Flexible Host Research Articles

Simple dinitro substituted calix[4]arene forming a honeycomb-like architecture with hydrophobic channels

A rather easily structured permethylated dinitro calix[4]arene was found to exhibit large, stable and rigid channels in the solid state. These were obtained as guest free as well as solvent filled species and proved to reversibly adsorb selected organic solvents. Combined use of QMB measurements and X-ray powder diffraction revealed the predominantly reversible interaction of dichloromethane vapour with the channel structure as well as the integrity of the nanopores during adsorption and desorption. Examination of the flexible host component by NMR spectroscopy revealed a mixture of interchanging conformational isomers which could explain the high sensitivity of the crystallization process from the employed solvents.

Single-crystal X-ray diffraction studies on structural transformations of porous coordination polymers.

X-Ray single-crystal diffraction has been the most straightforward and important technique in structural determination of crystalline materials for understanding their structure-property relationships. This powerful tool can be used to directly visualize the precise and detailed structural information of porous coordination polymers or metal-organic frameworks at different states, which are unique for their flexible host frameworks compared with conventional adsorbents. With a series of selected recent examples, this review gives a brief overview of single-crystal X-ray diffraction studies and single-crystal to single-crystal transformations of porous coordination polymers under various chemical and physical stimuli such as solvent and gas sorption/desorption/exchange, chemical reaction and temperature change.

Nitrogen deposition alters plant–fungal relationships: linking belowground dynamics to aboveground vegetation change

Nitrogen (N) deposition rates are increasing globally due to anthropogenic activities. Plant community responses to N are often attributed to altered competitive interactions between plants, but may also be a result of microbial responses to N, particularly root-associated fungi (RAF), which are known to affect plant fitness. In response to N, Deschampsia cespitosa, a codominant plant in the alpine tundra at Niwot Ridge (CO), increases in abundance, while Geum rossii, its principal competitor, declines. Importantly, G.rossii declines with N even in the absence of its competitor. We examined whether contrasting host responses to N are associated with altered plant-fungal symbioses, and whether the effects of N are distinct from effects of altered plant competition on RAF, using 454 pyrosequencing. Host RAF communities were distinct (only 9.4% of OTUs overlapped). N increased RAF diversity in G.rossii, but decreased it in D.cespitosa. D.cespitosa RAF communities were more responsive to N than G.rossii RAF communities, perhaps indicating a flexible microbial community aids host adaptation to nutrient enrichment. Effects of removing D.cespitosa were distinct from effects of N on G.rossii RAF, and D.cespitosa presence reversed RAF diversity response to N. The most dominant G.rossii RAF order, Helotiales, was the most affected by N, declining from 83% to 60% of sequences, perhaps indicating a loss of mutualists under N enrichment. These results highlight the potential importance of belowground microbial dynamics in plant responses to N deposition.

Two-dimensional self-assemblies of telechelic organic compounds: structure and surface host–guest chemistry

Guiding the self-assembly of different types of functional molecules into well-defined structures on surfaces is beneficial for both fundamental surface and interface study and emerging application fields, especially molecular and organic electronics. This review focuses on understanding the two-dimensional self-assembly process of telechelic organics, which feature alkoxylene chains terminated with carboxyl groups. With the combined flexibility of alkyl chains and directionality of carboxyl groups, telechelic organics show unique assembly behaviour on two-dimensional surfaces. By increasing the length of the alkoxylene chains, the cavities in the nanoporous networks of telechelic trimesic acid (1,3,5-benzene tricarboxylic acid) derivatives change from hexagonal cavities to irregular cavities on a highly oriented pyrolytic graphite surface. The nanoporous networks provide a flexible host template for host-guest supramolecular chemistry because the cavities framed by the flexible alkoxylene chains can be changed in accordance with the sizes/shapes of the guest molecules. Furthermore, the terminal carboxylic group can form a hydrogen bond with another hydrogen bond partner, leading to multi-component structural motifs and hierarchical assemblies. The unique assembly behaviour of telechelic organics makes them promising structures as important building blocks for the design and construction of complex self-assembled nanoarchitectures.

