Benefits and risks of including the bromoform containing seaweed Asparagopsis in feed for the reduction of methane production from ruminants

The agricultural production of ruminants is responsible for 24% of global methane emissions, contributing 39% of emissions of this greenhouse gas from the agricultural sector. Strategies to mitigate ruminant methanogenesis include the use of methanogen inhibitors. For example, the seaweeds Asparagopsis taxiformis and Asparagopsis armata included at low levels in the feed of cattle and sheep inhibit methanogenesis by up to 98%, with evidence of improvements in feed utilisation efficiency. This has resulted in an increasing interest in and demand for these seaweeds globally. In response, research is progressing rapidly to facilitate Asparagopsis cultivation at large scale, and to develop aquaculture production systems to enable a high quality and consistent supply chain. In addition to developing robust strategies for sustainable production, it is important to consider and evaluate the benefits and risks associated with its production and subsequent use as an antimethanogenic feed ingredient for ruminant livestock. This review focuses on the relevant ruminal biochemical pathways, degradation, and toxicological risks associated with bromoform (CHBr3), the major active ingredient for inhibition of methanogenesis in Asparagopsis, and the effects that production of Asparagopsis and its use as a ruminant feed ingredient might have on atmospheric chemistry

Metallosupramolecular Helicates and Tetrahedra: transition metal-directed assembly of polypyridyl ligands

