Investigation of molecular order in liquid-crystalline solutions of cellulose triacetate using PMR spectroscopy

Liquid-crystalline solutions of cellulose triacetate (CTA) in trifluoroacetic acid (TFA)–CH₂Cl₂, TFA–1.2-dichloroethane (1,2-DCE) solvent mixtures were examined by means of PMR spectroscopy. CTA forms both cholesteric and nematic phases in these solvents depending on the CTA concentration. In cholesteric solutions the CH₂Cl₂ signal is initially a singlet and then splits into a doublet. The time dependence of the splitting and the effect of CTA concentration are reported. The results suggest that the cholesteric phase slowly changes into a nematic phase in the magnetic field. The splitting of the CH₂Cl₂ proton signal into a doublet and the 1,2-DCE signal into a quartet are due to direct magnetic dipole-dipole interactions. Rotation of the sample in the magnetic field results in the disappearance of the doublet or quartet and suggests that the solvent molecules are originally oriented in the direction of the magnetic field. In the biphasic region, immediate splitting of the CH₂Cl₂ proton signal suggests that the anisotropic phase is nematic.     

Mesomorphic solutions of cellulose triacetate in trifluoroacetic acid halogenated solvent mixtures: Phase separations and factors affecting the cholesteric pitch

Cellulose triacetate (CTA) forms cholesteric mesophases in trifluoroacetic acetic acid (TFA) and mixtures of TFA and CH₂Cl₂, 1,2-dichloroethane (1,2-DCE), and CHCl₃. Cholesteric pitches and solution flow times indicate that the order of solvent powers is TFA-CH₂Cl₂ > TFA-1,2-DCE > TFA > TFA-CHCl₃, which is the order of decreasing acidity of the solvent systems. With TFA-CH₂Cl₂ as solvent, the one-fourth power of the pitch varies inversely with the CTA concentration, and increases linearly with temperature. The pitch increases exponentially with time and increases faster the more acidic the solvent. In a magnetic field a cholesteric to nematic transition occurs. A minimum in solution viscosity occurs at 34% w/v of CH₂Cl₂ for solutions in TFA-CH₂Cl₂. The miscibility gap as a function of molecular weight depends on the solvent composition and is smaller the higher the acidity of the solvent. Agreement between the experimentally observed A and B points and the theoretical points is better for the Khokhlov and Semenov theory for semiflexible chains than for the original Flory theory or the Flory-Ronca modification.     

Some further observations on the systems cellulose/trifluoroacetic acid/CH2Cl2 and cellulose triacetate/TFA/CH2Cl2

There is little or no trifluoroacetylation of cellulose dissolved in TFA-CH₂Cl₂ admixtures. Both cellulose and cellulose triacetate (CTA)are slowly degraded in the solvent. Cellulose forms a mesophase as low as 4%(w/w)concentration, but CTA has a much higher critical concentration, 20% (w/w), in TFA-CH₂Cl₂. The cellulose behaves as a rigid rod in TFA-CH₂Cl₂ (70/30v/v) and its persistence length calculated using the lattice model approximates its chain length, presumably due to extensive interaction with the solvent. As expected, due to low polymer-solvent interactions, the persistence length of CTA in TFA-CH₂Cl₂ is only one-fourth the chain length.     

The liquid-crystalline properties of selected cellulose derivatives

The liquid-crystalline properties of three cellulose esters, phenylacetoxy cellulose (PAC), 4-methoxyphenylacetoxy cellulose (4MPAC), and p-tolylacetoxy cellulose (TAC) and two cellulose silyl ethers, trimethyl silyl cellulose (TMSC) and t-butyldimethylsilyl cellulose (TBDMSC), are reported. Hot-stage polarized light microscopy provided evidence regarding the formation of thermotropic mesophases in the PAC, 4MPAC, TAC, and TMSC in bulk form upon heating. The concomitant DSC data showed further evidence of the thermotropic nature of these materials. PAC, 4MPAC, TAC, and TMSC formed lyotropic mesophases at 44, 48, 50, and 27 wt%, respectively in CH₂Cl₂. The presence of fingerprint patterns in wholly anisotropic solutions in conjunction with optical rotation measurements confirmed the cholesteric nature of these liquid crystalline solutions. TBDMSC formed neither a lyotropic nor a thermotropic liquid-crystalline phase due to the low degree of substitution (DS 0.68) of this derivative. The hydroxyl substituents of PAC, 4MPAC, TAC, and TMSC may be readily removed under mild conditions to regenerate cellulose.     

