Spectroscopic investigations on the effect of N-acetyl-L-cysteine-capped CdTe Quantum Dots on catalase

A Smartphone-Integrated Ratiometric Fluorescence Sensor for the Ultrasensitive and Selective Detection of 5-Heneicosylresorcinol in Whole Wheat Foods

Precise on-site monitoring of alkylresorcinols, a vital biomarker, is crucial for verifying whole wheat foods and accurately quantifying the whole wheat content in various consumer and industrial products. Herein, for the first time, we introduce a novel ratiometric fluorescence sensor (CDs@ZIF-8/CdTe@MIP) for ultrasensitive and selective detection of alkylresorcinols. 5-Heneicosylresorcinol (C21:0 AR), the primary alkylresorcinol homologue in whole wheat grains, was selected as the target analyte. This analyte was specifically and selectively recognized by the incorporation of a molecularly imprinted polymer (MIP) layer. Within this nanoreactor, blue-emitting carbon dots embedded in zeolitic imidazolate framework-8 (CDs@ZIF-8) and orange-emitting CdTe quantum dots served as the self-calibration signal and response signal, respectively. Exploiting a photoinduced electron transfer effect between CdTe and C21:0 AR, the established fluorescence sensor exhibited remarkable sensing performance, offering wide linear responses in 0.005-1 μg·mL-1 and 1-80 μg·mL-1 concentration ranges, and achieving a low detection limit of 1.14 ng·mL-1. The proposed assay effectively detected C21:0 AR in real samples, including 8 whole wheat foods and 19 whole wheat grains, demonstrating good recoveries and relative standard deviation. Furthermore, an intelligent sensing platform was established by integrating CDs@ZIF-8/CdTe@MIP with a smartphone-assisted device, thus validating the feasibility of visual and on-site monitoring of C21:0 AR. Because of its rapid response, portability, cost-effectiveness, superior sensitivity, and high selectivity, the proposed sensor serves as a reliable method for the analysis of C21:0 AR, thus having substantial potential for on-site monitoring of whole wheat foods.

Nano-bio convergence unveiled: Systematic review on quantum dots-protein interaction, their implications, and applications

Quantum dots (QDs) are semiconductor nanocrystals (2-10 nm) with unique optical and electronic properties due to quantum confinement effects. They offer high photostability, narrow emission spectra, broad absorption spectrum, and high quantum yields, making them versatile in various applications. Due to their highly reactive surfaces, QDs can conjugate with biomolecules while being used, produced, or unintentionally released into the environment. This systematic review delves into intricate relationship between QDs and proteins, examining their interactions that influence their physicochemical properties, enzymatic activity, ligand binding affinity, and stability. The research utilized electronic databases like PubMed, WOS, and Proquest, along with manual reviews from 2013 to 2023 using relevant keywords, to identify suitable literature. After screening titles and abstracts, only articles meeting inclusion criteria were selected for full text readings. This systematic review of 395 articles identifies 125 articles meeting the inclusion criteria, categorized into five overarching themes, encompassing various mechanisms of QDs and proteins interactions, including adsorption to covalent binding, contingent on physicochemical properties of QDs. Through a meticulous analysis of existing literature, it unravels intricate nature of interaction, significant influence on nanomaterials and biological entities, and potential for synergistic applications harnessing both specific and nonspecific interactions across various fields.

Exploring In Vivo Pulmonary and Splenic Toxicity Profiles of Silicon Quantum Dots in Mice

