Formation mechanism of supramolecular hydrogels in the presence of L-phenylalanine derivative as a hydrogelator

A novel chiral hydrogelator, L-phenylalanine derivative can self-assemble in aqueous media at different pH values to form supramolecular hydrogels. The images of the FE-SEM indicate that different aggregates of TC(18)PheBu in morphology were formed, which further lead to the formation of spherical crystallites as observed by polarized optical microscope (POM). The FT-IR spectra of the supramolecular hydrogels reveal that intermolecular hydrogen-bonding and hydrophobic interactions are the driving forces for the self-assembly of TC(18)PheBu. Fluorescence spectra of TC(18)PheBu in aqueous solutions in the presence of pyrene as a probe further confirm the importance of hydrophobic interactions for the self-assembly. The circular dichroism (CD) spectra of TC(18)PheBu in supramolecular hydrogels in the presence of KF indicate that the hydrogen-bonding interaction can be disrupted by fluoride ions, which further confirm the importance of hydrogen bonding for the self-assembly of TC(18)PheBu.     

Supramolecular Hydrogels Based on L‐Phenylalanine Derivatives with a Positively Charged Terminal Group

A new hydrogelator based on L ‐phenylalanine with a long hydrophobic chain and positively charged terminus was synthesized, and its gelation behavior in H₂O was investigated. Polarized optical microscopy (POM), field emission scanning electron microscopy (FE‐SEM), and X‐ray diffraction (XRD) results indicate that the hydrogelator self‐assembles into fibres‐like aggregates which then lead to the formation of a hydrogel. ¹H‐NMR and CD spectra of hydrogels and aqueous solution revealed that intermolecular H‐bonding between the amide groups was the driving force for gelation. A luminescence study, in which ANS (8‐anilinonaphthalene‐1‐sulfonic acid) was used as a probe, indicated that the hydrophobic interactions between long chains were the driving force for gelation. Consequently, it was proved that the hydrogelator self‐assembles into fibre‐like aggregates and then forms supramolecular hydrogels through the H‐bonding and hydrophobic interactions.     

多金属氧酸盐杂化催化剂光催化降解有机杀虫剂六氯苯

 通过自组装技术制备了一系列多金属氧酸盐-有机胺-分子筛杂化催化剂K5［M(H2O)PW11O39］-(EtO)3Si(CH2)3NH2-MCM-48,用XRD,ICP-AES,UV/DRS,FT-IR,31P MAS NMR和N2吸附等手段对其组成和结构进行了表征,并以有机杀虫剂六氯苯为探针分子考察了其光催化活性. 结果表明,多金属氧酸盐杂化催化剂的光催化降解活性高于直接光解,能有效地降解污水中的六氯苯,且易分离,可循环使用.     

Supramolecular hydrogels based on the epitope of potassium ion channels

Imparting aromatic-aromatic interactions to the potassium binding epitope affords a supramolecular hydrogelator that responds to the K(+) concentration by self-assembly into nanofibers of different widths and crosslinking patterns, which illustrates a simple approach to generate biomimic materials based on tunable, hierarchical self-assembly of small molecules.     

Light-Responsive Arylazopyrazole Gelators: From Organic to Aqueous Media and from Supramolecular to Dynamic Covalent Chemistry

Versatile photoresponsive gels based on tripodal low molecular weight gelators (LMWGs) are reported. A cyclohexane-1,3,5-tricarboxamide (CTA) core provides face-to-face hydrogen bonding and a planar conformation, inducing the self-assembly of supramolecular polymers. The CTA core was substituted with three arylazopyrazole (AAP) arms. AAP is a molecular photoswitch that isomerizes reversibly under alternating UV and green light irradiation. The E isomer of AAP is planar, favoring the self-assembly, whereas the Z isomer has a twisted structure, leading to a disassembly of the supramolecular polymers. By using tailor-made molecular design of the tripodal gelator, light-responsive organogels and hydrogels were obtained. Additionally, in the case of the hydrogels, AAP was coupled to the core through hydrazones, so that the hydrogelator and, hence, the photoresponsive hydrogel could also be assembled and disassembled by using dynamic covalent chemistry.     

