Photodynamic Action of Methylene Blue on the Paramecium Membrane

An electrophysiological study of photodynamic action on the Paramecium membrane was carried out. In the presence of methylene blue (MB), light-spot stimulation of an anterior and a posterior part induced a depolarization and a hyperpolarization of the membrane, respectively. Under voltage-clamping, the anterior stimulation induced an inward current, while the posterior stimulation induced an outward current. The amplitudes of these currents were dependent on the membrane potential. When K⁺ channels were blocked with Cs⁺ and tetraethylammonium (TEA⁺), the posterior outward current was inhibited, while the anterior inward current was not inhibited. Intracellular application of the Ca²⁺ chelator, 1,2 -bis (2-aminophenoxy) ethane- N,N,N',N' -tetraacetic acid (BAPTA) also inhibited the posterior outward current, but the anterior inward current was unaffected. These results suggest that photodynamic action on the Paramecium membrane primarily opens the Ca²⁺ channels and the following influx of Ca²⁺ activates the Ca²⁺-dependent K⁺ channels localized mainly on the posterior part of the membrane.     

钙离子选择性双管复合微电极的研制

本文研制的钙离子选择性双管复合微电极尖端直径小至2.5μm,特别适用于活体组织细胞及临床微量试样中钙离子浓度的测定。用该电极测量了人体微量试样中钙离子浓度,并观察了大白鼠及家免心肌组织受激时钙离子活度的动态变化。     

DEVELOPMENT OF DOUBLE-BARRELED CALCIUM ION-SELECTIVE MICROELECTRODE

A new PVC matrix membrane double-barreled calcium ion-selective microelectrode based on liquid ion exchanger has been designed and constructed.The tip diameter of about 2.5μm as well as lower selectivity coefficients for K+,Na and Mg2+are adequate for in-tracellular measurements of Ca activities.The inner wall of the selective channel was made to be hydrophobic by treatment withalkyl-alcohols.By means of this microelectrode some physiologicalphenomena related to Ca2+activities have been studied,and Caconcentrations in clinical microsamples have also been determined.     

Particle-Wave Dualism in Nanoconfined Space:Ultrafast Substance Flow

Many researchers, however, found that (1) the flow of both liquid and gas through nanoscale pores is one to even seven orders of magnitude faster than that would be predicted from the classic Newton's mechanic theories, such as the Hagen-Poiseuille equation, the Bernoulli's principle, the Knudsen theory; (2) the seeming contradiction that K⁺ channels conduct K⁺ ions at maximal throughput rates while not permeating slightly smaller Na⁺ ions, which have perplexed scientists for decades. Herein we propose a possible explanation for the above phenomena based on the Wave-Particle Dualism. The quantum effect on ultrafast flow could possibly provide a new perspective for studying the nature of the ion and molecule channels, which are the backbones for the biology, and possibly promote the development of new methods for energy conversion, desalination of sea water and even information systems.     

Influence of cations on the proton leakage through anion-exchange membranes

In the recovery of acids from wastewaters or the regeneration of acids and bases from salts by electromembrane processes, the most important phenomenon which limits the current efficiency is the transport of protons through the anion-exchange membrane (AEM). In this work, the proton leakage through an AEM is studied with a system containing hydrochloric acid or sulfuric acid on the cathodic side and the mixture of acid with one homoanionic salt (Li⁺, Na⁺, K⁺, Cr³⁺, NH₄⁺, (CH₃)₄N⁺ and (C₂H₅)₄N⁺) on the anodic side. The proton leakage is quantified from the value of the proton transport number. The results are analyzed assuming that the rate determining step of proton leakage is the interfacial transfer reaction of protons from the aqueous anodic solution to the membrane. The proton leakage is enhanced by the polarizing power of the cation. The transfer of protons into the membrane seems to be catalyzed by the presence of a layer of adsorbed cations on the surface of the membrane. The presence of salt decreases the proton leakage but it is always greater with H₂SO₄ solutions compared to HCl solutions.     

