Effect of the acrylic acid content on the permeability and water uptake of poly(styrene-co-butyl acrylate) latex films

In this contribution, a theoretical modeling of the latex film formation is presented and compared to experimental results: water vapor permeability and latex film capacitance are studied as a function of acrylic acid content in poly(styrene-co-butyl acrylate) latex films. It has been shown that both water uptake and water vapor permeability are mainly affected by film morphology which in turn is defined by intercolloidal interaction and drying rate.     

Protein partitioning in poly(ethylene glycol)/sodium polyacrylate aqueous two-phase systems

The partition of hemoglobin, lysozyme and glucose-6-phosphate dehydrogenase (G6PDH) in a novel inexpensive aqueous two-phase system (ATPS) composed by poly(ethylene glycol) (PEG) and sodium polyacrylate (NaPA) has been studied. The effect of NaCl and Na(2)SO(4), pH and PEG molecular size on the partitioning has been studied. At high pH (above 9), hemoglobin partitions strongly to the PEG-phase. Although some precipitation of hemoglobin occurs, high recovery values are obtained particularly for lysozyme and G6PDH. The partitioning forces are dominated by the hydrophobic and electrochemical (salt) effects, since the positively charged lysozyme and negatively charged G6PDH partitions to the non-charged PEG and the strongly negatively charged polyacrylate enriched phase, respectively.     

Describing intrinsic noise in Chua's circuit

In this Letter we demonstrate that intrinsic inevitable noise effects, existing in realistic experiments with electronic circuits, are properly described theoretically using a Gaussian noise. For this we integrate numerically the equations of motion from the Chua circuit using a fourth-order stochastic Runge–Kutta integrator. Periodic structures in parameter space, related to periodic motion, start to be destroyed when the noise intensity is increased and vanish at a critical intensity value, for which only chaotic motion remains. We find the appropriate noise intensity interval which satisfactorily reproduces the parameter space from the corresponding experiment and it is in remarkable agreement with the estimated experimental noise. Present achievements should be applicable to describe noise effects in a wide number of electronic circuits.     

Maximum entropy approach for deducing amino Acid interactions in proteins

We present a maximum entropy approach for inferring amino acid interactions in proteins subject to constraints pertaining to the mean numbers of various types of equilibrium contacts for a given sequence or a set of sequences. We have carried out several kinds of tests for a two-dimensional lattice model with just two types of amino acids with very promising results. We also show that the method works very well even when the mean numbers of contacts are not known and therefore can be applied to real proteins.     

Preliminary investigation of the interaction between the R2R3 DNA binding domain of the oncoprotein c-Myb and DNA fragments

The interaction between the R2R3 DNA binding domain of the oncoprotein c-Myb and oligodeoxynucleotides was investigated by ¹H-NMR spectroscopy and fluorescence anisotropy assays. Titration of 12 and 16 base-pair DNA fragments containing the TAACGGTC sequence with R2R3 revealed the presence of two complexed forms (in a 40/60 ratio): either two complexes or two conformations in slow exchange at the NMR chemical shift time scale. The largest variations of imino proton chemical shifts were observed for the imino proton of the base pairs 2, 3, 4 and 6 of the DNA sequence, suggesting a direct involvement of these base pairs in the interaction. Using fluorescence anisotropy measurements, a dissociation constant of 5.12 ± 1.49 nM for the specific DNA-R2R3 complex was found, whereas a value of 2.7 ± 0.1 μM was determined for the nonspecific complex. © 1996 John Wiley & Sons, Inc.     

Drug Design Inspired by Nature: Crystallographic Detection of an Auto‐Tailored Protease Inhibitor Template

De novo drug discovery is still a challenge in the search for potent and selective modulators of therapeutically relevant target proteins. Here, we disclose the unexpected discovery of a peptidic ligand 1 by X‐ray crystallography, which was auto‐tailored by the therapeutic target MMP‐13 through partial self‐degradation and subsequent structure‐based optimization to a highly potent and selective β‐sheet peptidomimetic inhibitor derived from the endogenous tissue inhibitors of metalloproteinases (TIMPs). The incorporation of non‐proteinogenic amino acids in combination with a cyclization strategy proved to be key for the de novo design of TIMP peptidomimetics. The optimized cyclic peptide 4 (ZHAWOC7726) is membrane permeable with an IC₅₀ of 21 nm for MMP‐13 and an attractive selectivity profile with respect to a polypharmacology approach including the anticancer targets MMP‐2 (IC₅₀: 170 nm ) and MMP‐9 (IC₅₀: 140 nm ).     

Palladacyclopentadienyl complexes bearing purine‐based N‐heterocyclic carbenes: A new class of promising antiproliferative agents against human ovarian cancer

A complete protocol for the synthesis of new palladacyclopentadienyl complexes with purine‐based carbenes as supporting ligands is described. The new organometallic compounds were exhaustively characterized using NMR and infrared spectroscopies and elemental analysis. The single‐crystal X‐ray structure of complex 2b coordinating also a triphenylphosphine was resolved. Some of these complexes showed an antiproliferative activity comparable to or better than that of cisplatin on two human ovarian cancer lines: A2780 (cisplatin‐sensitive) and A2780cis (cisplatin‐resistant). Moreover, for complexes 2 and 3 (coordinating one purine‐based N‐heterocyclic carbene ligand and one phosphine) the cytotoxicity is associated with an evident induction of apoptosis. Finally, complexes 3 , bearing one purine‐based N‐heterocyclic carbene ligand and one 1,3,5‐triaza‐7‐phosphaadamantane, proved practically inactive on non‐tumour fibroblast cells (MRC‐5).     

Benzyl N‐[(Benzyloxy)methyl]carbamate: An Improved Aminomethylation Electrophile for the Synthesis of (Benzyloxy)carbonyl (Cbz)‐Protected Chiral β2‐Amino Acids

α‐Aminomethylation of (R)‐DIOZ‐alkylated (DIOZ=4‐isopropyl‐5,5‐diphenyloxazolidin‐2‐one) substrates is a key step in the asymmetric synthesis of β²‐amino acids, but it is unfortunately often accompanied by formation of transcarbamation by‐products. Aminomethylation was tested using a range of electrophiles, and the amount of by‐product formation was assessed in each case. Benzyl N‐[(benzyloxy)methyl]carbamate electrophile 3d is unable to form this by‐product due to its inherent benzyl substitution. Use of electrophile 3d showed an improved impurity profile in aminomethylation, thus leading to easier intermediate purification.