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Forced degradation of losartan potassium in acidic condition resulted into three potential unknown impurities. These unknown degradation products marked as LD-I, LD-II and LD-III were analyzed using a new reverse-phase high performance liquid chromatography (HPLC), eluting at 3.63, 3.73 and 3.91 relative retention times with respect to losartan potassium (LOS) peak. All three were isolated from reaction mass using preparative HPLC and their structures were elucidated using LC-MS/MS, multidimensional NMR and FTIR spectroscopic techniques, as 5(2),11(2)-dibutyl-5(4),11(4)-dichloro-1(1)H,5(1)H,7(1)H,11(1)H-1(5,1),7(1,5)-ditetrazola-5,11(1,5)-diimidazola-2,8(1,2),3,9(1,4)-tetrabenzenacyclododecaphane,(Z)-5(2),11(2)-dibutyl-5(4),11(4)-dichloro-1(1)H,5(1)H,7(2)H,11(1)H-1(5,1),7(2,5)-ditetrazola-5,11(1,5)-diimidazola-2,8(1,2),3,9(1,4)-tetrabenzenacyclododecaphane, and 5(2),11(2)-dibutyl-5(4),11(4)-dichloro-1(2)H,5(1)H,7(2)H,11(1)H-1(5,2),7(2,5)-ditetrazola-5,11(1,5)-diimidazola-2,8(1,2),3,9(1,4)-tetrabenzenacyclododecaphane, respectively. To best of our knowledge, all three degradation products are novel impurities which are not discussed at any form of publication yet.

Differential scanning calorimetry (DSC) is a primary technique for measuring the thermal properties of materials, which reflects the physico-chemical properties of drug substances. In the present study, it is used as a screening technique for assessing the compatibility of sitagliptin with some currently employed pharmaceutical excipients. The influence of processing conditions and their effects (simple blending, co-grinding or kneading) on drug stability was evaluated. Sitagliptin showed a sharp endothermic peak at 212.1 °C with an enthalpy change of 131.5 J g−1 indicating melting of drug. Facile transformation of dehydrated sitagliptin to monohydrate form was observed in some mixtures, disappearance of sharp melting endothermic peak of sitagliptin was observed in some mixtures. On the basis of DSC results, sitagliptin was found to be compatible with micro crystalline cellulose, croscarmellose, and pregelatinized starch. Some excipient interaction was observed with magnesium stearate, ascorbic acid, and citric acid. X-ray diffractometry and FT-IR were used as supportive tools in interpreting the DSC results. Overall, the excipients selected were compatible with the API and the mixtures are stable within the tested conditions. These results would be useful for formulation development of the film coated tablets of sitaglitptin.

An isocratic, stability-indicating, reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed for the quantitative determination of doxofylline and terbutaline sulphate, used for the treatment of respiratory problems. The chromatographic separation was achieved on a Zorbax-SB Phenyl 250 x 4.6mm x 5 μm column with the mobile phase consisting of a mixture of 25 mM ammonium acetate (pH 5.0) : acetonitrile (85:15 %v/v) at a flow rate of 1.0 ml/min. The eluate was monitored at 274 nm using a PDA detector. Forced degradation studies were performed on the bulk sample of doxofylline and terbutaline sulphate using acid (0.1N HCl), base (0.1N NaOH), oxidation (10% hydrogen peroxide), photolytic, and thermal degradation conditions. Good resolution was observed between the degradants and analytes. Degradation products resulting from the stress studies did not interfere with the detection of doxofylline and terbutaline sulphate, thus the assay is stability-indicating. The method has the requisite accuracy, selectivity, sensitivity, and precision for the simultaneous estimation of doxofylline and terbutaline sulphate in bulk and pharmaceutical dosage forms. The limit of quantitation and limit of detection were found to be 1.16 μg/ml and 0.38 μg/ml for doxofylline, 2.08 μg/ml and 0.62 μg/ml for terbutaline sulphate, respectively.

A simple, rapid, and stability-indicating RP-HPLC method for a combination of tenofovir disoproxil fumarate (TDF), emtricitabine (FTC), and efavirenz (EFV) was developed and validated with the help of a suitable statistical software as an application tool for the quality by design. The drugs individually, and in combination, were subjected to forced degradation (thermal, photolytic, hydrolytic, and oxidative stress conditions) and accelerated stability studies (40 ± 1°C/75 ± 3% RH for three months). Successful separation of combined drugs from degradation products was achieved by gradient elution on a reverse-phase C18 column, using a mobile phase containing phosphate buffer (pH 3.5): acetonitrile at 1.5 mL min−1 flow rate, detection wavelength 256 nm, column oven temperature 25°C, and injection volume 10 μL. Linearity was established in the range of 20–300 μg mL−1, 24.5–367.5 μg mL−1 and 60–900 μg mL−1 for FTC, TDF, and EFV, respectively. The method was successfully applied for quantifying the drugs in marketed dosage forms and on stability samples.

