On the lifetime of excited states of frustration model of spin glasses

An analysis of the low energy excited states of the ± J model of Ising spins on a square lattice is developped in terms of clustering of solidary spins. Two types of clusters are exhibited : entropic and pinned clusters regarding the occurence of potential barriers in the relaxation. The mean reversal time of these clusters is determined and interpreted as one dimensional random walk in phase space. The size dependence of this mean reversal time varies as n² (n denoting the number of spins in the cluster) or $\text{n}{}^2\text{x exp(?}\text{ΔE}\text{k}{}_{\mathrm{B}}\text{T}\text{)}$ where ΔE is the potential barrier, instead of n in the case of ferromagnetic Ising model.     

Cyclocondensation adducts from the lewis acid mediated reaction of 4-acetoxy-2-azetidinone with siloxydienes

A successful trapping of 1-azetin-4-one with siloxydienes as cyclocondensation adducts is described.     

Protein micropatterns using a pH-responsive polymer and light

Protein and peptide microarrays are popular candidates for medical diagnostics because of the possibility for high sensitivity and simultaneous marker screening. To realize the potential of these arrays, new strategies for ligand patterning are needed. We report a method for patterning proteins that utilizes a pH-responsive polymer, deep ultraviolet (DUV) light, and a photoacid generator (PAG). Poly(3,3'-diethoxypropyl methacrylate) (PDEPMA) contains reactive acetal side chains which are converted to aldehydes following treatment with acid. PDEPMA was spin-coated onto Si-SiO(2) substrates and was either chemically deprotected with 1 M HCl or photochemically deprotected by exposure to DUV in the presence of triphenylsulfonium triflate. Conversion to aldehyde groups was confirmed with Purpald and by reaction with a green fluorescent hydroxylamine. Protein microarrays were demonstrated by incubating photochemically patterned surfaces with an aldehyde-reactive biotin followed by red fluorescent streptavidin. This methodology provides a new substrate for the precise patterning of both peptides and proteins for various biological applications including medical sensors.     

Heptakis(2-O-methyl-3,6-di-O-sulfo)-beta-cyclodextrin: a single isomer, 14-sulfated beta-cyclodextrin for use as a chiral resolving agent in capillary electrophoresis

The first single-isomer, 14-sulfated beta-cyclodextrin, the sodium salt of heptakis(2-O-methyl-3,6-di-O-sulfo)-beta-cyclodextrin (HMdiSu) has been used to separate 24 pharmaceutical weak base enantiomers in pH 2.5 background electrolytes using capillary electrophoresis. For the weakly binding bases, the cationic effective mobilities decreased, approached zero, and then increased again. For the strongly binding bases, the cationic effective mobilities decreased, became anionic at very low concentrations of HMdiSu, passed an anionic mobility maximum, then decreased again as the HMdiSu concentration was increased. Viscosity corrections according to Walden's rule did not eliminate these unexpected effective mobility extrema. The mobility extrema were rationalized by extending the charged resolving agent migration model (CHARM model) to include ionic strength effects.     

Tuning the parameters for fast respirometry

The aerobic bacterial respiration rate is an indicator of microbial growth and metabolism, essential for monitoring the oxidation process and organic load content of samples in a diverse field of application from influent streams in wastewater treatment facilities to industrial fermentations. This paper looks at the influence of parameters, such as culture concentration and volume, sample surface area/volume ratio and headspace volume to achieve optimisation of respirometry measurement and thus design a bench-top respirometric device, based on the monitoring of the pressure changes in a closed chamber where a bacterial culture is allowed to respire in contact with a sample. Contrary to traditional respirometry, the goal is detection of bacterial respiration within 5 min in a minimal sample volume. Both qualitative and quantitative data could be derived using a simple equation and fine-tuning of the micro-manometric parameters of the device, with a most important finding being that minimal headspace volume in combination with elevated bacterial populations maximised absolute pressure change response and favoured high sensitivity at short response time, even though the conditions indicated oxygen-limitation. Furthermore, in comparison with a commercially available respirometer the typical respiration rate of stationary phase P. putida M10 gave oxygen uptake rate (OUR) and specific oxygen uptake rate (SOUR) of 38 μmol l⁻¹ min⁻¹ and 5 μmol g⁻¹ min⁻¹, respectively with the ‘classical’ system, while the μ-Warburg device designed here showed a typical response, for the culture with the same dry cell concentration, of 66 μmol l⁻¹ min⁻¹ for the OUR and 9 μmol g⁻¹ min⁻¹ for the SOUR. The remarkable outcome from this data, therefore, is that it appears that the high surface area/volume geometry of the μ-Warburg device design has achieved less respiration limitation, even though the sample is unstirred. This presents important insight regarding future respirometer design.