ABSTRACT
The synthesis and characterization of the tetrathiomolybdatorhodium(I) monoanionic complexes [L2Rh(µ-S)2MoS2](-) (L = CO (3), P(OPh)3 (4), P(O-o-Tol)3 (P(o-CH3C6H4)3; 5), P(OMe)3 (6), P(OEt)3 (7), P(O-i-Pr)3 (8); L2 = COD (1,5-cyclooctadiene; 2), cis-dppen (cis-Ph2PCHâCHPPh2; 9), dppe (Ph2PCH2CH2PPh2; 10), dppb (Ph2P(CH2)4PPh2; 11)) is presented. The complex 2 (NEt4(+) salt) was characterized by X-ray diffraction analysis. A detailed DFT study of the electronic structures of 2-4 and 6-8 has revealed the existence of extended electron delocalization over the four-membered Rh(µ-S)2Mo ring and hence the possibility of electronic communication between the metal centers. The electronic spectra were studied with TDDFT calculations, and the main absorption band in the visible region was assigned to ν(RhâMo) electron transfer transition, which is actually a HOMO-LUMO transition. The ν(RhâMo) transition was found to correlate linearly both with Tolman's electronic parameter of the phosphite ligands and the calculated HOMO-LUMO gap of the complexes, rendering it a well-defined ligand electronic parameter, which describes the net donating ability of monodentate and bidentate ligands (CO, COD, phosphites, diphosphines). The study of the variation of Δδ((31)P) and (1)J(Rh-P) of the phosphite complexes with respect to the QALE model electronic parameters χd, πp, and Ear has succeeded in the assessment of the σ and π effects on these NMR spectral parameters.
ABSTRACT
The control of nanocrystal structures at will is still a challenge, despite the recent progress of colloidal synthetic procedures. It is common knowledge that even small modifications of the reaction parameters during synthesis can alter the characteristics of the resulting nano-objects. In this work we report an unexpected factor which determines the structure of cobalt nanoparticles. Nanocrystals of distinctly different sizes and shapes have resulted from stock solutions containing exactly the same concentrations of [Co{N(SiMe(3))(2)}(2)(thf)], hexadecylamine, and lauric acid. The reduction reaction itself has been performed under identical conditions. In an effort to explain these differences and to analyze the reaction components and any molecular intermediates, we have discovered that the rate at which the cobalt precursor is added to the ligand solution during the stock solution preparation at room temperature becomes determinant by triggering off a nonanticipated side reaction which consumes part of the lauric acid, the main stabilizing ligand, transforming it to a silyl ester. Thus, an innocent mixing, apparently not related to the main reaction which produces the nanoparticles, becomes the parameter which in fine defines nanocrystal characteristics. This side reaction affects in a similar way the morphology of iron nanoparticles prepared from an analogous iron precursor and the same long chain stabilizing ligands. Side reactions are potentially operational in a great number of systems yielding nanocrystals, despite the fact that they are very rarely mentioned in the literature.
ABSTRACT
The present technique describes a simple, sensitive spot test for the rapid one-shot detection of dopamine in human urine using lipid films with incorporated resorcin[4]arene receptor that are synthesized by a chemical reaction with a methacrylate polymer on a glass fiber filter. The lipid films without the receptor provided fluorescence under a UV lamp. The use of the receptor in these films quenched this fluorescence, and the color became similar to that of the filters without the lipid films. A drop of dopamine or urine containing this stimulant provided a "switching on" of the fluorescence, which allows the rapid detection of this stimulant in human urine at 10(-8) M concentrations. The novelty of the present work is that it opens new routes in the field of biosensing, i.e., development of sensitive, rapid, and simple methods for detecting species based on the fluorescence of the lipid membranes on a polymer film, and provides a spot test technique for the rapid detection of dopamine. The effect of potent interferences including a wide range of compounds usually found in human urine (i.e., ascorbic aid, glucose, leucine, glycine, tartrate, citrate, bicarbonate, and caffeine) was examined using an aqueous buffered solution that contained the potent interference and dopamine at two lower concentration levels (i.e., 3 x 10(-8)-10(-8) M). The effect of proteins and lipids was also investigated at these two lower dopamine concentration levels in aqueous buffered solution. The results showed no interferences from all these constituents at concentrations usually found in human urine samples; for example, albumin up to 3.22 g/L concentration levels did not provide any interference (i.e., no fluorescence). A drop of urine containing this stimulant provided similar results, i.e., a "switching on" of the fluorescence that allows a technique for the rapid detection of this stimulant in human urine at 10(-8) M concentrations. The technique is not based on a calibration graph but is a semiquantitative method for the detection of dopamine in real samples of urine that can be complimentary to HPLC methods. The difference in color between the samples containing dopamine at concentration levels of 10(-8)-10(-7) M can be easily distinguished by naked eye and a digital camera. An increase of dopamine concentration from 10(-8) to 10(-7) M makes the color more blue whereas the color of the filters remains purple in the blank test (i.e., addition of a urine sample without dopamine or dopamine at concentration levels of 10(-9) M to the filters that contain the lipid membranes with incorporated receptor). The reproducibility of the method was checked in approximately 100 samples, and all of them were found to provide similar results. Note that it was also found that the colors remain stable in the samples containing dopamine for periods of more than two months.