This paper presents the effects on the distance protection scheme used by the transmission lines protection system when they are compensated in series by Thyristor Controlled Series Capacitor (TCSC). The usage of TCSC introduces problems to distance protection schemes as there is a change in the measurement of apparent impedance observed by the respective relay. The change seen by the relay measurement has to be corrected for accurate operation of the particular relay, for which we take the help of Artificial Neural Networks which is extensively tested for various test conditions in MATLAB Simulation environment. The relay operation accuracy used for distance protection is improved by using the Artificial Neural Networks training methods and it also shows the distance at which the faults has occurred.

Recent years have seen a rapid increase in the discovery of novel allelic variants of the human leukocyte antigen (HLA) genes. Commonly, only the exons encoding the peptide binding domains of novel HLA alleles are submitted. As a result, the IPD-IMGT/HLA Database lacks sequence information outside those regions for the majority of known alleles. This has implications for the application of the new sequencing technologies, which deliver sequence data often covering the complete gene. As these technologies simplify the characterization of the complete gene regions, it is desirable for novel alleles to be submitted as full-length sequences to the database. However, the manual annotation of full-length alleles and the generation of specific formats required by the sequence repositories is prone to error and time consuming. We have developed TypeLoader to address both these facets. With only the full-length sequence as a starting point, Typeloader performs automatic sequence annotation and subsequently handles all steps involved in preparing the specific formats for submission with very little manual intervention. TypeLoader is routinely used at the DKMS Life Science Lab and has aided in the successful submission of more than 900 novel HLA alleles as full-length sequences to the European Nucleotide Archive repository and the IPD-IMGT/HLA Database with a 95% reduction in the time spent on annotation and submission when compared with handling these processes manually. TypeLoader is implemented as a web application and can be easily installed and used on a standalone Linux desktop system or within a Linux client/server architecture. TypeLoader is downloadable from http://www.github.com/DKMS-LSL/typeloader.

Summary A simple, rapid, precise, and accurate, stability-indicating reversed phase high performance liquid chromatographic method was developed and validated for simultaneous determination of metformin HCl and repaglinide. The chromatographic separation was achieved on YMC Pack AM ODS (5 μm, 250 mm length × 4.6 mm i.d.) column at a detector wavelength of 210 nm, using an isocratic mobile phase consisting of methanol and 10 mM potassium dihydrogen phosphate buffer (pH 2.5) in a ratio of 70:30 v/v at a flow rate of 1 mL min−1. The retention times for metformin and repaglinide were found to be 2.6 and 11.3 min, respectively. The drugs were exposed to thermal, photolytic, hydrolytic, and oxidative stress conditions, and the stressed samples were analyzed by the proposed method. Validation of the method was carried out as per International Conference on Harmonization (ICH) guidelines. Linearity was established for metformin and repaglinide in the range of 5–200 μg mL−1 and 1–200 μg mL−1, respectively. The lim...

Polypill is a fixed dose combination, used as a single daily pill to achieve a large effect in preventing cardiovascular disease with minimal adverse effects. In the present study, gradient LC method was developed for simultaneous determination of the Polycap, that is, Atenolol, Hydrochlorothiazide, Aspirin, Ramipril, and Simvastatin, in presence of their major interaction/degradation products. The individual drug components and their major interaction/degradation products were well separated using reverse phase C18 column and a mobile phase containing Acetonitrile:Phosphate buffer (pH 2.3). Other instrumental parameters were flow rate, 1 mL min−1; detection wavelength, 230 nm; column oven temperature, 40°C; and injection volume, 5 µL. The combined drugs were subjected to stress conditions such as hydrolysis, oxidation, photolysis, and thermal decomposition. The method was validated for linearity, precision, accuracy, specificity, and robustness.

