Solubilities of Hexadecanoic and Octadecanoic Acids in Supercritical CO2 With and Without Cosolvents

The solubilities of hexadecanoic acid (palmitic acid) and octadecanoic acid (stearic acid) in supercritical carbon dioxide without cosolvents and with two cosolvents, namely, ethanol and 3-methyl-1-butanol, were determined at (308 and 318) K at pressures varying from (12.8 to 22.6) MPa. The solubility data, in both the absence and presence of cosolvents, were correlated by a model proposed by Mendez-Santiago and Teja.

Specific Small-Molecule Activator of Aurora Kinase A Induces Autophosphorylation in a Cell-Free System

Aurora kinases are essential for chromosomal segregation and cell division and thereby important for maintaining the proper genomic integrity. There are three classes of aurora kinases in humans: A, B, and C. Aurora kinase A is frequently overexpressed in various cancers. The link of the overexpression and tumorigenesis is yet to be understood. By employing virtual screening, we have found that anacardic acid, a pentadecane aliphatic chain containing hydroxylcarboxylic acid, from cashew nut shell liquid could be docked in Aurora kinases A and B. Remarkably, we found that anacardic acid could potently activate the Aurora kinase A mediated phosphorylation of histone H3, but at a similar concentration the activity of aurora kinase B remained unaffected in vitro. Mechanistically, anacardic acid induces the structural changes and also the autophosphorylation of the aurora kinase A to enhance the enzyme activity. This data thus indicate anacardic acid as the first small-molecule activator of Aurora kinase, which could be highly useful for probing the function of hyperactive (overexpressed) Aurora kinase A.

Stabilization of an All-Metal Antiaromatic Molecule (Al4Li4) Using BH and C as Caps

It has been reported by Pati et al. (J. Am. Chem. Soc. 2005, 127, 3496) that coordination with a transition metal can stabilize the “antiaromatic”, all-metal compound Al4Li4. Here, we report that it can also be stabilized by capping with a main group element like C and its isoelectronic species BH. Our calculations of binding energy, nuclear independent chemical shift, energy decomposition analysis, and molecular orbital analysis support the capping-induced stability, reduction of bond length alternation, and increase of aromaticity of these BH/C-capped Al4Li4 systems. The interaction between px and py orbitals of BH/C and the HOMO and LUMO of Al4Li4 is responsible for the stabilization. Our calculations suggest that capping can introduce fluxionality at room temperature.

Stabilizing High-Energy Crystal Structure in Silver Nanowires with Underpotential Electrochemistry

We demonstrate that commonly face-centered cubic (fcc) metallic nanowires can be stabilized in hexagonal structures even when their surface energy contribution is relatively small. With a modified electrochemical growth process, we have grown purely single-crystalline 4H silver nanowires (AgNWs) of diameters as large as 100 nm within nanoporous anodic alumina and polycarbonate templates. The growth process is not limited by the/Ag Nernst equilibrium potential, and time-resolved imaging with high-resolution transmission electron microscopy (TEM) indicates a kinematically new mechanism of nanowire growth. Most importantly, our experiments aim to separate the effects of confinement and growth conditions on the crystal structure of nanoscale systems.

Structure and Bonding in Cyclic Isomers of B2AlHnm (n = 3−6, m = −2 to +1): A Comparative Study with B3Hnm, BAl2Hnm and Al3Hnm†

The structure, bonding and energetics of B2AlHnm (n = 3−6, m = −2 to +1) are compared with corresponding homocyclic boron, aluminum analogues and BAl2Hnm using density functional theory (DFT). Divalent to hexacoordinated boron and aluminum atoms are found in these species. The geometrical and bonding pattern in B2AlH4− is similar to that for B2SiH4. Species with lone pairs on the divalent boron and aluminum atoms are found to be minima on the potential energy surface of B2AlH32−. A dramatic structural diversity is observed in going from B3Hnm to B2AlHnm, BAl2Hnm and Al3Hnm and this is attributable to the preference of lower coordination on aluminum, higher coordination on boron and the higher multicenter bonding capability of boron. The most stable structures of B3H6+, B2AlH5 and BAl2H4− and the trihydrogen bridged structure of Al3H32− show an isostructural relationship, indicating the isolobal analogy between trivalent boron and divalent aluminum anion.

