformation in which the palladium is coordinated to one CC bond in an η2-fashion. Variable temperature, 1H- and 31P{H}-NMR spectroscopy of 1 show two distinct dynamic processes in solution. In the 1H-NMR spectra, a rapid intramolecular exchange of coordinated and uncoordinated CC bonds is observed with the estimated ΔGex‡ being 14 kcal mol−1. In the 31P{H}-NMR spectra, a facile interconversion of the predominant s-trans, s-trans conformer with the minor s-trans, s-cis, and s-cis, s-cis conformers begins to occur at higher temperatures. Molecular mechanics calculations place the relative energies of the three isomers at 0, 0.9, and 4.7 kcal mol−1, respectively. An intramolecular mechanism for double bond exchange is proposed to occur via a symmetric transition state involving the s-cis, s-cis conformer. Strong coordination of dba to palladium in 1 is proposed to account for slow reactions with PhX where the relative rates of oxidative addition were found to increase in the order of X=Cl≪Br

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.

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.

Spectroscopy of jet-cooled phenylsilanes: the influence of hyperconjugation

Abstract Supersonic free jet spectra have been obtained for the compounds phenylsilane, phenyltrimethylsilane, and phenylpentamethyldisilane. Unlike the spectra of analogous alkylbenzenes, strong progression structures are seen for the silylbenzenes. It is argued that the spectroscopic differences arise from differences in hyperconjugation between the excited and ground states.

PHOTOLYSIS OF SOME ORGANOSILYLENE PRECURSORS IN A MOLECULAR BEAM

Abstract The condensed-phase organosilylene precursors PhMeSi(SiMe 3 ) 2 ( 1 ), PhSi(SiMe 3 ) 3 ( 2 ), and (Me 2 Si) 6 ( 3 ) were photolyzed in a molecular beam using a pulsed supersonic jet and mass spectrometric detection. Under ∼ 10 ns pulsed UV illumination, we have found for the gas-phase trisilane precursors 1 and 2 that one photon results in removal of only one −SiMe 3 group. Even at the highest laser power densities used, there is no evidence of removal of a second −SiMe 3 to form a silylene. On the other hand, a single photolysis photon was capable of producing the silylene for the cyclohexasilane ring precursor, 3 .

cis-Di­chloro(N,N,N′,N′-tetra­methyl-1,2-di­amino­ethane)­palladium(II)

The title compound, C6H16Cl2N2Pd, exhibits slightly distorted square-planar coordination about the metal atom, with normal Pd—Cl and Pd—N distances.

Structure of cis-[1,2-bis(dicyclohexylphosphino)ethane-P,P']dichloroplatinum(II) chloroform solvate

The structure of cis-PtCl 2 (dcpe) [dcpe=1,2-bis(dicyclohexylphosphino)ethane] consists of an approximately square planar Pt II ion coordinated by a chelating dcpe ligand and two Cl ions. The coordination sphere of the Pt shows a slight tetrahedral distortion, while the five-membered chelate ring is puckered about the mean coordination plane

Williamson ether synthesis: an efficient one-step route for surface modifications of silicon nanoparticles

A new synthetic route to mechanochemically produce silicon nanoparticles modified with biocompatible and chromophoric molecular compounds using the Williamson ether synthesis is described. This reaction allows a direct grafting of organic compounds such as phenol, hydroquinone and tetraethylene glycol to the silicon nanoparticle surface in an efficient fashion. Specifically, the formation of (phenoxy) hexyl silicon, (tetraethyleneglycoxy) hexyl silicon and (p-hydroxyphenoxy) hexyl silicon nanoparticles using the Williamson ether synthesis on chloroalkyl-terminated silicon nanoparticle is described. The resulting physical properties of the individual functionalised silicon nanoparticles were characterised by transmission electron microscopy, energy dispersive spectroscopy and photoluminescence, ultraviolet–visible, nuclear magnetic resonance and Fourier transformed infrared spectroscopies. The spectroscopic results show a direct bonding of the biocompatible and chromophoric molecules to the nanoparticles. Photoluminescence results show that the modified nanoparticles exhibit fluorescence in the blue spectral regions, consistent with other functionalised silicon nanoparticles formed by mechanochemistry, but that phenol and hydroquinone moieties result in silicon nanoparticles with broad, overlapping luminescence peaks, while the functionalisation with tetraethylene glycol has little effect on the overall optical properties.

Triclinic form of 1,2,4,5-tetra­cyclo­hexyl­benzene

The molecule of the title compound, C30H46, has a crystallographically imposed inversion center and the cyclohexyl groups are oriented with their methine H atoms pointing towards one another (H⋯H = 2.04 Å).