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In this work, the effects of various high molecular weight cationic poly(vinyl alcohols), CPVAs, on the fiber morphology and the properties of papers made from fractionated refined fibers were investigated. At first, bleached sulfite fibers were refined under various revolutions and then refined fibers were fractionated under various time intervals to obtain refined fibers with a similar fiber length and fines content. Then, 20 mg/g CPVAs with various charge densities was adsorbed on the fractionated refined fibers prior to making hand sheets. The results showed that the lower the charge density of CPVA, the higher the effectiveness of CPVA in improving the paper strength at any refining revolution. The reasons for such a phenomenon were perhaps the different configurations of CPVAs on the surface of the fibers and the different adhesion/repulsion forces developed between CPVA-modified fibers in hand sheets. Also, by reducing the freeness of the fractionated fibers (increasing the refining revolutions), the effect of CPVA in improving the paper strength was reduced. In this case, the CPVAs tended to cover the fibrils on the fiber surface, which was demonstrated by SEM observations, thus reducing the contact area of the fractionated refined fibers. [ABSTRACT FROM AUTHOR]

Mo2C MXene is a two-dimensional material, which can be applied as a co-catalyst to significantly enhance the photocatalytic performance of CdS for H2 production. To understand the effect of the synthesis process of Mo2C MXene nanosheets on the catalytic performance, in this paper, Mo2C MXene was made from Mo2Ga2C by hydrothermal etching in different etchants. Diverse cations (Li+, Na+, K+, or NH4+) in etchants resided on the surface of Mo2C MXene nanosheets. Then, the samples were used to construct CdS/Mo2C-MXene composites for photocatalytic H2 evolution. Among them, Mo2C MXene with Li+ shows the best photocatalytic H2 production rate of 22,048 μmol g–1 h–1 under visible light. The remarkable performance arises from the modification at the nanoscale of Mo2C MXene with Li+, thereby resulting in better photoabsorption behavior, high separation efficiency of photogenerated carriers, and fast charge transfer at the heterointerface. Moreover, the energy band structures explain that the changes of band gap and the position of the conductive band in the photocatalyst tuned by cations are also key to affect photocatalytic activities. [ABSTRACT FROM AUTHOR]

The recently reported bis(1-pyrenyl)azine, easily prepared in a one-step reaction from 1-pyrenecarboxaldehyde and hydrazine hydrate, is used as a receptor for the visual detection of Hg2+ and Cu2+ ions in solution in an undergraduate laboratory experiment. The receptor was also supported on both filter paper and a hydrophobic PTFE (polytetrafluoroethylene) membrane, and the resulting probe-coated sheets were successfully used for selective sensing of the same metal ions using optical and fluorescent spectroscopies. This project provides an opportunity to organic chemistry students to learn about the challenging problem of selectively detecting toxic metal ions, such as Cu2+ and Hg2+, in solution. [ABSTRACT FROM AUTHOR]

In this paper, we study the collapse of a mixed insoluble monolayer formed by a cationic matrix, dioctadecyl-dimethylammonium bromide (DOMA), and a tetra-anionic porphyrin, tetrakis(4-sulfonatophenyl)porphyrin (TSPP), in a molar ratio TSPP/DOMA = 1:4. During the collapse of this system, we visualized the formation of circular domains consisting exclusively of trilayer, although the domains coalescence was not observed. The coexistence of trilayer and monolayer at the final step of the collapse cannot be interpreted exclusively in terms of a thermodynamic phase equilibrium, intervening as an additional factor the anisotropic line tension of the domain. A high line tension implies a high resistance to the domain deformation, and the anisotropy of the line tension implies the lack of coalescence between these domains, which has been experimentally observed by Brewster angle microscopy for us. Under these circumstances, the domains of collapsed material could enclose monolayer regions where the local surface pressure drops thus stopping the collapse process. The collapse of the TSPP/DOMA system is reversible, that is, the return of the three-dimensional material to the monolayer fits into a simple kinetics according to the nucleation−growth-collision theory. As for the collapse, the reverse process is also affected by the line tension of the domains. This paper relates the high line tension and the anisotropic line tension of a given domains with the reversible nature of the collapse process. [ABSTRACT FROM AUTHOR]

Through the use of the Active Thermochemical Tables approach, the best currently available enthalpy of formation of HO2 has been obtained as ΔfH298°(HO2) = 2.94 ± 0.06 kcal mol-1 (3.64 ± 0.06 kcal mol-1 at 0 K). The related enthalpy of formation of the positive ion, HO2+, within the stationary electron convention is ΔfH298°(HO2+) = 264.71 ± 0.14 kcal mol-1 (265.41 ± 0.14 kcal mol-1 at 0 K), while that for the negative ion, HO2- (within the same convention), is ΔfH298°(HO2-) = −21.86 ± 0.11 kcal mol-1 (−21.22 ± 0.11 kcal mol-1 at 0 K). The related proton affinity of molecular oxygen is PA298(O2) = 100.98 ± 0.14 kcal mol-1 (99.81 ± 0.14 kcal mol-1 at 0 K), while the gas-phase acidity of H2O2 is ΔacidG298°(H2O2) = 369.08 ± 0.11 kcal mol-1, with the corresponding enthalpy of deprotonation of H2O2 of ΔacidH298°(H2O2) = 376.27 ± 0.11 kcal mol-1 (375.02 ± 0.11 kcal mol-1 at 0 K). In addition, a further improved enthalpy of formation of OH is briefly outlined, ΔfH298°(OH) = 8.93 ± 0.03 kcal mol-1 (8.87 ± 0.03 kcal mol-1 at 0 K), together with new and more accurate enthalpies of formation of NO, ΔfH298°(NO) = 21.76 ± 0.02 kcal mol-1 (21.64 ± 0.02 kcal mol-1 at 0 K) and NO2, ΔfH298°(NO2) = 8.12 ± 0.02 kcal mol-1 (8.79 ± 0.02 kcal mol-1 at 0 K), as well as H2O2 in the gas phase, ΔfH298°(H2O2) = −32.45 ± 0.04 kcal mol-1 (−31.01 ± 0.04 kcal mol-1 at 0 K). The new thermochemistry of HO2, together with other arguments given in the present work, suggests that the previous equilibrium constant for NO + HO2 → OH + NO2 was underestimated by a factor of ∼2, implicating that the OH + NO2 rate was overestimated by the same factor. This point is experimentally explored in the companion paper of Srinivasan et al. (next paper in this issue). [ABSTRACT FROM AUTHOR]

In this paper, treatment of N-(isonicotinoyl)-N'-nicotinoylhydrazine (inh) and Agl with excess Kl afforded a unique coordination polymeric cluster [[Agl(inh)]6(Kl)]n (1) with the hexagram cluster units centered by µ6-l. In the polymer these hexagram units are parallel to the ab plane and are linked by separated K+ centers through inh. Polymer 1 represents the first example of coinstantaneous cation-anion-induced supramolecular self-assembly with nanoscale inner cavities. The polymer's third-order nonlinear optical (NLO) properties were determined by the Z-scan technique in DMF solution. The results show that the polymer has strong third-order optical nonlinearities. The nonlinear absorptive index a2 and refractive index n2 are calculated to be 1.044 × 10-9 mW-1 and 2.827 × 10-11 esu, respectively. The values are comparable to those of the reported cluster polymers. The optical limiting experiments show that the present cluster exhibits a large optical limiting capacity. The value of the limiting threshold was measured as 0.53 J cm-2 from the optical limiting experimental data. This value is three times better than 1.6 J cm-2 of C60. This paper also gives a summary and comparison on the optical limiting properties of oligomeric and polymeric clusters. [ABSTRACT FROM AUTHOR]

