Sulfur Atoms Research Articles

Enhanced Electron Delocalization Induced by Ferromagnetic Sulfur doped C 3 N 4 Triggers Selective H 2 O 2 Production.

For the 2D metal-free carbon catalysts, the atomic coplanar architecture enables a large number of pzorbitals tooverlap laterally,thus formingπ-electron delocalization, and the delocalization degree of the central atom dominates the catalytic activity. Herein, designing sulfur-doped defect-rich graphitic carbon nitride (S-Nv-C3N4) materials as a model, we proposea strategy to promote localized electronpolarization by enhancing the ferromagnetism of ultra-thin 2D carbon nitride nanosheets.The introduction of sulfur (S)further promotes localized ferromagnetic coupling,thereby inducing long-range ferromagnetic ordering and accelerating the electron interface transport. Meanwhile, the hybridization of sulfur atoms breaks the symmetry and integrity of the unit structure, promoteselectron enrichment and stimulating electron delocalization at the active site. This optimization enhances the *OOH desorption, providing a favorable kinetic pathway for the production of hydrogen peroxide (H2O2). Consequently, S-Nv-C3N4exhibits high selectivity (>95%)and achieves a superb H2O2production rate,approaching4374.8ppm duringcontinuous electrolysisover 300-hour. According to theoreticalcalculationand in-situspectroscopy,the ortho-S configurationcan provide ferromagnetic perturbation incarbon active centers, leading to the electron delocalization, which optimizes the OOH* adsorption during the catalytic process.

Resolving Photoinduced Femtosecond Three-Dimensional Solute-Solvent Dynamics through Surface Hopping Simulations.

Photoinduced dynamics in solution is governed by mutual solute-solvent interactions, which give rise to phenomena like solvatochromism, the Stokes shift, dual fluorescence, or charge transfer. Understanding these phenomena requires simulating the solute's photoinduced dynamics and simultaneously resolving the three-dimensional solvent distribution dynamics. If using trajectory surface hopping (TSH) to this aim, thousands of trajectories are required to adequately sample the time-dependent three-dimensional solvent distribution functions, and thus resolve the solvent dynamics with sub-Ångstrom and femtosecond accuracy and sufficiently low noise levels. Unfortunately, simulating thousands of trajectories with TSH in the framework of hybrid quantum mechanical/molecular mechanical (QM/MM) can be prohibitively expensive when employing ab initio electronic structure methods. To tackle this challenge, we recently introduced a computationally efficient approach that combines efficient linear vibronic coupling models with molecular mechanics (LVC/MM) via electrostatic embedding [Polonius et al., JCTC 2023, 19, 7171-7186]. This method provides solvent-embedded, nonadiabatically coupled potential energy surfaces while scaling similarly to MM force fields. Here, we employ TSH with LVC/MM to unravel the photoinduced dynamics of two small thiocarbonyl compounds solvated in water. We describe how to estimate the number of trajectories required to produce nearly noise-free three-dimensional solvent distribution functions and present an analysis based on approximately 10,000 trajectories propagated for 3 ps. In the electronic ground state, both molecules exhibit in-plane hydrogen bonds to the sulfur atom. Shortly after excitation, these bonds are broken and reform perpendicular to the molecular plane on timescales that differ by an order of magnitude due to steric effects. We also show that the solvent relaxation dynamics is coupled to the electronic dynamics, including intersystem crossing. These findings are relevant to advance the understanding of the coupled solute-solvent dynamics of solvated photoexcited molecules, e.g., biologically relevant thio-nucleobases.

Synthesis of Novel 3-Deoxy-3-thio Derivatives of d-Glucosamine and Their Application as Ligands for the Enantioselective Addition of Diethylzinc to Benzaldehyde.

A series of novel thio-derivatives of d-glucosamine has been synthesized using double inversion procedures at the C3 atom. New compounds were applied as ligands for the diethylzinc addition to benzaldehyde and the products of the addition were obtained with a low to good enantiomeric ratio. The direction and the level of the asymmetric induction were highly dependent on the type of protecting groups on the nitrogen and sulfur atoms.

