The influence of flexible spacer and the chirality of the core on the formation of chiral nematic phase of symmetric dimers containing trifluoromethyl terminal

Seven symmetric liquid crystal (LC) dimers containing different chiral cores and LC arms have been synthesised, termed EPDA-(R,S)PD, TFBDA-(R,S)PD, TFBA-(R,S)PD, TFBDA-(R)PD, TFBA-(R)PD, TFBDA-IB and TFBA-IB, respectively. TFBDA-(R,S)PD, TFBA-(R,S)PD, TFBDA-(R)PD and TFBDA-IB displayed chiral smectic A (SmA*) phase, while EPDA-(R,S)PD, TFBA-(R)PD and TFBA-IB exhibited chiral nematic (N*) phase. The effects of flexible spacer, structural type of LC arms and the chirality of the cores on the thermal properties of the dimers and the formation of N* phase have been studied. The results indicated that the chiral core was prone to induce the N* phase in LC dimer that contained nematic arms although the chirality of the core is very weak, while for the smectic LC arms containing CF3 terminal, the removal of the flexible spacer between chiral core and rigid LC units was conducive to the formation of N* phase. For example, TFBDA-(R)PD and TFBDA-IB displayed SmA* phase, while TFBA-(R)PD and TFBA-IB exhibited N* phase. However TFBA-(R,S)PD did not display N* phase, which reminded us that the chirality of the core and the conformation of the dimer also played an influence in the formation of the LC phase.     

High Pressure Liquid Chromatographic Analysis and Dissolution of Famotidine in Tablet Formulation

Abstract

A reversed phase high pressure liquid chromatographic method was developed for the quantitation of famotidine in tablet formulation using a mobile phase consisting of 0.1M phosphate buffer (84%), acetonitrile (11%) and methanol (5%) at a pH of 6.5. The detection wavelength was set at 285 nm. The method is precise and adaptable for quality control purposes. The use of the analytical method hi studying tablet dissolution is described.     

A Facile Method to 1,4-Diacyl Semicarbazides: Syntheses of 1-Aryloxyacetyl-4-(4-Chlorobenzoyl)-Thiosemicarbazides and Semicarbazides

A facile method to diacyl semicarbazides is described. Reactions of 4-chlorobenzoyl chloride with ammonium thiocyanate first, then with aryloxyacetic acid hydrazides under phase transfer catalysis give 1-aryloxyacetyl-4-(4-chlorobenzoyl)-thiosemicarbazides (Ia-h). Compounds Ia-h on treatment with potassium iodate under reflux result in the formation of 1-aryloxyacetyl-4-(4-chlorobenzoyl)-semicarbazides (IIa-h) in excellent yields.     

Indirect Determination of Bromhexine by Atomic Absorption Spectrophotometry

Abstract

A new procedure for determination of Bromohexine is described. The method consists of extracting an ion pair between the Bromhexine and the inorganic complex Co(SCN)² ₄ and measuring Co in the organic phase by AAS at 240. 7 nm. The optimal experimental conditions: pH, concentration of Co(SCN)² ₄, shaking time, phase ratio, number of extractions and the linear range of calibration are studied.

The organic phase used is 1,2-dichloroethane. The standard deviation of the method is 10^?3. The interference of foreign substances which accompany the Bromhexine in pharmaceutical preparations is studied, and the method is applied to their quantitative determination in medicines.     

High Pressure Liquid Chromatographic Analysis of Orphenadrine Citrate and Acetaminophen in Pharmaceutical Dosage Forms

Abstract

An ion pair reversed phase high pressure liquid chromatographic method for the analysis of orphenadrine citrate (I) and acetaminophen (II) was developed. The mobile phase consisted of 20mM sodium-1-octane sulfonate in 50mM phosphate buffer (pH=3.0), mixed with 22.5% organic solvents (50:50, acetonitrile: methanol). The method is simple, reliable and could be adapted for quality control purposes.     