Zeolites with hierarchical structures are of particular interest because such structures can improve molecular diffusion, particularly that of bulky molecules. N,N,N,N',N',N'-Hexapropylpentanediammonium cations (Pr6-diquat-5), a simple diquaternary ammonium organic structure-directing agent (OSDA), can direct the formation of hierarchically and sequentially intergrown MFI zeolites without employing any mesoporogens. In this paper, the effects of OSDAs having structures similar to Pr6-diquat-5 but different lengths of alkyl spacers and/or different substituting groups on the phase selectivity and morphology of the resulting zeolites are presented. It was revealed that the number of carbon atoms between two charged nitrogens in the OSDAs significantly affected the intergrowth and morphology of the crystals formed. In addition, the propyl-substituted OSDAs were found to be very selective to the formation of MFI zeolite, whereas the butyl-substituted OSDAs were not. For Pr6-diquat-5, the condition for the formation of hierarchically and sequentially intergrown MFI zeolites was somewhat narrow with the optimized molar composition of 1 SiO2:0.2 Pr6-diquat-5:0.375-0.500 KOH:200 H2O:4 EtOH. Defect lines observed on the obtained zeolite crystals by a transmission electron microscope were considered to be connectors for such intergrowths. The unique intergrowth formed by Pr6-diquat-5 was surmised to be due to the unusual fitting of Pr6-diquat-5 inside the channels of MFI zeolite, which was explained by comparing molecular dimensions and stabilization energies of each OSDA. [ABSTRACT FROM AUTHOR]

G-quadruplex (GQ) structures formed from guanine-rich sequences are found throughout the genome and are overrepresented in the promoter regions of some oncogenes, at the telomeric ends of eukaryotic chromosomes, and at the 5′-untranslated regions of mRNA. Interaction of small molecule ligands with GQ DNA is an area of great research interest to develop novel anticancer therapeutics and GQ sensors. In this paper we examine the interactions of TMPyP4, its isomer TMPyP2 (containing N-methyl-2-pyridyl substituents, N-Me-2Py) as well as two metal derivatives ZnTMPyP4 and CuTMPyP4 with GQs formed by dT4G4 and dT4G4T in 100 mM K+ or Na+ conditions. The DNA sequences were chosen to elucidate the effect of the 3′-T on the stabilization effect of porphyrins, binding modes, affinities, and stoichiometries determined via circular dichroism melting studies, UV-vis titrations, continuous variation analysis, and fluorescence studies. Our findings demonstrate that the stabilizing abilities of porphyrins are stronger toward (dT4G4)4 as compared to (dT4G4T)4 (ΔTm is 4.4 vs -6.4 for TMPyP4; 12.7 vs 5.7 for TMPyP2; 16.4 vs 12.1 for ZnTMPyP4; and 1.9 vs -8.4 °C for CuTMPyP4) suggesting that the 3′G-tetrad presents at least one of the binding sites. The binding affinity was determined to be moderate (Ka ∼ 106-107 μM-1) with a typical binding stoichiometry of 1:1 or 2:1 porphyrin-to-GQ. In all studies, ZnTMPyP4 emerged as a ligand superior to TMPyP4. Overall, our work contributes to clearer understanding of interactions between porphyrins and GQ DNA. [ABSTRACT FROM AUTHOR]

This paper studies the wetting properties of seven phosphonium cation-based ionic liquids: trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphinate [P66614][(iC8)2PO2], trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate [P66614][BEHP], trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) imide [P66614][NTf2], tributyltetradecylphosphonium dodecylbenzenesulfonate [P44414][DBS], tributylethylphosphonium diethylphosphate [P4442][DEP], trihexyltetradecylphosphonium dicyanamide [P66614][DCA], and trihexyltetradecylphosphonium chloride [P66614][Cl]. The surface tension was analyzed using the Gibbs free energy in a temperature range of 293-353 K, obtaining the expected linear decrease with temperature rise. The contact angle was measured on four different surfaces (AISI 52100 steel, CrN, TiN, and ZrN) and all liquids with high surface tensions interacting with hydrophobic systems displayed high contact angles as expected. The polarity fraction (PF) and the spreading parameter (SP) were estimated to complete and improve the wetting characterization of these ionic liquids, finding TiN-[P66614][BEHP] and TiN-[P66614][(iC8)2PO2] as the most favorable surface-ionic liquid combinations from a wetting point of view. [ABSTRACT FROM AUTHOR]

Description of the local microscopic structure in ionic liquids (ILs) is a prerequisite to obtain a comprehensive understanding of the influence of the nature of ions on the properties of ILs. The local structure is mainly determined by the spatial arrangement of the nearest neighboring ions. Therefore, the main interaction patterns in ILs, such as cation-anion H-bond-like motifs, cation-cation alkyl tail aggregation, and ring stacking, were considered within the framework of the nearest-neighbor approach with respect to each particular interaction site. We employed classical molecular dynamics (MD) simulations to study in detail the spatial, radial, and orientational relative distribution of ions in a set of imidazolium-based ILs, in which the 1-butyl-3-methylimidazolium (C4mim+) cation is coupled with the acetate (OAc-), chloride (Cl-), tetrafluoroborate (BF4 -), hexafluorophosphate (PF6 -), trifluoromethanesulfonate (TfO-), or bis(trifluoromethanesulfonyl)amide (TFSA-) anion. It was established that several structural properties are strongly anion-specific, while some can be treated as universally applicable to ILs, regardless of the nature of the anion. Namely, strongly basic anions, such as OAc- and Cl-, prefer to be located in the imidazolium ring plane next to the C-H2/4-5 sites. By contrast, the other four bulky and weakly coordinating anions tend to occupy positions above/below the plane. Similarly, the H-bond-like interactions involving the H² site are found to be particularly enhanced in comparison with the ones at H4-5 in the case of asymmetric and/or more basic anions (C4mimOAc, C4mimCl, C4mimTfO, and C4mimTFSA), in accordance with recent spectroscopic and theoretical findings. Other IL-specific details related to the multiple H-bond-like binding and cation stacking issues are also discussed in this paper. The secondary H-bonding of anions with the alkyl hydrogen atoms of cations as well as the cation-cation alkyl chain aggregation turned out to be poorly sensitive to the nature of the anion. [ABSTRACT FROM AUTHOR]

This paper provides spectral characterizations of the two isomers of the 1-methylenepyrene cation, namely, the 1-pyrenemethylium and a pyrene-like isomer owing a tropylium cycle. Both are possible photodissociation products of the 1-methylpyrene cation and were proposed as potential contributors to the diffuse interstellar bands. In that respect, vibrational and electronic spectra are computed for the optimized structures at the density functional theory (DFT) and time-dependent (TD-)DFT levels. Finite temperature effects on these spectra are estimated from molecular dynamics simulations within the density functional-based tight-binding (DFTB) and TD-DFTB frameworks, these methods being first benchmarked against DFT and TD-DFT calculations. The computed spectra allow discrimination of the two isomers. When the temperature increases, bands are observed to redshift and merge. The isomerization mechanism is investigated with the metadynamics technique, a biased dynamics scheme allowing to probe reaction mechanisms with high energy barriers by investigating the free energy surface at various temperatures. Four pathways with similar barrier heights (3.5-4 eV) are found, showing that the interconversion process would only occur in interstellar clouds under photoactivation. The present study opens the way to simulations on larger methyl- and methylenePAHs of astrophysical interest and their experimental investigation. [ABSTRACT FROM AUTHOR]