Thiophene network polyamides (TPPA) with tri(4-aminophenyl)benzene: Synthesis and removal of Hg2+ from aqueous solution

In this study, the thiophenyl polyamide (TPPA) derived from tri(4-aminophenyl) benzene was synthesized for the removal of Hg2+ from the aqueous solution. The adsorbent was characterized by the Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, scanning electron microscopy, nitrogen adsorption–desorption, thermogravimetric analysis and differential scanning calorimetry. The adsorption capacity of Hg2+ is 518.7 mg g−1 at a dose of 1.1 g/L of adsorbent. TPPA was shown to have the following advantages: (i) the high selectivity for the excess metal ions Hg2+, (ii) the stability in the pH values ranging between 2 and 6, and (iii) the proper recyclability (87 % of Hg2+ can be removed in 5 adsorption–desorption cycles). Our analysis suggests the models of the pseudo-second-order kinetics and the Langmuir isotherm are suitable for the description of the adsorption of Hg2+ on the thiophene network polyamide. Our experimental and theoretical results reveal the relationship between the structures and the adsorption capacities of TPPA, identifying the oxygen atom (amide) and the sulphur atom (thiophene) as the most important chemical-reaction sites.

Novel Co(II), Cu(II) and Fe(II) Pentadentate Schiff base complexes: Synthesis, characterization, antimicrobial, antioxidant, and molecular docking studies

The compound H2L, which is a ligand with five coordinating atoms, consisting of three nitrogen atoms and two sulfur atoms (N3S2), was reacted with Fe(OAc)2, Cu(OAc)2.H2O, and Co(OAc)2·4H2O to form the corresponding metal complexes ([FeL], [CuL], [CoL]). Many techniques, including NMR (for ligand), FT-IR, UV–Vis, elemental analysis, and molar conductivity, were used to characterize the synthesized compounds. According to the spectrum of data, complex molecule structures have a distorted triangular bipyramidal geometry with five coordination locations. The compounds that exhibit non-electrolyte behavior in solution do not possess any conductivity features. Evaluation was performed to determine the antioxidant activity of the synthesized compounds in comparison to the stable free radical DPPH. The ligand and its metal complexes were evaluated for antibacterial activity against several Gram-positive and Gram-negative bacteria, as well as a yeast strain. In comparison to the common antibiotic Amoxycillin/Clavulanic Acid (AMC-30), the Schiff base ligand (H2L) and its Cu(II) metal complex showed noticeably larger inhibitory zones against S. aureus. All the compounds showed a high negative binding affinity for S. aureus amino acid molecules when they were docked. The results indicated that the metal complexes, particularly the cobalt complex, exhibited a higher affinity for binding compared to the free ligand.

Synthesis, characterization, and biological activity of cationic ruthenium-arene complexes with sulfur ligands.

Five cationic ruthenium-arene complexes with the generic formula [Ru(SAc)(S2C·NHC)(p-cymene)](PF6) (5a-e) were prepared in almost quantitative yields using a straightforward one-pot, two-step experimental procedure starting from [RuCl2(p-cymene)]2, an imidazol(in)ium-2-dithiocarboxylate (NHC·CS2) zwitterion, KSAc, and KPF6. These half-sandwich compounds were fully characterized by various analytical techniques and the molecular structures of two of them were solved by X-ray diffraction analysis, which revealed the existence of an intramolecular chalcogen bond between the oxygen atom of the thioacetate ligand and a proximal sulfur atom of the dithiocarboxylate unit. DFT calculations showed that the C=S…O charge transfer amounted to 2.4kcalmol-1. The dissolution of [Ru(SAc)(S2C·IMes)(p-cymene)](PF6) (5a) in moist DMSO-d6 at room temperature did not cause the dissociation of its sulfur ligands. Instead, p-cymene was slowly released to afford the 12-electron [Ru(SAc)(S2C·IMes)]+ cation that could be detected by mass spectrometry. Monitoring the solvolysis process by 1H NMR spectroscopy showed that more than 22days were needed to fully decompose the starting ruthenium-arene complex. Compounds 5a-e exhibited a high antiproliferative activity against human glioma Hs683 and human lung carcinoma A549 cancer cells. In particular, the IMes derivative (5a) was the most potent compound of the series, achieving toxicities similar to those displayed by marketed platinum drugs.

