Mutational effects on the folding dynamics of a minimized hairpin.

The fold stabilities and folding dynamics of a series of mutants of a model hairpin, KTW-NPATGK-WTE (HP7), are reported. The parent system and the corresponding DPATGK loop species display submicrosecond folding time constants. The mutational studies revealed that ultrafast folding requires both some prestructuring of the loop and a favorable interaction between the chain termini in the transition state. In the case of YY-DPETGT-WY, another submicrosecond folding species [Davis, C. M., Xiao, S., Raleigh, D. P., and Dyer, R. B. (2012) J. Am. Chem. Soc. 134, 14476-14482], a hydrophobic cluster provides the latter. In the case of HP7, the Coulombic interaction between the terminal NH3(+) and CO2(-) units provides this; a C-terminal Glu to amidated Ala mutation results in a 5-fold retardation of the folding rate. The effects of mutations within the reversing loop indicate the balance between loop flexibility (favoring fast conformational searching) and turn formation in the unfolded state is a major factor in determining the folding dynamics. The -NAAAKX- loops examined display no detectable turn formation propensity in other hairpin constructs but do result in stable analogues of HP7. Peptide KTW-NAAAKK-WTE displays the same fold stability as HP7, but both the folding and unfolding time constants are greater by a factor of 20.

Analysis of Drug-Related Impurties by HPLC in Ciprofloxacin Hydrochloride Raw Material.

Objectives: In this study, we report the quality control results of drug-related impurity analysis of seven raw materials of ciprofloxacin hydrochloride marketed in Algeria. Materials and Methods: According to the European Pharmacopoeia (Eur. Ph.), high-performance liquid chromatography (HPLC) was used to analyze (B, C, D and E) impurities, while thin layer chromatography (TLC) used to control impurity A. Results: HPLC analysis showed that the C1, C2, C3, C4, and C6 samples have individual contents of specified impurities (B, C, D, E), unspecified and the total of all present impurities conform to norms. The C5 sample contains a very high content (0.579%) of impurity C, which is a photodegradation product and the impurities total (0.625%) exceeding limit, while C7 sample has a slightly higher content (0.118%) of unspecified impurity. The control solution of impurity A was not migrated in all developed TLC plates, so the system is not compliant, for this reason, an HPLC analysis protocol was developed. Conclusion: The results showed that impurity A content conformed in all samples except for the C6 sample, which has equal content to the limit. Therefore, we recommend revising the detecting technique of impurity A by TLC in the Eur. Ph. or replacing it with a more sensitive technique such as HPLC.