Efficient calculation of temperature dependence of solid-phase free energies by overlap sampling coupled with harmonically targeted perturbation

We examine a method for computing the change in free energy with temperature of a crystalline solid. In the method, the free-energy difference between nearby temperatures is calculated via overlap-sampling free-energy perturbation with Bennett's optimization. Coupled to this is a harmonically targeted perturbation that displaces the atoms in a manner consistent with the temperature change, such that for a harmonic system, the free-energy difference would be recovered with no error. A series of such perturbations can be assembled to bridge larger gaps in temperature. We test this harmonically targeted temperature perturbation (HTTP) method through the application to the inverse-power soft potential, u(r)=ε(σ/r)(n), over a range of temperatures up to the melting condition. Three exponent values (n=12, 9, and 6) for the potential are studied with different crystal structures, specifically face-centered cubic (fcc), body-centered cubic (bcc), and hexagonal close packing. Absolute free energies (classical only) for each system are obtained by implementing the series to near-zero temperature, where the harmonic model becomes very accurate. The HTTP method is shown to provide very precise results, with errors in the free energy smaller than two parts in 10(5). An analysis of the thermodynamic stability of the various structures in the infinite-system limit confirms previous findings. In particular, for n=12 and 9, the fcc structure is stable for all temperatures up to melting, and for n=6, the bcc crystal becomes stable relative to fcc for temperatures above kT/ε=0.802±0.001. The effects of vacancies and other defects are not considered in the analysis.     

Synthesis,Antiproliferative, and Antiplatelet Activities of Oxime‐Containing 3,4‐Dihydroquinolin‐2(1H)‐One Derivatives

Some oxime‐containing 3,4‐dihydroquinolin‐2(1H)‐one derivatives were synthesized and evaluated for their antiplatelet and antiproliferative activities. These compounds were synthesized via alkylation of hydroxyl precursors followed by the reaction with NH₂OH. The preliminary assays indicated that (Z)‐7‐[2‐(4‐fluorophenyl)‐2‐(hydroxyimino)ethoxy]‐3,4‐dihydroquinolin‐2(1H)‐one (13c) is the most active against U46619 induced platelet aggregation with an IC₅₀ value of 3.51 μM. For the inhibition of AA‐induced aggregation, (E)‐6‐[2‐(hydroxyimino)propoxy]‐3,4‐dihydroquinolin‐2(1H)‐one (15 ) is the most potent with an IC₅₀ value of 1.85 μM. These oxime‐containing 3,4‐dihydroquinolin‐2(1H)‐one derivatives were inactive against thrombin induced platelet aggregation with an IC₅₀ value of greater than 26.78 μM. For the antiproliferative activity, most of these oxime‐containing 3,4‐dihydroquinolin‐2(1H)‐one derivatives were inactive while (Z)‐7‐[2‐(hydroxyimino)‐2‐(naphthalen‐2‐yl)ethoxy]‐3,4‐dihydroquinolin‐2(1H)‐one (13a) exhibited only marginal activities with GI₅₀ value of 7.63, 7.34 and 6.36 μM against the growth of NPC‐TW01, NCI‐H661, and Jurkat respectively.     

Investigation of photophysical properties of mer-tris(8-hydroxyquinolinato) aluminum (III) and its derivatives: DFT and TD-DFTcalculations

Optimized structures and photophysical properties of mer- and fac-Alq₃ have been generated by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Investigating the substitution effect in the Alq₃ derivatives, the role of the electron-donating (CH₃- and NH₂-) and electron-withdrawing (F-, CN-, NO₂- and phenyl-) groups with 2- to 7-substitution have been analyzed. According to the calculation results, the 4- and 5- substituted Alq₃ exhibit an apparent spectral shift relative to the non-substituted Alq₃. The HOMO, LUMO, E_g (the energy gap between LUMO and HOMO), (maximum absorption wavelength) and f (the relative oscillator strength) of mer-Alq₃ with the 4- or 5-phenyl substitution on the quinoline ligand in the ground electronic state were calculated by using the DFT/B3LYP/6-31G(d) and TD-DFT methods. 5-phenyl substituted mer-Alq₃ with an electron-donating substituent showed an increase in the π-delocalization as compared to the 4-phenyl substituted mer-Alq₃ derivatives. Similarly, 4-phenyl substituted mer-Alq₃ with electron-withdrawing substituents also exhibits increased π-delocalization in the pyridine ring as compared to the non-substituted Alq₃. Replacing the CH group at the 4, 5 and 4,5 positions of the quinoline ligand of mer-Alq₃ with the aza group (nitrogen atom) gives three Alq₃ analogous: AlX₃, Al(NQ)₃ and Al(NX)₃; the calculated energy gap E_g of these derivatives decreases in the order Al(NQ)₃>Al(NX)₃>AX₃. Four quinoline with group III metals Mq₃ complexes were investigated for the photophysical properties; the calculated energy gap E_g decreases in the order Tlq₃>Inq₃>Gaq₃>Alq₃. The photophysical properties of 4-hydroxy-8-methyl-1,5-naphthyridine (mND) chelated with group III metals (MmND₃ complexes) were investigated also; their calculated E_g have the opposite order as those of Mq₃ complexes.     

