Formation Of Self-assembled Structures Research Articles

C1 symmetric dual-carboxyl-functionalized BODIPY dye: Synthesis, photophysical properties, and self-assembly behavior via hydrogen bonding

A BODIPY derivatives 3 with phenylethynyl bridging two carboxyl groups was synthesized via Sonogashira cross-coupling reaction. The structure was characterized by 1HNMR and HRMS. Its photophysical properties and aggregation behavior in solution were studied by UV–Vis absorption and fluorescence spectroscopy. The compound 3 displays strong absorption and high fluorescence quantum yield. The investigations of UV–Vis and emission also revealed the formation of self-assembled structures in the solid state or liquid/state with translationally slipped π-stacks of BODIPY units driven by hydrogen bonding between the carboxyl groups. The thermodynamic properties of the BODIPY derivative were carried out by DSC and TGA, indicating it possesses high thermal stability. In addition, the self-assembly of the BODIPY derivative functionalized with two carboxyl groups was explicitly investigated by using scanning tunneling microscopy (STM). The highly ordered supramolecular self-assembly monolayers endow the novel carboxyl functionalized BODIPY with good potential for application in organic devices.

Stability of n-alkanes and n-perfluoroalkanes against horizontal displacement on a graphite surface.

The stability of adsorbed molecules on surfaces is fundamental and important for various applications, such as coating, lubrication, friction, and self-assembled structure formation. In this study, we investigated the structures and interaction energies (Eint) of propane, n-pentane, n-heptane, perfluoropropane, n-perfluoropentane, and n-perfluoroheptane adsorbed on the surface of C96H24 (a model surface of graphite). The changes in Eint (ΔEint = Eint - Eint(0)) associated with the horizontal displacement from the stable position were calculated using dispersion-corrected density functional theory (DFT; B3LYP-D3), where Eint(0) is the Eint at the stable position. The maximum value of ΔEint (ΔEint(max)) associated with the horizontal displacement increased as the chain length increased. The ΔEint(max) for the three n-alkanes were 1.10, 1.82, and 2.35 kcal mol-1, respectively. The values for n-perfluoroalkanes were 0.57, 0.83, and 1.04 kcal mol-1, respectively. The ΔEint(max) values for the n-alkanes were significantly larger than those for the corresponding n-perfluoroalkanes. The Eint(max) value per carbon atom of the n-alkanes (ca. 0.30 kcal mol-1) is approximately 2.5 times as large as that of n-perfluoroalkanes (ca. 0.12 kcal mol-1). The ΔEint associated with the horizontal displacement of propane and perfluoropropane on circumcoronene (C54H18) obtained by the B3LYP-D3 calculations are close to those obtained by the second order Møller-Plesset (MP2) and dispersion-corrected double hybrid DFT calculations, suggesting the sufficient accuracy of the ΔEint obtained by the B3LYP-D3. Thus, our quantitative analysis revealed the higher stability of n-alkanes against horizontal displacement on a graphite surface than that of n-perfluoroalkanes.

Self-assembled Structure Formation in Homo/Random Copolymers by Nanophase Separation

Self-assembled Structure Formation in Homo/Random Copolymers by Nanophase Separation

Multiple Actions of H2S-Releasing Peptides in Human β-Amyloid Expressing C. elegans.

Alzheimer's disease (AD) is a debilitating progressive neurodegenerative disorder characterized by the loss of cognitive function. A major challenge in treating this ailment fully is its multifactorial nature, as it is associated with effects like deposition of Aβ plaques, oxidative distress, inflammation of neuronal cells, and low levels of the neurotransmitter acetylcholine (ACh). In the present work, we demonstrate the design, synthesis, and biological activity of peptide conjugates by coupling a H2S-releasing moiety to the peptides known for their Aβ antiaggregating properties. These conjugates release H2S in a slow and sustained manner, due to the formation of self-assembled structures and delivered a significant amount of H2S within Caenorhabditis elegans. These conjugates are shown to target multiple factors responsible for the progression of AD: notably, we observed reduction in oxidative distress, inhibition of Aβ aggregation, and significantly increased ACh levels in the C. elegans model expressing human Aβ.

