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The design of soft biomaterials requires a deep understanding of molecular self-assembly. We introduce here a nanoscale infrared (IR) spectroscopy study of a two-component supramolecular gel to assess the system´s heterogeneity and supramolecular assembly. In contrast to far-field IR spectroscopy, near-field IR spectroscopy revealed differences in the secondary structures of the gelator molecules and non-covalent interactions at three distinct nano-locations of the gel network. A β-sheet arrangement is dominant in single and parallel fibres with a small proportion of an α-helix present, while the molecular assembly derives from strong hydrogen bonding. However, at the crossing point of two fibres, only the β-sheet motif is observed, with an intense π-π stacking contribution. Near-field nanospectroscopy can become a powerful tool for the nanoscale distinction of non-covalent interactions, while is expected to advance the existing spectroscopic assessments of supramolecular gels. peerReviewed

We report the effects of a laser-oxidized single layer graphene (SLG) surface on the self-assembly of amphiphilic gelator N-fluorenylmethoxycarbonyl-L-phenylalanine (Fmoc-Phe) towards an gel–SLG interface. Laser oxidation modulates the levels of hydrophobicity/hydrophilicity on the SLG surface. Atomic force, scanning electron, helium ion and scattering scanning nearfield optical microscopies (AFM, SEM, HIM, s-SNOM) were employed to assess the effects of surface properties on the secondary and tertiary organization of the formed Fmoc-Phe fibres at the SLG–gel interface. S-SNOM shows sheet-like secondary structures on both hydrophobic/hydrophilic areas of SLG and helical or disordered structures mainly on the hydrophilic oxidized surface. The gel network heterogeneity on pristine graphene was observed at the scale of single fibres by s-SNOM, demonstrating its power as a unique tool to study supramolecular assemblies and interfaces at nanoscale. Our findings underline the sensitivity of assembled structures to surface properties, while our characterization approach is a step forward in assessing surface–gel interfaces for the development of bionic devices. peerReviewed

In the last decades, synthesis and design of low molecular weight organogelators has gained increasing attention due to their versatile use in, for example, cosmetics, biomedicine and oil spill remediation. In this work, three potential gelators have been prepared from allylated d-mannose. Both the gelators and the corresponding gels formed were thoroughly characterized by crystallography, FTIR spectroscopy, SEM, rheometry and NMR spectroscopy, in solution and in solid state. The results showed that two of the compounds phase-selectively form gels with hydrocarbon solvents. The most promising gelator compound is alkene terminated, with the unsaturated end functionality not critical for gel formation, tentatively providing the possibility for customizing the gelation properties by further chemical modification. Alternatively, the alkene group could possibly be utilized as a linker for future coupling to carrier materials or surfaces to further increase the mechanical strength of the gel. peerReviewed

Herein, we introduce the first diphenylalanine dipeptide hydrogelator capped with the cinnamoyl functional group (Cin-L-F-L-F). We evaluate the effects of the cinnamoyl moiety on molecular self-assembly events and resultant physical properties of the hydrogel formed. In addition, we report our preliminary results of this dipeptide's cytotoxicity against glioblastoma (GBM) cancer cells. peerReviewed

A transient organo-gelation system with spatiotemporal dynamic properties is described. Here, the solvent actively controls a complex set of equilibria that underpin the dynamic assembly event. The observed metastability is due to the in situ formation of a secondary solvent, acting as an antagonist against the primary solvent of the organogel. peerReviewed

