Formation of Giant and Small Cyclic Complexes from a Flexible Tripeptide Ligand Controlled by Metal Coordination and Hydrogen Bonds.

Formation of giant cyclic complexes by the assembly of small, flexible units is demonstrated by connecting 14 artificial tripeptides (1) with 14 Ni(II) ions. Although tripeptide 1 is very flexible because of the presence of three CH2 groups in the main chain, it formed a tetradecanuclear cyclic complex ([114Ni14]28+) with a large cavity (diameter: ca. 2 nm). In this structure, three tripeptides are coordinated to each Ni(II) center by three different coordination sites in 1, forming a mesh-like structure. Crystal structure analysis and theoretical calculations indicate that the conformation of 1 was controlled by the formation of metal coordination bonds and intramolecular hydrogen bonds. Because of the structural flexibility, the cyclic framework formed both circular and ellipsoidal structures in the crystalline state, depending on the packing structure. In addition, by the conditions of the assembly process, the size of the cavities could be tuned either with a small decrement (dodecanuclear complex [112Ni12]24+) or a large decrement (octanuclear complexes [(1-3H+)4Ni8]4+), in which "shrunk" cavities with a 10-fold difference in diameter (<0.2 nm) were formed by tuning the tripeptide conformation through additional metal coordination to the tripeptide framework. Dynamic light scattering and mass spectrometry studies indicated that the giant cyclic complexes were also present in the solution state.

Humidity-Responsive ON/OFF Switching of Gas Inclusion by Using Cooperative Opening/Closing of Heterogeneous Crystalline Cavities in a Peptide NiII Macrocycle.

Humidity-responsive ON/OFF switching of CO2 inclusion, associated with cooperative structural changes of heterogeneous cavities in crystalline peptide NiII macrocycles, 1⋅NO3 , is demonstrated. The structural transformation between an "open form" and a "closed form" was caused by reversible water uptake into one of the cavities. The adsorption behavior of CO2 was studied with and without water vapor, combined with gas-composition analysis by using gas chromatography. The studies revealed that the open form of 1⋅NO3 adsorbs CO2 gas up to 34 g mol-1 , whereas the closed form adsorbs only a negligible amount of CO2 gas. Also, structural studies (X-ray and IR spectroscopies) and investigation of water-content dependence of CO2 adsorption revealed that the switching of gas inclusion occurred abruptly over a narrow range of water-vapor pressure and was caused by the cooperative opening of vacant space to give the open form due to the structural transformation by water uptake.

Effect of dietary fatty acid and micronutrient intake/energy ratio on serum diamine oxidase activity in healthy women.

OBJECTIVE: Serum diamine oxidase (DAO) activity varies to a greater extent in women than in men. DAO activity during the luteal phase was higher than that during the follicular phase in healthy women. Recent reports have indicated that duodenal lipid infusion increased DAO activity in the intestinal lymph in rats. The aim of this study was to elucidate the effect of dietary nutrient intake on serum DAO activity in healthy women. METHODS: Thirty-four healthy Japanese women were recruited. Food surveys were performed using dietary records for 3 d during both the follicular and luteal phases. Nutrient intake was calculated and expressed as the energy intake ratio. The correlation between DAO activity and nutrient intake was analyzed. RESULTS: Serum DAO activity in both phases was positively correlated with intake of long-chain fatty acids, saturated fatty acids, and monounsaturated fatty acids (P < 0.05). Intake of phosphorus, calcium, zinc, magnesium, iron, and vitamin B12 during the luteal phase was positively correlated with serum DAO activity (P < 0.05). CONCLUSION: In healthy women, serum DAO activity was influenced by dietary fatty acid and micronutrient intake.