镉基杂化晶体的介电相变和蓝白光致发光双重特性

通过采用容易无序的胺,我们合成了2种有机无机杂化晶体,分别为基于bempy （bempy=1-甲基-1-溴乙基吡咯烷阳离子）的溴盐化合物（bempy） Br （1）和镉基溴化物（bempy）₂CdBr₄（2）,并对其结构相变、介电相变和蓝白荧光进行了详细的表征分析。化合物1在测试温度范围内未观察到可逆相变,化合物2为高温介电相变,介电和差示扫描量热法测试表征其相变温度为357 K。同时,化合物1和2均具备蓝白光致发光特性,荧光测试表明,化合物1和2分别在538 nm和547、750 nm处存在发射峰。化合物2具备介电相变和蓝白光致发光的双重特性。     

A systematic study on the influences of linkage length on phase behaviours and charge carrier mobilities of discotic dimers

Two series of discotic dimers T3Dn and T5Dn based on hexapropoxytriphenylene (HAT3) and hexapentyloxytriphenylene(HAT5), respectively, with polymethylene linkage O(CH₂)_nO (n = 3–12) have been synthesised. Their mesomorphism was investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The results showed that side chains induced a phase transition from col_hp phase to col_h phase, namely dimers T3Dn (n = 6–12) based on HAT3 exhibiting a single col_hp phase, dimers T4Dn (n = 6, 7, 11, 12) based on HAT4 showing a highly ordered col_hp phase in low-temperature region and a col_h phase in high-temperature region, dimers T4Dn (n = 8–10) based on HAT4 displaying a single col_hp phase and dimers T5Dn (n = 6–11) based on HAT5 indicating a single col_h phase. Dimers T4Dn showed a phase competition between col_h phase and col_hp phase induced by linkages. Surprisingly, a unique phenomenon was found by us, that is, those compounds in which linkage lengths were twice those of side chains showed the largest enthalpies, the smallest intracolumnar spacings and the highest charge-carrier mobilities among their homologues, respectively, which implied that they formed the most highly ordered phase among their homologues.     

New chiral liquid crystal cyclic monomers based on diosgenin: synthesis and mesomorphism

A series of new chiral liquid crystal (LC) intermediate compounds (LC-C₁~LC-C₄) containing diosgenyl groups and the corresponding cyclic LC aliphatic carbonate monomers (LC-M₁~LC-M₄) were synthesised to investigate the relationship between their structures and phase behaviour. The chemical structures of the compounds obtained in this study were characterised using FT-IR, ¹H NMR and ¹³C NMR measurement. The phase behaviour and mesophase structure were investigated with polarising optical microscopy, differential scanning calorimetry and X-ray diffraction measurement. As a result, LC-C₁ and LC-C₂ showed focal conic texture of the choleteric phase, while LC-C₃ and LC-C₄ with longer spacer length showed fan-shaped texture of a smectic A phase. The monomers (LC-M₁~LC-M₄) all exhibited focal conic texture of the choleteric phase on heating and cooling cycles. Furthermore, the effect of the spacer length on phase behaviour of the LC compounds was discussed.     

A Simple Method for Synthesis of Methylene Dioximes Using Poly(ethylene glycol)‐400 as a Phase Transfer Catalyst

Abstract

A simple method for synthesis of methylene dioximes by reaction of ketoximes with dichloromethane in the presence of aqueous sodium hydroxide solution using poly (ethylene glycol)‐400 (PEG‐400) as a phase transfer catalyst is described.     

Thin Layer Chromatographic Analysis of Basic and Quaternary Drugs Extracted as Bis(2-ethylexyl)phosphate Ion-Pairs

Abstract

Thin layer chromatography in the normal and reversed phase mode is evaluated as a qualitative analysis method for various basic and quaternary drugs extracted as bis(2-ethylhexyl)phosphate ion-pairs. A combination of two thin layer chromatographic systems, a reversed phase system and a fairly apolar normal phase system, is shown to cover the analysis of drugs with different grades of polarity. Based on that, a method for screening of urine samples for drugs is described.     

Analytical Resolution of 4-ARYL-1,2,3,4,5,6,7,8-Octahydroquinazoline-2-Thiones using a Cellulose Chiral Stationary Phase

ABSTRACT

Racemic 4-aryl-1,2,3,4,5,6,7,8-octahydroquinazoline-2-thiones were resolved into their enantiomers by HPLC on cellulose tris(4-methylbenzoate) coated on silica gel using ethanol:n-hexane (70:30) as a mobile phase. A convenient method for preparation of cellulose tris(4-methylbenzoate) chiral stationary phase was described and the enantiomers were characterized by some chromatographic data.     

