Elucidating the Supramolecular Copolymerization of N- and C-Centered Benzene-1,3,5-Tricarboxamides: The Role of Parallel and Antiparallel Packing of Amide Groups in the Copolymer Microstructure

An in-depth study of the supramolecular copolymerization behavior of N- and C-centered benzene-1,3,5-tricarboxamides (N- and C-BTAs) has been conducted in methylcyclohexane and in the solid state. The connectivity of the amide groups in the BTAs differs, and mixing N- and C-BTAs results in supramolecular copolymers with a blocky microstructure in solution. The blocky microstructure results from the formation of weaker and less organized, antiparallel hydrogen bonds between N- and C-BTAs. In methylcyclohexane, the helical threefold hydrogen-bonding network present in C- and N-BTAs is retained in the mixtures. In the solid state, in contrast, the hydrogen bonds of pure BTAs as well as their mixtures organize in a sheet-like pattern, and in the mixtures long-range order is lost. Drop-casting to kinetically trap the solution microstructures shows that C-BTAs retain the helical hydrogen bonds, but N-BTAs immediately adopt the sheet-like pattern, a direct consequence of the lower stabilization energy of the helical hydrogen bonds. In the copolymers, the stability of the helical aggregates depends on the copolymer composition, and helical aggregates are only preserved when a high amount of C-BTAs is present. The method outlined here is generally applicable to elucidate the copolymerization behavior of supramolecular monomers both in solution as well as in the solid state.     

High-yield bacillus subtilis protease production by solid-state fermentation

A Bacillus subtilis isolate was shown to be able to produce extracellular protease in solid-state fermentations (SSF) using soy cake as culture medium. A significant effect of inoculum concentration and physiological age on protease production was observed. Maximum activities were obtained for inocula consisting of exponentially growing cells at inoculum concentrations in the range of 0.7–2.0 mg g⁻¹. A comparative study on the influence of cultivation temperature and initial medium pH on protease production in SSF and in submerged fermentation (SF) revealed that in SSF a broader pH range (5–10), but the same optimum temperature (37°C), is obtained when compared to SF. A kinetic study showed that enzyme production is associated with bacterial growth and that enzyme inactivation begins before biomass reaches a maximum level for both SF and SSF. Maximum protease activity and productivity were 960 U g⁻¹ and 15.4 U g⁻¹ h⁻¹ for SSF, and 12 U mL⁻¹ and 1.3 U mL⁻¹ h⁻¹ for SF. When SSF protease activity was expressed by volume of enzyme extract, the enzyme level was 10-fold higher and the enzyme productivity 45% higher than in SF. These results indicate that this bacterial strain shows a high biotechnological potential for protease production in solid-state fermentation.     

Calculation of Conformational Properties and Rouse Relaxation Times of PAMAM‐EDA Dendrimers under Different pH Conditions

A Monte Carlo study has been performed for protonated and non‐protonated coarse‐grained PAMAM‐EDA of generations (G) ranging from 2 to 6. This study calculates sizes, asphericities, and global and external dendrimer density profiles that confirm features previously found in other studies. It is shown that form factors do not change significantly with protonation. Diffusion coefficients, intrinsic viscosities, and Rouse relaxation times are computed as conformational averages. The hydrodynamic properties and their change with protonation are in good agreement with available experimental data. Some differences between the neutral and protonated molecules are noticeable in the case of the relaxation times corresponding to the higher generation numbers (G > 4). These features indicate that pH may play a role in the internal dynamics of dendrimers. The complex modulus curves have also been computed. When in reduced units to discount size effects, the protonation effect is seen to be very small.

