Browsing by Subject "Supramolecular chemistry"

Now showing 1 - 20 of 22

Open Access
A [5]Rotaxane-Based photosensitizer for photodynamic therapy
(WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Özkan, Melis; Keser, Yağmur; Hadi, Seyed Ehsan; Tuncel, Dönüş
A [5]rotaxane was synthesized through a catalytically self‐threading reaction in which CB6 serves as a macrocycle and acts as a catalyst for the 1,3‐dipolar cycloaddition reaction between the alkyne substituted porphyrin core and azide functionalized stopper groups by forming triazole. Application of this rotaxane as a photosensitizer in photodynamic therapy against cancer cells and in bacteria inactivation have also been demonstrated. This photosensitizer has an excellent water solubility and remains stable in biological media at physiological pH (7.4) for prolonged times. It has the ability to generate singlet oxygen efficiently; while it shows no dark cytotoxicity up to 300 µm to the MCF7 cancer cell line, it is photocytotoxic even at 2 µm and reduces the cell viability to around 70 % when exposed to white light. It also displays light‐triggered biocidal activity both against gram‐negative bacteria (Escherichia coli, E. coli) and gram‐positive bacteria (Bacillus subtilis). Upon white light irradiation for 1 min with a flux of 22 mW/cm2 of E. coli suspension incubated with [5]rotaxane (3.5 µm), a killing efficiency of 96 % is achieved, whereas in the dark the effect is recorded as only around 9 %.
Open Access
Bioactive supramolecular peptide nanofibers for regenerative medicine
(Wiley, 2014) Arslan, Elif; Garip, I. Ceren; Gulseren, Gulcihan; Tekinay, Ayse B.; Güler, Mustafa O.
Recent advances in understanding of cell-matrix interactions and the role of the extracellular matrix (ECM) in regulation of cellular behavior have created new perspectives for regenerative medicine. Supramolecular peptide nanofiber systems have been used as synthetic scaffolds in regenerative medicine applications due to their tailorable properties and ability to mimic ECM proteins. Through designed bioactive epitopes, peptide nanofiber systems provide biomolecular recognition sites that can trigger specific interactions with cell surface receptors. The present Review covers structural and biochemical properties of the self-assembled peptide nanofibers for tissue regeneration, and highlights studies that investigate the ability of ECM mimetic peptides to alter cellular behavior including cell adhesion, proliferation, and/or differentiation.
Open Access
Biocompatible supramolecular catalytic one-dimensional nanofibers for efficient labeling of live cells
(American Chemical Society, 2015) Khalily, M. A.; Gulseren, G.; Tekinay, A. B.; Güler, Mustafa O.
Understanding complex cellular functions requires study and tracking of biomolecules such as proteins, glycans, and lipids in their natural environment. Herein, we report the first supramolecular nanocatalyst for bioorthogonal click reaction to label live cells. This biocompatible and biodegradable nanocatalyst was formed by self-assembled peptide nanofibers complexed with copper ions. The supramolecular nanocatalyst enhanced azide-alkyne cycloaddition reaction rate under physiological conditions and was shown to be useful for efficient bioorthogonal labeling of live cells.
Open Access
“Clicked” Porphyrin-cucurbituril conjugate: a new multifunctional supramolecular assembly based on triglycosylated porphyrin and Monopropargyloxycucurbit[7]uril
(Wiley-VCH Verlag, 2018) Koç, Ahmet; Khan, Rehan; Tuncel, Dönüş
The design, synthesis, and characterization of a new multifunctional supramolecular assembly based on a photoactive glycosylated porphyrin and covalently attached monofunctionalized cucurbit[7]uril (CB7) are reported. To obtain the target supramolecular assembly, azido-functionalized tetraphenylporphyrin (TPP) was used as a building block. TPP was first glycosylated by copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, then a monopropargyloxy-functionalized-CB7 unit was conjugated to glycosylated TPP with a second CuAAC reaction. The host-guest chemistry of the assembly was investigated by 1H NMR experiments to establish the availability of the CB7 as a host. The imidazole-based guest, which is known to have high affinity toward CB7, was observed to form inclusion complex with CB7. It was also demonstrated that this supramolecular assembly can serve as an efficient photosensitizer for the generation of singlet oxygen.
Open Access
Controlled enzymatic stability and release characteristics of supramolecular chiral peptide amphiphile nanofiber gels
(Elsevier B.V., 2017) Zengin, A.; Cinar, G.; Güler, Mustafa O.
