One-Step Synthesis of N‑Heterocyclic Compounds from Carbohydrates over Tungsten-Based Catalysts

A one-step reaction system has been developed to convert glucose and other renewable carbohydrates into important N-heterocyclic compounds in ammonia solution. Under optimal conditions, 2-methyl pyrazine (MP) and 4(5)-methyl imidazole (MI) were produced within 15 min with combined yields of around 40%. While the formation of 4(5)-MI was identified as a noncatalytic process, the yield of 2-MP was highly influenced by the presence of catalysts. In particular, nearly 3-fold yield enhancement of 2-MP was achieved over several tungsten-based catalysts. Control experiments, isotope-labeling tests, ESI-MS, and NMR analysis revealed that the formation of 2-MP follows a fragmentation mechanism, while small tungsten clusters such as [HW₂O₇]⁻ and [W₄O₁₃]^2– were the catalytically active species facilitating both glucose fragmentation and the subsequent cyclization reaction to generate pyrazine rings. The work exemplifies the possibility of sustainable production of important <i>N</i>-containing, heterocyclic chemicals from woody biomass, where the identification and understanding of novel catalysts are the key

Kinetic Studies of Lignin Solvolysis and Reduction by Reductive Catalytic Fractionation Decoupled in Flow-Through Reactors

Reductive catalytic fractionation (RCF) is an effective active-stabilization strategy to selectively extract and depolymerize lignin into aromatic monomers. Here, the kinetics of RCF were investigated by using flow-through reactors to decouple the two limiting mechanistic steps, namely lignin solvolysis and reduction. When operating in a solvolysis-limited regime, apparent energy barriers of 63 ± 1 and 64 ± 2 kJ mol^–1 were measured for the solvent mediated lignin extraction of poplar using particle diameters of 0.5 < <i><i>d</i></i> < 1 mm and 0.075 < <i><i>d</i></i> < 0.25 mm, respectively. In contrast, when using mechanically stirred batch reactors, apparent barriers of 32 ± 1 and 39 ± 3 kJ mol^–1 were measured for particle diameters of 0.5 < <i>d</i> < 1 mm and 0.075 < <i>d</i> < 0.25 mm, respectively. The difference of activation barriers between flow and batch reactors indicated that lignin extraction under typical RCF conditions in a 100 mL batch reactor stirred at 700 rpm was mass-transfer limited. In the reduction-limited regime, cleavage of the β-O-4 bond in a model compound exhibited an apparent activation barrier of 168 ± 14 kJ mol^–1. This study demonstrates RCF occurs by two limiting processes that can be independently controlled. Furthermore, both controlling which process limits RCF and verifying if transport limitations exist, are critical steps to develop a mechanistic understanding of RCF and to design improved catalysts

Multiply Intercalator-Substituted Cu(II) Cyclen Complexes as DNA Condensers and DNA/RNA Synthesis Inhibitors

Many drugs that are applied in anticancer therapy such as the anthracycline doxorubicin contain DNA-intercalating 9,10-anthraquinone (AQ) moieties. When Cu­(II) cyclen complexes were functionalized with up to three (2-anthraquinonyl)­methyl substituents, they efficiently inhibited DNA and RNA synthesis resulting in high cytotoxicity (selective for cancer cells) accompanied by DNA condensation/aggregation phenomena. Molecular modeling suggests an unusual bisintercalation mode with only one base pair between the two AQ moieties and the metal complex as a linker. A regioisomer, in which the AQ moieties point in directions unfavorable for such an interaction, had a much weaker biological activity. The ligands alone and corresponding Zn­(II) complexes (used as redox inert control compounds) also exhibited lower activity