钾离子浓度依赖的铅离子稳定G-四链体构型转化

已有研究普遍认为铅离子(Pb²⁺)诱导富G适体链形成的G-四链体(Pb²⁺-G4)比钾离子(K⁺)诱导富G适体链形成的G-四链体(K⁺-G4)更为稳定,因而Pb²⁺可以置换K⁺-G4中的K⁺,而且K⁺的存在不影响Pb²⁺-G4的稳定性。有趣的是本研究发现K⁺ (20 μmol∙L⁻¹–1 mmol∙L⁻¹)不仅可以诱导10 µmol∙L⁻¹ Pb²⁺稳定的T2TT(Pb²⁺-T2TT,杂合G4结构)发生构型转换,甚至还可取代Pb²⁺-T2TT中的Pb²⁺,形成K⁺稳定的T2TT (K⁺-T2TT,平行G4结构),最终转化形成的K⁺-G4结构与单独K⁺诱导富G适体链形成K⁺-G4的构型基本一致。随后,进一步考察了另外7条富G适体链,发现这一转化过程具有一定的普适性。该研究结果为理解G4构型转化以及内嵌离子交换提供了新的视角,也为拓展G4在生化分析和生物领域的应用提供了新的理论基础。     

Unimolecular artificial transmembrane channel with terminal dihydrogen phosphate groups showing transport selectivity for ammonium

A new artificial transmembrane channel molecule bearing dihydrogen phosphate groups has been synthesized.The terminal dihydrogen phosphate groups enable the channel to be highly negatively charged at both ends of the channel structures.The artificial channel could incorporate into the lipid bilayer efficiently under low concentration.The channel displays high NH4+/K+selectivity due to the electrostatic interaction and hydrogen bonding between NH4+and the terminal dihydrogen phosphate groups.     

Ca2+ INFLUX INDUCED BY PHOTODYNAMIC ACTION IN HUMAN CEREBRAL GLIOMA (U-87 MG) CELLS: POSSIBLE INVOLVEMENT OF A CALCIUM CHANNEL

Abstract The plasma membrane has been implicated as a critical target of photodynamic action on cells. We have observed that the photosensitization of human cerebral glioma (U-87 MG) cells by hematoporphyrin derivative (HpD) causes a large increase in intracellular calcium [Ca²⁺]. This increase in [Ca²⁺]_i was solely due to the influx of extracellular Ca²⁺ through the plasma membrane and showed a dependence on HpD concentration, light dose and concentration of calcium in the extracellular medium. The magnitude of the Ca²⁺ influx decreased with increasing postirradiation time, which suggests that the cell membrane partially recovers from the photodynamic injury. The photoinduced Ca²⁺ influx was inhibited by the Ca²⁺ channel blocker diltiazem and the reducing agent dithioerythritol. These findings are discussed in terms of possible activation of a Ca²⁺ channel as a result of photosensitization.     

Studies of Permeabilities of Metallic Ions Through Crosslinked Chitosan Membranes

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温度和离子对紫膜LB膜光循环的影响

用闪光动力学光谱仪测量了水平拉制的紫膜LB膜中菌紫质中间体M₄₁₂的衰减过程,观察了温度和离子对M₄₁₂衰减过程的影响。实验结果表明:在一定的温度范围内(10℃-60℃),随着温度的升高,M₄₁₂的衰减速率加快。对M₄₁₂s的衰减的抑制作用,La³⁺在低浓度时就很明显,而K⁺则在较高浓度时才表现出来,Ca²⁺的影响不明显;La³⁺对M₄₁₂f的衰减无明显影响,K⁺和Ca²⁺则稍微加快了其速率,pH的变化(H⁺浓度)明显影响到M₄₁₂的衰减速率,尤其在高pH情况,M₄₁₂s的衰减比正常pH值时要慢一个数量级。     

Influence of K+, Na+ or Ca2+ Ions on the Interaction Between AmB and Saturated Phospholipids by Langmuir Technique

Interaction between amphotericin B(AmB) and cell membrane is influenced by different metal cations. In the presence of K⁺, Na⁺ or Ca²⁺ ions, the surface pressure-area isotherms and the elastic modulus of an amphotericindipalmitoylphosphatidylcholine(AmB-DPPC) mixed monolayer were discussed. And the excess free energy and entropies of mixing were calculated according to the surface pressure-area isotherms. The phase transition of the mixed monolayer needed a higher concentration of AmB in the sequence Na⁺ > pure buffer > K⁺ > Ca²⁺. When the molar fraction of AmB(x_AmB) was 0.5, the molecular interaction changed from attraction to repulsion and the mixed monolayer turned to ordered state from disorder state under the induction of K⁺ or Ca²⁺ ions at all surface pressure in our experiment. At high surface pressure, the disorder of monolayer enhanced in the presence of Na⁺ ions at x_AmB > 0.1. At different molar ratios of AmB, the influences of these metal cations were discrepant. These cations may influence AmB molecules to form pores on the monolayer. It is helpful to understand the reduction of AmB's toxicity as theoretical reference.     

