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A versatile approach to the synthesis of migration-resistant poly(vinyl chloride) (PVC) additives is described and a preliminary assessment of their properties is presented. The process involves th...

Plant seeds have long been promoted as a production platform for novel fatty acids such as the ω3 long-chain (≥ C20) polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) commonly found in fish oil. In this article we describe the creation of a canola (Brassica napus) variety producing fish oil-like levels of DHA in the seed. This was achieved by the introduction of a microalgal/yeast transgenic pathway of seven consecutive enzymatic steps which converted the native substrate oleic acid to α-linolenic acid and, subsequently, to EPA, docosapentaenoic acid (DPA) and DHA. This paper describes construct design and evaluation, plant transformation, event selection, field testing in a wide range of environments, and oil profile stability of the transgenic seed. The stable, high-performing event NS-B50027-4 produced fish oil-like levels of DHA (9–11%) in open field trials of T3 to T7 generation plants in several locations in Australia and Canada. This study also describes the highest seed DHA levels reported thus far and is one of the first examples of a deregulated genetically modified crop with clear health benefits to the consumer.

Nuclear Magnetic Resonance (NMR) is an analytical technique extensively used in almost every chemical laboratory for structural identification. This technique provides statistically equivalent signals in spite of using spectrometer with different hardware features and is successfully used for the traceability and quantification of analytes in food samples. Nevertheless, to date only a few internationally agreed guidelines have been reported on the use of NMR for quantitative analysis. The main goal of the present study is to provide a methodological pipeline to assess the reproducibility of NMR data produced for a given matrix by spectrometers from different manufacturers, with different magnetic field strengths, age and hardware configurations. The results have been analyzed through a sequence of chemometric tests to generate a community-built calibration system which was used to verify the performance of the spectrometers and the reproducibility of the predicted sample concentrations.

We report new structural motifs for Cu nanoclusters that conceptually represent seed crystals for large face-centred cubic (FCC) crystal growth. Kinetically controlled syntheses, high resolution mass spectrometry experiments for determination of the dication formulae and crystallographic characterisation were carried out for [Cu18 H16 (DPPE)6 ][BF4 ][Cl] (DPPE=bis(diphenylphosphino)ethane) and [Cu16 H14 (DPPA)6 ][(BF4 )2 ] (DPPA=bis(diphenylphosphino)amine) polyhydrido nanoclusters, which feature the unprecedented bifrustum and frustum metal-core architecture in metal nanoclusters. The Cu18 nanocluster contains two Cu9 frustum cupolae and the Cu16 nanocluster has one Cu9 frustum cupola and a Cu7 distorted hexagonal-shape base. Gas-phase experiments revealed that both Cu18 H16 and Cu16 H14 cores can spontaneously release H2 upon removal of one bisphosphine capping ligand.

Electrospray ionisation mass spectrometry (ESI-MS) was used to monitor the reaction of AgBF4, bis(diphenylphosphino)amine (dppa = (Ph2P)2NH = LPh) and NaBH4 in acetonitrile and thereby direct the synthesis of the silver nanocluster [Ag3(μ3-H)(μ3-BH4)LPh3](BF4), 3b·BF4, formed via reaction of AgBF4, bis(diphenylphosphino)amine (dppa = (Ph2P)2NH = LPh) and NaBH4 in acetonitrile. The X-ray structure of 3b·BF4 highlights that the cation adopts a planar trinuclear Ag3 geometry surrounded by three dppa ligands and coordinated on the bottom face by a μ3-hydride and on the top face by a μ3-BH4. The solution phase structure of 3b·BF4 was characterised by multinuclear NMR and DOSY NMR, which showed that the borohydride anion remains bound in the [Ag3(μ3-H)(μ3-BH4)LPh3]+ cluster cation in solution. ESI-MS and in situ1H and HSQC NMR spectroscopy reveals that 3b·BF4 reacts with CS2 in solution at the BH4 site to yield [Ag3(H)(S2CH)LPh3]+, 4b, which has to date eluded structural characterisation via X-ray crystallography due to lack of formation of suitable crystals. The gas-phase ion chemistry of [Ag3(H)(S2CH)LPh3]+ was examined under multistage mass spectrometry conditions using collision-induced dissociation (CID) and compared to that of the previously examined copper analogue, [Cu3(H)(S2CH)LPh3]+. While both cluster cations fragment via ligand loss, the CID spectra of the resultant [M3(H)(S2CH)LPh2]+ are different. Unlike [Cu3(H)(S2CH)LPh2]+, which solely undergoes loss of thioformaldehyde to give [Cu3(S)LPh2]+, [Ag3(H)(S2CH)LPh2]+ gives a richer CID spectrum with fragmentation channels that include ligand loss, CH2S loss and reductive elimination of dithioformic acid. DFT calculations exploring rearrangement and fragmentation of the model systems [M3(H)(S2CH)LMe2]+ ((Me2P)2NH = dmpa = LMe) were used to suggest plausible mechanisms and examine the energetics of the three competing channels: ligand loss, CH2S loss and reductive elimination of dithioformic acid.

