Denitrification is a distinct means of energy conservation, making use of N oxides as terminal electron acceptors for cellular bioenergetics under anaerobic, microaerophilic, and occasionally aerobic conditions. The process is an essential branch of the global N cycle, reversing dinitrogen fixation, and is associated with chemolithotrophic, phototrophic, diazotrophic, or organotrophic metabolism but generally not with obligately anaerobic life. Discovered more than a century ago and believed to be exclusively a bacterial trait, denitrification has now been found in halophilic and hyperthermophilic archaea and in the mitochondria of fungi, raising evolutionarily intriguing vistas. Important advances in the biochemical characterization of denitrification and the underlying genetics have been achieved with Pseudomonas stutzeri, Pseudomonas aeruginosa, Paracoccus denitrificans, Ralstonia eutropha, and Rhodobacter sphaeroides. Pseudomonads represent one of the largest assemblies of the denitrifying bacteria within a single genus, favoring their use as model organisms. Around 50 genes are required within a single bacterium to encode the core structures of the denitrification apparatus. Much of the denitrification process of gram-negative bacteria has been found confined to the periplasm, whereas the topology and enzymology of the gram-positive bacteria are less well established. The activation and enzymatic transformation of N oxides is based on the redox chemistry of Fe, Cu, and Mo. Biochemical breakthroughs have included the X-ray structures of the two types of respiratory nitrite reductases and the isolation of the novel enzymes nitric oxide reductase and nitrous oxide reductase, as well as their structural characterization by indirect spectroscopic means. This revealed unexpected relationships among denitrification enzymes and respiratory oxygen reductases. Denitrification is intimately related to fundamental cellular processes that include primary and secondary transport, protein translocation, cytochrome c biogenesis, anaerobic gene regulation, metalloprotein assembly, and the biosynthesis of the cofactors molybdopterin and heme D1. An important class of regulators for the anaerobic expression of the denitrification apparatus are transcription factors of the greater FNR family. Nitrate and nitric oxide, in addition to being respiratory substrates, have been identified as signaling molecules for the induction of distinct N oxide-metabolizing enzymes.

/pdf/cell-biology-and-molecular-basis-of-denitrification-red4l5iffz.pdf

Cell biology and molecular basis of denitrification.

Photodynamic therapy (PDT) was discovered more than 100 years ago, and has since become a well-studied therapy for cancer and various non-malignant diseases including infections. PDT uses photosensitizers (PSs, non-toxic dyes) that are activated by absorption of visible light to initially form the excited singlet state, followed by transition to the long-lived excited triplet state. This triplet state can undergo photochemical reactions in the presence of oxygen to form reactive oxygen species (including singlet oxygen) that can destroy cancer cells, pathogenic microbes and unwanted tissue. The dual-specificity of PDT relies on accumulation of the PS in diseased tissue and also on localized light delivery. Tetrapyrrole structures such as porphyrins, chlorins, bacteriochlorins and phthalocyanines with appropriate functionalization have been widely investigated in PDT, and several compounds have received clinical approval. Other molecular structures including the synthetic dyes classes as phenothiazinium, squaraine and BODIPY (boron-dipyrromethene), transition metal complexes, and natural products such as hypericin, riboflavin and curcumin have been investigated. Targeted PDT uses PSs conjugated to antibodies, peptides, proteins and other ligands with specific cellular receptors. Nanotechnology has made a significant contribution to PDT, giving rise to approaches such as nanoparticle delivery, fullerene-based PSs, titania photocatalysis, and the use of upconverting nanoparticles to increase light penetration into tissue. Future directions include photochemical internalization, genetically encoded protein PSs, theranostics, two-photon absorption PDT, and sonodynamic therapy using ultrasound.

/pdf/new-photosensitizers-for-photodynamic-therapy-5diko9hbsn.pdf

New photosensitizers for photodynamic therapy

Organic-chemical synthesis has always fascinated chemists and will not lose its importance in the future. It is a truism that all chemists—and others too—are dependent on the synthesis of those compounds with which they want to work. As a result, organic-chemical synthesis today is more than ever before the cutting edge of organic chemistry, biology, biochemistry, medicine, physics, and material science. Synthesis is also the basis of the chemical industry. For the passionate synthetic chemist, however, synthesis is much more than just a method for obtaining compounds; it is the expression of his creativity, intelligence, ability, and also his perseverance.

Sequential Transformations in Organic Chemistry: A Synthetic Strategy with a Future†

10. Patented Literature 2616 10.1. Esterification 2616 10.2. Ether Formation 2619 10.2.1. Etherification without Cyclization 2619 10.2.2. Etherification with Cyclization 2624 10.3. N-Alkylation 2625 10.4. Other Reactions 2627 11. Summary and Outlook 2628 12. Note Added in Proof 2628 13. Abbreviations Used in This Review 2629 14. Acknowledgments 2629 15. Supporting Information Available 2630 16. References 2630

Mitsunobu and Related Reactions: Advances and Applications

Porphyrin-based photosensitizers for use in photodynamic therapy

A sequence, based on a Mitsunobu displacement at the hydroxymethyl position of deuterium-labeled, N-substituted 2-(hydroxymethyl)pyrroles, is reported as a general procedure to determine the ability of the N-substituent to deactivate the heterocycle. An SN2 mechanism, in this reaction, has been shown to be favored over reaction via an azafulvenium intermediate, by employing N-(trifluoromethyl)sulfonyl as the deactivating group. Deuterium-labeling studies have demonstrated that suppression of contributions to the reaction from an azafulvenium intermediate is less effective with other deactivating groups, and the order for deactivation is triflyl > mesyl > BOC ≈ acetyl. The attachment of an electron-withdrawing group onto the nitrogen of a 2-formyl[formyl-d]pyrrole has also been shown to allow reduction to give a 2-(hydroxymethyl[methylene-d1])pyrrole of high configurational purity. The utility of the N-triflyl group to deactivate a pyrrole was demonstrated with the preparation of deuterium-labeled porphobi...

Synthesis and Properties of Ring-Deactivated Deuterated (Hydroxymethyl)pyrroles.

Stereochemical course of hydroxylation of dopamine by dopamine-beta-hydroxylase (ec1.14.17.1)

Biosynthesis of Porphyrins and Related Macrocycles. Part 47. Synthesis and Chemistry of 2H‐Pyrroles (Pyrrolenines) Related to the Proposed Spiro‐Intermediate for Porphyrin Biosynthesis.

Synthesis of 20‐methyl and 20‐cyano isobacteriochlorins: the wittig‐photochemical approach

Rk. in gegenwart von enzymen 1. mitt. synth. von deuterium- oder tritiummarkierten (3s)- und (3r)-phenylalaninen, stereochemischer verlauf der durch eine, ammoniak aus phenylalanin freisetzende, lyase katalysierten eliminierung

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