Spin label EPR suggests the presence of cholesterol rich domains in cultured insect cell membranes.

Different spin labels were incorporated to the membranes of cultured insect UFL-AG-286 cells in order to characterize their physical properties by Electron Paramagnetic Resonance spectroscopy (EPR). The spectrum of the spin label 12-SASL incorporated to cell membranes was similar as those obtained in membrane model systems composed of eggPC/cholesterol. However, the spectrum of the spin label CSL, chemically related to cholesterol, was drastically different in the two systems. Interestingly, when cell cholesterol content was reduced using methyl beta cyclodextrin, an EPR spectrum similar to those of model membranes was obtained. The analysis of these experiments suggests the existence of cholesterol rich regions in UFL-AG-286 cell membranes.

Arbutin blocks defects in the ripple phase of DMPC bilayers by changing carbonyl organization.

The effect of arbutin, a 4-hydroxyphenyl-beta-glucopyranoside, on dimyristoylphosphatidylcholine (DMPC) bilayers was studied by turbidimetry, EPR and FTIR spectroscopies. The disruption of DMPC multilamellar vesicles (MLV's) with monomyristoylphosphatidylcholine (lysoPC), a product of hydrolysis of phospholipase A(2) (PLA(2)), is more efficient at 18 degrees C, where DMPC MLV's are known to be in the ripple P(beta') phase, than at 10 degrees C (L(beta') flat gel phase). Disruption at 18 degrees C was inhibited by increasing concentrations of arbutin in the solution. This inhibition was correlated with the disappearance of the ripple phase in MLV's when arbutin is present. Shifts in FTIR carbonyl bands caused by arbutin or by temperature changes allow us to propose a model. It is interpreted that the changes in the water-hydrocarbon interface caused by arbutin, forcing a reaccommodation of the carbonyl groups, eliminate the topological defects in the lattice due to mismatches among regions with different area per lipid where lysoPC can insert.

Structure, Single Crystal EPR Spectra, and Exchange Interactions in [Cu(L-proline)(2)](2).5H(2)O and Cu(D,L-proline)(2).2H(2)O.

A new copper(II) compound, [Cu(L-proline)(2)](2).5H(2)O (C(20)Cu(2)H(42)N(4)O(13)) (called compound I) was synthesized and crystallized, and its structure was solved using X-ray methods. It is monoclinic, space group P2(1), with a = 11.187(1) Å, b = 12.172(3) Å, c = 11.661(1) Å, beta = 114.96(1) degrees, and Z = 2. There are two chemically different copper molecules (labeled A and B), both with the copper atom in a N(2)O(2) square planar coordination. Molecule type A has one water molecule in an apical position. Molecule B has water molecules in each of the two apical positions. Single-crystal EPR measurements have been performed in I and also in Cu(D,L-proline)(2).2H(2)O (compound II). From the similar angular variations of the position of the single resonance observed in both compounds, we evaluated the molecular g tensors. Interpretation of the molecular g tensors resulted in d(x)()()2(-)(y)()()2 orbital ground states. From the angular variations of the line width we calculated the magnitude of the exchange interactions coupling neighbor copper ions in each compound. In I copper ions type A at 7.25 Å are arranged in chains coupled through axial-equatorial bonds. The exchange coupling within these chains is |J/k| = 118 mK. The coupling between copper ions type B is weaker. However, the interactions between copper ions type A and B generate a three-dimensional magnetic network. Our data in compound II indicate that a superexchange pathway containing a weak hydrogen bond C-H- - -O is the path for an exchange interaction with |J'/k| = 48 mK between coppers in neighbor layers at 9.75 Å.