Reactions of alkynes with bis(triphenylphosphine)platinum-ethylene: A 31P-{1H} NMR study

Internally consistent assignments of the ³¹P-{¹H} NMR parameters of the complexes [Pt(RCCR′)(PPh₃)₂] are proposed, based on the premise that the magnitude of ¹J(PtP) depends mainly on the nature of the moiety CR trans to P. For a given R, ²J(PP) correlates with ¹J(PtP) for thebond trans to CR. The alkynes PhCCSnEt₃, PhCCSnPh₃, Me₃SiCCCl, Me₃SiCCBr, Et₃SiCCI and MeCCI undergo oxidative addition reactions with [Pt(C₂H₄)(PPh₃)₂]; the intermediate alkyne complex was detected for PhCCSnEt₃, Me₃SiCCCl and Me₃CCBr. The triyne Me(CC)₃Me forms platinum(0) complexes by coordination with the central or terminal CC bond and appears also to give a platinum(II) complex by oxidative addition.     

193-nm photodissociation of acryloyl chloride to probe the unimolecular dissociation of CH2CHCO radicals and CH2CCO

The work presented here uses photofragment translational spectroscopy to investigate the primary and secondary dissociation channels of acryloyl chloride (CH2==CHCOCl) excited at 193 nm. Three primary channels were observed. Two C-Cl fission channels occur, one producing fragments with high kinetic recoil energies and the other producing fragments with low translational energies. These channels produced nascent CH2CHCO radicals with internal energies ranging from 23 to 66 kcal/mol for the high-translational-energy channel and from 50 to 68 kcal/mol for the low-translational-energy channel. We found that all nascent CH2CHCO radicals were unstable to CH2CH + CO formation, in agreement with the G3//B3LYP barrier height of 22.4 kcal/mol to within experimental and computational uncertainties. The third primary channel is HCl elimination. All of the nascent CH2CCO coproducts were found to have enough internal energy to dissociate, producing CH2C: + CO, in qualitative agreement with the G3//B3LYP barrier of 39.5 kcal/mol. We derive from the experimental results an upper limit of 23 +/- 3 kcal/mol for the zero-point-corrected barrier to the unimolecular dissociation of the CH2CHCO radical to form CH2CH + CO.     

Tripyrrolidinophosphoric acid triamide as an activator in samarium diiodide reductions

The electrochemical and spectrophotometric characterization of the complex formed from samarium diiodide and 4 equiv of tripyrrolidinophosphoric acid triamide (TPPA) is presented. Kinetic studies indicate that the SmI(2)/TPPA complex possesses reactivity greater than the complex formed between samarium diiodide and 4 equiv of HMPA. Examples of the use of SmI(2)/TPPA in synthesis are presented.     

Non-nucleoside building blocks for copper-assisted and copper-free click chemistry for the efficient synthesis of RNA conjugates

Novel non-nucleoside alkyne monomers compatible with oligonucleotide synthesis were designed, synthesized, and efficiently incorporated into RNA and RNA analogues during solid-phase synthesis. These modifications allowed site-specific conjugation of ligands to the RNA oligonucleotides through copper-assisted (CuAAC) and copper-free strain-promoted azide-alkyne cycloaddition (SPAAC) reactions. The SPAAC click reactions of cyclooctyne-oligonucleotides with various classes of azido-functionalized ligands in solution phase and on solid phase were efficient and quantitative and occurred under mild reaction conditions. The SPAAC reaction provides a method for the synthesis of oligonucleotide-ligand conjugates uncontaminated with copper ions.     

Ferrocenyl-substituted fluorescent anthracenes and anthraquinones

The synthesis of a range of ferrocene-substituted ethynylanthracenes and 1,1^′-(bis-(2-ethenylanthraquinoyl)ferrocene has been achieved. The synthesis relies on the production of ferrocenylanthraquinones as key precursors. The products were obtained in the reactions of ferrocenylanthraquinones with phenylethynyllithium or trimethylsilylethynyllithium followed by reduction with tin chloride. The key products such as 1- and 2-ferrocenyl(9,10-bis-phenylethynyl)anthracenes have been characterised by X-ray single crystal diffraction.     