Gradual permeability loss due to physical aging and the trade-off relationship between permeability and selectivity has largely hindered the advancement of membrane technology. In our prior works, porous aromatic framework (PAF-1) and poly-dichloroxylene (p-DCX) incorporated mixed matrix membranes (MMMs) have shown excellent anti-aging properties, achieved through polymer side chains adsorbing within PAF-1 or p-DCX pores. Advantageously, antiaging behaviour was usually also accompanied by enhanced membrane permeability due to the high porosity of the PAF-1 or p-DCX additive. However, these works mostly focused on polymers with moderate selectivities, such as polymers of intrinsic microporosity (PIM-1) and poly-trimethylsilyl-propyne (PTMSP). In this work, we investigated the anti-aging properties of PAF-1 and p-DCX in a highly selective polyimide (PI) polymer and demonstrated its potential for industrial CO2 separation. As anticipated, PI membranes demonstrated a slower CO2 aging rate with the addition of PAF-1 and p-DCX, for both single gases under low-pressure and mixed gas under high-pressure measurements. Additionally, the CO2 permeability was significantly enhanced, and consequently the mixed-gas performance of the composite PI-based membranes surpassed 2008 Upper Bounds for both CO2/N2 and CO2/CH4 separation.

The Labyrinthulomycetes or Labyrinthulea are a class of protists that produce a network of filaments that enable the cells to glide along and absorb nutrients. One of the main two Labyrinthulea groups is the thraustochytrids, which are becoming an increasingly recognised and commercially used alternate source of long-chain (LC, ≥C20) omega-3 containing oils. This study demonstrates, to our knowledge for the first time, the regiospecificity of the triacylglycerol (TAG) fraction derived from Australian thraustochytrid Aurantiochytrium sp. strain TC 20 obtained using 13C nuclear magnetic resonance spectroscopy (13C NMR) analysis. The DHA present in the TC 20 TAG fraction was determined to be concentrated in the sn-2 position, with TAG (16:0/22:6/16:0) identified as the main species present. The sn-2 preference is similar to that found in salmon and tuna oil, and differs to seal oil containing largely sn-1,3 LC-PUFA. A higher concentration of sn-2 DHA occurred in the thraustochytrid TC 20 oil compared to that of tuna oil.

Hydrogen at present is mainly produced from fossil fuels for use in ammonia synthesis, the petrochemical industry, and chemical production. In the future, hydrogen will be increasingly used as an energy vector. Although water electrolysis to produce hydrogen with renewable electricity offers a clean process, the approach is energy intensive, requiring a large renewable resource footprint. Methanol-water co-electrolysis can reduce the energy input by > 50%; its electrochemical oxidation poses complex issues such as poisoning of the catalyst, sluggish oxidation kinetics, and degradation over time. The addition of nano-sized SnO2 to PtRu/C catalyst, to reduce noble metal loading, has been shown here to reduce catalyst leaching and increase the chemical, micro-structural, and performance stability of the methanol-water co-electrolysis process during extended periods of testing. The electrochemical characterization, analysis of the methanol solution, and exit gases, post-cell testing, revealed complete oxidation of methanol with little performance degradation. This is further supported by the stability of the catalyst composition and structure as revealed by the post-mortem XRD and XPS analysis of the cell. The energy balance calculations show that methanol-water co-electrolysis can significantly reduce the renewable energy footprint, and the process can become carbon neutral if bio-methanol is used with renewable electricity.

Chemical absorption using aqueous amine-based solutions is the leading method for large-scale CO2 capture in industrial plants. This technology, however, still faces many challenges, in particular the high-energy requirements for solvent regeneration, which limit the economic viability of the technology. To guide the development of more energy-efficient amine solvents, this work studied the effect of molecular characteristics of diamines, including carbon chain length and type of amino functional group, on CO2 absorption and desorption performances. Six linear terminal diamines [NH2CH2CH2–R, where R = NH2, NHCH3, N(CH3)2, CH2NH2, CH2NHCH3, and CH2N(NH3)2] were investigated, and two monoamines, monoethanolamine (NH2CH2CH2OH, MEA) and 3-aminopropanol (NH2CH2CH2CH2OH, 3AP), were also tested as benchmarks. The CO2 absorption capacity in each amine was measured at 40 °C under atmospheric pressure using different CO2 gas partial pressures. 13C and 1H nuclear magnetic resonance spectroscopies were used to identi...

