Binding Constants Research Articles

Complex formation between n-alkyltrimethylammonium bromides and water-soluble calix[n]arenes

Abstract Complex formation between n-alkyltrimethylammonium bromides and water-soluble calix[n]arenes (n = 4, 6, 8) (CALXSn) was studied by potentiometric titration and molecular dynamic simulation. The binding isotherms were found to be composed of two phases; the first phase is strong specific binding to a few sites and the second phase is cooperative binding to the residual sites. Binding constant for the first specific binding was found to increase with an increase in the number of ring members of CALXSn. Binding constants for CALXS4 and CALXS6 systems did not change significantly with the length of the surfactant's alkyl chain and with the pH change from 7.0 to 12.5, while that for CALXS8 systems tended to increase with an increase in the alkyl-chain length. The specific binding disappeared with the pH increase. The thermodynamic parameters showed an enthalpy-entropy compensation relation with a compensation temperature of 289 K. The second phase was observed mainly for n-dodecyltrimethylammonium-CALXSn systems. The cooperativity parameter was found to increase with an increase in the number of ring member of CALXSn and is attributed to the contribution of increasing conformational flexibility of CALXSn as the number of ring members increases. MD simulation on CALXSn with and without n-alkyltrimethylammonium ion provided structural interpretation for the features of binding data.

New Ru(III) 2,6-Bis(2-benzimidazolyl)Pyridine Complexes Bearing p-sub-Benzyl Thiosemicarbazones Schiff Base: Synthesis, Characterization, DNA Binding and Anti-cancer Activity.

The six mononuclear Schiff's base Ru(III) complexes viz., [Ru(BZP)(LA)2].2NO3 (MRA), [Ru(BZP)(LB)2].2NO3 (MRB), [Ru(BZP))(LC)2].2NO3 (MRC), [Ru(BZP))(LD)2].2NO3 (MRD), [Ru(BZP)(LE)2].2NO3 (MRE) and [Ru(BZP)(LF)2].2NO3 (MRF), [(BZP = 2,6-bis(2-benzimidazolyl)pyridin], were synthesized using of p-sub-benzylthiosemicarbazones (BTS) [(Sub = 4-NO2 (LA), 4-N(CH3)2 (LB), 4-Cl (LC), 4-OCH3 (LD), 4-OCH2Ph (LE), 4-OH (LE)] and 4-OH (LF), as an ancillary ligand. The thiosemicarbazones ligands (LA-LF) were obtained by the condensation of p-substituted benzaldehyde and thiosemicarbazide. These complexes were characterized by elemental analysis, IR, ESR, ESI-MS, electronic absorption spectroscopy. The geometry was optimized by theoretical calculation using DFT and structure reveals that MRA-MRF adopt octahedral geometry. Further, the complexes were examined for anticancer against Leukemia cancer cell line K562 and shown significant responses to these cells. Moreover, DNA binding studies were studied with all complexes MRA-MRF and the binding constant (Kb) were found 1.54 x 104, 2.87 x 104, 1.67 x 104, 1.98 x 104 and 1.59 x 104, respectively. It was found that DNA binds in intercalation mode which is also validate by the Docking studies.

α-Synuclein Iron-Responsive-Element RNA and Iron Regulatory Protein Affinity Is Specifically Reduced by Iron in Parkinson’s Disease

