Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.     

Mimicking the atmospheric OH-radical-mediated photooxidation of isoprene: formation of cloud-condensation nuclei polyols monitored by electrospray ionization mass spectrometry

Recently, it has been proposed (M. Claeys et al., Science 2004; 303: 1173) that the atmospheric OH-radical-mediated photooxidation of isoprene is a source of two major secondary organic aerosol (SOA) components, that is, 2-methylthreitol and 2-methylerythritol. These diastereoisomeric tetrols, which were characterized for the first time in the fine size fraction (<2.5 microm aerodynamic diameter) of aerosols collected in the Amazon rain forest during the wet season, were proposed to enhance the capability of the aerosols to act as cloud-condensation nuclei. In the present study, we performed the oxidation of isoprene in aqueous solution under conditions that attempted to mimic atmospheric OH-radical-induced photooxidization, and monitored and characterized on-line the reaction products via electrospray ionization mass (and tandem mass) spectrometry in the negative ion mode. The results show that the reaction of isoprene with photo- or chemically generated hydroxyl radicals indeed yields 2-methyltetrols. Other polyols were also detected, and they may therefore be considered as plausible SOA components eventually formed in normal or more extreme OH-radical-mediated photooxidation of biogenic isoprene.     

A comparative study on various spectrometries with thin layer chromatography for simultaneous analysis of drotaverine and nifuroxazide in capsules

Three spectrophotometric methods including Vierordt's method, derivative, ratio spectra derivative, and thin layer chromatography (TLC)-UV densitometric method were developed for simultaneous determination of drotaverine HCl (DRT) and nifuroxazide (NIF) in presence of its impurity, 4-hydroxybenzohydrazide (4-HBH). In Vierordt's method, (E(1 cm)(1%)) values were calculated at 227 and 368 nm in the zero-order spectra of DRT and NIF. By derivative spectrophotometry, the zero-crossing method, drotaverine HCl was determined using the second derivative at 245 nm and the third derivative at 238 nm, while nifuroxazide was determined using the first derivative at 399 nm and the second derivative at 411 nm. The ratio spectra derivative spectrophotometry is basedon the measure of the amplitude at 459 nm for DRT and at 416 nm for NIF in the first derivative of the ratio spectra. Calibration graphs of the three spectrophotometric methods were plotted in the range 1-10 mug/ml of DRT and 2-20 mug/ml of NIF. TLC-UV densitometric method was achieved on silica gel plates using ethyl acetate : methanol : ammonia 33% (10 : 1 : 0.1 v/v/v) as the mobile phase. The Rf values were 0.74, 0.50, 0.30+/-0.01 for DRT, NIF and 4-HBH, respectively. On the fluorescent plates, the spots were located by fluorescence quenching and the densitometrical area were measured at 308 and 287 nm with linear range 0.2-4 mug/spot and 0.6-12 mug/spot for DRT and NIF, respectively. The proposed methods have been successfully applied to the commercial pharmaceutical formulation without any interference of excipients. Mean recoveries, relative standard deviations and the results of the proposed methods were compared with those obtained by applying the alternate methods.     

RNA-mediated synthesis of palladium nanoparticles on Au surfaces

RNA catalysts for the shape-controlled synthesis of Pd particles from the precursor complex trisdibenzylideneacetone dipalladium ([Pd2(DBA)3] were recently discovered in our laboratory (J. Am. Chem. Soc. 2005, 127, 17814-17818). In the work described here, RNA codes for hexagonal Pd platelets and Pd cubes were covalently immobilized on gold surfaces and evaluated for their activity toward particle synthesis. When coupled to gold via oligoethylene glycol linkers, both RNA sequences were able to catalyze the formation of Pd particles with the same shape control previously observed in solution. For low surface coverages, the average distance between RNA molecules on the surface was estimated at ca. 300 nm, yet large (e.g., dimensions of hundreds of nanometers) Pd hexagons and cubes still formed. This surprising result suggests that a single RNA molecule may be sufficient for nucleating and controlling the shapes of these particles. Finally, the use of surface-bound RNA as a tool for directing the orthogonal synthesis of materials on surfaces was demonstrated. Patterning the RNA code for Pd hexagons next to the code for Pd cubes, followed by incubation in a solution containing [Pd2(DBA)3], resulted in the spontaneous formation of spatially distinct spots of hexagonal and cubic particles.     

