Gd(III) chelates as NMR probes of protein-protein interactions. Case study: rubredoxin and cytochrome c3

Two cyclen-derived Gd probes, [Gd-DOTAM](3+) and [Gd-DOTP](5-) (DOTAM = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetamide; DOTP = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylenephosphonate)), were assessed as paramagnetic relaxation enhancement (PRE)-inducing probes for characterization of protein-protein interactions. Two proteins, Desulfovibrio gigas rubredoxin and Desulfovibrio gigas cytochrome c(3), were used as model partners. In a (1)H NMR titration it was shown that [Gd-DOTP](5-) binds to cytochrome c(3) near heme IV, causing pronounced PREs, characterized by line width broadenings of the heme methyl resonances at ratios as low as 0.08. A K(d) of 23 ± 1 μM was calculated based on chemical shift perturbation of selected heme methyl resonances belonging to three different heme groups, caused by allosteric effects upon [Gd-DOTP](5-) binding to cytochrome c(3) at a molar ratio of 2. The other probe, [Gd-DOTAM](3+), caused PREs on a well-defined patch near the metal center of rubredoxin (especially the patch constituted by residues D19-G23 and W37-S45, which broaden beyond detection). This effect was partially reversed for some resonances (C6-Y11, in particular) when cytochrome c(3) was added to this system. Both probes were successful in causing reversible PREs at the partner binding site, thus showing to be good probes to identify partners' binding sites and since the interaction is reversible to structurally characterize protein complexes by better defining the complex interface.     

Calorimetric aspects of adsorption of pesticides 2,4-<Emphasis Type="SmallCaps">d</Emphasis>, diuron and atrazine on a magadiite surface

H-magadiite was applied to remove the pesticides 2,4-d, diuron, and atrazine from water. The H-magadiite containing herbicides adsorbed were investigated by FTIR, DRX, N₂ adsorption and desorption isotherms, and surface area. Calorimetric studies were carried out to determine the heat of interaction between pesticides and magadiite. It was possible to ride the cycle of interaction of magadiite–pesticide for a better understanding of the process involved. From the results of the thermal effect of the interaction of magadiite–pesticide, the thermochemical parameters can be determined by using the relationship between the data obtained from adsorption and calorimetry results. The interaction of pesticide–magadiite follows the sequence of adsorption: diuron > atrazine > 2,4-d. The ΔH values for the interactions were determined to be −20.62 ± 1.08, −24.04 ± 0.86–26.34 ± 0.93 kJ mol⁻¹ for 2,4-d, diuron and atrazine, respectively. All the interactions were spontaneous, enthalpically and entropically favored demonstrating the effectiveness and efficiency of the method.     

Numerical study on the two-phase flow distribution in a T-junction

The main objective of this paper is to investigate the ability of a two-dimensional two-fluid computer code to predict the phase separation in a T-junction. A new semi-implicit numerical scheme is developed for solving the two-fluid model equations. Special attention is directed to the modelling of the constitutive for the interfacial friction term. Detailed distribution of void fraction, pressure and velocities are obtained for an air–water mixture in a vertical tee. Good agreement was obtained between the computer code results and the experimental data for the phase separation in the T-junction.     

A thermally stimulated discharge currents study of the molecular motions in two polysiloxane side-chain liquid crystalline polymers

The technique of thermally stimulated depolarization currents was used to study the dipolar relaxation mechanisms in two side-chain liquid-crystalline polysiloxanes. The studied polymers have the same mesogenic side-group, but they differ in the number (or density) of side groups attached to the main chain. In both cases three different relaxations were observed: one in the vitreous state, one in the liquid crystalline phase, and the glass transition relaxation. The features of those thermally stimulated discharges are discussed and some suggestions are made concerning the attribution of those discharges at the molecular level. © 1995 John Wiley & Sons, Inc.     

The mechanism of solvolysis of methyl perchlorate in hydroxylic solvents: calculation of the cavity terms

From standard Gibbs energies of transfer, corrected for cavity or nonelectrostatic effects, it is concluded that the solvolysis of methyl perchlorate takes place through a looser-than-usual S_N2 transition state with a charge separation of about 0.52 units.     

