Overview: recent progress in three-dimensional atom probe instruments and applications.

Over the last few years there have been significant developments in the field of three-dimensional atom probe (3DAP) analysis. This article reviews some of the technical compromises that have led to different instrument designs and the recent improvements in performance. An instrument has now been developed, based around a novel reflectron configuration combining both energy compensation and focusing elements, that yields a large field of view and very high mass resolution. The use of laser pulsing in the 3DAP, together with developments in specimen preparation methods using a focused ion-beam instrument, have led to a significant widening in the range of materials science problems that can be addressed with the 3DAP. Recent studies of semiconductor materials and devices are described.     

Identifying acetylated lignin units in non-wood fibers using pyrolysis-gas chromatography/mass spectrometry

A series of non-wood plant fibers, namely kenaf, jute, sisal and abaca, have been analyzed upon pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) of the whole material. The pyrolysis products mainly arise from the carbohydrate and lignin moieties of the fibers. The lignin-derived phenols belonged to the p-hydroxyphenylpropanoid (H), guaiacylpropanoid (G) and syringylpropanoid (S) structures, and showed a high S/G ratio of between 2.0 and 5.4, the highest corresponding to kenaf. Among the lignin-derived phenols released, small amounts of sinapyl and coniferyl acetates (in both cis- and trans-forms) were identified for the first time upon Py-GC/MS of lignocellulosic materials. Acetylation of the sinapyl and coniferyl alcohols was at the gamma-position of the side chain. The release of these alcohols derived from intact acetylated lignin units upon pyrolysis seems to indicate that the native lignin in the fibers selected for this study is at least partially acetylated. Sinapyl (and coniferyl) acetates have recently been suggested to be authentic lignin precursors involved in the polymerization of lignin along with the normal sinapyl and coniferyl alcohols. Py-GC/MS will offer a convenient and rapid tool for analyzing naturally acetylated lignins, as well as to screen plant materials for the presence of acetylated units in lignin.     

A study of substituent effect on 1H and 13C nmr spectra of N‐ and C‐substituted carbazoles

¹H and ¹³C nmr spectra of several N‐ and C‐substituted carbazoles (Series 1, 2, 3 and 4) were measured. Correlations between chemical shifts and substituent constants show that these parameters describe properly the substituent effect on the nmr phenomena. Atomic charge densities for carbazoles of Series 1, 2, 3 and 4 were calculated by using the semi empirical PM3 method. These values also show a linear correlation with the ¹³C chemical shifts. The synthesis of several carbazole derivatives 1a – 1g, 2a – 2g, 3a – 3j and 4a – 4g have been carried out according to literature procedures. The carbazoles 3i, 3j and 4c have been synthesized and fully characterized for the first time.     

Assigning the C-15 configuration of 15-hydroxy-, 15-methoxy-, 15-ethoxy-hexahydrofurofuran neoclerodane diterpenoids

Examination of ¹H and ¹³C NMR spectra allows the establishment of rules for assigning the correct configuration at C-15 of 15-hydroxy-, 15-methoxy-, 15-ethoxy-hexahydrofurofuran neoclerodane diterpenoids. The structure of several diterpenoids has been assigned or ammended.     

Structure-Reactivity Correlations in the Dissociative Hydrolysis of 2',4'-Dinitrophenyl 4-Hydroxy-X-benzenesulfonates

The hydrolysis reactions of several title esters in water at 60 degrees C follow the rate law k(obs) = (k(a) + k(b)[OH(-)])/(1 + a(H)/K(a)), where K(a) is the ionization constant of the hydroxy group of the ester and k(b) is the second-order rate constant for the S(N)2(S) attack of hydroxide ion on the ionized ester. Hammett and Br?nsted correlations are consistent with a previous proposal that the mechanism related to k(a) is dissociative. An unusual relationship between k(a) values and redox equilibrium constants for substituted quinones is found to hold: this finding further supports the dissociative nature of the pathway related to k(a).     

