Aggregation Properties In Solution Research Articles

Microscopic growth of pyridinium oxime based amphipathic on graphite: Effect of relative position of substituents

AbstractAmphipathic molecules with surfactant like properties have several applications ranging from healthcare to the chemical industry. Their ability to form thin films on surfaces with ordered and controllable patterns determines their applicability. Here, we report two pyridinium oxime‐based surfactants, which possess similar aggregation properties in solution, but exhibit substantially different assembly on highly oriented pyrolytic graphite (HOPG) surface. The two compounds are regioisomers with the oxime unit placed either in meta or para position of the pyridinium ring. While the para isomer assembled to anisotropic one‐dimensional (1D) islands and long rod‐like structures, the meta isomer formed two‐dimensional (2D) islands on the HOPG surface. This difference is rationalized through molecular level force‐field calculations that show anisotropy in the growth of the para isomer resulting from an effective overlap of the alkyl chains and oxime groups, which is distinctly not feasible in the assembly of the meta isomer. The assembly of these compounds is compared with another oxime‐containing compound of similar structure, but without the charged pyridinium unit. The charged unit seems to be crucial for the preferential formation of multilayer islands even at low coverage.

Human γS-Crystallin Mutation F10_Y11delinsLN in the First Greek Key Pair Destabilizes and Impairs Tight Packing Causing Cortical Lamellar Cataract.

Aromatic residues forming tyrosine corners within Greek key motifs are critical for the folding, stability, and order of βγ-crystallins and thus lens transparency. To delineate how a double amino acid substitution in an N-terminal-domain tyrosine corner of the CRYGS mutant p.F10_Y11delinsLN causes juvenile autosomal dominant cortical lamellar cataracts, human γS-crystallin c-DNA was cloned into pET-20b (+) and a p.F10_Y11delinsLN mutant was generated via site-directed mutagenesis, overexpressed, and purified using ion-exchange and size-exclusion chromatography. Structure, stability, and aggregation properties in solution under thermal and chemical stress were determined using spectrofluorimetry and circular dichroism. In benign conditions, the p.F10_Y11delinsLN mutation does not affect the protein backbone but alters its tryptophan microenvironment slightly. The mutant is less stable to thermal and GuHCl-induced stress, undergoing a two-state transition with a midpoint of 60.4 °C (wild type 73.1 °C) under thermal stress and exhibiting a three-state transition with midpoints of 1.25 and 2.59 M GuHCl (wild type: two-state transition with Cm = 2.72 M GuHCl). The mutant self-aggregates upon heating at 60 °C, which is inhibited by α-crystallin and reducing agents. Thus, the F10_Y11delinsLN mutation in human γS-crystallin impairs the protein's tryptophan microenvironment, weakening its stability under thermal and chemical stress, resulting in self-aggregation, lens opacification, and cataract.

Role of Torsional Flexibility in the Film Formation Process in Two π-Conjugated Model Oligomers.

The performance of solution-processed organic semiconductor devices is heavily influenced by the morphology of the active layer. Film formation is a complex process, with the final morphology being the result of the interplay between processing parameters and molecular properties, which is only poorly understood. Here, we investigate the influence of molecular stiffness by using two model oligomers, TT and CT, which differ only in the rotational flexibility of their central building block. We monitor absorption and emission simultaneously in situ during spin coating. We find that film formation takes place in four similar stages for both compounds. However, the time scales are remarkably different during the third stage, where electronically interacting aggregates are created. While this process is fast for the stiff CT, it takes minutes for the flexible TT. By comparing with previously determined aggregation properties in solution, we conclude that even though aggregate formation concurs with a planarization process, a certain amount of backbone flexibility is beneficial for establishing ordered structures during film formation. Here, the elongated time window in the case of the flexible compound can further allow for better processing control.