Cytogenetic analysis of two related Deltochilum (Coleoptera,Scarabaeidae) species: Diploid number reduction,extensive heterochromatin addition and differentiation

Male mitotic and meiotic chromosomes of two species of the genus Deltochilum (Scarabaeidae) were analyzed through conventional staining, C-banding, base-specific fluorochromes, silver nitrate staining (AgNO₃) and FISH (45S rDNA). The two species possessed karyotypes with 2n = 14, neo-XY and meta-submetacentric chromosomes. The analysis of constitutive heterochromatin (CH) revealed mainly diphasic chromosomes in the two species, showing heterochromatic long arms. Silver nitrate staining labeled the blocks corresponding to CH in D. (Deltohyboma) aff morbillosum while in D. (Deltohyboma) calcaratum, AgNO₃ staining revealed only the CH blocks of the diphasic autosomes. The fluorochrome staining revealed in D. (D.) calcaratum the diphasic autosomes and the sex chromosomes with CMA₃⁺ blocks, and in D. (D.) aff morbillosum, the GC-rich sequences were restricted to the terminal regions of the long arms of the pairs 1 and 2 and the X. The FISH revealed 45S rDNA sites in two autosomic pairs and in the X chromosome. The analyses performed allowed for the identification of cytogenetic markers and the discussion of possible chromosome rearrangements that have been involved in the karyotypic differentiation of these species mainly related to the repetitive genome.     

Fourth-order image formation by spontaneous parametric down-conversion: The effect of anisotropy

We analyze the transfer of angular spectrum and fourth-order image formation in two-photon states generated by spontaneous parametric down-conversion in both type I and type II phase matchings. We show how the image transfer from the pump beam to the two-photon field is affected by the anisotropy of the nonlinear crystal and by the coupling between frequency and wave vector. We also show how the distortion produced by the anisotropy can be compensated by the frequency bandwidth in type II phase matching.     

Dielectric study of the slow motional processes in the polymorphic States of anhydrous caffeine

Molecular mobility in crystalline anhydrous caffeine was studied by the dielectric technique of thermally stimulated depolarization currents (TSDC). Two relaxational processes were found, one appearing at approximately -10 degrees C that is ascribed to a reorientational glass transition, and a higher temperature one that probably arises from local molecular motions that are precursors of diffusion and sublimation. The experimental results suggest that both crystalline phases II and I of caffeine, that have distinct crystal structures, are solid rotator phases. Furthermore, this dynamic reorientational disorder shows a reorientational glass transition at the same temperature in phase II and in metastable phase I.     

Quantum communication through chains with diluted disorder

We investigate a single-qubit state transfer protocol along a channel featuring diagonal diluted disorder. In the regime where the source and destination sites are weakly coupled to the channel, we report the possibility of transmitting quantum states with high fidelity as well as establishing end-to-end entanglement in that sort of configuration. We further discuss how the performance of the protocol depends upon the availability of extended states within the disordered channel.     

Adsorption equilibria of CO<Subscript>2</Subscript> and CH<Subscript>4</Subscript> in cation-exchanged zeolites 13X

Ion-exchange with different cations (Na⁺, NH₄ ⁺, Li⁺, Ba²⁺ and Fe³⁺) was performed in binderless 13X zeolite pellets. Original and cation-exchanged samples were characterized by thermogravimetric analysis coupled with mass spectrometry (inert atmosphere), X-ray powder diffraction and N₂ adsorption/desorption isotherms at 77 K. Despite the presence of other cations than Na (as revealed in TG-MS), crystalline structure and textural properties were not significantly altered upon ion-exchange. Single component equilibrium adsorption isotherms of carbon dioxide (CO₂) and methane (CH₄) were measured for all samples up to 10 bar at 298 and 348 K using a magnetic suspension balance. All of these isotherms are type Ia and maximum adsorption capacities decrease in the order Li > Na > NH₄–Ba > Fe for CO₂ and NH₄–Na > Li > Ba for CH₄. In addition to that, equilibrium adsorption data were measured for CO₂/CH₄ mixtures for representative compositions of biogas (50 % each gas, in vol.) and natural gas (30 %/70 %, in vol.) in order to assess CO₂ selectivity in such scenarios. The application of the Extended Sips Model for samples BaX and NaX led to an overall better agreement with experimental data of binary gas adsorption as compared to the Extended Langmuir Model. Fresh sample LiX show promise to be a better adsorption than NaX for pressure swing separation (CO₂/CH₄), due to its higher working capacity, selectivity and lower adsorption enthalpy. Nevertheless, cation stability for both this samples and NH₄X should be further investigated.