A unique family of stable and water-soluble S-nitrosothiol complexes

Nitric oxide-releasing thiolated starch nanoparticles embedded in gelatin sponges for wound dressing applications

This study introduces a novel wound dressing by combining nitric oxide-releasing thiolated starch nanoparticles (NO-TS NPs) with gelatin. First, starch was thiolated (TS), and then its nanoparticles were prepared (TS NPs). Subsequently, NPs were covalently bonded to sodium nitrite to obtain NO-releasing TS NPs (NO-TS-NPs) that were incorporated into gelatin sponges at various concentrations. The resulting spherical TS NPs had a mean size of 85.42 ± 5.23 nm, which rose to 100.73 ± 7.41 nm after bonding with sodium nitrite. FTIR spectroscopy confirmed S-nitrosation on the NO-TS NPs' surface, and morphology analysis showed well-interconnected pores in all sponges. With higher NO-TS NPs content, pore size, porosity, and water uptake increased, while compressive modulus and strength decreased. Composites exhibited antibacterial activity, particularly against E. coli, with enhanced efficacy at higher NPs' concentrations. In vitro release studies demonstrated Fickian diffusion, with faster NO release in sponges containing more NPs. The released NO amounts were non-toxic to fibroblasts, but samples with fewer NO-TS NPs exhibited superior cellular density, cell attachment, and collagen secretion. Considering the results, including favorable mechanical strength, release behavior, antibacterial and cellular properties, gelatin sponges loaded with 2 mg/mL of NO-TS NPs can be suitable for wound dressing applications.

Biological Mechanisms of S-Nitrosothiol Formation and Degradation: How Is Specificity of S-Nitrosylation Achieved?

The modification of protein cysteine residues underlies some of the diverse biological functions of nitric oxide (NO) in physiology and disease. The formation of stable nitrosothiols occurs under biologically relevant conditions and time scales. However, the factors that determine the selective nature of this modification remain poorly understood, making it difficult to predict thiol targets and thus construct informatics networks. In this review, the biological chemistry of NO will be considered within the context of nitrosothiol formation and degradation whilst considering how specificity is achieved in this important post-translational modification. Since nitrosothiol formation requires a formal one-electron oxidation, a classification of reaction mechanisms is proposed regarding which species undergoes electron abstraction: NO, thiol or S-NO radical intermediate. Relevant kinetic, thermodynamic and mechanistic considerations will be examined and the impact of sources of NO and the chemical nature of potential reaction targets is also discussed.

Biological control of S-nitrosothiol reactivity: potential role of sigma-hole interactions

S-Nitrosothiols (RSNOs) are ubiquitous biomolecules whose chemistry is tightly controlled in vivo, although the specific molecular mechanisms behind this biological control remain unknown. In this work, we demonstrate, using high-level ab initio and DFT calculations, the ability of RSNOs to participate in intermolecular interactions with electron pair donors/Lewis bases (LBs) via a σ-hole, a region of positive electrostatic potential on the molecular surface at the extension of the N-S bond. Importantly, σ-hole binding is able to modulate the properties of RSNOs by changing the balance between two chemically opposite (antagonistic) resonance components, R-S⁺[double bond, length as m-dash]N-O^- (D) and R-S^-/NO⁺ (I), which are, in addition to the main resonance structure R-S-N[double bond, length as m-dash]O, necessary to describe the unusual electronic structure of RSNOs. σ-Hole binding at the sulfur atom of RSNO promotes the resonance structure D and reduces the resonance structure I, thereby stabilizing the weak N-S bond and making the sulfur atom more electrophilic. On the other hand, increasing the D-character of RSNO by other means (e.g. via N- or O-coordination of a Lewis acid) in turn enhances the σ-hole bonding. Our calculations suggest that in the protein environment a combination of σ-hole bonding of a negatively charged amino acid sidechain at the sulfur atom and N- or O-coordination of a positively charged amino acid sidechain is expected to have a profound effect on the RSNO electronic structure and reactivity.

Protein S-Nitrosylation: Determinants of Specificity and Enzymatic Regulation of S-Nitrosothiol-Based Signaling

SIGNIFICANCE

Protein S-nitrosylation, the oxidative modification of cysteine by nitric oxide (NO) to form protein S-nitrosothiols (SNOs), mediates redox-based signaling that conveys, in large part, the ubiquitous influence of NO on cellular function. S-nitrosylation regulates protein activity, stability, localization, and protein-protein interactions across myriad physiological processes, and aberrant S-nitrosylation is associated with diverse pathophysiologies. Recent Advances: It is recently recognized that S-nitrosylation endows S-nitroso-protein (SNO-proteins) with S-nitrosylase activity, that is, the potential to trans-S-nitrosylate additional proteins, thereby propagating SNO-based signals, analogous to kinase-mediated signaling cascades. In addition, it is increasingly appreciated that cellular S-nitrosylation is governed by dynamically coupled equilibria between SNO-proteins and low-molecular-weight SNOs, which are controlled by a growing set of enzymatic denitrosylases comprising two main classes (high and low molecular weight). S-nitrosylases and denitrosylases, which together control steady-state SNO levels, may be identified with distinct physiology and pathophysiology ranging from cardiovascular and respiratory disorders to neurodegeneration and cancer.

