Multicomponent Supramolecular Systems: Self‐Organization in Coordination‐Driven Self‐Assembly

The self‐organization of multicomponent supramolecular systems involving a variety of two‐dimensional (2 D) polygons and three‐dimensional (3 D) cages is presented. Nine self‐organizing systems, SS₁ – SS₉ , have been studied. Each involves the simultaneous mixing of organoplatinum acceptors and pyridyl donors of varying geometry and their selective self‐assembly into three to four specific 2 D (rectangular, triangular, and rhomboid) and/or 3 D (triangular prism and distorted and nondistorted trigonal bipyramidal) supramolecules. The formation of these discrete structures is characterized using NMR spectroscopy and electrospray ionization mass spectrometry (ESI‐MS). In all cases, the self‐organization process is directed by: 1) the geometric information encoded within the molecular subunits and 2) a thermodynamically driven dynamic self‐correction process. The result is the selective self‐assembly of multiple discrete products from a randomly formed complex. The influence of key experimental variables ‐ temperature and solvent ‐ on the self‐correction process and the fidelity of the resulting self‐organization systems is also described.     

A Carbon Dioxide Bubble‐Induced Vortex Triggers Co‐Assembly of Nanotubes with Controlled Chirality

It is challenging to prepare co‐organized nanotube systems with controlled nanoscale chirality in an aqueous liquid flow field. Such systems are responsive to a bubbled external gas. A liquid vortex induced by bubbling carbon dioxide (CO₂) gas was used to stimulate the formation of nanotubes with controlled chirality; two kinds of achiral cationic building blocks were co‐assembled in aqueous solution. CO₂‐triggered nanotube formation occurs by formation of metastable intermediate structures (short helical ribbons and short tubules) and by transition from short tubules to long tubules in response to chirality matching self‐assembly. Interestingly, the chirality sign of these assemblies can be selected for by the circulation direction of the CO₂ bubble‐induced vortex during the co‐assembly process.     

Desymmetrization of 3,3′‐Bis(acylamino)‐2,2′‐bipyridine‐Based Discotics: The High Fidelity of Their Self‐Assembly Behavior in the Liquid‐Crystalline State and in Solution

Two novel nonsymmetrical disc‐shaped molecules 1 and 2 based on 3,3′‐bis(acylamino)‐2,2′‐bipyridine units were synthesized by means of a statistical approach. Discotic 1 possesses six chiral dihydrocitronellyl tails and one peripheral phenyl group, whereas discotic 2 possesses six linear dodecyloxy tails and one peripheral pyridyl group. Preorganization by strong intramolecular hydrogen bonding and subsequent aromatic interactions induce self‐assembly of the discotics. Liquid crystallinity of 1 and 2 was determined with the aid of polarized optical microscopy, differential scanning calorimetry, and X‐ray diffraction. Two columnar rectangular mesophases (Col_r) have been identified, whereas for C₃‐symmetrical derivatives only one Col_r mesophase has been found. 1 In solution, the molecularly dissolved state in chloroform was studied with ¹H NMR spectroscopy, whereas the self‐assembled state in apolar solution was examined with optical spectroscopy. Remarkably, these desymmetrized discotics, which lack one aliphatic wedge, behave similar to the symmetric parent compound. To prove that the stacking behavior of discotics 1 and 2 is similar to that of reported C₃‐symmetrical derivatives, a mixing experiment of chiral 1 with C₃‐symmetrical 13 has been undertaken; it has shown that they indeed belong to one type of self‐assembly. This helical J‐type self‐assembly was further confirmed with UV/Vis and photoluminescence (PL) spectroscopy. Eventually, disc 2 , functionalized with a hydrogen‐bonding acceptor moiety, might perform secondary interactions with molecules such as acids.     

Dependence on Oil Chain‐Length of the Curvature Elastic Properties of Nonionic Surfactant Films: Droplet Growth from Spheres to a Bicontinuous Network

Using NMR self‐diffusion and ²H‐NMR relaxation experiments, we have investigated growth of oil‐in‐water microemulsion droplets when spontaneous curvature is lowered, starting at emulsification failure boundary. We compare two ternary nonionic microemulsion systems, containing penta‐ethylene glycol dodecyl ether (C₁₂E₅), and decane or hexadecane, at same surfactant‐to‐oil ratio and approximately the same spontaneous curvature. Droplet growth in microemulsions appears in general to be only minor. Quantitative differences between the two systems indicate differences in the curvature elastic constants.     