Post-synthetic exchange (PSE) and defect engineering have emerged as powerful techniques for tuning the properties and introducing novel functionality to metal organic frameworks (MOFs). Growing evidence suggests that each technique plays a key role in the mechanism of the other: linker coordination chemistry is pivotal to defective frameworks, while defect sites can help initiate PSE. Here, the intersection of these approaches is explored by exchanging an MOF with linkers already present within the framework. Post-synthetic annealing (PSA) modifies an MOF’s properties by redistributing the framework’s mixture of bound linker/modulator species. Using changes to the polymer-additive interactions in poly-1-trimethylsilyl-1-propyne nanocomposites observed through aging, we demonstrate that PSA causes one linker species to preferentially accumulate on the MOF’s crystal surface. Reaction conditions are shown to affect molecular composition of the resulting annealed UiO-66 MOFs, a finding explained through esta...

Ein neuer Ansatz zur Synthese von Heterohexa- und Heterodecametallaten unter nichtwassrigen, mikrowellengestutzten Reaktionsbedingungen wurde entwickelt. Die zwei neuartigen Molybdovanadate wurden isoliert und im festen sowie gelosten Zustand mittels Einkristall-Rontgenbeugung, FT-IR-, UV/Vis- und multinuklearer NMR-Spektroskopie sowie ESI-MS charakterisiert. Die relativen Stabilitaten der moglichen Strukturisomere beider Polyoxometallatsysteme wurden mithilfe von dispersionskorrigierten DFT-Rechnungen untersucht.

The reactions between silver salts and borohydrides produce a rich set of products that range from discrete mononuclear compounds through to silver nanoparticles and colloids. Previous studies using electrospray ionization mass spectrometry (ESI-MS) to track the cationic products in solutions containing sodium borohydride, silver(i) tetrafluoroborate and the bisphosphine ligands, L, bis(diphenylphosphino)methane (dppm) and bis(diphenylphosphino)amine (dppa) have identified the dications [Ag

The family of complexes of general formula [Co(Me ntpa)(Xdiox)]+ (tpa = tris(2-pyridylmethyl)amine, n = 0-3 corresponds to successive methylation of the 6-position of the pyridine rings; X = Br4, Cl4, H4, 3,5-Me2, 3,5- tBu2; diox = dioxolene) was investigated by density functional theory (DFT) calculations to predict the likelihood of valence tautomerism (VT). The OPBE functional with relativistic and solvent corrections allowed accurate reproduction of trends in spin-state energetics, affording the prediction of VT in complex [Co(Me3tpa)(Br4diox)]+ (1+). One-electron oxidation of neutral precursor [CoII(Me3tpa)(Br4cat)] (1) enabled isolation of target compounds 1(PF6) and 1(BPh4). Solution variable-temperature UV-vis absorption and Evans method magnetic susceptibility data confirm DFT predictions that 1+ exists in a temperature-dependent valence tautomeric equilibrium between low-spin Co(III)-catecholate and high-spin Co(II)-semiquinonate forms. The solution VT transition temperature of 1+ is solvent-tunable with critical temperatures in the range of 291-359 K for the solvents measured. Solid-state magnetic susceptibility measurements of 1(PF6) and 1(BPh4) reveal the onset of VT transitions above room temperature.

Membranes are particularly attractive for lowering the energy intensity of separations as they eliminate phase changes. While many tantalizing polymers are known, limitations in selectivity and stability slightly preclude further development. Mixed-matrix membranes may address these shortcomings. Key to their realization is the intimate mixing between the polymer and the additive to eliminate nonselective transport, improve selectivity, and resist physical aging. Polymers of intrinsic microporosity (PIMs) have inherently promising gas transport properties. Here, we show that porous additives can improve transport and resist aging in PIM-1. We develop a simple, low-cost, and scalable hyper-cross-linked polymer (poly-dichloroxylene, pDCX), which was hydroxylated to form an intimate mixture with the polar PIM-1. Solvent variation allowed control of physical aging rates and improved selectivity for smaller gases. This detailed study has allowed many interactions within mixed matrix membranes to be directly elucidated and presents a practical means to stabilize porous polymers for separation applications.

