Microwave spectrum and conformational composition of 1-vinylimidazole

The microwave spectrum of 1-vinylimidazole has been investigated in the 21-80 GHz spectral region. The spectra of two conformers have been assigned. One of these forms is planar, while the other is nonplanar with the imidazole ring and the vinyl group forming an angle of 15(4)° from coplanarity. The planar form is found to be 5.7(7) kJ/mol more stable than the nonplanar rotamer by relative intensity measurements. The spectra of 10 vibrationally excited states of the planar form and one excited-state spectrum of the nonplanar form were assigned. The vibrational frequencies of several of these states were determined by relative intensity measurements. The microwave work has been augmented by quantum chemical calculations at the CCSD/cc-pVTZ, MP2/cc-pVTZ, and B3LYP/cc-pVTZ levels of theory. The B3LYP calculations predict erroneously that both forms of 1-vinylimidazole are planar, whereas the MP2 and CCSD calculations correctly predict the existence of a planar and a nonplanar conformer of this compound.     

Complexation of metal ion with poly(1-vinylimidazole) resin prepared by radiation-induced polymerization with template metal ion

Poly(1-vinylimidazole) (PVI) resin was prepared with Ni²⁺, Co²⁺, or Zn²⁺ as a template to study the adsorption of metal ions. The metal-1-vinylimidazole complex was copolymerized and crosslinked with 1-vinyl-2-pyrrolidone by γ-ray irradiation and the template metal ion was removed by treating the polymer complex with an acid. These PVI resins adsorbed metal ions more effectively than the PVI resin prepared without the template. The number of adsorption sites (As) and the stability constant (K) of Ni²⁺ complex were larger for the PVI resin prepared with the Ni ion template, caused by the smaller dissociation rate constant of Ni ion from the resin. The composition of the Ni²⁺ complex in the resin remained constant. This suggests that the complexation proceeded via a one-step mechanism.     

Palladium(II) Complexes of 1-vinylimidazole

Two new co-ordination compounds of Pd^II with 1-vinylimidazole of the formulae [PdL₄]Cl₂·3H₂O and trans-[PdL₂Cl₂], where L is a 1-vinylimidazole molecule, have been obtained. The compounds were characterised by spectroscopic, molar conductivity, thermogravimetric and magnetochemical measurements. Single crystal X-ray structure analyses of the complexes were also carried out. The compounds are diamagnetic with square-planar coordinatination around the palladium(II) ions. Other physico-chemical properties of the both complexes are compatible with their structures.     

4(5)-vinylimidazole by dehydrobromination of 1-triphenylmethyl-4-(2-bromoethyl)imidazole

1-Triphenylmethyl-4-(2-bromoethyl)imidazole undergoes elimination upon basic treatment providing an easy approach to 4(5)-vinylimidazole whereas the N-unsubstituted analogue leads only to substitution products.     

Monolithic rod columns for HPLC based on divinylbenzene-styrene copolymer with 1-vinylimidazole and 4-vinylpyridine

Monolithic chromatographic columns for HPLC based on divinylbenzene-styrene both with 1-vinylimidazole and with 4-vinylpyridine are prepared. The monoliths were synthesized in glass tubes with the inner diameter of 2?mm. Texture, hydrodynamic and chromatographic properties of the prepared columns were studied. Linear solvation energy relationships model was applied for the characterization of columns selectivity It is shown that changing the on 1-vinylimidazole or 4-vinylpyridine content in the initial solution allows to change the selectivity of the columns. An examples of small molecules and some proteins separations are presented.     

