4,897 research outputs found
Synthesis and inclusion behavior of a heterotritopic receptor based on hexahomotrioxacalix[3]arene
A heterotritopic hexahomotrioxacalix[3]arene receptor with the capability of binding two alkali metals and a transition metal in a cooperative fashion was synthesized. The binding model was investigated by using ÂčH NMR titration experiments in CDClââCDâCN (10:1, v/v), and the results revealed that the transition metal was bound at the upper rim and the alkali metals at the lower and upper rims. Interestingly, the alkali metal ions Liâș and Naâș bind at the lower and upper rim respectively depending on the dimensions of the alkali metal ions versus the size of the cavities formed by the calix[3]arene derivative. The hexahomotrioxacalix[3]arene receptor acts as a heterotritopic receptor, binding with the transition metal ion Agâș and the alkali metals ions Liâș and Naâș. These findings were not applicable to other different sized alkali metals, such as Kâș and Csâș
A possible role of alkali metal ions in the synthesis of pure-silica molecular sieves
Pure-silica ZSM-12 is synthesized in the presence and absence of alkali metal ions; addition of alkali metal ions at constant hydroxide ion concentration increases the crystallization rate of ZSM-12, and it is suggested that alkali metal ions participate in both the nucleation and crystal growth processes
Prussian Blue-coated interdigitated array electrodes for possible analytical application
Thin films of iron(III) hexacyanoferrate(II) (Prussian Blue) were electrochemically deposited on interdigitated array (IDA) electrodes, yielding systems which can be considered as chemiresistors in sensing alkali metal ion concentrations in an adjacent electrolyte. This is due to the fact that the conductivity of the film being measured by a steady-state current on application of a voltage to the two-fingered electrodes of the IDA depends on both the redox stare of the film and the cation concentration in the electrolyte. From the dependence of the steady-state current on the electrode (bias) potential at variable cation concentrations for different alkali metal ions and for mixtures of alkali metal ions, the possibilities of analytical application were elucidated. In addition, by using the methods of staircase coulometry and scanning conductivity, the electron diffusion coefficient De was determined as a function of the redox state of Prussian Blue. It is concluded that Prussian Blue-coated IDA electrodes are, in principle, suitable as chemiresistors for the determination of alkali metal ion concentrations with increasing selectivity in the series Li < Na < K < Rb < Cs
Ăber einen energieunabhĂ€ngigen austausch der alkali-ionen Li+, Na+, K+, Rb+ und Cs+ GEGEN H+ in der membran intakter und desintegrierter rattenlebermitochondrien
Abstract1.1. The energy-independent exchange of alkali metal cations against protons was investigated in intact and disintegrated mitochondria. The exchange is not specific for different alkali metal ions.2.2. In intact mitochondria the apparent Km for the energy-independent exchange range from 5 to 25 mM (Cs+, Rb+, K+ 5â10 mM; Na+ 15 mM; Li+ 20 mM). At all ions studied the maximum release of protons was 15â20 nval/mg protein.3.3. In disintegrated mitochondria there are no differences between the alkali metal ions (apparent Km 30 mM; maximum H+-release 50 nval/mg protein).4.4. Directly accessible binding sites seem to exist in the outer membrane. Binding sites in the inner membrane are accessible only after disintegration, but not after addition of valinomycin + rotenone
Theory of Distinct Crystal Structures of Polymerized Fullerides AC60, A=K, Rb, Cs: the Specific Role of Alkalis
The polymer phases of AC60 form distinct crystal structures characterized by
the mutual orientations of the (C60-)n chains. We show that the direct electric
quadrupole interaction between chains always favors the orthorhombic structure
Pmnn with alternating chain orientations. However the specific quadrupolar
polarizability of the alkali metal ions leads to an indirect interchain
coupling which favors the monoclinic structure I2/m with equal chain
orientations. The competition between direct and indirect interactions explains
the structural difference between KC60 and RbC60, CsC60.Comment: 4 pages, 2 figures, 1 tabl
Affinity capillary electrophoretic study of K+/Na+ selectivity of hexaarylbenzene-based polyaromatic receptor
Affinity capillary electrophoretic (ACE) study has proved the selectivity of hexaarylbenzene-based polyaromatic receptor (R) for K+ ion over Na+ ion. The apparent binding constants of the R complexes with K+ and Na+ ions were determined from the dependence of effective electrophoretic mobility of R on the concentration of the above alkali metal ions in the background electrolyte using a non-linear regression analysis. The apparent binding constants (Kb) of the K-R+ and NaâR+ complexes in methanolic medium were evaluated as log Kb = 3.20 ± 0.22 for the KâR+ complex, and log Kbâ
â0.7 for the NaâR+ complex
Catalysis by alkali and alkaline-earth metal ions in nucleophilic attack of methoxide ion on crown ethers bearing an intra-annular acetoxy group
Rates of reaction of methoxide ion with crown ethers bearing an intra-annular acetoxy group are markedly enhanced by alkali and alkaline-earth metal bromides as a result of much stronger interactions of the metal ions with transition states than with reactants.\ud
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Rates of reactions of methoxide ion with crown ethers bearing an intra-annular acetoxy group markedly enhanced by alkali and alkaline-earth metal bromides as a result of much stronger interactions of the metal ion with transition state than with reactants
Photoemission of a doped Mott insulator: spectral weight transfer and qualitative Mott-Hubbard description
The spectral weight evolution of the low-dimensional Mott insulator TiOCl
upon alkali-metal dosing has been studied by photoelectron spectroscopy. We
observe a spectral weight transfer between the lower Hubbard band and an
additional peak upon electron-doping, in line with quantitative expectations in
the atomic limit for changing the number of singly and doubly occupied sites.
This observation is an unconditional hallmark of correlated bands and has not
been reported before. In contrast, the absence of a metallic quasiparticle peak
can be traced back to a simple one-particle effect.Comment: 4 pages, 4 figures, related theoretical work can be found in
arXiv:0905.1276; shortene
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