Silicon-based quantum dots (SiQDs) represent a special class of nanoparticles due to their low toxicity and easily modifiable surface properties. For this reason, they are used in applications such as bioimaging, fluorescent labeling, drug delivery, protein detection techniques, and tissue engineering despite a serious lack of information on possible in vivo effects. The present study aimed to characterize and evaluate the in vivo toxicity of SiQDs obtained by laser ablation in the lung and spleen of mice. The particles were administered in three different doses (1, 10, and 100 mg QDs/kg of body weight) by intravenous injection into the caudal vein of Swiss mice. After 1, 6, 24, and 72 h, the animals were euthanized, and the lung and spleen tissues were harvested for the evaluation of antioxidant enzyme activity, lipid peroxidation, protein expression, and epigenetic and morphological changes. The obtained results highlighted a low toxicity in pulmonary and splenic tissues for concentrations up to 10 mg SiQDs/kg body, demonstrated by biochemical and histopathological analysis. Therefore, our study brings new experimental evidence on the biocompatibility of this type of QD, suggesting the possibility of expanding research on the biomedical applications of SiQDs.

Role of CdTe quantum dots on peripheral Immunocytes and selenoprotein P: immunotoxicity at the molecular and cellular levels

The extensive product and application of cadmium-quantum dots (Cd-QDs), one kind of semiconductor nanomaterials, lead to prolonged exposure to the environment. Cd-QDs have shown good properties in biomedical and imaging-related fields; the safety of Cd-QDs limits the application of these materials and technologies, however. The systematic distribution of CdTe QDs in organisms has been ascertained in previous studies. Nevertheless, it is relatively less reported about the toxicity of CdTe QDs to immune macromolecules and organs. Based on this, immunocytes (including lymphocyte subsets-CD4+ T and CD8+ T cells, splenocytes) and selenoprotein P (SelP) were chosen as targets for CdTe QDs immunotoxicity studies. Results indicate that CdTe QDs induced cytotoxicity to CD4+ T cells, CD8+ T cells and splenocytes by reducing cell viability and causing apoptosis as CdTe QDs and Cd2+ enter cells. At the molecular level, the direct interaction between CdTe QDs and SelP is proved by multispectral measurements, which demonstrated the alteration of protein structure. The combined results show that CdTe QDs induced adverse effects on the immune system at the cellular and molecular levels. This research contributes to a better understanding of CdTe QDs cause harmful damage to the immune system and provides new strategies for the inhibition and treatment of health damages caused by CdTe QDs.

Application of Se-Met to CdTe QDs significantly reduces toxicity by modulating redox balance and inhibiting apoptosis

Cadmium tellurium quantum dots (CdTe QDs) as one of the most widely used QDs have been reported the toxicity and biosafety in recent years, little work has been done to reduce their toxicity however. Based on the mechanisms of toxicity of CdTe QDs on liver target organs such as oxidative stress and apoptosis previously reported by other researchers, we investigated the mechanism of action of trace element selenium (Se) to mitigate the hepatotoxicity of CdTe QDs. The experimental results showed that Se-Met at 40-140 μg L-1 could enhance the function of intracellular antioxidant defense system and the molecular structure of related antioxidant enzymes by reduce the production of ROS by 45%, protecting the activity of antioxidants and up-regulating the expression of selenoproteins with antioxidant functions, Gpx1 increase 225% and Gpx4 upregulated 47%. In addition, Se-Met could alleviate CdTe QDs-induced apoptosis by regulating two apoptosis-inducing factors, as intracellular caspase 3/9 expression levels were reduced by 70% and 87%, decreased Ca2+ concentration, and increased mitochondrial membrane potential measurements. Overall, this study indicates that Se-Met has a significant protective effect on the hepatotoxicity of CdTe QDs. Se-Met can be applied to the preparation of CdTe QDs to inhibit its toxicity and break the application limitation.

