Discussion on the method for the measurement of the flexural modulus of coupled materials and reasons of the shifts of theQ −1 maxima caused by coupling

Summary When measuringQ ^–1 and the flexural resonance frequency of bars clamped at one end, constituted by a viscoelastic polymeric material glued to a rigid support of modulusE ₁, it is possible to calculate the componentsE ₂ andE ₂ of the complex elastic modulus of the polymeric material examined. In this work the minimum (critical) value of the ratioa=E ₂ /E ₁=a _c and the values of the ratioQ ₂ ^–1/Q ^–1=F ₁ are evaluated beyond which no exact calculation ofE ₂ and ofQ ₂ ^–1 is possible.Within the confidence limits of the linear viscoelasticity theory, these values depend on the accuracy of measurement of both frequency and resonance curve, as well as on the instrument employed, on the operating temperature and on the ratio between the thicknesses of the two coupled materials.In order to keep outside the critical conditions, the most convenient method involves the use of measurements of coupled test-pieces having different ratiosz between their thicknesses and of supports having different modulusE ₁, depending on the field of temperature of the analysis ofE ₂ and tg ₂ concerning and E.P.R. elastomer and a vulcanized cis-1,4 polyisoprene in very wide ranges of temperature comprising the glass transition. Moreover, it is demonstrated by analysis the shift on the temperature axis of the tg maximum of the composite test-piece with respect to the position of the tg maximum of the polymeric material alone.With 11 figures and 1 table     

Marine Sediments and Snow from Ross Sea Region (Antarctica) Dating by 210Pb Method

Abstract

²¹⁰Pb is widely used to determine accumulation rates in order to obtain a time scale in environmental samples. The most accurate method uses the determination of ²¹⁰Pb via its grand-daughter ²¹⁰Po by alpha spectrometry. Unfortunately this method requires a complex wet-chemistry procedure to achieve the separation of ²¹⁰Po from its matrix. In this work a simplified procedure for the chemical separation of ²¹⁰Po is proposed and applied to three marine sediment cores and a 10 m snow core collected in Antarctica. The calculated sedimentation rates for marine sediments range from 0.053 to 0.071 cm y^?1. The mean annual accumulation rate for the snow is 16.6 cm y^?1 w.e. A comparison with literature data in the same region is given.     

Boosting Conjugate Addition to Nitroolefins Using Lithium Tetraorganozincates: Synthetic Strategies and Structural Insights

We report the first transition metal catalyst- and ligand-free conjugate addition of lithium tetraorganozincates (R₄ZnLi₂) to nitroolefins. Displaying enhanced nucleophilicity combined with unique chemoselectivity and functional group tolerance, homoleptic aliphatic and aromatic R₄ZnLi₂ provide access to valuable nitroalkanes in up to 98 % yield under mild conditions (0 °C) and short reaction time (30 min). This is particularly remarkable when employing β-nitroacrylates and β-nitroenones, where despite the presence of other electrophilic groups, selective 1,4 addition to the C=C is preferred. Structural and spectroscopic studies confirmed the formation of tetraorganozincate species in solution, the nature of which has been a long debated issue, and allowed to unveil the key role played by donor additives on the aggregation and structure of these reagents. Thus, while chelating N,N,N’,N’-tetramethylethylenediamine (TMEDA) and (R,R)-N,N,N’,N’-tetramethyl-1,2-diaminocyclohexane (TMCDA) favour the formation of contacted-ion pair zincates, macrocyclic Lewis donor 12-crown-4 triggers an immediate disproportionation process of Et₄ZnLi₂ into equimolar amounts of solvent-separated Et₃ZnLi and EtLi.     

Superior Antibacterial Activity of Integral Lemon Pectin Extracted via Hydrodynamic Cavitation

Pectin extracted via hydrodynamic cavitation in water only from waste lemon peel and further isolated via freeze drying displays significant antibacterial activity against Staphylococcus aureus, a Gram positive pathogen which easily contaminates food. The antibacterial effect of the new IntegroPectin is largely superior to that of commercial citrus pectin, opening the way to advanced applications of a new bioproduct now obtainable in large amounts and at low cost from citrus juice industry's waste.     

Introduction of 4(S)-oxazolidineacetic acid, 2-oxo (D-Oxac) motif in a polypeptide chain: synthesis and conformational analysis

A four step synthesis of 4(S)-oxazolidineacetic acid, 2-oxo benzyl ester (D-Oxac-OBn) from L-Asp-OH in 45% overall yield is reported. The formation of by-products is completely avoided, by microwave irradiation and by the use of caesium carbonate as base. Moreover the synthesis and IR and 1H NMR conformational analysis of the tetramers Boc-L-Val-D-Oxac-L-Ala-OBn and Boc-L-Val-D-Oxac-Aib-L-Ala-OBn in solution is reported.     

Full enzymatic hydrolysis of commercial sucrose laurate by immobilized-stabilized derivatives of lipase from Thermomyces lanuginosa

Sucrose laurate is a detergent that is useful for various biochemical applications because it is a green compound and is easily degradable after hydrolysis with a lipase or esterase. One problem observed in the process of sucrose laurate degradation is that most commercial detergent preparations are impure, necessitating the hydrolysis of all of the sucrose esters present in the preparation, all of them with detergent properties. In this article, a highly active catalyst, which is able to perform the hydrolysis of commercial sucrose laurate, is presented. The use of glyoxyl agarose preparations of a previously aminated Thermomyces lanuginosa lipase (TLL) enabled complete hydrolysis, in less than 30 min, of all of the compounds that comprise the mixture. In addition, this derivative is stable in the presence of 20% ethanol, which is necessary to prevent microbial contamination.