Conformational Changes In Structure Research Articles

Steric and Electronic Influence of Excited-State Decay in Cu(I) MLCT Chromophores.

ConspectusFor the past 11 years, a dedicated effort in our research group focused on fundamentally advancing the photophysical properties of cuprous bis-phenanthroline-based metal-to-ligand charge transfer (MLCT) excited states. We rationalized that, by gaining control over the numerous factors limiting the more widespread use of CuI MLCT photosensitizers, they would be readily adopted in numerous light-activated applications given the earth-abundance of copper and the extensive library of 1,10-phenanthrolines developed over the last century. Significant progress has been achieved by recognizing valuable structure-property concepts developed by other researchers in tandem with detailed ultrafast and conventional time-scale investigations, in-silico-inspired molecular designs to predict spectroscopic properties, and applying novel synthetic methodologies. Ultimately, we achieved a plateau in exerting cooperative steric influence to control CuI MLCT excited state decay. This led to combining sterics with π-conjugation and/or inductive electronic effects to further exert control over molecular photophysical properties. The lessons gleaned from our studies of homoleptic complexes were recently extended to heteroleptic bis(phenanthrolines) featuring enhanced visible light absorption properties and long-lived room-temperature photoluminescence. This Account navigates the reader through our intellectual journey of decision-making, molecular and experimental design, and data interpretation in parallel with appropriate background information related to the quantitative characterization of molecular photophysics using CuI MLCT chromophores as prototypical examples.Initially, CuI MLCT excited states, their energetics, and relevant structural conformation changes implicated in their photophysical decay processes are described. This is followed by a discussion of the literature that motivated our research in this area. This led to our first molecular design in 2013, achieving a 7-fold increase in excited state lifetime relative to the current state-of-the-art. The lifetime and photophysical property enhancement resulted from using 2,9-branched alkyl groups in conjunction with flanking 3,8-methyl substituents, a strategy we adapted from the McMillin group, which was initially described in the late 1990s. Applications of this newly conceived chromophore are presented in solar hydrogen-producing photocatalysis, photochemical upconversion, and photosensitization of [4 + 4] anthracene dimerization of potential interest in thermal storage of solar energy in metastable intermediates. Ultrafast transient absorption and fluorescence upconversion spectroscopic characterization of this and related CuI molecules inform the resultant photophysical properties and vice versa, so the most comprehensive structure-property understanding becomes realized when these experimental tools are collectively utilized to investigate the same series of molecules. Computationally guided structural designs generated newly conceived molecules featuring visible light-harvesting and 2,9-cycloalkane substituted complexes. The latter eventually produced record-setting excited state lifetimes in molecules leveraging both cooperative steric influence and electronic inductive effects. Using photoluminescence data from structurally homologous CuI MLCT excited states collected over 44 years, an energy gap correlation successfully modeled the data spanning a 0.3 eV emission energy range. Finally, a new research direction is revealed detailing structure-photophysical property relationships in heteroleptic CuI phenanthroline chromophores that are photoluminescent at room temperature.

Mechanistic analysis of Riboswitch Ligand interactions provides insights into pharmacological control over gene expression

Riboswitches are structured RNA elements that regulate gene expression upon binding to small molecule ligands. Understanding the mechanisms by which small molecules impact riboswitch activity is key to developing potent, selective ligands for these and other RNA targets. We report the structure-informed design of chemically diverse synthetic ligands for PreQ1 riboswitches. Multiple X-ray co-crystal structures of synthetic ligands with the Thermoanaerobacter tengcongensis (Tte)-PreQ1 riboswitch confirm a common binding site with the cognate ligand, despite considerable chemical differences among the ligands. Structure probing assays demonstrate that one ligand causes conformational changes similar to PreQ1 in six structurally and mechanistically diverse PreQ1 riboswitch aptamers. Single-molecule force spectroscopy is used to demonstrate differential modes of riboswitch stabilization by the ligands. Binding of the natural ligand brings about the formation of a persistent, folded pseudoknot structure, whereas a synthetic ligand decreases the rate of unfolding through a kinetic mechanism. Single round transcription termination assays show the biochemical activity of the ligands, while a GFP reporter system reveals compound activity in regulating gene expression in live cells without toxicity. Taken together, this study reveals that diverse small molecules can impact gene expression in live cells by altering conformational changes in RNA structures through distinct mechanisms.

