Self-assembled Nanoaggregates Research Articles

Cobalt (II) porphyrin nanoaggregates as sacrificial templates to improve the peroxidase-like activity of light-controlled TiO2-based nanozymes for colorimetric determination of amikacin

Although porphyrin modification can improve the peroxidase-like activity of some inorganic nanozymes, it is hardly studied that metal porphyrin self-assembled nanoaggregates as sacrificial templates to turn on the peroxidase-like activity of inorganic nanozymes under light illumination. In this work, cobalt (II) 5,10,15,20-Tetrakis (4-carboxylpheyl)porphyrin (CoTCPP) self-assembled nanoaggregates are firstly used as soft templates to prepare TiO2-based nanozymes with the enhanced peroxidase-like activity. Interestingly, CoTCPP nanoaggregates can be changed into Co oxide nanoparticles dispersed into the nanosphere composites. Furthermore, the peroxidase-like activity of CoTCPP-TiO2 nanospheres can be controlled by light illumination. Comparatively, CoTCPP-TiO2 nanoshperes exhibit the highest peroxidase-like activity of three nanospheres (CoTCPP-TiO2, H2TCPP-TiO2 and TiO2) with similar morphology under the light illumination. Other than the existence of oxygen vacancy, the formation of heterostructure between TiO2 and a small amount of Co3O4 are ascribed to increase the catalytic activity of CoTCPP-TiO2 composites. Thus, a facile and convenient colorimetric sensing platform has been constructed and tuned by light illumination for determining H2O2 and amikacin in a good linear range of 20–100 and 50–100 μM with a limit of detection (LOD) of 3.04 μM and 1.88 μM, respectively. The CoTCPP-TiO2 based colorimetric sensing platform has been validated by measuring the amikacin residue in lake water.

Low-Hysteresis and Tough Ionogels via Low-Energy-Dissipating Cross-Linking.

Low-hysteresis merits can help polymeric gel materials survive from consecutive loading cycles and promote life span in many burgeoning areas. However, it is a big challenge to design low-hysteresis and tough polymeric gel materials, especially for ionogels. This can be attributed to the fact that higher viscosities of ionic liquids (ILs) would increase chain friction of polymeric gels and eventually dissipate large amounts of energy under deformation. Herein, a chemical design of ionogels is proposed to achieve low-hysteresis characteristics in both mechanical and electric aspects via hierarchical aggregates formed by supramolecular self-assembly of quadruple H-bonds in a soft IL-rich polymeric matrix. These self-assembled nanoaggregates not only can greatly reinforce the polymeric matrix and enhance resilience, but also exhibit low-energy-dissipating features under stress conditions, simultaneously benefiting for low-hysteresis properties. These aggregates can also promote toughness and subsequent anti-fatigue properties in response to external cyclic mechanical stimuli. More importantly, these ionogels are presented as a model system to elucidate the underlying mechanism of the low hysteresis and fatigue resistance. Based on these findings, it is further demonstrated that the supramolecular low-hysteresis strategy is universal.

Self-Assembled Borneol-Guanidine-Based Amphiphilic Polymers as an Efficient Antibiofilm Agent.

Biofilm-associated infections remain a tremendous obstacle to the treatment of microbial infections globally. However, the poor penetrability to a dense extracellular polymeric substance matrix of traditional antibacterial agents limits their antibiofilm activity. Here, we show that nanoaggregates formed by self-assembly of amphiphilic borneol-guanidine-based cationic polymers (BGNx-n) possess strong antibacterial activity and can eliminate mature Staphylococcus aureus (S. aureus) biofilms. The introduction of the guanidine moiety improves the hydrophilicity and membrane penetrability of BGNx-n. The self-assembled nanoaggregates with highly localized positive charges are expected to enhance their interaction with negatively charged bacteria and biofilms. Furthermore, nanoaggregates dissociate on the surface of biofilms into smaller BGNx-n polymers, which enhances their ability to penetrate biofilms. BGNx-n nanoaggregates that exhibit superior antibacterial activity have the minimum inhibitory concentration (MIC) of 62.5 μg·mL-1 against S. aureus and eradicate mature biofilms at 4 × MIC with negligible hemolysis. Taken together, this size-variable self-assembly system offers a promising strategy for the development of effective antibiofilm agents.

