Infrared studies of rotational isomerism in α-halogeno-acetamides

Infrared spectra of fluoroacetamide, chloroacetamide, and iodoacetamide have been recorded in the solid, liquid, and vapour phases in the region 4000–200 cm^?1. A complete vibrational frequency assignment of the fundamental and non-fundamental bands has been made for each of these molecules. The results show that each of these compounds exists as an equilibrium mixture of gauche and trans isomers. Enthalpy differences (ΔH) between these isomers were calculated for each of these compounds in the liquid and vapour phases. The trans form is the most stable of the rotational isomers in all three phases.     

Gas chromatographic analysis of xylidine isomers on heteroaromatic compounds

Summary Nicotinic acid, picolinic acid, isonicotinic acid, histidine and other amphoteric heteroaromatic compounds, uracil, thymine, isatin and other heteroaromatic compounds having imino and carbonyl groups as well as IH-benzotriazole, benzoguanamine and guanidine phosphate effectively resolved all the xylidine (dimethylaniline) isomers. Furthermore, the mixed phases of nicotinamide + p-amino-benzoic acid and melamine+barbituric acid also provided an appreciable resolution. These analyses were carried out using a support which were not treated with an alkali.     

Enantiomeric Separation of Rotenone and Rotenolone on Chiral Stationary Phases

Abstract

Analytical and preparative high-performance liquid chromatoqraphic procedures have been developed for separation of optical antipodes of rotenone and rotenolone on three chiral stationary phases. Rotenone enantiomers were resolved on (+)-poly (triphenylmethylmethacrylate)-bonded silica, whereas optical resolution of rotenolone enantiomers was accomplished by using a (R)-N-3,5-dinitrobenzoylphenylglycine silica column (DNBPG). In experiments where resolution of enantiomers was achieved, each antipodal pair in both rotenone and rotenolone series was sufficiently resolved, although simultaneous resolution of all four isomers of rotenone and rotenolone was not accomplished. In all cases, the elution of (-)-(6aβ, 12aβ)-enantiomers preceded that of their antipodes. Separation factors (α) obtained with the covalent DNBPG stationary phase were slightly higher than those observed with the ionic valiant. The method has been applied to the resolution of racemates of deguelin and tephrosin.     

High Performance Liquid Chromatography of Dithiolthiones

Abstract

Sixteen dithiolthiones including oltipraz (5-(2-Pyrazinyl)-4-methyl-1-1, 2 dithiol-3-thione) and anethol dithiolthione (P-methoxyphenyl-1,2-dithiol-3-thione) have been studied using an isocratic high performance liquid chromatographic system. The retention characteristics of these compounds were determined using a conventional C 18 reverse phase column and a μ Bondapack phenyl column. The mobile phases used consisted of several concentrations of methanol and water. All compounds studied were adequately detected in the nanogram range (30–100 ng on column) using ultra violet detection (UV) set at 300 nm. Several analogs and isomers were separated. The retention characteristics of the 16 compounds studied are reported for both columns using 4 mobile phases and chromatograms of reference standards are presented.     

Normal Phase TLC Separation of Enantiomers Using Chiral Ion Interaction Agents

Abstract

A method for the thin layer chromatographic (TLC) separation of enantiomers and diastereomers involving the use of chiral ion interaction agents is described. Several aromatic amino alcohols were resolved by TLC on diol and/or high performance silica gel plates using a mobile phase containing (1R)-(-)- ammonium-10-camphorsulfonate or N-benzoxycarbonyl-glycyl-L-proline (ZGP). Many of these chiral aromatic amino alcohols are of pharmacological importance as α- and β-adrenergic blockers, adrenergic compounds, and anti-glaucoma agents. A comparison was made between various N-CBZ-amino acid derivatives as chiral counter ions/chiral mobile phase additives (CMAs). These separations could not be achieved on other normal phase TLC stationary phases including microcrystalline cellulose, alumina and ordinary silica gel plates.     

Separation of isomers of nitro-polycyclic aromatic hydrocarbons

Since positional isomers of several nitro-polycyclic aromatic hydrocarbons (nitro-PAH) contain widely different mutagenic properties, methods for separating the isomers were investigated. High performance liquid chromatography with dichloromethane in hexane on silica gave the best resolution for the majority of the compounds. A few groups of isomers were better resolved with other modifiers or with reversed phases. Of the reversed phase systems, methanol-water gave better resolution than acetonitrile-water. With dichloromethane/hexane on silica, the retention was found to depend on the presence of a bay nitro group (first), the number of H atoms peri to the nitro group (second), and the length/breadth ratio of the molecule (third). Front electron density calculations were combined with the structure-retention relations in making tentative structure assignments of minor isomers of nitro-PAH.     