Esterolytic activity of imidazole-containing polymers. Hydrophobic influences in copoly[1-alkyl-4- or 5-vinylimidazole/4(5)-vinylimidazole]-catalyzed hydrolysis of 3-nitro-4-acyloxybenzoic acids

Water-soluble copolymers containing imidazole and N-alkylated imidazole pendant groups have been synthesized in order to investigate the hydrophobic interactions between polymeric catalysts and long alkyl chain ester substrates. Copoly[1-methyl-4-vinyl-imidazole/4(5)-vinylimidazole],copoly[1-methyl-5-vinylimidazole/4(5)-vinylimidazole], copoly[1-ethyl-5-vinylimidazole/4-(5)-vinyl-imidazole] and copoly[1-propyl-5-vinylimidazole/4(5)-vinylimidazole] were synthesized and their catalytic activity toward 3-nitro-4-acyloxybenzoic acid substrates (S_n^?) was determined in 28.5% ethanol–water and in water and compared with that of the mixtures of homopolymers. Hydrophobic interactions were important for rate enhancement of the hydrolysis of long-chain ester substrates compared to that of short-chain ester substrates. The copolymers catalyzed the hydrolysis of 3-nitro-4-dodecanoyloxy-benzoic acid (S₁₂^?) about two times faster than the mixtures at pH 7.11 in 28.5% ethanol–water. The hydrolysis of S₁₂^? by the copolymers was about five times faster in water than 28.5% ethanol–water.     

Electrosynthesis of metal-containing polymeric coatings based on 1-vinylimidazole and acrylamide

Possibility of electrochemical formation of metal-polymeric nanocomposites and coatings on purely iron and steel electrodes by combining the electrochemically initiated (co)polymerization of 1-vinylimidazole and acrylamide with the cathodic deposition of metals was studied. Polymeric coatings were formed by the method of contact exchange of metals. The structure and selected properties of metal-polymeric coatings were examined. It was found that silver nanoparticles are uniformly distributed in the polymeric matrix. A thermogravimetric analysis demonstrated that the metal-polymers synthesized possess a high thermal stability.     

Esterolytic activity of imidazole-containing polymers. Synthesis and characterization of copoly[1-alkyl-4- or 5-vinylimidazole/4(5)-vinylimidazole] and its catalytic activity in the hydrolysis of p-nitrophenyl acetate

The water-soluble monomers, 1-methyl-4-vinylimidazole, 1-methyl-5-vinylimidazole, 1-ethyl-5-vinylimidazole, and 1-propyl-5-vinylimidazole have been synthesized, polymerized, and copolymerized with 4(5)-vinylimidazole. The copolymers were characterized by ¹⁴C-labeling, NMR, pK_a determination and viscosity measurements. The monomer reactivity ratios determined by ¹⁴C counting are r₁ = 1.04; r₂ = 0.94 [M₁ = 4(5)-vinylimidazole, M₂ = 1-methyl-4-vinylimidazole] and r₁ = 1.01; r₂ = 0.86 [M₁ = 4(5)-vinylimidazole, M₂ = 1-methyl-5-vinylimidazole]. The esterolytic activity of the copolymers for the hydrolysis of p-nitrophenyl acetate (PNPA) at pH 7–8 in 28.5% ethanol–water was higher than that of the mixtures of homopolymers. At pH 5–6 the esterolytic activities of the copolymers and the mixtures were similar. The most efficient esterolytic activity for PNPA hydrolysis at pH 7.11 in 28.5% ethanol–water occurred for copolymers containing 75 mole % 4(5)-vinylimidazole and for copolymers containing 1-methyl-4-vinylimidazole rather than 1-methyl-5-vinylimidazole.     

The esterolytic activity of poly(1-methyl-4- and -5-vinylimidazole) in water.

