DFT study on electronic properties of single- and double-shell icosahedral fullerenes

Multi-shell fullerenes are widely studied for their interesting properties although comparative studies on single- and multi-shell structures remain scarce. In this work, important electronic features of single- and double-shell icosahedral fullerenes as a function of their sizes were calculated in the framework of the density functional theory. Fully optimized structures were used to get the gap between the highest occupied molecular and the lowest unoccupied molecular orbital (H-L gap), electronegativity, softness and density of the electronic states. This work shows that the H-L gap of the single-shell fullerenes decreases nonlinearly as the nanoparticles size increases, whereas for the double-shell fullerenes an opposite trend is obtained. A decrease of the H-L gap is found going from single- to double-shell fullerenes with similar external sizes, up to a diameter of 3.13 nm. The electron density of states revealed that isolated peaks give way to more dense electronic states for nanoparticles with diameters above 2 nm.     

Hetero-tripodal hydroxypyridonate gadolinium complexes: syntheses, relaxometric properties, water exchange dynamics, and human serum albumin binding

The synthesis and relaxometric properties of hetero-tripodal hydroxypyridonate-terephthalamide gadolinium (Gd(3+)) chelates with differing structural features for probing human serum albumin (HSA) interactions are reported. The Gd(3+) complexes are divided into two series. The first series (3-5) features a benzyl derivative connected to the hydroxypyridonate (HOPO) moiety. The second series of complexes (6-10) has the common feature of a poly(ethylene glycol) (PEG) attached to the terephthalamide (TAM) moiety and is nonbenzylated. The water exchange of the complexes is in the fast exchange regime with rates (k(ex)) in the range 0.45-1.11 x 10(8) s(-1). The complexes have a moderate interaction with HSA with association constants (K(A)'s) in the range 0.7-8.6 x 10(3) M(-1). Protein binding results in an enhancement in proton relaxivity from 7.7-10.4 mM(-1) s(-1) (r(1p)) to 15-29 mM(-1) s(-1) (r(1p)(b)). It is concluded that the interaction of the complexes with HSA (i) is enhanced by the presence of benzyl groups, (ii) is entropically driven, and (iii) results in a lower hydration number (q).     

Total synthesis of mycalamide A

This communication describes a concise and efficient total synthesis of mycalamide A by the convergent coupling of pederic acid unit with the mycalamine unit. The left-half, (+)-7-benzoylpederic acid, was synthesized from (2R,3R)-3-methylpent-4-en-2-ol in seven steps and 34.6% overall yield through a route that features a one-step Pd(II)-catalyzed tandem Wacker/Heck cyclization reaction to prepare the tetrahydropyran ring system. The right-half, the mycalamine unit, was synthesized in 21 steps and 10.5% overall yield from diethyl d-tartrate. Effective, stereoselective methods were developed for the assembly of the two parts to yield either mycalamide A or C(10)-epi-mycalamide A.     

Organic,inorganic and total mercury determination in fish by chemical vapor generation with collection on a gold gauze and electrothermal atomic absorption spectrometry

A method for organic, inorganic and total mercury determination in fish tissue has been developed using chemical vapor generation and collection of mercury vapor on a gold gauze inside a graphite tube and further atomization by electrothermal atomic absorption spectrometry. After drying and cryogenic grinding, potassium bromide and hydrochloric acid solution (1 mol L^− 1 KBr in 6 mol L^− 1 HCl) was added to the samples. After centrifugation, total mercury was determined in the supernatant. Organomercury compounds were selectively extracted from KBr solution using chloroform and the resultant solution was back extracted with 1% m/v L-cysteine. This solution was used for organic Hg determination. Inorganic Hg remaining in KBr solution was directly determined by chemical vapor generation electrothermal atomic absorption spectrometry. Mercury vapor generation from extracts was performed using 1 mol L^− 1 HCl and 2.5% m/v NaBH₄ solutions and a batch chemical vapor generation system. Mercury vapor was collected on the gold gauze heated resistively at 80 °C and the atomization temperature was set at 650 °C. The selectivity of extraction was evaluated using liquid chromatography coupled to chemical vapor generation and determination by inductively coupled plasma mass spectrometry. The proposed method was applied for mercury analysis in shark, croaker and tuna fish tissues. Certified reference materials were used to check accuracy and the agreement was better than 95%. The characteristic mass was 60 pg and method limits of detection were 5, 1 and 1 ng g^− 1 for organic, inorganic and total mercury, respectively. With the proposed method it was possible to analyze up to 2, 2 and 6 samples per hour for organic, inorganic and total Hg determination, respectively.     

Opinion Dynamics on Networks under Correlated Disordered External Perturbations

We study an influence network of voters subjected to correlated disordered external perturbations, and solve the dynamical equations exactly for fully connected networks. The model has a critical phase transition between disordered unimodal and ordered bimodal distribution states, characterized by an increase in the vote-share variability of the equilibrium distributions. The fluctuations (variance and correlations) in the external perturbations are shown to reduce the impact of the external influence by increasing the critical threshold needed for the bimodal distribution of opinions to appear. The external fluctuations also have the surprising effect of driving voters towards biased opinions. Furthermore, the first and second moments of the external perturbations are shown to affect the first and second moments of the vote-share distribution. This is shown analytically in the mean field limit, and confirmed numerically for fully connected networks and other network topologies. Studying the dynamic response of complex systems to disordered external perturbations could help us understand the dynamics of a wide variety of networked systems, from social networks and financial markets to amorphous magnetic spins and population genetics.     

Atmospheric Pressure RF (13.56 MHz) Glow Discharge: Characterization and Application to “In Line” Waste Water Treatment

In this work the results obtained from the experimental study of an Atmospheric Pressure Glow Discharge (APGD) appear, generated in Helium (He) and dry air mixture by using a radio frequency (RF 13.56 MHz) power source. The external conditions of the discharge, its macroscopic parameters (i.e., electronic number density n_e and temperature T_e) and the results of its application to in line industrial and domestic waste water treatment are presented.     

Studies toward the asymmetric synthesis of the right part of the mycalamides

Described herein is the asymmetric synthesis of a functionalized, trioxadecalin unit that comprises the right-hand part of the mycalamides and related natural products. The synthetic route involves a 16-step sequence that accomplishes the formation of two heterocyclic rings and the generation of five stereocenters. The synthesis commenced with a C2-symmetric starting material, diethyl D-tartrate, and took advantage of a relay of diastereoselective reactions to extend this four-carbon chain and introduce new chiral centers. Subsequent electrophile-mediated cyclization afforded the desired pyran ring, which was then transformed into the desired, functionalized trioxadecalin skeleton.     

The Use of Diamond Electrodes in the Interface Biodiesel/Water

A boron‐doped diamond electrode was used at the interface of biodiesel and water in conjunction with square‐wave voltammetry to promote the detection of a model molecule (ferrocene). The addition of LiClO₄ to the oil phase increased the detection of ferrocene five‐fold as compared with an unsupported oil phase. A cathodic surface pretreatment of the BDD electrode caused no oscillation of currents and promoted a high stability within the system. Our successful use of this system suggests the possibility for its application in the analysis of other contaminants within biodiesel including liposoluble pesticides and glycerol.