On the reaction of L-ascorbic acid with propylamine under various conditions: quantification of the main products by HPLC/DAD

 The reaction of _L-ascorbic acid (AA) with proteins (protein ascorbylation) has a considerable impact on food processing and health. So far four products have been isolated and identified which can be formed from AA and lysine derivatives. Thus, 2-deoxy-2-(propylamino)ascorbic acid, 3-deoxy-3-(propylamino)ascorbic acid, oxalic acid monopropylamide and oxalic acid dipropylamide were synthesized and an HPLC system for their separation and quantification was developed. Then, mixtures of AA and propylamine, as a model compound for lysine derivatives, were reacted under various conditions and product yields were determined in relation to reaction time, temperature, amine concentration and pH value. The results were discussed in detail and can help to evaluate the contribution of the four products to protein and lysine ascorbylation under different conditions. Received: 2 September 1997 / Revised version: 27 November 1997     

Flavonoid concentrations in the inner leaves of head lettuce genotypes

Typical HPLC profiles of phenolics from head lettuce (butter lettuce) genotypes showed quercetin (Qu) compounds Qu 3-O-glucuronide, Qu 3-O-(6-malonylglucoside), an acidic luteolin (Lu) glycoside, chlorogenic acid and chicoric acid as the main compounds in outer and - except the Lu conjugate - inner leaves.The outer leaves of some genotypes additionally contained cyanidin 3-O-(6-malonylglucoside). The generally marginal flavonoid concentrations of the cores of lettuce heads increased between 10-fold and 20-fold during the illumination of opened inner leaves. This indicated the competence of inner leaves of lettuce heads to perform the light-dependent flavonoid biosynthesis. After hydrolysis of flavonoid extracts from 15 head lettuce varieties, Qu concentrations were detected between 19.4 and 152.1 µg/g dry plant material (DW) in inner leaves and from 417.3 to 2482.7 µg/g DW in outer leaves. While the Qu concentrations of the inner leaves of most genotypes, including the commercial varieties, amounted to about 3% of those found in outer leaves, these proportions were 15% and 19% in two genotypes. Two other varieties showed relatively high Qu values of cores in connection with maximum flavonoid levels of outer leaves. It is indicated that such genotypes may be useful in increasing the flavonoid concentrations in the inner leaves of commercial head lettuce varieties by conventional breeding methods.     

Formamidinium‐Based Dion‐Jacobson Layered Hybrid Perovskites: Structural Complexity and Optoelectronic Properties

Layered hybrid perovskites have emerged as a promising alternative to stabilizing hybrid organic–inorganic perovskite materials, which are predominantly based on Ruddlesden‐Popper structures. Formamidinium (FA)‐based Dion‐Jacobson perovskite analogs are developed that feature bifunctional organic spacers separating the hybrid perovskite slabs by introducing 1,4‐phenylenedimethanammonium (PDMA) organic moieties. While these materials demonstrate competitive performances as compared to other FA‐based low‐dimensional perovskite solar cells, the underlying mechanisms for this behavior remain elusive. Here, the structural complexity and optoelectronic properties of materials featuring (PDMA)FA_n–1Pb_nI_3n+1 (n = 1–3) formulations are unraveled using a combination of techniques, including X‐ray scattering measurements in conjunction with molecular dynamics simulations and density functional theory calculations. While theoretical calculations suggest that layered Dion‐Jacobson perovskite structures are more prominent with the increasing number of inorganic layers (n), this is accompanied with an increase in formation energies that render n > 2 compositions difficult to obtain, in accordance with the experimental evidence. Moreover, the underlying intermolecular interactions and their templating effects on the Dion‐Jacobson structure are elucidated, defining the optoelectronic properties. Consequently, despite the challenge to obtain phase‐pure n > 1 compositions, time‐resolved microwave conductivity measurements reveal high photoconductivities and long charge carrier lifetimes. This comprehensive analysis thereby reveals critical features for advancing layered hybrid perovskite optoelectronics.     

The use of toxicokinetic and toxicodynamic data in risk assessment: an international perspective

