Infrared Study of Solid Dispersions of β-Cyclodextrin with Naphthalene Derivitaves

The inclusion complexes of β-cyclodextrin (β-CD) with naphthalene and some of its derivatives in the solid state have been studied by infrared spectroscopy. Digital subtraction, deconvolution and curve fitting have been used to investigate the interactions between the naphthalene derivatives andβ-CD. Several preparation methods for the solid dispersions have been tested, using FTIR as an effective tool to evaluate the interactions at the molecular level. The effects of temperature and humidity on the spectra have been also analyzed. A carbonyl moiety in the guest molecule can increase the stability of the complex by establishing specific interactions with the hydroxyl groups of the CD cavity rims. The stability of the complexes is higher for 2-naphthylacetate than that for 1-naphthyl acetate, andso is the degree of association of its carbonyl groups. On the other hand, 2-acetylnaphthaleneforms very stable inclusioncomplexes although its carbonyl groups appear to be significantly less associated.     

Structural characteristics of some soluble and insoluble β-cyclodextrin polymers

Several β-cyclodextrin polymers (βCDP) have been obtained by cross-linking β-cyclodextrin (βCD) with the reagent epichlorohydrin (EP). It is expected that these polymers are capable of retaining different organic molecules by adsorbing them on its network and also by forming inclusion complexes with βCDs. In this work, two soluble polymers containing 39% and 48% βCD and other insoluble ones with 65% and 74% βCD have been studied. The total amount of CD in the polymers could not be available for complexation. This parameter has been calculated by means of the decrease of colour intensity of phenolphthalein solutions when different amounts of βCDP were added. The insoluble polymer with 74% βCD appears to possess less CD available than that with 65% βCD, probably due to the higher cross-linking degree of the former. On the other hand, a higher availability of CD is found for the soluble polymer which contains 48% βCD. Moreover, the amount of glycerol monoether groups formed as a side effect during the cross-linking process has been determined and related to the epichlorohydrin content, structure and swelling properties of the polymers. It is concluded that, varying the synthesis conditions, it is possible to induce structural modifications in the hydrogel networks which can improve their practical applications.     

Study of the miscibility of poly(vinyl pyridines) with poly(vinyl acetate), poly(vinyl alcohol) and their copolymers

Miscibility of poly(4-vinyl pyridine) (P4VP) and poly(2-vinyl pyridine) (P2VP) with poly(viny acetate) (PVAc), poly(vinyl alcohol) PVA and poly(vinyl acetate-co-alcohol) (ACA copolymers) has been investigated over a wide composition range. Differentiaal scanning calorimetry (DSC) results indicate that P2VP is immiscible with PVAC, PVA, and their copolymers over the whole composition range. In turn, P4VP appears to be immiscible with PVAC and PVA, but miscible with some ACA copolymers in certain range of composition. The P4VP-ACA phase diagram for different copolymer compositions has been determined. The variation of the glass transition temperature with composition for miscible mixtures was found to follow the Gordon-Taylor equation, with the parameter κ dependent upon copolymer composition. FTIR analysis of blends reveal the existence of specific interactions via hydrogen bonding between hydroxyl groups and the nitrogen of the pyridinic ring, which appear to be decisive for miscibility. © 1994 John Wiley & Sons, Inc.     

Self-assembled supramolecular gels of reverse poloxamers and cyclodextrins

A series of supramolecular aggregates were prepared using a poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO) block copolymer and β- or α-cyclodextrins (CD). The combination of β-CD and the copolymer yields inclusion complexes (IC) with polypseudorotaxane structures. These are formed by complexation of the PPO blocks with β-CD molecules producing a powder precipitate with a certain crystallinity degree that can be evaluated by X-ray diffraction (XRD). In contrast, when combining α-CD with the block copolymer, the observed effect is an increase in the viscosity of the mixtures yielding fluid gels. Two cooperative effects come into play: the complexation of PEO blocks with α-CD and the hydrophobic interactions between PPO blocks in aqueous media. These two combined interactions lead to the formation of a macromolecular network. The resulting fluid gels were characterized using different techniques such as differential scanning calorimetry (DSC), viscometry, and XRD measurements.     

Analysis of the Rotational Structure of CO2 by FTIR Spectroscopy

A physical chemistry experiment is described that involves the determination of some spectroscopic parameters of carbon dioxide, a molecule that obeys Bose-Einstein statistics. The main advantage of this experiment is that the spectra are easily recorded, not requiring a gas cell, because the sensitivity and resolution of conventional FTIR spectrometers is good enough to record spectra with a high signal-to-noise ratio and good resolution of the fine rotational structure. From the rotational lines of the antisymmetric stretching band, the moments of inertia and the bond lengths of CO₂ in the fundamental and the first-excited state can be accurately obtained. The particular case that carbon dioxide represents helps students understand the restrictions that symmetry and statistics impose on some molecules and the consequences that they have on the absorption of radiation.     

