Amphiphilic Amino Acid Research Articles

Self-assembly of biomimetic light-harvesting complexes capable of hydrogen evolution

Biomimetics provides us a new perspective to understand complex biological process and strategy to fabricate functional materials. However, a great challenge still remains to design and fabricate biomimetic materials using a facile but effective method. Here, we develop a biomimetic light harvesting architecture based on one-step co-assembly of amphiphilic amino acid and porphyrin. Amphiphilic amino acid can self-assemble into nanofibers via π-stacking and hydrogen binding interactions. Negatively charged porphyrin adsorbs on the surface of the assembled nanofibers through electrostatic force, and the nanofibers further organize into porous urchin-like microspheres induced presumably by hydrophobic interaction. The assembled amphiphilic amino acid nanofibers work as a template to tune the organization of porphyrin with an architecture principle analogous to natural light harvesting complex. The co-assembled microspheres exhibit enhanced light capture due to the light reflection in the porous structure. Reaction center (platinum nanoparticles) can be effectively coupled with the light harvesting microspheres via photoreduction. After visible light illumination, hydrogen evolution occurs on the hybrid microspheres.

New Amphiphilic Amino Acid Derivatives for Efficient DNA Transfection <i>in Vitro</i>

Nucleic acids-based therapies have recently developed as next-generation agents for treating and preventing viral infection, cancer, and genetic disorders, but their use is still limited due to its relatively poor delivery into targeted cells. We designed and synthesized new amphiphilic amino acid derivatives (cysteine-based) of low molecular weight, formed by the same pentapeptide (AG2: WWCOO) N-acylated, with different hydrophobic chains containing from 12 to 18 carbons, named AG2-Cn (N), which dimerize by oxidation in the presence of pLenti-CMV-GFP Puro plasmid (P) in the respective gemini. We determined transfection efficiency, critical micelle concentration, particle size, ζ-potential and cytotoxicity for the derivatives obtained. We found that all the synthesized compounds were active for DNA delivery and had greater ability to transfect CHO-K1 cells. In particular, AG2-C18 is a promising carrier for gene delivery because it showed no cytotoxicity and its activity was greater than or equal to the commercial actives currently used.

Spontaneous Formation of Vesicles by Self-Assembly of Nicotinyl Amino Acid Amphiphiles: Application as “Turn-On” Fluorescent Sensors for the Selective Detection of Trace-Level Hg(II) in Water

In this paper, the three nicotinic acid-based amphiphiles, sodium 6-dodecylnicotinic glycinate, sodium 6-dodecylnicotinic alaninate, and sodium 6-dodecylnicotinic valinate, were synthesized, and the effect of the headgroup on the self-assembly properties was investigated. The interfacial properties were determined by tensiometry measurement. A steady-state fluorescence technique was used to investigate the microenvironment of the self-assemblies. The amphiphiles form vesicles in water, and the size of the aggregates decreases with increase in the hydrophobicity of the headgroup. Gel permeation chromatography and kinetic studies were performed to establish the entrapping and releasing properties of the vesicles. The arrangement of the hydrocarbon chains in the lamella was examined by X-ray diffraction study. Circular dichroism spectra suggested formation of chiral structure through aggregation of the chiral amphiphiles. It has been demonstrated that the amphiphiles have the feasibility to be developed for ...

ChemInform Abstract: Chemoselective O‐Acylation of Hydroxyamino Acids and Amino Alcohols under Acidic Reaction Conditions: History, Scope and Applications

AbstractReview: 112 refs.

Chemoselective O-acylation of hydroxyamino acids and amino alcohols under acidic reaction conditions: History, scope and applications.