In this paper, with the example of two different polymorphs of KEu(MoO4)2, the influence of the ordering of the A-cations on the luminescent properties in scheelite related compounds (A',A")n[(B',B")O4]m is investigated. The polymorphs were synthesized using a solid state method. The study confirmed the existence of only two polymorphic forms at annealing temperature range 923-1203 K and ambient pressure: a low temperature anorthic a-phase and a monoclinic high temperature β-phase with an incommensurately modulated structure. The structures of both polymorphs were solved using transmission electron microscopy and refined from synchrotron powder X-ray diffraction data. The monoclinic β-KEu(MoO4)2 has a (3+1)-dimensional incommensurately modulated structure (superspace group I2/b(aβ0)00, a = 5.52645(4) Å, b = 5.28277(4) Å, c = 11.73797(8) Å, γ = 91.2189(4)o, q = 0.56821(2)a*-0.12388(3)b*), whereas the anorthic a-phase is (3+1)-dimensional commensurately modulated (superspace group I1(aβγ)0, a = 5.58727(22) Å, b = 5.29188(18)Å, c = 11.7120(4) Å, a = 90.485(3)o, β = 88.074(3)o, q = 91.0270(23)o, q = 1/2a* + 1/2c*). In both cases the modulation arises due to Eu/K cation ordering at the A site: the formation of a 2-dimensional Eu3+ network is characteristic for the a-phase, while a 3-dimensional Eu3+-framework is observed for the β-phase structure. The luminescent properties of KEu(MoO4)2 samples prepared under different annealing conditions were measured, and the relation between their optical properties and their structures is discussed. [ABSTRACT FROM AUTHOR]

Despite strong electrostatic repulsion,like-charged ions in aqueoussolution can effectively attract each other via ion–water interactions.In this paper we investigate such an effective interaction of like-chargedions in water by using the 3D-RISM-SCF method (i.e., electronic structuretheory combined with three-dimensional integral equation theory formolecular solvents). Free energy profiles are calculated at the CCSD(T)level for a series of molecular ions including guanidinium (Gdm+), alkyl-substituted ammonium, and aromatic amine cations.Polarizable continuum model (PCM) and mean-field QM/MM free energycalculations are also performed for comparison. The results show thatthe stability of like-charged ion pairs in aqueous solution is determinedby a very subtle balance between interionic interactions (includingdispersion and π-stacking interactions) and ionic solvation/hydrophobiceffects and that the Gdm+ion has a rather favorable characterfor like-charge association among all the cations studied. Furthermore,we investigate the like-charge pairing in Arg-Ala-Arg and Lys-Ala-Lystripeptides in water and show that the Arg-Arg pair has a contactfree-energy minimum of about −6 kcal/mol. This result indicatesthat arginine pairing observed on protein surfaces and interfacesis stabilized considerably by solvation effects. [ABSTRACT FROM AUTHOR]

Electrospray ionization (ESI) in the negative ion mode has received less attention in fundamental studies than the positive ion electrospray ionization. In this paper, we study the efficiency of negative ion formation in the ESI source via deprotonation of substituted phenols and benzoic acids and explore correlations of the obtained ionization efficiency values (logIE) with different molecular properties. It is observed that stronger acids (i.e., fully deprotonated in the droplets) yielding anions with highly delocalized charge [quantified by the weighted average positive sigma (WAPS) parameter rooted in the COSMO theory] have higher ionization efficiency and give higher signals in the negative-ion ESI/MS. A linear model was obtained, which equally well describes the logIE of both phenols and benzoic acids (R2 = 0.83, S = 0.40 log units) and contains only an ionization degree in solution (α) and WAPS as molecular parameters. Both parameters can easily be calculated with the COSMO-RS method. The model was successfully validated using a test set of acids belonging neither to phenols nor to benzoic acids, thereby demonstrating its broad applicability and the universality of the above-described relationships between IE and molecular properties. [ABSTRACT FROM AUTHOR]

Thermal conductivity is an importantthermophysical propertyof ionic liquids (ILs). In this paper, a database for the thermalconductivity of ILs was established by collecting experimental datafrom literature covering the period from 2007 to 2013, including 359data points, 45 ILs. The influences of temperature and the alkyl chainlength of the cation on thermal conductivity were also discussed.A topological index method was proposed to estimate the thermal conductivityof ILs based on collected data which were divided into training (299data points, 38 ILs) and testing (60 data points, 7 ILs) sets. Thetotal average absolute deviation between the calculated and literaturedata was found to be 2.3%, with 2.1% for the training set and 2.9%for the testing set. The topological index method guarantees satisfactoryprecision with a simple form and can be easily expanded to new kindsof ILs. [ABSTRACT FROM AUTHOR]

This paper has at its objective the assembling of liposomal assembliesonto nanoparticles. In this manner, one generates nanoparticles witha high loading capacity. Thus, spherical spherical polycationic “brushes”(SPBs) were synthesized by graft polymerizing a cationic monomer,(trimethylammonium)ethylmethacrylate chloride, onto the surface ofmonodisperse polystyrene particles, ca. 100 nm in diameter. Theseparticles were complexed with small unilamellar anionic liposomes,40–60 nm in diameter, composed of egg lecithin (EL) and anionicphosphatidylserine (PS1-) in PS1-/EL ratios from 0.10 to 0.54, a key parameter designated as ν.These complexes were then characterized according to electrophoreticmobility, dynamic light scattering, conductivity, fluorescence, andcryogenic transmission electron microscopy, with the following mainconclusions: (a) All added liposomes are totally associated with SPBsup to a certain saturation concentration (specific for each νvalue). (b) The number of liposomes per SPB particle varies from 40(ν = 0.1) to 14 (ν = 0.5). (c) At sufficiently high liposomeconcentrations, the SPBs experience an overall change from positiveto negative charge. (d) SPB complexes tend to aggregate when theirinitial positive charge has been precisely neutralized by the anionicliposomes. Aggregation is impeded by either positive charge at lowerlipid concentrations, or negative charge at higher lipid concentrations.(e) The liposomes remain intact (i.e., do not leak) when associatedwith SPBs, at ν ≤ 0.5. (f) Complete SPB/liposome dissociationoccurs at external [NaCl] = 0.3 M for ν = 0.1 and at 0.6 M for ν= 0.5. Liposomes with ν = 0.54 do not dissociate from the SPBseven in NaCl solutions up to 1.0 M. (g) Complexation of the PS1-/EL liposomes to the SPBs induces flip-flop of PS1-from the inner leaflet to the outer leaflet. (h)The differences in the ability of PS1-(a cylindricallipid) and CL2-(a conical lipid) to create membranesdefects are attributed to geometric factors. [ABSTRACT FROM AUTHOR]