Synthesis of Cu@ZnO Core−Shell Nanocomposite through Digestive Ripening of Cu and Zn Nanoparticles

The synthesis of colloids of copper and zinc nanoparticles by solvated metal atom dispersion (SMAD) is described. The as-prepared colloids with a large size distribution of the particles are transformed into colloidal nanoparticles of a narrow size distribution by the digestive ripening process which involves refluxing the colloid at or near the boiling point of the solvent in the presence of a passivating ligand. The copper nanoparticles of 2.1 ± 0.3 nm and zinc nanoparticles of 3.9 ± 0.3 nm diameters have thus been obtained. Digestive ripening of the as-prepared copper and zinc colloids together in the presence of a passivating agent gave Cu@ZnO core−shell nanoparticles, with an average diameter of 3.0 ± 0.7 nm. Particles synthesized in this manner were characterized by UV−visible spectroscopy, high-resolution electron microscopy, energy-filtered electron microscopy, and powder X-ray diffraction methods which confirm the core−shell structure.

The GAF Domain of the cGMP-Binding, cGMP-Specific Phosphodiesterase (PDE5) Is a Sensor and a Sink for cGMP

We describe here a novel sensor for cGMP based on the GAF domain of the cGMP-binding, cGMP-specific phosphodiesterase 5 (PDE5) using bioluminescence resonance energy transfer (BRET). The wild type GAFa domain, capable of binding cGMP with high affinity, and a mutant (GAFaF163A) unable to bind cGMP were cloned as fusions between GFP and Rluc for BRET2 assays. BRET2 ratios of the wild type GAFa fusion protein, but not GAFaF163A, increased in the presence of cGMP but not cAMP. Higher basal BRET2 ratios were observed in cells expressing the wild type GAFa domain than in cells expressing GAFaF163A. This was correlated with elevated basal intracellular levels of cGMP, indicating that the GAF domain could act as a sink for cGMP. The tandem GAF domains in full length PDE5 could also sequester cGMP when the catalytic activity of PDE5 was inhibited. Therefore, these results describe a cGMP sensor utilizing BRET2 technology and experimentally demonstrate the reservoir of cGMP that can be present in cells that express cGMP-binding GAF domain-containing proteins. PDE5 is the target for the anti-impotence drug sildenafil citrate; therefore, this GAF-BRET2 sensor could be used for the identification of novel compounds that inhibit cGMP binding to the GAF domain, thereby regulating PDE5 catalytic activity.

Self-assembly of a nanoscopic platinum(II) double square cage

Self-assembly of a rigid tripyridyl linker with a bidentate 90 degrees Pt(II) acceptor yielded a somewhat unusual double square cage, representing the first example of Pt(II) cage of such shape. Multinuclear NMR as well as single-crystal structure analysis characterized the cage.

To Dope Mn2+ in a Semiconducting Nanocrystal

It has been an outstanding problem that a semiconducting host in the bulk form can be doped to a large extent, while the same host in the nanocrystal form is found to resist any appreciable level of doping rather stubbornly, this problem being more acute in the wurtzite form compared to the zinc blende one. In contrast, our results based on the lattice parameter tuning in a ZnxCd1−xS alloy nanocrystal system achieves 7.5% Mn2+ doping in a wurtzite nanocrystal, such a concentration being substantially higher compared to earlier reports even for nanocrystal hosts with the “favorable” zinc-blende structure. These results prove a consequence of local strains due to a size mismatch between the dopant and the host that can be avoided by optimizing the composition of the alloyed host. Additionally, the present approach opens up a new route to dope such nanocrystals to a macroscopic extent as required for many applications. Photophysical studies show that the quantum efficiency per Mn2+ ion decreases exponentially with the average number of Mn2+ ions per nanocrystal; en route, a high quantum efficiency of 25% is achieved for a range of compositions.

