κ-卡拉胶热可逆凝胶化行为研究

用固体小角激光散射方法研究κ 卡拉胶 (KC)的热可逆凝胶化行为 .以散色斑点的突停点温度为体系的凝胶化点Tgel,考察了溶液中加入Na+ ,K+ ,NH+4,Ca2 + ,Cu2 + ,Zn2 + 等抗衡离子对Tgel的影响 .结果是随抗衡离子浓度增大Tgel上升 ;Tgel与Na+ 的浓度呈线性关系 ,与K+ ,NH+4,Ca2 + ,Cu2 + ,Zn2 + 等离子浓度的平方根成线性关系 ;另外 ,还得到 30℃时KC在KCl盐溶液中的溶胶 凝胶相图 ,并对比了KC在NaCl溶液中透析前后Tgel的变化 .     

Ions and ion pairs in anionic activated polymerization of ϵ-caprolactam

The effect of concentration of the catalytic system on the initial rate of the anionic activated polymerization of ?-caprolactam (AAPC) has been studied. It is shown that the data can be rationalized only by considering (along with side reactions such as Claisen condensation) the fact that chain growth involves both free anions and ion pairs. The possibility of formation of various associates is discussed. Quantum-chemical calculations suggest that, in the alkali metal lactamate molecule, negative charge is delocalized among the O and N heteroatoms. A possible structure for the ion pair of catalyst is suggested. The states of the Li, Na and K lactamate molecules under the conditions for AAPC are determined from conductivity measurements. Kinetic studies of AAPC with various counter ions are also described. For the Li salt, the kinetic data conflict with the results of conductometric measurements. Suppression of the dissociation of sodium caprolactamate by addition of a neutral electrolyte, sodium tetraphenylborate, results in a drastic decrease in the initial rate of polymerization, suggesting that AAPC proceeds through both free anions and ion pairs. The possibility of polymerization through the ion-coordinative mechanism is considered.     

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.     

Extraction mechanism of monovalent ion-pairs by polyurethane foams

The extractability sequence of K(+) approximately Rb(+) > Cs(+) > Na(+) > Li(+) for the extraction with polyether foam suggests that the cation chelation mechanism might be operative. However, the same order was obtained for the extraction with 100% polypropylene oxide polyether foam which does not normally adopt a helical structure to form oxygen-rich cavities as easily or as effectively as polyethylene oxide to accommodate alkali metal ions. This result indicates that a hole-size/cation-diameter relationship may not be required for the high extraction of K(+). The extraction of alkali metal DPAs and hydroxides from methanol demonstrates the importance of the solvent effect. It indicates that the water-structure enforced ion-pairing (WSEIP) is the driving force for extraction of the ion-pairs. The extraction mechanism for ionic species can be described as an ion-pair extraction process. The overall effect of ion-pair formation in water and interaction of the extracted ions with foam appears to determine the extractability of the ions of the extractable ion-pair.     

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.     

Theoretical and gas-phase studies of specific cationized purine base quartet

Guanine tetraplexes are biological non-covalent systems stabilized by alkali cations. Thus, self-clustering of guanine, xanthine and hypoxanthine with alkali cations (Na(+), K(+) and Li(+)) is investigated by electrospray ionization mass spectrometry (ESI-MS) in order to provide new insights into G-quartets, hydrogen-bonded complexes. ESI assays displayed magic numbers of tetramer adducts with Na(+), Li(+) and K(+), not only for guanine, but also for xanthine bases. The optimized structures of guanine and xanthine quartets have been determined by B3LYP hybrid density functional theory calculations. Complexes of metal ions with quartets are classified into different structure types. The optimized structures obtained for each quartet explain the gas-phase results. The gas-phase binding sequence between the monovalent cations and the xanthine quartet follows the order Li(+) > Na(+) > K(+), which is consistent with that obtained for the guanine quartet in the literature. The smallest stabilization energy of K(+) and its position versus the other alkali metal ions in guanine and xanthine quartets is consistent with the fact that the potassium cation can be located between two guanine or xanthine quartets, for providing a [gua(or (xan))(8)+K](+) octamer adduct. Even if an abundant octamer adduct with K(+) for xanthine was detected by ESI-MS, it was not the case for guanine.     

