Dependency of fentanyl analogue protomer ratios on solvent conditions as measured by ion mobility-mass spectrometry.

Recently, our group has shown that fentanyl and many of its analogues form prototropic isomers ("protomers") during electrospray ionization. These different protomers can be resolved using ion mobility spectrometry and annotated using mobility-aligned tandem mass spectrometry fragmentation. However, their formation and the extent to which experimental variables contribute to their relative ratio remain poorly understood. In the present study, we systematically investigated the effects of mixtures of common chromatographic solvents (water, methanol, and acetonitrile) and pH on the ratio of previously observed protomers for 23 fentanyl analogues. Interestingly, these ratios (N-piperidine protonation vs. secondary amine/O = protonation) decreased significantly for many analogues (e.g., despropionyl ortho-, meta-, and para-methyl fentanyl), increased significantly for others (e.g., cis-isofentanyl), and remained relatively constant for the others as solvent conditions changed from 100% organic solvent (methanol or acetonitrile) to 100% water. Interestingly, pH also had significant effects on this ratio, causing the change in ratio to switch in many cases. Lastly, increasing conditions to pH ≥ 4.0 also prompted the appearance of new mobility peaks for ortho- and para-methyl acetyl fentanyl, where all previous studies had only showed one single distribution. Because these ratios have promise to be used qualitatively for identification of these (and emerging) fentanyl analogues, understanding how various conditions (i.e., mobile phase selection and/or chromatographic gradient) affect their ratios is critically important to the development of advanced ion mobility and mass spectrometry methodologies to identify fentanyl analogues.

Linear isomer but not branched isomers of perfluorooctane sulfonate in plasma is associated with eicosapentaenoic acid, a seafood consumption biomarker.

BACKGROUND: Per- and polyfluoroalkyl substances (PFAS) are global contaminants. Seafood consumption is a possible PFAS exposure route to humans while the isomer specific analysis has not been conducted. METHODS: Perfluorooctane sulfonate (PFOS), perfluoroheptane sulfonate (PFHpS) and perfluorohexane sulfonate (PFHxS) were investigated in residents of Kyoto, Japan (n = 51). The relationship between plasma PFAS and seafood consumption biomarker, the ratio of eicosapentaenoic acid to arachidonic acid (EPA/AA) was examined by multiple regression analysis. RESULTS: Linear PFOS concentrations showed a significant positive correlation with the EPA/AA ratio in plasma samples (ß = 6.80, p = 0.0014). Linear PFHpS was marginally associated with EPA/AA ratio (ß = 0.178, p = 0.0874). Branched PFOS isomers and PFHxS had no associations with EPA/AA ratios. CONCLUSION: Seafood intake may be a significant exposure pathway for PFAS, such as PFOS but the isomers differ.

A novel cinnamic and caffeic acid-conjugated peptide analogs with anticonvulsant and analgesic potency: Comparative analyses of trans/cis isomers.

The novel cinnamic acid (CA) (H4-CA, H5-CA, and H7-CA) and caffeic acid (KA) (H4-KA, H5-KA, and H7-KA) hemorphin analogs have recently been synthesized and their trans isomers have been tested for antiseizure and antinociceptive activity. In the present study, the cis forms of these compounds were tested and compared with their trans isomers in seizure and nociception tests in mice. The cis-H5-CA and H7-CA compounds showed efficacy against psychomotor seizures, whereas the trans isomers were ineffective. Both the cis and trans KA isomers were ineffective in the 6-Hz test. In the maximal electroshock (MES) test, the cis isomers showed superior antiseizure activity to the trans forms of CA and KA conjugates, respectively. The suppression of seizure propagation by cis-H5-CA and the cis-H5-KA was reversed by a kappa opioid receptor (KOR) antagonist. Naloxone and naltrindole were not effective. The cis-isomers of CA conjugates and cis-H7-KA produced significantly stronger antinociceptive effects than their trans-isomers. The cis-H5-CA antinociception was blocked by naloxone in the acute phase and by naloxone and KOR antagonists in the inflammatory phase of the formalin test. The antinociception of the KA conjugates was not abolished by opioid receptor blockade. None of the tested conjugates affected the thermal nociceptive threshold. The results of the docking analysis also suggest a model-specific mechanism related to the activity of the cis-isomers of CA and KA conjugates in relation to opioid receptors. Our findings pave the way for the further development of novel opioid-related antiseizure and antinociceptive therapeutics.

LC-MS/MS of isomeric N-and O-glycopeptides on mesoporous graphitized carbon column.

