Na^+/CaO催化剂上的甲烷氧化偶联

研究了不同碱金属离子对CaO的促进作用,发现以Na~+的添加效果最好。在此基础上,研究了不同含钠化合物对CaO的促进作用,并用脉冲反应技术研究Na~+/CaO催化剂表面氧物种的特性及其作用。CaO表面上存在非选择性氧化的氧物种。Na~+对CaO的修饰作用是抑制非选择性氧化。当表面上的非选择性氧化的氧物种消耗后,体相的晶格氧会向表面迁移,以补充消耗掉的表面氧物种。消耗掉的表面氧物种也可由气相氧补充。CH_4脉冲和混合气脉冲说明仅靠[Na~+O~-]中心不足以使甲烷转化成C_2产物,必须有气相氧的参与才能使甲烷转化成C_2产物。     

Poly(ethylene glycol) doubly and singly cationized by different alkali metal ions: Relative cation affinities and cation-dependent resolution in a quadrupole ion trap mass spectrometer

Structural information of gas phase complexes of poly(ethylene glycol) (PEG) cationized by one or two different alkali metal ions is inferred from MS and MS/MS experiments performed with an electrospray quadrupole ion trap mass spectrometer. The rationale for selecting PEG was that its sites for cation binding are non-selective with respect to the repeating monomeric unit of the polymer, but there is selectivity with respect to the formation of an inner coordination sphere specific to each metal ion. The dissociation of [M1+ M2+ (EO23)], where EO23 = linear polymer of ethylene oxide, 23 units in length, resulted in loss of one of the alkali metal ions, with preference for loss of the larger cation, with no fragmentation of the PEG backbone for Na, K, Rb, and Cs. Li was not examined in this portion of the study. The selectivity for loss of the larger alkali metal ion was [Na+ K+ (EO23)] to [Na+ (EO23)] + K+ at 100%; [K+ Rb+ (EO23)] to [K+ (EO23)] + Rb+ at 93%; and [Rb+ Cs+ (EO23)] to [Rb+ (Eo23)] + Cs+ at 99%. The resolution of [M+ (EOx)] for x = 20-30 was dependent on the alkali metal ion, with the highest resolution observed for Cs+ and the lowest for Na+. These results are discussed with respect to the packing of the oxygen atoms on PEG (M.W.(avg) = 1000) around an alkali metal ion of different radius, and how this packing leads to an ensemble of unique structures, and therefore mobilities for [M+ (EOx)].     

The special five-membered ring of proline: An experimental and theoretical investigation of alkali metal cation interactions with proline and its four- and six-membered ring analogues

The interaction of the alkali metal cations, Li+, Na+, and K+, with the amino acid proline (Pro) and its four- and six-membered ring analogues, azetidine-2-carboxylic acid (Aze) and pipecolic acid (Pip), are examined in detail. Experimentally, threshold collision-induced dissociation of the M+(L) complexes, where M = Li, Na, and K and L = Pro, Aze, and Pip, with Xe are studied using a guided ion beam tandem mass spectrometer. From analysis of the kinetic energy dependent cross sections, M(+)-L bond dissociation energies are measured. These analyses account for unimolecular decay rates, internal energy of reactant ions, and multiple ion-molecule collisions. Ab initio calculations for a number of geometric conformations of the M+(L) complexes were determined at the B3LYP/6-311G(d,p) level with single-point energies calculated at MP2(full), B3LYP, and B3P86 levels using a 6-311+G(2d,2p) basis set. Theoretical bond energies show good agreement with the experimental bond energies, which establishes that the zwitterionic form of the alkali metal cation/amino acid, the lowest energy conformation, is formed in all cases. Despite the increased conformational mobility in the Pip systems, the Li+, Na+, and K+ complexes of Pro show higher binding energies. A meticulous examination of the zwitterionic structures of these complexes provides an explanation for the stability of the five-membered ring complexes.     