碱—碱土—稀土催化剂发射光谱的研究

用Eu~(3+)的发射光谱探讨了O~-物种的形成。对M/MgO、M/CaO体系(M为碱金属)的研究发现,Li~+、Na~+可进入MgO晶格;Li~+、Na~+、K~+可进入CaO晶格。由于Li~+不能进入La_2O_3晶格,故不能形成O~-物种,表明不同的催化剂体系在甲烷氧化偶联反应中会形成不同的活性中心。     

Anionic polymerization. III. Polymerization of butadiene with alkali metal alkoxide-modified alkali metal system

A high molecular weight polybutadiene was prepared in hexane solvent by using alkali metal (Li, Na, K) and metal tert-butoxide (Li, Na, K) as a polymerization initiator. The microstructure of polybutadiene varies, depending on the type of modifiers and polymerization and temperatures. The results and mechanistic implications of this study are discussed.     

Structure and energetics of poly(ethylene glycol) cationized by Li(+), Na(+), K(+) and Cs(+): a first-principles study

Density functional theoretical methods, including several basis sets and two functional, were used to collect information on the structure and energetic parameters of poly(ethylene glycol) (PEG), also referred to as poly(ethylene oxide) (PEO), coordinated by alkali metal ions. The oligomer chain is found to form a spiral around the alkali cation, which grows to roughly two helical turns when the oligomer size increases to about the decamer for each alkali ion. Above this size, the additional monomer units do not build the spiral further for Li(+) and Na(+); instead, they form less organized segments outside or next to the initial spiral. The distance of the first layer of co-ordinating O atoms from the alkali cation is 1.9-2.15 ? for Li(+), 2.3-2.5 ? for Na(+), 2.75-3.2 ? for K(+) and 3.5-3.8 ? for Cs(+) complexes. The number of O atoms in the innermost shell is five, six, seven and eleven for Li(+), Na(+), K(+) and Cs(+). The collision cross sections with He increase linearly with the oligomer to a very good approximation. No sign of leaning towards the 2/3 power dependence characterizing spherical particles is observed. The binding energy of the cation to the oligomer increases up to polymerization degree of about 10, where it levels off for each alkali-metal ion, indicating that this is approximately the limit of the oligomer size that can be influenced by the alkali cation. The binding energy-degree of polymerization curves are remarkably parallel for the four cations. The limiting binding energy at large polymerization degrees is about 544 kJ mol(-1), 460 kJ mol(-1), 356 kJ mol(-1) and 314 kJ mol(-1) for Li, Na, K and Cs, respectively. The geometrical features are compared with the X-ray and neutron diffraction data on crystalline and amorphous phases of conducting polymers formed by alkali-metal salts and PEG. The implications of the observations concerning collision cross sections and binding energies to ion mobility spectroscopy and mass spectrometry are discussed.     

Molecular switch triggered by solvent polarity: synthesis,Acid-base behavior,alkali metal ion complexation,and crystal structure

The synthesis and characterization of the new tetraazamacrocycle L, bearing two 1,1'-bis(2-phenol) groups as side-arms, is reported. The basicity behavior and the binding properties of L toward alkali metal ions were determined by means of potentiometric measurements in ethanol/water 50:50 (v/v) solution (298.1+/-0.1 K, I=0.15 mol dm(-3)). The anionic H(-1)L(-) species can be obtained in strong alkaline solution, indicating that not all of the acidic protons of L can be removed under the experimental conditions used. This species behaves as a tetraprotic base (log K(1)=11.22, log K(2)=9.45, log K(3)=7.07, log K(4)=5.08), and binds alkali metal ions to form neutral [MH(-1)L] complexes with the following stability constants: log K(Li)=3.92, log K(Na)=3.54, log K(K)=3.29, log K(Cs)=3.53. The arrangement of the acidic protons in the H(-1)L(-) species depends on the polarity of the solvents used, and at least one proton switches from the amine moiety to the aromatic part upon decreasing the polarity of the solvent. In this way two different binding areas, modulated by the polarity of solvents, are possible in L. One area is preferred by alkali metal ions in polar solvents, the second one is preferred in solvents with low polarity. Thus, the metal ion can switch from one location to the other in the ligand, modulated by the polarity of the environment. A strong hydrogen-bonding network should preorganize the ligand for coordination, as confirmed by MD simulations. The crystal structure of the [Na(H(-1)L)].CH(3)CN complex (space group P2(1)/c, a=12.805(1), b=20.205(3), c=14.170(2) A, beta=100.77(1) degrees, V=3601.6(8) A(3), Z=4, R=0.0430, wR2=0.1181), obtained using CH(2)Cl(2)/CH(3)CN as mixed solvent, supports this last aspect and shows one of the proposed binding areas.     

