Self-assembly of small polycyclic aromatic hydrocarbons on graphite: a combined scanning tunneling microscopy and theoretical approach

Self-assembled monolayers of chrysene and indene on graphite have been observed and characterized individually with scanning tunneling microscopy (STM) at 80 K under low-temperature, ultrahigh vacuum conditions. These molecules are small, polycyclic aromatic hydrocarbons (PAHs) containing no alkyl chains or functional groups that are known to promote two-dimensional self-assembly. Energy minimization and molecular dynamics simulations performed for small groups of the molecules physisorbed on graphite provide insight into the monolayer structure and forces that drive the self-assembly. The adsorption energy for a single chrysene molecule on a model graphite substrate is calculated to be 32 kcal/mol, while that for indene is 17 kcal/mol. Two distinct monolayer structures have been observed for chrysene, corresponding to high- and low-density assemblies. High-resolution STM images taken of chrysene with different bias polarities reveal distinct nodal structure that is characteristic of the molecular electronic state(s) mediating the tunneling process. Density functional theory calculations are utilized in the assignment of the observed electronic states and possible tunneling mechanism. These results are discussed within the context of PAH and soot particle formation, because both chrysene and indene are known reaction products from the combustion of small hydrocarbons. They are also of fundamental interest in the fields of nanotechnology and molecular electronics.     

Thermal behavior of some new chromium complexes with potential biological importance

Summary This paper reports the investigation of the thermal stability of three new complexes of Cr(III) with acrylate anion, [Cr₂(C₃H₃O₂)₄(OH)₂(H₂O)₄], [Cr₃O(C₃H₃O₂)₆(C₃H₄O₂)₃](C₃H₃O₂)×5H₂O and [Cr₂(C₃H₃O₂)₅(OH)] ×2H₂O, respectively. This type of complexes is important in proper carbohydrate and lipid metabolism of mammals. The thermal decomposition steps were evidenced. The thermal transformations are complex processes according to TG and DTG curves including dehydration and oxidative degradation of acrylate ion processes. The final product of decomposition is the chromium(III) oxide.     

Kalihinols from two Acanthella cavernosa sponges: inhibitors of bacterial folate biosynthesis

Acanthella spp. sponges have been prolific sources of highly functionalized diterpene antibiotics. Two Acanthella cavernosa sponges were investigated based on the activity of their extracts in a screen designed to detect bacterial folate biosynthesis inhibitors. Bacillus subtilis PY79 strain harboring a lacZ reporter gene fusion to a trimethoprim-responsive promoter (PpanB) was used for the screen. The ability of kalihinols to inhibit bacterial folate biosynthesis was investigated resulting in preliminary structure activity relationships. Eight kalihinol type diterpenes were isolated from two Philippine Acanthella cavernosa specimens including two new 10- and 15-formamido-kalihinol F analogs.     

Kinetics of methane combustion on Fe2O3/TiO2 catalysts

The objective of this work was to study the kinetics of methane combustion for a series of Fe₂O₃/TiO₂ catalysts. An increase in activity is observed as iron loading increases, and can be attributed to an increase of surface coverage by Fe₂O₃ species. Kinetic studies revealed that the reaction orders with respect to methane, oxygen, carbon dioxide and water are 1, 0, 0 and -1 respectively. This revised version was published online in June 2006 with corrections to the Cover Date.     

Fabrication of thermoset polyester microfluidic devices and embossing masters using rapid prototyped polydimethylsiloxane molds

Plastics are increasingly being used for the fabrication of Lab-on-a-Chip devices due to the variety of beneficial material properties, affordable cost, and straightforward fabrication methods available from a range of different types of plastics. Rapid prototyping of polydimethylsiloxane (PDMS) devices has become a well-known process for the quick and easy fabrication of microfluidic devices in the research laboratory; however, PDMS is not always an appropriate material for every application. This paper describes the fabrication of thermoset polyester microfluidic devices and masters for hot embossing using replica molding techniques. Rapid prototyped PDMS molds are convienently used for the production of non-PDMS polymeric devices. The recessed features in the cast polyester can be bonded to a second polyester piece to form an enclosed microchannel. Thermoset polyester can withstand moderate amounts of pressure and elevated temperature; therefore, the cast polyester piece also can be used as a master for embossing polymethylmethacrylate (PMMA) microfluidic systems. Examples of enclosed polyester and PMMA microchannels are presented, and we discuss the electroosmotic properties of both types of channels, which are important for analytical applications such as capillary electrophoresis.     

Cooperative and Orthogonal Switching in the Solid State Enabled by Metal-Organic Framework Confinement Leading to a Thermo-Photochromic Platform

Cooperative behavior and orthogonal responses of two classes of coordinatively integrated photochromic molecules towards distinct external stimuli were demonstrated on the first example of a photo-thermo-responsive hierarchical platform. Synergetic and orthogonal responses to temperature and excitation wavelength are achieved by confining the stimuli-responsive moieties within a metal–organic framework (MOF), leading to the preparation of a novel photo-thermo-responsive spiropyran-diarylethene based material. Synergistic behavior of two photoswitches enables the study of stimuli-responsive resonance energy transfer as well as control of the photoinduced charge transfer processes, milestones required to advance optoelectronics development. Spectroscopic studies in combination with theoretical modeling revealed a nonlinear effect on the material electronic structure arising from the coordinative integration of photoresponsive molecules with distinct photoisomerization mechanisms. Thus, the reported work covers multivariable facets of not only fundamental aspects of photoswitch cooperativity, but also provides a pathway to modulate photophysics and electronics of multidimensional functional materials exhibiting thermo-photochromism.     

