MRI of an angiomyolipoma

Angiomyolipomas are uncommon, benign tumors of the kidney with certain characteristic diagnostic features. We report a case of this condition in which MRI helped to characterize the lesion.     

ZnO porous structures synthesized by CTAB-assisted hydrothermal process

ZnO porous structures have been fabricated by cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal process. X-ray diffraction (XRD) pattern indicated that the synthesized ZnO porous structures were hexagonal. It is found that CTAB influences the morphology of ZnO structures. On the basis of structural information provided by XRD, SEM, and TEM, a growth mechanism is proposed for the formation of ZnO porous structures.     

An analysis and interpretation of the Michaelis-menten kinetics of immobilized enzymes perturbed by film diffusion

The determination of kinetic parameters such as the apparent Michaelis constant (K_m app.) of enzymic reactions occurring at a mixed interface, that is, at a solid/liquid interface where the catalyst is bound to the solid phase, can lead to values that are too high when an unstirred layer is present. The perturbatior, for which an equation is derived in this paper, depends on the thickness of the unstirred layer, the maximal catalytic rate, and the diffusion constant. An additional error is introduced by the graphical determination of K_m using the Lineweaver-Burk plot since after transformation the relation is not linear if an unstirred layer is present. A numerical example shows that apparent Michaelis constants obtained from in vitro experiments involving immobilized enzymes can lead to misleading results originating from conditions used in experiments such as stirring rate (CSTR-continuous stirred tank reactors) or flow rate (packed-bed reactors) of substrate. This can partly be explained by a greater bias of the K_m determination caused by unstirred layers of the liquid medium (substrate) being present around the solid particles onto which the enzyme molecules are attached.     

Effect of substituent on the mechanism of oxidation of anilines by acidic iodate. A kinetic study

The nature of the substituent is found to exhibit a profound influence on the mechanism of oxidation of anilides by iodate. The process appears to be smooth with electron-releasing groups, while it involves consecutive reactions with electron-withdrawing groups. Azobenzenes and quinones are obtained as the major products with electron-releasing and withdrawing groups, respectively.

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Cerium(III) ion catalysis in the oxalic acid-bromate reaction: Anomalous kinetic behavior of oxalic acid

The kinetics of cerium(III) ion catalyzed Br(V) oxidation of oxalic acid in the presence of HClO₄/H₂SO₄ and mercury(II)-a bromide removing ion, exhibits second order each in [br(V)] and [acid], 0.4 and zero order in [Ce(III)]. However, the kinetic behavior of oxalic acid is anomalous with –0.7, zero and 1.4 order. The chemistry underlying the phenomena is discussed.

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Br(V), Ce(III), HClO₄/H₂SO₄ (II), , [Br(V)], [], 0,4 [Ce(III)]. , , .. –0,7, 0 1,4. , .

     

Hydration layer of a cationic micelle, C(10)TAB: structure, rigidity, slow reorientation, hydrogen bond lifetime, and solvation dynamics

We report a theoretical study of the structure and dynamics of the water layer (the hydration layer) present at the surface of the cationic micelle decyltrimethylammonium bromide (DeTAB) by using atomistic molecular dynamics simulations. The simulated micelle consisted of 47 surfactant molecules (and an equal number of bromide ions), in good agreement with the pioneering light scattering experiments by Debye which found an aggregation number of 50. In this micelle, three partially positively charged methyl groups of each surfactant headgroup face the surrounding water. The nature of the cationic micellar surface is found to play an important role in determining the arrangement of water which is quite different from that in the bulk or on the surface of an anionic micelle, like cesium perfluorooctanoate. Water molecules present in the hydration layer are found to be preferentially distributed in the region between the three partially charged methyl headgroups. It is found that both the translational and rotational motions of water exhibit appreciably slower dynamics in the layer than those in the bulk. The solvation time correlation function (TCF) of bromide ions exhibits a long time component which is found to originate primarily from the interaction of the probe with the micellar headgroups. Thus, the decay of the solvation TCF is controlled largely by the residence time of the probe in the surface. The residence time distribution of the water molecules also exhibits a slow time component. We also calculate the collective number density fluctuation in the layer and find a prominent slow component compared to the similar quantity in the bulk. This slow component demonstrates that water structure in the hydration layer is more rigid than that in the bulk. These results demonstrate that the slow dynamics of hydration layer water is generic to macromolecular surfaces of either polarity.