Polymerization of an Elaidic Acid Langmuir Film Prepared on a Terbium-Containing Subphase

The UV-induced polymerization of an elaidic acid Langmuir film prepared on a terbium-containing subphase has been studied. The polymerization caused changes in pressure/area isotherms. The irradiated film in its more condensed state is in a liquid phase while the monomer film is in a solid phase. The dynamics of the irradiated films was investigated by following the evolution of the film area at a constant pressure. For the longer irradiation times, an expansion of the film area was observed. Scanning force microscopy and IR spectroscopy have been used to study the monolayer after its transfer onto a solid support. IR spectroscopic measurements indicated the presence of an oxygen-containing copolymer. Scanning force microscopy images revealed a modification of the structure of the film after irradiation. Copyright 1999 Academic Press.     

Synthesis and characterization of isomeric polyesters based on sebacic acid and hexanediols

Isomeric homopolymers and random copolyesters based on sebacic acid and isomeric hexanediols were synthesized by condensation techniques and characterized by NMR, GPC, intrinsic viscosity, and DSC. Among the homopolymers, only the polyester derived from the linear 1,6-hexanediol was found to be crystalline. Typical melting points were 65–70°C, depending on molecular weight, and a T_g of ?62°C was measured on a high molecular weight sample. Other isomeric homopolymers derived from the branched diols 2-methyl-2-ethyl-1,3-propanediol and 2,5-hexanediol were amorphous tacky fluids with glass temperatures of ?69 and ?66°C, respectively. In the case of the random copolymers, NMR analysis was particularly useful in determining the copolymer composition or the diol isomer ratio. DSC data indicated that all the random copolymers containing the linear 1,6-diol were crystallizable and their melting points depended on copolymer composition. The heat of fusion per repeat unit of poly(hexamethylene sebacate) was found to be 32 cal/g from measurements of the molecular weight dependence of the melting point.     

Trifluoromethyl-containing pyrazolinyl (p-tolyl) sulfones: The synthesis and structure of promising antimicrobial agents

The regiospecific synthesis of a novel series of nine 4-phenyl- and 3-alkyl(aryl)-5-hydroxy-5-trifluoromethyl-4,5-dihydro-1H-1-tosylpyrazoles (pyrazolinyl p-tolyl sulfones), as well as their antimicrobial activity against yeast, such as fungi, bacteria, and alga are reported. The 1-p-tosyl-2-pyrazolines were obtained from the cyclocondensation reaction of 3-phenyl- and 4-alkyl(aryl)-1,1,1-trifluoro-4-alkoxy-3-alken-2-ones, [where alkyl = H, Me and aryl are -C₆H₅, 4-CH₃C₆H₄, 4-OCH₃C₆H₄, 4-FC₆H₄, 4-ClC₆H₄, 4-BrC₆H₄,] with p-tosylhydrazine in a yield of 58-92% when toluene was employed as solvent. The best activity was obtained when the structure possessed a 4-fluorophenyl substituent linked at the carbon-3 of the pyrazoline ring. Subsequently, the dehydration reaction of 3-(4-fluorophenyl) substituted 2-pyrazoline with thionyl chloride/pyridine in benzene as solvent furnished the corresponding 1H-pyrazole in only a moderate yield (49%).     

Allylic alkylation and amination using mixed (NHC)(phosphine) palladium complexes under biphasic conditions

