Self-crosslinkable polymers. I. Copolymerization of glycidyl methacrylate with 2-vinylpyridine and 2-vinyl-5-ethylpyridine

A soluble and self-crosslinkable linear copolymer with pendant epoxy and pyridyl groups was obtained from glycidyl methacrylate (M₁) and 2-vinylpyridine (M₂) or 2-vinyl-5-ethylpyridine (M₂) by the action of azobisisobutyronitrile. The monomer reactivity ratios were determined in tetrahydrofuran at 60°C: r₁ = 0.510, r₂ = 0.620 with 2-vinylpyridine and r₁ = 0.57, r₂ = 0.62 with 2-vinyl-5-ethylpyridine. These were consistent with the calculated values with the reported Q and e values for these monomers. The intrinsic viscosities of the copolymers with 2-vinylpyridine and with 2-vinyl-5-ethylpyridine were found to be 0.17–0.19 and 0.26–0.38, respectively, in tetrahydrofuran at 30°C; they were independent of the copolymer composition. The copolymers were amorphous, had no clear melting points, and became insoluble crosslinked polymers under heating without further addition of any curing agents.     

Determination of very low levels of inorganic and organic mercury in natural waters by cold-vapor atomic absorption spectrometry after preconcentration on a chelating resin

Inorganic and organic mercury at ng l^?1 levels in fresh waters are collected simultaneously on a column of a dithiocarbamate-treated resin and quantitatively eluted with slightly acidic aqueous thiourea solution. Mercury vapor is generated from inorganic mercury by reduction with alkaline SnCl₂ solution, and from inorganic and organic mercury with a CdCl₂SnCl₂ solution, for determination by cold-vapor atomic absorption spectrometry. The range of determination is 0.2–5,000 ppt (ng l^?1) for 20-l water samples.     

Block copolymer from α,ω-dihydroxyl polystyrene and polyethylene glycol

α,ω-Dihydroxyl polystyrene was synthesized by the addition of styrene oxide to polystyryl dianion initiated with sodium naphthalene. Diglyme was found to be an unsuitable solvent for the preparation of low molecular weight compounds. Block copolymerization of the α,ω-dihydroxyl polystyrenes (M?_n = 2250, 3140, and 6200) with poly(ethylene glycols) (M?_n = 404, 1960, and 5650) was pursued by introducing urethane linkages with 4,4′-diphenylmethane diisocyanate. The mechanical, thermal, and viscoelastic properties, solution viscosity, molecular weight distribution, and moisture absorption of the block copolymers obtained were examined. Incorporation of styrene blocks was found to disturb the crystallization and fusion of poly(ethylene glycol) blocks. Films cast from benzene solution were soft and elastic and absorbed up to 5.8% moisture.     

Asymmetric synthesis of permethric acid. stereochemistry of chiral copper carbenoid reaction

The most effective optical isomer (1$\text{R}$-$\text{cis}$) of permethric acid ($\text{2}$, R = H), a potent intermediate in the production of synthetic pyrethroid, was enantioselectively prepared.     

Magnetic susceptibilities of UO2ThO2 solid solutions

The magnetic susceptibility of UO₂ThO₂ solid solutions has been measured from room temperature to 2.0 K. The magnetic moment and the Weiss constant have been determined in the temperature range in which the Curie-Weiss law holds. For the solid solutions showing antiferromagnetic transition, the Néel temperature has been also determined. These values decrease monotonically with increasing ThO₂ concentration. The results were analyzed using the molecular field theory which includes the interaction between next-nearest neighbor spins. The interactions between nearest neighbor spins, J₁, and those between next-nearest neighbor spins, J₂, both decrease with increasing ThO₂ concentration. The change of J₁ with composition is larger than that of J₂. The effect of magnetic dilution with ThO₂ is considered to be stronger on the interaction between nearest neighbor uranium ions.     

Rate constant of the reaction of NO3 with CH2I2 measured with use of cavity ring-down spectroscopy

We have applied cavity ring-down spectroscopy to a kinetic study of the reaction of NO₃ with CH₂I₂ in 25–100 Torr of N₂ diluent at 298 K. The rate constant of reaction of NO₃ + CH₂I₂ is determined to be (4.0 ± 1.2) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ in 100 Torr of N₂ diluent at 298 K. The rate constant increases with increasing pressure of buffer gas below 100 Torr. The reaction of CH₂I₂ with NO₃ has the potential importance at nighttime in the atmosphere.     