Amino acids, whether natural, semisynthetic or synthetic, are among the most important and useful chiral building blocks available for organic chemical synthesis. In principle, they can function as inexpensive, chiral and densely functionalized starting materials. On the other hand, the use of amino acid starting materials routinely necessitates protective group chemistry, and in reality, large-scale preparations of even the simplest side-chain derivatives of many amino acids often become annoyingly strenuous due to the necessity of employing protecting groups, on one or more of the amino acid functionalities, during the synthetic sequence. However, in the case of hydroxyamino acids such as hydroxyproline, serine, threonine, tyrosine and 3,4-dihydroxyphenylalanine (DOPA), many O-acyl side-chain derivatives are directly accessible via a particularly expedient and scalable method not commonly applied until recently. Direct acylation of unprotected hydroxyamino acids with acyl halides or carboxylic anhydrides under appropriately acidic reaction conditions renders possible chemoselective O-acylation, furnishing the corresponding side-chain esters directly, on multigram-scale, in a single step, and without chromatographic purification. Assuming a certain degree of stability under acidic reaction conditions, the method is also applicable for a number of related compounds, such as various amino alcohols and the thiol-functional amino acid cysteine. While the basic methodology underlying this approach has been known for decades, it has evolved through recent developments connected to amino acid-derived chiral organocatalysts to become a more widely recognized procedure for large-scale preparation of many useful side-chain derivatives of hydroxyamino acids and related compounds. Such derivatives are useful in peptide chemistry and drug development, as amino acid amphiphiles for asymmetric catalysis, and as amino acid acrylic precursors for preparation of catalytically active macromolecular networks in the form of soluble polymers, crosslinked polymer beads or nanoparticulate systems. The objective of the present review is to increase awareness of the existence and convenience of this methodology, assess its competitiveness compared to newer and more elaborate procedures for chemoselective O-acylation reactions, spur its further development, and finally to chronicle the informative, but poorly documented history of its development.

Amphiphilic amino acids: a key to adsorbing proteins to nanopatterned surfaces?

It has been suggested that amphiphilic amino acids play an important role in the adsorption of proteins on nanostructured surfaces with an ordered, striped domain structure such as those presented by monolayer-protected metal nanoparticles (MPMNs). We have proposed and now further explore this hypothesis by studying the adsorption behaviour of proteins on MPMN surfaces by molecular dynamics (MD) simulations. Our atomistic MD simulations of lysozyme (Lyz) on nanostructured surfaces, including single component surfaces and several theoretical nanopatterns of different spacing, presented here confirm the special role of amino acids containing sidechain amines in facilitating direct protein adsorption to MPMN surfaces. While we have previously demonstrated that an amphiphilic amino acid lysine is responsible for selective adsorption behaviour of Cyt C on nanostructured surfaces, in the case of Lyz it is the amphipathic character of arginine that enables the protein to form close contacts with both polar and non-polar surface ligands simultaneously. This renders it especially important for interactions with surfaces composed of adjacent nano-scale chemical domains. Arg is also capable of forming close contacts with homogeneous hydrophobic and hydrophilic ligand surfaces. We have also found that other amphiphilic amino acids, such as tyrosine and tryptophan, interact with surfaces via water-mediated contacts. Bridging water molecules adopt orientations which differ from those of simple surface-adsorbed waters, with the specificity of their orientations facilitating the protein-surface contacts. Our findings suggest that not only nanopatterned surfaces can be designed to selectively interact with different proteins but proteins may be engineered to specifically interact with nanomaterials by targeted incorporation of synthetic amino acids which can mimic natural amphiphilic amino acids possessing multiple affinities to different chemical motifs.

Cloud droplet activation mechanisms of amino acid aerosol particles: insight from molecular dynamics simulations

Atmospheric amino acids constitute a large fraction of water-soluble organic nitrogen compounds in aerosol particles, and have been confirmed as effective cloud condensation nuclei (CCN) materials in laboratory experiments. We present a molecular dynamics (MD) study of six amino acids with different structures and chemical properties that are relevant to the remote marine atmospheric aerosol–cloud system, with the aim of investigating the detailed mechanism of their induced changes in surface activity and surface tension, which are important properties for cloud drop activation. Distributions and orientations of the amino acid molecules are studied; these l-amino acids are serine (SER), glycine (GLY), alanine (ALA), valine (VAL), methionine (MET) and phenylalanine (PHE) and are categorised as hydrophilic and amphiphilic according to their affinities to water. The results suggest that the presence of surface-concentrated amphiphilic amino acid molecules give rise to enhanced Lennard–Jones repulsion, which in turn results in decreased surface tension of a planar interface and an increased surface tension of the spherical interface of droplets with diameters below 10 nm. The observed surface tension perturbation for the different amino acids under study not only serves as benchmark for future studies of more complex systems, but also shows that amphiphilic amino acids are surface active. The MD simulations used in this study reproduce experimental results of surface tension measurements for planar interfaces and the method is therefore applicable for spherical interfaces of nano-size for which experimental measurements are not possible to conduct.