A validated specific stability indicating reversed-phase high-performance liquid chromatography method was developed for the quantitative determination of Amsacrine as well as its related substances determination in bulk samples, in presence of degradation products, and its process related impurities. Forced degradation studies were performed on bulk samples of Amsacrine as per International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human use (ICH) prescribed stress conditions using acid, base, oxidative, thermal stress, and photolytic degradation to show the stability indicating power of the method. Significant degradation was observed during basic hydrolysis, slight degradation was observed in oxidative and thermal stress, and no degradation was observed in other stress conditions. The chromatographic method was optimized using the samples generated from forced degradation studies and the impurity spiked solution. Good resolution between the peaks corresponds to process-related impurities and degradation products from the analyte were achieved on Inertsil ODS column using the mobile phase consists a mixture of 1.0% triethyl amine in 20 mM potassium dihydrogen orthophosphate, with pH adjusted to 6.5, with ortho phosphoric acid in water and acetonitrile using a simple linear gradient. The detection was carried out at wavelength 248 nm. The mass balance in each case was in between 99.4% to 99.9%, indicating that the developed method was stability-indicating. Validation of the developed method was carried out as per ICH requirements. The developed method was found to be suitable to check the quality of bulk samples of Amsacrine at the time of batch release and also during its stability studies.

A novel, sensitive and precise UHPLC method has been developed and validated for the simultaneous determination of the all the active components of a Polypill viz Zycad, i.e., Aspirin (ASP) Atorvastatin (ATV), Ramipril (RMP) and Metoprolol (MTP) in Zycad tablet dosage form in the presence of degradation products. Forced degradation of individual as well as combination of all the drug substances components of Polypill was conducted in accordance with ICH guidelines. Acidic, basic, neutral, and oxidative hydrolysis, thermal stress, and photolytic degradation were used to assess the stability-indicating power of the method. Use of 100 × 2.1 mm, 1.7 µm stationary phases with simple mobile phase combination buffer consisting of 0.1% Perchloric acid (adjusted to pH 2.5) and Acetonitrile, delivered in a gradient mode and quantitation was carried out using ultraviolet detection at 215 nm with a flow rate of 0.6 mL?min–1. The method was optimized using samples generated by forced degradation studies. The method was validated for linearity, accuracy (recovery), precision, Specificity and robustness. The method was linear in the range of 37.5 to 150.0 µg?mL–1 for ASP, 5.0 to 20.0 µg?mL–1 for ATV and 2.5 to 10.0 µg?mL–1 for RMP and 25.0 to 100.0 µg?mL–1 for MTP.

Summary A new, sensitive, stability-indicating, and cost and time-effective isocratic reversed-phase UHPLC method has been developed for quantitative analysis of felbamate, an antiepileptic drug, both in the bulk drug and in pharmaceutical dosage forms. Chromatographic separation of felbamate and its two impurities was achieved on a C18 column with a simple buffer-methanol mobile phase; the run time was 8 min. Quantification was achieved by ultraviolet detection. Resolution between the impurities was >2.0. Response was a linear function of concentration over the range 0.1–3.0 μg mL−1, correlation coefficient >0.999, for felbamate and the impurities. The method is capable of detecting the two impurities at levels of 0.002% (0.02 μg mL−1) of the test concentration of 1.0 mg mL−1 (1 μL injection). The same sensitivity was achieved for all the degradation products formed during stress studies in which the drug was subjected to hydrolysis, oxidation, photolysis, and thermal degradation. Substantial degradation...

A novel, sensitive, stability indicating RP-LC method has been developed for the quantitative determination of mitotane, its impurity in both bulk drugs and pharmaceutical dosage forms. Efficient chromatographic separation was achieved using a C18 stationary phase with simple mobile phase combination delivered in an isocratic mode and quantitation was by ultraviolet detection at a wavelength of 230 nm. The mobile phase consisted of buffer and acetonitrile (25:75, v/v) delivered at a flow rate of 1.0 mL min−1. Buffer consisted of 10 mM potassium dihydrogen orthophosphate monohydrate, pH adjusted to 2.5 by orthophosphoric acid. In the developed LC method the resolution (Rs) between mitotane and its impurity namely Imp-1 was found to be greater than 2.5. Regression analysis shows an r value (correlation coefficient) greater than 0.999 for mitotane and its impurity. This method was capable to detect the impurity of mitotane at a level of 0.003% with respect to test a concentration of 0.2 mg mL−1 for a 10 μL injection volume. The inter- and intra-day precision values for mitotane and its impurity was found to be within 2.0% RSD. The method has shown good and consistent recoveries for mitotane in bulk drugs (99.2–101.5%), pharmaceutical dosage forms (98.2–103.1%) and for its impurity (99.7–102.1%). The test solution was found to be stable in diluent for 48 h. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. Considerable degradation was found to occur in basic stress hydrolysis. The stress samples were assayed against a qualified reference standard and the mass balance was found close to 99.97%. The developed RP-LC method was validated with respect to linearity, accuracy, precision and robustness.