Supramolecular bioarchitectures formed by assembly of achiral or chiral building blocks play important roles in various biochemical processes. Stereochemistry of amino acids is important for structural organization of peptide and protein assemblies and structure-microenvironment interactions. In this study, oppositely charged peptide amphiphile (PA) molecules with L-, D- and mixture of L- and D-amino acid conformations are coassembled into supramolecular nanofibers and formed self-supporting gels at pH 7.4 in water. The enzymatic stability of the PA nanofiber gels was studied in the presence of proteinase K enzyme, which digest a broad spectrum of proteins and peptides. The structural changes on the chiral PA nanofibers were also analyzed at different time periods in the presence of enzymatic activity. Controlled release of a model cargo molecule through the chiral PA nanofiber gels was monitored. The diffusivity parameters were measured for all gel systems. Release characteristics and the enzymatic stability of the peptide nanofiber gels were modulated depending on organization of the chiral PA molecules within the supramolecular assemblies.
Open Access
Cucurbituril-based supramolecular constructs for the diverse applications of nanomedicine
(2020-08) Özkan, Melis
The supramolecular chemistry of cucurbiturils (CBs) has been rapidly advancing to span wide range of nanomedicine applications including but not limited to pharmaceutical drug formulation and delivery, bio/medical imaging and sensing, cancer therapy, tissue engineering, development of antibacterial/antiviral agents and protein modification. Owing to unique recognition properties and low cytotoxicity, the supramolecular assemblies of CBs are particular promises for biomedicine tasks. Inspired by these developments, three multifunctional supramolecular constructs of CBs containing photoactive conjugated compounds were prepared to be utilized in nanomedicine applications covering antimicrobial and anticancer photodynamic therapy (PDT), combined PDT and photothermal therapy (PTT) for the inactivation of bacteria, drug delivery and cellular imaging. A stable rotaxane, namely [5]-rotaxane, based on photoactive alkynesubstituted porphyrin and azide-substituted stopper group was synthesized through 1,3-dipolar cycloaddition reaction. Herein, cucurbit[6]uril (CB6) acts as both macrocycle and catalysis for the reaction and encapsulates formed triazole ring inside its cavity. [5]-rotaxane was further investigated and results revealed that it has ability to generate reactive oxygen species (ROS) including singlet oxygens in high yield even under quite low fluence of light and short exposure time and this, in turn, renders it ideal photosensitizer which remains stable at physiological pH (7.4) for prolonged times. By taking the advantages of aforementioned properties, [5]-rotaxane was employed as a broad-spectrum antibacterial agent against Gram-negative and Gram-positive bacteria as well as anticancer agent against human breast cancer cell line (MCF-7) via visible-light-induced generation of ROS. [5]-rotaxane possess negligible dark cytotoxicity upon complexation with CB6 and it can afford efficacious PDT of cancer and infectious diseases caused by bacteria. Another multifunctional photoactive supramolecular assembly was built through covalently binding of four cucurbit[7]uril (CB7) molecules, functioning as receptor, to a tetraphenyl porphyrin core using suitable linkers. In addition to its light-promoted antibacterial property, here, main objective was to combine chemo- and photodynamic cancer therapy which makes this study novel. Presence of CB7, enables host-guest interactions with anticancer drug, doxorubicin hydrochloride (DOX), and therefore this system was used to carry drug molecules achieving synergistic PDT and chemotherapy. Finally, CB7-capped hybrid nanoparticles (NPs) made up of red-emitting conjugated oligomer (COL) and gold nanoparticles (Au-NPs) were obtained through one-pot synthetic method. These hybrid NPs were found to own high photostability, thermal reversibility and high ROS generation capacity. Benefitting from these properties, combined photodynamic and photothermal killing efficiency of NPs towards Gram-positive and Gram-negative bacteria was verified. Additionally, cellular imaging capability of them was shown owing to their inherently fluorescent characteristics and this feature could be utilized for image-guided PDT applications.
