A metallosupramolecular tetrahedron with a huge internal cavity

A huge molecular tetrahedral complex forms quantitatively by self-assembly from four ligands L-H6 and four titanium(IV) ions; in the solid state it encapsulates four [K(DIMF)3]+ units in its interior.     

Total synthesis of LL-Z1640-2 utilizing a late-stage intramolecular Nozaki-Hiyama-Kishi reaction

A total synthesis of LL-Z1640-2 (2), a potent and selective kinase inhibitor, has been completed. The key step of the convergent synthesis utilized a late-stage intramolecular Nozaki-Hiyama-Kishi (NHK) reaction to close the macrocycle at the C6′-C7′ bond.     

Total synthesis of anhydrolycorinone utilizing sequential intramolecular Diels-Alder reactions of a 1,3,4-oxadiazole

A convergent total synthesis of anhydrolycorinone is detailed, enlisting sequential intramolecular Diels-Alder reactions of a suitably substituted 2-amino-1,3,4-oxadiazole defining a novel oxadiazole --> furan --> benzene Diels-Alder strategy.     

Simultaneous multi-element analysis by inductively-coupled plasma emission spectrometry utilizing micro-sampling techniques with internal standard

A micro-sampling technique, which requires sample volumes of less than 100 μl, is used for multi-element analysis by i.c.p. emission spectrometry. One drop of sample solution in a teflon cup is nebulized through a capillary tube. Internal standardization with yttrium improves the precision of measurement. The method is applied to the analysis of serum and whole blood samples, after dilution or digestion.     

Specific molecular recognition by cage-type cyclophanes having a helically twisted and cylindrical internal cavity

Cage-type cyclophanes, which are constructed with two rigid 2,11,20-triaza[3.3.3]paracyclophane skeletons and three chiral bridging components, were prepared. Temperature-dependent ¹H NMR measurements in (CD₃)₂SO indicate that the molecular framework of the cage-type cyclophane having a cylindrical internal cavity is more rigid than those of the corresponding non-cage hosts. The guest-binding behavior of the cage-type hosts toward various guests was examined by electronic absorption spectroscopy and electrospray ionization (ESI) mass spectrometry. The present hosts were found to bind anionic guests, such as 1-hydroxy-2,4-dinitronaphthalene-7-sulfonate, 2-hydroxy-1-(phenylazo)naphthalene-6,8-disulfonate, 2,7-bis[(4-methyl-2-sulfophenyl)azo]-1,8-dihydroxynaphthalene-3,6-disulfonate, 8-anilinonaphthalene-1-sulfonate, 6-p-toluidinonaphthalene-2-sulfonate, naphthalene-1-sulfonate, and 3,5-bis(methoxycarbonyl)benzene-1-sulfonate, to form host-guest complexes. The computer-aided molecular modeling study reveals that the three pyridinium moieties bound to the chiral - and -valine residues in the bridging segments undergo chiral twist in the same directions. However, the twisted direction in the host bearing -valine residues is opposite to that evaluated for the host bearing -valine residues so that the former and latter cage-type cyclophanes furnish M and P-helical cavities, respectively, as reflected in their circular dichroism (CD) spectra. The chirality-based molecular recognition of the cage-type hosts toward enantiomeric guests such as bilirubin-IX and pamoic acid in aqueous media was investigated by CD spectroscopy.     

Total synthesis of (+)-isoschizandrin utilizing a samarium(II) iodide-promoted 8-endo ketyl-olefin cyclization

The 13-step synthesis of (+)-isoschizandrin reported herein features a samarium(II) iodide-promoted 8-endo ketyl-olefin coupling to assemble the eight-membered ring present in the target concomitantly with the required functionality and stereochemistry. In constructing (+)-isoschizandrin as a single atropisomer, the synthesis utilizes a kinetic resolution of a seven-membered lactone using a CBS-oxazaborolidine.     

Total synthesis of acosamine and daunosamine utilizing a diastereoselective intramolecular [3+2] cycloaddition

A total synthesis of daunosamine (3) and acosamine (4) has been accomplished via a diastereoselective intramolecular nitrone-olefin cyclization. In the key step the chiral nitrone 12a cyclized to give two isoxazolidines 13a and 14a in an 82:18 ratio. Further elaboration of 13a led to daunosamine and acosamine. The effects of olefin substitution on the diastereoselectivity of the cycloaddition was also examined.     