Ionic Liquids Based Cocktails as a Composite Redox Electrolyte for Natural Dye-Sensitized Solar Cells

Fatty-imidazolinium electrolytes, waste graphite dispersed composite electrolytes like cocktails (1,3-methyl octyl-1,2,3-benzotiazolium acetate–cis-oleyl-imidazolinium iodide), and graphite exfoliation using cis-oleyl-imidazolinium acetate have been studied to enhance the efficiency of a newly developing dye-sensitized solar cells (DSSCs). The DSSCs were fabricated in a sandwich structure and characterized using Solar Simulator. The graphite exfoliation was conducted by sonication and microwave energy, as well as the electrochemical method. Cis-oleyl-imidazolinium iodide efficiency (0.53%) was highest than stearyl-imidazolinium iodide and palmityl-imidazolinium iodide because cis-oleyl-imidazolinium iodide has a double bond and the longest alkyl chain which triggered a self-assembly structure formation and increased the rate of I-/I3- transport in cells. Then, the efficiency of DSSCs-based composite electrolytes was in the range of 0.020– 0.203%. Dispersion of 0.05% of the graphite results in efficiency enhancement of about 100%, but the greater fraction (0.10%) of the graphite causes a poor performance (lower efficiency), possibly due to interference of the internal electron transportation routes in the DSSC by insoluble graphite. After exfoliation, the conductivity of synthetic graphite (11.58 x 10-1 S/cm), new battery graphite (9.32 x 10-1 S/cm), and battery waste graphite (7.96 x 10-1 S/cm) were increased respectively 10 times, 2 times, and 4 times from the graphite before exfoliation due to changes in crystallinity, the distance between layers, crystal size, formation of multilayer graphene, and the occurrence of π to π* transition. This enhancement of solar conversion efficiency can give a new contribution to the development of DSSC.

ß-Sheet Induced Helical Self-Assembly Structure Formation by Dityrosine Dipeptide: Crystallographic Evidence and Other Biophysical Studies

Self-assembled structures derived from short peptides are a versatile class of organic building blocks which have shown great potential in a wide range of domains. In the current study, side-chain protected dityrosine based short peptide (TP) was synthesized, and its conformation accompanied by a self-assembly pattern was investigated through several spectroscopic studies and single crystal X-ray analysis. The single crystal X-ray analysis of TP confirmed that it exhibited a ß-sheet pattern which further self-assembled to form ß-sheet-promoted helical architectures by various noncovalent interactions. To the best of our knowledge, this is the first crystallographic report of a side-chain protected dityrosine based short peptide adopting ß-sheet-promoted helical structures. Morphological analysis of TP also revealed ß-sheet as well as helical conformations. NMR study suggested that both amide hydrogens of TP are involved in intermolecular hydrogen bonding. Moreover, CD spectroscopy established the self-assembly phenomenon of TP in the solution state by showing both corresponding ß-sheet and α-helix bands. Hirshfeld surface analysis and DFT study also concluded similar results. These kinds of small peptide units mimicking important protein secondary structures like helical assembly would be of pivotal significance as they may act as small peptidomimetics, mimicking the protein "Hotspot" area.

Chiral Fibers Formation Upon Assembly of Tetraphenylalanine Peptide Conjugated to a PNA Dimer.

Self‐assembly of biomolecules such as peptides, nucleic acids or their analogues affords supramolecular objects, exhibiting structures and physical properties dependent on the amino‐acid or nucleobase composition. Conjugation of the peptide diphenylalanine (FF) to peptide nucleic acids triggers formation of self‐assembled structures, mainly stabilized by interactions between FF. In this work we report formation of homogeneous chiral fibers upon self‐assembly of the hybrid composed of the tetraphenylalanine peptide (4F) conjugated to the PNA dimer adenine‐thymine (at). In this case nucleobases seem to play a key role in determining the morphology and chirality of the fibers. When the PNA “at” is replaced by guanine‐cytosine dimer “gc”, disordered structures are observed. Spectroscopic characterization of the self‐assembled hybrids, along with AFM and SEM studies is reported. Finally, a structural model consistent with the experimental evidence has also been obtained, showing how the building blocks of 4Fat arrange to give helical fibers.