A new, sensitive, stability indicating gradient RP-LC related substances and assay method has been developed for the quantitative determination of entacapone in bulk drugs. Efficient chromatographic separation was achieved on a C18 stationary phase with simple mobile phase combination of buffer and acetonitrile. Buffer consisted of 0.1% orthophosphoric acid, delivered in a gradient mode and quantitation was carried out using ultraviolet detection at 220 nm with a flow rate of 1.5 mL min−1. In the developed LC method the resolution (Rs) between entacapone and its three potential process impurities were found to be >2.0. Regression analysis showed an r2 value (correlation coefficient) >0.99 for entacapone and its three potential impurities. This method was capable to detect all three process impurities of entacapone at a level of 0.003% with respect to test concentration of 0.5 mg mL−1 for a 20 μL injection volume. The inter- and intra-day precision values for all three impurities and for entacapone was found to be within 2.0% RSD. The method has shown good and consistent recoveries for entacapone in bulk drugs (99.2–101.5%) and its three impurities (99.5–102.2%). The test solution was found to be stable in diluent for 48 h. The drug substances were subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. Considerable degradation was found to occur in acid stress, base stress and oxidative conditions. The stressed test solutions were assayed against the qualified working standard of entacapone and the mass balance in each case was close to 99.7% indicating that the developed method was stability-indicating. The developed RP-LC method was validated with respect to linearity, accuracy, precision and robustness.

A novel, sensitive, stability-indicating gradient RP-LC method has been developed for quantitative analysis of balsalazide disodium and its related impurities both in the bulk drug and in pharmaceutical dosage forms. Efficient chromatographic separation was achieved on a C18 stationary phase with a simple mobile-phase gradient prepared from methanol and phosphate buffer (10 mm potassium dihydrogen orthophosphate monohydrate, adjusted to pH 2.5 by addition of orthophosphoric acid). The mobile-phase flow rate was 1.0 mL min−1. Quantification was achieved by use of ultraviolet detection at 240 nm. Under these conditions resolution of balsalazide disodium from its three potential impurities was greater than 2.0. Regression analysis resulted in a correlation coefficient greater than 0.99 for balsalazide disodium and all three impurities. This method was capable of detecting the three impurities at 0.003% of the test concentration of 0.3 mg mL−1, using an injection volume of 10 μL. Inter-day and intra-day precision for all three impurities and for balsalazide disodium was within 2.0% RSD. Recovery of balsalazide disodium from the bulk drug (99.2–101.5%) and from pharmaceutical dosage forms (99.8–101.3%), and recovery of the three impurities (99.1–102.1%) was consistently good. The test solution was found to be stable in 70:30 (v/v) methanol–water for 48 h. When the drug was subjected to hydrolytic, oxidative, photolytic, and thermal stress, acidic and alkaline hydrolysis and oxidizing conditions led to substantial degradation. The RP-LC method was validated for linearity, accuracy, precision, and robustness.

A simple, sensitive gradient RP-LC assay method has been developed for the quantitative determination of vardenafil HCl in bulk drug and in pharmaceutical dosage forms, used to treat erectile dysfunction. The developed method is also applicable for the related substances determination. Efficient chromatographic separation was achieved on a C18 stationary phase with simple mobile phase combination delivered in a gradient mode and quantification was carried out using ultraviolet detection at a flow rate of 1.0 mL min−1. In the developed LC method the resolution between vardenafil and its four potential impurities was found to be greater than 3.0. Regression analysis shows an r2 value (correlation coefficient) greater than 0.99 for vardenafil and its four impurities. This method was capable of detecting all four impurities of vardenafil at a level of 0.009% with respect to test concentration of 1.0 mg mL−1 for a 10 μL injection volume. The method has shown good and consistent recoveries for vardenafil (98.4–100.6%) and its four impurities (93.5–106.2%). The test solution was found to be stable in the diluent for 48 h. Mass balance was found close to 99.4%.

