Hydrated Clay for Catalyst Removal in Copper Mediated Atom Transfer Radical Polymerization

A simple method has been described to remove catalyst from the copper mediated atom transfer radical polymerization (ATRP) of benzyl methacrylate and methyl methacrylate in anisole at 25 °C using hydrated natural clay (sodium montmorillonite, Na‐clay). The method consists of (1) addition of hydrated clay (Cu^I/clay ≈ 5 wt.‐%) either during or after the polymerization, (2) oxidation of catalyst complex by exposing the terminated reaction mixture in air, and (3) filtration to obtain catalyst free polymer solution. A strong coordination of CuBr‐ligand complex onto hydrated clay (10 wt.‐% < H₂O/clay < 30 wt.‐%) upon oxidation resulted in polymers with no or insignificant residual catalyst (<1.74 ppm), as determined by UV‐vis and atomic absorption spectroscopy. The recovered clay exhibited expanded intercalary layers and absence of polymer within it.

     

Ionothermal Synthesis of Imide-Linked Covalent Organic Frameworks

Covalent organic frameworks (COFs) are an extensively studied class of porous materials, which distinguish themselves from other porous polymers in their crystallinity and high degree of modularity, enabling a wide range of applications. COFs are most commonly synthesized solvothermally, which is often a time-consuming process and restricted to well-soluble precursor molecules. Synthesis of polyimide-linked COFs (PI-COFs) is further complicated by the poor reversibility of the ring-closing reaction under solvothermal conditions. Herein, we report the ionothermal synthesis of crystalline and porous PI-COFs in zinc chloride and eutectic salt mixtures. This synthesis does not require soluble precursors and the reaction time is significantly reduced as compared to standard solvothermal synthesis methods. In addition to applying the synthesis to previously reported imide COFs, a new perylene-based COF was also synthesized, which could not be obtained by the classical solvothermal route. In situ high-temperature XRPD analysis hints to the formation of precursor–salt adducts as crystalline intermediates, which then react with each other to form the COF.     

Determination of Dipeptidyl Peptidase-4 Inhibitors by Spectrophotometric and Chromatographic Methods

Dipeptidyl peptidase-4 (DPP-4) inhibitors are a novel class of oral anti-diabetic agents used in the treatment of type 2 diabetes mellitus and work to enhance the effect of incretin hormones. There has been significant research on wide range of analytical techniques that could be useful in the estimation of DPP-4 inhibitors in formulations and biological matrices. Analytical methods such as ultraviolet (UV) spectrophotometry, mass spectroscopy, NMR spectroscopy, HPLC, high pressure thin layer chromatography, ultra performance liquid chromatography, liquid chromatography?mass spectrophotometry and capillary zone electrophoresis have been reported for the estimation of DPP-4 inhibitors in single and/or in combination with other drugs. This comprehensive review covers most of the spectrophotometric and chromatographic methods described for the determination of sitagliptin, alogliptin, vildagliptin, linagliptin, saxagliptin and teneligliptin in pure forms, in different pharmaceutical dosage forms and biological fluids. From the review it can be deduced that a large number of chromatographic methods have been developed, and HPLC-UV methods have been commonly used in the detection and evaluation of DPP-4 inhibitors.     

Strained tridecane cage systems

Hexacyclo[6.5.0.0^2,7.0^4,12.0^5,10.0^9.13]tridecane (HCTD) contains two four-membered, two five-membered and two six-membered rings fused into a cage structure which contains about 77.0 kcal/mol of strain energy. Attempts to prepare the thioketal from the diketone of HCTD led to a skeletal rearrangement to produce a cage with one four-membered, four five-membered, and two six-membered rings fused into a cage (RHCTD). The corresponding RHCTD hydrocarbon has a strain energy 13.7 kcal/mol less than that of the starting tridecane (HCTD) which provides the driving force for the rearrangement. The X-ray structures of two HCTD derivatives and one RHCTD derivative are reported. The bond lengths in the three reported structures are normal for cages of this type. The structure of tetracyclo[6.3.0.0^3,7.0^4,11]undecane-5,10-dione mono(ketene 1,3-propanedithioacetal) is discussed also.     

Stress Degradation Behavior of Desipramine Hydrochloride and Development of Suitable Stability-Indicating LC Method

A simple reverse phase liquid chromatographic method was developed for the quantitative determination of desipramine hydrochloride and its related impurities in bulk drugs which is also stability-indicating. During the forced degradation at hydrolysis, oxidative, photolytic and thermal stressed conditions, the degradation results were only observed in the oxidative stress condition. The blend of the degradation product and potential impurities were used to optimize the method by an YMC Pack Pro C₁₈ stationary phase. The LC method employs a linear gradient elution with the water–acetonitrile–trifluoroacetic acid as mobile phase. The flow rate was 1.0 mL min^?1 and the detection wavelength 215 nm. The stressed samples were quantified against a qualified reference standard and the mass balance was found close to 99.0% (w/w) when the response of the degradant was considered to be equal to the analyte (i.e. desipramine). The developed RP-LC method was validated in agreement with ICH requirements.     