Quinomycins with an unusual N-methyl-3-methylsulfinyl-alanine residue from a Streptomyces sp.

Four new echinomycin congeners, quinomycins M-P (1-4) were isolated from the cultures of the soil-derived Streptomyces sp. CPCC205575. The planar structures were determined by comprehensive analyses of NMR and HRESIMS/MS data. The absolute configurations were elucidated by the advanced Marfey's method combined with biosynthetic gene analysis. Compounds 1-4 represent the first examples of quinomycin-type natural products with the sulfur atom at the N,S-dimethylcysteine residue oxidized as a sulfoxide group forming the unusual N-methyl-3-methylsulfinyl-alanine residue. Bioassay results revealed that the oxidation of the sulfur atom at the Cys or Cys' residues led to dramatic decrease of cytotoxicity and antimicrobial activity.

Tracking the history of polycyclic aromatic compounds in London through a River Thames sediment core and ultrahigh resolution mass spectrometry

Polycyclic aromatic compounds (PACs), including polycyclic aromatic hydrocarbons (PAHs) and heteroatom-containing analogues, constitute an important environmental contaminant class. For decades, limited numbers of priority PAHs have been routinely targeted in pollution investigations, however, there is growing awareness for the potential occurrence of thousands of PACs in the environment. In this study, untargeted Fourier transform ion cyclotron resonance mass spectrometry was used for the molecular characterisation of PACs in a sediment core from Chiswick Ait, in the River Thames, London, UK. Using complex mixture analysis approaches, including aromaticity index calculations, the number of molecular PAC components was determined for eight core depths, extending back to the 1930s. A maximum of 1676 molecular compositions representing PACs was detected at the depth corresponding to the 1950s, and a decline in PAC numbers was observed up the core. A case linking the PACs to London’s coal consumption history is presented, alongside other possible sources, with some data features indicating pyrogenic origins. The overall core profile trend in PAC components, including compounds with oxygen, sulfur, nitrogen, and chlorine atoms, is shown to broadly correspond to the 16 priority PAH concentration profile trend previously determined for this core. These findings have implications for other industry-impacted environments.

DFT studies on electronic and structure properties of PbSe1-xSx alloys for thermoelectric materials using VCA and RS

In this work, Density Functional Theory (DFT) was employed to investigate the crystal structure and electronic properties of lead selenide (PbSe) and lead sulfide (PbS) semiconductors and their pseudo binary alloys PbSe1-xSx. The virtual crystal approximation (VCA) and randomly substituted solid models were employed to study these materials. In addition, the thermoelectric properties as function of the alloy composition were studied. Lattice parameters obtained using the generalized gradient approximation (GGA) were compared with theoretical and experimental results. The electronic bands were calculated for different sulfur compositions (0≤x ≤ 1, Δx = 0.1) using the Generalized Gradient Approximation of TB09LDA (MGGA). It was observed that the transition from the valence band to the conduction band takes place at the L point, which agrees with previous theoretical investigations. Slight deviations from Vegard's law were observed in the lattice parameters and bandgap of the alloys, especially for the sulfur-rich alloys. Effective band diagrams obtained from the unfolding of supercell band diagrams, reported for the first time for this system, show that the impacts of alloy disorder are low in the vicinity of the L point. The influence of the alloy composition on the transport properties was studied within the framework of Boltzmann's semiclassical theory. The electrical conductivity shows a thermally activated increase which influences the total thermal conductivity above T > 600–700 K, and the figure of merit ZT. Seebeck coefficient dependence with the chemical potential suggests an ambipolar behavior of the alloys, which present both n and p character. The alloys have the ZT maxima above 900 K influenced by the PbSe1-xSx alloy composition. Remarkably, the alloy with x = 0.5 present a maximum ZT value comparable to that of PbSe, which indicates that is promising to substituting selenium by sulfur atoms to tailor the thermoelectrical properties. This work shows the suitability of the VCA approximation and the band unfolding method, to describe the composition-dependent properties of the PbSe1-xSx pseudo binary alloys.