Simultaneous Determination of Interfacial Molarities of Amide Bonds, Carboxylate Groups, and Water by Chemical Trapping in Micelles of Amphiphiles Containing Peptide Bond Models

Chemical trapping is a powerful approach for obtaining experimental estimates of interfacial molarities of weakly basic nucleophiles in the interfacial regions of amphiphile aggregates. Here, we demonstrate that the chemical probe 4-hexadecyl-2,6-dimethylbenzenediazonium ion (16-ArN(2)(+)) reacts competitively with interfacial water, with the amide carbonyl followed by cleavage of the headgroups from the tail at the amide oxygen, and with the terminal carboxylate groups in micelles of two N-acyl amino-acid amphiphiles, sodium N-lauroylsarcosinate (SLS) and sodium N-lauroylglycinate (SLG), simple peptide bond model amphiphiles. Interfacial molarities (in moles per liter of interfacial volume) of these three groups were obtained from product yields, assuming that selectivity toward a particular nucleophile compared to water is the same in an aqueous reference solution and in the interfacial region. Interfacial carboxylate group molarities are ~1.5 M in both SLS and SLG micelles, but the concentration of the amide carbonyl for SLS micelles is ~4.6-5 times less (ca. 0.7 M) than that of SLG micelles (~3 M). The proton on the secondary N of SLG helps solubilize the amide bond in the aqueous region, but the methyl on the tertiary N of SLS helps solubilize the amide bond in the micellar core, reducing its reaction with 16-ArN(2)(+). Application of chemical trapping to proteins in membrane mimetic interfaces should provide insight into the topology of the protein within the interface because trapping of the amide carbonyl and cleavage at the C-N bond occurs only within the interface, and fragment characterization marks those peptide bonds located within the interface.

Role of non-covalent interactions in the molecular organization of N-n-hexadecanoyl amino acid amphiphiles with hydrophobic Cα-side chains in Tris buffer (pH 9.3)

Role of non-covalent interactions on the molecular packing of N-n-hexadecanoyl amino acid amphiphiles (NHAA) has been studied using a set of corresponding L-amino acid (glycine, alanine, valine, proline and phenylalanine) derivatives in 50mM Tris buffer at pH 9.3. Self-assembly properties in aqueous dispersion were characterized by various physical techniques like tensiometry, fluorimetry, UV–vis spectroscopy, circular dichroism (CD) and differential scanning calorimetry (DSC). The results reveal that the hydrophobic interaction plays the driving role for such self assembly phenomena which is synergistically influenced by additional non-covalent interactions among the surfactants arising from the amino acid units present on the molecular backbone. Despite major similarities in structural elements (except their Cα-side chain residues) among all the NHAA amphiphiles described here, three issues were found to be important towards their self assembly properties viz, (a) optimal intermolecular distance that arises from van der Waals repulsions of the side chain residues and the electrostatic repulsions among anionic head groups; (b) intermolecular H-bonding and π–π type attractive interaction that reduces the intermolecular distance and (c) the effective solvation of the head groups required for the self assembly. Since, primary amide group is ubiquitous for all the amphiphiles except NHPro, the strength of H-bonding interaction among the amphiphiles was also investigated and found to be affected by the nature of the Cα-side chain residues. NHPhe was found to be unique compared to others due to the π–π type attractive interaction operative at the aromatic Cα-side chain while for others, the repulsive interactions among the Cα-side chain residues make them behave differently. Optimized non-covalent interactions with requisite solvation of the head group, molecular packing was found to be better for NHAla, while such packing was affected by van der Waals repulsion among the bulky Cα substituents (e.g. isopropyl group for NHVal) or stabilized by π–π interaction (for NHPhe) and intermolecular H-bonding interaction via amide linkages. The self-assembly behavior was found to be complex for proline based system (NHPro) where the hydrophobic effect and the steric disposition of the cyclic side chain significantly influence its molecular packing as well as its other self assembly properties. The characterization of thermodynamic parameters reveals that the hydrophobicity of Cα-substituents lowers the free energy of micellization. The DSC studies show that Krafft Temperature and enthalpy of solution were affected by the nature of the Cα-substituents. The van der Waals repulsion among the bulky substituents increases the intermolecular separation reducing the strength of the molecular packing as well as the aggregation number. An invariant CD signature for NHPhe at its non aggregated and aggregated state indicates a unique non-chiral self assembly and a new π–π dimeric molecular organization model for NHPhe amphiphiles has been proposed to rationalize this behavior.

