Self-Associated 1,8-Naphthalimide as a Selective Fluorescent Chemosensor for Detection of High pH in Aqueous Solutions and Their Hg2+ Contamination.

A novel diamino triazine based 1,8-naphthalimide (NI-DAT) has been designed and synthesized. Its photophysical properties have been investigated in different solvents and its sensory capability evaluated. The fluorescence emission of NI-DAT is significantly impacted by the solvent polarity due to its inherent intramolecular charge transfer character. Moreover, the fluorescence emission quenched at higher pH as a result of photo-induced electron transfer (PET) from triazine moiety to 1,8-naphthalimide after cleaving hydrogen bonds in the self-associated dimers. Furthermore, the new chemosensor exhibited a good selectivity and sensitivity towards Hg2+ among all the used various cations and anions in the aqueous solution of ethanol (5:1, v/v, pH = 7.2, Tampon buffer). NI-DAT emission at 540 nm was quenched remarkably only by Hg2+, even in the presence of other cations or anions as interfering analytes. Job's plot revealed a 2:1 stoichiometric ratio for NI-DAT/Hg2+ complex, respectively.

Multiple Hydrogen Bonds-Reinforced Hydrogels with High Strength, Shape Memory, and Adsorption Anti-Inflammatory Molecules.

The research on multiple hydrogen bonds (H-bonds) hydrogels have gradually aroused wide interest. In this paper, a multiple H-bonds-reinforced poly(acrylamide-co-2-vinyl-4,6-diamino-2-vinyl-1,3,5-triazine)/tannic acid (P(Am-co-VDT)/TA) hydrogels are prepared. The results suggest that the prepared hydrogel has two types of H-bonds crosslinking regions: A "soft" region of H-bonds between the diaminotriazine (DAT) moieties on the polymer chains and the TA pyrogallol/catechol groups, and a "hard" region of H-bonds forming by DAT moieties with itself. The hard crosslinking region exhibits significantly higher activation energy than the soft region. Such soft and hard dual physically crosslinked networks dramatically enhance the mechanical properties of P(Am-co-VDT)/TA hydrogels in a synergistic manner (tensile strength is 2.34 MPa, elongation at break is 410%). Due to the multiple hydrogen bonds, the hydrogel has good pH sensitivity and rapid response to shape memory within a few minutes. In addition, the hydrogels have the capacity of physical adsorption of the anti-inflammatory drug diclofenac sodium and other molecules with a specific spatially arranged chemical composition. These hydrogels with high mechanical strength, excellent shape memory behavior, and capacity of adsorption of anti-inflammatory drug could be attractive candidates for applications in the fields of biomedicine, tissue engineering, and medical materials.

Integrated Functional High-Strength Hydrogels with Metal-Coordination Complexes and H-Bonding Dual Physically Cross-linked Networks.

With the deepening of research on high-strength hydrogels, the multi-functional study of hydrogels has become a hot spot. In this paper, a dual cross-linked physical high-strength hydrogels is prepared by a relatively simple method. 2-Vinyl- 4,6-Diamino-2-vinyl-1,3,5-triazine (VDT) induces the formation of the first cross-linking points through the interaction of hydrogen bonds with poly(acrylamide-co-acrylic acid) (PAm-co-Ac) chains, then the secondary physical cross-linkers Fe3+ that introduce ionic coordinates between Fe3+ and -COO- groups. Due to the synergistic effect of hydrogen bonding and ionic coordination, hydrogels possess high tensile strength (approx. 4.34 MPa), large elongation (approx. 17.64 times), and good healing properties under alkali solution after cutting into two pieces. Meanwhile, VDT contains diaminotriazine functional groups that easily form hydrogen bonds so that the polymer of hydrogels could absorb 5-fluorouridine. In addition, the contribution of ionic polymer segments enables pH to be sensitive to hydrogels and facilitates the adsorption of a large number of ionic monomers to form ionic conductive networks, the prepared hydrogel capacitor device has very high sensitivity to pressure and deformation, and can detect the movement behavior of the human body. The dual-physical cross-linked hydrogels had a selective adsorption to biological small molecules and could be assembled into a flexible wearable device with high sensitivity.

Poly(vinyl diaminotriazine): From Molecular Recognition to High-Strength Hydrogels.

Poly(2-vinyl-4,6-diamino-1,3,5-triazine), (PVDT) with diaminotriazine residues is found to form not only intramolecular hydrogen bonds, but also three robust, complementary hydrogen bonds with nucleobases such as thymine and uracil. Taking advantage of the three complementary hydrogen bonds, molecular recognition of a nucleic acid base has been investigated in previous work. Over the past few years, the use of PVDT has been extended to the construction of gene delivery vectors and nonswellable, high-strength hydrogels by copolymerization with a hydrophilic monomer and/or crosslinker. In particular, many fascinating properties, such as excellent mechanical properties, stimuli responsiveness, the shape memory effect, and biodegradability, have emerged in PVDT-based hydrogels. In this article, the molecular recognition and self-assembly of diaminotriazine are introduced first, and then a particular focus is placed on the development of PVDT-based high performance hydrogels, especially their biorelated applications.