BACKGROUND: The study of glycopeptides is associated with challenges regarding the microheterogeneity of different isomeric glycans occupying the same glycosylation sites in glycoproteins. It is immensely valuable to perform both qualitative and quantitative site-specific glycosylation analysis of glycopeptide isomers due to their link to several diseases. Achieving isomeric separation of glycopeptides is particularly challenging due to the low abundance of glycopeptides as well as inefficient ionization. Although some methods have demonstrated the isomeric separation of glycopeptides, a more efficient nanoflow-based stationary phase is needed for the isomeric separation of both N- and O-glycopeptides. RESULTS: In this study, the separation of N- and O-glycopeptide isomers at 75 °C was achieved with an in-house packed 1 cm long mesoporous graphitized carbon (MGC) column. Different gradient compositions of the optimized mobile phase for separating permethylated glycans on MGC column were tested, and we observed efficient separation of N- and O-glycopeptide isomers at a gradient elution time of 120 min. After achieving the isomeric separation of sialylated glycopeptides from model glycoproteins derived from bovine fetuin, the separation of isomeric glycopeptides derived from asialofetuin, α-1 glycoprotein and human blood serum were also demonstrated. Furthermore, the developed method for the separation of isomeric N- and O-glycopeptide on MGC column showed high reproducibility over three months. We observed an average retention time shift of 1 min and consistent resolution of separated peaks throughout three months. SIGNIFICANCE AND NOVELTY: MGC column can serve as an efficient tool for obtaining the isomeric separation of N- and O-glycopeptide from complex biological samples in future studies. This will enable a more profound understanding of the roles played by isomeric N- and O-glycopeptide in important biological processes and their correlations to various disease progressions.

Determination of Flavonolignan Compositional Ratios in Silybum marianum (Milk Thistle) Extracts Using High-Performance Liquid Chromatography.

Milk thistle is one of the most popular ingredients in the liver protection products market. Silymarin is the main component of milk thistle and contains multiple isomers. There have been few studies focusing on the compositional ratios of silymarin isomers. In this study, we developed an HPLC method for the separation and quantification of silymarin isomers, thereby elucidating their compositional ratios. Through the analysis of more than 40 milk thistle extract products on the market, we found that the ratios, specifically Ratio 1 (the silybin B content to the silybin A content, SBNB/SBNA) and Ratio 2 (the sum of the contents of silybin B and isosilybin B to the sum of the contents of silybin A and isosilybin A, (SBNB + IBNB)/(SBNA + IBNA)), are highly consistent across milk thistle extracts, averaging approximately 1.58 and 1.28, respectively. Furthermore, such ratios were verified in milk thistle seed samples. This study introduces significant findings concerning the stable ratios among silymarin isomers in milk thistle extracts and seeds, thereby offering an innovative approach for quality assurance of milk thistle extracts.

Synthesis of 3,4-Disubstituted Maleimide Derivatives via Phosphine-Catalyzed Isomerization of α-Succinimide-Substituted Allenoates Cascade γ'-Addition with Aryl Imines.

3,4-disubstituted maleimides find wide applications in various pharmacologically active compounds. This study presents a highly effective approach for synthesizing derivatives of 3,4-disubstituted maleimides through the direct isomerization of α-succinimide-substituted allenoates, followed by a cascade γ'-addition and aryl imines using PR3 as a catalyst. The resulting series of 3,4-disubstituted maleimides exhibited excellent stereoselectivities, achieving yields of up to 86%. To our knowledge, the phosphine-mediated γ'-addition reaction of allenoates is seldom reported.

Integrating HexNAcQuest with Glycoproteomics Data Analysis Software to Distinguish HexNAc Isomers on Peptides.

Recently, HexNAcQuest was developed to help distinguish peptides modified by HexNAc isomers, more specifically O-linked ß-N-acetylglucosamine (O-GlcNAc) and O-linked α-N-acetylgalactosamine (O-GalNAc, Tn antigen). To facilitate its usage (particularly for datasets from glycoproteomics studies), herein we present a detailed protocol. It describes example cases and procedures for which users might need to use HexNAcQuest to distinguish these two modifications.

Characterization of different-sized human αA-crystallin homomers and implications to Asp151 isomerization.