Electrocatalytic effect of the oxide film at Pt anodes on Cl• recombination kinetics in chlorine evolution

In aqueous medium, Cl₂ evolution on noble metal anodes occurs on a surface oxide film, the properties of which, rather than those of the metal, determine the kinetics of the reaction. The kinetics of Cl₂ evolution on an oxidized Pt electrode in aqueous KCl are compared with those for Cl₂ evolution on a demonstrably unoxidized Pt surface in anhydrous trifluoroacetic acid (TFA) as solvent. Hence the effects of development of an oxide film on Pt in aqueous medium can be determined in relation to the kinetic behaviour of Cl₂ evolution on the unoxidized Pt metal surface. In both TFA and water, and their mixtures, it is shown that Cl₂ evolution kinetics are recombination-controlled and non-diffusion-controlled limiting currents, i_lim, are observed. The i_lim values in aqueous medium, i.e. for the oxide-covered surface, are some 45 times larger than on the free Pt surface in TFA; since the mechanism is shown to be the same in the two solvents, and their mixtures, this observation indicates a substantial electrocatalytic enhancement of the recombination rate for Cl^? on the oxide in comparison with the Pt metal surface. This is presumably due to weaker binding of Cl^? on oxidized Pt than on the “bare” Pt surface. Effects due to specific adsorption of Cl^? ion are also important and give rise to dependence of the recombination catalysis on Cl^? ion concentration. A method is proposed for analyzing the recombination kinetics by means of linear plots which give both the recombination rate constant and the quasi-equilibrium constant for the prior Cl^? ion discharge step as a function of water content.     

Studies on the macrocycle mediated transport of some metal cations through a bulk liquid membrane system using kryptofix 22

Competitive transport experiments involving Fe⁺³, Cr⁺³, Ni⁺², Co⁺², Ca⁺², Mg⁺² and K⁺ metal cations from an aqueous source phase through some organic membranes into an aqueous receiving phase have been carried out using 4,13-diaza-18-crown-6 (kryptofix 22) as an ionophore present in the organic membrane phase. Fluxes and selectivities for competitive of the metal cations transport across bulk liquid membranes have been determined. A good selectivity was observed for K⁺ cation by kryptofix 22 in 1,2-dichloroethane (1,2-DCE) membrane system. The sequence of selectivity for potassium ion in the organic solvents was found to be: 1,2-DCE > DCM (dichloromethane) >CHCl₃. The transport of K⁺ cation was also studied in the DCM-1,2-DCE, CHCl₃-1,2-DCE and CHCl₃-DCM binary mixed solvents as membrane phase. A non-linear relationship was observed between the transport rate of K⁺ ion and the composition of these binary mixed solvents. The amount of K⁺ transported follows the trend: DCM-DCE > CHCl₃-DCE > CHCl₃-DCM in the bulk liquid membrane studies. Then, the selective transport of K⁺ cation through a DCM-1,2-DCE bulk liquid membrane was studied by kryptofix 22 as an efficient carrier. The highest transport efficiency was obtained by investigating the influence of different parameters such as the concentration of kryptofix 22 in the membrane phase, pH of the source and the receiving phases and the equilibrium time of the transport process. Maximum transport value of 71.62 ± 1.61% was observed for K⁺ ion after 4 hours, when its concentration was 4 × 10^–3 M.     

Effect of trifluoroacetic acid upon Boc-aminoacyl- and Box-peptidyl-resins. Description of a new polymeric support for solid phase peptide synthesis.

The behavior of Boc-aminoacyl- and Boc-peptidyl-OCH₂-resins towards TFA/CH₂Cl₂ solutions has been studied. The results obtained point out the difficulty of finding an optimum TFA concentration which achieves total deprotection without substantial acidolytic losses. The synthesis of a new polymeric support which minimizes this problem is described.     

Volumetric properties of dilute aqueous solutions of cobalt amine type salts. Part 2. Densities at 15 and 5°C

Apparent molar volumes have been determined by density measurements of aqueous solutions for a series of salts [Co(L)₃]X₃, where X=Cl^– and Br^– and L¹=1,2-diaminoethane (en), L²=1,2-diaminopropane (pn) and L³=1,3-diaminopropane (tn) at 15°C and 5°C. Apparent molar volumes at infinite dilution for the complex cations at 0°C are estimated. The resulting values are related to the structure of solvent water molecules around the ions.     

Iron(III) Chloride Catalyzed Oxidative Coupling Reaction of 1,2‐Diarylethylene Derivatives

A nontoxic FeCl₃ catalyzed intramolecular oxidative coupling reaction was developed for mild synthesis of a series of phenanthrenes with different substituents. The method involves cross dehydrogenative coupling of a variety of 1,2‐diarylethylene derivatives with di‐tert‐butylperoxide (DTBP) as a sole oxidant at room temperature in CH₂Cl₂/TFA (9:1 V/V) to yield phenanthrenes in good to excellent yields.     