Non-covalent interactions of alkali metal cations with singly charged tryptic peptides

The complexes formed by alkali metal cations (Cat(+) = Li(+), Na(+), K(+), Rb(+)) and singly charged tryptic peptides were investigated by combining results from the low-energy collision-induced dissociation (CID) and ion mobility experiments with molecular dynamics and density functional theory calculations. The structure and reactivity of [M + H + Cat](2+) tryptic peptides is greatly influenced by charge repulsion as well as the ability of the peptide to solvate charge points. Charge separation between fragment ions occurs upon dissociation, i.e. b ions tend to be alkali metal cationised while y ions are protonated, suggesting the location of the cation towards the peptide N-terminus. The low-energy dissociation channels were found to be strongly dependant on the cation size. Complexes containing smaller cations (Li(+) or Na(+)) dissociate predominantly by sequence-specific cleavages, whereas the main process for complexes containing larger cations (Rb(+)) is cation expulsion and formation of [M + H](+). The obtained structural data might suggest a relationship between the peptide primary structure and the nature of the cation coordination shell. Peptides with a significant number of side chain carbonyl oxygens provide good charge solvation without the need for involving peptide bond carbonyl groups and thus forming a tight globular structure. However, due to the lack of the conformational flexibility which would allow effective solvation of both charges (the cation and the proton) peptides with seven or less amino acids are unable to form sufficiently abundant [M + H + Cat](2+) ion. Finally, the fact that [M + H + Cat](2+) peptides dissociate similarly as [M + H](+) (via sequence-specific cleavages, however, with the additional formation of alkali metal cationised b ions) offers a way for generating the low-energy CID spectra of 'singly charged' tryptic peptides.     

A joint experimental and theoretical study of cation-pi interactions: multiple-decker sandwich complexes of ferrocene with alkali metal ions (Li+, Na+, K+, Rb+, Cs+)

A systematic study of cation-pi interactions between alkali metal ions and the cyclopentadienyl ring of ferrocene is presented. The alkali metal (Li+, Na+, K+, Rb+, Cs+) salts of the ditopic mono(pyrazol-1-yl)borate ligand [1,1'-fc(BMe2pz)2]2- crystallize from dimethoxyethane as multiple-decker sandwich complexes with the M+ ions bound to the pi faces of the ferrocene cyclopentadienyl rings in an eta5 manner (fc = (C5H4)2Fe; pz = pyrazolyl). X-ray crystallography of the lithium complex reveals discrete trimetallic entities with each lithium ion being coordinated by only one cyclopentadienyl ring. The sodium salt forms polyanionic zigzag chains where each Na+ ion bridges the cyclopentadienyl rings of two ferrocene moieties. Linear columns [-CpR-Fe-CpR-M+-CpR-Fe-CpR-M+-](infinity) (R = [-BMe2pz]-) are established by the K+, Rb+, and Cs+ derivatives in the solid state. According to DFT calculations, the binding enthalpies of M+-eta5(ferrocene) model complexes are about 20% higher as compared to the corresponding M+-eta6(benzene) aggregates when M+ = Li+ or Na+. For K+ and Rb+, the degree of cation-pi interaction with both aromatics is about the same. The binding sequence along the M+-eta5(ferrocene) series follows a classical electrostatic trend with the smaller ions being more tightly bound.     

Nickel hexacyanoferrate membrane as a coated wire cation-selective electrode

Nickel hexacyanoferrates containing alkali metal cations as counter ions were used to prepare ion-selective electrodes for potentiometric sensing of intercalated species in the coated wire electrode (CWE) configuration. All the electrodes developed display a quasi-Nernstian response towards potassium ion, whereas the highest sensitivity is generally achieved when Cs+ is the counter cation in the sensing material. The selectivity constants of the electrodes were calculated by the matched potential method considering K+ as the primary ion. The selectivity order is Cs+ > K+ > Na+ > Li+ and reflects the effective dimension of the hydrated cations.     

Determination of stability constants of valinomycin complexes with ammonium and alkali metal ions by capillary affinity electrophoresis

Capillary affinity electrophoresis (CAE) has been employed to investigate quantitatively the interactions of valinomycin, macrocyclic depsipeptide antibiotic ionophore, with univalent cations, ammonium and alkali metal ions, K(+), Cs(+), Na(+), and Li(+), in methanol. The study involved measuring the change in effective electrophoretic mobility of valinomycin while the cation concentrations in the BGE were increased. The corresponding apparent stability (binding) constants of the valinomycin-univalent cation complexes were obtained from the dependence of valinomycin effective mobility on the cation concentration in BGE using a nonlinear regression analysis. The calculated apparent stability constants of the above-mentioned complexes show the substantially higher selectivity of valinomycin for K(+) and Cs(+) ions over Li(+), Na(+), and NH(4)(+) ions. CAE proved to be a suitable method for the investigation of both weak and strong interactions of valinomycin with small ions.     

