ABSTRACT
The interaction of cyclodextrins (CDs) with structure-controlled polymers is expected to provide significant insights into macromolecular recognition. However, the interaction of CDs with structure-controlled polymers has been an underexamined issue of investigation. Herein, alternating amphiphilic cooligomers (oligoCnAH, where n denotes the carbon number of alkyl groups; n = 4, 8, and 12) were synthesized by copper(I)-catalyzed azide-alkyne cycloaddition polymerization of heterodimers of 4-azido-5-hexynoic acid (AH) derivatives carrying N-alkylamide and t-butyl (tBu) ester side chains, followed by hydrolysis of the tBu ester, to study the interaction of CDs with oligoCnAH by 1H NMR, nuclear Overhauser effect spectroscopy, and pulse-field-gradient spin-echo NMR. These NMR studies indicated that αCD interacted with oligoC4AH, αCD and ßCD interacted with oligoC8AH, and all CDs interacted with oligoC12AH. Based on the equilibrium models proposed, the binding constants were evaluated for the binary mixtures, which showed interaction. Comparing the interactions of the CDs/oligoC12AH binary mixtures with those of the binary mixtures of CDs and alternating copolymers of sodium maleate and dodecyl vinyl ether (polyC12M), it is concluded that oligoC12AH forms less stable micelles than does polyC12M presumably because of the lower molecular weight, the hydrophilic amide groups in the side chain, and the longer interval between neighboring C12 groups in oligoC12AH.
ABSTRACT
Ruthenium(II)-catalyzed azide-alkyne cycloaddition (RuAAC) polymerization of t-butyl 4-azido-5-hexynoate (tBuAH), i.e., a heterobifunctional monomer carrying azide and alkyne moieties, was investigated in this study. RuAAC of the monofunctional precursors of tBuAH yielded a dimer possessing a 1,5-disubstituted 1,2,3-triazole moiety. 1H NMR data showed that the dimer was a mixture of diastereomers. Polymerization of tBuAH using ruthenium(II) (Ru(II)) catalysts produced oligomers of Mw ≈ (2.7-3.6) × 103 consisting of 1,5-disubstituted 1,2,3-triazole units (1,5-units) as well as 1,4-disubstituted 1,2,3-triazole units (1,4-units). The fractions of 1,5-unit (f1,5) were roughly estimated to be ca. 0.8 by comparison of signals of the methine and triazole protons in 1H NMR spectra, indicating that RuAAC proceeded preferentially and thermal Huisgen cycloaddition (HC) somehow took place during the polymerization. The oligomer samples obtained were also characterized by solubility test, size exclusion chromatography (SEC), ultraviolet-visible (UV-Vis) absorption spectroscopy, and thermogravimetric analysis (TGA). The UV-Vis and TGA data indicated that the oligomer samples contained a substantial amount of Ru(II) catalysts. To the best of our knowledge, this is the first report on dense 1,2,3-triazole oligomers consisting of 1,5-units linked via a carbon atom.
ABSTRACT
THO2 is a component of the THO-TREX (transcription and export factor) complex that participates in mRNA metabolism and export from the nucleus in yeast and animal cells. Here we report that tobacco putative THO2-related protein (NtTHO2) is a microtubule-associated protein, which directly binds to microtubules in vitro and co-localizes with cortical microtubules in vivo. We purified endogenous NtTHO2 by cycles of microtubule polymerization-depolymerization from crude extracts of tobacco BY-2 miniprotoplasts. Purified NtTHO2 sedimented with microtubules in vitro. Immunofluorescence revealed that NtTHO2 was present in both the nucleus and cytoplasm. In interphase, cytoplasmic NtTHO2 was localized along cortical microtubules. In the mitotic phase, NtTHO2 was localized to the mitotic spindle but not to either the preprophase band or the phragmoplast. In mature cells of seedling roots, and in BY-2 cells in which proliferation was stopped by removing 2,4-D, NtTHO2 staining was confined mainly to the nucleolus. These results suggest that NtTHO2 is a multifunctional protein that participates in mRNA metabolism, and also functions within the cortical microtubules and mitotic spindle.