Analytical performance characteristics of thin and thick film amperometric microcells

The analytical performance of amperometric microcells with different electrode geometries is compared for enzyme activity measurements. The microcells were fabricated with thin film photolithography or thick film screen-printing in four different designs. The cells made with the thin film process used flexible substrate with microelectrode array or a circular, disk-shaped working electrode. The screen-printed working electrodes had semicircle or disk shape on ceramic chips. Putrescine oxidase (PUO) activity measurement was used as a model. The determination of PUO activity is important in the clinical diagnosis of premature rupture of the amniotic membrane. An electropolymerized m-phenylenediamine size-exclusion layer was used to eliminate common interferences. The size exclusion layer revealed also to be advantageous in protecting the electrodes from fouling by putrescine (enzyme substrate). The electrode fouling of bare electrodes was insignificant for screen-printed electrodes, but very severe for electroplated platinum working electrodes. The microelectrode array electrodes demonstrated smaller RSD and higher normalized sensitivities for hydrogen peroxide and PUO activity. All the other electrodes were demonstrating comparable analytical performances.     

Horsepower requirements for high-solids anaerobic digestion

Applied Biochemistry and Biotechnology - Improved organic loading rates for anaerobic bioconversion of cellulosic feedstocks are possible through high-solids processing. Additionally, the reduction...     

Photocycle kinetics: analysis of Raman data from bacteriorhodopsin.

A recently developed algorithm for analyzing photocycle kinetics was applied to recently obtained Raman data for the time course of bacteriorhodopsin (bR) and its intermediates, L, M, N and O. The algorithm allows all possible transitions between any of the intermediates in the kinetic model. The best fit to all the Raman data required the transitions L in equilibrium with M in equilibrium with N----O----bR and also the branch L in equilibrium with N. The rates are moderately well determined and smooth as a function of pH. From the ratios of forward and backward rates the differences in free energy of the L, M and N states are no larger than 1.5 kcal. The possibility that only the sum of the L and N concentrations is well determined, but not the individual L and N concentrations, was investigated. The model L in equilibrium with M in equilibrium with N----O----bR satisfactorily fitted condensed L + N data and gave predicted individual L and N concentrations considerably different than those measured individually. The possibility of Raman invisible states, such as two Ms or two Ns was also investigated. Models with two Ns were not successful and it cannot yet confidently be concluded which model with two Ms is best. However, the model, L in equilibrium with M1----M2----N----O----bR plus the branch L----N, fits the data better with the same number of parameters as the best model with only one M intermediate. This provides strong support for two Ms in the bR photocycle.     

Role of s-p orbital mixing in the bonding and properties of second-period diatomic molecules

Qualitative molecular orbital theory is widely used as a conceptual tool to understand chemical bonding. Symmetry-allowed orbital mixing between atomic or fragment orbitals of different energies can greatly complicate such qualitative interpretations of chemical bonding. We use high-level Amsterdam Density Functional calculations to examine the issue of whether orbital mixing for some familiar second-row homonuclear and heteronuclear diatomic molecules results in net bonding or antibonding character for a given molecular orbital. Our results support the use of slopes of molecular orbital energy versus bond distance plots (designated radial orbital-energy slope: ROS) as the most useful criterion for making this determination. Calculated atomic charges and frontier orbital properties of these molecules allow their acid-base chemistry, including their reactivities as ligands in coordination chemistry, to be better understood within the context of the Klopman interpretation of hard and soft acid-base theory. Such an approach can be extended to any molecular species.     

Proof of the first order phase transition in the Slater KDP model

The Slater KDP model defined on d-dimensional tetrahedral lattices is proved to have a phase transition for which the entropy and energy are discontinuous functions at a transition temperaturekT _c =/ln2, independent of dimensionality.     

Development of a novel,two-step process for treating municipal biosolids for beneficial reuse

Modern municipal sewage waste treatment plants use conventional mechanical and biological processes to reclaim wastewaters. This process has an overall effect of converting a water pollution problem into a solid waste disposal problem (sludges or biosolids). An estimated 10 million tons of biosolids, which require final disposal, are produced annually in the United States. Although numerous disposal options for biosolids are available, including land application, landfilling, and incineration, disposal costs have risen, partly because of increased federal and local environmental restrictions(1). A novel, thermomechanical biosolids pre-treatment process, which allows for a variety of potential value-added uses, was developed. This two-step process first employs thermal explosive decompression to inactivate or kill the microbial cells and viruses. This primary step also results in the rupture of a small amount of the microbial biomass and increases the intrinsic fluidity of the biosolids. The second step uses shear to effect a near-complete rupturing of the microbial biomass, and shears the nondigested organics, which increases the overall surface area. Pretreated biosolids may be subjected to a secondary anaerobic digestion process to produce additional fuel gas, and to provide for a high-quality, easily dewatered compost product. This novel biosolids pretreatment process was recently allowed a United States patent.     

TESTING KINETIC MODELS FOR THE BACTERIORHODOPSIN PHOTOCYCLE—II. INCLUSION OF AN O TO M BACKREACTION

Abstract Using previously established procedures we have tested a kinetic model of bacteriorhodopsin involving a backreaction from O to M. This model is superior to the previously tested models involving only unidirectional reaction paths. However, the spectrum of O is still too strongly temperature dependent in the red. Therefore, at least one additional feature is necessary to obtain a completely consistent kinetic model of the bacteriorhodopsin photocycle.