Biotinylated Theranostic Amphiphilic Polyurethane for Targeted Drug Delivery.

In the area of drug delivery aided by stimuli-responsive polymers, the biodegradability of nanocarriers is one of the major challenges that needs to be addressed with the utmost sincerity. Herein, a hydrogen sulfide (H2S) responsive hydrophobic dansyl-based trigger molecule is custom designed and successfully incorporated into the water-soluble polyurethane backbone, which is made of esterase enzyme susceptible urethane bonds. The amphiphilic polyurethanes, PUx (x = 2 and 3) with a biotin chain end, formed self-assembled nanoaggregates. A hemolysis and cytotoxicity profile of doxorubicin (DOX)-loaded biotinylated PU3 nanocarriers revealed that it is nonhemolytic and has excellent selectivity toward HeLa cells (biotin receptor-positive cell lines) causing ∼60% cell death while maintaining almost 100% cell viability for HEK 293T cells (biotin receptor-negative cell lines). Furthermore, better cellular internalization of DOX-loaded fluorescent nanocarriers in HeLa cells than in HEK 293T cells confirmed receptor-mediated endocytosis. Thus, this work ensures that the synthesized polymers serve as biodegradable nanocarriers for anticancer therapeutics.

Less is More: Asymmetric D-A Type Agent to Achieve Dynamic Self-Assembled Nanoaggregates for Long-Acting Photodynamic Therapy.

To enhance the phototheranostic performance, agents with high reactive oxygen species (ROS) generation, good tumor-targeting ability, and prolonged retention are urgently needed. However, symmetric donor-acceptor (D-A) type agents usually produce spherical nanoaggregates, leading to good tumor targeting but inferior retention. Rod-like nanoaggregates are desired to extend their retention in tumors; however, this remains a challenge. In particular, agents with dynamically changeable shapes that integrate merits of different morphologies are seldomly reported. Therefore, self-assembled organic nanoaggregates with smart shape tunability are designed here using an asymmetric D-A type TIBT. The photoluminescence quantum yield in solids is up to 52.24% for TIBT. TIBT also exhibits high ROS generation in corresponding nanoaggregates (TIBT-NCs). Moreover, dynamic self-assembly in shape changing from nanospheres to nanorods occurrs in TIBT-NCs, contributing to the enhancement of ROS quantum yield from 0.55 to 0.72. In addition, dynamic self-assembly can be observed for both in vitro and in vivo, conferring TIBT-NCs with strong tumor targeting and prolonged retention. Finally, efficient photodynamic therapy to inhibit tumor growth is achieved in TIBT-NCs, with an inhibition rate of 90%. This work demonstrates that asymmetric D-A type agents can play significant roles in forming self-assembled organic nanoaggregates, thus showing great potential in long-acting cancer therapy.

Random ionic polymers: Salt-triggered reversible vesicular self-assembly in water

NaCl salt as an external stimulus triggers the self-assembly of ionic polymers and offers a convenient route to structuring vesicular reversible polymeric nanoparticles. In this contribution, amphiphilic random imidazolium ionic polymers are synthesized by roping the partial anion exchange and the choice of N-substituent. These polymers are evaluated for their self-assembly behavior in water, and it is strengthened by dye encapsulation application in water through self-assembly. The effects of salt and pH study demonstrated the reversibility of self-assembly. The self-assembled nano-aggregates are thermoresponsive at the upper critical solution temperature (UCST) (Cp 47 °C). The synergic balance between hydrogen bonding and ionic self-assembly is attributed to the constituents in the macromolecular structure, making these polyionic liquids (PILs) a “smart” responsive system in water upon the addition of external stimuli, such as NaCl and KPF6. This self-assembly is acquired with partial anion exchange and salt balance in the water. The unusual interfacial activity of polymer to form a regular shape eventually to surfaces organic dye molecule serving as a type of stabilizer or scavenger evidenced by nano-size and vesicular morphology analysis.

Nanoaggregates of Disulfide-Decorated TrxR Inhibitor Promote Cellular Uptake, Selective Targeting, and Antitumor Efficacy.

