Characterization,thermal and ceramic properties of phyllite clays from southeast Spain

Journal of Thermal Analysis and Calorimetry - The present research studied a set of phyllite clays from several deposits in southeast Spain. These phyllite clays have traditionally been used as...     

Dimensional Matching versus Induced‐Fit Distortions: Binding Affinities of Planar and Curved Polyaromatic Hydrocarbons with a Tetragold Metallorectangle

A tetragold(I) rectangle‐like metallocage containing two pyrene‐bis‐imidazolylidene ligands and two carbazolyl‐bis‐alkynyl linkers is used for the encapsulation of a series of polycyclic aromatic hydrocarbons (PAHs), including corannulene. The binding affinities obtained for the encapsulation of the planar PAHs guests in CD₂Cl₂ are found to exponentially increase with the number of π‐electrons of the guest (1.3 > logK >6.6). For the bowl‐shaped molecule of corannulene, the association constant is much lower than the expected one according to its number of electrons. The molecular structure of the host–guest complex formed with corannulene shows that the molecule of the guest is compressed, while the host is expanded, thus showing an interesting case of artificial mutual induced‐fit arrangement.     

Expanding the applicability of magnetic ionic liquids for multiclass determination in biological matrices based on dispersive liquid–liquid microextraction and HPLC with diode array detector analysis

Monitoring biological samples at trace levels of chemicals from anthropogenic actions such as pesticides, pharmaceuticals, and hormones has become a very important subject. This work describes a method for the determination of eight compounds of different chemical classes in human urine samples. Dispersive liquid–liquid microextraction based on magnetic ionic liquids was used as the sample preparation procedure. The main parameters of the method, such as sample dilution, type, and volume of disperser solvent, amount of magnetic ionic liquids, extraction time, and pH were optimized by univariate and multivariate procedures. Validation was performed using a urine sample of a male volunteer in order to obtain a calibration curve and the main analytical parameters of merit such as limits of detection and quantification. Values varied from 3.0 to 7.5 µg/L and from 10 to 25 µg/L, respectively. Satisfactory precisions of 21% for intraday (n = 3) and 16% for interday (n = 9) were achieved. Accuracy was evaluated by relative recovery assays using different urine samples and ranged from 75 to 130%. Robustness was assured by the Lenth method. The validated procedure was applied to five urine samples from different volunteers and the hormone estrone was found in one sample.     

A Theoretical Study of the Interaction of Hydrogen and Oxygen with Palladium or Gold Adsorbed on Pyridine‐Like Nitrogen‐Doped Graphene

The interaction of H₂ and O₂ molecules in the presence of nitrogen‐doped graphene decorated with either a palladium or gold atom was investigated by using density functional theory. It was found that two hydrogen molecules were adsorbed on the palladium atom. The interaction of these adsorbed hydrogen molecules with two oxygen molecules generates two hydrogen peroxide molecules first through a Eley–Rideal mechanism and then through a Langmuir–Hinshelwood mechanism. The barrier energies for this reaction were small; therefore, we expect that this process may occur spontaneously at room temperature. In the case of gold, a single hydrogen molecule is adsorbed and dissociated on the metal atom. The interaction of the dissociated hydrogen molecule on the surface with one oxygen molecule generates a water molecule. The competitive adsorption between oxygen and hydrogen molecules slightly favors oxygen adsorption.     

Determination of the inclusion complex constant between oleuropein and cyclodextrins by complexation theory

Oleuropein (OLE) is a major phenolic compound of olive leaf (Olea europaea) and has many therapeutic properties associated with olive leaf extracts. This work concerns the determination of the inclusion complex constant between OLE and cyclodextrins (CDs), based on the competition of two guests for the CD cavity, one being a dye and the other OLE. The dye used was methylorange (MO) and pH 3 was selected, since MO molar absorptivity at 500 nm is at maximum in this condition. A solution of MO, OLE, and α-CD or β-CD, with citrate buffer was used for determining the absorbance values. From these data and by appropriate mathematical modeling, the equilibrium constant for the formation of OLE:CD complexes were obtained: for OLE:α-CD K = 1,352.4 L mol^?1 (R ² = 0.9975) and for OLE:β-CD K = 1,827.9 L mol^?1 (R ² = 0.9991). The results show that OLE has a greater affinity for β-CD than for α-CD and given the relatively high constants, OLE:CD complexes have potential for giving longer shelf lives for OLE medicinal and food additive preparations.     