The water solubility of poly(1-Me-5-VIm) has made it possible to achieve phenomenal rate enhancements and to gain even greater insight into the mechanism of catalysis by polymeric imidazoles. The poly(1-Me-5-VIm)-catalyzed hydrolysis of S12- exhibited saturation in excess catalyst nad in excess substrate. Inhibition of the poly(1-Me-5-Vim) catalyzed hydrolysis of Sn- type substrates by analog inhibitors was also observed. The saturation apparently did not follow a simple Michaelis-Menten mechanism; however, the results could be rationalized by analogy to certain enzymatic systems. Multisite enzymes have long been known to display kinetic patterns different from that exhibited by enzymes with only one active site, i.e. such phenomena as sigmoidal rate vs [S] plots. These phenomena may arise entirely as a result of the multisite nature of the enzyme. Consequently, a synthetic macromolecular catalyst with multiple sites might also be expected to display such characteristics. The poly(1-Me-5-VIm)-catalyzed hydrolysis of S12- is apparently the first synthetic system in which such phenomena have been observed. The intermediacy of an apolar polymer substrate complex for the poly(1-Me-5-VIm)-catalyzed hydrolysis of S12- in water was given support by studies of the effect of temperature on the rate of hydrolysis. Activation parameters were determined for catalysis by 1,5-DMIm and by poly(1-Me-5-VIm). These results showed that the rate enhancement exhibited by the polymer was due entirely to a favorable entropy term.     

Synthesis and thermal behavior of RAFT-based copolymers of acrylonitrile and 1-vinylimidazole

The copolymers of acrylonitrile and 1-vinylimidazole with a narrow molecular weight distribution (MWD) were synthesized for the first time by the reversible addition–fragmentation chain transfer (RAFT) polymerization in a DMSO solution in the presence of acetic acid. Their thermal behavior difference upon heating in argon and in air along with ability to melt make them promising precursors for carbon fiber production.     

Microwave spectrum, structure, tautomeric, and conformational composition of 4-vinylimidazole

The microwave spectra of the two conformers each, of the 1H and 3H tautomers of 4-vinylimidazole, have been measured in the 48-72 GHz spectral region. The 4-vinylimidazole was generated in situ by the facile decarboxylation of urocanic acid at its vaporization temperature of 220 °C. The recognition of this reaction casts doubt on the reliability of a previous published spectroscopic study apparently mistakenly thought to be of uncontaminated vaporized urocanic acid, a natural product of great interest in skin cancer etiology. Quantum chemical theoretical predictions of the structures of each of ten possible conformers∕tautomers of urocanic acid and four of 4-vinylimidazole were performed at the ab initio MP2∕cc-pVTZ level, with vibrational predictions at the B3LYP∕cc-pVTZ and M062X∕cc-pVTZ levels. The predicted values of rotational constants for all the urocanic acid species were found to be quite inconsistent with those of the four observed spectra. For the 4-vinylimidazole isomers, the calculated relative energies suggested that all four species would have substantial equilibrium mole fractions at 220 °C. The isomers were identified by matching the observed and calculated rotational constants. The resulting assignment was found to be consistent with the predicted and observed (14)N nuclear quadrupole hyperfine multiplet patterns for a suitable rotational transition, and with the observed versus empirically calculated inertial defects. With one exception, the predicted structures were found to be planar. Resembling the case of 1-vinylimidazole, where one conformer is nonplanar, one isomer of 4-vinylimidazole was found to be quasiplanar. This seems to belong to a class of spontaneous symmetry-breaking observed in the molecular structure of some otherwise planar vinyl aromatic compounds.     