Raman spectroscopy and molecular dynamics simulations of protein microgels at the oil-water interface

The real-time structural changes of the molecular space conformation of myofibrillar protein microgels (MPM) after heat treatment (90 °C, 30 min) were analyzed by molecular dynamics simulation, and the structural properties and changes of MPM at the oil-water interface were analyzed by the combination of Raman spectroscopy and molecular dynamics simulation. The shift in the oil ratio had a major impact on the transformation of disulfide bonds within the protein molecule. Simultaneously, it caused tryptophan and tyrosine residues (I850 cm−1/ I850 cm−1 > 1) to become exposed, increasing the locations of amino acid residues in the protein that interact with the oil phase. HIPE with different oil phases influenced the change in spatial structural conformation of MPM, and there was a flexible structural change in the molecular space. The HIPE system, which was stabilized by 3.0 wt% MPM and 0.75 oil phase, exhibited a thixotropic recovery of >70 % and the highest elastic modulus G′ (822.14 Pa) based on the rheological behavior. It is expected to provide a theoretical basis for the development and utilization of high internal phase emulsion stabilized by microgel protein in food industry.

Adaptability to the environment of protease by secondary structure changes and application to enzyme-selective hydrolysis

The reactions involving enzymes are significantly influenced by various environmental factors. Clarity of how the activity and structure of proteases impact their function is crucial for more efficient application of enzymes as a tool. The impact of temperature, pH, and ionic strength on changes in protease activity, secondary structure, and protein conformation during enzymatic hydrolysis were investigated in this study. The enzymatic activity and secondary structure of acid-base protease were found to undergo significant modifications under different physical conditions, as demonstrated by UV spectrophotometry and FTIR spectroscopy analysis. Specifically, variations in α-helix and β-fold content were observed to correlate with changes in enzyme activity. Molecular simulation analysis revealed that physical conditions have varying effects on the protease, particularly influencing enzyme activity and secondary structure. Evaluation of the proteases indicated alterations in both enzyme activity and structure. This treatment selectively hydrolyzed β-lactoglobulin and reduced sensitization. These findings offer novel perspectives on the functionalities and regulatory mechanisms of proteases, as well as potential industrial applications.

Effects of ultrasound pretreatment on the structure, IgE binding capacity, functional properties and bioactivity of whey protein hydrolysates via multispectroscopy and peptidomics revealed

Whey protein is an important food ingredient, but it is also considered a major food allergen. The aim of this study was to investigate the effect of ultrasound pretreatment on the structure, IgE binding capacity, functional properties and biological activity of whey protein isolate (WPI) hydrolysates (WPH), including WPI hydrolyzed by a combination of enzymes from Bromelain and ProteAXH (BA-WPI) and WPI hydrolyzed by a combination of enzymes from Papain W-40 and ProteAXH (PA-WPI). The IgE binding capacity of BA-WPI and PA-WPI was reduced to 40.28% and 30.17%, respectively, due to disruption/exposure/shielding of conformational and linear epitopes. The IgE binding capacity of sonicated WPI was increased, but ultrasound pretreatment further reduced the IgE binding capacity of the hydrolysates to 32.89% and 28.04%. This is due to the fact that ultrasound pretreatment leads to conformational changes including increased α-helix and β-sheet structure, exposure of aromatic amino acids, surface hydrophobicity, and increased sulfhydryl content, which increases the accessibility of allergenic epitopes to WPI by the enzyme. Multispectral and LC-MS/MS results further indicated that ultrasound pretreatment altered the conformational and primary structural changes of the hydrolysates. The thermograms showed that ultrasound pretreatment mainly altered the epitope spectra of β-lactoglobulin hydrolysates, while it had less effect on the epitope spectra of α-lactalbumin hydrolysates. Additionally, ultrasound pretreatment significantly improved the foaming properties, antioxidant activity, and α-glucosidase inhibition of the hydrolysates without impairing the solubility and emulsification properties of the hydrolysates. Therefore, ultrasound pretreatment is a feasible method to reduce the allergenicity of WPH and to improve their functional properties and bioactivity. Notably, ultrasonic pretreatment improved the effectiveness and efficiency of WPI hydrolysis, which is a feasible method to produce high-quality protein feedstock in a green, efficient, and economical way.

