Nanoparticles from cationic copolymer and DNA that are soluble and stable in common organic solvents

DNA by virtue of its superlative ability to self-assemble has found use beyond biological research in the design and fabrication of nanomaterials. However, developing novel DNA-based materials for chemical applications might be restricted due to the insoluble nature of DNA in most common organic solvents. In this Communication, we are reporting the first demonstration of making DNA soluble in a variety of nonbiological solvents such as acetonitrile, benzene, dimethyl sulfoxide (DMSO), and tetrahydrofuran with the help of poly(ethylene glycol) (PEG)-based cationic random copolymers. Because of complex formation between cationic copolymer and anionic DNA, nanoparticles are formed. These nanoparticles are expected to exhibit micelle-like structures with a nanometric core of cationic units neutralized by phosphate anions of DNA, surrounded by a shell of PEG segments. As PEG is soluble in the organic solvents used in this study, nanoparticles are stable in these solvents, making entrapped DNA soluble in these organic solvents.     

Temperature-sensitive dendritic micelles

Syntheses up to three generations have been achieved of biaryl-based amphiphilic dendrons with a charge-neutral pentaethylene glycol as the hydrophilic part and a decyl chain as the hydrophobic part. Studies on the temperature-dependent characteristics revealed that these dendrons exhibit a generation-dependent lower critical solution temperature (LCST). This behavior is attributed to the combination of the amphipathic nature of the hydrophilic pentaethylene glycol side chain and dendritic effect. Interestingly, this biaryl-based scaffold also maintains the ability to form a micelle-like assembly in polar solvents and an inverted micelle-like assembly in apolar solvents. Polarity of the dendritic interior was investigated using dye-based microenvironment studies. The aggregation behavior of these micelles was analyzed by fluorescence spectroscopy and dynamic light scattering. Critical micelle concentrations (CMC) of these assemblies were investigated using fluorescence excitation spectra of the sequestered guest molecule, pyrene.     

Organogel from L-leucine-containing surfactant in nonpolar solvents

 Alkyl (S)-2-ammonium-2-isobutylacetate p-toluenesulfonate formed organogel in nonpolar solvents. The gels exhibited thermally reversible sol–gel phase transitions. UV spectroscopic study suggested that dodecyl (S)-2-ammonium-2-isobutylacetate p-toluenesulfonate forms reversed micelle-like aggregate at low concentration in a nonpolar solvent. Circular dichroism spec-troscopy indicated that component molecules of the reversed micelle-like aggregate are cooperatively organized and result in chiral aggregate. The huge fibrous aggregate responsible for gelation was observed with transmission electron microscopy. The accumulation and rearrangement of reversed micelle-like aggregate resulted in the formation of huge fibrous aggregates. A gathering of numerous fibrous aggregates formed the three-dimensional network to immobilize the isotropic liquid. Received: 24 June 1997 Accepted: 3 October 1997     

Aggregation and dispersion of small hydrophobic particles in aqueous electrolyte solutions

The effect of salts on the solvent-induced interactions between hydrophobic particles dispersed in explicit aqueous solution is investigated as a function of the salt's ionic charge density by molecular dynamics simulations. We demonstrate that aggregates of the hydrophobic particles can be formed or dissolved in response to changes in the charge density of the ions. Ions with high charge density increase the propensity of the hydrophobic particles to aggregate. This corresponds to stronger hydrophobic interactions and a decrease in the solubility (salting-out) of the hydrophobic particles. Ions with low charge density can either increase or decrease the propensity for aggregation depending on whether the concentration of the salt is low or high, respectively. At low concentrations of low charge density ions, the aggregate forms a "micelle-like" structure in which the ions are preferentially adsorbed at the surface of the aggregate. These "micelle-like" structures can be soluble in water so that the electrolyte can both increase the solubility and increase aggregation at the same time. We also find, that at the concentration of the hydrophobic particles studied (approximately 0.75 m), the aggregation process resembles a first-order transition in finite systems.     

