Supramolecular liquid‐crystalline polyurethane

A novel supramolecular liquid‐crystalline polyurethane was prepared by mixing the polyurethane containing a pendant pyridyl unit as H‐bond acceptor and 4‐dodecyloxybenzoic acid as H‐bond donor. Intermolecular hydrogen bond formation was confirmed by Fourier transform infrared spectroscopy. The liquid‐crystalline behaviour of the complex formed was established by differential scanning calorimetry, polarizing optical microscopy and X‐ray diffractometry. The complex exhibited highly ordered smectic and nematic phases. The smectic‐nematic and nematic‐isotropic transitions were observed at 89°C and 120°C, respectively.     

Distigmasterol-Modified Acylglycerols as New Structured Lipids—Synthesis,Identification and Cytotoxicity

Plant sterols, also referred as phytosterols, have been known as bioactive compounds which have cholesterol-lowering properties in human blood. It has been established that a diet rich in plant sterols or their esters alleviates cardiovascular diseases (CVD), and also may inhibit breast, colon and lung carcinogenesis. Phytosterols, in their free and esterified forms, are prone to thermo-oxidative degradation, where time and temperature affect the level of degradation. Looking for new derivatives of phytosterols with high thermo-oxidative stability for application in foods, our idea was to obtain novel structured acylglycerols in which two fatty acid parts are replaced by stigmasterol residues. In this work, asymmetric (1,2- and 2,3-) distigmasterol-modified acylglycerols (dStigMAs) were synthesized by the covalent attachment of stigmasterol residues to sn-1 and sn-2 or sn-2 and sn-3 positions of 3-palmitoyl-sn-glycerol or 1-oleoyl-sn-glycerol, respectively, using a succinate or carbonate linker. The chemical structures of the synthesized compounds were identified by NMR, HR-MS, and IR data. Moreover, the cytotoxicity of the obtained compounds was determined. The dStigMAs possessing a carbonate linker showed potent cytotoxicity to cells isolated from the small intestine and colon epithelium and liver, whereas the opposite results were obtained for compounds containing a succinate linker.     

Self‐organization of liquid crystalline 3,4,5‐tris[(11‐methacryloyl‐undecyl‐1‐oxy)‐4‐benzyloxy]benzoates in low‐shrinkage methacrylate mixtures

Crystallization and supramolecular aggregation of 3,4,5‐tris[(11‐methacryloyl‐undecyl‐1‐oxy)‐4‐benzyloxy]benzoate (1), 2‐methyl‐(1,4,7,10,13‐pentaoxabenzocyclopentadecane)‐3,4,5‐tris[(11‐methacryloyl‐undecyl‐1‐oxy)‐4‐benzoxyloxy]benzoate (2) and its 1 : 1 sodium triflate complex (2a) are described in solutions of methacrylate monomers. Formation of gels and subsequent polymerization yielded “supramolecular interpenetrating networks” consisting of an isotropic polymethacrylate resin, percolated by supramolecular aggregates of the solute, which are covalently connected to the resin phase. Compound 1 formed whisker‐type crystals, while 2 self‐organizes in networks of elongated supramolecular fibrils with diameters corresponding to the twofold length of one molecule. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 631–640, 2000     

HRMS Characterization,Antioxidant and Cytotoxic Activities of Polyphenols in Malus domestica Cultivars from Costa Rica

There is increasing interest in research into fruits as sources of secondary metabolites because of their potential bioactivities. In this study, the phenolic profiles of Malus domestica Anna and Jonagold cultivars from Costa Rica were determined by Ultra Performance Liquid Chromatography coupled with High Resolution Mass Spectrometry (HRMS) using a quadrupole-time-of-flight analyzer (UPLC-QTOF-ESI MS), on enriched-phenolic extracts from skins and flesh, obtained through Pressurized Liquid Extraction (PLE). In total, 48 different phenolic compounds were identified in the skin and flesh extracts, comprising 17 flavan-3-ols, 12 flavonoids, 4 chalcones, 1 glycosylated isoprenoid and 14 hydroxycinnamic acids and derivatives. Among extracts, the flesh of Jonagold exhibits a larger number of polyphenols and is especially rich in procyanidin trimers, tetramers and pentamers. Evaluating total phenolic content (TPC) and antioxidant activities using ORAC and DPPH procedures yields higher values for this extract (608.8 mg GAE/g extract; 14.80 mmol TE/g extract and IC₅₀ = 3.96 µg/mL, respectively). In addition, cytotoxicity evaluated against SW620 colon cancer cell lines and AGS gastric cancer cell lines also delivered better effects for Jonagold flesh (IC₅₀ = 62.4 and 60.0 µg/mL, respectively). In addition, a significant negative correlation (p < 0.05) was found between TPC and cytotoxicity values against SW620 and AGS adenocarcinoma (r = −0.908, and −0.902, respectively). Furthermore, a significant negative correlation (p < 0.05) was also found between the number of procyanidins and both antioxidant activities and cytotoxicity towards SW620 (r = −0.978) and AGS (r = −0.894) cell lines. These results align with Jonagold flesh exhibiting the highest abundance in procyanidin oligomers and yielding better cytotoxic and antioxidant results. In sum, our findings suggest the need for further studies on these Costa Rican apple extracts—and particularly on the extracts from Jonagold flesh—to increase the knowledge on their potential benefits for health.     

