Vapor sorption in emptied clathrate samples of syndiotactic polystyrene

The analysis of chloroform vapor sorption at 35°C in semicrystalline syndiotactic polystyrene samples shows remarkably different sorption isotherms, depending on the crystalline form of the samples. In particular, “emptied” clathrate (“emptied” δ form) samples are characterized by higher equilibrium sorption levels and the differences are particularly relevant for low vapor activities. Moreover, sorption kinetics detected at a vapor activity equal to 0.5 show that in the case of “emptied” δ form samples the sorption rate is much higher than for the other semicrystalline samples. The larger sorption equilibrium uptakes and sorption rates of the “emptied” δ form samples are essentially due to their ability to absorb chloroform, already for low activities, by clathration in the crystalline phase. The measured equilibrium uptakes and sorption kinetics suggest that “emptied” δ form samples of syndiotactic polystyrene could be suitable for removing polluting chlorinated compounds from vapor and liquid streams. © 1997 John Wiley & Sons, Inc.     

Copper(II) Complex Containing 4-Fluorophenoxyacetic Acid Hydrazide and 1,10-Phenanthroline: A Prostate Cancer Cell-Selective and Low-Toxic Copper(II) Compound

Prostate Cancer (PCa) is the second leading cause of cancer-related deaths among men worldwide. The treatment of advanced cases is based on chemotherapy, which lacks specificity and efficacy, due to severe side effects and resistance to the traditional drugs. Copper complexes have shown antitumoral efficacy and low toxicity, being considered a promising class of metal-based drugs for the treatment of malignant neoplasms. Thus, the present study aimed to evaluate the cellular effects of a copper(II) complex with 4-fluorophenoxyacetic acid hydrazide and 1,10-phenanthroline (1) on PCa cell lines, as well as the mutagenic/recombinogenic and anticarcinogenic potential of 1 in Drosophila melanogaster. PNT-2 (non-tumorigenic), LNCaP (hormone-responsive PCa) and PC-3 (androgen-independent PCa) cells were cultured, and cytotoxicity was assessed using the MTT assay. The expression levels of the proliferation markers Ki-67 and Cyclin D1 were analyzed by flow cytometry. Furthermore, the Somatic Mutation and Recombination Test (SMART) and the Epithelial Tumor Test (ETT) were performed. Complex 1 was selective to LNCaP cells, significantly reducing Ki-67 and Cyclin D1 expression levels. Sub-toxic concentrations of complex 1 were defined by the toxicity test in D. melanogaster, and no mutagenic/recombinogenic/carcinogenic effects were observed. Anticarcinogenic potential was observed in D. melanogaster, suggesting modulating activity of the complex 1 against Doxorubicin, a drug used as control by its carcinogenic properties. Therefore, complex 1 is a possible starting point for the development of new antitumor agents for the treatment of PCa.     

Biodereplication of Antiplasmodial Extracts: Application of the Amazonian Medicinal Plant Piper coruscans Kunth

Improved methodological tools to hasten antimalarial drug discovery remain of interest, especially when considering natural products as a source of drug candidates. We propose a biodereplication method combining the classical dereplication approach with the early detection of potential antiplasmodial compounds in crude extracts. Heme binding is used as a surrogate of the antiplasmodial activity and is monitored by mass spectrometry in a biomimetic assay. Molecular networking and automated annotation of targeted mass through data mining were followed by mass-guided compound isolation by taking advantage of the versatility and finely tunable selectivity offered by centrifugal partition chromatography. This biodereplication workflow was applied to an ethanolic extract of the Amazonian medicinal plant Piper coruscans Kunth (Piperaceae) showing an IC₅₀ of 1.36 µg/mL on the 3D7 Plasmodium falciparum strain. It resulted in the isolation of twelve compounds designated as potential antiplasmodial compounds by the biodereplication workflow. Two chalcones, aurentiacin (1) and cardamonin (3), with IC₅₀ values of 2.25 and 5.5 µM, respectively, can be considered to bear the antiplasmodial activity of the extract, with the latter not relying on a heme-binding mechanism. This biodereplication method constitutes a rapid, efficient, and robust technique to identify potential antimalarial compounds in complex extracts such as plant extracts.     

