Supramolecular hydrogel formed by glucoheptonamide of l-lysine: simple preparation and excellent hydrogelation ability

We describe the simple preparation of new l-lysine derivatives with a gluconic or glucoheptonic group, their hydrogelation properties, and the thermal and mechanical properties of the supramolecular hydrogels. The l-lysine derivatives with a gluconic group have no hydrogelation ability, while the l-lysine-glucoheptonamide derivatives functioned as hydrogelators. Their hydrogelation abilities increased with the decreasing length of the spacer between the l-lysine segment and the glucoheptonic group. The compound, which has no spacer, formed a supramolecular hydrogel at 0.05 wt % in pure water. The thermal stability and high mechanical strength of the supramolecular hydrogels based on this compound significantly depended on the aqueous solutions. Electron microscopy and FTIR studies demonstrated that the hydrogelators created a three-dimensional network through hydrogen bonding and hydrophobic interactions in the supramolecular hydrogel. In addition, it was found that hydrophobic interactions played an important role in the thermal stability of the supramolecular hydrogel.     

Supramolecular gels formed by amphiphilic low-molecular-weight gelators of N alpha,N epsilon-diacyl-L-lysine derivatives

Simple L-lysine derivatives, N(alpha)-hexanoyl-N(epsilon)-lauroyl-L-lysine (1), its alkali metal salts (2-4), and two-component compounds that consist of 1 with 2 to 4, were synthesized and their hydrogelation and organogelation properties were studied. Addition of hydrochloric acid to an aqueous solution of the alkali metal salt at room temperature produced a translucent hydrogel. This hydrogelation occurred as a result of a change in nanostructure from micelle-like aggregates to nanofibers, which was induced by partial protonation of the carboxylate to form a carboxylic acid. On the other hand, two-component low-molecular-weight gelators exhibited amphiphilic gelation behavior and functioned as not only hydrogelators, but also as organogelators. FTIR studies revealed that lateral ionic interactions between the carboxylate, alkali metal cation, carboxylic acid, and protons, in addition to hydrogen-bonding and van der Waals interactions play a very important role in hydrogelation. Furthermore, it was found that the water-insoluble carboxylic acid compound underwent a precipitation-dissolution transition with a thermally reversible sol-gel transition in the two-component gelator systems.     

Synthesis of Temperature-Sensitive Poly(N-isopropylacrylamide) Hydrogel with Improved Surface Property

A new PNIPA hydrogel was synthesized by carrying out the polymerization in the gelated corn starch aqueous solution. This PNIPA hydrogel has an improved surface property and does not form the disadvantageous bubbles during the shrinking process. This change is due to the hydrogen bonds between the corn starch and the hydrophilic side groups of the PNIPA chains, which let the starch act as the long graft-like chains of the PNIPA hydrogel. During the reswelling process, this PNIPA hydrogel exhibits a sigmoidal swelling pattern. This hydrogel with improved surface property may be very useful for the potential applications of the temperature-sensitive hydrogel. Copyright 2000 Academic Press.     

扫描电化学显微镜在水凝胶微孔阵列表征中的新应用

水凝胶微孔阵列是细胞培养的新型基板软材料,其微孔形貌对细胞的行为产生直接的影响.但传统水凝胶微孔阵列形貌的表征手段缺乏在水溶液中原位和可逆表征的能力.本文以水溶液中的氧气为还原电对,应用扫描电化学显微镜(SECM)对水溶液中的聚乙二醇二甲基丙烯酸酯水凝胶微孔阵列的形貌进行了原位表征,得到了水凝胶微孔阵列表面的二维孔径和三维形貌信息,开发出采用SECM对水凝胶微孔阵列形貌进行原位、可逆、无损表征及提供三维形貌信息的新方法.     

Structure and properties of an exceptional low molecular weight hydrogelator

Research for low molecular weight (LMW) hydrogelators has become an area of increasing interest due to many possible new applications for such compounds. They might serve as templates for nanostructures or in biomedical applications and even in drug discovery. In this investigation, we explored the structure-gelling relations of a LMW hydrogelator that can form a hydrogel in water at room temperature. To this end, various analytical techniques such as nuclear magnetic resonance, rheology, X-ray scattering, birefringence, and microscopy were applied to gain better insight on the structure of the gel and to provide an explanation for this unique gelation behavior.     

