Structure and physical properties of [µ-Tris(1,4-bis(tetrazol-1-yl)butane-N4,N4‘')iron(II)] Bis(hexafluorophosphate), a new Fe(II) spin-crossover compound with a three-dimensional threefold interlocked crystal lattice

[μ-Tris(1,4-bis(tetrazol-1-yl)butane-N4,N4‘)iron(II)] bis(hexafluorophosphate), [Fe(btzb)3](PF6)2, crystallizes in a three-dimensional 3-fold interlocked structure featuring a sharp two-step spin-crossover behavior. The spin conversion takes place between 164 and 182 K showing a discontinuity at about T1/2 = 174 K and a hysteresis of about 4 K between T1/2 and the low-spin state. The spin transition has been independently followed by magnetic susceptibility measurements, 57Fe-Mössbauer spectroscopy, and variable temperature far and midrange FTIR spectroscopy. The title compound crystallizes in the trigonal space group P30¯(No. 147) with a unit cell content of one formula unit plus a small amount of disordered solvent. The lattice parameters were determined by X-ray diffraction at several temperatures between 100 and 300 K. Complete crystal structures were resolved for 9 of these temperatures between 100 (only low spin, LS) and 300 K (only high spin, HS), Z = 1 [Fe(btzb)3](PF  6)2:  300 K (HS), a = 11.258(6) Å, c = 8.948(6) Å, V = 982.2(10) Å3; 100 K (LS), a = 10.989(3) Å, c = 8.702(2) Å, V = 910.1(4) Å3. The molecular structure consists of octahedral coordinated iron(II) centers bridged by six N4,N4‘ coordinating bis(tetrazole) ligands to form three 3-dimensional networks. Each of these three networks is symmetry related and interpenetrates each other within a unit cell to form the interlocked structure. The Fe−N bond lengths change between 1.993(1) Å at 100 K in the LS state and 2.193(2) Å at 300 K in the HS state. The nearest Fe separation is along the c-axis and identical with the lattice parameter c.

Polymer-lipid interactions:biomimetic self-assembly behaviour and surface properties of poly(styrene-alt-maleic acid) with diacylphosphatidylcholines

Abstract Various lubricating body fluids at tissue interfaces are composed mainly of combinations of phospholipids and amphipathic apoproteins. The challenge in producing synthetic replacements for them is not replacing the phospholipid, which is readily available in synthetic form, but replacing the apoprotein component, more specifically, its unique biophysical properties rather than its chemistry. The potential of amphiphilic reactive hypercoiling behaviour of poly(styrene-alt-maleic acid) (PSMA) was studied in combination with two diacylphosphatidylcholines (PC) of different chain lengths in aqueous solution. The surface properties of the mixtures were characterized by conventional Langmuir-Wilhelmy balance (surface pressure under compression) and the du Noüy tensiometer (surface tension of the non-compressed mixtures). Surface tension values and 31P NMR demonstrated that self-assembly of polymer-phospholipid mixtures were pH and concentration-dependent. Finally, the particle size and zeta potential measurements of this self-assembly showed that it can form negatively charged nanosized structures that might find use as drug or lipids release systems on interfaces such as the tear film or lung interfacial layers. The structural reorganization was sensitive to the alkyl chain length of the PC.

Downcore rock-magnetic properties of ICDP Core 5045-1, Lake Ohrid

The bulk magnetic mineral record from Lake Ohrid, spanning the past 637 kyr, reflects large-scale shifts in hydrological conditions, and, superimposed, a strong signal of environmental conditions on glacial-interglacial and millennial timescales. A shift in the formation of early diagenetic ferrimagnetic iron sulfides to siderites is observed around 320 ka. This change is probably associated with variable availability of sulfide in the pore water. We propose that sulfate concentrations were significantly higher before ~320 ka, due to either a higher sulfate flux or lower dilution of lake sulfate due to a smaller water volume. Diagenetic iron minerals appear more abundant during glacials, which are generally characterized by higher Fe/Ca ratios in the sediments. While in the lower part of the core the ferrimagnetic sulfide signal overprints the primary detrital magnetic signal, the upper part of the core is dominated by variable proportions of high- to low-coercivity iron oxides. Glacial sediments are characterized by high concentration of high-coercivity magnetic minerals (hematite, goethite), which relate to enhanced erosion of soils that had formed during preceding interglacials. Superimposed on the glacial-interglacial behavior are millennial-scale oscillations in the magnetic mineral composition that parallel variations in summer insolation. Like the processes on glacial-interglacial timescales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock-magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi-level contribution to environmental reconstructions, since the magnetic properties can mirror both environmental conditions on land and intra-lake processes.

