Capture of benzhydryl chloride ion pairs by cobalt nitrate

A case is presented where a transition metal salt, Co(NO₃)₂, intervenes in the solvolysis of benzhydryl chloride, after the rate determining ionization step. This is in contrast to the behavior of other salts which intervene early and promote the ionization reaction. This novel behavior of Co(NO₃)₂ permits for the first time the detection of two ion pair intermediates in the solvolysis of an alkyl chloride which generates an open carbonium ion.     

Gamma radiation effects on molecular characteristic of vegetable tannins

The influence of gamma radiation on tannins extracted from Pinus caribaea bark and on tannin acid has been investigated in this study with the aim of searching for evidences of structural and/or conformational changes. To fulfill this purpose, the samples of tannins, such as tannic acid and P. caribaea tannin bark, were irradiated at different doses (from 5 to 35 kGy) using a cobalt-60 gamma irradiator. The changes were analyzed by a Fourier transform infrared spectrometry and by high resolution liquid chromatography. The results pointed out some structural and conformational changes under the effects of gamma radiation for doses higher than 5 kGy for P. caribaea tannin bark. However, no changes were detected on the irradiated tannic acid. The observed behavior suggests the loss of carbonyl groups. This could be associated to a decarboxylation process with the corresponding release of CO₂ from the molecule. Evidences of some conformational changes were also noted.     

Thermally controlled preferential molecular aggregation state in a thiacarbocyanine dye

Herein we report the experimental and theoretical study of the temperature dependence of a thiacarbocyanine dye in its monomer, H- and J-aggregates states. We demonstrate the ability to control the ratio of monomer, H- and/or J-aggregates with heat. We link such a control to the conformation dependence of the molecule. An alternative way to gain access to the dominating species without changing the concentration as a complete switching mechanism between all the present species is proposed. The results presented in this work lead to a better understanding of thiacarbocyanine dye's behavior.     

A Micellar Multitasking Device: Sensing pH Windows and Gauging the Lipophilicity of Drugs with Fluorescent Signals

A multitasking fluorescent device can be obtained by forming micelles of Triton X‐100, containing a lipophilic macrocyclic Cu²⁺ complex and the coordinating fluorophore Coumarin 343 (C343), which features a COOH moiety. At low pH the two micellised components do not interact, and the fluorescence of Courmarin 343 (C343) is intense. At intermediate pH, C343 is deprotonated and coordinates to the Cu²⁺ centre in its apical position, with fluorescence quenching. At higher pH the deprotonated C343 is displaced from Cu²⁺ by the formation of an OH^? complex, and the fluorescence is revived. This allows the system to carry out its first task as it behaves as an “on–off–on” fluorescent sensor for pH windows. The “off” part of the window ranges from pH 6 to 8. In this interval, in which the carboxylate form of C343 is apically coordinated to the Cu²⁺ complex inside micelles, the device carries out its second task, that is, it behaves as a gauge for lipophilicity. For pHs between 6 and 8, molecules containing a COOH group are in their COO^? form and distribute between bulk water and micelles proportionally to their lipophilicity. Upon entering the micelle, their COO^? moiety competes for coordination with C343, displacing it from the Cu²⁺ centre, and this results in fluorescence revival, the intensity of which is also proportional to the lipophilicity of the examined molecule. We have chosen the physiological pH value (7.4) as the working pH, and we have examined the lipophilicity of fatty acids and of the widely used family of non‐steroidal anti‐inflammatory drugs (NSAIDs). The device successfully measures their lipophilicity, expressing it with an “off–on” type fluorescent signal, as demonstrated by the correlation of the fluorescence increase with the logarithmic water/octanol partition coefficient (log P) and with the difference between the pK_a observed in micelles and that measured in water for NSAIDs.     

Synthesis and characterization of large colloidal cobalt particles

Large colloidal environmentally stable silica-coated cobalt particles were synthesized by combining the sodium borohydride reduction in aqueous solution and the St?ber method. Low size polydisperse cobalt spheres with an average size of 95 nm were synthesized by using a borohydride reduction method and were subsequently coated with a thin layer of silica by means of hydrolysis and condensation of tetraethylorothosilicate (TEOS) in an aqueous/ethanolic solution. The large uniform cobalt spheres consist of smaller metallic Co clusters, explaining the superparamagnetic behavior of the spheres. The particles were investigated by transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM).     

Total synthesis of (-)-mucocin

[reaction: see text] An enantioselective total synthesis of (-)-mucocin has been completed. A combination of asymmetric glycolate aldol additions and ring closing metathesis reactions were exploited to construct the C18-C34 and C7-C17 fragments. A selective cross-metathesis reaction was employed as the key step to couple two complex fragments.     

Nanosphere dispersed liquid crystals for tunable negative-zero-positive index of refraction in the optical and terahertz regimes

An analysis of aligned nematic liquid crystal cells containing core-shell nanospheres shows that it is possible to devise a new type of metamaterial whose index of refraction is tunable from negative, through zero, to positive values. The design parameters for the constituents can be scaled for application in the optical as well as very long wavelength (e.g., terahertz and microwave) regions.