On the Nature of the Rotational Energy Barrier of Atropisomeric Hydrazides

N-N atropisomers represent a useful class of compounds that has recently received important attention from many research groups. This article presents an in-depth analysis of the energy barrier needed for the racemization process of atropoisomeric hydrazides, combining an experimental and computational approach. The focus is on examining how electronic and steric factors impact the racemization process. The results obtained indicate that the barrier observed during the racemization process mainly arises from an increase in the p-orbital character of the nitrogen atoms

Expanding the use of dynamic electrostatic repulsion reversed-phase chromatography: An effective elution mode for peptides control and analysis

Bioactive peptides are increasingly used in clinical practice. Reversed-phase chromatography using formic or trifluoroacetic acid in the mobile phase is the most widely used technique for their analytical control. However, sometimes it does not prove sufficient to solve challenging chromatographic problems. In the search for alternative elution modes, the dynamic electrostatic repulsion reversed-phase was evaluated to separate eight probe peptides characterised by different molecular weights and isoelectric points. This technique, which involves TBAHSO4 in the mobile phase, provided the lowest asymmetry and peak width at half height values and the highest in peak capacity (about 200 for a gradient of 30 min) and resolution concerning the classic reversed-phase. All analyses were performed using cutting-edge columns developed for peptide separation, and the comparison of the chromatograms obtained shows how the dynamic electrostatic repulsion reversed-phase is an attractive alternative to the classic reversed-phase

Squamous cell carcinoma of the brain with sarcoma-like stroma

A cerebral neoplasm containing a well differentiated epidermoid cyst surrounded by islands of infiltrating squamous cell carcinoma and a pleomorphic spindle cell stroma was described. By immunoperoxidase staining all these components contained keratin. The lesion was therefore similar to malignant squamous cell lesions with sarcoma-like stroma occurring in other body sites

A Brief Review of Nozzle Spray Drop Size Measurement Techniques

Spray application of Plant Protection Products (PPP) is affected by many factors, among which drop size distribution is the most important. In fact, the correct spray spectrum ensures the required dose on the target, minimizes off-target losses due to evaporation, drift and run-off, and enhances the operator safety in terms of inhalation and dermal exposure. This study reports a brief review of the most common drop size measurement techniques present in the literature