Ion-transfer voltammetry at 1,6-dichlorohexane|water and 1,4-dichlorobutane|water interfaces

The usefulness of 1,6-dichlorohexane (1,6-DCH) and 1,4-dichlorobutane (1,4-DCB) as organic solvent (O) for ion-transfer voltammetry at O|water (W) interface has been examined, and the results are compared with those with 1,2-dichloroethane (1,2-DCE). The width of potential window of the 0.1 M tetraoctylammonium tetrakis(4-chlorophenyl)borate (O)|0.05 M Li₂SO₄ (W) interface increased in the sequence: O = 1,6-DCH > 1,4-DCB > 1,2-DCE. The voltammetric behavior of the transfer of various cations and anions at the 1,6-DCH|W and 1,4-DCB|W interfaces has been shown to be of reversible nature, and the midpoint potentials or the reversible half-wave potentials have been determined. The midpoint potentials of hydrophilic ions have also been determined by the analysis of anodic final rise or cathodic final decent of the voltammograms with the O|W interfaces, where the W contains a salt of the hydrophilic ion. Also, the effect of ion-pair formation in O on the midpoint potentials has also been discussed.     

Synthesis and crystal structure of a new N-(2,6-dichlorobenzoyl)-N′,N″-bis(pyrrolidinyl)-phosphoric triamide as a carrier and competitive bulk liquid membrane transport of six metal cations

The competitive metal ion transport experiments of Co⁺², Cd⁺², Ag⁺, Pb⁺², Ni⁺², and Cu⁺² were carried out by N-(2,6-dichlorobenzoyl)-N′,N″-bis(pyrrolidinyl)-phosphoric triamide as a carrier in organic membrane phase. 2,6-Cl₂C₆H₃C(O)NHP(O)[NC₄H₈]₂ has been synthesized and characterized by mass spectrometry IR spectroscopy and single crystal X-ray diffraction. The asymmetric unit of title phosphoric triamide contains one symmetrically independent molecule. The source phase contained equimolar concentrations of metal ions at pH 5 and the receiving phase being buffered at pH 3. The following solvents were examined as membrane: chloroform (CHCl₃), nitrobenzene (NB), 1,2-dichloroethane (1,2-DCE), dichloromethane (DCM), dichloromethane/1,2-dichloroethane (DCM/1,2-DCE). The obtained results show that the selectivity and efficiency of transport for these heavy metal cations change with the nature of the ligand and also the organic solvents, which were used as liquid membrane in these experiments. A good selectivity was observed for Pb⁺² cation by this ligand in all membrane systems. Moreover, the selectivity of metal cations in DCM is higher than other solvents. A non-linear relationship was found between the percent of transport of Pb⁺² cation by this ligand and the compositions of DCM/1,2-DCE and binary solution by this ligand. The effect of several factors such as the nature of carboxylic acids (stearic, fumaric and maleic acid) as surfactant in the membrane phase and the time of transport on transport efficiency of Pb⁺² cation were investigated.     

Crystal structure and photoreactivity of a halogen‐bonded cocrystal based upon 1,2‐diiodoperchlorobenzene and 1,2‐bis(pyridin‐4‐yl)ethylene

The formation of a photoreactive cocrystal based upon 1,2‐diiodoperchlorobenzene ( 1,2‐C₆I₂Cl₄ ) and trans‐1,2‐bis(pyridin‐4‐yl)ethylene ( BPE ) has been achieved. The resulting cocrystal, 2( 1,2‐C₆I₂Cl₄ )·( BPE ) or C₆Cl₄I₂·0.5C₁₂H₁₀N₂, comprises planar sheets of the components held together by the combination of I…N halogen bonds and halogen–halogen contacts. Notably, the 1,2‐C₆I₂Cl₄ molecules π‐stack in a homogeneous and face‐to‐face orientation that results in an infinite column of the halogen‐bond donor. As a consequence of this stacking arrangement and I…N halogen bonds, molecules of BPE also stack in this type of pattern. In particular, neighbouring ethylene groups in BPE are found to be parallel and within the accepted distance for a photoreaction. Upon exposure to ultraviolet light, the cocrystal undergoes a solid‐state [2 + 2] cycloaddition reaction that produces rctt‐tetrakis(pyridin‐4‐yl)cyclobutane ( TPCB ) with an overall yield of 89%. A solvent‐free approach utilizing dry vortex grinding of the components also resulted in a photoreactive material with a similar yield.     