Synthesis, characterization, drug-loading capacity and safety of novel pH-independent amphiphilic amino acid copolymer micelles.

A novel block copolymer containing two polymeric components, poly(L-aspartic acid)-b-poly (L-phenylalanine) (PAA-PPA), was synthesized and its potential for the preparation of copolymer micelles with a poorly water-soluble drug was investigated in this study. The chemical structure and physical properties of PAA-PPA were characterized by FTIR, 1H NMR and TG. The degree of polymerization of PAA-PPA was calculated by analyzing the relative area of N-CH signal and C-CH3 of 1H NMR spectra. The critical micelle concentration (CMC) of the PAA-PPA achieved a minimum of 11.1 mg/L. Studies on the drug-free PAA-PPA solutions showed PAA-PPA aggregation into micellar type in the sub-150 nm size range. Furthermore, the size of the PAA-PPA micelles was found to be pH-independent between the pH range of 4.0 and 8.0, which could be favorable to avoid the limitation of the size change at the specified pH value seeking drug stability. 4-amino-2-trifluoromethyl-phenyl retinate (ATPR) was studied as a poorly water-soluble model drug. The drug-loading and entrapment efficiency of the ATPR-loaded PAA-PPA micelles were 30.9 wt% and 87.9 %, respectively. The high drug-loading and entrapment efficiency were due to the synergistic effect of the micellar encapsulation and the binding interaction between drug and PAA-PPA. The ATPR-loaded PAA-PPA micelles showed a narrow size distribution, low zeta potential, high drug-loading capacity and good stable. The PAA-PPA was safer than Tween-80 and Cremophor EL (CrmEL) as an injectable pharmaceutical adjuvant for ATPR as indicated by the hemolysis and cytotoxicity studies. The novel amphiphilic amino acid copolymer can be considered as a prospective injectable delivery system for ATPR in terms of the pH-independent, greater drug-loading capacity and safety.

High performance controlled reactors from micellar assemblies of aromatic amino acid amphiphiles for nanoparticle synthesis

The micellar assemblies of lauryl esters of tyrosine (LET) and phenylalanine (LEP) show extraordinary emulsification properties. The structural similarity in respect of the aromatic ring between the dispersed phase, styrene, and the surfactants facilitates solubilization of styrene up to four times the weight of LEP and 11times that of LET. We propose that the solubilization site varies between core in the LEP and shell in the LET micelles. LET affords double emulsions, water in oil in water (w/o/w) over a narrow phase composition, for example at R=7.15, where R represents ratio of weight of styrene to LET. A schematic model depicting the solubilization site of styrene at different regions in LET and LEP micelles has been proposed. On polymerization, the emulsions with LET and LEP micelles generated high molecular weight polymer nanoparticles of size 12–49nm with low polydispersity index (Pd). This demonstrates that micellar assemblies act as templating controlled reactors for the polymerization reaction. We demonstrate that PS nanoparticle dispersion of size 49nm with polymer weight fraction as high as 42.80% could be produced from emulsions with the LET surfactant, in contrast to LEP that is 50% less efficient. Polymerization of these emulsions occurs predominantly through a micellar nucleation mechanism. It is significant to note that under the same conditions, the control experiments with sodium dodecylsulfate (SDS) micelles resulted in polymers with broad distribution, Pd>3.0 in molecular weight.

Synthesis and Self-Assembly Behavior of Chiral Amphiphilic Diblock Copolymers Bearing L-Phenylalanine

