Novel Thermally-Accessible Structural Changes of Chiral and Some Related Cu（ll） Complexes

A mononuclear chiral copper（ll） complex, [Cu（RRchxn）2（C（CN）3）2]＇H20 （RRchxn = （1R, 2R）-diaminocyclohexane） （RRchxnH）, and its deuterated compound, [Cu（RRchxn）2（C（CN）3）z].D20 （RRchxnD）, and their isomers, [Cu（trchxn）2（C（CN）3）2]＇H20 （trchxn = trans-l,2-diaminocyclohexane） （trchxnH） and [Cu（trchxn）2（C（CN）3）2]＇D20 （trchxnD） have been prepared and characterized by means of 1R （infrared）, electronic, and CD （circular dichroism） spectra, magnetic susceptibility, and variable-temperature X-ray crystallography as single crystals or powder. Interestingly, depending on grain size of samples, RRchxnH exhibits the monoclinic form and the orthorhombic form, which are distinguished by systematic absence and powder XRD （X-ray diffraction） patterns clearly. Although single crystals did not exhibit phase transition, powder XRD patterns of RRchxnH and weakly hydrogen bonded RRchxnD emerged low-temperature phase of monoclinic in the orthorhombic patterns only around 200-220 K. However, as a control, powder XRD patterns of both trchxnH and trchxnD did not exhibit such phase transition clearly.     

Order/Disorder in Protein and Peptide-Based Biomaterials

Nature utilizes both order and disorder (or controlled disorder) to achieve exceptional materials properties and functions, while synthetic supramolecular materials mostly exploit just supramolecular order, thus limiting the structural diversity, responsiveness and consequent adaptive functions that can be accessed. Herein, we review the emerging field of supramolecular biomaterials where disorder and order deliberately co-exist, and can be dynamically regulated by considering both entropic and enthalpic factors in design. We focus on sequence-structure relationships that govern the (cooperative) assembly pathways of protein and peptide building blocks in these materials. Increasingly, there is an interest in introducing dynamic features in protein and peptide-based structures, such as the remarkable thermo-responsiveness and exceptional mechanical properties of elastin materials. Simultaneously, advances in the field of intrinsically disordered proteins (IDPs) give new insights about their involvement in intracellular liquid-liquid phase separation and formation of disordered, dynamic coacervate structures. These have inspired efforts to design biomaterials with similar dynamic properties. These hybrid ordered/disordered materials employ a combination of intramolecular and supramolecular order/disorder features for construction of assemblies that are dynamically reconfigurable. The assembly of these dynamic structures is mainly entropy-driven, relying on electrostatic and hydrophobic interactions and is mediated in part through the adopted (unstructured) protein conformation or by introducing an oppositely charged guest for peptide building blocks. Examples include design of protein building blocks composed of disordered repeat sequences of elastin-like polypeptides in combination with ordered regions that adopt a secondary structure, the co-assembly of proteins with peptide amphiphiles to achieve reconfigurable, yet highly stable membranes or tyrosine-containing tripeptides with sequence-controlled order/disorder that upon enzymatic oxidation give rise to melanin-like polymeric pigments with customizable properties. The resulting hybrid materials with controlled disorder can be metastable, and sensitive to various external stimuli giving rise to insights that are especially attractive for the design of responsive and adaptive materials.     

Cyclodextrin-Based Multistimuli-Responsive Supramolecular Assemblies and Their Biological Functions

Cyclodextrins (CDs), which are a class of cyclic oligosaccharides extracted from the enzymatic degradation of starch, are often utilized in molecular recognition and assembly constructs, primarily via host–guest interactions in water. In this review, recent progress in CD-based supramolecular nanoassemblies that are sensitive to chemical, biological, and physical stimuli is updated and reviewed, and intriguing examples of the biological functions of these nanoassemblies are presented, including pH- and redox-responsive drug and gene delivery, enzyme-activated specific cargo release, photoswitchable morphological interconversion, microtubular aggregation, and cell–cell communication, as well as a geomagnetism-controlled nanosystem for the suppression of tumor invasion and metastasis. Moreover, future perspectives and challenges in the fabrication of intelligent CD-based biofunctional materials are also discussed at the end of this review, which is expected to promote the translational development of these nanomaterials in the biomedical field.     