A simple, sensitive gradient RP-LC assay method has been developed for the quantitative determination of amtolmetin guacyl in bulk drug, used as anti-inflammatory drug. The developed method is also applicable for related substances determination. Efficient chromatographic separation was achieved on a C18 stationary phase with simple mobile phase combination delivered in a gradient mode and quantification was carried out using ultraviolet detection at 313 nm at a flow rate of 1.0 mL min−1. In the developed LC method the resolution between Amtolmetin Guacyl and its three potential impurities was found to be greater than 2.0. Regression analysis shows an r value (correlation coefficient) greater than 0.99 for amtolmetin guacyl and its three impurities. This method was capable to detect all three impurities of amtolmetin guacyl at a level of 0.002% with respect to test concentration of 0.5 mg mL−1 for a 10 μL injection volume. The inter- and intra-day precision values for all three impurities and for amtolmetin guacyl was found to be within 2.0% RSD at its specification level. The method has shown good and consistent recoveries for amtolmetin guacyl (99.2–101.5%) and its three impurities (94.5–104.8%). The test solution was found to be stable in diluent for 48 h. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. Considerable degradation was found to occur in oxidative stress conditions. The stress samples were assayed against a qualified reference standard and the mass balance was found close to 99.6%. The developed RP-LC method was validated with respect to linearity, accuracy, precision and robustness.

A new and accurate chiral liquid chromatographic method has been developed for the separation and quantification of (S,R,S)-enantiomer (unwanted enantiomer) and (R,R,R)-isomer (key intermediate) of aprepitant in bulk drug and formulation samples of apprepitant. The elution time was approximately 20 min using an immobilized amylose-based chiral stationary phase (Chiralpak-IA). The mobile phase was n-hexane and ethanol (90:10, v/v) and was delivered at a flow rate of 1.0 mL min−1. Detection was carried out with a wavelength set to 220 nm. The resolution factor between enantiomers was found to be greater than five. Limit of detection for both (S,R,S) enantiomer and (R,R,R) isomer of aprepitant was 0.035 µg, and limit of quantification for both (S,R,S) enantiomer and (R,R,R) isomers of aprepitant was 0.1 µg, for a 10 µL injection. The developed method showed excellent linearity (r > 0.999) for both isomers. When the method was applied to bulk drug samples and in pharmaceutical formulations recoveries were obtained ranging from 97.2 to 103.1%. Aprepitant sample solutions were found to be stable when characterized over a period of 48 h.

A new and accurate chiral liquid chromatographic method has been developed for determination of the enantiomeric purity of montelukast sodium (R enantiomer) in bulk drugs and dosage forms. Normal phase chromatographic separation was performed on an immobilized amylose-based chiral stationary phase with n-hexane–ethanol–1,4-dioxane–trifluoroacetic acid–diethylamine 65:25:10:0.3:0.05 (v/v) as mobile phase at a flow rate of 1.0 mL min−1. The elution time was approximately 15 min. The resolution (RS) between the enantiomers was >3. The mobile phase additives trifluoroacetic acid and diethylamine played a key role in achieving chromatographic resolution between the enantiomers and also in enhancing chromatographic efficiency. Limits of detection and quantification for the S enantiomer were 0.07 and 0.2 μg, respectively, for a test concentration of montelukast sodium of 1,000 μg mL−1 and 10 μL injection volume. The linearity of the method for the S enantiomer was excellent (R2 > 0.999) over the range from the LOQ to 0.3%. Recovery of the S enantiomer from bulk drug samples and dosage forms ranged from 97.0 to 103.0%, indicative of the high accuracy of the method. Robustness studies were also conducted. The sample solution stability of montelukast sodium was determined and the compound was found to be stable for a study period of 48 h.

High-resolution heat-capacity and optical-reflectivity measurements have been conducted near the smectic-A to hexatic-B transition in thin free-standing films of the liquid-crystal compound 64COOBC. We find an unexpected dependence on film thickness of the integrated magnitude of the heat-capacity anomalies as the films undergo layer-by-layer transitions. We measure the penetration depths of the ordering from the surface and next-to-surface layers which are pertinent to the highly correlated thermal behavior.

We report a set of material characterizations on the nematic mixture Mischung V. With these measurements, as well as previously known results, Mischung V becomes the second nematic liquid crystal possessing a complete set of known physical parameters relevant for electroconvection, enabling quantitative comparison with theoretical predictions to be made. Additionally, we have identified a stable dopant which induces in Mischung V the electrical conductivity necessary for observing the conduction regime of electroconvection. Mischung V is thus validated as a suitable substitute for materials that have traditionally been chosen for these types of experiments. However, Mischung V does not present the same experimental difficulties as traditional materials.

