On the difficulties of predicting the adsorption of volatile organic compounds at low pressures in microporous solid: the example of ethyl benzene

Adsorption isotherms of toluene and ethyl benzene, at 25 degrees C and 40 degrees C, were determined in two microporous activated carbons and one zeolite. Significant differences were found in the adsorption behavior, at low pressures, between the two vapors on the same adsorbent material. The quantities of adsorbed ethyl benzene at 25 degrees C, in the low-pressure region, were lower than what was observed at 40 degrees C in all the studied adsorbents, contrary to what was found for toluene. This fact was not related to kinetic effects at the two temperatures nor to vapor swelling of the adsorbents structure. Also, there was no molecular sieving since at high pressures the toluene and ethyl benzene occupied the same adsorption space. The differences found in the ethyl benzene adsorption at the two temperatures pose difficulties in the analysis of the adsorption data and, therefore, in the prediction of results. This is discussed in the analysis of the results with the application of the Dubinin-Astakhov equation and in the estimation of the isosteric heats of adsorption. The adsorption potentials of two possible ethyl benzene conformations were estimated for the adsorption in the pores of activated carbon from the Horvath and Kawazoe model, and the values compared with those found experimentally. The results were interpreted in terms of the ethyl benzene conformation effects when the molecule is confined in pores that are about the same size of one of the conformations.     

Study on Synthesis and NMR Characterization of 2,3-O-Hydroxyethyl Cellulose Depending on Synthesis Conditions

The synthesis of hydroxyethyl celluloses with regioselective functionalization in position 2 and 3 starting from triphenylmethyl (trityl) cellulose is described. The effects of reaction conditions upon both the degree of substitution and the distribution of the hydroxyethyl moieties were investigated in detail. The interest was not only focused on regioselective functionalization within the anhydroglucose unit but also on the formation of oxyethylene side chains. To avoid the formation of oxyethylene side chains, 2-(2-bromoethoxy)tetrahydropyran was used as etherifying agent in comparison with 2-bromoethanol. By acidic hydrolysis, both protecting groups – trityl at 6 position and tetrahydropyran at the hydroxyethyl substituent – can be simultaneously cleaved off. The hydroxyethyl celluloses were characterized by one- and two-dimensional NMR spectroscopy in order to determine the substitution pattern.     

Stability and migration of metal ions in G4-wires by molecular dynamics simulations

We present a molecular dynamics investigation of guanine quadruple helices based on classical force fields. We analyze the dependence of the helical conformation on various compositional factors, such as the length of the G4-wire, as well as the incorporation into the helix channel of alkali ions of different species and in different amounts. In compliance with previous indications, our results suggest that monovalent alkali cations assist the stability of the quadruplex arrangement against disruption on the few nanoseconds time scale in the order of increasing van der Waals radius. Whereas very short G4-wire fragments immediately unfold in the absence of coordinating metal ions or in the presence of tiny ions (e.g., Li+) in agreement with the experimental evidence that empty short guanine quadruplexes are not formed in any synthetic conditions, our simulations show that longer empty helices do not discompose. This finding supports the possibility of producing long G4-wires with different guanine-cation stoichiometries than those routinely known. The classical trajectories allow us to identify different stationary axial sites for the different metal species, which are confirmed by complementary quantum calculations.     

Association Phenomena of Poly(arylene ether sulfone)s in Dimethylformamide

Three poly(arylene ether sulfone)s (two polymers and one copolymer) containing diphenylfluorene, phenolphthalein and 2,4-bis[(4-chlorophenyl)sulfonyl]-1-(phenyltio) benzene)] units were synthesized by the classical Williamson polyetherification reaction. The association phenomenon in N,N-dimethylformamide (DMF) was investigated by different methods: gel permeation chromatography (GPC), viscosity, atomic force microscopy (AFM), fluorescence spectroscopy and dynamic light scattering (DLS). Both AFM and DLS measurements evidenced the formation of aggregates with spherical or ellipsoidal shape at a concentration around 0.05 wt.%. This behavior could be explained by dipole-dipole interactions between macromolecular chains, probably with the participation of solvent molecules, and by H-bonds involving hydroxyl end groups.     

BSDEs with a random terminal time driven by a monotone generator and their links with PDEs

In this paper, we study one-dimensional backward stochastic differential equations (BSDE) with a random terminal time driven by a monotone generator, and their links with elliptic partial differential equations. Firstly, we present the case of BSDEs driven by a strictly monotone generator, and next we consider BSDEs driven by a monotone generator.     

Thermosensitive and Switchable Terpyridine‐Functionalized Metallo‐Supramolecular Poly(N‐isopropylacrylamide)

Metallo‐supramolecular polymers offer attractive possibilities to combine the properties of polymers with the characteristics offered by the metal–ligand coordination. Here we present for the first time the combination of metal‐bis(terpyridine) complexes and lower critical solution temperature (LCST) polymers that can be switched by addressing either the thermosensitive polymer or the metal complex. We describe a new strategy for the synthesis of poly(N‐isopropylacrylamide) (PNIPAM) end functionalized with a terpyridine moiety, which is further used for the preparation of Fe^II and Zn^II‐bis(terpyridine PNIPAM). The comparison of the LCST behavior of the uncomplexed ligands and their metal complexes that bear different counter ions is included. Furthermore, the switchability of the synthesized Fe^II system is demonstrated by a decomplexation reaction followed by the characterization of the uncomplexed ligand.