CO and NO in medicine

Fluorescent small molecule donors

Small molecule donors (SMDs) play subtle roles in the signaling mechanism and disease treatments. While many excellent SMDs have been developed, dosage control, targeted delivery, spatiotemporal feedback, as well as the efficiency evaluation of small molecules are still key challenges. Accordingly, fluorescent small molecule donors (FSMDs) have emerged to meet these challenges. FSMDs enable controllable release and non-invasive real-time monitoring, providing significant advantages for drug development and clinical diagnosis. Integration of FSMDs with chemotherapeutic, photodynamic or photothermal properties can take full advantage of each mode to enhance therapeutic efficacy. Given the remarkable properties and the thriving development of FSMDs, we believe a review is needed to summarize the design, triggering strategies and tracking mechanisms of FSMDs. With this review, we compiled FSMDs for most small molecules (nitric oxide, carbon monoxide, hydrogen sulfide, sulfur dioxide, reactive oxygen species and formaldehyde), and discuss recent progress concerning their molecular design, structural classification, mechanisms of generation, triggered release, structure-activity relationships, and the fluorescence response mechanism. Firstly, from the large number of fluorescent small molecular donors available, we have organized the common structures for producing different types of small molecules, providing a general strategy for the development of FSMDs. Secondly, we have classified FSMDs in terms of the respective donor types and fluorophore structures. Thirdly, we discuss the mechanisms and factors associated with the controlled release of small molecules and the regulation of the fluorescence responses, from which universal guidelines for optical properties and structure rearrangement were established, mainly involving light-controlled, enzyme-activated, reactive oxygen species-triggered, biothiol-triggered, single-electron reduction, click chemistry, and other triggering mechanisms. Fourthly, representative applications of FSMDs for trackable release, and evaluation monitoring, as well as for visible in vivo treatment are outlined, to illustrate the potential of FSMDs in drug screening and precision medicine. Finally, we discuss the opportunities and remaining challenges for the development of FSMDs for practical and clinical applications, which we anticipate will stimulate the attention of researchers in the diverse fields of chemistry, pharmacology, chemical biology and clinical chemistry. With this review, we hope to impart new understanding thereby enabling the rapid development of the next generation of FSMDs.

Cationic Carbon Monoxide-Releasing Polymers as Antimicrobial and Antibiofilm Agents by the Synergetic Activity

Recent studies indicate that carbon monoxide-releasing molecules (CORMs), a class of organometallic compounds, exert antibacterial activities through the delivery of carbon monoxide (CO) molecules. We developed a new-class CO-delivery system by conjugating classical low-molecular-weight CORMs (i.e., [Ru(CO)3Cl2]2 and Mn(CO)5Br) onto a positively charged carrier, polyimidazolium (PIM), giving cationic CO-releasing polymers Ru@PIM and Mn@PIM, respectively. Compared with low-molecular-weight CORMs, our polymeric CO vehicles showed improved water solubility, reduced cytotoxicity, significantly extended CO-releasing duration, and enhanced antimicrobial ability against both planktonic and biofilm microorganisms. Ru@PIM and Mn@PIM inhibited the growth of a broad spectrum of free Gram-positive and Gram-negative bacteria as well as fungus with the lowest minimum inhibitory concentration (MIC) at 8 μg/mL. They were effective in preventing pathogenic Pseudomonas aeruginosa biofilm formation with biofilm reduction by more than 92% at 16 μg/mL and 99% at 32 μg/mL. They also demonstrated potent dispersal efficacy on recalcitrant well-established biofilms through a synergetic activity with a biofilm log10 reduction of 2.5-3.2 ≥ 64 μg/mL and nearly 2.0 at the concentration of as low as 16 μg/mL. This CO-releasing system may retain long-time antimicrobial ability after the complete release of CO molecules owing to the cationic structure. The novel CO-releasing polymers have great potential as antimicrobial and antibiofilm agents in biomedical applications.