Artificial ion channel formed by cucurbit[n]uril derivatives with a carbonyl group fringed portal reminiscent of the selectivity filter of K+ channels

Novel artificial ion channels (1 and 2) based on CB[n] (n = 6 and 5, respectively) synthetic receptors with carbonyl-fringed portals (diameter 3.9 and 2.4 A, respectively) can transport proton and alkali metal ions across a lipid membrane with ion selectivity. Fluorometric experiments using large unilamellar vesicles showed that 1 mediates proton transport across the membranes, which can be blocked by a neurotransmitter, acetylcholine, reminiscent of the blocking of the K+ channels by polyamines. The alkali metal ion transport activity of 1 follows the order of Li+ > Cs+ approximately Rb+ > K+ > Na+, which is opposite to the binding affinity of CB[6] toward alkali metal ions. On the other hand, the transport activity of 2 follows the order of Li+ > Na+, which is also opposite to the binding affinity of 2 toward these metal ions, but virtually no transport was observed for K+, Rb+, and Cs+. It is presumably because the carbonyl-fringed portal size of 2 (diameter 2.4 A) is smaller than the diameters of these alkali metal ions. To determine the transport mechanism, voltage-clamp experiments on planar bilayer lipid membranes were carried out. The experiments showed that a single-channel current of 1 for Cs+ transport is approximately 5 pA, which corresponds to an ion flux of approximately 3 x 107 ions/s. These results are consistent with an ion channel mechanism. Not only the structural resemblance to the selectivity filter of K+ channels but also the remarkable ion selectivity makes this model system unique.     

偏钛酸型锂离子交换剂表面性质与选择吸附性研究

本文采用Li渗入于TiO2经高温热力学重结晶制备偏钛酸型锂离子交换剂,其对碱金属、碱土金属溶液中的Li+ 具有特殊选择吸附性,其次序为Li+>Mg2+>Ca2+>Na+,K+。对交换剂表面性质以及Li+ 在固-液界面的选择吸附特性进行了研究。通过对某气田卤水提锂实验表明:该交换剂对低Li+ 含量卤水中Li+ 的选择性吸附效果显著,对Mg2+、Ca2+、Na+、K+ 的分离效果好,Li+ 的富集倍数达9倍,并具有较好的循环稳定性。     

Ion selectivity of crown ethers investigated by UV and IR spectroscopy in a cold ion trap

Electronic and vibrational spectra of benzo-15-crown-5 (B15C5) and benzo-18-crown-6 (B18C6) complexes with alkali metal ions, M(+)?B15C5 and M(+)?B18C6 (M = Li, Na, K, Rb, and Cs), are measured using UV photodissociation (UVPD) and IR-UV double resonance spectroscopy in a cold, 22-pole ion trap. We determine the structure of conformers with the aid of density functional theory calculations. In the Na(+)?B15C5 and K(+)?B18C6 complexes, the crown ethers open the most and hold the metal ions at the center of the ether ring, demonstrating an optimum matching in size between the cavity of the crown ethers and the metal ions. For smaller ions, the crown ethers deform the ether ring to decrease the distance and increase the interaction between the metal ions and oxygen atoms; the metal ions are completely surrounded by the ether ring. In the case of larger ions, the metal ions are too large to enter the crown cavity and are positioned on it, leaving one of its sides open for further solvation. Thermochemistry data calculated on the basis of the stable conformers of the complexes suggest that the ion selectivity of crown ethers is controlled primarily by the enthalpy change for the complex formation in solution, which depends strongly on the complex structure.     