Forced degradation of Ebastine (1-(4-(1,1-dimethylethyl)phenyl)-4-(4-(diphenylmethoxy) piperidin-1-yl)butan-1-one) drug substance in ultraviolet light condition resulted into an unknown significant degradation product. This degradation product was analyzed using a newly developed reverse-phase HPLC, where it was eluted at 2.73 relative retention time to Ebastine peak. UV degradation product was isolated from reaction mass using preparative HPLC and its structure was elucidated using high resolution MS, multidimensional NMR and FTIR spectroscopic techniques. UV degradation product has been characterized as 2-(4-(benzhydryloxy)piperidin-1-yl)-1-(4-(tert-butyl)phenyl)-2-methylcyclopropanol. (1)H and (13)C NMR chemical shift values were generated using computational chemistry for possible two diastereomers (7R10S and 7R10R) and later 7R10R was confirmed (and its enantiomer) as final structure given it showed close agreement with experimental NMR data. Formation of UV degradation product as a recemic mixture was further verified by computational chemistry evaluation, chiral HPLC and polarimetery. To best of our knowledge, this is a novel degradation product which is not discussed at any form of publication yet.

In this report, we emphasize the importance of public monographs with reference materials, coupled with careful process and change control and attention to GMPs, as a means of advancing access to good quality, safe, and effective medicines, with emphasis on available and incoming biologic medicines. With adequate control of articles covered by a monograph, these public standards can form the basis for a global public quality platform that covers reference products, non-interchangeable reference products, biosimilars, and interchangeable biosimilars. Working collaboratively with all stakeholders, new approaches allow these public standards to emerge nationally and globally in a timely way. Yet, there are increasing limitations in the availability of public standards for biologic medicines, which may reverse many decades of progress. Solutions are considered in this report.

Forced degradation of Amlodipine Besylate (AMD) in acidic condition gave rise to a potential unknown impurity. This unknown acid degradation product (ADP) was evaluated using a new-reverse-phase high performance liquid chromatography (HPLC), where it was eluted at 1.24 relative retention time to AMD peak. ADP was isolated using preparative HPLC from degradation mixture. Later, structure of ADP was elucidated using high resolution MS, multidimensional NMR and FTIR spectroscopic techniques, and characterized as ethyl-6-(2-chlorophenyl)-8-methyl-3,4,6,7-tetrahydro-2H-benzo[b][1,4]oxazine-5-carboxylate. The presence of ADP recemic mixture was confirmed by polarimeter and chiral HPLC. Given the complexity associated with ADP generation, single crystal X-ray crystallography technique was used to confirm proposed structure. In addition, reaction mechanism was postulated and confirmed using computational chemistry. To our knowledge, it is a novel impurity and not reported elsewhere.

Several new T- shaped liquid crystalline dimesogenic compounds were synthesized and their LC properties were characterized. These T-shaped dimesogens consist of substituted fluorene and substituted biphenyl units connected by flexible spacer units of varying lengths. The compounds were characterized for their liquid crystallinity by differential scanning calorimetry (DSC) and polarizing microscopy. All the compounds were found to exhibit enantiotropic nematic phase.

High-resolution heat-capacity and optical-reflectivity measurements have been conducted on thin free-standing films of n-hexyl-4′-n-pentanoyloxy-biphenyl-4-carboxylate (64COOBC). The data suggest incomplete layer-by-layer liquid-hexatic transitions. The transition in extremely thin films shows a diverging heat-capacity anomaly. The results are compared with those reported in other compounds, and discussed in the context of the theory of two-dimensional melting.

Syntheses and mesomorphic properties of dimesogens incorporating dissimilar mesogenic units viz. cholesterol and substituted biphenyls are reported.

Temperature dependences of the optical anisotropy and elastic constants of nematic laterally connected dimers, in which two rod-like 2,7-disubstituted fluorene moieties are linked through their 9-positions by flexible-OOC(CH2)m COO- residues, were determined by using the Freedericksz method of threshold transitions in a magnetic field. It was shown that the possibility of rotation of the mesogenic groups about their short axes influences the dependence of the order parameter on spacer length. No marked dependence of splay and bend elastic constants on spacer length was observed. The results are compared with literature data for polymer and low molecular mass nematics.

