Self-aggregation In Aqueous Solution Research Articles

Development of self-assembled monolayer of stearic acid grafted chitosan on mild steel and inhibition of corrosion in hydrochloric acid

Abstract Chitosan (CS) based systems are extensively used as a green alternative for corrosion protection of mild steel (MS) possessing good film-forming properties, chelation with metal and nontoxic nature. In this study, a self-assembled monolayer of stearic acid grafted chitosan was developed via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide mediated coupling reaction and casted on the MS surface. From the fluorescence intensity of the fluorescent probe pyrene, the critical micelle concentration (66 μg/mL) of self-aggregates in aqueous solution was determined. The purified chitosan grafted films were characterized by apposite analytical techniques. The film developed was employed for corrosion protection of MS in 0.5 and 1 N HCl via electrochemical and non-electrochemical techniques. The results showed that stearic acid grafted chitosan (CSA) films do offer better corrosion protection to MS than bare CS film.

Self-aggregation in aqueous solution of amphiphilic cationic calix[4]arenes. Potential use as vectors and nanocarriers

Abstract The self-aggregation of four amphiphilic cationic calix[4]arenes, CALIX, in aqueous solutions was investigated in this work. The nature of the polar group present at the upper rim as well as the length of the hydrophobic tails attached to the lower rim was varied. All the calixarenes present two critical aggregation concentrations, CAC1 and CAC2. For [CALIX] CAC2 micelles and a wide distribution of vesicles were found. Cell viability experiments show that calixarene micelles and several of the calixarene vesicles investigated could be used as biocompatible nanocarriers. On this basis, the study of the interactions between the cationic calixarene aggregates (micelles and vesicles) and calf thymus DNA, ctDNA, were done and the results indicated that most of them strongly interact with the polynucleotide, inverting its charge. Micelles totally compact the ctDNA, while vesicles only partially cause conformational changes in the nucleic acid. Therefore, the CALIX micelles show potential as vectors in gene therapy. The encapsulation of the antineoplastic drug doxorubicin into the calixarene aggregates was also investigated. A high encapsulation efficiency was found for micelles and, specially, for vesicles. However, DOX-loaded calixarene vesicles present low stability at 37 °C, which is a serious restriction in their use as nanocarriers for this drug. The release of DOX from the calixarene micelles shows that they could lengthen the half-life of free doxorubicin in the body and, as a result, lower amounts of drug could be used in the cancer treatments diminishing the important side effects of DOX.

Supramolecular protection-mediated one-pot synthesis of cationic gold nanoparticles

Despite the extended use of cationic gold nanoparticles (AuNPs) in biomedical applications, direct one-pot synthesis of AuNPs with tunable size in aqueous media is limited due to the deleterious electrostatic attraction between AuCl4-anions and positively charged ligands. This paper describes the one-pot synthesis of cationic gold nanoparticles with size tunability based on host-guest chemistry. As the host molecule, cucurbit[7]uril inhibits self-aggregation in aqueous solution by threading positively charged guest ligands, which provides a shielding effect on the ligands. Reduction of the mixtures by directly adding NaBH4 generates cationic AuNPs with narrow size distributions. Furthermore, their potential in biomedical applications is demonstrated by siRNA transfection experiments. This approach relying on supramolecular-mediated interactions may provide new insights into organic/inorganic reactions that involve electrostatic disturbance.

Squaramide—Naphthalimide Conjugates as “Turn-On” Fluorescent Sensors for Bromide Through an Aggregation-Disaggregation Approach

