Shape Memory Hydrogels Based on Noncovalent Interactions

Shape memory polymers (SMPs) are polymeric materials that are capable of fixing temporary shape and recovering the permanent shape in response to external stimuli. In particular, supramolecular interactions and dynamic covalent bond have recently been introduced as temporary switches to construct supramolecular shape memory hydrogels (SSMHs), arising as promising materials since they can exhibit excellent cycled shape memory behavior at room temperature. On the other hand, hydrogels, conventionally, are flexible but sometimes extremely soft, and they can be easily damaged under external force, which could limit their long-time application. Therefore, self-healing hydrogels that can be rapidly auto-repaired when the damage occurs have been recently developed to solve this problem. These materials present more than one triggering stimulus that can be used to induce the shape memory and self-healing effect. These driven forces can be originated from hydrogen bonds, hydrophobic interactions, and reversible covalent bonds, among others. Beyond all these, hybrid organic-inorganic interactions represent an interesting possibility due to their versatility and favorable properties that allow the fabrication of multiresponsive hydrogels. In this chapter, shape memory hydrogels based on noncovalent interactions are described

Tetra­kis(μ2-ferrocene­carboxyl­ato-κ2 O:O′)bis­[(methanol-κO)copper(II)] methanol disolvate

The complex mol­ecule of the title compound, [Cu2Fe4(C5H5)4(C6H4O2)4(CH3OH)2]·2CH3OH, lies about an inversion centre and contains two centrosymetrically related CuII atoms bridged by four O:O′-bidentante ferrocene­carboxyl­ate anions, leading to a dimeric tetra­bridged unit with a paddle-wheel geometry. The CuII atom has a distorted square-pyramidal coordination environment with four O atoms from four ferrocene­carboxyl­ate ligands in basal positions and an O atom from a methanol mol­ecule in an apical position. One of the two crystallographically independent ferrocenyl groups has a staggered conformation, while the other is eclipsed. The mol­ecules are connected into a chain along the b axis by O—H⋯O hydrogen bonds involving coordinated and uncoordinated methanol mol­ecules and the O atom from a ferrocene­carboxyl­ate unit

Vegetation pattern modulates ground arthropod diversity in semi-arid Mediterranean steppes

The ecological functioning of dryland ecosystems is closely related to the spatial pattern of the vegetation, which is typically structured in patches. Ground arthropods mediate key soil functions and ecological processes, yet little is known about the influence of dryland vegetation pattern on their abundance and diversity. Here, we investigate how patch size and cover, and distance between patches relate to the abundance and diversity of meso-and microarthropods in semi-arid steppes. We found that species richness and abundance of ground arthropods exponentially increase with vegetation cover, patch size, and patch closeness. The communities under vegetation patches mainly respond to patch size, while the communities in the bare-soil interpatches are mostly controlled by the average distance between patches, independently of the concurrent changes in vegetation cover. Large patches seem to play a critical role as reserve and source of ground arthropod diversity. Our results suggest that decreasing vegetation cover and/or changes in vegetation pattern towards small and over-dispersed vegetation patches can fast lead to a significant loss of ground arthropods diversity in drylands

Thermostructural behavior in a series of lanthanide-containing polyoxotungstate hybrids with copper(II) complexes of the tetraazamacrocycle cyclam: a single-crystal-to-single-crystal transformation study

