Toroidal surgeries on hyperbolic knots

For a hyperbolic knot in , a toroidal surgery is Dehn surgery which yields a -manifold containing an incompressible torus. It is known that a toroidal surgery on is an integer or a half-integer. In this paper, we prove that all integers occur among the toroidal slopes of hyperbolic knots with bridge index at most three and tunnel number one.

     

Supramolecular graphyne: a C(sp)-H...N hydrogen-bonded unique network structure of 2,4,6-triethynyl-1,3,5-triazine

The crystallization of 2,4,6-triethynyl-1,3,5-triazine (2) leads to a pi-stacked layered structure of a C(sp)-H...N hydrogen-bonded unique hexagonal network structure, which may be regarded as a supramolecular analogue of a hitherto unknown graphyne network: in-plane intermolecular interactions are short and linear H...N contacts (2.31 and 2.34 A) and the interlayer separation is 3.23 A.     

Redox-controlled, reversible rearrangement of a tris(2-pyridylthio)methyl ligand on nickel to an isomer with an “N,S-confused” 2-pyridylthiolate arm

Interchange between the nickel +2 and +3 oxidation states precisely controls the reversible rearrangement of the tris(2-pyridylthio)methanide (tptm) ligand in the organometallic nickel(II) complex [{Ni(μ-Br)-(tptm)}(2)] (2). Oxidation of 2 first gives the corresponding Ni(III) complex [{Ni(μ-Br)(tptm)}(2)][PF(6)](2) (4). However, in solution the tptm ligand in 4 slowly undergoes a rearrangement, in which the N and S atoms of one of the pyridylthiolate arms exchange Ni and C bonding partners, thereby resulting in an "N,S-confused" isomer of tptm in the product, [NiBr(bpttpm)]PF(6) (5; bpttpm= bis(2-pyridylthio)(2-thiopyridinium)-methyl). Reduction of 5 reverses this ligand rearrangement and 2 is reformed quantitatively. The individual steps involved in these unusual ligand rearrangements were investigated by a number of methods, including voltammetric analysis, and a mechanism for this process is proposed. X-ray crystal structure determinations of the key compounds 2, 4 and 5 have been obtained.     

Evaluation of the Intracellular Signaling Activities of κ-Opioid Receptor Agonists,Nalfurafine Analogs; Focusing on the Selectivity of G-Protein- and β-Arrestin-Mediated Pathways

Opioid receptors (ORs) are classified into three types (μ, δ, and κ), and opioid analgesics are mainly mediated by μOR activation; however, their use is sometimes restricted by unfavorable effects. The selective κOR agonist nalfurafine was initially developed as an analgesic, but its indication was changed because of the narrow safety margin. The activation of ORs mainly induces two intracellular signaling pathways: a G-protein-mediated pathway and a β-arrestin-mediated pathway. Recently, the expectations for κOR analgesics that selectively activate these pathways have increased; however, the structural properties required for the selectivity of nalfurafine are still unknown. Therefore, we evaluated the partial structures of nalfurafine that are necessary for the selectivity of these two pathways. We assayed the properties of nalfurafine and six nalfurafine analogs (SYKs) using cells stably expressing κORs. The SYKs activated κORs in a concentration-dependent manner with higher EC₅₀ values than nalfurafine. Upon bias factor assessment, only SYK-309 (possessing the 3S-hydroxy group) showed higher selectivity of G-protein-mediated signaling activities than nalfurafine, suggesting the direction of the 3S-hydroxy group may affect the β-arrestin-mediated pathway. In conclusion, nalfurafine analogs having a 3S-hydroxy group, such as SYK-309, could be considered G-protein-biased κOR agonists.     

Thermoluminescence and ESR phenomena in X-ray irradiated mixed alkaline-alkaline earth metal sulfates—I

Abstract

Thermoluminescence (TL) and ESR phenomena induced by X-ray irradiation of the mixed samples of K₂SO₄ and alkaline earth metal sulfate (MgSO₄ or BaSO₄) were investigated in terms of the reactivities and the crystallogrpahic properties. A high intensive TL resulted from the diffusion of a small amount of Mg²⁺ into K₂SO₄ crystals. The amount formed of K₂Mg₂(SO₄)₃, langbeinite, compound had a maximum at the stoichiometric composition. From the ESR measurements, SO^? ₃ radicals were found to be easily formed in the langebeinite by excitation. Both the TL and the ESR phenomena were hardly observed in the K₂SO₄–BaSO₄ system due to little diffusion of Ba²⁺ with much larger radius than Mg²⁺. The results were mainly discussed on the basis of the radii of the component cations in these systems. In addition, the fundamental data as to the application to the ESR dosimetry were obtained.     

Solving polynomial least squares problems via semidefinite programming relaxations

A polynomial optimization problem whose objective function is represented as a sum of positive and even powers of polynomials, called a polynomial least squares problem, is considered. Methods to transform a polynomial least square problem to polynomial semidefinite programs to reduce degrees of the polynomials are discussed. Computational efficiency of solving the original polynomial least squares problem and the transformed polynomial semidefinite programs is compared. Numerical results on selected polynomial least square problems show better computational performance of a transformed polynomial semidefinite program, especially when degrees of the polynomials are larger.     

Remote asymmetric induction with vinylketene silyl n,o-acetal

A highly regio- and diastereoselective TiCl4-mediated vinylogous Mukaiyama aldol reaction using the chiral vinylketene silyl N,O-acetal has been developed. The present vinylogous Mukaiyama aldol reaction provides a unique and effective means of controlling remote asymmetric induction. The methyl group at the alpha-position is important in achieving a high level of stereoselectivity. From a synthetic point of view, this methodology can provide a one-step construction of delta-hydroxy-alpha,gamma-dimethyl-alpha,beta-unsaturated carbonyl unit that is seen in many natural polyketide products.     

Reversed-phase HPLC separation of the enantiomers of denopamine after derivatization with GITC chiral reagent

Summary A reversed-phase high-performance liquid chromatographic (HPLC) method was developed to determine the optical purity of denopamine, which is a new cardiotonic agent having an asymmetric carbon in a molecule. The enantiomers were converted to diastereomeric thiourea derivatives using 2,3,4,6-Tetra-O-acetyl--D-glucopyranosyl isothiocyanate (GITC) reagent. Separation of the enantiomers of denopamine as diastereomers was successfully achieved by reversed-phase HPLC within 10 min using an ODS column and UV detection. Derivatization of denopamine proceeded rapidly under the alkaline conditions and the ambient temperature. This method was applied to the determination of the optical purity of denopamine drug substances and those in tablets. The favorable UV absorption of the derivatives enabled the optical antipode to be determined down to the 0.2% level.