RECENT PUBLICATIONS

Latest publications
 
A comparative assessment of the activity and structure of phlorotannins from the brown seaweek Carpophyllum flexuosum

Posted 15 December 2017

Rui Zhang, Alexander Yuen, Tony Masters and Thomas Maschmeyer et al.  Algal Research, 29, 130-141, 2018.   DOI:  10.1016/j.algal.2017.11.027

Abstract:

The extraction and antioxidant activity of phlorotannins from the brown seaweeds Carpophyllum flexuosum, Carpophyllum plumosum and Ecklonia radiata was investigated to identify an optimised extraction process for novel anti-oxidant extracts. Subsequently, the composition of the most active phlorotannin extracts was determined. Microwave assisted extraction (MAE) using water was the most efficient extraction process with shorter processing times and a higher purity product than obtained with any of the other methods tested. MAE resulted in the fast, effective decomposition of the cellular structure, as identified through scanning electron microscopy (SEM), and this related directly to the efficiency of extraction. Phlorotannins extracted from C. flexuosum by MAE had the strongest antioxidant activity (62.1 mg gallic acid equivalents (GAE)/g dw of seaweed) and more than 5.5-fold greater 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability than ascorbic acid after 7-day incubation periods at 30 °C and at 60 °C. Six major chemical species of phlorotannin, belonging to the fuhalol group, were identified within the MAE extract using NMR and HPLC-MS. The results confirm phlorotannins from C. flexuosum to be promising natural, bio-derived and bio-compatible antioxidants, while identifying the most effective method to extract the constituents and retain antioxidant activity.

Systematic tuning of Zn(II) frameworks with furan, thiophene, and selenophene dipyridyl and dicarboxylate ligands

Posted 15 December 2017

Carol Hua and Deanna D'Alessandro.  Crystal Growth & Design, 17 (12), 6262-6272, 2017.   DOI:  10.1021/acs.cgd.7b00940

Abstract:

Twelve Zn(II) frameworks with furan, thiophene, and selenophene dicarboxylate and dipyridyl ligands have been synthesized by solvothermal methods in both the presence and the absence of water to investigate the subtle differences in structure and properties of the framework with changes in the linearity of the ligands. The large change in the ligand bend angle (10°) of the furan ring when compared to either thiophene or selenophene results in the formation of a number of frameworks with unexpected topologies. By using only ligands containing thiophene and selenophene, which differ in their ligand bend angle by only 2°, a series of four isostructural Zn(II) paddlewheel frameworks were obtained and their subtle differences investigated using UV/vis/NIR spectroscopy and gas adsorption experiments with N2, H2, and CO2.

Bromozincate ionic liquids in the Knoevenagel condensation reactions

Posted 15 December 2017

Lisa Player, Bun Chan, Peter Turner, Tony Masters and Thomas MaschmeyerApplied Catalysis B: Environmental, 223, 228-233, 2018.   DOI:  10.1016/j.apcatb.2017.09.021

Abstract:

Ionic liquids (ILs) have been widely promoted as functional replacements of volatile organic solvents; however restricting their use to conventional solvents constrains their potential. One means of enhancing their utility is through the development of dual purpose ILs, capable of acting as both solvent and catalyst. A series of bromozincate ILs was synthesised, and the Lewis acidities probed spectroscopically. Furthermore, the crystal and molecular structure of [C2Py]2[ZnBr4] was determined through single-crystal X-ray diffraction. The ILs were then used in a model reaction, aimed at probing effects of both IL Lewis acidity and structural organisation on the reaction outcome.

The influence of the ancillary ligand on the potential of cobalt(III) complexes to act as chaperones for hydroxamic acid-based drugs

Posted 15 December 2017

Bradley Green, Anna Renfrew, Alexandra Glenister, Peter Turner and Trevor Hambley. Dalton Transactions, 46 (45), 15897-15907, 2017.  DOI:  10.1039/c7dt03645k

Abstract:

Cobalt(III) chaperones are a promising class of bioreductive prodrugs under investigation for the delivery of cytotoxic ligands to hypoxic solid tumours. Here we investigate a series of cobalt complexes as chaperones for hydroxamic acid ligands, comparing the properties of the cyclic cyclen (1,4,7,10-tetraazacyclododecane) ancillary ligand with the tripodal tpa (tris-(2-pyridylmethyl)amine) and tren (tris-(2-aminoethyl)amine). A small library of complexes containing several different hydroxamic acids, including the MMP inhibitor Marimistat and the fluorescent ligand C343haH2, were prepared and their pKa values, reduction potentials, and in some cases X-ray crystal structures, were determined. The antiproliferative actitivity of the series was evaluated against DLD-1 colon cancer cells and the cellular accumulation of the fluorescent C343haH2 complexes was monitored by ICPMS and confocal fluorescence microscopy, revealing that the nature of the ancillary ligand significantly influences the complexes’ properties, cytotoxicity and cellular distribution.