Chitosan gel film bandages: correlating structure, composition, and antimicrobial properties

Chitosan gel films were successfully obtained by evaporation cast from chitosan solutions in aqueous acidic solutions of organic acids (lactic and acetic acid) as gel film bandages, with a range of additives that directly influence film morphology and porosity. We show that the structure and composition of a wide range of 128 thin gel films, is correlated to the antimicrobial properties, their biocompatibility and resistance to biodegradation. Infrared spectroscopy and solid-state 13C nuclear magnetic resonance spectroscopy was used to correlate film molecular structure and composition to good antimicrobial properties against 10 of the most prevalent Gram positive and Gram negative bacteria. Chitosan gel films reduce the number of colonies after 24 h of incubation by factors of ∼105–107 CFU/mL, compared with controls. For each of these films, the structure and preparation condition has a direct relationship to antimicrobial activity and effectiveness. These gel film bandages also show excellent stability against biodegradation with lysozyme under physiological conditions (5% weight loss over a period of 1 month, 2% in the first week), allowing use during the entire healing process. These chitosan thin films and subsequent derivatives hold potential as low-cost, dissolvable bandages, or second skin, with antimicrobial properties that prohibit the most relevant intrahospital bacteria that infest burn injuries.

Crystallographic and magnetic identification of secondary phase in orientated Bi 5Fe 0.5Co 0.5Ti 3O 15 ceramics

The fabrication of highly-oriented polycrystalline ceramics of Bi 5Fe 0.5Co 0.5Ti 3O 15, prepared via molten salt synthesis and uniaxial pressing of high aspect ratio platelets is reported. Electron backscatter images show a secondary phase within the ceramic which is rich in cobalt and iron. The concentration of the secondary phase obtained from scanning electron microscopy is estimated at less than 2% by volume, below the detection limit of x-ray diffraction (XRD). The samples were characterized by x-ray diffraction, polarization-electric field measurements, superconducting quantum interference device as a function of sample orientation and vibrating sample magnetometry as a function of temperature. It is inferred from the data that the observed ferromagnetic response is dominated by the secondary phase. This work highlights the importance of rigorous materials characterisation in the study of multiferroics as small amounts of secondary phase, below the limit of XRD, can lead to false conclusions.

Magnetic properties of maar lake sediments from Otago, New Zealand

Foulden Maar is a highly resolved maar lake deposit from the South Island of New Zealand comprising laminated diatomite punctuated by numerous diatomaceous turbidites. Basaltic clasts found in debris flow deposits at the base of the cored sedimentary sequence yielded two new 40Ar/39Ar dates of 24.51±0.24 Ma and 23.38±0.24 Ma (2sigma). The younger date agrees within error with a previously published 40Ar/39Ar date of 23.17±0.19 Ma from a basaltic dyke adjacent to the maar crater. The diatomite is inferred to have been deposited over several tens of thousands of years in the latest Oligocene/earliest Miocene, and may have overlapped with the period of rapid glaciation and subsequent deglaciation of Antarctica known as the Mi-1 event. Sediment magnetic properties and SEM measurements indicate that the magnetic signal is dominated by pseudo-single domain pyrrhotite. The most likely source of detrital pyrrhotite is schist country rock fragments from the inferred tephra ring created by the phreatomagmatic eruption that formed the maar. Variations in magnetic concentration and lamina thickness indicate a decrease in erosional input and increase in diatom productivity throughout the depositional period, suggesting a long-term (tens of thousands of years) climatic change in New Zealand in the latest Oligocene/earliest Miocene.