Supportedionic liquid membranes (SILMs) are promising tools for the separationof carbon dioxide from other gases. In this paper, new imidazolium,pyrrolidinium, piperidinium, and morpholinium ionic liquids with atriethylene glycol side chain and tosylate anions, as well as theirsymmetrical dicationic analogues, have been synthesized and incorporatedinto SILMs. The selectivities for CO2/N2andCO2/CH4separations have been measured. Theselectivities exhibited by the dicationic ionic liquids are up totwo times higher than the values of the corresponding monocationicionic liquids. Quantum chemical calculations have been used to investigatethe difference in the interaction of carbon dioxide with monocationicand dicationic ionic liquids. The reason for the increased gas separationselectivity of the dicationic ionic liquids is two-fold: (1) a decreasein permeance of nitrogen and methane through the ionic liquid layer,presumably due to their less favorable interactions with the gases,while the permeance of carbon dioxide is reduced much less; (2) anincrease in the number of interaction sites for the interactions withthe quadrupolar carbon dioxide molecules in the dicationic ionic liquids,compared to the monocationic analogues. [ABSTRACT FROM AUTHOR]

Major alteration or even destruction of the hydration shell around interacting molecules and ions in solution is an important process that determines how hydrated substances interact. Therefore, the direct observation of structural changes in hydration shells around solutes in close contact with other solutes or surfaces is important for understanding chemical processes that take place in solution. In the work described in this paper, time-resolved IR absorption measurements were performed to study the interaction of hydrated Na+ or tetrapropylammonium cation (Pr4N+) with a hydrophobic CO-covered Pt surface; the adsorption force between cations and the surface was controlled by using an electrochemical system. We found that the hydrophobic hydration shell of Pr4N+ is initially stabilized on the hydrophobic surface, but application of a strong force to the cation approaching CO destroys the water layers between them. This process is rather slow, taking a few hundred milliseconds. Hydrophilic Na+ behaves quite differently from Pr4N+ due to the different structure of its hydration shell. These experimental results are supported by molecular dynamics simulations. [ABSTRACT FROM AUTHOR]

This paper presents a computational approach to the deliberate design of host architectures that recognize and bind specific guests. De novo molecule building software, HostDesigner, is interfaced with molecular mechanics software, PCModel, providing a tool for generating and screening millions of potential structures. The efficacy of this computer-aided design methodology is illustrated with a search for bis-amidoxime chelates that are structurally organized for complexation with the uranyl cation. [ABSTRACT FROM AUTHOR]

In this paper, a new synthetic way to modify naphthalene diimide (NDI) at "shoulder" positions is reported. The key step of the transformation is the intramolecular cyclization involving ethynyl and imidecarbonyl groups. The structure of the intermediate pyrylium cation was confirmed by X-ray crystal structural analysis. New conjugated molecules 1a-g were successfully synthesized in acceptable yields. Their absorption and fluorescence spectra were measured. Among them 1c-f are strongly emissive in solutions. Furthermore, 1b-f are also fluorescent in their solid states; in particular, 1b exhibits a typical aggregation-induced enhanced emission feature. Yellow-emissive microfibrils of 1d show potential optical waveguide behavior. HOMO/LUMO energies of 1a-f were determined based on their cyclic voltammograms. The results also reveal that HOMO/LUMO energies of these new conjugated molecules are influenced by the two flanking moieties. Notably, the thin film of 1c that is emissive shows p-type semiconducting behavior with hole mobility up to 0.0063 cm² V-1 s-1 based on the transfer and output characteristics of the OFET (organic field effect transistor). [ABSTRACT FROM AUTHOR]

Heterolysis rate constants k1 of differently substituted 1,3-diarylallyl halides and carboxylates have been determined in various solvents. The linear free energy relationship log k1 = sf(Nf + Ef) was found to predict the heterolysis rates (log k1) of 1,3-diarylallyl derivatives with a standard deviation of 0.26, corresponding to a factor of 1.82 in k1, and maximum deviation in k1 of a factor of 5. Some systematic deviations are evident, however. Thus, 1,3-diarylallyl carboxylates always react faster and 1,3-diarylallyl chlorides always react more slowly than calculated by the quoted correlation equation when both types of leaving groups were used to determine the electrofugality parameters Ef. As 1,3-diarylalyl cations are generated faster in solvolysis reactions and also react faster with nucleophiles than benzhydrylium ions of similar thermodynamic stabilities, i.e., Lewis acidities, one can conclude that the reactions involving 1,3-diarylallyl cations proceed with lower intrinsic barriers than those involving benzhydrylium ions. The electrofugality parameters Ef of 1,3-diarylallylium ions determined in this work were combined with the electrophilicity parameters E of the corresponding cations as well as with the results on ion pair dynamics reported in preceding papers for generating the full mechanistic spectrum of 1,3-diarylallyl solvolyses. [ABSTRACT FROM AUTHOR]

Room temperature ionic liquids (ILs) are effective matrices in secondary ion mass spectrometry (SIMS) and matrix assisted laser desorption ionization (MALDI). In this paper, we examine the role of proton transfer in the mechanism of secondary ion enhancement using IL matrices in SIMS. We employ hydrogenated and deuterated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) as analytes to investigate the origin of proton transfer. The data indicate that protons from the IL anion transfer to the analyte in solution leading to an increase in the secondary ion intensity of the protonated molecular ion. The chemical identity of the matrix cation also affects analyte signal intensities. Using deuterated DPPC we observe that protons (deuterium) from the DPPC tail group react with the cation of the IL liquid leading to an increase in (cation + D) ion intensities. Further, the data suggest that the transfer kinetics of deuterium (hydrogen) is correlated with the secondary ion enhancements observed. The highest secondary ion enhancements are observed for the least sterically hindered cation. Neither the proton affinity nor the pK of the IL cation have a large effect on the analyte ion intensities, suggesting that steric factors are important in determining the efficacy of IL matrices for a given analyte. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In this paper, four organic–inorganic hybrid complexeswereprepared using a cationic surfactant dimethyldioctadecylammonium (DODA)to replace the counter cations of four Keggin-type polyoxometalate(POM) clusters with gradually increased negative charges, PW12O403–, SiW12O404–, BW12O405–, and CoW12O406–. The formedsurfactant-encapsulated POM (SEP) complexes showed typical amphiphilicproperties and can be spread onto the air–water interface toform Langmuir monolayers. The interfacial behavior of the SEP monolayerfilms was systemically studied by multiple in situand ex situcharacterization methods includingBrewster angle microscopy (BAM), atomic force microscopy (AFM), reflection–absorptioninfrared (RAIR), and X-ray photoelectron spectroscopy (XPS). We foundthat the increasing alkyl chain density of SEPs leads to an enhancedstability and a higher collapse pressure of SEP Langmuir monolayers.Moreover, a second layer evolved as patterns from the initial monolayersof all the SEPs, when the surface pressures approached the collapsevalues. The rational combination of alkyl chain density and surfacepressure can precisely control the size and the morphology of SEPpatterns transforming from disk-like to leaf-like structures on amicrometer scale. The pattern formation was demonstrated to be drivenby the self-optimized surface energy of SEP monolayers. This findingcan direct a new strategy for the fabrication of POM-hybrid filmswith controllable patterns, which should be instructive for designingPOM-based thin film devices. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of discrete, moleculariron-oxoclusters is pursued in the interest of molecular magnets, bioinspiredmaterials and models for the geochemical aqueous-mineral interface.Iron-oxo clusters are challenging to synthesize in water, due to theextremely acidic and reactive nature of dissolved iron species, andthus require chelating ligands to passivate and neutralize the clustersurface. The 2-hydroxy-1,3-N,N,N′,N′-diamino-propanetetraaceticacid (HPDTA) ligand has been used to isolate several Al and Fe clustergeometries, including the square clusters Fe4(HPDTA)2and Al4(HPDTA)2. While prior reportson the Fe4(HPDTA)2cluster have focused on themagnetic properties, no solution characterization has been carriedout. Using electrospray ionization mass-spectrometry (ESI-MS) we showthis anionic Fe4(HPDTA)2cluster can be dissolvedintact in water, and recrystallized with virtually any metal as acountercation. The bonding of the metal cation to the square faceof the cluster trends with ionic radii of the cations, as shown bystructural characterization of Fe4(HPDTA)2withLi+, Na+, Cs+, Mg2+, Ba2+, La3+, Eu3+, and Zn2+.This trend is similar to that observed for association of cationson metal oxide surfaces in the environment. Furthermore, protonationof the bridging oxo ligands of this series of Fe4(HPDTA)2clusters is variable (0, 1, or 2 protons), and structuresas a function of protonation is discussed. This paper, largely structuralin nature, sets the foundation for future aqueous phase studies ofiron-oxo molecular clusters as models for the oxide-water interfacein the natural aqueous environment. [ABSTRACT FROM AUTHOR]

