Monomers In Organic Solvents Research Articles

Anion‐(π)n‐π Catalytic Micelles

AbstractAnion‐π catalysis operates by stabilizing anionic transition states on π‐acidic aromatic surfaces. In anion‐(π)n‐π catalysis, π stacks add polarizability to strengthen interactions. In search of synthetic methods to extend π stacks beyond the limits of foldamers, the self‐assembly of micelles from amphiphilic naphthalenediimides (NDIs) is introduced. To interface substrates and catalysts, charge‐transfer complexes with dialkoxynaphthalenes (DANs), a classic in supramolecular chemistry, are installed. In π‐stacked micelles, the rates of bioinspired ether cyclizations exceed rates on monomers in organic solvents by far. This is particularly impressive considering that anion‐π catalysis in water has been elusive so far. Increasing rates with increasing π acidity of the micelles evince operational anion‐(π)n‐π catalysis. At maximal π acidity, autocatalytic behavior emerges. Dependence on position and order in confined micellar space promises access to emergent properties. Anion‐(π)n‐π catalytic micelles in water thus expand supramolecular systems catalysis accessible with anion‐π interactions with an inspiring topic of general interest and great perspectives.

Anion-(π)n-π Catalytic Micelles.

Anion-π catalysis operates by stabilizing anionic transition states on π-acidic aromatic surfaces. In anion-(π)n-π catalysis, π stacks add polarizability to strengthen interactions. In search of synthetic methods to extend π stacks beyond the limits of foldamers, the self-assembly of micelles from amphiphilic naphthalenediimides (NDIs) is introduced. To interface substrates and catalysts, chargetransfer complexes with dialkoxynaphthalenes (DANs), a classic in supramolecular chemistry, are installed. In π-stacked micelles, the rates of bioinspired ether cyclizations exceed rates on monomers in organic solvents by far. This is particularly impressive considering that anion-π catalysis in water has been elusive so far. Increasing rates with increasing π acidity of the micelles evince operational anion-(π)n-π catalysis. At maximal π acidity, autocatalytic behavior emerges. Dependence on position and order in confined micellar space promises access to emergent properties. Anion-(π)n-π catalytic micelles in water thus expand supramolecular systems catalysis accessible with anion-π interactions with an inspiring topic of general interest and great perspectives.

Preparation of arctiin moleculary imprinted polymers with 4-vinylpyridine and Allyl-β-cyclodextrin as binary monomers under molecular crowding conditions

This paper reported a feasible method to prepare molecularly imprinted polymer (MIPs) using 4-vinylpyridine (4-VP) and Allyl-β-cyclodextrin (β-CD) as binary functional monomer in the presence of polystyrene (PS). This is the first time that a surrounding of macromolecular crowding was established to improve the imprinting effect of cyclodextrins as monomer in organic solvents. The morphological and characteristics of the polymers with macromolecular crowding reagents were investigated by scanning electron microscope (SEM), fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and nitrogen adsorption experiments. The MIPs were synthesized with 4-VP and β-CD as binary functional monomers, a series of experiments were conducted to compare with the control groups. Furthermore, the selectivity of MIP for analogues experiment showed that the β-CD/4-VP MIP has higher specific recognition for arctiin than β-CD/4-VP NIP. A purification method by β-CD/4-VP MIPs coupled with macromolecular crowding reagents was developed for extraction arctiin from Arctium lappa L. In the MIP-SPE process, the optimal washing and eluting reagents are methanol/water (5:5) and methanol/acid (9:1), respectively. When using the β-CD/4-VP MIPs as SPE absorbent, the mean recoveries for arctiin were 87% with purity of 95%. All the results indicate that this synthetic method using 4-VP and β-CD as binary functional monomers in the presence of PS is a promising method for the preparation of selective adsorbents for arctiin analysis in Arctium lappa L.

Self-Assembled 2,3-Dicyanopyrazino Phenanthrene Aggregates as a Visible-Light Photocatalyst.

In this study, 2,3-dicyanopyrazino phenanthrene (DCPP), a commodity chemical that can be prepared at an industrial scale, was used as a photocatalyst in lieu of Ru or Ir complexes in C-X (X = C, N, and O) bond-forming reactions under visible-light irradiation. In these reactions, [DCPP]n aggregates were formed in situ through physical π-π stacking of DCPP monomers in organic solvents. These aggregates exhibited excellent photo- and electrochemical properties, including a visible light response (430 nm), long excited-state lifetime (19.3 μs), high excited-state reduction potential (Ered([DCPP]n*/[DCPP]n·-) = +2.10 V vs SCE), and good reduction stability. The applications of [DCPP]n aggregates as a versatile visible-light photocatalyst were demonstrated in decarboxylative C-C cross-coupling, amidation, and esterification reactions.