Emergent Catalytic Behavior of Self‐Assembled Low Molecular Weight Peptide‐Based Aggregates and Hydrogels

We report a series of short peptides possessing the sequence (FE)_n or (EF)_n and bearing l ‐proline at their N‐terminus that self‐assemble into high aspect ratio aggregates and hydrogels. We show that these aggregates are able to catalyze the aldol reaction, whereas non‐aggregated analogues are catalytically inactive. We have undertaken an analysis of the results, considering the accessibility of catalytic sites, pK_a value shifts, and the presence of hydrophobic pockets. We conclude that the presence of hydrophobic regions is indeed relevant for substrate solubilization, but that the active site accessibility is the key factor for the observed differences in reaction rates. The results presented here provide an example of the emergence of a new chemical property caused by self‐assembly, and support the relevant role played by self‐assembled peptides in prebiotic scenarios. In this sense, the reported systems can be seen as primitive aldolase I mimics, and have been successfully tested for the synthesis of simple carbohydrate precursors.     

N,N′‐Methylenediimidazolium Salts: From Self‐Assembly to an Efficient DNAse Protection System

We have developed N,N′‐dialkylmethylenediimidazolium salts ([C_nC_nDIM][X]₂) that self‐organize into multilayered cationic vesicles and can interact with DNA. These preorganized systems form complexes with linear DNA and protect it from DNase I cleavage.     

Developing a Self‐Healing Supramolecular Nucleoside Hydrogel Based on Guanosine and Isoguanosine

Recently, supramolecular hydrogels have attracted increasing interest owing to their tunable stability and inherent biocompatibility. However, only few studies have been reported in the literature on self‐healing supramolecular nucleoside hydrogels, compared to self‐healing polymer hydrogels. In this work, we successfully developed a self‐healing supramolecular nucleoside hydrogel obtained by simply mixing equimolar amounts of guanosine (G) and isoguanosine (isoG) in the presence of K⁺. The gelation properties have been studied systematically by comparing different alkali metal ions as well as mixtures with different ratios of G and isoG. To this end, rheological and phase diagram experiments demonstrated that the co‐gel not only possessed good self‐healing properties and short recovery time (only 20 seconds) but also could be formed at very low concentrations of K⁺. Furthermore, nuclear magnetic resonance (NMR), powder X‐ray diffraction (PXRD), and circular dichroism (CD) spectroscopy suggested that possible G₂isoG₂‐quartet structures occurred in this self‐healing supramolecular nucleoside hydrogel. This co‐gel, to some extent, addressed the problem of isoguanosine gels for the applications in vivo, which showed the potential to be a new type of drug delivery system for biomedical applications in the future.     

Two‐Dimensional Self‐Assembly of a Porphyrin–Polypyridyl Ruthenium(II) Hybrid on HOPG Surface through Metal–Ligand Interactions

The synthesis and self‐assembly behavior of porphyrin–polypyridyl ruthenium(II) hybrid, which consists of a flexible alkyl chain attached with two conjugated moieties is described. The electronic absorption spectrum and emission spectra show that the [C₈‐TPP‐(ip)Ru(phen)₂](ClO₄)₂, abbreviated as (C₈ip)TPPC has optical properties. Scanning tunneling microscopy (STM) studies found that the π–π interaction and metal–ligand interaction allow (C₈ip)TPPC to form self‐assembled structure and have an edge‐on orientation on the highly oriented pyrolytic graphite (HOPG) surface. The multidentate structure in (C₈ip)TPPC molecules act as linkers between the molecules and form metal–ligand coordination, which forces the assembly process in the direction of stable columnar arrays. In addition, although the sample was stored for two months in ambient conditions, STM experiments showed that the order of (C₈ip)TPPC self‐assembly only slightly decreased which indicates that the self‐assembled monolayer is stable. This work demonstrates that introducing a metal‐ligand in the porphyrin‐polypyridyl compound is a useful strategy to obtain novel surface assemblies.     

