Nuclear techniques in structural chemistry

The discovery of radioactivity started the nuclear research. The nuclear techniques are very powerful tools in structural chemistry, as well. We would like to support this statement by two examples in this paper. We present a series of Mössbauer measurements which give information about the coordination structure of some dibutyltin (IV) complexes of carbohydrate derivates. The other example will demonstrate how the positron lifetime spectra can reflect the temperature dependence of water structure.     

Correlations between high-momentum secondaries in pp collisions at √s= 44.7 and 62.3 GeV

In pp collisions at √s = 44.7 and 62.3 GeV, where each proton fragments into at least one low-p_{T, high-x} meson or baryon, no correlations between the particle momenta are found for ππ, πK, KK, and pπ pairs. The ππ data show a preference for the formation of electrically neutral ππ systems. The KK data show the influence of strangeness conservation. For pp and pΛ final states, the momentum dependence of the correlation ratio R can be described by the scaling variable z = (1 ? x₁)(1 ? x₂). Small deviations from factorization are discussed.     

Icems and dcems study of Fe layers evaporated onto Al and Si

Thin layers of⁵⁷Fe (2.5 nm, 10 nm and 70 nm thickness), vacuum evaporated onto Al and Si plates, have been investigated by conversion electron Mössbauer spectroscopy (CEMS). The measurements were performed employing both a proportional counter and a channeltron for conventional and ultrahigh-vacuum integral CEMS (UHV-ICEMS) studies, respectively, and a channeltron for depth-selective CEMS (DCEMS). The phase analysis of the layers on base of experimental results has indicated the presence of metallic iron and one or two iron compounds, ascribed to iron reaction products formed with the residual gas during evaporation. These products are most likely rather stable iron nitrides, are more or less clustered and are distributed throughout the whole layer.     

Mössbauer investigation of austenite formation together with Cr depletion in aged turbine blade steels

Mössbauer spectroscopy and hardness measurements were used to study annealing effect on turbine blade steels. Hyperfine field distribution method was applied to follow the changes in the concentration of alloying elements being in the martensite after various heat treatments. Our results imply that upon annealing at a given temperature (400–640°C), formation of austenite takes place (similarly as found earlier [1] in some cases), simultaneously with a significant depletion (up to 4%) of Cr (and other alloying elements) in the martensite.     

Theory of coherence effects in time-dependent delayed fluorescence. II. Application to two- and three-dimensional crystals

A recently developed theory of the effects of transport coherence of triplet excitons on the time dependence of delayed fluorescence in molecular crystals is applied to two- and three-dimensional crystals. Manifestations of anisotropy are studied for arbitrary coherence and it is shown that the mean-square-velocity tensor can be extracted explicitly in the coherent limit.     

The production of high-momentum particles and resonances in pp collisions at the CERN intersecting storage rings

Data are reported on the momentum distributions of Λ, Λ (1520), φ (1020), $\text{Λ}\text{and}\text{p}$, inclusively produced between 1° and 2° with respect to one of the primary proton beams at the CERN Intersecting Storage Rings. In addition, the decay angular distribution of the Λ(1520), the ratio of the cross sections for the production of Σ^? (1385) and Σ⁺ (1385) and the ratios among different charge states of the pairs Λπ, ΛK, Δ⁺⁺ (1232)π and ππ have been measured. These data are confronted with current ideas on fragmentation.     

Mössbauer Investigation of Electrodeposited Sn–Zn,Sn–Cr,Sn–Cr–Zn and Fe–Ni–Cr Coatings

⁵⁷Fe and ¹¹⁹Sn CEMS, XRD and electrochemical measurements were used to investigate the effect of the preparation parameters and the components on the structure and phase composition of electrodeposited Fe-Ni-Cr alloys in connection with their corrosion behavior. XRD of the electrodeposits reflect an amorphous-like character. ⁵⁷Fe CEM spectra of Fe-Ni-Cr electrodeposited samples, prepared in a continuous flow plating plastic circulation cell with variation of current density, electrolyte velocity and temperature, can be evaluated as a doublet associated with a highly disordered paramagnetic solid solution phase. This phase was identified earlier in Fe-Ni-Cr electrodeposits that were prepared by another plating method and contained both ferromagnetic and paramagnetic metastable phases [1]. This is the first time that we have succeeded to prepare Fe-Ni-Cr alloys containing only the metastable paramagnetic phase. The effect of the plating parameters on the structure is also analysed by the quadrupole splitting distribution method. ¹¹⁹Sn CEM spectra of all Sn-containing plated alloys show a broad line envelop which can be decomposed at least into two components. One can be associated with β-tin. The other one can be assigned to an alloy phase. The structure and distribution of microenvironments of these phases depends on the plating parameters especially on the parameters of the reverse pulse applied. This revised version was published online in August 2006 with corrections to the Cover Date.     

