Influence of odd-even effect and intermolecular interactions in 2D molecular layers of bisamide organogelators

Supramolecular Organo/hydrogel-Fabricated Long Alkyl Chain α-Amidoamides as a Smart Soft Material for pH-Responsive Curcumin Release

Low-molecular-mass gelators, due to their excellent biocompatibility, low toxicological profile, innate biodegradability and ease of fabrication have garnered significant interest as they self-assemble through non-covalent interactions. In this study, we have designed and synthesized a series of six α-amidoamides by varying the hydrophobic alkyl chain length (C12-C22), which were well characterized using different spectral techniques. These α-amidoamides formed self-assembled aggregates in a DMSO/water solvent system affording organo/hydrogels at 0.66% w/v, which is the minimum gelation concentration (MGC) making them as remarkable supergelators. The various functionalities present in these gelators such as amides and alkyl chain length pave the way toward excellent gelation mechanism through hydrogen bonding and van der Waals interaction as evidenced from FTIR spectroscopy. Notably, as the chain length increased, organo/hydrogels became more thermally stable. Rheological results showed that the stability and strength of these gelators were considerably impacted by variations in chain length. The SEM morphology revealed dense sheet architectures of the organo/hydrogel samples. Organo/hydrogels have a significant impact on the advancement of innovative drug delivery systems that respond to various stimuli, ushering in a new era in pharmaceutical technology. Inspired by this, we encapsulated curcumin, a chemopreventive medication, into the gel core and further released via gel-to-sol transition induced by pH variation at 37 °C, without any alteration in structure-activity relationship. The drug release behavior was observed by UV-vis spectroscopy. Moreover, cell viability and cell invasion experiments demonstrate that the gel formulations exhibit high biocompatibility and low cytotoxicity. Among the tested formulations, 5e+Cur exhibited remarkable efficacy in controlling A549 cell migration, suggesting significant potential for applications in the pharmaceutical industry.

Amidoamine Oxide Surfactants as Low-Molecular-Weight Hydrogelators: Effect of Methylene Chain Length on Aggregate Structure and Rheological Behavior

Rheology control is an important issue in many industrial products such as cosmetics and paints. Recently, low-molecular-weight compounds have attracted considerable attention as thickeners/gelators for various solvents; however, there is still a significant need for molecular design guidelines for industrial applications. Amidoamine oxides (AAOs), which are long-chain alkylamine oxides with three amide groups, are surfactants that act as hydrogelators. Here, we show the relationship between the length of methylene chains at four different locations of AAOs, the aggregate structure, the gelation temperature T_gel, and the viscoelasticity of the formed hydrogels. As seen from the results of electron microscopic observations, the aggregate structure (ribbon-like or rod-like) can be controlled by changing the length of methylene chain in the hydrophobic part, the length of methylene chain between the amide and amine oxide groups, and the lengths of methylene chains between amide groups. Furthermore, hydrogels consisting of rod-like aggregates showed significantly higher viscoelasticity than those consisting of ribbon-like aggregates. In other words, it was shown that the gel viscoelasticity could be controlled by changing the methylene chain lengths at four different locations of the AAO.

Molecular Arrangement and Thermal Properties of Bisamide Organogelators in the Solid State

The crystal structure and phase behavior of bisamide gelators are investigated using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy, X-ray diffraction (XRD), and molecular modeling, aiming at a better understanding of bisamide gel systems. A homologous series of bisamide model compounds (nBAs) was prepared with the (CH₂)_n spacer between the two amide groups, where n varies from 5 to 10, and with two symmetric C17 alkyl tails. With increasing spacer length, the thermal properties show a clear odd-even effect, which was characterized using our newly developed analytical model DSC_N(T). Using XRD, all studied nBA compounds turn out to have a layer-like structure. The XRD patterns of the odd BA series are very similar but show marked differences compared to the XRD patterns of the even series, which in turn are very similar. The odd-membered 5BA molecules are nearly perpendicular to the stacked layers, as described by a pseudo-orthorhombic unit cell, whereas the even-membered 6BA molecules are tilted at an angle with respect to the layer normal, as described by a triclinic unit cell. In both the odd and even series, the inter-layer interaction is the van der Waals interaction. The 6BA hydrogen bonding scheme is very similar to that of Nylon 6,10 α, unlike the 5BA H bonding scheme. The packing of the C17 alkyl tails in the 5BA layers is similar to polyethylene, and unlike 6BA. The slightly higher crystalline density of 6BA (1.038 g cm^-3) as compared to 5BA (1.018 g cm^-3) explains the higher melting point, higher enthalpy of fusion, and the observed shift of N-H stretch bands to higher wave numbers. The structural differences observed between the odd and even BA series reflect the different structure-directing effect of parallel versus antiparallel amide hydrogen bonding motifs. These differences underlie the observed odd-even effect in the thermal properties of nBA compounds.

Turning Nonselective Inhibitors of Type I Protein Arginine Methyltransferases into Potent and Selective Inhibitors of Protein Arginine Methyltransferase 4 through a Deconstruction-Reconstruction and Fragment-Growing Approach

Protein arginine methyltransferases (PRMTs) are important therapeutic targets, playing a crucial role in the regulation of many cellular processes and being linked to many diseases. Yet, there is still much to be understood regarding their functions and the biological pathways in which they are involved, as well as on the structural requirements that could drive the development of selective modulators of PRMT activity. Here we report a deconstruction–reconstruction approach that, starting from a series of type I PRMT inhibitors previously identified by us, allowed for the identification of potent and selective inhibitors of PRMT4, which regardless of the low cell permeability show an evident reduction of arginine methylation levels in MCF7 cells and a marked reduction of proliferation. We also report crystal structures with various PRMTs supporting the observed specificity and selectivity.

Supramolecular Glycolipid-Based Hydro-/Organogels with Enzymatic Bioactive Release Ability by Tuning the Chain Length and Headgroup Size

Designing of supramolecular hydro-/organogels having desired properties, biocompatibility, and stimuli responsiveness is a challenging task. Herein, the gelation ability of amphiphilic glycolipid-based gelators in a wide range of solvents is explored. The structure-function relationship was established by varying the chain length and polar headgroup size of amphiphilic gelators. The prepared hydro-/organogels were characterized by employing several techniques such as differential scanning calorimetry (DSC), rheology, field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), etc. The thermal stability of hydro-/organogels increased with an increase in chain length. Rheological analysis depicted that variation in chain length and headgroup size of amphiphilic gelators significantly affected the gel strength and stability. The self-assembled morphology of hydro-/organogel samples revealed the compact entangled fibrillar network structures. After comparing the energy-minimized molecular length with the d-spacing value obtained by XRD, interdigitated bilayer packing in the gel network was established. The bioactive encapsulation and enzymatic release study of hydro-/organogels portrayed their potential application in the biomedical field. To our delight, glycolipid 16M (C16 chain length) formed a molecular hydrogel with injectable and thixotropic behaviors. High critical strain value, thixotropy, injectability, thermoreversibility, and faster bioactive release for the 16M-W hydrogel proved crucial to predict its future applications. Overall, glycolipid amphiphiles designed by upholding proper hydrophilic-lipophilic balance can form multifunctional supramolecular hydrogels with excellent implementation in the drug delivery system.