Thermodynamics for single-molecule stretching experiments

We show how to construct nonequilibrium thermodynamics for systems too small to be considered thermodynamically in a traditional sense. Through the use of a nonequilibrium ensemble of many replicas of the system which can be viewed as a large thermodynamic system, we discuss the validity of nonequilibrium thermodynamics relations and analyze the nature of dissipation in small systems through the entropy production rate. We show in particular that the Gibbs equation, when formulated in terms of average values of the extensive quantities, is still valid, whereas the Gibbs-Duhem equation differs from the equation obtained for large systems due to the lack of the thermodynamic limit. Single-molecule stretching experiments are interpreted under the prism of this theory. The potentials of mean force and mean position, now introduced in these experiments in substitution of the thermodynamic potentials, correspond respectively to our Helmholtz and Gibbs energies. These results show that a thermodynamic formalism can indeed be applied at the single-molecule level.     

Finite-size effects in microrheology

We propose a model to explain finite-size effects in intracellular microrheology observed in experiments. The constrained dynamics of the particles in the intracellular medium, treated as a viscoelastic medium, is described by means of a diffusion equation in which interactions of the particles with the cytoskeleton are modeled by a harmonic force. The model reproduces the observed power law behavior of the mean square displacement in which the exponent depends on the ratio between particle-to-cytoskeleton-network sizes.     

Properties of mesoporous tungstosilicic acid/titania composites prepared by sol-gel method

The tungstosilicic acid/titania composites were prepared by the sol-gel method. Titanium isopropoxide was used as titania precursor, and urea as a low-cost template. The tungstosilicic acid (TSA) was added in the same step as that in which titania hydrogel is formed. The TSA-modified samples only showed the characteristic peaks of anatase phase of titanium oxide in the XRD patterns, indicating that the presence of TSA retarded the crystallization of the anatase phase and its transformation into the rutile phase. Spherical particles with sizes between 200 and 700 nm, formed by aggregation of nanoparticle aggregates (4-50 nm in size), were observed. The particle size increased when the TSA content was raised and also increased slightly with the thermal treatment temperature. Mesoporous materials were obtained, with a mean pore diameter higher than 3.1 nm. Both the increase of the TSA concentration in the solid and the calcination temperature led to a decrease in the specific surface area of the samples. The main heteropolyoxometallate species present in the composites is the [SiW₁₂O₄₀]⁴⁻ anion for the composites calcined up to 500 °C. The band gap energy decreased as a result of the introduction of TSA into the titania matrix, though it remained almost constant with the calcination temperature increase.     

The Successive Projections Algorithm for interval selection in trilinear partial least-squares with residual bilinearization

In this work the Successive Projection Algorithm is presented for intervals selection in N-PLS for three-way data modeling. The proposed algorithm combines noise-reduction properties of PLS with the possibility of discarding uninformative variables in SPA. In addition, second-order advantage can be achieved by the residual bilinearization (RBL) procedure when an unexpected constituent is present in a test sample. For this purpose, SPA was modified in order to select intervals for use in trilinear PLS. The ability of the proposed algorithm, namely iSPA-N-PLS, was evaluated on one simulated and two experimental data sets, comparing the results to those obtained by N-PLS. In the simulated system, two analytes were quantitated in two test sets, with and without unexpected constituent. In the first experimental system, the determination of the four fluorophores (l-phenylalanine; l-3,4-dihydroxyphenylalanine; 1,4-dihydroxybenzene and l-tryptophan) was conducted with excitation-emission data matrices. In the second experimental system, quantitation of ofloxacin was performed in water samples containing two other uncalibrated quinolones (ciprofloxacin and danofloxacin) by high performance liquid chromatography with UV–vis diode array detector. For comparison purpose, a GA algorithm coupled with N-PLS/RBL was also used in this work. In most of the studied cases iSPA-N-PLS proved to be a promising tool for selection of variables in second-order calibration, generating models with smaller RMSEP, when compared to both the global model using all of the sensors in two dimensions and GA-NPLS/RBL.     

Supramolecular Stabilization of Metastable Tautomers in Solution and the Solid State

This work presents a successful application of a recently reported supramolecular strategy for stabilization of metastable tautomers in cocrystals to monocomponent, non‐heterocyclic, tautomeric solids. Quantum‐chemical computations and solution studies show that the investigated Schiff base molecule, derived from 3‐methoxysalicylaldehyde and 2‐amino‐3‐hydroxypyridine ( ap ), is far more stable as the enol tautomer. In the solid state, however, in all three obtained polymorphic forms it exists solely as the keto tautomer, in each case stabilized by an unexpected hydrogen‐bonding pattern. Computations have shown that hydrogen bonding of the investigated Schiff base with suitable molecules shifts the tautomeric equilibrium to the less stable keto form. The extremes to which supramolecular stabilization can lead are demonstrated by the two polymorphs of molecular complexes of the Schiff base with ap . The molecules of both constituents of molecular complexes are present as metastable tautomers (keto anion and protonated pyridine, respectively), which stabilize each other through a very strong hydrogen bond. All the obtained solid forms proved stable in various solid‐state and solvent‐mediated methods used to establish their relative thermodynamic stabilities and possible interconversion conditions.     

Mild Method for Ullmann Reaction of 2‐Chlorobenzoic Acids and Aminothiazoles or Aminobenzothiazoles under Ultrasonic Irradiation

One‐pot syntheses of 5H‐[1,3]thiazolo[2,3‐b]quinazolin‐5‐one, 12H‐[1,3]benzothiazolo[2,3‐b]quinazolin‐12‐one, and corresponding derivatives were developed using the copper‐catalyzed Ullmann condensation. The use of ultrasonic irradiation enhanced yields and reduced the reaction time to minutes.     

Tungstophosphoric Acid Supported on Zirconia: A Recyclable Catalyst for the Green Synthesis on Quinoxaline Derivatives under Solvent-Free Conditions

Abstract

A green, simple, and fast procedure has been developed for the preparation of quinoxaline derivatives by a condensation of 1,2-diamines with 1,2-dicarbonyl compounds in the presence of zirconium oxide modified with tungstophosphoric acid (H₃PW₁₂O₄₀) as a heterogeneous catalyst, in a solvent-free medium using conventional heating. Quinoxaline derivatives were formed in short-time periods and excellent yields (65–100%). The reaction work-up is very simple and the catalyst can be easily separated from the reaction mixture and reused several times in subsequent reactions without appreciable loss of the catalytic activity.

Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfer, and Silicon and the Related Elements for the following free supplemental files: Additional text.     

Entanglement Between Demand and Supply in Markets with Bandwagon Goods

Whenever customers’ choices (e.g. to buy or not a given good) depend on others choices (cases coined ‘positive externalities’ or ‘bandwagon effect’ in the economic literature), the demand may be multiply valued: for a same posted price, there is either a small number of buyers, or a large one—in which case one says that the customers coordinate. This leads to a dilemma for the seller: should he sell at a high price, targeting a small number of buyers, or at low price targeting a large number of buyers? In this paper we show that the interaction between demand and supply is even more complex than expected, leading to what we call the curse of coordination: the pricing strategy for the seller which aimed at maximizing his profit corresponds to posting a price which, not only assumes that the customers will coordinate, but also lies very near the critical price value at which such high demand no more exists. This is obtained by the detailed mathematical analysis of a particular model formally related to the Random Field Ising Model and to a model introduced in social sciences by T.C. Schelling in the 70’s.