Evaluation of new pregnane derivatives as 5alpha-reductase inhibitor

The objective of this study was to synthesize several new pregnane derivatives and evaluate them as antiandrogens. From the commercially available 16-dehydropregnenolone acetate (7), two new steroidal compounds were synthesized: 17alpha-hydroxy-17beta-methyl-16beta-phenyl-D-homoandrosta-1,4,6-triene-3,20-dione (18) and 17alpha-acetoxy-17beta-methyl-16beta-phenyl-D-homoandrosta-1,4,6-triene-3,20-dione (19). The 5alpha-reductase inhibitory effect of the new compounds 18 and 19 together with the previously synthesized intermediates 7, 8, 13, 16, and 17 was determined in three different models: gonadectomized hamster flank organs diameter size, incorporation of [1,2-(14)C]sodium acetate into lipids in flank organs and conversion of [3H]testosterone (T) to [3H]dihydrotestosterone (DHT) by Penicillium crustosum. The evaluation of these steroids was carried out with three different controls: one group was treated with vehicle, the second with T and the third group with T plus finasteride. The pharmacological results from this work demonstrated that T significantly increases the diameter of the pigmented spot on the flank organs (p<0.05) as well as the incorporation of labeled sodium acetate into lipids in gonadectomized hamster flank organs (from 0.125 to 0.255 nmol per gland). In this study we also observed that broth of Penicillium crustosum converted [3H]T to [3H]DHT in a manner comparable to that of the flank organs. All experiments indicated that finasteride as well as steroids 7, 8, 13, 16-19 reduced significantly the conversion of T to DHT in P. crustosum. These compounds also decrease the size of the pigmented spot in the flank organs as well as reducing the incorporation of radiolabeled sodium acetate into lipids; T and the control sample (treated with vehicle only) were used for comparison. Apparently the presence of the 4,6-diene-3,20-dione moiety and also the C-17 ester group produce a higher inhibitory effect on the parameters used. PPThe data from this study indicated also that the three models used for the pharmacological evaluation exhibited comparable results.     

Ethylenediamine effect on Co2+ uptake by zeolite Y

Co²⁺ ion exchange, at room temperature, from aqueous cobalt — sodium chloride solutions with NaY zeolite has been studied. The effect of contact time on the shape of the sorption curves of Co²⁺ using zeolite Y dehydrated at 600°C is similar to the one found in our previous work with a zeolite dehydrated at 150 °C. A fast sorption uptake is observed in which 1.8 meq of Na⁺ ions/g of zeolite are replaced by cobalt ions followed by a desorption process where the uptake decreases to 1.2 meq/g zeolite. The Co²⁺ sorption using zeolite Y dehydrated at 600 °C is increased when ethylenediamine solution is passed through the zeolite. The Co²⁺ sorption uptake, initially 2.0 meq/g, incrases to 2.8 meq/g of zeolite. This behavior is explained by the location and coordination of cobalt in zeolite Y sites. It is suggested that the highest uptake process is due to the blocking of zeolite sites by a Co complex compound.     

From nitrides to carbides: topotactic synthesis of the eta-carbides Fe3Mo3C and Co3Mo3C

The molybdenum bimetallic interstitial carbides Fe(3)Mo(3)C and Co(3)Mo(3)C have been synthesized by temperature-programmed reaction (TPR) between the molybdenum bimetallic interstitial nitrides Fe(3)Mo(3)N and Co(3)Mo(3)N and a flowing mixture of CH(4) and H(2) diluted in Ar. These compounds have been characterized by X-ray diffraction, laser Raman spectroscopy, elemental analysis, energy dispersive analysis of X rays, thermal analysis (in air) and scanning electron microscopy (field emission). Their structures have been refined from X-ray powder diffraction data. These carbides crystallize in the cubic system, space group Fd3m[a= 11.11376(6) and 11.0697(3)[Angstrom] for Fe and Co compounds, respectively].     

A fluorimetric study of pindolol and its complexes with cyclodextrins

Spectrofluorimetric characteristics of pindolol have been investigated with the aim of using this technique for analytical determinations. Other monosubstituted indole derivatives, 4-methoxy and 5-methoxyindole, have been also studied for comparative purposes. Corrected excitation and emission wavelengths in different solvents are reported and the effect of solvent on the Stokes shifts of these compounds has been analysed using the Lippert equation. In addition, the Stokes shift of pindolol has been determined in dioxan-water solvent mixtures and the presence of specific solvent effects is discussed. The fluorescence of pindolol is pH dependent, the quantum yields determined in water are lower than those in other solvents. With respect to the sensitivity, it has been found that the detection limits in aqueous solutions are improved in the presence of beta and methyl-beta-cyclodextrin. Finally, a fluorimetric analysis of the interaction between pindolol and different cyclodextrins has been carried out in order to determine the apparent stability constants of the complexes and the thermodynamic parameters associated to complexation.     

Photophysical properties of neutral and cationic tetrapyridinoporphyrazines

We describe the synthesis and photophysical properties of a series of neutral and cationic 3,4-tetrapyridinoporphyrazines, potential lead photosensitizers for photodynamic inactivation of bacteria. Tetracationic TPyPzs exist essentially as monomers in aqueous systems, but the presence of trialkylated compounds due to incomplete quaternization of the outer nitrogen atoms induces severe aggregation. The absorption, fluorescence, triplet, and singlet oxygen quantum yields for both the neutral and cationic compounds are comparable to those of the related phthalocyanines.