A novel compound consisting of a cationic porphyrin covalently attached to a derivative of polymyxin B has been synthesized and presents enhanced activity and targeting properties compared to the usual cationic porphyrins recognized as efficient photosensitizers in photodynamic antimicrobial chemotherapy (PACT). A synthesis pathway was established to preserve the bactericidal activity of the peptide. Accordingly, the N-terminal amino acid (l-2,4-diaminobutyric acid) of polymyxin B (PMB) was switched for a cysteine residue. Then, the resulting derivative of PMB was covalently bound to 5-(4-aminophenyl)-10,15,20-tri(4-N-methylpyridyl)-21H,23H-porphyrin using a thiol-maleimide "click" coupling. The peptide-coupled photosensitizer has demonstrated an improved PACT efficiency compared to the cationic porphyrin alone. This enhancement has been observed against Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli in particular. Flow cytometry analyses and confocal imaging microscopy demonstrated that the porphyrin-peptide conjugate selectively adhered to the cell walls of either Gram-positive or Gram-negative bacteria, thus justifying the damages induced by singlet oxygen production.

Potential of hydrogen (pH) is one of the most relevant parameters characterizing aqueous solutions. In biology, pH is intrinsically linked to cellular life since all metabolic pathways are implicated into ionic flows. In that way, determination of local pH offers a unique and major opportunity to increase our understanding of biological systems. Whereas the most common technique to obtain these data in analytical chemistry is to directly measure potential between two electrodes, in biological systems, this information has to be recovered in-situ without any physical interaction. Based on their non-invasive optical properties, fluorescent pH-sensitive probe are pertinent tools to develop. One of the most notorious pH-sensitive probes is fluorescein. In addition to excellent photophysical properties, this fluorophore presents a pH-sensitivity around neutral and physiologic domains. This review intends to shed new light on the recent use of fluorescein as pH-sensitive probes for biological applications, including targeted probes for specific imaging, flexible monitoring of bacterial growth, and biomedical applications.

In order to highlight the potential of photodynamic antimicrobial chemotherapy in case of infections by antibiotic resistant-strains, a new antimicrobial peptide conjugate has been synthesized, consisting of a derivative of polymyxin B and a cationic porphyrin covalently attached together to a spacer. A polymyxin-derived moiety was subjected to a primary structural modification in the replacement of four diaminobutyrate residues with lysine ones. This modification was done in order to strongly reduce bactericidal activity, with the aim to eliminate the potential rise of polymyxin-resistant strains. Despite this modification, this new conjugate displayed a strong photobactericidal activity against Gram-positive as well as Gram-negative bacteria. It was further shown that this conjugate was able to strongly stick to the cell walls of either kind of strain, thus helping to inactivate bacteria through the production of reactive oxygen species under light irradiation.

Despite advances achieved over the last decade, infections caused by multi-drug-resistant bacterial strains are increasingly becoming important societal issues that need to be addressed. New approaches have already been developed in order to overcome this problem. Photodynamic antimicrobial chemotherapy (PACT) could provide an alternative to fight infectious bacteria. Many studies have highlighted the value of cationic photosensitizers in order to improve this approach. This study reports the synthesis and the characterization of cationic porphyrins derived from methylimidazolium and phenylimidazolium porphyrins, along with a comparison of their photophysical properties with the well-known N-methylpyridyl (pyridinium) porphyrin family. PACT tests conducted with the tetracationic porphyrins of these three families showed that these new photosensitizers may offer a good alternative to the classical pyridinium porphyrins, especially against S.aureus and E.coli. In addition, they pave the way to new cationic photosensitizers by the means of derivatization through amide bond formation.

Following light irradiation, a new nanomaterial, elaborated from CNCs, chlorin-e6 and polymyxin B, demonstrated efficiency against Gram-negative bacteria (Escherichia coli,Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus,Staphylococcus epidermidis).

This article describes a new synthetic method for obtaining three water soluble porphyrins. The more sophisticated porphyrin [5-(4-N-dodecylpyridyl)-10,15,20-tri(4-N-methylpyridyl)-21H,23H-porphyrin tetraiodide], also named C12 porphyrin, was obtained through a three step methodology. The improvements, compared to syntheses described in the literature, mostly concern the purification procedures. The photophysical properties of the three porphyrins are described and the C12 porphyrin presents a very good (1)O2 yield compared to its chemical intermediates. This porphyrin seems to be a very promising candidate for PDT applications.

Establishing the rapid and accurate diagnosis of sepsis is a key component to the improvement of clinical outcomes. The ability of analytical platforms to rapidly detect pathogen-associated molecular patterns (PAMP) in blood could provide a powerful host-independent biomarker of sepsis. A novel concept was investigated based on the idea that a pre-bound and fluorescent ligand could be released from lectins in contact with high-affinity ligands (such as PAMPs). To create fluorescent ligands with precise avidity, the kinetically followed TEMPO oxidation of yeast mannan and carbodiimide coupling were used. The chemical modifications led to decreases in avidity between mannan and human collectins, such as the mannan-binding lectin (MBL) and human surfactant protein D (SP-D), but not in porcine SP-D. Despite this effect, these fluorescent derivatives were captured by human lectins using highly concentrated solutions. The resulting fluorescent beads were exposed to different solutions, and the results showed that displacements occur in contact with higher affinity ligands, proving that two-stage competition processes can occur in collectin carbohydrate recognition mechanisms. Moreover, the fluorescence loss depends on the discrepancy between the respective avidities of the recognized ligand and the fluorescent mannan. Chemically modulated fluorescent ligands associated with a diversity of collectins may lead to the creation of diagnostic tools suitable for multiplex array assays and the identification of high-avidity ligands.

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