Stability Indicating Hplc Method for the Determination of Sparfloxacin (Spar)

ABSTRACT

A rapid, sensitive and stability indicating method for the determination of sparfloxacin (SPAR) by RP - HPLC has been developed on a Merck RP - Select B (5 μm; 12.5 cm x 4.0 mm) column using a mobile phase of water: acetonitrile: triethylamine (80 : 20 : 0.2 v/v) pH of which was adjusted to 2.6 with orthrophosphoric acid. The flow rate was 1 ml / min. and the detection was carried out at 304 nm using Waters 486 variable wavelength detector. The retention time for SPAR was 7.2 min. Linearity range was from 8 - 1000 ppm. The method showed good precision and accuracy when applied to two brands of tablets containing SPAR. In alkaline media SPAR is stable where as it undergoes degradation in acidic and oxidising conditions generating different degradation products the nature of which is required to be established. The proposed method nicely separates the degraded products from SPAR and hence can be used as stability indicating method for the assay of SPAR.     

Preparative Isolation of Pyrrolizidine Alkaloids Derived from Senecio Vulgaris

Abstract

A large scale method for the isolation of pyrrolizidine alkaloids has been adapted from a previously published analytical method. This method is a reverse phase high pressure liquid chromatography technique, utilizing a .005 M KH₂ PO₄ (pH 6.3) — methanol solvent system. The pyrrolizidine alkaloids derived from Senecio vulgaris (common groundsel) have been utilized in this system.     

On the Use of the Knox Equation. II. the Efficiency Measurement Problem

Abstract

The Knox equation, which relates the reduced plate height, h, to the reduced linear velocity, v, has a great importance in column and stationary phase testing. Significant A, B, and C terms of the Knox equation cannot be obtain with erroneous plate heights, h. Four methods for efficiency determination, the inflection (0.6H) method, the height/area method, an asymmetry based (0.1H) method and the moment method, were critically compared using 200 real chromatograms. Efficiency obtained using Gaussian assuming methods were highly overestimated, while the asymmetry based method gave quite acceptable results. Using the exponentially modified Gaussian model, it is demonstrated that the b/a ratio (the sum b + a is the peak-width at 10% of the peak height) is not an empirical figure of merit but can be related to a “peak skew” expression.     

Optimization of the Extraction Conditions and Simultaneous Quantification by RP-LC of Six Alkaloids in Evodiae Fructus

A reversed phase liquid chromatographic (LC) method coupled with DAD (250 nm) has been developed and validated for simultaneous quantification of six alkaloids, dehydroevodiamine (1), wuzhuyuamide-I (2), 5-hydroxyrutaecarpine (3), 14-formyldihydrorutaecarpine (4), evodiamine (5) and rutaecarpine (6), in 12 batches evodiae fructus [the dried, unripe fruits of Evodia rutaecarpa (Juss.) Benth. or E. rutaecarpa (Juss.) Benth. var. officinalis (Dode) Huang, E. rutaecarpa (Juss.) Benth. var. bodinieri (Dode) Huang] as a traditional Chinese medicine. The method was carried out by a C₁₈ column (250 × 4.6 mm) with a gradient mobile phase of methanol, acetonitrile, and phosphoric acid–triethylamine–buffer solution. The contents of 1–6 in the evodiae fructus could easily be determined within 70 min. The experimental results were satisfactory for the intra-day and inter-day precision and accuracy of the method for simultaneous determination. The linear calibration ranges of 1–6 were 40–1,000, 20–500, 1–100, 10–500, 40–1,000 and 80–1,000 μg mL⁻¹. The recoveries of 1–6 were 97.43–103.73% with RSDs from 0.21 to 1.99%. The limits of detection for 1–6 were 2.0, 2.0, 0.1, 1.0, 5.0 and 5.0 μg mL⁻¹, and the limits of quantification were 6.6, 6.6, 0.3, 3.3, 16.5 and 16.5 μg mL⁻¹. The method was successfully applied to the quantification of six alkaloids in the evodiae fructus.     

Conformational in the IR spectra of 1′-hydroxyethyl derivatives of 1,4-benzo-and 5,8-dihydroxy-1,4-naphthoquinones: A DFT study