Magnetic properties of the oceanic igneous rocks (Table 1)

Hysteresis measurements have been carried out on a suite of ocean-floor basalts with ages ranging from Quaternary to Cretaceous. Approximately linear, yet separate, relationships between coercivity (Bc) and the ratio of saturation remanence/saturation magnetization (Mrs/Ms) are observed for massive doleritic basalts with low-Ti magnetite and for pillow basalts with multi-domain titanomagnetites (with x= 0.6). Even when the MORB has undergone lowtemperature oxidation resulting in titanomaghemite, the parameters are still distinguishable, although offset from the trend for unoxidized multidomain titanomagnetite. The parameters for these iron oxides with different titanium content reveal contrasting trends that can be explained by the different saturation magnetizations of the mineral types. This plot provides a previously underutilized and non-destructive method to detect the presence of low-titanium magnetite in igneous rocks, notably MORB.

Isotopic and magnetic provenance characterization of distal IRD in the Galicia Interior Basin (NW Iberia)

The sediments of the Galicia Interior Basin in NW Iberia Margin are of particular palaeoclimatic interest as they are located at the boundary where the climatic oscillations of the glacial interval were interrupted by extreme events such as Heinrich events. These events are well characterized in Northern North Atlantic areas, but little is known about their occurrence beyond the Ruddiman belt. This study presents a combined environmagnetic and geochemical approach to the provenance and characterization of distal ice-rafted detritus (IRD) that occurred during the last glacial period in core CI12PC3 from the Galicia Interior Basin. The last six Heinrich Layers were identified by their magneto-mineralogical and geochemical properties. Their Sr and Nd isotopic signatures indicated that the Laurentide Ice Sheet was the major source for HL1, HL2, HL4 and HL5. However, the European ice sheets also influenced the initial development stages of HL1, HL2, HL4. HL3, HL6 and partially HL1, HL2 and HL4 were influenced by more juvenile provinces, such as Iceland/Faroes sheets and/or by the Fram Strait/East Greenland nearby areas. Separate provenance analyses of the coarse and fine fractions in the studied Heinrich Layers also indicated that IRDs and glacial flour sources might not always be the same. Our results shed unequivocal evidence that Canadian-sourced distal IRD are preceded by European-sourced IRD, at least from the H4. In our view, LIS and EIS instabilities registered in the Iberian Margin respond to the same climate forcing at different velocities.

The structural and mechanical integrity of historic wood

Little is known about historic wood as it ages naturally. Instead, most studies focus on biological decay, as it is often assumed that wood remains otherwise stable with age. This PhD project was organised by Historic Scotland and the University of Glasgow to investigate the natural chemical and physical aging of wood. The natural aging of wood was a concern for Historic Scotland as traditional timber replacement is the standard form of repair used in wooden cultural heritage; replacing rotten timber with new timber of the same species. The project was set up to look at what differences could exist both chemically and physically between old and new wood, which could put unforeseen stress on the joint between them. Through Historic Scotland it was possible to work with genuine historic wood from two species, Oak and Scots pine, both from the 1500’s, rather than relying on artificial aging. Artificial aging of wood is still a debated topic, with consideration given to whether it is truly mimicking the aging process or just damaging the wood cells. The chemical stability of wood was investigated using Fourier-transform infrared (FTIR) microscopy, as well as wet chemistry methods including a test for soluble sugars from the possible breakdown of the wood polymers. The physical properties assessed included using a tensile testing machine to uncover possible differences in mechanical properties. An environmental chamber was used to test the reaction to moisture of wood of different ages, as moisture is the most damaging aspect of the environment to wooden cultural objects. The project uncovered several differences, both physical and chemical, between the modern and historic wood which could affect the success of traditional ‘like for like’ repairs. Both oak and pine lost acetyl groups, over historic time, from their hemicellulose polymers. This chemical reaction releases acetic acid, which had no effect on the historic oak but was associated with reduced stiffness in historic pine, probably due to degradation of the hemicellulose polymers by acid hydrolysis. The stiffness of historic oak and pine was also reduced by decay. Visible pest decay led to loss of wood density but there was evidence that fungal decay, extending beyond what was visible, degraded the S2 layer of the pine cell walls, reducing the stiffness of the wood by depleting the cellulose microfibrils most aligned with the grain. Fungal decay of polysaccharides in pine wood left behind sugars that attracted increased levels of moisture. The degradation of essential polymers in the wood structure due to age had different impacts on the two species of wood, and raised questions concerning both the mechanism of aging of wood and the ways in which traditional repairs are implemented, especially in Scots pine. These repairs need to be done with more care and precision, especially in choosing new timber to match the old. Within this project a quantitative method of measuring the microfibril angle (MFA) of wood using polarised Fourier transform infrared (FTIR) microscopy has been developed, allowing the MFA of both new and historic pine to be measured. This provides some of the information needed for a more specific match when selecting replacement timbers for historic buildings.