This thesis reports the synthesis of a range of polypyridyl ligands and their subsequent incorporation into transition metal-directed assembly experiments. These latter experiments were designed to assess the viability of subsequent metal-template reductive amination procedures for the preparation of pseudocryptands, mono- and dinuclear cryptates and larger polycyclic compounds.\ud \ud The synthesis of polypyridyl derivatives for use in the current project employed a range of modern coupling procedures, including Stille and Suzuki cross-couplings. The former was used to synthesise a range of bipyridines, notably the regioselective cross-coupling between 2,5-dibromopyridine and 2-trimethylstannyl-5-methylpyridine to afford 5-bromo-5'-methylbipyridine (I) in high yield. As well, the reaction of 2- trimethylstannyl-5-methylpyridine and 6,6'-dichloro-3,3 -bipyridine in a bis-Stille cross-coupling allowed the synthesis of 5,5'-dimethyl-2,2';5',5";2",2""-quaterpyridine (II), often in yields in excess of 90 %. Alternatively, quaterpyridine II could be synthesised by two other methods: a Ni(0)-homocoupling reaction or a modified Suzuki coupling, both using bromobipyridine I as the starting material.\ud \ud The interaction of quaterpyridine II with a range of transition metals, including Fe(II), Co(II), Ni(II) and Ru(II) was investigated. The resulting metal-complexes were characterised using a combination of NMR techniques, ESI-HRMS, X-ray crystallography and elemental analysis. The more labile first row transition metals yielded M₄L₆ host-guest complexes of type [M₄(II)₆()anion]⁷⁺ (where M = Fe(II), Co(II) and Ni(II) and anion = [FeCl₄]⁻, BF₄⁻ and PF₆⁻). There is also evidence that the [Fe₄(II)₆]⁸⁺ host encapsulates [FeCl₄]₂⁻, a rare example of the inclusion of a doubly charged species. Interestingly, a series of ¹⁹F NMR experiments revealed that the [Fe₄(II)₆]⁸⁺ host selectively binds PF₆⁻ over BF₄⁻; an observation that most probably reflects a size based recognition process. Furthermore, a successful synthetic procedure for isolation of the empty cage (free of an encapsulated anion) was developed, indicating that anion templation is not essential for the formation of [Fe₄(II)₆]⁸⁺.\ud \ud The interaction of quaterpyridine II with RuCl₃ in ethylene glycol using microwave heating was found to yield a rare dinuclear helicate, [Ru₂(II)₃]⁴⁺, in 36% yield. The racemate of this product was resolved by cation exchange chromatography on C-25 Sephadex with 0.1 M (-)-O,O' -dibenzoyl-L-tartaric acid as eluent. Circular dichroism measurements were made to assess the success of the separation of the two enantiomers and the crystallisation of enantiopure material has allowed the assignment of the M-[Ru₂(II)₃]⁴⁺ and P-[Ru₂(II)₃]⁴⁺ forms using X-ray crystallography. In turn, an equilibrium dialysis experiment with calf thymus DNA indicated that M-[Ru₂(II)₃]⁴⁺ binds preferentially over the P-[Ru₂(II)₃]⁴⁺. Furthermore, the use of a Sepharose-immobilized AT dodecanucleotide column resulted in the successful separation of the M-and P-enantiomers; M-[Ru₂(II)₃]⁴⁺ was strongly retained whilst P-[Ru₂(II)₃]⁴⁺ essentially eluted with the solvent front. Less efficient (but still satisfactory) separations were observed with other DNA motifs; for example, on employing a GC 12-mer and bulge and hairpin sequences. In each case M-[Ru₂(II)₃]⁴⁺ bound to the column more strongly than the P-enantiomer.\ud \ud To investigate the effect that rigidly bridged quaterpyridines might have on analogous octahedral metal-directed assembly outcomes, quaterpyridines III and IV were synthesised. These ligands were prepared in high yield by bis-Suzuki coupling reactions between bromobipyridine I and appropriate bis-pinacol-diboronic esters using microwave heating.\ud \ud The interaction of quaterpyridines III and IV with octahedral metal ions resulted in mixtures of [M₂L₃]⁴⁺ and [M₄L₆]⁸⁺ complexes (M = Fe(II) or Ni(II) and L = III or IV). [Fe₂L₃]⁴⁺ and [Fe₄L₆]⁸⁺ were adequately inert to allow their chromatographic separatation and subsequent characterization. A level of control over the relative ratio of these products was demonstrated using a combination of reaction times and the degree of dilution employed for their synthesis; short reaction times and high dilution favoured the formation of [M₂L₃]⁴⁺ (e.g. [Ni₂(III)₃]⁴⁺), while long reaction times and normal dilution favoured the formation of [M₄L₆]⁸⁺ (e.g. [Fe₄(III)₆()PF₆]⁷⁺). Interestingly, M₂L₃ and M₄L₆ complexes incorporating quaterpyridines III and IV are fluorescent. With respect to the latter, on interaction with BPh₄- the larger tetrahedron, [Fe₄(IV)₆]⁸⁺, yields a change in fluorescence (a fluorescent signal). These observations suggest that complexes incorporating ligands III and IV might find application as fluorescent sensors.\ud \ud The isolation of a number of interesting M₂L₃ and M₄L₆ complexes led to the possibility that analogous metal-directed assembly procedures employing appropriately substituted quaterpyridines, related to III and IV, might allow for the metal-template synthesis of dinuclear cryptates and larger tetranuclear polycyclic species. With this in mind a number of bipyridyl and quaterpyridyl derivatives were synthesized with salicyloxy functionality to allow for subsequent reductive amination procedures. In this regard, dialdehydes V – VII were synthesised and reacted with Fe(II) in a 2:3 ratio. The resulting products were characterised by NMR and ESI-HRMS, revealing a series of M₂L₃ and M₄L₆ precursor complexes, including [Fe₄(V)₆](BF₄)₈, [Fe₂(VI)₃](PF₆)₈, [Fe₄(VI)₆](PF₆)₈, [Fe₄(VII)₆](PF₆)₈ and [Fe₄(VII)₆](PF₆)₈. As was the case for the interaction of quaterpyridines III and IV with Fe(II), the interaction of VI and VII with Fe(II) yielded mixtures of M₂L₃ and M₄L₆ complexes; the product ratio of which could also be controlled.\ud \ud Preliminary experiments revealed that reductive amination of [Fe₂(VI)₃](PF₆)₈ using NH₄OAc and NaCNBH₃ in acetonitrile yields the dinuclear cryptate [Fe₂(L¹)](PF₆)₈ (L¹ = the corresponding cryptand). Reductive amination of the precursor complexes [Fe₄(V)₆](BF₄)₈ and [Fe₄(VII)₆](PF₆)₈ under these same conditions revealed the production of the unique tetranuclear polycyclic species [Fe₄(L²)](BF₄)₈ and [Fe₄(L³)](PF₆)₈ (L² and L³ = the corresponding metal-free polycyclic ligands). The successful syntheses of the latter species required a total of twelve successive in situ imine condensation/reduction reactions from a total of fourteen components

Electrogenerated polypyridyl ruthenium hydride and ligand activation for water reduction to hydrogen and acetone to iso-propanol

The complex [Ru(tpy)(bpy)(S)]2+ (tpy = 2,2':6',2''-terpyridine, bpy = 2,2'-bipyridine, S = solvent) is an electrocatalyst for water or proton reduction to hydrogen and for reduction of acetone to iso-propanol in CH3CN. Electrocatalysis is initiated by sequential 1e− reductions at the tpy and bpy ligands followed by addition of water to give a ruthenium hydride intermediate. Significant rate enhancements for hydrogen evolution are observed with added weak acids, such as H2PO4−, for the latter, with a rate enhancement of 104 compared to water. The reactivity of the in situ electrogenerated hydride toward hydride transfer is promoted by ligand reduction

