Artifacts aggregation

SEC analysis shows that some samples have a blmodal MWD. At this time it is not possible to tell whether the bimodallty is an artifact of the polymerization mechanism or, perhaps, a consequence of partial hydrolysis of the polymer i.e., the high MW shoulder in Figure 5 may be due to the formation of aggregates through Intermolecular dipolar interactions of P-OH side groups or to polymer molecules crosslinked by P-O-P bonds. 

However, careful kinetic measurements on related systems showed the invalidity of wire-type behavior [41]. Furthermore, Sen and coworkers [42] recently showed that the appearance of rapid, long-distance charge transfer for metallointercalators may be an artifact caused by the formation of aggregates. Currently, there are no data that clearly support the existence of a coherent transfer process in DNA over a distance greater than one or two base pairs [43, 44]. 

Finally, a feedback mechanism has often been used to explain observed (negative and positive) deviations from the Scatchard type plots or nonunity slopes of the nonsaturated portion of the logarithmic Michaelis-Menten plots (e.g. [209]). When no artifacts are present (cf. [197,198]), deviations can indeed be interpreted to indicate that the intrinsic stability or dissociation rate constants vary with the number of occupied transport sites. Nonetheless, several other physical explanations, including multiple carriers, non 1 1 binding, carrier aggregation, etc. must also be considered. 

The clusters which obey Eq. (61) are self similar to each other. Sometimes, however, the curve flattens at large molar masses and may form another straight line with a different exponent. Such behavior is an indication of a limitation in the separation capability of the column (or some other artifacts) or it is the result of large particles with a different fractal behavior. These particles can be aggregates or clusters of a higher branching density. Similar behavior can be observed also from the molar mass dependence of the viscosity. An example will be shown in the next section. 

Great care has to be taken in the analytical characterization of synthetic cyclic peptides.[73] The major side reactions during cyclization are epimerization of the C-terminal amino acid residue and cyclodimerization. Cyclodimers can be detected by mass spectrometry, although the analysis is not trivial, because artifacts do occur in some ionization techniques such as ES-MS as a result of aggregation.1 1 Ll 121 Real dimers can be detected as double-charged particles with mlz values identical to the cyclic monomers, but with a mass difference of 0.5 amu in the resolved isotope signals. The mass difference of the corresponding monomer is 1 amu. The cyclodimerization has received some attention as a direct method for the synthesis of C2-symmetrical cyclic peptides.[62 67 94113 115]... 

If preparative or instrumental artifact is ruled out, the universal occurrence of red-shifted Cotton effects with a-helical character in all the membranes studied points to a common property of the proteins in biological membranes. The ORD results from lipid-free mitochondrial structural protein and erythrocyte ghost protein are consistent with assigning the red shift in these membranes to aggregated protein. It is, therefore, reasonable that similar protein-protein association may occur in all membranes. Ionic requirements for membrane stability could then reflect in part the requirements for protein-protein association. To some extent the molecular associations which stabilize membranes, therefore, may be protein-protein as well as lipid-lipid in nature. 

If the tc term in Foltmann s equation is replaced by r, the intercept of the plot, x, approaches zero. This indicates that the difference between t and tc is not a lag time between enzymic action and aggregation, but is an artifact of the measurement method. The x term added to Storch and Segelcke s equation by Holter is not necessary if r is used instead of tc (Collinge and Brown 1986). 

The effect of varying slurry concentrations of silica/solvent on the available hydroxyl concentration per unit surface area is shown in Figure 9. This effect has not been observed previously, and it may be an artifact arising from the manner in which the experiments were performed. Many finely divided silicas occur as aggregates (48) which are unlikely to be broken up at higher slurry concentrations. Any reactive hydroxyl... 

One of the main causes of artifacts in the spectroscopy of proteins is the frequent tendency of proteins to aggregate, either during the folding step in recovery from inclusion bodies or as a result of the delicate balance of solubility of many proteins. For this reason, it is important to pay strict attention to monitoring aggregation (see Strategic Planning, discussion of Clarification of Solutions). 

Given the difficulties one should view with suspicion any deconvolution features that are not repeatable, that are functions of a particular constraint, and those that occur at the extremes of the range. Often these are artifacts. A physical explanation for multiple peaks should be sought. Initial aggregation should lead to doublets (Figure 5) and triplets, and fusion should lead to a continuum. Invoking aggregation to explain widely spaced peaks is not sufficient. 

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