Effective conversion of cellobiose and glucose to sorbitol using non-noble bimetallic NiCo/HZSM-5 catalyst

The tandem hydrolysis and hydrogenation of saccharides into sorbitol is an especially attractive reaction in the conversion of biomass. Here, an economical and efficient bimetallic catalyst for the transformation of glucose and cellobiose into sorbitol is reported. Non-precious metal based catalysts such as NiCo, Ni, and Co, were prepared via modified impregnation method, and NiCo/HZSM-5 showed superior performance for the synthesis of sorbitol (86.9% from cellobiose, 98.6% from D-glucose). Various characterizations, such as Brunner-Emmet-Teler (BET), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), confirmed that NiCo alloy formed and highly dispersed in NiCo/HZSM-5 catalyst. The high performance of fabricated catalyst would be attributed to the formation of nickel-cobalt alloy over HZSM-5 zeolite surface. High temperature and H₂ pressure were favorable for the tandem hydrolysis and hydrogenation reaction. Besides, the reaction pathway was also proposed based on the kinetics study. Cellobitol was detected as the intermediate in the reaction mixture. Furthermore, in the catalytic stability study, it was found that active metal species of NiCo/HZSM-5 were stable. The deactivation of catalyst would be due to the covering of acidic sites over NiCo/HZSM-5.     

Control of light in a quantized four level graphene atomic system via self and cross-Kerr nonlinearity

We investigate self and cross-Kerr nonlinearity in a four level quantized graphene atomic medium. The absorption, dispersion, transmission and subluminal/superluminal behaviors of a probe light field are studied. An amplification of the probe light field is observed in the absorption spectrum. The normal and anomalous slope of dispersion is also investigated at the positive/negative absorption region. It is shown that Kerr nonlinearity invert and enhance the subluminal/superluminal behaviors of the pulse and self-Kerr effect is found to be more subluminal/superluminal as compared to cross-Kerr effect. The results show significant applications in information storage, self and cross phase modulation and lasing without inversion.     

Time gap for temporal cloak based on spectral hole burning in atomic medium

We demonstrate the possibility of creating a time gap in the slow light based on spectral hole burning in a fourlevel Doppler broadened sodium atomic system. A time gap is also observed between the slow and the fast light in the hole burning region and near the burnt hole region, respectively. A cloaking time gap is attained in microseconds and no distortion is observed in the transmitted pulse. The width of the time gap is observed to vary with the inverse Doppler effect in this system. Our results may provide a way to create multiple time gaps for a temporal cloak.     

Water-mediated synthesis of disubstituted 5-aminopyrimidines from vinyl azides under microwave irradiation

An efficient and ecofriendly method for the synthesis of disubstituted 5-aminopyrimidines from vinyl azides and urea or thiourea was developed. This reaction proceeds under microwave irradiation conditions in the presence of water as a solvent. The remarkable features of this new protocol are high conversion, short reaction times, cleaner reaction profiles and straightforward procedure.     

Development of Stability Indicating HPLC–UV Method for Determination of Daclatasvir and Characterization of Forced Degradation Products

A simple and sensitive stability indicating high performance liquid chromatography method was developed for quantification of Daclatasvir hydrochloride in bulk and tablet dosage forms. The analysis was performed on water symmetry analytical column (150 mm?×?3.9 mm, 5 µm), packing octyl silica (Si-[CH₂]₇-CH₃) C8. Mobile phase containing potassium phosphate buffer (pH 2.0) and acetonitrile (38: 62) v/v was used at flow rate 0.7 mL min^?1 for isocratic elution. Detection was performed on 304 nm using UV detector. The method was validated appropriately according to the requirements of United State Pharmacopeia and International Conference on Harmonization guideline Q2 (R1). Recovery, precision, linearity and specificity of the method were assured. The correlation coefficient for linearity ranged from 2 to 24 µg mL^?1 was (r?>?0.9999). The limits of detection and quantification of Daclatasvir were 0.08 and 0.28 µg mL^?1, respectively. Stability studies of Daclatasvir were performed under various stressed conditions, i.e., hydrolytic (acidic, basic and neutral), oxidation, photolytic and thermal conditions, according to International Conference on Harmonization Q1A (R2) and QIB Guidelines. The degradation products were resolved using proposed method and further characterized by MS, NMR and IR spectroscopic analyses. The proposed method was successfully applied to assay determination of bulk drugs and tablet dosage forms.     