The Triple Crown: NO, CO, and H2S in cancer cell biology

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) are three endogenously produced gases with important functions in the vasculature, immune defense, and inflammation. It is increasingly apparent that, far from working in isolation, these three exert many effects by modulating each other's activity. Each gas is produced by three enzymes, which have some tissue specificities and can also be non-enzymatically produced by redox reactions of various substrates. Both NO and CO share similar properties, such as activating soluble guanylate cyclase (sGC) to increase cyclic guanosine monophosphate (cGMP) levels. At the same time, H2S both inhibits phosphodiesterase 5A (PDE5A), an enzyme that metabolizes sGC and exerts redox regulation on sGC. The role of NO, CO, and H2S in the setting of cancer has been quite perplexing, as there is evidence for both tumor-promoting and pro-inflammatory effects and anti-tumor and anti-inflammatory activities. Each gasotransmitter has been found to have dual effects on different aspects of cancer biology, including cancer cell proliferation and apoptosis, invasion and metastasis, angiogenesis, and immunomodulation. These seemingly contradictory actions may relate to each gas having a dual effect dependent on its local flux. In this review, we discuss the major roles of NO, CO, and H2S in the context of cancer, with an effort to highlight the dual nature of each gas in different events occurring during cancer progression.

The emergence and advancement of Tsuji-Trost reaction triggered carbon monoxide recognition and bioimaging

Considering that carbon monoxide is both a vital gasotransmitter and an obnoxious gas, tremendous efforts have been dedicated toward its recognition through various methods. However, the fluorescent light-up approach through the exploration of optical markers remains one of the most convenient methods owing to its several advantages. Amongst the different approaches towards the development of CO responsive optically active molecular markers, the Tsuji-Trost reaction-based CO recognition strategy has remained one of the most significant areas of interest across researchers working in this field. However, there have been no attempts to exclusively summarize the commendable work done in this area yet. The current review, therefore, attempts to summarize the developments of various optical probes following this reaction strategy until the year 2022. This review provides detailed mechanistic insights into the Tsuji-Trost mediated CO detection strategy. Besides, discussions on the strategic development and employment of probes based on various allyl derivatives - allyl carbamate/carbonate/ethers - will provide a thorough understanding of the detection method. The significant advancements of the Tsuji-Trost reaction as an interesting strategy that is accepted and extensively explored for monitoring CO in various media including air, aqueous solutions and living systems have been elaborately discussed. Various potential applications and utilization of these developed fluorogenic probes for tracing CO in different living systems have been examined systematically. Moreover, monitoring of exogenous/endogenous CO levels, modulation of intracellular CO concentration under various induced conditions and bioimaging of CO in in vivo models have also been detailed here. Briefly, this review summarizes the current prospects of this detection method and the future directions in related fields.

Sawhorse-type ruthenium complexes with triazolopyrimidine ligands - what do they represent in terms of cytotoxic and CORM compounds?

Three sawhorse-type ruthenium(I) complexes containing purine analogs such as triazolopyrimidines of the general formula [Ru₂(CO)₄(μ-OOCCH₃)₂(L)₂], where L is 1,2,4-triazolo[1,5-a]pyrimidine (tp for 1), 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp for 2) and 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine (dptp for 3), have been synthesized and characterized by elemental analysis, infrared analysis, multinuclear magnetic resonance spectroscopic techniques (¹H, ¹³C, ¹⁵N), and single-crystal X-ray diffraction (for 1 and 2). By assay with myoglobin, the photo-activated CO-releasing molecule (PhotoCORM) character of (1-3) has been confirmed, thus indicating the possibility of use in CO-based therapies. The importance of UV-induced modification has been investigated in the context of anticancer properties. Complexes (1) and (2) have been thoroughly screened for their in vitro cytotoxicity against various cancer cell lines: MCF-7 (breast cancer), HeLa (cervical cancer) and C32 (melanoma), as well as L929 normal fibroblasts in the dark and presence of UV-A light (365 nm). The results were compared with those for cisplatin and two reference ruthenium complexes, namely NAMI-A and KP1019. The most hydrophilic [Ru₂(CO)₄(μ-OOCCH₃)₂(tp)₂] (1) (log P = -1.12) was found to be more cytotoxic than (2), despite the lower cellular uptake measured by ICP-MS toward HeLa cells. Importantly, photo-induced stimulation of cells with (1) resulted in a lower decrease in the viability of L929 normal cells (IC₅₀ = 154.7 ± 6.5 μM) in comparison with HeLa cancer cells (IC₅₀ = 66.7 ± 3.4 μM). The photo-induced stimulation of (1) and (2) increases ROS generation, and their anticancer activity may be a partially ROS-dependent phenomenon.