Aggregation Behavior and Electron‐Transfer Reaction of Dendritic Perylene Bisimide, Accompanied by the Formation of Highly Stable Anionic Radical Species

AbstractA polyethylene‐glycol‐functionalized perylene bisimide (PEPBI) was synthesized. Its concentration‐, solvent‐ and temperature‐dependent visible spectra were measured and its aggregation states were analyzed. PEPBI exists as an aggregate dimer in aqueous solution or predominantly as a monomer in organic solvents. The anionic surfactant sodium dodecylbenzenesulfonate (SDBS) can disperse PEPBI as a monomer in aqueous solution. The fluorescence of these solutions depends on the concentration of PEPBI and SDBS. The reduction of aggregated PEPBI with Na2S is slow and the monoanion radical as well as dianion species are the main forms of monomer. PEPBI exists predominantly as monomers in DMF and reacts with Na2S much faster. Interestingly, the anionic radical species exist in H‐aggregate form at low PEPBI concentrations and J‐aggregation occurs at high concentration. The dianion species is EPR‐silent and its color highly depends on its concentration in DMF.

Concentration effects in homopolymerization of amine- and amide-containing (meth)acrylic monomers in organic solvents

The dependences of the initial reduced rate of radical homopolymerization on the initial concentration of the monomers were studied for toluene and dimethylformamide solutions of four amine-containing (meth)acrylic esters and amides, and also for N-(n-butyl)acrylamide and n-butyl methacrylate taken for comparison. The concentration effects are similar for all the methacrylic monomers and are specific in the case of acrylamides {N-(n-butyl)acrylamide and N-[3-(dimethylamino)propyl]acrylamide}, which is associated with the specific features of the structure of the prereaction monomeric associates.

Raman spectroscopic investigations on intermolecular interactions in aggregates and crystalline forms of trans‐astaxanthin

Astaxanthin is a carotenoid naturally found in microbial organisms, microalgae, and many crustaceans. Its consumption has led to beneficial effects such as pigmentation of marine animals, and it favorably addresses several human health issues as a result of its high important antioxidant property. Several companies produce synthetic trans‐astaxanthin for dietary purposes in aquaculture, where it is mainly used for pigmentation. It is known that trans‐astaxanthin manifests itself as a monomer in organic solvents, as aggregates in aqueous solutions of organic solvents, or as crystalline solids. These forms display unique optical and structural properties, which have an impact on biological systems. In this work, we report on detailed Raman investigations, in conjunction with optical absorption spectroscopy, of monomer, aggregates, and crystalline forms of trans‐astaxanthin. The Raman and optical absorption spectroscopic investigations of trans‐astaxanthin aggregates were performed as a function of time, showing the formation of card‐packed aggregates after 2 h, and head‐to‐tail aggregates after 24 h in a 10% acetone–water astaxanthin solution. For the crystalline trans‐astaxanthin, a pointwise Raman mapping evidenced the presence of two distinct crystal structures. The Raman modes of these crystal structures (A and B) were correlated with the intermolecular interactions present in chloroform solvated (AXT‐Cl) and unsolvated (un‐AXT) trans‐astaxanthin single crystals. Both crystal structure A and the card‐packed aggregates have similar intermolecular π stacking interactions as AXT‐Cl. The crystal structure B and the head‐to‐tail aggregates showed linear chain features as in un‐AXT. This work also clearly demonstrates that Raman spectroscopy is a powerful tool to distinguish the crystal structures present in crystalline powder of trans‐astaxanthin. Copyright © 2012 John Wiley & Sons, Ltd.

The effects of aggregation, protein binding and cellular incorporation on the photophysical properties of benzoporphyrin derivative monoacid ring A (BPDMA)

Absorption, fluorescence and laser flash photolysis spectroscopies were used to investigate the effects of self-aggregation, binding to human serum albumin and incorporation in cancer cells on the photophysics of benzoporphyrin derivative monoacid ring A (BPDMA). Aggregation of BPDMA has been studied in mixtures of methanol and phosphate-buffered saline (PBS). The extent of aggregation was dependent on dye concentration and solvent composition, becoming particularly marked in mixtures containing less than 30% methanol. A dimerization constant K d or 9 × 10 6 M −1 was determined by fluorescence experiments for BPDMA in pure PBS. In addition to spectral modifications, aggregation induces a lowering of the fluorescence and intersystem crossing quantum yields. Human serum albumin binds BPDMA with an association constant K b of 5.2 × 10 5 M −1 in PBS. When bound to HSA, BPDMA displays photophysical properties very similar to the monomer in organic solvents. The molar ratio [HSA]/[BPDMA] corresponding to complete binding of the dye was determined to be approximately 10. Efficient generation of the triplet state of BPDMA was also observed from aqueous cellular suspensions containing incorporated photosensitizer.

Synthesis of electrically conductive polypyrrole films by interphase oxidative polymerization

AbstractPolypyrrole (PPy) films were synthesized by interface polymerization reactions between aqueous solutions of FeCl3 and solutions of pyrrole monomer in organic solvents. The polymerizations were studied using various organic solvents, and flexible and uniform PPy films were obtained using benzene or toluene as solvents. It was found that polymerization time and organic solvents strongly affect the thickness and conductivity of the films, but the atomic composition of the PPy films was independent of the reaction conditions. The mechanism of the film growth at the interface is discussed on the basis of film properties and the observation of the film surface using scanning electron microscopy.

