The RNA polymerase inhibitor tiacumicin B is currently undergoing phase III clinical trial for treatment of Clostridium difficile associated diarrhea with great promise. To understand the biosynthetic logic and to lay a foundation for generating structural analogues via pathway engineering, the tiacumicin B biosynthetic gene cluster was identified and characterized from the producer Dactylosporangium aurantiacum subsp. hamdenensis NRRL 18085. Sequence analysis of a 110,633 bp DNA region revealed the presence of 50 open reading frames (orfs). Functional investigations of 11 orfs by in vivo inactivation experiments, preliminarily outlined the boundaries of the tia-gene cluster and suggested that 31 orfs were putatively involved in tiacumicin B biosynthesis. Functions of a halogenase (TiaM), two glycosyltransferases (TiaG1 and TiaG2), a sugar C-methyltransferase (TiaS2), an acyltransferase (TiaS6), and two cytochrome P450s (TiaP1 and TiaP2) were elucidated by isolation and structural characterization of the metabolites from the corresponding gene-inactivation mutants. Accumulation of 18 tiacumicin B analogues from 7 mutants not only provided experimental evidence to confirm the proposed functions of individual biosynthetic enzymes, but also set an example of accessing microbial natural product diversity via genetic approach. More importantly, biochemical characterization of the FAD-dependent halogenase TiaM reveals a sequentially acting dihalogenation step tailoring tiacumicin B biosynthesis.

Polyfluorenes (P1 and P2) with phosphonate groups in the side chains were designed and synthesized. Their absorption and photoluminescence spectra in solutions are solvent dependent and exhibit a red shift up to 14 and 6 nm, respectively, with increasing solvent polarity. The polymers are highly soluble in ethanol with a solution photoluminescence quantum yield of 0.74. Polymer P2 in thin film cast from ethanol shows high intrachain order as revealed by red-shifted absorption spectrum and emission spectrum along with well-resolved vibronic structure. Both P1 and P2 are highly sensitive and selective Fe 3+ sensory materials, and the sensitivity is much higher than that of model compounds 3 and 4. The highest sensitivity was observed with polymer P1, and a 210-fold fluorescence quenching in dichloromethane was achieved. Polymer light-emitting diodes (PLEDs) were also fabricated to investigate the electroluminescent properties. A luminous efficiency of 1.49 cd/A with Commission Internationale de L'Eclairage (CIE) coordinates of (0.171, 0.131) at 100 cd/m 2 and a maximum brightness of 1750 cd/m 2 have been demonstrated.