Browsing by Author "Nonappa, Nonappa"

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Caffeine as a gelator
(2016-03-02) Nonappa, Nonappa; Kolehmainen, Erkki
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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.
Cationic polymers for DNA origami coating-examining their binding efficiency and tuning the enzymatic reaction rates
(2016-06-14) Kiviaho, Jenny; Linko, Veikko; Ora, Ari; Tiainen, Tony; Järvihaavisto, Erika; Mikkilä, Joona; Tenhu, Heikki; Nonappa, Nonappa; Kostiainen, Mauri A.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
DNA origamis are fully tailored, programmable, biocompatible and readily functionalizable nanostructures that provide an excellent foundation for the development of sophisticated drug-delivery systems. However, the DNA origami objects suffer from certain drawbacks such as low cell-transfection rates and low stability. A great deal of studies on polymer-based transfection agents, mainly focusing on polyplex formation and toxicity, exists. In this study, the electrostatic binding between a brick-like DNA origami and cationic block-copolymers was explored. The effect of the polymer structure on the binding was investigated and the toxicity of the polymer-origami complexes evaluated. The study shows that all of the analyzed polymers had a suitable binding efficiency irrespective of the block structure. It was also observed that the toxicity of polymer-origami complexes was insignificant at the biologically relevant concentration levels. Besides brick-like DNA origamis, tubular origami carriers equipped with enzymes were also coated with the polymers. By adjusting the amount of cationic polymers that cover the DNA structures, we showed that it is possible to control the enzyme kinetics of the complexes. This work gives a starting point for further development of biocompatible and effective polycation-based block copolymers that can be used in coating different DNA origami nanostructures for various bioapplications.
Cooperative colloidal self-assembly of metal-protein superlattice wires
(2017-09-22) Liljeström, Ville; Ora, Ari; Hassinen, Jukka; Rekola, Heikki; Nonappa, Nonappa; Heilala, Maria; Hynninen, Ville; Joensuu, Jussi J.; Ras, Robin; Törmä, Päivi; Ikkala, Olli; Kostiainen, Mauri
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Material properties depend critically on the packing and order of constituent units throughout length scales. Beyond classically explored molecular self-assembly, structure formation in the nanoparticle and colloidal length scales have recently been actively explored for new functions. Structure of colloidal assemblies depends strongly on the assembly process, and higher structural control can be reliably achieved only if the process is deterministic. Here we show that self-assembly of cationic spherical metal nanoparticles and anionic rod-like viruses yields well-defined binary superlattice wires. The superlattice structures are explained by a cooperative assembly pathway that proceeds in a zipper-like manner after nucleation. Curiously, the formed superstructure shows right-handed helical twisting due to the right-handed structure of the virus. This leads to structure-dependent chiral plasmonic function of the material. The work highlights the importance of well-defined colloidal units when pursuing unforeseen and complex assemblies.
Crystalline Cyclophane–Protein Cage Frameworks
(2018-07-13) Beyeh, Ngong; Nonappa, Nonappa; Liljeström, Ville; Mikkilä, Joona; Korpi, Antti; Bochicchio, Davide; Pavan, Giovanni M.; Ikkala, Olli; Ras, Robin H. A.; Kostiainen, Mauri
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Cyclophanes are macrocyclic supramolecular hosts famous for their ability to bind atomic or molecular guests via noncovalent interactions within their well-defined cavities. In a similar way, porous crystalline networks, such as metal–organic frameworks, can create microenvironments that enable controlled guest binding in the solid state. Both types of materials often consist of synthetic components, and they have been developed within separate research fields. Moreover, the use of biomolecules as their structural units has remained elusive. Here, we have synthesized a library of organic cyclophanes and studied their electrostatic self-assembly with biological metal-binding protein cages (ferritins) into ordered structures. We show that cationic pillar[5]arenes and ferritin cages form biohybrid cocrystals with an open protein network structure. Our cyclophane–protein cage frameworks bridge the gap between molecular frameworks and colloidal nanoparticle crystals and combine the versatility of synthetic supramolecular hosts with the highly selective recognition properties of biomolecules. Such host–guest materials are interesting for porous material applications, including water remediation and heterogeneous catalysis.
