Hexagonal Lyotropic Liquid Crystalline Phase Research Articles

Metastable and stable phase diagrams and thermodynamic properties of the cetyltrimethylammonium bromide (CTAB)/water binary system

The thermodynamic properties of the cationic surfactant cetyltrimethylammonium bromide (CTAB)/water system were investigated using differential scanning calorimetry (235–395 K) and adiabatic calorimetry (78–320 K), and the stable phase diagram was established, in which the locations of phase boundaries were precisely determined. The micellar phase and the lyotropic liquid crystalline (LC) phases were found to transform into a metastable gel phase via rapid cooling, and a metastable phase diagram was also constructed. The hexagonal LC phase was found to consist of two types of phases with different thermodynamic characteristics. The transitions from the separated two-phase “CTAB crystal + solution” to the micellar and LC phases were also investigated, and it was found that the transition occurs in a two-step manner, wherein the transitions at lower temperatures depended on the thermal history. The enthalpy of fusion of the ice that coexisted with the CTAB crystal did not provide any evidence for the CTAB crystal being hydrated by non-freezing water.

Bioimaging Applications of Non-Lamellar Liquid Crystalline Nanoparticles.

Self-assembling processes of amphiphilic lipids in water give rise to complex architectures known as lyotropic liquid crystalline (LLC) phases. Particularly, bicontinuous cubic and hexagonal LLC phases can be dispersed in water forming colloidal nanoparticles respectively known as cubosomes and hexosomes. These non-lamellar LLC dispersions are of particular interest for pharmaceutical and biomedical applications as they are potentially non-toxic, chemically stable, and biocompatible, also allowing encapsulation of large amounts of drugs. Furthermore, conjugation of specific moieties enables their targeting, increasing therapeutic efficacies and reducing side effects by avoiding exposure of healthy tissues. In addition, as they can be easy loaded or functionalized with both hydrophobic and hydrophilic imaging probes, cubosomes and hexosomes can be used for the engineering of multifunctional/theranostic nanoplatforms. This review outlines recent advances in the applications of cubosomes and hexosomes for in vitro and in vivo bioimaging.

Lyotropic liquid crystalline nano templates for synthesis of ZnS cogwheels

Herein, we are reporting on the synthesis of zinc sulphide (ZnS) nano/microstructures via soft templating method. Hexagonal lyotropic liquid crystalline phases derived from binary mixtures of potassium soap and water (at different concentraions10:90, 30:70 and 50:50 wt%) are used as soft templates. Flower and hollow resilient cogwheels like (average diameter 100–500 nm) morphologies of ZnS have been obtained from10:90, 30:70 and 50:50 wt:wt% lyotropic templates as confirmed via SEM analysis. All the synthesized ZnS samples exhibit cubic zinc blende crystal structure as confirmed from the XRD measurements. Experimental finding and analysis infer that new kind of morphologies that are obtained for ZnS is not exactly resulted from the templated effect. Flower and cogwheel-like morphologies are results of orientational attachment of ZnS nuclei or coalescence of ZnS crystallite in the vicinity of the hexagonal lyotropic template. The mechanism responsible for such anisotropic growth has also been discussed. Comparing with all ZnS morphologies, cogwheel-like structures show best optical properties as they exhibit a lower band gap of 3.91 eV, low Urbach energy 0.66 eV and smaller dislocation density 16.83 nm−2.

Exceptional Catalytic Activities and Sensing Performance of Palladium Decorated Anisotropic Gold Nanoparticles

AbstractThe present perspective explores the effect of composition and morphology on the catalytic and surface enhanced Raman scattering (SERS) sensing applications of anisotropic bimetallic gold‐palladium (Au−Pd) nanoparticles. The morphology of the nanoparticles was controlled by a ‘soft’ templating approach by using a hexagonal lyotropic liquid crystalline phase. The mesophases comprised of toluene‐swollen surfactant cylinders, doped with the gold (Au) and palladium (Pd) precursors, stabilized by a monolayer of surfactant and co‐surfactant molecules, arranged in a hexagonal lattice in water as continuous medium. Anisotropic nanostructures of Au having very small Pd nanoparticles deposited on their surface were produced when hexagonal mesophases containing Au and Pd precursors were subjected to gamma irradiation. The synthesized nanomaterials were thoroughly characterized using X‐ray diffraction (XRD), transmission electron microscopy (TEM) and X‐ray photoemission spectroscopy (XPS). These nanomaterials showed exceptionally high catalytic activities for the reduction of 4‐nitrophenol with the normalized rate constant of the bimetallic Au−Pd catalyst being 1.5 times higher than the best catalyst that is reported in the literature. These bimetallic Au−Pd nanostructures also demonstrated very good enhancement for Raman signals of methylene blue by demonstrating an enhancement factor of the order of 106 and a detection limit as low as 0.1 nM.