碱金属离子对甘氨酸五肽气相解离过程的影响

为了获得更多的多肽结构信息,采用结构简单的甘氨酸五肽(简写为GGGGG或G5)作为模型,研究了碱金属离子(Li+、Na+、K+、Rb+)对甘氨酸五肽GGGGG气相解离过程的影响.将一定化学计量比的甘氨酸五肽分别和四种碱金属盐溶液混合后,静置10h,使反应达到平衡.电喷雾质谱结果表明,四种碱金属离子均可以在溶液中与甘氨酸五肽形成非共价复合物,其中主要组分为碱金属离子与G5配合比为1:1和2:1的非共价复合物.质谱碰撞诱导解离(CID)时的碰撞能量为25eV.气相碰撞诱导解离实验结果表明,在配合比为1:1的复合物中,其碎片化程度按照Li+、Na+、K+、Rb+的次序依次减小,Rb+的复合物碎裂过程中生成了不常见的c、z离子;在配合比为2:1的复合物中,其碎片化程度按照Li+、Na+、K+、Rb+的次序依次增大.与1:1的非共价复合物相比,Na+、K+、Rb+的2:1复合物的气相解离显得更加容易.除Li+外,两个碱金属离子对G5的活化能力明显较单个碱金属离子强,它们可以诱导多肽在更多位点断裂,生成更多类型的碎片离子.     

Structures and energetics of the cation-pi interactions of Li+, Na+, and K+ with cup-shaped molecules: effect of ring addition to benzene and cavity selectivity

The interactions of alkali metal cations (Li (+), Na (+), and K (+)) with the cup-shaped molecules, tris(bicyclo[2.2.1]hepteno)benzene and tris(7-azabicyclo[2.2.1]hepteno)benzene have been investigated using MP2(FULL)/6-311+G(d,p)//MP2/6-31G(d) level of theory. The geometries and interaction energies obtained for the metal ion complexation with the cup-shaped systems trindene and benzotripyrrole are compared with the results for benzene-metal ion complexes to examine the effect of ring addition to the benzene on structural and binding affinities. The cup-shaped molecules exhibit two faces or cavities (top and bottom). Except for one of the conformers of tris(7-azabicyclo[2.2.1]hepteno)benzene), the metal ions prefer to bind with the top face over bottom face of the cup-shaped molecules. The selectivity of the top face is due to strong interaction of the cation with the pi cloud not only from the central six-membered ring but also from the pi electrons of rim C=C bonds. In contrast, the metal ions under study exhibit preference to bind with the bottom face rather than top face of tris(7-azabicyclo[2.2.1]hepteno)benzene) when the lone pair of electrons of three nitrogen atoms participates in binding with metal ions. This bottom face selectivity could be ascribed to the combined effect of the cation-pi and strong cation-lone pair interactions. As evidenced from the values of pyramidalization angles, the host molecule becomes deeper bowl when the lone pair of electrons of nitrogen atoms participates in binding with cation. Molecular electrostatic potential surfaces nicely explain the cavity selectivity in the cup-shaped systems and the variation of interaction energies for different ligands. Vibrational frequency analysis is useful in characterizing different metal ion complexes and to distinguish top and bottom face complexes of metal ions with the cup-shaped molecules.     

碱金属离子改性对纳米HZSM-5沸石丁烯裂解催化性能的影响

利用NH3-TPD表征和小型固定床反应评价研究了不同碱金属离子浸渍改性对纳米HZSM-5沸石的酸度及混合碳四液化气中丁烯催化裂解性能的影响。结果表明,尽管锂、钠、钾改性在达到最佳乙烯和丙烯选择性时对应的负载量不同,但其最佳乙烯和丙烯选择性为50％～60％。碱金属离子改性催化剂在连续运转过程中其催化活性缓慢下降,但乙烯和...     

Self-assembled organometallic [12]metallacrown-3 complexes

The reaction of [(arene)RuCl2]2 (arene = C6H6, cymene, C6H3Et3, or C6Me6) or [Cp*RhCl2]2 with 3-hydroxy-2-pyridone in the presence of Cs2CO3 gives trinuclear metallamacrocyclic complexes. The self-assembly process was shown to be completely diastereoselective, and a racemic mixture of complexes with M(R)M(R)M(R) or MsMsMs (M=Ru, Rh) configuration was obtained. Plausible mononuclear intermediates of the formula [(arene)RuCl(C5H4NO2)] (arene = cymene, C6Me6) have been isolated and characterized. A structurally related trimer was synthesized by using [(cymene)RuCl2]2 and 3-acetamido-2-pyridone instead of 3-hydroxy-2-pyridone. The macrocycles were shown to be highly potent ionophores for Na+ and/or Li+ with negligible affinities for the larger cation K+. The selectivities of the receptors depend on the pi-ligand present: whereas the (C6H6)Ru- and (cymene)Ru complexes bind both Li+ and Na+, the (C6Me6)Ru-, (C6H3Et3)Ru-, and Cp*Rh complexes bind exclusively Li+. For all receptors, the presence of alkali metal ions can be detected electrochemically: the peak potential is shifted by > 300 mV toward anionic potential upon binding. This behavior was utilized to detect Li+ and Na+ colorimetrically. Single crystal X-ray analyses have been carried out on eight complexes, four of which are bound to an alkali metal halide ion pair. Structural parameters, which affect the affinity and selectivity are discussed. A computational study on [[MX][12]crown-3] complexes (M =Li, Na; X=Cl, Br, I) was performed in order to compare relevant bond lengths and angles of the energy-minimized structures with those of the organometallic receptors.     

