Eng Wui Tan

Adhesive Secretions of Live Mussels Observed in Situ by Attenuated Total Reflection–Infrared Spectroscopy

The chemical species involved in the adhesion of blue mussels (Mytilus galloprovincialis) and greenshell mussels (Perna canaliculus) to surfaces has been investigated using in situ attenuated total reflection infrared (ATR-IR) spectroscopy. Mussel spat ranging in size from 0.5 to 25 mm were placed in a flow cell containing a ZnSe multiple internal reflection prism and supplied with temperature-controlled seawater. Distinctively different absorption spectra were obtained when the mussels were predominantly moving across the surface or forming permanent bonds. With limited movement, the absorption spectrum was characteristic of protein with peaks near 1647 cm−1 (amide I), 1543 cm−1 (amide II), and 1235 cm−1 (amide III). When the mussels were observed to be moving across the surface of the ATR-IR crystal there was a strong broad absorption maximum around 1200–900 cm−1 (carbohydrate polymers), presumably due to the secretion of a weakly acidic mucopolysaccharide. Distinct differences in the spectra obtained from the adhesive secretions of blue or greenshell mussels were not observed. The data presented is the first reported use of IR spectroscopy to obtain in situ, real-time, chemical data on the interactions between invertebrates and substrates immersed in sea water.

UV-induced photodegradation of oseltamivir (Tamiflu) in water

Environmental context Oseltamivir (Tamiflu) is widely used to prevent and treat influenza but conventional wastewater processes involving sedimentation and biotic oxidation do not appear to significantly remove it from sewage, leading to its discharge into the environment. A range of advanced oxidation processes (AOPs) involving photolysis of aqueous solutions of oseltamivir with UV alone, UV/H2O2 and UV/H2O2/FeII is demonstrated to lead to photodegradation of oseltamivir to products with no ecotoxicity observed. These AOPs may therefore offer potentially environmentally friendly sewage water treatment options. Abstract Aqueous solutions of the antiviral drug oseltamivir phosphate (OSP, Tamiflu, (3R,4R,5S)-ethyl 4-acetamido-5-amino-3-(pentan-3-yloxy)cyclohex-1-enecarboxylate) were degraded using advanced oxidation processes (AOPs) involving photodegradation with UV alone, UV/H2O2 and UV/H2O2/FeII (photo-Fenton reaction). The photodecay of the parent OSP in all three cases followed first-order kinetics with respective rate constants of 0.21, 1.56 and 1.75 min–1 at 20°C in pH 7 phosphate-buffered Milli-Q water. The rate of UV/H2O2 photolysis in the presence of 2-methylpropan-2-ol was significantly slower with an approximate first-order rate constant of 0.13 min–1 suggesting the involvement of •OH in the degradation process. NMR spectroscopy, mass spectrometry and high-performance liquid chromatography (HPLC) with UV diode array detection were used to identify the crude photoproduct as the hydroxylated OSP derivative (3S,4R,5S)-ethyl 4-acetamido-5-amino-2-hydroxy-3-(pentan-3-yloxy)cyclohexanecarboxylate that occurs by an unknown mechanism. OSP and this crude photoproduct demonstrated no effect on the survival of Quinquelaophonte sp. over 96 h.

Mimicking subsecond neurotransmitter dynamics with femtosecond laser stimulated nanosystems

Existing nanoscale chemical delivery systems target diseased cells over long, sustained periods of time, typically through one-time, destructive triggering. Future directions lie in the development of fast and robust techniques capable of reproducing the pulsatile chemical activity of living organisms, thereby allowing us to mimic biofunctionality. Here, we demonstrate that by applying programmed femtosecond laser pulses to robust, nanoscale liposome structures containing dopamine, we achieve sub-second, controlled release of dopamine – a key neurotransmitter of the central nervous system – thereby replicating its release profile in the brain. The fast delivery system provides a powerful new interface with neural circuits, and to the larger range of biological functions that operate on this short timescale.

Penta­fluoro­phenyl 3-chloro-3-phenyl­propanoate

The structural analysis of the title compound, C15H8ClF5O2, confirms the position of the Cl atom at C-3.

