Solvent-Controlled Self-Assembled Oligopyrrolic Receptor

We report a fully organic pyridine-tetrapyrrolic U-shaped acyclic receptor 10, which prefers a supramolecular pseudo-macrocyclic dimeric structure (10)₂ in a less polar, non-coordinating solvent (e.g., CHCl₃). Conversely, when it is crystalized from a polar, coordinating solvent (e.g., N,N-dimethylformamide, DMF), it exhibited an infinite supramolecular one-dimensional (1D) “zig-zag” polymeric chain, as inferred from the single-crystal X-ray structures. This supramolecular system acts as a potential receptor for strong acids, e.g., p-toluenesulfonic acid (PTSA), methane sulfonic acid (MSA), H₂SO₄, HNO₃, and HCl, with a prominent colorimetric response from pale yellow to deep red. The receptor can easily be recovered from the organic solution of the host–guest complex by simple aqueous washing. It was observed that relatively stronger acids with pK_a < −1.92 in water were able to interact with the receptor, as inferred from ¹H NMR titration in tetrahydrofuran-d₈ (THF-d₈) and ultraviolet–visible (UV–vis) spectroscopic titrations in anhydrous THF at 298 K. Therefore, this new dynamic supramolecular receptor system may have potentiality in materials science research.     

DAG‐Width and Circumference of Digraphs

We prove that every digraph of circumference l has DAG‐width at most l. This is best possible and solves a recent conjecture from S. Kintali (ArXiv:1401.2662v1 [math.CO], January 2014).¹ As a consequence of this result we deduce that the k‐linkage problem is polynomially solvable for every fixed k in the class of digraphs with bounded circumference. This answers a question posed in J. Bang‐Jensen, F. Havet, and A. K. Maia (Theor Comput Sci 562 (2014), 283–303). We also prove that the weak k‐linkage problem (where we ask for arc‐disjoint paths) is polynomially solvable for every fixed k in the class of digraphs with circumference 2 as well as for digraphs with a bounded number of disjoint cycles each of length at least 3. The case of bounded circumference digraphs is still open. Finally, we prove that the minimum spanning strong subdigraph problem is NP‐hard on digraphs of DAG‐width at most 5.     

Forbidden subgraphs for chorded pancyclicity

We call a graph $G$ pancyclic if it contains at least one cycle of every possible length $m$, for $3\le m\le \left|V\left(G\right)\right|$. In this paper, we define a new property called chorded pancyclicity. We explore forbidden subgraphs in claw-free graphs sufficient to imply that the graph contains at least one chorded cycle of every possible length $4,5,\dots ,\left|V\left(G\right)\right|$. In particular, certain paths and triangles with pendant paths are forbidden.     

Quantitative Bestimmung organischer Verbindungen

Ohne Zusammenfassung     

The infrared spectrum of isothiazole in the range 600–1500 cm−1, including a high-resolution study of the v 11(A′) band at 818 cm−1 and the v 16(A″) band at 727 cm−1, together with ab initio studies of the full spectrum

Abstract

The gas-phase high-resolution infrared spectrum of isothiazole in the range 600–1500 cm^?1 has been recorded, and revised band centres obtained for a number of vibrations. An analysis of the v ₁₁(A′) band at 818 cm^?1 and the v ₁₆(A″) band at 727 cm^?1 has been performed, using the Watson Hamiltonian, A-reduction, III^r representation. These were combined with previous microwave spectral data to provide combined analyses for rotational constants and quartic centrifugal distortion constants Δ _J , Δ _JK , Δ _K , δ _j and δ _K . These extend the knowledge derived from previous microwave and IR spectral studies. The equilibrium structures and the derived harmonic frequencies were calculated by ab initio methods, using a variety of basis sets with MP2, MP4 and CCSD(T) methods, and a comparison of these with experimental data is discussed. At a pragmatic level, the closest correlation of the rotational constants with experiment is not obtained with the most sophisticated methodology. Similarly, the vibration frequencies and intensities also vary strongly with the procedure. In particular, we found that the cc-pVTZ+MP2 results probably provide the best numerical comparison with experimental IR data for this molecule.     

An Efficient Synthesis of the Indole Acetic Acid Metabolite of MK-0462

A palladium-catalyzed coupling of iodoaniline 2 with bis-TES propargyl alcohol 3 gives indole-3-methanol 4b in 72% yield. Displacement of the hydroxy group of 4b by sodium cyanide followed by hydrolysis of the cyano group and desilylation provides the indole acetic acid metabolite, L-749,335 (1), of the 5-HT_1D receptor agonist MK-0462.     

Synthesis and single crystal X-ray analysis of two griseofulvin metabolites

The two phenols, 6-O-desmethyl griseofulvin and 4-O-desmethyl griseofulvin are metabolites of the antifungal drug griseofulvin. Herein, we present an improved synthesis of the 6-phenol derivative, and an unequivocal proof of both structures by single-crystal X-ray analysis.