Novel chiral amphiphilic diblock copolymers bearing L-phenylalanine was synthesized using a “click” reaction of N3-L-phenylalanine and MPEO-b-PGPE. The structure and composition of copolymers were characterized by 1H-NMR and elemental analysis. Additionally, the self-assembly behavior of these chiral copolymers was investigated in sodium dihydrogen phosphate buffer (pH 4.5): the CMC of copolymer MPEO-b-PGTP determined by the measurement of surface tension was 2.1 mg/mL; the size and morphology of the micelles were studied using TEM; the specific optical rotation ([α]25D) of the micellar solutions was also measured; the result indicated that the copolymers can form chiral micelles in sodium dihydrogen phosphate buffer (pH =4.5).In recent years, the synthesis, structure and properties of optically active polymer have been paid attention by scientists owing to its potential applications in chiral separation, asymmetric adsorption, chiral synthesis[1]. The amphiphilic block polymers bearing amino acid possess not only the characteristics of the conventional amphiphilic block copolymer, but also good optically activity and biocompatibility. So it can be employed as nanoreactors for asymmetrical catalysis and materials for drug delivery. But there have been few reports published on the synthesis of chiral amphiphilic copolymers bearing amino acid. Sutthira Sutthasupa reported the synthesis of amino acid-based norbornene block copolymer with ester and carboxyl groups as hydrophobic and hydrophilic units[2]. O’Reilly group synthesized the amino acid-based chiral amphiphilic block copolymers using RAFT technique, and elucidated its self-assembly into spherical micelles with optically active hydrophobic core[3]. In the present work, chiral amphiphilic diblock copolymers bearing L-phenylalanine (L-Phe) pendants poly(ethylene oxide)-b-poly (glycidyl triazolyl-L-phenylalanine) (MPEO-b-PGTP) have been synthesized by the modification of poly(ethylene oxide)-b-poly (propargyl glycidyl ether) (MPEO-b-PGPE) with L-phenylalanine.

Quantum-Chemical Analysis of Thermodynamics of Two-Dimensional Cluster Formation of Racemic α-Amino Acids at the Air/Water Interface

The quantum-chemical semiempiric PM3 method is used to calculate the thermodynamic parameters of clusterization for the racemic α-amino acids C(n)H(2n+1)CHNH(2)COOH with n=5-15 at 278 and 298 K. Possible relative orientations of the monomers in the heterochiral clusters are considered. It is shown that, for the racemic mixtures of α-amino acids, the formation of heterochiral 2D films is most energetically preferable with the alternating (rather than "checkered") packing of the enantiomers with opposite specific rotation. The two enantiomeric forms of α-amino acids in the heterochiral 2D clusters are tilted with respect to the normal to the q direction at angles of φ(1)=20° and φ(2) = 33°, whereas the single enantiomeric forms are oriented at an angle of δ=9° with respect to the normal to the p direction. It is shown that the heterochiral 2D film based on the α-amino acid structures oriented at the angle φ(2)=33° with respect to the normal to the q direction possesses a rectangular unit cell with the geometric parameters a = 4.62 Å and b = 10.70 Å and the tilt angle of the alkyl chain of the molecule with respect to the interface t(2)=35°, which is in good agreement with the X-ray structural data a=4.80 Å, b=9.67 Å, and t(2)=37°. The parameters of the lattice structure of monolayers formed by amphiphilic amino acids are shown to be determined by the "a" type of the intermolecular H-H interactions, whereas the tilt angle of the molecules with respect to the interface depends on the volume and the structure of the functional groups involved in the hydrophilic part of the molecule. Spontaneous clusterization of the racemic form of α-amino acids at the air/water interface at 278 K takes place if the alkyl chain length is equal or higher than 12-13 carbon atoms, whereas for 298 K this clusterization threshold corresponds to 14 carbon atoms in the hydrocarbon chain. These values agree with the experimental data.

Stimulus responsive self-assembly of Gemini Amphiphilic Pseudopeptides

Amphiphilic amino acid derived compounds are very interesting for the design of building blocks able to self-assemble into highly ordered nanostructures, in a hierarchical and controlled fashion. With this aim, the modular synthesis and the full characterization of simple Gemini Amphiphilic Pseudopeptides (GAPs) have been carried out. These compounds were designed to establish intermolecular interactions in a hierarchical way to finally render supramolecular assemblies into well-ordered nanostructures, such as fibers, tubes, tapes or spherical vesicles. Different structural variables have been implemented, such as the amino acid side chain, the length of the central spacer and the nature of the hydrophobic tails. Besides, the effect of the environment was systematically checked, by performing the studies in solvents of different polarities (chloroform, methanol or aqueous methanol) and at different pHs (neutral, basic and acidic). The non-covalent self-assembling abilities and the structural features of the GAPs have been studied in the solid (SEM, TEM and FT-IR) and in the solution states (NMR, UV, CD, FT-IR and fluorescence spectroscopy). Moreover, the connection between the solution and the solid states has been established by monitoring the slow evaporation of the solvent by ATR FT-IR. This study has allowed the establishment of a relationship between the chemical structures of the GAPs and their abilities to form nanostructures. In some optimal cases (especially for the valine derivatives with medium-length spacers and two decyloxybenzyl hydrophobic tails), they behaved as stimulus responsive self-assembling nano-structures, which form amorphous materials from non-polar solvents, nano-fibers from polar environments at neutral or basic pH and vesicles when become protonated at acidic pH values. A reasonable structural model to explain the experimental observations can be proposed through the combination of the results from the different techniques.