Applicability of the BioArena System to Investigation of the Mechanisms of Biological Effects

JPC – Journal of Planar Chromatography – Modern TLC - Bioautography can be extended to a complex system called BioArena by linking different steps to it, for example dissolving a...     

Evidence of a water layer in solid-contact polymeric ion sensors

This paper presents the very first direct structural evidence for the formation of a 100 +/- 10 A water layer in coated-wire polymeric-membrane ion-selective electrodes (ISEs).     

Synthesis, potentiometric, kinetic, and NMR Studies of 1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid)-4,10-bis(methylenephosphonic acid) (DO2A2P) and its complexes with Ca(II), Cu(II), Zn(II) and lanthanide(III) ions

A cyclen-based ligand containing trans-acetate and trans-methylenephosphonate pendant groups, H 6DO2A2P, was synthesized and its protonation constants (12.6, 11.43, 5.95, 6.15, 2.88, and 2.77) were determined by pH-potentiometry and (1)H NMR spectroscopy. The first two protonations were shown to occur at the two macrocyclic ring N-CH 2-PO 3 (2-) nitrogens while the third and fourth protonations occur at the two phosphonate groups. In parallel with protonation of the two -PO 3 (2-) groups, the protons from the NH (+)-CH 2-PO 3 (2-) are transferred to the N-CH 2-COO (-) nitrogens. The stability constants of the Ca (2+), Cu (2+), and Zn (2+) (ML, MHL, MH 2L, and M 2L) complexes were determined by direct pH-potentiometry. Lanthanide(III) ions (Ln (3+)) form similar species, but the formation of complexes is slow; so, "out-of-cell" pH-potentiometry (La (3+), Eu (3+), Gd (3+), Y (3+)) and competitive spectrophotometry with Cu(II) ion (Lu (3+)) were used to determine the stability constants. By comparing the log K ML values with those of the corresponding DOTA (H 4DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and DOTP (H 8DOTP = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethylenephosphonic acid) complexes, the order DOTA < DO2A2P < DOTP was found for all the metal ion complexes examined here with the exception of the Ca (2+) complexes, for which the order is reversed. The relaxivity of Gd(DO2A2P) decreases between pH 2 and 7 but remains constant in the pH range of 7 < pH < 12 ( r 1 = 3.6 mM (-1) s (-1)). The linewiths of the (17)O NMR signals of water in the absence and presence of Gd(DO2A2P) (at pH = 3.45 and 8.5) between 274 and 350 K are practically the same, characteristic of a q = 0 complex. Detailed kinetic studies of the Ce (3+) and Gd (3+) complexes with DO2A2P showed that complex formation is slow and involves a high stability diprotonated intermediate Ln(H 2DO2A2P)*. Rearrangement of the diprotonated intermediate into the final complex is an OH (-) assisted process but, unlike formation of Ln(DOTA) complexes, rearrangement of Ln(H 2DO2A2P)* also takes place spontaneously likely as a result of transfer of one of the protons from a ring nitrogen to a phosphonate group. The order of the OH (-) assisted formation rates of complexes is DOTA > DO2A2P > DOTP while the order of the proton assisted dissociation rates of the Gd (3+) complexes is reversed, DOTP > DO2A2P > DOTA. (1)H and (13)C NMR spectra of Eu(DO2A2P) and Lu(DO2A2P) were assigned using two-dimensional correlation spectroscopy (2D COSY), heteronuclear multiple quantum coherence (HMQC), heteronuclear chemical shift correlation (HETCOR), and exchange spectroscopy (EXSY) NMR methods. Two sets of (1)H NMR signals were observed for Eu(DO2A2P) characteristic of the presence of two coordination isomers in solution, a twisted square antiprism (TSAP) and a square antiprism (SAP), in the ratio of ~93% and ~7%, respectively. Line shape analysis of the (1)H NMR spectra of Lu(DO2A2P) gave lower activation parameters compared to La(DOTP) for interconversion between coordination isomers. This indicates that the Ln(DO2A2P) complexes are less rigid probably due to the different size and spatial requirements of the carboxylate and phosphonate groups.