Piling Up Pillar[5]arenes To Self‐Assemble Nanotubes

New liquid‐crystalline pillar[5]arene derivatives have been prepared by grafting first‐generation Percec‐type poly(benzylether) dendrons onto the macrocyclic scaffold. The molecules adopt a disc‐shaped structure perfectly suited for self‐organization into a columnar liquid‐crystalline phase. In this way, the pillar[5]arene cores are piled up, thus forming a nanotubular wire encased within a shell of peripheral dendrons. The capability of pillar[5]arenes to form inclusion complexes has been also exploited. Specifically, detailed binding studies have been carried out in solution with 1,6‐dicyanohexane as the guest. Inclusion complexes have also been prepared in the solid state. Supramolecular organization into the Col_h mesophase has been deduced from X‐ray diffraction data and found to be similar to that observed within the crystal lattice of a model inclusion complex prepared from 1,4‐dimethoxypillar[5]arene and 1,6‐dicyanohexane.     

Progress in Symmetric and Asymmetric Superlattice Quantum Well Infrared Photodetectors

Herein, two challenges are addressed, which quantum well infrared photodetectors (QWIPs), based on III‐V semiconductors, face, namely: photodetection within the so‐called “forbidden gap”, between 1.7 and 2.5 microns, and room temperature operation using thermal sources. First, to reach this forbidden wavelength range, a QWIP which consists of a superlattice structure with a central quantum well (QW) with a different thickness is presented. The different QW in the symmetric structure, which plays the role of a defect in the otherwise periodic structure, gives rise to localized states in the continuum. The proposed InGaAs/InAlAs superlattice QWIP detects radiation around 2.1 microns, beyond the materials bandoffset. Additionally, the wavefunction parity anomaly is explored to increase the oscillator strength of the optical transitions involving higher order states. Second, with the purpose of achieving room temperature operation, an asymmetric InGaAs/InAlAs superlattice, in which the QW with a different thickness is not in the center, is used to detect infrared radiation around 4 microns at 300 K. This structure operates in the photovoltaic mode because it gives rise to states in the continuum which are localized in one direction and extended in the other, leading to a preferential direction for current flow.     

The Nature of Nonclassical Carbonyl Ligands Explained by Kohn–Sham Molecular Orbital Theory

When carbonyl ligands coordinate to transition metals, their bond distance either increases (classical) or decreases (nonclassical) with respect to the bond length in the isolated CO molecule. C−O expansion can easily be understood by π-back-donation, which results in a population of the CO's π*-antibonding orbital and hence a weakening of its bond. Nonclassical carbonyl ligands are less straightforward to explain, and their nature is still subject of an ongoing debate. In this work, we studied five isoelectronic octahedral complexes, namely Fe(CO)₆²⁺, Mn(CO)₆⁺, Cr(CO)₆, V(CO)₆⁻ and Ti(CO)₆²⁻, at the ZORA-BLYP/TZ2P level of theory to explain this nonclassical behavior in the framework of Kohn–Sham molecular orbital theory. We show that there are two competing forces that affect the C−O bond length, namely electrostatic interactions (favoring C−O contraction) and π-back-donation (favoring C−O expansion). It is a balance between those two terms that determines whether the carbonyl is classical or nonclassical. By further decomposing the electrostatic interaction ΔV_elstat into four fundamental terms, we are able to rationalize why ΔV_elstat gives rise to the nonclassical behavior, leading to new insights into the driving forces behind C−O contraction.     

Evaluation by Fourier Transform Infrared Spectroscopy of the different crystalline forms in syndiotactic polystyrene samples

Fourier transform infrared (FTIR) spectra of syndiotactic polystyrene (s-PS) semicrystalline samples have been examined by using the spectral subtraction approach. For the crystalline forms including trans-planar chains (trigonal α and orthorhombic β) a number of conformational and structural order effects, not previously described in the literature, have been identified. A method based on the results of the spectral subtraction analysis has been developed for the determination of the crystallinity degree and compared with the standard method based on the wide-angle X-ray diffraction patterns. The spectral subtraction analysis on FTIR spectra allows also an easy evaluation of the amount of α and β crystalline phases (often simultaneously present in melt-crystallized samples) although both contain chains in a same conformation. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1055–1066, 1997