Trap-State Dynamics in Visible-Light-Emitting ZnO:MgO Nanocrystals

Oleate-capped ZnO:MgO nanocrystals have been synthesized that are soluble in nonpolar solvents and which emit strongly in the visible region (450−600 nm) on excitation by UV radiation. The visible emission involves recombination of trap states of the nanocrystalline ZnO core and has a higher quantum yield than the band gap UV exciton emission. The spectrally resolved dynamics of the trap states have been investigated by time-resolved emission spectroscopy. The time-evolution of the photoluminescence spectra show that there are, in fact, two features in the visible emission whose relative importance and efficiencies vary with time. These features originate from recombination involving trapped electrons and holes, respectively, and with efficiencies that depend on the occupancy of the trap density of states.

Self-assembly of a nanoscopic platinum(II) double square cage

Self-assembly of a rigid tripyridyl linker with a bidentate 90 degrees Pt(II) acceptor yielded a somewhat unusual double square cage, representing the first example of Pt(II) cage of such shape. Multinuclear NMR as well as single-crystal structure analysis characterized the cage.

Ternary Iron(III) complex showing photocleavage of DNA in the photodynamic therapy window

A new ternary iron(III) complex [FeL(dpq)] containing dipyridoquinoxaline (dpq) and 2,2-bis(3,5-di-tert-butyl-2-hydroxybenzyl)aminoacetic acid (H3L) is prepared and structurally characterized by X-ray crystallography. The high-spin complex with a FeN3O3 core shows a quasi-reversible iron(III)/iron(II) redox couple at -0.62 V (vs SCE) in DMF/0.1 M TBAP and a broad visible band at 470 nm in DMF/Tris buffer. Laser photoexcitation of this phenolate (L)-to-iron(III) charge-transfer band at visible wavelengths including red light of >= 630 nm leads to cleavage of supercoiled pUC19 DNA to its nicked circular form via a photoredox pathway forming hydroxyl radicals.

Unusual Hydrogenation of Fumarate Anion Followed by Metal−Carbon Bond Formation: Synthesis and Characterization of Two Metallochelates

The treatment of [M(dppf)(H2O)2](OTf)2 (dppf =1,1′-bis(diphenylphosphino)ferrocene; M = Pd, Pt) with 1 equiv of disodium fumarate in methanol medium showed an unusual hydrogenation of the ethylenic bond followed by the formation of metallochelates linking M through one of the carboxylates and the β-carbon with respect to COO−. Despite the possibility of formation of a [2 + 2] or [4 + 4] self-assembled macrocycle, the reduction of fumarate to succinate, and in particular the linking through the β-carbon, is unique since a similar treatment using disodium succinate instead of disodium fumarate yielded an expected metallochelate where both the carboxylates were coordinated to the square-planar metal.

Thermotropic and hydration studies of membranes formed from gemini pseudoglyceryl lipids possessing polymethylene spacers

Membrane formation from gemini pseudoglyceryl lipids bearing n-C14H29 and n-C16H33 chains has been reported. These lipid aggregates have been characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), high sensitivity differential scanning calorimetry (DSC), and Paldan fluorescence studies. The length of the spacer between the cationic ammonium headgroups has been varied from -(CH2)(3)- (propandiyl) to -(CH2)(12)- (dodecandiyl) in these lipids. All gemini lipids were found to generate stable suspensions in aqueous media. Electron microscopic studies revealed the smaller size of the gemini lipid aggregates as compared to their monomeric lipid counterparts. DLS measurements showed that the gemini lipid suspensions with a -(CH2)(8)- spacer length were bigger in size than that of other analogues. DSC studies suggest the unusual behavior of the gemini lipids bearing -(CH2)3- propanediyl spacer based lipids. These observations were consistent irrespective of the hydrocarbon chain lengths of the lipids. Paldan fluorescence based hydration studies showed that the hexadecyl chain based gemini lipid aggregates bearing a -(CH2)(12)- spacer were the most hydrated in their gel states among all the gemini lipid series investigated herein.