Heterogeneous bilayer molecular structure at a liquid-solid interface

Hexaphenylbenzene (HPB) derivatives, HPB-6a and HPB-6pa, can form a supramolecular network which is stabilized by the intermolecular hydrogen bonding between carboxyl group at an octanoic acid/graphite interface. The observation of the heterogeneous bilayer structure formed exclusively by coronene and HPB-6pa at the octanoic acid/graphite interface is reported. Pronounced selectivity of coronene for the supramolecular networks with different sizes is reflected through the formation of bilayer structure for HPB-6pa network with the introduction of coronene as the guest species, indicating stronger interactions between HPB-6pa and coronene.     

Conformationally pre-organized and pH-responsive flat dendrons: synthesis and self-assembly at the liquid-solid interface

Efficient Cu-catalyzed 1,3-dipolar cycloaddition reactions have been used to prepare two series of three regioisomers of G-1 and G-2 poly(triazole-pyridine) dendrons. The G-1 and G-2 dendrons consist of branched yet conformationally pre-organized 2,6-bis(phenyl/pyridyl-1,2,3-triazol-4-yl)pyridine (BPTP) monomeric and trimeric cores, respectively, carrying one focal and either two or four peripheral alkyl side chains. In the solid state, the conformation and supramolecular organization were studied by means of a single crystal X-ray structure analysis of one derivative. At the liquid-solid interface, the self-assembly behavior was investigated by scanning tunneling microscopy (STM) on graphite surfaces. Based on the observed supramolecular organization, it appears that the subtle balance between conformational preferences inherent in the dendritic backbone on the one side and the adsorption and packing of the alkyl side chains on the graphite substrate on the other side dictate the overall structure formation in 2D.     

Albumin-fatty acid interactions at monolayer interface

The fluid mosaic model of Singer and Nicolson in 1972 shows how proteins are embedded in membranes. To elucidate the interactions between proteins and the surrounding lipids, stearic acid (SA) and bovine serum albumin (BSA) were used as lipid-protein components to mimic the normal membrane bilayer environment using the Langmuir-Blodgett technique. Surface pressure (π)-molecular area (A) isotherms were recorded for the SA monolayer in the presence of BSA on water. The mixed monolayer was successfully transferred onto an oxidized silicon wafer and imaged by tapping mode atomic force microscopy (AFM). Miscibility, compressibility and thermodynamic stability of the mixed system were examined. A large negative deviation of A_ex, together with the minimum value of ΔG_ex, was observed when the mole fraction of BSA (X_BSA) was 0.8, indicating this to be the most stable mixture. In a compressibility analysis, X_BSA was observed at below 50 mN m^-1, denoting a liquid-expanded phase and showing the occurrence of a strong interaction of SA with BSA molecules in this phase. AFM observations supported the quantitative data indicating that BSA was strongly attracted onto the membrane surface as predicted.     

Physical interactions at carbon nanotube-polymer interface

Mechanical properties of carbon nanotube (CNT) reinforced polystyrene rod and CNT reinforced epoxy thin film were studied and the CNT-polymer interface in these composites was examined. Transmission and scanning electron microscopy examinations of CNT/polystyrene (PS) and CNT/epoxy composite showed that these polymers adhered well to CNT at the nanometer scale. Molecular mechanics simulations and elasticity calculations were used to quantify some of the important interfacial characteristics that critically control the performance of a composite material. In the absence of chemical bonding between CNT and the matrix, it is found that the non-bond interactions, consist of electrostatic and van der Waals forces, result in CNT-polymer interfacial shear stress (at 0 K) of about 138 and 186 MPa, respectively, for CNT/epoxy and CNT/PS. The high interfacial shear stress calculated, about an order of magnitude higher than micro fiber reinforced composites, is believed attributed to intimate contact between the two solid phases at the molecular scale. Simulations and calculations also showed that local non-uniformity of CNT and mismatch of the coefficients of thermal expansions between CNT and polymer matrix also promote the stress transfer ability between the two.     

The volume expansion factor for liquid-solid transition at the triple point

The volume expansion factor associated with the liquid-solid transition at the triple point, ε = v_{ι t} /v_{s t},is a fluid characterizing parameter that finds utility in the prediction of the transport properties of substances in their dense gaseous and saturated and compressed liquid states. Values of this factor were independently established from the generalized treatment of self-diffusivity, viscosity and thermal conductivity involving information relating to these transport properties for monatomic, diatomic, and polyatomic substances and hydrocarbons of all types of molecular complexity. These values, derived from each of these transport properties, were found to be consistent and in agreement with each other and corresponding experimental measurements. This factor has been applied to the development of a relationship capable for its generalized prediction using information relating to Z_ono the critical compressibility factor and T_RT the reduced temperature at the triple point. Values of e obtained from limited experimental measurements were compared with values predicted by this method and were found to be in close agreement with corresponding values resulting from experimental measurements. Therefore, this development can be made to apply in a generalized manner to all types of substances.     