Three self-assembled nanoaggregates (CPUL1-LA NAs, CPUL1-DA NAs, and CPUL1-AA NAs) were constructed through lipoic acid (LA), dithiodipropionic acid (DA), and adipic acid (AA) decorated TrxR inhibitor (CPUL1), respectively. Measurements of DLS, TEM, UV-vis, fluorescence, 1H NMR, ITC, and MTT assays verified disulfide-containing CPUL1-LA NAs and CPUL1-DA NAs spontaneously assembled carrier-free nanoparticles in aqueous solution, which possessed high drug contents, excellent stability, improved cytotoxicity against HUH7 hepatoma cells, and potential biosafety because of low cytotoxicity against L02 normal cells. In contrast, disulfide-free CPUL1-AA NAs happened to aggregate and precipitate after 48 h, which showed distinct instability in aqueous solution. Thus, disulfide units seemed to be crucial for constructing controllable and stable nanoaggregates. While measuring the reduction of nanoaggregates by TrxR/NADPH and GSH/GR/NADPH, cyclic disulfide of LA and linear disulfide of DA were verified to endow the nanoaggregates with targeting ability to respond specifically to TrxR over GSH. Furthermore, by tests of flow cytometry, fluorescence images, and CLSM, both CPUL1-LA NAs and CPUL1-DA NAs displayed a faster cellular uptake characteristic to be internalized by cancer cells and could generate more abundant ROS to induce cell apoptosis than that of free CPUL1, resulting in significantly improved antitumor efficacy against HUH7 cells in vitro.

Synthesis of degradable PLA-based diblock copolymers with dual acid/reduction-cleavable junction

The development of biocompatible polylactide (PLA)-based block copolymers for constructing self-assembled nanoaggregates degradable in response to endogenous stimuli found in cell environments is promising for enhanced/controlled drug delivery in pharmaceutical science. Despite advances in the synthesis of various PLA-based nanoassemblies featured with only a single stimulus response, the design and development of advanced nanoassemblies integrated with two endogenous stimuli-responsive cleavable linkages for dual stimuli response is challenging. Here we report an approach to the synthesis of a new PLA-based diblock copolymer having dual reduction-cleavable disulfide and acid-labile acetal linkages at the block junction. Key to the approach is the use of a double-head initiator designed uniquely with both acetal and disulfide linkages as well as with both OH and bromine terminal groups. Our comprehensive results from structural analysis and degradation through chemical transition suggest the requirement of a rational combination of controlled polymerization techniques and facile coupling reactions for the synthesis of well-controlled PLA-based diblock copolymer having both disulfide and acetal linkages. The main reason is attributed to the instability of acetal linkages under ROP condition with a tin catalyst at an elevated temperature. The resultant copolymer self-assembles to form shell-sheddable nanoassemblies that are disintegrated in response to dual acid/reduction. This work demonstrates the importance in the development of efficient polymerization strategies by utilizing well-established polymerization techniques to synthesize novel functional copolymers with complicated architectures and various functionalities sensitive to reaction environments.

Discovery of Self-Assembling π-Conjugated Peptides by Active Learning-Directed Coarse-Grained Molecular Simulation.

Electronically active organic molecules have demonstrated great promise as novel soft materials for energy harvesting and transport. Self-assembled nanoaggregates formed from π-conjugated oligopeptides composed of an aromatic core flanked by oligopeptide wings offer emergent optoelectronic properties within a water-soluble and biocompatible substrate. Nanoaggregate properties can be controlled by tuning core chemistry and peptide composition, but the sequence-structure-function relations remain poorly characterized. In this work, we employ coarse-grained molecular dynamics simulations within an active learning protocol employing deep representational learning and Bayesian optimization to efficiently identify molecules capable of assembling pseudo-1D nanoaggregates with good stacking of the electronically active π-cores. We consider the DXXX-OPV3-XXXD oligopeptide family, where D is an Asp residue and OPV3 is an oligophenylenevinylene oligomer (1,4-distyrylbenzene), to identify the top performing XXX tripeptides within all 203 = 8000 possible sequences. By direct simulation of only 2.3% of this space, we identify molecules predicted to exhibit superior assembly relative to those reported in prior work. Spectral clustering of the top candidates reveals new design rules governing assembly. This work establishes new understanding of DXXX-OPV3-XXXD assembly, identifies promising new candidates for experimental testing, and presents a computational design platform that can be generically extended to other peptide-based and peptide-like systems.