Biphenylyl-1,2,4-oxadiazole based liquid crystals – synthesis,mesomorphism, effect of lateral monofluorination

ABSTRACT

Aiming at developing a new type of materials for functional applications, three series of new compounds were prepared, 3-(biphenylyl)-1,2,4-oxadiazoles, Series I; laterally mono-fluorinated 3-(biphenylyl)-1,2,4-oxadiazoles, Series II; and 5-(biphenylyl)-1,2,4-oxadiazoles, Series III. Liquid crystalline properties of these compounds were studied using differential scanning calorimetry and polarizing optical microscopy. Ten of the thirteen compounds in Series I are mesogenic forming either N or SmA phases depending on the length-to-width molecular ratio. Mesogens of the positional isomers, Series III are both N and SmA. Monofluorination of the biphenylyl group at either the central or the terminal phenylene rings, Series III, resulted in the formation of nematic mesogens with low phase transition temperatures and broad nematic phase range.     

Separation of Mycotoxins,Polycyclic Aromatic Hydrocarbons,Quinones, and Heterocyclic Compounds on Cyclodextrin Bonded Phases: An Alternative LC Packing

Abstract

β-Cyclodextrin and γ-cyclodextrin chiral bonded phases were previously shown to be useful in the separation of enantiomers, diastereomers and structural isomers. In this work it is demonstrated that these stationary phases are also useful in more routine separations. As such, they provide an alternative to the popular reverse phase packings. Because the selectivity of cyclodextrin packings is often unique they can be used to compliment conventional columns, particularly when separating complex mixtures where peak overlap is a problem. The separation of several important classes of compounds is used to demonstrate the general utility of this packing.     

A chiral induced ferroelectric liquid crystal phase transition with a vanishingly small enthalpy

Abstract

Information on molecular interactions that give rise to the stabilization of various ferroelectric, liquid-crystalline mesophases is important to the realization of their potential utility in a wide variety of optical devices. Understanding the roles that optical activity and optical purity play in the formation and properties of the various smectic phases is therefore of particular interest. In order to study this relationship three new liquid-crystalline materials were prepared, one as a racemic mixture, the other two as the optically active analogues. The optically active isomers appear to exhibit a different mesophase morphology from the racemate. The chiral compounds apparently possess two extra ferroelectric mesophases in comparison to the racemic mixture. The transitions to and from these phases have extremely small enthalpies. An attempt is made to explain the results for the chiral compounds in terms of differing dipolar couplings in the chiral ferroelectric phases. In the racemic mixture these interactions are compromised or scrambled by a loss of asymmetry thus destabilizing these extra phases.     

Bonded Cyclodextrin Stationary Phase Columns for the Separation of Cis/Trans Cyclohexane Derivatives

Abstract

Cyclohexane derivatives are important in the manufacture of monomers for the preparation of polyester polymers. The separation of cis/trans isomers of these derivatives has been investigated by using a bonded cyclodextrin column. This stationary phase offers excellent selectivity for the separation of these compounds. Although the efficiency of this column with the cyclohexane derivatives is less than the efficiency with nitroanalines, its excellent selectivity enabled adequate separation of the isomers of all but one of the compounds studied. A strategy for enhancing the efficiency and selectivity of this stationary phase is presented.     

Integrated multidimensional and comprehensive 2D GC analysis of fatty acid methyl esters

Fatty acid methyl ester (FAME) profiling in complex fish oil and milk fat samples was studied using integrated comprehensive 2D GC (GC × GC) and multidimensional GC (MDGC). Using GC × GC, FAME compounds – cis‐ and trans‐isomers, and essential fatty acid isomers – ranging from C18 to C22 in fish oil and C18 in milk fat were clearly displayed in contour plot format according to structural properties and patterns, further identified based on authentic standards. Incompletely resolved regions were subjected to MDGC, with Cn (n = 18, 20) zones transferred to a ²D column. Elution behavior of C18 FAME on various ²D column phases (ionic liquids IL111, IL100, IL76, and modified PEG) was evaluated. Individual isolated Cn zones demonstrated about four‐fold increased peak capacities. The IL100 provided superior separation, good peak shape, and utilization of elution space. For milk fat‐derived FAME, the ²D chromatogram revealed at least three peaks corresponding to C18:1, more than six peaks for cis/trans‐C18:2 isomers, and two peaks for C18:3. More than 17 peaks were obtained for the C20 region of fish oil‐derived FAMEs using MDGC, compared with ten peaks using GC × GC. The MDGC strategy is useful for improved FAME isomer separation and confirmation.     