The reactivity of melamine-urea-formaldehyde resins is of key importance in the manufacture of engineered wood products such as medium density fibreboard (MDF) and other wood composite products. Often the MDF manufacturing plant has little available information on the resin reactivity other than details of the resin specification at the time of batch manufacture, which often occurs off-site at a third-party resin plant. Often too, fresh resin on delivery at the MDF plant is mixed with variable volume of aged resin in storage tanks, thereby rendering any specification of the fresh resin batch obsolete. It is therefore highly desirable to develop a real-time, at-line or on-line, process analytical technology to monitor the quality of the resin prior to MDF panel manufacture. Near infrared (NIR) spectroscopy has been calibrated against standard quality methods and against 13C nuclear magnetic resonance (NMR) measures of molecular composition in order to provide at-line process analytical technology (PAT), to monitor the resin quality, particularly the formaldehyde content of the resin. At-line determination of formaldehyde content in the resin was made possible using a six-factor calibration with an R 2(cal) value of 0.973, and R 2(CV) value of 0.929 and a root-mean-square error of cross-validation of 0.01. This calibration was then used to generate control charts of formaldehyde content at regular four-hourly periods during MDF panel manufacture in a commercial MDF manufacturing plant.

An electrospray ionization mass spectrometry (ESI-MS) survey of the types of cationic copper clusters formed from an acetonitrile solution containing a 1:1:20 mixture of tetrakis(acetonitrile)copper(I) tetrafluoroborate [Cu(MeCN)4(BF4)], bis(diphenylphosphino)amine (dppa = (Ph2P)2NH = L), and NaBH4 revealed a major peak, which based on both the accurate masses and isotope distribution was assigned as [Cu3(BH4)(H)(L)3]+. This prompted synthetic efforts resulting in isolation of the dppa ligated trinuclear copper hydride nanoclusters, [Cu3(μ2-Cl)(μ3-H)(L)3](BF4) and [Cu3(μ3-BH4)(μ3-H)(L)3](BF4), which were subsequently structurally characterized using high resolution ESI-MS, X-ray crystallography, NMR, and IR spectroscopy. The X-ray structures reveal a common structural feature of the cation, in which the three copper(I) ions adopt a planar trinuclear Cu3 geometry coordinated on the bottom face by a μ3-hydride and surrounded by three dppa ligands. ESI-MS of [Cu3(μ2-Cl)(μ3-H)(L)3](BF4) and [Cu3(μ3-BH4)(μ3-H)...

The global interest in hydrogen/fuel cell systems for distributed power generation and transport applications is rapidly increasing. Many automotive companies are now bringing their pre-commercial fuel cell vehicles in the market, which will need extensive hydrogen generation, distribution and storage infrastructure for fueling of these vehicles. Electrolytic water splitting coupled to renewable sources offers clean on-site hydrogen generation option. However, the process is energy intensive requiring electric energy >4.2 kWh for the electrolysis stack and >6 kWh for the complete system per m3 of hydrogen produced. This paper investigates using ethanol as a renewable fuel to assist with water electrolysis process to substantially reduce the energy input. A zero-gap cell consisting of polymer electrolyte membrane electrolytic cells with Pt/C and PtSn/C as anode catalysts were employed. Current densities up to 200 mA cm−2 at 70 °C were achieved at less than 0.75 V corresponding to an energy consumption of about 1.62 kWh m−3 compared with >4.2 kWh m−3 required for conventional water electrolysis. Thus, this approach for hydrogen generation has the potential to substantially reduce the electric energy input to less than 40% with the remaining energy provided by ethanol. However, due to performance degradation over time, the energy consumption increased and partial oxidation of ethanol led to lower conversion efficiency. A plausible ethanol electro-oxidation mechanism has been proposed based on the Faradaic conversion of ethanol and mass balance of the by-products identified and quantified using 1H nuclear magnetic resonance spectroscopy and gas chromatography.

Herein we report the first photochromic polyoxometalate (POM)-based diarylethene (DAE) coordination complex, prepared by ligation of two cobalt(III)-incorporated borotungstates [BIIIWVI11O39CoIII]6– with the ditopic pyridyl-containing diarylethene (C25H16N2F6S2). The solution-state composition, structure, and stability of the assembly were probed using 1H and 19F nuclear magnetic resonance spectroscopy (NMR), electrospray ionization quadrupolar time-of-flight mass spectrometry (ESI-QTOF-MS), ultraviolet–visible spectroscopy (UV–vis), and small-angle X-ray scattering (SAXS), revealing that the complex self-organizes to adopt a molecular dumbbell structure due to electrostatic and steric considerations. This conformation is a prerequisite for the photocyclization reaction. The assembly was found to be switchable between two states using visible light due to the perturbation of the DAE electronic structure on coordination to the POM. We present photophysical data, including the reaction quantum efficiency of...

