EPR spectroscopy of tooth enamel: the tooth radicals and the microcrystal alignment

The paramagnetic radicals induced by radiation in dental enamel are very important because they can be related to the crystalline structure of hydroxyapatite. The R-value, that is, the ratio of the amplitude of the lines of the EPR signal due to radiation, is a measure of the degree of microcrystal alignment in human tooth enamel. The aim of this study is to underline the importance of a correct evaluation of the R-value, by using the current method to increase reproducibility in EPR spectroscopy of tooth enamel. Data with and without correction show a significant difference and, consequently, they give rise to a different valuation of microcrystal alignment.     

Feeding behaviour in ciliated protists

Ciliates are unicellular organisms characterized by the presence of cilia (at least in the juvenile stage), an oral cavity, nuclear dualism, conjugation, equatorial division plane in binary fission, and alveolar pellicular organization. Ciliates play an important role in the general economy of marine, fresh-water and soil environments, being essential links in the food chain. This article reviews the different feeding behaviours present in these protista together with the related digestive processes.     

Cholinergic Compounds. VI. Synthesis of epiallo Desethermuscarine

Recently, the synthesis of desethermuscarine ^1-3 and of two of its three possible isomers, allo– and epi– desethermuscarine, ^4,5 was reported. These substances, having muscarinic activity, have shown to be extremely interesting in the study of the cholinergic receptor. As a result, the role of the ether oxygen in muscarinic activity appears to be revised. Yet, due to lack of data on the fourth isomer, a complete picture of the activity of these compounds is impossible to date.     

A simple model for a two-stage chemical reaction with diffusion

We analyse the evolution of a two-stage chemical reaction betweentwo neighbouring plumes of reactants. Under the assumption thatthe plumes are approximately Gaussian we derive a system ofordinary differential equations for the total amount, the centroidand the variance of each reactant. We compare the solution ofthese equations with full numerical simulation of the reaction.Excellent agreement is obtained, with solution of the near-Gaussianmodel requiring considerably less computational effort thanthe full simulations. Of key importance is the yield of thereaction, and we discuss this feature in particular.     

An EPR study of lipid vesicles as paramagnetic agent vectors

Paramagnetic nitroxides have been proposed as probes in electron paramagnetic resonance (EPR) imaging and in clinical diagnosis. However, nitroxides are rapidly reducedin vivo to hydroxylamines, diamagnetic EPR-inactive species. Reduction occurs in blood via soluble agents such as ascorbic acid, as well as in the cells via enzymatic and non-enzymatic endocellular systems. To prevent the reduction, a water soluble nitroxide, i.e., potassium peroxylamine disulfonate, is entrapped in reverse phase evaporation vesicles. The loaded liposomes have a high entrapment capacity, and vesicles with the encapsulated agent are stable for days, even at room temperature. The vesiclesin vitro can almost completely prevent the reduction of the entrapped nitroxide by ascorbic acid. In blood of a rat, enriched with a homogenate of rat liver proteins, the vesicles are able to greatly prolong the life time of the nitroxide. In particular, the encapsulated nitroxide has a half-life of more than one hour, compared to two minutes for free nitroxide under the same conditions. Due to these protective effects, the lipid vesicles might be useful as a delivery system for paramagnetic agents.     

A complex photoreceptive structure in the cyanobacterium Leptolyngbya sp

Among the terrestrial epilithic cyanobacteria isolated from Roman hypogea at extremely low light intensity, a non-heterocystous strain, belonging to the genus Leptolyngbya, showed a marked photobehavior. These red cyanobacteria possess an orange spot at the tip of the apical cell. Micro-spectrophotometric analysis of this tip showed an absorption spectrum with two bands, centered at 456 and 504 nm, respectively. Experiments on photo-orientation impairment of these cells, and micro-spectrophotometric analysis of the tip of impaired trichomes showed that a rhodopsin-like protein might be present in this structure. All these data could support the hypothesis of the presence of a complex photoreceptive system in this prokaryote.