In situ particle zeta potential evaluation in electroosmotic flows from time-resolved microPIV measurements

A time-resolved microPIV method is presented to measure in an EOF the particles zeta potential in situ during the transient start-up of a microdevice. The method resolves the electrophoretic velocity of fluoro-spheres used as tracer particles in microPIV. This approach exploits the short transient regime of the EOF generated after a potential drop is imposed across a microchannel and before reaching quasisteady state. During the starting of the transient regime, the electrophoretic effect is dominant in the center of the channel and the EOF is negligible. By measuring the velocity of the tracer particles with a microPIV system during that starting period, their electrophoretic velocity is obtained. The technique also resolves the temporal evolution of the EOF with three regions identified. The first region occurs before the electroosmotic effect reaches the center of the channel, the second region extends until the EOF reaches steady state, and thereafter is the third region. The two time constants separating these regions are also obtained and compared to the theory. The zeta potential of 860 nm diameter polystyrene particles is calculated for different solutions including borate buffer, sodium chloride, and deionized water. Results show that the magnitudes of the electrophoretic and electroosmotic velocities are in the range of |300| to |700| μm/s for these measurements. The zeta potential values are compared to the well-established closed cell technique showing improved accuracy. The method also resolves the characteristic response time of the EOF, showing small but important deviations from current analytical predictions. Additionally, the measurements can be performed in situ in microfluidic devices under actual working EOF conditions and without the need for calibrations.     

Formation of Schiff bases of O-phosphorylethanolamine and O-phospho-D,L-serine with pyridoxal 5'-phosphate. experimental and theoretical studies

Pyridoxal 5'-phosphate (PLP) is a B(6) vitamer acting as an enzyme cofactor in various reactions of aminoacid metabolism and inhibiting glycation of biomolecules. Nonenzymatic glycation of aminophospholipids alters the stability of lipid bilayers and cell function as a result. Similarly to protein glycation, aminophospholipid glycation initially involves the formation of a Schiff base. In this work, we studied the formation of Schiff bases between PLP and two compounds mimicking the polar head of natural aminophospholipids, namely: O-phosphorylethanolamine and O-phospho-D,L-serine. Based on the results, the pH-dependence of the microscopic constants of the two PLP-aminophosphate systems studied is identical with that for PLP-aminoacid systems. However, the rate and equilibrium formation constants for the Schiff bases of the aminophosphates are low relative to those for the aminoacids. A theoretical study by density functional theory of the formation mechanism for the Schiff bases of PLP with the two aminophospholipid analogues confirmed that the activation energy of formation of the Schiff bases is greater with aminophosphates; on the other hand, that of hydrolysis is essentially similar with aminoacids and aminophosphates.     

Unveiling the complex pattern of intermolecular interactions responsible for the stability of the DNA duplex

Herein, we provide new insights into the intermolecular interactions responsible for the intrinsic stability of the duplex structure of a large portion of human B-DNA by using advanced quantum mechanical methods. Our results indicate that (i) the effect of non-neighboring bases on the inter-strand interaction is negligibly small, (ii) London dispersion effects are essential for the stability of the duplex structure, (iii) the largest contribution to the stability of the duplex structure is the Watson–Crick base pairing – consistent with previous computational investigations, (iv) the effect of stacking between adjacent bases is relatively small but still essential for the duplex structure stability and (v) there are no cooperativity effects between intra-strand stacking and inter-strand base pairing interactions. These results are consistent with atomic force microscope measurements and provide the first theoretical validation of nearest neighbor approaches for predicting thermodynamic data of arbitrary DNA sequences.

Advanced electronic structure methods provide a new insight into the intermolecular interactions responsible for the intrinsic stability of the duplex structure of human DNA.     