A fluorescence nanoprobe of N-Acetyl-L-Cysteine capped CdTe QDs for sensitive detection of nitrofurazone

A method was established for detecting the content of nitrofurazone (NFZ) by fluorescence quenching of N-Acetyl-L-Cysteine (NAC) coated cadmium telluride quantum dots (CdTe QDs). By means of transmission electron microscopy (TEM) and multispectral methods such as fluorescence and ultraviolet visible spectra (UV-vis), the synthesized CdTe QDs were characterized. The quantum yield (φ) of CdTe QDs was measured as 0.33 by reference method. The CdTe QDs had a better stability, the RSD of fluorescence intensity was 1.51% in three months. NFZ quenching the emission light of CdTe QDs was observed. The analyses of Stern-Volmer and time-resolved fluorescence suggested the quenching was static. The binding constants (K_a) between NFZ and CdTe QDs were 1.14 × 10⁴ (293 K), 0.74 × 10⁴ (303 K) and 0.51 × 10⁴ (313 K) L mol^-1. The hydrogen bond or van der Waals force was the dominated binding force between NFZ and CdTe QDs. The interaction was further characterized by UV-vis absorption as well as Fourier transform infrared spectra (FT-IR). Using fluorescence quenching effect, a quantitative determination of NFZ was carried out. The optimal experimental conditions were studied and determined as following: pH was 7 and contact time was 10 min. The effects of reagent addition sequence, temperature and the foreign substances including some metals (Mg²⁺; Zn²⁺; Ca²⁺; K⁺; Cu²⁺), glucose, bovine serum albumin (BSA) and furazolidone on the determination were studied. There was a high correlation between the concentration of NFZ (0.40 - 39.63 μg mL^-1) and F₀/F with the standard curve F₀/F = 0.0262c + 0.9910 (r = 0.9994). The detection limit (LOD) reached 0.04 μg mL^-1 (3S₀/S). The contents of NFZ in beef and bacteriostatic liquid were detected. The recovery of NFZ was 95.13% - 103.03% and RSD was 0.66% - 1.37% (n = 5).

Intrinsic mechanisms for the inhibition effect of graphene oxide on the catalysis activity of alpha amylase

Comprehending the interactions between graphene oxide (GO) and enzymes is critical for understanding the toxicities of GO. In this study, the inherent interactions of GO with α-amylase as a typical enzyme, and the impacts of GO on the conformation and biological activities of α-amylase were systematically investigated. The results reveal that GO formed ground-state complex with α-amylase primarily via hydrogen bonding and van der Waals interactions, thus quenching the intrinsic fluorescence of the protein statically. Particularly, the strong interactions altered the microenvironment of tyrosine and tryptophan residues, caused rearrangement of polypeptide structure, and reduced the contents of α-helices and β-sheets, thus changing the conformational structure of α-amylase. According to molecular docking results, GO binds with the amino acid residues (i.e., His299, Asp300, and His305) of α-amylase mainly through hydrogen bonding, which is in accordance with in vitro incubation experiments. As a consequence, the ability of α-amylase to catalyze starch hydrolysis into glucose was depressed by GO, suggesting that GO might cause dysfunction of α-amylase. This study discloses the intrinsic binding mechanisms of GO with α-amylase and provides novel insights into the adverse effects of GO as it enters organisms.

Silicon dioxide nanoparticles adsorption alters the secondary and tertiary structures of catalase and undermines its activity

The expanding production and use of nanomaterials in various fields caused big concern for human health. Oxidative stress is the most frequently described mechanism of nanomaterial toxicity. A state of oxidative stress can be defined as the imbalance of reactive oxygen species (ROS) production and antioxidant enzyme activities. Although nanomaterials-triggered ROS generation has been extensively investigated, little is known regarding the regulation of antioxidant enzyme activities by nanomaterials. This study used two typical nanomaterials, SiO₂ nanoparticles (NPs) and TiO₂ NPs, to predict their binding affinities and interactions with antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD). The molecular docking results showed that CAT and SOD had different binding sites, binding affinity, and interaction modes with SiO₂ NPs and TiO₂ NPs. The binding affinities of the two NPs to CAT were more potent than those to SOD. Consistently, the experimental work indicated NPs adsorption caused the perturbation of the second and tertiary structures of both enzymes and thus resulted in the loss of enzyme activities.