In this paper we report the characterization of the dichloromethane(DCM)/water interface in terms of density profile, width, and surfacestructure. The use of steered molecular dynamics (SMD) to study thetransfer of the K+cation from the organic layer to thewater layer is also described. The corresponding free energy is insemiquantitative agreement with published experimental and theoreticalresults. The transference of the K+cation from the waterlayer toward the DCM layer occurs with concomitant water transportas a water microdroplet that detaches itself from the water layerafter ca. 16 Å of penetration into the organic layer by breakingthe thin water thread that unites both. Complexation of the watermicrodroplet by a polyethylene-glycol type podand induces the lossof water molecules from the water microdroplet to bulk DCM and, eventually,to the water layer. [ABSTRACT FROM AUTHOR]

This study reports the characteristic fragmentation patterns from two polysiloxane polymers that form ordered overlayer on silver substrates. Results are compared for the bombardment of various monatomic and polyatomic projectiles of Cs, C (10 keV), Bi, and Bi (25 keV) in the high mass range time-of-flight secondary ion mass spectrometry (TOF-SIMS) spectra. Results are reported from sub-monolayer (solution cast) coverages of poly(dimethylsiloxane)s with the number average molecular weights (M) of 2200 and 6140 Da, respectively, and Langmuir-Blodgett monolayers of poly(methylphenylsiloxane) with molecular weights (MW) from 600 and 1000 Da. For each film, Bi projectiles resulted in the emission of positive silver cluster ions from the substrate under the polymer overlayer and peaks corresponding to silver cluster ions with larger mass were observed by impact of polyatomic 25 keV Bi projectiles. In addition, depending on the change of energy of Bi, a different pattern of fragments was observed. With Cs and C impact, however, the emission of silver cluster ions was not detected. In the case of C impact for PDMS-6140, peaks corresponding to silver-cationized intact oligomers were not observed. In this paper, these results are explained by the possible bombardment mechanism for each projectile, based on its mass, energy, and split trajectories of the component atoms under the polyatomic impact. [ABSTRACT FROM AUTHOR]

Nonbonding valence electrons, better known as lone pairs, are found us all anions as well as in canons in their lower oxidation states. In this paper the properties of lone pans are analyzed using a bond valence model defined in terms of a core and-valence-shell picture, which can be reduced to the point charges of the ionic model A bond is defined in terms of the electrostatic flux linking the atoms. When the lone pairs are inactive, they are uniformly distributed around the valence shell and the ion behaves like a main group ion that has no lone pairs. In this state it can be assigned a bonding strength that obeys the valence matching rule (for stable bonds the cation and anion bonding strengths should not differ by more than a factor of 2). However, when an ion with a lone pair has a bonding strength less than half that of the counterion, it has the flexibility to form a stronger bond by converting lone pair electron density to bonding electron density in the region where the valence shells overlap. To conserve the number of lone pairs, bonding electron density elsewhere in the valence shell is converted to lone pairs. The result is the adoption of an anisotropic coordination environment with fewer bonds but bonds whose enhanced strength matches the higher bonding strength of the counterion. This analysis raises questions about the validity of a number of traditional ideas on the nature of chemical bonds It shows that lone pairs do not form dative bonds. In a neutral molecule, the base function that is often attributed to a lone pair is always accompanied by an acid function, and both functions must be simultaneously activated. Electron-pair bonds, which are found only around strongly bonding cations, normally result in the formation of molecules, explaining why the models developed to describe molecular structures are unable to give good descriptions of extended crystal structures. [ABSTRACT FROM AUTHOR]

2,4-Dinitroanisole (DNAN) is being used as a replacement for 2,4,6-trinitrotoluene (TNT) as a less-sensitive melt-cast medium explosive than TNT. In this paper, we studied the surface-enhanced Raman spectroscopy (SERS) analysis of DNAN using Ag nanoparticles (AgNPs) modified by l-cysteine methyl ester hydrochloride. Due to the formation of a Meisenheimer complex between DNAN and the modifier, the modified AgNPs can detect 20 μg/L (0.2 ng) and 0.1 mg/L (1 ng) DNAN in deionized water and aged tap water, respectively. Three other chemicals (l-cysteine, N-acetyl-l-cysteine, and l-cysteine ethyl ester hydrochloride) were used as AgNPs modifiers to study the mechanism of the SERS of DNAN. It was confirmed that the amino group of l-cysteine methyl ester hydrochloride was the active group and that the methyl ester group significantly contributed to the high SERS sensitivity of DNAN. In order to further test the mechanism of Meisenheimer complex formation, the effect of anions and cations present in natural water on the SERS of DNAN was studied. It was found that CO32-, Cl–, and K+at 100 mg/L did not negatively affect the SERS of 10 mg/L DNAN, while SO42-, Na+, Mg2+, and Ca2+at 100 mg/L significantly quenched the SERS of 10 mg/L DNAN. The negative effect of the bivalent cations could be offset by SO42-. [ABSTRACT FROM AUTHOR]

The diffusion of charged polymers into the pores of cellulose fibers has not yet been fully understood due to the complexity of the interaction between polymers and fibers. In this paper, the diffusion of cationic-modified poly(vinyl alcohol) (CPVA) with tailored charge densities and a relatively high molecular weight into the pores of bleached aspen high-yield pulp (via a chemi-thermomechanical pulping process) was quantitatively investigated via an adsorption analysis, charge density analysis, and solute exclusion technique (SET). The results showed that the adsorption of the low-charged CPVA was substantially higher than that of the high-charged CPVA on fibers. The surface charge density analysis confirmed that approximately 17 mg/g of the high-charged CPVA adsorbed on the outer surface and on the macropores of fibers and the remaining (23 mg/g) diffused into the pores. The SET analysis confirmed that the pore size of fibers was more significantly reduced by applying the low-charged CPVA than the high-charged one. The influencing factors for the diffusion of CPVA into the large and small pores were related to the repulsion force developed between the adsorbed polymers and approaching polymers, entropy increase, and the polymer flexibility. The Brunauer–Emmett–Teller surface area analysis showed an increase in the surface area of fibers upon CPVA adsorption. It was proposed that the diffused CPVA prevented complete fiber pore collapse during drying, which eventually increased the surface area of fibers. [ABSTRACT FROM AUTHOR]

