Evaluation of Thiol Raman Activities and pKa Values Using Internally Referenced Raman-Based pH Titration

Benchmarking Thiolate-Driven Photoswitching of Cyanine Dyes

Carbocyanines are among the best performing dyes in single-molecule localization microscopy (SMLM), but their performance critically relies on optimized photoswitching buffers. Here, we study the versatile role of thiols in cyanine photoswitching at varying intensities generated in a single acquisition by a microelectromechanical systems (MEMS) mirror placed in the excitation path. The key metrics we have analyzed as a function of the thiolate concentration are photon budget, on-state and off-state lifetimes and the corresponding impact on image resolution. We show that thiolate acts as a concentration bandpass filter for the maximum achievable resolution and determine a minimum of ∼1 mM is necessary to facilitate SMLM measurements. We also identify a concentration bandwidth of 1-16 mM in which the photoswitching performance can be balanced between high molecular brightness and high off-time to on-time ratios. Furthermore, we monitor the performance of the popular oxygen scavenger system based on glucose and glucose oxidase over time and show simple measures to avoid acidification during prolonged measurements. Finally, the impact of buffer settings is quantitatively tested on the distribution of the glucose transporter protein 4 within the plasma membrane of adipocytes. Our work provides a general strategy for achieving optimal resolution in SMLM with relevance for the development of novel buffers and dyes.

Chiral-Solvent-Mediated Manganese-Based Hierarchical Supraparticles with Chiroptical Activity

In this study, manganese-based multiply hierarchical chiral supraparticles (SPs), with an anisotropy factor (g-factor) of 0.102 and circular dichroism (CD) intensity of 260 mdeg at 530 nm, are successfully synthesized with polar-solvent-mediated strategies. Notably, the g-factor of the SPs is further enhanced to 0.121 by the addition of an external chiral solvent, generating a chiral biased environment, which increases their CD intensity to 320 mdeg at 500 nm. The mechanism underlying the different chirality is proposed to be a difference in the angle of tilt of ±33° between the two enantiomers of the chiral SPs, which involves a difference of ±7° between the orientation of individual nanoplatelets. Chiral solvents induce the angle between adjacent nanoplatelets to get smaller than the original structure that leads to their higher anisotropic value. These findings potentially provide a practical method for the construction of complex chiral superstructures and the regulation of chiroptical activity.

Electrophile versus oxidant modification of cysteine residues: Kinetics as a key driver of protein modification

Humans have widespread exposure to both oxidants, and soft electrophilic compounds such as alpha,beta-unsaturated aldehydes and quinones. Electrophilic motifs are commonly found in a drugs, industrial chemicals, pollutants and are also generated via oxidant-mediated degradation of biomolecules including lipids (e.g. formation of 4-hydroxynonenal, 4-hydroxyhexenal, prostaglandin J2). All of these classes of compounds react efficiently with Cys residues, and the particularly the thiolate anion, with this resulting in Cys modification via either oxidation or adduct formation. This can result in deleterious or beneficial effects, that are either reversible (e.g. in cell signalling) or irreversible (damaging). For example, acrolein is a well-established toxin, whereas dimethylfumarate is used in the treatment of multiple sclerosis and psoriasis. This short review discusses the targets of alpha,beta-unsaturated aldehydes, and particularly two prototypic cases, acrolein and dimethylfumarate, and the factors that control the selectivity and kinetics of reaction of these species. Comparison is made between the reactivity of oxidants versus soft electrophiles. These rate constants indicate that electrophiles can be significant thiol modifying agents in some situations, as they have rate constants similar to or greater than species such as H₂O₂, can be present at higher concentrations, and are less efficiently removed by protective systems when compared to H₂O₂. They may also induce similar or higher levels of modification than highly reactive oxidants, due to the very low concentrations of oxidants formed in most in vivo situations.

Stereoselective Growth of Small Molecule Patches on Nanoparticles

Patchy nanoparticles featuring tunable surface domains with spatial and chemical specificity are of fundamental interest, especially for creating three-dimensional (3D) colloidal structures. Guided assembly and regioselective conjugation of polymers have been widely used to manipulate such topography on nanoparticles; however, the processes require presynthesized specialized polymer chains and elaborate assembly conditions. Here, we show how small molecules can form 3D patches in aqueous environments in a single step. The patch features (e.g., size, number, conformation, and stereoselectivity) are modulated by a self-polymerizable aromatic dithiol and comixed ligands, which indicates an autonomous assembly mechanism involving covalent polymerization and supramolecular assembly. Moreover, this method is independent of the underlying nanoparticle material and dimension, offering a streamlined and powerful toolset to design heterogeneous patches on the nanoscale.