Non-monotonous enzyme-assisted self-assembly profiles resulting from reaction-diffusion processes in host gels

Reaction–diffusion (RD) processes are responsible for surface and in-depth micropatterning in inanimate and living matter. Here we show that enzyme-assisted self-assembly (EASA) of peptides is a valuable tool to functionnalize host gels. By using a phosphatase distributed in a host hydrogel, the diffusion of phosphorylated peptides from a liquid/host gel interface leads to the spontaneous formation of a pattern of dephosphorylated peptide self-assembly presenting at least two self-assembly maxima. Variation of enzyme and peptide concentrations change the pattern characteristics. When a peptide drop is deposited on a phosphatase functionalized gel, a self-assembly pattern is also formed both along the gel-solution interface and perpendicular to the interface. This self-assembly pattern induces a local change of the gel mechanical properties measured by nanoindentation. Its appearance relies on the formation of self-assembled structures by nucleation and growth processes which are static in the hydrogel. This process presents great similarities with the Liesegang pattern formation and must be taken into account for the functionalization of hydrogels by EASA. A mechanism based on RD is proposed leading to an effective mathematical model accounting for the pattern formation. This work highlights EASA as a tool to design organic Liesegang-like microstructured materials with potential applications in biomaterials and artificial living systems design.

A new aggregation induced emission enhancement (AIEE) dye which self-assembles to panchromatic fluorescent flowers and has application in sensing dichromate ions.

We report for the very first time the crystal structure and self-assembly of a new aggregation-induced emission enhancement (AIEE) dye 4-(5-methoxythiazolo[4,5-b]pyridin-2-yl)-N,N-dimethylaniline (TPA) and its application in sensing dichromate ions. TPA reveals cyan blue emission under UV and visible light. The self-assembly properties of TPA were studied extensively by scanning electron microscopy (SEM) which revealed the formation of beautiful flower-like morphologies. These structures revealed both green and red fluorescence under FITC and rhodamine filters respectively when observed through fluorescence microscopy connoting the panchromatic emission properties of TPA from blue to red. The interactions which cause self-assembled structure formation in TPA were also validated theoretically using density functional theory (DFT) calculations. Crystal and molecular structure analysis of TPA was carried out via single-crystal X-ray diffraction to visualize the intermolecular interactions occurring in the solid-state and to study the structure-photophysical property relationship in the aggregated state. The photophysical properties of TPA were also studied extensively by UV-visible and fluorescence spectroscopy and its quantum yield and fluorescence lifetime were calculated by time-correlated single-photon counting (TCSPC). Interestingly, TPA could efficiently sense dichromate (Cr2O72-) ions in an acidic medium and an interesting morphological transition from a fluorescent flower to non-fluorescent disassembled structures could also be observed. The limit of detection of TPA for Cr2O72- ions was found to be as low as 5.5 nM, suggesting its exceptional sensitivity. More importantly, TPA could selectively sense Cr2O72- ions in real water samples even in the presence of other metal ions routinely present in polluted water, hence making it practically useful for water quality monitoring.

Tight Binding of Plasmid DNA With Self-Assembled Tetramethylguanidinium Conjugated Polyethylenimine Suppresses Transfection Efficiency

Here, we have demonstrated that on modification of linear polyethylenimine (lPEI, LP) with amphiphilic 3-bromopropyltetramethylguanidinium (PTMG) linker, the transfection efficiency exhibited by the modified polymers decreased while cell viability improved. A series of LP-PTMG polymers was synthesized by the reaction of varying amounts of 3-bromopropyl tetramethylguanidinium linker with lPEI (25 kDa). These modified polymers interacted efficiently with pDNA and formed nanosized complexes as shown by dynamic light scattering analysis. The size of the complexes in the series LP-PTMG/pDNA was observed in the range of ∼178–205 nm. The interaction of modified polymers with plasmid DNA was stronger than linear PEI as evidenced by heparin release assay which showed ∼83% pDNA release from LP-PTMG-3/pDNA complexes in comparison to ∼95% in lPEI/pDNA complexes on treatment with same amount of heparin suggesting the formation of self-assembled structures in modified polymers. The transfection studies in HeLa and Chinese hamster ovary cells showed a decrease in transfection efficiency of LP-PTMG polymers, the reason for this may be strong binding of modified polymers with pDNA due to accumulation of charge on the surface. This finding showed the significance of optimum binding of polymer and DNA to form polyplexes as well as release of DNA from the polyplexes.

