Various mixed liquid crystals containing crown ether‐cholesteryl liquid crystal, benzo‐15‐crown‐5‐COO‐C27H45 (B15C5‐COOCh), with various common cholesteric liquid crystals, e.g., cholesteryl chloride, cholesteryl benzoate and cholesteryl palmitate, were prepared and studied using polarizing microscopy and differential scanning calorimetry. Investigating the concentration effect of B15C5‐COOCh in mixed liquid crystals revealed that the addition of B15C5‐COOCh resulted in wider phase transition temperature ranges of these cholesteryl liquid crystals. The stability of these B15C5‐COOCh/cholesteryl mixed liquid crystals was studied using comprehensive graphic molecular modeling computer programs (Insight II and Discover) to calculate their molecular energy and stability energy. The effect of salts, e.g. Na+, Co3+, Y3+ and La3+, on the transition temperature range of the mixed liquid crystals was also investigated. The crown ether cholesteric liquid crystal B15C5‐COOCh was applied both as a surfactant and an ion transport carrier to transport metal ions through liquid membranes. Cholesteryl benzo‐15‐crown‐5 exhibited distinctive characteristics of a surfactant and the critical micellar concentration (CMC) of the surfactant was investigated by the pyrene fluorescence probe method. Cholesteryl benzo‐15‐crown‐5 was successfully applied as a good ion transport carrier (Ionophore) to transport various metal ions, e.g. Li+, Na+, La3+, Fe3+ and Co3+, through organic liquid membranes. The transport ability of the cholesteryl benzo‐15‐crown‐5 surfactant for these metal ions was in the order: Co3+ ≥ Li+ > Fe3+ > Na+ > La3+. 相似文献
5,5′‐Bistetrazole‐1,1′‐diolate‐based energetic salts from alkaline (Li+, K+, and Na+) and alkaline earth metal salts (Mg2+, Ca2+, and Ba2+) were synthesized in a simple, straightforward manner and were characterized by IR and NMR spectroscopy, and elemental analysis. Single‐crystal X‐ray diffraction of 4 salts (Li+, Na+, K+, and Mg2+) is given. The X‐ray structures show that in the title compounds, the metal atoms are bonded to the nitrogen and oxygen in the bistetrazole ring to form the sandwich structure. In addition, thermal stabilities of all title compounds were determined with differential thermal analysis‐thermal gravity analysis. All these new materials exhibit excellent thermal stabilities, high density, and excellent insensitivity to impact (h 50 > 60 cm). Especially, the potassium salt is of interest as potential “green heat‐resistance explosive” with high density and high thermal stability as well as low sensitivity. 相似文献
Organic structure‐directing agent (OSDA)‐free synthesis of zeolite beta is a subject of both scientific and industrial interest. Herein, we report a comprehensive investigation into the effects of various parameters on the seed‐assisted crystallization of zeolite beta in the absence of OSDA. The crystallization behavior of “OSDA‐free beta” is strongly governed by the chemical composition of the starting Na+‐aluminosilicate gel as well as by the Si/Al ratios of the calcined beta seed crystals, which are prepared using tetraethylammonium hydroxide (TEAOH). Furthermore, OSDA‐free beta seed crystals can be used to form zeolite beta, termed “green beta”. XRD, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, and 27Al magic angle spinning NMR analyses showed that the OSDA‐free beta and green beta were of high purity and crystallinity. The nitrogen adsorption–desorption of OSDA‐free beta and green beta revealed higher surface areas and larger volumes in the micropore region than those of the beta seeds synthesized with OSDA after calcination. These results provide a robust and reliable process for the environmentally friendly production of high‐quality zeolite beta in a completely OSDA‐free Na+‐aluminosilicate system. 相似文献
Novel dual molecular‐ and ion‐recognition responsive poly(N‐isopropylacrylamide‐co‐benzo‐12‐crown‐4‐acrylamide) (PNB12C4) linear copolymers with benzo‐12‐crown‐4 (B12C4) as both guest and host units are prepared. The copolymers exhibit highly selective sensitivities toward γ‐cyclodextrin (γ‐CD) and Na+. The presence of γ‐CD induces the lower critical solution temperature (LCST) of PNB12C4 copolymer to shift to a higher value due to the formation of 1:1 γ‐CD/B12C4 host‐guest inclusion complexes, while Na+ causes a negative shift in LCST due to the formation of 2:1 “sandwich” B12C4/Na+ host‐guest complexes. Regardless of the complexation order, when γ‐CD and Na+ coexist with PNB12C4, competitive complexation actions of B12C4 as both guest and host units toward γ‐CD and Na+ finally form equilibrium 2:2:1 γ‐CD/B12C4/Na+ composite complexes, and the final LCST values of PNB12C4 copolymer reach almost the same level. The results provide valuable guidance for designing and applying PNB12C4‐based smart materials in various applications.
