Distribution of amines in water/AOT/n-hexane reverse micelles: influence of the amine chemical structure

The distribution of different aliphatic and aromatic amines: n-butylamine (n-BA), isobutylamine (i-BA), tert-butylamine (t-BA), piperidine (PIP), N,N-dimethylaniline (DMA) and N-methylaniline (MA) in water/sodium 1,4-bis(2-ethylhexyl)sulfosuccinate(AOT)/n-hexane reverse micelles was investigated by steady-state fluorescence measurements. The partition constants were measured by an indirect method based on the effect that amine partitioning exert on the bimolecular rate of the reaction between a microphase incorporated fluorophore (Ru(bpy)2+(3)) and the quencher, (Fe(CN)3-(6)). For MA, that can act as a quencher of the fluorophore a direct method was used. The results show that primary amines have larger partition constants than the secondary ones. For tertiary amines the distribution constants were practically negligible. Laser flash photolysis experiments confirmed that tertiary amines, both aliphatic and aromatic, are not incorporated to the micellar pseudophase. The effect of the amine structure on the partition constant was analyzed through linear solvation free energy relationships (LSER) using solute parameters and compared with those obtained for alcohols. Hydrogen bond interactions with the AOT polar heads appear to be the main driving force for the distribution of amines between the organic and micellar pseudophases, whereas the size of the alkyl or aromatic group tends to hinder it.     

Systematic study of steric and spatial contributions to molecular recognition by non-covalent imprinted polymers.

Although molecular imprinting is a widely accepted method for producing template specific polymers, the general rules for prediction and control of the binding and catalytic properties of these materials are still not fully understood. One reason for this is the problematic structural analysis of the active sites in the polymers, which are not amenable to X-ray crystallography or microscopic techniques due to their amorphous and heterogeneous nature. Therefore, molecular probes have been the most informative agents for the analysis of the structure of active sites. This paper focuses on the steric and geometrical aspects of shape recognition in non-covalent imprinted polymers, with particular effort to minimize other factors contributing to molecular recognition by the polymers. Chiral amine compounds with systematic changes in spatial, distal and conformational components of sterically controlled molecular recognition were investigated for use as non-covalent imprinted polymers. Chromatographic studies revealed that steric and spatial interactions influence the selectivity properties of imprinted polymers in a predictable fashion.     

Polymers of tertiary amines

Polymers of tertiary amines and their hydrochlorides of molecular weights in the range 300–2000 have been prepared, starting from trans-1,4-dichlorobutene-2, and primary amines. The polymers present interesting solubility properties. Variation of the reaction conditions leads to crosslinked insoluble polymers. Reaction of the soluble tertiary amine polymers with organic acid dichlorides leads to polymers of tertiary amine–amides, a new type of polymer.     

Size-selective shell cross-linked interior functionalized siloxane nanocages

A new structure, consisting of a shell cross-linked, 2 nm size siloxane nanocage containing propylamine groups tethered to the interior face of the shell was synthesized, starting with micelles of the surfactant molecule, (triethoxysilyl)propylcetylcarbamate. After hydrolysis of the ethoxysilyl groups and condensation and capping of the silanols to form a cross-linked, one-atom-layer-thick siloxane shell, the carbamate was converted to amine, releasing the cetyl group from the structure and resulting in the desired spherical nanocage. The intermediates in the synthesis process and the final structure were characterized by 1H and 29Si NMR, DLS, TEM, and mass spectroscopy. The amine groups tethered to the interior surface of the shell react readily with ninhydrin but do not interact with the larger ZnTPP, indicating molecular size selectivity by the cross-linked shell. The structure also exhibits confinement effect in the amine-catalyzed decarboxylation of acetoacetic acid, exhibiting higher activity and higher selectivity for acetal than (aminopropyl)triethoxysilane.     