Glutathione Transferases as Detoxification Agents: Structural and Functional Studies

Glutathione transferases (GSTs) are a diverse family of enzymes that catalyze the glutathione-dependent detoxification of toxic compounds. GSTs are responsible for the conjugation of the tripeptide glutathione (GSH) to a wide range of electrophilic substrates. These include industrial pollutants, drugs, genotoxic carcinogen metabolites, antibiotics, insecticides and herbicides. In light of applications in biomedicine and biotechnology as cellular detoxification agents, detailed structural and functional studies of GSTs are required. Plant tau class GSTs play crucial catalytic and non-catalytic roles in cellular xenobiotic detoxification process in agronomically important crops. The abundant existence of GSTs in Glycine max and their ability to provide resistance to abiotic and biotic stresses such as herbicide tolerance is of great interest in agriculture because they provide effective and suitable tools for selective weed control. Structural and catalytic studies on tau class GST isoenzymes from Glycine max (GmGSTU10-10, GmGSTU chimeric clone 14 (Sh14), and GmGSTU2-2) were performed. Crystal structures of GmGSTU10-10 in complex with glutathione sulfenic acid (GSOH) and Sh14 in complex with S-(p-nitrobenzyl)-glutathione (Nb-GSH) were determined by molecular replacement at 1.6 Å and 1.75 Å, respectively. Major structural variations that affect substrate recognition and catalytic mechanism were revealed in the upper part of helix H4 and helix H9 of GmGSTU10-10. Structural analysis of Sh14 showed that the Trp114Cys point mutation is responsible for the enhanced catalytic activity of the enzyme. Furthermore, two salt bridges that trigger an allosteric effect between the H-sites were identified at the dimer interface between Glu66 and Lys104. The 3D structure of GmGSTU2-2 was predicted using homology modeling. Structural and phylogenetic analysis suggested GmGSTU2-2 shares residues that are crucial for the catalytic activity of other tau class GSTs–Phe10, Trp11, Ser13, Arg20, Tyr30, Leu37, Lys40, Lys53, Ile54, Glu66 and Ser67. This indicates that the catalytic and ligand binding site in GmGSTU2-2 are well-conserved. Nevertheless, at the ligandin binding site a significant variation was observed. Tyr32 is replaced by Ser32 in GmGSTU2-2 and thismay affect the ligand recognition and binding properties of GmGSTU2-2. Moreover, docking studies revealed important amino acid residues in the hydrophobic binding site that can affect the substrate specificity of the enzyme. Phe10, Pro12, Phe15, Leu37, Phe107, Trp114, Trp163, Phe208, Ile212, and Phe216 could form the hydrophobic ligand binding site and bind fluorodifen. Additionally, side chains of Arg111 and Lys215 could stabilize the binding through hydrogen bonds with the –NO2 groups of fluorodifen. GST gene family from the pathogenic soil bacterium Agrobacterium tumefaciens C58 was characterized and eight GST-like proteins in A. tumefaciens (AtuGSTs) were identified. Phylogenetic analysis revealed that four members of AtuGSTs belong to a previously recognized bacterial beta GST class and one member to theta class. Nevertheless, three AtuGSTs do not belong to any previously known GST classes. The 3D structures of AtuGSTs were predicted using homology modeling. Comparative structural and sequence analysis of the AtuGSTs showed local sequence and structural characteristics between different GST isoenzymes and classes. Interactions at the G-site are conserved, however, significant variations were seen at the active site and the H5b helix at the C-terminal domain. H5b contributes to the formation of the hydrophobic ligand binding site and is responsible for recognition of the electrophilic moiety of the xenobiotic. It is noted that the position of H5b varies among models, thus providing different specificities. Moreover, AtuGSTs appear to form functional dimers through diverse modes. AtuGST1, AtuGST3, AtuGST4 and AtuGST8 use hydrophobic ‘lock–and–key’-like motifs whereas the dimer interface of AtuGST2, AtuGST5, AtuGST6 and AtuGST7 is dominated by polar interactions. These results suggested that AtuGSTs could be involved in a broad range of biological functions including stress tolerance and detoxification of toxic compounds.

