Synthesis of imidazo[4,5-d]pyridazine nucleosides related to inosine

Several imidazo[4,5-d]pyridazine nucleosides which are structurally similar to inosine were synthesized. Anhydrous stannic chloride-catalyzed condensation of persilylated imidazo[4,5-d]-pyridazin-4(5H)one (1) and imidazo[4,5-d]pyridazine-4,7(5H,6H)dione ( 16 ) with 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-ribofuranose ( 3 ) provided (after sodium methoxide deblocking) 6-β-D-ribo furanosylimidazo[4,5-d]pyridazin-4(5H)one (5) and 3,6-di-(β-D-ribofuranosyI)imidazo[4,5-d]pyridazin-4-one ( 7 ); and 1-(β-D-ribofuranosyl)imidazo[4,5-d]pyridazine-4,7(5H,6H)dione ( 19 ) and 1,5 or 6-di-(β-D-ribofuranosyl)imidazo[4,5-d ]pyridazine-4,7(5H or 6H)dione ( 21 ), respeeitvely. 4,7-Diehloro-1-β-D-ribofuranosylimidazo[4,5-d]pyridazine ( 12 ) and dimethyl 1-β-D-ribofuranosylimidazole-4,5-dicarboxylate ( 26 ), both prepared from stannic chloride-catalyzed ribosylations of the corresponding heterocycles, were converted in several steps to 3-β-D-ribo-furanosy limidazo[4,5-d]pyridazin-4(5H)one ( 14 ) and nucleosidc 19 , respectively. Acid-catalyzed isopropylidenation of mesomeric betaine 7 or nuclcoside 14 provided 3-(2,3-isopropylidene-β-D-ribofuranosyl)imidazo[4,5-d]pyrizin-4(5H)one ( 31 ). 1-β-D-Ribofuranosylimidazo[4,5-d]-pyridazine ( 29 ) was obtained in several steps from nueleoside 12 . The structure of the nucleosides was established by the use of carbon-13 and proton nmr.     

Anodic stripping voltammetry with flow injection analysis

A flow cell with a wall-jet electrode design is used for anodic stripping voltammetry of lead at concentrations of about 10^?7 mol dm^?3. Maximum peak heights are obtained for narrow nozzle diameters and short nozzle-to-electrode distances. Linear calibration plots are obtainedfor almost four decades of change in concentration and can be extended by judicious choice of sample volume. Increasing sample throughput rates by increasing the solution flow rate decreases the analytical signal. Square wave voltammetry provides shorter analysis times and better sensitivity than differential pulse voltammetry.     

A new algorithm for computing the Geronimus transformation with large shifts

A monic Jacobi matrix is a tridiagonal matrix which contains the parameters of the three-term recurrence relation satisfied by the sequence of monic polynomials orthogonal with respect to a measure. The basic Geronimus transformation with shift α transforms the monic Jacobi matrix associated with a measure dμ into the monic Jacobi matrix associated with dμ/(x − α) + Cδ(x − α), for some constant C. In this paper we examine the algorithms available to compute this transformation and we propose a more accurate algorithm, estimate its forward errors, and prove that it is forward stable. In particular, we show that for C = 0 the problem is very ill-conditioned, and we present a new algorithm that uses extended precision.     

Sulfonate salts of the therapeutic agent dapsone: 4‐[(4‐aminophenyl)sulfonyl]anilinium benzenesulfonate monohydrate and 4‐[(4‐aminophenyl)sulfonyl]anilinium methanesulfonate monohydrate

Dapsone, formerly used to treat leprosy, now has wider therapeutic applications. As is the case for many therapeutic agents, low aqueous solubility and high toxicity are the main problems associated with its use. Derivatization of its amino groups has been widely explored but shows no significant therapeutic improvements. Cocrystals have been prepared to understand not only its structural properties, but also its solubility and dissolution rate. Few salts of dapsone have been described. The title salts, C₁₂H₁₃N₂O₂S⁺·C₆H₅O₃S⁻·H₂O and C₁₂H₁₃N₂O₂S⁺·CH₃SO₃⁻·H₂O, crystallize as hydrates and both compounds exhibit the same space group (monoclinic, P2₁/n). The asymmetric unit of each salt consists of a 4‐[(4‐aminophenyl)sulfonyl]anilinium monocation, the corresponding sulfonate anion and a water molecule. The cation, anion and water molecule form hydrogen‐bonded networks through N—H…O=S, N—H…O_water and O_water—H…O=S hydrogen bonds. For both salts, the water molecules interact with one sulfonate anion and two anilinium cations. The benzenesulfonate salt forms a two‐dimensional network, while the hydrogen bonding within the methanesulfonate salt results in a three‐dimensional network.     

