Chiral and extended π-conjugated bis(2-pyridyl)phospholes as assembling N,P,N pincers for coordination-driven synthesis of supramolecular [2,2]paracyclophane analogues

Chiral, π-conjugated 3,4-butano-1-phenyl-2,5-bis(2-pyridyl)phosphole derivatives 1a(2,2') and 1a(3) with chiral trans-1,2-diol moieties and fused pinene derivatives, respectively, were prepared from the corresponding chiral diynes by using the Fagan-Nugent method. Their UV/Vis absorption and chiroptical properties (optical rotation and circular dichroism) were studied. Their behavior as N,P,N chelates towards coordination of Cu(I) and formation of chiral supramolecular assemblies with π-conjugated ditopic dicyano ligands was investigated. Chiral C(2)-symmetric rectangles that are [2,2]paracyclophane analogues were obtained, as demonstrated by X-ray crystallography. During the course of this study, the first stable water-soluble phosphole derivative (1a(2)·2 HCl) was prepared. Furthermore, achiral 3,4-butano-1-phenyl-2,5-bis(aza[4]helicene)phosphole 1a(4) was synthesized and displays extended π conjugation. A supramolecular rectangle was obtained by coordination to Cu(I) and assembly with a dicyano stilbene. This coordination-driven supramolecular assembly contains a total of four aza[4]helicene moieties and displays two types of π-π stacking interactions in the solid state, that is, between two helicene moieties and between one helicene and a bridging dicyano ligand. All the supramolecular arrangements are discussed by comparing them with previous work on the parent 3,4-butano-1-phenyl-2,5-bis(2-pyridyl)phosphole.     

Determination of aflatoxins and ochratoxin A in ginseng and other botanical roots by immunoaffinity column cleanup and liquid chromatography with fluorescence detection

Mycotoxins are toxic secondary metabolites produced by certain molds and are common contaminants of many important food crops, such as grains, nuts, and spices. Some mycotoxins are found in fruits, vegetables, and botanical roots. These contaminants have a broad range of toxic effects, including carcinogenicity, immunotoxicity, neurotoxicity, and reproductive and developmental toxicity. The public health concerns related to both acute and chronic effects of mycotoxins in animals have prompted more than 100 countries to establish regulatory limits for some of the well-known mycotoxins, such as the aflatoxins (AFL). Our research focused on method development for 2 of these toxins, AFL and ochratoxin A (OTA), in ginseng and other selected botanical roots. Methods using an immunoaffinity column (IAC) cleanup, liquid chromatographic separation, and fluorescence detection were modified and evaluated. Two types of IAC cleanup were evaluated: IAC for AFL, and IAC for both AFL and OTA. Three derivatization techniques to enhance the fluorescence of the AFL were compared: precolumn trifluoroacetic acid, postcolumn bromination, and postcolumn ultraviolet irradiation. No derivatization was needed for OTA. Results for AFL using the single analyte IAC cleanup and the 3 derivatization techniques were all comparable for ginseng and for other roots such as ginger, licorice, and kava-kava. Recoveries of added AFL for ginseng at levels from 2 to 16 ng/g were about 80%. Using IAC cleanup for both AFL and OTA recoveries of added AFL for ginseng at 4-16 ng/g were about 70%, and for ginger, licorice, and kava-kava were about 60%. Recoveries of added OTA for ginseng, ginger, and echinacea at 4 ng/g were about 55%.     

Aza[6]helicene Platinum Complexes: Chirality Control of cis–trans Isomerism

It was serendipitously observed that cis‐[PtCl₂(NCEt)PPh₃] reacted differently with either racemic or enantiopure 4‐aza[6]helicene, giving respectively cis (racemic) and trans (enantiopure) [Pt^IICl₂(4‐aza[6]helicene)PPh₃] complexes. This unexpected reactivity is explained through a dynamic process (crystallization‐induced diastereoselective transformation) and enables a new aspect of reactivity in chiral transition‐metal complexes to be addressed.     