A series of 14 isostructural [Cu(cyclam)](2)[{Cu(cyclam)}4{(a-GeW11O39)Ln(H2O)-(OAc)(12)].18H(2)O (1-Ln, where Ln = La Lu; cyclam = 1,4,8,11-tetraazacyclotetradecane) polyoxometalate-based hybrids reported herein represent (i) the first example of a twodimensional covalent hybrid lattice involving the [{(aXWI 1039)Ln(H2O)(OAc)}2in- archetype and (ii) the first structural characterization of such a dimeric polyoxotungste for Ln = La and Pr as well as for the combination of X = Ge and Ln = Ce, Nd, Sm, or Lu. Compounds 1-Ln have been characterized by elemental analyses, infrared spectroscopy, and thermogravimetric analysis, and their thermostructural behavior has been monitored by powder and single-crystal Xray diffraction. The title compounds undergo two single-crystal-to-single-crystal transformations triggered dehydration leading to the [{Cu(cydam)}6{(alpha-GeW11O39)Ln(H2O)(OAc)}2]-4H(2)O intermediate (2-Ln, where Ln = Eu or Er) and [Cu(cyclam)]0.5[{Cu(cyclam)}55{(alpha-GeW11O39)Ln(0Ac)}2] (3-Ln, where Ln = Ce or Eu) final anhydrous phases, the latter evidencing a coordinatively unsaturated derivative of the dimeric archetype for the first time. These transitions involve formation and disruption of Cu Opom bonds that result in different {Cu(cydam)}(2+) moieties grafting onto and being released from Keggin surfaces, which reduces the dimensionality of 1-Ln to one-dimensional covalent assemblies for 2-Ln and 3-Ln. While all 3-Ln phases rehydrate fully upon exposure to air for 24 h, the kinetics governing the crystal transitions back toward 1Ln through 2-Ln depend on the nature of Ln. Under ambient moisture, the anhydrous structures fully revert back to the parent framework for Ln = La Sm, while the samples containing Eu to Lu afford mixtures of 1-Ln and 2-Ln and require immersion in water for the structural reversion to reach completion. Single-crystal X-ray diffraction analyses of the rehydrated 1R-Ln samples (Ln = Ce, Eu, and Er) support these observations.This work was funded by Eusko Jaurlaritza/Gobierno Vasco (Grant PIBA2018-59 and ELKARTEK bG18 10(2018/00054), MINECO (Grant MAT2017-89553-P), and UPV/EHU (Grants PPG17/37 and GIU17/050). S.R. thanks Obra Social la Caixa, Fundacion Caja Navarra, and UPNA for a research contract in the framework of the program "Captación del Talento". Technical and human support provided by SGIker (UPV/EHU) is gratefully acknowledged

Arabidopsis SWC4 Binds DNA and Recruits the SWR1 Complex to Modulate Histone H2A.Z Deposition at Key Regulatory Genes

Deposition of the H2A.Z histone variant by the SWR1 complex (SWR1-C) in regulatory regions of specific loci modulates transcription. Characterization of mutations in Arabidopsis thaliana homologs of yeast SWR1-C has revealed a role for H2A.Z exchange in a variety of developmental processes. Nevertheless, the exact composition of plant SWR1-C and how it is recruited to target genes remains to be established. Here we show that SWC4, the Arabidopsis homolog of yeast SANT domain protein Swc4/Eaf2, is a DNA-binding protein that interacts with SWR1-C subunits. We demonstrate that the swc4-1 knockout mutant is embryo-lethal, while SWC4 RNAi knockdown lines display pleiotropic phenotypic alterations in vegetative and reproductive traits, including acceleration of flowering time, indicating that SWC4 controls post-embryonic processes. Transcriptomic analyses and genome-wide profiling of H2A.Z indicate that SWC4 represses transcription of a number of genes, including the floral integrator FT and key transcription factors, mainly by modulating H2A.Z deposition. Interestingly, SWC4 silencing does not affect H2A.Z deposition at the FLC locus nor expression of this gene, a master regulator of flowering previously shown to be controlled by SWR1-C. Importantly, we find that SWC4 recognizes specific AT-rich DNA elements in the chromatin regions of target genes and that SWC4 silencing impairs SWR1-C binding at FT. Collectively, our data suggest that SWC4 regulates plant growth and development by aiding SWR1-C recruitment and modulating H2A.Z deposition.This work was supported by grants BIO2010-15589, BIO2013-43098-R, and BIO2016-77559-R to J.A.J. and M.P., and grant RYC-2013-14689 to P.C. from the Spanish Ministerio de Economia y Competitividad (MINECO/FEDER, EU), and Marie Curie FP7-PEOPLE-2011-IEF grant 298790 to P.C. and J.A.J. from the European Commission. The CBGP is a Severo Ochoa Center of Excellence (SEV-2016-0672). The CNIC is supported by the Spanish Ministerio de Economia, Industria y Competitividad and the Pro CNIC Foundation, and is also a Severo Ochoa Center of Excellence (SEV-2015-0505).S

Six tris(bipyridyl)iron(II) complexes with 2-substituted 1,1,3,3-tetracyanopropenide, perchlorate and tetrafluoridoborate anions; order versus disorder, hydrogen bonding and C - N⋯π interactions