Encased Gold Nanoparticle Synthesis as a Probe for Oleuropein Self-Assembled Structure Formation.

Stable oleuropein-coated gold nanoparticles in aqueous media were synthesized for the first time. Oleuropein (OLE) concentration in the reaction medium was found to greatly influence the outcome and stability of the resulting nanocolloid, with a marked decrease in particle size being found for the more concentrated oleuropein solutions. The protection mechanisms involved in the stabilized nanosystems were analyzed. Oleuropein self-assembled structures were found to be formed at a concentration threshold of [OLE] > 5 × 10−5 M, and observed through the use of CryoSEM imaging. Those structures were responsible for both the increased stability and the decrease in size observed at the more concentrated solutions.

A dual thermoresponsive and antifouling zwitterionic microgel with pH triggered fluorescent “on-off” core

A unique, tailor-made, zwitterionic, dual thermoresponsive and fluorescent microgel probe was synthesized via Reversible Addition Fragmentation chain-Transfer (RAFT) polymerization. Microgels were prepared via oil in water (o/w) emulsion polymerization where poly(carboxybetaine) (PCB) acted as a macro-RAFT reagent as well as an emulsifier. The presence of poly(N-vinylcaprolactam) (PNVCL) in the microgel system imparts the thermoresponsiveness to the system and the presence of a rhodamine derivative as fluorophore makes it responsive to pH change of the system by showing a fluorescence emission at 580 nm (reddish orange color). The dual thermoresponsiveness [i.e. the presence of upper critical solution temperature (UCST @ 12 °C) as well as lower critical solution temperature (LCST @ 33 °C)] of the microgels was studied via UV–visible spectroscopy (UV–vis) and temperature responsive dynamic light scattering (DLS) analyses. Presence of the PCB in the corona-crosslinked microgel, played a vital role in the formation of self-assembled structure as well as in protein immobilization (antifouling activity). Antifouling property was studied using UV–vis spectroscopy where bovine serum albumin (BSA) was taken as a model protein. The presence of the pH-responsive fluorescence, thermoresponsiveness as well as antifouling properties makes this zwitterionic microgel system a potential a potential candidate for medical diagnostics and for drug delivery vehicles.

Nucleotide-Selective Templated Self-Assembly of Nanoreactors under Dissipative Conditions.

Nature adopts complex chemical networks to finely tune biochemical processes. Indeed, small biomolecules play a key role in regulating the flux of metabolic pathways. Chemistry, which was traditionally focused on reactions in simple mixtures, is dedicating increasing attention to the network reactivity of highly complex synthetic systems, able to display new kinetic phenomena. Herein, we show that the addition of monophosphate nucleosides to a mixture of amphiphiles and reagents leads to the selective templated formation of self-assembled structures, which can accelerate a reaction between two hydrophobic reactants. The correct matching between nucleotide and the amphiphile head group is fundamental for the selective formation of the assemblies and for the consequent up-regulation of the chemical reaction. Transient stability of the nanoreactors is obtained under dissipative conditions, driven by enzymatic dephosphorylation of the templating nucleotides. These results show that small molecules can play a key role in modulating network reactivity, by selectively templating self-assembled structures that are able to up-regulate chemical reaction pathways.

The formation of self-assembled structures of C60 in solution and in the volume of an evaporating drop of a colloidal solution

The results of experiments on the self-aggregation of C60 fullerene molecules both inside a two-component solvent (xylene/tetrahydrofuran) and in the volume of an evaporating drop of C60 colloidal solution on a flat substrate surface are presented. The investigations of C60 solutions using dynamic light scattering, transmission electron microscopy and UV–Vis absorption spectroscopy methods revealed the possibility of synthesis of fractal nanoaggregates with a diameter of up to ~135 nm at low concentrations of C60 in the solutions. The final geometric dimensions of C60 nanoaggregates were determined by the initial concentration of fullerene in the solvent medium. Using the scanning electron microscopy method, we have shown that in an open dissipative system – in the volume of an evaporating droplet of the colloidal solution of fullerene C60 sessile on the surface of a flat glass substrate, large quasispherical nanoaggregates with an average diameter of ~380–800 nm are formed. The physical features and regularities that characterize the processes of self-aggregation of fullerene particles in the volume of a drying drop were determined.

