Ring-rearrangement metathesis of substituted dihydropyrans and dihydrofurans

The rearrangement of dihydropyrans and dihydrofurans featuring appending olefins has been studied. The rearranged products bear resemblance with polyunsaturated di- and trisaccharides. Examples of functionalization prior to, or following, rearrangement are provided suggesting that the method should be useful for the synthesis of nonclassical saccharides. This work also illustrates the power of cascade methatetic processes for increasing molecular complexity starting from relatively simple heterocycles.     

The Katona cycle proof of the Erdős–Ko–Rado theorem and its possibilities

In this paper we give a framework for applying Katona’s cycle proof of the Erd?s–Ko–Rado theorem to other objects. We also show how this method can be realized as a result using homomorphisms of graphs.     

Reconstructing bulk isotope ratios from compound‐specific isotope ratios

Carbon isotope analysis by bulk elemental analysis coupled with isotope ratio mass spectrometry has been the mainstay of δ¹³C analyses both at natural abundance and in tracer studies. More recently, compound‐specific isotope analysis (CSIA) has become established, whereby organic constituents are separated online by gas or liquid chromatography before oxidation and analysis of CO₂ for constituent δ¹³C. Theoretically, there should be concordance between bulk δ¹³C measurements and carbon‐weighted δ¹³C measurements of carbon‐containing constituents. To test the concordance between the bulk and CSIA, fish oil was chosen because the majority of carbon in fish oil is in the triacylglycerol form and ～95% of this carbon is amenable to CSIA in the form of fatty acids. Bulk isotope analysis was carried out on aliquots of oil extracted from 55 fish samples and δ¹³C values were obtained. Free fatty acids (FFAs) were produced from the oil samples by saponification and derivatised to fatty acid methyl esters (FAMEs) for CSIA by gas chromatography/combustion/isotope ratio mass spectrometry. A known amount of an internal standard (C15:0 FAME) was added to allow analyte quantitation. This internal standard was also isotopically calibrated in both its FFA (δ¹³C = ?34.30‰) and FAME (δ¹³C = ?34.94‰) form. This allowed reporting of FFA δ¹³C from measured FAME δ¹³C values. The bulk δ¹³C was reconstructed from CSIA data based on each FFA δ¹³C and the relative amount of CO₂ produced by each analyte. The measured bulk mean δ¹³C (SD) was ?23.75‰ (1.57‰) compared with the reconstructed bulk mean δ¹³C of ?23.76 (1.44‰) from CSIA and was not significantly different. Further analysis of the data by the Bland‐Altman method did not show particular bias in the data relative to the magnitude of the measurement. Good agreement between the methods was observed with the mean difference between methods (range) of 0.01‰ (?1.50 to 1.30). Copyright © 2010 John Wiley & Sons, Ltd.     

The in situ oxidation-Wittig reaction of alpha-hydroxyketones

In situ oxidation-Wittig methodology has been applied to alpha-hydroxyketones avoiding the problems normally associated with alpha-ketoaldehydes; the procedure is practically simple, and in many cases gives high yields of the product gamma-ketocrotonates; the procedure has also been successfully utilised with ethyl glycolate and glycolaldehyde dimer.     

What is 'unfreezable water', how unfreezable is it,and how much is there?

Water that remains unfrozen at temperatures below the equilibrium bulk freezing temperature, in the presence of ice, is sometimes called unfreezable or bound. This paper analyses the phenomenon in terms of quantitative measurements of the hydration interaction among membranes or macromolecules at freezing temperatures. These results are related to analogous measurements in which osmotic stress or mechanical compression is used to equilibrate water of hydration with a bulk phase. The analysis provides formulas to estimate, at a given sub-freezing temperature, the amount of unfrozen water due to equilibrium hydration effects. Even at tens of degrees below freezing, this hydration effect alone can explain an unfrozen water volume that considerably exceeds that of a single 'hydration shell' surrounding the hydrophilic surfaces. The formulas provided give a lower bound to the amount of unfrozen water for two reasons. First, the well-known freezing point depression due to small solutes is, to zeroth order, independent of the membrane or macromolecular hydration effect. Further, the unfrozen solution found between membranes or macromolecules at freezing temperatures has high viscosity and small dimensions. This means that dehydration of such systems, especially at freezing temperatures, takes so long that equilibrium is rarely achieved over normal experimental time scales. So, in many cases, the amount of unfrozen water exceeds that expected at equilibrium, which in turn usually exceeds that calculated for a single hydration shell.     

Effects of chlorine gas exposure on the optical properties of rhodium phthalocyanine films

We investigated the effects of exposing rhodium phthalocyanine films deposited on glass substrates by the Lagmuir-Blodgett technique to chlorine gas. The visual aspect of the films is altered upon chlorination, changing in color from blue to transparent. We performed optical absorption and Raman Scattering measurements on our films prior to and after exposing it to chlorine gas. We observed a pronounced quenching of the characteristic triplet centered around the Q-absorption band at 662 nm as a result of chlorine incorporation. Another absorption band, in the near UV part of the spectrum, is not greatly affected by the process. No new optical structures appear as a consequence of chlorination. Equivalent effects were observed in the Raman spectra. Leaving the previously exposed films in air for several hours results in a slow partial recovery of the optical spectra. This recovery, as well as the amount of original quenching, depends on the amount of time during which the film was exposed to chlorine.     

Competitive facilitated transport through liquid membranes

A mathematical model is presented which solves the dimensionless, transient, non-linear partial differential equations governing the competitive facilitated transport of two gases through a liquid membrane. The model incorporates the mass transfer coefficients in the boundary conditions for the free gas concentrations. Several studies were carried out. A comparison of this model with a steady-state “equilibrium core” model was excellent. Through varying the dimensionless parameters, it was found that gas I would have a higher steady-state facilitation factor than gas 2 if k₁ >k₂ and k_-1k_-2. The boundary conditions and mass transfer coefficients were also varied to see their effects on the facilitation factors. The idea of pumping one of the gases against its concentration gradient was shown to be theoretically possible.