Elucidation of the chemical structure and formation mechanism of humins is a requisite to further improve the efficiency of acid‐catalyzed biomass conversion. Through a low‐temperature approach, the key intermediates resulting in the formation of 5‐hydroxymethylfurfural (HMF)‐derived humins were captured, revealing multiple elementary reactions such as etherification, esterification, aldol condensation, and acetalization. Through humin characterization, it was found out that the aldol condensation moiety between aldehyde group and levulinic acid is critical to justify the characteristic IR peaks (1620 and 1710 cm−1) and aromatic fragments from pyrolysis GC–MS. Based on the investigations by means of HPLC–MS/MS, IR, pyrolysis GC–MS, and SEM, the structural models of humins at different temperatures were proposed, which are comprised of the elementary reaction types confirmed by the key intermediates. Humin structures with varying content of aldol condensation could be controllably synthesized under different reaction conditions (temperature and time), demonstrating the evolution process of HMF‐derived humins.
Cochlear noise injury is the second most frequent cause of sensorineural hearing loss, after aging. Because calcium dysregulation is a widely recognized contributor to noise injury, we examined the potential of calcium channel blockers to reduce noise-induced hearing loss (NIHL) in mice. We focused on two T-type calcium blockers, trimethadione and ethosuximide, which are anti-epileptics approved by the Food and Drug Administration. Young C57BL/6 mice of either gender were divided into three groups: a 'prevention' group receiving the blocker via drinking water before noise exposure; a 'treatment' group receiving the blocker via drinking water after noise exposure; and controls receiving noise alone. Trimethadione significantly reduced NIHL when applied before noise exposure, as determined by auditory brainstem recording. Both ethosuximide and trimethadione were effective in reducing NIHL when applied after noise exposure. Results were influenced by gender, with males generally receiving greater benefit than females. Quantitation of hair cell and neuronal density suggested that preservation of outer hair cells could account for the observed protection. Immunocytochemistry and RT-PCR suggested that this protection involves direct action of T-type blockers on α1 subunits comprising one or more Ca v 3 calcium channel types in the cochlea. Our findings provide a basis for clinical studies testing T-type calcium blockers both to prevent and treat NIHL.
A type III polyketide synthase cDNA and the corresponding gene (PcPKS2) were cloned from Polygonum cuspidatum Sieb. et Zucc. Sequencing results showed that the ORF of PcPKS2 was interrupted by three introns, which was an unexpected finding because all type III PKS genes studied so far contained only one intron at a conserved site in flowering plants, except for an Antirrhinum majus chalcone synthase gene. Besides the unusual gene structure, PcPKS2 showed some interesting characteristics: (1) the CHS "gatekeepers" Phe215 and Phe265 are uniquely replaced by Leu and Cys, respectively; (2) recombinant PcPKS2 overexpressed in Escherichia coli efficiently afforded 4-coumaroyltriacetic acid lactone (CTAL) as a major product along with bis-noryangonin (BNY) and p-hydroxybenzalacetone at low pH; however, it effectively yielded p-hydroxybenzalacetone as a dominant product along with CTAL and BNY at high pH. Beside p-hydroxybenzalacetone, CTAL and BNY, a trace amount of naringenin chalcone could be detected in assays at different pH. Furthermore, 4-coumaroyl-CoA and feruloyl-CoA were the only cinnamoyl-CoA derivatives accepted as starter substrates. PcPKS2 did not accept isobutyryl-CoA, isovaleryl-CoA or acetyl-CoA as substrate. DNA gel blot analysis indicated that there are two to four PcPKS2 copies in the P. cuspidatum genome. RNA gel blot analysis revealed that PcPKS2 is highly expressed in the rhizomes and in young leaves, but not in the roots of the plant. PcPKS2 transcripts in leaves were induced by pathogen infection, but not by wounding.
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