John Webb

The major lateral radula teeth of chitons (Mollusca: Polyplacophora) are composite materials, incorporating a variety of biominerals within an organic scaffold. While magnetite is ubiquitous to these teeth in all Polyplacophorans whose radulae have been described to date, this is not the case for the biominerals of the tooth core. In situ analsysis, using energy dispersive spectroscopy, to determine the distribution of elements in chiton teeth, and Raman spectroscopy, to identify the biominerals present, has been undertaken in the mature teeth of seven chiton species representing three families in the suborder Chitonina. The results show the tooth core to be comprised of a variety of elements, with the main biominerals identified as limonite, lepidocrocite and hydroxyapatite. Along with Ischnochiton australis, all five representatives of the Chitonidae deposit an apatitic mineral in their tooth core, while Plaxiphora albida does not deposit any calcium biomineral. With the exception of Acanthopleura echinata, the hydrated iron (III) oxide, limonite, is found in all species, including I. australis, which has relatively small amounts of iron in its tooth core. The lack of any evidence for a phosphate mineral in species that possess high levels of phosphorus in their core, challenges the long accepted notion that the presence of phosphorus implies its deposition as a biomineral. The combined techniques of energy dispersive spectroscopy and Raman spectroscopy provide a simple and effective means to evaluate, in situ, the biomineralisation strategies employed by chitons. While the results from this study are inconclusive in determining whether biomineralisation strategies reflect phylogenetic affinities in chitons, an extension of the study to include a wider range of chiton taxa could provide a basis for the utilisation of radula tooth biomineralisation as a systematic tool in this class of molluscs.

Drug-induced spoliation of hydrogels as contact lenses or as implants in the anterior eye is a frequent occurrence in clinical practice. This study explores the capacity of three commercial multipurpose solutions for contact lens care to reduce the spoliation of poly(2-hydroxyethyl methacrylate) (PHEMA) specimens exposed to a simulated aqueous humour formulation and to three topical drugs commonly administered after insertion of artificial corneas (Predsol, Optimol and Depo-Ralovera). ReNu MultiPlus® (Bausch & Lomb), Complete® Blink-N-Clean™ Lens Drops (Allergan) and Complete Protein Remover Tablets dissolved in Complete® ComfortPLUS™ (both from Allergan) were evaluated. All multipurpose solutions were able to dislodge passively the deposits formed on hydrogels in the simulated aqueous and in the presence of Predsol and Optimol, but none were effective against the deposits induced by Depo-Ralovera. A reduction of the calcium content in deposits caused by Predsol and Optimol was confirmed after treatment with the protein remover preparation, while the other multipurpose solutions caused the complete removal of the deposits. In experiments designed to evaluate the preventive action of the multipurpose solutions, no such effects were observed regardless of the drug involved. The prospect of using multipurpose solutions as eye drops following implantation of a hydrogel artificial cornea is a valid alternative for reducing device spoliation, however it appears to depend on the nature of the postoperative medication.

The sequence and ultimate pattern of mineralisation in the major lateral radula teeth of two species of limpet, namely Patelloida alticostata and Scutellastra laticostata (Mollusca : Patellogastropoda), have been elucidated using energy dispersive, Raman and infrared spectroscopies. In both species, iron is the first element infiltrated into the teeth and, in the form of goethite, occupies the posterior cutting surface of the tooth cusps, whereas silica mineralises the rest of the tooth. The first onset of mineralisation, as judged by the initial influx of iron, occurs in the junction zone, the region separating the tooth cusp from the tooth base. Although differences between the two species do exist, the general pattern of tooth mineralisation is very similar, suggesting that the mineralisation of iron and silica is a very ancient character, both in this group and among molluscs as a whole.

A simple procedure was developed to compare chelating agents for 153Sm complexes as a preliminary step to synthesise bifunctional analogues. Several variables affecting the efficiency of complex stability were investigated, such as the pre-organisation concept, cavity size, and the nature of coordination sites. Four semi-rigid agents incorporating carboxylic and/or phosphonic groupings fixed at trans-1,2-diaminocyclohexane were evaluated for their 153Sm chelation properties, and competition studies were performed. Data on the stability of the best chelating agent compound 3: trans-cyclohexane-1,2-bis(aminomethylphosphonic)-N,N′-bis(ethyl-2- iminodiacetic acid) in human serum are presented.

