Wei Li

Electrochemical considerations for determining absolute frontier orbital energy levels of conjugated polymers for solar cell applications.

Narrow bandgap conjugated polymers in combination with fullerene acceptors are under intense investigation in the field of organic photovoltaics (OPVs). The open circuit voltage, and thereby the power conversion efficiency, of the devices is related to the offset of the frontier orbital energy levels of the donor and acceptor components, which are widely determined by cyclic voltammetry. Inconsistencies have appeared in the use of the ferrocenium/ferrocene (Fc + /Fc) redox couple, as well as the values used for the absolute potentials of standard electrodes, which can complicate the comparison of materials properties and determination of structure/property relationships.

Anion-Free Bambus[6]uril and Its Supramolecular Properties

Methods for the preparation of anion-free bambus[6]uril (BU6) are presented. They are based on the oxidation of iodide anion, which is bound inside the macrocycle, utilizing dark oxidation by hydrogen peroxide or photooxidation in the presence of titanium dioxide. Anion-free BU6 was found to be insoluble in any of the investigated solvents; however, it dissolves in methanol/chloroform (1:1) or acetonitrile/water (1:1) mixtures in the presence of the tetrabutylammonium salt of a suitable anion. The association constants with halide ions, BF(4)(-), NO(3)(-), and CN(-), were measured by (1)H NMR spectroscopy. The highest association constant (8.9×10(5) M(-1)) was found for the 1:1 complex of BU6 with I(-) in acetonitrile/water mixture. A number of crystal structures of BU6 complexes with various anions were obtained. The influence of the anion size on the macrocycle diameter is discussed together with an unusual arrangement of the macrocycles into separate layers.

Peptide-Conjugated PAMAM Dendrimer as a Universal DNA Vaccine Platform to Target Antigen-Presenting Cells

DNA-based vaccines hold promise to outperform conventional antigen-based vaccines by virtue of many unique features. However, DNA vaccines have thus far fallen short of expectations, due in part to poor targeting of professional antigen-presenting cells (APC) and low immunogenicity. In this study, we describe a new platform for effective and selective delivery of DNA to APCs in vivo that offers intrinsic immune-enhancing characteristics. This platform is based on conjugation of fifth generation polyamidoamine (G5-PAMAM) dendrimers, a DNA-loading surface, with MHC class II-targeting peptides that can selectively deliver these dendrimers to APCs under conditions that enhance their immune stimulatory potency. DNA conjugated with this platform efficiently transfected murine and human APCs in vitro. Subcutaneous administration of DNA-peptide-dendrimer complexes in vivo preferentially transfected dendritic cells (DC) in the draining lymph nodes, promoted generation of high affinity T cells, and elicited rejection of established tumors. Taken together, our findings show how PAMAM dendrimer complexes can be used for high transfection efficiency and effective targeting of APCs in vivo, conferring properties essential to generate effective DNA vaccines.

Combining Proton and Electron Transfer to Modulate the Stability of Cucurbit[7]uril Complexes

(Ferrocenylmethyl)methylammonium (1H(+)) is an excellent cationic guest for inclusion complexation by the cucurbit[7]uril host. However, deprotonation of the guest leads to a decrease of 14.8 kJ mol(-1) in the overall stability of its inclusion complex, and one-electron oxidation of the guests ferrocene residue further diminishes the complex stability by another 12.3 kJ mol(-1). Overall, guest deprotonation followed by its oxidation constitutes an accessible method to lower the equilibrium association constant for the CB7·1H(+) complex by more than 4 orders of magnitude.

The cucurbituril ‘portal’ effect

This work focuses on the effect of cucurbit[n]uril (CBn) hosts on the microenvironment of molecular subunits that are located adjacent to the CBn binding site in inclusion complexes. The set of data presented here includes previously reported electrochemical and electron paramagnetic resonance spectroscopic data, primarily obtained with ferrocene-containing guests, as well as new electrochemical data recorded with 4,4′-bipyridinium (viologen) derivatives. Most of the data were obtained with cucurbit[7]uril (CB7) complexes, and the rest were collected with cucurbit[8]uril (CB8) complexes. The experimental data compiled here clearly suggest that the microenvironment adjacent to the CBn portals in the complexes exhibits increased polarity compared with the bulk aqueous solution.