Formation of metal complex ions from amino acid in the presence of Li+, Na+ and K+ by electrospray ionization: metal replacement of hydrogen in the ligands

Alkali metal cations easily form complexes with proteins in biological systems; understanding amino acid clusters with these cations can provide useful insight into their behaviors at the molecular level including diagnosis and therapy of related diseases. For the purpose of characterization of basic interaction between amino acids and alkali metal, each of the 20 naturally occurring amino acids were ionized in the presence of lithium, sodium and potassium cations by electrospray ionization, and the resulting product ions were analyzed. We focus our attention on the gas phase alkali metal ion-proton exchanged complexes in current study, specifically complexes with serine, threonine, asparagine and glutamine, which share characteristic pattern unlike other amino acids. All amino acids generated [M + H](+) and [M + Na](+) ions, where M stands for the neutral amino acid. Serine, threonine, asparagine and glutamine generated cluster ions of [nM - nH + (n + 1)Na](+) and [nM - (n - 1)H + (n - 1)Na + K](+) , where n = 1-7. While the (M - H + Li) and (M - H + K) species were not observed, the neutral (M - H + Na) species formed by proton-sodium cation exchange had a highly stable cyclic structure with ketone and amine ligand sites, suggesting that (M - H + Na) serves as a building block in cluster ion formation. Cluster ion intensity distributions of [nM - nH + (n + 1)Na](+) and [nM - (n - 1)H + (n - 1)Na + K](+) showed a magic number at n = 3 and 4, respectively. Extensive B3LYP-DFT quantum mechanical calculations were carried out to elucidate the geometry and energy of the cluster ions, and they provided a reasonable explanation for the stability and structure of the cluster ions.     

Dissociation of alkaliated alanine in the gas phase: the role of the metal cation

The dissociation of prototypical metal-cationized amino acid complexes, namely, alkaliated alanine ([Ala+M]+, M+ = Li+, Na+, K+), was studied by energy-resolved tandem mass spectrometry with an ion-trap mass analyzer and by density functional theory. Dissociation leads to formation of fragment ions arising from the loss of small neutrals, such as H2O, CO, NH3, (CO+NH3), and the formation of Na+/K+. The order of appearance threshold voltages for different dissociation pathways determined experimentally is consistent with the order of critical energies (energy barriers) obtained theoretically, and this provides the necessary confidence in both experimental and theoretical results. Although not explicitly involved in the reaction, the alkali metal cation plays novel and important roles in the dissociation of alkaliated alanine. The metal cation not only catalyzes the dissociation (via the formation of loosely bound ion-molecule complexes and by stabilizing the more polar intermediates and transition structures), but also affects the dissociation mechanisms, as the cation can alter the shape of the potential energy surfaces. This compression/expansion of the potential energy surface as a function of the alkali metal cation is discussed in detail, and how this affects the competitive loss of H2O versus CO/(CO+NH3) from [Ala+M]+ is illustrated. The present study provides new insights into the origin of the competition between various dissociation channels of alkaliated amino acid complexes.     

