Tai-Chu Lau

Impact of marine fish farming on water quality and bottom sediment: A case study in the sub-tropical environment

Abstract Field studies were carried out to determine and compare the impact of marine fish farming activities on the water quality and bottom sediment at four fish culture sites with different hydrographic and culture conditions in a sub-tropical environment where trash fish is used as feed. The major impact identified was on the sea bottom, resulting in the development of reducing and anoxic sediments, high sediment oxygen demand, production of hydrogen sulphide and elimination/decrease in benthos. The impact on water quality was less conspicuous. A decrease in dissolved oxygen was observed at all sites while increases in ammonia, inorganic P, nitrate and nitrite were observed only at sites with poor tidal flushing and high stocking density. However, no significant changes in total suspended solids, light extinction coefficient, chlorophyll a, phaeopigment and E. coli were found near the fish rafts at any sites. Environmental impacts vary considerably between sites, and were significantly reduced at sites with good water circulation and low stocking density. Despite the high organic and nutrient loadings generated by marine fish farming activities, the impacts on water quality and sediments at all sites were localised and did not appear to extend beyond a distance of 1–1.5 km from the fish rafts. Results of the present study also do not support the suggestion that marine fish farming activities have caused eutrophication on a large scale.

Chemical and Visible‐Light‐Driven Water Oxidation by Iron Complexes at pH 7–9: Evidence for Dual‐Active Intermediates in Iron‐Catalyzed Water Oxidation

In recent decades, tremendous efforts have been devoted by chemists to develop efficient, cost-effective catalytic methods for solar-driven water oxidation, which would provide an unlimited source of protons and electrons for the production of hydrogen and other renewable fuels. However, to be economically viable, the catalysts for water oxidation should be made from earth-abundant materials; so far only a few cobalt, manganese, iron, and copper water-oxidation catalysts (WOCs) have been developed. Among the first-row transition metals, iron is probably the most desirable to be used in WOCs because it is the most abundant and relatively nontoxic. Collins, Bernhard, and co-workers recently reported the use of an iron(III) complex bearing a tetraamido macrocyclic ligand (Fe-TAML) to catalyze water oxidation by Ce at approximately pH 1 with a turnover number (TON) of 18 and turnover frequency (TOF) of greater than 1.3 s . Subsequently, Fillol and Costas et al. , also reported that a number of iron complexes bearing tetradentate Ndonor ligands can catalyze water oxidation at low pH with TON> 350 and > 1000 using Ce and IO4 , respectively. Herein, we report chemical and light-driven water oxidation catalyzed by a number of iron complexes and iron salts at pH 7–9 in borate buffer. We provide evidence that at this pH range, Fe2O3 particles are produced, which are the actual catalyst for water oxidation. The catalytic activity of various iron complexes towards water oxidation at pH 7–9 was investigated by a chemical method using [Ru(bpy)3](ClO4)3 (bpy = bipyridine) as the terminal oxidant (Table 1). [Ru(bpy)3] 3+ is commonly used as an oxidant in this pH range because of its relative stability and high redox potential (E = 1.21 V), whereas Ce, the other commonly used oxidant, is stable only at low pH values. Initially we investigated the complex cis-Fe(mcp)Cl2 (mcp = N,N’-dimethyl-N,N’-bis(2-pyridylmethyl)cyclohexane-1,2-diamine; Figure S1), because it was recently reported to be a highly active catalyst for water oxidation by Ce or IO4 at low pH. In our hands, when we used this complex as a catalyst and (NH4)2Ce(NO3)6 as the oxidant in unbuffered water, we obtained a TON of 290 15, in reasonable agreement with the value of 320 15 reported in the literature. However, when we used [Ru(bpy)3](ClO4)3 as the oxidant at pH 7–9 in borate buffer, no oxygen was produced (after subtracting the background signal) from this complex (Table 1, entry 2 and Figure S2). On the other hand, when other iron complexes such as [Fe(bpy)2Cl2]Cl, [Fe(tpy)2]Cl2, cis-[Fe(cyclen)Cl2]Cl, and trans-Fe(tmc)Br2 (where tpy = 2,2’:6’,2’’-terpyridine, cyclen = 1,4,7,10-tetraazacyclodecane, and tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) were used as catalysts, oxygen evolution readily occurred, with TON ranging from 19 to 108 (Table 1, entries 3–6). Notably, simple iron salts such as Fe(ClO4)3 is even more active than the other iron complexes (Table 1, entry 7; Table S1 and Figure S3). The maximum TOF of 9.6 s 1 is higher than those of other earth-abundant artificial catalysts such as [Co4(H2O)2(aPW9O34)2] 10 (5 s ) and Fe-TAML (1.3 s ). In the absence of an iron catalyst, 8% yield of oxygen was also detected (Table 1, entry 1), which comes from background oxidation of water by [Ru(bpy)3] . No oxygen could be detected when the reaction was carried out in phosphate buffer (Table S1, entry 8), which is attributed to the formation of the very insoluble FePO4 (Ksp = 9.92 10 ). On the other Table 1: Iron-catalyzed water oxidation by [Ru(bpy)3](ClO4)3 at pH 8.5 in borate buffer.