Formation of supramolecular polymers and discrete dimers of perylene bisimide dyes based on melamine-cyanurates hydrogen-bonding interactions

Melamine-linked perylene bisimide dyes (MPBIs) bearing an ethylene or trimethylene group as linker moieties were synthesized, and their self-aggregation and coaggregation with cyanurates through complementary triple hydrogen bonds have been investigated. UV/vis studies revealed that both the MPBIs self-assemble in nonpolar organic solvent through pi-pi stacking interaction between perylene cores, giving self-aggregates with nearly identical thermal stabilities. Upon addition of 1 equiv of cyanurate components, however, the stabilities of the resulting aggregates were dramatically changed between the two systems, suggesting the formation of different types of hydrogen-bonded supramolecular species. Dynamic light scattering and atomic force microscopic studies revealed that the system featuring ethylene linker moieties generates a discrete dimer of MPBI supported by two cyanurate molecules, whereas the system featuring trimethylene linker moieties affords extended supramolecular polymers hierarchically organizing into nanoscopic fibers. These results demonstrate that it is possible to obtain distinct supramolecular species by just changing the number of carbon atoms at the linker moieties of MPBI components. The present strategy for the fabrication of discrete or polymeric supramolecular assemblies should be applicable to other functional pi-conjugated molecules.     

Performance and selectivity of polymeric pseudostationary phases for the electrokinetic separation of amino acid derivatives and peptides

Two polymeric pseudostationary phases, one an acrylamide polymer and the second a siloxane polymer, have been investigated for the separation of naphthalene-2,3-dicarboxaldehyde (NDA)-derivatized amino acids and small peptides. The dervatized amino acids were detected by UV absorbance and laser-induced fluorescence (LIF) detection. The polymers provided very high efficiency and good selectivity for the separation of the amino acids. The separation selectivity using the polymers was significantly different from that of SDS micelles, and there were subtle differences in selectivities between the polymers. Although very good detection limits were obtained with LIF detection, a significant background signal was observed when the polymers were not washed to remove fluorescent impurities. The polymers did not separate the peptides very well. It is postulated that the fixed covalent structure of the polymers prevents them from interacting strongly or efficiently with the peptides, which are large in relation to the analytes typically separated by electrokinetic chromatography using polymers.     

Membrane-mimetic films of asymmetric phosphatidylcholine lipid bolaamphiphiles

Membrane-spanning phospholipid bolaamphiphiles either alone or as a constituent of a multicomponent lipid membrane may prove to be facile building blocks for generating robust bioactive membrane-mimetic assemblies. We have previously reported the synthesis of asymmetric dialkyl phospholipid bolaamphiphiles that contain ester linked phosphatidylcholine and amine functionalities at opposite chain ends. In this report, we describe the synthesis of phospholipid bolaamphiphiles that are conjugated to biotin via the terminal amine with or without a poly(ethylene oxide) spacer arm of varying chain length. The behavior of biotinylated bolaamphiphiles as a self-assembled monolayer at an air-water interface was characterized by epi-fluorescence microscopy and revealed that domain structure and pi-A isotherms were substantially influenced by linker type and size. Substrate bound assemblies were produced by Langmuir-Blodgett deposition onto planar substrates coated with an avidin derivatized polyelectrolyte multilayer. Significantly, external reflectance infrared spectroscopy confirmed the fabrication of bolaamphiphile thin films that display extended stability in vitro.     

Interpenetrating polymer networks from polyurethanes and methacrylate polymers. II. Interpenetrating polymer networks with opposite charge groups

Interpenetrating polymer networks (IPNs) with opposite charge groups (tertiary amine and carboxyl groups) made from polyurethanes and methacrylate polymers have been synthesized and their properties and morphology, studied. With increasing carboxyl group concentration the mechanical properties and compatibility between the component networks were significantly improved, possibly because of the negative (or zero) free energy produced by the interaction contribution between the tertiary amine groups in the polyurethanes and the carboxyl groups in the methacrylate polymers determined by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The improved molecular mixing in these IPNs was thought to be due to the influence of the opposite charge groups in these systems.     

