Seaweed Allelopathy Against Coral: Surface Distribution of a Seaweed Secondary Metabolite by Imaging Mass Spectrometry

Coral reefs are in global decline, with seaweeds increasing as corals decrease. Although seaweeds inhibit coral growth, recruitment, and survivorship, the mechanism of these interactions is poorly understood. Here, we used field experiments to show that contact with four common seaweeds induces bleaching on natural colonies of Porites rus. Controls in contact with inert, plastic mimics of seaweeds did not bleach, suggesting seaweed effects resulted from allelopathy rather than shading, abrasion, or physical contact. Bioassay-guided fractionation of the hydrophobic extract from the red alga Phacelocarpus neurymenioides revealed a previously characterized antibacterial metabolite, neurymenolide A, as the main allelopathic agent. For allelopathy of lipid-soluble metabolites to be effective, the compounds would need to be deployed on algal surfaces where they could transfer to corals on contact. We used desorption electrospray ionization mass spectrometry (DESI-MS) to visualize and quantify neurymenolide A on the surface of P. neurymenioides, and we found the molecule on all surfaces analyzed, with highest concentrations on basal portions of blades.     

Head‐to‐Head Prenyl Synthases in Pathogenic Bacteria

Many organisms contain head‐to‐head isoprenoid synthases; we investigated three such types of enzymes from the pathogens Neisseria meningitidis, Neisseria gonorrhoeae, and Enterococcus hirae. The E. hirae enzyme was found to produce dehydrosqualene, and we solved an inhibitor‐bound structure that revealed a fold similar to that of CrtM from Staphylococcus aureus. In contrast, the homologous proteins from Neisseria spp. carried out only the first half of the reaction, yielding presqualene diphosphate (PSPP). Based on product analyses, bioinformatics, and mutagenesis, we concluded that the Neisseria proteins were HpnDs (PSPP synthases). The differences in chemical reactivity to CrtM were due, at least in part, to the presence of a PSPP‐stabilizing arginine in the HpnDs, decreasing the rate of dehydrosqualene biosynthesis. These results show that not only S. aureus but also other bacterial pathogens contain head‐to‐head prenyl synthases, although their biological functions remain to be elucidated.     

A cobalt metal‐organic framework with small pore size for adsorptive separation of CO2 over N2 and CH4

In this study, a new cobalt‐based metal‐organic framework (MOF), [ (μ₃‐OH)₂(ipa)₅(C₃O₂)(DMF)₂] (CoIPA) was synthesized. The crystal structure analysis shows that CoIPA is constructed by Co₆(μ₃‐OH)₂ units linked by isophthalic acid forming a sxb topology and it possesses a small pore size of about 4 Å. The new MOF has been characterized using multiple experimental methods. Monte Carlo and Molecular Dynamic simulations were employed to investigate adsorption equilibrium and kinetics in terms of capacity and diffusivity of CO₂, N₂, and CH₄ on CoIPA. The gas adsorption isotherms collected experimentally were used to verify the simulation results. The activated CoIPA sample exhibits great gas separation ability at ambient conditions for CO₂/N₂ and CO₂/CH₄ with selectivity of around 61.4 and 11.7, respectively. The calculated self‐diffusion coefficients show a strong direction dependent diffusion behavior of target molecules. This high adsorption selectivity for both CO₂/N₂ and CO₂/CH₄ makes CoIPA a potential candidate for adsorptive CO₂ separation. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4532–4540, 2017     

Elastic Constants of Erbia Single Crystals

The elastic properties of single-crystalline erbia (Er₂O₃) at room temperature have been investigated using resonant ultrasound spectroscopy. The three independent stiffness constants of anisotropic Er₂O₃ cubic type-C crystals have been measured. The values of the stiffness constants were c ₁₁= 256.4 GPa, c ₁₂= 146.8 GPa, and c ₄₄= 75.2 GPa. From the stiffness constants, the estimated values for dense polycrystalline erbia for Young's modulus, the shear modulus, the bulk modulus, and Poisson's ratio at room temperature were 179 GPa, 67 GPa, 183.3 GPa, and 0.337, respectively. The value of Young's modulus is a minimum along [001] and a maximum along [111]. The value of the shear modulus is independent of the direction in the (001) and (111) planes, whereas it decreases in (11¯0) from 75 GPa along [001] to 55 GPa along [110].     