Background Due to unmet need for bone augmentation, our aim was to promote osteogenic differentiation of human adipose stem cells (hASCs) encapsulated in gellan gum (GG) or collagen type I (COL) hydrogels with bioactive glass (experimental glass 2-06 of composition [wt-%]: Na2O 12.1, K2O 14.0, CaO 19.8, P2O5 2.5, B2O3 1.6, SiO2 50.0) extract based osteogenic medium (BaG OM) for bone construct development. GG hydrogels were crosslinked with spermidine (GG-SPD) or BaG extract (GG-BaG). Methods Mechanical properties of cell-free GG-SPD, GG-BaG, and COL hydrogels were tested in osteogenic medium (OM) or BaG OM at 0, 14, and 21 d. Hydrogel embedded hASCs were cultured in OM or BaG OM for 3, 14, and 21 d, and analyzed for viability, cell number, osteogenic gene expression, osteocalcin production, and mineralization. Hydroxyapatite-stained GG-SPD samples were imaged with Optical Projection Tomography (OPT) and Selective Plane Illumination Microscopy (SPIM) in OM and BaG OM at 21 d. Furthermore, Raman spectroscopy was used to study the calcium phosphate (CaP) content of hASC-secreted ECM in GG-SPD, GG-BaG, and COL at 21 d in BaG OM. Results The results showed viable rounded cells in GG whereas hASCs were elongated in COL. Importantly, BaG OM induced significantly higher cell number and higher osteogenic gene expression in COL. In both hydrogels, BaG OM induced strong mineralization confirmed as CaP by Raman spectroscopy and significantly improved mechanical properties. GG-BaG hydrogels rescued hASC mineralization in OM. OPT and SPIM showed homogeneous 3D cell distribution with strong mineralization in BaG OM. Also, strong osteocalcin production was visible in COL. Conclusions Overall, we showed efficacious osteogenesis of hASCs in 3D hydrogels with BaG OM with potential for bone-like grafts.

Herein we report silver(i) directed infinite coordination polymer network (ICPN) induced self-assembly of low molecular weight organic ligands leading to metallogelation. Structurally simple ligands are derived from 3-aminopyridine and 4-aminopyridine conjugates which are composed of either pyridine or 2,2'-bipyridine cores. The cation specific gelation was found to be independent of the counter anion, leading to highly entangled fibrillar networks facilitating the immobilization of solvent molecules. Rheological studies revealed that the elastic storage modulus (G') of a given gelator molecule is counter anion dependent. The metallogels derived from ligands containing a bipyridine core displayed higher G' values than those with a pyridine core. Furthermore, using single crystal X-ray diffraction studies and 1H-15N two-dimensional (2D) correlation NMR spectroscopy, we show that the tetracoordination of silver ions enables simultaneous coordination polymerization and metallosupramolecular cross-linking. The resulting metallogels show spontaneous, in situ nanoparticle (d < 2-3 nm) formation without any additional reducing agents. The silver nanoparticle formation was followed using spectroscopic studies, and the self-assembled fibrillar networks were imaged using transmission electron microscopy (TEM) imaging.

Six bile acid alkyl amide derivatives were studied with respect to their gelation properties. The derivatives were composed of three different bile acids with hexyl or cyclohexyl side chains. The gelation behaviour of all six compounds were studied for 36 solvents with varying polarities. Gelation was observed mainly in aromatic solvents, which is characteristic for bile‐acid‐based low molecular weight gelators. Out of 108 bile acid‐solvent combinations, a total of 44 gel systems were formed, 28 of which from lithocholic acid derivatives, only two from deoxycholic acid derivatives, and 14 from cholic acid derivatives. The majority of the gel systems were formed from bile acids with hexyl side chains, contrary to the cyclohexyl group, which seems to be a poor gelation moiety. These results indicate that the spatial demand of the side chain is the key feature for the gelation properties of the bile acid amides., The gelation abilities of a series of six bile acid alkyl amides were studied. Gelation was observed mainly in aromatic solvents by lithocholyl derivatives. One of the cholyl derivatives formed exclusively flawless gels, speculated to stem from its ability to form H‐bonded 2D polymers contrary to 1D bilayered structures of the other derivatives. The shape of the side chain (linear vs. cyclic) clearly had an impact on the self‐assembly properties.