A Robust Palladium(II)–Porphyrin Complex as Catalyst for Visible Light Induced Oxidative CH Functionalization

A series of palladium(II)-porphyrin complexes that display dual emissions with lifetimes up to 437 μs have been synthesized. Among the four complexes, PdF20TPP is an efficient and robust catalyst for photoinduced oxidative C-H functionalization by using oxygen as terminal oxidant. α-Functionalized tertiary amines were obtained in good to excellent yields by light irradiation (λ>400 nm) of a mixture of PdF20TPP, tertiary amine, and nucleophile (cyanide, nitromethane, dimethyl malonate, diethyl phosphite, and acetone) under aerobic conditions. Four examples of intramolecular cyclized amine compounds could be similarly prepared. Comparison of the UV-visible absorption spectra before and after the photochemical reaction revealed that PdF20TPP was highly robust (>95 % recovery). The practical application of PdF20TPP has been revealed by the photochemical reactions performed by using a low catalyst loading (0.01 mol %) and on a 10 mmol scale. The PdF20TPP catalyst could sensitize photoinduced oxidation of sulfides to sulfoxides in excellent yields. Mechanistic studies revealed that the photocatalysis proceeded by singlet-oxygen oxidation.

Formation of molecular radical cations of enkephalin derivatives via collision-induced dissociation of electrospray-generated copper (II) complex ions of amines and peptides

Fragmentation of some electrospray-generated complex ions, [63CuII(amine)M].2+, where M is an enkephalin derivative, produces the radical cation of the peptide, M.+. This ion has only been observed when M contains a tyrosyl or tryptophanyl residue plus a basic residue, typically arginyl or lysyl. A typical viable amine is diethylenetriamine. Collision-induced dissociation (CID) of the M.+ ion yields a prominent [M − 106].+ product ion for tyrosine-containing peptides, and a prominent [M − 129].+ ion for a tryptophan-containing peptide. These fragment ions are formed as a result of elimination of the tyrosyl and tryptophanyl side chains. Dissociation of these ions, in turn, produces second generation product ions, many of which are typically absent in the fragmentation of protonated peptide ions. Structures for some of these unusual ions are proposed.

Efficient catalytic oxidation of alkanes by Lewis acid/[Os(VI)(N)Cl4]- using peroxides as terminal oxidants. Evidence for a metal-based active intermediate.

The oxidation of alkanes by various peroxides ((t)BuOOH, H2O2, PhCH2C(CH3)2OOH) is efficiently catalyzed by [Os(VI)(N)Cl4](-)/Lewis acid (FeCl3 or Sc(OTf)3) in CH2Cl2/CH3CO2H to give alcohols and ketones. Oxidations occur rapidly at ambient conditions, and excellent yields and turnover numbers of over 7500 and 1000 can be achieved in the oxidation of cyclohexane with (t)BuOOH and H2O2, respectively. In particular, this catalytic system can utilize PhCH2C(CH3)2OOH (MPPH) efficiently as the terminal oxidant; good yields of cyclohexanol and cyclohexanone (>70%) and MPPOH (>90%) are obtained in the oxidation of cyclohexane. This suggests that the mechanism does not involve alkoxy radicals derived from homolytic cleavage of MPPH but is consistent with heterolytic cleavage of MPPH to produce a metal-based active intermediate. The following evidence also shows that no free alkyl radicals are produced in the catalytic oxidation of alkanes: (1) The product yields and distributions are only slightly affected by the presence of O2. (2) Addition of BrCCl3 does not affect the yields of cyclohexanol and cyclohexanone in the oxidation of cyclohexane. (3) A complete retention of stereochemistry occurs in the hydroxylation of cis- and trans-1,2-dimethylcyclohexane. The proposed mechanism involves initial O-atom transfer from ROOH to [Os(VI)(N)Cl4](-)/Lewis acid to generate [Os(VIII)(N)(O)Cl4](-)/Lewis acid, which then oxidizes alkanes via H-atom abstraction.