Mesostructure and physical properties of aqueous mixtures of the ionic liquid 1-ethyl-3-methyl imidazolium octyl sulfate doped with divalent sulfate salts in the liquid and the mesomorphic states.

This paper extends the study of the induced temperature change in the mesostructure and in the physical properties occurring in aqueous mixtures of the ionic liquid 1-ethyl-3-methyl imidazolium octyl-sulfate [EMIm][OSO4]. For some compositions, these mixtures undergo a phase transition between the liquid (isotropic in the mesoscale) and the mesomorphic state (lyotropic liquid crystalline) at about room temperature. The behavior of mixtures doped with a divalent metal sulfate was investigated in order to observe their applicability as electrolytes. Calcium sulfate salt is almost insoluble even in the 20 wt% water mixture. The magnesium salt, in contrast, can be dissolved up to concentrations of 730 ppm in the same mixture and it has a profound impact on its properties. Six aqueous mixtures (with water content from 10 wt% to 33 wt%) of [EMIm][OSO4] were saturated with magnesium sulfate salt, producing the ternary mixture [EMIm][OSO4] + H2O + MgSO4. Viscosity, density and ionic conductivity for these samples were measured from 10 °C to 90 °C. In addition, SAXS, FTIR, diffussion NMR and Raman spectroscopy of the most interesting samples have been performed, and structural data indicate a transition between a hexagonal lyotropic liquid crystalline phase below and an isotropic solution phase above room temperature. The octyl sulfate anions of the cylindrical micelles in the hexagonal phase are coordinated with water molecules through H-bonds (about four per sulfate anion), while the [EMIm] cations seem to be poorly coordinated and so free to move. Inorganic salt addition reinforces that network, increasing the phase transition temperature.

Structural Investigation of Bulk and Dispersed Inverse Lyotropic Hexagonal Liquid Crystalline Phases of Eicosapentaenoic Acid Monoglyceride.

Recent studies demonstrated the potential therapeutic use of newly synthesized omega-3 (ω-3) polyunsaturated fatty acid (PUFA) monoglycerides owing to their beneficial health effects in various disorders including cancer and inflammation diseases. To date, the research was mainly focused on exploring the biological effects of these functional lipids. However, to the best of our knowledge, there is no report on the hydration-mediated self assembly of these lipids that leads to the formation of nanostructures, which are attractive for use as vehicles for the delivery of drugs and functional foods. In the present study, we investigated the temperature-composition phase behaviour of eicosapentaenoic acid monoglyceride (MAG-EPA), which is one of the most investigated ω-3 PUFA monoglycerides, during a heating-cooling cycle in the temperature range of 5-60 °C. Experimental synchrotron small-angle X-ray scattering (SAXS) evidence on the formation of a dominant inverse hexagonal (H2) lyotropic liquid crystalline phase and its temperature-induced transition to an inverse micellar solution (L2 phase) is presented for the fully hydrated bulk MAG-EPA system and its corresponding dispersion. We produced colloidal MAG-EPA hexosomes with an internal inverse hexagonal (H2) lyotropic crystalline phase in the presence of F127, a well-known polymeric stabilizer, or citrem, which is a negatively charged food-grade emulsifier. In this work, we report also on the formation of MAG-EPA hexosomes by vortexing MAG-EPA in excess aqueous medium containing F127 at room temperature. This low-energy emulsification method is different than most reported studies in the literature that have demonstrated the need for using a high-energy input during the emulsification step or adding an organic solvent for the formation of such colloidal nonlamellar liquid crystalline dispersions. The designed nanoparticles hold promise for future drug and functional food delivery applications due to their unique structural properties and the potential health-promoting effects of MAG-EPA.