Chiral Amphiphilic Secondary Amine-Porphyrin Hybrids for Aqueous Organocatalysis.

Two chiral proline-derived amphiphilic 5-substituted-10,15,20-tris(4-sulfonatophenyl)porphyrins were prepared, and their pH-dependent supramolecular behavior was studied. In neutral aqueous solutions, the free-base form of the hybrids is highly soluble, allowing enamine-based organocatalysis to take place, whereas under acidic conditions, the porphyrinic protonated core of the hybrid leads to the formation of self-assembled structures, so that the hybrids flocculate and their catalytic activity is fully suppressed. The low degree of chirality transfer observed for aqueous Michael and aldol reactions strongly suggests that these reactions take place under true “in water” organocatalytic conditions. The highly insoluble catalyst aggregates can easily be separated from the reaction products by centrifugation of the acidic reaction mixtures, and after neutralization and desalting, the sodium salts of the sulfonated amine-porphyrin hybrids, retaining their full catalytic activity, can be recovered in high yield.

Importance of the fatty acid chain length on in vitro and in vivo anticancer activity of fattigation-platform albumin nanoparticles in human colorectal cancer xenograft mice model

The aims of this study were to design different chain length fatty acid-conjugated albumin nanoparticles (ANPs) and evaluate their anticancer activity in the HCT116 human colorectal cancer xenograft mouse model. Doxorubicin hydrochloride (DOX·HCl) was chosen as a model drug. The different chain lengths of fatty acids (butyric acid; C4, and stearic acid; C18) in albumin conjugates exhibited different physicochemical properties and anticancer activity. Fatty acid-conjugated albumin aided the formation of self-assembled structures with an average size of approximately 200 nm and a negative charge when incubated with excess DOX in an aqueous solution. DOX-loaded long-chain C18-conjugated ANPs allowed efficient encapsulation of hydrophobic DOX into the core of the self-assembled structure, enabling higher drug loading, enhanced colloidal stability and controlled release behavior in PBS pH 7.4 medium as compared with free DOX·HCl or non-fatty acid conjugated ANPs. Furthermore, DOX-loaded fatty acid-conjugated ANPs showed an increased cellular uptake intensity and cytotoxic effects in vitro. In vivo, HCT116 xenograft model experiments confirmed that DOX-loaded C18-conjugated ANPs showed improved anticancer activity and reduced side effects compared with the DOX-treated groups. The long-chain fatty acid-conjugated ANPs synergistically activated the interaction with the free-fatty acid receptor (FFAR) on HCT116 colorectal cancer cells as compared with short-chain C4 or other non-conjugated ANPs. Specifically, DOX-loaded C18-conjugated NPs exhibited significant performance to overexpressed FFAR4 on HCT116 colorectal cancer cells. The fatty acid chain length in the fattigation-platform system could be a promising molecular moiety to improve targeting efficiency and drug accumulation in various cancer therapy.

Luminescence of irradiated lithium, sodium and magnesium fluorides nanocrystals: Formation of self-assembled structures and point defects with new properties

The luminescence and absorption properties of LiF, NaF and MgF2 nanocrystals containing radiation-induced point defects with new properties are investigated. The influence of temperature, at which nanocrystals are maintained after their manufacture, on the efficiency and kinetics of such defects formation is examined. For LiF samples, the activation energy of fotmation processes is determined. X-ray diffraction reflections are compared for LiF nanocrystals, unannealed and annealed after fabrication, unannealed and irradiated with γ-rays or electrons, as well as those manufactured by fragmentation of an irradiated crystal plate. Conclusions are drawn about the processes of self-assembled nanostructures formation, the presence of which is a prerequisite for the creation of radiation-induced point defects with new properties.

Investigation of α/γ hybrid peptide self-assembled structures with antimicrobial and antibiofilm properties.

