Dissociation Of Disulfide Bonds Research Articles

In Silico Investigation of the Mechanism of Disulfide Bond Dissociation by New Frustrated Lewis Pairs.

Understanding the mechanism of disulfide bond cleavage is important in various scientific disciplines including organic synthesis, catalysis, and biochemistry. In this study, an in silico investigation has been carried out for the dissociation of disulfide bonds using newly designed frustrated Lewis pairs (FLPs). The study revealed that the cleavage of the disulfide bond by the FLP P(tBu)3/B(C2NBSHF2)3 can also be used like the conventional FLP (tBu)3P/B(C6F5)3. It has been observed that the reaction is almost thermoneutral in the gas phase but exothermic in nonpolar solvents, such as toluene, heptane, and hexane. Furthermore, the natural bond orbital (NBO) describes insights into the role of FLPs in facilitating this reaction. Additionally, reaction force and force constant studies shed light on the energy requirements for completing the reaction and the synchronous nature of the dissociation process, respectively. Reaction electronic flux (REF) and its separations give the pattern of electronic activity during the chemical reaction. Extended transition state-natural orbitals for chemical valence (ETS-NOCV) and principal interacting orbital (PIO) analysis provide valuable information about the orbital interactions during the chemical reaction.

Insights into the Zintl Cluster Mediated Disulfide Bond Separation: A DFT Study

AbstractDisulfide bond cleavage plays a crucial role in various chemical and biological processes. In recent years, developing novel and efficient catalysts for disulfide bond cleavage has garnered significant attention. This manuscript presents a comprehensive density functional theory (DFT) study on the separation of a disulfide bond by a well‐known Nona‐silicide Zintl cluster, Si94−. It is a single‐step exothermic reaction process that proceeds via the SN2 mechanism. This study also investigates the electronic activity, electron transfer process, and other electronic properties associated with the disulfide bond dissociation by the Si9‐Zintl cluster using the M06‐2X computational method.

Bioinspired Thermoplastic Elastomer with Flexible, Self-Healing Capabilities.

The self-healing property of biological tissues gives humans inspiration to endow artificial synthetic materials with self-healing functions. Herein, we report a thermoplastic elastomer that can be self-repaired in a short time, which uses dual dynamic bonds (hydrogen bonds and disulfide bonds) coupled to realize its self-healing function through the rapid conversion of dynamic hydrogen bonds between the hard and soft segments, as well as the dynamic bonding and dissociation of disulfide bonds. Furthermore, the maximum tensile strength and strain of the elastomer can reach 17.4 MPa and 3780%, respectively, and the maximum self-healing rate is close to 100% (temperature: 90 °C, time: 5 h). The arrays' arrangement and reversibility of hydrogen bonds endow the elastomer with high toughness and self-healing properties and thus solve the problem that ordinary polymers cannot self-heal.

Photoclick Reaction Constructs Glutathione-Responsive Theranostic System for Anti-Tuberculosis.

Tuberculosis (TB) is a virulent form of an infectious disease that causes a global burden due to its high infectivity and fatality rate, especially the irrepressible threats of latent infection. Constructing an efficient strategy for the prevention and control of TB is of great significance. Fortunately, we found that granulomas are endowed with higher reducibility levels possibly caused by internal inflammation and a relatively enclosed microenvironment. Therefore, we developed the first targeted glutathione- (GSH-) responsive theranostic system (RIF@Cy5.5-HA-NG) for tuberculosis with a rifampicin- (RIF-) loaded near-infrared emission carrier, which was constructed by photoclick reaction-actuated hydrophobic-hydrophobic interaction, enabling the early diagnosis of tuberculosis through granulomas-tracking. Furthermore, the loaded rifampicin was released through the dissociation of disulfide bond by the localized GSH in granulomas, realizing the targeted tuberculosis therapy and providing an especially accurate treatment mapping for tuberculosis. Thus, this targeted theranostic strategy for tuberculosis exhibits the potential to realize both granulomas-tracking and anti-infection of tuberculosis.

Ion-Conducting Dynamic Solid Polymer Electrolyte Adhesives.

