Stability and enzymatic studies with omeprazole:hydroxypropyl-β-cyclodextrin

Omeprazole (OME) exhibits low stability to light, heat and humidity. In stress conditions OME stability should improve under inclusion complex form with hydroxypropyl-β-cyclodextrin (HPβCD). Stability of OME, its physical mixture (PM) with HPβCD and OME:HPβCD inclusion complex was assessed during 60 days. The inclusion complexes were prepared by kneading and freeze-drying techniques and characterized by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). A molecular modelling was also held to predict the most probable tridimensional conformation of inclusion complex OME:HPβCD. The inhibitory activity of free and complexed OME on selected enzymes, namely, papain (protease model of the proton pump) and acetylcholinesterase (enzyme present in cholinergic neurons and also involved in Alzheimer’s disease) was compared. The results obtained show that HPβCD do not protect against OME degradation, in any prepared powder, in the presence of light, heat and humidity. This may indicate that the reactive group of OME is not included in the HPβCD cavity. This fact is supported by molecular modelling data, which demonstrated that 2-pyridylmethyl group of OME is not included into the cyclodextrin cavity. In relation to enzymatic assays it was observed that free OME and OME in the binary systems showed identical inhibitory activity on papain and acethylcolinesterase, concluding that HPβCD do not affect OME activity on these two enzymes.     

Innovative Cross-Linked Polyurethane Networks Based on Cyclodextrins and Polyethylene Glycols: Inclusion Capacity and Potential Use as Controlled Release Carrier for Nifedipine

Summary: Polymers derived from cyclodextrins show several biomedical applications. In this paper, six cross-linked polyurethane networks based on β-cyclodextrin (βCD) or hydroxypropyl-β-cyclodextrin (HPβCD) and polyethylene glycols (PEG 400, PEG 1500 or PEG 4000) were synthesized by the usual two-step polymerization method. The polymers were characterized by Fourier-transformed infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and X-ray diffraction (XRD). The inclusion capacity was evaluated by the discoloration method of a phenolphthalein solution. In order to explore their potential use as controlled drug delivery systems, dissolution profiles and release behavior of inclusion complexes between PUR/TDI/βCD/PEG4000 or PUR/TDI/HPβCD/PEG1500 and nifedipine (NIF) were investigated. FTIR assignments confirmed the formation of urethane linkages. XRD patterns revealed that the crystallinity decreased mainly due to the crosslinking process. TGA showed three stages of mass loss attributed to water loss, cleavage of urethane bonds and volatilization of decomposition products. The inclusion capacity of cyclodextrins cross-linked with polyurethane was suitably maintained. Dissolution profiles demonstrated that the inclusion complexes PUR/TDI/βCD/PEG4000-NIF and PUR/TDI/HPβCD/PEG1500-NIF are feasible systems for controlling drug release, showing a biexponential release behavior.     

Aqueous biphasic systems: a boost brought about by using ionic liquids

During the past decade, ionic-liquid-based Aqueous Biphasic Systems (ABS) have been the focus of a significant amount of research. Based on a compilation and analysis of the data hitherto reported, this critical review provides a judicious assessment of the available literature on the subject. We evaluate the quality of the data and establish the main drawbacks found in the literature. We discuss the main issues which govern the phase behaviour of ionic-liquid-based ABS, and we highlight future challenges to the field. In particular, the effect of the ionic liquid structure and the various types of salting-out agents (inorganic or organic salts, amino acids and carbohydrates) on the phase equilibria of ABS is discussed, as well as the influence of secondary parameters such as temperature and pH. More recent approaches using ionic liquids as additives or as replacements for common salts in polymer-based ABS are also presented and discussed to emphasize the expanding number of aqueous two-phase systems that can actually be obtained. Finally, we address two of the main applications of ionic liquid-based ABS: extraction of biomolecules and other added-value compounds, and their use as alternative approaches for removing and recovering ionic liquids from aqueous media.     