树枝状聚(醚-酰胺)基胶束的制备及其形貌研究

采用ε-己内酯(CL)开环聚合的方法首先合成树枝状聚(醚-酰胺)基(DPEA)星形聚合物star-PCL,再与异氰酸基封端的PEG(PEG-NCO)偶合制备了两亲性树枝状聚(醚-酰胺)基星形嵌段聚合物star-PCL-b-PEG.利用FT-IR、1H-NMR和GPC分析测试手段对star-PCL-b-PEG的结构进行了表征.通过滴加选择性溶剂的方法,制备了star-PCL-b-PEG以水为介质的类似"平头"聚集体胶束溶液.采用荧光光谱法测得star-PCL-b-PEG水溶液的临界胶束浓度(CMC)为1.623mg/L;采用激光光散射仪测得其在浓度0.15mg/mL和0.5mg/mL的流体力学半径分别为86.2nm和224.6nm,其多分散指数分别为0.115和0.197.透射电镜(TEM)观察发现胶束的形貌受共溶剂的特性,初始聚合物浓度,水含量等因素的影响.     

Micelle-like particles based on self-assembly of rod-like FPEEK and coil-like PVA

The self-assembly of a rod-like polymer [hydroxyl-terminated trifluoromethylphenyl-substituted fluorinated poly(ether ether ketone) (FPEEK)] and a coil-like polymer (polyvinyl alcohol, PVA) in water has been studied. It was found that this polymer pair could form micelle-like particles. Hydrogen bonding between the hydroxy groups of rod-like FPEEK and coil-like PVA, and parallel packing of the rod-like FPEEK are the main factors affecting the formation of micelle-like particles. Over a broad range, when the FPEEK/PVA mass ratio or the tetrahydrofolate/H₂O volume ratio is decreased, the diameter of micelle-like particles is decreased. The diameters (around 250 nm) of micelle-like particles measured by scanning electron microscopy and dynamic light scattering are similar, but are different from that measured by transmission electron microscopy (around 150 nm). Thus, it can be concluded that micelle-like particles have a core–shell structure and the cores of micelles are composed of FPEEK, and that the shells of micelles are composed of PVA. When polyethylene glycol was used instead of PVA, micelle-like particles were also formed, but the average diameter was bigger than that of the particles formed by PVA and FPEEK. This work was supported by the National Nature Science Foundation of China (50203004).     

Polyoxometalate-Engineered Building Blocks with Gold Cores for the Self-Assembly of Responsive Water-Soluble Nanostructures

The controlled assembly of gold nanoparticles (AuNPs) with the size of quantum dots into predictable structures is extremely challenging as it requires the quantitatively and topologically precise placement of anisotropic domains on their small, approximately spherical surfaces. We herein address this problem by using polyoxometalate leaving groups to transform 2 nm diameter gold cores into reactive building blocks with hydrophilic and hydrophobic surface domains whose relative sizes can be precisely tuned to give dimers, clusters, and larger micelle-like organizations. Using cryo-TEM imaging and ¹H DOSY NMR spectroscopy, we then provide an unprecedented “solution-state” picture of how the micelle-like structures respond to hydrophobic guests by encapsulating them within 250 nm diameter vesicles whose walls are comprised of amphiphilic AuNP membranes. These findings provide a versatile new option for transforming very small AuNPs into precisely tailored building blocks for the rational design of functional water-soluble assemblies.     

Aggregates of poly-functional amphiphilic molecules in water and oil phases

The solvation and aggregate formation of complex amphiphilic molecules such as tetra-acids in polar and nonpolar phases are studied via Molecular Dynamics simulations. The nonpolar core of tetra-acid molecules is found to be effectively impermeable for water molecules resulting in a low solubility in the polar solvent, while nonpolar solvent molecules sufficiently solvate the amphiphilic molecules considered, enabling an open conformation of their molecular structure. The rigidity of the core region of the tetra-acid molecules has been found to play a crucial role in their behavior in both polar and nonpolar phases. In the polar phase, simulations have shown that tetra-acids form micelle-like structures with a small aggregation number, confirming previous experimental work. The identification of a case of study in which micelle-like structures can form only with a small aggregation number enables the study via Molecular Dynamics of micelle-micelle interactions. Micelle stability and dispersion in the polar phase under different conditions can be therefore investigated. In the nonpolar phase, the preferential interactions between carboxyl groups, the affinity of the tetra-acids with the solvent molecules, and the structural characteristics of the central core moiety of the tetra-acids have been found to possibly induce a web like array, or network.     