Evolution of tree killing in bark beetles (Coleoptera: Curculionidae): trade-offs between the maddening crowds and a sticky situation

AbstractBark beetles (Coleoptera: Curculionidae: Scolytinae) play important roles in temperate conifer ecosystems, and also cause substantial economic losses. Although their general life histories are relatively similar, different species vary markedly in the physiological condition of the hosts they select. Most of ∼6000 known species colonise dead or stressed trees, a resource they share with a large diversity of insects and other organisms. A small number of bark beetle species kill healthy, live trees. These few are of particular interest as they compete directly with humans for resources. We propose that tree killing evolved when intense interspecific competition in the ephemeral, scarce resource of defence-impaired trees selected for genotypes that allowed them to escape this limitation by attacking relatively healthy trees. These transitions were uncommon, and we suggest they were facilitated by (a) genetically and phenotypically flexible host selection behaviours, (b) biochemical adaptations for detoxifying a wide range of defence compounds, and (c) associations with symbionts, which together aided bark beetles in overcoming formidable constitutive and induced host defences. The ability to detoxify terpenes influenced the evolutionary course of pheromonal communication. Specifically, a mate attraction system, which was exploited by intraspecific competitors in locating poorly defended hosts, became a system of cooperative attack in which emitters benefit from the contributions responders make in overcoming defence. This functional shift in communication was driven in part by linkage of beetle semiochemistry to host defence chemistry. Behavioural and phenological adaptations also improved the beetles’ abilities to detect when tree defences are impaired, and, where compatible with life history adaptations to other selective forces, for flight to coincide with seasonally predictable host stress agents. We propose a conceptual model, whereby the above mechanisms enable beetles to concentrate on those trees that offer an optimal trade-off between host defence and interspecific competition, along dynamic gradients of tree vigour and stand-level beetle density. We offer suggestions for future research on testing elements of this model.

Flexible host choice and common host switches in the evolution of generalist and specialist cuckoo bees (Anthophila: Sphecodes).

Specialization makes resource use more efficient and should therefore be a common process in animal evolution. However, this process is not as universal in nature as one might expect. Our study shows that Sphecodes (Halictidae) cuckoo bees frequently change their host over the course of their evolution. To test the evolutionary scenario of host specialization in cuckoo bees, we constructed well-supported phylogenetic trees based on partial sequences of five genes for subtribe Sphecodina (Halictini). We detected up to 17 host switches during Sphecodes evolution based on 37 ingroup species subject to mapping analysis of the hosts associated with the cuckoo bee species. We also examine the direction of evolution of host specialization in Sphecodes using the likelihood ratio test and obtain results to support the bidirectional evolutionary scenario in which specialists can arise from generalists, and vice versa. We explain the existence of generalist species in Sphecodes based on their specialization at the individual level, which is recently known in two species. Our findings suggest flexible host choice and frequent host switches in the evolution of Sphecodes cuckoo bees. This scenario leads us to propose an individual choice constancy hypothesis based on the individual specialization strategy in cuckoo bees. Choice constancy has a close relationship to flower constancy in bees and might be an extension of the latter. Our analysis also shows relationships among the genera Microsphecodes, Eupetersia, Sphecodes and Austrosphecodes, a formerly proposed Sphecodes subgenus. Austrosphecodes species form a basal lineage of the subtribe, and Microsphecodes makes it paraphyletic.

Solvent and Pressure Effects on the Motions of Encapsulated Guests: Tuning the Flexibility of a Supramolecular Host

The supramolecular host assembly [Ga4L6](12-) [1; L = 1,5-bis(2,3-dihydroxybenzamido)naphthalene] contains a flexible, hydrophobic interior cavity that can encapsulate cationic guest molecules and catalyze a variety of chemical transformations. The Ar-CH2 bond rotational barrier for encapsulated ortho-substituted benzyl phosphonium guest molecules is sensitive to the size and shape of the host interior space. Here we examine how changes in bulk solvent (water, methanol, or DMF) or applied pressure (up to 150 MPa) affect the rotational dynamics of encapsulated benzyl phosphonium guests, as a way to probe changes in host cavity size or flexibility. When host 1 is dissolved in organic solvents with large solvent internal pressures (∂U/∂V)T, we find that the free energy barrier to Ar-CH2 bond rotation increases by 1-2 kcal/mol, compared with that in aqueous solution. Likewise, when external pressure is applied to the host-guest complex in solution, the bond rotational rates for the encapsulated guests decrease. The magnitude of these rate changes and the volumes of activation obtained using either solvent internal pressure or applied external pressure are very similar. NOE distance measurements reveal shorter average host-guest distances (~0.3 Å) in organic versus aqueous solution. These experiments demonstrate that increasing solvent internal pressure or applied external pressure reduces the host cavity size or flexibility, resulting in more restricted motions for encapsulated guest molecules. Changing bulk solvent or external pressure might therefore be used to tune the physical properties or reactivity of guest molecules encapsulated in a flexible supramolecular host.