Alloxazine-Based Ligands and Their Ruthenium Complexes as NADH Oxidation Catalysts and G4 Binders.

Flavin-like ligands (L-1 and L-2) with extended π-conjugation were synthesized using microwave-assisted techniques. An N,N-chelating fragment was integrated into alloxazine units, providing binding sites for metal ions while retaining redox activity. The complexation capability of L-1 and L-2 with two prototypical Ru-scaffolds was examined to design Ru(II) complexes (M-1 and M-2), whose electronic properties were studied and compared with their corresponding ligands via absorption and emission spectroscopy, computational analysis (density functional theory (DFT) and time-dependent DFT (TD-DFT)), and cyclic voltammetry (CV). The ability of L-1 and M-1 to undergo alloxazine/isoalloxazine tautomerization was demonstrated to play a crucial role in the photocatalytic oxidation of NADH, including under green and red wavelengths. Moreover, the interaction of M-1 and M-2 with B-DNA and G-quadruplex structures was investigated. M-2 showed high stabilization of Kit1 and h-Telo oligonucleotides. Meanwhile, M-1 demonstrated switchable emissive properties with B-DNA and induced conformational changes in the h-Telo G-quadruplex structure.

Glycan-shielded homodimer structure and dynamical features of the canine distemper virus hemagglutinin relevant for viral entry and efficient vaccination.

Canine distemper virus (CDV) belongs to morbillivirus, including measles virus (MeV) and rinderpest virus, which causes serious immunological and neurological disorders in carnivores, including dogs and rhesus monkeys, as recently reported, but their vaccines are highly effective. The attachment glycoprotein hemagglutinin (CDV-H) at the CDV surface utilizes signaling lymphocyte activation molecule (SLAM) and Nectin-4 (also called poliovirus-receptor-like-4; PVRL4) as entry receptors. Although fusion models have been proposed, the molecular mechanism of morbillivirus fusion entry is poorly understood. Here, we determined the crystal structure of the globular head domain of CDV-H vaccine strain at 3.2 Å resolution, revealing that CDV-H exhibits a highly tilted homodimeric form with a six-bladed β-propeller fold. While the predicted Nectin-4-binding site is well conserved with that of MeV-H, that of SLAM is similar but partially different, which is expected to contribute to host specificity. Five N-linked sugars covered a broad area of the CDV-H surface to expose receptor-binding sites only, supporting the effective production of neutralizing antibodies. These features are common to MeV-H, although the glycosylation sites are completely different. Furthermore, real-time observation using high-speed atomic force microscopy revealed highly mobile features of the CDV-H dimeric head via the connector region. These results suggest that sugar-shielded tilted homodimeric structure and dynamic conformational changes are common characteristics of morbilliviruses and ensure effective fusion entry and vaccination.

Glycan-shielded homodimer structure and dynamical features of the canine distemper virus hemagglutinin relevant for viral entry and efficient vaccination

Canine distemper virus (CDV) belongs to morbillivirus, including measles virus (MeV) and rinderpest virus, which causes serious immunological and neurological disorders in carnivores, including dogs and rhesus monkeys, as recently reported, but their vaccines are highly effective. The attachment glycoprotein hemagglutinin (CDV-H) at the CDV surface utilizes signaling lymphocyte activation molecule (SLAM) and Nectin-4 (also called poliovirus-receptor-like-4; PVRL4) as entry receptors. Although fusion models have been proposed, the molecular mechanism of morbillivirus fusion entry is poorly understood. Here, we determined the crystal structure of the globular head domain of CDV-H vaccine strain at 3.2 Å resolution, revealing that CDV-H exhibits a highly tilted homodimeric form with a six-bladed β-propeller fold. While the predicted Nectin-4-binding site is well conserved with that of MeV-H, that of SLAM is similar but partially different, which is expected to contribute to host specificity. Five N-linked sugars covered a broad area of the CDV-H surface to expose receptor-binding sites only, supporting the effective production of neutralizing antibodies. These features are common to MeV-H, although the glycosylation sites are completely different. Furthermore, real-time observation using high-speed atomic force microscopy revealed highly mobile features of the CDV-H dimeric head via the connector region. These results suggest that sugar-shielded tilted homodimeric structure and dynamic conformational changes are common characteristics of morbilliviruses and ensure effective fusion entry and vaccination.