An anionic siloxane polymer as a pseudostationary phase for electrokinetic chromatography

A novel polymeric pseudostationary phase for electrokinetic chromatography is introduced and characterized. Siloxane polymers are of interest for this application because of the range of chemistries that could be developed based on these backbones, and because successful development of siloxane polymers would make it possible to employ much of the stationary phase chemistry developed in the past thirty years. A commercially available water-soluble siloxane with a hydroxy-terminated alkyl group was converted to the sulfate derivative. This siloxane polymer is water-soluble, effectively eliminating this limitation associated with siloxane polymers. When employed as a pseudostationary phase, this compound provided rapid, efficient, and selective separations. The electrophoretic mobility of the polymer was less than sodium dodecyl sulfate (SDS) and poly(sodium 10-undecenylsulfate), providing a compressed migration time range, which is the main limiting factor for this polymer. The chemical selectivity of the siloxane sulfate was somewhat different than SDS micelles. The siloxane was employed in buffers modified with a large amount of acetonitrile to separate a number of polynuclear aromatic hydrocarbons. The addition of acetonitrile caused an apparent discontinuity in the electrophoretic mobility of the polymer, which may indicate a change in the structure with increasing organic solvent content.     

Alkyl modified anionic siloxanes as pseudostationary phases for electrokinetic chromatography. I. Synthesis and characterization

Anionic water soluble siloxane polymers have been synthesized and characterized for electrokinetic chromatography. Siloxane polymers are of interest in electrokinetic chromatography because of the wide variety of chemistries that can be developed based on these backbones, including much of the stationary phase chemistry developed in the last 30 years. The siloxanes in this study have a sulfonate functional group. The siloxanes have different length alkyl chains (C8, C12, C18) attached to the backbone in differing densities. The methylene selectivity generally increases with increasing alkyl chain length and with increasing alkyl chain density. The electrophoretic mobility appears to pass through a maximum as more alkyl chain is added to the siloxane backbone. The efficiency also would seem to pass through a maximum as more alkyl chain is added. The chemical selectivities of the siloxane polymers are very different from sodium dodecyl sulfate but are similar to each other.     

Poly(2-imidazolin-5-ones)—A new class of heterocyclic polymers

The reaction of bisazlactones (2-oxazolin-5-ones) with primary diamines containing additional secondary or tertiary amine functionality (e.g., diethylenetriamine, triethylenetetramine, or N-methyliminobispropylamine) readily produces polyamides which serve as precursors to a new class of heterocyclic polymers. Thermal cyclodehydration takes place under relatively mild conditions (180–200°C) to produce water-soluble polymers containing the 2-imidazolin-5-one heterocycle. Model reactions have been studied to verify this mode of cyclization and confirm the proposed polymer structure.     

Photoinduced electron transfer in double-bridged porphyrin-fullerene triads

Electron and energy transfer reactions of porphyrin-porphyrin-fullerene triads (P2P1C) with controllable sandwich-like structures have been studied using spectroscopic and electrochemical methods. The stabile, stacked structure of the molecules was achieved applying a two-linker strategy developed previously for porphyrin-fullerene dyads. Different triad structures with altered linker positions, linker lengths, and center atoms of the porphyrin rings were studied. The final charge-separated (CS) state and the different transient states of the reactions have been identified and energies of the states estimated based on the experimental results. In particular, a complete CS state P2(+) P1C- was achieved in a zinc porphyrin-free-base porphyrin-fullerene triad (ZnP2t9P1C) in both polar (benzonitrile) and nonpolar (toluene) solvents. The lifetime of this state was longer living in the nonpolar solvent. An outstanding feature of the ZnP2t9P1C triad is the extremely fast formation of the final CS state, P2(+) P1C-. This state is formed after primary excitation of either zinc porphyrin or free-base porphyrin chromophores in less than 200 fs. Although the intermediate steps between the locally excited states and the final CS state were not time-resolved for this compound, the process is clearly multistep and the fastest ever observed for porphyrin-based compounds.     