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.     

Fabrication of poly(ethylene glycol) hydrogel microstructures using photolithography

The fabrication of hydrogel microstructures based upon poly(ethylene glycol) diacrylates, dimethacrylates, and tetraacrylates patterned photolithographically on silicon or glass substrates is described. A silicon/silicon dioxide surface was treated with 3-(trichlorosilyl)propyl methacrylate to form a self-assembled monolayer (SAM) with pendant acrylate groups. The SAM presence on the surface was verified using ellipsometry and time-of-flight secondary ion mass spectrometry. A solution containing an acrylated or methacrylated poly(ethylene glycol) derivative and a photoinitiator (2,2-dimethoxy-2-phenylacetophenone) was spin-coated onto the treated substrate, exposed to 365 nm ultraviolet light through a photomask, and developed with either toluene, water, or supercritical CO2. As a result of this process, three-dimensional, cross-linked PEG hydrogel microstructures were immobilized on the surface. Diameters of cylindrical array members were varied from 600 to 7 micrometers by the use of different photomasks, while height varied from 3 to 12 micrometers, depending on the molecular weight of the PEG macromer. In the case of 7 micrometers diameter elements, as many as 400 elements were reproducibly generated in a 1 mm2 square pattern. The resultant hydrogel patterns were hydrated for as long as 3 weeks without delamination from the substrate. In addition, micropatterning of different molecular weights of PEG was demonstrated. Arrays of hydrogel disks containing an immobilized protein conjugated to a pH sensitive fluorophore were also prepared. The pH sensitivity of the gel-immobilized dye was similar to that in an aqueous buffer, and no leaching of the dye-labeled protein from the hydrogel microstructure was observed over a 1 week period. Changes in fluorescence were also observed for immobilized fluorophore labeled acetylcholine esterase upon the addition of acetyl acholine.     

Photopolymerization of poly(ethylene glycol) diacrylate on eosin-functionalized surfaces

We describe a new method that allows photopolymerization of hydrogels to occur on surfaces functionalized with eosin. In this work, glass and silicon surfaces were derivatized with eosin and photopolymerization was carried out using visible light (514 nm). This mild condition may have advantages over methods that use ultraviolet (UV) light (e.g., for encapsulation of cells and proteins, in drug screening, or in biosensing applications). The hydrogel formed on the modified surface is remarkably stable for an extended period of time. The resultant hydrogel was hydrated for more than 18 months without suffering delamination from the substrate surface. This strongly suggests covalent attachment of the hydrogel to the surface. Contact angle titration measurements and X-ray photoelectron spectroscopy analysis of eosin surfaces before and after irradiation in the presence of triethanolamine suggest that the eosin radical is responsible for the covalent attachment of the gel onto the substrate surface. This method allows for 2-D patterning of hydrogels, which is demonstrated here using the microcontact printing technique. However, noncontact photolithography could be used to form similar patterns by directing light through a mask. This method can be easily implemented to form arrays of fluorophores and proteins in situ.     

Pristine Carbon‐Nanotube‐Included Supramolecular Hydrogels with Tunable Viscoelastic Properties