Cross-linked polymer electrolytes containing structurally dynamic disulfide bonds have been synthesized to investigate their combined ion transport and adhesive properties. Dynamic network polymers of varying cross-link densities are synthesized via thiol oxidation of a bisthiol monomer, 2,2'-(ethylenedioxy)diethanethiol, and tetrathiol cross-linker, pentaerythritol tetrakis(3-mercaptopropionate). At optimal loading of lithium bis(trifluoromethane-sulfonyl-imide) (LiTFSI) salt, the ionic conductivities (σ) at 90 °C are about 1 × 10-4 and 1 × 10-5 S/cm at the lowest and highest cross-linking, respectively. Notably, in comparison to the equivalent nondynamic network, the dynamic network shows a positive deviation in σ above 90 °C, which suggests the enhancement of ion transport occurs from the difference in structural relaxation on account of the dissociation of disulfide bonds. Lap shear adhesion and conductivity tests on ITO-coated glass substrates reveal the dynamic network exhibits a higher adhesive shear strength of 0.2 MPa (vs 0.03 MPa for the nondynamic network) and higher σ after the application of external stimulus (UV light or heat). The adhesive strength and σ are stable over multiple debonding/rebonding cycles and, thus, demonstrating the utility of these structurally dynamic networks as solid polymer electrolyte adhesives.

Anticancer Effect of Intracellular-Delivered Doxorubicin Using a Redox-Responsive LMWSC-g-Lipoic Acid Micelles

To induce a quick-drug release, lipoic acid (LA) was introduced to amine group of low molecular weight water-soluble chitosan (LMWSC) by coupling agent. The disulfide bond (-S-S-) of lipoyl group from LMWSC-grafted lipoic acid (LL) can response to glutathione (GSH) at cytoplasm with reducing environment, where LL can rapidly be disassembled via dissociation of disulfide bond (-S-S-) by GSH. The doxorubicin (DOX)-encapsulated LL (LLDOX) was prepared by dialysis method, which allowed quick release of DOX by destabilization of inner-hydrophobic core of LL when disulfide bond (-S-S-) was dissociated by GSH. To demonstrate a redox-responsive release behavior of LLDOX, its drug release was accomplished under PBS buffer (pH 7.4) and GSH (10 mM) condition. In addition, the particle size and morphology of LL and LLDOX were respectively confirmed by DLS and TEM. The particle sizes of LL30% and LL60% were indicated as 268.8±30.9 and 308.1±11.9 nm, respectively. In addition, particle size of LLDOX was decreased more than that of LL. Also, surface charge of LLDOX was displayed to strong positive charge (LLDOX30%: 12.6±0.5 mV, LLDOX60%: 9.6±1.1 mV). Moreover, their morphological structure has a spherical shape. The cytotoxicity LL and LLDOX was confirmed by using MTT assay. Besides, to investigate the intracellular uptake of DOX from LLDOX against HeLa and AGS cell lines, fluorescence image was observed by using fluorescence microscopy. These results suggest that LL is an excellent as a drug carrier due to high anticancer effect by rapid drug release with redox-responsive effect.

Exploring ECD on a Benchtop Q Exactive Orbitrap Mass Spectrometer.

As the application of mass spectrometry intensifies in scope and diversity, the need for advanced instrumentation addressing a wide variety of analytical needs also increases. To this end, many modern, top-end mass spectrometers are designed or modified to include a wider range of fragmentation technologies, for example, ECD, ETD, EThcD, and UVPD. Still, the majority of instrument platforms are limited to more conventional methods, such as CID and HCD. While these latter methods have performed well, the less conventional fragmentation methods have been shown to lead to increased information in many applications including middle-down proteomics, top-down proteomics, glycoproteomics, and disulfide bond mapping. We describe the modification of the popular Q Exactive Orbitrap mass spectrometer to extend its fragmentation capabilities to include ECD. We show that this modification allows ≥85% matched ion intensity to originate from ECD fragment ion types as well as provides high sequence coverage (≥60%) of intact proteins and high fragment identification rates with ∼70% of ion signals matched. Finally, the ECD implementation promotes selective disulfide bond dissociation, facilitating the identification of disulfide-linked peptide conjugates. Collectively, this modification extends the capabilities of the Q Exactive Orbitrap mass spectrometer to a range of new applications.