Hydrogen‐Bond‐Driven Controlled Molecular Marriage in Covalent Cages

A supramolecular approach that uses hydrogen‐bonding interaction as a driving force to accomplish exceptional self‐sorting in the formation of imine‐based covalent organic cages is discussed. Utilizing the dynamic covalent chemistry approach from three geometrically similar dialdehydes ( A , B , and D ) and the flexible triamine tris(2‐aminoethyl)amine ( X ), three new [3+2] self‐assembled nanoscopic organic cages have been synthesized and fully characterized by various techniques. When a complex mixture of the dialdehydes and triamine X was subjected to reaction, it was found that only dialdehyde B (which has OH groups for H‐bonding) reacted to form the corresponding cage B₃X₂ selectively. Surprisingly, the same reaction in the absence of aldehyde B yielded a mixture of products. Theoretical and experimental investigations are in complete agreement that the presence of the hydroxyl moiety adjacent to the aldehyde functionality in B is responsible for the selective formation of cage B₃X₂ from a complex reaction mixture. This spectacular selection was further analyzed by transforming a nonpreferred (non‐hydroxy) cage into a preferred (hydroxy) cage B₃X₂ by treating the former with aldehyde B . The role of the H‐bond in partner selection in a mixture of two dialdehydes and two amines has also been established. Moreover, an example of unconventional imine bond metathesis in organic cage‐to‐cage transformation is reported.     

A numerical evaluation of chamber methodologies used in measuring the δ13C of soil respiration

Measurement of the δ¹³C value of soil‐respired CO₂ (δ_r) has become a commonplace method through which ecosystem function and C dynamics can be better understood. Despite its proven utility there is currently no consensus on the most robust method with which to measure δ_r. Static and dynamic chamber systems are both commonly used for this purpose; however, the literature on these methods provides evidence suggesting that measurements of δ_r made with these chamber systems are neither repeatable (self‐consistent) nor comparable across methodologies. Here we use a three‐dimensional (3‐D) numerical soil‐atmosphere‐chamber model to test these chamber systems in a ‘surrogate reality’. Our simulations show that each chamber methodology is inherently biased and that no chamber methodology can accurately predict the true δ_r signature under field conditions. If researchers intend to use δ_r to study in situ ecosystem processes, the issues with these chamber systems need to be corrected either by using diffusive theory or by designing a new, unbiased δ_r measurement system. Copyright © 2009 John Wiley & Sons, Ltd.     

Biomimetic Artificial Inorganic Enzyme‐Free Self‐Propelled Microfish Robot for Selective Detection of Pb2+ in Water

The availability of drinking water is of utmost importance for the world population. Anthropogenic pollutants of water, such as heavy‐metal ions, are major problems in water contamination. The toxicity assays used range from cell assays to animal tests. Herein, we replace biological toxicity assays, which use higher organisms, with artificial inorganic self‐propelled microtubular robots. The viability and activity of these robots are negatively influenced by heavy metals, such as Pb²⁺, in a similar manner to that of live fish models. This allows the establishment of a lethal dose (LD₅₀) of heavy metal for artificial inorganic microfish robots. The self‐propelled microfish robots show specific response to Pb²⁺ compared to other heavy metals, such as Cd²⁺, and can be used for selective determination of Pb²⁺ in water. It is a first step towards replacing the biological toxicity assays with biomimetic inorganic autonomous robotic systems.     

Almost Enclosed Buckyball Joints: Synthesis,Complex Formation,and Computational Simulations of Pentypticene‐Extended Tribenzotriquinacene

We report the synthesis of a tribenzotriquinacene‐based (TBTQ) receptor ( 3 ) for C₆₀ fullerene, which is extended by pentiptycene moieties to provide an almost enclosed concave ball bearing. The system serves as a model for a self‐assembling molecular rotor with a flexible and adapting stator. Unexpectedly, nuclear magnetic resonance spectroscopic investigations reveal a surprisingly low complex stability constant of K₁=213±37 M ^?1 for [C₆₀? 3 ], seemingly inconsistent with the previously reported TBTQ systems. Molecular dynamics (MD) simulations have been conducted for three different [C₆₀?TBTQ] complexes to resolve this. Because of the dominating dispersive interactions, the binding energies increase with the contact area between guest and host, however, only for rigid host structures. By means of free‐energy calculations with an explicit solvent model it can be shown that the novel flexible TBTQ receptor 3 binds weakly because of hampering entropic contributions.     

