Electro-Optic Intensity Modulator for Broadband Optical Communications

An LiNbO 3 electro-optic grating modulator, composed of coplanar microstrip electrodes with periodic small fins and an airbridge structure, is presented. The small fins slow down the microwave propagating speed, while the effect of the airbridge is the reduction of the effective index. The modulator design has good performance in terms of wavelength selection and high-speed characteristics. The microwave and optical analysis are carried out using the three-dimensional finite difference method and coupled mode equations.     

Solute—Solvent interactions in water-rich mixtures. I. Ionic conductances in water—Acetonitrile mixtures at 25°C

Conductance measurements oni-Am₃BuNI (TABI), NaBPh₄, NaI, NaBr, NaCl, and KCl are reported for aqueous mixtures containing up to 20 mole% acetonitrile at 25°C. Experimental data were analyzed by the 1965 Fuoss-Onsager-Skinner equation. Limiting ionic equivalent conductances in water-acetonitrile mixtures were calculated assuming that the contribution to the limiting conductance foriAm₃BuNBPh₄ is the same for both ions involved. The trends observed for the limiting ionic conductance-viscosity products for several ions in these water-rich solvents are discussed in terms of structural effects and ion-solvent interaction.     

Ionic enthalpies of transfer from water to water-sulfolane mixtures

NaCl, NaBr, NaI, NaClO₄, KCl, KClO₄, NaBPh₄, and Ph₄PBr solution enthalpies were measured in water-sulfolane mixtures at 30°C. Ionic enthalpies of transfer from water to mixed solvents were calculated on the basis of the assumption H _s ^o (BPh ₄ ^– )=H _s ^o (Ph₄P⁺). The variation of the ionic enthalpies of transfer with solvent composition is discussed in terms of ion-solvent interactions and of the effects caused by sulfolane on the structure of water.     

Excess heat capacities and excess volumes of binary liquid mixtures of chloroform with cyclic ethers at 298.15 K

Molar excess heat capacities at constant pressure, C^E_p, of binary liquid mixtures chloroform + oxolane, chloroform + 1,3-dioxolane, chloroform + oxane, and chloroform + 1,4-dioxane have been determined at 298.15 K from measurements of volumetric heat capacities in a Picker flow microcalorimeter. A precision of ±0.04 J K^?1 mole^? was achieved by using the stepwise procedure. Experimental molar excess heat capacities are compared with values derived from H^E results at different temperatures. Excess molar volumes, V^E, for the same systems at 298.15 K have been determined by measuring the density of the pure liquids and solutions with a high-precision digital flow densimeter.     

One-pot multicomponent synthesis of 2,3-dihydropyrans: new access to furanose-pyranose 1,3-C-C-linked-disaccharides

An efficient synthesis of 2,3-dihydropyrans from different terminal alkynes was developed. The 2,3-dihydropyrans were obtained in a few minutes through a microwave-assisted multicomponent enyne cross-metathesis/hetero-Diels-Alder reaction. Starting from C-ethynyl-ribofuranose, a new multicomponent approach to furanose-pyranose 1,3-C-C-linked disaccharides was also developed.     

Chlorophyllide a/cyclodextrin interaction in aqueous solution

The interactions between Chlorophyllide a (Chlide), a pigment having the same structure of Chl a without the phytilic tail, and two CDs having the same moieties but different cavity size, the hydroxypropyl- β -cyclodextrin and the hydroxypropyl-γ-cyclodextrin, were studied in aqueous solutions by means of absorption, fluorescence spectroscopy, circular dichroism and isothermal titration calorimetry. The results obtained indicate that both cyclodextrins are able to modify the aggregation equilibrium of the pigment favouring the monomeric form. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enthalpies of transfer of ubiquinone-0 from water to aqueous surfactant solutions at various temperatures

Mixing and dilution enthalpies of aqueous solutions of 2,3-dimethoxy-5-methyl-1,4-benzoquinone (UQ₀) and of N,N-dimethyl-dodecylamine-N-oxide (DDAO) were measured and used to calculate the enthalpies of transfer δH(W →W +S) of UQ₀ from water to DDAO aqueous solutions at 20‡, 25‡, 30‡, and 35‡C. From the dependence of δH(W →W +S) on surfactant concentration, the distribution constant between aqueous and micellar phases and the standard transfer enthalpy of UQ₀ from water to DDAO micelles were evaluated along with the standard transfer free energy and entropy. The approach used required knowledge of the CMC and micellization enthalpy at each temperature. Thus, the thermodynamics of micellization of DDAO was studied by means of dilution enthalpy measurements at the several temperatures.     

Interaction between chlorophyll a and b-cyclodextrin derivatives in aqueous solutions

Cyclodextrins (CDs) are widely used as delivery systems of poorly water soluble drugs in pharmacological applications. The delivery system produces an increase of aqueous solubility of the drug and significant modifications in its physico-chemical and pharmacological properties. In this paper we report the results of our study on aqueous solutions of chlorophyll a, a natural pigment useful as sensitizer in the photodynamic therapy, and two CDs: hydroxypropyl- b-cyclodextrin and heptakis(2,6-di-O-methyl)-b-cyclodextrin. The interactions between chlorophyll and CDs and the effect produced by the presence of the CDs on the aggregation of chlorophyll were studied by calorimetric and UV-Vis spectrophotometric measurements respectively. This revised version was published online in July 2006 with corrections to the Cover Date.