Characterization of a capacitance-coupled contactless conductivity detection system with sidewall electrodes on a low-voltage-driven electrophoresis microchip

A new type of capacitance-coupled contactless conductivity detection (C⁴D) system with sidewall electrodes was proposed for integration on a silicon-on-isolator–poly(dimethylsiloxane) (SOI-PDMS) hybrid low-voltage-driven electrophoresis microchip. By a microelectromechanical system process, the sidewall electrodes were fabricated precisely at either side of the separation channel. The area of the capacitor electrodes was the maximum value to improve the detection sensitivity with an enhanced capacitance effect. According to the simulation results, the structural parameters of the sidewall electrodes were determined as 550-μm length, 15-μm width, 80-μm separation distance, and 1-μm isolator thickness. The integrated microdevice with the SOI-PDMS hybrid electrophoresis microchip was very compact and the size was only 15 cm × 15 cm × 10 cm (width × length × height), which permitted miniaturization and portability. The detector performance was evaluated by K⁺ testing. The detection limit of the conductivity detector was determined to be 10^-9 and 10^-6 M for K⁺ in the static and electric-driven modes, respectively. Finally, the C⁴D was applied to low-voltage-driven electrophoresis on a microchip to carry out real-time measurement of the separation of amino acids. The separations of 10^-4 M lysine and phenylalanine in the low-voltage-driven electrophoresis mode were performed with an electric field of 300 V/cm and were completed in less than 15 min with a resolution of 1.3. The separation efficiency was found to be 1.3 × 10³ and 2.8 × 10³ plates for lysine and phenylalanine, respectively, with a migration time reproducibility of 2.7 and 3.2%. The conductivity detection limit of amino acids achieved was 10^-6 M. The proposed method for the construction of a novel C⁴D integrated on an SOI-PDMS hybrid low-voltage-driven electrophoresis microchip showed the most extensive integration and miniaturization of a microdevice, which is a further crucial step toward the realization of the “lab-on-a-chip” concept.     

Quantitation of formate by solid-phase microextraction and gas chromatography--mass spectrometry utilizing a [13C]formate internal standard

A new method for the analysis of formic acid was developed using gas chromatography-electron impact ionization mass spectrometry in the selected ion monitoring mode and solid-phase microextraction. Using this method with [13C]formic acid as an internal standard, the peak area ratio of [12C]formic acid/[13C]formic acid was not affected by differing methanol or sulfuric acid concentrations during the esterification and fiber adsorbing step. In comparison, the peak area ratio of formic acid/acetonitrile as detected by conventional GC with flame ionization detection was greatly affected by methanol or sulfuric acid concentrations. The formic acid calibration curve of our method showed excellent linearity over the range 5 to 200 microM. The within- and between-run assay relative standard deviations for the formic acid concentration were all less than 1.70%.     

Total synthesis of optically active lycopladine A by utilizing diastereoselective protection of carbonyl group in a 1,3-cyclohexanedione derivative

We successfully synthesized two enantiomers of bicyclic enones, (7R,7aR)- and (7S,7aS)-9, from the hemiacetal 2a, which we first synthesized from the symmetrical diketone 1a via diastereoselective carbon-oxygen bond formation between one of the carbonyl groups and the chiral alcohol on the C2 side chain in a 2,2-disubstituted 1,3-cycloalkanedione derivative. We also report the total synthesis of natural (+)-lycopladine A [(+)-6] from (7R,7aR)-9 and the formal synthesis of unnatural (-)-lycopladine A [(-)-6] from (7S,7aS)-9.     