Highly stable surface modifications of poly(3-caprolactone) (PCL) films by molecular self-assembly to promote cells adhesion and proliferation

In this paper, we report a simple and versatile surface coating method to functionalize poly(3-caprolactone) (PCL) films by molecular self-assembly of a hydrogelator.     

Chiral self-dimerization of vanadium complexes on a SiO2 surface for asymmetric catalytic coupling of 2-naphthol: structure, performance, and mechanism

Vanadium monomers with chiral tridentate Schiff-base ligands were supported on SiO(2) through a chemical reaction with surface silanols, where we found a new chirality creation by the self-dimerization of the vanadyl complexes on the surface. The chiral self-dimerization and the role of surface silanols in the self-assembly were investigated by means of X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), diffuse-reflectance ultraviolet/visible (DR-UV/VIS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), electron spin resonance (ESR), and density functional theory (DFT) calculations. The surface vanadyl complexes had a distorted square-pyramidal conformation with a V=O bond. FT-IR spectra revealed that the Ph-O moiety of Schiff-base ligands was converted to Ph-OH by a surface-concerted reaction between the vanadium precursors and surface SiOH groups. The Ph-OH in an attached vanadyl complex interacted with a COO moiety of another vanadyl complex by hydrogen bonding to form a self-dimerized structure at the surface. The interatomic distance of V-V in the surface self-assembly was evaluated to be 0.40 +/- 0.05 nm by ESR after O(2) adsorption. The self-dimerized V structure on SiO(2) was modeled by DFT calculations, which demonstrated that two vanadium monomers with Ph-OH linked together by two hydrogen bonds and their V=O groups were directed opposite to each other. The surface self-dimerization of the vanadium precursors fixes the direction of the V=O bond and the plane of the Schiff-base ligand. Thus, a new chiral reaction field was created by two types of chirality: the chiral Schiff-base ligand and the chiral V center. We have also found that the chiral self-dimerized vanadyl complexes exhibit remarkable catalytic performance for the asymmetric oxidative coupling of 2-naphthol: 96% conversion, 100% selectivity to 1,1'-binaphthol (BINOL), and 90% enantiomeric excess (ee). Increasing the vanadium loading on SiO(2) caused a dramatic swell of enantioselectivity, and the maximum 90% ee was observed on the supported catalyst with the full coverage of the vanadyl complex (3.4 wt % vanadium). This value is equivalent to the maximum ee reported in homogeneous catalysis for the coupling reaction. Furthermore, the supported vanadium dimers were reusable without loss of the catalytic performance. To our knowledge, this is the first heterogeneous catalyst for the asymmetric oxidative coupling of 2-naphthol.     

Absorption of 10-hydroxycamptothecin on Fe3O4 magnetite nanoparticles with layer-by-layer self-assembly and drug release response

In this paper, the structural and zeta potential properties of 10-hydroxycamptothecin (HCPT) were investigated by FT-IR and zeta potential analyzer under different pH. The anticancer drug HCPT as a model drug was used to prepare a high-performance and relatively easy-to-fabricate system on Fe(3)O(4) magnetite nanoparticles by using a polystyrene sulfonate (PSS) and HCPT interlayer self-assembly method. The results obtained from FT-IR and XRD confirmed that HCPT was molecularly dispersed into the nanoparticles. The method holds not only environment-friendly characteristics and the ability to mimic the self-organization process in biological systems but also greatly decreases adjuvant polymers. In addition, the system has an ideal drug payload for the delivery of insoluble HCPTs.     

A family of low-molecular-weight hydrogelators based on L-lysine derivatives with a positively charged terminal group