Metabolic engineering of the omega-3 (ω3) long chain polyunsaturated fatty acid biosynthesis pathway has generated fish oil-like levels of pharmaceutically and nutritionally important docosahexaenoic acid (DHA) in plant seeds. However, the majority of DHA has been accumulated at the sn-1 and sn-3 positions of triacylglycerol (TAG) in these engineered seeds, leaving only a minor amount (~10%) at sn-2 position and indicating a strong discrimination (or, a very poor specificity) for DHA by seed lysophosphatidic acid acyltransferases (LPAATs), which mediate the acylation of sn-2 position of glycerol backbone. In order to increase the level of DHA at sn-2 position of TAG and to increase overall DHA level in seeds, we attempted to discover DHA-preferring LPAATs. Several lysophosphatidic acid acyltransferases (LPAATs) for acylation of the sn-2 position of the TAG glycerol backbone were investigated for substrate preference for DHA. In transiently expressing these LPAATs in Nicotiana benthamiana, a Mortierella alpina LPAAT had the highest substrate specificity for accumulating DHA onto oleoyl-lysophosphatidic acid (oleoyl-LPA), while the plant LPAATs tested showed lower preference for DHA. In a competition assay with a pool of four ω3 acyl-Coenzyme A (CoA) substrates involved in the DHA biosynthesis pathway, LPAATs from both M. alpina and Emiliana huxleyi showed a high preference for DHA-CoA acylation onto oleoyl-LPA. When docosahexaenoyl-LPA was used as the acyl receiver, M. alpina LPAAT also showed a high preference for DHA-CoA. Stable overexpression of M. alpina LPAAT in an Arabidopsis line that expressed the DHA biosynthesis pathway significantly increased both the total DHA levels and the distribution of DHA onto the sn-2 position of seed TAG. LC-MS analysis of the seed TAG species also confirmed that overexpression of M. alpina LPAAT increased di-DHA and tri-DHA TAGs, suggesting that the M. alpina LPAAT could enrich DHA at the TAG sn-2 position, leading to a metabolic engineering of oil seed for channeling DHA into the sn-2 position of TAG and to a higher DHA level.

Borohydrides react with silver salts to give products that span multiple scales ranging from discrete mononuclear compounds through to silver nanoparticles and colloids. The cluster cations [Ag3(H)(BH4)L3](+) are observed upon electrospray ionization mass spectrometry of solutions containing sodium borohydride, silver(I) tetrafluoroborate and bis(dimethylphosphino)methane (L(Me)) or bis(diphenylphosphino)methane (L(Ph)). By adding NaBH4 to an acetonitrile solution of AgBF4 and L(Ph), cooled to ca. -10 °C, we have been able to isolate the first mixed silver hydride borohydride nanocluster, [Ag3(μ3-H)(μ3-BH4)L(Ph)3]BF4, and structurally characterise it via X-ray crystallography. Combined gas-phase experiments (L(Me) and L(Ph)) and DFT calculations (L(Me)) reveal how loss of a ligand from the cationic complexes [Ag3(H)(BH4)L3](+) provides a change in geometry that facilitates subsequent loss of BH3 to produce the dihydride clusters, [Ag3(H)2Ln](+) (n = 1 and 2). Together with the results of previous studies (Girod et al., Chem. - Eur. J., 2014, 20, 16626), this provides a direct link between mixed silver hydride/borohydride nanoclusters, silver hydride nanoclusters, and silver nanoclusters.

Reversible deactivation radical polymerisation (RDRP) has enabled chemists to generate polymers with precision control over molecular weight and molecular structure. Despite recent advances in the field of template polymerisation, control of the repeat unit sequence requires further development. We describe herein the synthesis of sequence-regulated copolymers of styrene-thymine and maleic anhydride.

We report new structural motifs for Cu nanoclusters that conceptually represent seed crystals for large face-centred cubic (FCC) crystal growth. Kinetically controlled syntheses, high resolution mass spectrometry experiments for determination of the dication formulae and crystallographic characterisation were carried out for [Cu