Bioactive Seed Layer for Surface‐Confined Self‐Assembly of Peptides

The design and control of molecular systems that self‐assemble spontaneously and exclusively at or near an interface represents a real scientific challenge. We present here a new concept, an active seed layer that allows to overcome this challenge. It is based on enzyme‐assisted self‐assembly. An enzyme, alkaline phosphatase, which transforms an original peptide, Fmoc‐FFY(PO₄^2?), into an efficient gelation agent by dephosphorylation, is embedded in a polyelectrolyte multilayer and constitutes the “reaction motor”. A seed layer composed of a polyelectrolyte covalently modified by anchoring hydrogelator peptides constitutes the top of the multilayer. This layer is the nucleation site for the Fmoc‐FFY peptide self‐assembly. When such a film is brought in contact with a Fmoc‐FFY(PO₄^2?) solution, a nanofiber network starts to form almost instantaneously which extents up to several micrometers into the solution after several hours. We demonstrate that the active seed layer allows convenient control over the self‐assembly kinetics and the geometric features of the fiber network simply by changing its peptide density.     

Size Matters! On the Way to Ionic Liquid Systems without Ion Pairing

Several, partly new, ionic liquids (ILs) containing imidazolium and ammonium cations as well as the medium‐sized [NTf₂]^? (0.230 nm³; Tf=CF₃SO₃^?) and the large [Al(hfip)₄]^? (0.581 nm³; hfip=OC(H)(CF₃)₂) anions were synthesized and characterized. Their temperature‐dependent viscosities and conductivities between 25 and 80 °C showed typical Vogel–Fulcher–Tammann (VFT) behavior. Ion‐specific self‐diffusion constants were measured at room temperature by pulsed‐gradient stimulated‐echo (PGSTE) NMR experiments. In general, self‐diffusion constants of both cations and anions in [Al(hfip)₄]^?‐based ILs were higher than in [NTf₂]^?‐based ILs. Ionicities were calculated from self‐diffusion constants and measured bulk conductivities, and showed that [Al(hfip)₄]^?‐based ILs yield higher ionicities than their [NTf₂]^? analogues, the former of which reach values of virtually 100 % in some cases.From these observations it was concluded that [Al(hfip)₄]^?‐based ILs come close to systems without any interactions, and this hypothesis is underlined with a Hirshfeld analysis. Additionally, a robust, modified Marcus theory quantitatively accounted for the differences between the two anions and yielded a minimum of the activation energy for ion movement at an anion diameter of slightly greater than 1 nm, which fits almost perfectly the size of [Al(hfip)₄]^?. Shallow Coulomb potential wells are responsible for the high mobility of ILs with such anions.     

Exploring the Effect of Ligand Structural Isomerism in Langmuir–Blodgett Films of Chiral Luminescent EuIII Self‐Assemblies

Here we have investigated the influence of the antenna group position on both the formation of chiral amphiphilic Eu^III‐based self‐assemblies in CH₃CN solution and, on the ability to form monolayers on the surface of quartz substrates using the Langmuir–Blodgett technique, by changing from the 1‐naphthyl ( 2(R) , 2(S) ) to the 2‐naphthyl ( 1(R) , 1(S) ) position. The evaluation of binding constants of the self‐ assemblies in CH₃CN solution was achieved using conventional techniques such as UV/Visible and luminescence spectroscopies along with more specific circular dichroism (CD) spectroscopy. The binding constants obtained for EuL , EuL₂ and EuL₃ species in the case of 2‐naphthyl derivatives were comparable to those obtained for 1‐naphthyl derivatives. The analysis of the changes in the CD spectra of 1(R) and 1(S) upon addition of Eu^III not only allowed us to evaluate the values of the binding constants but the resulting recalculated spectra may also be used as fingerprints for assignment of the chiral self‐assembly species formed in solution. The obtained monolayers were predominantly formed from EuL₃ (≈85 %) with the minor species present in ≈15 % EuL₂ .     