Induction of Chirality in Atomically Thin ZnSe and CdSe Nanoplatelets: Strengthening of Circular Dichroism via Different Coordination of Cysteine-Based Ligands on an Ultimate Thin Semiconductor Core

Chiral nanostructures exhibiting different absorption of right- and left-handed circularly polarized light are of rapidly growing interest due to their potential applications in various fields. Here, we have studied the induction of chirality in atomically thin (0.6-1.2 nm thick) ZnSe and CdSe nanoplatelets grown by a colloidal method and coated with L-cysteine and N-acetyl-L-cysteine ligands. We conducted an analysis of the optical and chiroptical properties of atomically thin ZnSe and CdSe nanoplatelets, which was supplemented by a detailed analysis of the composition and coordination of ligands. Different signs of circular dichroism were shown for L-cysteine and N-acetyl-L-cysteine ligands, confirmed by different coordination of these ligands on the basal planes of nanoplatelets. A maximum value of the dissymmetry factor of (2-3) × 10^-3 was found for N-acetyl-L-cysteine ligand in the case of the thinnest nanoplatelets.

Response of earthworm coelomocytes and catalase to pentanone and hexanone: a revelation of the toxicity of conventional solvents at the cellular and molecular level

Organic solvents like 2-pentanone and 2-hexanone which are widely used in industrial production make up a large proportion of the source of chemical pollution. What is worrisome is that the cellular and molecular toxicity of 2-pentanone and 2-hexanone has not been reported yet. Based on this, earthworms and catalase (CAT) were chosen as target receptors for the toxicity studies. The cytotoxicity of 2-pentanone and 2-hexanone was revealed by measuring the multiple intracellular indicators of oxidative stress. At the molecular level, changes in the structure and function of CAT were characterized in vitro by the spectroscopy and molecular docking. The results show that 2-pentanone and 2-hexanone that induced the accumulation of reactive oxygen species can eventually reduce coelomocytes viability, accompanying by the regular changes of antioxidant activity and lipid peroxidation level. In addition, the exposure of 2-pentanone and 2-hexanone can shrink the backbone structure of CAT, quench the fluorescence, and misfold the secondary structure. The decrease in enzyme activity should be attributed to the structural changes induced by surface binding. This study discussed the toxicological effects and mechanisms of conventional solvents at the cellular and molecular level, which creatively proposed a joint research method.

New insights into the release mechanism of Cd2+ from CdTe quantum dots within single cells in situ

Cadmium-quantum dots (Cd-QDs) possess unique properties as optoelectronic devices for sensitive detection in food and biomedicine fields. However, the toxic effects of Cd-QDs to single cells is still controversial, due to the release mechanism of QDs to Cd²⁺in situ and the cytotoxic effects of QDs and Cd²⁺ respectively are still unclear. In this paper, the release rule of Cd²⁺ from CdTe QDs within single cells was investigated in situ by using flow cytometry method and the dose-response relationships were explored. Besides, an all-inclusive microscopy system was optimized for live cell imaging to observe the real-time entry process of CdTe QDs into cells. We found that intracellular CdTe QDs and Cd²⁺ contents were increased based on the dosage and exposing time. A dissociated saturation of Cd²⁺ from CdTe QDs was exist within cells. CdTe QDs induced more serious cytotoxicity on kidney cells than hepatocytes. The toxicity of oxidative stress, cell apoptosis effects induced by CdTe QDs and Cd²⁺ are also in consistent with this result. This research develops analytical method to quantify the uptake and release of Cd-QDs to primary cells in situ and can provide technical support in studying the cytotoxicity portion contributed by nanoparticles (NPs) and metal ions.

