Solid-phase synthesis of novel trimers containing a phenylstatine core and analysis by high-resolution magic angle spinning

Here we describe a multistep solid-phase synthetic approach for the addition of amino acid residues to both the C- and N-termini of a phenylstatine core, yielding a library aimed at the development of structure-activity relationships in the S2 and S2' regions of the aspartyl proteases. Optimization of the synthetic strategy was performed on the basis of the in situ analysis of the compounds bound to the solid support through high-resolution magic angle spinning NMR Spectroscopy (HR-MAS NMR).     

TGA/FTIR studies of segmented aliphatic polyurethanes and their nanocomposites prepared with commercial montmorillonites

Nanocomposites prepared with segmented polyurethane (SPU) and commercially available nanoclays (Cloisite™ Na⁺, Cloisite™ 15A, Cloisite™ 30B) were studied using thermogravimetric analysis coupled with Fourier Transform Infrared Spectroscopy (TGA/FTIR). The results showed that the thermal degradation of unfilled SPU and the 4, 6 and 10 wt% hand mixed nanocomposites occurred in two stages being the first due to degradation of hard segments and the second due to the degradation of soft segments. It was also found that the thermal stability of these nanocomposites was not improved by increasing nanoclay concentration except for SPU/Cloisite™ 15A nanocomposites were a 40 °C increase was observed. In a similar manner, FTIR spectra of the evolved gases obtained after the thermal degradation of these nanocomposites were qualitatively similar to the unfilled polymer except in those containing Cloisite™ 30B where isocyanate absorptions were detected. In contrast, SPU/Cloisite™ 30B nanocomposites prepared by in-situ polymerization, exhibited higher thermal stability than the corresponding hand mixed nanocomposites. In addition, these nanocomposites exhibited the presence of carbon dioxide in the evolved gases during its second degradation stage which was not observed in the hand mixed nanocomposites. In this case, it can be said that the presence of clays in the nanocomposites has a significant effect on the thermal degradation pathways.     

Absorption Spectra of 4‐Nitrophenolate Ions Measured in Vacuo and in Solution

From blue to red: While four π‐conjugated nitrophenolates absorb within a relatively narrow region in solution, they cover the entire visible spectrum when isolated in vacuo (see picture). The work combines gas‐ and solution‐phase spectroscopy and provides the first benchmark of theoretical excitation energies for nitrophenolates.

     

Study of the factors that control the ratio of the products between 5-fluorouracil, uracil, and tetrahydrobenzoxazepine O,O-acetals bearing electron-withdrawing groups on the nitrogen atom

(RS)-1-(2-Nitrobenzenesulfonyl)- and (RS)-1-(4-nitrobenzenesulfonyl)-3-methoxy-1,2,3,5-tetrahydro-4,1-benzoxazepines are better substrates than 1-acyl-3-methoxy-1,2,3,5-tetrahydro-4,1-benzoxazepine derivatives for the Lewis acid mediated condensation reaction with pyrimidine bases to give O,N-acetals. Acetonitrile, stannic chloride, 50 degrees C, and a reaction time higher than 48 h are the optimum conditions for such condensation reactions. Under these conditions, 5-fluorouracil preferably links to the aminalic carbon through its N-1" position, while the attachment of the uracil fragment is through N-3" or N-1" of the cyclic or acyclic products, respectively. The causes that influence the course of the reactions are analyzed and discussed. Examination of the (1)H NMR spectra revealed the presence of a single form for the secondary amine 11 and of two conformers for the tertiary sulfonamides 7a,b, 9a,b, and 10b and for the amides 7d and 13, with the following distribution: 7a, 59/41; 7b, 53/47; 9a, 52/48; 9b, 59/41; 10b, 56/44; 7d, 50/50; 13, 80/20. On increasing the temperature, the (1)H NMR spectrum (DMSO-d(6)) of 7b showed coalescence at 110 degrees C. The torsional barrier determined [DeltaG(c)++ value of 19.0 +/- 0.2 kcal.mol(-1) (79.1 +/- 1.0 kJ.mol(-1))] proved to be the highest ever observed for sulfonamide moieties.     