Tetrathiafulvalene carboxylate-based anode material for high-performance sodium-ion batteries.

Organic electrode materials are promising to be applied in sodium ion batteries (SIBs) due to their low cost and easily modified molecular structures. Nevertheless, low conductivity and high solubility in electrolytes still limit the development of organic electrodes. In this work, a carboxylate small molecule (BDTTS) based on tetrathiafulvalene is developed as anode material for SIBs. BDTTS has a large rigid π-conjugated planar structure, which may reduce solubility in the electrolyte, meanwhile facilitating charge transporting. Experimental results and theoretical calculations both support that apart from the four carbonyl groups, the sulfur atoms on tetrathiafulvalene also provide additional active sites during the discharge/charge process. Therefore, the additional active sites can well compensate for the capacity loss caused by the large molecular weight. The as-synthesized BDTTS electrode renders an excellent capacity of 230 mAh g-1 at a current density of 50 mA g-1 and an excellent long-life performance of 128 mAh g-1 at 2C after 500 cycles. This work enriches the study on organic electrodes for high-performance SIBs and paves the way for further development and utilization of organic electrodes.

Structure Optimization and Passivation Strategy Toward Efficient Integrated Perovskite/Pseudo‐Planar Heterojunction Solar Cells

AbstractBroadening near‐infrared (NIR) spectral response by virtue of organic bulk heterojunction (BHJ) is intensively explored to enhance power conversion efficiency (PCE) of perovskite solar cells (PSCs). However, the complex photovoltaic morphology and undesirable conductivity in BHJ structure can lead to the severe loss of photovoltaic performance, which are still urgent challenges for the commercialization of integrated PSCs (IPSCs). Recently, the gradual development of pseudo‐planar heterojunction (PPHJ) structure with excellent vertical phase separation and improved charge transfer can hopefully provide more opportunities for IPSCs. Herein, an optimization strategy is reported employing PPHJ structure with hydrophobic long alkyl chains as the NIR light‐absorbing layer in the devices, with which the light response of the IPSCs is extended to 920 nm. Owing to the lone electron pairs in the sulfur atoms, D18‐Cl has functioned as an effective additive that can effectively modulate the growth of the perovskite and passivate the defects. As a result, the optimized device has achieved an impressive PCE of 23.25%, while the short‐circuit current is enhanced from 22.93 to 25.14 mA cm−2. The long‐term and humidity stability of integrated perovskite/PPHJ solar cells are significantly elevated compared with IPSCs based on BHJ.

Exploring the nanoscale: AFM-IR visualization of cysteine adsorption on gold nanoparticles