Polymers of sodium-N-undec-10-ene-1-oyl taurate and sodium-N-undec-10-ene-1-oyl aminoethyl-2-phosphonate as pseudostationary phases for electrokinetic chromatography

The use of micelle polymers, a class of polysoaps with a polymerized hydrophobic interior and a charged hydrophillic exterior, as pseudostationary phases in electrokinetic chromatography has generated significant interest. Their stable structure has been shown to provide significant advantages over conventional micelles when used as pseudostationary phases. In previous studies, micelle polymers have had carboxylate and sulfate head groups. These chemistries have limitations: carboxylate micelle polymers precipitate out of solution at pH less than seven or eight and sulfate head groups are not stable to hydrolysis and are hydrolyzed during polymerization. Additionally, while the chemical selectivity of conventional micelles varies with head group chemistry, no significant differences in chemical selectivity were observed between analogous polymers with sulfate and carboxylate groups. To overcome the limitations of carboxylate and sulfate head groups, and to further investigate the chemical selectivity of micelle polymers, poly(sodium-N-undec-10-ene-1-oyl-taurate) and poly(sodium-N-undec-10-ene-1-oyl-ethyl-2-phosphonate) micellar polymers have been synthesized and characterized as pseudostationary phases. These polymers have amide functionality and stable, strongly acidic sulfonate and phosphonate head groups. These polymers did provide improved solubility at low pH, and are stable under the conditions studied. The chromatographic performance and chemical selectivity of the polymers has been studied by several methods, including linear solvation energy relationships. Poly(sodiumN-undec-10-ene-1-oyl-taurate) has greater electrophoretic mobility than other polymers of this type, and can be used for the separation of hydrophobic compounds. The polymers do exhibit unique selectivity, but the differences in selectivity are not significant for the majority of compounds studied.     

Photostabilizing activity of tertiary hindered amines

The influence of the N-alkyl group of tertiary hindered amines on the photostabilization of polymers was studied. The photostabilizing effects of the tertiary amine derivatives of 4-benzoyloxy-2,2,6,6-tetramethylpiperidine ( 1a ) in polypropylene were compared. All tertiary amine derivatives having α-H to hindered N showed higher effectiveness than 1a . Model liquid phase photoxidations were carried out by irradiating (UV-lamp) the solutions of tertiary hindered amines containing tert-butyl hydroperoxide as a photoinitiator. The tertiary hindered amines were oxidized more easily than corresponding parent hindered amine and converted to the parent amine, which was identified as its salt, resulting from the carboxylic acid produced from the N-alkyl group by oxidation. The thermal reaction of the tertiary hindered amines with tert-butyl hydroperoxide was also studied in the liquid phase. The tertiary hindered amines decomposed tert-butyl hydroperoxide more rapidly than the parent secondary hindered amine, and generated the parent amine. It was also found that the photostabilizing effects of tertiary hindered amines for polyolefins were higher than that of the parent secondary hindered amine.     

SYNTHESIS OF CONDENSATION POLYMERS OF SALICYLIC ACID, FORMALDEHYDE AND ALKYL PRIMARY AMINES AND ITS APPLICATION AS A CATALYST FOR THE HYDROLYSIS OF p-NITROPHENYL ACETATE (PNPA) IN AQUEOUS SOLUTION

As a model of serine hydrolase, the condensation polymers of salicylic acid, formaldehyde and methyl amine, n-propyl amine, n-hexyl amine or n-lauryl amine were prepared by polycondensation catalyzed by sulfuric acid. It was confirmed by potentiometric titration and infrared spectrum that the polymers containing tertiary amino group possess the structure which resembles the internal salt of amino acid in weak basic and weak acidic solution:     