α-Synuclein (α-Syn) is implicated in the pathophysiology of Parkinson’s disease (PD) and plays a significant role in neuronal degeneration. Iron response proteins (IRPs) bind to iron response elements (IREs) found in the 5′-untranslated regions (5′-UTRs) of the messenger RNA that encode the α-Syn gene. This study used multi-spectroscopic approach techniques to investigate the impact of iron on α-Syn IRE RNA binding to IRP1. The formation of a stable complex between α-Syn RNA and IRP1 was suggested by fluorescence quenching results. Fluorescence measurements showed that α-Syn RNA and IRP1 had a strong interaction, with a binding constant (Ka) of 21.0 × 106 M−1 and 1:1 binding stoichiometry. About one binding site per IRP1 molecule was suggested by the α-Syn RNA binding. The Ka for α-Syn RNA•IRP1 with added Fe2+ (50 μM) was 6.4 μM−1. When Fe2+ was added, the Ka of α-Syn RNA•IRP1 was reduced by 3.3 times. These acquired Ka values were used to further understand the thermodynamic characteristics of α-Syn RNA•IRP1 interactions. The thermodynamic properties clearly suggested that α-Syn RNA binding to IRP1 was an entropy-favored and enthalpy-driven event, with significant negative ΔH and small positive ΔS. For α-Syn RNA•IRP1, the Gibbs free energy (ΔG) was −43.7 ± 2.7 kJ/mol, but in the presence of Fe2+, it was −36.3 ± 2.1 kJ/mol. These thermodynamic calculations indicated that hydrogen bonding as well as van der Waals interactions might help to stabilize the complex formation. Additionally, far-UV CD spectra verified α-Syn RNA•IRP1 complex formation, and α-Syn RNA and Fe2+ induce secondary structural alteration of IRP1. According to our findings, iron alters the hydrogen bonding in α-Syn RNA•IRP1 complexes and induces a structural change in IRP1. This suggests that iron selectively affects the thermodynamics of these RNA–protein interactions.

Exploring the physicochemical interactions and loading strategies of mesoporous silicon dioxide nanoparticles for drug delivery.

Mesoporous silica nanoparticles play an important role in drug delivery due to their high surface area, porous structure, tunable pore size, chemical stability and functionalization capability. Such properties make them a good candidate for drug encapsulation. However, molecular binding is another parameter that govern drug loading apart of pores' structure and size. There is a lack of comprehensive reviews on that topic nowadays. This paper overviews the latest publications on the physicochemical aspects of the interaction of mesoporous silica nanoparticles with drugs. The review is focused primarily on a such parameters of the intermolecular binding between a drug and silica nanoparticle as a binding constant, enthalpy and entropy changes and experimental methods with the emphasis on the principles of thermodynamic parameters characterization. Such information would be very important for the development and optimization of drug delivery strategies based on mesoporous silica nanoparticles.

Investigation of mono-nuclear cobalt(II) complexes with a tri-dentate quinoxalyl-hydrazone ligand for their potential in biological research and interaction with ct-DNA.

The condensing reaction of 2-hydroxy-1-naphthaldehyde with quinoxalyl-2-carbohydrazide resulted in synthesizing of a novel derivative of hydrazone quinoxalyl ligand (H2dpq). The bonding behavior between H2dpq and Co(II) ion was investigated in molar ratios of 1: 1 and 2: 1 to produce two different complexes, Codpq and Co(dpq)2, respectively. Their chemical structure was verified using several spectroscopic approaches. The characterization envolved micro-C, H, and N-elemental analyses, thermogravimetric investigations, as well as the examination of their magnetic and conductance properties. The inhibitory effects of H2dpq (the free ligand) and its Co(II)-chelates on the growing up of three specific bacterial series, three specific fungal series, and three famous human cancer cell lines were evaluated based on their structure features. The study referred to the pivotal function of Co(II) and its ratio in the two complexes. The antioxidant activity was determined for all current compounds within DPPH and SOD assays, reporting respectable antioxidant reactivity. The interaction of H2dpq, Codpq, and Co(dpq)2 with calf thymus DNA (ct-DNA) was assessed by analyzing through the alterations in the viscometric and spectrophotometric properties. Determination of binding constant (Kb, 13.12, 16.02, and 16.82×107mol-1dm3), Gibb's free energy (∆Gb≠, were -40.21, -46.13, and -46.67kJmol-1), and the chromism mode (hypo-character) were employed for H2dpq, Codpq, and Co(dpq)2 to assess the interactive modes, respectively. Rewardingly, the monometallic-chelates Co(II)-complexes displayed modified binding action more than that of H2dpq against ct-DNA.

Probing the interaction mechanism of tigecycline with γ-globulin and hemoglobin in the absence and presence of amikacin.