Synthesis, multiphase characterization, and helicity control in chiral DACH-linked oligothiophenes

A new class of chiral oligothiophenes is described. Mono-, bi-, ter-, and quarterthiophenes have been linked to enantiopure trans-1,2-cyclohexanediamine (DACH) via diamino or diimino moieties. The stereochemistry of DACH, the type of linker, and oligothiophene size determine the conformational flexibility of these molecules and consequently their molecular and supramolecular helicity in solution and in the solid state. The case of diaminobis(bithiophene), which inverts helicity and shows chiral amplification in the transition from solution to film, is described in detail. Based on the combined use of circular dichroism in solution and in the solid state, single-crystal/thin-film X-ray diffraction, and polarized optical microscopy, a working mechanism has been proposed to explain this unexpected behavior.     

Precipitate flotation-separation, speciation and hydride generation atomic absorption spectrometric determination of selenium(IV) in food stuffs

A method for flotation and determination of selenium(IV) in foodstuffs using p-chlorophenylthiosemicarbazide (HCPT) was investigated. At pH  2, selenium(IV) forms a 1:1 reddish-brown precipitate with HCPT easily floated using oleic acid (HOL) surfactant. The separated complex was dissolved in 4 M HCl and diluted in 10-ml double-distilled water (DDW). Selenium(IV) content in the eluate was determined by hydride generation atomic absorption spectrometry (HG-AAS) at 196.4 nm using sodium borohydride. The HCPT–Se(IV) complexes formed in absence and presence of oleic acid were characterized by elemental analysis, mass and infrared spectral studies. The mode of chelation between Se(IV) and HCPT is proposed to be through S and N coordination. Interferences, on the flotation process, from various foreign ions were avoided by adding excess HCPT. The proposed flotation methodology was successfully applied to the analysis of selenium in real foodstuffs and natural water spiked with known amounts of Se(IV) with a preconcentration factor of 100 and a detection limit of 20 pg. Application was also extended to separate Se(IV) successfully from Se(VI) in their synthetic mixtures. The separation mechanism is proposed to be due to hydrogen bond formation between the COOH group of HOL and –NH of the HCPT–Se(IV) complex.     

Intermolecular aza‐wittig reaction: One‐step synthesis of pyrazolo[1,5‐a]pyrimidine and imidazo[1,2‐b]pyrazole derivatives

Pyrazolo[1,5‐a]pyrimidine and imidazo[1,2‐b]pyrazole derivatives were synthesized via intermolecular aza‐Wittig reaction of 5‐(triphenylphosphoranylideneamino)‐3‐phenylpyrazole 3 derived from 5‐amino‐3‐phenylpyrazole with some selected α‐chloroketones.     

Quantum chemical mass spectrometry: ab initio prediction of electron ionization mass spectra and identification of new fragmentation pathways

The electron ionization mass spectra of four organic compounds are predicted based on the results of quantum chemical calculations at the DFT/B3LYP/6‐311 + G* level of theory. This prediction is performed ‘ab initio’, i.e. without any prior knowledge of the thermodynamics or kinetics of the reactions under consideration. Using a set of rules determining which routes will be followed, the fragmentation of the molecules' bonds and the complete resulting fragmentation pathways are studied. The most likely fragmentation pathways are identified based on calculated reaction energies ΔE when bond cleavage is considered and on activation energies ΔE^? when rearrangements are taken into account; the final intensities of the peaks in the spectrum are estimated from these values. The main features observed in the experimental mass spectra are correctly predicted, as well as a number of minor peaks. In addition, the results of the calculations allow us to propose fragmentation pathways new to empirical mass spectrometry, which have been experimentally verified using tandem mass spectrometry measurements. Copyright © 2016 John Wiley & Sons, Ltd.     

Application of the aza-Wittig reaction for efficient synthesis of diversely substituted benzo[f]Chromeno[2,3-d]pyrimidine and benzo[f]chromeno[2,3-d][1,2,4]triazolopyrimidine derivatives

An efficient synthesis of novel benzo[f]Chromeno[2,3-d]pyrimidine and unknown benzo[f]chromeno[2,3-d][1,2,4]triazolopyrimidine derivatives is described utilizing ethyl-2-amino-4-phenyl-4H-benzo[f]chromene-3-carboxylate as precursor via aza-Wittig reaction. The process proved to be simple, high-yielding, and efficient.     

Solvent effects on the electronic absorption spectra and acid strength of some substituted pyridinols.

The electronic absorption spectra of some substituted pyridinols in organic solvents of different polarities are studied. Also, the solvent effects on the intramolecular charge transfer bands are discussed using various solvent parameters. The acid-base equilibria of the compounds used are studied spectrophotometrically in various mixed aqueous solvents at 25 degrees C and 0.1 M ionic strength (NaClO4). Furthermore, the influence of the solvents on the dissociation constants and tautomeric equilibria of a pyridinol derivatives are discussed. The effect of molecular structure of the pyridinols on the pK's is also examined.