Proton conductivity and luminiscence properties of lanthanide aminotriphosphonates

Metal phosphonates are multifunctional solids with tunable properties, such as internal H-bond networks, and high chemical and thermal stability [1]. In the present work, we describe the synthesis, structural characterization, luminescent properties and proton conduction performance of a new family of isostructural cationic compounds with general formula [Ln(H4NMP)(H2O)2]Cl·2H2O [Ln = La3+, Pr3+, Sm3+, Gd3+, Tb3+, Dy3+, Ho3+, H6NMP = nitrilotris(methylphosphonic acid)]. These solids are formed by positively charge layers, which consist of isolated LnO8 polyhedra and bridge chelating NMP2- ligands, held apart by chloride ions and water molecules. This arrangement result in extended interlayer hydrogen networks with possible proton transfer pathways. The proton conductivity of Gd3+ sample, selected as prototype of the series, was measured. In the range between range 25º and 80 ºC, the conductivity increase with the temperature up to a maximum value of 3.10-4 S·cm-1, at relative humidity of 95 %. The activation energy obtained from the Arrhenius plot (Figure 1) is in the range corresponding to a Grotthuss transfer mechanism.

Photoconductivity and electrical properties of diamond films grown by MPCVD

The electrical and photoconductive features of as-grown microwave-plasma-assisted chemical-vapour deposition (MPCVD) diamond films are studied in correlation with magnetic results obtained from electron paramagnetic resonance (EPR). Also, the morphology is analysed by atomic force microscopy (AFM) showing [111] crystals with a good uniformity of the deposit. The photoresponse as well the current-voltage features observed show an efficient photogeneration of carriers while the optoelectronic characteristics of the metal-diamond junction have an ideality factor of 1.6 together with a rectification ratio of about 10(4) at +/-2.5 V. The nature of the mechanisms responsible for the conduction is discussed. (C) 1998 Elsevier Science S.A.

Photoconductivity and electrical properties of diamond films grown by MPCVD

The electrical and photoconductive features of as-grown microwave-plasma-assisted chemical-vapour deposition (MPCVD) diamond films are studied in correlation with magnetic results obtained from electron paramagnetic resonance (EPR). Also, the morphology is analysed by atomic force microscopy (AFM) showing [111] crystals with a good uniformity of the deposit. The photoresponse as well the current-voltage features observed show an efficient photogeneration of carriers while the optoelectronic characteristics of the metal-diamond junction have an ideality factor of 1.6 together with a rectification ratio of about 10(4) at +/-2.5 V. The nature of the mechanisms responsible for the conduction is discussed. (C) 1998 Elsevier Science S.A.

Experimentally and coupled CFD/CSD assisted structural and aeroelastic modelling of the Javelin UAV outboard wing section

This study presents the procedure followed to make a prediction of the critical flutter speed for a composite UAV wing. At the beginning of the study, there was no information available on the materials used for the construction of the wing, and the wing internal structure was unknown. Ground vibration tests were performed in order to detect the structure’s natural frequencies and mode shapes. From tests, it was found that the wing possesses a high stiffness, presenting well separated first bending and torsional natural frequencies. Two finite element models were developed and matched to experimental results. It has been necessary to introduce some assumptions, due to the uncertainties regarding the structure. The matching process was based on natural frequencies’ sensitivity with respect to a change in the mechanical properties of the materials. Once experimental results were met, average material properties were also found. Aerodynamic coefficients for the wing were obtained by means of a CFD software. The same analysis was also conducted when the wing is deformed in its first four mode shapes. A first approximation for flutter critical speed was made with the classical V - g technique. Finally, wing’s aeroelastic behavior was simulated using a coupled CFD/CSD method, obtaining a more accurate flutter prediction. The CSD solver is based on the time integration of modal dynamic equations, requiring the extraction of mode shapes from the previously performed finite-element analysis. Results show that flutter onset is not a risk for the UAV, occurring at velocities well beyond its operative range.