Biomimetic Synthesis of Hierarchically Porous Nanostructured Metal Oxide Microparticles—Potential Scaffolds for Drug Delivery and Catalysis

Hierarchically porous hybrid microparticles, strikingly reminiscent in their structure of the silica skeletons of single-cell algae, diatoms, but composed of titanium dioxide, and the chemically bound amphiphilic amino acids or small proteins can be prepared by a simple one-step biomimetic procedure, using hydrolysis of titanium alkoxides modified by these ligands. The growth of the hierarchical structure results from the conditions mimicking the growth of skeletons in real diatoms--the self-assembly of hydrolysis-generated titanium dioxide nanoparticles, templated by the microemulsion, originating from mixing the hydrocarbon solvent and water on action of amino acids as surfactants. The obtained microsize nanoparticle aggregates possess remarkable chemical and thermal stability and are promising substrates for applications in drug delivery and catalysis. They can be provided with pronounced surface chirality through application of chiral modifying ligands. They display also high selectivity in sorption of phosphorylated biomolecules or medicines as demonstrated by (1)H and (31)P NMR studies and by in vitro modeling using (32)P-marked ATP as a substrate. The release of the adsorbed model compounds in an inert medium is a very slow process directed by desorption kinetics. It is enhanced, however, noticeably in contact with biological fluids modeling those of the tissues suffering inflammation, which makes the produced material highly attractive for application in medical implants. The developed synthetic approach has been applied successfully also for the preparation of analogous hybrid microparticles based on zirconium dioxide or aluminum sesquioxide.

Reversible peptide particle formation using a mini amino acid sequence

Interest in nanostructures, artificial compartments and smart materials is steadily increasing as a result of beneficial applications in sensors, tissue engineering, nanoreactors and drug delivery systems. Block copolymers, peptide-based hybrid materials, expressed protein-like copolymers, and peptides that self-assemble in aqueous solution fulfill the demands of such applications while providing maximum biocompatibility. Herein, we focus on the formation of self-assembled particles using an amphiphilic amino acid (AA) sequence derived by solid-phase peptide synthesis (SPPS) and describe its purification and characterisation. The prepared undecamer features a repetitive L-tryptophan and D-leucine [LW-DL] motif representing the hydrophobic block, and an N-terminally attached hydrophilic (lysine or acetylated lysine) section. For peptides containing charged lysine, aggregation into micelles and a minor fraction of peptide particles was observed. Charge shielding with anionic counter ions shifted the equilibrium towards the larger peptide aggregates, with their size depending on the counter ion's position in the Hofmeister series. Similarly, the corresponding uncharged (acetylated) peptide was also demonstrated to assemble into micelles and subsequently into peptide particles, termed ‘peptide beads’, which we hypothesise to be multicompartment micelles. The formation of the peptide beads was studied as a function of temperature and solvent composition by means of electron paramagnetic resonance (EPR), dynamic and static light scattering, fluorimetry and electron microscopy. The results suggest an equilibrium between single peptide molecules, micelles, and peptide beads. Interestingly once formed the peptide beads show high mechanical stability and preserve their shape and dimensions even after isolation from solution.

Synthesis, physical-chemical and biological properties of amphiphilic amino acid conjugates of nitroxides

Due to the dual property of synthetic nitroxide compounds to either act as probe or antioxidant, efforts toward their selective targeting using specific ligands have been extensively explored. Herein, we report the synthesis of novel amphiphilic nitroxides in which the nitroxyl group is grafted onto an amphiphilic carrier comprising a lactobionamide polar group, a non-polar alkyl chain and an amino acid as scaffold. Piperidine and pyrrolidine nitroxides such as 4-amino-TEMPO (4-AT) and 3-carboxyproxyl (3-CP), respectively, were grafted onto the amphiphilic carriers. To further investigate the effect of the nature of the chain on the physical-chemical and biological properties of nitroxides, hydrogenated or perfluorinated alkyl chains were used. The self-aggregation properties in aqueous media of these surfactant-like nitroxides were confirmed by dynamic light scattering (DLS) as well as electron paramagnetic resonance (EPR) spectroscopy, and were correlated with their respective lipophilicity. The effect of the carrier groups on the electrochemical property of nitroxides was investigated using cyclic voltammetry, and the rates of reduction using ascorbate as reducing agent were measured. Finally, their cytoprotective property against toxic concentrations of hydrogen peroxide using bovine aortic endothelial cells was also investigated.