Heterocyclic 1,3,4-oxadiazole as columnar core

The synthesis, characterization and mesomorphic properties of a new type of liquid crystalline compound, the 2,5-bis(3,4,5-trialkoxyphenyl)-1,3,4-oxadiazoles, 3a-3h, are reported. These heterocyclic compounds are derived from unsaturated 1,3,4-oxadiazole as the core group, and obtained by the condensation reaction of 3,4,5-trialkoxybenzoic acid N-(3,4,5-trialkoxybenzoyl)-hydrazides and phosphorus oxychloride in toluene under reflux. All compounds were characterized by ¹H and ¹³C NMR spectroscopy, and elemental analysis. The mesomorphic properties of these and the related compounds 1, 2 were characterized and studied by differential scanning calorimetry and polarizing optical microscopy. The formation of columnar mesophases was found to be dependent on the numbers of alkoxy sidechains. The compounds 3 exhibited hexagonal columnar (Col_h) phases, however compounds 1, 2 formed crystalline phases. Compounds 3b-3e with shorter carbon chains were room temperature liquid crystals. Polar induction by nitrogen and/or oxygen atoms on the heterocyclic core ring might be responsible for the formation and better observed mesomorphic properties in this type of compound.     

The Structure of 2,4-Diorganyl-2,4-Dithioxo-1,3,2λ5,4λ5-Dithiadiphosphetanes in Solution

Abstract

Compounds of the overall composition RPS₂, so called perthiophosphonic acid anhydrides, prefer a dimeric structure in szlution, as it has already been known for the solid compounds. Following compounds [RP(S)S]₂ with R=methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, cyclohexyl, phenyl, 4-methoxy-phenyl and 3,5-dimethyl-piienyl were prepared and characterized by iJJR spectroscopy. The 3,5-ditert-butyl-4-hydroxy-phenyl-compound [1] was also investigated. NHR investigations give evidence for the existence of conligurational isomers of the 2,4-Diorganyl-2,4-dithi-oxo-1,3,2λ⁵,4λ⁵-dithiadiphosphetanes. In solutions an equllibrium between cis and trans isomers is established. The concentration of the two isomers depends on the kind of P and the solvent used. In general the trans isomer has a nigher concentration than the cis isomer. The easy preparation of unsymmetrical compounds by mixing solutions of compounds with different R shows a continous dissociation and association process of the PSPS-ring. This result underlines the existence of a monomeric compound of low concentration as intermediate. An interesting result is obtained for the isopropyl compound. After dissolving e.g. in CDC1₃ almost 90% of the compound is transformed into the other isomer. The progress of the transformation can be followed by NXR spectroscopy. In all other cases the equilibrium state is immediately achieved after preparation of the solution.     

Reversed-Phase High-Performance Liquid Chromatography of Unsubstituted Aminobenzoic Acids

Abstract

High-performance liquid chromatographic (HPLC) characteristics of three position isomers of aminobenzoic acids (potential metabolites of important anesthetic drugs), were delineated with respect to their interactions with various mobile phases and stationary phases. HPLC with five hydrocarbonaceous phase, β-cyclodextrin silica (CDS), macrophase MP-1 polymer (MP), macroporous polystyrene/divinylbenzene (MPD), octadecylsilica (ODS), and propylphenylsilica (PPS), yielded results explicable in terms of substituent effects derived from the bifunctional amino– and carboxy groups. For cases where mobile phases contained sulfonates or quaternary ammonium salts both having longer chain alkyls, retention of analytes on all but CDS appeared to proceed predominantly via an ion-pairing mechanism. The extent of the corresponding counter-ion effects decreased in the order: MPD > ODS > PPS > MP, while the analyte retention order paralleled thier pH₂ values. On the other hand, an inverse relationship between the magnitude of capacity factors (k′) and pK₁ values of the title compounds was observed in experiments that produced retention data incompatible with ion-pair interaction rationales. The unique HPLC results obtained with the CDS phase are compared with those obtained with other phases.     

Liquid chromatography of jasmonic acid amine conjugates

Summary Racemic jasmonic acid (3R,7R/3S,7S)-(±)-JA) was chemically conjugated with different biogenic amines originating from aliphatic and aromatic α-amino acids by decarboxylation. The resulting isomeric compounds were subjected to reversed-phase high-performance liquid chromatography (HPLC) and to HPLC on the chiral stationary phases Chiralpak AS and Nucleodex β-PM. Under reversed-phase conditions, all the homologous amine derivatives tested could be separated from each other except the JA-conjugates containing 2-phenyl-ethylamine and 3-methylbutylamine. On both chiral supports the (3R,7R)-(−)-JA conjugates eluted earlier than those of the enantiomeric counterpart (3S,7S)-(+)-JA. On Chiralpak AS all the isomers studied could be separated to baseline with a mobile phase containingn-hexane and 2-propanol. The calculated resolution factors were between 1.80 and 4.17. The pairs of isomers were also chromatographed on the cyclodextrin stationary phase Nucleodex β-PM with methanol-triethylammonium acetate buffer as mobile phase. Under these conditions resolution factors were between 0.74 and 1.29. The individual isomers were chiroptically characterized by measurement of their circular dichroism.     

