Synthesis and mass spectrum of 3-(3′-pyridinyloxymethyl)pyridine and polarography of its dialkyl diquaternary salts

3-(3′-Pyridinyloxymethyl)pyridine is prepared by reaction of 3-hydroxymethylpyridine with 3-bromopyridine and converted to the 1,1′-dimethyl and 1,1′-diethyl diquaternary salts with alkyl iodides. The salts are reduced polarographically at a potential (E_o) of about - 1.02 to - 1.10 V in the pH range of 5.5-8.5.     

Palladium-Catalyzed Carbonylation and Coupling Reactions of Aryl Chlorides and Amines

The palladium-catalyzed amidation of electron-deficient aryl chlorides proceeds readily in the presence of low CO pressures and a slight excess of an iodide salt. The rates of amidation are accelerated over those without added salt, and iodide is preferred over bromide or chloride. More electron-rich aryl chlorides were not effectively amidated, either with or without added iodide. We postulate that an intermediate anionic palladium(0) iodide complex is responsible for the enhanced reactivity.     

Conformational Study of Naringenin in the Isolated and Solvated States by Semiempirical and Ab Initio Methods

Naringenin is a natural widespread flavanone occurring in different foodstuffs that presents several important biological activities. Although its properties are well documented, its mechanisms of action are still controversial. The present article reports a conformational analysis of naringenin, using the semiempirical AM1 and ab initio methods, at the Hartree–Fock level of theory. The 3-21G, 3-21G*, 6-31G, and 6-31G** basis sets were used. The electron correlation effects were included through the Møller–Plesset second-order perturbation theory. The solvation of naringenin has been investigated through the standard SCRF, the supermolecule (SM), and the combined SM/SCRF models. The results have shown that there are two degenerate forms of naringenin, differing mainly by the orientation of a hydroxyl group (C4—OH). The energy barrier for the interconversion between them is ca. 6 kcal.mol^–1, suggesting some conjugation between the -system of the aromatic B ring and the hydroxyl group (C4—OH).     

Electron-impact ionization of CCl4 and CCl2F2

Absolute partial and total cross sections for electron-impact ionization of CCl4 and CCl2F2 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for production of CCl3(+), CCl2(+), CCl+, C+, Cl2(+), and CCl3(2+) from CCl4; and for production of CCl(2)F+, CClF2(+), CClF(+), (CCl+ + CF2(+)), Cl+, CF+, F+, and C+ from CCl2F2. Data are also reported for formation of (CCl2(+),Cl+) and (CCl+, Cl+) ion pairs from CCl4. The total cross section for each target is obtained as the sum of the partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly charged ions is +/- 5-7 %. The present partial cross sections for lighter fragment ions are found to be considerably greater than had been previously reported but the most recent total cross section measurements agree well with those reported here. Neither the binary-encounter-Bethe theory nor the Deutsch-Mark theory reproduces the experimental cross sections correctly for both targets.     

Self-assembling a molecular pegboard

This paper describes the design, construction, and application of a self-assembled, chemically addressable DNA nanogrid composed of DNA tiles of nanometer dimensions. This self-assembled structure permits precise placement of molecules at predetermined locations on a "molecular pegboard". We used the indexed DNA nanogrids to identify single molecules of DNA that hybridize at particular locations.     

Energy transfer between 1,3-dimethylxanthine and europium(III) in aqueous solution

Luminescence of 1,3-dimethylxanthine in solution is impaired owing to collisional deactivation by solvent molecules and matrix interferences. Energy absorbed by 1,3-dimethylxanthine has been transferred to trivalent europium which emits narrow-band radiation in a region distant from background interferences. The enhanced luminescence of trivalent europium was utilized for the determination of 1,3-dimethylxanthine in buffered aqueous solution. An analytically useful range from 1.1 × 10^?5?5.0 × 10^?4 M and a detection limit of 1.1 × 10^?5 M were obtained. The methodology for the analytical procedure was determined.     

Developments on carbon dioxide reduction: Their promise,achievements, and challenges

CO₂ reduction processes continue to be developed for electrosynthesis, energy storage applications, and environmental remediation. A number of promising materials have shown high activity and selectivity to target reduction products. However, the progress has been mainly at a small laboratory scale, and the technical challenges of large scale CO₂ reduction have not been considered adequately. This review covers recent advancements in catalyst materials and cell designs. The leading materials for CO₂ reduction to a number of useful products are presented with their corresponding cell and reactor designs. The latest efforts to progress to industrially relevant scales are discussed, along with the challenges that must be met for carbon dioxide reduction to be a viable route for mass scale production.     