Binding and displacement study of gentamicin, 5-fluorouracil, oxytetracycline and rolitetracycline with (BSA: Drug2) complex using spectroscopic and calorimetric techniques: Biophysical approach

Understanding of energetics of interactions between drug and protein is essential in pharmacokinetics and pharmacodynamics study. The binding affinity (K) helps in investigating how tightly or loosely drug is bound to protein. The binding, displacement, conformational change and stability study of drugs- gentamicin (GM), 5-fluorouracil (5FU), oxytetracycline (OTC) and rolitetracycline (RTC) with bovine serum albumin (BSA) has been carried out in presence of each other drug by fluorescence, UV–visible spectroscopy, molecular docking, circular dichroism techniques and thermal denaturation method. The site marker study and docking methods have confirmed that 5FU and GM are able to bind at site 1 and OTC and RTC at site II of BSA. The order of their binding affinities with BSA for the binary system were as GM <5FU < OTC < RTC with the order of 102 < 103 < 105 < 105–6 M−1. The displacement study has shown that higher affinity drug decreases the equilibrium constant of another drug already in bound state with BSA if both these drugs are having the same binding site. Therefore 5FU, GM (binding site 1) drugs were not able to displace OTC and RTC (binding site 2) and vice-versa as they are binding at two different sites. The binding constant values were found to be decreasing with increasing temperature for all the systems involved which suggests static or mixed type of quenching, however can only confirmed with the help of TCSPC technique. The ΔG0 (binding energy) obtained from docking method were in accordance with the ITC method. From molecular docking we have determined the amino acid residues involved in binding process for binary and ternary systems by considering first rank minimum binding energy confirmation. From CD it has been observed that RTC causes most conformational change in secondary and tertiary structure of BSA due to the presence of pyrrole ring. OTC-RTC with higher affinity showed highest melting temperature Tm values while low affinity drugs in (5FU-GM) combination showed lowest Tm value. 5FU showed large endothermic denaturation enthalpy ΔHd0 due to the presence of highly electronegative fluorine atom in the pyridine analogue.

Dual decoration of quinoa protein isolate by different dietary polyphenols with covalent and noncovalent approaches: Structure characterization, conformational changes and functional properties

Naringenin (Nar) showed diverse biological activities as well as limited stability and bioavailability. In this study, polyphenol-grafted quinoa protein isolate (QPI) nanoparticles were synthesized and utilized for encapsulating Nar to improve its stability and enhance its antioxidant capacity. Initially, the study investigated the effects of different types of polyphenols (dihydrocaffeic acid [DA] and dihydromyricetin [DHM]) and different QPI/polyphenol mass ratios (10:1, 10:2.5, 10:5, 10:7.5, 10:10) on the structural properties and conformational changes of the conjugates. Results from polyphenol binding equivalents, SDS-PAGE analysis, and reactive group changes confirmed the covalent binding between QPI and polyphenols, with DHM showing higher reactivity and binding strength to QPI. Subsequently, Nar was encapsulated in QPI-polyphenol nanoparticles (Nar@conjugates), with Nar@DHMgQ displaying a spherical structure and higher EE (82.33%) and LC (8.98%). Furthermore, Nar@conjugates exhibited superior thermal stability, free radical scavenging ability, and controlled release characteristics. Nar@conjugates effectively maintained cell viability, reduced reactive oxygen species (ROS) levels, and restored intracellular antioxidant enzyme activity under oxidative stress conditions. These findings suggested a promising approach for delivering hydrophobic bioactive compounds like Nar in functional foods and pharmaceuticals.