Risk assessment of chemicals is a process which is usually based on data derived from animal testing in which the exposure of animals results in toxicological effects. By extrapolation, the dose/exposure in humans, which will not result in toxicological effects ('safe dose', 'safe exposure'), is estimated. Traditional approaches use 'safety factors' or 'uncertainty factors' to extrapolate from animal to man and from the 'mean' subject to the general population, including sensitive subgroups. Traditionally, a default factor of 10 has been used to account for interspecies variation. It is proposed that this factor be subdivided into a subfactor to address the toxicokinetic aspects and a second subfactor for the toxicodynamic aspects. Likewise, a default factor of 10 with subfactors is proposed to account for the intraspecies variability. In the framework of the International Program on Chemical Safety's (IPCS) project on the Harmonization of Approaches to the Assessment of Risk from Exposure to Chemicals, an activity has been initiated to provide guidance to risk assessors on the use of quantitative chemical specific data to account for interspecies variation and interindividual variability in risk assessment. To address the toxicokinetic aspects, the active species, the relevant internal exposure and the adequate metrics must be considered. Data quality and availability, in vitro or in vivo, the route of administration and the relevant dose level are relevant information for interspecies extrapolation. The availability of experimental data, including the relevance of the population studied, the number of subjects and/or samples obtained in the relevant group allow one to estimate the population distribution, e.g. difference between central tendency and given percentiles. In a similar fashion, the toxicodynamic data must be addressed. In addition to the identification of the active chemical species, the relevant endpoint must be determined. In extrapolation from animal to man, in most of the cases, the definitive endpoint (e.g. anemia) is lacking. It can be substituted by in vitro data (e.g. in vitro hemolysis) if it is a key event and relevant for the toxicity in animal as well as in humans. In extrapolating from animal to man, the dose-effect relationship plays an important role. To account for the toxicodynamic variability in the human population, similar aspects have to be taken into consideration, which have been discussed for toxicokinetics. The IPCS document is available at the IPCS website and risk assessors are invited to use the framework and report back their experience with it to enable revision and improvement.     

Metal-Metal Coordination Chemistry: Free Clusters of Group 12 Elements with Sodium

A systematic study of the mass spectra of particles formed in a supersonic nozzle expansion of Zn, Cd, and Hg vapors together with Na was performed. The particles discussed in this paper contain only one heavy atom and less than 12 Na ligands. Mass spectra from the neutral particles were generated by photoionization at five wavelengths (250, 260, 280, 300, and 320 nm) with a slit width corresponding to 16.5 and 3.3 nm, respectively. The abundances were corrected to relative differential ionization cross-sections. Photoionization potentials for Na_n M with 5 < n < 10 and M = Zn, Cd, Hg were measured. Below n = 6 no mixed clusters were found. The first abundance maximum occurred for all M at n = 8. A second maximum was with n = 16 or n = 18 (not covered in this paper). This selectivity can be rationalized by recent ab initio calculations by Fantucci et al. (J. Chem. Phys.; in press) and by jellium calculations, which give a closed shell at n = 8 with the occupations 1s²1p⁶2s². Ionization potentials clearly show a level reversal to 1p-2s-1d in contrast to the homonuclear jellium with 1p-1d-2s. This is similar to previous results with K_nMg (Kappes, M. et al., Chem. Phys. Lett., 1985, 119 : 11). Molecular dynamics simulations with empirical potentials show that the heavy metal migrates to the center of a cube in the frozen asymptote of Na_gM. At finite temperatures and for larger central atoms, a square antiprismal arrangement seems to be more stable.     

Pyrane-derivatives as fragrances and flavors-a study on structure/odour relationships

Summary In this study several 2/H-3,4-dihydropyrane-derivatives, substituted with different unsaturated alkyl groups, have been synthesized. These compounds exhibit pleasant green, fruity and flowery fragrances. The syntheses start from 2H-3,4-dihydropyrane-2-carbaldehydes which are available by dimerisation of acroleine, meth-ylacroleine and ethylacroleine. It was shown that it is possible to induce dimerisation by ultrasonic irradiation. Subsequent Wittig and Horner-Emmons olefinations lead to the desired pyrane derivatives. The odorous character of these compounds is fully described and remarkable structure/odour relationships are discussed.

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Pyran-Derivate als Aroma- und Duftstoffe. Eine Studie über Struktur/Geruchs-Beziehungen

Zusammenfassung In der vorliegenden Untersuchung werden die Synthese und der Geruch verschiedener 2H-3,4-Dihydropyrane, die unterschiedliche olefinische Seitenketten tragen, beschrieben. Alle diese Verbindungen besitzen ein ausgeprägtes grünes, fruchtiges und blumiges Aroma. Die Synthesen nehmen ihren Ausgang von den durch Dimerisation von Acrolein, Methyl- und Ethyl-acrolein zugänglichen 2H-3,4-Dihydropyran-2-carbalde-hyden, wobei gezeigt werden konnte, daß durch Ultraschall-Bestrahlung ebenfalls Dimerisation induziert werden kann. Anschließende Wittig- bzw. Horner-Emmons Reaktionen führen zu den gewünschten Zielverbindungen. Die Geruchseigenschaften dieser Substanzen werden ausführlich beschrieben und etwaige Struktur/Wirkungsbeziehungen diskutiert.