Revised Robertson's test theory of special relativity: Space-time structure and dynamics

The experimental testing of the Lorentz transformations is based on a family of sets of coordinate transformations that do not comply in general with the principle of equivalence of the inertial frames. The Lorentz and Galilean sets of transformations are the only member sets of the family that satisfy this principle. In the neighborhood of regular points of space-time, all members in the family are assumed to comply with local homogeneity of space-time and isotropy of space in at least one free-falling elevator, to be denoted as Robertson'sab initio rest frame [H. P. Robertson,Rev. Mod. Phys. 21, 378 (1949)].Without any further assumptions, it is shown that Robertson's rest frame becomes a preferred frame for all member sets of the Robertson family except for, again, Galilean and Einstein's relativities. If one now assumes the validity of Maxwell-Lorentz electrodynamics in the preferred frame, a different electrodynamics spontaneously emerges for each set of transformations. The flat space-time of relativity retains its relevance, which permits an obvious generalization, in a Robertson context, of Dirac's theory of the electron and Einstein's gravitation. The family of theories thus obtained constitutes a covering theory of relativistic physics.A technique is developed to move back and forth between Einstein's relativity and the different members of the family of theories. It permits great simplifications in the analysis of relativistic experiments with relevant Robertson's subfamilies. It is shown how to adapt the Clifford algebra version of standard physics for use with the covering theory and, in particular, with the covering Dirac theory.Part of this work was done at the Department of Physics, Utah State University, Logan, Utah 84322.     

The spherical-model limit in a random field

The spherical-model limitn of then-vector model in a random field, with either a statistically independent distribution or with long-range correlated random fields, is studied to demonstrate the correctness of the replica method in which then and replica limits limits are interchanged, provided the replica and thermodynamic limits are taken in the right order, in the case of long-range correlated random fields. A scaling form for the two-point correlation function relevant to the first-order phase transition below the lower critical dimensionality of the random system is also obtained.     

Amphiphilic cyclodextrin carriers embedding porphyrins: charge and size modulation of colloidal stability in heterotopic aggregates

The interaction between the anionic 5,10,15,20-tetrakis(4-sulfonatophenyl)-21H,23H-porphyrin (TPPS) and cationic vesicles formed by heptakis(2-omega-amino-O-oligo(ethylene oxide)-6-hexylthio)-beta-cyclodextrin (SC6CDNH2) has been investigated in detail through a combination of elastic light scattering (ELS), quasi-elastic light scattering (QELS), zeta potential measurements, and time-resolved fluorescence anisotropy. ELS experiments provided the first structural characterization of these cationic vesicles both in the absence and in the presence of TPPS porphyrin, modeling the system as a spherical particle described by a single thin shell form factor. The structure of mixed hetero-aggregates is modulated by charge and size of the two components as function of different porphyrin/cyclodextrin (CD) molar ratios. At the limiting molar ratio studied, the absolute value of zeta potential (/zeta/ = 12.5 mV) seems to be a reference value for the formation of stable colloidal CD vesicular aggregates at thermodynamic equilibrium. New insights on the structure of these heterotopic colloids have been obtained by analysis of rotational correlation times at different molar ratios exploiting time-resolved fluorescence anisotropy experiments. At high porphyrin loads, the anisotropy decays behave as monoexponentials and the rotational correlation times (1-2 ns) together with the r(0) values close to zero suggest the presence of small amounts of TPPS embedded in a hydrophobic environment either in monomeric or in aggregated form. At the lower porphyrin/CD molar ratios, the anisotropy decays exhibit a double-exponential behavior showing a predominant component with a slow rotational correlation time (20-25 ns) and limiting anisotropy values of approximately 0.15. This component has been assigned to molecules that are more stabilized onto the CD vesicles, that is, porphyrins embedded into the oligo-ethylene "wall" of the CD vesicles. Scanning near-field optical microscopy of the samples evaporated on glass surfaces gave further insights on the morphology and optical properties of these systems, confirming the embedding of TPPS on the vesicles and evidencing the role of the solvent.     

Molecular shape effects and quantum theory

Certain features of the chemist's molecular structure model, viz. size and shape, are retrieved even in the best non-adiabatic variational calculations thus far carried out for ground states of H ₂ ⁺ and H₂. Those features do not conflict with the full symmetry of exact molecular eigenstates, once they are properly understood as correlation effects.     

Development of a capillary electrophoretic method for the separation of diastereoisomers of a new human immunodeficiency virus protease inhibitor

A capillary electrophoretic (CE) method was developed for the separation of diastereoisomers of a new human immunodeficiency virus (HIV) protease inhibitor TMC114. In total 16 isomers of this drug have been synthesized (eight pairs of enantiomers). We succeeded in the separation of the eight diastereoisomers, but no enantiomers could be separated. Because of the high similarity and water-insolubility of these isomers, the separation is a real challenge. Different CE modes were tried out: capillary zone electrophoresis (CZE), nonaqueous capillary electrophoresis (NACE), micellar electrokinetic capillary chromatography (MEKC), and microemulsion electrokinetic capillary chromatography (MEEKC). Only MEEKC offered resolution of these compounds.     

