Adsorption controversies

The most possible reason may be in the higher free energy of the protein adsorption on PolyPROPYL A materials. Chemisorbed neutral poly(succinimide) of molecular weight 13000 apparently forms a diffuse interface as predicted by theory (see Sect. 2.2). Controversially, a short polyethyleneimine exists on a surface in a more flat conformation exhibiting almost no excluded volume and producing... 

The use of internal standards is somewhat controversial.115 There is agreement that an internal standard may be used as a correction for injection volume or to correct for pipetting errors. If an internal standard is included before sample hydrolysis or derivatization, it must be verified that the recovery of the internal standard peak is highly predictable. Ideally, the internal standard is unaffected by sample handling. Using an internal standard to correct for adsorptive or chemical losses is not generally approved, since the concentration of the standard may be altered by the conditions of sample preparation. An example of internal vs. external standards is given in Chapter 4. 

Hence, it appeared that the story was complete and the adsorption of hydrogen on platinum understood. However, considerable controversy was arising even as the definitive experiments were being performed. In 1959, Schuldiner carried out kinetic measurements on the H2-evolution reaction... 

Puschmann et al. also carried out a SEXAFS analysis giving an adsorption site shown as A in the inset to Figure 8. The adsorption site of the formate species on copper surfaces in general has, however, proved to be controversial [22,23]. Most recent... 

The question of the species involved in these unusual adsorption states is still controversial. No direct inforaation (such as spectroscopic data) on the nature of the species is available. Only electrocheaical data have been obtained and these require several cross deterainations and careful discussion taking into account the whole experiaental data set and the parallel behaviour of the (100) and (111) orientations. 

Most earlier papers dealt with the mercury electrode because of its unique and convenient features, such as surface cleanness, smoothness, isotropic surface properties, and wide range of ideal polarizability. These properties are gener y uncharacteristic of solid metal electrodes, so the results of the sohd met electrolyte interface studies are not as explicit as they are for mercury and are often more controversial. This has been shown by Bockris and Jeng, who studied adsorption of 19 different organic compounds on polycrystaUine platinum electrodes in 0.0 IM HCl solution using a radiotracer method, eUipsometry, and Fourier Transform Infrared Spectroscopy. The authors have determined and discussed adsorption isotherms and the kinetics of adsorption of the studied compounds. Their results were later critically reviewed by Wieckowski. ... 

The cellular uptake of AS-ODN is an energy-dependent process and takes place in a saturable and sequence-independent manner [120,121]. The exact mechanism of uptake remains controversial. From in vitro experiments, some authors have proposed that the uptake is endocytic and mediated by membrane receptor proteins. The receptor responsible for the cellular uptake of AS-ODNs was reported to consist of both a 30-kDa protein [122] and an 80-kDa membrane protein [121]. However, other workers have argued that AS-ODN binding to membrane proteins is relatively non-specific and is mostly charge associated, consistent with adsorptive endocytosis or fluid-phase pinocytosis [101]. As a result of these conflicting reports, it is unlikely that in vitro data can be safely extrapolated to what occurs in the intact organism. 

Since it is relatively easy to fit experimental adsorption data to a theoretical equation, there is some controversy as to what constitutes a satisfactory description of adsorption. From a practical point of view, any theory that permits the amount of material adsorbed to be related to the specific surface area of the adsorbent and that correctly predicts how this adsorption varies with temperature may be regarded as a success. From a theoretical point of view, what is desired is to describe adsorption in terms of molecular properties, particularly in terms of an equation of state for the adsorbed material, where the latter is regarded as a two-dimensional state of matter. 

Several methods used during the last 30 years in attempts to measure the specific surfaces of coals include gas and vapor adsorption and heats of immersion. The specific surface value obtained for a given coal can vary according to both the type of method used and the particular variant of the method used—e.g., vapor adsorption at different temperatures. The consequent controversies that have been evoked by such contradictory results have led to considerable confusion. Growing evidence suggests that the concept of "specific surface/ when applied to sorbents containing pores with diameters of a few tenths A. or less, has no physical meaning. 

Although these reactions have been researched extensively and are the subjects of numerous patents, the precise reaction mechanism is not fully understood. The controversy has mostly centered on the nature of the oxygen species responsible for ethylene oxide formation (103). The results of various surface characterization studies indicate that there are at least three types of adsorbed oxygen species on silver monoatomic chemisorbed oxygen, diatomic (molecular) oxygen, and subsurface oxygen. The first results from a dissociative adsorption of oxygen on a silver surface ... 

---