Exploring the mechanism and inhibitory effect of robinin on xanthine oxidase using multi-spectroscopy and molecular dynamics simulation methods

Xanthine oxidase (XOD) is a key enzyme in purine metabolism that is tightly associated with hyperuricemia (HUA). Natural flavonoids can inhibit XOD activity. In this study, the inhibitory activity and mechanism of the novel flavonoid robinin on XOD were analyzed using enzyme inhibition kinetics, multispectral techniques, molecular docking, and molecular dynamics (MD) simulations. Robinin reversibly inhibited the activity of XOD in a mixed competitive manner, with an IC50 value of 31.79 ± 0.15 μg/mL. Moreover, robinin spontaneously binds to a specific site on XOD and effectively quenches its intrinsic fluorescence via a single static quenching mechanism. The combination of XOD and robinin induced secondary structure rearrangement and conformational changes in XOD and prevented the entry of substrates, thus producing a strong inhibitory effect. Molecular docking and MD simulation revealed that robinin mainly binds to XOD through hydrogen bonding and hydrophobic interactions to form more stable complexes with a binding energy of −7.4 kcal/mol. Overall, this study established a theoretical reference for robinin as a promising natural XOD inhibitor for relieving HUA.

Mild extraction of faba bean (Vicia faba L.) proteins against conventional methods: Impact on physicochemical and thermal characteristics

Faba bean (high- and low-tannin) protein isolates were water extracted followed by dialysis or micellization in comparison to concentrates from conventional alkali extraction + acid precipitation, and salt-based extraction (1% NaCl) + dialysis. Protein fractions were characterised for secondary structure conformational changes, crystalline structure, particle size distribution in aqueous suspension and thermal properties. Mild water or salt extraction did not influence particle size distribution. Based on XRD, FTIR and CD, β-sheet structures were the most abundant secondary structures and water extraction + dialysis had minimal impact on their native conformation. DSC results showed an association between protein purity, glass transition temperature and endothermic enthalpy. High melting temperature above glass transition confirms the suitability of faba bean proteins for thermal/extrusion processing. Fractionation method was a more significant determinant of physicochemical characteristics compared to the cultivar. Further exploration of the techno-functional characteristics of faba bean proteins is essential for value-added food applications.

Revealing the interaction mechanism between bovine serum albumin (BSA) and a fluorescent coumarin derivative: A multispectroscopic and in silico approach

The interaction of biomacromolecules with each other or with the ligands is essential for biological activity. In this context, the molecular recognition of bovine serum albumin (BSA) with 4-(Benzo[1,3]dioxol-5-yloxymethyl)-7-hydroxy-chromen-2-one (4BHC) is explored using multispectroscopic and computational techniques. UV–Vis spectroscopy helped in predicting the conformational variations in BSA. Using fluorescence spectroscopy, the quenching behaviour of the fluorophore upon interaction with the ligand is examined, which is found to be a static type of quenching; fluorescence lifetime studies further verify this. The binding constant is discovered to be in the range of 104 M−1, which indicates the moderate type of association that results in reversible binding, where the transport and release of ligands in the target tissue takes place. Fourier-transform infrared spectroscopy (FT-IR) measurements validate the secondary structure conformational changes of BSA after complexing with 4BHC. The thermodynamic factors obtained through temperature-dependent fluorescence studies suggest that the dominant kind of interaction force is hydrophobic in nature, and the interaction process is spontaneous. The alterations in the surrounding microenvironment of the binding site and conformational shifts in the structure of the protein are studied through 3D fluorescence and synchronous fluorescence studies. Molecular docking and molecular dynamics (MD) simulations agree with experimental results and explain the structural stability throughout the discussion. The outcomes might have possible applications in the field of pharmacodynamics and pharmacokinetics.

Photo-transformations of 2-aminothiazole-4-carboxylic acid in low-temperature matrices

The structure, spectroscopic properties and photo-induced conformational changes of 2-aminothiazole-4-carboxylic acid (ACA) isolated in argon and nitrogen matrices were studied using matrix-isolation FTIR spectroscopy and DFT calculations undertaken at the B3LYPD3/6–311++G(3df,3pd) level of theory. Out of 18 stable isomers, the three most stable structures with the five-membered ring stabilized by two C=C and C=N double bonds and with different arrangement of the carboxyl group were identified in both matrices after deposition. Conformer ACA1 has trans and conformers ACA2 and ACA3 have cis conformation of the COOH group and the calculated abundance of 69.5%, 18.2% and 12.2%, respectively. Following irradiation at 285 nm, a rotation of the OH group around the C–O bond in ACA1 was detected leading to increase of ACA2. The corresponding reverse photo-rotamerization was detected at 296 nm, resulting in the recovery of the initial isomer ACA1. Upon NIR irradiation a dominant process was rotamerization within the carboxylic group leading to changes in the population of the ACA1 trans and ACA2 cis forms.