Iron antimony oxide selective oxidation catalysts – an inelastic neutron scattering study

The inelastic neutron scattering spectra of allyl iodide (3-iodopropene, CH₂=CHCH₂I) and allylpalladium chloride, and allyl iodide dosed onto activated iron(III) oxide and iron antimonate catalysts at room temperature have been determined to characterise the adsorbed allyl species. The spectra are energy loss vibrational spectra in the range 16–4000 cm⁻¹. Allyl iodide is not decomposed on the surface and interacts through the localised C = C bond, more strongly with iron antimonate than with iron(III) oxide. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photochemical free-volume generation in poly(methyl methacrylate) photoresists

The dissolution rates of poly(methyl methacrylate) [PMMA] thin films on quartz substrates are studied by a combination of laser interferometry and fluorescence quenching methods. In this way one can monitor the penetration, rate of the solvent (2-butanone, 2-pentanone) into the film. When these films were prepared containing 2 to 8 percent Meldrum's diazo (1) as a dopant, the dopant acted as a mild retarder of film dissolution. Upon irradiation at 254 nm, 1 is converted to CO, N₂ + acetone, and this process leads to a pronounced acceleration' of the PMMA film dissolution rate.     

Crosslinking vs. interdiffusion rates in melamine-formaldehyde cured latex coatings: A model for waterborne automotive basecoat

Designing optimal formulations for automotive waterborne basecoats can be fairly complex, often requiring knowledge of events that occur at the molecular level. The ultimate performance of the coating can depend upon the success with which this knowledge is applied. We examine a system in which an aqueous dispersion of an acrylic latex with -OH functionality reacts with a melamine derivative when heated. We use fluorescence-labeling and energy transfer measurements to obtain information on the relative rates of crosslinking and interparticle polymer diffusion in these films. We show that temperature and particle morphology play an important role in the development of film properties. Finally, these energy transfer experiments provide information on the location of the melamine-formaldehyde resin in the dry film before the onset of crosslinking. This system can serve as a model for waterborne basecoat development in many automotive applications. Presented at the 1998 Annual Meeting of the Federation of Societies for Coatings Technology, on October 15, 1998, in New Orleans, LA. Department of Chemistry, 80 St. George St., Toronto, Canada M5S 3H6. Finishes Division, 377 Fairall St., Ajax, ON Canada L1S 1R7.     

Using an additive to control the electrospinning of fibres of poly(ε‐caprolactone)

Electrospinning is a route to polymer fibres with diameters considerably smaller than available from most fibre‐producing techniques. We explore the use of a low molecular weight compound as an effective control additive during the electrospinning of poly(ε‐caprolactone). This approach extends the control variables for the electrospinning of nanoscale fibres from the more usual ones such as the polymer molecular weight, solvent and concentration. We show that through the use of dual solvent systems, we can alter the impact of the additive on the electrospinning process so that finer as well as thicker fibres can be prepared under otherwise identical conditions. As well as the size of the fibres and the number of beads, the use of the additive allows us to alter the level of crystallinity as well as the level of preferred orientation of the poly(ε‐caprolactone) crystals. This approach, involving the use of a dual solvent and a low molar mass compound, offers considerable potential for application to other polymer systems. Copyright © 2010 Society of Chemical Industry     

Interactions of binary liquid mixtures with polysaccharides studied using multi-dimensional NMR relaxation time measurements

Nuclear magnetic resonance transverse T₂ relaxation time has proven to be a valuable parameter for characterizing liquid/polymer interactions. This measurement is applicable to many food, personal care, and cosmetic products that contain multi-component liquid mixtures. Here, we investigate the interactions of corn starch with water/glycerol mixtures of different weight compositions and explore liquid exchange dynamics; such a system is relevant to the personal care industry. We use a combination of chemical shift resolved ¹H T₂ relaxation measurements and corresponding two-dimensional T₂ relaxation exchange experiments using both a conventional experimental protocol and a modified method with the addition of NMR chemical shift selectivity. Two relaxation regimes were evident for the hydroxyl ¹H (found in both water and glycerol) whilst three relaxation regimes are evident for the aliphatic glycerol ¹H associated here with strongly bound, weakly bound, and free (bulk) liquid, respectively. At higher water contents preferential absorption of glycerol was evident. T₂-T₂ exchange maps with a range of storage times reveal molecular exchange rates between all three regimes due to self-diffusion. Rapid exchange of water between the bulk and bound locations was evident in the case of pure water. Exchange rates for hydroxyl ¹H was considerably reduced by the inclusion of glycerol.