Open Access
Design and synthesis of self-assembling peptides for fabrication of functional nanomaterials
(2016-12) Khalily, Mohammad Aref
Self-assembling peptides are a class of supramolecular polymers, which exploit noncovalent interactions such as hydrogen bonding, hydrophobic, electrostatic, charge-transfer complex, π-π, and van der Waals interactions to generate well-defined supramolecular nanostructures including nanospheres, nanosheets, nanotubes, and nanofibers. These versatile peptide-based supramolecular nanomaterials have been utilized in variety of applications including catalysis, sensing, light harvesting, optoelectronic, bioelectronic and tissue engineering. In this thesis, use of supramolecular peptide nanofibers formed by specially designed short peptide sequences that can form sheet-like hydrogen bonded structures for controlled synthesis of nanometer scale functional materials were explored. Specifically, n-type and p-type β-sheet forming short peptide sequences were synthesized, which assemble separately into well-ordered nanofibers in aqueous media. These p-type and n-type nanofibers coassemble via hydrogen bonding and electrostatic interactions to generate highly uniform supramolecular n/p-coassembled 1D nanowires. This smart molecular design ensures alternating arrangement of D and A chromophores within n/p-coassembled supramolecular nanowires. Supramolecular n/p- coassembled nanowires were found to be formed by alternating A-D-A unit cells having an association constant of (KA) of 5 x 105 M-1. Moreover, I designed and synthesized β-sheet forming peptide nanofibers to fabricate different metal and metal oxide nanostructures in highly controlled manner using wet chemistry and atomic layer deposition techniques. These hybrid organic-inorganic nanostructures were employed in model Suzuki coupling, alkyne-azide cycloaddition and hydrolysis of ammonia borane reactions.
Open Access
The effect of cucurbit[n]uril on the solubility, morphology, and the photophysical properties of nonionic conjugated polymers in an aqueous medium
(2010) Tuncel, D.; Artar, M.; Hanay, S. B.
The effects of cucurbit[n]uril on the dissolution and the photophysical properties of nonionic conjugated polymers in water are described. For this purpose, a fluorine-based polymer, namely, poly[9,9-bis{6(N,N-dimethylamino) hexyl}fluorene-co-2,5-thienylene (PFT) was synthesized and characterized by spectroscopic techniques including 1D and 2D NMR, UV-vis, fluorescent spectroscopy, and matrix-assisted laser desorption mass spectrometry (MALDI-MS). For the first time, it was demonstrated that a nonionic conjugated polymer can be made soluble in water through an inclusion complex formation with CB8. The structure of the complex was elucidated by NMR experiments including 1H and selective 1D-NOESY. This complex emits green and is highly fluorescent with fluorescent quantum yield of 35%. In contrast, CB6 or water-soluble CB7 although they are chemically identical to CB8 do not have any effect on the dissolution and photophysical properties of PFT. By preparing a protonated version of PFT, the optical properties of PFT in methanol, protonated PFT and PFT@CB8 in water have been studied and compared. It was also observed that the morphology of the polymer PFT was affected by the presence of CB8. Thus CB8-assisted self-assembly of polymer chains leads to vesicles formation; these structures were characterized by DLS, AFM, SEM, and TEM fluorescent optical microscopy.
Open Access
Fabrication of supramolecular n/p-nanowires via coassembly of oppositely charged peptide-chromophore systems in aqueous media
(American Chemical Society, 2017-07) Khalily, M. A.; Bakan, G.; Kucukoz, B.; Topal, A. E.; Karatay, A.; Yaglioglu, H. G.; Dana, A.; Güler, Mustafa O.
Fabrication of supramolecular electroactive materials at the nanoscale with well-defined size, shape, composition, and organization in aqueous medium is a current challenge. Herein we report construction of supramolecular charge-transfer complex one-dimensional (1D) nanowires consisting of highly ordered mixed-stack π-electron donor-acceptor (D-A) domains. We synthesized n-type and p-type β-sheet forming short peptide-chromophore conjugates, which assemble separately into well-ordered nanofibers in aqueous media. These complementary p-type and n-type nanofibers coassemble via hydrogen bonding, charge-transfer complex, and electrostatic interactions to generate highly uniform supramolecular n/p-coassembled 1D nanowires. This molecular design ensures highly ordered arrangement of D-A stacks within n/p-coassembled supramolecular nanowires. The supramolecular n/p-coassembled nanowires were found to be formed by A-D-A unit cells having an association constant (KA) of 5.18 × 105 M-1. In addition, electrical measurements revealed that supramolecular n/p-coassembled nanowires are approximately 2400 and 10 times more conductive than individual n-type and p-type nanofibers, respectively. This facile strategy allows fabrication of well-defined supramolecular electroactive nanomaterials in aqueous media, which can find a variety of applications in optoelectronics, photovoltaics, organic chromophore arrays, and bioelectronics.
Open Access
Hierarchical self-assembly of histidine-functionalized peptide amphiphiles into supramolecular chiral nanostructures
(American Chemical Society, 2017) Koc, M. H.; Ciftci, G. C.; Baday, S.; Castelletto, V.; Hamley, I. W.; Güler, Mustafa O.
