Donor- and/or acceptor-substituted expanded radialenes: theory, synthesis, and properties.

The synthesis of donor- (D) and/or acceptor (A)-expanded [4]radialenes has been developed on the basis of readily available dibromoolefin (7), tetraethynylethene (10 and 20), and vinyl triflate (12) building blocks. The successful formation of D/A radialenes relies especially on (1) effective use of a series alkynyl protecting groups, (2) Sonogashira cross-coupling reactions, and (3) the development of ring closing reactions to form the desired macrocyclic products. The expanded [4]radialene products have been investigated by spectroscopic (UV-vis absorption and emission) and quantum chemical computational methods (density functional theory and time dependent DFT). The combined use of theory and experiment provides a basis to evaluate the extent of D/A interactions via the cross-conjugated radialene framework as well as an interpretation of the origin of D/A interactions at an orbital level.

Synthesis and derivatization of expanded [n]radialenes (n=3, 4).

Versatile, iterative synthetic protocols to form expanded [n]radialenes have been developed (n=3 and 4), which allow for a variety of groups to be placed around the periphery of the macrocyclic framework. The successful use of the Sonogashira cross-coupling reaction to complete the final ring closure demonstrates the ability of this reaction to tolerate significant ring strain while producing moderate to excellent product yields. The resulting radialenes show good stability under normal laboratory conditions in spite of their strained, cyclic structures. The physical and electronic characteristics of the macrocycles have been documented by UV-visible spectroscopy, electrochemical methods, and X-ray crystallography (four derivatives), and these studies provide insight into the properties of these compounds as a function of pendent substitution in terms of conjugation and donor/acceptor functionalization.

Pyridinones are not antioxidants as shown by kinetics of free radical autoxidation, but they prevent radical oxidations catalyzed by toxic heavy metals.

Three 2-methyl-3-hydroxypyridinones, 1-methyl-, 1; 1-(4-methoxy)phenyl-, 2; and 1-(4-dimethylamino)phenyl-, 3, were discovered not to possess strong antioxidant properties contrary to literature reports. These pyridinones were not active chain-breaking antioxidants toward peroxyl radicals generated from styrene or methyl oleate initiated by azobis-2-methylpropylnitrile (AIBN) in solution compared to known phenolic antioxidants, 2,2,5,7,8-pentamethyl-6-hydroxychroman (PMHC) or 2,6-di-tert-butyl-4-methoxyphenyl (DBHA). Pyridinone 2 exhibited weak antioxidant activity in cumene, kinh = 1.3 × 10(3) M(-1) s(-1), compared to 2,6-di-tert-butyl-4-methylphenol (BHT), kinh = 4.3 × 10(3) M(-1) s(-1). The pyridinones were not active antioxidants during lipid peroxidation initiated by azobis-2-amidinopropane·2HCl (ABAP) in aqueous-lipid dispersions of 0.50 M sodium dodecyl sulfate (SDS) micelles where 2 did not inhibit peroxidation of methyl oleate at pH 7.0 or 4.0, while BHT exhibited effective suppression of oxygen uptake. In addition, 2 did not exhibit any cooperative antioxidant effect in combination with Trolox during inhibited peroxidation of linoleic acid in micelles. Pyridinones were effective preventative antioxidants in aqueous-lipid dispersions against reactions initiated by heavy metal ions, notably copper; for example, 2 blocked peroxidation of linoleic acid initiated by Cu ions in SDS micelles. In particular, both 2 and 3 were active in preventing the rapid pro-oxidation effects, "spikes", of very rapid oxygen uptake when phenolic antioxidants PMHC or Trolox were added to peroxidations initiated by Cu(2+). A proposal is given to account for such pro-oxidant effects.

Enhanced osteoblast adhesion on self-assembled nanostructured hydrogel scaffolds.

The objective of the current in vitro study was to improve properties of a commonly used hydrogel for implant applications by incorporating novel self-assembled helical rosette nanotubes (HRNs). Since traditional methods (such as autografts and allografts) used to treat bone defects present various disadvantages (such as donor tissue shortage, extensive inflammation, possible disease transmission, and poor new bone growth), which may lead to implant failure, much effort has been devoted to creating a novel bone substitute that biomimics the nanoscale features of natural bone in order to improve bone growth. HRNs (formed by chemically immobilizing two DNA base pairs) are a novel type of soft nanomaterial that biomimics natural nanostructured components of bone (such as collagen) since they are 3.5 nm in diameter and self-assemble into a helical structure in aqueous solutions. Because HRNs undergo a phase transition from a liquid to a viscous gel when heated to slightly above body temperatures or when added directly to serum-supplemented or serum-free media at body temperatures, they may provide an exciting therapy to heal bone fractures in situ. In this study, HRN-K1 (HRNs functionalized with lysine amino acids) was embedded in and coated on a model hydrogel [specifically, poly(2-hydroxyethyl methacrylate) or pHEMA]. The results of this study showed, for the first time, enhanced osteoblast (bone-forming cell) adhesion on HRN-K1 embedded in and coated on hydrogels compared to hydrogels without HRN-K1. Moreover, the results showed that embedding HRN-K1 into hydrogels can greatly decrease the polymerization time of pHEMA (especially at low temperatures). The presence of lysine in HRN-K1/hydrogels was shown to be one, but not only, property of HRN-K1 that enhanced osteoblast adhesion. In summary, the present results demonstrated that HRNs can improve properties of one particular hydrogel (pHEMA) and, thus, should be further investigated as a bone-healing material.