A simple theoretical approach to converging of Myoglobin-Assay with different pH values

Many metal carbonyl complexes have been synthesized and analyzed as CO-releasing agents. As in many bioactivity assays, differences between in-vitro and in-vivo studies in Myoglobin Assay have been observed. Adjustment of in-vitro conditions to in-vivo conditions is one way to overcoming this problem. Changing the conditions of each in-vivo assay is not possible considering the available grant, material, and labor facilities. In-silico methods are suitable as they provide better in-vitro conditions before experimental procedures. A method which is easy to employ on a basic computer could be more suitable to observe the assay convergence. In this study, global reactivity descriptors were used as an approach to investigate pH differences in myoglobin assay. Global reactivity descriptors of the molecules were compared with myoglobin assay results at different pH values and molecular docking results performed with optimized molecules in different solvents. The following complexes were studied: [Mn(CO)3(bpy)(L)]PF6 (bpy: 2,2-bipyridyl, L: benzylbenzimidazole, 4-chlorobenzylbenzimidazole).

Engineering macromolecular nanocarriers for local delivery of gaseous signaling molecules

In addition to being notorious air pollutants, nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S) have also been known as endogenous gaseous signaling molecules (GSMs). These GSMs play critical roles in maintaining the homeostasis of living organisms. Importantly, the occurrence and development of many diseases such as inflammation and cancer are highly associated with the concentration changes of GSMs. As such, GSMs could also be used as new therapeutic agents, showing great potential in the treatment of many formidable diseases. Although clinically it is possible to directly inhale GSMs, the precise control of the dose and concentration for local delivery of GSMs remains a substantial challenge. The development of gaseous signaling molecule-releasing molecules provides a great tool for the safe and convenient delivery of GSMs. In this review article, we primarily focus on the recent development of macromolecular nanocarriers for the local delivery of various GSMs. Learning from the chemistry of small molecule-based donors, the integration of these gaseous signaling molecule-releasing molecules into polymeric matrices through physical encapsulation, post-modification, or direct polymerization approach renders it possible to fabricate numerous macromolecular nanocarriers with optimized pharmacokinetics and pharmacodynamics, revealing improved therapeutic performance than the small molecule analogs. The development of GSMs represents a new means for many disease treatments with unique therapeutic outcomes.

Nitric oxide-releasing micelles with intelligent targeting for enhanced anti-tumor effect of cisplatin in hypoxia

Background

Hypoxic tumor microenvironment (TME) promotes tumor metastasis and drug resistance, leading to low efficiency of cancer chemotherapy. The development of targeted agents or multi-target therapies regulating hypoxic microenvironment is an important approach to overcome drug resistance and metastasis.

Methods

In this study, chitosan oligosaccharide (COS)-coated and sialic acid (SA) receptor-targeted nano-micelles were prepared using film dispersion method to co-deliver cisplatin (CDDP) and nitric oxide (NO) (denoted as CTP/CDDP). In addition, we explored the mechanisms by which NO reversed CDDP resistance as well as enhanced anti-metastatic efficacy in hypoxic cancer cells.

Results

Because of the different affinities of COS and SA to phenylboronic acid (PBA) under different pH regimes, CTP/CDDP micelles with intelligent targeting property increased cellular uptake of CDDP and enhanced cytotoxicity to tumors, but reduced systemic toxicity to normal organs or tissues. In addition, CTP/CDDP showed stimulus-responsive release in TME. In terms of anti-tumor mechanism, CTP/CDDP reduced CDDP efflux and inhibited epithelial-mesenchymal transition (EMT) process of tumor by down-regulating hypoxia-inducible factor-1α (HIF-1α), glutathione (GSH), multidrug resistance-associated protein 2 (MRP2) and matrix metalloproteinase 9 (MMP9) expression, thus reversing drug resistance and metastasis of hypoxic tumor cells.