Ferroelectric liquid crystals derived from (S)‐2‐(6‐methoxy‐2‐naphthyl)propionic acid with non‐fluorinated or semi‐fluorinated alkanes at a chiral terminal chain

Two series of ferroelectric liquid crystals derived from (S)‐2‐(6‐methoxy‐2‐naphthyl)propionic acid, with non‐fluorinated or semi‐perfluorinated alkanes positioned at a chiral terminal chain, have been synthesized and characterized by differential scanning calorimetry, polarizing optical microscopy and electro‐optical measurements. The non‐fluorinated compounds, 1‐hexyl (S)‐2‐{6‐[4‐(4‐alkanoyloxyphenyl)benzoyloxy]‐2‐napthyl}propionates exhibit rich mesomorphism—the BP_II, N*, TGB_A*, SmA* and SmC* phases. The fluorinated compounds display only the SmA* and SmC* phases, suggesting that the fluorination promotes the formation of smectic phases. In addition, the SmA* and SmC* phases of the fluorinated compounds have enhanced thermal stability as compared with the corresponding phases of the non‐fluorinated compounds. The spontaneous polarization (P _s values) for the non‐fluorinated compounds are higher than those of the fluorinated compounds at any reduced temperature below the SmA*–SmC* transition. The electro‐optical responses measured for these compounds in the ferroelectric phase displayed thresholdless, V‐shaped switching.     

Effects of deuteration on the structure and magnetic properties of bis-quinolinium tetrabromidocuprate(II) dihydrate

Abstract

The partially [d₆, 2] and fully [d₂₀, 3] deuterated analogues of (QuinH)₂CuBr₄·2H₂O (d₀, 1) were prepared and their crystal structures were determined [Quin = quinoline]. In both compounds, there is a clear disorder in the positions of the bromide ions which was resolved. This led to a reexamination of the structure of the parent, fully protonated compound (1) where a small percentage of previously unrecognized disorder was also observed and the structure rerefined. Variable temperature magnetization measurements over the range 1.8–310?K indicate that all three materials behave as magnetically well-isolated layers that can be evaluated using the 2D-quantum Heisenberg antiferromagnetic model. Final fitting results for the partially (J = ?5.96(5) K) and fully (J = ?5.77(2) K) deuterated compounds indicate slightly weaker exchange compared to the protonated compound (J = ?6.17(3) K), likely as a result of the increased disorder in the deuterated phases.     

Separations in Thin Layer and High Performance Liquid Chromatography Using Alkyl Silica Gel Bonded Phases

Abstract

Separations in thin layer (TLC) and high performance liquid chromatography (HPLC) using alkyl bonded phases were carried out under optimum solvent conditions for each of three phases, RP-2, RP-8 and RP-18. The phases were tested for their efficiency and resolving power using three groups of compounds in three binary organic-water mobile phases. The organic solvents were acetonitrile, methanol and tetrahydrofuran, which are widely used as solvent modifiers in reversed phase liquid chromatography.

The results showed that, unlike HPLC, TLC using RP-18 plates was the most, and RP-2 plates the least, efficient. A naphthalene and biphenyl mixture which was resolved by HPLC using any of the three solvents and columns was not resolved by TLC using any plate or solvent combination, unless the plate was prewashed with an organic modifier. The addition of NaCl (1–2% wt/vol) to the solvent for TLC speeded development unless an alcohol was used, but did not greatly affect the separation.     

Non-symmetrically (1,2,4- and 1,3,4-)oxadiazole homologous: synthesis,characterisation and study the effect of different substituents on their mesophase behaviours

We have previously demonstrated that the type of oxadiazole isomers is relatively affected on showing the liquid crystalline properties of the compounds that have the same chemical compositions. In this paper, we presented the synthesis and mesomorphic behaviour of related compounds that possess ester linkage with different substituted groups on para of the phenyl to six derivatives containing 1,3,4-oxadiazole and like another six containing 1,2,4-oxadiazole rings. The formation of these compounds was evidenced by FTIR, ¹H NMR, ¹³C NMR, elemental analysis and mass techniques. Their mesophase behaviours were studied by optical polarised microscopy (OPM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). All of them presented liquid crystalline properties with nematic (N), smectic A (SmA) and smectic C (SmC) phases typically to calamitic compounds. The effect of substituent group nature and the type of oxadiazole isomers on the liquid crystalline properties of these compounds are analysed and discussed.     

Determination of molecular diffusion coefficients in liquid-crystalline cholesteryl myristate using gas chromatography

Abstract

The molecular diffusion coefficients of xylene and picoline isomers have been determined at different temperatures in the three phases (smectic, cholesteric and isotropic) of cholesteryl myristate by gas chromatography. The results obtained are discussed in terms of molar volume, polarity and length-to-breadth ratio of the isomers.