Gemini表面活性剂(12-6-12)和DNA的相互作用

应用紫外光谱、荧光探针、zeta 电位、动态光散射和凝胶电泳等方法探讨了阳离子gemini 表面活性剂C₁₂H₂₅N⁺(CH₃)₂―(CH₂)₆―(CH₃)₂N⁺C₁₂H₂₅·2Br^-(12-6-12)与DNA之间的相互作用. 研究结果表明, 与传统表面活性剂相比, 偶联表面活性剂特殊的分子结构使其与DNA的作用更强烈. DNA引导表面活性剂在其链周围形成类胶束结构, 开始形成类胶束时对应的表面活性剂临界聚集浓度(CAC)比纯表面活性剂临界胶束浓度(CMC)低两个数量级. CAC与DNA的浓度无关, 而与表面活性剂之间的疏水作用以及表面活性剂与DNA之间的静电吸引作用密切相关. Zeta 电位和凝胶电泳结果显示了DNA链所带负电荷逐渐被阳离子表面活性剂中和的过程. 借助原子力显微镜(AFM)成功观察到了松散的线团状DNA, 球状体随机地分散在DNA链上形成类似于串珠的结构、尺寸较大的球形复合物以及其由于吸附多余的表面活性剂重新带正电而被溶解得到的较小DNA/12-6-12聚集体. 圆二色(CD)光谱结果显示, 12-6-12可以诱导DNA的构象发生改变.     

Formation of new hybrid structures: Fullerene C<Subscript>60</Subscript>–amphiphilic copolymer of <Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone with (di)methacrylates in isopropyl alcohol

New hybrid structures of fullerene C₆₀ and an amphiphilic copolymer of N-vinylpyrrolidone with lauryl methacrylate and triethylene glycol dimethacrylate have been obtained via solubilization of fullerene by individual macromolecules and their micelle-like aggregates that form in isopropyl alcohol. The volume ratios of copolymer and C₆₀ solutions in toluene at which there is suppression of aggregation of fullerene and fullerene–polymer particles and the existence of stable hybrid structures in solution have been found. With the use of absorption electron spectroscopy, it has been shown that, with time, fullerene undergoes binding to donor groups of the copolymer and forms a donor–acceptor complex. According to the data of optical microscopy, fullerene is homogeneously distributed as spherical aggregates in the solid polymer matrix.     

Salt effect on the interactions between gemini surfactant and oppositely charged polyelectrolyte in aqueous solution

The effect of alkali halides (NaBr, NaCl, KCl) on the interactions between the cationic gemini surfactant hexylene-1,6-bis(dodecyldimethylammonium bromide) (12-6-12) and the anionic polyelectrolyte sodium polyacrylate (NaPAA) in aqueous solution has been investigated by fluorescence emission spectroscopy, UV transmittance, zeta potential, and transmission electron microscopy (TEM). With increased addition of NaBr, a counterbalancing salt effect on the critical aggregation concentration (CAC) is observed. At low concentrations, NaBr facilitates the formation of micelle-like structures between surfactant and polyelectrolyte and results in a smaller CAC. At high concentrations, NaBr screens the electrostatic attraction between surfactant and polyelectrolyte and leads to a larger CAC. Upon the formation of micelle-like structures at high surfactant concentrations, the addition of NaBr is favorable for larger aggregates. The microstructure detected by TEM show that a global structure is generally formed in the presence of NaBr. The interactions also depend on ion species. Compared to NaBr, the addition of NaCl or KCl yields a smaller CAC.     