Platform-directed allostery and quaternary structure dynamics of SAMHD1 catalysis

SAMHD1 regulates cellular nucleotide homeostasis, controlling dNTP levels by catalysing their hydrolysis into 2’-deoxynucleosides and triphosphate. In differentiated CD4+ macrophage and resting T-cells SAMHD1 activity results in the inhibition of HIV-1 infection through a dNTP blockade. In cancer, SAMHD1 desensitizes cells to nucleoside-analogue chemotherapies. Here we employ time-resolved cryogenic-EM imaging and single-particle analysis to visualise assembly, allostery and catalysis by this multi-subunit enzyme. Our observations reveal how dynamic conformational changes in the SAMHD1 quaternary structure drive the catalytic cycle. We capture five states at high-resolution in a live catalytic reaction, revealing how allosteric activators support assembly of a stable SAMHD1 tetrameric core and how catalysis is driven by the opening and closing of active sites through pairwise coupling of active sites and order-disorder transitions in regulatory domains. This direct visualisation of enzyme catalysis dynamics within an allostery-stabilised platform sets a precedent for mechanistic studies into the regulation of multi-subunit enzymes.

Monitoring of DNA structural changes after incorporation of the phenylpyrazole insecticide fipronil

The use of insecticides presents a risk to the environment because they can accumulate in the water, soil, air, and organisms, endangering human and animal health. It is therefore essential to investigate the effects of different groups of insecticides on individual biomacromolecules such as DNA. We studied fipronil, which belongs to the group of phenylpyrazole insecticides. The interaction of fipronil with calf thymus DNA was investigated using spectroscopic methods (absorption and fluorescence spectroscopy) complemented with infrared spectroscopy and viscosity measurement. Fluorescence emission spectroscopy showed the formation of a fipronil/DNA complex with a combined static and dynamic type of quenching. The binding constant was 4.15 × 103 L/mol. Viscosity changes were recorded to confirm/disconfirm the intercalation mode of interaction. A slight change in DNA viscosity in the presence of fipronil was observed. The phenylpyrazole insecticide does not cause significant conformational changes in DNA structure or increase of its chain length. We hypothesize that fipronil is incorporated into the minor groove of the DNA macromolecule via hydrogen interactions as indicated by FT-IR and CD measurements.

Mechanistic Analysis of Riboswitch Ligand Interactions Provides Insights into Pharmacological Control over Gene Expression.

Riboswitches are structured RNA elements that regulate gene expression upon binding to small molecule ligands. Understanding the mechanisms by which small molecules impact riboswitch activity is key to developing potent, selective ligands for these and other RNA targets. We report the structure-informed design of chemically diverse synthetic ligands for PreQ1 riboswitches. Multiple X-ray co-crystal structures of synthetic ligands with the Thermoanaerobacter tengcongensis (Tte)-PreQ1 riboswitch confirm a common binding site with the cognate ligand, despite considerable chemical differences among the ligands. Structure probing assays demonstrate that one ligand causes conformational changes similar to PreQ1 in six structurally and mechanistically diverse PreQ1 riboswitch aptamers. Single-molecule force spectroscopy is used to demonstrate differential modes of riboswitch stabilization by the ligands. Binding of the natural ligand brings about the formation of a persistent, folded pseudoknot structure, whereas a synthetic ligand decreases the rate of unfolding through a kinetic mechanism. Single round transcription termination assays show the biochemical activity of the ligands, while a GFP reporter system reveals compound activity in regulating gene expression in live cells without toxicity. Taken together, this study reveals that diverse small molecules can impact gene expression in live cells by altering conformational changes in RNA structures through distinct mechanisms.