Parallel single-cell optical transit dielectrophoresis cytometer

In this work, we present an optical transit DEP flow cytometer for parallel single-cell analysis. Each cell's dielectric property is inferred from velocity perturbations due to DEP actuation in a microfluidic channel. Dual LED sources facilitate velocity measurement by producing two transit shadows for each cell passing through the channel. These shadows are detected using a 256-pixel linear optical array detector. Massively parallel analysis is possible as each pixel of the detector can independently analyze the passing cells. A wide channel (∼18 mm) was employed to carry many particles simultaneously, and the system was capable of detecting the velocity of over 200 cells simultaneously. We have achieved analysis rates for 10 µm diameter polystyrene spheres response exceeding 250 per second. With appropriate calibration, this DEP cytometer can quantitatively measure the dielectric response. The dielectric response (Clausius–Mossotti factor) of viable CHO cells was measured over the frequency range of 100 kHz to 6 MHz, and the obtained response matches the previously measured values by our group. The DEP cytometer uses simple modular components to achieve high throughput label-free single-cell dielectric analysis and can begin analyzing particles within 10 s after starting to pump the sample into the channel.     

Enantioselective total synthesis of (-)-kibdelone C

The kibdelones are aromatic polyketide natural products featuring isoquinolinone and tetrahydroxanthone ring systems. They display potent cytotoxicity toward a range of human cancer cell lines. Here, we present an enantioselective total synthesis of kibdelone C that utilizes a Shi epoxidation to establish the absolute and relative stereochemistry, an acid-catalyzed cyclization to form the tetrahydroxanthone, and a C-H arylation to complete the hexacyclic skeleton.     

The Crystal and Molecular Structure of Bis(cyclopentadienyldicarbonylchromium) (CrCr)

The crystal structure of bis(cyclopentadienyldicarbonyl-chromium) has been determined by x-ray diffraction. The compound crystalizes in the triclinic system, space group P1¯(C¹_i, No. 2) with unit cell parameters: a, 7.829(3); b, 14.543(6); c, 6.588(2)Å; α, 94.67(3), β, 110.70(3); γ, 104.04°(3); V, 699.1(4)ų; z=2. There are two independent molecules per unit cell located at the inversion centers at O,O,O and O, 1/2, O. The CrCr bond distances are, respectively 2.200(3) and 2.230(3), thus supporting their formulation as triple bonds. The CpCrCr angles in the two molecules are 165.0° and 158.7°, respectively. The structural features are compared with those of Cp₂Mo₂(CO)₄, which has a linear CpMoMoCp axis; and the differences rationalized in terms of electronic interactions of the Cp-ligand with the orbitals of the M₂ unit. The differences observed in the structures of the two independent molecules are also related to the proposed bonding model and to packing considerations.     

Anionic-initiated polymerization of β-nitrostyrenes

β-Nitrostyrene and many of its derivatives have been shown to yield high polymers via anionic initiation with alkoxide ions in protic solvents, e.g., alcohols. A study was conducted to determine the effect of certain substituents on the polymerization characteristics of representative monomers of this series and the properties of their polymers. A kinetic study was conducted and the relative rates of propagation were unexpectedly found to correlate well with brown's σ⁺ values. The rates of initiation of two representative monomers, β-nitrostyrene and p-methoxy-β-nitrostyrene, with sodium ethoxide were found to be 3.51 and 2.86 liter/mole sec, respectively. The rate of chain transfer in ethanol was studied qualitatively by using gel-permeation chromatography (GPC) to obtain molecular weight distribution (MWD) curves. The low values of the M _w/M _n ratios indicated little chain transfer in the protic solvent.     

Synthesis and Characterization of Water-Soluble Starch-Acrylamide Graft Copolymers

A series of water-soluble starch-polyacrylamide graft copolymers (ST-g-PAM) were prepared by Ce⁴⁺-initiated graft copolym-erizations of acrylamide (AM) onto starch (ST) dissolved in water at 30°C. The copolymers were found to contain 3-33% (wt) of ST. The structure of the copolymers, including the average number of grafts per chain and the efficiency of the initiator, was determined by acid-catalyzed degradation of the ST followed by size exclusion chromatography (SEC) analysis of the PAM chains and was found to be consistent with the presence or absence of free ST in the polymerization product prior to hydrolysis. The average number of grafts per starch molecule was found to be three or less, depending on conditions. The initiator efficiency (6–43%) was shown to decrease with increasing [Ce⁴⁺] and decreasing [AM], and this was found to be qualitatively in accord with the proposed mechanism of initiation and polymerization. The low efficiency was shown to be due, in part, to the low rate of reaction of Ce⁴⁺ compared to the polymerization rate. The copolymers were characterized by ultra-centrifugation, SEC, and viscometry.