Mechanistic Insight into Heptosyltransferase Inhibition by using Kdo Multivalent Glycoclusters

The synthesis of unprecedented multimeric Kdo glycoclusters based on fullerene and calix[4]arene central scaffolds is reported. The compounds were used to study the mechanism and scope of multivalent glycosyltransferase inhibition. Multimeric mannosides based on porphyrin and pillar[5]arenes were also generated in a controlled manner. Twelve glycoclusters and their monomeric ligands were thus assayed against heptosyltransferase WaaC, which is an important bacterial glycosyltransferase that is involved in lipopolysaccharide biosynthesis. It was first found that all the multimers interact solely with the acceptor binding site of the enzyme even when the multimeric ligands mimic the heptose donor. Second, the novel Kdo glycofullerenes displayed very potent inhibition (K_i=0.14 μm for the best inhibitor); an inhibition level rarely observed with glycosyltransferases. Although the observed “multivalent effects” (i.e., the enhancement of affinity of a ligand when presented in a multimeric fashion) were in general modest, a dramatic effect of the central scaffold on the inhibition level was evidenced: the fullerene and the porphyrin scaffolds being by far superior to the calix‐ and pillar‐arenes. We could also show, by dynamic light scattering analysis, that the best inhibitor had the propensity to form aggregates with the heptosyltransferase. This aggregative property may contribute to the global multivalent enzyme inhibition, but probably do not constitute the main origin of inhibition.     

A Perfect Match: Fullerene Guests in Star‐Shaped Oligophenylenevinylene Mesogens

Star‐shaped oligophenylenevinylene (OPV) mesogens are shape‐persistent and possess formally large void space. A mesogen with three styrene repeating units packs densely in a columnar helical arrangement. Attachment of one fullerene through a short spacer results in an exceptional increase of the mesophase stability. X‐ray scattering and modeling evidence a triple‐helical arrangement in which the fullerene perfectly fills the void space between the arms of the star mesogen.     

Phase behavior of blends of PCBM with amorphous polymers with different aromaticity

The phase behavior of [6,6]‐phenyl C₆₁‐butyric acid methyl ester (PCBM) blends with amorphous polymers with different degrees of aromaticity has been investigated by differential scanning calorimetry (DSC) and small‐angle neutron scattering (SANS). The polymers investigated are the homologous series of polystyrene (PS), poly(2‐vinyl‐naphthalene) (P2VN), and poly(9‐vinyl‐phenanthrene) (P9VPh). The DSC results show that the miscibility of PCBM in these polymers increases nonlinearly from 16.5 wt % in PS, 57.0 wt % in P2VN, and 74.9 wt % in P9VPh. The SANS results show that at all concentrations of PCBM, the blends are composed of two mixed phases. Analysis shows that the phase dimensions remain largely independent of PCBM content, but there is a strong dependence of the PCBM concentration difference in the two phases with increasing PCBM content. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 994–1001     

Simultaneous morphological stability and high charge carrier mobilities in donor–acceptor block copolymer/PCBM blends

Donor–acceptor block copolymers (BCP), incorporating poly(3‐hexylthiophene) (P3HT), and a polystyrene copolymer with pendant fullerenes (PPCBM) provide desired stable nanostructures, but mostly do not exhibit balanced charge carrier mobilities. This work presents an elegant approach to match hole and electron transport in BCP by blending with molecular PCBM without causing any macrophase separation. An insufficient electron mobility of PPCBM can be widely compensated by adding PCBM which is monitored by the space‐charge limited current method. Using X‐ray diffraction, atomic force microscopy, and differential scanning calorimetry, we verify the large miscibility of the PPCBM:PCBM blend up to 60 wt % PCBM load forming an amorphous, molecularly mixed fullerene phase without crystallization. Thus, blending BCP with PCBM substantially enhances charge transport achieving an electron mobility of μ_e=(3.2 ± 1.7) × 10^?4 cm²V^?1s^?1 and hole mobility of μ_h=(1.8 ± 0.6) × 10^?3 cm²V^?1s^?1 in organic field‐effect transistors (OFET). The BCP:PCBM blend provides a similarly high ambipolar charge transport compared to the established P3HT:PCBM system, but with the advantage of an exceptionally stable morphology even for prolonged thermal annealing. This work demonstrates the feasibility of high charge transport and stable morphology simultaneously in a donor–acceptor BCP by a blend approach. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1125–1136     

Relationship between reduction potentials and electron affinities of fullerenes and their derivatives

A linear relationship was found between the first reduction potentials (E°_red) and electron affinities (EA) for fullerenes C₆₀ and C₇₀, their hydro- and fluoro-derivatives, and aromatic hydrocarbons: E°_red = –3.04 + 0.81·EA. This equation was used to estimate the unknown values of EA = 2.45 eV for C₆₀H₂, 2.47 eV for C₇₀H₂, –0.15 eV for C₇₀H_36—38, –0.41 eV for C₇₀H_44—46, and E°_red = –1.74—–1.91 V (vs. Fc^0/+) for C₆₀H₁₈.     

Higher trifluoromethylated derivatives of C60, C60(CF3)16 and C60(CF3)18: Synthesis, structure, and theoretical study

Three isomers of C₆₀(CF₃)₁₆ and one isomer of C₆₀(CF₃)₁₈ have been isolated by HPLC from a mixture prepared by trifluoromethylation of C₆₀ with CF₃I in a glass ampoule at 380-400 °C. The molecular structures of the four new compounds have been determined by means of X-ray single crystal diffraction and discussed in terms of mechanistic pathways of their formation and relative stability according to the DFT calculations.