These observations agree with TEM observations of sectioned walls. In the secondary callose wall, for which no structure is visible using TEM, cryo-FESEM also revealed a 50 nm lattice consisting of longer fibers, approximately 10-15 nm wide, with rod-like, thinner interconnections at angles of approximately 90
degrees with the longer fibers. Such architecture may reflect functional needs with respect to porosity and mechanical strength. The wall does not form a mechanical barrier to interaction with the environment and is gained at low cost. Cryo-FESEM additionally revealed another special feature of the wall: the tubes Galardin were tiled with scales or rings that were highly conspicuous after pectin extraction with EDTA. These rings cause the typical banding patterns of pectin that are commonly seen in pollen tubes during oscillatory growth, as confirmed by staining with toluidine blue as well as by DIC microscopy. Growth analysis by VEC-LM showed that the ring-or scale-like structures of the primary wall consist of material deposited prior to the growth pulses. The alternating band pattern
seen in the callose wall is probably imposed by constrictions resulting from the rings of the primary wall.”
“A copolymer comprising of 2-acrylamido-2-methyl Stattic price propane sulfonic acid (AMPS (R)) and itaconic acid (molar ratio 1 : 0.32) was synthesized by aqueous free radical polymerization and probed as high temperature retarder for oil well cement. Characteristic properties of the copolymer including molar masses (Mw and Mn), polydispersity index and anionic Protein Tyrosine Kinase inhibitor charge amount were determined. The copolymer possesses a Mw of similar to 2 x 105 g/mol and is highly anionic. HT/HP consistometer tests confirmed effectiveness of the retarder at temperatures up to 200 degrees C. The working mechanism of NaAMPS (R)-co-itaconic acid was found to rely exclusively on its huge calcium binding capacity (5 g calcium/g copolymer). It reduces the amount of freely dissolved, nonbound calcium ions present in cement pore solution and thus hinders the growth of cement hydrates because of lack of calcium. The value for the
calcium binding capability is 46 times higher than the stoichiometric amount per ?COO- functionality. Consequently, calcium also coordinates to other donor atoms present in the retarder. NaAMPS (R)-co-itaconic acid also adsorbs onto cement, as was evidenced by TOC analysis of cement filtrates, zeta potential measurement and decreased rheology of cement pastes. However, adsorption plays no role in the retarding mechanism of this copolymer. Combination of NaAMPS (R)-co-itaconic acid retarder with a common CaAMPS (R)-co-NNDMA fluid loss additive (FLA) revealed that competitive adsorption on cement between these two admixtures occurs. The retarder fills interstitial adsorption sites on cement located between those occupied by the larger FLA molecules.