The interaction mechanism of tigecycline with γ-globulin and hemoglobin in the absence and presence of amikacin was investigated through multipectral, molecular docking and molecular dynamics simulation. The results show that tigecycline and γ-globulin/hemoglobin forms a ground state complex without or with amikacin. The presence of amikacin slightly increases the binding constant of tigecycline to γ-globulin/hemoglobin, but all are of moderate binding affinity, at 104Lmol-1. The equilibrium fraction of unbound tigecycline fu is >90%, but the presence of amikacin reduces the free concentration of tigecycline in γ-globulin and hemoglobin. Whether amikacin is present or not, the interaction between tigecycline and γ-globulin/hemoglobin is a synergistic interaction driven by enthalpy and entropy. Non-covalent forces are primarily hydrophobic interactions, but also include electrostatic forces and hydrogen bonds. In the presence of amikacin, the effect of tigecycline on the skeleton structure of γ-globulin/hemoglobin is more significant. The effect of tigecycline and/or amikacin on the secondary structure of γ-globulin/hemoglobin is not significant, while the secondary structure changes in different systems are not the same. Molecular docking shows that γ-globulin/hemoglobin-tigecycline (first)-amikacin ternary system is the most stable. Molecular dynamics simulation explores the stability and dynamic behavior of γ-globulin/hemoglobin-tigecycline complex without or with amikacin.

An introduction to multiway modeling of fluorescence excitation-emission measurements to estimate the interaction of maprotiline hydrochloride and DNA, and quantify the drug-DNA binding constant

An introduction to multiway modeling of fluorescence excitation-emission measurements to estimate the interaction of maprotiline hydrochloride and DNA, and quantify the drug-DNA binding constant

A physicochemical investigation of the complex formation by β-cyclodextrin with Triton X-100 and Triton X-114 and their aggregation behaviour in aqueous solution: an experimental approach.

The complexation behavior and binding affinity of Triton X-100 (TX-100) and Triton X-114 (TX-114) with β-cyclodextrin (β-CD) were extensively studied in an aqueous medium using a comprehensive suite of experimental techniques. These techniques allowed for the evaluation of key physicochemical parameters, including critical micelle concentration (cmc), aggregation number (Nagg), Stern-Volmer constant, and particle size distribution. These metrics were instrumental in understanding the underlying mechanism of the host-guest interaction between β-CD and Triton-X. Dynamic light scattering (DLS) data provided strong evidence for the formation of inclusion complexes, demonstrating significant hydrophobic interactions between the hydrophobic regions of Triton-X and the cavity of β-CD. The disruption of micellar structures, caused by β-CD encapsulating the hydrophobic moieties of the surfactants, was clearly observed. This process also resulted in an increased CMC, further underscoring the impact of β-CD on the aggregation behavior of the surfactants. To quantify the interaction, the Benesi-Hildebrand method was utilized to determine the stoichiometry and binding constants of the β-CD/Triton-X complexes. The results confirmed a well-defined 1 : 1 binding mode, indicating the precise incorporation of the surfactant's hydrophobic tails into the β-CD cavity while leaving the hydrophilic regions exposed to the aqueous environment. This selective binding mechanism alters the thermodynamics of micellization and disrupts the native micellar equilibrium of the surfactant systems. This systematic and comparative investigation is among the few studies that thoroughly examine the interactions between Triton-X surfactants and β-CD. Such research not only enhances our understanding of these complexes, but also reveals their significant potential for various applications. In drug delivery, for example, β-CD/Triton-X complexes can improve the solubility, stability, and bioavailability of hydrophobic drugs. In supramolecular chemistry, these complexes serve as model systems for studying host-guest interactions and self-assembly processes. Furthermore, their ability to modulate surfactant behaviour opens avenues for their use in material science, cosmetics, and industrial formulations, where precise control over micelle formation and aggregation is essential. This study underscores the versatility and utility of β-CD in interacting with non-ionic surfactants, offering insights that can be applied to other amphiphilic systems and paving the way for innovative applications in diverse fields.

Ru(II)-Based Multitopic Hosts for Fullerene Binding: Impact of the Anion in the Recognition Process.

