Crosslinked penicillin acylase aggregates for synthesis of β-lactam antibiotics in organic medium

Crosslinked enzyme aggregates (CLEAs) of a partially purified penicillin acylase from a recombinant Escherichia coli strain have been produced as a novel type of biocatalysts well endowed to perform in organic media. Different protein precipitants were studied and glutaraldehyde was used as the crosslinking agent. Precipitation curves were obtained for all precipitants to determine the concentrations at which all the protein precipitated out of the solution. The effect of the glutaraldehyde-to-protein ratio was studied with respect to process recovery and the specific activity and stability of the biocatalyst. Recovery of penicillin acylase activity was moderately high, about 50%; major losses of enzyme activity were produced at the precipitation step. Specific activities of all CLEAs were very high, which is one of the advantages of using nonsupported biocatalysts. Ammonium sulfate and tert-butyl alcohol were the best precipitants at a glutaraldehyde-protein mass ratio of 2 and were selected to perform the kinetically controlled synthesis of ampicillin in 60% (v/v) ethylene glycol medium. At comparable conversion yields, volumetric and specific antibiotic productivity were much higher for CLEAs than for carrier-bound penicillin acylases.     

Attenuation of the depolarizing field in a thin film model relaxor

The behavior of the polarization in a microscopic statistical model for a thin film relaxor placed between two metallic electrodes is studied by numerical simulations. Depolarization fields different from zero, due to a non-perfect compensation of surface charges at the metallic electrodes, are taken into account. Different thicknesses and different values of the compositional charge disorder density for the relaxor are considered. Depolarization field is found to be extremely attenuated for large values of the number density of charge carriers in the relaxor. In such a case, field attenuation allows for the existence of a homogeneous ferroelectric ground state.     

Properties of nano-scale soliton-like excitations in two-dimensional lattice layers

Nano-scale soliton-like supersonic, intrinsic localized excitations in two-dimensional atomic anharmonic lattice layers are here considered. We study the propagation, the velocity and other soliton-like features at head-on collisions of such lattice excitations created by using suitable initial mechanical and thermal conditions. Noteworthy is that narrow, highly-energetic solitons moving along one lattice row are very robust, accompanied by weak anti-phase oscillations in the lateral direction.     

Analytic extension of non quasi-analytic Whitney jets of Roumieu type

Let (M_r)_{r∈? 0} be a logarithmically convex sequence of positive numbers which verifies M₀ = 1 as well as M_r ≥ 1 for every r ∈ ? and defines a non quasi-analytic class. Let moreover F be a closed proper subset of ?ⁿ. Then for every function ? on ?ⁿ belonging to the non quasi-analytic (M_r)-class of Roumieu type, there is an element g of the same class which is analytic on ?ⁿ F and such that D^α ?(x) = D^αg(x) for every σ ∈ ?₀ ⁿ SBAP and x ∈ F.     

Application of a Heuristic Scheduling Rule for a Tyre Testing Department

This paper presents the development and application of a heuristic scheduling rule for the Testing Department of a tyre and rubber company. The company had set down five major objectives for this department: (1) minimize average flow-time; (2) maintain an average flow-time of less than two weeks; (3) maintain pre-set maximum individual test flow times; (4) assign a higher priority to important jobs; (5) maintain a balanced mix between truck and passenger tyres. A composite scheduling rule was designed to meet these objectives which contains the following four components: (a) slack-time per remaining operation; (b) shortest processing time; (c) an urgency factor to prioritize important jobs; (d) a balancing factor to enable a desired proportion between truck and passenger tyres. This composite rule is tested against the existing scheduling scheme used by the foreman and against the simple S.P.T. rule. The results are very encouraging.     

Parallel Versus Antiparallel β-Sheet Structure in Cyclic Peptide Hybrids Containing γ- or δ-Cyclic Amino Acids

Cyclic peptides with disc-shaped structures have emerged as potent building blocks for the preparation of new biomaterials in fields ranging from biological to material science. In this work, we analyze in depth the self-assembling properties of a new type of cyclic peptides based on the alternation of α-residues and cyclic δ-amino acids (α,δ-CPs). To examine the preferred stacking properties adopted by cyclic peptides bearing this type of amino acids, we carried out a synergistic in vitro/in silico approximation by using simple dimeric models and then extended to nanotubes. Although these new cyclic peptides (α,δ-CPs) can interact either in a parallel or antiparallel fashion, our results confirm that although the parallel β-sheet is more stable, it can be switched to the antiparallel stacking by choosing residues that can establish favorable cross-strand interactions. Moreover, the subsequent comparison by using the same methodology but applied to α,γ-CPs models, up to the moment assumed as antiparallel-like d,l -α-CPs, led to unforeseen conclusions that put into question preliminary conjectures about these systems. Surprisingly, they tend to adopt a parallel β-sheet directed by the skeleton interactions. These results imply a change of paradigm with respect to cyclic peptide designs that should be considered for dimers and nanotubes.     

Modeling of pore formation in phase inversion processes: analysis of pore formation mechanism

The phase inversion process is the most important preparation process of porous polymer membranes. Recently, a numerical model based on first principles to predict pore structures has been proposed (Hopp-Hirschler and Nieken in J Membr Sci 564:820–831, 2018). This model enables a detailed investigation of the mechanism of pore formation in porous polymer membranes. This follow-up presents investigations of the mechanism of nucleation of pores during the phase inversion process in 1D. Pores originate due to accumulation of over-saturated mixtures inside a diffuse interface between homogeneous and demixed polymer solutions behind the precipitation front. This is caused by an expansion of the width of the diffuse interface and time-dependent concentration profiles which finally lead to a change of sign of total diffusive mass flux inside of the diffuse interface. As a result, oscillating compositions behind the precipitation front lead to formation of pores. It is concluded that large surface tension leads to initially small pore sizes. In the second part, a detailed discussion of directional diffusion behind the precipitation front is presented in 2D, which is responsible for different pore structures, e.g., finger or sponge pores. Depending on the dominant direction of diffusion finger pores, lamella structures or sponge pores are formed. This picture can straightforwardly be extended to 3D structures.