Motion of a spin probe in hexagonal and lamellar potassium palmitate

Summary Nitroxyl radical Tempol dissolved in the hexagonal liquid-crystalline phase of potassium palmitate experienced a homogeneous time averaged environment. In the lamellar phase the radicals were distributed in two environments of different solvent polarities, which was demonstrated by simulation of the spectra.In both phases the nitroxyl probes were able to tumble comparatively freely (the rotational correlation time a was 0.15–0.9 ns).

---

Zusammenfassung Das Nitroxylradikal Tempol wurde zur Untersuchung der Molekülbeweglichkeit in den verschiedenen Phasen im System Kaliumpalmitat — H₂O benutzt. Die hexagonale, flüssig-kristalline Phase erscheint homogen; in der lamellaren Phase wurden zwei verschiedene Umgebungen mit unterschiedlicher Lösungsmittelpolarität festgestellt. In beiden Phasen waren die Nitroxylradikale relativ frei beweglich ( = 0,15–9,9 nsec).

     

1H NMR spectra and stereochemistry of cis- and trans-5,6-dimethyl-2-oxo-1,4-dioxans

The ¹H NMR spectra of isomeric 5,6-dimethyl-2-oxo-1,4-dioxans have been recorded and the pertinent chemical shifts and coupling constants determined. The parameters indicate that both isomers exist as an equilibrium mixture of interconverting half chair ring conformations.     

On the stereochemistry of 1,4-diheterocyclanes. IV—carbon-13 NMR spectra and structural properties of 1,4-dioxane-2,3-diols and their methyl-substituted derivatives

The 1,4-dioxane-2,3-diols and a number of their methyl-substituted derivatives were synthesized and their ¹³C NMR spectra measured. The configurational properties were studied on the basis of the spectral data and chemical equilibration. For the parent compound the trans configuration is slightly more stable. The hydroxyl groups are predominantly axial. Introduction of a methyl group at the 2 position causes the cis configuration of the hydroxyl substituents to become more stable. The substituent effects on the chemical shifts were calculated and used to test the conformational homogeneity of the compounds. The results indicate a biased (chair) conformation for all the methyl-substituted derivatives which were studied. Methyl groups have strongly predominating equatorial orientation in each case studied.     

Studies on stereoselective [2+2] cycloadditions between N,N-dialkylhydrazones and ketenes

Staudinger-like cycloadditions between chiral, non-racemic N,N-dialkylhydrazones 1 and functionalized ketenes constitute an efficient methodology for the stereoselective construction of the beta-lactam ring. The potential for fine tuning of the dialkylamino auxiliary structure, the availability of a high-yielding deprotection method for the release of the free azetidinones, and the high thermal and chemical stability of hydrazones as N-dialkylamino imines are highlighted as the key elements for the success of the strategy. This last aspect is of particular importance concerning generality: even hydrazones from easily enolizable aldehydes or from formaldehyde reacted to afford the corresponding cycloadducts with high chemical and stereochemical yields. The syntheses of the beta-amino-alpha-hydroxyacids (2R,3S)-phenylisoserine (42) and (2R,3S)-norstatin (45) were accomplished as illustrative examples of the synthetic utility of this procedure. A model system for the cycloaddition of g series auxiliaries was studied by ab initio computational methods. The collected results support a two-step mechanism through zwitterionic intermediates, and explain the observed absolute and relative stereochemistry in terms of the preferred outward cycloaddition to the Re face of the hydrazone.     

Alcoholic Fermentation with Flocculant Saccharomyces cerevisiae in Fed-Batch Process

Studies have been conducted on selecting yeast strains for use in fermentation for ethanol production to improve the performance of industrial plants and decrease production costs. In this paper, we study alcoholic fermentation in a fed-batch process using a Saccharomyces cerevisiae yeast strain with flocculant characteristics. Central composite design (CCD) was used to determine the optimal combination of the variables involved, with the sucrose concentration of 170 g/L, a cellular concentration in the inoculum of 40 % (v/v), and a filling time of 6 h, which resulted in a 92.20 % yield relative to the theoretical maximum yield, a productivity of 6.01 g/L h and a residual sucrose concentration of 44.33 g/L. With some changes in the process such as recirculation of medium during the fermentation process and increase in cellular concentration in the inoculum after use of the CCD was possible to reduce the residual sucrose concentration to 2.8 g/L in 9 h of fermentation and increase yield and productivity for 92.75 % and 9.26 g/L h, respectively. A model was developed to describe the inhibition of alcoholic fermentation kinetics by the substrate and the product. The maximum specific growth rate was 0.103 h^?1, with K _I and K _s values of 109.86 and 30.24 g/L, respectively. The experimental results from the fed-batch reactor show a good fit with the proposed model, resulting in a maximum growth rate of 0.080 h^?1.     

Compact middle-wave infrared Fabry-Perot interferometer with double metallic subwavelength gratings

We demonstrate a compact middle-wave IR (MWIR) Fabry-Perot (FP) interferometer by replacing the traditional distributed Bragg reflectors consisting of thick multilayer films with two identical metallic subwavelength gratings. The transmission efficiency, resonance peak position, and finesse of the FP interferometer can be controlled by tuning the structural parameters. The performance of the MWIR FP interferometer is verified by experiment, which shows its potential application as, for example, narrowband MWIR filter for gas detection.     

Emerging methods and tools for environmental risk assessment, decision-making, and policy for nanomaterials: summary of NATO Advanced Research Workshop

Nanomaterials and their associated technologies hold promising opportunities for the development of new materials and applications in a wide variety of disciplines, including medicine, environmental remediation, waste treatment, and energy conservation. However, current information regarding the environmental effects and health risks associated with nanomaterials is limited and sometimes contradictory. This article summarizes the conclusions of a 2008 NATO workshop designed to evaluate the wide-scale implications (e.g., benefits, risks, and costs) of the use of nanomaterials on human health and the environment. A unique feature of this workshop was its interdisciplinary nature and focus on the practical needs of policy decision makers. Workshop presentations and discussion panels were structured along four main themes: technology and benefits, human health risk, environmental risk, and policy implications. Four corresponding working groups (WGs) were formed to develop detailed summaries of the state-of-the-science in their respective areas and to discuss emerging gaps and research needs. The WGs identified gaps between the rapid advances in the types and applications of nanomaterials and the slower pace of human health and environmental risk science, along with strategies to reduce the uncertainties associated with calculating these risks.     

On the terminology of voice research

This article reviews problems associated with establishment of a scientifically accurate, internationally recognized, multilingual terminology to describe voice. Two strategies for developing terminology are discussed: consensus and dictation. Ontological decisions are considered an integral part of developing terminology. We conclude that terminological problems should be solved by a terminological committee—as yet to be established—as they average from problems in interpreting the literature and the results of voice research. A comprehensive bibliography and audio tape of the multilingual terminology describing voice would help facilitate adaptation and understanding of the terms defined.     

The 13C,H coupling constants in structural and conformational analysis. IV–The rotational dependence of the long-range CH couplings of the aldehyde and hydroxyl protons in salicylaldehyde

The proton-coupled ¹³C NMR spectrum of salicylaldehyde was analysed. The second-order character of the seven independent sub-spectra allowed the signs of most of the couplings to be determined. The input values for the analyses were obtained from the known J(CH) values of benzene, phenol and benzaldehyde using the additivity principle. In most instances, very good agreement between the calculated and observed values was obtained. Significant couplings of the ring carbons to both the aldehyde and hydroxyl protons were also observed. The magnitude of these couplings was very dependent on the stereochemical relationships between the coupled nuclei.