γ-Cyclodextrin/alkylthiol inclusion compounds crystals as substrates for the formation and immobilization of gold nanoparticles produced by magnetron sputtering

In this work, we report the nanodecoration of microcrystals of inclusion compound (IC) of γ-cyclodextrin (γ-CD) that contain octanethiol, decanethiol and dodecanethiol. Crystals of these ICs provide a suitable environment for nucleation, growth and immobilization of gold nanoparticles that were obtained by the magnetron sputtering technique. The use of γ-CD IC substrates with a specific surface morphology (i.e., the functional group of the guest molecule faces outward preferentially from a crystal plane) is an efficient method for the preparation of AuNPs with low size dispersion, which is due to the high affinity between the functional group of the surfactant alkylthiol guest with the metal nanoparticles.     

Single‐Molecule‐Magnet Behavior in the Family of [Ln(OETAP)2] Double‐Decker Complexes (Ln=Lanthanide,OETAP=Octa(ethyl)tetraazaporphyrin)

Double‐decker complexes of lanthanide cations can be readily prepared with tetraazaporphyrins (porphyrazines). We have synthesized and characterized a series of neutral double‐decker complexes [Ln(OETAP)₂] (Ln=Tb³⁺, Dy³⁺, Gd³⁺, Y³⁺; OETAP=octa(ethyl)tetraazaporphyrin). Some of these complexes show analogous magnetic features to their phthalocyanine (P_c) counterparts. The Tb³⁺ and Dy³⁺ derivatives exhibit single‐molecule magnet (SMM) behavior with high blocking temperatures over 50 and 10 K, respectively. These results confirm that, in double‐decker complexes that involve Tb or Dy, the (N₄)₂ square antiprism coordination mode has an important role in inducing very large activation energies for magnetization reversal. In contrast with their P_c counterparts, the use of tetraazaporphyrin ligands endows the presented [Ln(OETAP)₂] complexes with extraordinary chemical versatility. The double‐decker complexes that exhibit SMM behavior are highly soluble in common organic solvents, and easily processable even through sublimation.     

Association of Valdecoxib,a Nonsteroidal Anti‐Inflammatory Drug,with Human Serum Albumin

Valdecoxib addition quenches the intrinsic human serum albumin (HSA) fluorescence. This allows an evaluation of the drug–protein association. However, both the number of binding sites and their affinity for the drug depend upon the methodology employed for their evaluation and the employed protein concentration. In this work, we measured the effect of valdecoxib on HSA fluorescence yield over a wide range of experimental conditions and discuss the validity of the binding parameters derived from the different data treatments: Stern–Volmer, Scatchard, double logarithmic, quadratic equation, Benesi–Hilderand, and Encinas–Lissi. It is proposed that a combination of Encinas–Lissi and Scatchard treatments of the data renders the most reliable results. From these data, it is concluded that HSA presents three high‐affinity binding sites for valdecoxib (K_as = 4.5 × 10⁴ m ^?1) and several secondary sites of smaller activity.     

Ring Contraction Through Epoxide Rearrangement: A Formal Synthesis of Capsorubin

An eight-step synthesis of the cyclopentane keto-alcohol 2, which has previously been converted in one step into the carotenoid pigment capsorubin (1), is described. The key step in our synthesis is a stereospecific epoxide rearrangement with ring contraction, thus producing the cyclopentane ring from an epoxide of a cyclohexene.