A bis(diphenylphosphino)methane-ligated trinuclear silver hydride nanocluster, [Ag3((Ph2P)2CH2)3(μ3-H)](BF4)2, featuring three silver(I) ions coordinated to a μ3-hydride, and its deuteride analogue, [Ag3((Ph2P)2CH2)3(μ3-D)](BF4)2, have been isolated and structurally characterized using electrospray ionization mass spectrometry (ESI-MS), X-ray crystallography, NMR and IR spectroscopy. The position of the deuteride in [Ag3((Ph2P)2CH2)3(μ3-D)](BF4)2 was determined by neutron diffraction. ESI-MS of [Ag3L3(μ3-H/D)](BF4)2 [L = ((Ph2P)2CH2)2] produces [Ag3L3(μ3-H/D)](2+) and [Ag3L3(μ3-H/D)(BF4)](+). A rich gas-phase ion chemistry of [Ag3L3(μ3-H/D)](2+) is observed under conditions of collision-induced dissociation (CID) and electron-capture dissociation (ECD). CID gives rise to the following complementary ion pairs: [Ag3L2](+) and [L+(H/D)](+); [Ag2(H/D)L2](+) and [AgL](+); [Ag2(H/D)L](+) and [AgL2](+). ECD gives rise to a number of dissociation channels including loss of the bis(phosphine) ligand, fragmentation of a coordinated bis(phosphine) ligand via C-P bond activation, and loss of a hydrogen (deuterium) atom with concomitant formation of [Ag3L3](+). Under CID conditions, [Ag3L3(μ3-H/D)(BF4)](+) fragments via ligand loss, the combined loss of a ligand and [H,B,F4], and cluster fragmentation to give [Ag2(BF4)L2](+) and [Ag2(L-H)L](+) [where (L-H) = (Ph2P)2CH(-)].

Fragment screening is becoming widely accepted as a technique to identify hit compounds for the development of novel lead compounds. In neighboring laboratories, we have recently, and independently, performed a fragment screening campaign on the HIV-1 integrase core domain (IN) using similar commercially purchased fragment libraries. The two campaigns used different screening methods for the preliminary identification of fragment hits; one used saturation transfer difference nuclear magnetic resonance spectroscopy (STD-NMR), and the other used surface plasmon resonance (SPR) spectroscopy. Both initial screens were followed by X-ray crystallography. Using the STD-NMR/X-ray approach, 15 IN/fragment complexes were identified, whereas the SPR/X-ray approach found 6 complexes. In this article, we compare the approaches that were taken by each group and the results obtained, and we look at what factors could potentially influence the final results. We find that despite using different approaches with little overlap of initial hits, both approaches identified binding sites on IN that provided a basis for fragment-based lead discovery and further lead development. Comparison of hits identified in the two studies highlights a key role for both the conditions under which fragment binding is measured and the criteria selected to classify hits.

We report a new approach for the synthesis of heterohexa- and heterodecametalates via the use of non-aqueous, microwave-assisted reaction conditions. The two novel molybdovanadates have been isolated and characterized in the solid and solution states using single-crystal X-ray diffraction, FT-IR, UV/Vis, multinuclear NMR spectroscopy, and ESI-MS. The relative stabilities of the possible structural isomers were probed using dispersion-corrected DFT calculations for both polyoxometalate systems.

Metalloenzymes preorganize the reaction environment to steer substrate(s) along the required reaction coordinate. Here, we show that phosphine ligands selectively facilitate protonation of binuclear silver hydride cations, [LAg2(H)]+ by optimizing the geometry of the active site. This is a key step in the selective, catalysed extrusion of carbon dioxide from formic acid, HO2CH, with important applications (for example, hydrogen storage). Gas-phase ion-molecule reactions, collision-induced dissociation (CID), infrared and ultraviolet action spectroscopy and computational chemistry link structure to reactivity and mechanism. [Ag2(H)]+ and [Ph3PAg2(H)]+ react with formic acid yielding Lewis adducts, while [(Ph3P)2Ag2(H)]+ is unreactive. Using bis(diphenylphosphino)methane (dppm) reshapes the geometry of the binuclear Ag2(H)+ scaffold, triggering reactivity towards formic acid, to produce [dppmAg2(O2CH)]+ and H2. Decarboxylation of [dppmAg2(O2CH)]+ via CID regenerates [dppmAg2(H)]+. These gas-phase insights inspired variable temperature NMR studies that show CO2 and H2 production at 70 °C from solutions containing dppm, AgBF4, NaO2CH and HO2CH., Designing catalysts and understanding the influence of ligands for particular transformations remains a highly challenging task. Here, the authors show that bisphosphine ligands can alter the geometry of the active site in silver catalysts, driving protonation and ultimately extrusion of carbon dioxide from formic acid.