Responses of catalase and superoxide dismutase to low-dose quantum dots on molecular and cellular levels

With the wider application of cadmium-containing quantum dots (Cd-QDs) in biomedical fields, it is easier for people to be exposed. Studies have suggested that Cd-QDs could release cadmium ion and induce oxidative effects due to the disruption of redox equilibrium. Antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD), play an important role in organisms to resist the negative impact of exogenous substances. Molecular mechanisms of antioxidant enzymes with Cd-QDs remain unclear, however. In this study, structural and functional changes of CAT and SOD have been investigated under low dose Cd-QDs exposure. Cell viability, malondialdehyde (MDA) level, CAT and SOD activities were influenced by Cd-QDs in hepatocytes of mice. To further investigate the responses of CAT and SOD to Cd-QDs, multiple spectroscopic, calorimetric and activity measurements were carried out. Similar interaction patterns were observed that result in interaction force, structural and functional changes: Cd-QDs combine with CAT and SOD through hydrophobic forces; Intrinsic fluorescence of proteins was statically quenched by Cd-QDs and new complexes were formed; Also, the skeleton and secondary structure (with α-helix decrease) of CAT and SOD was influenced. Taken together, we suggest that Cd-QDs chosen in this study induce oxidative stress effects to hepatocytes but have not caused serious oxidative stress damage at concentrations below 10 μg/mL. MPA-CdSe/ZnS QDs caused the lowest level of oxidative stress which is associated with the induction of antioxidant proteins. This paper presents responses of CAT and SOD to low-dose Cd-QDs, and provides a reference for evaluating health damages caused by Cd-QDs.

Exploring the conformational changes in fibrinogen by forming protein corona with CdTe quantum dots and the related cytotoxicity

This study describes synthesis of N‑acetyl‑l‑cysteine-capped CdTe quantum dots (QDs) and investigates their interaction with plasma protein fibrinogen (FIB) and the structural changes of FIB. It is shown that the interaction of QDs with FIB is a spontaneous process and the major driving forces are van der Waals forces and hydrogen bonds. Multi-spectroscopic measurements show that the intrinsic fluorescence of FIB was quenched and secondary and tertiary structures were altered due to the interaction with QDs. In addition, the aggregation state of FIB was altered in the presence of QDs. Furthermore, the formed complexes of FIB with QDs reduced the cytotoxicity of QDs. The coating of FIB on QDs could lower intracellular QDs uptake and therefore result in less released cadmium ions and ROS productions. This study, therefore, might be helpful to the comprehensive understanding of QDs toxicity and provide evidence for assessing the safe application of nanoparticles.

The interaction of silica nanoparticles with catalase and human mesenchymal stem cells: biophysical, theoretical and cellular studies

Aim

Nanoparticles (NPs) have been receiving potential interests in protein delivery and cell therapy. As a matter of fact, NPs may be used as great candidates in promoting cell therapy by catalase (CAT) delivery into high oxidative stress tissues. However, for using NPs like SiO₂ as carriers, the interaction of NPs with proteins and mesenchymal stem cells (MSCs) should be explored in advance.

Methods

In the present study, the interaction of SiO₂ NPs with CAT and human MSCs (hMSCs) was explored by various spectroscopic methods (fluorescence, circular dichroism (CD), UV-visible), molecular docking and dynamics studies, and cellular (MTT, cellular morphology, cellular uptake, lactate dehydrogenase, ROS, caspase-3, flow cytometry) assays.

Results

Fluorescence study displayed that both dynamic and static quenching mechanisms and hydrophobic interactions are involved in the spontaneous interaction of SiO₂ NPs with CAT. CD spectra indicated that native structure of CAT remains stable after interaction with SiO₂ NPs. UV-visible study also revealed that the kinetic parameters of CAT such as Km, Vmax, Kcat, and enzyme efficiency were not changed after the addition of SiO₂ NPs. Molecular docking and dynamics studies showed that Si and SiO₂ clusters interact with hydrophobic residues of CAT and SiO₂ cluster causes minor changes in the CAT structure at a total simulation time of 200 ps. Cellular assays depicted that SiO₂ NPs induce significant cell mortality, change in cellular morphology, cellular internalization, ROS elevation, and apoptosis in hMSCs at higher concentration than 100 µg/mL (170 µM).