The development of multitopic hosts for fullerene recognition based on nonplanar corannulene (C20H10) structures presents challenges, primarily due to the requirement for synergistic interactions with multiple units of this polycyclic aromatic hydrocarbon. Moreover, increasing the number of corannulene groups in a single chemical structure while avoiding the cost of increasing flexibility has been scarcely explored. Herein, we report the synthesis of a family of multitopic Ru(II)-polypyridyl complexes bearing up to six units of corannulene arranged by pairs, offering a total of three molecular tweezers. All of them are fixed by the central atom and organized in an octahedral structure. Their fullerene recognition capabilities have been thoroughly demonstrated toward C60 and C70 showing that they can reasonably accommodate up to three fullerenes per host in a noncooperative manner. There are, however, some features that diverge from comparable hosts in the literature, such as the low value of several association constants. This behavior, supported by theoretical studies, is attributed to the presence of two noninnocent BAr4F anions that interfere with the supramolecular binding through ion pair formation. These findings highlight the crucial role of selecting compatible ionic species in supramolecular host design as they can significantly influence the recognition process.

A Novel Rhodamine Functionalized Schiff Base Type Ratiometric Fluorescent Chemosensor for the Sensing of Hg2+ Ions; Experimental and Theoretical Approach.

A new Rhodamine functionalised Schiff Base sensor 3',6'-bis(diethylamino)-2-((4-hydroxybenzylidene)amino)spiro[isoindoline-1,9'-xanthen]-3-one (SBRB1) was designed and synthesized. The recognition ability of sensor SBRB1 towards Hg2+ was studied by using UV-Vis and fluorescence spectroscopy. The fluorescence results showed that the sensor SBRB1 has specific selectivity as well as sensitivity towards Hg2+ among other competitive metal ions as the fluorescence intensity at 479nm quenched only in the presence of Hg2+. This sensitivity towards Hg2+ was due to the chelation between ligand and Hg2+. From the fluorescence titration the binding constant and detection limit of SBRB1:Hg2+ complex were calculated and found to be 5.114 106 M-1 and 2.91 10-5 M respectively. It showed The 1:1 complexation between SBRB1 and Hg2+ whichwas conformed from the DFT and TD-DFT study of SBRB1 in both solvent and gas phase.

Spectrophotometric and computational characterization of charge transfer complex of selumetinib with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and its utilization in developing an innovative green and high throughput microwell assay for analysis of bulk form and pharmaceutical formulation

For paediatric patients suffering from neurofibromatosis, Selumetinib (SEL) is the only approved drug. Here an original ecofriendly and high pace method is introduced using 96- microwell spectrophotometric assay (MW-SPA) to measure SEL content in bulk and commercial pharmaceutical formulation (Koselugo® capsules). This assay was relied on in-microwell formation of a coloured charge transfer complex (CTC) upon interaction of SEL with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The complex was fully characterized by spectrophotometric and computational studies. The CTC exhibited an absorbance maximum (λmax) at 440 nm. The ease of reaction occurrence, complex stability and its high absorptivity were proved by measuring its association constant (0.63 × 102 L/ mol), standard free energy change (-10.31 KJ/mol), molar absorptivity (ε) (3.78 × 103 L/mol/cm), and the SEL: DDQ stoichiometric ratio (1:1). Establishments of the optimum values of the applied conditions in 96-well assay plate were refined regarding DDQ concentration, reaction time, temperature, and solvents. Validation of the assay was according to the ICH guidelines. The assay was linear in SEL’ concentrations ranged from 10 to 200 µg/well, with limits of detection and quantitation of 4.1 and 12.5 µg/well, respectively. Then, the assay was efficaciously adapted to accurately and precisely determine SEL content in bulk form and Koselugo® capsules. The assay environmental safety was documented by three different comprehensive metric tools. Additionally, assessment of the assay’s rate demonstrated its high throughput, enabling the processing of large number of samples in pharmaceutical quality control laboratories. The successful development of this assay provides a valuable fast and green analytical tool for ensuring the quality control of SEL’s bulk form and capsules.

Deciphering Binding Potential of Naphthalimide-Coumarin Conjugate with c-MYC G-Quadruplex for Developing Anticancer Agents: A Spectroscopic and Molecular Modeling Approach.

