Volodymyr Sashuk

[(NHC)(NHCewg)RuCl2(CHPh)] Complexes with Modified NHCewg Ligands for Efficient Ring‐Closing Metathesis Leading to Tetrasubstituted Olefins

Imidazolium salts (NHC(ewg)HCl) with electronically variable substituents in the 4,5-position (H,H or Cl,Cl or H,NO(2) or CN,CN) and sterically variable substituents in the 1,3-position (Me,Me or Et,Et or iPr,iPr or Me,iPr) were synthesized and converted into the respective [AgI(NHC)(ewg)] complexes. The reactions of [(NHC)RuCl(2)(CHPh)(py)(2)] with the [AgI(NHC(ewg))] complexes provide the respective [(NHC)(NHC(ewg))RuCl(2)(CHPh)] complexes in excellent yields. The catalytic activity of such complexes in ring-closing metathesis (RCM) reactions leading to tetrasubstituted olefins was studied. To obtain quantitative substrate conversion, catalyst loadings of 0.2-0.5 mol % at 80 degrees C in toluene are sufficient. The complex with the best catalytic activity in such RCM reactions and the fastest initiation rate has an NHC(ewg) group with 1,3-Me,iPr and 4,5-Cl,Cl substituents and can be synthesized in 95 % isolated yield from the ruthenium precursor. To learn which one of the two NHC ligands acts as the leaving group in olefin metathesis reactions two complexes, [(FL-NHC)(NHC(ewg))RuCl(2)(CHPh)] and [(FL-NHC(ewg))(NHC)RuCl(2)(CHPh)], with a dansyl fluorophore (FL)-tagged electron-rich NHC ligand (FL-NHC) and an electron-deficient NHC ligand (FL-NHC(ewg)) were prepared. The fluorescence of the dansyl fluorophore is quenched as long as it is in close vicinity to ruthenium, but increases strongly upon dissociation of the respective fluorophore-tagged ligand. In this manner, it was shown for ring-opening metathesis ploymerization (ROMP) reactions at room temperature that the NHC(ewg) ligand normally acts as the leaving group, whereas the other NHC ligand remains ligated to ruthenium.

Highly reproducible, stable and multiply regenerated surface-enhanced Raman scattering substrate for biomedical applications

We fabricated a Surface Enhanced Raman Scattering (SERS)-active surface based on photo-etched and Au-coated GaN. The highest enhancement factor (EF) in SERS and high reproducibility of spectra were obtained from surfaces covered with bunched nanopillars which were produced by relatively long defect-selective photo-etching. The surfaces exhibited SERS enhancements of the order of 2.8 × 106 for malachite green isothiocyanate (MGITC) and 2 × 106 for p-mercaptobenzoic acid (PMBA). These SERS enhancement factors were comparable to those of conventional SERS substrates, while the EF for MGITC was two orders of magnitude larger than the corresponding one reported for the SERS platform made on porous GaN. The standard deviation of the relative intensity of the 1180 cm−1 mode of MGITC was less than 5% for 100 randomly distributed locations across a single platform and less than 10% between different platforms. The SERS signal of MGITC at our GaN/Au surface (kept under ambient conditions) was extremely stable. We could not detect any peak shift or appreciable change of intensity even after three months. We used these surfaces to detect biological molecules such as amino acids and bovine serum albumin (BSA) at low concentration and with short detection time. We developed simple and effective cleaning procedures for our substrates. After cleaning, the same substrate could be used multiple times retaining the SERS activity. We are not aware of any other multiply regenerated SERS substrate which provides simultaneously such high stability with high enhancement, good uniformity, and high reproducibility.

Olefin cross-metathesis with vinyl halides

The first successful example of olefin cross-metathesis with chloroalkenes is reported.

