The reaction of a mixture of [NPCl2]n and Cs2CO3 first with (R)-(+)-1,1′-binaphthyl-2,2′diol (HO-C10H6-C10H6-OH) (binaphthol) and subsequently with phenol (HO-C6H5) in refluxing 1,4dioxane gave the series of the optically active random copolymers {[NP(O2C20H12)]x[NP(OC6H5)2]1-x}n (2). Absolute molecular weight distributions and radius of gyration have been determined by size exclusion chromatography, using simultaneously multiangle light scattering and differential refractive index detectors. The dependence of the dimensions of the polymers on the molecular weight through the corresponding scaling laws is studied. In addition, a stereochemical study of homopolymers [NP(O 2C20H12)]n 1 and copolymers 2 based on the CD exciton chirality method is also included. The reaction of the partially substituted polymer [NP(R-O2C20H12)0.4(Cl2)0.6]n with the stoichiometric amount of racemic binaphthol, or with a large excess of the latter, in the presence of Cs2CO3 gave the same polymer [NP(R-O2C20H12)0.4-(rac-O2C20H12)0.4]n [(-)-3] irrespective of the amount of racemic binaphthol used, showing no enantiomeric induction by the R-binaphthoxy units already present in the polymer.

Four different pectinesterase isoforms, with different isoelectric points, have been detected and purified from sweet cherries (Prunus avium L.):  a basic form (PE I, pI > 8.66), a neutral form (PE II, pI = 7.05), and two acidic forms (PE III, pI = 6.36); PE IV, pI = 5.24). The molecular weight (MW) of PE I was 35.4 kDa determined by sodium dodecyl sulfate−polyacrylamide gel electrophoresis (SDS−PAGE) and 27.2 kDa determined by filtration through Sephadex G-75 SF. PEs II−IV had the same MW in SDS−PAGE (49.8 kDa) as by filtration through Sephadex G-75 SF (55.9 kDa). PEs I and IV appeared to be the most abundant forms, with K m values of 1.03 and 74.6 μg·mL-1 apple pectin, respectively. The PE isoforms differ in optimum pH and thermal stability, PEs II and IV being the most thermostable. All four isoforms are activated by calcium and sodium cations and inactivated by d-galacturonic acid. Keywords: Sweet cherries; Prunus avium L.; Rosaceae; pectinesterase; isoenzymes; cell wall

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In this study the authors analysed which objective mechanical parameters, obtained by means of penetration, shear and Kramer shear cell tests, best explain the results obtained through sensorial assessment of the texture of six varieties of sweet cherry, and the changes undergone therein during the freezing process. The results suggest that the mechanical parameters selected should be independent of sample weight and volume, and that sample preparation should be as non-destructive as possible. All the mechanical test parameters used in this work discriminate between varieties, but not all are useful for assessing the effect of freezing. The maximal force displayed on the shear-test curve is the parameter that best reflects the firmness of the product whether fresh or frozen. The slope of the penetration-test curve best reflects the variations in turgidity of the fruit as a consequence of freezing.

: Thermal and calcium pretreatments applied to preserve the sweet cherry texture by the freezing/thawing process produced biochemical changes in the pectic substances and ultrastructural alterations to the cells and tissues, which were visible under scanning electron microscopy. Partial dehydration of the epidermic tissue caused by calcium (100 mM CaCl2) and thermal (50 °C/10 min) pretreatment attenuated the surface damage produced by freezing. However, pretreatment at 70 °C/2 min caused partial destruction of the epidermic tissue and plasmolysis of the parenchymatic cells. After freezing, the cell walls in the parenchymatic tissue of the fruits pretreated with 100 mM CaCl2 exhibited swelling as a result of gelling of the cell‐wall pectic material. Thermal pretreatments increased the ethylenediaminetetraacetic acid (EDTA)‐soluble pectin fraction and reduced the degree of pectin esterification. Thermal treatments at 70 °C, without immersion in calcium, reduced the water‐ and pectinase‐soluble pectin fractions, whereas immersion in calcium prevented depolymerization of these fractions. Immersion in 100 mM CaCl2 increased the water‐soluble pectin fraction.

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A rapid and sensitive method of detecting pectinesterase activity following electrophoresis or isoelectric focusing in polyacrylamide gels is described. The method uses ruthenium red and requires no addition of substrate when making the gels, thus obviating direct enzyme-substrate contact during electrophoresis. Because of its versatility, the method can be used in a wide variety of applications, such as plant and microbial taxonomy, enzyme purification and characterization, or as an analytical method in fresh and processed plant technology.

The polycondensation of methyl N-(l2-hydroxydodecanoyl)-o-aminoalkanoates (HO(CH3, lCONH(CH3xCOOCH,) has been studied as a source of the alternating polyesteramides [O(CH2), ,CONH(CH2)xCO],, and the properties of the products compared with those of equivalent random copolymers of similar co-unit ratio. Polymerization of the esters with x = 10 and 1 1 occurred straight-forwardly, giving crystalline products which were distinguishable from the random counterparts by DSC but not by 67 MHz l3C NMR. For x = 5 the reaction was complicated by progressive partial elimination of the amide moiety as 6-hexanolactam and by transamidation leading, for the polymer of highest amide content obtained, to an imperfect structure with ca. 76% of the sub-units in alternating arrangement, the remainder being composed of oligoester and diamide units. This deviation from ideality has been elucidated by a study of the 13C NMR spectra of a wide range of model compounds which has yielded criteria for the recognition of oligomeric iminohexanoyl units, and by the NMR and MS examination of the products of aminolytic degradation. The results explain the multiple signals found in the 13C NMR spectra of the imperfectly alternating polymer (x = 5) and of its random analogues.