Self-assembled nano-aggregates of fluorinases demonstrate enhanced enzymatic activity, thermostability and reusability.

Three SAP (self-assembling peptide)-tagged fluorinases (FLAs), namely, FLA-ELK16, FLA-L6KD and FLA-18A (named after the SAP used for tagging FLA) were successfully engineered. All three SAP-tagged FLAs could be highly over-expressed using engineered E. coli host cells despite being in the form of aggregates (inclusion bodies). It was noted that all three SAP-tagged FLAs exhibited enzymatic activity. It was also observed that all three SAP-tagged FLAs were capable of self-assembly to form nano-sized particles with different dimensions in aqueous solutions. Strikingly, one of the SAP-tagged FLA (FLA-L6KD) displayed improved enzyme activity, thermostability and reusability, which is potentially ideal for bio-transformation. FLA is an exotic enzyme that is capable of catalysing the formation of C-F bonds using inorganic fluorine ions as substrates. This significant feature enables it to incorporate [18F]-fluoride into different small molecules to generate radiopharmaceuticals in PET (positron emission tomography) labeling. In addition, fluorinase is greatly valuable in synthetic biology for incorporating the fluorine element into building blocks to produce non-natural organofluorines or as a biocatalyst for transforming non-native substrates. Our method would be a further step in making FLA-based biocatalysis even 'greener' by enhancing the enzymatic activity, thermostability and reusability of FLA through the introduction of nano-sized aggregates. Enzymes are such nontrivial biomaterials, which can be manifested in different scenarios. Our research expands their reach and tunes their properties by tagging SAP partners. Thus, this methodology can be put into the 'toolbox' of enzymologists, which can be further explored and generalised for others.

Revealing the Sequence-Structure-Electronic Property Relation of Self-Assembling π-Conjugated Oligopeptides by Molecular and Quantum Mechanical Modeling.

Self-assembled nanoaggregates of π-conjugated synthetic peptides present a biocompatible and highly tunable alternative to silicon-based optical and electronic materials. Understanding the relationship between structural morphology and electronic properties of these assemblies is critical for understanding and controlling their mechanical, optical, and electronic responses. In this work, we combine all-atom classical molecular simulations with quantum mechanical electronic structure calculations to ascertain the sequence-structure-electronic property relationship within a family of Asp-X-X-quaterthiophene-X-X-Asp (DXX-OT4-XXD) oligopeptides in which X is one of the five amino acids {Ala, Phe, Gly, Ile, Val} ({A, F, G, I, V}). Molecular dynamics simulations reveal that smaller amino acid substituents (A, G) favor linear stacking within a peptide dimer, whereas larger groups (F, I, V) induce larger twist angles between the peptides. Density functional theory calculations on the dimer show the absorption spectrum to be dominated by transitions between carbon and sulfur p orbitals. Although the absorption spectrum is largely insensitive to the relative twist angle, the highest occupied molecular orbital strongly localizes onto one molecule within the dimer at large twist angles, impeding the efficiency of transport between molecules. Our results provide a fundamental understanding of the relation between peptide orientation and electronic structure and offer design precepts for rational engineering of these systems.

Controlling Supramolecular Chirality in Peptide-π-Peptide Networks by Variation of the Alkyl Spacer Length.

