Stimuli-Responsive Gelators From Carbamoyl Sugar Derivatives and Their Responses to Metal Ions and Tetrabutylammonium Salts

Carbohydrate-based low molecular weight gelators (LMWGs) are interesting compounds with a variety of applications. In this research, a library of nineteen carbamate derivatives of N-acetyl-D-glucosamine were synthesized and characterized, and several derivatives were found to be effective LMWGs. They formed gels in pump oils as well as mixtures of water with ethanol or water with DMSO. The structures of the carbamoyl chains played an important role in the gelation properties, short chain aliphatic derivatives and phenyl carbamates formed gels in more solvents than certain aromatic and dimeric carbamates. The phenyl carbamate gelator was also selected for the encapsulation of naproxen sodium, and the drug slowly diffused from the gel to the aqueous phase as indicated by UV-vis spectroscopy. In addition, we also found that the p-methoxyl benzyl carbamate derivative showed interesting stimuli-responsive gelation properties in the presence of metal salts and tetrabutylammonium salts. The gels were characterized using optical microscopy, scanning electron microscopy, rheology and other methods. The self-assembling mechanisms of the gelators were studied using 1H NMR spectroscopy. The preparation, characterization, and molecular assembling properties of these compounds are reported. The results obtained from this study are useful for the design of other LMWGs and the sugar derivatives can be explored for different biological applications. The formation of spontaneous ionic gels can be applicable for a plethora of applications including catalysis and environmental remediation

Recently Developed Carbohydrate Based Gelators and Their Applications

Carbohydrate based low molecular weight gelators have been an intense subject of study over the past decade. The self-assembling systems built from natural products have high significance as biocompatible materials and renewable resources. The versatile structures available from naturally existing monosaccharides have enriched the molecular libraries that can be used for the construction of gelators. The bottom-up strategy in designing low molecular weight gelators (LMWGs) for a variety of applications has been adopted by many researchers. Rational design, along with some serendipitous discoveries, has resulted in multiple classes of molecular gelators. This review covers the literature from 2017-2020 on monosaccharide based gelators, including common hexoses, pentoses, along with some disaccharides and their derivatives. The structure-based design and structure to gelation property relationships are reviewed first, followed by stimuli-responsive gelators. The last section focuses on the applications of the sugar based gelators, including their utilization in environmental remediation, ion sensing, catalysis, drug delivery and 3D-printing. We will also review the available LMWGs and their structure correlations to the desired properties for different applications. This review aims at elucidating the design principles and structural features that are pertinent to various applications and hope to provide certain guidelines for researchers that are working at the interface of chemistry, biochemistry, and materials science

Synthesis and Self-Assembling Properties of Carbohydrate- and Diarylethene-Based Photoswitchable Molecular Gelators

Carbohydrate-based low-molecular-weight gelators are interesting new materials with many potential applications. These compounds can be designed to include multiple stimuli-responsive functional groups. In this study, we designed and synthesized several chemically responsive bola-glycolipids and dimeric carbohydrate- and diarylethene-based photoswitchable derivatives. The dimeric glycolipids formed stable gels in a variety of solvent systems. The best performing gelators in this series contained decanedioic and dithienylethene (DTE) spacers, which formed gels in eight and nine of the tested solvents, respectively. The two new DTE-containing esters possessed interesting photoswitching properties and DTE derivative 7 was found to have versatile gelation properties in many solvents, including DMSO solutions at low concentrations. The gels formed by these compounds were stable under acidic conditions and tended to hydrolyze under basic conditions. Several gels were used to absorb rhodamine B and Toluidine blue from aqueous solutions. In this study, we demonstrated the rational design of molecular gelators which incorporated photoresponsive and pH responsive functions, leading to the discovery of multiple effective stimuli-responsive gelators

The Development of Novel Carbohydrate-Based Gelators and Their Applications as Advanced Soft Materials

Low molecular weight gelators (LMWGs) are attractive molecules that have been explored extensively due to their practical applications in many disciplines. These small molecules self-assemble forming solid-like gels via three-dimensional cross-linked networks with the solvent as the key component within the matrix. Carbohydrate-based LMWGs are small molecules that can form solid-like gels in water, organic solvents, and aqueous solutions. They have great potential to be utilized in different applications because carbohydrates are biocompatible and can be made from easily accessible and renewable resources. Designing gelators is still a challenge within the field, even though researchers have developed tools to predict gelation and other properties. Therefore, research on the structure and properties of different gelator templates remains valuable to the field. The research in this dissertation comprises of three projects discussed in chapters 2-4. For the first project, we have studied several monosaccharide ester derivatives that can function as stimuli responsive gelators in organic solvents, water, and aqueous solutions. The results from project one demonstrated that these stimuli-responsive gelators have the potential to be utilized for dye removal and as controlled delivery carriers for various drug molecules. In the second project, we have studied a variety of glycolipid gelators containing ester, ether and amine functional groups. Their applications for enzyme immobilization as well as the encapsulation and release of model drugs have been studied. The third project examined a series of dimeric glycolipids and evaluated the influence of structure on the gelation properties, as well as their uses as soft materials for dye absorption studies. Overall, several functionalized gelators and their resulting gels are stimuli-responsive to bases and lipases. Other representative gels were able to successfully encapsulate naproxen sodium as well as hydroxychloroquine sulfate and allow for their sustained release over time. The hydrogel from project two had the ability to encapsulate α-amylase and facilitated retention of its activity. This was illustrated from the recorded production of maltose by the gel throughout the experiment. In addition to that, the gels absorbed toluidine blue and rhodamine B from an aqueous solution demonstrating their potential usage in environmental remediation

Synthesis and Self-Assembling Properties of Cationic Glycolipids

Low molecular weight gelators derived from carbohydrates are quite important molecules with a vast amount of applications in many different fields. Monosaccharide based compounds can be modified at different positions with a variety of functional groups to investigate their impact on the gelation process and obtain advanced functional biomaterials. Herein, we have synthesized and studied the gelation properties of several monosaccharides with amino functionalities and some of their respective quaternary ammonium salts. Two series of analogues with variable carbon chain lengths between the amino group and the sugar moiety were examined. Certain derivatives were found to be effective gelators in organic solvents. The amines were converted to their respective ammonium salts with different acids to investigate the possibility of forming spontaneous hydrogels. We also studied other glycolipid based organogelators for their applications in drug delivery and for binding pollutants and dyes. In this presentation, the effect of changing the carbon spacer on both the amines and their salts will be demonstrated; their gelation properties and applications will also be discussed.https://digitalcommons.odu.edu/sciences_achievement/1017/thumbnail.jp