A single urea or amide functionality in a dumbbell‐shaped guest can be “clipped” by a macrocycle generated from a diamine and a dialdehyde through the templating effect of a Na+ ion (see scheme). The resulting imine‐containing rotaxanes can then be reduced to allow isolation of stable amine‐based rotaxanes. 相似文献
The successful deployment of advanced energy‐conversion systems depends critically on our understanding of the fundamental interactions of the key adsorbed intermediates (hydrogen *H and hydroxyl *OH) at electrified metal–aqueous electrolyte interfaces. The effect of alkali metal cations (Li+, Na+, K+, Cs+) on the non‐Nernstian pH shift of the step‐related voltammetric peak of the Pt(553) electrode is investigated over a wide pH window (1 to 13) by means of experimental and computational methods. The co‐adsorbed alkali cations along the step weaken the OH adsorption at the step sites, causing a positive shift of the potential of the step‐related peak on Pt(553). Density functional calculations explain the observations on the identity and concentration of alkali cations on the non‐Nernstian pH shift, and demonstrate that cation–hydroxyl co‐adsorption causes the apparent pH dependence of “hydrogen” adsorption in the step sites of platinum electrodes. 相似文献
We apply our previously developed deconvolution method and interpretation to analyze changes in the OH stretching band [ν(OH) band] of low‐concentration (≤0.2 m) aqueous solutions of NaCl and KCl. We treat these simple, monovalent ions as defects in the hydrogen‐bond network of pure water and quantify the changes in the spectra at low defect concentration with an “order parameter”. Order‐parameter analysis of difference spectra of the two solutions leads to hydration numbers of 7.0±1.0 and 5.9±0.3 for K+ and Na+, respectively. Additionally, we find that changes in the ν(OH) band due to low concentrations of ions result from changes in the topology of the hydrogen‐bond network. 相似文献
Heteroditopic hexahomotrioxacalix[3]arene receptors that are capable of binding an anion and a cation simultaneously in a cooperative fashion were synthesized. The structure of one of the triamide derivatives was confirmed by single‐crystal X‐ray diffraction. The binding of alkali metals at the lower rim, and the binding of anions (chloride, bromide) at the upper rim, has been investigated by using 1H NMR titration experiments. Alkali metal binding at the lower rim controls the calix cavity. Li+‐ion binding to the lower rim can improve the binding ability of anions at the upper rim amide moiety by a factor of 15, thus suggesting a strong positive allosteric effect for anion recognition. However, when a Na+ cation is bound to the ionophoric site on the lower rim, the calix cavity is changed from a “flattened cone” to a more‐upright form, which is favored for intramolecular hydrogen bonding between the neighboring NH and C?O groups; this change can block the inclusion of anions onto the amide moiety at the upper rim, which strongly suggests a negative allosteric effect of Na+‐ion binding, which controls the cooperative recognition system. 相似文献
The forces between two molecularly smooth mica surfaces were measured over a range of concentrations in aqueous Li+, Na+, K+ and Cs+ chloride solutions. Deviations from DLVO forces in the form of additional short-range repulsive “Hydration” forces were observed only above some critical bulk concentration, which was different for each electrolyte. These observations are interpreted in terms of the corresponding ion exchange properties at the mica surface. “hydration” forces apparently arise when hydrated cations adsorbed on mica are prevented from desorbing as two interacting surfaces approach. dehydration of the cations leads to a repulsive hydration force. A simple site-binding model was successfully applied to describe the charging behavior of interacting mica surfaces . By subtraction of the DLVO-regulation theory from the total measured force the net hydration force was obtained for mica surfaces apparently fully covered with adsorbed cations. The magnitude of this extra force followed the series Na+ > Li+ > K+ > Cs+ and, in each case, could be described by a double-exponential decay. 相似文献
Two biscatecholester ligands with oligoether spacers were used to prepare dinuclear titanium(IV) triscatecholate based helicates. In the case of Li4[( 1 / 2 )3Ti2], “classical” helicates with three internally bound Li+ ions and syn‐oriented ligands in the complex units (fac/fac isomer) were obtained. In the case of the sodium salt Na4[( 2 )3Ti2], a different homochiral dinuclear triple‐stranded helicate with two internally bound Na+ ions was formed. The complex units are anti‐configured, and two of the ligand spacers are connecting internal with external positions of the helicate (mer/mer isomer). Removal of the sodium ions and addition of lithium ions leads to the switching from one topology to the other with an expanded helicate [( 2 )3Ti2]4? as an intermediate. Switching back to the “non‐classical” helicate cannot be observed because severe structural rearrangements would be required. 相似文献