Solvent Extraction of Alkali Metal Picrates by Lipophilic Cyclodextrin Derivatives

Lipophilic cyclodextrin (CD) derivatives were prepared to extract alkali metal cations from a water phase into an organic phase. The extraction equilibrium constant, K ex, was determined by the solvent extraction method using UV absorption spectroscopy. Hydroxyl groups at the carbons in the 2,6-positions of CD molecules were dipropylated to add the hydrophobicity for dissolving into organic solvents, and furthermore hydroxyl groups at the carbons in the 3-position of these derivatives were acylated as complexing sites with the alkali metal cations. These CD derivatives formed a 1 : 1 complex with alkali metal cations, except for the case of Li+, and transported the alkali metal cations from a water phase into a benzene phase. The initial concentrations of alkali metal cation and picrate anion in the water phase and that of the CD derivatives in the organic phase strongly influenced the extraction equilibrium. Extraction of the alkali metal cation by the derivative without acyl groups was not detected. K ex values of these CD derivatives are of the same order of magnitude as or larger than those of crown ethers. The order of the K ex values in all cases is Li+ < Na+ < K+ Rb+ Cs+, although these CD derivatives have no special selectivity for the alkali metal cations. The cation extraction mechanism was interpreted by an induced-fit mechanism.     

Fragmentation study of rutin, a naturally occurring flavone glycoside cationized with different alkali metal ions, using post-source decay matrix-assisted laser desorption/ionization mass spectrometry.

A post-source decay matrix-assisted laser desorption/ionization mass spectrometric (PSD-MALDI-MS) study of rutin, a naturally occurring flavone glycoside cationized with different alkali metal ions, is reported. The fragmentations of rutin were performed by selecting the [R + Cat]+ peaks for PSD, where R represents a rutin molecule and Cat an alkali metal ion (Li+, Na+, K+). The PSD-MALDI mass spectra showed, depending on Cat, different fragmentation patterns with respect to both the quality and quantity of the fragment ions formed. The intensity of fragmentation decreased in the order Li+ > Na+ > K+. The fragmentation mechanism and an explanation for the observed differences are suggested.     

Conductance Study of 1 : 1 19-Crown-6 Complexes with Various Mono- and Bivalent Metal Ions in Water

Formation constants (ML) of 1 : 1 19-crown-6 (19C6) complexes with mono- (M+) and bivalent metal ions (M2+) were determined in water at 25 °C by conductometry. The KML value of 19C6 for M+ and M2+ decreases in the order Rb+ K+ > Tl+ > Na+ = Ag+ > Li+ Cs+ and Pb2+ > Ba2+ > Sr2+ > Cd2+ > Ca2+, respectively. The selectivity for the neighboring alkali metal ions in the periodic table is lower for 19C6 than for 18-crown-6 (18C6) except for the case of Rb+ and Cs+. The same is true for the alkaline earth metal ions. Generally, the KML values of 19C6 with M2+ are greater than those with M+. For Na+ and the ions which are smaller in size than Na+ (Li+, Ca2+, Cd2+), the KML value is larger for 19C6 than for 18C6, but the contrary holds for all the other ions of larger sizes than Na+. The limiting ionic molar conductivity (°) of the 19C6–K+ complex in water at 25 °C was determined to be 43. Although 19C6 is larger than 18C6, the 19C6–K+ complex is much more mobile in water than the 18C6–K+ complex.     

冠醚配合物的热力学性质的研究 III. 碱金属离子与18C6甲基衍生物配位反应的电导研究

The coordination reaction of Na+, K+, Rb+ and Cs+ with benzo- 15-crown-5, 18-crown-6 and the newly synthesized cyclic polyethers 2, 3-benzo-8, 15-dimethyl-18-crown-6, 2, 3-benzo-8, 11, 15-trimethyl-18-crown-6 in methanol at 25`C has been studied by conductometric titration. The stability constants for the 1:1 coordination compounds were calculated. The marked selectivity of 18-crown-6 toward alkali metal ions was not found in its methyl derivatives. The induction effect of the benzene ring and methyl group on polyether ring reduced the stability of the coordination compounds. In methanol, the stability sequence of te compounds of alkali metal ions with 18-crown-6 was K+>Rb+>Cs+>Na+, that of its dimethyl derivative was K+>Rb+>Na+>Cs+ and that of its trimethyl derivative was K+>Na+>Rb+>Cs+, that is, the methyl substituent had a weaker influence on the stability of Na+ compound than on that of Rb+ or Cs+ compound. In the range of concentration studied, decrease in equivalent conductance is in agreement with the prediction on the basis of the structure of the complexes. The above results may give a clue for modifying the structure of a crown ether for specified selectivity.