Spectroscopic, mass spectrometry, and semiempirical investigations of a new 2-(2-methoxyethoxy)ethyl ester of Monensin A and its complexes with monovalent cations

A new 2-(2-methoxyethoxy)ethyl ester of Monensin A (MON7) has been synthesized and its capability of complex formation with Li⁺, Na⁺, and K⁺ cations has been studied by ESI MS, ¹H and ¹³C NMR, FT-IR, and PM5 semiempirical methods. ESI mass spectrometry indicates that MON7 forms complexes with Li⁺, Na⁺, and K⁺ of exclusively 1:1 stoichiometry which are stable up to cv = 70 V. The formation of complexes between MON7 and Na⁺ cations is strongly favored. Starting from about cv = 90 V fragmentation of the respective complexes is observed, primarily characterized by several dehydration steps. The structures of the MON7 complexes with Li⁺, Na⁺, and K⁺ cations are stabilized by intramolecular hydrogen bonds in which the OH groups are always involved. The structures are visualized and discussed in detail. It has been proved that the formation of a pseudo crown ring structure formed by MON7 is preferred in complexes with Na⁺ cations.     

Exit transition state of endohedral X@Si20H20 complexes (X=Li, Na, K, Be, Mg)

The kinetic stability of endohedral X@Si₂₀H₂₀ complexes (X=Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺) has been studied at the B3LYP/6-31G* level of density functional theory (DFT). The transition states (TS) are investigated by the QST3 method of Gaussian 98 package and demonstrated with Intrinsic reaction coordinate (IRC). It is found that K⁺@Si₂₀H₂₀ cluster has the most stable structure kinetically, that the exit barrier heights (H_exit) for K⁺ expulsion from or insertion in the cage are 187.38 and 205.58 kcal/mol, respectively. However, the smallest Be²⁺ dication is not endohedrally encapsulated and the Be²⁺@Si₂₀H₂₀ cluster is expected to be the least stable structure kinetically. By comparison, other endohedral complexes have a moderate kinetic stability.     

On the affinities of ammonia and water for Li, Na and K

The affinities of ammonia for Na⁺ and K⁺, recently determined experimentally, have been computed by the ab initio SCF method using ended polarized gaussian basis sets and shown to be satisfactory Furthermore, the corresponding values computed at the same level of accuracy for the three cations Li⁺, Na⁺, K⁺ and the two ligands NH₃ and H₂O are shown to yield the order Li⁺ > Na⁺ > K⁺ for each ligand and NH₃ > H₂O for each ion, in agreement with experiment. An analysis of the factors involved in the binding provides a consistent rationalization of these regularities and of some observed correlations.     

Equilibrium of ion-exchange polymeric membrane with aqueous salt solution and its thermodynamic modeling

A thermodynamic model is proposed to describe distribution of the components between a liquid solution and a swollen membrane undergoing structural transformations. Free energy contributions related to formation of solution-filled micro-cavities in the membrane interior are estimated. Formation of the cavities of different shape is accounted for by using the Helfrich expressions for the bending energy of a curved interface. Three adjustable parameters of the model are related to the hydrophobic polymer matrix of the membrane, while the electrostatic contribution is estimated explicitly. Structural changes in the membrane are described as a transition from spherical to cylindrical cavities. Predominance of cavities having definite shape (spheres, cylinders) results in a specific shift of the Donnan equilibrium, which thus, becomes dependent on the structure of the membrane on the mesoscale. The results of model calculations are compared with the experimental data on the distribution of ions (H⁺, Li⁺, Cs⁺, K⁺, Na⁺, Ca²⁺, Mg²⁺) between the aqueous solution and the membrane. Different types of predicted thermodynamic behavior of the membrane in the liquid solution, including the hysteresis of ion-exchange equilibrium curves, are discussed. The model takes into account the effect of micro-inhomogeneties and helps to establish a link between molecular characteristics of the perfluoropolymer membrane and its macroscopic behavior in the liquid solution.     