Plasmon mediated super-absorber flexible nanocomposites for metamaterials

A flexible host has been selected to achieve, for the first time, functional nanocomposites based on CdSe@ZnS core-shell type quantum dots (QDs) and Au nanoparticles (NPs), simultaneously dispersed in a polymer matrix. Coherent interactions between QDs and plasmonic Au NPs embedded in PDMS films have been demonstrated to lead to a relevant enhancement of the absorption cross-section of the QDs, remarkably modifying the optical response of the entire system. Optical and time resolved spectroscopy studies revealed an active gain-plasmon feedback behind the super-absorbing overall effect.

Guest encapsulation and coronene–C60 exchange in supramolecular zinc porphyrin tweezers, grids and prisms

Using a variant of the HETPHEN concept, heteroleptic 2D and 3D metallosupramolecular structures, such as tweezer T, grid G and tetragonal prism P, were fabricated quantitatively and characterised by (1)H NMR, (13)C NMR, (1)H-(1)H COSY, DOSY as well as ESI-MS. All structures encapsulate C60, with P showing the highest binding affinity (Kassoc = 3.3 × 10(6) M(-1)). The association constant increases along the series T < G < P, most likely due to the enhanced structural rigidity and better coplanarity of the two zinc porphyrin units. In contrast to T and G, the tetragonal prism P shows notable encapsulation of coronene (Kassoc = 1.1 × 10(4) M(-1)). In T and G, on the other hand, complexation of coronene is kinetically inhibited by the bulky mesityl rings at the porphyrin periphery. As illustrated in the facile displacement of coronene by C60 in coronene@P to furnish C60@P, P behaves as a flexible and guest-adaptive host.

A second combinatorial immune receptor in monocytes/macrophages is based on the TCRγδ

Recent evidence indicates that monocytes and macrophages express T cell receptor (TCR)αβ-like combinatorial immune receptors. Here, we demonstrate the presence of a second recombinatorial immunoreceptor, which is structurally based on the TCR γ- and δ-chains, in human and murine monocytes and differentially activated macrophages (referred to here as TCRLmγδ). In vitro, infection of macrophages with mycobacteria and gram positive or gram negative bacteria induced expression of donor-specific and differential TCRLm Vδ repertoires indicating that the novel immunoreceptor represents a dynamic flexible host defense system that responds to bacterial challenge. In vivo, we find that TCRLmγδ bearing macrophages, which express highly restricted repertoires of the antigen-binding Vδ chain, accumulate in the cerebrospinal fluid in acute bacterial meningitis and in advanced lesions of atherosclerosis. These results identify an as yet unrecognized monocyte/macrophage subpopulation that bears combinatorial TCRLm γδ immune receptors, and is associated with both acute and chronic inflammatory diseases. Moreover, they indicate that the monocytic lineage uses the same bipartite system of TCRαβ/TCRγδ-based combinatorial immune receptors that is present in T cells. Our findings suggest specific roles of monocytes/macrophages in various inflammatory conditions and lend further evidence that flexible immune recognition in higher vertebrates operates on a broader cellular basis than previously thought.

A Taco Complex Derived from a Bis-Crown Ether Capable of Executing Molecular Logic Operation through Reversible Complexation