Cube‐in‐Cube Hollow Cu9S5 Nanostructures with Enhanced Photocatalytic Activities in Solar H2 Evolution

Hydrogen produced from water under solar energy is an ideal clean energy source, and the efficiency of hydrogen production usually depends on the catalytic systems based on new compounds and/or a unique nanostructure. Herein, well‐defined cube‐in‐cube hollow Cu₉S₅ nanostructures have been successfully prepared with Cu₂O nanocubes and CS₂ as precursors, and single‐shell hollow Cu₉S₅ nanocubes could be obtained by replacing CS₂ with Na₂S. The formation mechanism of cube‐in‐cube hollow nanostructures has been proposed based on the Kirkendell effect and an outward self‐assembly process. Further studies revealed that the cube‐in‐cube hollow Cu₉S₅ nanostructures exhibited better photocatalytic activity toward solar H₂ evolution and would be a promising photocatalyst in the solar hydrogen industry.     

Tuning the Chirality of Block Copolymers: From Twisted Morphologies to Nanospheres by Self‐Assembly

New advances into the chirality effect in the self‐assembly of block copolymers (BCPs) have been achieved by tuning the helicity of the chiral‐core‐forming blocks. The chiral BCPs {[N?P(R)‐O₂C₂₀H₁₂]_200?x[N?P(OC₅H₄N)₂]_x}‐b‐ [N?PMePh]₅₀ ((R)‐O₂C₂₀H₁₂=(R)‐1,1′‐binaphthyl‐2,2′‐dioxy, OC₅H₄N=4‐pyridinoxy (OPy); x=10, 30, 60, 100 for 3 a – d , respectively), in which the [N?P(OPy)₂] units are randomly distributed within the chiral block, have been synthesised. The chiroptical properties of the BCPs ([α]_D vs. T and CD) demonstrated that the helicity of the BCP chains may be simply controlled by the relative proportion of the chiral and achiral (i.e., [N?P(R)‐O₂C₂₀H₁₂] and [N?P(OPy)₂], respectively) units. Thus, although 3 a only contained only 5 % [N?P(OPy)₂] units and exhibited a preferential helical sense, 3 d with 50 % of this unit adopted non‐preferred helical conformations. This gradual variation of the helicity allowed us to examine the chirality effect on the self‐assembly of chiral and helical BCPs (i.e., 3 a – c ) and chiral but non‐helical BCPs (i.e., 3 d ). The very significant influence of the helicity on the self‐assembly of these materials resulted in a variety of morphologies that extend from helical nanostructures to pearl‐necklace aggregates and nanospheres (i.e., 3 b and 3 d , respectively). We also demonstrate that the presence of pyridine moieties in BCPs 3 a – d allows specific decoration with gold nanoparticles.     

Measurement of Residual Dipolar Couplings of Organic Molecules in Multiple Solvent Systems Using a Liquid‐Crystalline‐Based Medium

Residual dipolar coupling (RDC), a robust anisotropic NMR parameter for structural elucidation of organic molecules, is only accessible in an anisotropic environment. Herein, we introduce a novel alignment medium based on the molecular self‐assembly of oligopeptide amphiphile (OPA). This medium is compatible with different intermediate and polar solvent systems, such as CD₃OD, [D₆]DMSO, and D₂O. The preparation of the OPA‐based medium is simple and rapid, while only very weak background signals were observed from OPAs. Furthermore, we show that the purity of OPA has only a minor influence on the quality of the RDC data. These advantages allow RDC measurements of organic molecules with different polarities and solubilities with high efficiency and accuracy.     

Molecular dynamics simulation of liquid water and ice nanoclusters using a new effective HFD‐like model

We have determined a new two‐body interaction potential of water by the inversion of viscosity collision integrals of water vapor and fitted to achieve the Hartree–fock dispersion‐like (HFD‐like) potential function. The calculated two‐body potential generates the thermal conductivity, viscosity, and self‐diffusion coefficient of water vapor in an excellent accordance with experimental data at wide temperature ranges. We have also used a new many‐body potential as a function of temperature and density with the HFD‐like pair‐potential of water to improve the two‐body properties better than the SPC, SPC/E, TIP3P, and TIP4P models. We have also used the new corrected potential to simulate the configurational energy and the melting temperatures of the (H₂O)₅₀₀, (H₂O)₈₆₄, (H₂O)₂₀₄₈, and (H₂O)₆₉₁₂ ice nanoclusters in good agreement with the previous simulation data using the TIP4P model. The extrapolated melting point at the bulk limit is also in better agreement with the experimental bulk data. The self‐diffusion coefficients for the ice nanoclusters also simulated at different temperatures. © 2017 Wiley Periodicals, Inc.