[Fe(C5Ar5)(CO)2Br] complexes as hydrogenase mimics for the catalytic hydrogen evolution reaction

Posted 15 December 2017

Ellen Hemming, Peter Turner, Leo Corcilius, Jason Price, Tony Masters and Thomas Maschmeyer et al.  Applied Catalysis B:  Environmental, 223, 234-241, 2018.  DOI:  10.1016/j.apcatb.2017.04.053

Abstract:

A new iron-based hydrogenase mimic, [Fe(C5(p-C6H4Br)5)(CO)2Br], was synthesised and characterised using X-ray crystallography. Two analogous catalytic precursors, [Fe(C5Ar5)(CO)2Br] (Ar = C6H5; p-C6H4Br), were also analysed electrochemically in order to investigate how bulkier and more electron withdrawing C5Ar5 ligands affect the catalytic generation of hydrogen from trichloroacetic acid. Compared to previously reported iron-based cyclopentadienyl analogues, these complexes were found to have smaller overpotentials and larger turnover numbers. The [Fe(C5(p-C6H4Br)5)(CO)2Br] complex was found to be the most efficient of the two catalytic precursors with a turnover number of 25, an overpotential of around 310 mV and a faster rate of reaction compared to [Fe(C5Ph5)(CO)2Br].

Mixed valency as a strategy for achieving charge delocalization in semiconducting and conducting framework materials

Posted 15 December 2017

Ryuichi Murase, Chanel Leong and Deanna D'AlessandroInorganic Chemistry, 56 (23), 14373-14382, 2017. DOI:  10.1021/acs.inorgchem.7b02090

Abstract:

The fundamentally important phenomenon of mixed valency has been discussed in detail over the past 50 years, predominantly in the context of dinuclear complexes, which are used as model systems for understanding electron delocalization in more complex biological and physical systems. Very recently, mixed valency has been shown to be an important mechanism for charge transfer, leading to delocalization and conductivity in two- and three-dimensional framework materials such as metal–organic frameworks and related systems including covalent organic frameworks and semicrystalline semiconducting metal–organic graphenes. This Viewpoint provides a current perspective on the field of mixed-valence frameworks, where the property is either intrinsic or generated postsynthetically via an external stimulus. Aspects of the spectroscopy and applications of these materials are also discussed, highlighting the future potential for exploiting mixed valency in extended solid-state systems.

The mechanism of the spontaneous detonation of ammonium nitrate in reactive grounds

Posted 15 December 2017

Alex Djerdjev, Pramith Priyananda, James Beattie, Chiara Neto, and Brian Hawkett. Journal of Environmental Chemical Engineering, 6 (1), 281-288, 2018.  DOI:  10.1016/j.jece.2017.12.003

Abstract:

The mechanism of the decomposition of ammonium nitrate fuel oil (ANFO) and of ammonium nitrate (AN) emulsions has been investigated. The formation of NO gas bubbles at the end of an induction period was observed, which led to the evolution of brown NO2 gas on contact with air. Inhibition of the decomposition reaction could be achieved by reducing the NO concentration in the gas phase, with inhibitors not in physical contact with the reaction mixture. NO adsorbing clay minerals (hydrotalcite) were effective inhibitors, indicating multiple mechanisms of inhibition. A central role is assigned to nitrous acid (HNO2): sequestering NO prevents its formation, base inhibitors keep it in the non-reactive form of the nitrite ion (pKa of HNO2 ∼ 3), and urea in acidic conditions decomposes it to harmless N2. Our results have implications in industries where NOx emissions can cause significant environmental problems for both aquatic and marine life as well as for human health.

Covalent bonding in the hydrogen molecule

Posted 15 December 2017

George Bacskay et al. The Journal of Physical Chemistry A, 121 (48), 9330-9345, 2017.  DOI:  10.1021/acs.jpca.7b08963

Abstract:

This work addresses the continuing disagreement between two schools of thought concerning the mechanism of covalent bonding. According to Hellmann, Ruedenberg, and Kutzelnigg, covalent bonding is a quantum mechanical phenomenon whereby lowering of the kinetic energy associated with electron sharing, i.e., delocalization, is the key stabilization mechanism. The opposing view of Slater, Feynman, and Bader has maintained that the source of stabilization is electrostatic potential energy lowering due to electron density redistribution to binding regions between nuclei. Following our study of H2+ we present an analogous detailed study of H2 where bonding involves an electron pair with repulsion and correlation playing a significant role in its properties. We use a range of different computational approaches to study and reveal the relevant contributions to bonding as seen in the electron density and corresponding kinetic and potential energy distributions. The energetics associated with the more complex electronic structure of H2, when examined in detail, clearly agrees with the analysis of Ruedenberg; i.e., covalent bonding is due to a decrease in the interatomic kinetic energy resulting from electronic delocalization. Our results support the view that covalent bonding is a quantum dynamical phenomenon requiring a properly quantized kinetic energy to be used in its description.