Enantioselective synthesis of tetranuclear quadruple helicates

Quadruple helical structures are assembled around a tetranuclear cubane structure using four chiral tridentate ligands and two ligands coordinating diagonally across a face. Stereoselectivity in the complex formation is observed.     

Electric dipole (hyper)polarizabilities of spatially confined LiH molecule

In this study we report on the electronic contributions to the linear and nonlinear static electronic electric dipole properties, namely the dipole moment (μ), the polarizability (α), and the first-hyperpolarizability (β), of spatially confined LiH molecule in its ground X (1)Σ(+) state. The finite-field technique is applied to estimate the corresponding energy and dipole moment derivatives with respect to external electric field. Various forms of confining potential, of either spherical or cylindrical symmetry, are included in the Hamiltonian in the form of one-electron operator. The computations are performed at several levels of approximation including the coupled-cluster methods as well as multi-configurational (full configuration interaction) and explicitly correlated Gaussian wavefunctions. The performance of Kohn-Sham density functional theory for the selected exchange-correlation functionals is also discussed. In general, the orbital compression effects lead to a substantial reduction in all the studied properties regardless of the symmetry of confining potential, however, the rate of this reduction varies depending on the type of applied potential. Only in the case of dipole moment under a cylindrical confinement a gradual increase of its magnitude is observed.     

Mechanisms of fibrinogen adsorption on latex particles determined by zeta potential and AFM measurements

The adsorption of fibrinogen on polystyrene latex particles was studied using the concentration depletion method combined with the AFM detection of residual protein after adsorption. Measurements were carried out for a pH range of 3.5-11 and an ionic strength range of 10(-3)-0.15 M NaCl. First, the bulk physicochemical properties of fibrinogen and the latex particle suspension were characterized for this range of pH and ionic strength. The zeta potential and the number of uncompensated (electrokinetic) charges on the protein were determined from microelectrophoretic measurements. It was revealed that fibrinogen molecules exhibited amphoteric characteristics, being on average positively charged for pH <5.8 (isolectric point) and negative otherwise. However, the latex particles did not show any isoelectric point, remaining strongly negative for this pH range. Afterward, systematic measurements of the electrophoretic mobility of fibrinogen-covered latex were carried out as a function of the amount of adsorbed protein, expressed as the surface concentration. A monotonic increase in the electrophoretic mobility (zeta potential) of the latex was observed in all cases, indicating a significant adsorption of fibrinogen on latex for pH below 11. It was also proven that fibrinogen adsorption was irreversible, with the maximum surface concentration varying between 2.5 and 5 × 10(3) μm(-2) (weight concentration of a bare molecule was 1.4 to 2.8 mg m(-2)). These measurements revealed two main adsorption mechanisms of fibrinogen: (i) the unoriented (random) mechanism prevailing for lower ionic strength, where adsorbing molecules significantly penetrate the fuzzy polymeric layer on the latex core and (ii) the side-on adsorption mechanism prevailing for pH > 5.8 and a higher ionic strength of 0.15 M. It was also shown that in the latter case, variations in the zeta potential with the protein coverage could be adequately described in terms of the electrokinetic model, previously formulated for planar substrate adsorption. On the basis of these experimental data, an efficient procedure of preparing fibrinogen-covered latex particles of controlled monolayer structure and coverage was envisaged.     

Combining chromatography and chemometrics for the characterization and authentication of fats and oils from triacylglycerol compositional data—A review

The characterization and authentication of fats and oils is a subject of great importance for market and health aspects. Identification and quantification of triacylglycerols in fats and oils can be excellent tools for detecting changes in their composition due to the mixtures of these products. Most of the triacylglycerol species present in either fats or oils could be analyzed and identified by chromatographic methods. However, the natural variability of these samples and the possible presence of adulterants require the application of chemometric pattern recognition methods to facilitate the interpretation of the obtained data. In view of the growing interest in this topic, this paper reviews the literature of the application of exploratory and unsupervised/supervised chemometric methods on chromatographic data, using triacylglycerol composition for the characterization and authentication of several foodstuffs such as olive oil, vegetable oils, animal fats, fish oils, milk and dairy products, cocoa and coffee.     