Supramolecular Aggregation of a New Substituted Bis(salicylaldiminato)zinc(II) Schiff-Base Complex Derived from trans-1,2-Diaminocyclohexane

In this contribution is reported the synthesis, characterization, and aggregation properties in solution of a novel Zn(II) complex, (R)-2, derived from the enantiopure chiral trans-1,2-diaminocyclohexane and a substituted salicylaldehyde. Detailed 1H NMR, DOSY NMR, optical absorption, and circular dichroism spectroscopic studies and chemical evidence allowed to investigate the nature of aggregate species in solution. The high solubility of (R)-2 in solution of the non-coordinating chloroform solvent leads to formation of various aggregates, some of them consisting of large oligomers estimated to contain up to 27 monomeric units. The chiral trans-stereochemistry of the bridging diamine favors a different aggregation mode in these complexes, both in the oligomers and dimers, involving a tetrahedral coordination geometry around the metal center. Overall data suggest the formation of helical oligomers, (ZnL)n, in freshly prepared chloroform solutions which, by standing or heating, evolve towards a more thermodynamically stable, dinuclear double-helicate Zn2L2 dimer.

Supramolecular Aggregates of Defined Stereochemical Scaffolds: Aggregation/Deaggregation in Schiff-Base Zinc(II) Complexes Derived from Enantiopure trans-1,2-Diaminocyclohexane.

This contribution explores, through detailed 1H NMR, DOSY NMR, optical absorption, and circular dichroism spectroscopic studies, the aggregation properties in solution of noncoordinating solvents of some new ZnII Schiff-base complexes, (R)-1, (S)-1, and (R)-2, derived from the chiral trans-1,2-diaminocyclohexane. It is found that chloroform solutions of 1 are characterized by the presence of three species, the predominance of which consists of large oligomeric aggregates. For chloroform solutions of 1, upon heating or standing, all species are irreversibly converted into a dimer, 1C, which is very stable and hardly disaggregable. Analysis of 1H NMR, UV/vis, and CD spectroscopic data and chemical evidence allow proposing a double helicate Zn2L2 structure with a tetrahedral coordination around the ZnII ions for 1C, as a consequence of the defined stereochemistry of the trans-1,2-diaminocyclohexane chelate bridge. This represents a different, uncommon aggregation mode in ZnII complexes of tetradentate Schiff-bases.

Conjugated polymers with m-pyridine linkages: synthesis, photophysics, solution structure and film morphology

The synthesis of two π-conjugated polymers whose structures include m-pyridyl linkages that create regularly spaced bends and disrupt π-conjugation along the polymer backbones is described. The π-conjugated segments in the two polymers were comprised of p-(2,5-dialkoxyphenylene)vinylene, p-phenylenevinylene and 2,7-carbazole subunits. Additionally, each m-pyridylene unit is enshrouded within a steric cleft provided by 2,6-diaryl substitution of the pyridyl ring, thus minimizing inter-chain interactions of these sites. The concentration-dependence of photophysical characteristics along with small angle neutron scattering (SANS) was employed to resolve solution aggregation properties and atomic force microscopy was employed to assess the surface morphology of polymer films.

Asymmetrically end capping perylene diimide with POSS and C60 for controlled self assembly

Perylene diimide dye asymmetrically end capped with POSS and C60 has been synthesized and fully characterized. Aggregation properties in solution have been investigated in detail using UV/vis and fluorescence spectroscopy, differential scanning calorimeter (DSC), and X-ray diffraction. Concentration dependent UV/vis measurements revealed that PDI characteristic peaks decreased gradually with intensity reversal appearing less dramatic at higher concentration, an indication of good control on the π–π interaction. Neither new peak nor peak shifting was observed during aggregation. Solubility of the dye in organic solvents increased as a result of easy solvation of the PDI due to POSS weakening the π-system.