Self-Catalytic Sol−Gel Synergetic Replication of Uniform Silica Nanotubes Using an Amino Acid Amphiphile Dynamically Growing Fibers as Template

The aggregation behavior of a novel histidine derivative surfactant N-dodecanoyl-L-histidine (DHis) in aqueous solution was investigated. By mixing with cationic/anionic surfactant, an interesting phase transition over time from transparent homogeneous solution to jelly and finally to fibrous floccules was observed with aggregates growth taken place in the systems. Making use of the growing fibrous structures in the DHis/DTEAB and DHis/SDS systems as surface charge tunable dynamic template, we achieved sol-gel replication of silica and titania nanotubes in mild conditions, respectively. The possible mechanism underlying the formation of silica nanotubes was proved to be synergistically self-catalyzed hydrolysis and condensation of silica precursors depositing on the template surface. In particular, by optimizing the sol-gel process, silica nanotubes with tunable sizes in diameter and uniform wall thickness could be obtained in high yield. The large specific surface area and peculiar photoluminescence property of the silica nanomaterials indicated that the synthetic nanotubes were well-defined in both morphology and physical properties. Importantly, this fibrous aggregates could be universally used in opposite charged inorganic precursors to accomplish inorganic oxide nanotubes via sol-gel replication process, which may provide a general route for the construction of one-dimensional nanostructures in aqueous media.

Foam nest components of the túngara frog: a cocktail of proteins conferring physical and biological resilience.

The foam nests of the túngara frog (Engystomops pustulosus) form a biocompatible incubation medium for eggs and sperm while resisting considerable environmental and microbiological assault. We have shown that much of this behaviour can be attributed to a cocktail of six proteins, designated ranaspumins (Rsn-1 to Rsn-6), which predominate in the foam. These fall into two discernable classes based on sequence analysis and biophysical properties. Rsn-2, with an amphiphilic amino acid sequence unlike any hitherto reported, exhibits substantial detergent-like surfactant activity necessary for production of foam, yet is harmless to the membranes of eggs and spermatozoa. A further four (Rsn-3 to Rsn-6) are lectins, three of which are similar to fucolectins found in teleosts but not previously identified in a land vertebrate, though with a carbohydrate binding specificity different from previously described fucolectins. The sixth, Rsn-1, is structurally similar to proteinase inhibitors of the cystatin class, but does not itself appear to exhibit any such activity. The nest foam itself, however, does exhibit potent cystatin activity. Rsn-encoding genes are transcribed in many tissues of the adult frogs, but the full cocktail is present only in oviduct glands. Combinations of lectins and cystatins have known roles in plants and animals for defence against microbial colonization and insect attack. Túngara nest foam displays a novel synergy of selected elements of innate defence plus a specialized surfactant protein, comprising a previously unreported strategy for protection of unattended reproductive stages of animals.

Counterion dependent hydrogelation of amino acid based amphiphiles: switching from non-gelators to gelators and facile synthesis of silver nanoparticles

With the growing importance of hydrogels in scientific applications, the search for low molecular weight hydrogelators (LMWH), with simultaneous logical structural correlation is continuously increasing. In the present work, counterion variation of amino acid based amphiphiles was done to qualitatively evaluate its contribution towards hydrogelation. Further changes in the molecular skeleton of the amino acid amphiphile were done along with counterion variation to establish the importance of π–π interactions of aromatic planar ring in hydrogelation. An efficient conversion of a non-gelator to gelator molecule was achieved simply by changing the counterions to aromatic carboxylates. Role of the counterion in the mechanism of gelation process through the self-assembly of amino acid based amphiphiles has been discussed. The formation of supramolecular structures during hydrogelation was investigated by FESEM, CD, FT-IR, luminescence, 2D-NOESY and rheological studies. Interestingly, the L-tryptophan containing amphiphile hydrogelators were further utilized for synthesis of Ag nanoparticles under mild conditions without any need for high temperature, alkaline medium and external reducing agent. The nanoparticles obtained were characterized by UV-Vis, TEM, AFM and XRD experiments.