Triquinoline- versus Fullerene-Based Cycloparaphenylene Ionic Complexes: Comparison of Photoinduced Charge-Shift Reactions

A triquinoline cationic moiety (TQ⋅H⁺) has recently been designed as a novel molecular unit for supramolecular chemistry. In addition to some useful features, TQ⋅H⁺ has strong electron-acceptor properties, which renders the molecular cation a unique element in nanochemistry. TQ⋅H⁺ is found to form complexes with coronene (COR) and cycloparaphenylene (CPP). In this work, we report a computational study of photoinduced electron transfer in supramolecular complexes TQ⋅H⁺-COR, TQ⋅H⁺⊂[12]CPP and (TQ⋅H⁺-COR)⊂[12]CPP. The electron-transfer rates are estimated by using the semi-classical approach. The results are compared with the data previously obtained for a structurally similar inclusion complex Li⁺@C₆₀⊂[10]CPP. In particular, we found a red solvatochromic shift for charge-shift bands in the TQ⋅H⁺-complexes unlike a blueshift showed by Li⁺@C₆₀⊂[10]CPP. This distinction is explored in terms of electronic and structural features of the systems.     

Predictive Catalysis in Olefin Metathesis with Ru-based Catalysts with Annulated C60 Fullerenes in the N-heterocyclic Carbenes

Predictive catalysis must be the tool that does not replace experiments, but acts as a selective agent, so that synthetic strategies of maximum profitability are used in the laboratory in a surgical way. Here, nanotechnology has been used in olefin metathesis from homogeneous Ru-NHC catalysts, specifically annulating a C₆₀ fullerene to the NHC ligand. Based on results with the C₆₀ in the backbone, a sterile change with respect to the catalysis of the metal center, an attempt has been made to bring C₆₀ closer to the metal, by attaching it to one of the two C−N bonds of the imidazole group of the SIMes (1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) ligand (reference NHC ligand of the 2^nd generation Grubbs catalysts) to increase the steric pressure of C₆₀ in the first sphere of reactivity of the metal. The DFT calculated thermodynamics and the kinetics of SIMes-derived systems show that they are efficient catalysts for olefin metathesis.     

Studies on the pauson-khand reaction. Exclusive formation of angularly fused triquinanes from bicyclo[3.3.0]oct-2-ene and propargyl derivatives

Reaction of bicyclo[3.3.0]oct-2-ene with different hexacarbonyl dicobalt complexes of propargyl derivatives leads, under a great variety of experimental conditions, to the exclusive formation of angularly fused triquinanes, the corresponding reduced products being formed if the reaction is run at high temperature. The intermediacy of a π-allyl complex is suggested in order to account for these results, as well as for the presence of minor amounts of Diels-Alder adducts in the reaction mixture.     

New synthesis of pyrido[2,3-d]pyrimidines. III. Nucleophilic substitution on 4-amino-2-halo and 2-amino-4-halo-5,6-dihydropyrido[2,3-d]pyrimidin-7(8H)-ones

As the third step of a new general synthesis of pyrido[2,3-d]pyrimidines, the substitution of the halogens by several nucleophiles has been carried out. Yields are between good and high in every case, even when 4-halogenated compounds have a neighbouring methyl group in C5.     

Direct entry to the all-cis tricyclo[5.2.1.O4,10]decane (perhydrotriquinacene) skeleton by a cobalt mediated intramolecular cyclization

The perhydrotriquinacene skeleton has been synthesized by a Pauson-Khand bis-annulation process.     

Model independent fitting to theZ line shape

An improved model independent formula to fit theZ line shape parameters is presented. The accuracy of the QED radiative corrections used in the formula is estimated, as is the absolute accuracy of the formula itself. The precision of the formula is compared with existing fitting formulae, in terms of cross sections produced and in terms of theZ parameters returned from a fit. The errors which the LEP-SLC experiments can expect to achieve on theZ parameters are examined as a function of total integrated luminosity. The formula presented here can fit theZ parameters with high accuracy: below 1 MeV for theZ mass, the order of 1 MeV for total width, and below 0.04% for the hadronic and leptonic peak cross sections. Such biases will remain much below the expected experimental uncertainties from LEP and SLC.