One-dimensional copper(II) coordination polymers bridged both by mu-trans-oxamidates and phenyldicarboxylates: Synthesis, crystal structure and DNA binding studies

Two new one-dimensional copper(II) polymers with formulae of [Cu₂(H₂O)₂(dmapox)(ipa)₂]_n (1) and [Cu₂(H₂O)₂(dmapox)(tpa)₂]_n (2), where dmapox, ipa and tpa stand for the dianion of N,N′-bis[3-(dimethylamino)propyl]oxamide, isophthalic acid and terephthalic acid respectively, have been synthesized and characterized by elemental analysis, conductivity measurement, IR and electronic spectral studies. The crystal structures of the two complexes have been determined by X-ray single-crystal diffraction. The structures of 1 and 2 consist of one-dimensional copper(II) coordination polymeric chain constructed both by the bis-tridentate trans-dmapox and bis-monodentate phenyldicarboxylate bridging ligands. In the two complexes, the environment around the copper(II) atoms can be described as distorted square-pyramid and the Cu···Cu separations through μ-trans-dmapox and phenyldicarboxylato bridging ligands are 5.245(5) Å and 8.212(3) Å for 1, 5.237(8) Å and 11.171(1) Å for 2, respectively. The binding properties of the two copper(II) polymers with herring sperm DNA (HS-DNA) have been investigated by using absorption and emission spectral and electrochemical techniques and viscometry. The results show that the two copper(II) complexes interact with the HS-DNA in the mode of intercalation with the intrinsic binding constants of 1.22(±0.2) × 10⁴ M⁻¹ and 1.45(±0.3) × 10⁴ M⁻¹ for 1 and 2, respectively.     

Biological characterization of Sorona polymer from corn-derived 1,3-propanediol

The Sorona family of polymers, based on corn-derived 1,3-propanediol, have recently been developed as novel bio-based materials for use in plastics, films, and fibers. In the present study, Sorona polymers were investigated for their effects on cell survival and inflammatory cell activation using in vitro mouse cell cultures. Cytotoxicity of Sorona polymers was evaluated by placing material samples in direct contact with 3T3 fibroblast cells. Both Sorona plastic and Sorona films were non-cytotoxic to fibroblasts. The inflammatory potential of Sorona samples was evaluated by exposing J774 macrophage cells to material samples, and measuring TNF-α release from macrophages. Sorona plastic and Sorona films did not elicit inflammatory TNF-α release from macrophages. These results indicate that Sorona polymers are non-cytotoxic and non-inflammatory. While the 1,3-propanediol component of Sorona 3GT is manufactured in a bacterial fermentation process, the absence of an inflammatory response to Sorona film and Sorona plastic is highly encouraging. The results are significant for the design of materials that utilize bio-based polymers.     

Molecular homochirality and the parity-violating energy difference. A critique with new proposals

Previous proposals for the origin of molecular homochirality, based on the effect of the weak neutral current (WNC) on enantiomers, and the amplification of the resultant parity-violating energy difference (PVED), are possibly flawed. The additive amplification of PVED in crystals and polymers ("Yamagata hypothesis") cannot lead to detectable levels of optical activity, the original theory apparently overestimating PVED by a factor equal to Avogadro's number. An alternative theory based on the irreversible and spontaneous evolution of a dynamically fluctuating system is apparently impractical. However, the nonlinear amplification of PVED via autocatalytic polymerization may be possible as indicated by a simplified physico-chemical approach. This may also occur during crystallization and melting, and form the basis of the second order asymmetric transformation. (Thus, reported differences in the melting points of enantiomers in several cases may well be real). Also, the preponderance of racemic compounds over conglomerates may be based on the destabilization of the conglomerate by the action of the WNC on the crystalline lattice. The WNC may also be involved in the anomalous scattering of X-rays, which possibly arises from their circular polarization: the current theory would need to be revised accordingly.     

