Polymorphism and Thermodynamic Stability of Zn7Sb2O12

The composition Zn_2.33Sb_0.67O₄ (or Zn₇Sb₂O₁₂) exists in two polymorphic forms. The thermodynamically stable, low-temperature orthorhombic β form transforms to the high-temperature cubic α-polymorph with a spinel structure at 1225°±25°C. The transformation is fully reversible but slower in the α→β direction and therefore, it is easy to preserve the high-temperature α-polymorph to lower temperatures where it is kinetically stable but thermodynamically metastable. It is also possible to synthesize the α-polymorph directly at low temperatures, e.g., 900°C. This synthesis, of a phase that is thermodynamically stable only at high temperatures, but which has sufficient kinetic stability to exist metastably at low temperatures, represents an example of Ostwald's law of successive reactions in which the first phase to crystallize from a reaction mixture is not necessarily the equilibrium phase of lowest free energy. The crystal structure of the α-polymorph has been confirmed by Rietveld refinement of X-ray powder diffraction data to be an inverse spinel, (Zn)[Sb_2/3Zn_4/3]O₄, in which octahedral sites contain a disordered, random mixture of Zn and Sb and tetrahedral sites are fully occupied by Zn.     

A novel random mutagenesis approach using human mutagenic DNA polymerases to generate enzyme variant libraries

The in vitro MutaGen procedure is a new random mutagenesis method based on the use of low-fidelity DNA polymerases. In the present study, this technique was applied on a 2 kb gene encoding amylosucrase, an attractive enzyme for the industrial synthesis of amylose-like polymers. Mutations were first introduced during a single replicating step performed by mutagenic polymerases pol beta and pol eta. Three large libraries (>10(5) independent clones) were generated (one with pol beta and two with pol eta). The sequence analysis of randomly chosen clones confirmed the potential of this strategy for the generation of diversity. Variants generated by pol beta were 4-7-fold less mutated than those created with pol eta, indicating that our approach enables mutation rate control following the DNA polymerase employed for mutagenesis. Moreover, pol beta and pol eta provide different and complementary mutation spectra, allowing a wider sequence space exploration than error-prone PCR protocols employing Taq polymerase. Interestingly, some of the variants generated by pol eta displayed unusual modifications, including combinations of base substitutions and codon deletions which are rarely generated using other methods. By taking advantage of the mutation bias of naturally highly error-prone DNA polymerases, MutaGen thus appears as a very useful tool for gene and protein randomisation.     

Validation of a PCR-based method for the detection of various rendered materials in feedstuffs using a forensic DNA extraction kit

A method trial was initiated to validate the use of a commercial DNA forensic kit to extract DNA from animal feed as part of a PCR-based method. Four different PCR primer pairs (one bovine pair, one porcine pair, one ovine primer pair, and one multispecies pair) were also evaluated. Each laboratory was required to analyze a total of 120 dairy feed samples either not fortified (control, true negative) or fortified with bovine meat and bone meal, porcine meat and bone meal (PMBM), or lamb meal. Feeds were fortified with the animal meals at a concentration of 0.1% (wt/wt). Ten laboratories participated in this trial, and each laboratory was required to evaluate two different primer pairs, i.e., each PCR primer pair was evaluated by five different laboratories. The method was considered to be validated for a given animal source when three or more laboratories achieved at least 97% accuracy (29 correct of 30 samples for 96.7% accuracy, rounded up to 97%) in detecting the fortified samples for that source. Using this criterion, the method was validated for the bovine primer because three laboratories met the criterion, with an average accuracy of 98.9%. The average false-positive rate was 3.0% in these laboratories. A fourth laboratory was 80% accurate in identifying the samples fortified with bovine meat and bone meal. A fifth laboratory was not able to consistently extract the DNA from the feed samples and did not achieve the criterion for accuracy for either the bovine or multispecies PCR primers. For the porcine primers, the method was validated, with four laboratories meeting the criterion for accuracy with an average accuracy of 99.2%. The fifth laboratory had a 93.3% accuracy outcome for the porcine primer. Collectively, these five laboratories had a 1.3% false-positive rate for the porcine primer. No laboratory was able to meet the criterion for accuracy with the ovine primers, most likely because of problems with the synthesis of the primer pair; none of the positive control DNA samples could be detected with the ovine primers. The multispecies primer pair was validated in three laboratories for use with bovine meat and bone meal and lamb meal but not with PMBM. The three laboratories had an average accuracy of 98.9% for bovine meat and bone meal, 97.8% for lamb meal, and 63.3% for PMBM. When examined on an individual laboratory basis, one of these four laboratories could not identify a single feed sample containing PMBM by using the multispecies primer, whereas the other laboratory identified only one PMBM-fortified sample, suggesting that the limit of detection for PMBM with this primer pair is around 0.1% (wt/wt). The results of this study demonstrated that the DNA forensic kit can be used to extract DNA from animal feed, which can then be used for PCR analysis to detect animal-derived protein present in the feed sample.     