Self-assembled supramolecular organic materials with π-functionalities are of great interest because of their applications as biocompatible nanoelectronics. A detailed understanding of molecular parameters to modulate the formation of hierarchical structures can inform design principles for materials with engineered optical and electronic properties. In this work, we combine molecular-level characterization techniques with all-atom molecular simulations to investigate the subtle relationship between the chemical structure of peptide-π-peptide molecules and the emergent supramolecular chirality of their spontaneously self-assembled nanoaggregates. We demonstrate through circular dichroism measurements that we can modulate the chirality by incorporating alkyl spacers of various lengths in between the peptides and thienylene-phenylene π-system chromophores: even numbers of alkyl carbons in the spacer units (0, 2) induce M-type helical character whereas odd numbers (1, 3) induce P-type. Corroborating molecular dynamics simulations and explicating machine learning analysis techniques identify hydrogen bonding and hydrophobic packing to be the principal discriminants of the observed chirality switches. Our results present a molecular-level design rule to engineer chirality into optically and electronically active nanoaggregates of these peptidic building blocks by exploiting systematic variations in the alkyl spacer length.

Efficacious fungicidal potential of composite derived from nano-aggregates of Cu-Diclofenac complexes and ZnO nanoparticles

The composite-based formulations have appeared as prominent “antimicrobial materials” because it provide superior antimicrobial efficacy than single component based therapeutic formulations. Herein, we report the synergistically enhanced antifungal activity of the composite developed from self-assembled nano-aggregates of copper complexes of non-steroidal anti-inflammatory drug, diclofenac (Cu-Dc) in combination with zinc oxide (ZnO) nanoparticles. The composites (ZnO-Cu-Dc) were prepared at different weight ratios (Cu-Dc/ZnO; 1:0.125–1:2) and characterized thoroughly by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), fourier-transform infrared spectroscopy (FT-IR) and dynamic light scattering (DLS) measurements which revealed them to be nanostructured aggregates. The composite mediated treatments showed substantially increased zones of inhibition in agar well-diffusion method against a human pathogenic fungus (Candida albicans) and three plant pathogenic fungi (Penicillium funiculosum, Aspergillus niger and Fusarium oxysporum). Notably, the individual treatments using the respective concentrations of ZnO nanoparticles did not show any inhibitory activity against all the fungal strains. Optical density measurements profiled maximum reduction in fungal growth for composite treatment when compared to that of ZnO nanoparticles and Cu-Dc complexes alone. The morphological analysis of fungal cell growth by SEM and optical microscopic studies evidenced maximum deformation of biofilm mass for composite mediated treatment. Concisely, the ZnO-Cu-Dc, a composite system has been developed which can be utilized as an effective formulation against fungal infections.

Twisted-Intramolecular-Charge-Transfer-Based Turn-On Fluorogenic Nanoprobe for Real-Time Detection of Serum Albumin in Physiological Conditions.

Two cyanine-based fluorescent probes, ( E)-2-(4-(diethylamino)-2-hydroxystyryl)-3-ethyl-1,1-dimethyl-1 H-benzo[ e]indol-3-ium iodide (L) and ( E)-3-ethyl-1,1-dimethyl-2-(4-nitrostyryl)-1 H-benzo[ e]indol-3-ium iodide (L1), have been designed and synthesized. Of these two probes, the twisted-intramolecular-charge-transfer (TICT)-based probe, L, can preferentially self-assemble to form nanoaggregates. L displayed a selective turn-on fluorescence response toward human and bovine serum albumin (HSA and BSA) in ∼100% aqueous PBS medium, which is noticeable with the naked eye, whereas L1 failed to sense these albumin proteins. The selective turn-on fluorescence response of L toward HSA and BSA can be attributed to the selective binding of probe L with HSA and BSA without its interfering with known drug-binding sites. The specific binding of L with HSA led to the disassembly of the self-assembled nanoaggregates of L, which was corroborated by dynamic-light-scattering (DLS) and transmission-electron-microscopy (TEM) analysis. Probe L has a limit of detection as low as ∼6.5 nM. The sensing aptitude of probe L to detect HSA in body fluid and an artificial-urine sample has been demonstrated.