Protein-responsive imprinted polymers with specific shrinking and rebinding

Stimuli-responsive protein imprinted polymers were obtained via a combination of molecular imprinting and reversible stimuli-responsive polymer using lysozyme or cytochrome c as template, N-isopropylacrylamide (NIPA) as major monomer, methacrylic acid (MAA) and acrylamide (AAm) as functional co-monomers, and N,N-methylenebisacrylamide (MBAAm) as crosslinker. The molecularly imprinted polymers (MIPs) can respond not only to external stimuli such as temperature and salt concentration, but also to the corresponding template protein with significant specific volume shrinking. This specific shrinking behavior was attributed to the synergistic effect of multiple-site weak interactions (electrostatic force, hydrogen bonding and hydrophobic interaction) and the cavity effect. The MIPs showed highly selective adsorption of template proteins with specific shrinking compared with the non-imprinted polymers. The results indicated that the MIPs seemed to change shape to accommodate the conformation of the template protein leading to the formation of a shape complementary cavity.     

Chelating efficiency and thermal, mechanical and decay resistance performances of chitosan copper complex in wood-polymer composites

Wood–polymer composites (WPC) have been extensively used for building products, outdoor decking, automotive, packaging materials, and other applications. WPC is subject to fungal and termite attacks due to wood components enveloped in the thermoplastic matrix. Much effort has been made to improve decay resistance of WPC using zinc borate and other chemicals. In this study, chitosan copper complex (CCC) compounds were used as a potential preservative for wood–HDPE composites. CCC was formulated by reacting chitosan with copper salts under controlled conditions. Inductively coupled plasma (ICP) analytical results indicated that chitosan had high chelating efficiency with copper cations. CCC-treated wood–HDPE composites had a thermal behavior similar to untreated and zinc borate-treated wood–HDPE composites. Incorporation of CCC in wood–HDPE composites did not significantly influence board density of the resultant composites, but had a negative effect on tensile strength at high CCC concentration. In comparison with solid wood and the untreated wood–HDPE composites, 3% CCC-treated wood–HDPE composites significantly improved the decay resistance against white rot fungus Trametes versicolor and brown rot fungus Gloeophyllum trabeum. Especially, CCC-treated wood–HDPE composites were more effectively against the brown rot than the untreated and chitosan-treated wood–HDPE composites. Moreover, CCC-treated wood–HDPE composites performed well as zinc borate-treated wood–HDPE composites on fungal decay resistance. Accordingly, CCC can be effectively used as a preservative for WPC.     

Thioredoxin as a fusion tag for carrier-driven crystallization

Structural investigations are frequently hindered by difficulties in obtaining diffracting crystals of the target protein. Here, we report the crystallization and structure solution of the U2AF homology motif (UHM) domain of splicing factor Puf60 fused to Escherichia coli thioredoxin A. Both modules make extensive crystallographic contacts, contributing to a well-defined crystal lattice with clear electron density for both the thioredoxin and the Puf60-UHM module. We compare two short linker sequences between the two fusion domains, GSAM and GSPPM, for which only the GSAM-linked fusion protein yielded diffracting crystals. While specific interdomain contacts are not observed for both fusion proteins, NMR relaxation data in solution indicate reduced interdomain mobility between the Trx and Puf60-UHM modules. The GSPPM-linked fusion protein is significantly more flexible, albeit both linker sequences have the same number of degrees of torsional freedom. Our analysis provides a rationale for the crystallization of the GSAM-linked fusion protein and indicates that in this case, a four-residue linker between thioredoxin A and the fused target may represent the maximal length for crystallization purposes. Our data provide an experimental basis for the rational design of linker sequences in carrier-driven crystallization and identify thioredoxin A as a powerful fusion partner that can aid crystallization of difficult targets.     

Novel fold of VirA, a type III secretion system effector protein from Shigella flexneri

VirA, a secreted effector protein from Shigella sp., has been shown to be necessary for its virulence. It was also reported that VirA might be related to papain-like cysteine proteases and cleave alpha-tubulin, thus facilitating intracellular spreading. We have now determined the crystal structure of VirA at 3.0 A resolution. The shape of the molecule resembles the letter "V," with the residues in the N-terminal third of the 45-kDa molecule (some of which are disordered) forming one clearly identifiable domain, and the remainder of the molecule completing the V-like structure. The fold of VirA is unique and does not resemble that of any known protein, including papain, although its N-terminal domain is topologically similar to cysteine protease inhibitors such as stefin B. Analysis of the sequence conservation between VirA and its Escherichia coli homologs EspG and EspG2 did not result in identification of any putative protease-like active site, leaving open a possibility that the biological function of VirA in Shigella virulence may not involve direct proteolytic activity.     

