SmCP-networked films obtained by in situ photopolymerization of neat reactive banana-shaped liquid crystals

The synthesis and characterization of reactive banana-shaped compounds have been carried out, and their ability to be photopolymerized in their SmCP mesophase has been assessed. The presence of a SmCP liquid crystalline phase in these compounds has been confirmed by X-ray studies. The polymerization of these molecules has been demonstrated by calorimetric techniques as well as by the preparation and characterization of SmCP-ordered free films that are mechanically stable at room temperature. Furthermore, polymerized films exhibit second harmonic generation activity at room temperature in the absence of an electric field.     

Use of beta-cyclodextrins to prevent modifications of the properties of carbopol hydrogels due to carbopol-drug interactions

Carbomers are carboxyvinylic derivatives that are widely used in the manufacture of hydrogel dosage forms. Because of their anionic nature and large number of acid groups, they tend to interact with cationic substances, and with other hydrophilic polymers containing alcohol groups. Here, we report a study of interactions between the carbomer Carbopol and the cationic drug propranolol hydrochloride in the solid state and in solution, and of the effects of such interactions on the properties of the hydrogel. We found that the drug forms an insoluble ionic complex with the polymer, modifying all of the hydrogel properties studied (swelling, release, bioadhesion). The inclusion of beta-cyclodextrin in the formulation reduces polymer/drug interactions, so that hydrogel properties remain unchanged. This is probably attributable to formation of inclusion complexes of beta-cyclodextrin and the drug, so that the drug is prevented from interacting with the polymer.     

Controlling ultralong room temperature phosphorescence in organic compounds with sulfur oxidation state

Sulfur oxidation state is used to tune organic room temperature phosphorescence (RTP) of symmetric sulfur-bridged carbazole dimers. The sulfide-bridged compound exhibits a factor of 3 enhancement of the phosphorescence efficiency, compared to the sulfoxide and sulfone-bridged analogs, despite sulfone bridges being commonly used in RTP materials. In order to investigate the origin of this enhancement, temperature dependent spectroscopy measurements and theoretical calculations are used. The RTP lifetimes are similar due to similar crystal packing modes. Computational studies reveal that the lone pairs on the sulfur atom have a profound impact on enhancing intersystem crossing rate through orbital mixing and screening, which we hypothesize is the dominant factor responsible for increasing the phosphorescence efficiency. The ability to tune the electronic state without altering crystal packing modes allows the isolation of these effects. This work provides a new perspective on the design principles of organic phosphorescent materials, going beyond the rules established for conjugated ketone/sulfone-based organic molecules.

Sulfur lone pairs in bridged dimers enhance intersystem crossing and phosphorescence through orbital mixing and electrostatic screening.     

Intramolecular interactions in the triplet excited states of benzophenone-thymine dyads

Time-resolved and product studies on the synthesized dyads 1 and 2 have provided evidence that the benzophenone-to-thymine orientation strongly influences intramolecular photophysical and photochemical processes. The prevailing reaction mechanism has been established as a Paterno-Büchi cycloaddition to give oxetanes 3-6; however, the ability of benzophenone to achieve a formal hydrogen abstraction from the methyl group of thymidine has also been evidenced by the formation of photoproducts 7 and 8. These processes have been observed only in the case of the cisoid dyad 1. Adiabatic photochemical cycloreversion of the oxetane ring is achieved upon direct photolysis to give the starting dyad 1 in its excited triplet state. The photobiological implications of the above results are discussed with respect to benzophenone-photosensitized damage of thymidine.     

Spectrophotometric study of the acid-base equilibria of an imidazobenzodiazepine,midazolam, and its determination in pharmaceutical formulations

The acid-base behaviour of midazolam, a psychotropic drug derived from imidazobenzodiazepine family, has been studied spectro-photometrically. This compound hydrolyzes at pH values lower than 4. Reversible cleavage of the azomethine bond takes place and the open-ring compound is in equilibrium with the closed-ring compound (protonated form of the parent drug). Absorbance-time data (measured at 225 nm and for different pH values) have been evaluated by a pseudo-first order logarithmic approach, leading to different apparent kinetic constants, depending on pH and temperature. A simple mechanism of hydrolysis, corresponding to fast protonation and slow hydrolysis with opening of the ring is in good agreement with the kinetic results. From data obtained at pH values greater than 4, the deprotonation constant of the nitrogen atom at position 2 of the imidazole ring has been calculated and a pK_a value of 5.50 ± 0.05 obtained. In addition, a Spectrophotometric method has been developed which allows the determination of midazolam at concentrations from 1.23 × 10^–6 M to 3.38 × 10^–5 M. This method has been applied to a pharmaceutical formulation midazolam; the Dormicum error, in terms of relative standard deviation, was lower than 1.5%.     