The crystal engineering of coordination polymers has aroused interest due to their structural versatility, unique properties and applications in different areas of science. The selection of appropriate ligands as building blocks is critical in order to afford a range of topologies. Alkali metal cations are known for their mainly ionic chemistry in aqueous media. Their coordination number varies depending on the size of the binding partners, and on the electrostatic interaction between the ligands and the metal ions. The two‐dimensional coordination polymer poly[tetra‐μ‐aqua‐[μ4‐4,4′‐(diazenediyl)bis(5‐oxo‐1H‐1,2,4‐triazolido)]disodium(I)], [Na2(C4H2N8O2)(H2O)4]n, (I), was synthesized from 4‐amino‐1H‐1,2,4‐triazol‐5(4H)‐one (ATO) and its single‐crystal structure determined. The mid‐point of the imino N=N bond of the 4,4′‐(diazenediyl)bis(5‐oxo‐1H‐1,2,4‐triazolide) (ZTO2−) ligand is located on an inversion centre. The asymmetric unit consists of one Na+ cation, half a bridging ZTO2− ligand and two bridging water ligands. Each Na+ cation is coordinated in a trigonal antiprismatic fashion by six O atoms, i.e. two from two ZTO2− ligands and the remaining four from bridging water ligands. The Na+ cation is located near a glide plane, thus the two bridging O atoms from the two coordinating ZTO2− ligands are on adjacent apices of the trigonal antiprism, rather than being in an anti configuration. All water and ZTO2− ligands act as bridging ligands between metal centres. Each Na+ metal centre is bridged to a neigbouring Na+ cation by two water molecules to give a one‐dimensional [Na(H2O)2]n chain. The organic ZTO2− ligand, an O atom of which also bridges the same pair of Na+ cations, then crosslinks these [Na(H2O)2]n chains to form two‐dimensional sheets. The two‐dimensional sheets are further connected by intermolecular hydrogen bonds, giving rise to a stabile hydrogen‐bonded network. 相似文献
The dynamic potential response of an 18‐crown‐6 based ion‐selective electrode towards Li+, Na+, K+ and Ca2+, in a flow‐injection system is studied. Different double nonmonotonic transient signals are obtained for the different ions. The influence of the flow‐injection variables and of ion concentration on the signals is studied. Two signal parameters, the relative return rates, are found to be characteristic for each ion and are constant for a concentration range of 1–3 decades. The nonmomotonic transient signals obtained are explained by reference to the theoretical models reported. 相似文献
The hydration, state, and mobility of protons and Li+, Na+, and Cs+ ions in MF-4SK perfluorinated sulfonic acid cation-exchange membranes doped with silicon dioxide and phosphotungstic acid
have been investigated by NMR and impedance spectroscopy. The dopants increase the moisture content of the membrane and change
the system of pores and channels in which ion transport takes place. At low humidities, the dopant particles are involved
in ion transport. The greatest effect is observed for the membranes doped with both SiO2 and phosphotungstic acid. The water molecules sorbed by dopant particles as a material participate in the hydration of alkali
metal cations in the membrane. 相似文献
Molecular recognition of small molecules and ions by artificial receptors in microheterogeneous media such as micelles and vesicles can, in principle, provide better models of biological systems in comparison with bulk solutions. In this work we have investigated the complexation of an organic fluorescent probe with amphiphilic calixarene receptor below and above the critical micelle concentration (CMC). For concentrations below the CMC, the probe forms a host–guest complex with the calixarene behaving like a traditional host–guest system operating in bulk solution. Above the CMC, multiple equilibrium processes are established and the probe can exchange between the recognition site of the calixarene in the monomeric state, micellized state and/or the micellar hydrophobic core. Careful analysis of the results obtained from NMR spectroscopy and fluorescence experiments allowed us to propose a quantitative model to describe the system. The increment of the local concentration of Na+ counterions at the Stern layer displace the dye to the micelle core through competitive binding of Na+ in the cavity of the receptor and is decisive for the observed self‐sorting behavior. 相似文献
Molecular evolution, with self‐organization of simple molecules towards complex functional systems, provides a new strategy for biomimetic architectonics and perspectives for understanding the complex processes of life. However, there remain many challenges to fabrication of systems comprising different types of units, which interact with one another to perform desired functions. Challenges arise from a lack of stability, dynamic properties, and functionalities that reconcile with a given environment. A co‐assembling fiber system composed of simple peptide and porphyrin is presented. This material is considered a prebiotic assembly of molecules that can be rather stable and flexibly self‐functionalized with the assistance of visible light in a “prebiotic soup”; acidic (pH 2), hot (70 °C), and mineral‐containing (Na+, Ti4+, Pt2+, and so forth) water. The co‐assembled peptide–porphyrin fiber, with self‐mineralized reaction centers, may serve as a primitive photobacteria‐like cellular model to achieve light harvesting, energy transfer, and ultimately sustainable hydrogen evolution. 相似文献