An Unprecedented Structural Interconversion in Solution of Aggregate Zinc(II) Salen Schiff-Base Complexes

This contribution explores the aggregation properties in solution of noncoordinating solvents of a series of amphiphilic Zn(salen) derivatives, through detailed (1)H NMR, DOSY NMR, and optical absorption spectroscopic studies. It is found that these aggregate species are involved in a unique structural interconversion between two defined dimers, A and B, driven by the concentration of water dissolved in chloroform. Dilute CHCl(3) solutions are characterized by the presence of dimeric species, A, in which both Zn(II) atoms of the Zn(salen) units mutually interact through a Zn···O axial coordination, likely adopting a square-base pyramidal structure. Investigations to higher concentrations indicate the existence of a new dimeric species, B, in equilibrium to that observed at lower concentrations, involving a coordination mode interconversion of an intermediate monomer presumably from a square-pyramidal to a trigonal bipyramidal structure. This behavior may be related to the nonconjugated, conformational flexible nature of the bridging diamine of the Schiff base, and is influenced by the solvent polarity. Variable-temperature (1)H NMR studies indicate the existence of a nonequivalent species B' in a fluxional equilibrium with species B.

Synthesis and Characterization of Poly-l-lysine-Grafted Silica Nanoparticles Synthesized via NCA Polymerization and Click Chemistry

Polypeptide polymer-grafted silica nanoparticles are of considerable interest because the ordered secondary structure of the polypeptide grafts imparts novel functional properties onto the nanoparticle composite. The synthesis of poly-L-lysine-grafted silica nanoparticles would be of particular interest because the high density of cationic charges on the surface could lead to many applications such as gene delivery and antimicrobial agents. In this work, we have developed a "grafting-to" approach using a combination of NCA polymerization and "click chemistry" to synthesize poly-L-lysine-grafted silica nanoparticles with a high graft density of 1 chain/nm(2). The covalent attachment of poly-L-lysine to silica nanoparticles (PLL-silica) was confirmed using a variety of techniques such as (13)C CP MAS NMR, TGA, and IR. This methodology was then extended to graft poly-L-lysine-b-poly-L-leucine copolymer (PLL-b-PLLeu-silica) and poly-L-benzylglutamate (PLBG-silica) onto silica nanoparticles. All of these polypeptide-grafted nanoparticles show interesting aggregation properties in solution. The efficacy of PLL-silica and PLL-b-PLLeu-silica as antimicrobial agents was tested on both gram-negative E. coli and gram-positive Bacillus subtilis.

Novel dyes derived from hydrazones. Part 4. Synthesis and characterizations of 2-{4-[(2 E)-2-(1-arylylidene)hydrazino]phenyl}ethylene-1,1,2-tricarbonitrile

Novel tricyanovinyl derived from hydrazones have been prepared by the reaction of tetracyanoethylene and phenylethylidene hydrazone, and these dyes showed absorption in the region of 500–593 nm. The dyes showed pronounced solvatochromic effects as the polarity of the solvents increased. Some of the new dyes were studied to show the aggregation properties in solution as the concentration changed. Most of the dyes studied showed change in the absorption spectrum and hence the position of the maximum absorption bands. The thermal stability of some of the prepared dyes was studied in polymethylmethacrylate film at 80 °C; the annulations on the aromatic group showed less thermal stability of the dyes.

Novel dyes derived from hydrazones: Part 3. Synthesis and characterizations of 2-[4-(1-phenylethylidene)hydrazino]phenylethylene-1,1,2-tricarbonitrile

Novel tricyanovinyl dyes derived from hydrazones have been prepared by the reaction of tetracyanoethylene and phenylethylidene hydrazone, and these dyes showed absorption in the region of 500 nm. The dyes showed pronounced solvatochromic effects as the solvent's polarity increased. Some of the new dyes were studied to show their aggregation properties in solution as the concentration changed. Most of the dyes studied showed change in the absorption spectrum and hence the position of the maximum absorption bands. The thermal stability of some of the prepared dyes was studied in poly(methyl methacrylate) film at 80 °C; the substitution on the aromatic group showed less thermal stability of the dyes.

