Microwave activation of the electro-oxidation of glucose in alkaline media

The oxidation of glucose is a complex process usually requiring catalytically active electrode surfaces or enzyme modified electrodes. In this study the effect of high intensity microwave radiation on the oxidation of glucose in alkaline solution at Au, Cu, and Ni electrodes is reported. Calibration experiments with the Fe(CN)(6)(3-/4-) redox system in aqueous 0.1 M NaOH indicate that strong thermal effects occur at both 50 and 500 mu m diameter electrodes with temperatures reaching 380 K. Extreme mass transport effects with mass transport coefficients of k(mt) > 0.01 m s(-1) (or k(mt) > 1.0 cm s(-1)) are observed at 50 mu m diameter electrodes in the presence of microwaves. The electrocatalytic oxidation of glucose at 500 mu m diameter Au, Cu, or Ni electrodes immersed in 0.1 M NaOH and in the presence of microwave radiation is shown to be dominated by kinetic control. The magnitude of glucose oxidation currents at Cu electrodes is shown to depend on the thickness of a pre-formed oxide layer. At 50 mu m diameter Au, Cu, or Ni electrodes microwave enhanced current densities are generally higher, but only at Au electrodes is a significantly increased rate for the electrocatalytic oxidation of glucose to gluconolactone observed. This rate enhancement appears to be independent of temperature but microwave intensity dependent, and therefore non-thermal in nature. Voltammetric currents observed at Ni electrodes in the presence of microwaves show the best correlation with glucose concentration and are therefore analytically most useful.

A review and simplification of the in vitro incubation medium

The requirement to rapidly and efficiently evaluate ruminant feedstuffs places increased emphasis on in vitro systems. However, despite the developmental work undertaken and widespread application of such techniques, little attention has been paid to the incubation medium. Considerable research using in vitro systems is conducted in resource-poor developing countries that often have difficulties associated with technical expertise, sourcing chemicals and/or funding to cover analytical and equipment costs. Such limitations have, to date, restricted vital feed evaluation programmes in these regions. This paper examines the function and relevance of the buffer, nutrient, and reducing solution components within current in vitro media, with the aim of identifying where simplification can be achieved. The review, supported by experimental work, identified no requirement to change the carbonate or phosphate salts, which comprise the main buffer components. The inclusion of microminerals provided few additional nutrients over that already supplied by the rumen fluid and substrate, and so may be omitted. Nitrogen associated with the inoculum was insufficient to support degradation and a level of 25 mg N/g substrate is recommended. A sulphur inclusion level of 4-5 mg S/g substrate is proposed, with S levels lowered through omission of sodium sulphide and replacement of magnesium sulphate with magnesium chloride. It was confirmed that a highly reduced medium was not required, provided that anaerobic conditions were rapidly established. This allows sodium sulphide, part of the reducing solution, to be omitted. Further, as gassing with CO2 directly influences the quantity of gas released, it is recommended that minimum CO, levels be used and that gas flow and duration, together with the volume of medium treated, are detailed in experimental procedures. It is considered that these simplifications will improve safety and reduce costs and problems associated with sourcing components, while maintaining analytical precision. (c) 2005 Elsevier B.V. All rights reserved.

Microwave activation of the electro-oxidation of glucose in alkaline media

The oxidation of glucose is a complex process usually requiring catalytically active electrode surfaces or enzyme-modified electrodes. In this study the effect of high intensity microwave radiation on the oxidation of glucose in alkaline solution at Au, Cu, and Ni electrodes is reported. Calibration experiments with the Fe(CN)63–/4– redox system in aqueous 0.1 M NaOH indicate that strong thermal effects occur at both 50 and 500 µm diameter electrodes with temperatures reaching 380 K. Extreme mass transport effects with mass transport coefficients of kmt > 0.01 m s–1(or kmt > 1.0 cm s–1) are observed at 50 µm diameter electrodes in the presence of microwaves. The electrocatalytic oxidation of glucose at 500 µm diameter Au, Cu, or Ni electrodes immersed in 0.1 M NaOH and in the presence of microwave radiation is shown to be dominated by kinetic control. The magnitude of glucose oxidation currents at Cu electrodes is shown to depend on the thickness of a pre-formed oxide layer. At 50 µm diameter Au, Cu, or Ni electrodes microwave enhanced current densities are generally higher, but only at Au electrodes is a significantly increased rate for the electrocatalytic oxidation of glucose to gluconolactone observed. This rate enhancement appears to be independent of temperature but microwave intensity dependent, and therefore non-thermal in nature. Voltammetric currents observed at Ni electrodes in the presence of microwaves show the best correlation with glucose concentration and are therefore analytically most useful.

Photocatalytic degradation of humic acid in saline waters part 2. Effects of various photocatalytic materials

The present study explores for the first time, the effectiveness of photocatalytic oxidation of. humic acid (HA) in the increasingly important highly saline water. TiO2 (Degussa P25), TiO2 (Anatase), TiO2 (Rutile), TiO2 (Mesoporous) and ZnO dispersions were used as catalysts employing a medium pressure mercury lamp. The effect of platinum loading on P25 and zinc oxide was also investigated. The zinc oxide with 0.3% platinum loading was the most efficient catalyst. The preferred medium for the degradation of HA using ZnO is alkaline, whereas for TiO2 it is acidic. In addition, a comparative study of HA decomposition in artificial seawater (ASW) and natural seawater (NSW) is reported, and the surface areas and band gaps of the catalysts employed were also determined. A spectrophotometric method was used to estimate the extent of degradation of HA. (C) 2003 Elsevier Science B.V. All rights reserved.