Electrical behaviour of native cellulose nanofibril/carbon nanotube hybrid aerogels under cyclic compression
(2016) Wang, Miao; Anoshkin, Ilya V.; Nasibulin, Albert G.; Ras, Robin H A; Nonappa, Nonappa; Laine, Janne; Kauppinen, Esko I.; Ikkala, Olli
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Hybrid aerogels consisting of cellulose nanofibers (CNF) and modified few-walled carbon nanotubes (FWCNT) are investigated under cyclic mechanical compression to explore "electrical fatigue". For this purpose the FWCNTs were hydrophilized, thus promoting their aqueous dispersibility to allow FWCNT/CNF hybrid hydrogels, followed by freeze-drying to obtain hybrid aerogels. The optimized composition consisting of FWCNT/CNF 20/80 wt/wt showed conductivity of 10-5 S cm-1 as promoted due to double percolation, and showed only small changes in electrical and mechanical behaviour upon cycling 100 times. The electrical behaviour under cycled compression shows good stability and reversibility.
Electron Tomography of Whole Mounts
(2019-06-21) Nonappa, Nonappa; Engelhardt, Peter
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Rapid progress in the instrumentation, sample preparation methods, and computational power have triggered a revolution in electron tomography methods. Herein, we adapted a straightforward freeze-drying method using tert-butanol for electron tomography of whole mount colloids. This approach will overcome some of the common artifacts in electron microscopy specimen preparation.
Engineered protein cages for selective heparin encapsulation
(2021-02-07) Välimäki, Salla; Liu, Qing; Schoonen, Lise; F. M. Vervoort, Daan; Nonappa, Nonappa; Linko, Veikko; Nolte, Roeland J. M.; C. M. van Hest, Jan; Kostiainen, Mauri
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
A heparin-specific binding peptide was conjugated to a cowpea chlorotic mottle virus (CCMV) capsid protein, which was subsequently allowed to encapsulate heparin and form capsid-like protein cages. The encapsulation is specific and the capsid-heparin assemblies display negligible hemolytic activity, indicating proper blood compatibility and promising possibilities for heparin antidote applications.
Experimental and Simulation Study of the Solvent Effects on the Intrinsic Properties of Spherical Lignin Nanoparticles
(2021-11-11) Zou, Tao; Nonappa, Nonappa; Khavani, Mohammad; Vuorte, Maisa; Penttilä, Paavo; Zitting, Aleksi; Valle-Delgado, Juan José; Elert, Anna Maria; Silbernagl, Dorothee; Balakshin, Mikhail; Sammalkorpi, Maria; Österberg, Monika
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Spherical lignin nanoparticles (LNPs) fabricated via nanoprecipitation of dissolved lignin are among the most attractive biomass-derived nanomaterials. Despite various studies exploring the methods to improve the uniformity of LNPs or seeking more application opportunities for LNPs, little attention has been given to the fundamental aspects of the solvent effects on the intrinsic properties of LNPs. In this study, we employed a variety of experimental techniques and molecular dynamics (MD) simulations to investigate the solvent effects on the intrinsic properties of LNPs. The LNPs were prepared from softwood Kraft lignin (SKL) using the binary solvents of aqueous acetone or aqueous tetrahydrofuran (THF) via nanoprecipitation. The internal morphology, porosity, and mechanical properties of the LNPs were analyzed with electron tomography (ET), small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), and intermodulation AFM (ImAFM). We found that aqueous acetone resulted in smaller LNPs with higher uniformity compared to aqueous THF, mainly ascribing to stronger solvent–lignin interactions as suggested by MD simulation results and confirmed with aqueous 1,4-dioxane (DXN) and aqueous dimethyl sulfoxide (DMSO). More importantly, we report that both LNPs were compact particles with relatively homogeneous density distribution and very low porosity in the internal structure. The stiffness of the particles was independent of the size, and the Young’s modulus was in the range of 0.3–4 GPa. Overall, the fundamental understandings of LNPs gained in this study are essential for the design of LNPs with optimal performance in applications.