Electrochemical analysis of gold nanoparticles multifunctionalised with Cytochrome c and a zinc Porphyrin

Cytochrome c (Cyt c), known for its functional redox capabilities, plays a pivotal role in biological processes such as the electron transport chain and apoptosis. However, understanding how different conjugation strategies impact its structural and redox characteristics is limited. To fill this gap, we investigated the effects of conjugating Cyt c and a zinc(II) porphyrin (Zn Porph) to gold nanoparticles (AuNPs). We used circular dichroism (CD) spectroscopy to detect structural conformational changes in Cyt c upon conjugation and time-of-flight secondary ion mass spectrometry (ToF-SIMS) to identify protein orientation. Cyt c was predicted to have different orientations depending on the size of AuNPs and methods used to conjugate the protein, it was hypothesised that the orientation of Cyt c may influence the redox properties of the protein. The electrochemical properties of Cyt c were assessed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). We used DPV-based to determine the heterogeneous rate constant (k0). The results show a lower k0for conjugated Cyt c than free Cyt c, likely due to structural changes in the protein. The spatial orientation of Cyt c had minimal influence on k0, while ligand density and AuNP size had an effect. The k0 value of Zn Porph did not decrease on conjugation. Despite these changes, Cyt c and Zn Porph maintained their electrochemical capabilities after conjugation.

Characterization of the interactions between Fulvic acid and Trypsin with Spectroscopic and Molecular Docking technology.

The interaction mechanism between trypsin and fulvic acid was analyzed by multispectral method and molecular docking simulation. The fluorescence spectra showed that fulvic acid induced static quenching of trypsin. The validity of this conclusion was further substantiated through the computation of the binding constants. The thermodynamic parameters show that the reaction is mainly controlled by van der Waals force and hydrogen bond force, and the reaction is spontaneous. In addition, based on the obtained binding distance, there may be a non-radiative energy transfer between the two. The ultraviolet spectrum showed that fulvic acid could shift the absorption peak of trypsin, indicating that fulvic acid had an effect on the secondary structure of trypsin. According to the synchronous fluorescence spectrum results, fulvic acid primarily interacts with tryptophan residues in trypsin and induces alterations in their microenvironment. Three-dimensional fluorescence spectrum and circular dichroism further proves this conclusion. The molecular docking simulation reveals that the interaction between the two groups primarily arises from hydrogen bonding and van der Waals forces. The findings suggest that FA has the ability to induce conformational changes in trypsin's secondary structure.

Anticancer Study on IrIII and RhIII Half-Sandwich Complexes with the Bipyridylsulfonamide Ligand.

Organometallic half-sandwich complexes [(η5-Cp)IrCl(L)]PF6 (1) and [(η5-Cp)RhCl(L)]PF6 (2) were prepared using pentamethylcyclopentadienyl chloride dimers of iridium(III) or rhodium(III) with the 4-amino-N-(2,2'-bipyridin-5-yl)benzenesulfonamide ligand (L) and ammonium hexafluorophosphate. The crystal structures of L, 1, and 2 were analyzed in detail. The coordination reactions of the ligand with the central ions were confirmed using various spectroscopic techniques. Additionally, the interactions between sulfaligand, Ir(III), and Rh(III) complexes with carbonic anhydrase (CA), human serum albumin (HSA), and CT-DNA were investigated. The iridium(III) complex (1) did not show any antiproliferative properties against four different cancer cell lines, i.e., nonsmall cell lung cancer A549, colon cancer HCT-116, breast cancer MCF7, lymphoblastic leukemia Nalm-6, and a nonmalignant human embryonic kidney cell line HEK293, due to high binding affinity to GSH. The sulfonamide ligand (L) and rhodium(III) complex (2) were further studied. L showed competitive inhibition toward CA, while complexes 1 and 2, uncompetitive. All compounds interacted with HSA, causing a conformational change in the protein's α-helical structure, suggesting the induction of a more open conformation in HSA, reducing its biological activity. Both L and 2 were found to induce cell death through a caspase-dependent pathway. These findings position L and 2 as potential starting compounds for pharmaceutical, therapeutic, or medicinal research.