Chain-End Effects on Supramolecular Poly(ethylene glycol) Polymers.

In this work we present a fundamental analysis based on small-angle scattering, linear rheology and differential scanning calorimetry (DSC) experiments of the role of different hydrogen bonding (H-bonding) types on the structure and dynamics of chain-end modified poly(ethylene glycol) (PEG) in bulk. As such bifunctional PEG with a molar mass below the entanglement mass Me is symmetrically end-functionalized with three different hydrogen bonding (H-bonding) groups: thymine-1-acetic acid (thy), diamino-triazine (dat) and 2-ureido-4[1H]-pyrimidinone (upy). A linear block copolymer structure and a Newtonian-like dynamics is observed for PEG-thy/dat while results for PEG-upy structure and dynamics reveal a sphere and a network-like behavior, respectively. These observations are concomitant with an increase of the Flory-Huggins interaction parameter from PEG-thy/dat to PEG-upy that is used to quantify the difference between the H-bonding types. The upy association into spherical clusters is established by the Percus-Yevick approximation that models the inter-particle structure factor for PEG-upy. Moreover, the viscosity study reveals for PEG-upy a shear thickening behavior interpreted in terms of the free path model and related to the time for PEG-upy to dissociate from the upy clusters, seen as virtual crosslinks of the formed network. Moreover, a second relaxation time of different nature is also obtained from the complex shear modulus measurements of PEG-upy by the inverse of the angular frequency where G' and G'' crosses from the network-like to glass-like transition relaxation time, which is related to the segmental friction of PEG-upy polymeric network strands. In fact, not only do PEG-thy/dat and PEG-upy have different viscoelastic properties, but the relaxation times found for PEG-upy are much slower than the ones for PEG-thy/dat. However, the activation energy related to the association dynamics is very similar for both PEG-thy/dat and PEG-upy. Concerning the segmental dynamics, the glass transition temperature obtained from both rheological and calorimetric analysis is similar and increases for PEG-upy while for PEG-thy/dat is almost independent of association behavior. Our results show how supramolecular PEG properties vary by modifying the H-bonding association type and changing the molecular Flory-Huggins interaction parameter, which can be further explored for possible applications.

Supramolecular Dimerization in a Polymer Melt from Small-Angle X-Ray Scattering and Rheology: A Miscible Model System.

We present a structural and dynamic study on the simplest supramolecular hetero-association, recently investigated by the authors to prepare architectural homogeneous structures in the melt state, based on the bio-inspired hydrogen-bonding of thymine/diaminotriazine (thy-DAT) base-pairs. In the combination with an amorphous low Tg poly(butylene oxide) (PBO), no micellar structures are formed, which is expected for nonpolar polymers because of noncompatibility with the highly polar supramolecular groups. Instead, a clear polymer-like transient architecture is retrieved. This makes the heterocomplementary thy-DAT association an ideal candidate for further exploitation of the hydrogen-bonding ability in the bulk for self-healing purposes, damage management in rubbers or even the development of easily processable branched polymers with built-in plasticizer. In the present work, we investigate the temperature range from Tg + 20 °C to Tg + 150 °C of an oligomeric PBO using small-angle X-ray scattering (SAXS) and linear rheology on the pure thy and pure DAT monofunctionals and on an equimolar mixture of thy/DAT oligomers. The linear rheology performed at low temperature is found to correspond to fully closed-state dimeric configurations. At intermediate temperatures, SAXS probes the equilibrium between open and closed states of the thy-DAT mixtures. The temperature-dependent association constant in the full range between open and closed H-bonds and an enhancement of the monomeric friction coefficient due to the groups is obtained. The thy-DAT association in the melt is more stable than the DAT-DAT, whereas the thy-thy association seems to involve additional long-lived interactions.

Gene-modified cell detachment on photoresponsive hydrogels strengthened through hydrogen bonding.

Photoresponsive hydrogels are potentially useful as drug delivery and cell culture media, but there has been no report on manipulation of cell attachment/detachment and gene transfection simultaneously on the surface of this single gel. In the present study, strong light sensitive hydrogels were prepared mechanically by photoinitiated copolymerization of spiropyran-containing monomer, 2-vinyl-4,6-diamino-1,3,5-triazine, hydrogen bonding monomer, oligo(ethylene glycol) methacrylate and polyethylene glycol diacrylate (PEGDA, Mn=575). The multiple hydrogen bondings of diaminotriazine residues could contribute to the increase in compressive strengths of the photosensitive hydrogels up to 5.1MPa. UV (365nm) irradiation led to detachment of adhered cells as a result of the increased surface hydrophilicity caused by a switch from hydrophobic spiropyran to hydrophilic merocyanine form. Furthermore, selective detachment of cells could also be achieved by UV light illumination on the specified gel surface. Hydrogen bonding between diaminotriazines were shown to tightly anchor the PVDT/pDNA complex particles on the gel surface, where reverse gene transfection was achieved. Following up with UV irradiation triggered the unharmful detachment of gene-modified cells from the gel surface. It is envisioned that this photosensitive hydrogel holds potential as a versatile platform for operating gene delivery and controlled harvest of desired cells for tissue engineering.