Detailed conformational analysis of the molecule of ′-hydroxyethyl-1,4-benzoquinone (3) by the B3LYP/cc-pVTZ method revealed predominance of rotamers with the free 1′-OH group in the gas phase. B3LYP/cc-pVTZ calculations with inclusion of solvent (cyclohexane) effect in the framework of the polarizable continuum model predict an increase in the percent-age of such rotamers compared to the corresponding gas-phase values. The results obtained are in qualitative agreement with the experimentally observed pattern of v(OH) bands in the IR spectrum of compound 3 in cyclohexane (hexane) solution. Conformational analysis, including tautomerism and rotamerism, of 2-ethyl-1′,5,8-trihydroxy-1,4-naphthoquinone (2) was performed by the B3LYP method with the 6-31G(d), 6-311G(d), 6-311G(d,p), and cc-pVDZ basis sets. The most abundant tautomeric form of compound 2 is form A in which the substituent bearing 1′-OH group is in the quinonoid nucleus. In the gas phase, the percentage of all rotamers in form A is about 86% (among them, the proportion of rotamers with the free 1′-OH group is more than 60%). The main reason for splitting of the v(OH) bands in the IR spectra of compounds 2 and 3 in solutions in nonpolar solvents is the equilibrium between rotamers with a relatively weak intramolecular hydrogen bond between the 1′-OH group and the carbonyl group and those having no this bond.     

Determination of Copper by Faas After Preconcentration with Lead-4-Methylpiperidinedithiocarbamate on Microcrystalline Naphthalene By Solid Phase Extraction

ABSTRACT

By using the Pb-4-methylpiperidinedithiocarbamate complex (Pb(4-MPDC)₂) on microcrystalline naphthalene in a column a method was developed for the preconcentration of copper in water samples prior to its determination by FAAS. In this method, copper in liquid phase quantitatively replaces lead on the Pb(4-MPDC)₂-naphthalene solid phase in the column, forming solid Cu(4-MPDC)₂ complex.

Afterwards, copper on Cu(4-MPDC)₂-naphthalene can be easily eluted by potassium cyanide into the aqueous phase, and the Cu is measured by FAAS. The optimum experimental parameters such as pH, flow rate, sample volume, Pb(4-MPDC)₂-naphthalene ratio, concentration of the potassium cyanide solution and effect of matrix ions for the preconcentration of copper were investigated. The obtained recovery was nearly 100 %, when the enrichment factor was 100 for standard solutions and spiked water samples. The proposed method has been employed for the determination of copper in various standard metal alloys and natural water samples.     

Indirect Determination of Lidocaine by Atomic Absorption Spectrophotometry

Abstract

A new procedure for determining lidocaine chlorhydrate is described. The method consists of extracting an ion pair composed of Lidocaine and the inorganic complex Co(SCN)₄ ^2- into an organic solvent (1, 2 dichloroethane), then measure the Co in the organic phase by A.A.S. at 240.7 mm. Optimal experimental conditions concerning pH, Co(SCN)₄ ^?2 concentration, shaking time, phase ratio, number of extractions and linear range for calibration are studied. The method has a standard deviation of 10^?2. Two pharmaceutical preparations containing lidocaine, have been analyzed with very good results.     

Determination of Tetracycline and Related Compounds by High-Performance Liquid Chromatography

Abstract

An isocratic high-performance liquid chromatography method for the determination of tetracycline and its related compounds is described. The method uses a reverse phase (C₁₈) column, a modified acetonitrile/water mobile phase, and banzoic acid as the internal standard. Elution of all compounds of interest is complete within seven minutes. Results are presented for thirteen commercial capsule formulations and are compared with results by microbiological assay and thin-layer chromatographic methods.     

V-shaped switching in binary mixtures of an achiral swallow-tailed material with the antiferroelectric liquid crystal (S)-MHPOBC

An achiral swallow-tailed material, 2-propylpentyl 4-(4′-decyloxybiphenyl-4-carbonyloxy)benzoate, p, showing SmA and SmC_alt phases was prepared for mixing (by weight percentage) with an antiferroelectric liquid crystal, (S)-MHPOBC, m, for the study. The binary mixture p/15/m85 using (S)-MHPOBC (85%) as a host doped with achiral material (15%) resulted in a phase sequence SmA-SmC*-SmC*_A. The electro-optic response of this mixture in the ferroelectric SmC* phase displayed V-shaped switching, while that in the antiferroelectric SmC*_A phase displayed a double hysteresis switching. The mixture p85/m15 possessed SmA* and SmC*_A phases; V-shaped switching was found in the antiferroelectric SmC*_A phase of this mixture. These optical phenomena implied that a binary mixture containing a larger amount of achiral swallow-tailed material and/or possessing relatively lower polarization favours the occurrence of V-shaped switching in the antiferroelectric phase. The results of this work also suggested that thresholdless V-shaped switching in chiral smectic liquid crystals can be achieved by mixing an achiral swallow-tailed material with an antiferroelectric liquid crystal.