Site-specific modifications of aspartate residues spontaneously occur in crystallin, the major protein in the lens. One of the primary modification sites is Asp151 in αA-crystallin. Isomerization and racemization alter the crystallin backbone structure, reducing its stability by inducing abnormal crystallin-crystallin interactions and ultimately leading to the insolubilization of crystallin complexes. These changes are considered significant factors in the formation of senile cataracts. However, the mechanisms driving spontaneous isomerization and racemization have not been experimentally demonstrated. In this study, we generated αA-crystallins with different homo-oligomeric sizes and/or containing an asparagine residue at position 151, which is more prone to isomerization and racemization. We characterized their structure, hydrophobicity, chaperone-like function, and heat stability, and examined their propensity for isomerization and racemization. The results show that the two differently sized αA-crystallin variants possessed similar secondary structures but exhibited different chaperone-like functions depending on their oligomeric sizes. The rate of isomerization and racemization of Asp151, as assessed by the deamidation of Asn151, was also found to depend on the oligomeric sizes of αA-crystallin. The predominant isomerization product via deamidation of Asn151 in the different-sized αA-crystallin variants was L-ß-Asp in vitro, while various modifications occurred around Asp151 in vivo. The disparity between the findings of this in vitro study and in vivo studies suggests that the isomerization of Asp151 in vivo may be more complex than what occurs in vitro.

Indole-3-pyruvate: Analysis and Control of Tautomerism and Reactivity.

It is well-known in biochemistry that structure confers function, meaning that chemical structural elucidation is critical to truly understanding the function of a given metabolite. Indole-3-pyruvate (IPyA) exists in an equilibrium between the keto and enol tautomeric forms. IPyA is suggested to play a role in immune function; however, determining whether the tautomeric forms function differently can only be studied if an analytical method is capable of distinguishing between the two forms. Herein, we describe the use of UHPLC-HRMS to gain insight into the physical variables that govern IPyA tautomer equilibrium, reactivity, and detection limit. We use hydrogen-deuterium exchange (HDX) to identify enol and keto peaks, and we show that tautomers exhibit a valley of fronting followed by a tailing peak shape (though separation is still attainable) and identical MS/MS spectra. We observed drastically different ratios of keto and enol forms in different solvents, which is an important consideration for in vitro studies. IPyA was found to be highly unstable with accelerated reactivity in peroxides. Through in vitro reactivity studies, IPyA produced a myriad of known and unknown metabolites via nonenzymatic processes, many of which were mapped in vivo via the analysis of human plasma. Finally, we show that vitamin C (ascorbic acid) can slow this reactivity and enable sensitive detection in whole blood.

Ultrafast, Selective, and Highly Sensitive Nonchromatographic Analysis of Fourteen Cannabinoids in Cannabis Extracts, Δ8-Tetrahydrocannabinol Synthetic Mixtures, and Edibles by Cyclic Ion Mobility Spectrometry-Mass Spectrometry.

The diversity of cannabinoid isomers and complexity of Cannabis products pose significant challenges for analytical methodologies. In this study, we developed a method to analyze 14 different cannabinoid isomers in diverse samples within milliseconds by leveraging the unique adduct-forming behavior of silver ions in advanced cyclic ion mobility spectrometry-mass spectrometry. The developed method achieved the separation of isomers from four groups of cannabinoids: Δ3-tetrahydrocannabinol (THC) (1), Δ8-THC (2), Δ9-THC (3), cannabidiol (CBD) (4), Δ8-iso-THC (5), and Δ(4)8-iso-THC (6) (all MW = 314); 9α-hydroxyhexahydrocannabinol (7), 9ß-hydroxyhexahydrocannabinol (8), and 8-hydroxy-iso-THC (9) (all MW = 332); tetrahydrocannabinolic acid (THCA) (10) and cannabidiolic acid (CBDA) (11) (both MW = 358); Δ8-tetrahydrocannabivarin (THCV) (12), Δ8-iso-THCV (13), and Δ9-THCV (14) (all MW = 286). Moreover, experimental and theoretical traveling wave collision cross section values in nitrogen (TWCCSN2) of cannabinoid-Ag(I) species were obtained for the first time with an average error between experimental and theoretical values of 2.6%. Furthermore, a workflow for the identification of cannabinoid isomers in Cannabis and Cannabis-derived samples was established based on three identification steps (m/z and isotope pattern of Ag(I) adducts, TWCCSN2, and MS/MS fragments). Afterward, calibration curves of three major cannabinoids were established with a linear range of 1-250 ng·ml-1 for Δ8-THC (2) (R2 = 0.9999), 0.1-25 ng·ml-1 for Δ9-THC (3) (R2 = 0.9987), and 0.04-10 ng·ml-1 for CBD (4) (R2 = 0.9986) as well as very low limits of detection (0.008-0.2 ng·ml-1). Finally, relative quantification of Δ8-THC (2), Δ9-THC (3), and CBD (4) in eight complex acid-treated CBD mixtures was achieved without chromatographic separation. The results showed good correspondence (R2 = 0.999) with those obtained by gas chromatography-flame ionization detection/mass spectrometry.