This study focuses on the adsorption process of L-cysteine (Cys), a sulfur-containing amino acid, onto monolayers of gold nanoparticles (AuNPs) prepared through distinct protocols on mica substrates. Two types of AuNPs were prepared using two different methods: the first employed a physical approach, which combined the Inert Gas Condensation (IGC) technique with the magnetron sputtering method, while the second utilized a chemical method involving the reduction of tetrachloroauric acid with trisodium citrate (TC). The characterization of AuNPs was performed using transmission electron microscopy (TEM) and atomic force microscopy (AFM), of up to 5 ± 1.3 nm for bare AuNPs obtained through vacuum techniques, and up to 12 ± 5 nm for negatively charged, citrate-stabilized TCAuNPs(−). The application of spectroscopic techniques based on the surface-enhanced effects allows for describing the adsorption process in both micro- and nanoscale systems: Cys/bare AuNPs and Cys/ TCAuNPs(−). The commonly used surface-enhanced Raman spectroscopy (SERS) technique provided insights into adsorption behaviours at the microscale level. In the case of TCAuNPs(−), an interaction involving the lone electron pair of sulfur (S) atom and metal surface, while on the bare AuNPs, S is adsorbed on the surface, but the cleavage of the SH group is not discernible. Nanoscale analysis was complemented using AFM combined with the surface-enhanced infrared absorption spectroscopy (AFM-SEIRA) technique. AFM-SEIRA map indicated the formation of hot spot which were predominantly located between aggregated TCAuNPs(−) and on specific NPs surfaces (area between NPs and gold-coated tip). Results from the SERS and AFM-SEIRA techniques were in good agreement, underscoring the comprehensive understanding achieved through the chosen experimental approach regarding the Cys interactions with layers of AuNPs.

Efficient Mineralization of Lithium Bis(pentafluoroethanesulfonyl)imide and Related Electrolyte Fluorochemicals Using Superheated Water.

Lithium bis(pentafluoroethanesulfonyl)imide, Li[N(SO2C2F5)2], a typical fluorochemical aimed at better electrochemical performance of battery electrolytes, in superheated water was studied for its waste treatment. When Li[N(SO2C2F5)2] was reacted in pure superheated water at 300 °C, little F- ions were produced. In contrast, complete mineralization of the fluorine, sulfur, and nitrogen atoms in Li[N(SO2C2F5)2] was achieved when the reaction was performed in the presence of KMnO4. Specifically, when Li[N(SO2C2F5)2] was treated for 18 h with 158 mM of KMnO4, the F- and SO42- yields were 101 and 99%, respectively, and the sum of the NO3- and NO2- yields was 101%. In the gas phase, trace CO2 was detected and no CHF3, which has high global warming potential, was formed. Furthermore, the fluorine, sulfur, and nitrogen atoms in the analogues K[N(SO2C4F9)2] and K[N(SO2CF2)2CF2] also underwent complete mineralization using the same approach.

Unlocking the NIR‐II AIEgen for High Brightness through Intramolecular Electrostatic Locking

Fluorescent imaging and biosensing in the near‐infrared‐II (NIR‐II) window holds great promise for non‐invasive, radiation‐free, and rapid‐response clinical diagnosis. However, it’s still challenging to develop bright NIR‐II fluorophores. In this study, we report a new strategy to enhance the brightness of NIR‐II aggregation‐induced emission (AIE) fluorophores through intramolecular electrostatic locking. By introducing sulfur atoms into the side chains of the thiophene bridge in TSEH molecule, the molecular motion of the conjugated backbone can be locked through intramolecular interactions between the sulfur and nitrogen atoms. This leads to enhanced NIR‐II fluorescent emission of TSEH in both solution and aggregation states. Notably, the encapsulated nanoparticles (NPs) of TSEH show enhanced brightness, which is 2.6‐fold higher than TEH NPs with alkyl side chains. The in vivo experiments reveal the feasibility of TSEH NPs in vascular and tumor imaging with a high signal‐to‐background ratio and precise resection for tiny tumors. In addition, polystyrene nanospheres encapsulated with TSEH are utilized for antigen detection in lateral flow assays, showing a signal‐to‐noise ratio 1.9‐fold higher than the TEH counterpart in detecting low‐concentration antigens. This work highlights the potential for developing bright NIR‐II fluorophores through intramolecular electrostatic locking and their potential applications in clinical diagnosis and biomedical research.

Unlocking the NIR-II AIEgen for High Brightness through Intramolecular Electrostatic Locking.