The syntheses of two new squaramide-naphthalimide conjugates (SQ1 and SQ2) are reported where both compounds have been shown to act as selective fluorescence “turn on” probes for bromide in aqueous DMSO solution through a disaggregation induced response. SQ1 and SQ2 displayed a large degree of self-aggregation in aqueous solution that is disrupted at increased temperature as studied by 1H NMR and Scanning Electron Microscopy (SEM). Moreover, the fluorescence behavior of both receptors was shown to be highly dependent upon the aggregation state and increasing temperature gave rise to a significant increase in fluorescence intensity. Moreover, this disaggregation induced emission (DIE) response was exploited for the selective recognition of certain halides, where the receptors gave rise to distinct responses related to the interaction of the various halide anions with the receptors. Addition of F− rendered both compounds non-emissive; thought to be due to a deprotonation event while, surprisingly, Br− resulted in a dramatic 500–600% fluorescence enhancement thought to be due to a disruption of compound aggregation and allowing the monomeric receptors to dominate in solution. Furthermore, optical sensing parameters such as limits of detection and binding constant of probes were also measured toward the various halides (F−, Cl−, Br−, and I−) where both SQ1 and SQ2 were found to sense halides with adequate sensitivity to measure μM levels of halide contamination. Finally, initial studies in a human cell line were also conducted where it was observed that both compounds are capable of being taken up by HeLa cells, exhibiting intracellular fluorescence as measured by both confocal microscopy and flow cytometry. Finally, using flow cytometry we were also able to show that cells treated with NaBr exhibited a demonstrable spectroscopic response when treated with either SQ1 or SQ2.

Experimental and computational study of guanidinoacetic acid self-aggregation in aqueous solution

In this work for the first time the physicochemical and thermal properties of guanidinoacetic acid (GAA) and its aqueous solutions have been performed to test for its viability as a potential dietary supplement. Thermal stability, viscosity, solubility and experimental density are determined. From measured densities the volumetric properties were estimated and discussed in the scope of GAA self-aggregation in aqueous solutions using experimental and computational results. Based on thermal stability and solubility measurements, it is found that GAA is more thermally stable but less soluble comparing to creatine due to a self-aggregation process that occurs at GAA concentrations higher than 0.013mol·dm−3. Existence of self-aggregation influences the macroscopic properties of aqueous GAA solutions, but also its bioavailability.

Mesoscopic simulation of alkylimidazoline self-aggregation in aqueous solution

ABSTRACTA dissipative particle-dynamics method was used to simulate the self-aggregation behavior of 15 alkylimidazoline surfactants of different structures. The effects of concentration and structure of hydrophilic and lipophilic groups of the alkylimidazolines on the configuration and aggregation number (Nagg) of the micelles were also explored. Results show that the concentration of the alkylimidazoline has a significant influence on the configuration of the micelles generated. More specifically, alkylimidazolines of different concentrations are found to generate different structures (spherical, rod-shaped, layered, and interlaced) in aqueous solution. At low (1–10 wt%) and medium (40 wt%) concentrations, the micelles generated in aqueous solution are spherical and rod-shaped, respectively. At higher concentrations (80 wt%), the micelles generated present interlaced shapes with rod-shaped and layered micelles when the length of the lipophilic chain is greater than C13 or the hydrophilic group is Hc. Nagg is strongly dependent on alkylimidazoline concentration and increases as concentration increases. Nagg is also greatly dependent on the structure of the hydrophilic and lipophilic groups present: it increases as the chain length of the lipophilic group increases but decreases as that of the hydrophilic group increases.

Morphology transition of self-aggregates of poly(amino acid)-drug conjugates

Abstract In this paper, we report morphology tunable self-aggregates of poly(amino acid)-drug conjugates. Amphiphilic drug-grafted polymers were synthesized by grafting hydrophobic phytosphingosine (PHS) onto two different hydrophilic poly(amino acid)s backbones, and the hydrophilic/hydrophobic ratio were controlled by varying the number of grafted drugs. The amphiphilic poly(amino acid)-g-PHS formed self-aggregates in aqueous solution, and morphology transitions of the self-aggregates from sphere to ellipsoid to cylindrical micelles were observed with increasing number of grafted phytosphingosines. Morphologies of self-aggregates were further confirmed by small angle neutron scattering, showing that the obtained self-aggregates consisted of a thin poly(amino acid) shell and a PHS core. The morphological changes of PHS-grafted poly(amino acid) were interpreted using geometrical changes of building blocks arising from the decrease of the hydrophilic part per PHS with increasing number of PHS grafts.

