Simultaneous determination of hydroquinone, resorcinol, phenol, m-cresol and p-cresol in untreated air samples using spectrofluorimetry and a custom multiple linear regression-successive projection algorithm

In this study, a novel, simple, and efficient spectrofluorimetric method to determine directly and simultaneously five phenolic compounds (hydroquinone, resorcinol, phenol, m-cresol and p-cresol) in air samples is presented. For this purpose, variable selection by the successive projections algorithm (SPA) is used in order to obtain simple multiple linear regression (MLR) models based on a small subset of wavelengths. For comparison, partial least square (PLS) regression is also employed in full-spectrum. The concentrations of the calibration matrix ranged from 0.02 to 0.2 mg L⁻¹ for hydroquinone, from 0.05 to 0.6 mg L⁻¹ for resorcinol, and from 0.05 to 0.4 mg L⁻¹ for phenol, m-cresol and p-cresol; incidentally, such ranges are in accordance with the Argentinean environmental legislation. To verify the accuracy of the proposed method a recovery study on real air samples of smoking environment was carried out with satisfactory results (94-104%). The advantage of the proposed method is that it requires only spectrofluorimetric measurements of samples and chemometric modeling for simultaneous determination of five phenols. With it, air is simply sampled and no pre-treatment sample is needed (i.e., separation steps and derivatization reagents are avoided) that means a great saving of time.     

Structure conversions of cellulose IIII crystal models in solution state: a molecular dynamics study

This paper re-examines our previous molecular dynamics (MD) study on cellulose III_I crystal models with finite dimensions solvated in explicit water molecules. Eight crystal models, differing in a constituent lattice plane and dimensions, were studied. One calculation allowed for O–H and C–H bond stretching, and had a small time step of 0.5 fs. The other calculation adopted non-scaling factors of the 1–4 non-bonded interactions. As in our previous study, in the former MD calculations, six of the eight crystal models exhibited structure conversion with cooperative chain slippages generated by a progressive fiber bend. This converted the initial non-staggered chain packing of cellulose III_I into a near one-quarter staggering and gave the crystal model a triclinic-like configuration. In contrast, in the non-1–4 scaling MD calculations, all of the eight crystal models retained the initial cellulose III_I crystal structure. Another series of non-1–4 scaling MD calculations were performed for the four crystal models containing chains with a degree of polymerization (DP) of 40 at 370 K, which simulated hot water treatment to convert cellulose III_I to Iβ. Some of the hydroxymethyl groups irreversibly rotated from gt into tg conformation. This accompanied exchange of the intrasheet hydrogen bonding scheme along the (1 ?1 0) lattice plane from O2–O6 to O3–O6. The original corrugated (1 ?1 0) chain sheet was partly converted into a cellulose I-like flat chain sheet.     

Supramolecular hemoprotein-gold nanoparticle conjugates

Interaction of apohemoprotein with a covalently immobilized heme moiety onto a gold nanoparticle surface resulted in supramolecular hemoprotein-gold nanoparticle conjugates. The addition of an apohemoprotein dimer further led to a densely-packed hemoprotein-gold nanoparticle assembly, which was visualized by TEM and AFM measurements.     

Real polarizers and faster than light signaling

An imperfection of real polarizers (as opposite to ideal ones) seems to provide a method for faster than light signaling, threatening the structural stability of quantum field theory. The cause of the unphysical result is explained, and the problem of structural stability is solved.     

The dependence of catalytic activities of secondary functional beta-cyclodextrins on cavity structures.

Secondary imidazole-appended beta-cyclodextrin 5 with a nondistorted cavity synthesized from a novel intermediate 3-amino-3-deoxy-beta-cyclodextrin exhibits much greater catalytic activity in the ester hydrolysis than its isomer 6 with a distorted cavity, indicating that the catalytic activities of secondary functional cyclodextrins are dependent on cavity structures.     

Organocatalytic asymmetric Mannich-type reaction of N-sulfonylimines with isocyanoacetate leading to optically active 2-imidazoline-4-carboxylates

The first asymmetric Mannich-type reaction of methyl isocyanoacetate with N-sulfonylimines catalyzed by cinchona alkaloid derivatives yielded 2-imidazolines with high diastereoselectivities and good enantioselectivities (up to >99:1 dr and 70% ee). This reaction provided a convenient route to access various substituted 2-imidazoline-4-carboxylates and related α,β-diamino acids in high enantiomeric purities.     

Interest rate option pricing and volatility forecasting: An application to Brazil

Assessing the markets perception of future interest and inflation rate volatility is of crucial importance to assess the evolution of expectations in an inflation targeting framework. This article aims to evaluate the information content of implied volatilities extracted from a Brazilian interest-rate call option. We compared the predictive performance of three different approaches: one using the traditional [Black F. The pricing of commodity contracts. J Financ Econ 1976;3:167–79] method, another one using the extended-Vasicek model, and in the third approach, we use a GARCH(2, 1) model. The empirical evidence was more favorable to the extended-Vasicek method. Moreover, extended-Vasicek’s implied volatilities could predict around 33% (adjusted R²) of the variations in realized volatility. Further research could test for the predictive content of long memory options such as those suggested in Wang et al. [Wang X-T, Qiu W-Y, Ren F-Y. Option pricing of fractional version of the Black–Scholes model with Hurst exponent H being in . Chaos, Solitons & Fractals 2001;12:599–608; Wang X-T, Ren F-Y, Liang X-Q. A fractional version of the Merton model. Chaos, Solitons & Fractals 2003;15:455–63].