Natural and abundant plant triterpenoids are attractive starting materials for the synthesis of conformationally rigid and chiral building blocks for functional soft materials. Here, we report the rational design of three oleanolic acid–triazole–spermine conjugates, containing either one or two spermine units in the target molecules, using the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction. The resulting amphiphile-like molecules 2 and 3, bearing just one spermine unit in the respective molecules, self-assemble into highly entangled fibrous networks leading to gelation at a concentration as low as 0.5% in alcoholic solvents. Using step-strain rheological measurements, we show rapid self-recovery (up to 96% of the initial storage modulus) and sol ⇔ gel transition under several cycles. Interestingly, rheological flow curves reveal the thixotropic behavior of the gels. To the best of our knowledge, this kind of behavior was not shown in the literature before, neither for a triterpenoid nor for its derivatives. Conjugate 4, having a bolaamphiphile-like structure, was found to be a nongelator. Our results indicate that the position and number of spermine units alter the gelation properties, gel strength, and their self-assembly behavior. Preliminary cytotoxicity studies of the target compounds 2–4 in four human cancer cell lines suggest that the position and number of spermine units affect the biological activity. Our results also encourage exploring other triterpenoids and their derivatives as sustainable, renewable, and biologically active building blocks for multifunctional soft organic nanomaterials. peerReviewed

Over the past six decades, nuclear magnetic resonance spectroscopy has been an integral part of synthetic organic and organometallic chemistry, as well as biochemistry. Beyond solution state experiments, increasing developments have opened new avenues to study materials in their solid state. Between two extremes (i.e., solution and solid), there exist several other forms of materials, especially soft materials such as gels and liquid crystals. Traditionally gels have been studied using solution state NMR spectroscopic methods. However, the viscosity of complex viscoelastic fluids such as gels affects the molecular tumbling, which in turn affects the chemical shift anisotropy and dipolar and quadrupolar interactions, resulting in broad spectral lines. Therefore, the importance of solid state (SS) NMR in understanding the structural details of self-assembled soft materials has remained unexplored for several decades. Nevertheless, promising results in understanding weak interactions in polymer gels have been explored using solid state cross polarization (CP) and high resolution (HR) magic angle spinning (MAS) NMR spectroscopy. However, similar studies and the possibility to utilize SS NMR spectroscopy to study hydro- and organogels derived from low molecular weight gelators have been limited until recently. In this chapter, we will focus on the application of SS NMR to study xerogels, aerogels and native gels with selected examples.

Square planar platinum(ii) complexes are attractive building blocks for multifunctional soft materials due to their unique optoelectronic properties. However, for soft materials derived from synthetically simple discrete metal complexes, achieving a combination of optical properties, thermoresponsiveness and excellent mechanical properties is a major challenge. Here, we report the rapid self-recovery of luminescent metallogels derived from platinum(ii) complexes of perfluoroalkyl and alkyl derivatives of terpyridine ligands. Using single crystal X-ray diffraction studies, we show that the presence of synergistic platinum-platinum (PtMIDLINE HORIZONTAL ELLIPSISPt) metallopolymerization and fluorine-fluorine (FMIDLINE HORIZONTAL ELLIPSISF) interactions are the major driving forces in achieving hierarchical superstructures. The resulting bright red gels showed the presence of highly entangled three-dimensional networks and helical nanofibres with both (P and M) handedness. The gels recover up to 87% of their original storage modulus even after several cycles under oscillatory step-strain rheological measurements showing rapid self-healing. The luminescence properties, along with thermo- and mechanoresponsive gelation, provide the potential to utilize synthetically simple discrete complexes in advanced optical materials.

The self-assembly properties of nine low-molecular-weight gelators (LMWGs) based on bile acid alkyl amides were studied in detail. Based on the results, the number of hydroxyl groups attached to the steroidal backbone plays a major role in the gelation, although the nature of the aliphatic side chain also modulates the gelation abilities. Of the 50 gel systems studied, 35 are based on lithocholic acid and 15 on cholic acid derivatives. The deoxycholic acid derivatives did not form any gels. The gelation occurred primarily in aromatic solvents and the gels manifested typical fibrous or spherical morphologies. The 13C cross-polarized magic angle spinning (CPMAS) NMR spectra measured on the crystalline materials and the corresponding wet organogels were analogous, suggesting that the chemical environments, that is, the intermolecular interactions found in the two materials were similar. The single-crystal X-ray structures of all nine bile-acid amide derivatives studied revealed very similar molecular conformations in the solid state and gave insights into the possible intermolecular interactions in the gel state. peerReviewed