Formation of negative ions via resonant low-energy electron capture by cysteine and cystine methyl esters

The processes of resonance low-energy free electron attachment to methyl esters of some sulfur-containing amino acids were studied. The long-lived molecular negative ions of cystine dimethyl ester formed in the valence state via the Feshbach nuclear excited resonance mechanism were detected by mass spectrometry. The reactions of disulfide bond dissociation were identified in an electron energy range of 0—1 eV. They can be considered as model reactions regarding processes of peptide decomposition due to the resonance interaction with low-energy electrons. Predissociation of short-lived molecular ions of cysteine methyl ester formed by capture of electrons with energies of ~1.6 eV is accompanied by the intra-ionic transfer of negative charge from the carbonyl group to the sulfur atom leading to the elimination from the latter of hydrogen atom.

Mesoporous carbon nanoparticles capped with polyacrylic acid as drug carrier for bi-trigger continuous drug release.

A pH and redox responsive bi-trigger continuous drug release nanocarrier is developed by capping mesoporous carbon nanoparticles (MCNs) with polyacrylic acid (PAA), termed as PAA-ss-MCN. The nanocarrier contains disulfide bond units and exhibits pH responsive behavior. It provides promising potential for drug loading due to the internal uniform channels and large surface area of MCNs. PAA grafted on the exterior surface of MCNs acts as a gating layer, generating a novel nano-container and a pH-responsive intelligent nanovalve. By loading doxorubicin (DOX) in PAA-ss-MCN, its sequential release is achieved via two approaches: (1) the intracellular acidic environment induces partial release from the surface of the PAA gating layer, (2) release of the drug sealed in nanochannels via disruption of the integrity of the nanocarrier by glutathione (GSH) caused dissociation of disulfide bonds in the physiological environment. As a result, release of 62% loaded drug is readily achieved. After culturing with HeLa cells, DOX transports into the cell interior and therein exhibits pH- and GSH-sensitive release. As most tumor sites exhibit more acidic environments or high redox potential, the pH- and GSH-sensitive releasing capability of PAA-ss-MCN is particularly useful for controllable drug delivery by taking advantage of the inherent characteristics of tumor cells.

Dibenzyl disulfide adsorption on Cu(111) surface: a DFT study

The adsorption of dibenzyl disulfide (DBDS) on a Cu(111) surface model was investigated by using density functional calculations, considering energetic and electronic aspects. Several complexes were generated, where the bridge, hollow hcp, hollow fcc and top adsorption sites were considered. The results show that the Cu–S interaction guides the final complexes, and a secondary π–Cu weak interaction confers an extra stability. The complexes were grouped as physi- or chemisorption according to their adsorption energy applying a distortion decomposition model, with a preference by a double interaction of S with Cu (i.e., hollow hcp and bridge sites). A degree of disulfide bond dissociation was observed in the complexes, being correlated with adsorption energies. From an electronic aspect, it was found that the electronic flow from copper to DBDS occurs in the most stable complexes, checked with charge analysis. These results are in agreement with experimental revelations of copper corrosion on power transformers.

Theoretical study of dibenzyl disulfide adsorption on Cu7 cluster as a first approximation to sulfur-induced copper corrosion process

The adsorption of dibenzyl disulfide (DBDS) on a pentagonal bipyramid Cu-7 cluster was investigated by using density functional calculations, from energetic and electronic viewpoints. The resulting complexes are mainly driven by Cu center dot center dot center dot S interaction, and an extra stabilization can be conferred by a secondary pi center dot center dot center dot Cu weak interaction. They were classified as physi- or chemisorption according to their binding energy, and by applying a distortion/interaction decomposition model. Disulfide bond dissociation was observed in the most stable complexes, which includes higher distortion energy. From an electronic viewpoint, an electronic flow from copper to DBDS was observed.