SPECTROSCOPIC STUDY OF ALUMINUM PHTHALOCYANINE CHLORIDE (AlPcCl) IN HOMOGENEOUS AND MICRO-HETEROGENEOUS MEDIA CONSISTING OF P-123 AND F-127 POLYMERIC MICELLES

Aluminum phthalocyanine chloride (AlPcCl) is a photoactive compound which has been used as a photosensitizer (PS) in photodynamic therapy (PDT). Its spectroscopic properties have been studied in solvents of different polarities (ethanol, acetone, dimethylsulfoxide and chloroform). Its solubility has been found to decrease with increasing solvent polarity, together with full self-aggregation in aqueous solution. The binding of AlPcCl to the copolymer PluronicTM micellar class P-123 and F-127 used as solubilizer/carriers was studied. Greater interaction between the more hydrophobic copolymer P-123 and AlPcCl was observed, besides a complex interaction profile involving different AlPcCl forms (self-aggregate/monomeric form) in the copolymers. Time- and temperature-dependent structural organization of AlPcCl in the copolymers was also observed. Thus, AlPcCl has a strong tendency to self-aggregate with increasing solvent polarity, an effect also observed in micellar media.

The influence of sodium chloride on the self-association and chromonic mesophase formation of Edicol Sunset Yellow

We have investigated the effect of an inorganic electrolyte (sodium chloride) on the aggregation behaviour and liquid crystals of Edicol Sunset Yellow. Edicol self-aggregates in aqueous solution to form single molecule stacks, which then become ordered to form nematic and hexagonal (columnar) mesophases at high concentrations. We have employed changes in the 1H nuclear magnetic resonance (NMR) chemical shifts to monitor the aggregate formation in solution. A single spectrum is observed at all concentrations because the exchange between Edicol monomers in solution and those in stacks is fast on the NMR time scale. The results show that at low Edicol concentrations (<1 wt%) the concentration of aggregates is small, but at high concentrations (20 wt%) the fraction of monomers is tiny. At low Edicol concentrations, low levels of salinity appear to alter aggregate shape and size, resulting in a disaggregation/aggregation effect occurring over four orders of magnitude of added electrolyte. However, little alteration is seen in the fraction of aggregates. At high electrolyte levels, when the Debye length is comparable to the stack lengths (a few nanometres), the fraction of aggregates increases, presumably because of the reduced intra-stack electrostatic repulsion. Importantly, we have also shown that the isodesmic theory of aggregation (equal K) is too simple to describe accurately the aggregation process from the monomer to the pre-nematic phase concentrations. NMR quadrupole splittings indicate that there is no specific Na+ ion binding to the stacks. At the very highest concentrations of Edicol and sodium chloride the aggregates and mesophases are destabilised. The reason for this has yet to be elucidated.

Binding of Multivalent Anionic Porphyrins to V3 Loop Fragments of an HIV‐1 Envelope and Their Antiviral Activity

Interactions of multivalent anionic porphyrins and their iron(III) complexes with cationic peptides, V3(Ba-L) and V3(IIIB), which correspond to those of the V3 loop regions of the gp120 envelope proteins of the HIV-1(Ba-L) and HIV-1(IIIB) strains, respectively, are studied by UV/Vis, circular dichroism, (1)H NMR, and EPR spectroscopy, a microcalorimetric titration method, and anti-HIV assays. Tetrakis(3,5-dicarboxylatophenyl)porphyrin (P1), tetrakis[4-(3,5-dicarboxylatophenylmethoxy)phenyl]porphyrin (P2), and their ferric complexes (Fe(III)P1 and Fe(III)P2) were used as the multivalent anionic porphyrins. P1 and Fe(III)P1 formed stable complexes with both V3 peptides (binding constant K>10(6) M(-1)) through combined electrostatic and van der Waals interactions. Coordination of the His residues in V3(Ba-L) to the iron center of Fe(III)P1 also played an important role in the complex stabilization. As P2 and Fe(III)P2 form self-aggregates in aqueous solution even at low concentrations, detailed analysis of their interactions with the V3 peptides could not be performed. To ascertain whether the results obtained in the model system are applicable to a real biological system, anti-HIV-1(BA-L) and HIV-1(IIIB) activity of the porphyrins is examined by multiple nuclear activation of a galactosidase indicator (MAGI) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. There is little correlation between chemical analysis and actual anti-HIV activity, and the size rather than the number of the anionic groups of the porphyrin is important for anti-HIV activity. All the porphyrins show high selectivity, low cytotoxicity, and high viral activity. Fe(III)P1 and Fe(III)P2 are used for the pharmacokinetic study. Half-lives of these iron porphyrins in serum of male Wistar rats are around 4 to 6 h owing to strong interaction of these porphyrins with serum albumin.

