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Tuning Gel State Properties of Supramolecular Gels by Functional Group Modification.

ABSTRACT: The factors affecting the self-assembly process in low molecular weight gelators (LMWGs) were investigated by tuning the gelation properties of a well-known gelator N-(4-pyridyl)isonicotinamide (4PINA). The N-H???N interactions responsible for gel formation in 4PINA were disrupted by altering the functional groups of 4PINA, which was achieved by modifying pyridyl moieties of the gelator to pyridyl N-oxides. We synthesized two mono-N-oxides (INO and PNO) and a di-N-oxide (diNO) and the gelation studies revealed selective gelation of diNO in water, but the two mono-N-oxides formed crystals. The mechanical strength and thermal stabilities of the gelators were evaluated by rheology and transition temperature (Tgel) experiments, respectively, and the analysis of the gel strength indicated that diNO formed weak gels compared to 4PINA. The SEM image of diNO xerogels showed fibrous microcrystalline networks compared to the efficient fibrous morphology in 4PINA. Single-crystal X-ray analysis of diNO gelator revealed that a hydrogen-bonded dimer interacts with adjacent dimers via C-H???O interactions. The non-gelator with similar dimers interacted via C-H???N interaction, which indicates the importance of specific non-bonding interactions in the formation of the gel network. The solvated forms of mono-N-oxides support the fact that these compounds prefer crystalline state rather than gelation due to the increased hydrophilic interactions. The reduced gelation ability (minimum gel concentration (MGC)) and thermal strength of diNO may be attributed to the weak intermolecular C-H???O interaction compared to the strong and unidirectional N-H???N interactions in 4PINA.

SUBMITTER: Ghosh D

PROVIDER: S-EPMC6804314 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Tuning Gel State Properties of Supramolecular Gels by Functional Group Modification.

Ghosh Dipankar D Mulvee Matthew T MT Damodaran Krishna K KK

Molecules (Basel, Switzerland) 20190925 19

The factors affecting the self-assembly process in low molecular weight gelators (LMWGs) were investigated by tuning the gelation properties of a well-known gelator N-(4-pyridyl)isonicotinamide (4PINA). The N-H∙∙∙N interactions responsible for gel formation in 4PINA were disrupted by altering the functional groups of 4PINA, which was achieved by modifying pyridyl moieties of the gelator to pyridyl N-oxides. We synthesized two mono-N-oxides (INO an ...[more]

PMID: 31557821

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Project description:H2S is a gasotransmitter with several physiological roles, but its reactivity and short half-life in biological media make its controlled delivery difficult. For biological applications of the gas, hydrogels have the potential to deliver H2S with several advantages over other donor systems, including localized delivery, controlled release rates, biodegradation, and variable mechanical properties. In this study, we designed and evaluated peptide-based H2S-releasing hydrogels with controllable H2S delivery. The hydrogels were prepared from short, self-assembling aromatic peptide amphiphiles (APAs), functionalized on their N-terminus with S-aroylthiooximes (SATOs), which release H2S in response to a thiol trigger. The APAs were studied both in solution and in gel forms, with gelation initiated by addition of CaCl2. Various substituents were included on the SATO component of the APAs in order to evaluate their effects on self-assembled morphology and H2S release rate in both the solution and gel phases. Transmission electron microscopy (TEM) images confirmed that all H2S-releasing APAs self-assembled into nanofibers above a critical aggregation concentration (CAC) of ∼0.5 mg/mL. Below the CAC, substituents on the SATO group affected H2S release rates predictably in line with electronic effects (Hammett σ values) according to a linear free energy relationship. Above the CAC, circular dichroism, infrared, and fluorescence spectroscopies demonstrated that substituents influenced the self-assembled structures by affecting hydrogen bonding (β-sheet formation) and π-π stacking. At these concentrations, electronic control over release rates diminished, both in solution and in the gel form. Rather, the release rate depended primarily on the degree of organization in the β-sheets and the amount of π-π stacking. This supramolecular control over release rate may enable the evaluation of H2S-releasing hydrogels with different release rates in biological applications.

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Tuning Gel State Properties of Supramolecular Gels by Functional Group Modification.

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Tuning Gel State Properties of Supramolecular Gels by Functional Group Modification.

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