Fabrication of biopolymer-based optical fibers for short-distance applications
(2021-12-14) Sanouillet, Alizée
Perustieteiden korkeakoulu | Master's thesis
The extraordinary ability of optical fibers to control and propagate light has sparked a revolution in modern high-capacity communication networks. Beyond data networks, the state-of-the-art glass and plastic optical fibers have also been studied for numerous biomedical applications, including laser surgery, optogenetics, phototherapy and biosensing. However, commercial optical fibers have several disadvantages due to their brittle nature, non-biocompatibility and non-degradability necessary for biomedical applications. Therefore, there is a need to develop optical fibers from biopolymers that are biocompatible and biodegradable. Because of their biocompatible nature, biopolymer optical fibers can remain in the human body for a long time without iliciting an immune response. Because of their biodegradable nature, surgical removal after their use is not necessary. This thesis aimed to identify critical parameters to fabricate and characterize biopolymer optical fibers using environmentally benign fiber spinning methods. Three types of biopolymers, viz., alginate, carboxymethylcellulose and methylcellulose, were used for fiber preparation. The hydrogels prepared from the biopolymers were used for fiber extrusion using either wet-spinning or dry-jet wet spinning. The fibers were ionically cross-linked using metal ions under ambient conditions. The resulting fibers were then optically characterized for their waveguiding properties using the cutback method. The optical characterization suggests that the alginates-based fibers are not suitable for waveguiding due to very little light propagation. Interestingly, carboxymethylcellulose fibers displayed very low optical loss. This is on par or better than biopolymer optical fibers reported in the literature. The results encourage to explore further the potential of naturally abundant and renewable biomaterials for short-distance optical fibers.
Halogenation Dictates Architecture of Amyloid Peptide Nanostructures
(2017) Pizzi, Andrea; Pigliacelli, Claudia; Gori, Alessandro; Nonappa, Nonappa; Ikkala, Olli; Demitri, Nicola; Terraneo, Giancarlo; Castelletto, Valeria; Hamley, Ian W.; Bombelli, Francesca Baldelli; Metrangolo, Pierangelo
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Amyloid peptides yield a plethora of interesting nanostructures though difficult to control. Here we report that depending on the number, position, and nature of the halogen atoms introduced at either one or both phenylalanine benzene rings of the amyloid [small beta] peptide-derived core-sequence KLVFF, four different architectures were obtained in a controlled manner. Our findings demonstrate halogenation may develop as a general strategy to engineer amyloidal peptide self-assembly and obtain new amyloidal nanostructures.
Hierarchical self-assembly from nanometric micelles to colloidal spherical superstructures
(2017) Bertula, Kia; Nonappa, Nonappa; Myllymäki, Teemu T.T.; Yang, Hongjun; Zhu, Xiaoxia; Ikkala, Olli
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We report sequential self-assembly of low molecular weight asymmetric star-like polymers from nanometric spherical micelles (core diameter 8–12 nm) to colloidal spherical superstructures (d > 500–1000 nm) in aqueous media, as directed by quadruple hydrogen bonding moieties activated by solvent exchanges. The molecules consist of a rigid asymmetric steroidal cholic acid (CA) core, whose hydroxyl groups are first grafted with four oligomeric allyl glycidyl ether (AGE) chains involving six repeat units. The allylic double bonds are thiol-clicked with cysteamine (HS-(CH2)2-NH2), and in the final step their amino end groups are conjugated with 2-ureido-4[1H]-pyrimidinone (UPy) via isocyanate chemistry using UPy-(CH2)6-NCO to obtain asymmetric star-like facially amphiphilic molecules denoted as CA[(AGE-NH2)6]4-(UPy)n. They self-assemble into spherical micelles in dimethyl sulfoxide (DMSO), which suppresses the dimerization of UPys. Solvent exchange from DMSO to water activates the inter-micellar hydrogen bonds via the peripheral UPy units, which triggers the formation of spherical submicron to micron scale superstructures. Based on three-dimensional (3D) reconstruction using transmission electron tomography (ET), we show that such structures are composed of densely packed micellar network. Our work shows that surfactant-like molecules, characteristically leading to micelles, can undergo complex and hierarchical self-assembly to microscale by equipping the solubilising chains with hydrogen bonding units that can be switched ON and OFF by sequential solvent exchanges.
