Influence of mixed and multivalent counterions in overcharging of DNA-like spherocylindrical macroions

The influence of multivalent and mixed valency counterions on the ground-state energetics of overscreening of a core DNA-like model (sphero)cylindrical macroion is investigated using an earlier developed energy minimization numerical simulation algorithm. The effects of mono-, di-, tri-, and tetravalent counterions, and mixed valency (mono- plus di-) counterions are compared and contrasted. It is seen that the depth of the minimum in the excess ground-state energy (over the neutral reference state) versus the number of overcharging counterions increases as counterion valency changes from mono- to tetra- testifying to the efficiency of the overcharging process due to multivalent counterions. The influence of (i) the presence of mixed valency counterions and (ii) counterion size on the energetics is also investigated.     

Molecular dynamics and neutron scattering study of the dependence of polyelectrolyte dendrimer conformation on counterion behavior

Atomistic molecular dynamics (MD) simulations and contrast variation small angle neutron scattering (SANS) have been combined to investigate the Generation-5 polyelectrolyte polyamidoamine starburst dendrimer. This work reveals the dendrimer conformational dependence on counterion association at different levels of molecular charge. The accuracy of the simulations is verified through satisfactory comparison between modeled results, such as excess intra-dendrimer scattering length density distribution and hydration level, and their experimental counterparts. While the counterion distributions are not directly measureable with SANS, the spatial distribution of the counterions and their dendrimer association are extracted from the validated MD equilibrium trajectories. It is found that the conformation of the charged dendrimer is strongly dependent on the counterion association. Sensitivity of the distribution of counterions around charged amines to the counterion valency is qualitatively explained by adopting Langmuir adsorption theory. Moreover, via extending the concept of electrical double layer for compact charged colloids, we define an effective radius of a charged dendrimer including the spatial distribution of counterions in its vicinity. Within the same framework, the correlation between the strength of intra-dendrimer electrostatic repulsion and the counterion valency and dynamics is also addressed.     

Effects of multivalent salt addition on effective charge of dilute colloidal solutions

The effective charge Z* is often invoked to account for the accumulation of counterions near the colloid with intrinsic charge Z. Although the ion concentrations c(i) are not uniform in the solution due to the presence of the charged particle, their chemical potentials are uniform everywhere. Thus, on the basis of ion chemical potential, effective ion concentrations c(i)*, which can be experimentally measured by potentiometry, are defined with the pure salt solution as the reference state. The effective charge associated with the charged particle can then be determined by the global electroneutrality condition. Monte Carlo simulations are performed in a spherical Wigner-Seitz cell to obtain the effective charge of the colloid. In terms of the charge ratio alpha=Z*/Z, the effects of added salt concentration, counterion valency, and particle charge are examined. The effective charge declines with increasing salt concentration and the multivalent salt is much more efficient in reducing the effective charge of the colloidal solution. Moreover, the extent of effective charge reduction is decreased with increasing intrinsic charge for a given concentration of added salt. Those results are qualitatively consistent with experimental observations by electrophoresis.     

Complex formation in Aerosol OT reversed micelles between sodium counterion and Kryptofix 221D macrobicyclic ligand

The interaction between 5-decyl-4,7,13,16,21-pentaoxa-1,10-diazabicyclo-[8,8,5]-tricosan (Kryptofix 221D) and reversed micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in n-heptane as a function of AOT and water concentration was investigated by a calorimetric technique. The solubilization of the cryptand in the reversed AOT micelles produces an exothermic effect that increases with R (R=[water]/[AOT]) and is slightly dependent on AOT concentration. Processes due to the formation of a 1:1 complex between the cryptand and the sodium counterion of the AOT and to the transfer of Kryptofix 221D from bulk n-heptane to the micellar palisade layer have been taken into account to rationalize the experimental results. The peculiar solvation state of the sodium counterions near the water-AOT interface has also been considered.In part from the Doctor in Biology thesis of F. Pinio in the University of Palermo.     

