Probe efficiency improvement with remote and transmission line tuning and matching.

In certain nuclear magnetic resonance (NMR) applications in which accessibility to the gantry is limited, performing optimal tuning and matching represents a major problem. Here, we discuss a method of tuning NMR probe circuits and matching their impedances which uses cables with different impedance values. This simple but efficient method may be advantageous compared with much more difficult perfect tuning and matching.     

Propylene polymerization in liquid monomer with a Ziegler-Natta catalyst in bench scale reactors. Kinetics and model to predict reaction yields

The study of new catalytic systems is critical in order to develop improved and cost effective polymerization processes. One of the methods to evaluate the performance of a catalytic system is by means of bench scale reactors. Despite its difference in size with large scale industrial plants, bench scale reactors have proved to be a valuable tool to understand the behavior of the catalytic system during the polymerization. In this work, a method to estimate the kinetic parameters of propylene polymerization over a conventional Ziegler Natta catalyst is evaluated. Thus, it was possible to set up a semi-empirical model to correlate the reaction yield with the polymerization time, the hydrogen content in the reactor and the reaction temperature. This model proves to be useful to evaluate the performance of a catalytic system within the range of normal operating conditions. A brief study on the particle size distribution of the products is also carried out.     

Total solid-phase synthesis of the azathiocoraline class of symmetric bicyclic peptides

Thiocoraline is a potent antitumor agent isolated from the marine organism Micromonospora sp. This symmetric bicyclic depsipeptide binds the minor groove of DNA. Here we report two solid-phase strategies for the syntheses of azathiocoraline and its analogues. The thioester linkage was replaced by an amide bond to improve the compound's pharmacokinetic properties. The first strategy is based on a convergent (4+4) approach, whilst the second is a stepwise synthesis, cyclizations in both approaches occurring on the solid support. These two strategies were designed to overcome problems caused by the presence of consecutive noncommercial N-methyl amino acids, to avoid epimerization during cyclization and/or fragment condensation, and to form the disulfide bridge under solid-phase conditions. The heterocyclic moiety was added in the last step of the synthesis to assist the preparation of libraries of new compounds with potential therapeutic applications.     

Analysis of recombinant human erythropoietin glycopeptides by capillary electrophoresis electrospray–time of flight-mass spectrometry

Capillary electrophoresis electrospray–mass spectrometry was used to detect and characterize the great variety of O- and N-glycopeptide glycoforms of recombinant human erythropoietin (rhEPO) using an orthogonal accelerating time-of-flight mass spectrometer to obtain their exact molecular masses (CE–TOF-MS). rhEPO was digested with trypsin and Glu-C and analyzed by CE–TOF-MS to detect O₁₂₆, N₈₃, N₂₄–N₃₈ and N₂₄ and N₃₈ glycopeptide glycoforms, respectively. Neuraminidase was first used to enhance the detection of the glycopeptides and detect all possible glycoforms contained in each glycosylation site. O₁₂₆ and N₈₃ glycopeptides were extensively characterized. Twelve sialoforms corresponding to 5 different glycoforms were detected in N₈₃, and for the first time, a sulfated sialoform of this glycopeptide was also detected. In the case of O₁₂₆, different sialoforms with different types of sialic acids (Neu5Gc and Neu5Ac) were detected and an estimation of the relative percentage of Neu5Gc versus Neu5Ac was also carried out for this glycopeptide. N₂₄ and N₃₈ glycosylation sites were also characterized by CE–TOF-MS after Glu-C digestion and these results permitted to rule out some glycan combinations for N₂₄–N₃₈ glycopeptide glycoforms. This study provided a reliable glycopeptide map of rhEPO and may be regarded as an excellent starting point to analyze rhEPO glycopeptides in biological fluids and detect the use of this hormone in sports.     