Supramolecular assembly of isomeric SN-38 prodrugs regulated by conjugation sites.

Supramolecular polymers (SPs) are an emerging class of drug transporters employed to improve drug therapy. Through the rational design of self-assembling monomers, one can optimize the properties of the resulting supramolecular nanostructures, such as size, shape, surface chemistry, release, and, therefore, biological fates. This study highlights the design of isomeric SN38 prodrugs through the conjugation of hydrophilic oligo(ethylene glycol) (OEG) with hydroxyls at positions 10 and 20 on hydrophobic SN-38. Self-assembling prodrug (SAPD) isomers 10-OEG-SN38 and 20-OEG-SN38 can self-assemble into giant nanotubes and filamentous assemblies, respectively, via aromatic associations that dominate self-assembly. Our study reveales the influence of modification sites on the assembly behavior and ability of the SN38 SAPDs, as well as drug release and subsequent in vitro and in vivo antitumor effects. The SAPD modified at position 20 exhibits stronger π-π interactions among SN38 units, leading to more compact packing and enhanced assembly capability, whereas OEG at position 10 poses steric hindrance for aromatic associations. Importantly, owing to its higher chemical and supramolecular stability, 20-OEG-SN38 outperforms 10-OEG-SN38 and irinotecan, a clinically used prodrug of SN38, in a CT26 tumor model, demonstrating enhanced tumor growth inhibition and prolonged animal survival. This study presents a new strategy of using interactions among drug molecules as dominating features to create supramolecular assemblies. It also brings some insights into creating effective supramolecular drug assemblies via the engineering of self-assembling building blocks, which could contribute to the optimization of design principles for supramolecular drug delivery systems.

Synthesis of Thiazolidin-4-Ones Derivatives, Evaluation of Conformation in Solution, Theoretical Isomerization Reaction Paths and Discovery of Potential Biological Targets.

Thiazolin-4-ones and their derivatives represent important heterocyclic scaffolds with various applications in medicinal chemistry. For that reason, the synthesis of two 5-substituted thiazolidin-4-one derivatives was performed. Their structure assignment was conducted by NMR experiments (2D-COSY, 2D-NOESY, 2D-HSQC and 2D-HMBC) and conformational analysis was conducted through Density Functional Theory calculations and 2D-NOESY. Conformational analysis showed that these two molecules adopt exo conformation. Their global minimum structures have two double bonds (C=N, C=C) in Z conformation and the third double (C=N) in E. Our DFT results are in agreement with the 2D-NMR measurements. Furthermore, the reaction isomerization paths were studied via DFT to check the stability of the conformers. Finally, some potential targets were found through the SwissADME platform and docking experiments were performed. Both compounds bind strongly to five macromolecules (triazoloquinazolines, mglur3, Jak3, Danio rerio HDAC6 CD2, acetylcholinesterase) and via SwissADME it was found that these two molecules obey Lipinski's Rule of Five.

Position Matters: Pyridine Regioisomers Influence Secondary Structure and Micelle Morphology in Polymer-Homopolypeptide Micelles.

Polymer-homopolypeptide block copolymers are a class of bioinspired materials that combine the processability and stability of synthetic polymers with the biocompatibility and unique secondary structures of peptides, such as α-helices and ß-sheets. These properties make them ideal candidates for a wide variety of applications, for example, in the pharmaceutical field, where they are frequently explored as building blocks for polymeric micelle drug delivery systems. While homopolypeptide side chains can be furnished with an array of different moieties to impart the copolymers with desirable properties, such as stimulus responsivity, pyridine derivatives represent an underutilized functional group for this purpose. Additionally, the interplay between polypeptide side chain structure, secondary conformation, and micelle morphology is not yet well understood, particularly in the case of structural regioisomers. Therefore, in this work, a series of polymer-homopolypeptide copolymers were prepared from a poly(ethylene glycol)-b-poly(glutamic acid) (PEG-b-PGA) backbone, where the pendant carboxylic acid groups were covalently conjugated to a series of pyridine regioisomers by carbodiimide coupling. These pyridine regioisomers differed only in the position of the nitrogen heteroatom, ortho, meta or para, relative to the linking group, generating a series of PEG-b-poly(pyridinylmethyl glutamate) (PEG-b-PMG) copolymers. Following self-assembly of the copolymers in aqueous solutions, dynamic light scattering (DLS) revealed differences in micelle hydrodynamic diameter (Dh) (ranging from ∼60 to 120 nm), while transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) revealed distinctive morphologies ranging from ellipsoidal, to cylindrical, and disc-like, suggesting that subtle changes in positional isomers in the polypeptide block may influence the micelle structure. Analysis of the PEG-b-PMG copolymer micelles by circular dichroism (CD) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy revealed that differences in the morphology were associated with changes in polypeptide secondary structure, which in turn was influenced by the position of the pyridine heteroatom. Overall, these findings contribute to the broader understanding of the relationship between polypeptide structure and micelle morphology and serve as useful insight for the rational design of polymer-polypeptide nanoparticles.