Pore wall thickness and interpore influence on adsorption of alkanes in carbons using explicit pore models

In modeling of activated carbons, the pores are often assumed to be slit-shaped formed of a constant number of graphene layers. X-ray diffraction studies show that micropores are formed between stacks of different numbers of graphene layers. In this study, we investigate, through the grand canonical Monte Carlo method, the influence on the adsorbed alkanes densities of pore walls with different graphene layers thickness and the related interpore adsorbate interaction when the pore wall has only one graphene layer. All studies of thickness and interpore interaction to date were performed using the Steele 10-4-3 potential model. Instead of Steele model, we propose explicit models made up of graphene layers of discrete carbon atoms. We also investigated the sensitivity of the system to the cut-off and solid-fluid parameter. With our explicit model we found that the influence of the number of carbon layers is not significant for n>2 as previously observed by Steele model??DFT studies. The system was also insensitive to cut-off and well deep parameter variations. A new pore model with an extra dummy graphene wall was proposed to investigate the interpore interaction. The interpore interaction study with the alkanes series C1 to C4 shows that the retention capacity of heavier alkanes is the same whether for activated carbons with few layers (stronger interpore interaction) as for carbons with two or more layers (stronger solid-fluid interaction) assuming negligible surface mediation. The explicit models proposed can be successfully used in the elaboration of virtual porous carbon models to reproduce wall thickness and interpore adsorbate interactions phenomena.     

Positive ground state solutions for the critical Klein–Gordon–Maxwell system with potentials

This paper deals with the Klein–Gordon–Maxwell system when the nonlinearity exhibits critical growth. We prove the existence of positive ground state solutions for this system when a periodic potential V$V$ is introduced. The method combines the minimization of the corresponding Euler–Lagrange functional on the Nehari manifold with the Brézis and Nirenberg technique.     

Total Hadronic Cross-Section Data and the Froissart–Martin Bound

The energy dependence of the total hadronic cross section at high energies is investigated with focus on the recent experimental result by the Total Elastic and Diffractive Cross-section Measurement Collaboration at 7?TeV and the Froissart?CMartin bound. On the basis of a class of analytical parametrization with the exponent ?? in the leading logarithm contribution as a free parameter, different variants of fits to pp and $\bar{\textrm{p}}$ p total cross-section data above 5?GeV are developed. Two ensembles are considered, the first comprising data up to 1.8?TeV and the second also including the data collected at 7?TeV. We show that in all fit variants applied to the first ensemble, the exponent is statistically consistent with ???=?2. Applied to the second ensemble, however, the same variants yield ?? values above 2, a result already obtained in two other analysis, by Amaldi et al. and by the UA4/2 Collaboration. As recently discussed by Azimov, this faster-than-squared-logarithm rise does not necessarily violate unitarity. Our results suggest that the energy dependence of the hadronic total cross section at high energies still constitutes an open problem.     

The approximation to a fixed point

In a spherically complete ultrametric space, a strictly contracting mapping has a fixed point. We indicate in this paper how this fixed point can either be reached or approximated.     

2D Raman spectroscopy study of dolomite and cyanobacterial extracellular polymeric substances from Khor Al‐Adaid sabkha (Qatar)

Dolomite precipitation, limited at low temperature, appears to be impacted by microbial extracellular polymeric substances (EPS). The presence of dolomites has been reported in the extreme environments of Arabian Gulf sabkhas. Many of these sites are characterized by extensive growth of cyanobacterial mats that are recognized as key producers of EPS. However, no information has been gathered on the cyanobacterial EPS involvement in dolomite precipitation. The objective of this study was to obtain in situ information on the spatial distribution of cyanobacterial EPS and dolomite in Khor Al‐Adaid sabkha (Qatar) sediments by chemical mapping. For this purpose, in situ 2D Raman spectroscopy and atomic force microscopy were applied. Additionally, samples were analyzed with scanning electron microscopy and X‐ray diffraction. Raman fingerprints of dolomite (300, 725, and 1098 cm⁻¹), cyanobacteria, and their EPS (1000, 1130, 1148, and 1508 cm⁻¹) were observed widely distributed in the top 2 cm of the sabkhas sediments. 2D chemical imaging of sediment layers characterized minerals and organic matter of microbial origins at high spatial resolution. Raman mapping indicated small dolomite clusters (<2 µm) embedded in a dense cyanobacterial EPS matrix. The spatial distribution showed that small dolomite clusters are closely associated with cyanobacterial EPS and organic carbon. Our results prove that cyanobacterial molecules are closely related to dolomite in the sabkhas sediments. This study demonstrated that Raman mapping is a robust and sensitive technique for acquisition of in situ information on cell–mineral interactions. Copyright © 2013 John Wiley & Sons, Ltd.