A family of L-lysine-based low-molecular-weight compounds with various positively charged terminals (pyridinium and imidazolium derivatives) was synthesized and its gelation behavior in water was investigated. Most of the compounds can be very easily synthesized in high yields (total yields >90 %), and they function as excellent hydrogelators that form hydrogels below 1 wt %; particularly, N(epsilon)-lauroyl-N(alpha)-[11-(4-tert-butylpyridinium)undecanoyl]-L-lysine ethyl ester (2 c) and N(epsilon)-lauroyl-N(alpha)-[11-(4-phenylpyridinium)undecanoyl]-L-lysine ethyl ester (2 d), which are able to gel water at concentration of only 0.2 wt %. This corresponds to a gelator molecule that entraps more than 20 000 water molecules. All hydrogels are very stable and maintain the gel state for at least 9 months. TEM observations demonstrated that these hydrogelators self-assemble into a nanoscaled fibrous structure; a three-dimensional network is then formed by the entanglement of the nanofibers. An FTIR study in [D(6)]DMSO/D(2)O and in CHCl(3) revealed the existence of intermolecular hydrogen bonding between the amide groups. This was further supported by a (1)H NMR study in [D(6)]DMSO/H(2)O. A luminescence study, in which ANS (1-anilino-8-naphtharenesulfonic acid) was used as a probe, indicated that the hydrogelators self-assemble into nanostructures possessing hydrophobic pockets at a very low concentration. Consequently, it was found that the driving forces for self-assembly into a nanofiber are hydrogel bonding and hydrophobic interactions.     

Directing Foldamer Self-Assembly with a Cyclopropanoyl Cap

The rational design of self-assembling organic materials is extremely challenging due to the difficulty in precisely predicting solid-state architectures from first principles, especially if synthons are conformationally flexible. A tractable model system to study self-assembly was constructed by appending cyclopropanoyl caps to the N termini of helical α/β-peptide foldamers, designed to form both N−H⋅⋅⋅O and C^α−H⋅⋅⋅O hydrogen bonds, which then rapidly self-assembled to form foldectures (foldamer architectures). Through a combined analytical and computational investigation, cyclopropanoyl capping was observed to markedly enhance self-assembly in recalcitrant substrates and direct the formation of a single intermolecular N−H⋅⋅⋅O/C^α−H⋅⋅⋅O bonding motif in single crystals, regardless of peptide sequence or foldamer conformation. In contrast to previous studies, foldamer constituents of single crystals and foldectures assumed different secondary structures and different molecular packing modes, despite a conserved N−H⋅⋅⋅O/C^α−H⋅⋅⋅O bonding motif. DFT calculations validated the experimental results by showing that the N−H⋅⋅⋅O/C^α−H⋅⋅⋅O interaction created by the cap was sufficiently attractive to influence self-assembly. This versatile strategy to harness secondary noncovalent interactions in the rational design of self-assembling organic materials will allow for the exploration of new substrates and speed up the development of novel applications within this increasingly important class of materials.     

溶剂对镍（域）金属有机骨架结构的影响

通过乙酸镍和4-咪唑-1-基-苯甲酸( HL)在不同溶剂热条件下合成了3个新型金属有机骨架化合物[Ni(L)2]n·DMF(1), Ni(H2 O)2(L)2(2)和 Ni(L)2(CH3 OH)2(3)。化合物1是用 N,N-二甲基甲酰胺(DMF)作为溶剂合成的具有菱形孔道的三维骨架化合物;化合物2是在DMF/H2O(体积比4︰1)中合成的水作为终端配体参与配位的二维层状化合物,并通过层与层之间的氢键作用构筑形成了三维超分子结构;当溶剂为甲醇时,得到了二维层状化合物3,且甲醇作为终端配体参与配位。磁学和电化学性质研究结果表明,化合物1~3中相邻镍离子之间存在反铁磁相互作用;在一定的电势范围内出现一对明显的Ni (Ⅱ)/Ni(Ⅲ)氧化还原峰,表明化合物1~3是潜在的磁性材料或电催化剂材料。     

Design and preparation of a novel fluorescent naphthalimide derivative supramolecular self-assembly system and its bioimaging application

ABSTRACT

A novel fluorescent naphthalimide derivative gelator (N-18) was designed and characterised which could form a stable gel in 1,4-dioxane/H₂O (2/1, v/v), methyl sulfoxide (DMSO), ethanol/H₂O (4/1, v/v), acetone/H₂O (2/1, v/v) and methanol. The self-assembly process of molecule N-18 in the five solvents was carefully investigated by the field emission scanning electron microscope, UV-vis absorption spectra, fluorescence emission spectra, fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and water contact angle experiments. Different structures from microbelts to helical nanofibers were formed in the self-assembly process. Hydrogen bonding and π–π stacking interaction were the mainly driving forces for the formation of gel. At the same time, the hydrophobic surface with the contact angles of 133°–142° was observed on the xerogel films N-18 from the above five solvents. Interestingly, molecule N-18 could be applied in bioimaging in a living cell.     