Conclusions

The designed micelles significantly enhanced anti-tumor effects both in vitro and in vivo. These results suggested that CTP/CDDP represented a promising strategy to treat resistance and metastatic tumors.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00989-z.

Carbon Monoxide and Nitric Oxide as Examples of the Youngest Class of Transmitters

The year 2021 is the 100th anniversary of the confirmation of the neurotransmission phenomenon by Otto Loewi. Over the course of the hundred years, about 100 neurotransmitters belonging to many chemical groups have been discovered. In order to celebrate the 100th anniversary of the confirmation of neurotransmitters, we present an overview of the first two endogenous gaseous transmitters i.e., nitric oxide, and carbon monoxide, which are often termed as gasotransmitters.

Enhanced luminescence intensity of near-infrared-sensitized upconversion nanoparticles via Ca2+ doping for a nitric oxide release platform

Light-induced NO release based on exogenous NO donors has attracted substantial attention in clinical applications; the induction light source usually converts near-infrared light to blue or ultraviolet light. However, the low efficiency of near-infrared light-assisted chemical light energy conversion remains a challenge, especially for NaYF4:Yb3+/Tm3+ photoconverting near-infrared light to ultraviolet (UV) and blue light. In this paper, a luminescence-enhanced strategy is reported by doping Ca2+ into NaYF4:Yb3+/Tm3+ and coating it with NaGdF4 through a two-step solvothermal method. Then, UCNPs modified with methyl-β-cyclodextrin (M-β-CD) are loaded on a ruthenium nitrosyl complex [(3)Ru(NO)(Cl)] as nitric oxide release-molecules (NORMs). X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) data demonstrated that Ca2+ was successfully doped into NaYF4:Yb3+/Tm3+ nanoparticles as the core, and a pure hexagonal phase, NaYF4, was obtained from the doping of Ca2+. TEM revealed that the crystallinity was significantly improved after Ca2+ doping, and the core-shell structure was successfully synthesized, with NaGdF4 directionally grown on the NaYF4:Ca/Yb/Tm core. Fluorescence tests showed that, especially in the ultraviolet and blue light excitation wavelength regions, the UC emission intensity of the Ca-doped NaYF4:Yb3+/Tm3+@NaGdF4 core-shell UCNPs increased by 302.95 times vs. NaYF4:Yb3+/Tm3+ UCNPs. Finally, the release of NO was tested by the Griess method. Under 980 nm irradiation, the cell viability distinctly decreased with increasing UCNPs@M-β-CD-NORMs concentration. This study shows that NORM release of NO is triggered by enhanced up-converted UV and blue light, which can be used for the development of UV photo-sensitive drugs.

Methionine-based carbon monoxide releasing polymer for the prevention of biofilm formation

A new water-soluble methionine-based CO releasing polymer shows slow and spontaneous release of CO with sustained-release kinetics, preventing biofilm formation against Pseudomonas aeruginosa.

A turn-on and lysosome-targeted fluorescent NO releaser in water media and its application in living cells and zebrafishes

Due to the high activity and difficult to transport of nitric oxide, the controlled release of nitric oxide has been a new trend in the research on the biological effect of nitric oxide. In this paper, a water-soluble and turn-on fluorescent NO donor Rh-NO was synthesized. Upon 525 nm irradiation, the fluorescence of the Rh-NO at 568 nm enhanced with the quantum yield (Φ_F) of Rh-NO changing from 5.08% to 35.96%. The mechanism of NO releasing was proved by HRMS and the Dan. The releasing time of 6 min and the releasing yield of 0.61 proved the superiority of Rh-NO. Excellent cell activity above 80% of Rh-NO and Rh guaranteed that nitric oxide was released from Rh-NO in lysosome and zebrafishes successfully, which provided a good platform to understand the biological effects of nitric oxide in lysosomes.