Toward chaperone-assisted crystallography: protein engineering enhancement of crystal packing and X-ray phasing capabilities of a camelid single-domain antibody (VHH) scaffold

A crystallization chaperone is an auxiliary protein that binds to a target of interest, enhances and modulates crystal packing, and provides high-quality phasing information. We critically evaluated the effectiveness of a camelid single-domain antibody (V(H)H) as a crystallization chaperone. By using a yeast surface display system for V(H)H, we successfully introduced additional Met residues in the core of the V(H)H scaffold. We identified a set of SeMet-labeled V(H)H variants that collectively produced six new crystal forms as the complex with the model antigen, RNase A. The crystals exhibited monoclinic, orthorhombic, triclinic, and tetragonal symmetry and have one or two complexes in the asymmetric unit, some of which diffracted to an atomic resolution. The phasing power of the Met-enriched V(H)H chaperone allowed for auto-building the entire complex using single-anomalous dispersion technique (SAD) without the need for introducing SeMet into the target protein. We show that phases produced by combining SAD and V(H)H model-based phases are accurate enough to easily solve structures of the size reported here, eliminating the need to collect multiple wavelength multiple-anomalous dispersion (MAD) data. Together with the presence of high-throughput selection systems (e.g., phage display libraries) for V(H)H, the enhanced V(H)H domain described here will be an excellent scaffold for producing effective crystallization chaperones.     

Crystal structure of human coactosin-like protein at 1.9 A resolution

Human coactosin-like protein (CLP) shares high homology with coactosin, a filamentous (F)-actin binding protein, and interacts with 5LO and F-actin. As a tumor antigen, CLP is overexpressed in tumor tissue cells or cell lines, and the encoded epitopes can be recognized by cellular and humoral immune systems. To gain a better understanding of its various functions and interactions with related proteins, the crystal structure of CLP expressed in Escherichia coli has been determined to 1.9 A resolution. The structure features a central beta-sheet surrounded by helices, with two very tight hydrophobic cores on each side of the sheet. CLP belongs to the actin depolymerizing protein superfamily, and is similar to yeast cofilin and actophilin. Based on our structural analysis, we observed that CLP forms a polymer along the crystallographic b axis with the exact same repeat distance as F-actin. A model for the CLP polymer and F-actin binding has therefore been proposed.     

Cyanide Self-Addition,Controlled Adsorption,and Other Processes at Layered Double Hydroxides

Layered double hydroxides (LDH) are anion-exchangingmaterials of the type M(III)-M(II)_x(OH)_(2x+2)Y thatoccur abundantly in nature, and can concentrate, protect, andactivate simple organic anionic species of possible relevance tothe earliest organisms. We now wish to report progress in thefollowing areas:1) Internal vs. external uptake of anions. Ferrocyanidedoes not displace carbonate from synthetic hydrotalcite (Mg:AlLDH carbonate) but is nevertheless taken up on the outside of theparticles. In other cases, anion uptake is controlled byspecific hydrogen bonding requirements rather than by chargedensity alone, a feature that can be used to control whetheruptake will be both internal and external, or external only. These two findings taken together have important implications forspecific catalysis by LDH, since specific hydrogen bonding willaffect the individual and relative conformations of substrateanions, and anions occupying space in the interlayer will beunder tighter constraints than those adsorbed externally.2) Specific reactions catalyzed by LDH. We have found thatthe LDH Mg₂Al(OH)₆Cl catalyzes the self-addition ofcyanide, to give in a one-pot reaction at low concentrations anincreased yield of diaminomaleonitrile and in addition, at higher( 0.05M) concentrations, a purple-pink material that adheres tothe LDH. We are investigating whether this reaction also occurswith hydrotalcite itself, what is the minimum effectiveconcentration of cyanide, and what can be learned about theproducts and how they compare with those reported at high HCNconcentrations in the absence of catalyst.