Stereoselective Solid-State Synthesis of Biologically Active Cyclobutane and Dicyclobutane Isomers via Conformation Blocking and Transference.

Conformations in the solid state are typically fixed during crystallization. Transference of "frozen" C=C conformations in 3,5-bis((E)-2-(pyridin-4-yl)vinyl)methylbenzene (CH3-3,5-bpeb) by photodimerization selectively yielded cyclobutane and dicyclobutane isomers, one of which (Isomer 2) exhibited excellent in vitro anti-cancer activity towards T-24, 7402, MGC803, HepG-2, and HeLa cells.

Exploring Release, Isomerization, and Absorption of Cypermethrin in Pacific Oysters (Crassostrea gigas) with Different Processing Methods during In Vivo Digestion: Insights from a Gastrointestinal Tract Quantitative Tracing Method.

Cypermethrin (CP) is a neurotoxic insecticide found accumulated in oysters, one of the most commonly consumed seafoods, posing potential health risks to the human body. We designed a gastrointestinal tracing method allowing for accurate quantification of the propulsion of chyme and further established the mouse in vivo digestion model to explore the behavior of CP in the digestion of raw, steamed, and roasted oysters. The results showed that bioaccumulation of CP in oysters may be accompanied by the biotransformation of CP. Thermal processing decreased both the CP content in oysters and its bioaccessibility. The small intestine is the main site for CP digestion and absorption. The cis-isomers of CP might finally accumulate in the body at a higher ratio and further become the predominant configuration for toxic effects. Taken together, the study contributes to the risk assessment of the dietary exposure of CP from aquatic products.

Hyphenation of Liquid Chromatography and Trapped Ion Mobility - Mass Spectrometry for Characterization of Isomeric Phosphatidylethanolamines with Focus on N-Acylated Species.

In prior research, hydrophilic interaction liquid chromatography coupled to tandem mass spectrometry (HILIC-MS/MS) has demonstrated applicability for characterizing regioisomers in lipidomics studies, including phosphatidylglycerols (PG) and bis(monoacyl)glycerophosphates (BMP). However, there are other lipid regioisomers, such as phosphatidylethanolamines (PE) and lyso-N-acyl-PE (LNAPE), that have not been studied as extensively. Therefore, hyphenated mass spectrometric methods are needed to investigate PE and LNAPE regioisomers individually. The asymmetric structure of LNAPE favors isomeric species, which can result in coelution and chimeric MS/MS spectra. One way to address the challenge of chimeric MS/MS spectra is through mobility-resolved fragmentation using trapped ion mobility spectrometry (TIMS). Therefore, we developed a multidimensional HILIC-TIMS-MS/MS approach for the structural characterization of isomeric phosphatidylethanolamines in both negative and positive ionization modes. The study revealed the complementary fragmentation pattern and ion mobility behavior of LNAPE in both ionization modes, which was confirmed by a self-synthesized LNAPE standard. With this knowledge, a distinction of regioisomeric PE and LNAPE was achieved in human plasma samples. Furthermore, regioisomeric LNAPE species containing at least one unsaturated fatty acid were noted to exhibit a change in collision cross-section in positive ionization mode, leading to a lipid characterization with respect to fatty acyl positional level. Similar mobility behavior was also observed for the biological LNAPE precursor N-acyl-PE (NAPE). Application of this approach to plasma and cereal samples demonstrated its effectiveness in regioisomeric LNAPE and NAPE species' elucidation.

Comparison of α and ß-acid isomerization in hops and beer using HPLC, confocal microscopy, spectrofluorimetry and chemical analysis of metabolites and essential oils in flowers of different hop cultivars produced in Brazil.