Ammonium ionic liquid as modulator of the critical micelle concentration of ammonium surfactant at aqueous solution: Conductimetric and dynamic light scattering (DLS) studies

We report measurements of self aggregation in aqueous solution of an ionic liquid (IL), didecyl-dimethylammonium nitrate ([DDA][NO 3]) and a surfactant hexadecyl-trimethylammonium bromide (CTAB) and of mixtures of these two salts. The electrical conductivity and dynamic light scattering (DLS) measurements were used for the characterization of the aggregation process. The conductivity measurements were performed at three temperatures. The critical micelle concentration (CMC) was determined at different temperatures and at different ratio of two salts. The effect of IL on the micellization of CTAB has been discussed. Our results suggest that organized structures formed by CTAB and [DDA][NO 3] self assembly in domains of several hundred nanometers size. The micellar solubility of the salicylic acid in mixed salt aqueous solutions was determined to probe the physical properties of these assemblies. We have observed, that the micellar solubility enhancement was only slightly influenced by the nature of micelles present in aqueous solution. This proves that salicylic acid solubilization is enthalpy driven.

Modification of the Nanoscale Structure of the J-Aggregate of a Sulfonate-Substituted Amphiphilic Carbocyanine Dye through Incorporation of Surface-Active Additives

The amphiphilic dye 3,3'-bis(2-sulfopropyl)-5,5',6,6'-tetrachloro-1,1'-dioctylbenzimidacarbocyanine (C8S3) self-aggregates in aqueous solution to form tubular J-aggregates with a diameter of 17.0 +/- 0.5 nm, a wall thickness of approximately 4 nm, and a length exceeding several hundred nanometers. The absorption spectrum shows the typical features expected for tubular J-aggregates with several sharp and red-shifted absorption bands. Morphological investigations using cryo-transmission electron microscopy (cryo-TEM) and spectroscopic investigations reveal a high stability of the tubular morphology but a tendency of the aggregates to assemble into ropelike bundles after several weeks of storage. It is found that aggregation in solutions containing additives such as alcohols or surfactants results in the formation of new types of aggregates. A second type of tubular aggregate with a diameter of 13.0 +/- 0.5 nm is observed when the solutions contain more than 10 wt % MeOH. On the time scale of days these tubular aggregates transform into ribbonlike structures characterized by a new absorption spectrum, and they convert after several weeks into giant tubes with diameters of up to 500 nm.

A novel chitosan oligosaccharide–stearic acid micelles for gene delivery: Properties and in vitro transfection studies