Functionalised siloxane macromonomers, with properties designed for application as an injectable, in situ curable accommodating intraocular lens (A-IOL), were prepared via re-equilibration of a phenyl group-containing polysiloxane of very high molecular weight with octamethylcyclotetrasiloxane (D₄) and 2,4,6,8-tetra(n-propyl-3-methacrylate)-2,4,6,8-tetramethyl-cyclotetrasiloxane (D₄(AM)) in toluene using trifluoromethanesulfonic acid as a catalyst. Hexaethyldisiloxane was used as an end group to control the molecular weight of the polymer. The generated polymers had a consistency suitable for injection into the empty lens capsule. The polymers contained a low ratio of polymerisable groups so that, in the presence of a photo-initiator, they could be cured on demand in situ within 5 min under irradiation of blue light to form an intraocular lens within the lens capsule. All resulting polysiloxane soft gels had a low elastic modulus and thus should be able to restore accommodation. The pre-cure viscosity and post-cure modulus of the generated polysiloxanes were controlled by the end group and D₄(AM) concentrations respectively in the re-equilibration reactions. The refractive index could be precisely controlled by adjusting the aromatic ratio in the polymer to suit such application as an artificial lens. Lens stretching experiments with both human and non-human primate cadaver lenses of different ages refilled with polysiloxane polymers provided a significant increase in amplitude of accommodation (up to 4 D more than that of the respective natural lens). Both in vitro cytotoxicity study using L929 cell lines and in vivo biocompatibility study in rabbit models demonstrated the non-cytotoxicity and ocular biocompatibility of the polymer.

The structures of the “Z” and “R” substituents of a RAFT agent (Z–C(S)S–R) determine a RAFT agent’s ability to control radical polymerization. In this paper we report new acid/base switchable N-aryl-N-pyridyl dithiocarbamates (R = −CH2CN, Z = −N(Py)(Ar)) which vary in substituent at the 4-position of the aryl ring and the use of these to control molecular weight and dispersity. In their protonated form, the new RAFT agents are more effective in controlling polymerization of the more activated monomer, methyl acrylate (MA), whereas in their neutral form they provide more effective control of the polymerization of less activated monomers, N-vinyl carbazole (NVC) and vinyl acetate (VAc). For each polymerization, the apparent chain transfer coefficient (Ctrapp) shows a good correlation with Hammett parameters. Dithiocarbamates with more electron-withdrawing aryl ring substituents have the higher Ctrapp. This demonstrates the influence of polar effects on Ctrapp and supports the hypothesis that the activity of...

A phosphine-free selenium nanocrystal precursor solution has been synthesized by heating elemental selenium powder in 1-octadecene (ODE). This mixture was characterized by UV−vis absorption, photoluminescence excitation (PLE), nuclear magnetic resonance (NMR), Se X-ray absorption spectroscopy (Se-XAS), electron impact mass spectrometry (EIMS), and inductively coupled plasma atomic emission spectroscopy (ICP-AES) to establish identifiable spectroscopic and chemical signatures that can be correlated to the chemical efficacy of the precursor for the growth of metal selenide nanocrystals. Highly temperature dependent rates of selenium dissolution and deactivation of the resultant precursor are demonstrated and optimal preparation times for the most reactive precursor are determined. Distinctive features in the PLE spectrum provide a rapid estimate of the reactivity of the as-prepared Se-ODE precursor. NMR and XAS data strongly indicate both Se−Se and Se−C bonding are present in the precursor solution, suggest...

Ruthenium-alkylidene catalysed ring closing metathesis (RCM) provides a convenient method for the synthesis of cyclic dicarba peptide analogues. Sequences devoid of turn-inducing residues, however, can often fail to cyclise. A combination of pseudoproline (ΨPro) insertion and microwave irradiation can be used to enhance RCM yield in these problematic sequences. This strategy is illustrated in the synthesis of a dicarba human growth hormone (hGH) fragment. The structural changes associated with cystine to dicarba replacement were found to change the metabolic profile of the peptide.

The enzyme-resistant starch (ERS) content in processed high amylose and regular maize starches has been studied, with and without acid dextrinisation. The physicochemical and structural characteristics of the starches were analysed using a variety of techniques. The increase in ERS in high amylose maize starch with dextrinisation was related to the formation of a critical molecular weight fraction (MW ∼ 20,000) that could rearrange structurally. Further dextrinisation reduced the processed starch MW to below where it could still form ERS. Regular maize starch containing less than 30% amylose did not increase its resistance to amylase digestibility with acid dextrinisation, probably due to impairment of amylose rearrangement by the numerous branched amylopectin chains. The ERS, which is likely to form during the enzyme-digestion process, is a linear molecule with a maximum degree of polymerisation (DP) of 30, irrespective of the starch source, processing conditions applied or type and amount of acid used.