Conclusion

The current results suggest that low concentrations of SiO₂ NPs induce no substantial change or mortality against CAT and hMSCs, and potentially useful carriers in CAT delivery to hMSC.

PFOA and PFOS interact with superoxide dismutase and induce cytotoxicity in mouse primary hepatocytes: A combined cellular and molecular methods

This study investigated the adverse effects of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) on mouse primary hepatocytes by conducting cell viability, apoptosis, intracellular oxidative stress level, superoxide dismutase (SOD), catalase (CAT) activity and glutathione level assays. It was shown that PFOA and PFOS altered antioxidant enzymes activities and triggered oxidative stress, and thus exhibited cytotoxicity to the hepatocytes. Molecular mechanisms of SOD activities were measured and structural changes were explored by isothermal titration calorimetry and multiple spectroscopy. PFOA and PFOS bind to SOD via electrostatic forces with 7.634 ± 0.06 and 9.7 ± 0.4 sites, respectively, leading to structural and conformational changes. The overall results demonstrated that PFOS and PFOA are able to interact with SOD directly, resulting in producing oxidative stress and induce apoptosis.

Immobilization of Recombinant Human Catalase on Gold and Silver Nanoparticles

Human catalase cDNA was cloned into a pEX-C-His vector. Purified recombinant catalase was immobilized on nanoparticles. Gold and silver nanoparticles were synthesized in a variety of sizes by chemical reduction; no agglomerates or aggregates were observed in any of the colloids during dynamic light scattering or scanning transmission electron microscopy analysis. After immobilization on gold nanoparticles, recombinant catalase activity was found to be lower than that of the same amount of enzyme in aqueous solution. However, after 10 days of storage at room temperature, the activity of catalase immobilized on gold nanoparticles (AuNPs) of 13 and 20 nm and coverage of 133% was 68 and 83% greater than catalase in aqueous solution, respectively. During 10 days of experiment, percentage activity of catalase immobilized on those gold nanoparticles was higher in comparison to CAT in aqueous solution. Catalase immobilized on silver nanoparticles did not lose activity as significantly as catalase immobilized on AuNPs. Those results confirm the ability to produce recombinant human enzymes in a bacterial expression system and its potential use while immobilized on silver or gold nanoparticles.

One-pot synthesis of highly luminescent N-acetyl-l-cysteine-capped CdTe quantum dots and their size effect on the detection of glutathione

N-Acetyl-l-cysteine-capped CdTe QDs with a large size (3.68 nm) are more suitable for detecting glutathione than the small ones (1.99 nm).

Spectroscopic investigations on the conformational changes of lysozyme effected by different sizes of N-acetyl-l-cysteine-capped CdTe quantum dots

The effect of N-acetyl-l-cysteine-capped CdTe quantum dots (NAC-CdTe QDs) with different sizes on lysozyme was investigated by isothermal titration calorimetry (ITC), enzyme activity assays, and multi-spectroscopic methods. ITC results proved that NAC-CdTe QDs can spontaneously bind with lysozyme and hydrophobic force plays a major role in stabilizing QDs-lysozyme complex. Multi-spectroscopic measurements revealed that NAC-CdTe QDs caused strong quenching of the lysozyme's fluorescence in a size-dependent quenching manner. Moreover, the changes of secondary structure and microenvironment in lysozyme caused by the NAC-CdTe QDs were higher with a bigger size. The results of enzyme activity assays showed that the interaction between lysozyme and NAC-CdTe QDs inhibited the activity of lysozyme and the inhibiting effect was in a size-dependent manner. Based on these results, we conclude that NAC-CdTe QDs with larger particle size had a larger impact on the structure and function of lysozyme.