Magic Angle Spinning NMR of Macromolecular and Supramolecular Systems

Sideband patterns in single quantum and double quantum magic angle spinning NMR spectra are reviewed. Their use in elucidating non-covalent interactions, such as hydrogen bonds or pi-pi stacking, is demonstrated by studies of supramolecular systems of current interest. Moreover, the effects of local and collective motions are illustrated by examples from supramolecular and macromolecular science.     

Synthesis of water dispersible reduced graphene oxide via supramolecular complexation with modified β-cyclodextrin

A noncovalent functionalization of the edges of reduced graphene oxide (RGO) with β-cyclodextrin-graft-hyperbranched polyglycerol (β-CD-g-HPG) was successfully performed via a host-guest interaction. The results showed that β-CD-g-HPG disperses the graphene sheets better than pure β-CD or HPG. The resulted supramolecular structure is stable in neutral water medium more than one week. However, in acidic medium the host-guest interaction is collapsed and graphene nanosheets precipitate.     

Metallo‐supramolecular materials based on terpyridine‐functionalized polyhedral silsesquioxane

In this study, novel metallo‐supramolecular materials based on terpyridine‐functionalized polyhedral silsesquioxane were synthesized from 4′‐chloro‐2,2′:6′,2″‐terpyridine and amino‐group‐functionalized polyhedral oligomeric silsesquioxane. The obtained terpyridine‐functionalized polyhedral silsesquioxanes were converted to metallo‐supramolecular hybrid materials by coordination polycondensation reaction with Co(II) or Cu(II) ions. The supramolecular polymers created were characterized by means of structure, morphology and stimuli‐responsive performance employing scanning electron microscopy, amperometric techniques and UV–visible and Fourier transform IR spectroscopy. UV?visible and cyclic voltammetry studies showed that both the optical and electrochemical properties of metallo‐supramolecular materials are affected by the substituent at the pyridine periphery. The supramolecular polymers obtained exhibited electrochromism during the oxidation processes of cyclic voltammogram studies. As a result, these terpyridine‐functionalized polyhedral silsesquioxanes are good candidates for electronic, opto‐electronic and photovoltaic applications as smart stimuli‐responsive materials. © 2013 Society of Chemical Industry     

A Water‐Soluble Mechanochromic Luminescent Pyrene Derivative Exhibiting Recovery of the Initial Photoluminescence Color in a High‐Humidity Environment

Switching of the luminescence properties of molecular materials in response to mechanical stimulation is of fundamental interest and also has a range of potential applications. Herein, a water‐soluble mechanochromic luminescent pyrene derivative having two hydrophilic dendrons is reported. This pyrene derivative is the first example of a mechanochromic luminescent organic compound that responds to relative humidity. Mechanical stimulation (grinding) of this pyrene derivative in the solid state results in a change of the photoluminescence from yellow to green. Subsequent exposure to water vapor induces recovery of the initial yellow photoluminescence. The color change is reversible through at least ten cycles. It is also demonstrated that this compound can be applied as a mechano‐sensing material in frictional wear testing for grease, owing to its immiscibility in non‐polar solvents and its non‐crystalline behavior. Transmission electron microscope and atomic force microscope observations of samples prepared from dilute aqueous solutions of the pyrene derivative on suitable substrates, together with dynamic light scattering measurements for the compound in aqueous solution, indicate that this amphiphilic dumbbell‐shaped molecule forms micelles in water.     

Mechanochemical preparation of kaempferol intermolecular complexes for enhancing the solubility and bioavailability

Abstract

In this study, complexes of kaempferol (KF) with polysaccharide arabinogalactan (AG) and disodium glycyrrhizinate (Na₂GA) were prepared through mechanochemical technique to improve the solubility and bioavailability of KF. The physicochemical properties and the interactions of KF with AG/Na₂GA were investigated through dissolution, SEM, XRD, and DSC studies. The reduction of particle sizes and destruction of crystal forms revealed the formation of solid dispersion which may have assisted the dissolution of the drug. The accelerated stability study showed higher stability for KF–Na₂GA complex. In vivo pharmacokinetic study was performed to observe the plasma drug concentrations for KF complexes. Mechanochemical complexation of KF with AG/Na₂GA improved the pharmacological activity as evident by the inhibitory potential of the complexes towards carbohydrate metabolic enzymes. In vivo studies were performed in STZ-induced diabetic mice, where the group treated with KF–AG complex showed better liver and kidney function and lower blood glucose levels than pure KF. Therefore, mechanochemical complexes of KF with polysaccharide or glycyrrhizate may serve as a promising formulation for the treatment of diabetes.