ZS gratefully acknowledges the Algerian DGRSDT (Direction Générale de la Recherche Scientifique et du Développement Technologique) and Université Ferhat Abbas Sétif 1 for financial support.Structures are reported for six closely related salts of tris(bipyridyl)iron(II) cations, namely tris(2,2′-bipyridine)iron(II) bis(1,1,3,3-tetracyano-2-methoxypropenide) 0.776-hydrate, [Fe(C10H8N2)3](C8H3N4O)2.0.776H2O, (I), tris(2,2′-bipyridine)iron(II) 1,1,3,3-tetracyano-2-(propylsulfanyl)propenide perchlorate, [Fe(C10H8N2)3](C10H7N4S)(ClO4), (II), tris(5,5′-dimethyl-2,2′-bipyridine)iron(II) 1,1,3,3-tetracyano-2-methoxypropenide tetrafluoridoborate ethanol 0.926-solvate, [Fe(C12H12N2)3](C8H3N4O)(BF4).0.926C2H2O, (III), tris(5,5′-dimethyl-2,2′-bipyridine)iron(II) 1,1,3,3-tetracyano-2-ethoxypropenide tetrafluoridoborate, [Fe(C12H12N2)3](C9H5N4O)(BF4), (IV), tris(5,5′-dimethyl-2,2′-bipyridine)iron(II) 1,1,3,3-tetracyano-2-(ethylsufanyl)propenide tetrafluoridoborate, [Fe(C12H12N2)3](C9H5N4S)(BF4), (V), and tris(5,5′-dimethyl-2,2′-bipyridine)iron(II) 1,1,3,3-tetracyano-2-propoxypropenide tetrafluoridoborate, [Fe(C12H12N2)3](C10H7N4O)(BF4), (VI). In compound (I), one of the anions is disordered over two sets of atomic sites with equal occupancies while, in the second anion, just one of the C(CN)2 units is disordered, again over two sets of atomic sites with equal occupancies: the anionic components are linked by multiple C - H⋯N hydrogen bonds to form a three-dimensional framework. In compound (II), the polynitrile anion is disordered over two sets of atomic sites with occupancies in the approximate ratio 3:1, while the perchlorate anion is disordered over three sets of atomic sites: there are C - N⋯π interactions between the cations and the polynitrile anion. The polynitrile anion in compound (III) is fully ordered, but the tetrafluoridoborate anion is disordered over two sets of atomic sites with occupancies 0.671 (4) and 0.329 (4): the cations and the tetrafluoridoborate anions are linked by C - H⋯F interactions to form an interrupted chain. Compounds (IV) and (V) are isostructural and all of the ionic components are fully ordered in both of them: the cations and tetrafluoridoborate anions are linked into C22(12) chains. The polynitrile anion in compound (VI) is disordered over two sets of atomic sites with approximately equal occupancies, and here the chains formed by the cations and the tetrafluoridoborate anions are of the C22(13) type.Publisher PDFPeer reviewe

Consecutive single-crystal-to-single-crystal isomerization of novel octamolybdate anions within a microporous hybrid framework with robust water sorption properties

The 3D hybrid framework [{Cu(cyclam)}3(kMo8O27)]· 14H2O (1) (cyclam=1,4,8,11-tetraazacyclotetradecane) undergoes sequential single-crystal-to-singlecrystal transformations upon heating to afford two different anhydrous phases (2 a and 3a). These transitions modify the framework dimensionality and enable the isomerization of k-octamolybdate (k-Mo8) anions into λ (2 a) and μ (3 a) forms through metal migration. Hydration of 3 a involves condensation of one water molecule to the cluster to afford the γ-Mo8 isomer in 4, which dehydrates back into 3a through the 6a intermediate. In contrast, 2a reversibly hydrates to form 5, exhibiting the same Mo8 cluster as that of 1. It is remarkable that three of the Mo8 clusters (k, λ and μ) are new and that up to three different microporous phases can be isolated from 1 (2 a, 3a, and 6a). Water vapor sorption analyses show high recyclability and the highest uptake values for POM-based systems. The isotherms display an abrupt step at low humidity level desirable for humidity control devices or water harvesting in drylands.Funded by Eusko Jaurlaritza/Gobierno Vasco (EJ/GV, grants IT1722-22 and KK-2022/00045). E.R.B. thanks EJ/GV for her doctoral fellowship (PRE_2018_1_0143)