Microstructurally Controlled Polyisoprene or Polystyrene Diblock Copolymers of rac‐Lactide

AbstractSummary: A series of new polyisoprene‐block‐polylactide and polystyrene‐block‐polylactide diblock copolymers was prepared by combining the living anionic polymerization of isoprene or styrene, and the stereoselective ring‐opening polymerization of rac‐lactide. Aluminum and yttrium‐based polystyrene or polyisoprene macroinitiators yielded isotactic‐stereoblock and heterotactic‐enriched polylactide segments, respectively. A strong influence of the microstructure of the polylactide block on the aggregation properties in solution and morphological behavior of the solid materials in thin films has been observed.General strategy used for the preparation of the diblock copolymers, illustrated here for poly(isoprene‐block‐lactide). Poly(styrene‐block‐lactide) copolymers were prepared similarly.magnified imageGeneral strategy used for the preparation of the diblock copolymers, illustrated here for poly(isoprene‐block‐lactide). Poly(styrene‐block‐lactide) copolymers were prepared similarly.

Novel dyes derived from hydrazones. Part 2: synthesis and characterizations of N-methyl-4-tricyanovinylidenephenyl-hydrazones

Novel tricyanovinyl derived from N-methylhydrazones have been prepared by the reaction of tetracyanoethylene and N-methylbenzylidenehydrazone, and these dyes showed absorption in the region of 500 nm. The dyes showed pronounced solvatochromic effects as the solvents' polarity increased. Some of the new dyes were studied to show their aggregation properties in solution as the concentration changed. Most of the dyes studied showed change in the absorption spectrum and hence the position of the maximum absorption bands. The thermal stability of some of the prepared dyes was studied in poly(methyl methacrylate) film at 80 °C; the substitution on the aromatic aldehydes showed some improvement of the thermal stability of the dyes.

The effect of the chemokine rhMIP-1 alpha, and a non-aggregating variant BB-10010, on blast cells from patients with acute myeloid leukaemia.

The effects of recombinant macrophage inflammatory protein 1 alpha (rhMIP-1 alpha) on the proliferation of leukaemic blast cells from patients with acute myeloid leukaemia was assessed. Using the previously described [3H]thymidine incorporation index assay, the response of autonomous and growth factor responsive AML blast cells to the chemokine rhMIP-1 alpha was measured. In the case of autonomous proliferators, rhMIP-1 alpha had no inhibitory effect on [3H]thymidine incorporation and in 4/6 cases [3H]-thymidine incorporation was stimulated by rhMIP-1 alpha. In the presence of stem cell factor (SCF), a majority (8/9) of the samples which responded to this growth factor were inhibited when rhMIP-1 alpha was included in the assay medium. Similar results were obtained with GM-CSF-responsive samples; however, when these two cytokines were combined, only 3/14 were significantly inhibited. In the presence of human placental conditioned medium (HPCM), rhMIP-1 alpha significantly inhibited [3H]thymidine incorporation in only 2/10 of HPCM-responsive samples. In methylcellulose assays rhMIP-1 alpha had no consistent effect on colony/cluster formation in the presence of either GM-CSF + SCF or HPCM. Similar results were obtained with BB-10010, a mutant of rhMIP-1 alpha which has defined aggregation properties in solution. These data suggest that autonomously proliferating AML cells, and also some AML samples which require cytokines to proliferate, are non-responsive to the growth inhibitors rhMIP-1 alpha and BB-10010 in the presence of multiple growth factors.

ChemInform Abstract: Synthesis and Different Aggregation Properties in Solution of Alkyl‐ and Dialkyl Amide Surrounded Phthalocyanines.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis and different aggregation properties in solution of alkyl- and dialkyl amide surrounded phthalocyanines

The synthesis of dodecylaminocarbonylmethoxy substituted phthalocyanines 5ȁ7 and their precursors is described. It is demonstrated that aggregation in solution of dioctyl-aminocarbonylmethoxyphthalocyanines 1ȁ4 is induced by the presence of cations whilst hydrogen bonding is the only determinant force in the aggregation of 5ȁ7.