Screw dislocation-induced pyramidal crystallization of dendron-like macromolecules featuring asymmetric geometry

We report herein that dendron-shaped macromolecules AB_n crystallize into well-ordered pyramid-like structures from mixed solvents, instead of spherical motifs with curved structures, as found in the bulk. The design of the asymmetric molecular architecture and the choice of mixed solvents are applied as strategies to manipulate the crystallization process. In mixed solvents, the solvent selection for the Janus macromolecule and the existence of dominant crystalline clusters contribute to the formation of flat nanosheets. Whereas during solvent evaporation, the bulkiness of the asymmetric macromolecules easily creates defects within 2D nanosheets which lead to their spiral growth through screw dislocation. The size of the nanosheets and the growth into 2D nanosheets or 3D pyramidal structures can be regulated by the solvent ratio and solvent compositions. Moreover, macromolecules of higher asymmetry generate polycrystals of lower orderliness, probably due to higher localized stress.

The dendron-shaped macromolecules AB_n crystallize into well-ordered pyramid-like structures from mixed solvents, which is on the contrary to spherical motifs with curved structures in bulk.     

Ion-sensitive "isothermal" responsive polymers prepared in water

Ion-sensitive responsive polymers are prepared under fully aqueous conditions using controlled radical polymerization. Variations in comonomer content and sequence lead to temperature and salt-dependent solution behavior, with cloud-points ranging by +/-40 degrees C following addition of Hofmeister series salts. A "hybrid" block copolymer, composed of a statistical sequence of monomers tipped with a hydrophilic block, formed stable micelle-like assemblies that exhibited burst release of an encapsulated model drug in response to addition of a kosmotrope, Na2SO4, at room temperature.     

Self-assembly of trimesic acid at the liquid-solid interface-a study of solvent-induced polymorphism

A scanning tunneling microscope operated under ambient conditions was utilized to study the self-assembly of trimesic acid (TMA) at the liquid-solid interface. On a graphite substrate, two different open, loosely packed, two-dimensional hydrogen-bond networks were found. Both structures exhibit a periodic arrangement of approximately 1.0 nm wide cavities, which can be used for the co-adsorption of another species (guest) within the cells of this host system. These two polymorphs ("chickenwire" and "flower" structures) differ in their molecular packing density and hydrogen-bonding schemes. Using a homologous series of alkanoic acids as solvents, ranging from butyric to nonanoic, selective self-assembly of either the "flower" or "chickenwire" forms was achieved on a graphite surface. Solubility of TMA in these acid solvents was found to decrease with increasing chain length, and the longer-chain solvents favored formation of the chickenwire polymorph structure on the surface.     

Thermodynamics of temperature-sensitive polyether-modified poly(acrylic acid) microgels

The temperature-induced structural changes and thermodynamics of ionic microgels based on poly(acrylic acid) (PAA) networks bonded with poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) (Pluronic) copolymers have been studied by small-angle neutron scattering (SANS), ultra-small-angle neutron scattering (USANS), differential scanning calorimetry (DSC), and equilibrium swelling techniques. Aggregation within microgels based on PAA and either the hydrophobic Pluronic L92 (average composition, EO8PO52EO8; PPO content, 80%) or the hydrophilic Pluronic F127 (average composition, EO99PO67EO99; PPO content, 30%) was studied and compared to that in the solutions of the parent Pluronic. The neutron scattering results indicate the formation of micelle-like aggregates within the F127-based microgel particles, while the L92-based microgels formed fractal structures of dense nanoparticles. The microgels exhibit thermodynamically favorable volume phase transitions within certain temperature ranges due to reversible aggregation of the PPO chains, which occurs because of hydrophobic associations. The values of the apparent standard enthalpy of aggregation in the microgel suspensions indicate aggregation of hydrophobic clusters that are more hydrophobic than the un-cross-linked PPO chains in the Pluronic. Differences in the PPO content in Pluronics L92 and F127 result in a higher hydrophobicity of the resulting L92-PAA-EGDMAmicrogels and a larger presence of hydrophobic, densely cross-linked clusters that aggregate into supramolecular structures rather than micelle-like aggregates such as those formed in the F127-PAA-EGDMA microgels.     