反离子对氟表面活性剂的影响1. 表面活性及胶团化作用

通过表面张力和荧光探针法研究了全氟辛酸钠、全氟辛酸铵以及全氟辛酸四烷基铵[C₇F₁₅COON(C_nH_2n+1)₄, n＝1, 2, 3, 4]的表面活性以及胶团化作用, 系统地讨论了各种反离子, 特别是反离子大小的影响. 结果表明, 与普通碳氢表面活性剂不同, 反离子对这类氟表面活性剂的表面活性以及胶团化作用有很大影响. 表面活性剂的临界胶束浓度(cmc)随反离子的增大而下降; 饱和吸附层中平均每个分子所占的面积则大致随反离子的增大而增大. 而表面张力的变化则较为复杂. cmc时的表面张力随反离子的增大先上升(从全氟辛酸铵到全氟辛酸四乙铵)后下降(从全氟辛酸四乙铵到全氟辛酸四丁铵). 通过反离子的空间位阻、疏水性、插入以及电荷屏蔽效应对上述结果做了解释.     

Streaming potentials and conductivities of latex plugs. Influence of the valency of the counterion

Plugs consisting of polystyrene particles with sulphonate surface groups have been investigated in the presence of mono-, di- and trivalent counterions. The streaming potentials and conductivities of the plug and bulk solution have been measured. From the latter, the overall surface conductivity has been estimated. It is shown that for this system, accounting for the surface conductivity in the hydrodynamically stagnant layer is crucial to convert the streaming potentials into zeta potentials. The overall surface conductivity clearly depends on the charge of the counterion, and so do the ionic mobilities in the stagnant layer. The higher the valency of the counterion, the lower is the ionic mobility in the stagnant layer, but for all counterions, the ionic mobility in the stagnant layer is of the same order of magnitude as in the bulk. For the divalent counterions, no indications of specific interactions with the surface groups have been found.     

The shape of a flexible polymer in a cylindrical pore

We calculate the mean end-to-end distance R of a self-avoiding polymer encapsulated in an infinitely long cylinder with radius D. A self-consistent perturbation theory is used to calculate R as a function of D for impenetrable hard walls and soft walls. In both cases, R obeys the predicted scaling behavior in the limit of large and small D. The crossover from the three-dimensional behavior (D --> infinity) to the fully stretched one-dimensional case (D --> 0) is nonmonotonic. The minimum value of R is found at D approximately 0.46R(F), where R(F) is the Flory radius of R at D --> infinity. The results for soft walls map onto the hard wall case with a larger cylinder radius.     

Simulation Study of the Conformational Properties of Diblock Polyelectrolytes in Salt Solutions

Coarse-grained molecular dynamics simulations are performed to understand the behavior of diblock polyelectrolytes in solutions of divalent salt by studying the conformations of chains over a wide range of salt concentrations. The polymer molecules are modeled as bead spring chains with different charged fractions and the counterions and salt ions are incorporated explicitly. Upon addition of a divalent salt, the salt cations replace the monovalent counterions, and the condensation of divalent salt cations onto the polyelectrolyte increases, and the chains favor to collapse. The condensation of ions changes with the salt concentration and depends on the charged fraction. Also, the degree of collapse at a given salt concentration changes with the increasing valency of the counterion due to the bridging effect. As a quantitative measure of the distribution of counterions around the polyelectrolyte chain, we study the radial distribution function between monomers on different polyelectrolytes and the counterions inside the counterion worm surrounding a polymer chain at different concentrations of the divalent salt. Our simulation results show a strong dependence of salt concentration on the conformational properties of diblock copolymers and indicate that it can tune the self-assembly behaviors of such charged polyelectrolyte block copolymers.     

Aggregation and adsorption of sodium dioctylsulfosuccinate in aqueous ammonium chloride solution: role of mixed counterions

The critical micelle concentration (cmc) of sodium dioctylsulfosuccinate (AOT) was determined at 25 °C from surface tension and fluorescence methods in aqueous NH(4)Cl solution for assessing the influence of mixed counterions on the special counterion binding behavior (SCB) of AOT. The SCB of AOT refers to a sudden twofold increase in the value of the counterion binding constant (β) in aqueous medium when the concentration (c(*)) of the added 1:1 sodium salt is about 0.015 mol kg(-1), and it has been tested so far for sodium ion only. In the presence of sodium and ammonium mixed counterions also the SCB of AOT exist, but with lower c(*) (0.009 mol kg(-1) NH(4)Cl). Synergism in the cmc occurs due to mixed counterions. In the case of inorganic counterions, unlike the case with organic counterions, the cmc is dependent on the total counterion concentration in solution and negligibly on the specific type of counterion. Na(+) and NH(4)(+) bind almost equally to the micelle in the region of low β (below c(*)), but in the region of high β (above c(*)) NH(4)(+) binds predominantly. It has been shown that the theoretical expression for the surface excess of ionic surfactant+electrolyte system containing a single counterion can also be used to evaluate the surface excess in the presence of mixed counterions if the two counterions are considered to undergo Henry-type adsorption at the air-solution interface.     