Polycations with varying chemistries and architectureshave beensynthesized and used in DNA transfection. In this paper we connectpoly-l-lysine (PLL) architecture to DNA-binding strength,and in turn transfection efficiency, since experiments have shownthat graft-type oligolysine architectures [e.g., poly(cyclooctene-g-oligolysine)] exhibit higher transfection efficiency thanlinear PLL. We use atomistic molecular dynamics simulations to studystructural and thermodynamic effects of polycation–DNA bindingfor linear PLL and grafted oligolysines of varying graft lengths.Structurally, linear PLL binds in a concerted manner, while each oligolysinegraft binds independently of its neighbors in the grafted architecture.Additionally, the presence of a hydrophobic backbone in the graftedarchitecture weakens binding to DNA compared to linear PLL. The bindingfree energy varies nonmonotonically with the graft length primarilydue to entropic contributions. The binding free energy normalizedto the number of bound amines is similar between the grafted and lineararchitectures at the largest (Poly5) and smallest (Poly2) graft lengthand stronger than the intermediate graft lengths (Poly3 and Poly4).These trends agree with experimental results that show higher transfectionefficiency for Poly3 and Poly4 grafted oligolysines than for Poly5,Poly2, and linear PLL. [ABSTRACT FROM AUTHOR]

In the present paper we report combined experimental and theoretical studies of the UV-vis-NIR spectra of the mineral compounds malachite, rosasite, and aurichalcite and of the precursor compounds for Cu/ZnO catalysts. For the copper species in the minerals the crystal field splitting and the vibronic coupling constants are estimated using the exchange charge model of the crystal field accounting for the exchange and covalence effects. On this basis the transitions responsible for the formation of the optical bands arising from the copper centers in minerals are determined and the profiles of the absorption bands corresponding to these centers are calculated. The profiles of the absorption bands calculated as a sum of bands of their respective Cu species are in quite good agreement with the experimental data. In agreement with crystal chemical considerations, the Zn ions were found to be preferentially located on the more regular, i.e., less distorted, octahedral sites in zincian malachite and rosasite, suggesting a high degree of metal ordering in these phases. This concept also applies for the mineral aurichalcite, but not for synthetic aurichalcite, which seems to exhibit a lower degree of metal ordering. The catalyst precursor was found to be a mixture of zincian malachite and a minor amount of aurichalcite. The best fit of the optical spectrum is obtained assuming a mixture of contributions from malachite (0% Zn) and rosasite (38% Zn of [Zn + Cu]), which is probably due to the intermediate Zn content of the precursor (30%). [ABSTRACT FROM AUTHOR]

Smalt was commonly used as a pigment by artists between the 16th and 18th centuries. It is a powdered blue potash glass colored by cobalt ions and often degrades causing dramatic changes in the appearance of paintings. The ann of the work presented in this paper was to investigate the changes in the structure and environment around the cobalt ion on deterioration, to further our understanding of the basis of the loss of color. Particles of well-preserved and altered smalt in microsamples from paintings in the National Gallery, London, and the Louvre, Paris, were analyzed using synchrotron micro-X-ray absorption spectros- copy at the Co K-edge. X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) measurements showed that in intense blue particles the cobalt is predominantly present as Co2+ in tetrahedral coordination, whereas m colorless altered smalt the Co2+ coordination number in the glass structure is increased and there is a shift from tetrahedral toward octahedral coordination. The extent of this shift correlates clearly with the alkali content, indicating that it is caused by leaching of potassium cations, which act as charge compensators and stabilize the tetrahedral coordination of the cobalt ions that is responsible for the blue color. [ABSTRACT FROM AUTHOR]

Previous studies have shown environmentally persistent free radicals (EPFRs) form when chlorine- and hydroxy-substituted benzenes chemisorb on Cu(II)O-containing surfaces under postcombustion conditions. This paper reports the formation of EPFRs on silica particles containing 5% Fe(III)2O3. The EPFRs are formed by the chemisorption of substituted aromatic molecular adsorbates on the metal cation center followed by electron transfer from the adsorbate to the metal ion at temperatures from 150 to 400 °C. Depending on the nature of the adsorbate and the temperature, two organic EPFRs were formed: a phenoxyl-type radical, which has a lower g-value of 2.0024-2.0040, and a second semiquinone-type radical, with a g-value of 2.0050-2.0065. Yields of EPFRs were ∼10× lower for iron than copper, however, the half-lives of EPFRs on iron ranged from 24 to 111 h, compared to the half-lives on copper of 27 to 74 min. The higher oxidation potential of Fe(III)2O3 is believed to result in greater decomposition of the adsorbate, resulting in the lower EPFR yields, but increased stabilization of the EPFR once formed, resulting in the longer half-lives. [ABSTRACT FROM AUTHOR]

The one-electron oxidation potentials [EoxNHE(H2Q)], pKa (pKa1 and pKa2) values, and bond dissociation energies (BDE1 and BDE2) of 118 important p- and o-dihydroquinones in DMSO were systematically predicted for the first time by using DFT method and the PCM cluster continuum model. The calculated results agree well with the available experimental determinations. The study shows that all the five thermodynamic parameters correlate well with the Hammett substituent parameters σp (for p-H2Q, EoxNHE(H2Q·+/H2Q) = 1.66Σσp + 0.54, pKa1 = -5.69Σσp + 16.54, pKa2 = -5.19Σσp + 23.91, BDE1 = 3.43Σσp + 82.29, BDE2 = 4.64Σσp + 67.70 and for o-H2Q, EoxNHE(H2Q·+/H2Q) = 1.85Σσp + 0.46, pKa1 = -5.53Σσp + 13.28, pKa2 = -5.24Σσp + 26.70, BDE1 = 3.54Σσp + 82.08, BDE2 = 3.82Σσp + 75.93), which hints that we can get these thermodynamic parameters as long as the structure of the hydroquinones were known. The comparisons of the calculated five thermodynamic parameters between p-hydroquinones and o-hydroquinones and the number of the phenyl ring effects on these thermodynamic parameters were also studied. At last, intramolecular hydrogen bond energies in hydroquinones at neutral, radical cation, radical, anion different state were systematically calculated and analyzed. Combined with the papers published in our group before, we will have a systematic thermodynamic picture of the transfer details between different kinds of quinones and corresponding hydroquinones, which strongly promote the fast development of the understanding and applications of quinones. [ABSTRACT FROM AUTHOR]

Neutralization of carboxylic acid is an important means to avoid sialic acid dissociation when sialylated glycans are analyzed by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). In this paper, we describe a simple and rapid method to modify the sialic acids of sialylated glycans in the presence of methylamine and (7-azabenzotriazol-1 -yloxy) trispyrrolidinophosphonium hexafluorophosphate (PyAOP). After methylamidation, sialylated glycans can be analyzed by MALDI-MS without loss of the sialic acid moiety. The electrospray ionization mass spectrometry (ESI-MS) and MALDI-MS analysis of both 3'- and 6'-sialyllactose derivatives indicated that the quantitative conversion of sialic acids was achieved, regardless of their linkage types. This derivatization strategy was further validated with the N-glycans released from three standard glycoproteins (fetuin, human acid glycoprotein, and bovine acid glycoprotein) containing different types of complex glycans. Most importantly, this derivatization method enabled the successful characterization of N-glycans of sera from different species (human, mouse, and rat) by MALDI-MS. Because of the mild reaction conditions, the modification in sialic acid residues can be retained. This improvement makes it possible to detect sialylated glycans containing O-acetylated sialic acid moieties using MALDI-MS in positive-ion mode. [ABSTRACT FROM AUTHOR]