Metal-ion recognition-competitive bulk liquid membrane transport of transition and post-transition metal cations using a thioether donor acyclic ionophore

The competitive bulk liquid membrane transport of Cr³⁺, Co²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Ag⁺ and Pb²⁺ metal cations with a new synthetic sulfur donor acyclic ligand (pseudo-cyclic ionophore), i.e. 1-(2-[(2-hydroxy-3-phenoxypropyl)sulfanyl]ethylsulfanyl)-3-phenoxy-2-propanol; (C₂₀H₂₆O₄S₂), was examined using some organic solvents as membranes. The membrane solvents include: chloroform (CHCl₃), 1,2-dichloroethane (1,2-DCE), dichloromethane (DCM), nitrobenzene (NB), chloroform-nitrobenzene (CHCl₃-NB) and chloroform-dichloromethane (CHCl₃-DCM) binary mixtures. The transport process was driven by a back flux of protons, maintained by the buffering the source and receiving phases with pH 5 and 3, respectively. The aqueous source phase consisted of a buffer solution (CH₃COOH/CH₃COONa) at pH = 5 and containing an equimolar mixture of these seven metal cations. The organic phase contained the acyclic ligand, as an ionophore and the receiving phase consisted of a buffer solution (HCOOH/HCOONa) at pH = 3. For these systems that displayed transport behaviour, sole selectivity for Ag⁺ cation was observed under the employed experimental conditions in this investigation. The amount of Ag⁺ transported follows the trend: 1,2-DCE > CHCl₃ > DCM > NB in the bulk liquid membrane studies. The transport of the metal cations in CHCl₃-NB and CHCl₃-DCM binary solvents is sensitive to the solvent composition. The influence of the stearic acid, palmitic acid and oleic acid in the membrane phase on the ion transport was also investigated.     

NMR study of ordering in liquid crystalline solution of polybenzylglutamate of various molecular mass

¹H and ²H NMR spectra of fractionated poly-γ-benzyl-L-glutamate solutions are recorded at various temperatures. NMR signals of both these nuclei of solvent molecules (mixture of CD₂Cl₂ and CH₂Cl₂) appear to be doublets. Their splitting (30-130 Hz for protons and 200–600 Hz for deuterons) reduces when the polymer molecular mass grows. As the splitting is proportional to degree of orientation of solvent and solute molecules, it means that longer macromolecules are less oriented than shorter ones. One can explain such behavior in terms of persistent chain model, since the bended rods of less length can be better oriented along the director.     

Degradation and isomerization of 1,2-dichloroethenes by photocatalytic reactions

The photocatalytic degradation and isomerization of trans- and cis-1,2-dichloroethenes (1,2-DCEs) by TiO₂ photocatalyst have been investigated using gas chromatography. The reaction half-life of 1,2-DCEs in nitrogen was longer than in dry air and oxygen, and the initial concentration of them affects the extent of the isomerization. The results indicate that the oxygen molecule and chlorine atoms play an important role in the degradation and isomerization of 1,2-DCE. It is also apparent that the photocatalytic degradation of 1,2-DCEs occurs on the TiO₂ surface.     

Solutions of cellulose in DMAc + LiCl: migration of the solute in an electrical field

For solutions of cellulose (Solucell, M_w=230 kg mol^–1) in the mixed solvent DMAc (N,N-dimethylacetamide) + LiCl, it is demonstrated by means of an electrolysis cell, subdivided into six compartments, that cellulose migrates to the anode. This observation is interpreted in terms of a field-induced opening of associations between the [DMAc]_xLi⁺ complex and the [cellulose]Cl^– complex. This understanding is corroborated by the observed changes in the positions of the menisci in the electrode compartments of the electrolysis cell. Contrary to expectations, the rate of cellulose transport does not depend on its molar mass, at least under the present conditions.     

Electrochemical studies of iodine in an aluminium chloride-butylpyridinium chloride ionic liquid part II. Neutral and basic solvent composition

The electrochemical behavior of iodine in an ambient temperature molten salt system, aluminum chloride-N-(1-butyl)pyridinium chloride (BuPyCl), have been studied in basic (excess BuPyCl) and neutral (1.0:1.0 AlCl₃: BuPyCI mole ratio) melt compositions. Acid-base interactions of iodine in different oxidation states with the ionic solvent are observed. High stability of triiodide ion in neutral butylpyridinium tetrachloroaluminate indicates relatively weak intermolecular interactions in this solvent. In basic solutions polyhalogen equilibria involving iodine in different oxidation states and chloride ions are established. In iodine and tetraethylammonium triiodide solutions a mixture of ICI₂^?, I₂Cl^?, I₃^? and I^? ions forms. The formation constants of I₂Cl^? and I₃^? and the equilibrium constant for I₂Cl^? disproportionation are estimated.     