Growth and Crystal Structure of YbAl3（BO3）4

1 INTRODUCTION With the development of high power InGaAs laser diode (LD) as pump sources, the Yb3+-doped laser crystals have received much attention. Due to the simple energy level structure of the Yb3+ ions, the Yb3+-doped laser crystals have no concentration quenching, and have high quantum efficiency and low quantum defects even at high doping concentration of the Yb3+ ions[1, 2]. Therefore, the Yb3+-doped crystals are good candidates of media in the LD-pumped solid-state laser,…     

Synthesis and Crystal Structure of 3,3′-(Hexane-1,6-diyl)bis(1-acetyl-5,5-dimethylhydantoin),a New Inducer of Differentiation

1 INTRODUCTION Hexamethylenebis[acetamide] (HMBA) is an effective agent in phaseⅡclinical trial[1] that induces differentiation of certain types of tumors to nonmalignant phenotypes. In an attempt to discover more efficient inducers, a number of derivatives of HMBA have been synthesized and evaluated in vitro[2, 3]. The results proved that increasing the number of functional groups could enhance the anticancer activity. In addition, it was evident that compounds with six methylene i…     

Crystal Structure of Indenyl—3—indenyl

1 INTRODUCTION Indene is an intermediate used for the synthesis of organometallic complexes involving silylene-bridged indenyl[1～5]. In the process of synthesizing (CH3)(C6H5)Si(Ind)2[6], a new compound as a by-product which is a dimer of indene was obtained, and only one similar crystal was found in CCDC[7]. Up to now, there are no crystal structure reports on this kind of structure. The present paper will describe the crystal structure of the title compound. 2 EXPERIMEN…     

Langevin dynamics of semiflexible polyelectrolytes: rod-toroid-globule-coil structures and counterion distribution

We have investigated the nature of counterion condensation on uniformly charged semiflexible polyelectrolyte chains and the concomitant configurations by monitoring the role of chain stiffness, chain length, counterion valency, and the strength of electrostatic interaction. The counterion condensation is seen to follow the adsorption process and the effective polymer charge increases with chain stiffness. Size and shape, as calculated through the radius of gyration, effective persistence length, and hydrodynamic radius, are studied. Stable coil-like, globular, folded-chain, toroidal, and rodlike configurations are possible at suitable combinations of values of chain stiffness, chain length, electrostatic interaction strength, and the valency of counterion. For high strengths of electrostatic interactions, sufficiently stiff polyelectrolytes form toroids in the presence of multivalent counterions, whereas flexible polyelectrolytes form disordered globules. The kinetic features of the nucleation and growth of toroids are monitored. Several metastable structures are found to frustrate the formation of toroids. The generic pathway involves the nucleation of one primary loop somewhere along the chain contour, followed by a growth process where the rest of the chain is folded continuously on top of the primary loop. The dependence of the average radii of toroids on the chain length is found to be roughly linear, in disagreement with existing scaling arguments.     

Synthesis and Crystal Structure of Bis(nitrate)bis(N-n-octyl-α-pyrrolidone)uranyl (II)

1 INTRODUCTION Tri-butyl phosphate (TBP) has been widely used for the extraction reagent in Th-U fuel to separate uranium from thorium. However di-butyl phosphate (DBP) and butyl phosphate (MBP), the radiolytic products of TBP, exhibit some coordinated ability to the fission elements, such as Zr and Nb. The physical and chemical properties of amides and caprolactam are similar to those of TBP, and they selectively extract U(VI) and Th(VI). The principal advantages of amides an…     