This paper reports the synthesis, characterization, and application of two cationic bismuthate clusters by anion templating. The compounds were synthesized under mild hydrothermal treatment and characterized by powder and single-crystal X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis. The first material consists of a cationic hexanuclear bismuthate cluster octahedral in geometry and linked by 1,2-ethanedisulfonate molecules. This structure is thermally stable to about 235 °C. In the second compound, discrete cationic nonanuclear bismuthate clusters interact electrostatically with trifluoromethanesulfonate anions to pack into a nearly layered assembly. The material undergoes a transformation to Bi2O3 upon loss of the triflate groups at about 385 °C. Both materials demonstrate the use of sulfonate groups for the anion-directed assembly of these rare cationic inorganic structures. The application of the 3D octahedral bismuth cluster material toward acidic heterogeneous catalysis is also reported. [ABSTRACT FROM AUTHOR]

To design or simulate air separation by a pressure swing adsorption process (PSA), adsorption equilibrium data in the range of temperatures used in this kind of process are needed. Acquisition of coadsorption equilibrium data is time-consuming, and then a binary model based on pure substance isotherm measurements is usually used to simulate equilibrium in PSA. In this paper, adsorption equilibrium data for nitrogen and oxygen on five faujasite zeolites (NaX, NaLSX, KLSX, and two LiLSX) were obtained at (288, 303, and 318) K and at pressures up to 3000 kPa. Coadsorption equilibria of nitrogen and oxygen mixtures were measured at 400 kPa with an original volumetric apparatus which is able to keep a constant pressure in the measurement cell. The measurements were compared to isotherms calculated by an extended Langmuir−Freundlich model. The influence of compensation cation on the adsorption capacities and selectivities was also analyzed. [ABSTRACT FROM AUTHOR]

In this paper, a bifunctional electrochemical biosensor for highly sensitive detection of small molecule (adenosine) or protein (lysozyme) was developed. Two aptamer units for adenosine and lysozyme were immobilized on the gold electrode by the fonnation of DNA/DNA duplex. The detection of adenosine or lysozyme could be carried out by virtue of switching structures of aptamers from DNA! DNA duplex to DNAJtarget complex. The change of the interfacial feature of the electrode was characterized by cyclic voltammertic (CV) response of surface-bound [Ru(NH3)6]3+. On the other hand, DNA functionalized Au nanoparticles (DNA-AuNPs) were used to enhance the sensitivity of the aptasensor because DNA-AuNPs modified interface could load more [Ru(NH3)6]3+ cations. Thus, the assembly of two aptamer-contained DNA strands integrated with the DNA-AuNPs amplification not only improves the sensitivity of the electrochemical aptasensor but also presents a simple and general model for bifunctional aptasensor. The proposed aptasensor has low detection limit (0.02 nM for adenosine and 0.01 μg mL-1 for lysozyme) and exhibits several advantages such as high sensitivity and bifunctional recognition. [ABSTRACT FROM AUTHOR]

This paper describes a unique application of the fluoronium cation (F+) as an organocatalyst for mediating the reaction between N-substituted imines and ethyl diazoacetate affording excellent yields of N-substituted aziridines. [ABSTRACT FROM AUTHOR]

Chevrel phases (CPs), MxMo8T8 (M = metal, T = S, Se) are unique materials, which allow for a fast and reversible insertion of various cations at room temperatsre. In spite of extensive studies of these materials, the origin of their high ionic mobility remained unclear. In a previous paper we presented for the first time a proper classification of the very complex transport behavior of different cations in the Mo6T8 hosts: (i) apparent immobility of the large M cations such as Pb2+, Sn2+, Ag+ in the ternary phases, MMo8T8 (ii) coupled M+M' diffusion in the quaternary phases, MxM'yMo8T8, where both large and small cations can assist; (ii) cation trapping in the Mg-Mo8S8, Cd-Mo8S8, and Na-Mo8T8 systems; (iv) a combination of low- and high-rate diffusion kinetics at the first and last intercalation stages, respectively, for the Cu-Mo8S8, Mn-Mo8S8, and Cd-Mo8Se8 systems, and (v) a fast ionic transport for small cations such as Ni2+, Zn2+, and Li+. It was shown that this behavior could be understood by a relatively simple crystallographic analysis (mapping of all the cation sites and estimations of their potential energy according to the distances of these sites from adjacent anions and cations) of the diffusion routes, which differ for different cations. For this analysis, it was necessary to complete our knowledge about the cation location in the crystal structure for several CPs with known ionic mobility. This article presents the results of a combined Rietveld analysis of powder X-ray and high-resolution neutron diffraction profiles for NaMo8T8, ZnMo8T8, CdMo8T8, and MnMo8S8. All seven compounds can be defined as classic CPs, where cation delocalization from the center of the largest cavity between the Mo8T8 blocks decreases with the length of the ideal chemical bond, M-T. In addition, this work details the effect of the structural parameters on the ionic conductivity in CPs, namely, it shows how subtle changes in cation delocalization may be crucial for diffusion kinetics. [ABSTRACT FROM AUTHOR]

This paper analyses the interaction of Co+(d8, 1G, and 3F) and Co2+(d7, 4F) cations with (glycyl)nglycine (n= 1−3) oligomers. The structure, relative energies, and binding energies of the complexes formed have been theoretically determined by means of density functional methods. For all Co+complexes the ground spin state is the triplet one and the most stable structures show tricoordinated geometries. In contrast, for Co2+systems the lowest energy structures are tricoordinated (n= 1), tetracoordinated (n= 2), and pentacoordinated (n= 3). For both cobalt cations, interaction energies increase with the peptide length. Differences in the coordination properties of the ligands are discussed according to their length as well as to the electronic configuration of the metal cation, and results are compared to those previously obtained for the analogous Cu+/2+systems. The IR spectra of the most stable and low energy conformers have been simulated, and a discussion of the main vibrational features is provided. [ABSTRACT FROM AUTHOR]

The detailed oxidative decomposition mechanism of propylene carbonate (PC) in the lithium ion battery is investigated using density functional theory (DFT) at the level of B3LYP/6-311++G(d), both in the gas phase and in solvent. The calculated results indicate that PC is initially oxidized on the cathode to a radical cation intermediate, PC•+, and then decomposes through three pathways, generating carbon dioxide CO2and radical cations. These radical cations prefer to be reduced on the anode or by gaining one electron from PC, forming propanal, acetone, or relevant radicals. The radicals terminate by forming final products, including trans-2-ethyl-4-methyl-1,3-dioxolane, cis-2-ethyl-4-methyl-1,3-dioxolane, and 2,5-dimethyl-1,4-dioxane. Among all the products, acetone is most easily formed. The calculations in this paper give detailed explanations of the experimental findings that have been reported in the literature and clarify the role of intermediate propylene oxide in PC decomposition. Propylene oxide is one of the important intermediates. As propylene oxide is formed, it isomerizes forming a more stabile product, acetone. [ABSTRACT FROM AUTHOR]

