NMR-study of the stereochemistry and dynamic behaviour of thioacrylamides

Several model thioacrylamides, Me₂N CH = C(R) C(S) NMe₂ (R = H, Ph — 2a, b ) and (p)MeO C₆H₄ NH CHC(R) C(S) NMe₂ (R = H, Ph — 3a, b ) have been synthesized. The ¹H-n.m.r. spectra have been taken for discussing the E/Z-isomerism of the thioacrylamides and the assignment further strengthened by an added LIS-study. The 2-unsubstituted compounds have been found to exist exclusively in preferred configurations/conformations: 2a — E(s-cis); 3a — Z(s-cis); the 2-phenylsubstituted analogs are of divergent behaviour: in 2b the C(S) NMe₂ moiety is found to be twisted out of the common plane, and 3b prefers the flat s-trans conformations (E(s-trans) ⇌ Z(s-trans)). The compounds show restricted rotations about C¹, N- and C³, N-partial double bonds. The corresponding rotational barriers, determined as ΔG-values by dynamic n.m.r. spectroscopy, are discussed with respect to (i) the resonance branch at C¹, (ii) the influence of substituents, and (iii) the effect of steric hindrance in the thioacrylamide moiety generally.     

Prevalence of Salmonella in two Botswana abattoir environments

A 1-year study was carried out to investigate the prevalence of Salmonella in two abattoir environments coded "A" and "B" in Gaborone, Botswana. The total number of environmental samples collected from abattoirs A and B was 250 and 300, respectively. The samples were taken from soils in the corrals, knife blades, saw blades, cattle-drinking water, cattle feces, and feed. Preenrichment, enrichment, and selective/differential media, which enabled the favorable growth of Salmonella, were used in the study. Salmonellae were present in all sampled environments. The most common serotypes found in the environment at abattoir A were E1, C1, C2, and B. Serotypes B, C1, C2, C3, and E1 were common in abattoir B. Antigenic characterization of the salmonellae isolates showed that Salmonella Anatum, Salmonella Azteca, Salmonella Saintpaul, Salmonella Cerro, and Salmonella Westhampton were predominant in abattoir A, whereas Salmonella Anatum, Salmonella Mbandaka, Salmonella Molade, Salmonella Reading, and Salmonella Oranienburg were dominant in abattoir B. Implementing hazard analysis critical control point principles in work procedures would definitely reduce the gross contamination taking place in abattoirs.     

Novel wet-chemical routes to highly structured semiconductor layers for improved efficiency photovoltaic devices

There is increasing interest in using ZnO as an alternative to TiO₂ in photoelectrochemical (PEC) solar cells that employ high surface area nanostructured substrates. Columnar ZnO films may offer fundamental advantages over nanoporous TiO₂ such as improved electrical transport properties. We have grown perpendicularly orientated ZnO crystallites, on novel ZnO template layers, from aqueous solutions containing a zinc carboxylate salt and hexamethylenetetraamine (HMT). These films provide a high surface area substrate for subsequent overgrowth of semiconductor sensitizer layers of Cu_2–x S and Cu_2–x Se. Films have been characterized by spectroscopic methods (UV-VIS, photoluminescence, PL), microscopy (scanning electron microscopy, SEM) and X-ray diffraction (XRD) methods.     

Prevalence and antimicrobial susceptibility of Salmonella isolated from a variety of raw meat sausages in Gaborone (Botswana) retail stores

The objective of the study was to provide baseline data on the prevalence and antimicrobial susceptibility of Salmonella in different types of raw meat sausages directly accessible to the consumers in Gaborone, Botswana. A total of 300 raw sausages comprising 79 beef, 78 pork, 72 chicken, and 71 mutton samples were concurrently analyzed for the presence of Salmonella using a conventional culture method and a validated PCR method. The PCR assay results were in full concordance with those of the conventional culture method for the detection of Salmonella. Sixty-five (21.7%) of 300 samples were positive for Salmonella by both the conventional culture method and PCR assay. Even though more chicken samples contained Salmonella than did any other sausage type, the difference in the presence of Salmonella among the four sausages types was not significant. Eleven serotypes were identified, and Salmonella enterica subsp. salamae II was most prevalent in all the sausage types. Beef sausages generally had higher mesophilic bacterial counts than did the other three sausage types. However, higher microbial counts were not reflective of the presence of salmonellae. Susceptibility of the Salmonella enterica serotypes to 20 antimicrobial agents was determined, and Salmonella Muenchen was resistant to the widest array of agents and was mostly isolated from chicken sausages. Regardless of the meat of origin, all 65 Salmonella isolates were resistant to at least four antimicrobial agents: amikacin, gentamicin, cefuroxime, and tombramycin. This resistance profile group was the most common in all four sausage types, comprising 90% of all Salmonella isolates from beef, 71% from pork, 63% from mutton, and 35% from chicken. These results suggest that raw sausages pose a risk of transmitting multidrug-resistant Salmonella isolates to consumers.     

Synergistic Effect of Functionalized Carbon Nanotubes and Micron‐Sized Rubber Particles on the Mechanical Properties of Epoxy Resin

In this study, the synergistic effect of functionalized carbon nanotubes (fCNT) and micron‐sized rubber particles in improving the thermomechanical properties of epoxy resin is demonstrated. fCNT is mixed with carboxyl‐terminated butadiene acrylonitrile toughened epoxy (CTBNTE) by ultrasonication followed by the addition of curing agent and mixing with planetary shear mixer. A significant improvement is noticed in fracture toughness (≈ 200%) and thermal stability (≈ 12 °C) of fCNT‐filled CTBNTE system but only a marginal improvement in fracture toughness and thermal stability of pristine CNT‐filled CTBNTE relative to epoxy. Dispersion of fCNT is better than pristine CNT in the epoxy matrix. Scanning electron microscope (SEM) images of fractured surface of fCNT‐filled CTBNTE reveal plastic deformation zone, stress whitening, and overall rougher surface compared to pristine CNT‐filled CTBNTE. The findings of our work show promise for use of fCNT in conjunction with a rubber toughener as filler for improving the properties of epoxy resin for advanced structural applications.

     

Prevalence and antibiotic resistance profiles of Escherichia coli O157:H7 in beef products from retail outlets in Gaborone, Botswana

Four hundred meat samples (134 meat cubes, 133 minced meat, 133 fresh sausages) were collected from 15 supermarkets and butcheries in Gaborone, Botswana, between the summer months of October 2002 and March 2003. Samples were assayed for Escherichia coli O157 by selective enrichment in modified E. coli broth containing novobiocin, followed by immunomagnetic separation and plating onto sorbitol MacConkey agar supplemented with potassium tellurite. The isolates were biochemically and serologically confirmed by API 20E and O157 antisera, respectively. The prevalence rates for E. coli O157 were 5.22% in meat cube samples, 3.76% in minced meat samples, and 2.26% in fresh sausages. The isolates showed single, double, and triple antibiotic resistance. Fifty-three percent of them were resistant to cephalothin. Resistance was also recorded for sulphatriad (33%), colistin sulphate (26%), streptomycin (0.7%), and tetracycline (26%). It is recommended that the cause for antibiotic resistance be investigated using a larger number of samples from cattle, especially from ranching areas of the country.