Synthesis and characterization of cobalt acrylate–melamine co-crystals

A new co-crystal of tetraaqua acrylato cobalt (II) complex and melamine, [Co(acr)₂(H₂O)₄]·4MA·2DMF (acr = acrylate, MA = melamine, DMF = dimethylformamide), has been synthesized and characterized using IR, UV-Vis, thermogravimetric analysis, and single-crystal X-ray diffraction. The complex contains discrete unities of [Co(acr)₂(H₂O)₄], melamine, and DMF linked by hydrogen bonds. Investigations evidenced that Co(II) has an octahedral stereochemistry and both acrylate ions present unidentate coordination mode. Thermal decomposition occurs in four steps and denotes that melamine is lost at high temperatures, and this indicates a greater stability that may be associated with the presence of hydrogen bonds network.

     

Synthesis,characterization, molecular docking studies and in vitro screening of new metal complexes with Schiff base as antimicrobial and antiproliferative agents

A series of Cu(II), Co(II), Pd(II), Pt(II), Zn(II), Cd(II) and Fe(III) complexes were designed and synthesized using Schiff base 1‐phenyl‐2,3‐dimethyl‐4‐(N‐3‐formyl‐6‐methylchromone)‐3‐pyrazolin‐5‐one (HL). The new metal complexes were investigated using various physicochemical techniques including elemental and thermal analyses, molar electric conductivity and magnetic susceptibility measurements, as well as spectroscopic methods. Also, the crystal structures of ligand HL and the Pd(II) complex were determined using single‐crystal X‐ray diffraction analysis. For all compounds, the antimicrobial activity was studied against a series of standard strains: Staphylococcus aureus, Bacillus cereus, Enterococcus faecalis, Escherichia coli, Acinetobacter baumannii, Candida albicans, Candida krusei and Cryptococcus neoformans. The in vitro antiproliferative activity of the ligand and complexes was evaluated against ten cancer cell lines: MSC, A375, B16 4A5, HT‐29, MCF‐7, HEp‐2, BxPC‐3, RD, MDCK and L20B. At 10 μM concentration a significant cytotoxic effect of the Co(II), Pd(II) and Cd(II) complexes was observed against B16 4A5 murine melanoma cells. The Zn(II) complex is active against HEp‐2, RD and MDCK cancer cell lines, where IC₅₀ values vary between 1.0 and 77.6 and for BxPC‐3 the activity index versus doxorubicin is 3.7 times higher.     

Evaluating the biological potential of some new cobalt (II) complexes with acrylate and benzimidazole derivatives

This paper presents the synthesis, physico‐chemical and biological properties of four new coordination compounds with mixed ligands: acrylate ion (acr) and benzimidazole/benzimidazole derivatives with the general formula [Co(L) ₂ (acr) ₂ ]·nH ₂ O [ (1) L: benzimidazole (HBzIm), n: 0.5; (2) L: 2‐methylbenzimidazole (2‐MeBzIm), n: 0.5; (3) L: 5‐methylbenzimidazole (5‐MeBzIm), n: 0; (4) L: 5,6‐dimethylbenzimidazole (5,6‐Me₂BzIm), n: 0]. Their chemical formulae were achieved correlating the chemical analysis with mass spectrometry data, the ligands coordination modes were assigned by Fourier transform‐infrared measurements, and the trigonal bipyramidal geometry of cobalt ion in complexes was assigned by data correlation of UV–Vis‐NIR spectra and magnetic moments measurements. Single‐crystal X‐ray diffraction reveals a mononuclear structure with a pentacoordinated cobalt (II) ion, connected to two acrylato coordinated in different modes and two unidentate 5,6‐dimethylbenzimidazole ligands for compound (4) . The biological tests were performed against several microbial strains, the cytotoxicity was evaluated on HCT8 cellular lines and the cell cycle analysis was performed on HT29 cellular lines. Microbiological assays indicated that Co (II) complexes present a very good to good activity against Candida albicans 1760, Enterococcus faecium E5, Bacillus subtilis ATCC 6683 and Escherichia coli ATCC 25922. Predictive pharmacokinetic (ADME), toxicity and drug‐likeness profiles were evaluated for Co (II) complexes. Our results highlight that Co (II) complexes depicted in the present study are suitable to be used as efficient pharmacological agents.     

In Vitro Reconstitution Reveals a Central Role for the N-Oxygenase PvfB in (Dihydro)pyrazine-N-oxide and Valdiazen Biosynthesis

The Pseudomonas virulence factor (pvf) operon is essential for the biosynthesis of two very different natural product scaffolds: the (dihydro)pyrazine-N-oxides and the diazeniumdiolate, valdiazen. PvfB is a member of the non-heme diiron N-oxygenase enzyme family that commonly convert anilines to their nitroaromatic counterparts. In contrast, we show that PvfB catalyzes N-oxygenation of the α-amine of valine, first to the hydroxylamine and then the nitroso, while linked to the carrier protein of PvfC. PvfB modification of PvfC-tethered valine was observed directly by protein NMR spectroscopy, establishing the intermediacy of the hydroxylamine. This work reveals a central role for PvfB in the biosynthesis of (dihydro)pyrazine-N-oxides and valdiazen.