Hydrogen Sulfide: A Therapeutic Option in Systemic Sclerosis

Systemic sclerosis (SSc) is a lethal disease that is characterized by auto-immunity, vascular injury, and progressive fibrosis of multiple organ systems. Despite the fact that the exact etiology of SSc remains unknown, oxidative stress has been associated with a large range of SSc-related complications. In addition to the well-known detrimental properties of reactive oxygen species (ROS), gasotransmitters (e.g., nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S)) are also thought to play an important role in SSc. Accordingly, the diverse physiologic actions of NO and CO and their role in SSc have been previously studied. Recently, multiple studies have also shown the importance of the third gasotransmitter H₂S in both vascular physiology and pathophysiology. Interestingly, homocysteine (which is converted into H₂S through the transsulfuration pathway) is often found to be elevated in SSc patients; suggesting defects in the transsulfuration pathway. Hydrogen sulfide, which is known to have several effects, including a strong antioxidant and vasodilator effect, could potentially play a prominent role in the initiation and progression of vasculopathy. A better understanding of the actions of gasotransmitters, like H₂S, in the development of SSc-related vasculopathy, could help to create early interventions to attenuate the disease course. This paper will review the role of H₂S in vascular (patho-)physiology and potential disturbances in SSc. Moreover, current data from experimental animal studies will be reviewed. Lastly, we will evaluate potential interventional strategies.

Vesicles Functionalized with a CO-Releasing Molecule for Light-Induced CO Delivery

In this paper, a new type of methodology to deliver carbon monoxide (CO) for biological applications has been introduced. An amphiphilic manganese carbonyl complex (1.Mn) incorporated into the 1,2-distearoyl-sn-glycero-3-phosphocholine lipid vesicles has been reported first time for the photoinduced release of CO. The liposomes (Ves-1.Mn) gradually released CO under light at 365 nm over a period of 50 min with a half-time of 26.5 min. The CO-releasing ability of vesicles appended with 1.Mn complexes has been confirmed by myoglobin assay and infrared study. The vesicles appended with 1.Mn have the advantages of biocompatibility, water solubility, and steady and slow CO release. This approach could be a rational approach for applying various water-insoluble photoinduced CO donors in aqueous media by using vesicles as a nanocarrier for CO release.

The dichotomous role of H2S in cancer cell biology? Déjà vu all over again

Nitric oxide (NO) a gaseous free radical is one of the ten smallest molecules found in nature, while hydrogen sulfide (H2S) is a gas that bears the pungent smell of rotten eggs. Both are toxic yet they are gasotransmitters of physiological relevance. There appears to be an uncanny resemblance between the general actions of these two gasotransmitters in health and disease. The role of NO and H2S in cancer has been quite perplexing, as both tumor promotion and inflammatory activities as well as anti-tumor and antiinflammatory properties have been described. These paradoxes have been explained for both gasotransmitters in terms of each having a dual or biphasic effect that is dependent on the local flux of each gas. In this review/commentary, I have discussed the major roles of NO and H2S in carcinogenesis, evaluating their dual nature, focusing on the enzymes that contribute to this paradox and evaluate the pros and cons of inhibiting or inducing each of these enzymes.

Remote-controlled delivery of CO via photoactive CO-releasing materials on a fiber optical device

Although carbon monoxide (CO) delivery materials (CORMAs) have been generated, remote-controlled delivery with light-activated CORMAs at a local site has not been achieved. In this work, a fiber optic-based CO delivery system is described in which the photoactive and water insoluble CO releasing molecule (CORM) manganese(i) tricarbonyl [(OC)3Mn(μ3-SR)]4 (R = nPr, 1) has been non-covalently embedded into poly(l-lactide-co-d/l-lactide) and poly(methyl methacrylate) non-woven fabrics via the electrospinning technique. SEM images of the hybrid materials show a porous fiber morphology for both polymer supports. The polylactide non-woven fabric was attached to a fiber optical device. In combination with a laser irradiation source, remote-controlled and light-triggered CO release at 405 nm excitation wavelength was achieved. The device enabled a high flexibility of the spatially and timely defined application of CO with the biocompatible hybrid fabric in aqueous media. The rates of liberated CO were adjusted with the light intensity of the laser. CO release was confirmed via ATR-IR spectroscopy, a portable electrochemical CO sensor and a heterogeneous myoglobin assay.