Steric aspects of selectivity of organophosphorus extractants

This paper is devoted to the steric aspects of the efficiency and selectivity of extractants in the process of extraction of metal cations from acidic aqueous solution into a nonpolar phase. The extraction of uranium, plutonium, americium, and europium by tertiary carbamoylmethyl phosphine oxides and polydiphenylphosphinylmethyl benzenes have been studied. The separation factors of uranium and plutonium from americium are measured. Tertiary carbamoylmethyl phosphine oxides and diphenylphosphinylmethyl benzenes of the ortho type are characterized by unusually high separation factors. The diphenylphosphinylmethyl derivatives of benzene of the meta type do not possess a high selectivity in the process of separation of uranium and plutonium from americium, but are more efficient in extraction of americium.     

Polymers with double-decker and side-opened cage silsesquioxanes: Effects of cage structures on materials properties

Cage silsesquioxanes, also known as polyhedral oligomeric silsesquioxanes (POSS), serve as crucial building blocks in crafting precisely designed organic–inorganic hybrid materials, given that their well-defined silsesquioxane clusters can be adorned with organic substituents. While polymers with POSS in their main chains have been thoroughly examined, analyzing the correlation between cage structure and material properties in main-chain-type polymers remains challenging. This difficulty stems from the limited range of organic substituents on traditional POSS monomers, thereby precluding comparisons between polymers with unified substituents and different cage structures. In this study, we synthesized double-decker silsesquioxane (DDSQ) and side-opened POSS (SO-POSS) monomers, both featuring phenyl groups. Subsequent platinum-catalyzed hydrosilylation polymerization yielded main-chain-polymers. Both the cage and linker structures influence thermal stability and the glass transition temperature, while the hardness was primarily determined by the linker structure. This research is the first to elucidate the impact of cage structure on the material properties of main-chain-type POSS polymers.     

Pyridylalkylamine ligands and their palladium complexes: structure and reactivity revisited by NMR

Pyridylmethylamines or pma are versatile platforms for different catalytic transformations. Five pma‐ligands and their respective Pd complexes have been studied by liquid state NMR. By comparing ¹H, ¹³C and ¹⁵N chemical shifts for each pma/pma–Pd couple, a general trend for the metallacycle atoms concerns variations of the electronic distribution at the pendant arm, especially at the nitrogen atom of the ligand. Moreover, the increase of the chemical shift of the pendant arm nitrogen atom from primary to tertiary amine is also related to the increase of crowding within the complex. This statement is in good agreement with X‐ray data collected for several complexes. Catalytic results for the Suzuki–Miyaura reaction involving the pma–Pd complexes showed within this series that a sterically crowded and electron‐rich ligand in the metallacycle was essential to reach the coupling product with a good selectivity. In this context, NMR study of chemical shifts of all active nuclei especially in the metallacycle could give a trend of reactivity in the studied family of pma–Pd complexes. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of class I and II organic modifiers on retention and selectivity in vesicle electrokinetic chromatography

Vesicles are large aggregates of surfactant monomers consisting of a spherical bilayer surrounding an internal cavity of solvent. The bilayer structure allows vesicles to be attractive models for the study of various transmembrane and binding processes. The use of thermodynamically stable vesicles (TSV) formed from oppositely charged surfactants for use as a pseudostationary phase in electrokinetic chromatography (EKC) was first accomplished using dodecyltrimethylammonium bromide and sodium dodecyl sulfate (DTAB/SDS). Surfactant vesicles have demonstrated enhanced separation characteristics compared to conventional micelles in EKC, although only investigated in aqueous media. Organic modifiers have been widely studied and used in EKC to enhance separation conditions. In this study, vesicles formed from cetyltrimethylammonium bromide and sodium octyl sulfate (CTAB/SOS) were investigated in the presence of "class I and II" organic modifiers. Electrophoretic and chromatographic parameters were examined as well as linear solvation energy relationship analysis (LSER) to characterize the effects of the modifiers on retention and selectivity in EKC. LSER analysis is a useful way to quantitatively investigate solute/solvent interactions responsible for retention and selectivity.