Electrochemical glucose sensors on permselective non-conducting substituted pyrrole polymers

Our aim has been to construct biosensors which can be produced in large numbers for commerical use with high stability and selectivity. Thin-film technology is able to provide the high purity and reproducibility required of the electrode surface and the high spatial resolution of the electrode structure. A four-electrode electrochemical cell with an outer diameter of 2.5 mm possessing two identical working electrodes is produced by using glass sheets or Upilex foils as electrode carriers. These sheets, coated with thin titanium layers acting as an adhesion layer, are covered with platinum to form an electro-chemical electrode. After structuring, the conducting lines are isolated by silicon nitride or polyimide. To coat the platinum electrodes with polymeric layers new strategies in the synthesis of 1- and 3-substituted pyrroles have been developed to obtain 1-(carboxyalkyl) pyrroles, 2-(1-pyrrolo)-acetylglycine, 1-alkylpyrroles, 1-(4-carboxybenzyl)-pyrrole, 1-(4-nitrophenyl) pyrrole, 4-(3-pyrrolo)-4-ketobutyric acid and 3-((keto 4-nitrophenyl) methyl) pyrrole as monomers. New types of polymer-coated electrodes are prepared and characterized further by electrochemical oxidation and polymerization of these monomers in organic solvents. To couple enzymes and to activate terminal carboxy and nitro groups of the polymer, water-soluble carbodiimides and chloranil are found to give the best results. The activated electrodes are reacted immediately with glucose oxidase and the glucose sensors thus obtained are stored at 4 °C. Electrodes covered by substituted polypyrrole layers having no redox activity show two fundamental advantages: a significant increase of response per unit area due to the porous polymer and permeation control for interfering electroactive substances by the polymeric layer, resulting in a distinct increase in selectivity.

Low temperature polymerization and copolymerization of acetylenic monomers in vitrifying organic solvents

Polymerization and copolymerization of acetylenic monomers in organic solvents vitrifying at low temperatures have been studied and the reasons for their low polymerization capacity clarified. It is shown that the low yields and low molecular mass of the polymer formed are linked with inactivation of the growing macroradicals in the course of their interaction with the conjugated system of the polymer already formed and also with effective decay and steric screening of the active polymerization centres.

Electrophoresis of ganglioside micelles

AbstractGangliosides are known to exist as monomers in organic solvents and to aggregate in aqueous systems with the formation of high molecular weight micelles. It is shown here that the ganglioside micelles can be rendered visible by incorporation of a lipophilic dye and analyzed by conventional polyacrylamide gel electrophoresis. Mixed micelles of gangliosides and commonly used detergents as well as interaction products of ganglioside micelles with albumin were thus visualized by polyacrylamide gel electrophoresis for the first time.

Current status and prospects of development of polyphenylquinoxalines. Review

New tendencies in the development of the chemistry of polyheteroarylenes aimed at producing processable thermoreactive polymers are reviewed. A detailed analysis is made of the reaction of one-stage polyheterocyclization of tetrafunctional monomers in organic solvents leading to the formation of linear, defect-free, high molecular weight phenylquinoxaline polymers and copolymers and the main characteristics and the areas of practical use of the principal representatives of this polymer class.

Biosynthesis and characterization of [15N]actinomycin D and conformational analysis by nitrogen-15 nuclear magnetic resonance.

We describe the production and characterization of actinomycin D labeled with 15N at all twelve nitrogen positions. Cultures of Streptomyces parvulus were incubated in the presence of racemic [15N]glutamic acid and, following an initial delay, labeled antibiotic was produced. Evidence is presented that the D enantiomorph of glutamic acid was ultimately used for actinomycin biosynthesis. The 15N NMR spectrum at 10.14 and 20.47 MHz of the labeled drug in CDCl3 is presented. All nitrogens except the phenoxazone chromophore nitrogen are inverted when spectra are obtained under broad-band proton irradiation conditions. All 15N resonances have been assigned, and the proton-nitrogen one-bond coupling constants were determined in CDCl3 to be 92.5 +/- 0.3 Hz for the valine and threonine amide protons by both 1H and 15N NMR. 15N NMR spectra were also obtained in dimethyl sulfoxide, methanol, and water in order to probe solvent interactions with the peptide nitrogens and carbonyl groups. Large downfield shifts (greater than 5 ppm) were seen for the Pro, sarcosine, and methylvaline resonances when the solvent was changed from dimethyl sulfoxide to water. Smaller downfield shifts were observed for the Val and Thr peaks. These results are discussed in terms of a model for the solution conformation of the actinomycin pentapeptide rings based on different hydrogen-bonding interactions in the monomer in organic solvents and the dimer which is formed in water.