Hierarchical Supramolecular Cross-Linking of Polymers for Biomimetic Fracture Energy Dissipating Sacrificial Bonds and Defect Tolerance under Mechanical Loading
(2017-02-15) Myllymäki, Teemu T. T.; Lemetti, Laura; Nonappa, Nonappa; Ikkala, Olli
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Biological structural materials offer fascinating models how to synergistically increase the solid-state defect tolerance, toughness, and strength using nanocomposite structures by incorporating different levels of supramolecular sacrificial bonds to dissipate fracture energy. Inspired thereof, we show how to turn a commodity acrylate polymer, characteristically showing a brittle solid state fracture, to become defect tolerant manifesting noncatastrophic crack propagation by incorporation of different levels of fracture energy dissipating supramolecular interactions. Therein, poly(2-hydroxyethyl methacrylate) (pHEMA) is a feasible model polymer showing brittle solid state fracture in spite of a high maximum strain and clear yielding, where the weak hydroxyl group mediated hydrogen bonds do not suffice to dissipate fracture energy. We provide the next level stronger supramolecular interactions toward solid-state networks by postfunctionalizing a minor part of the HEMA repeat units using 2-ureido-4[1H]-pyrimidinone (UPy), capable of forming four strong parallel hydrogen bonds. Interestingly, such a polymer, denoted here as p(HEMA-co-UPyMA), shows toughening by suppressed catastrophic crack propagation, even if the strength and stiffness are synergistically increased. At the still higher hierarchical level, colloidal level cross-linking using oxidized carbon nanotubes with hydrogen bonding surface decorations, including UPy, COOH, and OH groups, leads to further increased stiffness and ultimate strength, still leading to suppressed catastrophic crack propagation. The findings suggest to incorporate a hierarchy of supramolecular groups of different interactions strengths upon pursuing toward biomimetic toughening.
Highly Luminescent Gold Nanocluster Frameworks
(2019) Chandra, Sourov; Nonappa, Nonappa; Beaune, Grégory; Som, Anirban; Zhou, Shaochen; Lahtinen, Jouko; Jiang, Hua; Timonen, Jaakko; Ikkala, Olli; Ras, Robin
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Metal nanoclusters (NCs) are being intensely pursued as prospective luminophores because of their tunable electronic and optical properties. Among the various fluorescent NCs, gold nanoclusters (GNCs) are attractive due to their biocompatibility and excellent photostability, even if so far, they have had limited application potential due to poor quantum yield (QY). In this context, a facile route is demonstrated to tune up the photophysical and photochemical activities of water‐borne luminescent GNCs through the formation of self‐assembled nanocluster superstructures. The approach involves the controlled introduction of Sn2+ ions, directing GNCs from individual particles into 3D spherical gold nanocluster colloidal frameworks (GNCFs). In these, the reduction in the nonemissive relaxation pathways leads to significant enhancement of luminescence signals (QY from ≈3.5% to ≈25%), likely owing to restricted movements of ligands. This approach paves ways for GNCFs as a potent agent for biomedical imaging and therapies, while their high photocatalytic activity is an added advantage
Hydrogen bonding asymmetric star-shape derivative of bile acid leads to supramolecular fibrillar aggregates that wrap into micrometer spheres
(2016-08-28) Myllymäki, Teemu; Nonappa, Nonappa; Yang, Hongjun; Liljeström, Ville; Kostiainen, Mauri A.; Malho, Jani-Markus; Zhu, X. X.; Ikkala, Olli
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We report that star-shaped molecules with cholic acid cores asymmetrically grafted by low molecular weight polymers with hydrogen bonding end-groups undergo aggregation to nanofibers, which subsequently wrap into micrometer spherical aggregates with low density cores. Therein the facially amphiphilic cholic acid (CA) is functionalized by four flexible allyl glycidyl ether (AGE) side chains, which are terminated with hydrogen bonding 2-ureido-4[1H]pyrimidinone (UPy) end-groups as connected by hexyl spacers, denoted as CA(AGE6-C6H12-UPy)4. This wedge-shaped molecule is expected to allow the formation of a rich variety of solvent-dependent structures due to the complex interplay of interactions, enabled by its polar/nonpolar surface-active structure, the hydrophobicity of the CA in aqueous medium, and the possibility to control hydrogen bonding between UPy molecules by solvent selection. In DMSO, the surfactant-like CA(AGE6-C6H12-UPy)4 self-assembles into nanometer scale micelles, as expected due to its nonpolar CA apexes, solubilized AGE6-C6H12-UPy chains, and suppressed mutual hydrogen bonds between the UPys. Dialysis in water leads to nanofibers with lateral dimensions of 20-50 nm. This is explained by promoted aggregation as the hydrogen bonds between UPy molecules start to become activated, the reduced solvent dispersibility of the AGE-chains, and the hydrophobicity of CA. Finally, in pure water the nanofibers wrap into micrometer spheres having low density cores. In this case, strong complementary hydrogen bonds between UPy molecules of different molecules can form, thus promoting lateral interactions between the nanofibers, as allowed by the hydrophobic hexyl spacers. The wrapping is illustrated by transmission electron microscopy tomographic 3D reconstructions. More generally, we foresee hierarchically structured matter bridging the length scales from molecular to micrometer scale by sequentially triggering supramolecular interactions.