Close-packed monolayers of charged Janus-type nanoparticles at the air–water interface

We present a new method to obtain close-packed monolayers composed of noble metal nanoparticles (NP) possessing well-defined permanent charge of either sign. The method is based on the fact that ligands forming the protecting layer exhibit ability to rearrange at the NPs surface. We demonstrate that if the protecting layer is composed of a mixture of hydrophobic and hydrophilic charged ligands in appropriate proportion, the NP exhibits properties of a Janus-type particle with one of the hemispheres hydrophilic and the other hydrophobic. Such amphiphilic NPs self-assemble into a monolayer of well defined surface charge at the air-water interface. Due to strong stabilizing effect of the lateral electrostatic repulsions, such monolayer can be compressed to form close-packed hexagonal structure, and then easily transferred onto a solid substrate with the Langmuir-Blodgett technique.

Formation and structure of PEI/DNA complexes: quantitative analysis

Controlled formation of gene delivery complexes (DNA and a vector, usually a cationic polymer) is one of the key challenges in developing efficient gene delivery systems. The researchers focused their procedures on the ratio of vector to DNA, neglecting the influence of concentration on the complex formation process. In this study we show, by studying the association of polyethylenimine (PEI) and 66-base pair (bp) DNA fragments, that the concentration of the gene delivery system greatly influences the formation of PEI/DNA complexes even at a fixed PEI/DNA ratio. We find that the charge and the size of PEI/DNA complexes are increasing functions of their concentration even in a highly dilute regime of concentrations. The number of PEI/DNA molecules in a complex was calculated from the measured charge and electrophoretic mobility. We established a model, on the basis of Smoluchowski theory, to explain the relation between the concentration and the size of PEI/DNA complexes. We analyzed the structure of the complexes and found out that a large proportion of space in the PEI/DNA complexes is occupied by the solvent. This study indicates that the influence of concentration should be seriously considered in gene delivery studies, since large PEI/DNA complexes can be prepared by scaling up their concentration simultaneously without increasing the dosage of PEI.

Kinetic trapping of the host–guest association intermediate and its transformation into a thermodynamic inclusion complex

The molecular recognition and self-assembly between host cucurbit[6]uril and guest adrenaline led to kinetic trapping and crystallization of the intermediate exclusion complex, which was characterized by X-ray diffraction. The crystalline kinetic complex undergoes slow spontaneous dissolution and subsequently recrystallizes as a thermodynamic inclusion complex.

Thiolate-Protected Nanoparticles via Organic Xanthates: Mechanism and Implications

The gold nanoparticles (AuNPs) stabilized with amine ligands are converted into robust thiolate-protected AuNPs in the presence of xanthates. This enables decoration of the AuNPs with a diversity of important functional groups, in particular, to introduce the thiol-sensitive unsaturated C-C bonds. The (1)H NMR study on the reaction mechanism provides a new insight into the great mystery of nanoscience-the fate of hydrogen upon the formation of the Au-S bond.

A Thermo- and Photo-Switchable Ruthenium Initiator For Olefin Metathesis.

A ruthenium carbene complex bearing azobenzene functionality is reported. The complex exists in the form of two isomers differing by the size of the chelate ring. Both isomers were isolated by applying kinetic or thermodynamic control during the synthesis and characterized by X-ray diffraction analysis. The isomerization of the complex was studied by UV/Vis spectroscopy. The stable isomer was tested as a catalyst in olefin metathesis. The complex was activated at about 100 °C to promote ring-closing and ring-opening polymerization metathesis reactions. The activation took place also at room temperature under middle ultraviolet radiation.

Autonomous Self‐Assembly of Ionic Nanoparticles into Hexagonally Close‐Packed Lattices at a Planar Oil–Water Interface

Lets get charged! Positively charged nanoparticles (NPs) spontaneously self-assemble into hexagonally close-packed lattices at a planar CH(2)Cl(2)-water interface. The self-assembly process is fully autonomous and occurs without any external manipulation.

Solid-state assembly of carboxylic acid substituted pillar[5]arene and its host–guest complex with tetracaine

The solid state structures of the carboxylic acid substituted pillar[5]arene PA5 host–guest complexes with ethanol and the anesthetic drug tetracaine are reported. PA5 forms an inclusion complex with ethanol in a 1 : 2 stoichiometry that assembles into hydrogen-bonded polymeric chains in the solid state. The macrocyclic cavity of PA5 can include large pharmaceutical molecules like tetracaine via a combination of different non-covalent interactions.