Dihydroanthracene bridged bis-naphthopyrans:A multimodal chromophore with mechano-and photo-chromic properties

Mechanochromophores based on bichromic molecular switches,such as bis-naphthopyanes,allow multimodal mechanochromic behavior beyond the typical binary response from single chromophores,which is important for distinguishing between multiple stress states through discrete changes in color.Spontaneously generated persistent and distinguishable multi-colors from activated bis-naphthopyanes remain challenging.And the versatility of bis-mechanophore design for advanced optical molecular systems and the fundamental insights into the corresponding mechano-reactivity are not enough.Here,we identify a dihydroanthracene bridged bis-naphthopyrans as a multimodal mechanochromophore in polymers.Bridging two pyrans with the sterically constrained dihydroanthracene is helpful to control the steric effect for the favorable formation of a distinctly appreciable bis-merocyanine(bis-MC)product.By varying the length of the polymer chains,the force delivered to the mechanophore is modulated,resulting in a gradient change in the relative distribution of two distinctly colored MC products and a multicolor mechanochromism.Mechanical activation of this bis-naphthopyanes proceeds via a mechanistically distinct pathway compared to the photochemical process.In addition,the bulk films can also achieve pronounced color changes when subjected to mechanical force.This study thus further expands the molecular diversity of mechanochromophores and tune the multimodal switch properties of bis-naphthopyrans based polymers.

Efficient production of 14α‑OH‑AD by engineered Mycolicibacterium neoaurum via coupled cofactor and reconstructed electron transport system

14α-hydroxy-androst-4-ene-3,17-dione(14α-OH-AD)is an important precursor for the synthesis of steroid drugs with anticancer and carcinolytic activity.Initially,14α-OH-AD was mostly synthesized by whole-cell fermentation of mold fungi using androstenedione(AD)as a substrate,which had difficulties in product isolation and purification as well as problems of high production cost.In this study,the source of the 14α-hydroxylase gene was expanded.And 14α-hydroxylase genes were heterologously expressed in Mycolicibacterium neoaurum(MNR)M3ΔksdD,which enabled the one-step biotransformation from the cheap substrate phytosterols(PS)to 14α-OH-AD,reducing the difficulty of product purification and production cost.What is more,to alleviate the problem of poor activity of 14α-hydroxylase,the 14α-hydroxylase gene was co-expressed with the electron transport chain element genes and the coenzyme regeneration genes,and a superior engineered strain MNR M3ΔksdD/pMV261-14α-G6PDH was obtained.Finally,the transformation conditions were optimized for the transformation of PS by the engineered strain.The molar yield of 14α-OH-AD reached to 60.4±2.3%(about 0.22 g/L productivity).This study investigated for the first time the effects of the tandem electron transport chain element genes and the tandem coenzyme regeneration genes on the 14α-hydroxylation reaction,providing a theoretical basis for the industrial production of 14α-OH-AD.