PEG-coumarin nanoaggregates as π–π stacking derived small molecule lipophile containing self-assemblies for anti-tumour drug delivery

Polymeric self-assemblies formed by non-covalent interactions such as hydrophobic interactions, hydrogen bonding, π–π stacking, host-guest and electrostatic interactions have been utilised widely and exhibit controlled release of encapsulated drug. Beside carrier-carrier interactions, small molecule amphiphiles exhibiting carrier-drug interactions have recently been an area of interest for cancer drug delivery, as most of the hydrophobic anti-tumour drugs are aromatic and exhibit π–π conjugated structure. In the present study PEG-coumarin (PC) conjugates forming self-assembled nanoaggregates were synthesised with PEG (polyethylene glycol) as hydrophilic block and coumarin as small molecule lipophilic segment. Curcumin (CUR) as model conjugated aromatic drug was loaded in to the nanoaggregates via dual hydrophobic and π–π stacking interactions. The interactions between the conjugates and CUR, drug release profile and in vitro anti-tumour efficacy were investigated in detail. CUR-loaded nanoaggregate self-assembly was driven by π–π interactions and a maximum loading level of about 18 wt.% (~60 % encapsulation efficiency) was achieved. The average hydrodynamic diameter (Dav) was in the range of 120–160 nm and a spherical morphology was observed by transmission electron microscopy (TEM). A sustained release of CUR was observed for 90 h. Cytotoxicity evaluation of CUR-loaded nanoaggregates on pancreatic cancer cell lines indicated higher efficacy, IC50 ~11 and ~15 μM as compared to free CUR, IC50 ~14 and ~20 μM on human pancreatic carcinoma (MIA PaCa-2) and human pancreatic duct epithelioid carcinoma (PANC-1) cell lines respectively. PC conjugates provided a new strategy of fabricating nanoparticles for drug delivery and may form the basis for the development of advanced biomaterials in near future.

Control of the hierarchical assembly of π-conjugated optoelectronic peptides by pH and flow.

Self-assembled nanoaggregates of π-conjugated peptides possess optoelectronic properties due to electron delocalization over the conjugated peptide groups that make them attractive candidates for the fabrication of bioelectronic materials. We present a computational and theoretical study to resolve the microscopic effects of pH and flow on the non-equilibrium morphology and kinetics of early-stage assembly of an experimentally-realizable optoelectronic peptide that displays pH triggerable assembly. Employing coarse-grained molecular dynamics simulations, we probe the effects of pH on growth kinetics and aggregate morphology to show that control of the peptide protonation state by pH can be used to modulate the assembly rates, degree of molecular alignment, and resulting morphologies within the self-assembling nanoaggregates. We also quantify the time and length scales at which convective flows employed in directed assembly compete with microscopic diffusion to show that flow influences cluster alignment and assembly rate during early-stage assembly only at extremely high shear rates. This suggests that observed improvements in optoelectronic properties at experimentally-accessible shear rates are due to the alignment of large aggregates of hundreds of monomers on time scales in excess of hundreds of nanoseconds. Our work provides new fundamental understanding of the effects of pH and flow to control the morphology and kinetics of early-stage assembly of π-conjugated peptides and lays the groundwork for the rational manipulation of environmental conditions to direct assembly and the attendant emergent optoelectronic properties.

Self-assembly of four- and two-antennary oligoglycines in aqueous medium

In aqueous media synthetic antennary oligoglycine molecules self-assemble into supramolecular structures like bulk hydrophilic aggregates (tectomers), vesicles, etc. The innate reason for the self-organization is the onset of highly cooperative network of intra- and intermolecular hydrogen bonds, resulting in ‘recognition-type’ interactions. The present study deals with the detailed investigation of the onset, the time evolution and the properties of the tectomers, formed from three types of synthetic oligoglycines: four-antennary (T4), two- antennary with octyl chain (T2-C8) and two-antennary with heptyl chain (T2-C7). Detailed size distributions and the electrophoretic mobilities of the aggregates are presented. The pH and the temperature of the investigated samples are strictly monitored and kept within prescribed value ranges. The impact of the addition of low molecular mass electrolyte (NaCl) on the size distributions of the obtained self-assemblies is also clarified. The basic result is the registration of predominantly bimodal size distribution of the self-assembled nanoaggregates. Only at high oligoglycine concentration the sizes distribution becomes monomodal. Insofar as the antennary oligoglycines are biocompatible, the pool of attained systematic data will be further implemented in the design and fine-tunning strategies of complex fluid formulations aimed at the entrapment of charged and/or hydrophobic nanospecies of various origin. The obtained results suggest that the self-assembled nanostructures of antennary olygoglycines have high potential for e.g. biomedical and water-purity-control applications.

