Light-responsive azo-containing organogels

While azo compounds are widely employed as radical initiators, they have rarely been used as stimuli-responsive motifs in macromolecular constructs. In this study, an azo-based cross-linker was prepared and reacted with poly(vinyl alcohol) to afford a series of stimuli-responsive organogels. Irradiation of these materials with UV light causes de-cross-linking and triggers a solid-to-liquid phase transition. Model adhesives with de-bonding-on-demand capability based on this design were explored

Azo-Containing Polymers with Degradation On-Demand Feature

Molecules comprising aliphatic azo moieties are widely used as radical polymerization initiators, but only a few studies have explored their usefulness as stimuli-responsive motifs in macromolecular constructs. The controlled degradation of azo-containing polymers has indeed remained largely unexplored. Here we present the syntheses of linear azo-containing polyamides and polyurethanes and report on their thermally and optically induced responses in solution and the solid state. We show that the stimuli- induced degradation behavior depends strongly on the nature of the polymer backbone, the state of matter, and in solution, on the nature of the solvent. The stimuli-responsive solid-state properties of the azo-containing materials may be particularly useful. In the case of the polyurethanes studied here, temperature- or light-induced cleavage of the azo motifs led to a controllable decrease in the molecular weight, which, in turn, caused a reduction of the elongation at break, modulus, and strength. The controlled degradation of the polymer in well-defined areas can be readily achieved via photopatterning, and this approach was shown to be useful to produce solid structures with graded mechanical properties

Quantitative Nano-characterization of Polymers Using Atomic Force Microscopy

The present article offers an overview on the use of atomic force microscopy (AFM) to characterize the nanomechanical properties of polymers. AFM imaging reveals the conformations of polymer molecules at solid– liquid interfaces. In particular, for polyelectrolytes, the effect of ionic strength on the conformations of molecules can be studied. Examination of force versus extension profiles obtained using AFM-based single molecule force spectroscopy gives information on the entropic and enthalpic elasticities in pN to nN force range. In addition, single molecule force spectroscopy can be used to trigger chemical reactions and transitions at the molecular level when force-sensitive chemical units are embedded in a polymer backbone

Triggered metal ion release and oxidation: ferrocene as a mechanophore in polymers

The introduction of mechanophores into polymers makes it possible to transduce mechanical forces into chemical reactions that can be used to impart functions such as self‐healing, catalytic activity, and mechanochromic response. Here, an example of mechanically induced metal ion release from a polymer is reported. Ferrocene (Fc) was incorporated as an iron ion releasing mechanophore into poly(methyl acrylate)s (PMAs) and polyurethanes (PUs). Sonication triggered the preferential cleavage of the polymers at the Fc units over other bonds, as shown by a kinetic study of the molar mass distribution of the cleaved Fc‐containing and Fc‐free reference polymers. The released and oxidized iron ions can be detected with KSCN to generate the red‐ colored [Fe(SCN)n(H2O)6−n)](3−n)+ complex or reacted with K4[Fe(CN)6] to afford Prussian blue

Pan-cancer Alterations of the MYC Oncogene and Its Proximal Network across the Cancer Genome Atlas

Although theMYConcogene has been implicated incancer, a systematic assessment of alterations ofMYC, related transcription factors, and co-regulatoryproteins, forming the proximal MYC network (PMN),across human cancers is lacking. Using computa-tional approaches, we define genomic and proteo-mic features associated with MYC and the PMNacross the 33 cancers of The Cancer Genome Atlas.Pan-cancer, 28% of all samples had at least one ofthe MYC paralogs amplified. In contrast, the MYCantagonists MGA and MNT were the most frequentlymutated or deleted members, proposing a roleas tumor suppressors.MYCalterations were mutu-ally exclusive withPIK3CA,PTEN,APC,orBRAFalterations, suggesting that MYC is a distinct onco-genic driver. Expression analysis revealed MYC-associated pathways in tumor subtypes, such asimmune response and growth factor signaling; chro-matin, translation, and DNA replication/repair wereconserved pan-cancer. This analysis reveals insightsinto MYC biology and is a reference for biomarkersand therapeutics for cancers with alterations ofMYC or the PMN

Modeling Ultrasound-Induced Moledular Weight Decrease of Polymers With Multiple Scissile Azo-Mechanophores

The azo moiety is receiving increasing attention as a stimuli-responsive trigger. Herein, we present an investigation of the mechanoresponsive behavior of a series of polyurethanes containing multiple randomly distributed azo motifs as scissile mechanophores, i.e., an entity that is preferentially cleaved upon application of a mechanical force. We made a systematic comparison of the ultrasound-induced cleavage of azo-containing polymers of different molecular weights and with varying azo content. We developed a mathematical model to describe the scission kinetics and the analysis of the rate constants showed that site-specific cleavage at the azo position was favored over random bond scission events. The proposed mathematical model appears to be a broadly useful method to characterize the ultrasound-induced molecular weight decrease of polymers containing multiple scissile mechanophores

Modeling ultrasound-induced molecular weight decrease of polymers with multiple scissile azo-mechanophores

The azo moiety is receiving increasing attention as a stimuli-responsive trigger. Herein, we present an investigation of the mechanoresponsive behavior of a series of polyurethanes containing multiple randomly distributed azo motifs as scissile mechanophores, i.e., an entity that is preferentially cleaved upon application of a mechanical force. We made a systematic comparison of the ultrasound-induced cleavage of azo-containing polymers of different molecular weights and with varying azo content. We developed a mathematical model to describe the scission kinetics and the analysis of the rate constants showed that site-specific cleavage at the azo position was favored over random bond scission events. The proposed mathematical model appears to be a broadly useful method to characterize the ultrasound-induced molecular weight decrease of polymers containing multiple scissile mechanophores.Peer reviewe