Nanoprecipitation of Biocompatible Poly(malic acid) Derivative,Its Ability to Encapsulate a Molecular Photothermal Agent and Photothermal Properties of the Resulting Nanoparticles

Biocompatible nanoparticles (NPs) of hydrophobic poly(benzyl malate) (PMLABe) were prepared by nanoprecipitation. The influence of nanoprecipitation parameters (initial PMLABe, addition rate, organic solvent/water ratio and stirring speed) were studied to optimize the resulting formulations in terms of hydrodynamic diameter (Dh) and dispersity (PDI). PMLABe NPs with a Dh of 160 nm and a PDI of 0.11 were isolated using the optimized nanoprecipitation conditions. A hydrophobic near infra-red (NIR) photothermally active nickel-bis(dithiolene) complex (Ni8C12) was then encapsulated into PMLABe NPs using the optimized nanoprecipitation conditions. The size and encapsulation efficiency of the NPs were measured, revealing that up to 50 weight percent (wt%) of Ni8C12 complex can efficiently be encapsulated with a slight increase in Dh of the corresponding Ni8C12-loaded NPs. Moreover, we have shown that NP encapsulating Ni8C12 were stable under storage conditions (4 °C) for at least 10 days. Finally, the photothermal properties of Ni8C12-loaded NPs were evaluated and a high photothermal efficiency (62.7 ± 6.0%) waswas measured with NPs incorporating 10 wt% of the Ni8C12 complex.     

Synthèse enzymatique d’esters de fructose

The enzymatic synthesis of esters is well documented in the literature. A number of parameters have been revised to optimize the operating conditions, in view of a more industrial approach. The experimental conditions presented here are now superior to those of literature and the yields of esters show 78% of fructose laurate. Analytical methods have been perfected and rapid methods (based on different TLC conditions depending on the desired information), accurate methods (based on HPLC) and several purification methods were developed.     

Silver-layered double hydroxides self-assemblies

New inorganic ensembles type layered double hydroxides enriched with silver ions were investigated in terms of thermal behavior and structural evolution by means of TG-FTIR analysis. The studies were focused on two classes of layered precursors, actually distinguished only by the nature of the divalent metal ions, in order to correlate the influence of the clay structure with the thermal behavior of the silver-anionic clay ensembles. The understanding of the thermal degradation mechanism, which is essential to advance the potential applications, requires supplementary characterization techniques such as XRD and FTIR analyses. The thermal analysis performed at three different heating rates revealed the three thermal degradation stages typical for LDHs structure, but different from sample to sample as a consequence of the different interactions between the clay layers and the interlayer anions. The interpretation of the 3D FTIR spectra of the gaseous species resulting in each stage of the thermal degradation process, by means of standard IR spectra, indicates CO₂ and H₂O as main evolved gasses. Moreover, the evolution curves of the gaseous species released by the thermal degradation in air of the studied anionic clays point out that the two gaseous components are eliminated into the temperature ranges corresponding to those given by TG–DTG. The comparative study of the silver-LDH ensembles from the perspective of the structural evolution during the controlled heating suggest a better response from the ensemble with structure consisting of magnesium as divalent cation in the clay network, meaning a better thermal stability.     

Substrate and enzyme concentration dependence of the Henri–Michaelis–Menten model probed by numerical simulation

The use of the classic Henry–Michaelis–Menten (HMM) model (or simply, Michaelis–Menten model) to study the substrate and enzyme concentration dependence of enzyme catalysis is a very important step in understanding many biochemical processes, including microbial growth. Although the HMM model has been extensively studied, the conditions in which the substrate concentration is not in excess have still not been adequately defined mathematically. This lack of definition occurs despite at the cellular and molecular levels most systems generally do not operate in a state of substrate excess. In the present work, we describe an approach for studying enzyme reactions in which substrate concentrations are not in excess. Our results show that the use of extent of reactions and numerical simulation of the velocities of reaction provides an important advance in this field and furnishes results not obtained in previous studies involving these aspects. This approach, in association with knowledge of the rate constants, provides a direct and easy means of examining the single substrate–enzyme profile during product formation at any enzyme–substrate ratio. This approach is more direct than previous models that required the use of empirical equations with arbitrary constants.