Relative silver(I) ion binding energies of α-amino acids : A determination by means of the kinetic method

The relative silver(I) ion binding energies of 19 α-amino acids have been measured by means of the kinetic method. In general, they are similar to the relative copper(I) ion binding energies of corresponding amino acids although there are differences that can be accounted for by differences in silver(I) and copper(I) chemistry. The correlation with proton basicities is comparatively poorer. Again, the differences between silver(I) and proton binding can be attributed to differences in silver(I) and proton chemistry. The relative silver(I) binding energies measured are best described as relative basicities or ΔΔGAg°’s. The observed internal consistency during construction of a silver(I) ion basicity ladder implies that ΔΔSAg° is approximately zero except when histidine and lysine are involved. For 16 α-amino acids, their relative silver(I) ion basicities ≈ relative silver(I) ion affinities or ΔΔG° Ag ≈ ΔΔHAg°.

Characterization of the product ions from the collision-induced dissociation of argentinated peptides

Tandem mass spectrometry performed on a pool of 18 oligopeptides shows that the product ion spectra of argentinated peptides, the [bn + OH + Ag]+ ions and the [yn − H + Ag]+ ions bearing identical sequences are virtually identical. These observations suggest strongly that these ions have identical structures in the gas phase. The structures of argentinated glycine, glycylglycine, and glycylglycylglycine were calculated using density functional theory (DFT) at the B3LYP/DZVP level of theory; they were independently confirmed using HF/ LANL2DZ. For argentinated glycylglycylglycine, the most stable structure is one in which Ag+ is tetracoordinate and attached to the amino nitrogen and the three carbonyl oxygen atoms. Mechanisms are proposed for the fragmentation of this structure to the [b2 + OH + Ag]+ and the [y2 − H + Ag]+ ions that are consistent with all experimental observations and known calculated structures and energetics. The structures of the [b2 − H + Ag]+ and the [a2 − H + Ag]+ ions of glycylglycylglycine were also calculated using DFT. These results confirm earlier suggestions that the [b2 − H + Ag]+ ion is an argentinated oxazolone and the [a2 − H + Ag]+ an argentinated immonium ion.

Kinetics and mechanism of G-quadruplex formation and conformational switch in a G-quadruplex of PS2.M induced by Pb2+

DNA sequences with guanine repeats can form G-quartets that adopt G-quadruplex structures in the presence of specific metal ions. Using circular dichroism (CD) and ultraviolet-visible (UV–Vis) spectroscopy, we determined the spectral characteristics and the overall conformation of a G-quadruplex of PS2.M with an oligonucleotide sequence, d(GTG3TAG3CG3TTG2). UV-melting curves demonstrate that the Pb2+-induced G-quadruplex formed unimolecularly and the highest melting temperature (Tm) is 72°C. The analysis of the UV titration results reveals that the binding stoichiometry of Pb2+ ions to PS2.M is two, suggesting that the Pb2+ ions coordinate between adjacent G-quartets. Binding of ions to G-rich DNA is a complex multiple-pathway process, which is strongly affected by the type of the cations. Kinetic studies suggest that the Pb2+-induced folding of PS2.M to G-quadruplex probably proceeds through a three-step pathway involving two intermediates. Structural transition occurs after adding Pb(NO3)2 to the Na+- or K+-induced G-quadruplexes, which may be attributed to the replacement of Na+ or K+ by Pb2+ ions and the generation of a more compact Pb2+–PS2.M structure. Comparison of the relaxation times shows that the Na+→Pb2+ exchange is more facile than the K+→Pb2+ exchange process, and the mechanisms for these processes are proposed.

Antiferromagnetic ordering in a novel five-connected 3D polymer {Cu2(2,5-Me2pyz)[N(CN)2]4}n (2,5-Me2pyz2,5-dimethylpyrazine)Electronic supplementary information (ESI) available: plot of the temperature dependence of the ac susceptibility (Fig. S1). See http://www.rsc.org/suppdata/nj/b1/b111012h/

Reaction of Na[N(CN)2] with CuSO4·5H2O and 2,5-Me2pyz produced {Cu2(2,5-Me2pyz)[N(CN)2]4}n (2,5-Me2pyz = 2,5-dimethylpyrazine), which is an unusual five-connected, two-fold interpenetrated network that orders antiferromagnetically at low temperature.

Cerium(IV)-Driven Water Oxidation Catalyzed by a Manganese(V)–Nitrido Complex†

The study of manganese complexes as water-oxidation catalysts (WOCs) is of great interest because they can serve as models for the oxygen-evolving complex of photosystem II. In most of the reported Mn-based WOCs, manganese exists in the oxidation states III or IV, and the catalysts generally give low turnovers, especially with one-electron oxidants such as Ce(IV) . Now, a different class of Mn-based catalysts, namely manganese(V)-nitrido complexes, were explored. The complex [Mn(V) (N)(CN)4 ](2-) turned out to be an active homogeneous WOC using (NH4 )2 [Ce(NO3 )6 ] as the terminal oxidant, with a turnover number of higher than 180 and a maximum turnover frequency of 6 min(-1) . The study suggests that active WOCs may be constructed based on the Mn(V) (N) platform.