Reactive oligo(dimethylsiloxane) mesogens and their nanostructured thin films.

Oligo(dimethylsiloxane)-based reactive mesogens were prepared and shown to form room-temperature smectic phases which were 'frozen-in' by photopolymerization. Homeotropically aligned, nanostructured thin films were obtained by spincoating, and micropatterning was demonstrated. These hybrid reactive mesogens are suitable for the preparation of aligned nanostructured polymer thin films with potential applications ranging from stimuli responsive coatings to nanoporous membranes.

Reactions of mercaptans with cytochrome c oxidase and cytochrome c.

1. The steady-state oxidation of ferrocytochrome c by dioxygen catalyzed by cytochrome c oxidase, is inhibited non-competitively towards cytochrome c by methanethiol, ethanethiol, 1-propanethiol and 1-butanethiol with Ki values of 4.5, 91, 200 and 330 microM, respectively. 2. The inhibition constant Ki of ethanethiol is found to be constant between pH 5 and 8, which suggests that only the neutral form of the thiol inhibits the enzyme. 3. The absorption spectrum of oxidized cytochrome c oxidase in the Soret region shows rapid absorbance changes upon addition of ethanethiol to the enzyme. This process is followed by a very slow reduction of the enzyme. The fast reaction, which represents a binding reaction of ethanethiol to cytochrome c oxidase, has a k1 of 33 M-1 . s-1 and a dissociation constant Kd of 3.9 mM. 4. Ethanethiol induces fast spectral changes in the absorption spectrum of cytochrome c, which are followed by a very slow reduction of the heme. The rate constant for the fast ethanethiol reaction representing a bimolecular binding step is 50 M-1 . s-1 and the dissociation constant is about 2 mM. Addition of up to 25 mM ethanethiol to ferrocytochrome c does not cause spectral changes. 5. EPR (electron paramagnetic resonance) spectra of cytochrome c oxidase, incubated with methanethiol or ethanethiol in the presence of cytochrome c and ascorbate, show the formation of low-spin cytochrome alpha 3-mercaptide compounds with g values of 2.39, 2.23, 1.93 and of 2.43, 2.24, 1.91, respectively.

Evaluation of strained alkynes for Cu-free click reaction in live mice.

INTRODUCTION: We report on our evaluation of the strain-promoted cyclooctyne-azide cycloaddition reaction for use in tumor pretargeting, comprising a side-by-side comparison of probes 1-3 bearing three distinct cyclooctyne moieties based respectively on the 1st and 2nd generation difluorinated cyclooctyne and the 1st generation dibenzocyclooctyne. METHODS: The probes were synthesized and labeled with (177)Lu with high yields. The probe stability and reactivity towards azides were evaluated in PBS and mouse serum, and their blood clearance, biodistribution and in vivo reactivity were evaluated in tumor-free mice. RESULTS: In serum the three probes exhibited sufficient stability for a pretargeting application with half-lives of 12-19h. In PBS, probes 2 and 3 were more reactive towards azido-conjugated Rituximab (Rtx-N3) than 1, but in contrast to 1, their reactivity decreased in mouse serum and mouse serum albumin solutions, as a result of covalent and non-covalent interactions with albumin. Biodistribution data confirmed the interactions with serum proteins in circulation: (177)Lu-1 showed a fast elimination from blood (t1/2,ß = 0.31h), while (177)Lu-2 and (177)Lu-3 were retained in blood for longer periods of time (t1/2,ß = 1.08 and 3.58h, respectively). Dual isotope biodistribution experiments assessing the reaction between (125)I-Rtx-N3 and (177)Lu-1-3 in circulation in mice showed a very limited retention of 2 and 3 in blood rich organs, indicating a minimal reactivity, while no such retention was observed for 1. CONCLUSION: The low reactivity of the studied cyclooctynes, and their serum interactions preclude their use at the low in vivo concentrations typical for pretargeting applications.