Ion solvation by channel carbonyls characterized by 17O solid-state NMR at 21 T

Recently available ultrahigh magnetic fields offer new opportunities for studies of quadrupole nuclei in biological solids because of the dramatic enhancement in sensitivity and resolution associated with the reduction of second-order quadrupole interactions. Here, we present a new approach for understanding the function and energetics of ion solvation in channels using solid-state 17O NMR spectroscopy of single-site 17O-labeled gramicidin A. The chemical shift and quadrupole coupling parameters obtained in powder samples of lyophilized material are similar to those shown in the literature for carbonyl oxygens. In lipid bilayers, it is found that the carbonyl 17O anisotropic chemical shift of Leu10, one of the three carbonyl oxygens contributing to the ion binding site in gramicidin A, is altered by 40 ppm when K+ ion binds to the channel, demonstrating a high sensitivity to such interactions. Moreover, considering the large breadth of the carbonyl 17O chemical shift (>500 ppm), the recording of anisotropic 17O chemical shifts in bilayers aligned with respect to magnetic field B0 offers high-quality structural restraints similar to 15N and 13C anisotropic chemical shifts.     

Helical water chains in aquapores of organic hexahost: remarkable halogen-substitution effect on the handedness of water helix

Water helices surrounding the nano-channels of trichlorophloroglucinol and tribromophloroglucinol have different handedness, PMPMPM and PPPMMM (P = right-handed, M = left-handed), depending on halogenhalogen interactions between the host molecules.     

A representation theorem for weak automorphisms of a universal algebra

Given a group G and a descending chainG ₀,G ₁,...,G _n, of normal subgroups ofG, we prove that there exists a universal algebra , such that the chain ...W_n( )...W₁( }) W₀( )W( ) is isomorphic to the chain ...G _n ...G ₁G ₀G, where W( ) is the group of weak automorphisms of , and W_n( ) is the group of weak automorphisms of that leaves alln-ary operations fixed.We also prove that there are an infinite number of non-isomorphic algebras that satisfy the above.These results are a generalization of those proved by J. Sichler, in the special case when G=G₀, and G₁=G₂=...=G_n=....Presented by J. Mycielski.This paper comprises part of the author's doctoral dissertation at the University of Notre Dame in 1983. The author wishes to express her deep gratitude to Professor Abraham Goetz for suggesting this problem, for being extremely generous with his time and experience, and for giving her his constant encouragement. The author also thanks the reviewer for his helpful comments.     

Thermochromism in nickel(II) complexes: thermal, solid state H NMR and single crystal X-ray analysis of bis-(N,N-dimethyl-1,2-ethanediamine) nickel(II) perchlorate

The complex bis-(N,N-dimethyl-1,2-ethanediamine) nickel(II) perchlorate undergoes a first-order thermochromic phase transition at ca. 476 K, changing its color from orange to red. The room temperature X-ray crystal structure determination showed that the nickel ion possesses a square-planar geometry with two five membered chelate rings, in the δλ conformation, forming the NiN₄ chromophore. The broad-line ¹H NMR indicates the onset of a dynamic disorder of diamine chelate rings at the phase transition temperature region, while T₁ measurement of ¹H affords the activation energy of the puckering metal chelate rings to be 26 kJ mol⁻¹. The electronic spectrum revealed that a weakening of ligand field around the nickel is associated with the phase transition.     

A method for the purification of bulk amount of thorium from its daughter products

A method has been developed to purify bulk amounts of natural thorium from its daughter products. The method is based on anion exchange separation of Th from Pb, Bi, Tl, Ra using Dowex 1 X 8 anion exchange resin conditioned to 2M HCl. The method has several advantages over other methods, namely the decontamination is quite high, Th separation is quantitative and it is suitable for the purification of bulk amounts of Th in a reasonably short time.     

Luminescence of Ce3+ in Y2SiO5 nanocrystals: Role of crystal structure and crystal size

Here, we report the role of crystal structure and crystal size on the photoluminescence properties of Ce3+ ions in Y2SiO5 nanocrystals. The emission at 430 nm (5d1 --> 4f1) and lifetime of the excited state of Ce3+ ion doped Y2SiO5 nanocrystals are found to be sensitive to the crystal structure, crystal size, and dopant concentration. It is found that the overall lifetime tau of 0.5 mol % Ce doped Y2SiO5 nanocrystals are 8.78 and 3.45 ns for 1000 and 1100 degrees C heat-treated samples with the same crystal structure (X1-Y2SiO5 phase), respectively. However, a significant increase in the overall lifetime (35.21 ns) is observed for the 1300 degrees C annealed 0.5 mol % Ce doped Y2SiO5 sample having a different crystal structure (X2-Y2SiO5 phase). We found that the decay kinetic is biexponential. It is explained that the fast component arises due to sequential hole-electron capture on the luminescent ions and the slow component arises from isolated ions. Our analysis suggests that modifications of radiative and nonraditive relaxation mechanisms are due to local symmetry structure of the host lattice and crystal size, respectively.     

4‐Amino derivatives of 7‐nitro‐2,1,3‐benzoxadiazole: the effect of the amino moiety on the structure of fluorophores

The crystal structures of three 4‐amino derivatives of 7‐nitro‐2,1,3‐benzoxa­diazole with increasing substituent ring size, viz. 7‐nitro‐4‐(pyrrolidin‐1‐yl)‐2,1,3‐benzoxa­diazole, C₁₀H₁₀N₄O₃, 7‐nitro‐4‐(piperidin‐1‐yl)‐2,1,3‐benzoxa­diazole, C₁₁H₁₂N₄O₃, and 4‐(azepan‐1‐yl)‐7‐nitro‐2,1,3‐benzoxa­diazole, C₁₂H₁₄N₄O₃, have been determined in order to understand their photophysical behaviour. All three were found to crystallize in centrosymmetric space groups. There is considerable electron delocalization compared with the parent compound, although the five‐membered oxa­diazole ring apparently does not participate in this. The length of the C—N bond between the amino N atom and the 7‐nitro­benzoxa­diazole system is found to be shorter than in similar compounds, as is the C—N_nitro bond. In each structure, the nitro group lies in the plane of the benzoxa­diazole unit.