Research investigations involving pristine carbon nanotubes (CNTs) and their applications in diversified fields have been gathering enormous impetus in recent times. One such emerging domain deals with the hybridization of CNTs within hydrogels to form soft nanocomposites with superior properties. However, till now, reports on the inclusion of pristine CNTs within low‐molecular‐weight hydrogels are very scarce due to their intrinsic feature of remaining in the bundled state and strong repulsive behavior to the aqueous milieu. Herein, the synthesis of a series of amino acid/dipeptide‐based amphiphilic hydrogelators having a quaternary ammonium/imidazolium moiety at the polar head and a C16 hydrocarbon chain as the hydrophobic segment is reported. The synthesized amphiphiles exhibited excellent hydrogelation (minimum gelation concentration (MGC) ≈0.7–5 % w/v) as well as single‐walled carbon nanotube (SWNT) dispersion ability in aqueous medium. Interestingly, the dispersed SWNTs were incorporated into the supramolecular hydrogel formed by amphiphiles with an imidazolium moiety at the polar end through complementary cation–π and π–π interactions. More importantly, the newly synthesized hydrogelators were able to accommodate a significantly high amount of pristine SWNTs (2–3.5 % w/v) at their MGCs without affecting the gelating properties. This is the first time that such a huge amount of SWNTs has been successfully incorporated within hydrogels. The efficient inclusion of SWNTs to develop soft nanocomposites was thoroughly investigated by spectroscopic and microscopic methods. Remarkably, the developed nanocomposites showed manifold enhancement (≈85‐fold) in their mechanical strength compared with native hydrogel without SWNTs. The viscoelastic properties of these nanocomposites were readily tuned by varying the amount of incorporated CNTs.     

Surface precipitation of highly porous hydrotalcite-like film on Al from a zinc aqueous solution

A hydrotalcite-like film has been successfully deposited on an Al-bearing glass substrate based on an interface reaction between an Al layer and a zinc aqueous solution. The film selectively grew on the Al surface but not on the glass surface. The film on Al was composed of layered nanosheets of a hydrotalcite-like compound containing Al and Zn. Comparably, deposits on the plastic surface and precipitates in solution were wurzite-type ZnO with various morphologies depending upon the preparation conditions. At low supersaturation degrees, single crystals and superstructures of Zn-Al hydrotalcite were also obtained. This porous hydrotalcite film has a potential application as catalyst supports, environmental materials, or matrixes for hydrotalcite-based nanocomposite films. Using Al as a reaction interface makes it easy to coat porous hydrotalcites on a series of matrix materials varying in shapes and properties, which is important for achieving practical applications. In addition, the method developed should be widely applicable to other systems for the preparation of porous or oriented hydrotalcite-like thin films by an appropriate combination of divalent/trivalent solution-substrate systems.     

UV光引发表面接枝两性离子水凝胶层的制备及抗细菌黏附性能

采用聚合和交联的SiO₂有机/无机杂化溶胶作为基材, 通过与两性离子单体层之间的过渡层, 在紫外光作用下引发杂化溶胶和两性离子单体溶液中的双键反应, 使生成的杂化层在基材和表面的两性离子聚合物之间形成辅助性黏接作用, 从而在基材表面构筑两性离子水凝胶层. 通过傅里叶红外光谱(FTIR)、 原子力显微镜(AFM)和接触角测试等方法对所制备的两性离子水凝胶层和杂化层的表面进行了表征. 以空白玻璃片为对照样品, 以金黄色葡萄球菌和大肠杆菌为试验菌, 研究了用两性离子凝胶层修饰的玻璃表面的抗细菌黏附性能. 结果表明, 在SiO₂杂化过渡层中引入线型-Si-(CH₂)₂-O-链段可有效提高杂化过渡层对基材的附着力, 并改善其柔韧性. 与对照样品相比, 用两性离子凝胶层修饰的玻璃表面具有优异的抗菌黏附性能.     

Surface‐Assisted Self‐Assembly Strategies Leading to Supramolecular Hydrogels

Localized molecular self‐assembly processes leading to the growth of nanostructures exclusively from the surface of a material is one of the great challenges in surface chemistry. In the last decade, several works have been reported on the ability of modified or unmodified surfaces to manage the self‐assembly of low‐molecular‐weight hydrogelators (LMWH) resulting in localized supramolecular hydrogel coatings mainly based on nanofiber architectures. This Minireview highlights all strategies that have emerged recently to initiate and localize LMWH supramolecular hydrogel formation, their related fundamental issues and applications.     

