Dixon's Q-test and Student's t-test to assess analog internal standard response in nonregulated LC-MS/MS bioanalysis.

Aim: In bioanalytical assays, analyte response is normalized to an internal standard response. When the internal standard works well, it compensates for processing and detection variability. However, in case the internal standard introduces additional variability, due to addition errors or other issues, scientists need to identify this. Results: A new method, using a Q-test for outliers and a t-test to compare internal standard response from different sample types, is applied to 15 cases. The results show that the Q-test/t-test, which uses confidence level rather than arbitrary cut-points, is more discerning of deviations compared with widely used methods. Conclusion: This work may improve the quality of and rationale for the internal standard response monitoring method.

Evaluation, identification and impact assessment of abnormal internal standard response variability in regulated LC-MS bioanalysis.

Internal standard (IS) plays an important role in LC-MS bioanalysis by compensating for the variability of the analyte of interest in bioanalytical workflow. Due to the complexity of biological sample compositions and bioanalytical processes, a certain level of IS response variability across a run or a study is anticipated. However, an extensive variability may raise doubts to the accuracy of the measured results and also suggest nonoptimal analytical method. In this current paper, recent publications and guidelines regarding IS response in LC-MS bioanalysis were thoroughly reviewed with focus on the evaluation, identification and impact assessment of 'abnormal' IS response variability. A systematic decision tree was proposed to facilitate investigation into abnormal IS response variability after each run.

Peptide-Dendron Hybrids that Adopt Sequence-Encoded ß-Sheet Conformations.

Rational design rules for programming hierarchical organization and function through mutations of monomers in sequence-defined polymers can accelerate the development of novel polymeric and supramolecular materials. Our strategy for designing peptide-dendron hybrids that adopt predictable secondary and quaternary structures in bulk is based on patterning the sites at which dendrons are conjugated to short peptides. To validate this approach, we have designed and characterized a series of ß-sheet-forming peptide-dendron hybrids. Spectroscopic studies of the hybrids in films reveal that the peptide portion of the hybrids adopts the intended secondary structure.

Hexagonally Ordered Arrays of α-Helical Bundles Formed from Peptide-Dendron Hybrids.

Combining monodisperse building blocks that have distinct folding properties serves as a modular strategy for controlling structural complexity in hierarchically organized materials. We combine an α-helical bundle-forming peptide with self-assembling dendrons to better control the arrangement of functional groups within cylindrical nanostructures. Site-specific grafting of dendrons to amino acid residues on the exterior of the α-helical bundle yields monodisperse macromolecules with programmable folding and self-assembly properties. The resulting hybrid biomaterials form thermotropic columnar hexagonal mesophases in which the peptides adopt an α-helical conformation. Bundling of the α-helical peptides accompanies self-assembly of the peptide-dendron hybrids into cylindrical nanostructures. The bundle stoichiometry in the mesophase agrees well with the size found in solution for α-helical bundles of peptides with a similar amino acid sequence.