Structures and NMR Parameters of 1,2-Diphenylcyclobutanes

A new reaction scheme for obtaining cis and trans 1,2-diphenylcyclobutane is described. Using ¹H-NMR at 600 MHz, full spectral assignment was made for both isomers, obtaining all J coupling constants and chemical shifts. NMR results on cis and trans 1,2-diphenylcyclobutane are compared with the vicinal coupling constants obtained by the Barfield–Smith equations from the literature internal and dihedral angles of cyclobutane. In the trans isomer, in agreement with previous results on halo-cyclobutanes, the conformation with the phenyls in the pseudo-di-equatorial position is strongly preferred. On the contrary, the cis isomer fluctuates between the two equivalent conformations: phenyl pseudo-axial and pseudo-equatorial.     

Competition between glutathione and guanine for a ruthenium(II) arene anticancer complex: detection of a sulfenato intermediate

The organometallic anticancer complex [(eta6-bip)Ru(en)Cl]+ (1; bip = biphenyl, en = ethylenediamine) selectively binds to guanine (N7) bases of DNA (Novakova, O.; Chen, H.; Vrana, O.; Rodger, A.; Sadler, P. J.; Brabec, V. Biochemistry 2003, 42, 11544-11554). In this work, competition between the tripeptide glutathione (gamma-L-Glu-L-Cys-Gly; GSH) and guanine (as guanosine 3',5'-cyclic monophosphate, cGMP) for complex 1 was investigated using HPLC, LC-MS and 1H,15N NMR spectroscopy. In unbuffered solution (pH ca. 3), the reaction of 1 with GSH gave rise to three intermediates: an S-bound thiolato adduct [(eta6-bip)Ru(en)(GS-S)] (4) and two carboxylate-bound glutathione products [(eta6-bip)Ru(en)(GSH-O)]+ (5, 6) during the early stages (<6 h), followed by en displacement and formation of a tri-GS-bridged dinuclear Ru(II) complex [((eta6-bip)Ru)2(GS-mu-S)3]2- (7). Under physiologically relevant conditions (micromolar Ru concentrations, pH 7, 22 mM NaCl, 310 K), the thiolato complex 4 was unexpectedly readily oxidized by dioxygen to the sulfenato complex [(eta6-bip)Ru(en)(GS(O)-S)] (8) instead of forming the dinuclear complex 7. Under these conditions, competitive reaction of complex 1 with GSH and cGMP gave rise to the cGMP adduct [(eta6-bip)Ru(en)(cGMP-N7)]+ (10) as the major product, accounting for ca. 62% of total Ru after 72 h, even in the presence of a 250-fold molar excess of GSH. The oxidation of coordinated glutathione in the thiolato complex 4 to the sulfenate in 8 appears to provide a facile route for displacement of S-bound glutathione by G N7. Redox reactions of cysteinyl adducts of these Ru(II) arene anticancer complexes could therefore play a significant role in their biological activity.     

Capillary electrophoresis/mass spectrometry: a promising tool for the control of some physiologically hazardous compounds. I-derivatives of 3-quinuclidinol

A method based on the coupling of capillary electrophoresis with mass spectrometry (CE/MS) was developed for the monitoring of 3-quinuclidinol and its four N-alkyl derivatives (methyl, ethyl, propyl and isopropyl derivatives). A fragmentation study (collision-induced dissociation of ions in an ion trap) and optimization of the ion optics set-up for CE/MS experiments using direct infusion of a methanolic solution of the standards into the mass spectrometer were carried out in advance. Molecular ions of all quaternary compounds and the quasi-molecular ion [M + H]+ of free 3-quinuclidinol prevail in the mass spectra. In the MS/MS of propyl and isopropyl derivatives, the elimination of the alkyl chain dominates, leading to the ion at m/z 128. The fragmentation of the other compounds is more complex. Previous CE separation of the mixture of isobaric propyl and isopropyl derivatives is necessary for their unambiguous identification. A 10 mM ammonium acetate buffer (pH 4.0) is the optimum running electrolyte, allowing the CE separation of methyl, ethyl, propyl and isopropyl derivatives. A 0.5% (v/v) solution of acetic acid in methanol provides sufficient detection sensitivity when used as the sheath liquid. Limits of detection of 0.1 ppm for 3-quinuclidinol and 0.05 ppm for quaternary derivatives were achieved under the optimum conditions. The optimized method was applied to the determination of 3-quinuclidinol and related quaternary derivatives spiked into a sample of pond water. The experimental set-up for CE/MS/MS was investigated, which strongly increases the identification capability of the technique.     

On the automorphism groups of a special class of quasigroups

We investigate automorphism groups of 2-generated quasigroups, constructed in [6], and show that such quasigroups of odd order k ≥ 7 have only one nontrivial automorphism, whereas in the case of even order k ≥ 6 there are no nontrivial automorphisms.     

Polarity of chordal graphs

Polar graphs are a common generalization of bipartite, cobipartite, and split graphs. They are defined by the existence of a certain partition of vertices, which is NP-complete to decide for general graphs. It has been recently proved that for cographs, the existence of such a partition can be characterized by finitely many forbidden subgraphs, and hence tested in polynomial time. In this paper we address the question of polarity of chordal graphs, arguing that this is in essence a question of colourability, and hence chordal graphs are a natural restriction. We observe that there is no finite forbidden subgraph characterization of polarity in chordal graphs; nevertheless we present a polynomial time algorithm for polarity of chordal graphs. We focus on a special case of polarity (called monopolarity) which turns out to be the central concept for our algorithms. For the case of monopolar graphs, we illustrate the structure of all minimal obstructions; it turns out that they can all be described by a certain graph grammar, permitting our monopolarity algorithm to be cast as a certifying algorithm.     