Aqueous synthesis of functionalized copper sulfide quantum dots as near-infrared luminescent probes for detection of Hg2+, Ag+ and Au3

Stable water-soluble copper sulfide(Cu2S) quantum dots(QDs) with near-infrared emission were synthesized using N-acetyl-L-cysteine(NAC) as a modifier in aqueous solution and nitrogen atmosphere at room temperature. The product was characterized by TEM, XRD, XPS, FT-IR, FL and UV-VIS spectrometers. Effects of preparation conditions such as pH values, the molar ratio of reactants, temperature, and metal ions on the fluorescence properties of Cu2S QDs were discussed. Under optimal conditions, the prepared Cu2S QDs with average diameter about 2-5 nm show a near-infrared emission at 770 nm with the excitation wavelength of 466 nm, and have a good detection sensitivity for ions of Hg2+, Ag+ and Au3+, based on the characteristic of fluorescence quenching. The fluorescence quenching mechanism was proposed via electron transfer with cation exchange, which based on the theory of Hard-Soft-Acid-Base (HSAB) and Ksp value of metal-sulfide.

Investigating the Interaction of Fe Nanoparticles with Lysozyme by Biophysical and Molecular Docking Studies

Herein, the interaction of hen egg white lysozyme (HEWL) with iron nanoparticle (Fe NP) was investigated by spectroscopic and docking studies. The zeta potential analysis revealed that addition of Fe NP (6.45±1.03 mV) to HEWL (8.57±0.54 mV) can cause to greater charge distribution of nanoparticle-protein system (17.33±1.84 mV). In addition, dynamic light scattering (DLS) study revealed that addition of Fe NP (92.95±6.11 nm) to HEWL (2.68±0.37 nm) increases suspension potential of protein/nanoparticle system (51.17±3.19 nm). Fluorescence quenching studies reveled that both static and dynamic quenching mechanism occur and hydrogen bond and van der Waals interaction give rise to protein-NP system. Synchronous fluorescence spectroscopy of HEWL in the presence of Fe NP showed that the emission maximum wavelength of tryptophan (Trp) residues undergoes a red-shift. ANS fluorescence data indicated a dramatic exposure of hydrophobic residues to the solvent. The considerable reduction in melting temperature (T(m)) of HEWL after addition of Fe NP determines an unfavorable interaction system. Furthermore circular dichoroism (CD) experiments demonstrated that, the secondary structure of HEWL has not changed with increasing Fe NP concentrations; however, some conformational changes occur in tertiary structure of HEWL. Moreover, protein-ligand docking study confirmed that the Fe NP forms hydrogen bond contacts with HEWL.

Binding of copper to lysozyme: Spectroscopic, isothermal titration calorimetry and molecular docking studies

Although copper is essential to all living organisms, its potential toxicity to human health have aroused wide concerns. Previous studies have reported copper could alter physical properties of lysozyme. The direct binding of copper with lysozyme might induce the conformational and functional changes of lysozyme and then influence the body's resistance to bacterial attack. To better understand the potential toxicity and toxic mechanisms of copper, the interaction of copper with lysozyme was investigated by biophysical methods including multi-spectroscopic measurements, isothermal titration calorimetry (ITC), molecular docking study and enzyme activity assay. Multi-spectroscopic measurements proved that copper quenched the intrinsic fluorescence of lysozyme in a static process accompanied by complex formation and conformational changes. The ITC results indicated that the binding interaction was a spontaneous process with approximately three thermodynamical binding sites at 298K and the hydrophobic force is the predominant driven force. The enzyme activity was obviously inhibited by the addition of copper with catalytic residues Glu 35 and Asp 52 locating at the binding sites. This study helps to elucidate the molecular mechanism of the interaction between copper and lysozyme and provides reference for toxicological studies of copper.

Thermodynamic and conformational changes of protein toward interaction with nanoparticles: a spectroscopic overview

Nanoparticles (NPs) in different forms have been widely used in medicine and pharmaceutics for diagnosis and drug delivery.