Controlled Growth of Gold Nanostars: Effect of Spike Length on SERS Signal Enhancement.

Two different types of gold nanostars (Au NS), namely, short-spiked nanostars (SSNS) and long-spiked nanostars (LSNS), are prepared by using a hexagonal lyotropic liquid-crystalline (LLC) phase as a template. The formation, size and length of spikes or arms of the resultant Au NS are controlled by preparation in either a hexagonal LLC phase or an isotropic phase. These NS are anchored onto indium tin oxide (ITO) electrodes through a self-assembled monolayer of 3-mercaptopropyltrimethoxysilane, which acts as a linker molecule. Structural and morphological characterisations of SSNS- and LSNS-anchored ITO electrodes are performed by means of microscopic and spectroscopic analyses. Further electrochemical techniques, namely, cyclic voltammetry and electrochemical impedance spectroscopy, are also used to confirm the immobilisation of these Au NS on ITO electrodes and to study the electrochemical characteristics. These studies clearly reveal the formation of star-shaped, branched, anisotropic nanostructures of gold during the template preparation method and these Au NS are successfully anchored onto ITO electrodes through a covalent immobilisation strategy. Furthermore, the SERS activity of these Au NS is analysed by using glutathione and crystal violet as analytes and by employing glass and ITO as substrates. It is interesting to note that SSNS show a significant enhancement in SERS signals relative to those of LSNS.

High catalytic activities of palladium nanowires synthesized using liquid crystal templating approach

Synthesis of palladium (Pd) nanoparticles of various morphologies using swollen liquid crystalline (SLC) phases as structure directing templates is described in the present paper. The Pd precursor, bisdibenzyledene acetone palladium (Pd(DBA)2) was dissolved in the oil phase of a hexagonal lyotropic liquid crystalline phase. The characteristic nature of the hexagonal mesophase was confirmed using polarized optical microscopy. The hexagonal mesophases were exposed to hydrogen gas for the synthesis of Pd nanoparticles. The nanomaterials were characterized using UV–vis spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). These nanowires showed very good catalytic activity for reduction of 4- nitrophenol to 4-aminophenol when compared to the spherical Pd nanoparticles. A comparative study revealed that the catalytic activity of the nanowires was much better than even very small Pd nanoparticles that are reported in the literature. The nanowires also had a very good catalytic activity in Suzuki-Miyaura coupling reactions for the synthesis of biphenyl even using aryl chlorides as reactant.

Lipid-Based Liquid Crystals As Carriers for Antimicrobial Peptides: Phase Behavior and Antimicrobial Effect.

The number of antibiotic-resistant bacteria is increasing worldwide, and the demand for novel antimicrobials is constantly growing. Antimicrobial peptides (AMPs) could be an important part of future treatment strategies of various bacterial infection diseases. However, AMPs have relatively low stability, because of proteolytic and chemical degradation. As a consequence, carrier systems protecting the AMPs are greatly needed, to achieve efficient treatments. In addition, the carrier system also must administrate the peptide in a controlled manner to match the therapeutic dose window. In this work, lyotropic liquid crystalline (LC) structures consisting of cubic glycerol monooleate/water and hexagonal glycerol monooleate/oleic acid/water have been examined as carriers for AMPs. These LC structures have the capability of solubilizing both hydrophilic and hydrophobic substances, as well as being biocompatible and biodegradable. Both bulk gels and discrete dispersed structures (i.e., cubosomes and hexosomes) have been studied. Three AMPs have been investigated with respect to phase stability of the LC structures and antimicrobial effect: AP114, DPK-060, and LL-37. Characterization of the LC structures was performed using small-angle X-ray scattering (SAXS), dynamic light scattering, ζ-potential, and cryogenic transmission electron microscopy (Cryo-TEM) and peptide loading efficacy by ultra performance liquid chromatography. The antimicrobial effect of the LCNPs was investigated in vitro using minimum inhibitory concentration (MIC) and time-kill assay. The most hydrophobic peptide (AP114) was shown to induce an increase in negative curvature of the cubic LC system. The most polar peptide (DPK-060) induced a decrease in negative curvature while LL-37 did not change the LC phase at all. The hexagonal LC phase was not affected by any of the AMPs. Moreover, cubosomes loaded with peptides AP114 and DPK-060 showed preserved antimicrobial activity, whereas particles loaded with peptide LL-37 displayed a loss in its broad-spectrum bactericidal properties. AMP-loaded hexosomes showed a reduction in antimicrobial activity.