Diffraction aperture non-ideal behaviour of air coupled transducers array elements designed for NDT

Air coupled piezoelectric ultrasonic array transducers are a novel tool that could lead to interesting advances in the area of non-contact laminar material testing using Lamb wave's propagation techniques. A key issue on the development of such transducers is their efficient coupling to air media (impedance mismatch between the piezoelectric material and air is 90 dB or more). Adaptation layers are used in order to attain good matching and avoid possible serious signal degradation. However, the introduction of these matching layers modify the transducer surface behaviour and, consequently, radiation characteristics are altered, making the usual idealization criteria (of uniform surface movement) adopted for field simulation purposes inaccurate. In our system, we have a concave linear-array transducer of 64 elements (electrically coupled by pairs) working at 0.8 MHz made of PZ27 rectangular piezoceramics (15 mm x 0.3 mm) with two matching layers made of polyurethane and porous cellulose bonded on them. Experimental measurements of the acoustic aperture of single excited array elements have shown an increment on the geometrical dimensions of its active surface. A sub-millimeter vibrometer laser scan has revealed an extension of the aperture beyond the supposed physical single array element dimensions. Non-uniform symmetric apodized velocity surface vibration amplitude profile with a concave delay contour indicates the presumed existence of travelling wave phenomena over the surface of the outer array matching layer. Also, asymptotic propagation velocities around 2500 m/s and attenuation coefficient between 15 and 20 dB/mm has been determined for the travelling waves showing clear tendencies. Further comparisons between the experimental measurements of single array element field radiation diagram and simulated equivalent aperture counterpart reveal good agreement versus the ideal (uniform displaced) rectangular aperture. For this purpose an Impulse Response Method (IRM) has been used.     

Optimum spin-state selection for all multiplicities in the acquisition dimension of the HSQC experiment

Most conventional heteronuclear spin-state-selective (S(3)) NMR experiments only work for a specific multiplicity, typically IS spin systems. Here, we introduce a general and efficient IPAP strategy to achieve S(3) editing simultaneously for all multiplicities in the acquisition dimension of the HSQC experiment. Complementary in-phase (HSQC-IP) and anti-phase (HSQC-AP) data are separately recorded with a simple phase exchange of two 90 degrees proton pulses involved in the mixing process of the F2-coupled sensitivity-improved HSQC pulse sequence. Additive and subtractive linear combination of these IP/AP data generates simplified F2-alpha/beta-spin-edited HSQC subspectra for all IS, I(2)S, and I(3)S spin systems and combines enhanced and optimized sensitivity with excellent tolerance to unwanted cross-talk contributions over a considerable range of coupling constants. Practical aspects such as pulse phase settings, transfer efficiency dependence, inter-pulse delay optimization, and percentage of cross-talk are theoretically analyzed and discussed as a function of each I(n)S multiplicity. Particular emphasis on the features associated to spin-editing in diastereotopic I(2)S spin systems and application to the measurement of long-range proton-carbon coupling constants are also provided.     

Prosocial norms and degree heterogeneity in social networks

We provide empirical evidence to support the claims that social diversity promotes prosocial behavior. We elicit a real-life social network and its members’ adherence to a social norm, namely inequity aversion. The data reveal a positive relationship between subjects’ prosociality and several measures of centrality. This result is in line with the theoretical literature that relates the evolution of social norms to the structure of social interactions and argues that central individuals are crucial for the emergence of prosocial behavior.     

Ultrasonic velocity and amplitude characterization of magnetorheological fluids under magnetic fields

Variations in velocity of sound and amplitude of the signal of a commercial magnetorheological fluid under different magnetic fields are studied experimentally. Different factors such as orientation, uniformity, geometry and intensity of the magnetic field are investigated. An increase in the change of MR fluid acoustical properties is obtained when the magnetic field intensity is risen. In addition, these properties show an opposite behavior when a magnetic field is applied parallel or perpendicular to the ultrasound propagation. Experiments using an electromagnet and permanent magnets as the source of magnetic field are also compared. Properties such as anisotropy in sound velocity and amplitude make these materials interesting regarding applications.     

Simulation of the ion beam-plasma interaction processes for point-like ions in doped DT plasmas

The purpose of this work is to study the interaction between an ion beam and a doped deuterium-tritium (DT) plasma in a fast ignition nuclear fusion context. In order to analyze the influence of the dopants in the interaction process, we present a physical model to carry out spatial-temporal simulations of the stopping of an ion beam interacting with a doped plasma target, the plasma heating processes, and the formation of the ignition regions. We perform a set of numerical experiments where different concentrations of dopants are added to a fully ionized DT plasma. These simulations allow us to characterize the increase in the stopping power and the maximum temperatures achieved with the presence of impurities, as well as the reduction of the heated and ignition regions. This reduction in the ignition region indicates difficulties for the formation of an efficient hot spot when there are dopants in the DT plasma.     

Team syntegrity and democratic group decision making: theory and practice

Stafford Beer created Team Syntegrity as a methodology for social interaction that predisposes participants towards shared agreement among varied and sometimes conflicting interests, without compromising the legitimate claims and integrity of those interests. This paper outlines the methodology and the underlying philosophy, describing several applications in a variety of countries and contexts, indicating why such an approach causes us to re-think more traditional approaches to group decision processes, and relating Team Syntegrity to other systems approaches.