Transition metals (d-blocks) are recognized as playing critical roles in biology, and they most often act as cofactors in diverse enzymes; however, improper regulation of transition metal stores is also connected to serious disorders. Therefore, the monitoring and imaging of transition metals are significant for biological research as well as clinical diagnosis. In this article, efforts have been made to review the chemical sensors that have been developed for the detection of the first-row d-block metals (except Cu and Zn): Cr, Mn, Fe, Co, and Ni. We focus on the development of fluorescent sensors (fall into three classes: “turn-off”, “turn-on”, and ratiometric), colorimetric sensors, and responsive MRI contrast agents for these transition metals (242 references). Future work will be likely to fill in the blanks: (1) sensors for Sc, Ti, and V; (2) MRI sensors for Cr, Mn, Co, Ni; (3) ratiometric fluorescent sensors for Cr6+, Mn2+, and Ni2+, explore new ways of sensing Fe3+ or Cr3+ without the proton interference, as well as extend applications of MRI sensors to living systems.

Fluorescent, MRI, and colorimetric chemical sensors for the first-row d-block metal ions

Photoactive Ruthenium Nitrosyls: Effects of Light and Potential Application as NO Donors.

Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photoactivatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials.

The multiple roles nitric oxide (NO) plays as a bioregulatory, anticancer, antimicrobial and antioxidant agent has triggered an explosive interest in recent years in compounds able to deliver this diatomic radical for therapeutic purposes. A major issue associated with NO donors is the precise control of the NO release, which effect is highly concentration and flux dependent. Light represents a convenient non-invasive on/off trigger to deliver NO on demand since it allows the accurate control of site, timing and dosage. The assembling of NO photodonors through different approaches may lead to intriguing light-responsive molecular constructs including nanostructured films, polymers, gels, nanoparticles and molecular conjugates which exhibit promising potential in view of practical applications. This tutorial review illustrates the recent research from our and other laboratories towards the fabrication of these molecular assemblies, highlighting the logical design and the relevance in the biomedical field. Therefore, this review is aimed to be a source of inspiration for a wide range of scientists belonging to the chemical, materials science and biochemical communities, facing the common challenge of fabricating controllable NO dispensers.

Light-controlled nitric oxide delivering molecular assemblies.

Nitric oxide (NO) is involved in several physiological processes, such as the control of vascular tone, the inhibition of platelet aggregation, smooth muscle cell replication, the immune response, and wound healing processes. Several pathologies have been associated with dysfunctions in the endogenous production of NO. Thus, there is great interest in developing NO-releasing drugs and in matrices which are able to stabilize and release NO locally and directly in different tissues. Over the past few years, a very promising strategy for biocompatible NO-delivery systems has emerged based on the use of nanobiotechnology for targeted NO-release for biomedical applications. In this work, the current state-of-the-art approaches to NO-release from nanomeric materials, their preparation, and promising biomedical applications are reviewed. Such materials, comprised of dendrimers, liposomes, metallic and silica nanoparticles, polymeric micro and nanoparticles, semiconductor quantum dots, carbon nanotubes, and nanoporous solid materials exhibit exceptional potential in directly delivering NO in a controlled spatial and temporal manner with superior biocompatibility for pharmacological applications.

Jeane Bordini

Papers

Photochemical release of nitric oxide from a regenerable, sol-gel encapsulated Ru–salen–nitrosyl complex

A rhodamine-B-based turn-on fluorescent sensor for biological iron(III)

Acidity and photolability of ruthenium salen nitrosyl and aquo complexes in aqueous solutions