Effect of strain and nonparabolicity on interband transition energies of InAs/GaAs coupled double quantum dots

Strained potential profiles and electronic subband energies of InAs/GaAs coupled double quantum dots (DQDs) were calculated by using a three-dimensional finite-difference method (FDM) taking into account shape-based strain and nonparabolic effects. The interband transition energies from the ground electronic subband to the ground heavy-hole band (E₁-HH₁) in the InAs/GaAs DQDs, as determined from the FDM calculations taking into account strain and nonparabolic effects, were in reasonable agreement with the experimental peaks corresponding to the (E₁-HH₁) interband transition energies at several temperatures, as determined from the temperature-dependent photoluminescence spectra.     

Complex Gaussian quadrature of oscillatory integrals

We construct and analyze Gauss-type quadrature rules with complex- valued nodes and weights to approximate oscillatory integrals with stationary points of high order. The method is based on substituting the original interval of integration by a set of contours in the complex plane, corresponding to the paths of steepest descent. Each of these line integrals shows an exponentially decaying behaviour, suitable for the application of Gaussian rules with non-standard weight functions. The results differ from those in previous research in the sense that the constructed rules are asymptotically optimal, i.e., among all known methods for oscillatory integrals they deliver the highest possible asymptotic order of convergence, relative to the required number of evaluations of the integrand.     

Subgel studies of dimyristoylphosphatidylcholine bilayers

It is known that when bilayers of some saturated phosphatidylcholines are stored for 3 or more days at approximately 0 degrees C, a lamellar subgel (Lc) phase is detected at temperatures below the pretransition by differential scanning calorimetry (DSC). However, the subgel (Lc) phase and the corresponding subtransition (Lc--> Lbeta') for dimyristoylphosphatidylcholine (DMPC) has not been clearly characterized. In this study, using the temperature jump protocol first developed by Tristram-Nagle et al. for the dipalmitoylphosphatidylcholine (DPPC) system, new and accurate data characterizing the subgel formation and subtransition of DMPC were obtained through DSC and fluorescence spectroscopy with 1,6-diphenyl-1,3,5-hexatriene (DPH). It was discovered that the formation of the DMPC subgel phase requires incubation at temperatures of -5 degrees C or lower for 2 h or more. Kinetics of the subgel formation indicate that it is a very complex process and demonstrates that the planar gel phase is merely metastable below the subtransition, and not the thermodynamically stable phase. The subgel growth of DMPC is proven to be the dehydration of the headgroup region, and the subtransition is a process in which poorly hydrated DMPC becomes hydrated.     

Topological Expansion in the Complex Cubic Log–Gas Model: One-Cut Case

We prove the topological expansion for the cubic log–gas partition function

$$\begin{aligned} Z_N(t)= \int _\Gamma \cdots \int _\Gamma \prod _{1\le j<k\le N}(z_j-z_k)^2 \prod _{k=1}^Ne^{-N\left( -\frac{z^3}{3}+tz\right) }\mathrm{dz}_1\cdots \mathrm{dz}_N, \end{aligned}$$

where t is a complex parameter and \(\Gamma \) is an unbounded contour on the complex plane extending from \(e^{\pi \mathrm{i}}\infty \) to \(e^{\pi \mathrm{i}/3}\infty \). The complex cubic log–gas model exhibits two phase regions on the complex t-plane, with one cut and two cuts, separated by analytic critical arcs of the two types of phase transition: split of a cut and birth of a cut. The common point of the critical arcs is a tricritical point of the Painlevé I type. In the present paper we prove the topological expansion for \(\log Z_N(t)\) in the one-cut phase region. The proof is based on the Riemann–Hilbert approach to semiclassical asymptotic expansions for the associated orthogonal polynomials and the theory of S-curves and quadratic differentials.

     

A solution of structural ambiguity: s-Triazolo[1,5-a] – and s-triazolo[4.3-a] pyrimidines

The condensation of 3-amino-5-benzylthio-s-triazole ( 2 ) with acetylacetone in refluxing acetic acid has been reported to have given 3-benzylthio-5,7-dimethyl-s-triazolo[4,3-a]pyrimidine ( 3 ). However, it has now been established, with the aid of ¹³C spectra and a modification of the original synthetic work, that only 2-benzylthio-5,7-dimethyl-s-triazolo[1,5-a]pyrimidine ( 4 ) can be obtained by this method of condensation. The erroneously reported, but previously unknown 6 was synthesized and its structure and that of 4 was firmly established by ir, uv, pmr,¹³ C nmr, tlc and mixed melting point data. The correct structures of 3-mercapto-5,7-dimethyl-s-triazolo-[4,3-a]pyrimidine ( 5 ) and 2-mercapto-5,7-dimethyl-s-triazolo[1,5-a]pyrimidine ( 6 ) were also established and the facile rearrangement of 5 to 6 was demonstrated.