Cyanines derived from heptamethines were investigated in combination with iodonium salts as initiators of the radical polymerization of tripropylene glycol diacrylate and epoxides derived from bisphenol‐A‐diglycidylether. A new near‐infrared (NIR) LED prototype emitting at 805 nm with an exposure intensity of 1.2 W cm−2 facilitated initiation of both radical and cationic polymerization using sensitizers derived from cyanines. This new light‐emitting device has brought new insight into the photochemistry of cyanines with the general structure 1 because a combination of photonic and thermal processes strongly influences reaction pathways. In particular, cationic cyanines comprising a cyclopentene moiety and diphenylamino group in the center initiated the cationic polymerization of epoxides. Selective oxidation of this unit explains why specifically these derivatives may function as initiators for cationic polymerization. In contrast, when the diphenylamino group was replaced by a barbital group at the meso‐position cationic polymerization of epoxides was not initiated.
BackgroundInsufficient incorporation of heme is considered a central impeding cause in the recombinant production of active heme proteins. Currently, two approaches are commonly taken to overcome this bottleneck; metabolic engineering of the heme biosynthesis pathway in the host organism to enhance intracellular heme production, and supplementation of the growth medium with the desired cofactor or precursors thereof to allow saturation of recombinantly produced apo-forms of the target protein. In this study, we investigated the effect of both, pathway engineering and medium supplementation, to optimize the recombinant production of the heme protein horseradish peroxidase in the yeast Pichia pastoris.ResultsIn contrast to studies with other hosts, co-overexpression of genes of the endogenous heme biosynthesis pathway did not improve the recombinant production of active heme protein. However, medium supplementation with hemin proved to be an efficient strategy to increase the yield of active enzyme, whereas supplementation with the commonly used precursor 5-aminolevulinic acid did not affect target protein yield.ConclusionsThe yield of active recombinant heme peroxidase from P. pastoris can be easily enhanced by supplementation of the cultivation medium with hemin. Thereby, secreted apo-species of the target protein are effectively saturated with cofactor, maximizing the yield of target enzyme activity.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-014-0187-z) contains supplementary material, which is available to authorized users.
Cyaninderivate von Heptamethinen wurden mit Iodoniumsalzen auf ihre Fähigkeit zur Initiierung der radikalischen und kationischen Polymerisation von Tripropylenglykoldiacrylat und Epoxiden des Bisphenol‐A‐diglycidylether untersucht. Ein neuer Nahinfrarot(NIR)‐LED‐Prototyp, der bei 805 nm mit einer Strahlungsintensität von 1.2 W cm−2 emittiert, ermöglicht die Initiierung beider Polymerisationsarten. Dies liefert neue Einblicke in die Photochemie von Cyaninverbindungen des Strukturtyps 1, da die Kombination von photonischen und thermischen Prozessen den Reaktionsweg maßgeblich beeinflusst. Zum ersten Mal wird die Initiierung der kationischen Photopolymerisation von Epoxiden mit solchen NIR‐Absorbern beschrieben, wobei insbesondere Cyanine mit Cyclopentenyl‐ und Diphenylaminogruppen im Zentrum effizient sind. Die selektive Oxidation dieser Verbindung erklärt, weshalb speziell diese Derivate die kationische Polymerisation initiieren. Bei Austausch der Diphenylaminogruppe durch eine Barbituratgruppe in meso‐Position erfolgt hingegen keine Initiierung der kationischen Polymerisation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.