Liquid crystalline phase synthesis of nanoporous MnO2 thin film arrays as an electrode material for electrochemical capacitors

Three-dimensional (3D) MnO2 thin film arrays with nanoporous structure is electrodeposited on Ti foil from hexagonal lyotropic liquid crystalline phase. Low-angle X-ray diffraction (XRD), wide-angle XRD, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) are employed to study the morphology and the structure of the as-synthesized MnO2 materials. Galvanostatic charge/discharge measurements show the nanoporous, 3D electrode material exhibits excellent capacitive performance between the potential range of −0.1 to 0.9V, and a maximum specific capacitance as high as 462Fg−1 are achieved in 0.5M Na2SO4 solution at a charge/discharge current density of 4Ag−1.

Fabrication of a mesoporous Co(OH)2/ITO nanowire composite electrode and its application in supercapacitors

A novel mesoporous α-Co(OH)2/ITO NWs heterostructure has been successfully synthesized via a new method of combining chemical vapor deposition (CVD) on a titanium substrate and electrodeposition through a hexagonal lyotropic liquid crystalline (LLC) phase for electrochemical energy storage application. Electrochemical measurements demonstrate the improved ionic conductivity of an electrode and enhanced supercapacitive behavior, as compared to a mesoporous cobalt hydroxide film on a titanium current collector without indium tin oxide (ITO) NWs as “electron highways”. Galvanostatic charge–discharge measurements in 1 M KOH solution prove that the electrode of the as-prepared heterostructure possesses excellent electrochemical capacitance, in the potential range from −0.1 V to 0.5 V with a maximum specific capacitance of 1128 F g−1 at a discharge current density of 1 A g−1. The unique mesoporous α-Co(OH)2/ITO NWs heterostructure provides a high capacitance retention ratio at high discharge current densities and long-term electrochemical stability in an alkaline solution.

2D hexagonal mesoporous platinum films exhibiting biaxial, in-plane pore alignment

The synthesis of 2D hexagonal mesoporous platinum films with biaxial, in-plane pore alignment is demonstrated by electrodeposition through an aligned lyotropic liquid crystal templating phase. Shear force is used to align a hexagonal lyotropic liquid crystalline templating phase of an inexpensive and a commercially available surfactant, C16EO10, at the surface of an electrode. Electrodeposition and subsequent characterisation of the films produced shows that the orientation and alignment of the phase is transferred to the deposited material. Transmission electron microscopy confirms the expected nanostructure of the films, whilst transmission and grazing incidence small angle X-ray scattering analysis confirms biaxial, in plane alignment of the pore structure. In addition further electrochemical studies in dilute sulfuric acid and methanol show that the pores are accessible to electrolyte solution as indicated by a large current flow; the modified electrode therefore has a high surface area, that catalyses methanol oxidation, and the pores have a very large aspect ratio (of theoretical maximum 2 × 105). Films with such aligned mesoporosity will advance the field of nanotechnology where the control of pore structure is paramount. The method reported is sufficiently generic to be used to control the structure and order of many materials, thus increasing the potential for the development of a wide range of novel electronic and optical devices.

Nickel hydroxide deposited indium tin oxide electrodes as electrocatalysts for direct oxidation of carbohydrates in alkaline medium

In this work, the direct electrochemical oxidation of carbohydrates using nickel hydroxide modified indium tin oxide (ITO) electrodes in alkaline medium is demonstrated; suggesting the feasibility of using carbohydrates as a novel fuel in alkaline fuel cells applications. The chosen monosaccharides are namely glucose and fructose; disaccharides such as sucrose and lactose; and sugar acid like ascorbic acid for this study. ITO electrodes are chemically modified using a hexagonal lyotropic liquid crystalline phase template electrodeposition of nickel. Structural morphology, growth, orientation and electrochemical behaviour of Ni deposits are characterized using SEM, XRD, XPS and cyclic voltammetry (CV), respectively. Further electrochemical potential cycling process in alkaline medium is employed to convert these Ni deposits into corresponding nickel hydroxide modified electrodes. These electrodes are used as novel platform to perform the electrocatalytic oxidation of various carbohydrates in alkaline medium. It was found that bare and Ni coated ITO electrodes are inactive towards carbohydrates oxidation. The heterogeneous rate constant values are determined and calculated to be two orders of magnitude higher in the case of template method when compared to non-template technique. The observed effect is attributed to the synergistic effect of higher surface area of these deposits and catalytic ability of Ni(II)/Ni(III) redox couple.