Targeted and Non-Targeted Mechanisms for Killing Hypoxic Tumour Cells—Are There New Avenues for Treatment?

Purpose: A major issue in radiotherapy is the relative resistance of hypoxic cells to radiation. Historic approaches to this problem include the use of oxygen mimetic compounds to sensitize tumour cells, which were unsuccessful. This review looks at modern approaches aimed at increasing the efficacy of targeting and radiosensitizing hypoxic tumour microenvironments relative to normal tissues and asks the question of whether non-targeted effects in radiobiology may provide a new “target”. Novel techniques involve the integration of recent technological advancements such as nanotechnology, cell manipulation, and medical imaging. Particularly, the major areas of research discussed in this review include tumour hypoxia imaging through PET imaging to guide carbogen breathing, gold nanoparticles, macrophage-mediated drug delivery systems used for hypoxia-activate prodrugs, and autophagy inhibitors. Furthermore, this review outlines several features of these methods, including the mechanisms of action to induce radiosensitization, the increased accuracy in targeting hypoxic tumour microenvironments relative to normal tissue, preclinical/clinical trials, and future considerations. Conclusions: This review suggests that the four novel tumour hypoxia therapeutics demonstrate compelling evidence that these techniques can serve as powerful tools to increase targeting efficacy and radiosensitizing hypoxic tumour microenvironments relative to normal tissue. Each technique uses a different way to manipulate the therapeutic ratio, which we have labelled “oxygenate, target, use, and digest”. In addition, by focusing on emerging non-targeted and out-of-field effects, new umbrella targets are identified, which instead of sensitizing hypoxic cells, seek to reduce the radiosensitivity of normal tissues.     

Adaptive Sustainable Enterprises

Enterprises that want to compete in today’s dynamic markets need to be able to respond to the ever-increasing rates of change. At the same time enterprises strive to be ever more sustainable in terms of economic, environmental, societal, and cultural concerns. Enterprises are being challenged at all levels to meet the demands for sustainability and in a manner that can handle the complexity that is present. In this paper we suggest that enterprises need to integrate sustainability objectives with adaptive approaches to manage complexity and uncertainty. The overarching objective of the research is to explore how an enterprise can become both adaptive and sustainable by interweaving the deliberate and emergent in the context of strategy, organization, process, and information. This research seeks to model and develop several artefacts that assist with responses to complexity and uncertainty while also supporting goals of sustainability. In particular, we propose context aware adaptive and sustainable concepts, framework, lifecycle, architecture, and a prototypical implementation.     

New generation of amino coumarin methyl sulfonate-based fluorogenic substrates for amidase assays in droplet-based microfluidic applications

Droplet-based microfluidics is a powerful tool for biology and chemistry as it allows the production and the manipulation of picoliter-size droplets acting as individual reactors. In this format, high-sensitivity assays are typically based on fluorescence, so fluorophore exchange between droplets must be avoided. Fluorogenic substrates based on the coumarin leaving group are widely used to measure a variety of enzymatic activities, but their application in droplet-based microfluidic systems is severely impaired by the fast transport of the fluorescent product between compartments. Here we report the synthesis of new amidase fluorogenic substrates based on 7-aminocoumarin-4-methanesulfonic acid (ACMS), a highly water-soluble dye, and their suitability for droplet-based microfluidics applications. Both substrate and product had the required spectral characteristics and remained confined in droplets from hours to days. As a model experiment, a phenylacetylated ACMS was synthesized and used as a fluorogenic substrate of Escherichia coli penicillin G acylase. Kinetic parameters (k(cat) and K(M)) measured in bulk and in droplets on-chip were very similar, demonstrating the suitability of this synthesis strategy to produce a variety of ACMS-based substrates for assaying amidase activities both in microtiter plate and droplet-based microfluidic formats.     

Social regulation of serotonin in the auditory midbrain.

The neuromodulator serotonin regulates auditory processing and can increase within minutes in response to stimuli like broadband noise as well as nonauditory stressors. Little is known about the serotonergic response in the auditory system to more natural stimuli such as social interactions. Using carbon-fiber voltammetry, we measured extracellular serotonin in the auditory midbrain of resident male mice during encounters with a male intruder. Serotonin increased in the inferior colliculus (IC) over the course of a 15 minute interaction, but not when mice were separated with a perforated barrier. Several behaviors, including the amount of immobility and anogenital investigation performed by the resident, were correlated with the serotonergic response. Multiple intrinsic factors associated with individual mice also correlated with the serotonergic response. One of these was age: older mice had smaller serotonergic responses to the social interaction. In a second interaction, individual identity predicted serotonergic responses that were highly consistent with those in the first interaction, even when mice were paired with different intruders. Serotonin was also significantly elevated in the second social interaction relative to the first, suggesting a role for social experience. These findings show that during social interaction, serotonin in the IC is influenced by extrinsic factors such as the directness of social interaction and intrinsic factors including age, individual identity, and experience. (PsycINFO Database Record (c) 2011 APA, all rights reserved)