Direct sequencing of a disulfide-linked peptide with electrospray ionization tandem mass spectrometry.

Dissociation of disulfide is normally mandatory prior to disulfide peptide sequencing via electrospray ionization collision induced dissociation mass spectrometry (ESI-CID-MS). Herein, a facile method for directly sequencing intact disulfide peptides was proposed. The basic principles involved were electrolyte-enhanced corona discharge in ESI and the following oxidative cleavage reaction.

Adsorption behaviour of sulfur containing polymers to gold surfaces using QCM-D

We investigate the influences that functional group, polymer molecular weight and polymer molecular architecture have on the adsorption behaviour of some sulfur containing oligo(ethylene glycol) polymers to gold. QCM-D and XPS was used in this investigation revealing that disulfide functional groups bind with more mass deposited than dithio, trithio or thiols. This was observed with small di(ethylene glycol) polymers and with higher mass polymers. The effect of the sulfo-groups was not as apparent with higher mass polymers. Longer PEG pendent chains resulted in lower binding overall on the gold surface in comparison to shorter DEG chains caused by shielding of sulfur by the longer pendent chains. Thiols undergo two steps during the adsorption process while all other sulfur species adsorb in one step. XPS revealed the dissociation of disulfide bonds when binding to gold. These findings are important when forming stable polymer films on gold efficiently, with uses in applications from bio-fouling to polymer-lipid bilayers.

Deformation Model for Thioredoxin Catalysis of Disulfide Bond Dissociation by Force

We develop a theoretical model describing the effect of applied force on the rate of enzymatic dissociation of disulfide bonds (Wiita, A. P. et al., Nature 450:124–127, 2007). The timescale characterizing the extension of the 8-domain protein chain, in which every domain contains a disulfide bond, exhibits anomalous force dependence: The extension time first increases and then decreases with increasing force. This type of force dependence indicates catch-binding and is under active investigation in a variety of systems. The disulfide system presents the first example of a chemical catch-bond. The key difference between the deformation model developed here and the two-pathway model used in the original publication is the bond-deformation term in the force dependence of the dissociation rate constant. The bond-deformation concept provides a different interpretation of the phenomenon. Rather than invoking a new dissociation pathway, which is difficult to rationalize for a simple S–S bond, catch-binding is explained by a force-induced deformation in the protein system disfavoring bond dissociation by thioredoxin. The analysis of the experimental data is performed within the Michaelis–Menten kinetic mechanism of enzyme catalysis. A simplified version of the Michaelis–Menten mechanism containing only four parameters is found to provide a quantitative description of the key features of the experimental data.

Abnormal adsorption behavior of dimethyl disulfide on gold surfaces

Adsorption of dimethyl disulfide (DMDS) on gold colloidal nanoparticle surfaces has been examined to check its binding mechanism. Differently from previous results, DMDS molecules adsorbed on the gold surface at high concentration showed the S–S stretching band at ∼500 cm−1 in surface-enhanced Raman scattering (SERS) spectra, which indicates the presence of intact adsorption of DMDS molecules. However, it was found that the S–S bond of disulfides was easily cleaved on the gold surface at low concentration. These behaviors were not observed for diethyl disulfide (DEDS) or diphenyl disulfide (DPDS). Our results indicate that DMDS molecules with the shortest alkyl chains on the gold surface can be inserted into self-assembled monolayers (SAMs) without the S–S bond cleavage during self-assembly due to insufficient lateral van der Waals interaction and the low adsorption activity of disulfides, whereas DEDS with longer alkyl chains or DPDS with the weak disulfide bond dissociation energy would not. These unusual DMDS adsorption behaviors were examined by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). We also compared the bonding dissociation energy of the S–S bonds of various disulfides by means of a density functional theory (DFT) calculation.