Self-diffusion coefficient of water in Nafion-117 membrane with different monovalent counterions: a radiotracer study

The self-diffusion coefficient of water in Nafion-117 membrane in different cationic forms was measured by the transient radiotracer method, which is based on an analytical solution of Fick's second law. The self-diffusion coefficient of water in the membrane was obtained from the analysis of time-dependent isotopic-exchange rates of tritium tagged water between sample of Nafion-117 membrane and equilibrating water. This transient method does not require the knowledge of partition coefficient of water, which is an essential parameter in the radiotracer permeation method. In present work, self-diffusion coefficients of water in the Nafion-117 membrane with H⁺, Li⁺, Ag⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ monovalent counterions were obtained. The values of logarithm of self-diffusion coefficients were found to vary linearly as a function of polymer volume fraction except for membrane sample with H⁺ counterions. The self-diffusion coefficient of water in Nafion-117 membrane with H⁺ counterions was significantly different from the trend observed in the variation of self-diffusion coefficient of water as a function of polymer volume fraction in the membrane with other monovalent counterions. This observation seems to suggest that the physical structure of Nafion-117 membrane in H⁺ form may be quite different from the Nafion-117 membrane with other monovalent counterions. The high self-diffusion coefficient of water (1.67 × 10⁻⁶ cm²/s) in Nafion-117 membrane with Cs⁺ counterions indicates that the ionic clusters in Nafion-117 membrane are well connected even at low water content (8.2 wt.%) in the membrane.     

邻甲氧基羰基苄氧基取代杯[4]芳烃衍生物的合成及其性能研究

杯芳烃是继冠醚、环糊精之后的第三代主体分子[1].据文献[2,3]报道,在杯[4]芳烃下沿酚氧原子上连接乙酸酯得到的四取代衍生物对Na+有很高的选择性,核磁与晶体结构研究均证实这是由于羧酸酯的羰基和酚氧基参与了对Na+的配位,而且配位基团所形成的包络空间大小与钠离子相匹配.一般认为,随着包络空间改变,对金属离子的识别作用会有所变化[4].但目前对这方面的工作并没有给予更多的重视.我们发现,用2-溴甲基苯甲酸甲酯与杯[4]芳烃反应,得到了一种新的四取代杯[4]芳烃衍生物[2]萃取研究结果表明,该化合物对钾离子有较好的选择性.此外,在合成该衍生物的过程中,还得到了另一新的二取代衍生物(3).     

分子梭协助离子跨膜运输的机理研究

采用增强采样分子动力学模拟研究了一轮烷型分子梭协助K⁺跨膜转运的机制, 该轮烷由两亲性的轴和套在轴上的大冠醚环及连接在大冠醚环上的小冠醚环构成, 轴上有3个带正电的结合位点. 通过计算穿梭过程的自由能变化, 探索了溶剂(氯仿、 乙腈、 水、 氯仿-乙腈)以及中间结合位点对该轮烷穿梭运动的影响, 并分析了中间位点在其携带K⁺穿越细胞膜(采用水-氯仿-水模拟)过程中的重要作用. 结果表明, 改变溶剂不会改变轮烷(不携带K⁺)的运动模式, 但随着溶剂极性的增加穿梭所需克服的自由能能垒显著降低; 在氯仿-乙腈混合溶剂中, 中间结合位点的质子化状态, 不影响轮烷(不携带K⁺)的穿梭能垒; 然而在模拟细胞膜的环境中, 该结合位点的质子化与去质子化相比大幅降低了穿梭的能垒, 促进了K⁺的跨膜转运, 表明中间位点的质子化对于离子转运至关重要, 进一步分析表明轮烷中大环穿梭和小环摆动的协同作用, 也是加速离子跨膜转运的另一关键因素.     

Raman spectroscopic study of the conformational change of 12-crown-4 due to cation capture

Raman spectra of the Li⁺, Na⁺, K⁺, NH⁺₄, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺ complexes of 12-crown-4 and also 12-crown-4 in various states are observed. The spectra of 12-crown-4 change remarkably by complex formation with cations. Normal vibration calculations of various conformations of 12-crown-4 are carried out. On the basis of the observed spectra and the results of the calculations, the conformation of 12-crown-4 in the Li⁺, Na⁺, K⁺, NH⁺₄, Mg²⁺ complexes is found to have approximate D_2d symmetry, while that in the Ca²⁺, Sr²⁺, Ba²⁺ complexes is found to have approximate C_2V symmetry.     

ESI MS, spectroscopic and PM5 semiempirical studies of Colchicine complexes with lithium, sodium and potassium salts

The colchicine complexes with Li⁺, Na⁺ and K⁺ cations have been synthesized and studied by ESI MS, ¹H and ¹³C NMR, FT-IR and PM5 semiempirical methods. It has been shown that colchicine forms stable complexes of 1:1 stoichiometry with monovalent metal cations. For Li⁺ cations also formation of the 2:1 stoichiometry complexes has been detected. The most stable structures of the complexes are those in which the acetamide groups are involved in the coordination process. The structures of the colchicine complexes with Li⁺, Na⁺ and K⁺ cations are visualized and discussed in details.