Radiation preparation and swelling behavior of sodium carboxymethyl cellulose hydrogels

Sodium carboxymethyl cellulose (CMC) is a kind of degraded polymer under γ-irradiation. However, in this work, it has been found that CMC crosslinks partially to form hydrogel by radiation technique at more than 20% CMC aqueous solution. The gel fraction increases with the dose. The crosslinking reaction of CMC is promoted in the presence of N₂ or N₂O due to the increase of free radicals on CMC backbone, but gel fraction of CMC hydrogel is not high (<40%). Some important values related to this kind of new CMC hydrogel synthesized under different conditions, such as radiation yield of crosslinking G(x), gelation dose R_g, number average molecular weight of network M_c were calculated according to the Charlesby–Pinner equation. The results indicated that although crosslinked CMC hydrogel could be prepared by radiation method, the rate of radiation degradation of CMC was faster than that of radiation crosslinking due to the character of CMC itself. Swelling dynamics of CMC hydrogel and its swelling behavior at different conditions, such as acidic, basic, inorganic salt as well as temperature were also investigated. Strong acidity, strong basicity, small amount of inorganic salts and lower temperature can reduce swelling ratio.     

Growth and characterization of Fe3+-doped bis(thiourea)zinc(II) chloride crystals

Fe3+-doping at ～10 mol% in aqueous medium during crystal growth by slow evaporation solution method in bis(thiourea)zinc(II) chloride (BTZC) leads to form a new compound C2H8Cl2N4S2Zn0.93Fe0.07 (BTZCF) which crystallizes in orthorhombic structure with centrosymmetric space group Pnma though the parent compound BTZC crystallizes in noncentrosymmetric structure with space group Pn2(1)a. The interesting feature observed in this new crystal is that though it crystallizes in centrosymmetric structure, it exhibits positive SHG result (weak signal), quite likely due to possible surface effects or internal stress. The calculated first-order hyperpolarizability is 1.457×10(-30) esu which is ～5.5 times that of urea. Fe3+-doping enhances the transmittance to a significant extent. Comparison of the thermal analysis results by DSC reveals the incorporation of dopant into the crystalline matrix. The high resolution XRD studies reveal that the crystalline quality is improved considerably when the doping level is reached to ～10 mol%.     

Cyclohexane bis-urea compounds for the gelation of water and aqueous solutions

A new class of efficient hydrogelators has been developed by a simple modification of the peripheral substituents of cyclohexane bis-urea organogelators with hydrophilic hydroxy or amino functionalities. These bis-urea hydrogelators were synthesised in two or three steps using an alternative procedure to the common isocyanate method. Gelation was obtained with organic solvents, water and strongly basic aqueous solutions like 25% ammonia. Hydrogelation was found to depend on a delicate balance between the hydrophobicity of the alkyl chains, hydrophilicity of the terminal substituents and the enantiomeric purity of the compound. The hydrogels consisted of a network of fibers, in which all urea groups are involved in intermolecular hydrogen bonding. Most likely, gelation is driven by hydrophobic interactions of the methylene units, whereas hydrogen bond formation between the urea groups provides the necessary anisotropy of the aggregation and the high thermal stability of the gels.     

A Study on The Interactions Between Coordination Compounds and Supports

In this study the viewpoint is taken that the supported complexes react with active groups on the surface of the support to form new entities which may be called surface complexes.Various interactions between the support and the solute in solution of impregnation have been found,and these interactions may be divided into four calsses: (1) there is no noticeable chemical interaction between the dissolved coordination compound and the support,except the physical adsorption;(2) the metal ion of the complex is anchored on the surface through the surface group as a ligand forming a surface complex,or the support provides the central ion for the formation of a surface polynuciear complex through the bridging ligand of the complex;(3) the surface of the support provides the central ion for ligands dissociated from the complex or for the solvent molecules;(4) the metal hydroxide might be formed,when the acidity of the cation of the support is weaker than that of the metal ion of the complex in a aqueous solutio     

