Intramolecular Ketone-Olefin Radical Cyclization with Low-Valent Titanium Reagent: Synthesis of Benzopyrans

A novel protocol for intramolecular ketyl-olefin radical cyclization with low-valent titanium reagent is outlined. It allows the formation of the benzopyran nucleus from ortho-allyloxy propiophenones as the sole product in moderate yields via intramolecular radical cyclization.     

UV-Vis, fluorescence and NMR spectroscopic investigations on inclusion properties of a designed tetrahomocalix[8]arene with fullerenes C60 and C70 in solution

The present article reports the spectroscopic investigations on non-covalent interaction of fullerenes C(60) and C(70) with a macrocyclic receptor molecule, namely, 1,3,5,7-tetrahomo-p-tert-butylcalix[8]arene (1) in toluene. Jobs method of continuous variation reveals 1:1 stoichiometry for the fullerene complexes of 1. The most fascinating feature of the present study is that 1 binds selectively C(60) compared to C(70) as obtained from binding constant (K) data of C(60)-1 (K(C60-1)) and C(70)-1 (K(C70-1)) complexes which are enumerated to be 265,000 dm(3) mol(-1) and 63,43 dm(3) mol(-1), respectively, and selectivity in binding (K(C60-1)/K(C70-1)) is estimated to be 4.18 as obtained from UV-Vis study. Steady state fluorescence studies reveal quenching of fluorescence of 1 in presence of fullerenes and the K value of the C(60)-1 and C(70)-1 complexes are estimated to be 80,760 and 68,780 dm(3) mol(-1), respectively, with selectivity in binding (K(C60-1)/K(C70-1)) ~1.18. (1)H NMR analysis provides very good support in favor of strong binding between C(60) and 1. The high value of K value for C(60)-1 complex indicates that 1 forms an inclusion complex with C(60).     

Multiderivative Runge-Kutta processes for two-point boundary value problems

A class of finite difference schemes for the solution of a nonlinear system of first order differential equations with two point boundary conditions which shares properties with Runge-Kutta processes and gap schemes is discussed. The order conditions for the coefficients of these processes, techniques for reducing these order conditions in number and the symmetry conditions are given. A symmetricA-stable eight order process which has second, fourth and sixth orderA-stable processes embedded in it is given as an example.Research supported in part by the United States Air Force under contract AFOSR-89-0383.     

Converting dipyrrinones to lactim ethers to fluorescent <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-difluoroboryl derivatives

A high-yield straightforward conversion of lactams to lactim ethers is shown by the conversion of (10H)-dipyrrin-1-ones to (11H)-dipyrrin-1-ol methyl and ethyl ethers in 90% yield from heating in neat trimethyl or triethyl phosphite at 160°C. Unlike the parent dipyrrinones, which form intermolecularly hydrogen-bonded dimers in CHCl₃, their lactim ethers are shown to be monomeric by vapor pressure osmometry. The latter react with boron trifluoride etherate to N,N′-bridged BF₂ derivatives that exhibit strong fluorescence (φ_F 0.6–0.8) near 535 nm. X-Ray crystal structures were obtained of the lactim ethyl ether of kryptopyrromethenone and the BF₂ derivative of the lactim ethyl ether 2,3-diethyl-7,8-dimethyl-(10H)-dipyrrin-1-one. Correspondence: David A. Lightner, Department of Chemistry, University of Nevada, Reno, Nevada 89557-0020 USA.     

Experimental demonstration of terahertz metamaterial absorbers with a broad and flat high absorption band

We present the design, numerical simulations and experimental measurements of terahertz metamaterial absorbers with a broad and flat absorption top over a wide incidence angle range for either transverse electric or transverse magnetic polarization depending on the incident direction. The metamaterial absorber unit cell consists of two sets of structures resonating at different but close frequencies. The overall absorption spectrum is the superposition of individual components and becomes flat at the top over a significant bandwidth. The experimental results are in excellent agreement with numerical simulations.     

Assessment of DFT based optimized molecular structure-antioxidant efficacy relationship of trimethylgermanium(IV) complexes

Optimized molecular structure-antioxidant efficacy relationship of trimethylgermanium(IV) complexes involving biologically active bulky heterocyclic-O-donor ligands was investigated using density functional theory (DFT). The complexes

where R = -CH₂CH₃[L₍₁₎H],-C₆H₅[L₍₂₎H], p-ClC₆H₄-[L₍₃₎H] were prepared by the reaction of trimethylgermanium chloride with sodium salts of bulky heterocyclic-O-donor ligands in 1:1 M ratio in refluxing dry THF. The complexes were characterized by various spectroscopic techniques namely FTIR, ¹H and ¹³C NMR. The spectral evidences are indicative of a bidentate behaviour of the ligands in these complexes which adopt a pentacoordinated geometry. Computational studies of these complexes have been carried out using B3LYP/6-31G* basis set to obtain molecular geometry, ground state energy and other global reactivity parameters. The most stable geometry having lowest optimized energy was chosen and bond lengths and bond angles were computed. The HOMO-LUMO energies for the complexes have been computed in order to ascertain the energy distribution and reactivity behaviour. These complexes were evaluated for antioxidant activity using FRAP (ferric reducing antioxidant power) assay and demonstrated potential antioxidant activity of distinguishable magnitude.     

Enantiomeric Separation of Moxifloxacin and Its (R,R)-Isomer by Ligand-Exchange Chiral Chromatography

A new stereospecific LC method for the separation and quantification of moxifloxacin and its (R,R)-enantiomer in bulk drug was developed and validated by ligand-exchange liquid chromatography on a reversed phase column using aqueous mobile phase containing the chiral reagent l-isoleucine-Cu(II). The UV detector was operated at 293 nm. The flow rate of mobile phase was set at 0.9 mL min^?1. The achiral ODS column offers good separation of the two enantiomers in less than 20 min. The test concentration was 1,000 μg mL^?1 in the mobile phase. This method was capable of detecting the (R,R)-enantiomer of moxifloxacin up to 0.1 μg mL^?1 for a 20 μL injection volume. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. There was no interference of degradants with the (R,R)-enantiomer in the developed method. The developed chiral RP-LC method was validated with respect to linearity, accuracy, precision and robustness. The percentage recovery for the (R,R)-enantiomer in bulk drug samples ranged from 98.1 to 104.4%. The test solution was found to be stable in the mobile phase for 48 h after preparation.     

Investigations of the first order magnetic phase transition in dysprosium

The first order magnetic phase transition in polycrystalline sample of dysprosium (Dy) has been investigated in detail by dc-resistance vs. temperature (R-T) measurements. Distinct signature of coexistence of two magnetically ordered phases (i.e. ferromagnetic and antiferromagnetic), originating as a result of the metastable behavior associated with the first order phase transition (FOPT) is found near 90 K. By successfully recording the minor hysteresis loops within the hysteretic R-T regime of Dy, a varying degree of phase coexistence in the FOPT is demonstrated.