DNA-like interactions enhance the miscibility of supramolecular polymer blends

We have investigated the miscibility behavior, specific interactions, and supramolecular structures of blends of the DNA-like copolymers poly(vinylbenzylthymine-co-butyl methacrylate) (T-PBMA) and poly(vinylbenzyladenine-co-styrene) (A-PS) with respect to their vinylbenzylthymine (VBT) and vinylbenzyladenine (VBA) contents. ¹H nuclear magnetic resonance spectroscopy and one- and two-dimensional Fourier transform infrared spectroscopy revealed that hydrogen bonding occurred exclusively between the VBA and VBT units. In addition, size exclusion chromatography, dynamic light scattering, and viscosity analyses provided evidence for the formation of supramolecular network structures in these binary blend systems. A miscibility window existed in the A-PS/T-PBMA blend system when the VBT and VBA fractions in the copolymers were greater than 11 mol%, as predicted using the Painter-Coleman association model.     

Janus particle amphiphilicity and capillary interactions at a fluid interface

Studying the behavior of anisotropic particles at fluid interfaces is a rapidly expanding field, as understanding how the introduced anisotropy affects the resulting properties is essential in the engineering of interfacial systems. Surface anisotropic particles, also known as Janus particles (JPs), offer new possibilities for novel applications due to their amphiphilicity and stronger binding to fluid interfaces compared to homogeneous particles. Introducing surface anisotropy creates complexity as the orientation of interfacially bound particles affects interparticle interactions, a contributing factor to the microstructure formation. In this work, we have investigated the microstructure of JP monolayers formed at the air–water interface using particles with different degrees of amphiphilicity and examined the response of the networks to applied compressions. Our findings demonstrate that JPs amphiphilicity is a crucial factor governing their orientation at the interface, which in turn dictates the complexity of the capillary interactions present and the mechanical properties of the ensuing networks.     

A critical review on the cellular and molecular interactions at the interface of zirconia-based biomaterials

In the past few years, zirconia has gained a great attention among biomedical scientists due to its extraordinary strength and fracture toughness, negligible thermal conductivity, good biocompatibility and chemical inertness. In this regard, there is still room for the manipulation of zirconia-based biomaterials regarding the protein adsorption and subsequently cell responses to the surface. Protein adsorption on biomaterials surfaces start interpreting the construction and also arranging the surface characteristics into a biological language. In this review, the role of adsorbed proteins as key players in starting interactions between cells and zirconia-based biomaterials will be discussed in detail. The discussion will then highlight discussions on the implementation of innovative strategies to engineer the physiochemical properties of this class of biomaterials. It is expected that these promising solutions can better control proteins adsorption and cellular functions after implantation in the body.     

Polymeric supramolecular assemblies based on multivalent ionic interactions for biomedical applications

Oppositely charged polyelectrolytes can be used to form various types of self-assembled structures directed by multivalent ionic interactions. The supramolecular architectures that result are often referred to as polyion complexes (PICs). Synthetic polyion complexes are exciting candidates for biomedical applications. Their self-assembly capabilities give rise to hierarchical mesoscopic platforms such as micelles, membranes, and capsules through simple mixing processes. These complexes are also ideal candidates for the transport and delivery of biological agents since biomolecules, such as DNA and proteins can be easily incorporated through ionic interactions. PICs have therefore found use in drug delivery, diagnostics, gene therapy, biosensors and microreactors. In this paper, we briefly review examples of polymeric supramolecular assemblies based on multivalent ionic interactions for biomedical applications.     

Adsorption isotherms for thiourea at the mercury-solution interface

Double layer parameters for the adsorption of thiourea on mercury were obtained at constant charge and at constant potential on the electrode. In both cases the adsorption isotherm was found to be congruent on the electrical variable. The virial adsorption isotherm is quite adequate to describe the adsorption of thiourea but a different virial coefficient is needed in each case. The study of this simultaneous congruence led to the conclusion that when the adsorption of neutral molecules is considered in terms of the two electrical variables a much more convenient picture of the behaviour of the interface is obtained.     

Reactions at the polyimide-metal interface

Ultra-high-vacuum spectroscopic techniques are utilized to investigate the mechanism of the interfacial reactions of copper and titanium with polyimides. Ultra-violet photoemission spectroscopy of in situ deposited Cu on polyimides suggests that covalent interaction between the metal and the polymer is absent. Model studies confirm this finding. Alternatively, deposition of Ti onto polyimides shows the presence of strong covalent interaction between the imide moiety of the polymer backbone and the metal. Solution model studies support a mechanism for the Ti-polyimide reaction involving initial TiO bond formation followed by TiC bonding at higher coverages of material.     

