Synthesis of new crown ethers and their metal complexes: 1H and 13C NMR study

A new type of crown ethers containing a diphenyl ether unit has been prepared, the ring size ranging from 12 to 36. ¹H and ¹³C NMR spectra of both free ligands and their metal-ion complexes have been recorded. For 18- and 21-membered compounds a general downfield shift was observed for both methylene and aromatic proton resonances on metal-ion complexation. The stoichiometry of K⁺ and Na⁺ complexes was deduced from chemical shift dependence on metal-ion concentration. The K⁺ and Na⁺ complexes of 18- and 21-membered rings have a guest to host ratio of 1:1, whereas the K⁺ salt of the 15-membered ring exists as a 1:2 complex in solution. The ¹H shift observed on salt formation was attributed to electric-field and conformational effects. The ¹³C resonances for the aryl carbons, C-1, C-2 and C-3, and the α-methylene carbon in 15- and 18-membered rings were shifted upfield when an equivalent amount of KSCN was added in CDCI_3?DMSO-d₆. The shift changes were independent of the anion, and similar results were obtained for SCN^?, Br^?, and I^? salts. The upfield shift is explained by conformational factors. The spectral changes were slight for 12- and 36-membered rings. In 15- and 18-membered rings, complexation induces conformational changes which force the C-α carbon into the plane of the benzene ring. The solution conformation of these molecules is discussed.     

Third-order potential constants and dipole moment of SeO2 by microwave spectroscopy

The third-order potential constants of SeO₂ have been recalculated using the vibrational frequencies reported for matrix-isolated SeO₂. General trends of the constants are in good accord with the results obtained for other triatomic molecules, such as SO₂, O₃, and OF₂. The dipole moment was measured more accurately to be 2.62 ± 0.05 D.     

A numerical method for the solution of multi-point problems for ordinary differential equations with integral constraints

We propose a method for the solution of a system of nonlinear ordinary differential equations with integral constraints, by transforming to multi-point boundary value problems. Examples are given.     

Improvements in Carrier-to-Noise-Ratio (CNR) of Lightwave Amplitude Modulated Vestigial-Sideband (AM-VSB) Transmission Systems by the Use of Optical Isolators

In lightwave community antena television (CATV) systems as well as other optical fiber communication networks, a transmitted optical signal is known to be degraded by an intensity noise produced within the fiber due to the interference between the signal and doubly reflected light. We report on the improvements to the signal degradation due to the double Rayleigh backscattering by inserting optical isolators in the trunk lines of the systems. A carrier-to-noise ratio (CNR) has been calculated as a function of the number and the insertion loss of the isolators. The calculated results indicate that there is an optimum number of isolators, and if the insertion loss is less than 0.3 dB, the CNR degradation can be restored by more than 60%. To test the calculated results, we conducted experiments for the specific case of employing one isolator, and obtained good agreements between the two.     

Bidirectional and colorimetric recognition of sodium and potassium ions

Host 1 based on the phenolphthalein skeleton and two crown ether moieties demonstrated opposite behaviors toward sodium and potassium cations caused by bidirectional complexation. [reaction: see text]     

Li-intercalation into hexagonal boron nitride

A Li hexagonal boron nitride (hBN) intercalation compound (Li-hBNIC) was successfully synthesized by the annealing of powder or bulk hBN and Li at 1523 K. By an XRD analysis, a strong peak indicating the expansion of BN interlayer distance due to Li-intercalation was observed at an angle lower than that of hBN (0 0 2). In the sample, the interlayer distance and its expansion ratio were 3.76 Å and 12.6%, respectively, and these values were similar to those of a first stage Li-graphite intercalation compound (Li-GIC), LiC₆. The electrical conductivity of the sample was increased by several orders of magnitude, from 10⁻¹⁵ to 10⁻⁷ Ω⁻¹ cm⁻¹ at room temperature. Li de-intercalation was confirmed by the dispersion of the sample in purified water.     

Automatic design of illumination systems

The approach for autodesign of optical characteristics of different illumination units such as backlight systems, led arrays and light boxes is considered. Suggested software solution allows finding optimal configuration of lighting scheme for providing necessary distribution of output light. Additional preprocessing phase is introduced in design process, which provides reduction of design iterations and better convergence compared to conventional design methods, utilizing random fluctuations of design parameter between iterations. The results of several designs of different kinds of illumination systems are presented.     

Antikaon–Nucleon Dynamics and its Application to Few-Body Systems

We overview the recent progress in the investigation of the antikaon dynamics with single nucleon and with few-body nuclei, based on chiral SU(3) symmetry. We first show how the Λ(1405) resonance emerges from the coupled-channel ${\bar{K}N - \pi\Sigma}$ interaction. Next, we present the construction of an up-to-date ${\bar{K}N}$ interaction in response to the recent measurement of kaonic hydrogen. Finally, we discuss the possibility of the antikaon bound states in nuclei from the perspective of few-body physics.     

An Unprecedented Cyclization Mechanism in the Biosynthesis of Carbazole Alkaloids in Streptomyces

Carquinostatin A (CQS), a potent neuroprotective substance, is a unique carbazole alkaloid with both an ortho‐quinone function and an isoprenoid moiety. We identified the entire gene cluster responsible for CQS biosynthesis in Streptomyces exfoliatus through heterologous production of CQS and gene deletion. Biochemical characterization of seven CQS biosynthetic gene products (CqsB1–7) established the total biosynthetic pathway of CQS. Reconstitution of CqsB1 and CqsB2 showed that the synthesis of the carbazole skeleton involves CqsB1‐catalyzed decarboxylative condensation of an α‐hydroxyl‐β‐keto acid intermediate with 3‐hydroxybutyryl‐ACP followed by CqsB2‐catalyzed oxidative cyclization. Based on crystal structures and mutagenesis‐based biochemical assays, a detailed mechanism for the unique deprotonation‐initiated cyclization catalyzed by CqsB2 is proposed. Finally, analysis of the substrate specificity of the biosynthetic enzymes led to the production of novel carbazoles.     

On the nature of the and from their behavior in chiral dynamics

We study the behavior with the number of colors (N_c) of the Λ(1405) and Λ(1670) resonances obtained dynamically within the chiral unitary approach. The leading order meson–baryon interaction, used as the kernel of the unitarization procedure, manifests a nontrivial N_c dependence of the flavor SU(3) representation for baryons. As a consequence, the SU(3) singlet (or ) component of the Λ(1405) states remains bound in the large N_c limit, while the other components dissolve into the continuum. Introducing explicit SU(3) breaking, we obtain the N_c dependence of the excitation energy, masses and widths of the physical Λ(1405) and Λ(1670) resonances. The N_c behavior of the decay widths is found to be different from the general counting rule for a qqq state, indicating the dynamical origin of these resonances.