Acid dissociation of 2,2 '-dipyridylamine in non-aqueous medium when chelated to some Ru(II)N-4 cores

[Ru(2,2'-bipyridine)(2)(Hdpa)](BF4)(2) center dot 2H(2)O (1), [Ru(1,10-phenanthroline)(2)(Hdpa)] (PF6)(2) center dot CH2Cl2 (2) and [Ru(4,4,4',4'-tetramethyl-2,2'- bisoxazoline)(2)(Hdpa)] (PF6)(2) (3) are synthesized where Hdpa is 2,2'-dipyridylamine. The X-ray crystal structures of 1 and 2 have been determined. Hdpa in 1 and 2 is found to bind the metal via the two pyridyl N ends. Comparing the NMR spectra in DMSO-d(6), it is concluded that 3 has a similar structure. The pK(a) values (for the dissociation of the NH proton in Hdpa) of free Hdpa and its complexes are determined in acetonitrile by exploiting molar conductance. These correlate linearly with the chemical shift of the NH proton in the respective entities. (C) 2007 Elsevier B.V. All rights reserved.

Synthesis of fused cyclic systems containing medium-sized rings through tandem ROM-RCM of norbornene derivatives embedded in a carbohydrate template

A general approach for the synthesis of fused cyclic systems containing medium-sized rings (7-9) has been developed. The key steps involve a diastereoface-selective Diels-Alder reaction of the dienophiles 4a-d attached to a furanosugar with cyclopentadiene and ring opening (ROM)-ring closing metathesis (RCM) of the resulting norbornene derivatives 10a-d and 11a-d. Diels-Alder reaction of the dienophiles 4a-d with cyclopentadiene in the absence of a catalyst produced 10a-d as the major product arising through addition of the diene to the unhindered Si-face. The most interesting and new aspect of the Diels-Alder reaction of these dienophiles is the accessibility of the Re-face that was blocked by the alkenyl chains under Lewis acid catalysis producing the diastereoisomers 11a-d exclusively. The reversal of facial selectivity from an uncatalyzed reaction to a catalyzed one is unprecedented. The observed stereochemical dichotomy is attributed to rotation of the enone moiety along the or bond linking the sugar moiety during formation of the chelate 13. This makes the Re-face of the enone moiety in 4a-d unhindered. Diels-Alder reaction of the carbocyclic analogue 15 under Lewis acid catalysis produced a 1: 1 mixture of the adducts 16 and 17 confirming the participation of sugar ring oxygen in chelate formation. Finally ROM-RCM of 10a-d and 11a-d with Grubbs' catalyst afforded the cis-syn-cis and cis-anti-cis bicyclo-annulated sugars 21a-d and 23a-d, respectively, containing 7-9 membered rings.

Effect of culture medium and cryoprotectants on the growth and survival of probiotic lactobacilli during freeze drying

To investigate the effects of the medium and cryoprotective agents used on the growth and survival of Lactobacillus plantarum and Lactobacillus rhamnosus GG during freeze drying. A complex medium was developed consisting primarily of glucose, yeast extract and vegetable-derived peptone. Trehalose, sucrose and sorbitol were examined for their ability to protect the cells during freeze drying. Using standardized amount of cells and the optimized freeze drying media, the effect of the growth medium on cell survival during freeze drying was investigated. The results showed that glucose and yeast extract were the most important growth factors, while sucrose offered better protection than trehalose and sorbitol during freeze drying. When the cells were grown under carbon limiting conditions, their survival during freeze drying was significantly decreased. A clear relationship was observed between cell growth and the ability of the cells to survive during the freeze drying process. The survival of probiotic strains during freeze drying was shown to be dependent on the cryoprotectant used and the growth medium.

Alkaline phosphatase activity in pasteurized milk: a quantitative comparison of Fluorophos and colourimetric procedures

Fluorophos and colourimetric procedures for alkaline phosphatase (ALP) testing were compared using milk with raw milk additions, purified bovine ALP additions and heat treatments. Repeatability was between 0.9% and 10.1% for Fluorophos, 3.5% and 46.1% for the Aschaffenburg and Mullen (A&M) procedure and 4.4% and 8.8% for the Scharer rapid test. Linearity (R-2) using raw milk addition was 0.96 between Fluorophos and the Scharer procedure. Between the Fluorophos and the A&M procedures, R-2 values were 0.98, 0.99 and 0.98 for raw milk additions, bovine ALP additions and heat treatments respectively. Fluorophos showed greater sensitivity and was both faster and simpler to perform.

An enhanced relay-enabled medium access control protocol for wireless ad hoc networks

In this paper we propose an enhanced relay-enabled distributed coordination function (rDCF) for wireless ad hoc networks. The idea of rDCF is to use high data rate nodes to work as relays for the low data rate nodes. The relay helps to increase the throughput and lower overall blocking time of nodes due to faster dual-hop transmission. rDCF achieves higher throughput over IEEE 802.11 distributed coordination function (DCF). The protocol is further enhanced for higher throughput and reduced energy. These enhancements result from the use of a dynamic preamble (i.e. using short preamble for the relay transmission) and also by reducing unnecessary overhearing (by other nodes not involved in transmission). We have modeled the energy consumption of rDCF, showing that rDCF provides an energy efficiency of 21.7% at 50 nodes over 802.11 DCF. Compared with the existing rDCF, the enhanced rDCF (ErDCF) scheme proposed in this paper yields a throughput improvement of 16.54% (at the packet length of 1000 bytes) and an energy saving of 53% at 50 nodes.