Noncovalent attachment of pyro-pheophorbide a to a carbon nanotube

Pyrene mediated noncovalent attachment of a chlorophyll derivative, pyro-pheophorbide a, to a soluble single wall carbon nanotube is reported and the resultant CD, UV-Vis absorbance, fluorescence and 1H NMR spectra are discussed.     

Multipole interference in the second-harmonic optical radiation from gold nanoparticles

We provide experimental evidence of higher multipole (magnetic dipole and electric quadrupole) radiation in second-harmonic (SH) generation from arrays of metal nanoparticles. Fundamental differences in the radiative properties of electric dipoles and higher multipoles yield opposite interference effects observed in the SH intensities measured in the reflected and transmitted directions. These interference effects clearly depend on the polarization of the fundamental field, directly indicating the importance of multipole effects in the nonlinear response. We estimate that higher multipoles contribute up to 20% of the total emitted SH field amplitude for certain polarization configurations.     

A combined NMR, DFT, and X-ray investigation of some cinchona alkaloid O-ethers

Structures and conformational behavior of several cinchona alkaloid O-ethers in the solid state (X-ray), in solution (NMR and DFT), and in the gas phase (DFT) were investigated. In the crystal, O-phenylcinchonidine adopts the Open(3) conformation similar to cinchonidine, whereas the O-methyl ether derivatives of both cinchonidine and cinchonine are packed in the Closed(1) conformation. Dynamic equilibria in solutions of the alkaloids were revealed by combined experimental-theoretical spin simulation/iteration techniques for the first time. In the (1)H NMR spectra in CDCl3 and toluene-d8 at room temperature, Closed(1) conformation was observed for the O-silyl ethers as a separate set of signals. For O-methyl ether derivatives Closed(1) could be separated only at -30 degrees C in CDCl3 or toluene-d8 and for O-phenylcinchonidine at -70 degrees C in CDCl3/CD2Cl2. The ratio between the Closed(2) and Open(3) conformers was estimated by analyzing the vicinal coupling constant (3)J(H9,H8) at ambient and low temperatures. The observed conformational equilibria of O-(tert-butyldimethylsilyl)cinchonidine in CDCl 3 and toluene-d8 are in good agreement with the theoretically estimated equilibrium populations of the conformations according to Boltzmann statistics. The conformational equilibria of four cinchona alkaloid O-ether solutes in CDCl3 and toluene-d8 are discussed in the light of their relevance to the mechanism of 1-phenyl-1,2-propanedione (PPD) hydrogenation over cinchona alkaloid modified heterogeneous platinum catalysts. It was demonstrated that the conformation found to be abundant in the liquid phase has no direct correlation with the enantioselectivity of the PPD hydrogenation reaction.     

Synthesis and X‐ray Structures of the Polycyclic Dimers {[PhB(μ‐NtBu)2AsN(tBu)H]LiI}2 and [PhB(μ‐NtBu)2AsN(tBu)Li]2

The metathesis of [PhB(μ‐NtBu)₂]AsCl and tBuN(H)Li in 1:1 molar ratio in diethyl ether produced the amido derivative [PhB(μ‐NtBu)₂AsN(tBu)H] ( 1 ) in good yield. The lithiation of 1 with one equivalent of nBuLi afforded the lithium salt [PhB(μ‐NtBu)₂AsN(tBu)Li] ( 2a ). Both 1 and 2a were characterized by multinuclear NMR spectroscopy. The crystal structure of 2a is comprised of a U‐shaped, centrosymmetric dimer in which the monomeric [PhB(μ‐NtBu)₂AsN(tBu)]^?Li⁺ units are linked by Li‐N interactions to give a six‐rung ladder. Oxidation of 2a with one‐half equivalent of I₂ in diethyl ether resulted in hydrogen abstraction from the solvent to give the dimeric lithium iodide adduct {[PhB(μ‐NtBu)₂AsN(tBu)H]LiI}₂ ( 1 ·LiI) with a central Li₂I₂ ring.     