Diffusion and structure of water in polymers containing N-vinyl-2-pyrrolidone

Poly(N-vinyl-2-pyrrolidone) (PVP), a water-soluble polymer, is known for its excellent biocompatibility. It is generally recognized that the properties of polymers may be profoundly affected by the structure of water absorbed in them. In this study, Fourier transform infrared (FT-IR) in attenuated total reflection (ATR) and transmission mode was performed to examine the diffusion and structure of water in PVP and its copolymers. The obtained spectra were analyzed using two-dimensional (2D) IR with the aid of density functional theory (DFT) calculations. The 2D IR of time-resolved FT-IR/ATR spectra shows that type II water between 3300 and 3500 cm(-1) occurs earlier during the water absorption process, which is also demonstrated by transmission FT-IR at the initial stage of water absorption. Conversely, type II water changes last when desorption takes place. Results from DFT calculations indicate that type II water might be monomeric or dimeric water molecules interacting with a carbonyl group in the pyrrolidone moiety. Furthermore, it is found that vibrations less than 3300 cm(-1) (type I water) arise from water molecules involved in a carbonyl group interacting with more than two water molecules. It is reasonable that the transmission FT-IR spectra of film with an extra low water amount hardly show vibration bands below 3300 cm(-1); however, this region is distinct in the FT-IR/ATR spectra of fully swollen film. In addition, vibration bands between 3800 and 3500 cm(-1) (type III water) are assigned to free water or water with relatively weak hydrogen bonding, as supported by the transmission FT-IR spectra of polyacrylonitrile (PAN) and the calculation results. Therefore, the diffusion process and the structures of water in PVP and its copolymers can be successfully accessed on the basis of the 2D IR analysis and DFT calculations.     

Preparation,characterization and thermal behaviour of polymeric complex of cadmium hexamethylenetetramine nitrate

The preparation of cadmium nitrate complex with bridged hexamethylenetetramine-[{Cd(HMTA)(NO₃)₂(H₂O)₂}_n], CHNC, of polymeric nature has been reported here for the first time. It was characterized by X-ray crystallography, ¹H NMR, FT-IR and elemental analysis. The crystal structure is stabilized by hydrogen bonding between the oxygen atom of the nitrate group with the methyl hydrogen of HMTA and hydrogen of the coordinated water molecule via C–H⋯O and O–H⋯O interactions. The thermolysis of this complex was investigated by TG-DSC and ignition delay measurements. The model-free isoconversional and model-fitting kinetic approaches have been applied to isothermal TG data for kinetics investigation of thermal decomposition of the complex. At higher temperatures, the complex gets ignited to produce highly thermally stable residue most closely resembles CdO proved by XRD.     

Gelation Kinetics-Structure Analysis of pH-triggered Low Molecular Weight Hydrogelators

Properties such as shear modulus, gelation time, structure of supramolecular hydrogels are strongly dependent on self-assembly, gelation triggering mechanism and processes used to form the gel. In our work we extend reported rheology analysis methodologies to pH-triggered supramolecular gels to understand structural insight using a model system based on N−N’ Dibenzoyl-L-Cystine pH-triggered hydrogelator and Glucono-δ-Lactone as the trigger. We observed that Avrami growth model when applied to time-sweep rheological data of gels formed at lower trigger concentrations provide estimates of fractal dimension which agree well compared with visualization of the microstructure as seen via Confocal Laser Scanning Microscopy, for a range of gelator concentrations.     

Ni(II)-mediated self-assembly of artificial beta-dipeptides forming a macrocyclic tetranuclear complex with interior spaces for in-line molecular arrangement

Metal-mediated self-assembly of bioinspired molecular building blocks shows promise as an excellent strategy to provide well-defined metal arrays and nanoscopic metallo-architectures in a programmable way. Herein, we report Ni(II)-mediated self-assembly of artificial beta-dipeptides (1) which were prepared from a newly designed beta-amino acid bearing a propanediamine ligand as the side chain. The beta-dipeptide (1) has thus two sets of ligands, that is, each building block serves as a tridentate ligand with a bidentate propanediamine unit and an amide carbonyl group. Both C- and N-terminal tridentate ligands in 1 bind to two Ni(II) ions independently, and consequently, four beta-dipeptides are circularly arranged in a head-to-tail fashion to form a macrocyclic tetranuclear Ni(II) complex, Ni414(ClO4)8(H2O)10. The cyclic structure was determined by X-ray analysis and ESI-TOF mass spectrometry. The resulting unique twisted-boat structure allows the formation of isolated spaces for in-line hydrogen-bonded arrangement of water and anion molecules within a hole and two grooves rich in hydrogen bonding groups.     