The title compound, 4-(cholestroxycarbonyl)pentyloxy-4'-heptyloxycarbonylbiphenyl (C53H78O5), is a novel dimesogen comprising two mesogenic units dissimilar in nature. It crystallizes in the orthorhombic space group P212121 with cell parameters a = 6.241(3), b = 17.943(5), c = 43.13(5), Z = 4. The structure was solved using SHELXS (Sheldrick, 1997) and refined using SHELXL (Sheldrick, 1997). The final residual was R = 0.0803 for 1769 reflections with I < 2 σ(I). In the crystal phase the molecule is linear and the terminal groups show stretching with higher bond distances. The packing of the molecules shows imbrication, herringbone and stacking along the a, b, and c axes, respectively. The structure also exhibits an intermolecular hydrogen bond of the type CH…O. The space group suggests the possibility of a chiral mesophase.

The title compound, di-(2,7-disubstituted-9 fluorenyl)glutamate, C82 H86 O12 has been characterized thus: triclinic, P 1, a=16.173(5)A, b=16.233(5)A, c=14.320(5)A, alpha=91.124(5), beta=105.098(5), gamma=92.270(5), V=3625(1)A3, Z=2 and F.W.=1248.54, Dm=1.125 gcm-3, Dc=1.169g cm-3. F000=1356.00, lambda(Mo- K)=0.71069 A, mu=0.77cm-1,final R1 and omegaR2 are 0.094 and 0.28 respectively.

Electron-diffraction measurements have been conducted on thin free-standing liquid crystal films of n-pentyl-4′-n-pentanoyloxy-biphenyl-4-carboxylate (54COOBC). This compound undergoes the smectic-A-hexatic-B-crystal-B phase sequence, but its thin films exhibit power-law thermal anomalies at the smectic-A-hexatic-B transition which are not predicted in the theory of defect-mediated melting in two dimensions, despite the apparent absence of herringbone order. We have determined the 6n-fold bond-orientational order (BOO) parameters C6n and positional correlation length ζ in a two-layer film as a function of temperature in the hexatic-B phase. The results of C6n are consistent with the scaling relation C6n = C6°(n), where σ(n) = n 2, as expected in a two-dimensional XY system.

The syntheses and mesomorphic properties of novel laterally attached non-chiral and chiral dimers have been reported. The reported non-chiral dimers showed monotropic nematic phase and the chiral dimers showed monotropic cholesteric phase.

We have successfully prepared stable one-layer films of 54COOBC $[n$-pentyl-${4}^{\ensuremath{'}}\ensuremath{-}n$-pentanoyloxy biphenyl-4-carboxylate] in a small film hole $(\ensuremath{\approx}0.7$ mm in diameter) and conducted high-resolution optical reflectance measurements near the smectic-$A$\char21{}hexatic-$B$ transition. The stability of these films is contrary to experiences with all other compounds and also to heuristic understanding. We propose a modification to such understanding. Within the resolution of our measurements, data are in good agreement with those of two-layer films. The result gives a confirmation of two-dimensional behavior of two-layer films.

Motivated by the defect-mediated two-stage melting theory, extensive experiments have been concluded on free-standing films of a liquid-crystal sample which exhibits the isotropic-smectic-A–hexatic B-crystal-B bulk phase sequence. For a two-layer film, which is virtually two-dimensional, our calorimetric measurement shows an apparently divergent anomaly near the smectic-A-hexatic-B transition. Its anomaly has a dominant fluctuation contribution and can be fitted to a power law with an exponent α≈0.37±0.05, in disagreement with the theoretical prediction. Thicker films exhibit surface-initiated layer-by-layer (LBL) wetting transition upon cooling. Moreover, these films also exhibit interesting LBL thinning transitions above the bulk clearing temperature.

Molecular dynamics of side chain liquid crystalline polymers (LCP) and their components were studied using the technique of paramagnetic resonance. A cigar shape spin probe (COL) and a nearly spherical spin probe (TPL) were used to study the motions and order of the LCPs. Computer simulations of the observed spectra were performed. Both rotational correlation times and order parameters were extracted from these simulations. We found that LCPs containing 30 per cent and 50 per cent of mesogenic side chains had about the same viscosity as indicated by nearly equal tumbling times at the same temperature. In addition, the LCPs motion is considerably slower than that of the monomeric liquid crystal indicating that the spacer couples the motions of the side chains to those of the main chain. Rotations about axes perpendicular to the side chain are slowed more than rotations about an axis parallel to the side chain. DSC measurements were employed to study the phase transitions. The 30 and 50 per cent LC...