Contribution of individual zinc ligands to metal binding and peptide folding of zinc finger peptides

Little is known about the contribution of individual zinc-ligating amino acid residues for coupling between zinc binding and protein folding in zinc finger domains. To understand such roles of each zinc ligand, four zinc finger mutant peptides corresponding to the second zinc finger domain of Sp1 were synthesized. In the mutant peptides, glycine was substituted for one of four zinc ligands. Their metal binding and folding properties were spectroscopically characterized and compared to those of the native zinc finger peptide. In particular, the electronic charge-transfer and d-d bands of the Co(II)-substituted peptide complexes were used to examine the metal coordination number and geometry. Fluorescence emission studies revealed that the mutant peptides are capable of binding zinc despite removing one ligand. Circular dichroism results clearly showed the induction of an alpha-helix by zinc binding. In addition, the structures of certain mutant zinc finger peptides were simulated by molecular dynamics calculation. The information indicates that His23 and the hydrophobic core formed between the alpha-helix and the beta-sheet play an essential role in alpha-helix induction. This report demonstrates that each ligand does not contribute equally to alpha-helix formation and coordination geometry in the zinc finger peptide.     

NMR assignment methods for the aromatic ring resonances of phenylalanine and tyrosine residues in proteins

The unambiguous assignment of the aromatic ring resonances in proteins has been severely hampered by the inherently poor sensitivities of the currently available methodologies developed for uniformly 13C/15N-labeled proteins. Especially, the small chemical shift differences between aromatic ring carbons and protons for phenylalanine residues in proteins have prevented the selective observation and unambiguous assignment of each signal. We have solved all of the difficulties due to the tightly coupled spin systems by preparing regio-/stereoselectively 13C/2H/15N-labeled phenylalanine (Phe) and tyrosine (Tyr) to avoid the presence of directly connected 13C-1H pairs in the aromatic rings. The superiority of the new labeling schemes for the assignment of aromatic ring signals is clearly demonstrated for a 17 kDa calcium binding protein, calmodulin.     

Conversion of antennapedia homeodomain to zinc finger-like domain: Zn(II)-induced change in protein conformation and DNA binding

From the standpoint of protein dynamics and metalloprotein design, it is interesting to create an artificial protein which induces structural change and regulates its function by metal-ion binding. We engineered a novel protein, "Antennafinger (Ant-F)", whose structure and function can be controlled with Zn(II), by introducing the consensus sequence of a Cys(2)His(2)-type zinc finger protein into a non-metalloprotein scaffold, an Antennapedia homeodomain mutant (Ant-wt), selected using a motif-searching system. The circular dichroism studies demonstrate that Ant-F has secondary structures similar to Ant-wt and also changes its conformation due to Zn(II)-binding. The optical absorption spectra of the Co(II) complexes of Ant-F and its derivative proteins suggest that the geometry of the metal center of holo-Ant-F is tetrahedral and that the mutated Cys(2)His(2) residues are involved in the complex formation. In addition, the gel mobility shift assay reveals that the DNA binding activity of Ant-F can be regulated through Zn(II)-induced structural alteration. These results provide valuable information about the dynamic properties of proteins and a novel concept for metalloprotein design.     

Diastereoselective imino-aldol condensation of chiral 3-(p-Tolylsulfinyl)-2-furaldimine and ester enolates

(Ss)-3-(p-Tolylsufinyl)-2-furaldimine was synthesized, and condensation of the chiral furaldimine with lithium ester enolates has been examined. The product distribution of the reaction is dependent upon reaction conditions and on the kind of the substituent placed on the esters. Disubstituted ester enolate resulted in the exclusive formation of (4R)-beta-lactam, while unsubstituted, tert-butyl ester enolate preferentially gave (3R)-beta-amino ester. With the monosubstituted ester enolates, the condensation afforded (4R)-beta-lactams and/or (3R)-beta-amino esters as major products. This method has been applied to an efficient route to chiral furyl beta-lactams.