This study presents the reactive self-assembly of isocyanate functional and amphiphilic six-arm, star-shaped polyether prepolymers in water into nanogels. Intrinsic molecular amphiphilicity, mainly driven by the isophorone moiety at the distal endings of the star-shaped molecules, allows for the preparation of spherical particles with an adjustable size of 100-200 nm by self-assembly and subsequent covalent cross-linking without the need for organic solvents or surfactants. Covalent attachment of a fluorescence dye and either the cell-penetrating TAT peptide or a random control peptide sequence shows that only TAT-labeled nanogels are internalized by HeLa cells. The nanogels thus specifically enter the cells and accumulate in the perinuclear area in a time- and concentration-dependent manner.

Herein we report a multi‐component reaction approach for the development of a new class of hydrogelators based on the OxoTriphenylHexanOate (OTHO) backbone. A focused library of OTHOs has been synthesized and their hydrogelation features evaluated. The two most potent hydrogelators were studied by rheology revealing different stiffness, appearances and thixotropic behavior of the gels. The new gelators showcase the versatility of the OTHO backbone as a platform for the design of functionalized hydrogels with tunable gel properties. peerReviewed

Simple ML2 [M = Fe(II), Co(II), Ni(II)] complexes obtained from a perfluoroalkylamide derivative of 4-aminophenyl-2,2′,6,2′-terpyridine spontaneously, yet anion selectively, self-assemble into gels, which manifest an unprecedented rapid gel strength recovery, viz. self-healing, and thermal rearrangement in aqueous dimethyl sulfoxide. The key factor for gelation and rheological properties emerges from the fluorine–fluorine interactions between the perfluorinated chains, as the corresponding hydrocarbon derivative did not form metallogels. The perfluoro-terpyridine ligand alone formed single crystals, while its Fe(II), Co(II) or Ni(II) complexes underwent rapid gelation leading to highly entangled fibrillar networks visualized by electron microscopy. The thermodynamic parameters of gelation based on variable temperature NMR 1H and 19F resonances showed that gelation was enthalpically favourable and entropically disfavourable. The step strain rheological experiments revealed that the gels undergo rapid self-healing and the morphological features, thermal stability and mechanical properties were found to depend on the nature of the metal ion. peerReviewed

Caffeine (a stimulant) and ethanol (a depressant) may have opposite effects in our body, but under in vitro conditions they can “gel” together. Caffeine, being one of the widely used stimulants, continued to surprise the scientific community with its unprecedented biological, medicinal and physicochemical properties. Here, we disclose the supramolecular self-assembly of anhydrous caffeine in a series of alcoholic and aromatic solvents, rendering a highly entangled microcrystalline network facilitating the encapsulation of the solvents as illustrated using direct imaging, microscopy analysis and NMR studies.