Potentiometric studies on the complexation of copper(II) by phenolic acids as discrete ligand models of humic substances

Studies on the complexation of copper(II) by phenolic acids, as ligand models of humic substances were done by potentiometry. The acids under study were: 3,4-dihydroxyhydrocinnamic acid or hydrocaffeic acid (1), 3,4-dihydroxyphenylacetic acid (2) and 3,4-dihydroxybenzoic acid or protocatechuic acid (3). Acidity constants of the ligands and the formation constants of metal-ligand complexes were evaluated by computer programs. The carboxylic group of the phenolic acids has different pK_a1 values, being the dissociation constants intrinsically related with the distance between the function and the aromatic nucleus. The results obtained allow concluding that acidity constants of the catechol moiety of the compounds are similar with pK_a2 and pK_a3 values between 9.47-9.41 and 11.55-11.70. The complexation properties of the three ligands towards copper(II) ion are quite similar, being the species found not different either in nature or stability. Although the model ligands have some structural differences no significant differences were found in their complexation properties towards copper(II). So, it can be postulated that complexation process is intrinsically related with the presence of a catechol group.     

Can a single oxidant with two spin states masquerade as two different oxidants? A study of the sulfoxidation mechanism by cytochrome p450

Density functional calculations were performed on the sulfoxidation reaction by a model compound I (Cpd I) of cytochrome P450. By contrast to previous alkane hydroxylation studies, which exhibit a dominant low-spin (LS) pathway, the sulfoxidation follows a dominant high-spin (HS) reaction. Thus, competing hydroxylation and sulfoxidation processes as observed for instance by Jones et al. (Volz, T. J.; Rock, D. A.; Jones, J. P. J. Am. Chem. Soc. 2002, 124, 9724) are the result of a two-state reactivity scenario, whereby the hydroxylation originates from the LS pathway and the sulfoxidation from the HS pathway. In this manner, two spin states of a single oxidant (Cpd I) can be disguised as two different oxidants. The calculations rule out the possibility that a second oxidant (the ferric peroxide, Cpd 0 species) interferes in the observed results of Jones et al.     

Tetrametallic Reduction of Dinitrogen: Formation of a Tetranuclear Samarium Dinitrogen Complex

The cooperative attack of four (dipyrromethanyl)Sm(II) units on dinitrogen resulted in a novel tetranuclear samarium dinitrogen complex (shown schematically). The presence of halogen atoms inhibited reactivity with dinitrogen through the assembly of divalent samarium clusters. dipyrr=diphenylmethyldipyrrolide dianion.     

Lipase from a Brazilian StrainPenicillium citrinum Cultured in a Simple and Inexpensive Medium st]Heat-Denaturation, Kinetics, and pH Stability

This work is a study of lipase production by a Brazilian strain ofPenicillium citrinum using an inexpensive and simple medium without organic nitrogen sources and of some important industrial properties, including thermostability in relation to ionic strength. The maximal lipase activity (1585 U/L) was obtained whenPenicillium citrinum was cultured on 0.75% ammonium sulfate complemented with minerals salts instead of yeast extract. Although this activity was about 55% lower than that produced in medium with yeast extract (2850 U/L), the specific activity (7.8 U/mg proteins) was higher than that obtained with the yeast extract (4.9 U/mg proteins). The morphology of fungus changed totally, with yeast extract there are smooth, solid, and spherical pellets whereas on ammonium sulfate there are small “hairy” pellets uniformly suspended in the medium. The effect of ferrous (Fe⁺⁺) ions was carried out using medium MA with and without Fe⁺⁺ ions. Lipase production byPenicillium citrinum in medium MA requires Fe⁺⁺ ions, the absence of which caused a decreased of about 50% in the specific activity (3.5 U/mg proteins). The utilization of commercial, locally available oils as carbon sources, such as soybean oil (236 U/L) and corn oil (74 U/L) resulted in lower activity compared to olive oil, showing that lipase production byPenicillium citrinum is specifically induced by olive oil. Potassium concentration in the medium can effects the production of lipase (1 mM (1585 U/L), 10 mM (1290 U/L), and 30 mM (1238 U/L), 50 mM (195 U/L), and 100 mM (2 U/L). The crude culture filtered was susceptable to thermal deactivation. It was stable at pH 6.0, but was not stable at the optimum pH (8.0-8.5) at 50 mM. At the low ionic concentration (1-25 mM) this lipase was stable at low pH (3.5-4.0). The activation energy was 22.4 ±2.2 Kcal. mol 1.     

Supramolecular helical mesomorphic polymers. Chiral induction through H-bonding

The work described here concerns a challenge of general interest in supramolecular chemistry: the achievement of chiral helical organizations with controlled structures. This work provides a strategy to obtain supramolecular polymers in which a chiral helical conformation has been induced by a noncovalent association, that is, through hydrogen bonding. Polycatenar 2,4,6-triarylamino-1,3,5-triazines, which organize into columnar mesophases and are susceptible to H-bonding interactions, were chosen as a starting point to build up the chiral supramolecular structure. The stacking of these mesogens has been forced to wind in a helical way by means of H-bond association with (R)-3-methyladipic acid, within the mesophase. The optically active columnar organization has been studied in depth by optical microscopy, differential scanning calorimetry (DSC), X-ray diffraction, and circular dichroism. Formation of stable complexes between the triazine units and (R)-3-methyladipic acid has also been investigated by means of NMR diffusion-ordered spectroscopy (DOSY) experiments in chloroform.