An Apparent Interface Location as a Tool to Solve the Porous Interface Flow Problem

A new approach for solving the laminar flow problem above a porous medium is presented here, using an apparent interface for which both superficial velocity and intrinsic shear stress are continuous. The derivation of this approach is based on a detailed investigation of the Ochoa-Tapia and Whitaker (Int. J. Heat Mass Transfer 38:2635–2646, 1995a) jump condition and its sensitivity to the value of β (the jump condition coefficient) and to an error in the interface location. While the value of the jump condition coefficient is highly sensitive to the interface location, the new apparent interface approach does not require an a priori information about the location of the interface. This approach can be easily used knowing only one measurable parameter—the maximum velocity or the flow rate. Validation of the apparent interface approach against measurements from other works shows that it can be successfully used to predict the velocity profile for different geometrical models.     

Gallium(III) complexes of DOTA and DOTA-monoamide: kinetic and thermodynamic studies

Given the practical advantages of the (68)Ga isotope in positron emission tomography applications, gallium complexes are gaining increasing importance in biomedical imaging. However, the strong tendency of Ga(3+) to hydrolyze and the slow formation and very high stability of macrocyclic complexes altogether render Ga(3+) coordination chemistry difficult and explain why stability and kinetic data on Ga(3+) complexes are rather scarce. Here we report solution and solid-state studies of Ga(3+) complexes formed with the macrocyclic ligand 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, (DOTA)(4-), and its mono(n-butylamide) derivative, (DO3AM(Bu))(3-). Thermodynamic stability constants, log K(GaDOTA) = 26.05 and log K(GaDO3AM(Bu)) = 24.64, were determined by out-of-cell pH-potentiometric titrations. Due to the very slow formation and dissociation of the complexes, equilibration times of up to ～4 weeks were necessary. The kinetics of complex dissociation were followed by (71)Ga NMR under both acidic and alkaline conditions. The GaDOTA complex is significantly more inert (τ(1/2) ～12.2 d at pH = 0 and τ(1/2) ～6.2 h at pH = 10) than the GaDO3AM(Bu) analogue (τ(1/2) ～2.7 d at pH = 0 and τ(1/2) ～0.7 h at pH = 10). Nevertheless, the kinetic inertness of both chelates is extremely high and approves the application of Ga(3+) complexes of such DOTA-like ligands in molecular imaging. The solid-state structure of the GaDOTA complex, crystallized from a strongly acidic solution (pH < 1), evidenced a diprotonated form with protons localized on the free carboxylate pendants.     

A physicochemical model for analyzing DNA sequences

In search of an ab initio model to characterize DNA sequences as genes and nongenes, we examined some physicochemical properties of each trinucleotide (codon), which could accomplish this task. We constructed three-dimensional vectors for each double-helical trinucleotide sequence considering hydrogen-bonding energy, stacking energy, and a third parameter, which we provisionally identified with DNA-protein interactions. As this three-dimensional vector moves along any genome, the net orientation of the resultant vector should differ significantly for gene and nongene regions to make a distinction feasible, if the underlying model has some merits. An analysis of 331 prokaryotic genomes comprising a total of 294 786 experimentally verified genes (nonoverlapping) and an equal number of nongenes presents a proof of concept of the model without the need for further parametrization. Also, initial analyses on Saccharomyces cerevisiae and Arabidopsis thaliana suggest that the methodology is extendable to eukaryotes. The physicochemical model (ChemGenome1.0) introduced has the potential to be developed into a gene-finding algorithm and, more pressingly, could be employed for an independent assessment of the annotation of DNA sequences.     

High density preheating effects on Q-ball decays and inflation in the minimal supersymmetric standard model

Nonperturbative preheating decay of postinflationary condensates often results in a high density, low momenta, nonthermal gas. In the case where the nonperturbative classical evolution also leads to Q balls, this effect shields them from instant dissociation, and may radically change the thermal history of the Universe. For example, in a large class of inflationary scenarios, motivated by the minimal supersymmetric standard model and its embedding in string theory, the reheat temperature changes by a multiplicative factor of 10(12).     

A Triazacyclononane‐Based Bifunctional Phosphinate Ligand for the Preparation of Multimeric 68Ga Tracers for Positron Emission Tomography

For application in positron emission tomography (PET), PrP9 , a N,N′,N′′‐trisubstituted triazacyclononane with methyl(2‐carboxyethyl)phosphinic acid pendant arms, was developed as ⁶⁸Ga³⁺ complexing agent. The synthesis is short and inexpensive. Ga^III and Fe^III complexes of PrP9 were characterized by single‐crystal X‐ray diffraction. Stepwise protonation constants and thermodynamic stabilities of metal complexes were determined by potentiometry. The Ga^III complex possesses a high thermodynamic stability (log K_[GaL]=26.24) and a high degree of kinetic inertness. ⁶⁸Ga labeling of PrP9 is possible at ambient temperature and in a wide pH range, also at pH values as low as 1. This means that for the first time, the neat eluate of a TiO₂‐based ⁶⁸Ge/⁶⁸Ga generator (typically consisting of 0.1 M HCl) can be directly used for labeling purposes. The rate of ⁶⁸Ga activity incorporation at pH 3.3 and 20 °C is higher than for the established chelators DOTA and NOTA. Tris‐amides of PrP9 with amino acid esters were synthesized to act as models for multimeric peptide conjugates. These conjugates exhibit radiolabeling properties similar to those of unsubstituted PrP9 .     