Monochromatic sinks in nearly transitive arc-colored tournaments

Let T be the set of all arc-colored tournaments, with any number of colors, that contain no rainbow 3-cycles, i.e., no 3-cycles whose three arcs are colored with three distinct colors. We prove that if T∈T and if each strong component of T is a single vertex or isomorphic to an upset tournament, then T contains a monochromatic sink. We also prove that if T∈T and T contains a vertex x such that T−x is transitive, then T contains a monochromatic sink. The latter result is best possible in the sense that, for each n≥5, there exists an n-tournament T such that (T−x)−y is transitive for some two distinct vertices x and y in T, and T can be arc-colored with five colors such that T∈T, but T contains no monochromatic sink.     

Coupling Reaction of 4-Chloro-7-H-Pyrrolo[2,3-d]Pyrimidine with 2,3,5-Tri-O-Acetyl-β-D-Ribofuranosyl Chloride

Tubercidin (4-amino-7--D-riobofuranosyl-7-H-pyrrolo[2,3-d]pyrimidine) 1, an antibio-tic substance produced in the culture broth of Streptomyces tubericidus1, is an adenosine analog in which N-7 is replaced by a carbon atom. It has attracted much attention due to the biological activities for the growth inhibition of certain tumors, and many derivatives of tubercidin have been synthesized2-5.For the synthesis of tubercidin analogs, 4-chloro-7-H-pyrrolo[2,3-d]pyrimidine-2,3,5-tri-O-acetyl--D-r…     

Indirect measurements of streamwise solid fraction variations of granular flows accelerating down a smooth rectangular chute

In this study, we detail a method for estimating the flux-averaged solid fraction of a steady granular flows moving down an inclined rectangular chute using velocity measurements from along the perimeter cross section, combined with knowledge of the mass flow rate through the cross section. The chute is 5 cm wide and 150 cm long with an adjustable inclination angle. Four inclination angles, from 27° to 36° at 3° intervals, are tested. This angle range overlaps the internal friction angle of the glass beads, which are 4 mm nominal in diameter. Two slender mirrors are installed at the top and the bottom of the transparent chute to reflect images of the flow down the chute of the two surfaces. This allows photographic recording of the flow with a PIV imaging system and measurement of the flow depth. The mass flow rate can be calibrated simultaneously by collecting the accumulated mass at the chute exit. A linear interpolation scheme is proposed to interpolate the volume flow rate in each section of the chute. Sensitivity analysis suggests that the relative standard deviation of this scheme is about ±6%, i.e., the resultant solid volume fraction is only moderately dependent on the interpolation scheme for the tested cases. This is further confirmed by a direct intercepting method. Compared to the sophisticated magnetic resonance imaging (MRI) or the radioactive positron emission particle tracking (PEPT) methods, the present method is verified as a cost-effective and nonhazardous alternative for ordinary laboratories. Two distinct groups of streamwise dependence of the solid fractions are found. They are separated by the inclination angle of the chute and agreed with the internal friction angle. In the experiments using the two smaller inclination angles, the solid fraction ratios are found to be linear functions of the streamwise distance, while for the two larger inclination angles, the ratios have a nonlinear concave shape. All decrease with growing downstream distance.     

The Effect of the Buffering Capacity of the Supporting Electrolyte on the Electrochemical Oxidation of Dopamine and 4‐Methylcatechol in Aqueous and Nonaqueous Solvents

Dopamine was electrochemically oxidized in aqueous solutions and in the organic solvents N,N‐dimethyl‐formamide and dimethylsulfoxide containing varying amounts of supporting electrolyte and water, to form dopamine ortho‐quinone. It was found that the electrochemical oxidation mechanism in water and in organic solvents was strongly influenced by the buffering properties of the supporting electrolyte. In aqueous solutions close to pH 7, where buffers were not used, the protons released during the oxidation process were able to sufficiently change the localized pH at the electrode surface to reduce the deprotonation rate of dopamine ortho‐quinone, thereby slowing the conversion into leucoaminochrome. In N,N‐dimethylformamide and dimethylsulfoxide solutions, in the absence of buffers, dopamine was oxidized to dopamine ortho‐quinone that survived without further reaction for several minutes at 25 °C. The voltammetric data obtained in the organic solvents were made more complicated by the presence of HCl in commercial sources of dopamine, which also underwent an oxidation process.