Three isomeric forms of hydroxyphenyl‐2‐oxazoline: 2‐(2‐hydroxyphenyl)‐2‐oxazoline, 2‐(3‐hydroxyphenyl)‐2‐oxazoline and 2‐(4‐hydroxyphenyl)‐2‐oxazoline

Crystal structures are reported for three isomeric compounds, namely 2‐(2‐hydroxy­phenyl)‐2‐oxazoline, (I), 2‐(3‐hydroxy­phenyl)‐2‐oxazoline, (II), and 2‐(4‐hydroxy­phenyl)‐2‐oxazoline, (III), all C₉H₉NO₂ [systematic names: 2‐(4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenol, (I), 3‐(4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenol, (II), and 4‐(4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenol, (III)]. In these compounds, the deviation from coplanarity of the oxazoline and benzene rings is dependent on the position of the hydroxy group on the benzene ring. The coplanar arrangement in (I) is stabilized by a strong intra­molecular O—H⋯N hydrogen bond. Surprisingly, the 2‐oxazoline ring in mol­ecule B of (II) adopts a ³T₄ (^C2T_C3) conformation, while the 2‐oxazoline ring in mol­ecule A, as well as that in (I) and (III), is nearly planar, as expected. Tetra­mers of mol­ecules of (II) are formed and they are bound together via weak C—H⋯N hydrogen bonds. In (III), strong inter­molecular O—H⋯N hydrogen bonds and weak intra­molecular C—H⋯O hydrogen bonds lead to the formation of an infinite chain of mol­ecules perpendicular to the b direction. This paper also reports a theoretical investigation of hydrogen bonds, based on density functional theory (DFT) employing periodic boundary conditions.     

Hereditary Coreflective Subcategories of Categories of Topological Spaces

Let be an epireflective subcategory of the category Top of topological spaces that is not bireflective (e.g., the category of Hausdorff spaces, the category of Tychonoff spaces) and ℬ be a coreflective subcategory of . Extending the corresponding result obtained for coreflective subcategories of Top we prove that ℬ is hereditary if and only if it is closed under the formation of prime factors. As a consequence we obtain that every hereditary coreflective subcategory ℬ of containing a non-discrete space is generated by a class of prime spaces and if is a quotient-reflective subcategory of Top, then the assignment gives a bijection of the collection of all hereditary coreflective subcategories of Top that contain the class FG of all finitely generated spaces onto the collection of all hereditary coreflective subcategories of that contain . Some applications of these results in the categories of Hausdorff spaces, Tychonoff spaces and zero-dimensional Hausdorff spaces are presented.Mathematics Subject Classifications (2000) 18D15, 54B30.     

Tensor Products in Categories of Topological Spaces

In this paper symmetric monoidal closed structures on coreflective subcategories of the category of (Hausdorff) topological spaces are studied. We describe all such structures on the category of (Hausdorff) pseudoradial spaces and some of its subcategories and give an example of a coreflective subcategory of the category of Hausdorff topological spaces admitting a proper class of symmetric monoidal closed structures.     

Platinum (IV) Derivatives with Cinnamate Axial Ligands as Potent Agents Against Both Differentiated and Tumorigenic Cancer Stem Rhabdomyosarcoma Cells

To design an anticancer drug capable of inhibiting not only the proliferation of the differentiated tumor cells but also reducing the tumorigenic capability of cancer stem cells (CSCs), the new Pt^IV prodrugs with axial cinnamate ligands were synthesized. We demonstrate their superior antiproliferative activity in monolayer and 3D spheroid antiproliferative activity tests using panel of cancer cell lines. An outstanding activity was found against rhabdomyosarcoma cells, one of the most problematic and poorly treatable pediatric tumors. The results also suggest that the released Pt^II compound inhibits antiproliferative activity of cancer cells by DNA‐damage mediated mechanism; the released cinnamic acid can trigger processes leading to differentiation, making the CSCs more sensitive to killing by the platinum part of the complex. Pt^IV complex with axial cinnamate ligands is the first Pt^IV prodrug capable of overcoming CSCs resistance and induce death in both CSCs and bulk cancer.     

A Systematic Study of Coumarin–Tetrazine Light-Up Probes for Bioorthogonal Fluorescence Imaging

Fluorescent probes that light-up upon reaction with complementary bioorthogonal reagents are superior tools for no-wash fluorogenic bioimaging applications. In this work, a thorough study is presented on a set of seventeen structurally diverse coumarin–tetrazine probes that produce fluorescent dyes with exceptional turn-on ratios when reacted with trans-cyclooctene (TCO) and bicyclononyne (BCN) dienophiles. In general, formation of the fully aromatic pyridazine-containing dyes resulting from the reaction with BCN was found superior in terms of fluorogenicity. However, evaluation of the probes in cellular imaging experiments revealed that other factors, such as reaction kinetics and good cell permeability, prevail over the fluorescence turn-on properties. The best compound identified in this study showed excellent performance in live cell-labeling experiments and enabled no-wash fluorogenic imaging on a timescale of seconds.