Octanes

The adhesion forces and free energies of separation of structure II clathrate hydrates in vacuum and submerged in water and a model oil are investigated by molecular dynamics simulation. The water molecules are modeled by the TIP4P/ice model and the alkanes by the OPLS_AA force field. The results are compared with theory and earlier work. It is observed that the adhesive forces between the simulated surfaces have an effective range of no more than 1.5-2 nm. The hydrate-hydrate interaction force is attractive in vacuum and oil, larger in vacuum. In water the interaction force is very slightly repulsive on average and much weaker than in the two other systems with a larger uncertainty. In all cases the interaction is largely entropically driven. The separation energies in vacuum and oil (octane) are stronger than predicted by theory, with free energies of approximately 4 and 0.7 aJ, respectively, likely due to lack of polarization effects. The hydrate-hydrate interaction in water is too weak for quantitative comparisons to be made.

The mutually optimized combinations of vertex-degree weighted path indices and the vertex-degree vertex-distance weighted elements of the Universal matrix were applied in the way of TI new = ∑k N ×PN(a N ,b N ,...) + k ij ×u ij (a ij ,b ij ,c ij). They were correlated to the boiling points of octanes. Using the mutually optimized combination of vertex-degree weighted path indices P2(a 2 ,b 2 ,c 2), P3(a 3 ,b 3 ,c 3 ,d 3), and P4(a 4 ,b 4 ,c 4 ,d 4 ,e 4) there was observed R = 0.99950. When in addition to P2(a 2 ,b 2 ,c 2), P3(a 3 ,b 3 ,c 3 ,d 3), and P4(a 4 ,b 4 ,c 4 ,d 4 ,e 4) also P1(a 1 ,b 1) or u 72 (a 72 ,b 72 ,c 72) or u 76 (a 76 ,b 76 ,c 76) or u 62 (a 62 ,b 62 ,c 62) or u 74 (a 74 ,b 74 ,c 74) or u 52 (a 52 ,b 52 ,c 52) have been applied, then the goodnesses of up to R = 0.99988, S = 0.098, IC = 98.5% have been observed. The mutually optimized combinations of vertex-degree weighted path indices and the vertex-degree vertex-distance weighted elements of the Universal matrix are promising indices also for other physicochemical properties of octanes.

Improvement of catalytic efficiency of immobilized enzymes via materials engineering was demonstrated through the preparation of bioactive nanofibers. Bioactive poly-styrene (PS) nanofibers with a typical diameter of 120 nm were prepared and examined for catalytic efficiency for biotransformations. The nanofibers were produced by electrospinning functionalized PS, followed by the chemical attachment of a model enzyme, R-chymotrypsin. The observed enzyme loading as determined by active site titration was up to 1.4 % (wt/wt), corresponding to over 27.4 % monolayer coverage of the external surface of nanofibers. The apparent hydrolytic activity of the nanofibrous enzyme in aqueous solutions was over 65 % of that of the native enzyme, indicating a high catalytic efficiency as compared to other forms of immobilized enzymes. Furthermore, nanofibrous R-chymotrypsin exhibited a much-improved nonaqueous activity that was over 3 orders of magnitude higher than that of its native counterpart s...

A new method for the separation and identification of lipid classes by normal-phase HPLC on a cyanopropyl column is described. The use of a simple binary gradient, with toluene as a component, provided a rapid separation of non-polar as well as phospholipid classes. The inherent small differences in performances between possible non-polar eluent components of the gradient, such as hexane, heptane, and iso-octane, had a pronounced impact on retention times for individual phospholipid classes. Separation of molecular species within a lipid class could also be observed.

Dry reverse micelles of AOT in isooctane spontaneously undergo a microstructural transition to an organogel upon the addition of a phenolic dopant, p-chlorophenol. This microstructural evolution has been studied through a combination of light scattering, small-angle neutron ...

Injection of large volumes of samples in solvents other than mobile phase composition has been proved for some less hydrophobic compounds. Thus, the retention behavior of several compounds of pharmaceutical interest (isosorbide-2-nitrate, isosorbide-5-nitrate, tropicamide, pentoxifylline, and methyl p-hydroxybenzoate) was studied by using different hydrophobic solvents (n-hexane, n-heptane, or i-octane) as sample solvents. Two types of stationary phases were used: octyl and octadecyl modified silica (both of Zorbax Eclipse type). The experiments showed a linear dependence between capacity factor of each solute and sample injection volume, up to maximum volume values of about 680 microL for C8 stationary phase and 580 microL for C18 stationary phase, when the solutes are no longer retained in stationary phase. Injection of large volumes of these hydrophobic solvents is thus possible in RP-LC with a gradual reduction of retention and peak efficiency. Two major conditions are however necessary in order to apply such an injection approach: the solutes must have a proper solubility in hydrophobic solvents and meanwhile they have to be less hydrophobic than the sample solvent in order to avoid competition with solvent molecules in partitioning between mobile and stationary phases.

The commercially available monoterpene carvone has been efficiently converted into the tricyclo[3.2.1.0(2.7)]octane and bicyclo[3.2.1]octane systems characteristic of some biologically active compounds. The sequence used for this transformation involves as key features an intramolecular Diels-Alder reaction of a 5-vinyl-1,3-cyclohexadiene and a cyclopropane ring opening.