As learned from natural systems, self-assembly and self-sorting help in interconnecting different molecular logic gates and thus achieve high-level logic functions. In this context, demonstration of important logic operations using changes in optical responses due to the formation of molecular assemblies is even more desirable for the construction of a molecular computer. Synthesis of an appropriate divalent as well as a luminescent crown ether based host 1 and paraquat derivatives, 2(PF(6))(2) and 3(PF(6))(2), as guests helped in demonstrating a reversible [3](taco complex) (1·{2(PF(6))(2)}(2) or 1·{3(PF(6))(2)}(2)) formation in nonpolar solvent. Detailed (1)H NMR studies revealed that two paraquat units were bound cooperatively by the two crown units in 1. Because of preorganization, the flexible host molecule 1 adopts a folded conformation, where each of two paraquat units remain sandwiched between the two aromatic units of each folded crown ether moiety in 1. Disassembly of the "taco" complex in the presence of KPF(6) and reassembly on subsequent addition of DB18C6 was initially demonstrated by (1)H NMR spectral studies, which were subsequently corroborated through luminescence spectral studies. Further, luminescence spectral responses as output signals with appropriate and two independent molecular inputs could be correlated to demonstrate basic logic operation like OR and YES gates, while the results of the three molecular inputs could be utilized to demonstrate important logic operation like an INHIBIT gate.

Low-Energy Isomer Identification, Structural Evolution, and Magnetic Properties in Manganese-Doped Gold Clusters MnAun (n = 1–16)

The size-dependent electronic, structural, and magnetic properties of Mn-doped gold clusters have been systematically investigated by using relativistic all-electron density functional theory with generalized gradient approximation. A number of new isomers are obtained for neutral MnAu(n) (n = 1-16) clusters to probe the structural evolution. The two-dimensional (2D) to three-dimensional (3D) transition occurs in the size range n = 7-10 with manifest structure competitions. From size n = 13 to n = 16, the MnAu(n) prefers a gold cage structure with Mn atom locating at the center. The relative stabilities of the ground-state MnAu(n) clusters show a pronounced odd-even oscillation with the number of Au atoms. The magnetic moments of MnAu(n) clusters vary from 3 μ(B) to 6 μ(B) with the different cluster size, suggesting that nonmagnetic Au(n) clusters can serve as a flexible host to tailor the dopant's magnetism, which has potential applications in new nanomaterials with tunable magnetic properties.

Polymer-based miniature flexible capacitive pressure sensor for intraocular pressure (IOP) monitoring inside a mouse eye

This paper presents an ultra-thin and flexible polymer-based capacitive pressure sensor for intraocular pressure (IOP) monitoring in a mouse eye. Due to the size limitation of the anterior chamber in the mouse eye, a volume of approximately 700 × 700 × 150μm(3) on a small substrate is available for the MEMS capacitive pressure sensor. Moreover, the sensor would ideally be easily injectable into place. Further complicating the sensing is the need to operate the device on the curved surface of the anterior chamber with minimum damage to the eye tissue. Therefore, a thin and flexible substrate is required. We fabricate sensors by exploiting Parylene as a biocompatible structural material in a suitable form factor and 25μm thick liquid crystal polymer (LCP) as a soft and flexible host substrate. Using our approach, the flexibility and small form factor necessary for a mouse eye implant is achieved, along with the sensitivity required to monitor IOP fluctuations. This device will allow better study of glaucoma through close monitoring in mice after integration with other components.

Interplay of solvent in flexible behaviour of cyclohexane dinapthyl bis-thiourea system: conformational aspects

Trans-1,2-bis-3-(naphthalen-1-yl) thioureido cyclohexane (L) compound is a new host material with considerable structural adaptability over a range of solvents. An investigation of the binding behaviours of solvents to the flexible host L was carried out in the solid phase as well as in the solution phase. The formation of these solvent-induced polymorph and the structural similarities and dissimilarities in their packing motifs can be rationalised through multipoint solute–solvent non-covalent interactions. In addition to strong hydrogen bonds, different types of non-covalent intermolecular C–H·…O, C–H·…S, N–H·…S C–H·…π, π·…π and lone pair·…π interactions were found to stabilise the crystal structures. Powder X-ray diffraction, thermal analysis and optical microscopic studies were performed to support the crystallographic studies. Solvent-dependent NMR spectroscopy shows significant change in the peak position with changes in the solvents. Furthermore, solution-phase photo-physical (especially steady state and time-resolved fluorescence) studies were also carried out to emphasise the role of the solvent polarity on the conformational flexibility of the host through non-covalent interactions.

Selectivity of amides by host–guest inclusion

The mechanism of selectivity by enclathration of four amides, N-methylformamide (NMF), dimethylformamide (DMF), N-methylacetamide (NMA) and dimethylacetamide (DMA), has been investigated by employing a bulky, flexible host. We measured the two-component selectivity curves for a mixture of amides, whose proportions in the crystals were determined by 1H NMR spectroscopy. The crystal structures of the single guest inclusion compounds were elucidated and analyzed. The subtle changes in the torsional flexibility of the host were correlated to the selectivity. The packing factor, which represents the occupied vs. available space by the guest in the crystal structures correlates with the measured selectivities.