A dramatic improvement of the catalytic activity was observed when a phosphine was added in allylic alkylation reactions catalyzed by (NHC)Pd(η³-C₃H₅)Cl complexes. Consequently, several palladium complexes, generated in situ from different NHC-silver complexes, [Pd(η³-C₃H₅)Cl]₂ and PPh₃, were tested in this reaction to evaluate their potential. High reaction rates and conversions could be obtained with this catalytic system in the alkylation of allylic acetates with dimethylmalonate, particularly under biphasic conditions using water/dichloromethane and KOH 1 M as the base. These conditions are experimentally more convenient and gave higher reaction rates than the classical anhydrous conditions (NaH/THF). In this system, the phosphine is essential since no conversion was obtained when it is not present. The steric hindrance of the carbene ligand has a great influence on the activity and the stability of the catalytic system. The best NHC ligands for this reaction are either 1-mesityl-3-methyl-imidazol-2-ylidene or 1-(2,6-diisopropylphenyl)-3-methyl-imidazol-2-ylidene which are less bulky among the NHC tested. These two ligands led in 5 min to a complete conversion at 20 °C. The Pd-catalyzed allylic amination reaction using (E)-1,3-diphenylprop-3-en-yl acetate and benzylamine was also tested with (NHC)(PPh₃)Pd complexes and under the biphasic conditions. This reaction was found to be slower than the alkylation with dimethylmalonate but a complete conversion could be reached in 6 h at 20 °C using K₂CO₃ 1 M as the base. NMR experiments indicated that mixed (NHC)(PPh₃)Pd complexes are formed in situ but their structure could not be established exactly.     

Attachment of metal trications to peptides

Gas-phase complexes of triply charged metal ions with peptides may be readily produced using electrospray ionization, including for small peptides such as bradykinin and peptides with no basic residues such as insulin chain A. Attachment without charge-reduction is demonstrated for all trications studied: La(3+), Al(3+), Ga(3+), Fe(3+), V(3+), and Cr(3+). The intensities of adducts are often comparable to, or even exceed, those of protonated analogs in any charge state.     

Addition of activated olefins to cyclic N-acyliminium ions in ionic liquids

Organoindate(III) ionic liquid (BMI·InCl₄) was successfully employed in the nucleophilic addition of allyltrimethylsilane, silyl enol ethers and ketene silyl acetals to in situ generated cyclic N-acyliminium ions at room temperature without the need of an external Lewis acid. The corresponding α-substituted heterocycles were obtained in good yields and the recovered ionic liquid phase could be reused at least three times.     

Synthesis of tri- and tetrasubstituted furans catalyzed by trifluoroacetic acid

Substituted 2-hydroxy-3-acetylfurans are synthesized by alkylation of tert-butyl acetoacetate with an alpha-haloketone followed by treatment of the obtained intermediate with trifluoroacetic acid (TFA). A second alkylation of the intermediate followed by treatment with trifluoroacetic acid provides access to disubstituted 2-methylfurans.     

Monte Carlo evidence of non-equilibrium effects for ising model in a random field

Simulating an Ising model, up to sizes 150×150×150 in three and 225×225 in two dimensions, in a random field of strength ±H, we find a magnetization slowly decreasing with time if initially all spins are parallel. This decay is extremely slow for small random fields, so that a stable magnetization cannot be excluded. Below some freezing temperature, the system remains a single domain, with a finite magnetization in both two and three dimensions. If instead the system is cooled down in a constant random field, from temperatures above to temperatures below this freezing transition, then at the lower temperature the magnetization increases with time; this increase is very slow for large systems, with similar results in two and three dimensions.     

An efficient two-step total synthesis of the quaterpyridine nemertelline

Regioselective and univocal Suzuki cross-coupling reactions performed on halopyridinyl boronic acids provide a flexible and versatile route to a multigram scale synthesis of 2,2'-dichloro-3,4'-bipyridine 14, which allows couplings with excess pyridin-3-yl boronic acid to give a new and efficient two-step rapid synthesis of nemertelline, the quaterpyridine neurotoxin isolated from a Hoplonemertine sea worm.     

Design,scope and mechanism of highly active and selective chiral NHC–iridium catalysts for the intramolecular hydroamination of a variety of unactivated aminoalkenes

Chiral, cationic NHC–iridium complexes are introduced as catalysts for the intramolecular hydroamination reaction of unactivated aminoalkenes. The catalysts show high activity in the construction of a range of 5- and 6-membered N-heterocycles, which are accessed in excellent optical purity, with various functional groups being tolerated with this system. A major deactivation pathway is presented and eliminated by using alternative reaction conditions. A detailed experimental and computational study on the reaction mechanism is performed providing valuable insights into the mode of action of the catalytic system and pointing to future modifications to be made for this catalytic platform.

Chiral, cationic NHC–iridium complexes are introduced as catalysts for the intramolecular hydroamination reaction of unactivated aminoalkenes.