Assessment of the Validity of the Double Superhelix Model for Reconstituted High Density Lipoproteins: A COMBINED COMPUTATIONAL-EXPERIMENTAL APPROACH

For several decades, the standard model for high density lipoprotein (HDL) particles reconstituted from apolipoprotein A-I (apoA-I) and phospholipid (apoA-I/HDL) has been a discoidal particle ∼100 Å in diameter and the thickness of a phospholipid bilayer. Recently, Wu et al. (Wu, Z., Gogonea, V., Lee, X., Wagner, M. A., Li, X. M., Huang, Y., Undurti, A., May, R. P., Haertlein, M., Moulin, M., Gutsche, I., Zaccai, G., Didonato, J. A., and Hazen, S. L. (2009) J. Biol. Chem. 284, 36605-36619) used small angle neutron scattering to develop a new model they termed double superhelix (DSH) apoA-I that is dramatically different from the standard model. Their model possesses an open helical shape that wraps around a prolate ellipsoidal type I hexagonal lyotropic liquid crystalline phase. Here, we used three independent approaches, molecular dynamics, EM tomography, and fluorescence resonance energy transfer spectroscopy (FRET) to assess the validity of the DSH model. (i) By using molecular dynamics, two different approaches, all-atom simulated annealing and coarse-grained simulation, show that initial ellipsoidal DSH particles rapidly collapse to discoidal bilayer structures. These results suggest that, compatible with current knowledge of lipid phase diagrams, apoA-I cannot stabilize hexagonal I phase particles of phospholipid. (ii) By using EM, two different approaches, negative stain and cryo-EM tomography, show that reconstituted apoA-I/HDL particles are discoidal in shape. (iii) By using FRET, reconstituted apoA-I/HDL particles show a 28-34-Å intermolecular separation between terminal domain residues 40 and 240, a distance that is incompatible with the dimensions of the DSH model. Therefore, we suggest that, although novel, the DSH model is energetically unfavorable and not likely to be correct. Rather, we conclude that all evidence supports the likelihood that reconstituted apoA-I/HDL particles, in general, are discoidal in shape.

Synthesis and characterization of nanostructured Cu/ZnO/Al2O3 from lyotropic liquid crystalline templates

Abstract The hexagonal lyotropic liquid crystalline phases of nonionic surfactants AEO-9 were used to template directly the fabrication of nanostructured Cu/ZnO/Al2O3 oxides. The reaction between metal precursors and alkaline reacting substance dissolved within the aqueous domains of the liquid crystalline templates generated nanostructured oxides. Low-angle X-ray diffraction and transmission election microscopy characterization reveals the product as a hexagonal array of cylindrical pores with pore-to-pore separation of ca. 6.3 nm. Possessing ordered nanochannels, Cu/ZnO/Al2O3 oxides could find more potential application in catalysis.

LineardsDNA Partitions Spontaneously into the Inverse Hexagonal Lyotropic Liquid Crystalline Phases of Phospholipids

Recently, we reported that DNA associated with inverse hexagonal (H(II)) lyotropic liquid crystal phases of the lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) was actively transcribed by T7 RNA polymerase. Our findings suggested that key components of the transcription process, probably the T7 RNA polymerase and the DNA, remained associated with the monolithic H(II) phase throughout transcription. Here, we investigate the partitioning of DNA between an H(II) lyotropic liquid crystal phase and an isotropic supernatant phase in order to develop insights into the localization of DNA in liquid crystalline environments. Our results show that linear double stranded DNA (dsDNA) molecules partition spontaneously into monolithic preformed H(II) liquid crystal phases of DOPE. We propose that this process is driven by the increase in entropy due to the release of counterions from the DNA when it inserts into the aqueous pores of the H(II) phase.