A cascading biorefinery process targeting sulfated polysaccharides (ulvan) from Ulva ohnoi

We evaluated eight biorefinery processes targeting the extraction of ulvan from Ulva ohnoi. Using a factorial design the effect of three sequential treatments (aqueous extraction of salt; ethanol extraction of pigments; and Na2C2O4 or HCl (0.05 M) extraction of ulvan) were evaluated based on the yield (% dry weight of biomass) and quality (uronic acid, sulfate, protein and ash content, constituent sugar and molecular weight analysis) of ulvan extracted. The aqueous extraction of salt followed by HCl extraction of ulvan gave higher yields (8.2 +/- 1.1% w/w) and purity of ulvan than equivalent Na2C2O4 extracts (4.0 +/- 1.0% w/w). The total sugar content of HCl extracts (624-670 mu g/mg) was higher than Na2C2O4 extracts (365-426 mu g/mg) as determined by constituent sugar with ulvan specific monosaccharides contributing 94.7-96.2% and 70.1-84.0%, respectively. Ulvan extracted from U. ohnoi was 53.1 mol% rhamnose, 27.8 mol% glucuronic acid, 10.1 mol% iduronic acid, and 5.3 mol% xylose with molecular weights ranging from 10.5-312 kDa depending on the biorefinery process employed. Therefore, the extraction of high quality ulvan from U. ohnoi is facilitated by an aqueous pre-treatment and subsequent HCl-extraction of ulvan as part of a cascading biorefinery model delivering salt, ulvan, and a protein enriched residual biomass

Enrichment processes for the production of high-protein feed from the green seaweed Ulva ohnoi

New sources of protein are required to supplement current animal- and plant-protein. Here, we quantify the quality and yield of four protein-enriched biomass products (PEB-I to PEB-IV) and a protein isolate (PI) from the commercially produced seaweed Ulva ohnoi. To decrease the content of components of the biomass that may be undesirable in feed, we have developed a multi-step biorefinery process to produce salt, sulfated polysaccharides (ulvan), and protein products. The content of protein increased from 22.2 ± 0.4% dry weight (dw) in unprocessed biomass to between 39.5 ± 1.9% in the PEB-IV and 45.5 ± 0.8% in the PI. The quality (mol % of essential amino acids [EAA]) of the protein products was similar to soybean meal, with 41.6 ± 0.1 and 43.4 ± 0.1 mol% EAA in PEB-I and the PI, respectively. The yield of PEB products varied from 16.3 ± 0.8 to 41.0 ± 0.8% of the unprocessed biomass, with PEB-I > PEB-II=PEB-III > PEB-IV. The yield of all PEB products was more than four-fold greater than the PI (4.4%). Conservatively, the biomass productivity of U.ohnoi is 70 t dw ha−1 year−1 resulting in a projected annual production (t dw ha−1 year−1) of 24 t of salt, 4.3 t of ulvan, 29 t of PEB-I, or 3.2 t of PI using this biorefinery process. With nine-fold higher yield, and a protein product of similar quality to the PI, we recommend producing PEB-I by concentrating the protein through the extraction of salt and ulvan over the extraction of a PI for the development of food and feed products

Post-assembly covalent di- and tetracapping of a dinuclear [Fe2L3]4+ triple helicate and two [Fe4L6]8+ tetrahedra using sequential reductive aminations

The use of a highly efficient reductive amination procedure for the postsynthetic end-capping of metal-templated helicate and tetrahedral supramolecular structures bearing terminal aldehyde groups is reported. Metal template formation of a [Fe2L3]4+ dinuclear helicate and two [Fe4L6]8+ tetrahedra (where L is a linear ligand incorporating two bipyridine domains separated by one or two 1,4-(2,5-dimethoxyaryl) linkers and terminated by salicylaldehyde functions is described. Postassembly reaction of each of these "open" di- and tetranuclear species with excess ammonium acetate (as a source of ammonia) and sodium cyanoborohydride results in a remarkable reaction sequence whereby the three aldehyde groups terminating each end of the helicate, or each of the four vertices of the respective tetrahedra, react with ammonia then undergo successive reductive amination to yield corresponding fully tertiary-amine capped cryptate and tetrahedral covalent cages