A polythreaded three-dimensional architecture of undulated layers originated by the contribution of different supramolecular interactions

The structure of compound [Cd₂(NDC)₂(L)₂(H₂O)]·0.5DMF (1) (NDC = 1,4-naphthalenedicarboxylate, L = pyrazino[2,3-f][1,10]phenanthroline and DMF = N,N′-dimethylformamide) is reported. Two independent Cd(II) atoms in a distorted [CdO₄N₂] octahedral environment and three unique NDC ligands showing different coordination modes give strongly undulated two-dimensional grid motifs. Dangling L ligands are chelated to every Cd(II) atom decorating both sides of the layers. Due to the marked undulation of the layers, the large open windows are threaded by the dangling ligands of other layers producing a three-dimensional polythreaded supramolecular array that can be also described as a single three-dimensional framework if the extended columnar face-to-face π–π interactions are considered.     

Miscibility enhancement of supramolecular polymer blends through complementary multiple hydrogen bonding interactions

We have investigated the miscibility behavior and specific interactions of supramolecular poly[vinylbenzylthymine‐co‐(butyl methacrylate)] (T‐PBMA) and poly[(2‐vinyl‐4,6‐diamino‐1,3,5‐triazine)‐co‐styrene] (VDAT‐PS) blends with respect to their vinylbenzylthymine (VBT) and 2‐vinyl‐4,6‐diamino‐1,3,5‐triazine (VDAT) contents. Fourier transform infrared spectroscopy revealed that multiple hydrogen bonding interactions occurred exclusively between the VDAT and VBT units, which were stronger than adenine and thymine interactions. A miscibility window occurred in the VDAT‐PS/T‐PBMA blend system when the VBT and VDAT fractions in the copolymers were greater than 7 mol%, as predicted using the Painter–Coleman association model. Copyright © 2010 Society of Chemical Industry     

基于膜表面与界面作用的膜污染控制方法

膜污染控制是膜技术能否成功应用的关键因素之一。讨论了膜面粗糙度、亲水性和荷电性等性质对膜分离性能的影响,介绍了膜表面性质参数的表征方法,分析了颗粒污染物团聚、颗粒与胶体吸附、胶体大分子的变形等对膜污染形成的影响。最后对面向应用过程的陶瓷膜材料表面与界面控制方法进行了总结。膜污染的研究已从操作参数调节发展到表面与界面作用的控制,对提高膜分离性能,促进膜过程在更多领域的推广应用有重要意义。     

One-dimensional supramolecular assembly of an Mn12 single molecule magnet by ligand interactions

A new Mn₁₂ complex was synthesized using ligand substitution reaction of Mn₁₂–OAc with 4-(thiophen-3-yl)benzoic acid and complex’s structural and magnetic properties were analysed. [Mn₁₂O₁₂(O₂CC₆H₄C₄H₃S)₁₆(H₂O)₃]·14CH₂Cl₂ (1) crystallized in the P2₁/c space group. Intermolecular π–π interactions between phenyl and thiophene rings of two adjacent Mn₁₂ molecules result in one-dimensional supramolecular assembly of 1 in the crystal. On the other hand, steric repulsion between the neighbouring molecules causes unusual ligand arrangement and coordination geometry of Mn(III) ion with five coordination. The ac magnetic study of 1 gives U_eff = 69.98 K and 1/τ₀ = 1.456 × 10⁸ s^?1 and dc reduced magnetization measurement gives S = 10, g = 1.95 and D = ?0.425 cm^?1 showing that outer ligand distortion has little effect on the magnetic properties.     

Selectivity of heavy metal ions at acidic supramolecular surfaces

Langmuir monolayers containing surface carboxylic acid head groups were examined in order to characterize their selectivity to metal ion adsorption. Experimental data of ion adsorption obtained by surface isotherms and FTIR spectroscopy were analyzed using a thermodynamic-and-electrochemical model. Among bivalent ions examined (Cr²⁺, Pb²⁺, Cu²⁺, Cd²⁺, Zn²⁺, Ca²⁺, Ni²⁺, and Ba²⁺), Langmuir monolayers showed the highest selectivity to chromium ions. In addition, it was found that adsorption constants of the surface ions are quite different from binding constants of the bulk ions. The results show important implications to sensing and separating metal ions by the use of acidic supramolecular materials.     

Mechanical tuning of molecular machines for nucleotide recognition at the air-water interface

Molecular machines embedded in a Langmuir monolayer at the air-water interface can be operated by application of lateral pressure. As part of the challenge associated with versatile sensing of biologically important substances, we here demonstrate discrimination of nucleotides by applying a cholesterol-armed-triazacyclononane host molecule. This molecular machine can discriminate ribonucleotides based on a twofold to tenfold difference in binding constants under optimized conditions including accompanying ions in the subphase and lateral surface pressures of its Langmuir monolayer. The concept of mechanical tuning of the host structure for optimization of molecular recognition should become a novel methodology in bio-related nanotechnology as an alternative to traditional strategies based on increasingly complex and inconvenient molecular design strategies.