Poly(1-vinylimidazole) Prospects in Gene Delivery

Polymeric amines are being studied intensively as components of systems for gene delivery in genetic engineering and gene therapy of genetic disorders, including cancer. Despite remarkable achievements in the field, polymeric amines, such as polyethyleneimine, show some disadvantages. Strong interaction between the amine-containing polymer and nucleic acid hampers the release of nucleic acid in the cell cytoplasm. Amine groups can interact with the cell membrane which results in cell death. These limitations of polymeric amines stimulated an investigation of new structures for gene delivery. Imidazole-containing polymers have attracted attention as lesser basic substances, while they are able to interact with polymeric acids. Further development of imidazole-based gene delivery agents requires knowledge about some fundamental aspects of interaction between nucleic acids, and polymeric imidazoles. In this work, we studied the complexation of poly(1-vinylimidazole) and oligomeric DNA. We found that the number of active sites capable of binding with negatively charged phosphate groups is comparable with the number of protonated imidazole units in the case of high molecular weight polymer. The increase in polymer charge by 1-bromopropane quaternizating 1%?5% imidazole units or by decreasing the pH to 6.5?7 considerably increased the ability of poly(1-vinylimidazole) to interact with oligonucleotides. The pH sensitivity of this interaction is interesting for cancer gene therapy because the tumours have a lowered intercellular pH (stable oligonucleotide complex) and a higher extracellular pH which can lead to complex dissociation. Minimal critical length for complexation of quaternized poly(1-vinylimidazole) and DNA is below eight units which corresponds to polymers with amine groups. Fluorescence-tagged poly(1-vinylimidazole) samples were obtained and their potential for monitoring the polymer and polymer-oligonucleotide complex internalization into living cells was demonstrated.     

Reactions of 1-Halo-4-nitroanthraquinones with C-Nucleophiles

1-Fluoro-4-nitroanthraquinone reacts with C-nucleophiles, yielding the corresponding fluorine replacement products. Reactions of 1-chloro-4-nitroanthraquinone with the same nucleophiles result in formation of mixtures of dechlorination and denitration products whose ratio is determined by both charge and orbital interactions. Steric structure of the nucleophile can also affect the regioselectivity of substitution.     

Synthesis and Reactions of Some 1-Thiapyran-4-One Derivatives

The preparation of some 3,5-diarylidene-1-thipyran-4-one derivatives (Ia-e) was described. Oxidation of Ia, b and Ie with hydrogen peroxide gave the corresponding dioxides (IIa-c). Reaction of the 1-thiapyran-4-one derivatives with bromine, Grignard reagents, and amines were studied. Structural assignments are supported by spectral (UV, IR, and ¹HNMR) data.     

Synthesis and polymerization of 1,5-dioxo-1-methyl-4-azaphosphepane

1,5-Dioxo-1-methyl-4-azaphosphepane was synthesized and polymeized in the presence of water, stannic chloride, or phosphoric acid. Polymers obtained by using these catalysts were shown to have lower molecular weights than nylon 6 samples prepared under identical reaction conditions. Thermal and other physical properties of the phosphorus-containing polyamide are reported and compared with those of nylon 6.     

Crystal and molecular structures of the complexes of cobalt dichloride with 1-isopropenylimidazole and 1-vinylimidazole

The crystal and molecular structures of bis(1-isopropenylimidazole)dichlorocobalt (C₁₂H₁₆Cl₂·N₄Co) [R 0.036 (R _W 0.089) for 3229 unique reflections with I > 2σ(I)] and tetra(1-vinylimidazole)dichlorocobalt (C₂₀H₂₄Cl₂N₈Co) [R 0.031 (R _W 0.072) for 1863 unique reflections with I > 2σ(I)] were determined. In these molecular complexes, the monodentate terminal 1-alkenylimidazole ligands coordinate to the metal via a “pyridine” nitrogen atom. In C₁₂H₁₆Cl₂N₄Co, the Co atom has a distorted tetrahedral 2N,2Cl coordination. The coordination polyhedron of cobalt in C₂₀H₂₄Cl₂N₈Co is a strongly elongated 4N,2Cl octahedron. The Co-N and Co-Cl bonds [Co-N 2.015(2) and 2.032(4) Å; Co-Cl 2.229(2) Å] in the tetrahedral complex C₁₂H₁₆Cl₂N₄Co are shorter than those in the octahedral complex C₂₀H₂₄Cl₂N₈Co [Co-N 2.134(2) and 2.157(2) Å; Co-Cl 2.518(1) Å]. In the structures of both complexes there are short contacts involving the Cl atoms.