Application of automated docking to the binding of naphthalenes to βCD in water: correlation with spectrofluorimetric data

Automated semi-rigid docking has been explored as an alternative approach for the theoretical study of the inclusion complexes with cyclodextrins. To this purpose we have chosen as a model for the binding to βCD some naphthalene derivatives (naphthalene, 2-ethylnaphthalene, 2-acetylnaphthalene, 1-naphthyl acetate, 2-naphthyl acetate and 1-naphthol). For comparison purposes, the binding constants in water and the associated thermodynamic parameters have been obtained under the same experimental conditions by steady-state fluorescence spectroscopy. The calculations of the automated docking regarding the topology of the guest inside the cavity produce a cluster of structures that qualitatively agrees with fluorescence results and literature data. However, the predicted values of the free energy of binding are lower than the experimental ones by ca. −10 kJ mol⁻¹, and very close to the experimental enthalpy of binding deduced from the temperature dependence of the association constants. The differences are ascribed mainly to the assumption of rigidity of the CD into the auto-docking scheme.     

Structural and cathodoluminiscent properties of Zr0.95Ce0.05O2 nanopowders prepared by sol-gel and template methods

Nanopowders of Zr_0.95Ce_0.05O₂ composition have been prepared by a standard Pechini-type sol-gel process and by means of a colloidal crystal template approach. In the latter method, inverse opal Zr_0.95Ce_0.05O₂ powders were fabricated employing poly(methyl methacrylate) (PMMA) colloidal crystals as a template. The effects of the two different synthesis routes on the structure and microstructural characteristics of the prepared nanopowders were evaluated by X-ray diffraction and scanning electron microscopy. For both preparation routes, the X-ray diffraction analysis has shown that a tetragonal fluorite structure is formed with a crystallite size of ∼35-40 nm. The scanning electron microscopy measurements indicate that the powder obtained by the sol-gel Pechini-type process is comprised of nanoparticles that are arranged in agglomerates with shape and size relatively uniform whereas the inverse opal Zr_0.95Ce_0.05O₂ nanopowders exhibit the formation of macropores with a mean size of ∼100 nm. The cathodoluminescence spectra of the prepared Zr_0.95Ce_0.05O₂ nanomaterials have been measured in the 300-800 nm wavelength range. The powder prepared by sol-gel method yields a broad emission band centered at 482 nm whereas the emission from the inverse opal preparation is considerably less intense.     

Structural and luminescence characterization of synthetic Cr-doped Ni3(PO4)2

Ni_3–xCr_2x/3(PO₄)₂ (x=0 and 0.02) microcrystalline powders were obtained as single phases via a modified sol–gel Pechini-type in situ polymerizable complex method. The samples were characterized using scanning electron microscopy, X-ray diffraction, cathodoluminescence (CL), and thermoluminescence (TL) techniques. We found that Cr³⁺ doping modified the average particle and distribution. The mean particle size was 0.441 μm for Ni₃(PO₄)₂ and 0.267 μm for Ni_2.98Cr_0.013(PO₄)₂. The results also reveal that Cr³⁺ doping notably enhanced the CL and TL UV-blue emission.     

Rhythm Analysis during Cardiopulmonary Resuscitation Using Convolutional Neural Networks

Chest compressions during cardiopulmonary resuscitation (CPR) induce artifacts in the ECG that may provoque inaccurate rhythm classification by the algorithm of the defibrillator. The objective of this study was to design an algorithm to produce reliable shock/no-shock decisions during CPR using convolutional neural networks (CNN). A total of 3319 ECG segments of 9 s extracted during chest compressions were used, whereof 586 were shockable and 2733 nonshockable. Chest compression artifacts were removed using a Recursive Least Squares (RLS) filter, and the filtered ECG was fed to a CNN classifier with three convolutional blocks and two fully connected layers for the shock/no-shock classification. A 5-fold cross validation architecture was adopted to train/test the algorithm, and the proccess was repeated 100 times to statistically characterize the performance. The proposed architecture was compared to the most accurate algorithms that include handcrafted ECG features and a random forest classifier (baseline model). The median (90% confidence interval) sensitivity, specificity, accuracy and balanced accuracy of the method were 95.8% (94.6–96.8), 96.1% (95.8–96.5), 96.1% (95.7–96.4) and 96.0% (95.5–96.5), respectively. The proposed algorithm outperformed the baseline model by 0.6-points in accuracy. This new approach shows the potential of deep learning methods to provide reliable diagnosis of the cardiac rhythm without interrupting chest compression therapy.     

Complexation of ebastine with β-cyclodextrin derivatives

Complexation of ebastine (EB) with hydroxypropyl and methyl-β-cyclodextrin (HP-β-CD and Me-β-CD) was studied in aqueous solutions and in the solid state. The formation of inclusion complexes in aqueous solutions was analysed by the solubility method. The assays were designed using low CD concentrations compared with the solubility of these derivatives in order to avoid non-inclusion phenomena and to obtain a linear increase in EB solubility as a function of CD concentration. The values of complexation efficiency for HP-β-CD and Me-β-CD were 1.9 × 10^?2 and 2.1 × 10^?2, respectively. It seems that the non polar character of the methyl moiety slightly favoured complexation. In relation to solid state complexation, 1:1 EB:CD systems were prepared by kneading, and by heating a drug-CD mixture at 90 ºC. They were analysed using X ray diffraction analysis by comparison with their respective physical mixtures. A complex with a characteristic diffraction pattern similar to that of the channel structure of β-CD was formed with Me-β-CD in 1:1 melted and 1:2 EB:CD kneaded systems. Complexation with HP-β-CD was not clearly evidenced because only a slight reduction of drug crystallinity was detected. Finally, the loading of EB in two β-CD polymers cross-linked with epichlorohydrin yielded 7.3 and 7.7 mg of EB/g polymer respectively.