Residues within processed protein fragments bound to major histocompatibility complex class I (MHC-I) glycoproteins have been considered to function as a series of “independent pegs” that either anchor the peptide (p) to the MHC-I and/or interact with the spectrum of αβ-T-cell receptors (TCRs) specific for the pMHC-I epitope in question. Mining of the extensive pMHC-I structural database established that many self- and viral peptides show extensive and direct interresidue interactions, an unexpected finding that has led us to the idea of “constrained” peptides. Mutational analysis of two constrained peptides (the HLA B44 restricted self-peptide (B44DPα–EEFGRAFSF) and an H2-D b restricted influenza peptide (D b PA, SSLENFRAYV) demonstrated that the conformation of the prominently exposed arginine in both peptides was governed by interactions with MHC-I-orientated flanking residues from the peptide itself. Using reverse genetics in a murine influenza model, we revealed that mutation of an MHC-I-orientated residue (SSLEN F RAYV → SSLEN A RAYV) within the constrained PA peptide resulted in a diminished cytotoxic T lymphocyte (CTL) response and the recruitment of a limited pMHC-I specific TCR repertoire. Interactions between individual peptide positions can thus impose fine control on the conformation of pMHC-I epitopes, whereas the perturbation of such constraints can lead to a previously unappreciated mechanism of viral escape.

A study of the reactivity of a non-stabilised azomethine ylide, derived from N-(methoxymethyl)-N-(trimethylsilylmethyl)benzylamine, with nitro-substituted isatoic anhydrides was undertaken. N-Methyl-4-nitroisatoic anhydride underwent a 1,3-dipolar cycloaddition reaction exclusively at the isatoic anhydride C1-carbonyl group, followed by decarboxylative rearrangement to yield a benzo-1,3-diazepin-5-one derivative. In contrast, N-methyl-5-nitroisatoic anhydride underwent competing cycloaddition processes to the isatoic anhydride C1-carbonyl group and to the nitro-substituted aromatic ring. The dearomative addition reaction resulted in the formation of novel tetracyclic products.

Reversing the polarity of the cycloaddition partners in Dane’s steroid synthesis provides ready access to enantiomerically pure, functionally-rich steroidal structures.

Synthesis of the C6–C18 domain of pamamycin-607 was achieved in ten steps and 7% overall yield from commercially available d -norvaline. The key asymmetric transformations included a Paterson anti aldol addition, an anti selective reduction of the resultant β-hydroxy ketone and a cis selective Bartlett type ring closure.

Dicarba cyclic peptide analogues of the cystine-containing octapeptides octreotide, lanreotide, and vapreotide, all known somatostatin analogues, have been synthesized via an on-resin homogeneous metal-catalysed sequence involving ruthenium-catalysed ring-closing metathesis followed by rhodium-catalysed hydrogenation.Key words: dicarba-analogues of cystine-containing peptides, octreotide, vapreotide, and lanreotide; tandem ring-closing metathesis and hydrogenation.

Aging in super glassy polymers such as poly(trimethylsilylpropyne) (PTMSP), poly(4-methyl-2-pentyne) (PMP), and polymers with intrinsic microporosity (PIM-1) reduces gas permeabilities and limits their application as gas-separation membranes. While super glassy polymers are initially very porous, and ultra-permeable, they quickly pack into a denser phase becoming less porous and permeable. This age-old problem has been solved by adding an ultraporous additive that maintains the low density, porous, initial stage of super glassy polymers through absorbing a portion of the polymer chains within its pores thereby holding the chains in their open position. This result is the first time that aging in super glassy polymers is inhibited whilst maintaining enhanced CO2 permeability for one year and improving CO2/N2 selectivity. This approach could allow super glassy polymers to be revisited for commercial application in gas separations.

This study introduces a radical-free approach for generating polyacrylamide (PAM) hydrogels with no toxic residues remaining in the networks. Acrylamide and bisacrylamide, which are neurotoxins, are not used during the hydrogel synthesis and only nontoxic side products are generated. This is achieved using a gentle carbodiimide-mediated crosslinking (CMCL) reaction that does not require complex initiation systems and is effective in the presence of oxygen. This overcomes some of the key limitations related to PAM hydrogel synthesis using free-radical routes and maintains the advantages of synthetic hydrogels over biopolymers. In addition, the CMCL reaction allows for accurate placement of functional groups, which controls hydrogel structure and performance including mechanical strength, swelling capacity, and hydrophobic balance. This flexibility is demonstrated through the synthesis and rheological characterization of a library of structurally diverse hydrogels as well as spherical hydrogels. PAM-based hydrogels are used extensively in a broad number of applications, and this study demonstrates the applicability of this method as a nontoxic and radical-free complementary alternative route that can generate structures analogous to those prepared using free-radical routes.