It has been well accumulated that G-quadruplex (G4-DNA) has great anticancer relevance, and various heterocyclic moieties have been synthesized and examined as potent G4-DNA binders with promising anticancer activity. Here, we have synthesized a series of naphthalimide-triazole-coumarin conjugates by substituting various amines and further examine their anticancer activity against 60 human cancer cell lines at 10 μM. One and five dose concentration results reveal low values of MG-MID GI50 for compounds including 8a (3.18 μM), 8b (13.11 μM), 8e (7.68 μM) and 8f (1.75 μM). Further cell apoptosis manifests that all compounds can induce cell apoptosis in cancer cells by stabilizing the c-MYC promoter G-quadruplex. Therefore, the G-quadruplex-mediated pathway may be responsible for the apoptosis that these naphthalimide-coumarin compounds caused in cancer cells. Therefore, multispectroscopic techniques are employed to evaluate the binding of molecules with c-MYC G4-DNA where all four molecules readily bind to G4-DNA and stabilize it with a high binding constant, leading to inhibition of cancer cells and apoptosis of cancer cells. Binding studies toward ct-DNA disclose that these compounds do not interact with ds-DNA and thus selectively target G4-DNA to exert their anticancer activity. All the active compounds have greater affinity toward Human Serum Albumin (HSA) and can readily bind with HSA with a binding constant of 12 × 104 M-1 (8a), 13.0 × 104 M-1 (8b), 14.2 × 104 M-1 (8e), 16.3 × 104 M-1 (8f). Thus, the results disclose that inhibition and killing of cancer cells by these derivatives feasibly occur due to their ability to interact with c-MYC G-quadruplex forming promoters and their high affinity toward HSA unfold potent anticancer agents and can be taken further for clinical trials.

Site-wise dynamic defects in a non-conserving exclusion process

Motivated by the significant influence of the defects in the dynamics of the natural or man-made transportation systems, we propose an open, dynamically disordered, totally asymmetric simple exclusion process featuring bulk particle attachment and detachment. The site-wise dynamic defects might randomly emerge or vanish at any lattice location, and their presence slows down the motion of the particles. Using a mean-field approach, we obtain an analytical expression for both particle and defect density and validate them using Monte Carlo simulation. The study investigates the steady-state characteristics of the system, including phase transitions, analysis of boundary layers, and phase diagrams. Our approach streamlines the defect dynamics by integrating two parameters into one called the obstruction factor, which helps in determining an effective binding constant. The impact of the obstruction factor on the phase diagram is explored across various combinations of binding constants and detachment rates. A critical value of the obstruction factor is obtained, about which an infinitesimal change results in a substantial qualitative change in the structure of the phase diagrams. Further, the effect of the detachment rate is studied, and critical values along which the system observes a quantitative transition of the stationary phases are obtained as a function of the obstruction factor. Overall, the system shows stationary phases ranging from three to seven depending upon the value of the obstruction factor, the binding constant, and the detachment rate. Moreover, we scrutinized the impact of the obstruction factor on the shock dynamics and found no finite-size effect.

Characterization of insulin and bile acid complexes in liposome by different mass spectrometry techniques.

Insulin bound with ligand molecules can improve its bioavailability in oral formulations. In this work, the interactions between insulin and bile acids of taurocholic acid (TCA) and glycocholic acid (GCA) are characterized using different mass spectrometry (MS) methods. Electrospray (ESI)-MS analysis revealed that GCA and TCA could interact with insulin individually or together through non-covalent bonds, and the products included mGCA-insulin, nTCA-insulin, and mGCA-nTCA-insulin complexes. Their binding stoichiometry, relative intensity ratio (IRa), and binding affinity were determined. ESI-MS/MS data and the calculated association constants both suggest that TCA has stronger affinity to insulin than GCA. The mixtures of various insulin, GCA, andTCA complexes with different charge states were separated, and distinct trend lines were observed using ion mobility mass spectrometry (IMMS). Moreover, liposomes containing insulin and GCA and/or TCA were prepared, and directly characterized using ESI-MS, and the interaction products of insulin with GCA and TCA were found in the liposome formulation. AutoDock was used to simulate molecular binding and select binding sites between insulin and GCA or TCA to explore the interaction mechanisms. The findings in this work could help understand the mechanism of actionof insulin protection with bile acids in the body.

