SELECTED PUBLICATIONS
IR SPECTRA OF N-BU4M (M = SI, GE, SN, PB), N-BUAUPPH3-D15, AND “N-BU” ON A GOLD SURFACE
Observed and DFT-calculated IR spectra of n-Bu4M (M = Si, Ge, Sn, Pb), (CH3CH2CH213CD2)4Sn, and n-BuAuPPh3-d15 are reported and assigned. The asymmetric CH stretching vibration of the CH2 group adjacent to the metal atom appears as a distinct shoulder at ∼2934 cm–1, whereas for other CH2 groups it is located at ∼2922 cm–1. The characteristic peak at ∼2899 cm–1 is attributed to an overtone of a symmetric CH2 bend at ∼1445 cm–1. In n-BuAuPPh3-d15, the CH stretching vibrations of the butyl group are shifted to lower frequencies by ∼10 cm–1, and two possible rationalizations are offered.
MECHANISM OF SURFACE ALKYLATION OF A GOLD AEROGEL WITH TETRA-N-BUTYLSTANNANE-D36: IDENTIFICATION OF BYPRODUCTS
The formation of self-assembled monolayers on surfaces is often likely to be accompanied by the formation of byproducts, whose identification holds clues to the reaction mechanism but is difficult due to the minute amounts produced. We now report a successful identification of self-assembly byproducts using gold aerogel with a large specific surface area, a procedure likely to be applicable generally. Like a thin gold layer on a flat substrate, the aerogel surface is alkylated with n-butyl-d9 groups upon treatment with a solution of tetra-n-butylstannane-d36 under ambient conditions. The reaction byproducts accumulate in the mother liquor in amounts sufficient for GC-MS analysis. In chloroform solvent, they are butene-d8, butane-d10, octane-d18, and tributylchlorostannane-d27. In hexane, they are the same except that tributylchlorostannane-d27 is replaced with hexabutyldistannane-d54. The results are compatible with an initial homolytic dissociation of a C–Sn bond on the gold surface, followed by known radical processes.
LINQUATS: SYNTHESIS, CHARACTERIZATION, AND PROPERTIES OF LINEAR EXTENDED DIQUATS
We report an innovative synthetic route to linear extended diquats (linquats). Our approach is short and efficient and features a highly modular reaction sequence based on two-fold quaternization followed by the key intramolecular [2+2+2] alkyne cycloaddition. The physico-chemical properties of four new linquats were characterized by spectroscopic methods, X-ray crystallography, and electrochemistry complemented by information obtained from DFT calculations. Electron deficient N-heteroaromatic cations with linear extended diquat motif with high electron affinities have been recently recognized as attractive n-type semiconductors for chemical and biological sensing. Their advantageous redox properties such as very fast reversible electron transfers make the title compounds interesting for applications.
MODULAR SYNTHESIS OF HELICENE-LIKE COMPOUNDS BASED ON IMIDAZOLIUM MOTIF
Straightforward synthesis of novel mono- and tricationic helical compounds based on the imidazolium core has been developed. The synthetic route based on double [2+2+2] cycloaddition reactions of precursors with the imidazolium core motif is notably modular and reaches beyond established protocols used for the synthesis of imidazolium systems as well as beyond the reported protocols used to assemble compounds with helical frameworks. This approach opens rapid four-step access to a cationic species featuring nine ortho-annulated rings that represents the highest order helical nitrogen-based cationic system reported to date.
STUDY OF DNA-LIGAND INTERACTIONS BY PARTIAL FILLING AFFINITY CAPILLARY ELECTROPHORESIS
In this work, a new partial filling affinity capillary electrophoresis (PF-ACE) method has been developed and applied to investigation of non-covalent molecular interactions between double stranded DNA oligonucleotide (Dickerson dodecamer) and classical DNA intercalator ligand–ethidiumbromide (EtBr) or oligophenylene derivatives-based potential new type of DNA ligands. Binding constants of DNA–ligand complexes were determined from the dependence of migration time changes of DNA oligomer (applied as analyte) on the length of ligand zones introduced beforehand as plugs of various lengths (0–75 mm with 12.5 mm step) in hydroxypropylcellulose coated fused silica capillary of 50/375 μm I.D./O.D. and 400/300 mm total/effective length. PF-ACE experiments were performed in two background electrolytes, Tris-borate, pH 8.0, ionic strength 14.3 mM (BGE1), and sodium phosphate, pH 7.5, ionic strength 133 mM (BGE2). Binding constants of DNA–EtBr complex (ca 15 300 L/mol in the BGE1 and 4200 L/mol in the BGE2) were found to be significantly higher than those of DNA complexes with oligophenylene derivatives (ca 2200–3600 L/mol in the BGE1 and 1600–2300 L/mol in the BGE2).
ELECTRON TRANSFER TRIGGERS FAST DIMER/MONOMER SWITCHING OF PYRIDINIUM AND QUINOLINIUM CATIONS
N-Heteroaromatic cations with quaternary pyridine-type nitrogen atoms have a rich application potential due to their bioactivity, fluorescence, and redox properties. Reactivityof radicals formed by reduction of such compounds is of key importance. We report the electron transfer mechanismof four novel compounds containing pyridinium, quinolinium, and benzothiazolium moiety. The reduction of pyridinium and quinolinium derivatives by one electron yields radicals that very rapidly form σ-dimers. Dimers can be converted to parent cations by oxidation, which proceeds at considerably higher potentials. Hence the dimerization can be reversibly switched by application of the appropriate electrode potential. In contrast, in benzothiazolium derivative the electron transfer yields a stable radical in which the follow-up dimerization reaction is completely blocked. Analysis of experimental data as well as theoretical models led to the identification of dimerization sites in reduced pyridinium and quinolinium species. We show the advantage of using the combination of electrochemical impedance data and simulation of cyclic voltammograms for estimation of kinetic parameters of the heterogeneous electron transfer rates and the coupled chemical reactions.
NITROGEN HETEROAROMATIC CATIONS BY [2+2+2] CYCLOADDITION
Org. Biomol. Chem. 2011, 9, 450-462
A modular approach to the construction of monocationic quaternary N-heteroaromatic frameworks was developed capitalizing on a direct pyridine-type nitrogen quaternization followed by metal-catalyzed [2+2+2] cycloaddition with gaseous acetylene. The flexibility of the route is demonstrated on 12 diverse scaffolds based on pyridinium, quinolinium, thiazolium, benzothiazolium, imidazolium, and pyrimidinium. Electrochemical study revealed a quinolinium redox system with two electrochemically distinct forms that are interconverted by a homogeneous chemical reaction triggered by fast electron transfers (reduction at −0.7 V and oxidation at −0.05 V).