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Density and sound velocity for solutions of carbohydrates glucose, fructose and sucrose in water and in aqueous solutions of 10% w/w of polymers PPG400, PEG400, PEG4000, and PEG10000 were measured at T = (288.15, 293.15, 298.15, 303.15, and 308.15) K. From the measured experimental data, the isentropic compressibility values of the investigated solutions were determined and from which the values of the hydration numbers of the carbohydrates were calculated. Apparent molar volume and apparent molar isentropic compressibility of the carbohydrates in the investigated solutions were also determined and based of them the sweet properties of the carbohydrates were discussed. Finally, the infinite dilutions apparent molar properties for transfer of the carbohydrates from water to aqueous solutions of different polymers were studied and the results were discussed based on the different interactions exist in the solutions. [ABSTRACT FROM AUTHOR]

The article discusses the determination of hydration numbers, the average number of water molecules affected by solute-solvent interactions, of nonelectrolytes. It cites that various acoustic methods were used in identifying the hydration numbers of nonelectrolytes including Pasynski method, Yasunaga method, and Onori method. It states that among the compounds used in acoustic methods include alcohols, polymers, and amines. It says that hydration numbers are additive with the solute molecule.

Lipophilicity of chemicals and drug candidates is normally described in terms of octanol/water partitioning and log P. We investigated an alternate approach to lipophilicity determination using a mimic of an alkyl alcohol with compound partitioning quantified using acoustic sensing. A self-assembled monolayer composed of HSC10(CH2CH2O)6C18 was formed on planar gold electrodes of a piezoelectric acoustic sensor. The system was challenged with compounds covering a 4-log range of log D values. As compounds partitioned in the interfacial layer, changes in sensor resonant frequency were found to correlate with compound partition coefficients (log P) and with distribution coefficients (log D). Linear concordance (R² = 0.933) was established between log(-dF/Mwt) and log P and with log D in both water and biological buffers at variant pH (pH 5.2 to 7.8). In turn, drug pKa could be determined by profiling log D changes during pH titration. The lipophilicity/pH profile of a weakly basic drug (quinine; pKa = 7.95) was sigmoidal with respect to -dF/Mw values, with a profile inverse to that of a weakly acidic drug (naproxen; pKa = 4.15). [ABSTRACT FROM AUTHOR]

The polar lipid fraction E (PLFE) is a major tetraetherlipid componentin the thermoacidophilic archaeon Sulfolobus acidocaldarius. Using differential scanning and pressure perturbation calorimetryas well as ultrasound velocity and density measurements, we have determinedthe compressibilities and volume fluctuations of PLFE liposomes derivedfrom different cell growth temperatures (Tg= 68, 76, and 81 °C). The compressibility and volume fluctuationvalues of PLFE liposomes, which are substantially less than thosedetected from diester lipid membranes (e.g., DPPC), exhibit smallbut significant differences with Tg. Amongthe three Tgs employed, 76 °C leadsto the least compressible and most tightly packed PLFE membranes.This temperature is within the range for optimal cell growth (75–80°C). It is known that a decrease in Tgdecreases the number of cyclopentane rings in archael tetraetherlipids. Thus, our data enable us to present the new view that membranepacking in PLFE liposomes varies with the number of cyclopentane ringsin a nonlinear manner, reaching maximal tightness when the tetraetherlipids are derived from cells grown at optimal Tgs. In addition, we have studied the effects of pressure ontotal layer thickness, d, and neutron scatteringlength density, ρn, of a silicon–D2O interface that is covered with a PLFE membrane using neutron reflectometry(NR). At 55 °C, dand ρnarefound to be rather insensitive to pressure up to 1800 bar, suggestingminor changes of the thickness of the membrane’s hydrophobiccore and headgroup orientation upon compression only. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations with a combined quantum mechanical and molecular mechanical (QM/MM) potential have been carried out to investigate the squalene-to-hopene carbocation cyclization mechanism in squalene-hopene cyclase (SHC). The present study is based on free energy simulations by constructing the free energy surface for the cyclization steps along the reaction pathway. The picture that emerges for the carbocation cyclization cascade is a delicate balance of thermodynamic and kinetic control that ultimately favors the formation of the final hopanoids carbon skeleton, A key finding is that the five- to six-membered ring expansion process is not a viable reaction pathway for either C- or D-ring formation in the cyclization reaction. The only significant intermediate is the NB-bicyclic cyclohexyl cation (III), from which two asynchronous concerted reaction pathways lead to, respectively, the 6,6,6,5-tetracyclic carbon skeleton and the 6,6,6,6,5-pentacyclic hopanoids. Experimentally, these two products are observed to have 1% and 99% yields, respectively, in the wild-type enzyme. We conclude that the product distribution in the wild-type enzyme is dictated by kinetic control of these two reaction pathways. [ABSTRACT FROM AUTHOR]

Calculations at the B3LYP/6-311+G(d,p)//B3LYP/6-311+G(d,p) level involving the atoms-in-molecules (AIM) and electron localization function (ELF) methods have been carried out for a variety of PO-bond-containing molecules in an effort to further characterize the phosphoryl bond. One cannot distinguish the phosphoryl bond from a conventional PO double bond by comparing bond distances. Both the bond breaking energies and delocalization indices do divide into the three classes of single, double, and phosphoryl and tend to parallel each other. On the basis of the PO bond in HPO having a reference bond order of 2.0, the phosphoryl bond has a bond order of about 1.3. Examination of localized orbitals confirm our ideas that the phosphoryl bond is highly polar as, indeed, are the other PO bonds. What sets the phosphoryl bond apart is the high degree of back-bonding that contributes to the delocalization index (and covalent bond order) and provides for its stronger-than-single-bond character and short bond distance. [ABSTRACT FROM AUTHOR]

Compares and contrasts the most commonly used acoustic microsensor devices in chemical sensing and interfacial studies. Thickness-shear mode (TSM) sensors; Surface acoustic wave (SAW) devices; Surface transverse wave (STW) sensors; Flexural plate wave (FPW) sensors; Acoustic plate mode (APM) sensors; Operation and measurement methods; Mass sensitivity and detection limits; Mass detectors.

The article presents a discussion of the new approach to pattern fluorescent molecules which are not involved in an electrochemical reaction. The function and use of a scanning electrochemical microscopy (SECM) are also given attention. The technique that makes use of a click chemistry reaction in forming a covalent bond is also discussed.

The article presents a research on a separation method based on acoustic forces that works on a continuous flow of sample in a microfluidic device. The researchers had applied acoustic forces to move particle from one laminar stream to another in a microfluidic channel. The method works in a device that has a central microfuidic channel with an inlet jutting out from either side. They also demonstrated that acoustically inseparable particles could be separated by manipulating the density of the suspending buffer.