Substituent Effect on Cytotoxicity and Interaction Profile of DNA/BSA With Selected Terpyridine Derivatives of Ester/Ferrocene and Their Fe(III) and Ru(III) Complexes—A Comparative Analysis

ABSTRACTThe present work demonstrates the synthesis of ester and ferrocene groups containing new terpyridine‐based ligands (FRL and RL) and their selected meal complexes FR‐Fe, FR‐Ru, RL‐Fe, and RL‐Ru. Investigations on the influence of the ester and ferrocene groups on binding to DNA/BSA and anticancer activity were carried out. All these products were structurally characterized by using spectroscopic and analytical techniques. Notably, the molecular structures of both the ligands and the ester‐based Fe(III) complex were confirmed by single‐crystal X‐ray diffraction analysis. Additionally, theoretical calculations were employed to further establish the structures of the synthesized ligands and their metal complexes, which were subsequently utilized for molecular docking studies to evaluate their binding potential. The docking results revealed the best binding orientation with the lowest possible binding energy of −10.20 kcal/mol for the RL‐Fe complex with BSA and −8.30 kcal/mol for the FR‐Fe complex with DNA. Furthermore, the binding interactions of all the synthesized compounds were investigated using UV–visible absorption (UV) and fluorescence spectroscopy (FL). The binding sites and binding constants were determined using the Stern‐Volmer equation. Moreover, cytotoxicity assays were performed against lung cancer (A549), liver cancer (Hep G2), and normal Vero cell lines, with results benchmarked against cisplatin. Notably, the ligand (FRL) exhibited significant cytotoxic action with an IC50 of 54.51 μM compared to the related Fe(III) complex (FR‐Fe) (i.e., 69.86 μM) against A549 cells. But the complex FR‐Fe displayed IC50 of 56.19 μM against Hep G2 cells, demonstrating better potency over cisplatin.

Introducing Pyridone[α]-Fused BOPHYs as Red-Shifted Bright Fluorophore Potentially Useful as Non-fullerene Acceptors in Donor-Acceptor Dyads.

A series of 2-pyridone[α]-fused BOPHYs 6-8 were prepared via a two-step procedure involving the preparation of enamine, followed by an intramolecular heterocyclization reaction. In addition to being fully conjugated with the BOPHY core pyridone fragment, BOPHYs 7 and 8 have a pyridine group connected to the BOPHY core via one- or two -CH2- groups. New BOPHYs were characterized by spectroscopy as well as X-ray diffraction. Conjugation of the pyridone fragment into the BOPHY core results in a significant red shift of the absorption and fluorescence while maintaining extremely high fluorescence quantum yields. Axial coordination and photophysical properties of the supramolecular dyads formed between pyridine-appended pyridone-fused BOPHYs 7 and 8 with TPPF20Zn (TPPF20Zn = zinc 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin) were investigated using UV-vis and fluorescence spectroscopy and gave a binding constant in the range of 1.46 × 105 to 4.6 × 105 M-1. The electronic structures and excited-state properties of new BOPHYs 6-8 and their donor-acceptor assemblies with TPPF20Zn were studied by the density functional theory (DFT) and time-dependent DFT (TDDFT). The HOMO and HOMO - 1 of supramolecular complexes TPPF20Zn-7/8 are TPPF20Zn centered, while the LUMO is localized on the BOPHY entity, allowing potential HOMO → LUMO charge transfer from the TPPF20Zn donor to the BOPHY acceptor.

B,N‐Embedded Helical Nanographenes Showing an Ion‐Triggered Chiroptical Switching Function

AbstractIntramolecular oxidative aromatic coupling of 3,6‐bis(m‐terphenyl‐2’‐yl)carbazole provided a bis(m‐terphenyl)‐fused carbazole, while that of 3,6‐bis(m‐terphenyl‐2’‐yl)‐1,8‐diphenylcarbazole afforded a bis(quaterphenyl)‐fused carbazole. Borylation of the latter furnished a B,N‐embedded helical nanographene binding a fluoride anion via a structural change from the three‐coordinate boron to the four‐coordinate boron. The anionic charge derived from the fluoride anion is stabilized over the expanded π‐framework, which leads to the high binding constant (Ka) of 1×105 M−1. The four‐coordinate boron species was converted back to the parent three‐coordinate boron species with Ag+, and the chiroptical switch between the three‐coordinate boron and four‐coordinate boron species has been achieved via the ion recognition with the change in the color and glum values.