Effect of counterion species on colloidal crystal

The effect of counterion species on the colloidal crystal structure in a dispersion was carefully investigated as a function of the degree of neutralization (alpha) by the ultra-small-angle X-ray scattering technique. The nearest neighbor interparticle distance (2D(exp)) first increased with decreasing alpha, and then decreased after passing through the maximum. This behavior was confirmed for K(+), Li(+), Ca(2+), TMA(+) (tetramethylammonium) as a counterion, and Na(+) in our previous report (Harada, T.; Matsuoka, H.; Ikeda, T.; Yamaoka, H. Langmuir 2000, 16, 1612). However, the alpha value of the maximum position (alpha(max)) largely depended on the counterion species, and it was in the order K(+) < Na(+) < TMA(+) approximately Li(+). This behavior was well characterized by the specific features of each ion: the alpha(max) map could be well superimposed in the Stokes radius-crystal ion radius relationship of counterions. The alpha(max) dependence on Stokes radius was very similar to that of the B coefficient by Jones and Dole except in the case of Ca(2+). In principle, the smaller the value for B, the smaller alpha(max), indicating that a water structure breaker such as K(+) can more easily destroy the colloidal crystal structure. In other words, the effect of the counterion species on colloidal crystal stability follows the Hofmeister series. Including Ca(2+), the relationship was linear for the alpha(max) values plotted as a function of the limiting equivalent conductivity of small ions. A counterion with larger conductivity would be a stronger breaker for the colloidal crystal structure.     

Synthesis and Crystal Structure of Binuclear Copper （Ⅱ） Complex Containing （Dimethylaminomethyl）ferrocene

1 INTRODUCTION Transition metal complexes with ferrocene are of considerable interest in the past fifty years because of their novel structures and special properties[1, 2]. The chemistry of ferrocene and its derivatives has become richer and richer in the last decade. Many complexes containing ferrocenyl have been synthesized and characterized[3～5]. Recently we have reported the synthesis and crystal structure of dibromo[1,1?bis(diphenylphosphino)- ferrocene]cadmium (Ⅱ)[6]. Herein we…     

关于聚电解质单链抗衡离子浓度径向分布的研究

采用单分子荧光显微统计光谱技术,通过将pH响应型荧光探针分子精确标记于聚苯乙烯磺酸钠分子链末端,并通过不同长度的多肽链调节分子链与探针分子间的距离,有效测量了聚苯乙烯磺酸钠单分子链的抗衡离子浓度的空间分布.实验结果清晰展示了聚电解质分子链的抗衡离子云结构,并确定了抗衡离子浓度随着距离分子链末端长度的不同而发生变化的规律,为描述聚电解质抗衡离子浓度的径向分布特征提供了实验信息.     

Synthesis and Structural Characterization of a Cyano-bridged Dinuclear Neodymium(III)-iron(III) Complex [Nd(DMSO)_5(H_2O)_2](μ-CN)[Fe(CN)_5]

1 INTRODUCTION The Prussian-Blue analogues and hybridPrussian-Blue families have attracted great attentionfor decades due to their rich and interesting struc-tures and magnetic behaviors[1]. In order to find outthe features of the ligands to form var…     

单核镍(Ⅱ)配合物[Ni(IDB)_2][C_6H_4(OH)COO].ClO_4.CH_3CH_2OH.H_2O的合成和晶体结构

标题配合物是由三齿配体N, N-二(2-苯并咪唑亚甲基)胺(IDB)、Ni(ClO4)2·6H2O与水杨酸钠在乙醇溶液中反应得到的紫色晶体。用X-射线衍射测定了其单晶结构。结果表明,该晶体属三斜晶系,P 空间群,化学式:C41H43ClN10NiO9,Mr = 914.01,a = 11.010(2),b = 13.800(3),c = 15.550(3) 牛 = 100.75(3),?= 102.97(3), = 107.56(3)? V = 2111.3(7) ?,Z = 2,F(000) = 952,Dc = 1.438 g/cm3,(MoK) = 0.591 mm-1,8215个独立可观测点(I>2(I))。最终偏离因子R(I>2(I)):R = 0.0591, wR = 0.1325;R(全部数据): R = 0.1302,wR = 0.1572。结构分析表明,镍(Ⅱ)分别与2个IDB配体中的苯并咪唑的4个氮和胺基的2个氮配位形成畸变的八面体构型。