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As an important metabolic intermediate, 2-ketoisovalerate has significant potential in the pharmaceutical and biofuel industries. However, a low output through microbial fermentation inhibits its industrial application. The microbial production of 2-ketoisovalerate is representative whereby redox imbalance is generated with two molecules of NADH accumulated and an extra NADPH required to produce one 2-ketoisovalerate from glucose. To achieve efficient 2-ketoisovalerate production, metabolic engineering strategies were evaluated in Escherichia coli. After deleting the competing routes, overexpressing the key enzymes for 2-ketoisovalerate production, tuning the supply of NADPH, and recycling the excess NADH through enhancing aerobic respiration, a 2-ketoisovalerate titer and yield of 46.4 g/L and 0.644 mol/mol glucose, respectively, were achieved. To reduce the main by-product of isobutanol, the activity and expression of acetolactate synthase were modified. Additionally, a protein degradation tag was fused to pyruvate dehydrogenase (PDH) to curtail the conversion of pyruvate precursor into acetyl-CoA and the generation of NADH. The resulting strain, 050TY/pCTSDTQ487S-RBS55, was initially incubated under aerobic conditions to attain sufficient cell mass and then transferred to a microaerobic condition to degrade PDH and inhibit the remaining activity of PDH. Intracellular redox imbalance was relieved with titer, productivity and yield of 2-ketoisovalerate improved to 55.8 g/L, 2.14 g/L h and 0.852 mol/mol glucose. These results revealed metabolic engineering strategies for the production of a redox-imbalanced fermentative metabolite with high titer, productivity, and yield.

A multi-functional liposome has been developed that demonstrates reversible changes in color and fluorescence intensity in response to changes in pH. Addition of a pendant tryptophan moiety gives the assembly the ability to detect Escherichia coli. The sensor platform is made from a polymerized vesicular assembly of hydrazide-terminated diacetylene lipids and a BO558 fluorescent dye. The polymer backbone is responsible for the color change, while the organization induced by hydrogen bonding of the terminal hydrazide groups permits the reversibility of the color change. Fluorescence quenching is due to internal rearrangement of the liposome and occurs in both polymerized and unpolymerized structures.

Chiral diacetylenes featuring ester and urethane groups are readily prepared from amino acids and diynediols. The ability of the butadiyne moiety to undergo topotactic polymerization is dependent on both the length of the chain to the urethane group and the size of the amino acid. In some cases, the polymerization proceeds as well as the well-studied achiral parent compound, 4BCMU. The polymers form yellow solutions in good solvents where the chains adopt a random-coil configuration. Addition of a nonsolvent changes the solution color to red as the chains adopt a helical conformation.

We structurally designed and synthesized a novel class of self-layered supramolecular polymers containing DA derivatives that can be obtained as film-forming materials and processed into a various forms. We found that double H-bonds between the acid hard cores together with a remarkable molecular DA recognition allow for retaining more favorable packing of the reactive groups in spin-coated films or even in dispersed solutions with a high degree of local ordering, suitable for topochemical polymerization. The sample molecularly designed here could be topochemically polymerized by UV irradiation through 1,4 addition of the conjugated triple bonds between adjacent stacking molecules. A reversible thermochromism in the absorption characteristics of spin-coated terephthalic acid/diacetylene polymers was also observed.

Polydiacetylenes (PDAs) are ordered and uniquely conjugated polymers synthesized from diacetylene monomers by UV-initiated photoreaction or thermally. The amphiphilic PDAs with controlled spacing and orientation often accomplished by Langmuir–Blodgett (LB) technique provide possible applications in the area of the photolithography, nonlinear optics and chemical sensors. In this study, we synthesized an amphiphilic of diacetylene monomer, 2,5-bis-octadeca-5,7-diynyloxy-terephthalic acid (BODTA), containing a diacetylene moiety in each of two symmetric side chains. Stable Langmuir monolayers of BODTA were constructed, and successfully transferred on the solid substrates as the monomeric form to investigate the changes of the molecular interaction, packing and orientation induced by UV-induced polymerization. In situ spectroscopic and scanning probe microscopic analyses indicate that at lower surface pressure, BODTA spontaneously forms micro-scale domains, and merges together as surface pressure increases. The molecular orientation and intermolecular interaction of BODTA were significantly altered by UV-induced polymerization. We found that two different polymerization mechanisms may be involved as the intermolecular distance and relative orientation to adjacent molecules changes by controlling the degree of compression of the monolayer at the interface.

Full Paper: A convenient, low cost micro-patterning method using a new side group polymer containing phenol-phthalein is reported. A random copolymer of t-BOC-protected phenolphthalein methacrylate (t-BMPP) with methyl methacrylate (MMA) was prepared by radical copolymerization in dioxane. The negative-tone patterns of this polymer could be obtained by photo-deprotection of the t-BOC groups due to the effect of dissolution inhibition by the phenolic group of the phenolphthalein. The chemical and optical properties of the polymer were, as anticipated, very close to those of the corresponding phenolphthalein and the pH controlled colorimetric transition was reproducibly observed. The contrast in solubility and chromism upon alkaline treatment makes this polymer a promising candidate for investigating spatially-directed chromism and selective deposition of pH sensitive polymers.

A polymerizable quinizarin (Qz) dye precursor having both methacrylate and tert-butoxycarbonyl (t-BOC) groups has been prepared and radically copolymerized to obtain mono-t-BOC-protected quinizarin polymers as fluorescent imaging materials. The mono-t-BOC-protected quinizarin methacylate 3 (t-BQzMA) is a unique monomer having an acid-labile t-BOC blocking group along with a polymerizable methacrylate group. The t-BOC-protected quinizarin polymers obtained by copolymerization of t-BQzMA with methyl methacrylate were readily modified to regenerate phenol groups by deprotection of t-BOC groups in the quinizarin moieties with photochemical treatment in the presence of a photoacid generator. The polymers rendered color and fluorescent imaging properties based on a photolithographic method: fluorescent images obtained without wet development and fluorescent relief patterns after wet development followed by flood exposure.

Although a high electric energy density was recently reported for defect-modified poly(vinylidene fluoride) (PVDF) copolymers at millisecond discharge, they usually deliver less energy at a high pulse rate. In this letter, a low loss polystyrene (PS) was grafted as side chains onto the P(VDF-chlorotrifluoroethylene) main chain. After PVDF crystallization, dielectric PS side chains were segregated to the crystalline-amorphous interface, forming a finite confinement layer for ferroelectric PVDF crystals. We speculated that less space charge was induced during electric poling because of the nanoscale confinement effect. Consequently, a fast discharge speed and a relatively high energy density were achieved.