Controlling the hierarchical organization of self-assembling peptide amphiphiles into supramolecular nanostructures opens up the possibility of developing biocompatible functional supramolecular materials for various applications. In this study, we show that the hierarchical self-assembly of histidine- (His-) functionalized PAs containing d- or l-amino acids can be controlled by both solution pH and molecular chirality of the building blocks. An increase in solution pH resulted in the structural transition of the His-functionalized chiral PA assemblies from nanosheets to completely closed nanotubes through an enhanced hydrogen-bonding capacity and π-π stacking of imidazole ring. The effects of the stereochemistry and amino acid sequence of the PA backbone on the supramolecular organization were also analyzed by CD, TEM, SAXS, and molecular dynamics simulations. In addition, an investigation of chiral mixtures revealed the differences between the hydrogen-bonding capacities and noncovalent interactions of PAs with d- and l-amino acids.
Open Access
Local delivery of doxorubicin through supramolecular peptide amphiphile nanofiber gels
(Royal Society of Chemistry, 2017) Cinar, G.; Ozdemir, A.; Hamsici, S.; Gunay, G.; Dana, A.; Tekinay, A. B.; Güler, Mustafa O.
Peptide amphiphiles (PAs) self-assemble into supramolecular nanofiber gels that provide a suitable environment for encapsulation of both hydrophobic and hydrophilic molecules. The PA gels have significant advantages for controlled delivery applications due to their high capacity to retain water, biocompatibility, and biodegradability. In this study, we demonstrate injectable supramolecular PA nanofiber gels for drug delivery applications. Doxorubicin (Dox), as a widely used chemotherapeutic drug for breast cancer treatment, was encapsulated within the PA gels prepared at different concentrations. Physical and chemical properties of the gels were characterized, and slow release of the Dox molecules through the supramolecular PA nanofiber gels was studied. In addition, the diffusion constants of the drug molecules within the PA nanofiber gels were estimated using fluorescence recovery after the photobleaching (FRAP) method. The PA nanofiber gels did not show any cytotoxicity and the encapsulation strategy enhanced the activity of drug molecules on cellular viability through prolonged release compared to direct administration under in vitro conditions. Moreover, the local in vivo injection of the Dox encapsulated PA nanofiber gels (Dox/PA) to the tumor site demonstrated the lowest tumor growth rate compared to the direct Dox injection and increased the apoptotic cells within the tumor tissue for local drug release through the PA nanofiber gels under in vivo conditions.
Open Access
Molecular switch based on a cucurbit[6]uril containing bistable [3]rotaxane
(2007) Tuncel, D.; Özsar, Ö.; Tiftik, H. B.; Salih, B.
A bistable CB6-based [3]rotaxane with two recognition sites has been prepared very efficiently in a high yield synthesis through CB6 catalyzed 1,3-dipolar cycloaddition; this rotaxane behaves as a reversible molecular switch and exhibits conformational changes caused by the movement of rings under base, acid and heat stimuli from one location to the other. © The Royal Society of Chemistry.
Open Access
Multivalent presentation of cationic peptides on supramolecular nanofibers for antimicrobial activity
(American Chemical Society, 2017) Beter, M.; Kara, H. K.; Topal, A. E.; Dana, A.; Tekinay, A. B.; Güler, Mustafa O.
Noncovalent and electrostatic interactions facilitate the formation of complex networks through molecular self-assembly in biomolecules such as proteins and glycosaminoglycans. Self-assembling peptide amphiphiles (PA) are a group of molecules that can form nanofibrous structures and may contain bioactive epitopes to interact specifically with target molecules. Here, we report the presentation of cationic peptide sequences on supramolecular nanofibers formed by self-assembling peptide amphiphiles for cooperative enhanced antibacterial activity. Antibacterial properties of self-assembled peptide nanofibers were significantly higher than soluble peptide molecules with identical amino acid sequences, suggesting that the tandem presentation of bioactive epitopes is important for designing new materials for bactericidal activity. In addition, bacteria were observed to accumulate more rapidly on peptide nanofibers compared to soluble peptides, which may further enhance antibacterial activity by increasing the number of peptide molecules interacting with the bacterial membrane. The cationic peptide amphiphile nanofibers were observed to attach to bacterial membranes and disrupt their integrity. These results demonstrate that short cationic peptides show a significant improvement in antibacterial activity when presented in the nanofiber form.