High-resolution heat-capacity and optical-reflectivity measurements have been conducted near the smectic-A to hexatic-B transition in thin free-standing films of the liquid-crystal compound 64COOBC. We find an unexpected dependence on film thickness of the integrated magnitude of the heat-capacity anomalies as the films undergo layer-by-layer transitions. We measure the penetration depths of the ordering from the surface and next-to-surface layers which are pertinent to the highly correlated thermal behavior.

It is well known that the bend and twist elastic constants contain a term that diverges at the nematic\char21{}smectic-A phase transition according to a simple power law in reduced temperature; i.e., as where t=(T-${T}_{N\mathrm{\ensuremath{-}}\mathrm{Sm}\mathrm{\ensuremath{-}}\mathit{A})}$/${T}_{N\char21{}\mathrm{Sm}\mathrm{\ensuremath{-}}\mathit{A}}$. We report here a high-resolution light-scattering measurement of the twist constant exponent ${\ensuremath{\rho}}_{2}$ (=0.66\ifmmode\pm\else\textpm\fi{}0.03) in the four-decade range -6.5t-2.5. Within experimental uncertainty, this is the correlation length exponent predicted by the well-known three-dimensional XY model, a result originally predicted by de Gennes [Solid State Commun. 10, 753 (1972); Mol. Cryst. Liq. Cryst. 21, 49 (1973)] and later by dislocation-mediated melting models due to Helfrich [J. Phys. (Paris) 39, 1199 (1978)] and Dasgupta and Halperin [Phys. Rev. Lett. 47, 1566 (1981)]. This is the largest value of ${\ensuremath{\rho}}_{2}$ reported to date and by comparison with previous results reveals a clear trend of increasing ${\ensuremath{\rho}}_{2}$ with increasing nematic range. This trend suggests that smaller values of ${\ensuremath{\rho}}_{2}$ observed for previously studied materials, may in fact be effective exponents associated with critical-tricritical crossover behavior but leaves open the question of whether there exists a universal value of ${\ensuremath{\rho}}_{2}$.

A series of alkenyl substituted biphenyl benzoates having a lateral cyano substituent have been prepared. These liquid crystalline monomers were hydrosylylated with polymethylhydrosiloxane. The monomers have wide nematic range, and the polymers show wide range liquid crystallinity.

Esters in the homologous series n-alkyl-4′-n-pentanoyloxy-biphenyl-4-carboxylates (n4COOBC, n = 1–12) have been synthesized. Mesomorphic properties and phase transitions have been determined using polarizing hot-stage microscopy, DSC and x-ray. Phase transitions from SA-SB crystal and hexatic (tentatively) have been observed. The relationship between the incidence of hexatic phase and molecular structure has been discussed.

We present here the results of our detailed optical, X-ray, high pressure and dielectric studies on 4-nonyloxyphenyl-4'-nitrobenzoyloxybenzoate (DB90NO 2 ), a triply reentrant compound which exhibits the following sequence of transitions at atmospheric pressure on cooling the isotropic phase: I−N−A d −N re −A d(re) −N re −A 1 −C~−A 2 −C 2 . The existence of the A 2 phase, not reported so far in this compound, is clearly shown from our studies Etude par methodes optiques, diffraction RX et mesures dielectriques du nitro-4' benzoyloxy-4 benzoate de nonyloxy-4 phenyle presentant la sequence suivante de transitions en refroidissement: I−N−A d −N re −A d(re) −N re −A 1 −C~−A 2 −C 2

Three new series of compounds exhibiting nematic and smectic A phases have been prepared: 4- n-alkyl phenyl-3′-methoxy-4′-(4′-cyanobenzoyloxy) benzoate series, 4-cyanophenyl-3′-methoxy-4′-(4”- n-al...

The far-infrared absorption of terephthal-bis-butylaniline (TBBA) in the smectic H, VI, VII and crystalline phases has been studied in the range 30-650 cm−1. Spectra of the former three phases closely resemble each other over the entire spectral range. On transforming to the crystalline phase several new modes appear, especially in the low frequency region. When compared to the Raman spectra of these phases, the present results show interesting differences which allow for further deductions in characterizing the mesophases considered here. The lineshape of bands in the range 460-510 cm−1 is seen to exhibit changes dependent upon the phase of the sample. A band centered at 476±12 cm−1 exhibits a broadening in smectic H and VI phases as compared to phase Vll. This has been attributed to the occurrence of intramolecular reorientations of the butyl chain segments in the former two phases. From a study of the half-widths (HWHM) of the band, the mean correlation time of these reorientations is estimate...