     

Simple implementation of complex functionals: scaled self-consistency

We explore and compare three approximate schemes allowing simple implementation of complex density functionals by making use of self-consistent implementation of simpler functionals: (i) post-local-density approximation (LDA) evaluation of complex functionals at the LDA densities (or those of other simple functionals) (ii) application of a global scaling factor to the potential of the simple functional, and (iii) application of a local scaling factor to that potential. Option (i) is a common choice in density-functional calculations. Option (ii) was recently proposed by Cafiero and Gonzalez [Phys. Rev. A 71, 042505 (2005)]. We here put their proposal on a more rigorous basis, by deriving it, and explaining why it works, directly from the theorems of density-functional theory. Option (iii) is proposed here for the first time. We provide detailed comparisons of the three approaches among each other and with fully self-consistent implementations for Hartree, local-density, generalized-gradient, self-interaction corrected, and meta-generalized-gradient approximations, for atoms, ions, quantum wells, and model Hamiltonians. Scaled approaches turn out to be, on average, better than post approaches, and unlike these also provide corrections to eigenvalues and orbitals. Scaled self-consistency thus opens the possibility of efficient and reliable implementation of density functionals of hitherto unprecedented complexity.     

Proteome-on-a-chip: mirage, or on the horizon?

Proteomics has emerged as the next great scientific challenge in the post-genome era. But even the most basic form of proteomics, proteome profiling, i.e., identifying all of the proteins expressed in a given sample, has proven to be a demanding task. The proteome presents unique analytical challenges, including significant molecular diversity, an extremely wide concentration range, and a tendency to adsorb to solid surfaces. Microfluidics has been touted as being a useful tool for developing new methods to solve complex analytical challenges, and, as such, seems a natural fit for application to proteome profiling. In this review, we summarize the recent progress in the field of microfluidics in four key areas related to this application: chemical processing, sample preconcentration and cleanup, chemical separations, and interfaces with mass spectrometry. We identify the bright spots and challenges for the marriage of microfluidics and proteomics, and speculate on the outlook for progress.     

Nanospheres,Nanotubes, Toroids,and Gels with Controlled Macroscopic Chirality

The interaction of a highly dynamic poly(aryl acetylene) (poly‐ 1 ) with Li⁺, Na⁺_, and Ag⁺ leads to macroscopically chiral supramolecular nanospheres, nanotubes, toroids, and gels. With Ag⁺, nanospheres with M helicity and tunable sizes are generated, which complement those obtained from the same polymer with divalent cations. With Li⁺ or Na⁺, poly‐ 1 yields chiral nanotubes, gels, or toroids with encapsulating properties and M helicity. Right‐handed supramolecular structures can be obtained by using the enantiomeric polymer. The interaction of poly‐ 1 with Na⁺ produces nanostructures whose helicity is highly dependent on the solvation state of the cation. Therefore, structures with either of the two helicities can be prepared from the same polymer by manipulation of the cosolvent. Such chiral nanotubes, toroids, and gels have previously not been obtained from helical polymer–metal complexes. Chiral nanospheres made of poly(aryl acetylene) that were previously assembled with metal(II) species can now be obtained with metal(I) species.     

Determination of vapor pressure curves of warifteine and methylwarifteine by using thermogravimetry

Warifteine and methylwarifteine are bisbenzylisoquinoline alkaloids from Cissampelos sympodialis Eichl., produces a reversible, nonspecific, and noncompetitive antagonism of histamine, anti-allergic therapy, and used in the folk medicine for the treatment of airway respiratory diseases. Thermal techniques are used for several purposes, e.g., for thermal characterization, and measurement of the vapor pressure with objective of the quantitative determination. The objective of this study was to evaluate of the vapor pressure of the curves of warifteine and methylwarifteine by thermogravimetry analysis, how a fast and sensible method for quantitative determination. This method is based on the ratio of the Arrhenius, Langmuir, and Antoine equations for a reference material and the sample under investigation. The results showed these alkaloids follow zero-order kinetics with respect to volatilization. The vapor pressure curves of warifteine and methylwarifteine were plotted for the rates of 10, 15, and 20 °C min⁻¹. The proposed method also possesses the potential.     

Loaded and unloaded optical response of polyester model materials

The optical behavior of mixtures of rigid and flexible polyester resins when loaded and unloaded under constant strain-rate and varying test temperature are characterized. New evidence about the photoplastic method of analyzing deformed but unloaded models is presented through experiments with tensile or compressive uniaxial specimens, diametrically compressed disks and beams under pure bending, which were analyzed during loading, unloading and after being unloaded.