Isomeric Effect of Nano-Inhibitors on Aβ40 Fibrillation at The Nano-Bio Interface

Chemical and physical properties of nanobio interface substantially affect the conformational transitions of adjacent biomolecules. Previous studies have reported the chiral effect and charge effect of nanobio interface on the misfolding, aggregation, and fibrillation of amyloid protein. However, the isomeric effect of nanobio interface on protein/peptides amyloidosis is still unclear. Here, three isomeric nanobio interfaces were designed and fabricated based on the same sized gold nanoclusters (AuNCs) modified with 4-mercaptobenzoic acid (p-MBA), 3-mercaptobenzoic acid (m-MBA), and 2-mercaptobenzoic acid (o-MBA). Then three isomeric AuNCs were employed as models to explore the isomeric effect on the misfolding, aggregation, and fibrillation of Aβ₄₀ at nanobio interfaces. Site-specific replacement experiments on the basis of theoretical analysis revealed the possible mechanism of Aβ₄₀ interacting with isomeric ligands of AuNCs at the nanobio interfaces. The distance and orientation of -COOH group from the surface of AuNCs can affect the electrostatic interaction between isomeric ligands and the positively charged residues (R5, K16, and K28) of Aβ₄₀, which may affect the inhibition efficiency of isomeric AuNCs on protein amyloidosis. Actually, the amyloid fibrillation kinetics results together with atomic force microscope (AFM) images, dynamic light scattering (DLS) results and circular dichroism (CD) spectra indeed proved that all the three isomeric AuNCs could inhibit the misfolding, aggregation and fibrillation of Aβ₄₀ in a dose-dependent manner, and the inhibition efficiency was definitely different from each other. The inhibition efficiency of o-MBA-AuNCs was higher than that of m-MBA-AuNCs and p-MBA-AuNCs at the same dosage. These results provide an insight for isomeric effect at nanobio interfaces, and open an avenue for structure-based nanodrug design target Alzheimer's disease (AD) and even other protein conformational diseases.

A theoretical study on the pKa values of selenium compounds in aqueous solution

The pK_a values of different kinds of selenium compounds (R-SeH) were investigated by using the ωB97XD method with a SMD model.

Theoretical modeling of pKa's of thiol compounds in aqueous solution

The pK_a's of different kinds of thiols (R-SH) were investigated by using the M06-2X method with a SMD_sSAS model.

Simultaneous determination of the lipophilicity and dissociation constants of dialkyl phosphinic acids by negligible depletion hollow fiber membrane-protected liquid-phase microextraction

Determination of the physicochemical properties, especially the lipophilicity (expressed as the logarithm of distribution coefficient, log D) and dissociation constant (pK_a), is of great importance in the early stage of environmental risk assessment for an ionizable compound without these data. Currently, the log D and pK_a values of dialkyl phosphinic acids (DPAs), the environmental hydrolysates of aluminum dialkyl phosphinates (ADPs) that is one class of emerging phosphorus-containing flame retardants, are not available. In this study, the log D and pK_a values of three DPAs including methylethylphosphinic acid (MEPA), diethylphosphinic acid (DEPA) and methylcyclohexyl phosphinic acid (MHPA), were simultaneously determined by negligible depletion hollow fiber supported liquid phase microextraction (nd-HF-LPME) followed by ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). The pK_a and log D of DPAs were determined by curve-fitting the experimental data with equations derived on the basis of the Henderson-Hasselbalch equation and compared with model calculated data. For MEPA, DEPA and MHPA, the pK_a values were close and around 3, but the log Ds were strongly pH-dependent with values from -5.01 to 1.01. The log K_OW of the neutral form (logK_OW,HA) and ionic form (logK_OW,A) were in the range of -0.67-1.02 and -3.86--1.33, respectively. The experimentally determined pK_a values were highly in good agreement with ACD/pK_a predicted values and the measured log K_OW,HA values were closely related to KOWWIN calculated ones, suggesting ACD/pK_a and KOWWIN are good alternative methods to estimate pK_a and log K_OW of DPAs, respectively. As far as we know, this is the first report on the pK_a and log D data for DPAs, which are fundamental for the product design and evaluating the environmental behavior and effects of DPAs and ADPs.

Carbon disulfide. Just toxic or also bioregulatory and/or therapeutic?

The overview presented here has the goal of examining whether carbon disulfide (CS₂) may play a role as an endogenously generated bioregulator and/or has therapeutic value.