Alkyl linker effects on the coordination topology of ditopic di(2-pyridylmethyl)amine carboxylate ligands with ZnII and CuII: polymers vs. macrocycles

A series of ditopic ω-di(2-pyridylmethyl)amine carboxylic acid ligands incorporating a range of n-alkyl linkers (CnCOOH, n = 3–5, 7, 10 and 11) have been synthesised. Solution phase studies showed a 1 : 1 coordination stoichiometry between the ligands and M(ClO4)2·6H2O (M = ZnII or CuII) in all cases. The ZnII and CuII complexes were subsequently crystallised by liquid–liquid diffusion and the solid-state structures investigated by X-ray crystallography. The crystal structures obtained are entirely consistent with the 1 : 1 metal–ligand ratio of the solution-phase adducts. However, the coordination geometries and complex topologies are dependent on the alkyl chain length of the ligand CnCOOH. The ZnII and CuII complexes of the short alkyl chain ligands (n ≤ 5) exhibit 1D coordination polymeric structures with somewhat different conformations for {[Zn(C3COO)(H2O)](ClO4)·3.5H2O}n (1), {[Zn(C4COO)(H2O)]4(ClO4)4·1.5H2O}n (2), {[Zn(C5COO)(H2O)](ClO4)}n (3), {[Cu(C3COO)](ClO4)·MeOH}n (4), {[Cu(C4COO)(H2O)]2(ClO4)2·2H2O}n (5) and {[Cu(C5COO)(H2O)](ClO4)·2H2O}n (6). In contrast, the ligands with longer alkyl chains (n ≥ 7) participate in Zn2L2 metallomacrocyclic structures {[Zn(C7COO)(H2O)](ClO4)}2 (7), [Zn2(C10COO)2(H2O)2](ClO4)2·2H2O·MeOH (8) and {[Zn2(C11COO)2(H2O)2][Zn2(C11COO)2](ClO4)4·H2O}n (9). The formation of metallomacrocycles instead of the 1D coordination polymers is a persistent trend and, with identical crystal growth conditions and a non-coordinating anion employed, appears to be an effect of the longer alkyl chain.

CO2-triggered release from switchable surfactant impregnated liposomes

Incorporation of an amidine-based switchable surfactant into the lipid membrane of a liposome produces a system that is capable of triggered release upon in situ exposure to CO2. The amount of liposomal contents released is dependent on the concentration of switchable surfactant incorporated. A mechanism of the release is proposed.

The Synthesis of Multifunctionalized 1,3-Oxazin-4-ones from Donor–Acceptor Cyclopropanes

A series of electronically diverse imines were found to readily react with various donor-acceptor cyclopropyl acid chlorides, with complete regioselectivity, to form 1,3-oxazin-4-ones in moderate yields (25-48% over two steps). Select oxazinones underwent a base induced rearrangement to afford the corresponding cycloheptene-fused oxazinones in good yields (up to 70%).

Expedient Metal-Free Synthesis of 1,3-Oxazinen-4-ones

1,3-Oxazinen-4-ones are medicinally important scaffolds which have traditionally been accessed using a hetero-Diels-Alder approach or more recently using a cobalt-catalyzed three-component cycloaddition. Herein we report a novel strategy to access this scaffold which allows for the rapid and high yielding synthesis of 1,3-oxazinen-4-ones under ambient temperature and pressures with improved substrate scope.

Stereoselective radical bromination of α-chloro hydrocinnamic acid derivatives

Reaction of (S)-2-chloro-3-phenylpropanoic acid derivatives with NBS gave the corresponding 3-bromo-2-chloro derivatives with a preference for the formation of the (2R,3S) isomers over the (2R,3R) isomers. The stereoselectivity was affected by the nature of the carboxylic acid derivative. Reaction of ester derivatives was highly stereoselective while the reaction of amide derivatives showed varied stereoselectivity which depended on the nature of the amide. Theoretical studies at UHF/3-21G* level showed that the intermediate benzylic radical of the methyl ester, the methyl amide and the diisopropyl amide derivatives had different energy profiles with respect to rotation of the C2–C3 bond. The different stereoselectivity observed from reaction of the various acid derivatives could be attributed, at least in part, to different distribution of conformers of the radical intermediate.

Pulsatile release from pH triggered imidazoline switchable surfactant liposomes

The incorporation of an imidazoline (IDZ) based switchable surfactant into the lipid membrane of a liposome produces a system that can be triggered to release its solute upon pH change. However, unlike traditional pH-triggered controlled release systems, IDZ–liposomes are capable of undergoing multiple triggering events, resulting in solute release in a pulsatile manner. Furthermore near-total release can be achieved incrementally with temporal control. A mechanism for this reversible behaviour is also proposed, and dependence on the physical properties of the surfactant is discussed.