Coupling desorption electrospray ionization with ion mobility/mass spectrometry for analysis of protein structure: evidence for desorption of folded and denatured States

A desorption electrospray ionization (DESI) source has been coupled to an ion mobility time-of-flight mass spectrometer for the analysis of proteins. Analysis of solid-phase horse heart cytochrome c and chicken egg white lysozyme proteins with different DESI solvents and conditions shows similar mass spectra and charge state distributions to those formed when using electrospray to analyze these proteins in solution. The ion mobility data show evidence for compact ion structures [when the surface is exposed to a spray that favors retention of "nativelike" structures (50:50 water:methanol)] or elongated structures [when the surface is exposed to a spray that favors "denatured" structures (49:49:2 water:methanol:acetic acid)]. The results suggest that the DESI experiment is somewhat gentler than ESI and under appropriate conditions, it is possible to preserve structural information throughout the DESI process. Mechanisms that are consistent with these results are discussed.     

Novel pH-responsive nanoparticles

In this work we report a new type of pH-responsive micelle-like nanoparticle. Reversible nanoscale structures are formed in solutions of a pH-sensitive hydrophobic polyelectrolyte, poly( N-methacryloyl- l-valine) or poly( N-methacryloyl- l-phenylalanine), and nonionic surfactant (Brij 98) in the presence of hydrochloric acid. The influence of composition and pH on particles size and shape was investigated by a variety of methods. An entity's size and polydispersity could be varied in a broad range making them a perspective candidate as a drug carrier. Unlike the case of typical micelles, our results indicate the presence of cavities in the formed particles. A hypothetical model of a nanoparticle and mechanism of formation are proposed.     

Self-assembly of Yttrium-containing lacunary polyoxotungstate macroanions in solution with controllable supramolecular structure size by pH or solvent content

The self-assembly and the formation of "Blackberry" type supramolecular structures for a type of Yttrium-containing polyoxometalate (K 15Na 6(H 3O) 9[(PY 2W 10O 38) 4(W 3O 14)].9H 2O, or {P 4Y 8W 43}) macroanions is characterized by using static and dynamic light scattering techniques. {P 4Y 8W 43} macroions are found to form hollow, spherical, single-layer "blackberry" structures in water and water-acetone mixed solvents. Very interestingly, the blackberry size can be accurately controlled by either changing acetone content in water-acetone mixed solvents, or by changing solution pH in aqueous solution. The blackberry size increases with decreasing pH (lower charge density) or higher acetone content in the mixed solvent (lower dielectric constant) and the blackberry size can change in responding to the change of external conditions. This indicates that the {P 4Y 8W 43} macroanions possess the properties of both "strong electrolyte type" and "weak electrolyte type" macroions, as we outlined previously. This is due to the special chemical feature of such clusters, which can be treated as Na 2HPO 4-type electrolytes in solution. The kinetics of the blackberry formation can be controlled by temperature.     

The structure of the H3O+ hydronium ion in benzene

Infrared, X-ray structural, 1H NMR, and computational evidence for pi-solvation of H3O+ by benzene molecules is presented. A salt with a discrete [H3O.3benzene]+ cation can be isolated using a very weakly interacting carborane counterion, CHB11Cl11-. pi-Arene solvation of H3O+ explains the solubility of this salt in benzene solution. Similar results are indicated for the "Zundel-type" H5O2+ ion. These findings suggest structures for the active protonating species when strong acids are used as catalysts in arene solvents containing trace water. They are also relevant to structures that may be present in biological proton transport.     

Cobaltacarborane-phthalocyanine conjugates: Syntheses and photophysical properties

Syntheses of two new cobaltacarborane-phthalocyanine conjugates, one anionic (Pc 6) and one zwitterionic (Pc 7), were accomplished via cyclotetramerization of the corresponding cobaltacarborane-substituted phthalonitriles (4 or 5) with excess phthalonitrile in quinoline. X-ray structures of two phthalonitrile precursors (2 and 3) were obtained and are discussed, and the absorption and emission properties of the two cobaltacarborane-phthalocyanine conjugates in several solvents were investigated. The anionic conjugate 6 exists mainly as a monomer in polar organic solvents and has fluorescence quantum yields in the region 0.2-0.3. The zwitterionic conjugate 7 aggregates in solution and displays lower quantum yields ∼0.1 in organic solvents.