Tutkielman kirjallisessa osassa perehdyttiin siihen, kuinka kemialliset ja fysikaaliset tekijät vaikuttavat geelin muodostukseen ja siihen, kuinka näillä ärsykkeillä voidaan vaikuttaa geelin rakenteeseen, ominaisuuksiin tai olomuotoon. Kokeellisessa osassa tutkittiin kuinka jäähtymisprofiilin vaikutusta geelinmuodostuksen nopeuteen ja geelin rakenteeseen. Kokeissa käytettiin gelaattorina koolihapon ja L-metioniinimetyyliesterin amidia, joka liuotettiin ultraäänikäsittelyn ja lämmityksen avulla eri liuottimiin, jotka olivat o-ksyleeni, tolueeni, bentseeni ja tert-butyylibentseeni. Pääasiallisena tutkinnan kohteina olivat tolueenin, bentseenin ja tert-butyylibentseenin ja gelaattorin muodostamat geelit. Jäähdytysmenetelminä käytettiin normaalin huoneenlämpötilassa jäähdytyksen lisäksi jää- ja nestetyppijäähdytyksiä. Geelirakenteiden eroja pyrittiin selvittämään tutkimalla geeliä pyykäisyelektromikroskoopilla. Tämän lisäksi gelaattorin bentseenin ja tolueenin kanssa muodostamista geeleistä ajettiin VT NMR -spektrit välillä 30-70 oC. Bentseenissä muodostuneesta geelistä mitattiin myös 13C CPMAS NMR -spektri. Sen lisäksi, että työssä pyrittiin selvittämään jäähdytysnopeuden vaikutuksia geelin muodostumiseen ja rakenteeseen, selvitettiin eri menetelmien etuja ja haittoja SEM-näytteitä valmistettaessa. Menetelmistä tutkittiin voitelua, ilmakuivausta ja pakastekuivausta. Tulosten perusteella jäähdytyksen nopeus oli suoraan verrannollinen geelinmuodostusnopeuteen. Eri jäähdytysmenetelmillä saaduissa VT NMR- ja 13C CPMAS NMR –spektreissä ei havaittu suuria eroja, mutta pakastekuivaamalla valmistetuissa bentseenigeelinäytteissä eroja eri jäähdytysmenetelmillä saatujen geelien välillä havaittiin. Kun liuottimena käytettiin bentseeniä ja geeli muodostettiin antamalla sen jäähtyä huoneenlämpötilassa tai jäähdyttämällä sitä jäähauteessa, geelin perusrakenteen muodostavissa kennoissa havaittiin rihmastoa. Kun jäähdytys suoritettiin nestetyppihauteessa, tämä rihmasto puuttui täysin. Lisäksi nestetyppihauteessa jäähdytetystä geelistä muodostettu kserogeeli oli heikompi hitaammin jäähdytetyistä geeleistä muodostettuihin kserogeeleihin verrattuna. Tert-butyylibentseenigeelin rakenteen muodostaneet pallomaiset partikkelit vääristyivät nopean jäähdytyksen vuoksi. SEM-näytteenvalmistusmenetelmistä pakastekuivaus antoi selkeästi eniten tietoa geelin rakenteesta, mutta näytteen valmistus onnistui vain bentseenissä muodostuneista geeleistä. Ilmakuivaus tuotti enimmäkseen kiinteitä näytteitä, kun taas voitelemalla valmistetut näytteet enimmäkseen kasautuivat.

The research described in this thesis covers the synthesis, characterization and the study of the gelation ability of fteen pyrene based low molecular weight organogelators (LMOGs). The gelation and gel properties were investigated by rheometry, scanning electron microscopy, di erential scanning calorimetry, UV-Vis and uorescence spectroscopy. The pyrene based LMOGs form complexes with 2,4,7-trinitro uorenone (TNF) and self-assemble non-covalently through - stacking, donor-acceptor and van der Waals interactions to form thermoreversible gels, which remain stable at least for two years. The strongest gels were obtained in primary alcohols whereas the poor solubility of TNF restricted gelation in nonpolar hydrocarbons. It was observed that the gelation behavior of the two-component gelator system can be estimated in both nonpolar and polar solvents by using the Hansen solubility parameters and distance. The unknown solubility parameters of the gelators were estimated by a group contribution method. The gelation ability of the two-component system was found to correlate with the hydrogen bonding solubility parameter of the solvent. Electron microscopy showed that the gelation occurs due to self-assembly of the gelators into long gel bers that form an entangled gel network. The solvent and the structure of the pyrene based LMOG have a large e ect on the gel structure and; consequently, the properties. The gels with less ber bundles and denser gel network were more elastic and had higher stability and viscosity. The organogels are viscoelastic soft materials showing shear thinning behavior and a yield point. The e ect of the solvent, additives like pyrene, crosslinker molecule and aluminum nanoparticles, functionality and alkyl side chain length of the pyrene based gelator on the gel properties were studied by rheometry. The results of this work indicate that two- and three-component gelator systems open wide possibilities to control the gel properties in various solvents.