Crystal structures of lanthanide(III) complexes with cyclen derivative bearing three acetate and one methylphosphonate pendants

A series of lanthanide(III) complexes formulated as M[Ln(Hdo3ap)].xH(2)O (M = Li or H and Ln = Tb, Dy, Er, Lu, and Y) with the monophosphonate analogue of H(4)dota, 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic-10-methylphosphonic acid (H(5)do3ap), was prepared in the solid state and studied using X-ray crystallography. All of the structures show that the (Hdo3ap)(4-) anion is octadentate coordinated to a lanthanide(III) ion similarly to the other H(4)dota-like ligands, i.e., forming O(4) and N(4) planes that are parallel and have mutual angle smaller than 3 degrees . The lanthanide(III) ions lie between these planes, closer to the O(4) base than to the N(4) plane. All of the structures present the lanthanide(III) complexes in their twisted-square-antiprismatic (TSA) configuration. Twist angles of the pendants vary in the range between -24 and -30 degrees, and for each complex, they lie in a very narrow region of 1 degree. The coordinated phosphonate oxygen is located slightly above (0.02-0.19 Angstroms) the O(3) plane formed with the coordinated acetates. A water molecule was found to be coordinated only in the terbium(III) and neodymium(III) complexes. The bond distance Tb-O(w) is unusually long (2.678 Angstroms). The O-Ln-O angles decrease from 140 degrees [Nd(III)] to 121 degrees [Lu(III)], thus confirming the increasing steric crowding around the water binding site. A comparison of a number of structures of Ln(III) complexes with DOTA-like ligands shows that the TSA arrangement is flexible. On the other hand, the SA arrangement is rigid, and the derived structural parameters are almost identical for different ligands and lanthanide(III) ions.     

Mass spectrometry in structural and stereochemical problems—CCXXXV : A hidden hydrogen rearrangement in long chained anilides

The mass spectra of deuterium labeled hexananilides show an unexpected rearrangement of a hydrogen atom from C-4 with formation of a C₆H₇N⁺ ion. The decomposition of the McLafferty rearrangement ion in these compounds is shown to involve expulsion of the elements of ethynyl alcohol rather than ketene.     

Capillary electrophoresis—matrix-assisted laser-desorption ionization mass spectrometry of proteins

An “off-line” combination of capillary electrophoresis (CE) with matrix-assisted laser-desorption mass spectrometry (MALDI-MS) has been developed for the structural characterization of CE-separated peptides and proteins. Using a sheath flow interface, similar to that developed for “on-line” CE—fast atom bombardment MS and CE—electrospray MS, an efficient sample isolation procedure has been developed which is applicable to bioorganic compounds in aqueous buffer solutions. This isolation procedure, with subsequent transfer to the MALDI-MS sample target, has been successfully used for the direct analysis of CE-separated proteins of M _r up to 67 000, and a mixture of apolipoprotein AII monomer and homodimer, using sample amounts of less than 1 pmol.     

Cyclam (1,4,8,11-tetraazacyclotetradecane) with one methylphosphonate pendant arm: a new ligand for selective copper(ii) binding

The new ligand, [(1,4,8,11-tetraazacyclotetradecan-1-yl)methyl]phosphonic acid (H(2)te1P, H(2)L), was synthesized and its complexing properties towards selected metal ions were studied potentiometrically. The ligand forms a very stable complex with copper(ii)(logbeta(CuL)= 27.34), with a high selectivity over binding of other metal ions (i.e. logbeta(ZnL)= 21.03). The crystal structures of the free ligand (in its protonated form with bromide as counter-ion) and two copper(ii) complexes (obtained by crystallization at various pH) were determined. The free ligand adopts the common conformation for such macrocycles with the protonated nitrogen atoms in the corners of a virtual rectangle. In the trans-Br,O-[Cu(Br)(Hte1P)].H(2)O species, the central metal ion is surrounded by four in plane nitrogen atoms, one oxygen atom of the pendant moiety in the apical position and a bromide anion positioned trans to the oxygen atom, forming a distorted octahedral coordination sphere. In the compound [Cu(H(2)te1P)][Cu(Hte1P)]Br(3).6H(2)O, obtained from a highly acidic solution, the bromide anions are placed further away from the copper(ii) ion and the coordination environment (N(4)O) is thus square-pyramidal. In both structures, the protons are associated with non-coordinated phosphonate oxygen atoms.