Planar and Nonplanar Free‐Base Tetraarylporphyrins: β‐Pyrrole Substituents and Geometric Effects on Electrochemistry,Spectroelectrochemistry, and Protonation/Deprotonation Reactions in Nonaqueous Media

A series of planar and nonplanar free‐base β‐pyrrole substituted meso‐tetraarylporphyrins were characterized by electrochemistry, spectroelectrochemistry, and protonation or deprotonation reactions in neutral, acidic, and basic solutions of CH₂Cl₂. The neutral compounds are represented as H₂(P), in which P represents a porphyrin dianion with one of several different sets of electron‐withdrawing or ‐donating substituents at the messo and/or β‐pyrrole positions of the macrocycle. The conversion of H₂(P) to [H₄(P)]²⁺ in CH₂Cl₂ was accomplished by titration of the neutral porphyrin with trifluoroacetic acid (TFA) while the progress of the protonation was monitored by UV/Vis spectroscopy, which was also used to calculate logβ₂ for proton addition to the core nitrogen atoms of the macrocycle. Cyclic voltammetry was performed after each addition of TFA or TBAOH to CH₂Cl₂ solutions of the porphyrin and half‐wave potentials for reduction were evaluated as a function of the added acid or base concentration. Thin‐layer spectroelectrochemistry was used to obtain UV/Vis spectra of the neutral and protonated or deprotonated porphyrins under the application of an applied reducing potential. The magnitude of the protonation constants, the positions of λ_max in the UV/Vis spectra and the half‐wave or peak potentials for reduction are then related to the electronic properties of the porphyrin and the data evaluated as a function of the planarity or nonplanarity of the porphyrin macrocycle. Surprisingly, the electroreduction of the diprotonated nonplanar porphyrins in acid media leads to H₂(P), whereas the nonplanar H₂(P) derivatives are reduced to [(P)]^2? in CH₂Cl₂ containing 0.1 M tetra‐n‐butylammonium perchlorate (TBAP). Thus, in both cases an electrochemically initiated deprotonation is observed.     

Electronic spectral studies and solvent effects on the reaction of iodine with 1,4,8,11-tetraazacyclotetradecane

The reaction between iodine and 1,4,8,11-tetraazacyclotetradecane (TACTD) is studied photometrically in various solvents like CCl₄, CHCl₃, CH₂Cl₂ and 1,2-dichloroethane. The results reveal that in each solvent the (TACTD):I₂ ratio is 1:2 and the iodine complex is formulated as (TACTD)I⁺·I₃⁻. The obtained values of the formation constant (K), extinction coefficient (ε) and oscillator strength (ƒ) for the iodine complex are shown to be strongly dependent on the polarity of the solvent. A linear correlation is obtained between either (ƒ) or (ε) and the dielectric constant (D) of the solvent. The important role of the solvent is mainly suggested to be due to the interaction of the ionic iodine complex with the solvent.     

Cellulose wet wiper sheets prepared with cationic polymer and carboxymethyl cellulose using a papermaking technique

Carboxymethyl cellulose (CMC)-rich cellulose sheets were prepared with a cationic retention aid, poly[N,N,N-trimethyl-N-(2-methacryloxyethyl)ammonium chloride] (PTMMAC), using a papermaking technique. When 5% PTMMAC and 5% CMC were added to cellulose slurries, approximately 94% of the polymers were retained in the sheets by formation of polyion complexes between the two polymers. When the PTMMAC/CMC/cellulose sheets were soaked in solutions consisting of ethanol, water and calcium chloride (EtOH/H₂O/CaCl₂) with a weight ratio of 75:24:1, almost all PTMMAC and CMC molecules remained in the sheets, forming the structures of PTMMAC-N⁺Cl⁻ and CMC-COO⁻Ca²⁺Cl⁻ without dissolution of these molecules in the soaking solution. Thus, PTMMAC, CMC and calcium contents in the sheets were able to be determined on the basis of these PTMMAC and CMC structures from analytical data such as nitrogen, calcium and chlorine contents. The trade-off properties between sufficient wet strength in use and water-disintegrability after use can be added to the PTMMAC/CMC/cellulose sheets by selecting weight ratios of the EtOH/H₂O/CaCl₂ solution used as the impregnation liquid.