This paper reports a chemical approach for obtaining a silica-rich nanolayer on the surface of a vanadium-bearing silicate glass. The approach involves depletion of earth alkaline ions (Mg2橷 Ca2) from the glass surface by means of inward diffusion of those ions, i.e., diffusion from the surface to the interior of the glass. The inward diffusion is induced by the reduction of V5 V4誉, when the glass is heat-treated in H2/N2(1/99 v/v) at the glass transition temperature (Tg) for certain durations (ta). During the reduction of vanadium by H2, structurally bonded hydroxyl groups form and are incorporated into the glass structure. Both the V4橷 the hydroxyl contents increase with increasing taand hydrogen partial pressure. The inward diffusion enhances the hardness of the glass surface. The mechanism of the inward diffusion is suggested on the basis of a model describing the outward diffusion. The new approach provides a possibility to create a silica-rich nanolayer on glass surfaces by means of the inward diffusion process. [ABSTRACT FROM AUTHOR]

The present paper introduces the use of a weak cationexchange/crown ether column in the proteomics field. The 18-crown-6 ether functionality is well-known to selectively complex ammonium and monoalkylammonium ions, which should make this column highly suitable to trap peptides with free α-NH2 or free ϵ-NH2 groups from lysine side chains. This unique selection mechanism was put to the test in an N-teromics setup which aims for the enrichment of deliberately acetylated protein N-terminal peptides from a serum digest. It was demonstrated that peptides with free α-NH2 groups and peptides with α-amino-acetylated groups can be separated from each other using this weak cation-exchange/crown ether column. The peptides of interest, bearing no free primary amines, were found to be significantly enriched in the column's flow through. At the same time a favorable coenrichment of N-glycosylated peptides was observed. To obtain more insight in the contributions of the two distinct column functionalities, i.e., the weak cation exchanger and the crown ether, the experimental data were checked against a theoretical prediction of the outcome. [ABSTRACT FROM AUTHOR]

The sequential adsorption of oppositely charged polyelectrolytes called the “layer by layer” technique is a method for formation of ultrathin films with controlled thickness and interfacial properties. Composition of polyelectrolyte solutions, pH, and electrolyte concentration are important parameters governing formation of multilayer films. Since pH is the factor controlling charge of weak polyelectrolytes, the structure of multilayers should be sensitive to its value. In this paper we focused on formation of PE multilayer films composed from weak and strong polyelectrolytes. We used weak, branched polycation polyethyleneimine (PEI, 70 kDa) and strong polyanion poly-4-styrenesulfonate (PSS, 70 kDa) to form films by the layer-by-layer technique on the surface of silicon wafers under two deposition conditions: pH = 6 when PEI was strongly charged and pH = 10.5 when the charge density of PEI was low. Thicknesses of films were measured by single wavelength ellipsometry, and the results were confronted with ones concerning mass of the adsorbed films obtained by quartz crystal microbalance. We found that, depending on pH of the solutions, combination of weakly and strongly charged polyelectrolytes gave either linear or nonmonotonic increase of film thickness with a number of deposited PE layers. We observed a good correlation between multilayer film thickness and adsorbed mass. The atomic force microscopy images of surface topography of PEI/PSS films demonstrated large differences between films deposited at pH = 6 and 10.5. Additionally the cyclic voltamperometry was used to determine the differences in permeability of films formed at various pH conditions. [ABSTRACT FROM AUTHOR]

We report the preparation of a series of solid polymer electrolytes with different cations but with the same anion. We have chosen a PEO:PEG blend (at 40:60 by w/w) and complexed it with LiI, NaI, KI, NH4I, 1-ethyl-3-methylimidazolium iodide (EMII), and 1-hexyl-3-methylimidazolium iodide (HMII) with the same ion to monomer ratio. The role of different cations in terms of their size has been investigated on the conductivity of the polymer electrolyte films. The electrolyte properties have been explained in terms of the changes in the number of free charge carriers and the variation in crystallinity of the matrix. The cell performance of the dye-sensitized solar cells (DSSC) fabricated with these systems also showed strong dependence on the cation radii. The concept of ion intercalation and surface adsorption used for the liquid electrolyte systems has been extended to the polymer electrolytes and discussed in this paper. [ABSTRACT FROM AUTHOR]

In this paper we explored factors that determine the polarity of an Actin bundle formed with polycation through electrostatic interaction. We found that the polarity decreases with an increase in the polycation concentration while it hardly depends on the KCl salt concentration. Additionally, the polarity of the Actin bundle increases with an increase in the degree of polymerization of the polycation at a constant polymer concentration. From these results we proposed that the kinetics of nuclei formation determines the polarity of the Actin bundle. [ABSTRACT FROM AUTHOR]

Cinchona alkaloids occupy a privileged status due to their optimal possession of two desirable properties, namely catalytic efficiency and stereoselectivity. This paper proposes a new quantitative measure, the energy difference between the adducts formed by reand siface attack to Mosher’s cation (ΔMOSCAre−si) as a measure of stereoinductive potential, by taking the example of cinchona alkaloids. Other descriptors such as methyl cation affinities and the one based on continuous symmetry measures are also estimated and correlated with ΔMOSCAre−sivalues. [ABSTRACT FROM AUTHOR]

In situ synthesis of inorganic clusters in polyelectrolyte multilayers (PEMs) has typically relied on free carboxylic acid groups as the binding sites, limiting the scheme to the loading of cationic precursor reagents. The use of amine groups for similar purposes has not been demonstrated because of the challenge of incorporating free amine groups that are not paired with the oppositely charged groups residing on the polyanion of the PEM. In this paper, we use specific PEM assembly conditions to produce ultrathin conformal films of PAH/PAA (poly(allylamine hydrochloride)/poly(acrylic acid)) and PAH/PSS (poly(styrene sulfonate)) that upon suitable postassembly treatment undergo substantial molecular rearrangements that generate free amine groups in the films. These PEMs are capable of binding anionic precursors including complexes widely used for the synthesis of gold nanoparticles. On the basis of our understanding of the gold binding mechanisms, we demonstrate systematic control over the size and spatial distribution of gold nanoparticles in the films by changing the PEM assembly and postassembly treatment conditions. [ABSTRACT FROM AUTHOR]

Metal selenites and tellurites are a class of very important compounds. In this paper, the structures and properties of metal selenites or tellurites combining with transition-metal (TM) ions with the d° electronic configuration or tetrahedral MO4 building blocks of post-transition main-group elements were reviewed. Most compounds in the alkali or alkaline-earth-d° TM-SIV (or TeIV)-O systems exhibit extended anionic architectures composed of distorted octahedra of (d°) TM cations and tellurite or selenite groups. The distortion of the octahedron is always away from the lone-pair cation, and some of them exhibit excellent second-order nonlinear optical properties due to the adductive effects of two types of bond polarizations. Because of the high coordination number of LIII ions, most of compounds in the Ln-d° TM-SeIV (or TeIV)-O systems are not second-harmonic-generation active; however, they are able to emit strong luminescence in the visible or near-IR region; also in most cases, the d° TM cations are in tetrahedral geometry and are well separated from selenite or tellurite groups. It is also interesting to note that the selenite group is normally "isolated", whereas the TeOx (x = 3-5) can be polymerized into a variety of discrete polynuclear anionic clusters or extended architectures via Te-O-Te bridges. [ABSTRACT FROM AUTHOR]