Photochemestry, photophyisics and photoeletrochemestry of the ranelate ion

Abstract

Strontium ranelate (SrRan) is a drug available in more than 70 countries under the name of Protos or Protests. It is consumed in appreciable doses, such as teas (2 g/day), to prevent and treat Osteosporosis mainly in postmenopausal patients. Its efficiency has also been proven in very elderly patients, stimulating bone regeneration and reducing fractures. Its action involves the calcium receptors, increasing the formation of osteoblasts that act in the formation of the bone. At the same time, it induces the secretion of osteoprotegerin in osteoblasts, inhibiting the action of osteoclasts in their role of desorption and renewal of bone mineral components. Although strontium is a known calcium substitute in bone structure, its relevance may not be associated with this aspect, as many other sources of calcium are available and do not have the same effectiveness. Although strontium ranelate is non-toxic or non-toxic, it is being put on alert in several countries because of reports of increased risk of myocardial infarction in susceptible patients. From a chemical point of view, the most curious aspect of strontium ranelate is related to its molecular structure. In this structure there is a central thiophene nucleus, from which carboxylic and amino carboxylic arms, similar to EDTA, emerge as well as a nitrile group. The carboxylic groups retain the strontium ions in the structure, generating a three-dimensional framework similar to that of a MOF (Metal Organic Framework). Our attempt to isolate ranelic acid by treating strontium ranelate with 6 M HCl unexpectedly revealed the appearance of a navy blue color, which stands out due to the limpidity of the medium, generating a very vivid, characteristic tone after a few hours in conditions. Exposure to the sun greatly accelerates the process, which aroused our curiosity, since this transformation had not yet been reported in the literature. Only in 2018, when all data were placed in the puzzle, a pattern, corroborated by spectral and mass evidence, was formed that the blue dye would have a dimeric structure with a thiophene nucleus. The elucidation of this proposal is currently a great challenge, as it involves the isolation and characterization of the various intermediates, as well as the blue ranelate itself. It is known that the process is activated by acid, and only occurs by photochemical, steps still to be investigated. On the other hand, the blue product can be obtained by simple acidification of strontium ranelate and exposure to light. Once formed, the unprecedented dye showed to be quite stable even under sunlight for several weeks, and showed strong fluorescence, eliciting applications such as chemical/biological markers and even uses in dye-sensitized solar cells.These facts motivated the continuation of the work. But on another level of research, which may further expand the knowledge of a drug in commerce, whose chemistry remains almost unknown. All these aspects are still unpublished, and the relation with the optical excitation will be properly explored focusing on the photochemical, photophysical and photoelectrochemical processes, such as solar cell photosensitizers and blue OLED emitter. (AU)