Delivery of Antioxidant and Anti-inflammatory Agents for Tissue Engineered Vascular Grafts

The treatment of patients with severe coronary and peripheral artery disease represents a significant clinical need, especially for those patients that require a bypass graft and do not have viable veins for autologous grafting. Tissue engineering is being investigated to generate an alternative graft. While tissue engineering requires surgical intervention, the release of pharmacological agents is also an important part of many tissue engineering strategies. Delivery of these agents offers the potential to overcome the major concerns for graft patency and viability. These concerns are related to an extended inflammatory response and its impact on vascular cells such as endothelial cells. This review discusses the drugs that have been released from vascular tissue engineering scaffolds and some of the non-traditional ways that the drugs are presented to the cells. The impact of antioxidant compounds and gasotransmitters, such as nitric oxide and carbon monoxide, are discussed in detail. The application of tissue engineering and drug delivery principles to biodegradable stents is also briefly discussed. Overall, there are scaffold-based drug delivery techniques that have shown promise for vascular tissue engineering, but much of this work is in the early stages and there are still opportunities to incorporate additional drugs to modulate the inflammatory process.

Spin-Forbidden Excitation: A New Approach for Triggering Photopharmacological Processes with Low-Intensity NIR Light

Exposure to low-intensity radiation in the near-infrared (NIR) spectral region matching the optically transparent "phototherapeutic window" of biological tissues can be applied to directly populate spin-restricted excited states of light-responsive compounds. This unconventional and unprecedented approach is introduced herein as a new strategy to overcome some of the major unresolved problems observed in the rapidly emerging fields of photopharmacology and molecular photomedicine, where practical applications in living cells and organisms are still limited by undesired side reactions and insufficient light penetration. Water-soluble and biocompatible metal complexes with a significant degree of spin-orbit coupling were identified as target candidates for testing our new hypothesis. As a first example, a dark-stable manganese carbonyl complex acting as a visible-light-triggered CO-releasing molecule (Photo-CORM) is shown to be photoactivated by NIR radiation, although apparently no spectroscopically evident absorption bands are detectable in this low-energy region. This quite remarkable effect is ascribed to a strongly restricted, but obviously not completely forbidden optical population of the lowest triplet excited state manifold of the diamagnetic complex from the singlet ground state.

Nonmetallic carbon monoxide releasing molecules (CORMs)

Recent progress on nonmetallic carbon monoxide releasing molecules (CORMs) is reviewed.

Photoactivatable CO release from engineered protein crystals to modulate NF-κB activation

Photoactivatable CO releasing protein crystals were developed by immobilization of Mn carbonyl complexes in polyhedral crystals, which are spontaneously formed in insect cells. The photoactivatable CO release from the engineered protein crystals activates nuclear factor kappa B (NF-κB) upon stimulation by visible light irradiation with suppression of cytotoxicity of the Mn complex.

Functional Interactions between BKCaα-Subunit and Annexin A5: Implications in Apoptosis

Proteomic studies have suggested a biochemical interaction between α subunit of the large conductance, voltage- and Ca²⁺-activated potassium channel (BK_Caα), and annexin A5 (ANXA5), which we verify here by coimmunoprecipitation and double labelling immunocytochemistry. The observation that annexin is flipped to the outer membrane leaflet of the plasma membrane during apoptosis, together with the knowledge that the intracellular C-terminal of BK_Caα contains both Ca²⁺-binding and a putative annexin-binding motif, prompted us to investigate the functional consequences of this protein partnership to cell death. Membrane biotinylation demonstrated that ANXA5 was flipped to the outer membrane leaflet of HEK 293 cells early in serum deprivation-evoked apoptosis. As expected, serum deprivation caused caspase-3/7 activation and this was accentuated in BK_Caα expressing HEK 293 cells. The functional consequences of ANXA5 partnership with BK_Caα were striking, with ANXA5 knockdown causing an increase and ANXA5 overexpression causing a decrease, in single BK_Ca channel Ca²⁺-sensitivity, measured in inside-out membrane patches by patch-clamp. Taken together, these data suggest a novel model of the early stages of apoptosis where membrane flippage results in removal of the inhibitory effect of ANXA5 on K⁺ channel activity with the consequent amplification of Ca²⁺ influx and augmented activation of caspases.

