According to the pH-partition hypothesis the charged species of organic compounds do not contribute to lipid bilayer permeation as they generally show negligible partitioning into n-octanol. With this assumption, membrane permeation is related to the molar fraction of the neutral species at a particular pH. A recently developed permeation assay permits us to directly determine pH-dependent permeation of aromatic carboxylic acids. Tb(3+)-loaded liposomes are incubated with aromatic carboxylic acids and upon excitation at the absorption wavelength of the acid, permeation kinetics can be measured as an increase in Tb(3+) luminescence. The anions of the tested acids permeated egg phosphatidylcholine membranes only 12 (2-hydroxynicotinic acid), 66 (salicylic acid), and 155 (dipicolinic acid) times slower than the net neutral species. The anions, therefore, controlled the total permeation already at 1-2 pH units above their pK(a). These results indicate that in contrast to the expectations of the pH-partition hypothesis, lipid bilayer permeation of an acidic compound can be completely controlled by the anion at physiological pH.

Depending on the single rate constants and on the geometry of the system, lipid bilayer permeation may positively, negatively or not correlate with the bilayer affinity of the permeant.

Lipid-bilayer permeation is determinant for the disposition of xenobiotics in the body. It controls the pharmacokinetic behavior of drugs and is, in many cases, a prerequisite for intracellular targeting. Permeation of in vivo barriers is in general predicted from lipophilicity and related parameters. This article goes beyond the empirical correlations, and elucidates the processes and their interplay determining bilayer permeation. A flip-flop model for bilayer permeation, which considers the partitioning rate constants beside the translocation rate constants, is compared with the diffusion model based on Fick's first law. According to the flip-flop model, the ratios of aqueous volumes to barrier area can determine whether partitioning or translocation is rate-limiting. The flip-flop model allows permeation of anions and cations, and expands our understanding of pH-dependent permeation kinetics. Some experimental evidences for ion-controlled permeation at pH 7 are also included in this work.

Background The unmonitored use of complementary medicine in patients with cancer can be associated with an increased risk of safety‐related issues, such as lower adherence to conventional cancer therapies. Training oncology physicians to advise their patients about the effectiveness and safety of these therapies could improve this situation. Methods The objective of this study was to develop and pretest a consultation framework that has high potential to be widely implemented. The framework comprises: 1) a systematically developed and tested, manualized, guided consultation; and 2) blended learning training (e‐learning and communication skills training workshop) to upskill oncology physicians in advising their patients on complementary and integrative medicine (CIM). For this implementation study, mixed methods were used to develop the manual (literature review, consensus procedure, pilot testing) and the training (questionnaires and interviews with oncology physicians and patients with cancer and an examination of the skills in a setting with standardized patients). Results The training was tested with 47 oncology physicians from across Germany. The manual‐guided consultation (context: general information on the setting and communication techniques; inform: consultation duration and content; capture: previous CIM use; prioritize: focus on consultation; advise: evidence‐based CIM recommendations; discuss, advise, accept, or advise against other CIM; concretize advice: summary and implementation; and monitor: documentation) was considered suitable. The structure and time frame (maximum, 20 minutes) of the consultation as well as the training were feasible and well accepted. Conclusions The current study demonstrates that the KOKON‐KTO framework (a German acronym for Competence Network for Complementary Medicine ‐ Consultation Training for Oncology Physicians) is suitable for training oncology physicians. Its implementation can lead to better physician‐patient communication about CIM in cancer.