Fluorescent imaging and biosensing in the near-infrared-II (NIR-II) window holds great promise for non-invasive, radiation-free, and rapid-response clinical diagnosis. However, it's still challenging to develop bright NIR-II fluorophores. In this study, we report a new strategy to enhance the brightness of NIR-II aggregation-induced emission (AIE) fluorophores through intramolecular electrostatic locking. By introducing sulfur atoms into the side chains of the thiophene bridge in TSEH molecule, the molecular motion of the conjugated backbone can be locked through intramolecular interactions between the sulfur and nitrogen atoms. This leads to enhanced NIR-II fluorescent emission of TSEH in both solution and aggregation states. Notably, the encapsulated nanoparticles (NPs) of TSEH show enhanced brightness, which is 2.6-fold higher than TEH NPs with alkyl side chains. The in vivo experiments reveal the feasibility of TSEH NPs in vascular and tumor imaging with a high signal-to-background ratio and precise resection for tiny tumors. In addition, polystyrene nanospheres encapsulated with TSEH are utilized for antigen detection in lateral flow assays, showing a signal-to-noise ratio 1.9-fold higher than the TEH counterpart in detecting low-concentration antigens. This work highlights the potential for developing bright NIR-II fluorophores through intramolecular electrostatic locking and their potential applications in clinical diagnosis and biomedical research.

Operando Spectroscopic Monitoring of Metal Chalcogenides for Overall Water Splitting: New Views of Active Species and Sites

AbstractMetal‐based chalcogenides exhibit great promise for overall water splitting, yet their intrinsic catalytic reaction mechanisms remain to be fully understood. In this work, we employed operando X‐ray absorption (XAS) and in situ Raman spectroscopy to elucidate the structure–activity relationships of low‐crystalline cobalt sulfide (L−CoS) catalysts toward overall water splitting. The operando results for L−CoS catalyzing the alkaline hydrogen evolution reaction (HER) demonstrate that the cobalt centers in the bulk are predominantly coordinated by sulfur atoms, which undergo a kinetic structural rearrangement to generate metallic cobalt in S−Co−Co−S moieties as the true catalytically active species. In comparison, during the acidic HER, L−CoS undergoes local structural optimization of Co centers, and H2 production proceeds with adsorption/desorption of key intermediates atop the Co−S−Co configurations. Further operando characterizations highlight the crucial formation of high‐valent Co4+ species in L−CoS for the alkaline oxygen evolution reaction (OER), and the formation of such active species was found to be far more facile than in crystalline Co3O4 and Co‐LDH references. These insights offer a clear picture of the complexity of active species and site formation in different media, and demonstrate how their restructuring influences the catalytic activity.

Operando Spectroscopic Monitoring of Metal Chalcogenides for Overall Water Splitting: New Views of Active Species and Sites.

Metal-based chalcogenides exhibit great promise for overall water splitting, yet their intrinsic catalytic reaction mechanisms remain to be fully understood. In this work, we employed operando X-ray absorption (XAS) and in situ Raman spectroscopy to elucidate the structure-activity relationships of low-crystalline cobalt sulfide (L-CoS) catalysts toward overall water splitting. The operando results for L-CoS catalyzing the alkaline hydrogen evolution reaction (HER) demonstrate that the cobalt centers in the bulk are predominantly coordinated by sulfur atoms, which undergo a kinetic structural rearrangement to generate metallic cobalt in S-Co-Co-S moieties as the true catalytically active species. In comparison, during the acidic HER, L-CoS undergoes local structural optimization of Co centers, and H2 production proceeds with adsorption/desorption of key intermediates atop the Co-S-Co configurations. Further operando characterizations highlight the crucial formation of high-valent Co4+ species in L-CoS for the alkaline oxygen evolution reaction (OER), and the formation of such active species was found to be far more facile than in crystalline Co3O4 and Co-LDH references. These insights offer a clear picture of the complexity of active species and site formation in different media, and demonstrate how their restructuring influences the catalytic activity.