The present work describes the synthesis and characterization of α/γ hybrid peptides, Boc-Phe-γ4 -Phe-Val-OMe, P1; Boc-Ala-γ4 -Phe-Val-OMe, P2; and Boc-Leu-γ4 -Phe-Val-OMe, P3 together with the formation of self-assembled structures formed by these hybrid peptides in dimethyl sulfoxide (DMSO)/water (1:1). The self-assembled structures were characterized by infrared (IR) spectroscopy, circular dichroism (CD), and scanning electron microscopy (SEM). Further, α/γ hybrid peptide self-assembled structures were evaluated for antibacterial properties. Among all, the self-assembled peptide P1 exhibited the antimicrobial activity against Escherichia coli and Klebsiella pneumoniae, while self-assembled peptide P3 inhibited the biofilms of Salmonella typhimurium and Pseudomonas aeruginosa. In this study, we have shown the significance of self-assembled structures formed from completely hydrophobic α/γ hybrid peptides in exploring the antibacterial properties together with biofilm inhibition.

Hydrotrope-Driven Self-Assembly in CTAB/ n-Hexanol/Water/Heptane Reverse Micellar System.

Self-organization of nanoparticles into one-dimensional (1D) nanochains leads to new unpredicted physiochemical properties, which are further exploited to develop photonic or electronic devices. Thus, the controlled fabrication of 1D nanochains requires nanotemplate, which acts as building blocks for the self-assembly of nanoparticles. To address this issue, we designed a hydrotrope (sodium salicylate)-based CTAB/ n-hexanol/water/heptane reverse micellar system. Hydrotrope, herein, modulates electrostatic interactions between reverse micellar droplets and paves the way for the formation of self-assembled structures. Small-angle X-ray scattering studies were performed on the CTAB/heptane reverse micellar system by varying hydrotrope concentrations and water-to-surfactant ratios (W x). The aqueous content of the reverse micellar pool is determined from the W x value, where W x = [H2O]/[CTAB] and [CTAB] = 0.05 M. SAXS studies were performed for CTAB/heptane reverse micellar systems at three different W x values, that is, 6, 12, and 16 and represented by W6, W12, and W16, respectively. All SAXS profiles were modeled with a spherical form factor and a Baxter sticky hard sphere structure factor. The interaction between droplets was predicted in terms of stickiness parameter. The effect of W x on the formation of self-assembled structures and forces governing the assembly has been discussed in detail. For the W6 system, the electrostatic repulsion between reverse micellar droplets decreases, resulting in the formation of the 1D chain-like assembly of nanodroplets. In the case of the W12 system, the dual feature of the hydrotrope has been observed, it increases the size of the reverse micellar system and reduces electrostatic repulsion between droplets because of which the formation of chain-like assemblies cannot be determined with accuracy. For the W16 system, the decrease in micellar size with the increase in the hydrotrope concentration has been observed. Thus, our reverse micellar templates may provide a comprehensive method for the fabrication of high aspect ratio 1D nanochains of a variety of materials and harnessing their collective properties for magnetic, catalytic, and opto-electronic applications.

Dendrimer directed assembly of dicarboxylated hairy nanocellulose

HypothesisDendrimer-directed assembly of electrosterically stabilized nanocrystalline cellulose (ENCC) to form network structures was studied. ENCC is a member of the family of hairy nanocelluloses and consists of a crystalline rod and dicarboxylated cellulose chains (“hairs”) protruding from both ends, which are very reactive. We hypothesized that covalent linking of ENCC and dendrimers should lead to self-assembled hybrid network structures in which dendrimeric nodes connect cellulose nanorods. ExperimentsPolyamidoamine (PAMAM) dendrimers were covalently linked to ENCC by a bioconjugation reaction with different ratios of ENCC to PAMAM. To control the self-assembly process and prevent aggregation, acid hydrolysis of ENCC was performed to obtain crew-cut ENCC with shorter hairs and less negative charge. The formation of self-assembled structures from different PAMAM concentrations were analyzed using atomic force microscopy. FindingsIt was observed that depending on the concentration of PAMAM, various linear, star-shaped, and closed-loop structures were formed. Also, networks were formed with dendrimers acting as the nodes, connecting long cellulose rods, thus producing a network with a characteristic length of around 100–200 nm, which is difficult to obtain otherwise. We have demonstrated that the reactions of dendrimers with ENCC are solely occurring at the hairs and not at the crystalline regions.