Electrochemical and SEM properties of Co2+ ion in hexagonal mesophase of pluronic lyotropic liquid crystal template

The electrochemical and SEM properties of Co2+ ion in hexagonal mesophase of the pluronic lyotropic liquid crystal template are reported. The cyclic voltammetric studies evidenced the occurrence of two slow electron transfer reduction processes. Such a reaction presumably related to the reduction of Co2+ ion to Co metal. The hexagonal (H1) lyotropic liquid crystalline phases of P84 surfactant have been used to template the electrochemical deposition of nanostructured cobalt films as well as its uses as background electrolyte. Electrochemical studies show that these films have very high surface areas, which reveals that the deposited film exhibits promising properties. The electrode parameters of Co(II) ion in hexagonal meso phase of the lyotropic liquid crystal ternary system (pluronic P84/cobalt/p-xylene) is determined using cyclic voltammetry, deduced convolutive voltammetry and chronoamperometry techniques. The morphology of nanostructured deposited films of Co2+ ion in pluronic lyotropic liquid crystal template was investigated via scanning electron microscopy (SEM) technique.

Electrodeposition and characterization of ordered mesoporous cobalt hydroxide films on different substrates for supercapacitors

Novel ordered mesoporous cobalt hydroxide films have been successfully electrodeposited on different substrates, i.e., foamed nickel mesh and titanium plate, from cobalt nitrate dissolved in the aqueous domains of the hexagonal lyotropic liquid crystalline phase of Brij 56. Field emission scanning electron microscope (FESEM) and transmission electron microscopy (TEM) studies present that the as-deposited films have an interlaced nanosheet-like surface morphology and possess a regular nanostructure with hexagonal arrays of pores of nanometer dimension and extended periodicity. Various electrochemical test results show that the films on both substrates exhibit excellent electrochemical capacitive behavior due to the special ordered mesoporous nanostructure. Furthermore, it is obvious that the ordered mesoporous cobalt hydroxide film on foamed Ni mesh has much higher specific capacitance (maximum: 2646 F g −1) than that of the film on Ti plate (maximum: 1018 F g −1), which is mainly because that the foamed Ni mesh substrate with much larger surface area than Ti plate could enhance the utilization and the capacitance of Co(OH) 2 film greatly.

Effects of the electrodeposition potential and temperature on the electrochemical capacitance behavior of ordered mesoporous cobalt hydroxide films

Novel ordered mesoporous cobalt hydroxide film (designated H I-e Co(OH) 2) has been successfully electrodeposited from cobalt nitrate dissolved in the aqueous domains of the hexagonal lyotropic liquid crystalline phase of Brij 56. Experimental electrodeposition parameters such as deposition potentials and deposition temperatures are varied to analyze their influences on the electrochemical capacitor behavior. The films are physically characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to determine the effects of deposition potentials and temperatures on the surface morphology and nanostructure. Electrochemical techniques such as cyclic voltammetry (CV) and chronopotentiometry are applied to systematically investigate the effects of deposition potentials and temperatures on the capacitance of the films. The results demonstrated that the capacitive performance of the H I-e Co(OH) 2 film achieved the highest value when it is electrodeposited at −0.75 V under the deposition temperature of 50 °C.

Electrodeposition of ordered mesoporous cobalt hydroxide film from lyotropic liquid crystal media for electrochemical capacitors

A novel ordered mesoporous cobalt hydroxide film (designated HI-e Co(OH)2) has been successfully electrodeposited on titanium substrate from the hexagonal lyotropic liquid crystalline phase using surfactant Brij 56 as the structure-directing agent. Low-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies indicate that the film electrodeposited from the liquid crystal template has a regular nanostructure consisting of a hexagonal array of cylindrical pores. Cyclic voltammeter (CV) and galvanostatic charge/discharge measurements show that the ordered mesoporous HI-e Co(OH)2 film electrode has excellent electrochemical capacitance between a potential range of –0.1–0.45 V, and a maximum specific capacitance as high as 1084 F g–1 could be achieved in 2 M KOH solution at a charge–discharge current density of 4 A g–1. Meanwhile, the properties of Co(OH)2 film electrodeposited from aqueous solution without templates (designated Aq-e Co(OH)2) are also discussed for comparison.