Versatile functionalization of a crown ether/sec-ammonium salt-type rotaxane was accomplished. The rotaxane underwent reductive N-alkylation with sodium tri(acyloxy)borohydride or sodium tri(acyloxy)borohydride/arbitrary aldehyde in excellent yields. Structural switching based on reversible tert-ammonium/tert-amine conversion by acid and base was demonstrated as a pH-controlled molecular shuttle.

An early response to mechanical stimulation of bone cells in vitro is an increase in intracellular calcium concentration ([Ca 2+ ] i ). This study analyzed the [Ca 2+ ] i wave area, magnitude, duration, rise time, fall time, and time to onset in individual osteoblasts for two identical bouts of mechanical stimulation separated by a 30-min rest period. The area under the [Ca 2+ ] i wave increased in the second loading bout compared to the first. This suggests that rest periods may potentiate mechanically induced intracellular calcium signals. Furthermore, many of the [Ca 2+ ] i wave parameters were strongly, positively correlated between the two bouts of mechanical stimulation. For example, in individual primary osteoblasts, if a cell had a large [Ca 2+ ] i wave area in the first bout it was likely to have a large [Ca 2+ ] i wave area in the second bout (r 2 = 0.933). These findings support the idea that individual bone cells have "calcium fingerprints" (i.e., a unique [Ca 2+ ] i wave profile that is reproducible for repeated exposure to a given stimulus).

Pendant rotaxane switch-tethering poly(m-phenylene diethynylene) was synthesized by the polyoxidative coupling of a rotaxane containing an axle-terminal m-diethynylbenzene group and an optically active crown ether. The reversible helix-random coil transition of the polymer was successfully performed by the positional switching of the rotaxane wheel.

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Fanconi Anemia (FA), results from mutations in genes necessary for DNA damage repair and often leads to progressive bone marrow failure. Although the exhaustion of the bone marrow leads to cytopenias in FA patients as they age, evidence from human FA and mouse model fetal livers suggests hematopoietic defects originate in utero which may lead to deficient seeding of the bone marrow. To address this possibility, we examined the consequences of loss of Fancd2, a central component of the FA pathway. Examination of E14.5 Fancd2 knockout (KO) fetal livers showed a decrease in total cellularity and specific declines in long-term and short-term hematopoietic stem cell (LT- and ST-HSC) numbers. Fancd2 KO fetal liver cells display similar functional defects to Fancd2 adult bone marrow cells including reduced colony forming units, increased mitomycin C sensitivity, increased LT-HSC apoptosis and heavily impaired competitive repopulation, implying these defects are intrinsic to the fetal liver and not dependent on the accumulation of DNA damage during aging. Telomere shortening, an aging-related mechanism proposed to contribute to HSC apoptosis and bone marrow failure in FA, was not observed in Fancd2 KO fetal livers. In summary, loss of Fancd2 yields significant defects to fetal liver hematopoiesis, particularly the HSC population, which mimic key phenotypes from adult Fancd2 KO bone marrow independent of aging-accrued DNA damage.