Probing charge-transfer processes in helium nanodroplets by optically selected mass spectrometry (OSMS): charge steering by long-range interactions

Electron impact ionization of a helium atom in a helium nanodroplet is followed by rapid charge migration, which can ultimately result in the localization of the charge on an atomic or molecular solute. This process is studied here for the cases of hydrogen cyanide, acetylene, and cyanoacetylene in helium, using a new experimental method we call optically selected mass spectrometry (OSMS). The method combines infrared laser spectroscopy with mass spectrometry to separate the contributions to the overall droplet beam mass spectrum from the various species present under a given set of conditions. This is done by vibrationally exciting a specific species that exists in a subset of the droplets (for example, the droplets containing a single HCN molecule). The resulting helium evaporation leads to a concomitant reduction in the ionization cross sections for these droplets. This method is used to study the charge migration in helium and reveals that the probability of charge transfer to a solvated molecule does not approach unity for small droplets and depends on the identity of the solvated molecule. The experimental results are explained quantitatively by considering the effect of the electrostatic potential (between the charge and the embedded molecule) on the trajectory of the migrating charge.     

Structures and anion-binding properties of M4L6 tetrahedral cage complexes with large central cavities

Reaction of the bis-bidentate bridging ligand L(3), in which two bidentate chelating 3(2-pyridyl)pyrazole units are separated by a 3,3'-biphenyl spacer, with Co(II) salts affords tetranuclear cage complexes of composition [Co(4)(L(3))(6)]X(8)(X =[BF(4)](-), [ClO(4)](-), [PF(6)](-) or I(-)) in which four 6-coordinate Co(II) ions in an approximately tetrahedral array are connected by six bis-bidentate bridging ligands, one spanning each of the six edges of the Co(4) tetrahedron. In every case, X-ray crystallography reveals that the 'apical' Co(II) ion has a fac tris-chelate geometry, whereas the other three Co(II) ions have mer tris-chelate geometries, resulting in (non-crystallographic)C(3) symmetry for the cages; that this structure is retained in solution is confirmed by (1)H NMR spectroscopy of the paramagnetic cages. In every case one of the anions is located inside the central cavity of the cage, with the remaining seven outside. We found no clear evidence for an anion-based templating effect. The cage superstructure is sufficiently large to leave gaps in the centres of the faces through which the internal and external anions can exchange. Variable-temperature (19)F NMR spectroscopy was used to investigate the dynamic behaviour of the cages with X =[BF(4)](-) and [PF(6)](-) in MeCN solution: in both cases two separate signals, corresponding to external and internal anions, are clear at 233 K which have coalesced to a single signal at room temperature. Analysis of the linewidth of the minor signal (for the internal anion) at various temperatures below coalescence gave an activation energy for anion exchange of ca. 50 kJ mol(-1) in each case, a figure which suggests that anion exchange can occur via a conformational rearrangement of the cage superstructure in solution rather than opening of the cavity by cleavage of metal-ligand bonds.     

Stereoselective conjugate addition of benzyl phenylsulfonyl carbanions to enoates derived from d-mannitol

The conjugate addition of benzylic phenylsulfonyl carbanions (2a'-d') to enoates derived from d-(+)-mannitol (E- or Z-1a-c) was studied using THF and THF/HMPA as solvent. Under kinetic conditions (-78 degrees C), enoate E-1a,b led to a mixture of syn-(R,S) and anti-(S,S) adducts (55/45), and syn-(R,S) adducts were the main product obtained ( approximately 90/10) from enoate Z-1a. Under thermodynamic conditions (-78 degrees C to room temperature) syn-(R,S) adducts were also preferentially formed ( approximately 90/10), despite the geometry at the double bond in the acceptor. Enoate 1c (E/Z = 57/43), bearing an additional benzyl group at the alpha-position, also reacted with carbanions 2'a,b, under thermodynamic conditions, leading to syn-adducts in excellent de (control at the three newly generated stereogenic centers). The adducts were quantitatively transformed into the corresponding beta-gamma-disubstituted gamma-butyrolactones and alpha,beta,gamma-trisubstituted gamma-butyrolactones. (1)H NMR studies (NOE and J-coupling) of these lactones allowed us to determine their configuration at the newly generated chiral centers. The reduction of the C-S bond in adducts syn-(R,S) with Na/Hg, followed by treatment of the resulting products in aqueous acid media, led to enantioenriched beta-benzyl-gamma-hydroxymethyl-gamma-butyrolactones. The conformational equilibrium of enoates E- and Z-1b was evaluated by theoretical calculations (ab initio, MP2/6-31G), and a mechanistic rationale was proposed to explain the observed stereoselectivities.