The hydrated iron(III) oxide limonite is reported for the first time as a biomineral. In situ laser Raman spectra of the tooth cores from major lateral teeth of the chiton Plaxiphora albida are compared with those of synthetic and mineral iron phosphates and iron oxides. Raman spectra measured on iron phosphate and iron oxide standard materials are shown to be easily distinguishable from one another. The central tooth cores of mature P. albida teeth do not show any evidence for the presence of a separate iron phosphate mineral. Rather, in each tooth a narrow band of the hydrated iron(III) oxide limonite is shown to separate the magnetite of the tooth surface from a central core region comprising both lepidocrocite and limonite. The high concentration of phosphorus in P. albida tooth cores, previously observed by energy dispersive spectroscopy, is not associated with a separate iron phosphate mineral, indicating that this element may be adsorbed onto the surface of the iron oxide minerals present. The failure to detect a separate iron(III) phosphate is discussed with reference to other chiton species that display high levels of iron and phosphorus in the cores of their mature major lateral teeth.

The mineralisation of iron in the major lateral teeth of the chiton Acanthopleura echinata has been examined using light and electron microscopy, together with energy dispersive and Raman spectroscopy. The deposition of magnetite in the posterior region of the tooth cusp has been shown to occur simultaneously on two fronts, from both the anterior and posterior sides. In contrast, in the lepidocrocite region, the mineral is formed by aggregation over the whole region. In addition, evidence is presented for the existence of a thin veneer of ferrihydrite over the surface of the magnetite region. The veneer preserves this region from oxidation prior to use in the mature tooth. Data also suggest that the junction zone plays a vital role in the overall biomineralisation process, contributing large amounts of iron at critical stages of development.

Raman spectroscopic investigations of the major lateral teeth of the chitons Acanthopleura rehderi and Acanthopleura curtisiana indicate that, in addition to the magnetite of the cutting surface and a carbonated hydroxyapatite in the central tooth core, these species deposit limonite in place of the lepidocrocite reported for other members of the genus Acanthopleura. A comparison of the spectra from these species with those of Onithochiton quercinus, which also deposits limonite, indicates that the current assignment of these species to Acanthopleura may not be appropriate. Biomineralization of the major lateral teeth may be a useful parameter to include in the taxonomic classification of chiton species.

This study describes a simple, efficient synthesis pathway from trans-1,2-diaminocyclohexane that provides access to a new class of semi-rigid polyamine, polycarboxylic, and polyphosphonic ligands. The key steps in synthesis were the functionalisation (with an appropriate branching group) of a bisphosphonate diaminocyclohexane derivative and the introduction of methanephosphonic functions by a rarely used method.

Magnetic bacteria synthesize magnetite crystals with species-dependent morphologies. The molecular mechanisms that control nano-sized magnetite crystal formation and the generation of diverse morphologies are not well understood. From the analysis of magnetite crystal-associated proteins, several low molecular mass proteins tightly bound to bacterial magnetite were obtained from Magnetospirillum magneticumstrain AMB-1. These proteins showed common features in their amino acid sequences, which contain hydrophobic N-terminal and hydrophilic C-terminal regions. The C-terminal regions in Mms5, Mms6, Mms7, and Mms13 contain dense carboxyl and hydroxyl groups that bind iron ions. Nano-sized magnetic particles similar to those in magnetic bacteria were prepared by chemical synthesis of magnetite in the presence of the acidic protein Mms6. These proteins may be directly involved in biological magnetite crystal formation in magnetic bacteria.

The interactions between the cationic polymer chitosan (Chit) and iron(III) were investigated. The solution properties were studied by pH-metry, viscometry and dynamic light scattering. Solid state iron(III)–Chit samples were also prepared and characterized by IR spectroscopy and electron microscopy. In aqueous solutions, the precipitation pH of the iron(III) oxyhydroxide (FeOOH) is significantly shifted towards the higher pH values in the presence of Chit indicating that some interaction takes place between the iron(III) and the polymer. However, the additivity of the pH-metric titration curves, the lack of variation both in the viscometric and IR spectra of Chit in the presence and absence of iron(III), indicate the lack of direct complexation between the Chit and ferric ions. Isolated FeOOH nanospheres of 5–10 nm diameter were observed on the transmission electron microscopic pictures of samples obtained from solutions containing iron(III) and Chit, while from DLS measurements hydrodynamic units with a few hundred nm in diameter were identified. Our data support that Chit acts as steric stabilizer and inhibits the macroscopic aggregation of the subcolloidal FeOOH particles. Thus the iron(III)–Chit interactions offer a simple and economic way to fabricate nanometric size FeOOH spheres, morphologically similar to the core of iron(III)-storage protein, ferritin.