A cost-effective urgent care policy to improve patient access in a dynamic scheduled clinic setting

Patient no-show in outpatient clinics has been a long recognized issue, which negatively impacts clinic operational efficiency in terms of costs and patient access to care. One way to reduce these negative impacts is to allow urgent walk-ins during a clinic day. Some clinics allow random walk-ins and some purposely leave open time slots to accommodate them. The objective of this paper is to develop a cost-effective urgent care policy that is added on top of a full schedule and takes into account scheduled patients’ no-show rates to improve patient access to care in a dynamic clinic environment. The findings indicate that the proposed approach outperforms the current random and urgent slot approaches. This paper demonstrates a dynamic approach for accommodating urgent patients into a patient scheduling system, based on the prediction of an individual patient's no-show probability and the maximum number of urgent patients allowed.     

The closures of arithmetic progressions in the common division topology on the set of positive integers

In this paper we characterize the closures of arithmetic progressions in the topology T on the set of positive integers with the base consisting of arithmetic progressions {an + b} such that if the prime number p is a factor of a, then it is also a factor of b. The topology T is called the common division topology.     

LED pumped polymer laser sensor for explosives

A very compact explosive vapor sensor is demonstrated based on a distributed feedback polymer laser pumped by a commercial InGaN light‐emitting diode. The laser shows a two‐stage turn on of the laser emission, for pulsed drive currents above 15.7 A. The ‘double‐threshold’ phenomenon is attributed to the slow rise of the ∼30 ns duration LED pump pulses. The laser emits a 533 nm pulsed output beam of ∼10 ns duration perpendicular to the polymer film. When exposed to nitroaromatic model explosive vapors at ∼8 ppb concentration, the laser shows a 46% change in the surface‐emitted output under optimized LED excitation.     

Oxygen Uptake in the Vitamin B2-sensitized Photo-oxidation of Tyrosine and Tryptophan in the Presence of Uracil: Kinetics and Mechanism

Considering the significance of visible light-promoted reactions in complex biological media, the photo-oxidation of the amino acids (AAs) tyrosine (tyr) and tryptophan (trp) was studied in the presence of the naturally occurring oxidative scavenger uracil (ur). The involved photoprocesses, studied at pH 7 and 9, are driven through the reactive oxygen species (ROS) singlet molecular oxygen (O₂(¹Δ_g)), superoxide radical anion (O₂^•−) and hydrogen peroxide (H₂O₂). The effect on the effectiveness of the overall photo-oxidation process due to the presence of an added electron-donating substrate such as ur is not straightforwardly predictable. The addition of the pyrimidine compound, a much lesser photo-oxidizable substrate than the AAs themselves, produced different results: (1) antioxidative for tyr at pH 9, decreasing the overall rate of oxygen uptake; (2) synergistic for tyr at pH 7, increasing the oxidation rate more than the corresponding addition value of the respective individual rates and (3) no effect for trp at both pH values. The final result depends on the respective abilities of the substrates as quenchers of both the long-lived riboflavin triplet excited state and the generated ROS and the pH of the medium. An interpretation for the different cases is attempted through a kinetic and mechanistic analysis.     

Carbon monoxide-promoted carbene insertion into the aryl substituent of an N-heterocyclic carbene ligand: Buchner reaction in a ruthenium carbene complex

In the presence of carbon monoxide, ruthenium carbenes give a net insertion/ring expansion (Buchner reaction) into one of the aromatic rings of the N-heterocyclic carbene ligand. In alkene metathesis applications, the N-heterocyclic carbene ligand is both robust and typically inert to reactions with the metal-bound carbene. This unique reaction is completely regioselective. The complexes obtained through ring expansion were fully characterized in the solid state using X-ray crystallography and in solution using NMR and IR spectroscopy.     

Palladium-catalyzed C–H alkenylation of quinoxaline N-oxide enabled by a mono-N-protected amino acid

The efficient alkenylation of quinoxaline N-oxide was achieved via Pd-catalyzed C–H activation, using the assistance of a mono-N-protected amino acid. Further deoxygenation of the 2-styrylquinoxaline-N-oxides yielded the corresponding styrylquinoxaline derivatives.