Cooperation of Amphiphilicity and Crystallization for Regulating the Self-Assembly of Poly(ethylene glycol)-block-poly(lactic acid) Copolymers

Tuning the amphiphilicity of block copolymers has been extensively exploited to manipulate the morphological transition of aggregates. The introduction of crystallizable moieties into the amphiphilic copolymers also offers increasing possibilities for regulating self-assembled structures. In this work, we demonstrate a detailed investigation of the self-assembly behavior of amphiphilic poly(ethylene glycol)-block-poly(l-lactic acid) (PEG-b-PLLA) diblock copolymers with the assistance of a common solvent in aqueous solution. With a given length of the PEG block, the molecular weight of the PLA block has great effect on the morphologies of self-assembled nanoaggregates as a result of varying molecular amphiphilicity and polymer crystallization. Common solvents including N,N-dimethylformamide, dioxane, and tetrahydrofuran involved in the early stage of self-assembly led to the change in chain configuration, which further influences the self-assembly of block copolymers. This study expanded the scope of PLA-based copolymers and proposed a possible mechanism of the sphere-to-lozenge and platelet-to-cylinder morphological transitions.

A route to self-assemble suspended DNA nano-complexes.

Highly charged polyelectrolytes can self-assemble in presence of condensing agents such as multivalent cations, amphiphilic molecules or proteins of opposite charge. Aside precipitation, the formation of soluble micro- and nano-particles has been reported in multiple systems. However a precise control of experimental conditions needed to achieve the desired structures has been so far hampered by the extreme sensitivity of the samples to formulation pathways. Herein we combine experiments and molecular modelling to investigate the detailed microscopic dynamics and the structure of self-assembled hexagonal bundles made of short dsDNA fragments complexed with small basic proteins. We suggest that inhomogeneous mixing conditions are required to form and stabilize charged self-assembled nano-aggregates in large excess of DNA. Our results should help re-interpreting puzzling behaviors reported for a large class of strongly charged polyelectrolyte systems.

Lipopolysaccharide (LPS) and Protein-LPS complexes: Detection and Characterization by Gel Electrophoresis, Mass Spectrometry and Bioassays

A prerequisite to the discovery and characterization of lipopolysaccharide (LPS) interaction with specific receptors and the resulting pathophysiological effects is the comprehensive structural analysis of LPS species. This brief review is aimed to summarize the use of gel electrophoresis linked to other biochemical technologies for detecting and characterizing LPSs. Lipopolysaccharide aggregates alone or mixtures containing LPSs and proteins/peptides can be separated by native agarose gel electrophoresis (NAGE), after which LPSs are detected with imidazole and zinc salts. A double-staining process with Coomassie brilliant blue R-250 enables the use of NAGE for detecting and studying protein-LPS interactions. For compositional analysis, the LPS aggregates are separated, with high resolution, by surfactant-polyacrylamide gel electrophoresis. After reverse staining with zinc-imidazole and elution from gel microparticles, glycoform-specific LPSs are ready for structural and biological analysis. For sequence analysis based on tandem electrospray ionization mass spectrometry (ESI-MS/MS) of oligosaccharides, LPSs are subjected to mild acid hydrolysis, dephosphorylation and permethylation. Also, O-deacylated LPS forms can be analyzed by matrix-assisted laser desorption/ionization-time of flight-MS. By comparison to spectra of unpurified LPSs, mass spectra of the micropurified LPSs show reduce heterogeneity and increased signal-to-noise ratios. Furthermore, the micropurification of LPSs prior to MS allows a higher sensitivity of detection for less abundant LPS glycoforms. The micropurified LPS fractions can be used to form self-assembled nanoaggregates which may be detected by dynamic light scattering. The effect of the O-side chain length on the Z-potential of LPS aggregates may be estimated by measurements based on laser Doppler electrophoresis. The thus obtained glycoform-specific LPSs are not only intact chemically but also biologically active as tested by e.g. Limulus amoebocyte lysate test, TNF-α assay and agonistic effect on human Toll-like receptor 4.