Two new phenylbutanoids from inner bark of Betula pendula

Two phenylbutanoids, 7-{3R-[(4-hydroxyphenyl)butyl] beta-glucopyranosid-O-6-yl} 4-O-beta-glucopyranosylvanillin and 3-beta-glucopyranosyloxy-1-(4-hydroxyphenyl)-butanone were isolated from an aqueous methanol extract of the inner bark of Betula pendula. Their structures were determined by NMR spectroscopy and mass spectrometry. The complete assignment of proton and carbon signals was achieved by 1D and 2D NMR experiments: selective 1D TOCSY, HSQC, HMBC and DQF-COSY.     

3-Oxo-1,3-oxathiolanes-synthesis and stereochemistry

The compound 3-oxo-1,3-oxathiolane (6) and its cis - and trans - 2-methyl (7,8), 4-methyl (9,10), 5-methyl (11,12) and 2-p-nitrophenyl (13,14) derivatives were prepared by oxidizing the corresponding 1,3-oxathiolanes (1-5) with NaIO4 in water. The oxides were purified and their isomers separated using thin layer chromatography. The structural characterization was carried out with 1H NMR spectroscopy and molecular modeling. Compounds 8-10, 12, and 14 attain the half-chair type conformation with O1 above and C5 below the plane (HC1), but 6, 7, 11, and 13 are, for steric reasons, the mixtures with the alternative half-chair (HC2), where O1 is below and C5 above this plane. Accordingly, 6 appears based on the values of experimental coupling constants as an 81:19, 7 as a 37:63, 11 as a 33:67 and 13 as a 54:46 mixture of HC1 and HC2, respectively. The relative energies of these conformations, the values of the vicinal H,H-coupling constants and 1H chemical shifts were estimated for compounds 6-12 also by computational methods and they support nicely the conclusions based on experimental data.     

2(S)‐Amino‐3‐[1H‐imidazol‐4(5)‐yl]­propyl cyclo­hexylmethyl ether di­hydro­chloride and 2(S)‐amino‐3‐[1H‐imidazol‐4(5)‐yl]­propyl 4‐bromo­benzyl ether di­hydro­chloride

(Cyclo­hexyl­methyl­oxy­methyl)(1H‐imidazol‐4‐io­methyl)‐(S)‐ammonium dichloride, C₁₃H₂₅N₃O⁺·2Cl^?, and (4‐bromo­benzyl)(1H‐imidazol‐4‐io­methyl)‐(S)‐ammonium dichloride, C₁₃H₁₈BrN₃O⁺·2Cl^?, are model compounds with different biological activities for evaluation of the hist­amine H3‐receptor activation mechanism. Both title compounds occur in almost similar extended conformations.     

Theoretical studies on the interaction of oleoyl sarcosine with the surface of apatite

Quantum chemical methods were used to study interactions of models of oleoyl sarcosine (N-oleoyl-N-methyl-amino carboxylic acid) with the Ca²⁺ ion and the surface calcium of apatite. Geometry optimizations revealed that oleoyl sarcosine can form either bidentate or tridentate structures with Ca²⁺ ions. Modification of the functional group in the sarcosine model to investigate its influence on the interaction energies showed that the interaction energies vary with the group. Comparison of interactions of the Ca²⁺ ions and the surface calcium of apatite showed the interaction energies to change with the functional group in a similar way.     

A Projected Algebraic Multigrid Method for Linear Complementarity Problems

We present an algebraic version of an iterative multigrid method for obstacle problems, called projected algebraic multigrid (PAMG) here. We show that classical algebraic multigrid algorithms can easily be extended to deal with this kind of problem. This paves the way for efficient multigrid solution of obstacle problems with partial differential equations arising, for example, in financial engineering.     

Analysis of Rotenoids by High Temperature High Resolution Gas Chromatography-Mass Spectrometry

A short glass capillary column coated with PS-090 (20% phenyl–80% methylpolysiloxane, of 10 m × 0.30 mm i.d.; with 0.1 μm film thickness) was used to analyze samples from Tephrosia candida; eighteen rotenoids were separated and identified without derivatization by HT-HRGC and HT-HRGC-MS. The mass spectra show the typical fragmentation pattern for rotenoids, with the base peaks either at M⁺, or originating from RDA (Retro Diels-Alder) rearrangements. HT-HRGC and HT-HRGC-MS were shown to be extremely valuable and neglected techniques for structural studies as well as the routine analysis of rotenoids in crude extracts. Possible applications to other classes of aromatic natural products, e.g. flavonoids, are envisaged.