Polymerization of tetrahydrofuran: A radiochemical study of the initiation mechanism

¹⁴C-tagged triphenylmethyl hexachloroantimonate was used to initiate the polymerization of THF. An activity count on the polymers indicated no incorporation of initiator fragments into the macromolecule. On ascertaining the fate of the tagged trityl fragment it was found that the activity resided in the triphenylmethane isolated from the methanol supernatant. This indicates that at least one sequence of the initiation reaction in this polymerization involves hydride ion abstraction.     

The rotational spectrum and structure of the phosphine-hydrogen cyanide complex

The rotational spectrum of the weakly bound complex (PH₃, HCN) in its vibrational ground state has been observed by the technique of pulsed-nozzle, Fourier-transform microwave spectroscopy. The isotopic species (PH₃, HC¹⁴N), (PH₃, DC¹⁴N) and (PH₃, HC¹⁵N) exhibit spectra of the symmetric-top type from which accurate values of the spectroscopic constants B₀, D_J, D_JK and X_aa(¹⁴N) have been determined. For (PH₃, HC¹⁴N) the appropriate values are: B₀ = 1553.3709(1) MHz, D_J = 3.306(3) kHz, D_JK = 256.9(6) kHz and X_aa(¹⁴N) = ?4.3591(14) MHz. The geometry of the complex established from the spectroscopic constants is one of C_3v symmetry at equilibrium, with the HCN molecule lying along the C₃ axis of PH₃ and oriented so that it forms a hydrogen bond to the P atom. The effective distance from P to the C nucleus is r(P ? C) = 3.913 Å.     

The geometry and intermolecular binding of HCN…BrC1 probed by rotational spectroscopy

Ground-state rotational spectra of several isotopomers of a linear complex formed between HCN and BrCl were observed by pulsed-nozzle, F-T microwave spectroscopy and analysed to give the spectroscopic constants B₀, D_J, _χ(Br), _χ(Cl), and M_bb(Br). The order HCN…BrCl of the nuclei was established from the changes in the B₀ values on isotopic substitution. The small fractional electronic charge (δ ≈ 0.05) transferred from Br to Cl on complex formation and the intermolecular stretching force constant (k_σ ≈ 11 N m⁻¹) estimated from the spectroscopic constants indicates a weak interaction of HCN and BrCl, with little perturbation of the charge distribution of BrCl.     

First-order stark effect and electric dipole moment of H3P … HC15N by pulsed-nozzle fourier-transform microwave spectroscopy

The first-order Stark effect in the J = 4 ← 3, K = 1 transition of the weakly bound dimer H₃P … HC¹⁵ N has been obeserved and measured by pulsed-nozzle Fourier-transform microwave spectroscopy under the selection rules ΔM = O and ΔM = ± 1. The electric dipole moment μ= 4.046(47) D determined for H₃P … HC¹⁵ N has been interpreted in terms of an enhancement Δμ = 0.60 D on dimer formation.     

Immobilized metal-ion affinity chromatography of recombinant Fab protein OPG C11 in the presence of EDTA-Mg(II)

Undesired adsorption of host cell proteins poses a big challenge for immobilized metal-ion affinity chromatography (IMAC) purification. In this study, by using His6-tagged protein Fab OPG C11 from Escherichia coli fermentation as a model, we found that the presence of low concentrations of EDTA-Mg2+ in feed streams weakens the adsorption but makes it more specific towards polyhistidine tag. By combining EDTA-Mg2+ treatment and periplasmic extraction, we developed a one-step purification procedure for His6-tagged recombinant Fab OPG C11 using Ni-IDA (iminodiacetic acid) chromatography. This procedure eliminated the buffer exchange step after periplasmic extraction, which is usually required before IMAC in order to remove EDTA. In addition to savings on time and cost, this procedure eliminates undesired adsorption of most host cell proteins thus significantly improves the purity of polyhistidine-tagged recombinant proteins. The strategy of EDTA-Mg2+ treatment may have general application potentials.     

The synthesis and evaluation of trimeric X-ray contrast agents

Novel trimeric iodinated contrast agents with low osmolality have been prepared and evaluated with the aim of improving the already good safety profile of such agents. While the aim of low osmolality was achieved, the viscosity of the trimeric agents was found to be generally higher than current dimeric agents in clinical use.     

Chordal decomposition in operator-splitting methods for sparse semidefinite programs

Mathematical Programming - We employ chordal decomposition to reformulate a large and sparse semidefinite program (SDP), either in primal or dual standard form, into an equivalent SDP with smaller...     

Simultaneous determination of free-form amphetamine in rat's blood and brain by in-vivo microdialysis and liquid chromatography with fluorescence detection

The determination of amphetamine in rat's blood and brain simultaneously by micordiaysis technique and HPLC/fluorescence derivatization is described. Microdiaysis is used to sample rat's blood and brain fluid and the amphetamine content is evaluated by HPLC/fluorescence derivatization assay. Dansyl chloride is used as fluorescence derivatization reagent. The detection limit, linearity and precision associated with this assay were evaluated. Pharmarcokinetic parameters of amphetamine in rat's blood and brain are also reported.