Enantioselective synthesis of β-amino-diacids

An efficient route to orthogonally protected β-amino-diacids is described: chiral derivative 3 was shown to be a precursor of enantiopure substituted β-amino acids. The key step of the procedure is a diastereoselective reduction of β-enaminolactones 5 by NaBH₃CN in CH₂Cl₂. A study concerning the regio- and diastereoselectivity of alkylation of β-enaminolactone 3 is also presented.     

WAVELENGTH DEPENDENCE OF HEMATOPORPHYRIN DERIVATIVE PHOTODYNAMIC TREATMENT EFFECTS ON RAT EARS

The in vivo wavelength dependence of hematoporphyrin derivative (HpD) photodynamic treatment (PDT) has been studied. Ears of 136 rats were treated at six red and four blue-green laser wavelengths (615-635, 488-514.5 nm). Hematoporphyrin derivative was administered intraperitoneally (15 mg/kg) and 24 h later both ears were irradiated, at different wavelengths, for t = 6.5, 10 or 15 min at 60 mW/cm2. Four parameters (thickness, average erythema, eschar and loss of tissue) were quantified and a combined score (CS) of effects was established statistically. The maximum combined score during follow-up was taken as a measure for the biological effect. The light distribution in rat ears during irradiation with red and blue-green light was estimated from in vivo measurements and the transport theory. Statistical analysis of the combined score data yielded values for the relative biological effectiveness (RBE). Relative biological effectiveness maxima occurred at 501.7 and 625 nm. Analyzing erythema and loss of tissue separately yielded maxima at the same wavelengths. Quantitative agreement between the latter two sets of relative biological effectiveness values was obtained only when they were referred to the actual light energy fluence in tissue, rather than to the incident fluence. These relative biological effectiveness values are about 2.3 at 501.7 nm and 1.35 at 625 nm, taking relative biological effectiveness = 1 at 630 nm.     

Dissymmetrical U‐Shaped π‐Stacked Supramolecular Assemblies by Using a Dinuclear CuI Clip with Organophosphorus Ligands and Monotopic Fully π‐Conjugated Ligands

Reactions between the U‐shaped binuclear Cu^I complex A that bears short metal–metal distances and the cyano‐capped monotopic π‐conjugated ligands 1 – 5 that carry gradually bulkier polyaromatic terminal fragments lead to the formation of π‐stacked supramolecular assemblies 6 – 10 , respectively, in yields of 50–80 %. These derivatives have been characterized by multinuclear NMR spectroscopic analysis and X‐ray diffraction studies. Their solid‐state structures show the selective formation of U‐shaped supramolecular assemblies in which two monotopic π‐conjugated systems present large ( 6 , 7 , and 9 ) or medium ( 8 and 10 ) intramolecular π overlap, thus revealing π–π interactions. These assemblies self‐organize into head‐to‐tail π‐stacked dimers that in turn self‐assemble to afford infinite columnar π stacks. The nature, extent, and complexity of the intermolecular contacts within the head‐to‐tail π‐stacked dimer depend on the nature of the terminal polyaromatic fragment carried by the cyano‐capped monotopic ligand, but it does not alter the result of the self‐assembling process. These results demonstrate that the dinuclear molecular clip A that bears short metal–metal distances allows selective supramolecular assembly processes driven by the formation of intra‐ and intermolecular short π–π interactions in the resulting self‐assembled structures; thus, demonstrating that their shape is not only dictated by the symmetry of the building blocks. This approach opens perspectives toward the formation of extended π‐stacked columns based on dissymmetrical and functional π‐conjugated systems.     

Anisotropic light scattering and rheological study of the physical gelation of atactic polystyrene in carbon disulfide

The physical gelation of the solutions of atactic polystyrene (aPS) in carbon disulfide (CS₂) is studied by the excess of anisotropic light scattering δH_v and by the Theological properties. An abrupt jump of δH_v at gelation temperature shows that a part of the chains are stiffened upon gelation. This effect which is independent of aPS molecular weight strongly decreases with concentration. It is well correlated with an abrupt change of the plateau modulus ^GN which indicates the formation of additional entanglements in the gel phase with respect to the sol. The compatibility of these abrupt jumps with the thermodynamic theories used to interpret the concentration and molecular-weight dependence of the gelation temperature is discussed.