Sulfated Glycosaminoglycans as Inhibitors for Chlamydia Infections: Molecular Weight and Sulfation Dependence.

Glycosaminoglycans (GAGs) play a pivotal role in pathogen attachment and entry into host cells, where the interaction with GAGs is critical for a diverse range of bacteria and viruses. This study focuses on elucidating the specific interactions between sulfated GAGs and the adhesin OmcB (Outer membrane complex protein B) of Chlamydia species, examining how structural characteristics of GAGs, such as sulfation degree and molecular weight, influence their binding affinity and thereby affect bacterial infectivity. A surface-based binding assay is established to determine the binding constants of OmcB with various GAGs. It is shown that increased sulfation and higher molecular weight enhance GAG binding to OmcB. These findings are further validated using cell assays, which shows that the addition of sulfated GAGs reduces OmcB-cell binding and inhibits the attachment of C. pneumoniae elementary bodies (EBs), underscoring the pivotal role of specific GAGs in chlamydial infections. Notably, heparin exhibites a stronger inhibitory effect on OmcB compare to GAGs with similar sulfation degrees and molecular weights, suggesting that particular molecular architectures may optimize binding interactions.

A-D-A type fluorescent probe with dual quaternary-ammonium-salt anchors for turn on detection of HSA in wide emission gamut.

Human serum albumin (HSA) is a key protein implicates in various physiological and pathological conditions such as renal injury, diabetes mellitus. Herein, we report an AIE-active fluorescent probe (DNI-4) for detection of HSA with a "turn on" response covering visible and near-infrared region (500 - 800nm). Combining with a triphenylamine and two 1,8-naphthalimide moieties, the chromophore segment of DNI-4 forms a "A-D-A" type molecular architecture with the twisted intramolecular charge transfer property. Two quaternary ammonium salt moieties are introduced into the chromophore to give the probe (DNI-4), which has good hydrophilicity and can interact with HSA to form the dye-HSA aggregates with "turn-on" signal. DNI-4 demonstrates a good linear correlation over a low concentration range of HSA from 0 to 0.2μM (R2=0.9995), with a limit of detection (LOD) as low as 15nM. We tested the diameters and potential values of DNI-4 and HSA to disclose the variation in microstructure before and after the recognition event. Furthermore, we test and compare the sensitivity and association constants of DNI-4 and two control compounds, neutral DNI-1 and mono-quaternary-ammonium-salt-substituted DNI-5. The results indicate the electronic interaction is a key factor for recognition and DNI-4 with the most positive groups is the best probe for HSA. At last, DNI-4 is successfully applied to probe HSA in the Hela cells indicating the potential application in fluorescent sensing and bioimaging.

SPR is a fast and straightforward method to estimate the binding constants of cyclic dinucleotides to their binding partners, such as STING or poxin.

The development of small molecule drugs that target protein binders is the central goal in medicinal chemistry. During the lead compound development process, hundreds or even thousands of compounds are synthesized, with the primary focus on their binding affinity to protein targets. Typically, IC50 or EC50 values are used to rank these compounds. While thermodynamic values, such as the dissociation constant (KD), would be more informative, they are experimentally less accessible. In this study, we compare isothermal calorimetry (ITC) with surface plasmon resonance (SPR) using human STING, a key protein of innate immunity, and several cyclic dinucleotides (CDNs) that serve as its ligands. We demonstrate that SPR, with recent technological advancements, provides KDs that are sufficiently accurate for drug development purposes. To illustrate the versatility of our approach, we also used SPR to estimate the KD of poxin binding to cyclic GMP-AMP (cGAMP) that serves as a second messenger in the innate immune system. In conclusion, SPR offers a high benefit-to-cost ratio, making it an effective tool in the drug design process.