Open Access
Nanoengineering hybrid supramolecular multilayered biomaterials using polysaccharides and self-assembling peptide amphiphiles
(Wiley-VCH Verlag, 2017) Borges, J.; Sousa, M. P.; Cinar, G.; Caridade, S. G.; Güler, Mustafa O.; Mano, J. F.
Developing complex supramolecular biomaterials through highly dynamic and reversible noncovalent interactions has attracted great attention from the scientific community aiming key biomedical and biotechnological applications, including tissue engineering, regenerative medicine, or drug delivery. In this study, the authors report the fabrication of hybrid supramolecular multilayered biomaterials, comprising high-molecular-weight biopolymers and oppositely charged low-molecular-weight peptide amphiphiles (PAs), through combination of self-assembly and electrostatically driven layer-by-layer (LbL) assembly approach. Alginate, an anionic polysaccharide, is used to trigger the self-assembling capability of positively charged PA and formation of 1D nanofiber networks. The LbL technology is further used to fabricate supramolecular multilayered biomaterials by repeating the alternate deposition of both molecules. The fabrication process is monitored by quartz crystal microbalance, revealing that both materials can be successfully combined to conceive stable supramolecular systems. The morphological properties of the systems are studied by advanced microscopy techniques, revealing the nanostructured dimensions and 1D nanofibrous network of the assembly formed by the two molecules. Enhanced C2C12 cell adhesion, proliferation, and differentiation are observed on nanostructures having PA as outermost layer. Such supramolecular biomaterials demonstrate to be innovative matrices for cell culture and hold great potential to be used in the near future as promising biomimetic supramolecular nanoplatforms for practical applications.
Open Access
pH-triggered dethreading-rethreading and switching of cucurbit[6]uril on bistable [3]pseudorotaxanes and [3]rotaxanes
(2008) Tuncel, D.; Katterle, M.
A series of water-soluble [3]rotaxanes-(n+2) and [3]pseudorotaxanes-(n+2) with short (propyl, n=1) and long (dodecyl, n=10) aliphatic spacers have been prepared in high yields by a 1,3-dipolar cycloaddition reaction catalyzed by cucurbit[6]uril (CB6). The pH-triggered dethreading and rethreading of CB6 on these pseudorotaxanes was monitored by 1H NMR spectroscopy. A previously reported [3]rotaxane-12 that is known to behave as a bistable molecular switch has two recognition sites for CB6, that is, the diaminotriazole moieties and the dodecyl spacer. By changing the pH of the system, it is possible to observe more than one state in the shuttling process. At low pH values both CB6 units are located on the diaminotriazole moieties owing to an ion-dipole interaction, whereas at high pH values both of the CB6 units are located on the hydrophobic dodecyl spacer. Surprisingly, the CB6 units shuttle back to their initial state very slowly after reprotonation of the axle. Even after eighteen days at room temperature, only about 50 % of the CB6 units had relocated back onto the diaminotriazole moieties. The rate constants for the shuttling processes were measured as a function of temperature over the range from 313 to 333 K and the activation parameters (enthalpy, entropy, and free energy) were calculated by using the Eyring equation. The results indicate that this [3]rotaxane behaves as a kinetically controlled molecular switch. The switching properties of [3]rotaxane-3 have also been studied. However, even under extreme pH conditions this rotaxane has not shown any switching action, which confirms that the propyl spacer is too short to accommodate CB6 units.
Open Access
Presentation of functional groups on self-assembled supramolecular peptide nanofibers mimicking glycosaminoglycans for directed mesenchymal stem cell differentiation
(Royal Society of Chemistry, 2017) Yasa, Oncay; Uysal, Ozge; Ekiz, Melis Sardan; Güler, Mustafa O.; Tekinay, Ayse B.
Organizational complexity and functional diversity of the extracellular matrix regulate cellular behaviors. The extracellular matrix is composed of various proteins in the form of proteoglycans, glycoproteins, and nanofibers whose types and combinations change depending on the tissue type. Proteoglycans, which are proteins that are covalently attached to glycosaminoglycans, contribute to the complexity of the microenvironment of the cells. The sulfation degree of the glycosaminoglycans is an important and distinct feature at specific developmental stages and tissue types. Peptide amphiphile nanofibers can mimic natural glycosaminoglycans and/or proteoglycans, and they form a synthetic nanofibrous microenvironment where cells can proliferate and differentiate towards different lineages. In this study, peptide nanofibers were used to provide varying degrees of sulfonation mimicking the natural glycosaminoglycans by forming a microenvironment for the survival and differentiation of stem cells. The effects of glucose, carboxylate, and sulfonate groups on the peptide nanofibers were investigated by considering the changes in the differentiation profiles of rat mesenchymal stem cells in the absence of any specific differentiation inducers in the culture medium. The results showed that a higher sulfonate-to-glucose ratio is associated with adipogenic differentiation and a higher carboxylate-to-glucose ratio is associated with osteochondrogenic differentiation of the rat mesenchymal stem cells. Overall, these results demonstrate that supramolecular peptide nanosystems can be used to understand the fine-tunings of the extracellular matrix such as sulfation profile on specific cell types. © 2017 The Royal Society of Chemistry.