Circular dichroism sensor based on cadmium sulfide quantum dots for chiral identification and detection of penicillamine

A new chemical sensor based on the measuring of circular dichroism signal (CD) was fabricated from cysteamine capped cadmium sulfide quantum dots (Cys-CdS QDs). The chiral-thiol molecules, d-penicillamine (DPA) and l-penicillamine (LPA), were used to evaluate potentials of this sensor. Basically, DPA and LPA provide very low CD signals. However, the CD signals of DPA and LPA can be enhanced in the presence of Cys-CdS QDs. The CD spectra of DPA and LPA exhibited a mirror image profile. Parameters affecting the determination of DPA and LPA were thoroughly investigated in details. Under the optimized condition, the CD signals of DPA and LPA displayed a linear relationship with the concentrations of both enantiomers, ranging from 1 to 35 μM. Detection limits of this sensor were 0.49 and 0.74 μM for DPA and LPA, respectively. To demonstrate a potential application of this sensor, the proposed sensor was used to determine DPA and LPA in real urine samples. It was confirmed that the proposed detection technique was reliable and could be utilized in a broad range of applications.

Increasing the activity of immobilized enzymes with nanoparticle conjugation

The efficiency and selectivity of enzymatic catalysis is useful to a plethora of industrial and manufacturing processes. Many of these processes require the immobilization of enzymes onto surfaces, which has traditionally reduced enzyme activity. However, recent research has shown that the integration of nanoparticles into enzyme carrier schemes has maintained or even enhanced immobilized enzyme performance. The nanoparticle size and surface chemistry as well as the orientation and density of immobilized enzymes all contribute to the enhanced performance of enzyme-nanoparticle conjugates. These improvements are noted in specific nanoparticles including those comprising carbon (e.g., graphene and carbon nanotubes), metal/metal oxides and polymeric nanomaterials, as well as semiconductor nanocrystals or quantum dots.

Characterization of the interaction of FTO protein with thioglycolic acid capped CdTe quantum dots and its analytical application

CdTe quantum dots (QDs) were synthesized in aqueous solution using thioglycolic acid (TGA) as stabilizing agents. The interaction between TGA-CdTe QDs and fat mass and obesity-associated (FTO) protein was investigated by fluorescence, UV-visible absorption, synchronous fluorescence and three-dimensional fluorescence spectroscopy. Results revealed that TGA-CdTe QDs could strongly quench the intrinsic fluorescence of FTO protein with a static quenching procedure. Both the van der Waals and hydrogen bonding played a major role in stabilizing the complex. The binding constant and thermodynamic parameters at different temperatures were obtained. In addition, we found that the fluorescence intensity of QDs was significantly enhanced by the addition of FTO protein. Based on this, a sensitive method for detecting FTO protein was obtained in the linear range of 5.52×10(-9)-6.62×10(-7) mol L(-1) with the detection limit of 1.14×10(-9) mol L(-1). The influences of factors on the interaction between FTO protein and TGA-CdTe QDs were studied.

Effects of N-acetyl-L-cysteine-capped CdTe quantum dots on bovine serum albumin and bovine hemoglobin: isothermal titration calorimetry and spectroscopic investigations

The interactions of N-acetyl-L-cysteine-capped CdTe quantum dots (QDs) with bovine serum albumin (BSA) and bovine hemoglobin (BHb) were investigated by isothermal titration calorimetry (ITC), fluorescence, synchronous fluorescence, fluorescence lifetime, ultraviolet-visible absorption, and circular dichroism techniques. Fluorescence data of BSA-QDs and BHb-QDs revealed that the quenching was static in every system. While CdTe QDs changed the microenvironment of tryptophan in BHb, the microenvironment of BSA kept unchanged. Adding CdTe QDs affected the skeleton and secondary structure of the protein (BSA and BHb). The ITC results indicated that the interaction between the protein (BSA and BHb) and QDs-612 was spontaneous and the predominant force was hydrophobic interaction. In addition, the binding constants were determined to be 1.19 × 10(5) L mol(-1) (BSA-QDs) and 2.19 × 10(5) L mol(-1) (BHb-QDs) at 298 K. From these results, we conclude that CdTe QDs have a larger impact on the structure of BHb than BSA.