We used confocal microscopy and spectrofluorescence to characterize the emission spectra in hop flowers, to follow the isomerization processes in different hop preparations, and beers, to compare with HPLC extracted samples. Flowers of different hop cultivars produced in three regions of Brazil, were quantitated by HPLC and GC-MS. The fluorescence spectra showed two characteristic emission bands evaluated from different preparations. The isomerization process leads to a gradual decrease in fluorescence intensity as the reaction progresses. This demonstrates the valuable use of confocal microscopy and fluorescence spectroscopy for analysis of the correlation between bitter acid indices with fluorescence intensity and lifetime microscopy. Such techniques can be used directly in the flowers allowing rapid monitoring of the brewing process. Twenty-nine substances were characterized in the essential oils and some cultivars presented quantities of bitter acids and essential oil levels close to those expected for plants after more than three years of cultivation.

Mechanisms and high-value applications of phthalate isomers degradation pathways in bacteria.

Phthalate isomers are key intermediates in the biodegradation of pollutants including waste polyethylene terephthalate (PET) plastics and plasticizers. So far, an increasing number of phthalate isomer-degrading strains have been isolated, and their degradation pathways show significant diversity. In this paper, we comprehensively review the current status of research on the degrading bacteria, degradation characteristics, aerobic and anaerobic degradation pathways, and degradation genes (clusters) of phthalate isomers, and discuss the current shortcomings and challenges. Moreover, the degradation process of phthalate isomers produces many important aromatic precursor molecules, which can be used to produce higher-value derivative chemicals, and the modification of their degradation pathways holds good prospects. Therefore, this review also highlights the current progress made in modifying the phthalate isomer degradation pathway and explores its potential for high-value applications.

Ultrafast terahertz Stark spectroscopy reveals the excited-state dipole moments of retinal in bacteriorhodopsin.

The photoinduced all-trans to 13-cis isomerization of the retinal Schiff base represents the ultrafast first step in the reaction cycle of bacteriorhodopsin (BR). Extensive experimental and theoretical work has addressed excited-state dynamics and isomerization via a conical intersection with the ground state. In conflicting molecular pictures, the excited state potential energy surface has been modeled as a pure S[Formula: see text] state that intersects with the ground state, or in a 3-state picture involving the S[Formula: see text] and S[Formula: see text] states. Here, the photoexcited system passes two crossing regions to return to the ground state. The electric dipole moment of the Schiff base in the S[Formula: see text] and S[Formula: see text] state differs strongly and, thus, its measurement allows for assessing the character of the excited-state potential. We apply the method of ultrafast terahertz (THz) Stark spectroscopy to measure electric dipole changes of wild-type BR and a BR D85T mutant upon electronic excitation. A fully reversible transient broadening and spectral shift of electronic absorption is induced by a picosecond THz field of several megavolts/cm and mapped by a 120-fs optical probe pulse. For both BR variants, we derive a moderate electric dipole change of 5 [Formula: see text] 1 Debye, which is markedly smaller than predicted for a neat S[Formula: see text]-character of the excited state. In contrast, S[Formula: see text]-admixture and temporal averaging of excited-state dynamics over the probe pulse duration gives a dipole change in line with experiment. Our results support a picture of electronic and nuclear dynamics governed by the interaction of S[Formula: see text] and S[Formula: see text] states in a 3-state model.

Structure-activity relationship between gold nanoclusters and human serum albumin: Effects of ligand isomerization.

The interactions between gold nanoclusters (AuNCs) and proteins have been extensively investigated. Nevertheless, the structure-activity relationship between gold nanoclusters and proteins in terms of ligand isomerization remained unclear. Here, interactions between Au25NCs modified with para-, inter- and ortho-mercaptobenzoic acid (p/m/o-MBA-Au25NCs) and human serum albumin (HSA) were analyzed. The results of the multispectral approach showed that all three gold nanoclusters bound to the site I in dynamic modes to increase the stability of HSA. There were significant differences in the binding intensity, thermodynamic parameters, main driving forces, and binding ratios between these three gold nanoclusters and HSA, which might be related to the existence forms of the three ligands on the surface of AuNCs. Due to the different polarities of AuNCs themselves, the impact of three AuNCs on the microenvironment of amino acid residues in HSA was also different. It could be seen that ligand isomerization significantly affected the interactions between gold nanoclusters and proteins. This work will provide theoretical guidance for ligand selection and biological applications of metal nanoclusters.