Hydrogen Bonding Directed Colloidal Self-Assembly of Nanoparticles into 2D Crystals, Capsids, and Supracolloidal Assemblies
(2018-07) Nonappa, Nonappa; Ikkala, Olli
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Self-assembly of colloidal building blocks, like metal nanoparticles, is a rapidly progressing research area toward new functional materials. However, in-depth control of the colloidal self-assembly and especially hierarchical self-assembly is difficult due to challenges in controlling the size dispersities, shape/morphology, directionalities, and aggregation tendencies. Using either polydispersed or narrow-size dispersed nanoparticles, considerable progress has been achieved over the past few years. However, absolutely monodisperse nanoparticles could allow new options for rational designs of self-assemblies. Therein, atomically precise monolayer protected nanoclusters (d < 3 nm) have recently been synthesized with well-defined metal cores and surface ligands. Their dispersion behavior is commonly tuned by surfactant-like ligands. Beyond that, this study deals with approaches based on ligand-driven supramolecular interactions and colloidal monodispersity until atomic precision to tune the colloidal self-assembly and hierarchy from nanoscale to mesoscopic scale. Therein colloidal packing to self-assembled 2D crystals and closed virus capsid-inspired shells provide relevant research goals due to ever increasing potential of 2D materials and encapsulation. This study addresses the hydrogen bonding (H-bonding) directed self-assembly of atomically precise gold and silver nanoparticles and narrow size dispersed cobalt nanoparticles to free-standing 2D colloidal nanosheets, nanowire assemblies, capsid-like colloidal closed shells, as well as higher order structures.
In vivo self-assembly mechanisms of ferritin fusion proteins
(2018-08-20) Pääsky, Heini
Kemian tekniikan korkeakoulu | Master's thesis
Ferritins are spherical iron storage proteins and widely studied protein building blocks for many biomaterial applications. These protein particles are known to assemble into two-dimensional sheets into hexagonal plane. However, a ferritin fusion protein GFP-resilin-ferritin produced at VTT Ltd formed unprecedented spear-like supramolecularly self-assembled structures. The aim of this thesis was to gain molecular level insights into its self-assembly mechanisms. In this thesis, five fusion protein constructs were produced and their in vivo supramolecular assemblies were examined. Trichoderma reesei strain producing GFP-resilin-ferritin was cultivated and visualized with confocal microscopy for studying in vivo self-assembly mechanisms. Purification procedures including sonication and homogenization by mixer mill were attempted. New constructs expressing ferritin and HFBI-ferritin were designed, cloned and agroinfiltrated to Nicotiana benthamiana tobacco plants. Also, resilin fusion proteins ZERA-resilin and GFP-resilin-HFBI were expressed N. benthamiana. These four fusion proteins were purified from ground leaves by sucrose gradient ultracentrifugation. The in vivo self-assembly mechanisms of the fusion proteins were studied by confocal microscopy, whereas purified fusion proteins were investigated also by conventional and cryogenic transmission electron microscopy (Cryo-TEM) imaging. The new ferritin construct self-assembled into long thin spears similar to those of GFP-resilin-ferritin, thus indicating that ferritin would drive the spear-like self-assembly. Resilin fusion proteins ZERA-resilin and GFP-resilin-HFBI formed only spherical PBs, so it is suggested that resilin does not have an impact to spear-like assembly of GFP-resilin-ferritin. HFBI-ferritin formed spherical PB-like structures, which is likely due to PB-inducing fusion protein partner HFBI. Purified ferritin fusion proteins did not show similar self-assembled structures when observed with TEM. These observations provide insights for recombinant protein self-assembly research.
Infinite coordination polymer networks: metallogelation of aminopyridine conjugates and in situ silver nanoparticle formation
(2019-01-01) Tatikonda, Rajendhraprasad; Bulatov, Evgeny; Özdemir, Zulal; Nonappa, Nonappa; Haukka, Matti
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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.