Catechol oxidase activity of a series of new dinuclear copper(II) complexes with 3,5-DTBC and TCC as substrates: syntheses, X-ray crystal structures, spectroscopic characterization of the adducts and kinetic studies

A series of dinuclear copper(II) complexes has been synthesized with the aim to investigate their applicability as potential structure and function models for the active site of catechol oxidase enzyme. They have been characterized by routine physicochemical techniques as well as by X-ray single-crystal structure analysis: [Cu 2(H 2L2 (2))(OH)(H 2O)(NO 3)](NO 3) 3.2H 2O ( 1), [Cu(HL1 (4))(H 2O)(NO 3)] 2(NO 3) 2.2H 2O ( 2), [Cu(L1 (1))(H 2O)(NO 3)] 2 ( 3), [Cu 2(L2 (3))(OH)(H 2O) 2](NO 3) 2, ( 4) and [Cu 2(L2 (1))(N 3) 3] ( 5) [L1 = 2-formyl-4-methyl-6R-iminomethyl-phenolato and L2 = 2,6-bis(R-iminomethyl)-4-methyl-phenolato; for L1 (1) and L2 (1), R = N-propylmorpholine; for L2 (2), R = N-ethylpiperazine; for L2 (3), R = N-ethylpyrrolidine, and for L1 (4), R = N-ethylmorpholine]. Dinuclear 1 and 4 possess two "end-off" compartmental ligands with exogenous mu-hydroxido and endogenous mu-phenoxido groups leading to intermetallic distances of 2.9794(15) and 2.9435(9) A, respectively; 2 and 3 are formed by two tridentate compartmental ligands where the copper centers are connected by endogenous phenoxido bridges with Cu-Cu separations of 3.0213(13) and 3.0152(15) A, respectively; 5 is built by an end-off compartmental ligand having exogenous mu-azido and endogenous mu-phenoxido groups with a Cu-Cu distance of 3.133(2) A (mean of two independent molecules). The catecholase activity of all of the complexes has been investigated in acetonitrile and methanol medium by UV-vis spectrophotometric study using 3,5-di- tert-butylcatechol (3,5-DTBC) and tetrachlorocatechol (TCC) as substrates. In acetonitrile medium, the conversion of 3,5-DTBC to 3,5-di- tert-butylbenzoquinone (3,5-DTBQ) catalyzed by 1- 5 is observed to proceed via the formation of two enzyme-substrate adducts, ES1 and ES2, detected spectroscopically for the first time. In methanol medium no such enzyme-substrate adduct has been detected, and the 3,5-DTBC to 3,5-DTBQ conversion is observed to be catalyzed by 1- 5 very efficiently. The substrate TCC forms an adduct with 2- 5 without performing further oxidation to TCQ due to the high reduction potential of TCC (in comparison with 3,5-DTBC). But most interestingly, 1 is observed to be effective even in TCC oxidation, a process never reported earlier. Kinetic experiments have been performed to determine initial rate of reactions (3,5-DTBC as substrate, in methanol medium) and the activity sequence is 1 > 5 > 2 = 4 > 3. A treatment on the basis of Michaelis-Menten model has been applied for kinetic study, suggesting that all five complexes exhibit very high turnover number, especially 1, which exhibits turnover number or K cat of 3.24 x 10 (4) (h (-1)), which is approximately 3.5 times higher than the most efficient catalyst reported to date for catecholase activity in methanol medium.     

Growth of highly oriented crystalline polyaniline films by self-organization

Silicon substrates with (100) orientation were modified with amino-silane self-assembled monolayer (SAM) to provide amino (NH(2)) moieties at the substrate surface. Self-organization of polyaniline during chemical polymerization, on this modified surface, leads to the growth of highly oriented films at the substrate-polymer interface. The morphology studied using scanning electron microscopy and atomic force microscopy revealed the formation of polymer film with well faceted pyramidal crystallites. XPS and FTIR spectroscopy were used to analyze the chemical structure of the film. X-ray diffraction measurements show the crystalline nature of the polyaniline, whose lattice parameters are in agreement with the reported values. This study underlines the importance of a SAM in deciding the structure and morphology of the deposited polymer.     

Comparison of Spectroscopic and Lasing Properties of Different Types of Sol-Gel Glass Matrices Containing Rh-6G

Rhodamine-6G (Rh-6G) is embedded in sol-gel glass samples which have been prepared by three different methods namely: 1) using HCl as catalyst and glycerol as Drying Control Chemical Additive (DCCA), 2) using HCl as catalyst at 60 °C and drying at room temperature and 3) using HCl as catalyst at 60 °C and heated at 600 °C for 3 h. Comparative studies of spectroscopic and lasing properties of the three types of Rh-6G containing samples were carried out with the lapse of time upto 8 months. Photostability of Rh-6G containing sol-gel samples is measured in terms of half life under Nitrogen laser pumping as number of pulses of N₂ laser necessary to reduce the dye laser intensity to 50% of the original value and value is 7500 pulses at 1.67 Hz rate. The best performance of Rh-6G, as far as its spectroscopic and lasing properties are concerned was found in third type of host matrices using HCl as catalyst at 60 °C and heated at 600 °C for 3 h.