Self-assembled small molecular weight hydrogels of prodrugs

Prodrugs as building unit for construction of various hydrogelator in response to different stimulus (e.g., temperature, enzyme, pH value, ion).     

Different properties of H2O- and D2O-containing phospholipid-based reverse micelles near a critical temperature

Dipalmitoylphosphatidylcholine (DPPC)/water/pyridine reverse micelles have been found to transform from a clear liquid into a glass when the DPPC-to-water volume fraction is in the 0.78-0.89 range at 28 or 26 degrees C depending on whether water is H2O or D2O. Their study by SANS, FT-IR, and 1H NMR for this composition has shown remarkable effects of the isotopic nature of water on their structural and dynamic properties. By SANS, between 38 and 43.5 degrees C, micelles appear as either flexible polymer-like cylinders or short rods depending on whether water is H2O or D2O. On the basis of this dual aspect, micelles have been visualized as branched cylinders whose quasi-spherical branching points would be prone to assemble into short rods. In addition, when water contains more than 40% of D2O, a Bragg reflection emerges at 0.12 A(-1) on SANS spectra, evidencing an organization of micelles. In addition, FT-IR spectra show that DPPC phosphate groups are D bonded only when water is D2O. Consequently, we assumed that forces prone to organize the D2O-containing micelles are D-bonded water bridges between neighboring micelles at the level of their branching points. In fact, ab initio calculations have shown that water dimers are more stable when the bridging atom is D rather than H. These water bridges could be formed due to the fact that branching points, able to slide along micelles, keep close for a longer time when water is D2O than when it is H2O. Indeed, it has been shown experimentally that the lateral diffusion of phospholipid molecules in any layer is slower in the first case. Formation of such bridges triggers a deuteron migration between micelles evidenced by the 1/T1 relaxation rate of deuterons of water in D2O-containing micelles measured at 43 degrees C by 1H NMR.     

l-Lysine-based supramolecular hydrogels containing various inorganic ions

The preparation of supramolecular hydrogels containing various inorganic acids and salts using L-lysine-based hydrogelators is conducted and their thermal stabilities, gel strengths, FT-IR spectra, and electron micrographs are measured. These hydrogelators can form supramolecular hydrogels over a wide pH range and contain inorganic acids and salts. The supramolecular hydrogels based on ester-type hydrogelators have good thermal stabilities (high Tgel), while the hydrogelator with a carboxyl group forms a thermally sensitive gel with high mechanical strength. Furthermore, the gelation mechanism is discussed using FT-IR spectroscopy and TEM observations.     

Comparative Study on the Structure of Water in Reverse Micelles Stabilized with Sodium Bis(2-ethylhexyl) Sulfosuccinate or Sodium Bis(2-ethylhexyl) Phosphate in n-Heptane

The microstructure of water solubilized in H(2)O/surfactant/n-heptane ternary systems has been investigated by employing (1)H-NMR and FT-IR spectroscopic techniques. Two reverse micellar systems were prepared and studied, i.e., sodium bis(2-ethylhexyl) sulfosuccinate in n-heptane (H(2)O/AOT/n-heptane) and sodium bis(2-ethylhexyl) phosphate in n-heptane (H(2)O/NaDEHP/n-heptane). (1)H-NMR data showed that the chemical shift of water protons for the AOT and NaDEHP reverse micelles varied downfield and upfield, respectively, with an increase of the water content. The opposite shift directions with increasing water content are interpreted as due to a composition change of the solubilized water associated with head-groups and sodium counterions in reverse micellar systems. On the basis of deconvolution results of FT-IR spectra, a four-component model is proposed to interpret the FT-IR and (1)H-NMR results. Copyright 2000 Academic Press.