Stearic acid (SA) grafted chitosan oligosaccharide (CSO) (CSO–SA), which was synthesized by an 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)-mediated coupling reaction, was demonstrated to form micelle like structure by self-aggregation in aqueous solution. The critical micelle concentration (CMC) of CSO–SA with 15.4% amino substituted degree of CSO was about 0.035 mg/ml. The micelles with 1 mg/ml CSO–SA concentration had 70.6 nm volume average hydrodynamic diameter with a narrow size distribution and 46.4 ± 0.1 mV surface potential. Due to the cationic property, the micelles could compact the plasmid DNA to form micelle/DNA complexes nanoparticles, which can efficiently protect the condensed DNA from enzymatic degradation by DNase I. The volume average hydrodynamic diameter of CSO–SA micelle/DNA complex increased from 203 nm to 318 nm and decreased to 102 nm due to the variation of zeta potential when the N/P ratio increased from 0.25 to 3.6 and from 3.6 to 58. The IC 50 value of the CSO–SA micelle against A549 cells was 543.16 μg/ml, while the IC 50 of Lipofectamine™ 2000 was about 6 μg/ml. The in vitro transfection efficiency of CSO–SA micelles was investigated by using plasmid DNA (pEGFP-C1). The transfection efficiency with CSO–SA/DNA (N/P ratio is 29) was increased with the post-transfection time (in 76 h), while the optimal transfection of Lipofectamine™ 2000/DNA was obtained at 24 h. The transfection of CSO–SA was not interfered in the presence of 10% fetal bovine serum, which showed remarkable enhancement effect. The optimal transfection efficiency of CSO–SA micelles in A549 cells was about 15%, which was higher than that of CSO (about 2%) and approach to that of Lipofectamine™ 2000 (about 20%). The low cytotoxic biodegradable CSO–SA micelles could be used as an effective DNA condensation carrier for gene delivery system.

Controlling the Helicity of Tubular J-Aggregates by Chiral Alcohols

The achiral 3,3‘-bis(3-carboxypropyl)-5,5‘,6,6‘-tetrachloro-1,1‘-dioctylbenzimidacarbocyanine dye (C8O3) self-aggregates in aqueous solution to form optically active helical J-aggregates. A three-phasic circular dichroism (CD) spectrum with positive Cotton effect at 568 nm, negative Cotton effect at 582 nm, and positive Cotton effect at 605 nm (+,−,+) is usually found and ascribed to molecular excitons. The predominance of the (+,−,+) signature means that the generation of chirality is enantioselective. The CD signal increases by a factor of about 100 when the chiral (R)-2-octanol is added to an aggregated solution, and the CD signal is further amplified by a factor of about 5 when the alcohol is present in the solvent prior to aggregation. The signature of the CD signal reverses if the enantiomeric (S)-2-octanol is used instead, and for a molar alcohol/dye ratio R of about 20, the spectra become mirror images in good approximation; i.e., the chirality of the alcohol and the CD spectra of aggregates are c...

Self-aggregates of hydrophobically modified poly(2-hydroxyethyl aspartamide) in aqueous solution

Dehydrocholic acid (DHA) grafted poly(2-hydroxyethyl aspartamide) (PHEA)s were successfully synthesized and their self-aggregates in aqueous solution were characterized by fluorescence spectra and light scattering. PHEA was obtained by a simple reaction of ethanolamine with synthesized poly(succinimide) (PSI), and then PHEA-g-DHA was synthesized through an ester linkage between DHA and PHEA. The degree of substitution (DS) of DHA groups, defined by grafted mole%, was determined from both 1H-NMR and elemental analysis. The grafting reaction of DHA was retarded up to almost 10 mole% feed ratio of DHA/PHEA, but increased linearly above the threshold ratio. Nano-size self-aggregates in aqueous solution were examined with four DSs less than 10. As DS increased, the critical aggregation concentrations (CAC) of polymers were continuously reduced and the size of primary aggregates reduced to as small as 40 nm in diameter. When stored, the sonicated aggregates of high DS were destabilized, apparently forming large aggregates with small curvatures. The formation of irreversible interfused secondary structures would be induced by the curvature change or aggregation of primary particles. A simple calculation indicates that a small change of separation between grafted DHA groups may induce the large curvature shift, in fact, sphere-to-planar surface transition.