Open Access
Self-assembled peptide nanostructures for functional materials
(Institute of Physics Publishing, 2016) Ekiz, M. S.; Cinar, G.; Khalily, M. A.; Güler, Mustafa O.
Nature is an important inspirational source for scientists, and presents complex and elegant examples of adaptive and intelligent systems created by self-assembly. Significant effort has been devoted to understanding these sophisticated systems. The self-assembly process enables us to create supramolecular nanostructures with high order and complexity, and peptide-based self-assembling building blocks can serve as suitable platforms to construct nanostructures showing diverse features and applications. In this review, peptide-based supramolecular assemblies will be discussed in terms of their synthesis, design, characterization and application. Peptide nanostructures are categorized based on their chemical and physical properties and will be examined by rationalizing the influence of peptide design on the resulting morphology and the methods employed to characterize these high order complex systems. Moreover, the application of self-assembled peptide nanomaterials as functional materials in information technologies and environmental sciences will be reviewed by providing examples from recently published high-impact studies.
Open Access
Sequence-specific self-sorting of the binding sites of a ditopic guest by cucurbituril homologues and subsequent formation of a hetero[4]pseudorotaxane
(2009) Celtek, G.; Artar, M.; Scherman, O. A.; Tuncel, D.
Ties us together: The selectivity and recognition behavior of cucurbit[n]uril (CB[n]) homologues (n = 6,7,8) towards a ditopic guest containing two distinct binding sites is explored. CB6, CB7, and CB8 recognize and self-sort the binding sites according to their size, shape, and chemical nature. In the presence of both CB6 and CB8 a hetero[4]pseudorotaxane is formed. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.
Open Access
Spatial organization of functional groups on bioactive supramolecular glycopeptide nanofibers for differentiation of mesenchymal stem cells (MSCs) to brown adipogenesis
(American Chemical Society, 2016-12) Caliskan, O. S.; Sardan, Ekiz M.; Tekinay, A. B.; Güler, Mustafa O.
Spatial organization of bioactive moieties in biological materials has significant impact on the function and efficiency of these systems. Here, we demonstrate the effect of spatial organization of functional groups including carboxylate, amine, and glucose functionalities by using self-assembled peptide amphiphile (PA) nanofibers as a bioactive scaffold. We show that presentation of bioactive groups on glycopeptide nanofibers affects mesenchymal stem cells (MSCs) in a distinct manner by means of adhesion, proliferation, and differentiation. Strikingly, when the glutamic acid is present in the glycopeptide backbone, the PA nanofibers specifically induced differentiation of MSCs into brown adipocytes in the absence of any differentiation medium as shown by lipid droplet accumulation and adipogenic gene marker expression analyses. This effect was not evident in the other glycopeptide nanofibers, which displayed the same functional groups but with different spatial organization. Brown adipocytes are attractive targets for obesity treatment and are found in trace amounts in adults, which also makes this specific glycopeptide nanofiber system an attractive tool to study molecular pathways of brown adipocyte formation.
Open Access
Supramolecular assemblies constructed by cucurbituril-catalyzed click reaction
(2011) Tuncel, D.; Ünal, Ö.; Artar, M.
Cucurbituril homologues are multi-functional macrocycles that can find applications in many areas and have numerous interesting features setting them apart from the other macrocycles. Among them, the ability of one of the cucurbituril homologues, cucurbit[6]uril (CB6), to catalyze 1,3- dipolar cycloaddition in a regiospecific fashion is truly exceptional. Using this feature, small molecules can be clicked together to form complex structures in a very efficient way. Accordingly, in this article we review recent research involving the use of CB6-catalyzed 1,3-dipolar cycloaddition or the click reaction of CB6 in the construction of supramolecular assemblies including rotaxanes, pseudorotaxanes, polyrotaxanes, polypseudorotaxanes, molecular switches, machines, and nanovalves.