Integration of Carboxymethyl Cellulose Waveguides for Smart Textile Optical Sensors
(2022-12-08) Guridi Sotomayor, Sofia; Hokkanen, Ari; Jaiswal, Aayush Kumar; Nonappa, Nonappa; Kääriäinen, Pirjo
A4 Artikkeli konferenssijulkaisussa
The development of novel textile materials capable of controlled interaction with the environment has contributed to the growth of smart textiles. Nevertheless, the ubiquitous integration of plastic and electronic components into textile structures will bring new challenges regarding the use of material resources and waste management. Focusing on this problem, the present work explores the use of carboxymethyl cellulose (CMC)-based optical waveguides to create textile-based optical sensors. Following an interdisciplinary approach, the research was conducted by combining methods from textile design, material science, and photonics. CMC optical fiber and planar waveguide were compared in corresponding textile structures. We present the laboratory testing results of initial proof of concept samples of bio-based woven smart textiles demonstrating their touch, bending.. and water optical sensing capabilities.
Inverse Thermoreversible Mechanical Stiffening and Birefringence in a Methylcellulose/Cellulose Nanocrystal Hydrogel
(2018-07-09) Hynninen, Ville; Hietala, Sami; McKee, Jason R.; Murtomäki, Lasse; Rojas Gaona, Orlando; Ikkala, Olli; Nonappa, Nonappa
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We show that composite hydrogels comprising methyl cellulose (MC) and cellulose nanocrystal (CNC) colloidal rods display a reversible and enhanced rheological storage modulus and optical birefringence upon heating, i.e., inverse thermoreversibility. Dynamic rheology, quantitative polarized optical microscopy, isothermal titration calorimetry (ITC), circular dichroism (CD), and scanning and transmission electron microscopy (SEM and TEM) were used for characterization. The concentration of CNCs in aqueous media was varied up to 3.5 wt % (i.e, keeping the concentration below the critical aq concentration) while maintaining the MC aq concentration at 1.0 wt %. At 20 °C, MC/CNC underwent gelation upon passing the CNC concentration of 1.5 wt %. At this point, the storage modulus (G′) reached a plateau, and the birefringence underwent a stepwise increase, thus suggesting a percolative phenomenon. The storage modulus (G′) of the composite gels was an order of magnitude higher at 60 °C compared to that at 20 °C. ITC results suggested that, at 60 °C, the CNC rods were entropically driven to interact with MC chains, which according to recent studies collapse at this temperature into ring-like, colloidal-scale persistent fibrils with hollow cross-sections. Consequently, the tendency of the MC to form more persistent aggregates promotes the interactions between the CNC chiral aggregates towards enhanced storage modulus and birefringence. At room temperature, ITC shows enthalpic binding between CNCs and MC with the latter comprising aqueous, molecularly dispersed polymer chains that lead to looser and less birefringent material. TEM, SEM, and CD indicate CNC chiral fragments within a MC/CNC composite gel. Thus, MC/CNC hybrid networks offer materials with tunable rheological properties and access to liquid crystalline properties at low CNC concentrations.
Light-Triggered Reversible Supracolloidal Self-Assembly of Precision Gold Nanoclusters
(2020-03-25) Rival, Jose V.; Nonappa, Nonappa; Shibu, Edakkattuparambil Sidharth
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Monolayer thiol-protected noble metal nanoclusters are attractive nanoscale building blocks for well-defined colloidal superstructures. However, achieving facile reversible self-assembly of nanoclusters using external stimuli is still in its infancy. Herein, we report the synthesis and photon-assisted reversible self-assembly of thiolated azobenzene-stapled Au25 nanoclusters. Photoactivation of functionalized nanoclusters in dichloromethane by irradiating ultraviolet light at 345 nm results in a visual change and formation of disc-like colloidal superstructures (d ∼100-1000 nm). The superstructures readily disassemble into individual nanoclusters upon irradiating with visible light at 435 nm. Systematic changes in both the electronic absorption bands and nuclear magnetic resonance spectra of chromophores in solution suggest that the photoisomerization of surface ligands drives the self-assembly. High-resolution transmission electron microscopy, electron tomographic reconstruction, dynamic light scattering, and small-angle X-ray powder diffraction show that the disc-like superstructures contain densely packed nanoclusters. Long-range self-assembly and disassembly under ultraviolet and visible light, respectively, demonstrate reversible photoswitching in nanoclusters.