The attachment of modulators to a trimeric porin ion channel was investigated (see picture of the trimer with a crown ether modulator (orange)). The interplay of modulator and protein is essential for the conformational heterogeneity of the hybrid channel. Single‐site attachment in large pores is not sufficient to change the electrophysiological characteristics of the pores—such change requires additional noncovalent interactions or second‐site attachments.
Chromation and ferration are the latest additions to the concept of alkali‐metal‐mediated metalation, as described by J. Klett, R. E. Mulvey, and co‐workers in their Communication on page 3317 ff. While the more electropositive sodium is essential for the reaction, it is the less electropositive chromium or iron that actually performs deprotonation of benzene. This novel reactivity can be likened to a game of chess in which the queen (Na) holds the king in check, while the knight (Cr, Fe) scores checkm(etal)ate.
To date, poly(vinyl chloride) (PVC) is the most used polymer in the design of ion selective electrode (ISE) membranes. This paper is focused on the use of sulfonated poly(ether ether ketone) (SPEEK) as an alternative material to PVC for the design of ISEs. SPEEK of the desired degree of sulfonation is synthesized from poly(ether ether ketone) (PEEK). An NH4+-ISE has been chosen as a model electrode to study the efficiency of SPEEK as polymer matrix of the membrane. The material was evaluated in ionophore free ion exchanger membranes as well as in ion-selective electrodes membranes containing nonactine as ionophore. Analytical performance parameters of the prepared electrodes were evaluated. The electrodes show a slope between 50 and 60 mV dec−1 depending on both the calibration medium and the membrane composition. A linear range of response between 10−4 and 1.0 M and a lifetime of 1-2 months were obtained. The interferences of cations such us Ca2+, Na+, Li+ and K+ over the prepared ISEs are studied as well. Although the plasticizer in the SPEEK based membrane matrix is not necessary, its presence improves the sensibility. This makes SPEEK a good potential choice over alternative membrane matrices reported in the literature and a promising platform for the establishment of membrane components. 相似文献
16-membered meta,para-cyclophanes mimicking the vancomycin binding pocket (D-O-E ring) were designed and synthesized. The structural key features of these biaryl ether containing macrocycles are (1) the presence of beta-amino-alpha-hydroxy acid or alpha,beta-diamino acid as the C-terminal component of the cyclopeptide and (2) the presence of a hydrophobic chain or lipidated aminoglucose at the appropriate position. Cycloetherification by an intramolecular nucleophilic aromatic substitution reaction (S(N)Ar) is used as the key step for the construction of the macrocycle. The atropselectivity of this ring-closure reaction is found to be sensitive to the peptide backbone and chemoselective cyclization (phenol versus primary amine) is achievable. Glycosylation of phenol was realized with freshly prepared 3,4,6-tri-O-acetyl-2-N-lauroyl-2-amino-2-deoxy-alpha-D-glucopyranosyl bromide under phase-transfer conditions. Minimum inhibitory concentrations for all of the derivatives are measured by using a standard microdilution assay, and potent bioactivities against both sensitive and resistant strains are found for some of these compounds (MIC (minimum inhibitory concentration) = 4 microg mL(-1) against VRE). From these preliminary SAR studies, it was anticipated that both the presence of a hydrophobic substituent and an appropriate structure of the macrocycle were required for this series of compounds to be active against VRE. 相似文献
The structure and aromaticity of a royal crown-shaped molecule Li(3)-N(3)-Be are studied at the CCSD(T)/aug-cc-pVDZ level. This molecule is a charge-separated system and can be denoted as Li(3) (2+)N(3) (3-)Be(+). It is found that the Li(3) (2+) ring exhibits aromaticity mainly because the Li(3) (2+) ring can share the pi-electron with the N(3) (-3) ring. The 4n+2 electron counter rule can be satisfied for the Li(3) (2+) subunit if the shared pi valence electron of N(3) (3-) subunit is also taken into account. This new knowledge on aromaticity of a ring from the interactions between subunits is revealed first time in this paper. Li(3)-N(3)-Be can be also regarded as a molecule containing two superatoms (Li(3) and N(3)), which may be named as a "superomolecule." Li(3)-N(3)-Be is a new metal-nonmetal-metal type sandwich complex. The N(3) (3-) trianion in the middle repulses the electron clouds of the two metal subunits (mainly to the Li(3) superatom) to generate an excess electron, and thus Li(3)-N(3)-Be is also an electride. This phenomenon of the repulsion results in: (a) the HOMO energy level increased, (b) the electron cloud in HOMO distended, (c) the area of the negative NICS value extended, and (d) the VIE value lowered. So the superomolecule Li(3)-N(3)-Be is not only a new metal-nonmetal-metal type sandwich complex but also a new type electride, which comes from the interaction between the alkali superatom (Li(3)) and the nonmetal superatom (N(3)). 相似文献