CRITICAL ISSUES

The target specificity of protein S-nitrosylation and the stability and reactivity of protein SNOs are determined substantially by enzymatic machinery comprising highly conserved transnitrosylases and denitrosylases. Understanding the differential functionality of SNO-regulatory enzymes is essential, and is amenable to genetic and pharmacological analyses, read out as perturbation of specific equilibria within the SNO circuitry.

FUTURE DIRECTIONS

The emerging picture of NO biology entails equilibria among potentially thousands of different SNOs, governed by denitrosylases and nitrosylases. Thus, to elucidate the operation and consequences of S-nitrosylation in cellular contexts, studies should consider the roles of SNO-proteins as both targets and transducers of S-nitrosylation, functioning according to enzymatically governed equilibria.

Light-activated generation of nitric oxide (NO) and sulfite anion radicals (SO3˙−) from a ruthenium(ii) nitrosylsulphito complex

This manuscript describes the preparation of a new Ru(ii) nitrosylsulphito complex,trans-[Ru(NH₃)₄(isn)(N(O)SO₃)]⁺(complex1), its spectroscopic and structural characterization, photochemistry, and thermal reactivity.

Synthesis and structural characterisation of unprecedented primary N-nitrosamines coordinated to iridium(iv)

The one electron oxidation of the N-nitrosamine complexes [Ir^IIICl₅(RN(H)NO)]^2– (R = benzyl or n-butyl) was studied in detail.

Direct NMR detection of the unstable “red product” from the reaction between nitroprusside and 2-mercaptosuccinic acid

First NMR characterization of the unstable “red product” produced from the reaction between nitroprusside and organic thiolates.

Thiol redox biochemistry: insights from computer simulations

Thiol redox chemical reactions play a key role in a variety of physiological processes, mainly due to the presence of low-molecular-weight thiols and cysteine residues in proteins involved in catalysis and regulation. Specifically, the subtle sensitivity of thiol reactivity to the environment makes the use of simulation techniques extremely valuable for obtaining microscopic insights. In this work we review the application of classical and quantum-mechanical atomistic simulation tools to the investigation of selected relevant issues in thiol redox biochemistry, such as investigations on (1) the protonation state of cysteine in protein, (2) two-electron oxidation of thiols by hydroperoxides, chloramines, and hypochlorous acid, (3) mechanistic and kinetics aspects of the de novo formation of disulfide bonds and thiol-disulfide exchange, (4) formation of sulfenamides, (5) formation of nitrosothiols and transnitrosation reactions, and (6) one-electron oxidation pathways.

Copper(I) nitrosyls from reaction of copper(II) thiolates with S-nitrosothiols: mechanism of NO release from RSNOs at Cu

S-nitrosothiols (RSNOs) serve as ready sources of biological nitric oxide activity, especially in conjunction with copper centers. We report a novel pathway for the generation of NO within the coordination sphere of copper model complexes from reaction of copper(II) thiolates with S-nitrosothiols. Reaction of tris(pyrazolyl)borate copper(II) thiolates (iPr2)TpCu-SR (R = C6F5 or CPh3) with (t)BuSNO leads to formation of (iPr2)TpCu(NO) and the unsymmetrical disulfide RS-S(t)Bu. Quantum mechanical investigations with B3LYP-D3/6-311G(d) suggest formation of a κ(1)-N-RSNO adduct (iPr2)TpCu(SR)(R'SNO) that precedes release of RSSR' to deliver (iPr2)TpCu(NO). This process is reversible; reaction of (iPr2)TpCu(NO) (but not (iPr2)TpCu(NCMe)) with C6F5S-SC6F5 forms (iPr2)TpCu-SC6F5. Coupled with the facile, reversible reaction between (iPr2)TpCu(NO) and C6F5SNO to give (iPr2)TpCu-SC6F5 and 2 equiv NO, we outline a new, detailed catalytic cycle for NO generation from RSNOs at Cu.

Nitric oxide delivery by core/shell superparamagnetic nanoparticle vehicles with enhanced biocompatibility

We report the synthesis of Fe(3)O(4)/silica core/shell nanoparticles and their functionalization with S-nitrosothiols. These nanoparticles are of immense interest because of their nitric oxide (NO) release capabilities in human alveolar epithelial cells. Moreover, they act as large storage reservoirs of NO that can be targeted magnetically to the specific site with a sustainable release of NO for up to 50 h. Such nanoparticles provide an enhancement of the biocompatibility with released NO while allowing intracellular accumulation ascribed to their small size.

Zinc thiolate reactivity toward nitrogen oxides: insights into the interaction of Zn2+ with S-nitrosothiols and implications for nitric oxide synthase

Zinc thiolate complexes containing N(2)S tridentate ligands were prepared to investigate their reactivity toward reactive nitrogen species, chemistry proposed to occur at the zinc tetracysteine thiolate site of nitric oxide synthase (NOS). The complexes are unreactive toward nitric oxide (NO) in the absence of dioxygen, strongly indicating that NO cannot be the species directly responsible for S-nitrosothiol formation and loss of Zn(2+) at the NOS dimer interface in vivo. S-Nitrosothiol formation does occur upon exposure of zinc thiolate solutions to NO in the presence of air, however, or to NO(2) or NOBF(4), indicating that these reactive nitrogen/oxygen species are capable of liberating zinc from the enzyme, possibly through generation of the S-nitrosothiol. Interaction between simple Zn(2+) salts and preformed S-nitrosothiols leads to decomposition of the -SNO moiety, resulting in release of gaseous NO and N(2)O. The potential biological relevance of this chemistry is discussed.