A novel technique for simultaneous diagnosis and radioprotection by radioactive cerium oxide nanoparticles: study of cyclotron production of <Superscript>137m</Superscript>Ce

Application of nanoparticles in nuclear medicine has aimed to develop diagnosis and therapeutic techniques. Cerium oxide nanoparticles (CNPs) are expected to be useful for protection of healthy tissue from radiation-induced harm and could serve therapeutic function. Among a variety of cerium radioisotopes, ^137mCe (T _1/2 = 34.4 h, IT (99.22%), β⁺ (0.779%)) could be a novel candidate radionuclide in the field of diagnosis owing to its appropriate half-life, 99.91% natural abundance of target and its intense gamma line at 254.29 keV. In this study, ^137mCe excitation function via the ^natLa(p,3n) reaction was calculated by TALYS-1.2 and EMPIRE-3 codes. The excitation function calculations demonstrated that the ^natLa(p,3n)^137mCe reaction leads to the formation of the ^136/138Ce isotopic contamination in the 22–35 MeV energy range. Interestingly, the isotopic impurities of ^137mCe could serve radio protector function. Overall results indicate that the cyclotron produced ^137mCeO₂ nanoparticles by irradiation of a target encompassing lanthanum oxide nanoparticles could be a potent alternative for conventional diagnostic radionuclides with simultaneous radioprotection capacity.     

Spectral Hole Burning via Kerr Nonlinearity

Spectral hole burning is investigated in an optical medium in the presence of Doppler broadening and Kerr nonlinearity. The Kerr nonlinearity generates coherent hole burning in the absorption spectrum. The higher order Kerr nonlinearity enhances the typical lamb dip of the hole. Normal dispersion in the hole burning region while Steep anomalous dispersion between the two hole burning regions also enhances with higher order Kerr effect. A large phase shift creates large delay or advancement in the pulse propagation while no distortion is observed in the pulse. These results provide significant steps to improve optical memory, telecom devices, preservation of information and image quality.     

RP-HPLC Method for Simultaneous Determination of Sofosbuvir and Ledipasvir in Tablet Dosage Form and Its Application to In Vitro Dissolution Studies

A reversed-phase high-performance liquid chromatographic method was developed for the simultaneous determination of sofosbuvir and ledipasvir in tablet dosage form. The analysis was performed on Luna analytical column 250 × 4.6 mm, 5 µm, octyl silica packing (Si–[CH₂]₇–CH₃) C8, using ammonium acetate buffer solution pH 7.0 and acetonitrile 35:65 % v/v as mobile phase at flow rate of 0.7 mL min⁻¹ for isocratic elution. Detection of sofosbuvir and ledipasvir was performed on a UV detector at 245 nm. The retention times of sofosbuvir and ledipasvir were 4.468 ± 0.013 min and 8.242 ± 0.012 min, respectively, and the total run time was 20 min. The method was validated according to the requirements of the United States Pharmacopeia (category I). The overall recovery of both analytes was 100 ± 1 %; the relative standard deviation for precision and intraday precision was less than 2.0 %. The method was linear with correlation coefficient (r) >0.9999, limits of detection 0.485 and 0.175 µg mL⁻¹, and limits of quantification was 1.619 and 0.586 µg mL⁻¹ for sofosbuvir and ledipasvir, respectively. The method was successfully applied to the assay and in vitro dissolution studies of sofosbuvir and ledipasvir in tablet dosage form.