Catalytic performance of Fe-modified AlPO4 catalyst in cyclohexene skeletal isomerization

Iron-modified AlPO₄ catalysts (0.5–5 wt.% Fe₂O₃) have been prepared by impregnation until incipient wetness with different iron(III) salts. The resulting solids, after characterization by surface area, XRD and DRIFT measurements, were checked for their surface acidity through their catalytic activity towards cyclohexene skeletal isomerization test reaction. It was found that iron(III) increases the catalytic performance of AlPO₄ and besides, the iron(III) salt used strongly influences the activity. Thus, the catalysts prepared using complexed iron(III) salts as starting materials presented higher specific activity (and hence, acidity) than those prepared using iron(III) nitrate. Moreover, a maximum in activity was found for 2 wt.% Fe₂O₃.     

A validated solid-liquid extraction method for the HPLC determination of polyphenols in apple tissues Comparison with pressurised liquid extraction

A solid-liquid extraction procedure followed by reversed-phase high-performance liquid chromatography (RP-HPLC) coupled with a photodiode array detector (DAD) for the determination of polyphenols in freeze-dried apple peel and pulp is reported. The extraction step consists in sonicating 0.5 g of freeze-dried apple tissue with 30 mL of methanol-water-acetic acid (30:69:1, v/v/v) containing 2 g of ascorbic acid/L, for 10 min in an ultrasonic bath. The whole method was validated, concluding that it is a robust method that presents high extraction efficiencies (peel: >91%, pulp: >95%) and appropriate precisions (within day: R.S.D. (n = 5) <5%, and between days: R.S.D. (n = 5) <7%) at the different concentration levels of polyphenols that can be found in apple samples. The method was compared with one previously published, consisting in a pressurized liquid extraction (PLE) followed by RP-HPLC-DAD determination. The advantages and disadvantages of both methods are discussed.     

Joule heating effects in optimized insulator‐based dielectrophoretic devices: An interplay between post geometry and temperature rise

Insulator‐based dielectrophoresis (iDEP) is the electrokinetic migration of polarized particles when subjected to a non‐uniform electric field generated by the inclusion of insulating structures between two remote electrodes. Electrode spacing is considerable in iDEP systems when compared to electrode‐based DEP systems, therefore, iDEP systems require high voltages to achieve efficient particle manipulation. A consequence of this is the temperature increase within the channel due to Joule heating effects, which, in some cases, can be detrimental when manipulating biological samples. This work presents an experimental and modeling study on the increase in temperature inside iDEP devices. For this, we studied seven distinct channel designs that mainly differ from each other in their post array characteristics: post shape, post size and spacing between posts. Experimental results obtained using a custom‐built copper Resistance Temperature Detector, based on resistance changes, show that the influence of the insulators produces a difference in temperature rise of approximately 4°C between the designs studied. Furthermore, a 3D COMSOL model is also introduced to evaluate heat generation and dissipation, which is in good agreement with the experiments. The model allowed relating the difference in average temperature for the geometries under study to the electric resistance posed by the post array in each design.     

Fluorescent boron Schiff bases dyes for staining silk fibroin: Green synthesis,structural characterization,DFT, and photophysical properties

Five novel organoboron complexes were synthesized in just 15 min via microware irradiation, by one pot multicomponent reactions between diverse aryl aldehydes with benzoylhydrazide, or 4‐nitrobenzoylhidrazine and diphenyl boronic acid, in a 1:1:1 ratio in benzene. The products were characterized by ¹H, ¹³C, ¹¹B NMR, UV, IR, spectroscopy and high‐resolution mass spectrometry (HRMS). The molecular structure was also determined by single‐crystal X‐ray diffraction for two complexes, which showed the tetra‐coordination of the boron atoms giving rise to distorted tetrahedral molecular geometry with a strong intermolecular C‐H···π interactions. In spite of the low quantum yields exhibited by the series in solution, some complexes stained uniformly the silk fibroins emitting enough fluorescence to allow its characterization by confocal microscopy. Boron as chelate center of the five complexes resulted not to be toxic for B16F10 cells, these compounds are appropriate for their used in medical applications.