Laser treatment of keloids and hypertrophic scars

Lasers have been used in the treatment of hypertrophic scars and keloids for more than 20 years. Different laser systems have been examined; among them pulsed dye lasers are currently considered the laser of choice in these settings. The purpose of this study is to review the pertinent literature and provide updated information on different laser therapies available for treatment of keloids and hypertrophic scars. A Medline literature search was performed for relevant publications. In this review the results of published studies in the treatment and prevention of hypertrophic scars and keloids are presented. Suggested mechanisms of action are reviewed. A review of the optimal laser parameters to modulate treatment outcome will be discussed. Different lasers are effective in not only the treatment but also the prevention of hypertrophic scars and keloids, among them PDL is more promising. Most of the suggested theories are based on the selective photothermolysis in which the light energy emitted from a vascular laser is absorbed by hemoglobin, generating heat and leading to coagulation necrosis, neocollagenesis, collagen fiber heating with dissociation of disulfide bonds and subsequent collagen fiber realignment. The optimal laser is currently 585 nm PDL, although the recent results of Q-switched 532 nm frequency-doubled Nd:YAG are promising. Early use of lasers are beneficial, especially in those who are prone to develop these lesions.

Selective Disulfide Bond Cleavage in Gold(I) Cationized Polypeptide Ions Formed via Gas-Phase Ion/Ion Cation Switching

Gaseous multiply protonated disulfide-linked peptides have been subjected to reactions with AuCl2(-) ions to explore the possibility of effecting cation switching of Au+ for two protons and to determine whether cationization by Au+ ions affords selective dissociation of disulfide linkages. The incorporation of Au+ into several model disulfide-linked peptides proved to be straightforward. The primary ion/ion reaction channels were proton transfer, which does not lead to Au+ incorporation, and attachment of AuCl2(-) ions to the polypeptide cation, which does incorporate Au+. Fragmentation of the attachment product, the extent of which varied with peptide and charge state, led to losses of one or more molecules of HCl and, to some extent, cleavage of polypeptides at the disulfide linkage into its two constituent chains. Collisional activation of the intact metal-ion-incorporated peptides showed cleavage of the disulfide linkage to be a major, and in some cases exclusive, process. Cations with protons as the only cationizing agents showed only small contributions from cleavage of the disulfide linkage. These results indicate that Au+ incorporation into a disulfide-linked polypeptide ion is a promising way to effect selective dissociation of disulfide bonds. Cation switching via ion/ion reactions is a convenient means for incorporating gold and is attractive because it avoids the requirement of adding metal salts to the analyte solution.

Mapping of Protein Disulfide Bonds Using Negative Ion Fragmentation with a Broadband Precursor Selection

Fast mapping of disulfide bonds in proteins containing multiple cysteine residues is often required in order to assess the integrity of the tertiary structure of proteins prone to degradation and misfolding or to detect distinct intermediate states generated in the course of oxidative folding. A new method of rapid detection and identification of disulfide-linked peptides in complex proteolytic mixtures utilizes the tendency of collision-activated peptide ions to lose preferentially side chains of select amino acids in the negative ion mode. Cleavages of cysteine side chains result in efficient dissociation of disulfide bonds and produce characteristic signatures in the fragment ion mass spectra. While cleavages of other side chains result in insignificant loss of mass and full retention of the peptide ion charge, dissociation of external disulfide bonds results in physical separation of two peptides and, therefore, significant changes of both mass and charge of fragment ions relative to the precursor ion. This feature allows the fragment ions generated by dissociation of external disulfide bonds to be easily detected and identified even if multiple precursor ions are activated simultaneously. Such broadband selection of precursor ions for consecutive activation is achieved by lowering the dc/rf amplitude ratio in the first quadrupole filter of a hybrid quadrupole time-of-flight mass spectrometer. The feasibility of the new method is demonstrated by partial mapping of disulfide bridges within a 37-kDa protein containing 16 cysteine residues and complete disulfide mapping within a lysozyme (14.5 kDa) containing 8 cysteine residues. In addition to detecting peptide pairs connected by a single external disulfide, the new method is also shown to be capable of identifying peptides containing both external and internal disulfide bonds. The two major factors determining the efficiency of disulfide mapping using the new methodology are the effectiveness of proteolysis and the ability of the resulting proteolytic fragments to form multiply charged negative ions.