Mechanistic Studies on Bromocyclization of Unsaturated Thioester by Density Functional Theory and Experiment.

Using sulfur-containing nucleophiles in halocyclization has been underexplored notwithstanding their potential to generate novel S-heterocycles and despite the extensive exploration of oxygen, nitrogen, and carbon nucleophiles. In this study, we focused on the bromocyclization of alkenoic thioesters with N-bromoacetamide, which leads to the formation of cyclic bromosulfides. Investigation into the mechanistic pathways of these reactions revealed that the sulfur atom behaves as a nucleophile, leading to S-acetylsulfonium intermediates. HBr and Br2 played significant roles in these transformations.

Sulfite ion and gold (111) surface interaction mechanism

The interaction of a sulfite ion (SO32−) with the Au (111) surface has been studied using density functional theory. The results of the geometry optimization, the charge density distribution, and the density of states showed that sulfite ions exhibit a strong interaction with the Au (111) surface atoms, and they are adsorbed by forming a strong ionic bond that leads to the rearrangement of Au surface atoms. Consequently, this interaction leads to a charge transfer from the sulfite ion to Au surface atoms. The results proved a change in the geometry of the adsorbed sulfite ion, but it is not degraded on the gold surface because of the covalent bonds between sulfur and oxygen atoms.

32 Overview over methionine metabolism: Implications in swine nutrition and health

Abstract Methionine (Met) can be referred to as a functional amino acid (AA) because besides serving as a building block for protein bio-syntheses, it also performs many other biochemical and physiological functions in swine body, simply due to its unique chemical structure and cellular metabolism. As a sulfur-containing AA (SAA), a Met molecule, as its name indicates, contains a methyl group covalently bonded to a sulfur atom via a thioether bond. In terms of its functions, first of all, Met is the initiator for virtually all protein bio-syntheses. Secondly, Met can be easily oxidized to a sulfoxide via a covalent modification, and the resulting Met sulfoxide can be readily reduced back to Met. In the case of protein-bound Met, both Met and cysteine (Cys) residues are most susceptible to oxidation and this nature can protect many proteins from oxidative damages. The biochemical metabolism of Met involves transmethylation, remethylation, transsulfuration, and transamination pathways. The initial step of transmethylation is generation of S-adenosylmethionine (SAM) which is an essential methyl donor in a myriad of metabolic events that include the methylation of DNA, RNA, proteins, phospholipids, and some small molecules. These various methylations dictate the replicational, transcriptional and translational fidelities, mismatch repair, chromatin modelling, epigenetic modification, imprinting, as well as detoxification of xenobiotics, which are all topics of great interest and importance in swine health and production performance. SAM is also a key metabolite to produce homocysteine which can be remethylated back to Met via the remethylation pathway (known as methyl cycle). The transsulfuration pathway firstly converts homocysteine to cystathionine via a condensation with serine, and then cystathionine is cleaved to Cys plus α-ketobutyrate and ammonia. Transsulfuration pathway is irreversible, and that is why Met is an indispensable AA whose deficiency cannot be remedied by Cys, whereas Cys is dispensable when more Met is provided. Because of this metabolic interconversion between Met and Cys in the body, these two are generally grouped together as SAA (Met + Cys) in swine nutrition practice. That said, when tissue Met concentration is too great, Met can be catabolized via its transamination pathway which is minor and SAM-independent. Met toxicity is mainly caused by methanethiol and H2S, two major toxic metabolites in the transamination pathway. Synthesized from Met, a myriad of proteins and peptides are involved in the functioning of immune system for maintaining animal health. For example, SAM is also a precursor for synthesis of polyamines which can enhance immune cell proliferation during an immune challenge. Cys and its derivatives (e.g., glutathione and taurine), in addition to their antioxidative capacity, can ameliorate inflammation during an immune response. In short, Met is a unique SAA that has numerous indispensable biological functions for supporting swine health and production performance.