Transparent Superhydrophobic silica coatings on glass by sol-gel method

Wetting behavior of solid surfaces is a key concern in our daily life as well as in engineering and science. In the present study, we demonstrate a simple dip coating method for the preparation of Thermally stable, transparent superhydrophobic silica films on glass substrates at room temperature by sol-gel process. The coating alcosol was prepared by keeping the molar ratio of methyltriethoxysilane (MTES), trimethylmethoxysilane (TMMS), methanol (MeOH), water (H₂O) constant at 1:0.09:12.71:3.58, respectively with 13 M NH₄OH throughout the experiments and the films were prepared with different deposition time varied from 5 to 25 h. In order to improve the hydrophobicity of as deposited silica films, the films were derivatized with 10% trimethylchlorosilane (TMCS) as a silylating agent in hexane solvent for 24 h. Enhancement in wetting behavior was observed for surface derivatized silica films which showed a maximum static water contact angle (172°) and minimum sliding angle (2°) for 25 h of deposition time. The superhydrophobic silica films retained their superhydrophobicity up to a temperature of 550 °C. The silica films were characterized by field emission scanning electron microscopy (FE-SEM), surface profilometer, Fourier transform infrared (FT-IR) spectroscopy, thermo-gravimetric and differential thermal analysis (TG-DTA), percentage of optical transmission, water contact angle measurements. The imperviousness behavior of the films was tested with various acids.     

Trapezoid defect in 4H–SiC epilayers

A new type of extended defect was identified in 4H–SiC homoepitaxial epilayers. The defect has a characteristic trapezoidal shape with parallel sides perpendicular to the off-cut direction in ultraviolet photoluminescence intensity maps. Structural characterization of the defect using a transmission electron microscope revealed that the trapezoid defect consisted of multiple Frank type stacking faults. The faults originate in the substrate and propagate into the epilayer during epitaxy.     

Chiral,non-racemic diols,and α-amino acid-derived β-amino alcohols as templates for chiral catalysts in the Tsuji–Trost reaction

A commercially available collection of β-amino alcohols have been converted to their corresponding β-(o-diphenylphosphino) benzoyloxy(o-diphenylphosphino) benzamides and have been employed in the Tsuji–Trost asymmetric alkylation reaction with 1,3-diphenylpropenyl acetate. The best ligand was derived from l-tert-leucinol and when applied to the asymmetric allylic alkylation reaction, yielded the product in an enantiomeric ratio of 99.5:0.5 favoring the (S)-enantiomer.     

Trichloroisocyanuric Acid–Mediated One-Pot Synthesis of Unsymmetrical 2,5-Disubstituted 1,3,4-Oxadiazoles at Ambient Temperature

An efficient method for the one-pot synthesis of unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles has been developed using trichloroisocyanuric acid (TCCA) at ambient temperature. A wide variety of aromatic as well as heterocyclic aldehydes exhibit condensation with a variety of acylhydrazines followed by oxidative cyclization to yield corresponding unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles. The mild nature of the synthesis and short reaction time are notable advantages of the developed protocol.     

Efficient Synthesis of Substituted 2‐Amino‐3‐carbethoxythiophenes

A microwave‐assisted method for the synthesis of a variety of thiophene o‐aminoesters (2a–l) has been developed, starting from an appropriate aldehyde, methyl ketone or acetoacetate ester with ethyl cyanoacetate in the presence of elemental sulfur.     

β-Hydroxy and β-(o-diphosphino)benzoyloxy(o-diphosphino) benzamides as ligands for asymmetric allylic alkylation

Diphenylphosphinobenzoic acid was treated with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), DMAP, and with either one of two equivalents of (1R,2S)-norephedrine and (1S,2S)-pseudonorephedrine. This process yielded a series of β-hydroxy and β-(diphosphino) benzoyloxy(diphosphino)benzamides that were employed in the Tsuji–Trost asymmetric allylic alkylation process. It was determined that the diastereomeric geometry of the norephedrine series was superior to that of the pseudonorephedrine-based ligands. In addition, it was determined that the norephedrine-based β-(o-diphosphino)benzoyloxy(o-diphosphino)benzamide afforded the best enantiomeric ratio (94:6) favoring the (S)-enantiomer.     

Rapid and sensitive determination of major polyphenolic components in Euphoria longana Lam. seeds using matrix solid‐phase dispersion extraction and UHPLC with hybrid linear ion trap triple quadrupole mass spectrometry

A rapid and sensitive method for the extraction and determination of four major polyphenolic components in Euphoria longana Lam. seeds is presented for the first time based on matrix solid‐phase dispersion extraction followed by ultra high performance liquid chromatography with hybrid triple quadrupole linear ion trap mass spectrometry. Matrix solid‐phase dispersion method was designed for the extraction of Euphoria longana seed constituents and compared with microwave‐assisted extraction and ultrasonic‐assisted extraction methods. An Ultra high performance liquid chromatography with hybrid triple quadrupole linear ion‐trap mass spectrometry method was developed for quantitative analysis in multiple‐reaction monitoring mode in negative electrospray ionization. The chromatographic separation was accomplished using an ACQUITY UPLC BEH C₁₈ (2.1 mm × 50 mm, 1.7 μm) column with gradient elution of 0.1% aqueous formic acid and 0.1% formic acid in acetonitrile. The developed method was validated with acceptable linearity (r² > 0.999), precision (RSD ≤ 2.22%) and recovery (RSD ≤ 2.35%). The results indicated that matrix solid‐phase dispersion produced comparable extraction efficiency compared with other methods nevertheless was more convenient and time‐saving with reduced requirements on sample and solvent volumes. The proposed method is rapid and sensitive in providing a promising alternative for extraction and comprehensive determination of active components for quality control of Euphoria longana products.     