Polymer micelle-like aggregates of novel amphiphilic biodegradable poly(asparagine) grafted with poly(caprolactone)

Novel amphiphilic graft copolymers composed of poly(asparagine) (PAsn) as the hydrophilic backbone and poly(caprolactone) (PCL) as the hydrophobic segment were successfully synthesized by grafting PCL–HMDs to poly(succinimde). After tosylating PCL-diol with p-toluenesulfonylchloride (TsCl), tosylated poly(caprolactone) (PCL–OTs) was then reacted with hexamethylenediamine (HMD). The reaction of the amine terminated PCL with poly(succinimide) (PSI) and the following aminolysis resulted in poly(aspargine)- graft-poly(caprolactone) (PAsn- g-PCL). The degree of substitution (DS) and grafting reaction was confirmed by 13C NMR, FT-IR spectroscopy and elemental analysis. X-ray diffraction and DSC thermogram showed that the crystalline domain originated from PCL became apparent with an increase of DS. The amphiphilic comb-type graft polymer formed self-aggregates in aqueous solution when precipitated and dialysed against distilled water. Strong hydrophobic interaction of associated PCL grafts facilitated primary aggregate formation with DS, significantly reducing critical aggregation concentration and secondary aggregates also appeared in DLS measurements. Self-aggregates showed a bimodal size distribution originated from the self-aggregation and kinetically controlled particle aggregation, although the smaller primary aggregates was predominant. Spherical and dispersed aggregates of about 20 nm in diameter were observed by a transmission electron microscope.

Preparation and characterization of hydrophobically modified alginate

Biodegradable alginate-derived polymeric surfactants (APSs) with a linear alkyl group (C8, C12, C16) were synthesized by oxidation followed by reductive amination of 2,3-dialdehydic alginate. The oxidized alginates and all APSs were characterized by spectral and X-ray diffractometry analysis. The sonicated suspension test was employed to form self-aggregates in aqueous solution. In the case of 40% CHO-C8 APS, the lowest interfacial tension, 31.5 mNm−1, was obtained at the c.m.c. value of 1.35 g L−1. A biodegradability test on the 30% CHO-C12 APS system suggested that it would be attacked by a soil microorganism, Aspergillus niger.

Cholesterol-armed cyclen–Na+ complex as a chiral, helicated amphiphile for supramolecular architecture: self-aggregation and chirality induction in aqueous solution

An octadentate Na+ complex of chiral cholesterol-armed cyclen has a quadruple helicated structure and forms a stable self-aggregate in aqueous solution which offers chirality induction of achiral 5-dimethylaminonaphthalen-1-ylsulfonylglycine anion.

Self-aggregates of poly(aspartic acid) grafted with long alkyl chains

Biodegradable poly(aspartic acid) (PASP) containing octadecyl chain grafts has been synthesized by thermal polycondensation of aspartic acid, aminolysis by octadecylamine, and followed by hydrolysis of remaining succinimide in polymer backbone. The sonicated suspension formed self-aggregates in aqueous solution. Size exclusion chromatography and dynamic light scattering indicated that self-aggregates became compact and particle size was reduced as increasing the amount of substituted octadecyl chains. In the case of low degree of substitution, self-aggregates assembled loosely due to low hydrophobic interaction. In the concentration range of 0.05–1.0%, the stability of aggregates was maintained due to effective hydrophobic interaction and electrostatic repulsion. Below pH 3.2, macroscopic phase-separation appeared in aqueous solution due to attraction of protonated PASP backbone.

Synthesis and Cytotoxic Activity of Conjugates of Monomethoxy-Poly(Ethylene Glycol) End-Capped with Doxorubicin via Ester, Amide, or Schiffs Base Bond

Doxorubicin (adriamycin; ADR) which is one of the most clinically used antitumor agent, has undesirable side-effects. To reduce these side-effects, a macromolecular prodrug of ADR exhibiting high antitumor activity, the conjugate of PEG end-capped with ADR was developed. Tb effect intracellular release of ADR from the conjugate, ester, amide and Schiffs base bonds were employed as modes of bonding ADR to PEG. The MeO-PEG/Schiffs base/ADR conjugate readily released ADR under the lysosomal acidic conditions in vitro and very slowly ADR under physiological conditions. Moreover, the MeO-PEG/Schiffs base/ADR conjugate showed strong cytotoxic activity similar to free ADR against p388D1 lymphocytic leukemia cells in vitro. Fluorescence measurements suggest that the conjugate forms self-aggregates in aqueous solution.