Control of the charge-transfer interaction between a flexible porous coordination host and aromatic guests by framework isomerism

Based on 2,5-thiophenedicarboxylate (thdc), two isomorphic frameworks, [Zn(thdc)(dpNDI)]n, are assembled from zinc ions and N,N′-di(4-pyridyl)-1,4,5,8-naphthalenediimide (dpNDI). Because of the significant difference in their porous structures, these isomers show different charge-transfer interactions with electron-donating aromatic molecules.

Induction of host-plant preference in Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae)

The coconut hispine beetle, Brontispa longissima, is a serious invasive pest of coconut palm (Cocos nucifera) in Southeast Asia and the Pacific region. Recently, however, it has been reported that on Ishigaki Island, Japan, where C. nucifera is rare, the endemic palm Satakentia liukiuensis serves as a regular host. To explore this phenomenon, we examined the preferences of the beetle for the two palm hosts by choice tests and measurements of feeding amount using four different groups: naïve adults obtained from a colony reared on C. nucifera (NC); naïve adults from a colony reared on S. liukiuensis (NS); wild adults collected on C. nucifera on Ishigaki Island (WC); and wild adults collected on S. liukiuensis on Ishigaki Island (WS). Both NC and NS consumed significantly more C. nucifera leaves than S. liukiuensis leaves and were observed more often on the leaves of C. nucifera. These results suggest that B. longissima has an innate preference for C. nucifera. In contrast, field-collected adults (WC, WS) initially showed preferences for the species on which they were collected, but after exposure to the other host plant for 2 weeks, their preferences for that host increased. These results suggest that the feeding experience of B. longissima adults affected their subsequent host preferences. This flexible host preference may have facilitated the beetle’s successful establishment in novel Japanese habitats where the original host plant was rare.

Engineering of Linear Molecular Nanostructures by a Hydrogen-Bond-Mediated Modular and Flexible Host−Guest Assembly

The formation of a desired nanostructure with concomitant patterns and functions is of utmost importance in the field of surface molecular engineering and nanotechnology. We here present a flexible host-guest assembly, which steers the formation of linear molecular nanostructures on surfaces by a hydrogen-bond-mediated assembly process. A linear monodendron molecular template with periodic hydrogen-bond binding sites is shown to accommodate a variety of molecules with pyridylethynyl terminals. The unit cell parameters in the transverse direction of the linear pattern can be tuned from 3.4 to 7.3 nm in response to the packing of the guest molecules with different sizes, shapes, and aggregation number. The introduction of hydrogen-bonding partners into the host template and into guest molecules is responsible for the steering of the linear pattern of guest molecules. The modular approach could greatly facilitate the ordering of guest molecules with desired functional moieties.

Multiple growths of epitaxial lift-off solar cells from a single InP substrate

We demonstrate multiple growths of flexible, thin-film indium tin oxide-InP Schottky-barrier solar cells on a single InP wafer via epitaxial lift-off (ELO). Layers that protect the InP parent wafer surface during the ELO process are subsequently removed by selective wet-chemical etching, with the active solar cell layers transferred to a thin, flexible plastic host substrate by cold welding at room temperature. The first- and second-growth solar cells exhibit no performance degradation under simulated Atmospheric Mass 1.5 Global (AM 1.5G) illumination, and have a power conversion efficiency of ηp=14.4±0.4% and ηp=14.8±0.2%, respectively. The current-voltage characteristics for the solar cells and atomic force microscope images of the substrate indicate that the parent wafer is undamaged, and is suitable for reuse after ELO and the protection-layer removal processes. X-ray photoelectron spectroscopy, reflection high-energy electron diffraction observation, and three-dimensional surface profiling show a surface that is comparable or improved to the original epiready wafer following ELO. Wafer reuse over multiple cycles suggests that high-efficiency; single-crystal thin-film solar cells may provide a practical path to low-cost solar-to-electrical energy conversion.

Dynamic gas separation on a flexible single-crystal host

Dynamic gas separation on a flexible single-crystal host