The Shape of the Simplest Non-proteinogenic Amino Acid α-Aminoisobutyric Acid (Aib)

The simplest non-proteinogenic amino acid α-aminoisobutyric acid (Aib), an analogue of glycine and alanine, has been vaporized by laser ablation and probed by high-resolution Fourier transform microwave spectroscopic techniques. Comparison of the experimental rotational and ¹⁴N nuclear quadrupole constants with that predicted ab initio has allowed the identification of three conformers of Aib exhibiting three types of hydrogen-bond interactions I (NH⋅⋅⋅O=C, cis-COOH), II (OH⋅⋅⋅N, trans-COOH), and III (N−H⋅⋅⋅O−H, cis-COOH) within the amino acid backbone. The observation of conformer III, not detected previously for related proteinogenic amino acids with a nonpolar side chain in a supersonic expansion, indicates that the presence of the methyl groups should restrict the conformational relaxation from conformer Aib-III to Aib-I. For conformer Aib-II, the rotational spectra of the ¹³C isotopomers reveal a tunneling motion arising from the two equivalent methyl groups in the molecule. The observation of a single spectrum at the midpoint between those predicted for the two ¹³C of the methyl groups has been explained by considering a double-minimum potential function with a low-energy interconversion barrier for a large amplitude internal motion. This singular fact has been corroborated by the anomalous centrifugal distortion effects determined in conformer Aib-II.     

Non-emissive RuII Polypyridyl Complexes as Efficient and Selective Photosensitizers for the Photooxidation of Benzylamines

Five new Ru^II polypyridyl complexes bearing N-(arylsulfonyl)-8-amidoquinolate ligands and three of their biscyclometalated Ir^III congeners have been prepared and employed as photocatalysts ( PC s) in the photooxidation of benzylamines with O₂. In particular, the new Ru^II complexes do not exhibit photoluminescence, rather they harvest visible light efficiently and are very stable in solution under irradiation with blue light. Their non-emissive behavior has been related to the low electrochemical energy gaps and rationalized on the basis of theoretical calculations (DFT analysis) that predict low S₀←T₁ energy values. Moreover, the Ru^II complexes, despite being non-emissive, display excellent activities in the selective photocatalytic transformation of benzylamines into the corresponding imines. The presence of an electron-withdrawing group (-CF3) on the arene ring of the N-(arylsulfonyl)-8-amidoquinolate ligand improves the photocatalytic activity of the corresponding photocatalyst. Furthermore, all the experimental evidence, including transient absorption spectroscopy measurements suggest that singlet oxygen is the actual oxidant. The Ir^III analogues are considerably more photosensitive and consequently less efficient photosensitizers ( PS s).     

New (k; r)-arcs in the projective plane of order thirteen

A (k;r)-arc $\cal K$ is a set of k points of a projective plane PG(2, q) such that some r, but no r +1 of them, are collinear. The maximum size of a (k; r)-arc in PG(2, q) is denoted by m _r (2, q). In this paper a (35; 4)-arc, seven (48; 5)-arcs, a (63; 6)-arc and two (117; 10)-arcs in PG(2, 13) are given. Some were found by means of computer search, whereas the example of a (63; 6)-arc was found by adding points to those of a sextic curve $\cal C$ that was not complete as a (54; 6)-arc. All these arcs are new and improve the lower bounds for m _r (2, 13) given in [10, Table 5.4]. The last section concerns the nonexistence of (40; 4)-arcs in PG(2, 13).     

The adsorption of hydrogen on face centered tetragonal FePd surfaces

Adsorption of hydrogen on the ordered FePd face centered tetragonal alloy is investigated using a tight binding theoretical method. The changes in the electronic structure and bonding in the (100), (110) and (111) surfaces are analyzed. A simplified model for H diffusion to the bulk is also developed. The H-surface bond is achieved at the expense of the metal-metal bond being the Pd-Pd the more affected in the (100) and (110) cases.     

A new kinetic photometric method for the simultaneous determination of metals based on catalytic and activating effects

Summary The potential use of the activating effect of Pb(II) on the Mn(II)-catalysed oxidation of Tiron by hydrogen peroxide in the presence of 1,10-phenanthroline for the simultaneous determination of the two metals was investigated. The results obtained allowed the development of a new kinetic photometric method for the simultaneous determination of Pb(II) and Mn(II). The catalysed reaction was monitored by the initial rate method, which was applied to absorbance-time curves. Different Mn(II) concentrations were used to construct calibration graphs by plotting the slopes of the photometric curves obtained against the Mn(II) concentration at each Pb(II) concentration assayed. A new calibration graph was obtained in terms of the Pb(II) concentration from the slopes of such graphs. By applying the standard-addition method to the sample to be assayed a third graph was obtained, the slope and intercept of which provided the analytical concentration of Pb(II) and Mn(II), respectively. The optimized values of the different variables involved were used to determine Mn(II) and Pb(II) over the concentration ranges 1–5 and 200–800 ng/ml, respectively.