Photoinduced stepwise oxidative activation of a chromophore-catalyst assembly on TiO2

To probe light-induced redox equivalent separation and accumulation, we prepared ruthenium polypyridyl molecular assembly [(dcb)2Ru(bpy-Mebim2py)Ru(bpy)(OH2)]4+ (RuaII–RubII–OH2) with Rua as light-harvesting chromophore and Rub as water oxidation catalyst (dcb = 4,4'-dicarboxylic acid-2,2'-bipyridine; bpy-Mebim2py = 2,2'-(4-methyl-[2,2':4',4"-terpyridine]-2",6"-diyl)bis(1-methyl-1H-benzo[d]imidazole); bpy = 2,2'-bipyridine). When bound to TiO2 in nanoparticle films, it undergoes MLCT excitation, electron injection, and oxidation of the remote −RubII–OH2 site to give TiO2(e–)–RuaII–RubIII–OH23+ as a redox-separated transient. The oxidized assembly, TiO2–RuaII–RubIII–OH23+, similarly undergoes excitation and electron injection to give TiO2(e–)–RuaII–RubIV═O2+, with RubIV═O2+ a known water oxidation catalyst precursor. Injection efficiencies for both forms of the assembly are lower than those for [Ru(bpy)2(4,4'-(PO3H2)2bpy)]2+ bound to TiO2 (TiO2–Ru2+), whereas the rates of back electron transfer, TiO2(e–) → RubIII–OH23+ and TiO2(e–) → RubIV═O2+, are significantly decreased compared with TiO2(e–) → Ru3+ back electron transfer

Photostability of phosphonate-derivatized, Ru(II) polypyridyl complexes on metal-oxide surfaces

The photostability of [RuII(bpy)2(4,4'-(PO3H2)2bpy)]Cl2 (bpy = 4,4'-bipyridine) on nanocrystalline TiO2 and ZrO2 films was investigated using a standard measurement protocol. Stability was evaluated by monitoring visible light absorbance spectral changes, in real time, during 455 nm photolysis (30 nm fwhm, 475 mW/cm2) in a variety of conditions relevant to dye-sensitized solar cells and dye-sensitized photoelectrosynthesis cells. Desorption (kdes) and photochemical (kchem) processes were observed and found to be dependent upon solvent, anion, semiconductor, and presence of oxygen. Both processes are affected by oxygen with kdes and kphoto noticeably smaller in argon saturated solution. Desorption was strongly solvent and pH dependent with desorption rates increasing in the order: methanol (MeOH) ≈ acetonitrile (MeCN) < propylene carbonate (PC) < pH 1 pH 7. Photochemistry occurred in MeOH and PC but not in aqueous, 0.1 M HClO4 and MeCN. The anion and solvent dependence of kphoto strongly suggests the photoreaction involves ligand substitution initiated by population of metal centered d-d states. The relative stability of −PO3H2- versus −COOH-substituted [RuII(bpy)3]2+ was also quantitatively established

Multiple response optimisation of the aqueous extraction of high quality ulvan from Ulva ohnoi

Response surface methodology was used to determine the effects of the solvent pH, the temperature of extraction, and the duration of extraction on the yield, purity, molecular weight, viscosity, and total metal content of ulvan extracted from U. ohnoi. Quadratic models identified the optimised responses for yield (72.6%) purity (68.2% w/w), molecular weight (92.9 kDa), viscosity (491.1 s), and total metal content (~0 mg/kg). These responses occurred between a solvent pH of 2.2–4.0, an extraction temperature of 61.3–90.0 °C, and an extraction duration of 55.0–90.0 min. The overall desirability of the ulvan product was determined using a Derringer's desirability function, which identified a solvent pH of 2.92, an extraction temperature of 90 °C, and an extraction duration of 90 min. These extraction conditions minimise the requirement for downstream purification and are suitable for upscaling the extraction of a high quality ulvan product

Self-assembled bilayers on indium−tin oxide (SAB-ITO) electrodes: a design for chromophore−catalyst photoanodes

A novel approach for creating assemblies on metal oxide surfaces via the addition of a catalyst overlayer on a chomophore monolayer derivatized surface is described. It is based on the sequential self-assembly of a chromophore, [Ru(bpy)(4,4'-(PO3H2bpy)2)]2+, and oxidation catalyst, [Ru(bpy)(P2Mebim2py)OH2]2+, pair, resulting in a spatially separated chromophore−catalyst assembly