Cell-penetrating peptides (CPPs) are able to traverse cellular membranes and deliver macromolecular cargo. Uptake occurs through both endocytotic and nonendocytotic pathways, but the molecular requirements for efficient internalization are not fully understood. Here we investigate how the presence of tryptophans and their position within an oligoarginine influence uptake mechanism and efficiency. Flow cytometry and confocal fluorescence imaging are used to estimate uptake efficiency, intracellular distribution and toxicity in Chinese hamster ovarian cells. Further, membrane leakage and lipid membrane affinity are investigated. The peptides contain eight arginine residues and one to four tryptophans, the tryptophans positioned either at the N-terminus, in the middle, or evenly distributed along the amino acid sequence. Our data show that the intracellular distribution varies among peptides with different tryptophan content and backbone spacing. Uptake efficiency is higher for the peptides with four tryptophans in the middle, or evenly distributed along the peptide sequence, than for the peptide with four tryptophans at the N-terminus. All peptides display low cytotoxicity except for the one with four tryptophans at the N-terminus, which was moderately toxic. This finding is consistent with their inability to induce efficient leakage of dye from lipid vesicles. All peptides have comparable affinities for lipid vesicles, showing that lipid binding is not a decisive parameter for uptake. Our results indicate that tryptophan content and backbone spacing can affect both the CPP uptake efficiency and the CPP uptake mechanism. The low cytotoxicity of these peptides and the possibilities of tuning their uptake mechanism are interesting from a therapeutic point of view.

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Because of their unique photophysical properties, sensitively depending on environment, ruthenium dipyridophenazine (dppz) complexes are interesting as probes for cellular imaging with fluorescence microscopy. Here three complexes derivatized with alkyl ether chains of varied length, which exhibit distinctly different cellular staining patterns by confocal laser scanning microscopy, are studied regarding their binding preference for rRNA compared with calf thymus DNA (ct-DNA) and phospholipid membranes. Co-staining with commercial RNA and membrane-specific dyes shows that whereas the least lipophilic complex exclusively stains DNA inside the nucleus, the most lipophilic complex preferentially stains membrane-rich parts of the cell. Interestingly, only the intermediate lipophilic complex shows intense staining of the RNA-rich nucleoli. The intracellular localizations of the probes correlate with their binding preferences concluded from spectroscopy measurements.

The reaction of MoCl62" or MoCl6" with Mo(CO)4Cl3~inCH2Cl2 results in the formation of Mo2Cl,3" and MoCl92", respectively. The temperature dependence of the magnetic moment of the latter is shown to be hi accord with the thermal equilibrium 5 = */2 4* S = 3/2, while its infrared spectrum can be readily assigned assuming a bioctahedral, D3h structure. It is easily reduced to Mo2C193_. The reaction of Mo2Cl92' with Mo(CO)4Cl3" leads to Mo3C1123" whose trinuclear structure was verified from conductivity measurements. Both the electronic and the infrared spectra are in accord with a linear, trioctahedral, face-shared structure (unlike Re3Cl123"). Magnetic moments in solution are in qualitative agreement with the thermal equilibrium 5 = '/2 & S = 3/2.