Effect of various inorganic cations (Li,Na, K and Cs) and silica sources on the synthesis of the silica analogue of zeolite NCL-1 (Si-NCL-1)

The role of various inorganic cations such as Li, Na, K and Cs has been studied in the hydrothermal synthesis of the silica polymorph of zeolite NCL-1 (Si-NCL-1). The crystallization time decreases in the order (Cs + Na) > K > Na> (Li + Na) under otherwise identical gel composition and crystallization conditions. Further, the synthesis has been standardized using different silica sources including various fumed silicas with different surface area and particle size, through optimizing the OH⁻/Si molar ratio by adding the required amount of alkali hydroxide in the synthesis gel. Among different silica sources (fumed silicas, tetraethyl orthosilicate, silica sol etc.), fumed silicas with smaller particles (~0.007 μn) like Sigma S-5005, S-5130, and Cab-O-Sil-M5 were found to be quite effective and preferable for the synthesis of Si-NCL-1 molecular sieves. These materials were characterized through XRD, IR, SEM, sorption and surface area measurements.     

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。     

Solvent effects on the conformation of DNA dodecamer segment: a simulation study

Different solvent temperatures with five kinds of counterions are used to investigate solvent effects on the DNA microscopic structure. The dodecamer d (CGCGAATTCGCG) DNA segment is merged into the solvents and its conformation transition is studied with the molecular dynamics simulations in detail. For the simple point charge model of water molecule with Na(+) counterions, as temperature increases from 200 K to 343 K, the duplex DNA changes from stiff B form to a state between A form and B form, which we define as mixed (A-B) structure, with a double helix unwinding. To study the counterions effects, other four alkali cations, Li(+), K(+), Rb(+), or Cs(+) ions, are substituted for Na(+) ions at 298 K and 343 K, respectively. For the cases of Li(+), Rb(+), and Cs(+) ions, the duplex DNA becomes more flexible with sugar configuration changing form C2'-endo to C1'-endo type and the width and depth of minor groove at CpG and GpC steps moving towards A values, as the mass of the counterions decreasing. For the case of K(+) ions, DNA-K(+) interaction widens the width of minor and major grooves at ApA steps and TpT steps, respectively. It seems that the light ions (Li(+) or Na(+)) prefer to interact with the free phosphate oxygen atoms while the heavier ions (Rb(+) and Cs(+)) strongly interact with the base pairs.     

VUV-transitions in ionic rare-gas alkali molecules

Mixtures of rare-gases (Rg) and alkali vapors (A) were excited by helium and argon ions. VUV transitions observed between 131.1 nm and 189.9 nm were ascribed to the decay of (RgA)⁺ ions where Rg=Kr, Xe and A=Cs, Rb, K, Na, Li. In the (ArA)⁺ systems (A=Rb, K, Na, Li) transitions appeared between 114.1 nm and 124.7 nm. Since the final state is only weakly bound, the (RgA)⁺ ions seem to be promising candidates for storage media of VUV lasers.     

Zirconium phosphate dispersed on a cellulose fiber surface: preparation, characterization, and selective adsorption of Li+, Na+, and K+ from aqueous solution

Highly dispersed zirconium phosphate was prepared by reacting Cel/ZrO(2) (ZrO(2)=6.7 wt%; 0.56 mmol g(-1) of zirconium atom per gram of the material) with phosphoric acid. High power decoupling magic angle spinning (HPDEC-MAS)(31)P NMR and X-ray photoelectron spectroscopy data indicated that HPO(2-)(4) is the species present on the fiber surface. The X-ray diffraction patterns showed that zirconium hydrogen phosphate particles were amorphous and had an ion-exchange capacity, determined by ammonia gas adsorption, of 0.30 mmol g(-1). The ion-exchange capacities for Li(+), Na(+), and K(+) ions were determined from ion-exchange isotherms at 298 K and showed the following values (in mmol g(-1)): Li(+)=0.01, Na(+)=0.23, and K(+)=0.30. The higher affinity of the surface hydrogen phosphate particles for Na(+) and K(+) is due to its lamelar structure which permits easier diffusion of these two ions whose hydrated radii are smaller than that of Li(+).     

Analysis of carrageenans by matrix-assisted laser desorption/ionization and electrospray ionization mass spectrometry. I. kappa-Carrageenans.

Matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) mass spectra of small kappa-carrageenans are reported and discussed. MALDI spectra can be obtained in both positive and negative ion mode. In the absence of extraneous metal ions, positive ions are formed by the attachment of one Na(+) ion to the carrageenan, whereas for negative ions one Na(+) ion is detached from the sulfate group. Multiply charged species are not observed in MALDI. Intense ESI spectra can be obtained in negative ion mode and now multiply charged species are seen. Alkali exchange experiments show that in these small carrageenan anions one, but only one, alkali metal ion is bound in a bidentate coordination with two ionic sulfate groups. G2-type ab initio calculations on model ions HO(-) [M(+)] (-)OH (M = Li, Na, K, Cs), as well as arguments based on a simple Coulombic interaction model, show that the bidentate stabilization energy drops rapidly as the size of the alkali cation increases. Exchange of Na(+) with Li(+) leads to expulsion of the Na(+) ion generating, in ESI, intense multiply charged anions. An attempt is made to rationalize this behavior in terms of hydration effects.     

Cyclohexane as a Li+ selective ionophore

The M+[cyclohexane][Ar] (M = Li, Na, and K) cluster ions were investigated using infrared photodissociation spectroscopy in the C-H stretching region. The alkali metal cation binds to the cyclohexane ring above the ring on the S6 axis via eta3 coordination. The C-H stretching modes are perturbed due to binding of the metal cation and display a significant spread in frequency. The shifts are greatest for the Li+ and decrease for Na+ and K+ with increasing ionic radius. It has been observed that cyclohexane displays greater selectivity for Li+ over Na+ than the cyclic ether, 12-crown-4. The charge transfer interaction between Li+ and cyclohexane is believed to be responsible for the selectivity of Li+ over other alkali metal ions.     

Structural Study of Alkaline 1-Phenyl-1H-1, 2, 3, 4-tetrazole-5-thiolate Salts: An Example of Periodicity in Alkaline Cations

The alkaline 1-phenyl-1H-1, 2, 3, 4-tetrazole-5-thiolate salts, M[C₆H₅N₄CS] (M = Li ( 1 ), Na ( 2 ), K ( 3 ), Rb ( 4 ) and Cs ( 5 )) were obtained and characterized by means of mass spectrometry (FAB⁺) and NMR (¹H; ¹³C) spectroscopy. The structures of Na ( 2 ), K ( 3 ), Rb ( 4 ) and Cs ( 5 ) compounds were determined by X-ray diffraction methods. The ligand shows a rich variety of coordination patterns with the alkaline cations. The formation of a four-membered ring MSCN in the compounds with heavier alkali cations (K, Rb and Cs) is shown. In all the cations the coordination number around it increases with the ionic radius. Compounds with Cs⁺ and Rb⁺ exhibited the formation of Cs-C and Rb-C interactions with the phenyl group.     

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.     

Molecular structure and vibrational spectra of mixed MDyX4 (M = Li, Na, K, Rb, Cs; X = F, Cl, Br, I) vapor complexes: a computational and matrix-isolation infrared spectroscopic study

The structures, energetic, and vibrational properties of MDyX(4) (M = Li, Na, K, Rb, Cs; X = F, Cl, Br, I) mixed alkali halide/dysprosium halide complexes have been investigated by a joint computational and experimental, matrix-isolation Fourier-transform infrared spectroscopic (MI-IR), study. According to our DFT computations for the complexes with heavier halides and alkali metals the ground-state structure is the tridentate isomer; while at high temperatures the bidentate structural isomer dominates. The survey of various dissociation processes revealed the preference of the dissociation to neutral MX and DyX(3) fragments over ionic and radical dissociation products. Cationic complexes are considerably less stable at 1000 K than the neutral complexes, and they prefer to dissociate to M(+) + DyX(4)(?) fragments. The vapor species of selected mixtures of NaBr and CsBr with DyBr(3) and of CsI with DyI(3) in the temperature range 900-1000 K have been isolated in krypton and xenon matrices and investigated by infrared spectroscopy. Besides the characteristic vibrational frequencies of the monomeric and dimeric alkali halide species and of the dysprosium trihalide molecules, certain signals indicated the formation of MDyX(4) (M = Na, Cs; X = Br, I) mixed complexes. Comparison with the computed vibrational and thermodynamic characteristics of the relevant species lead to the conclusion that these complexes appear in the vapor predominantly as the C(2v)-symmetry bidentate isomer. This is the first time that this structure was identified in an experimental vibrational spectroscopic study. The signals appearing upon performing a thermal anneal cycle were tentatively assigned to the double complex M(2)DyX(5) (M = Na, Cs; X = Br, I). A structure in which one alkali atom is bound to dysprosium by three and the other by two bridges is proposed for these double complexes.