Hydrogelators of cyclotriveratrylene derivatives

Developing cavity-based supramolecular hydrogels is in its infancy because not many such hydrogelators are available. Reported herein is our creation of rigid cavitand cyclotriveratrylene (CTV) based hydrogelators from the molecular backbones of CTVs that were in limited cases shown to form organogels. For doing so deprotonable -COOH or protonable -NH(2) was introduced as terminal group into the rigid and hydrophobic CTV backbones. We thus successfully obtained optically anisotropic supramolecular hydrogels from these new CTVs hydrogelators with excellent thermostability and high tolerance towards strong electrolytes. The obtained CTV-1 and CTV-2 hydrogels are luminescent and exhibit reversible gel-to-sol and sol-to-gel transitions upon pH variations. The success in creating CTV-1 and CTV-2 hydrogelators on the basis of the skeleton of a CTV-organogelator suggests that balancing the hydrophilic and hydrophobic characters of the ionic and hydrophobic moieties well in the gelator molecule is important for designing a promising hydrogelator.     

Photo gel-sol/sol-gel transition and its patterning of a supramolecular hydrogel as stimuli-responsive biomaterials

In a focused library of glycolipid-based hydrogelators bearing fumaric amide as a trans-cis photoswitching module, several new photoresponsive supramolecular hydrogelators were discovered, the gel-sol/sol-gel transition of which was pseudo-reversibly induced by light. Studying the optimal hydrogel by NMR spectroscopy and various microscopy techniques showed that the trans-cis photoisomerization of the double bond of the fumaric amide unit effectively caused assembly or disassembly of the self-assembled supramolecular fibers to yield the macroscopic hydrogel or the corresponding sol, respectively. The entanglement of the supramolecular fibers produced nanomeshes, the void space of which was roughly evaluated to be 250 nm based on confocal laser scanning microscopy observations of the size-dependent Brownian motion of nanobeads embedded in the supramolecular hydrogel. It was clearly shown that such nanomeshes become a physical obstacle that captures submicro- to micrometer-sized substrates such as beads or bacteria. By exploiting the photoresponsive property of the supramolecular nanomeshes, we succeeded in off/on switching of bacterial movement and rotary motion of bead-tethered F(1)-ATPase, a biomolecular motor protein, in the supramolecular hydrogel. Furthermore, by using the photolithographic technique, gel-sol photopatterning was successfully conducted to produce sol spots within the gel matrix. The fabricated gel-sol pattern not only allowed regulation of bacterial motility in a limited area, but also off/on switching of F1-ATPase rotary motion at the single-molecule level. These results demonstrated that the photoresponsive supramolecular hydrogel and the resulting nanomeshes may provide unique biomaterials for the spatiotemporal manipulation of various biomolecules and live bacteria.     

配合物与载体相互作用的研究

本文研究了配合物与载体的相互作用。载体浸渍于配合物的溶液时,两者间的相互作用可分成四类:(1)无明显的化学作用;(2)配合物与载体通过桥联的配体作用;(3)载体阳离子与解离的配体作用;(4)载体促进金属水合离子的水解。     

Spherical phospholipid polymer hydrogels for cell encapsulation prepared with a flow-focusing microfluidic channel device

To prepare spherical polymer hydrogels, we used a flow-focusing microfluidic channel device for mixing aqueous solutions of two water-soluble polymers. Continuous encapsulation of cells in the hydrogels was also examined. The polymers were bioinspired 2-methacryloyloxyethyl phosphorylcholine polymer bearing phenyl boronic acid groups (PMBV) and poly(vinyl alcohol) (PVA), which spontaneously form a hydrogel in aqueous medium via specific molecular complexation upon mixing, even when they were in cell culture medium. The microfluidic device was prepared with polydimethylsiloxan, and the surface of the channel was treated with fluoroalkyl compound to prevent sticking of the polymers on the surface. The microfluidic channel process could control the diameter of the spherical hydrogels in the range of 30-90 μm and generated highly monodispersed diameter spherical hydrogels. We found that the polymer distribution in the hydrogel was influenced by the PVA concentration and that the hydrogel could be dissociated by the addition of d-sorbitol to the suspension. The single cells could be encapsulated and remain viable in the hydrogels. The localized distribution of polymers in the hydrogel may provide an environment for modulating cell function. It is concluded that the spontaneous hydrogel formation between PMBV and PVA in the flow-focusing microfluidic channel device is applicable for continuous preparation of a spherical hydrogel-encapsulating living cell.