Light-triggered CO delivery by a water-soluble and biocompatible manganese photoCORM

The discovery of salutary effects of low doses of carbon monoxide (CO) has spurred interest in designing exogenous molecules that can deliver CO to biological targets under controlled conditions. Herein we report a water-soluble photosensitive manganese carbonyl complex [MnBr(CO)3(pyTAm)] (2) (pyTAm = 2-(pyridyl)imino-triazaadamantane) that can be triggered to release CO upon exposure to visible light. Inclusion of a triazaadamantyl pharmacophore into the coligand of 2 improves its stability and solubility in water. Change in the coligand from 2-(pyridyl)imino-triazaadamantane to 2-(pyridyl)iminoadamantane (pyAm) or 2-(quinonyl)imino-triazaadamantane (qyTAm) dramatically alters these desired properties of the photoCORM. In addition to structures and CO-releasing properties of the three analogous complexes 1-3 from these three α-diimine ligands, theoretical calculations have been performed to determine the origin of Mn-CO bond labilization upon illumination. Rapid delivery of CO to myoglobin under physiological conditions attests the potential of 2 as a biocompatible photoCORM.

Toxicity, bio-distribution and metabolism of CO-releasing molecules based on cobalt

CO-releasing molecules (CORMs) containing [Co2(CO)6] moiety show many bioactivities, such as anti-inflammatory and antitumor cell proliferation. However, so far, no one knows their properties in vivo. So, here, we evaluated some these kind CORMs from drug-like properties including cytotoxicity, toxicity in vivo, distribution and metabolism. The results show all the tested complexes displayed antiproliferative activity to HeLa cell and HepG2 cell lines, and their IC50 values were 36-110µM against HeLa cells and 39-140µM against HepG2 cells. Toxicity tests of mice, we used oral acute toxic class method and got their LD50 values; among them, LD50 of complex 1 and complex 4 were in 2500-5000mgkg(-1) and complex 7 over 5000mgkg(-1). The developmental toxicities of the complexes were investigated in embryonic zebrafish. The mortality, hatch rate, malformation, heart rate, spontaneous movement, and larval behavior were examined, and we found both complexes 4 and 7 have not toxicity at low concentration (<1.0μM) but have higher toxicity at high concentration (>5.0μM). After several consecutive i.p administrations, tested complexes severely damaged rat liver and kidney in both functional and morphological aspects. Through metal ion measurement using ICP-AES, we found the tested complexes were unevenly distributed in tissues and organs; complex 4 has a big prone to collect in liver, whereas complex 7 easily enters to kidney. After administration 480min later, most of complex 7 excreted from kidney and entered urine, while complex 4 needed 9h at least. This results show cobalt did not accumulate, and could excrete with the urine. In vivo, Co(0) in complexes was oxidised to Co(II). In addition, the substituents significantly affected the rate of CO-release, cytotoxicity and their bio-distribution. In the view of these aspects, the CORMs based cobalt has a potential property to be a medicine.

A multifunctional nanoplatform for lysosome targeted delivery of nitric oxide and photothermal therapy under 808 nm near-infrared light

NIR light induced spatiotemporal delivery of NO to lysosome accompanied by hyperthermia was realized.

Emerging applications of metal–organic frameworks

Metal–organic frameworks are highly crystalline porous materials which present emerging opportunities in biotechnology, catalysis, microelectronics and photonics.

A combined experimental and DFT investigation on the structure and CO-releasing properties of mono and binuclear fac-ReI(CO)3 complexes with 5-pyridin-2-ylmethylene-amino uracils

New tricarbonyl rhenium(i) complexes with 5-substituted-6-amino-1,3-dimethyluracils are reported.

Synthesis of oxime-based CO-releasing molecules, CORMs and their immobilization on maghemite nanoparticles for magnetic-field induced CO release

Labile and intensely colored CORMs are stabilized in alginate–dextran composites.