*2.1. Micellization*

Hubbell et al. engineered the micellization technique as the CO-producer with reduced diffusion; creditably targeted to the distal tissue draining sites [59]. Micelles were synthesized by the tri-block copolymer composed of poly(ornithine acrylamide) block and poly(ethylene glycol) block (hydrophilic nature) hosted by [Ru(CO)3Cl-(ornithinate)] moieties with poly(n-butylacrylamide) block (hydrophobic nature). The CO-releasing micelles consists of a triblock copolymers (Figure 6): A hydrophilic poly(ethylene glycol) (PEG) fragment that stabilizes the micelles; a poly-OrnRu fragment that releases CO. A hydrophobic poly(n-butylacrylamide) fragment drives to construct the micelles forms.

**Figure 6.** Triblock copolymer assembles for releasing the CO at biological sites.

The micelles polymer can be used as a pharmaceutically acceptable carrier to solubilize the poorly soluble drugs and produces the therapeutic effect against the targeting sites. Probably it promotes the reduction in toxic effects of the drugs on normal tissues and organs. Significantly, the toxicity of the Ru(CO)3Cl moiety is well-reduced in the polymer micelle due to the stealth characteristic of the PEG fragment. Moreover, the micelles moderately respond to human monocytes against the lipopolysaccharide (LPS) -induced inflammatory disease model. Importantly, poly(ethylene glycol) attenuates the toxic feature of [Ru(CO)3Cl(amino acidate)] moieties. The addition of cysteine allows the release of CO from an occupied area with a slower rate as compared to [Ru(CO)3Cl(glycinate)] (CORM-3). The release of CO from micelles was tested in a myoglobin assay and it has been found to be slower than CORM-3. The diffusion of the Orn-Ru substrate is facing hindrance in the cells due to the micelles stereoscopic effect. Anyhow, the mechanism approach of CO-releasing is not obvious. It has been evidently proved through experiments that thiol compounds such as cysteine, glutathione and protein are compatible to induce the CO release from micelles.

Hiroshi Maeda et al. incorporated the tricarbonyldichlororuthenium dimer (CORM-2: [RuCl(μ-Cl)(CO)3]2) as water-soluble styrene-maleic acid and copolymer (SMA) while gaining the optimum half-life and numerous therapeutic effects [145]. They established the micellization structure for encapsulating the CORM-2 (SMA/CORM-2) (Figure 7). The micellization has good water solubility and it is compatible with the aqueous environment. The sustain CO kinetic profile performs well in vivo bioactivity such as murine model of inflammatory colitis. The half-life of this complex was almost 35-folds compared with the free CORM-2.

**Figure 7.** Tricarbonylchlororuthenium (II) dimer (CORM-2) synthesized with water-soluble styrene-maleic acid copolymer (SMA) for micellization CORMats.

In spite of the ligand exchange CO-release mechanism, photo light is able to disintegrate the CORMats moiety as the CO donor. Robert Igarashi and Yi Liao explored the micelle-based photo-CORMs synthesized by the cyclic α-diketones (α-DK) encapsulation [55]. These CORMs require visible photo light for releasing the embedded CO. This research demonstrates the therapeutic potential of CORMs. The photo-activated micelle CORMs strategy has been explained in Figure 8. During the study of these micelle CORMats on the cell proliferation, it has been found that no difference was monitored in the viability of cells in response to the micelles of DKs.

**Figure 8.** Synthesis route of unsaturated α-diketones (α-DKs) has been activated by photons energy.