The International Conference on Harmonisation Guidance in Practice: Stress Degradation Studies on Lamivudine and Development of a Validated Specific Stability-Indicating HPTLC Assay Method

A sensitive, selective, precise and stability-indicating high-performance thin-layer chromatographic method of analysis of lamivudine both as a bulk drug and in formulations was developed and validated. The solvent system consisted of carbon tetrachloride – methanol – chloroform - acetonitrile (7.0: 3.0: 2.0: 1.5, v/v/v/v). Densitometric analysis of lamivudine was carried out in the absorbance mode at 275 nm. This system was found to give compact spots for lamivudine (R_F value of 0.36 ± 0.02) following double development of chromatoplates with the same mobile phase. Lamivudine was subjected to acid and alkali hydrolysis, oxidation, dry heat and wet heat treatment and photo degradation. The drug undergoes degradation under acidic, basic conditions, oxidation, wet heat and photo degradation. Also the degraded products were well resolved from the pure drug with significantly different R_F values. Linearity was found to be in the range of 50 – 1000 ng spot^–1 with significantly high value of correlation coefficient. The linear regression analysis data for the calibration plots showed good linear relationship with r² = 0.9994 ± 0.05 in the working concentration range of 300 ng spot^–1 to 1000 ng spot^–1. The mean value of slope and intercept were 0.11 ± 0.08 and 10.47 ± 1.21, respectively. The method was validated for precision, robustness and recovery. The limit of detection and quantitation were 15 ng spot^–1 and 40 ng spot^–1 respectively. As the method could effectively separate the drug from its degradation products, it can be employed as a stability indicating one. Moreover, the proposed HPTLC method was utilized to investigate the kinetics of acid degradation process. Arrhenius plot was constructed and activation energy was calculated.     

The ICH guidance in practice: stress degradation studies on stavudine and development of a validated specific stability-indicating HPTLC assay method

A sensitive, selective, precise, and stability-indicating high-performance thin-layer chromatographic (HPTLC) method for the analysis of stavudine both as a bulk drug and in formulations is developed and validated. The solvent system consisted of toluene-methanol-chloroform-acetone (7.0:3.0:1.0:1.0, v/v/v/v). Densitometric analysis of stavudine is carried out in the absorbance mode at 270 nm. This system is found to give compact spots for stavudine (retention factor value of 0.45 +/- 0.05) following development of chromatoplates with the mobile phase. Stavudine is subjected to acid and alkali hydrolysis, oxidation, dry-heat and wet-heat treatment, and photo and UV degradation. The drug undergoes degradation under acidic and basic conditions, oxidation, and wet-heat degradation. Linearity is found to be in the range of 30-1000 ng/spot with a significantly high value of correlation coefficient. The linear regression analysis data for the calibration plots show a good linear relationship with r2 = 0.9997 +/- 0.05 in the working concentration range of 300 to 1000 ng/spot. The mean value of slope and intercept are 0.10 +/- 0.06 and 22.12 +/- 1.08, respectively. The method is validated for precision, robustness, and recovery. The limits of detection and quantitation are 10 and 30 ng/spot, respectively. The proposed HPTLC method is utilized to investigate the kinetics of the acid degradation process. Arrhenius plot is constructed and activation energy is calculated.     

Rapid densitometric method for simultaneous analysis of umbelliferone, psoralen, and eugenol in herbal raw materials using HPTLC

The term 'phenolics' refers to a vast array of biologically active compounds ubiquitous in plants, many of which have been used in traditional medicine for thousands of years. Umbelliferone, psoralen, and eugenol are widely occurring phenolic compounds of plant origin, for which many biological activities against chronic diseases have been reported. A simple HPTLC method has been developed for the simultaneous quantification of umbelliferone, psoralen, and eugenol. These three compounds were quantified in the dried fruit pulp of Aegle marmelos and in the fruit of Trachyspermum ammi and Foeniculam vulgare. The technique enables rapid and sensitive simultaneous analysis in different samples. The method was validated for precision, repeatability, and accuracy in accordance with ICH guidelines. The accuracy of the method was checked by a recovery study conducted at three different levels and the average percentage recovery was found to be 98.88% for umbelliferone, 100.104% for psoralen, and 99.33% for eugenol. The proposed HPTLC method for the simultaneous quantification of umbelliferone, psoralen, and eugenol was found to be simple, precise, specific, sensitive, and accurate. It can be used for routine quality control of herbal raw materials as well as formulations containing any or all of these compounds.