Considerations in the design of a microwave induced plasma utilizing the TM010 cavity for optical emission spectroscopy

A procedure is presented to determine the resonant frequency shift of the TM₀₁₀ cavity when dielectric material (the plasma discharge tube) is inserted. This allows convenient adjustment of the cavity diameter to yield a resonance frequency near 2.450 GHz when the plasma is ignited.The design of a unique plasma discharge tube is presented. This discharge tube utilizes a tangential plasma support gas flow (He or Ar) to generate a suspended plasma discharge which does not touch the wall of the discharge tube. The resulting discharge has superior spatial and temporal stability compared to previously reported plasma discharges.The use of TM₀₁₀ resonant cavities having 2 and 3 cm internal thicknesses is discussed. These cavities result in physically longer plasmas providing greater analyte residence times and enhanced analytical performance. Results with and without prior aerosol desolvation are presented.     

High-resolution cavity ringdown spectroscopy with a Fabry–Perot etalon at the cavity output

We demonstrate a cavity ringdown spectrometer that affords a frequency resolution higher than the conventional limit imposed by the bandwidth of a pulsed laser source. A Fabry–Perot etalon at the exit of a ringdown cavity disperses the frequency components of a broadband ringdown signal spatially, permitting a narrow-linewidth spectral measurement based on single-exponential decay signals. A proof of principle experiment is presented with the P(9) transition of the [50]_10⁰0⁰ band of C₂H₂. This technique is expected to be useful for in situ monitoring molecular concentration.     

The flame height of rectangular pool fires bounded by a sidewall with different distances and aspect ratios

Journal of Thermal Analysis and Calorimetry - This paper presents an investigation on the flame height of rectangular pool fires bounded by a sidewall. A series of experiments were conducted to...     

Högberg compounds with a functionalized box-like cavity

Preparations of the Högberg compounds (Ia–e) with functionalized box-like cavities, designed for complexation of soft cations like silver and copper(II), are described. The structure of1a was determined by X-ray analysis.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Marangoni natural convection in a cubical cavity filled with a nanofluid

Journal of Thermal Analysis and Calorimetry - Natural convection in a differentially heated cubical cavity filled with a water-based nanofluid under the Marangoni effect from the upper free surface...     

Chiral selector with multiple hydrogen-bonding sites in a macrocyclic cavity

Chiral macrocycles with the hydrogen bond donor/acceptor sites in the cavity were synthesized and covalently bonded to silica gel to give chiral stationary phases (CSPs), which showed excellent abilities to resolve various chiral compounds, such as benzoin and Co(acac)3, in HPLC. Various organic solvents could be used as the mobile phase to optimize the resolution efficiency of CSPs, and in some cases, even MeCN, MeOH, and CO(2) could be used for the complete resolution of enantiomers.     

Assay of cholesterol 7 alpha-hydroxylase utilizing a silica cartridge column and 5 alpha-cholestane-3 beta, 7 beta-diol as an internal standard

A simplified and accurate assay of cholesterol 7 alpha-hydroxylase activity using 5 alpha-cholestane-3 beta,7 beta-diol as an internal standard is described. Endogenous microsomal cholesterol was used as the substrate. Following incubation and addition of the internal standard, lipids extracted from the incubation mixture were applied to Bond-Elut silica cartridge columns. 7 alpha-Hydroxycholesterol, 7 beta-hydroxycholesterol, 7-ketocholesterol and the internal standard were quantitatively recovered by eluting the column with 6 ml of benzene-ethyl acetate (2:3, v/v) after removal of cholesterol with 6 ml of benzene-ethyl acetate (9:1, v/v). After trimethylsilylation, the mass of 7 alpha-hydroxycholesterol was determined by capillary gas chromatography with selected-ion monitoring. The method permits a faster, easier and more sensitive determination of the activity of cholesterol 7 alpha-hydroxylase in small samples.     

Restricted rotational motion of CO in a protein internal cavity: evidence for nonseparating correlation functions from IR pump-probe spectroscopy

The strongly restricted orientational motion of CO molecules trapped in the Xe4 internal cavity of myoglobin mutant L29W-S108L is investigated by polarization-dependent mid-infrared pump-probe spectroscopy at cryogenic temperatures. Following an ultrafast initial decay, the signal anisotropy reaches an asymptotic value that is significantly larger than the prediction from the well-known relation [see text], based on previously established potential parameters. This discrepancy is explained by showing that the full four-point correlation function describing third-order spectroscopy [see text] does not factorize in systems where its fast decay is dominated by restricted reorientation of the transition dipole moments.