Thirty years of haemoglobin electrochemistry

Studies on the interaction of 2,4-dibromophenol with human hemoglobin using multi-spectroscopic, molecular docking and molecular dynamics techniques

2,4-Dibromophenol (DBP) has several industrial applications, including as a wood preservative and flame retardant. This study investigated the interaction between DBP and human hemoglobin (Hb) using spectroscopic, molecular docking and molecular dynamic techniques. The UV-visible spectra showed ground-state complex formation between DBP and Hb. Fluorescence studies revealed that DBP binding caused significant quenching of Hb fluorescence by the static quenching mechanism. The binding of DBP to Hb is a spontaneous process that involves van der Waals forces and hydrogen bonds. There is one DBP binding site on each Hb molecule that is located at the α1β2 interface of Hb. DBP binding did not alter the microenvironment of tyrosine and tryptophan residues in Hb. Circular dichroism studies revealed that DBP increased the α-helical content of Hb. The intrinsic esterase activity of Hb was inhibited by DBP in a concentration-dependent manner. Molecular docking showed that DBP binds to Hb via hydrogen bonds, hydrophobic, van der Waals and π - π interactions. Molecular dynamics simulation confirmed that the Hb-DBP complex is stable. Overall, the results of this study clearly show that DBP induces structural changes and interferes with the function of Hb. This can have important implications for human health.Communicated by Ramaswamy H. Sarma.

Physicochemical mechanism of BSA, Hb, and dsDNA biomacromolecules with aq-NaCMC at 298.15-310.15 K interfaced with UV-vis fluorescence circular dichroism spectroscopy and in-silico for interacting activities

The 0.2-0.8mg% @ 0.2 mg% bovine serum albumin (BSA 66), hemoglobin (Hb 64.5), and double stranded deoxyribonucleic acid (dsDNA 130 kDa) with water and 0.25, 0.50, and 1.00 g% aqueous carboxymethyl cellulose sodium salt (NaCMC) thermodynamically, kinetically, and tentropically stable homogeneous solutions via resonating energy transfer were designed. Density (ρ), viscosity (η), surface tension (γ), friccohesity (σ), Gibbs free energy (ΔG_b), chemical potential (μ), frictional volume (ϕ), apparent molar volume (V₂), hydrodynamic radius (R_h), and isentropic compressibility (k_sϕ) at 298.15, 304.15, and 310.15 K were studied. UV-Vis spectrophotometry, fluorescence spectroscopy, circular dichroism (CD), MALDI TOF, and in-silico study via reorientational activities have elucidated structural recognition. The ρ, η, γ, σ, ΔG_b, μ, V₂, ϕ, R_h, and k_sϕ physicochemical properties (PCPs) have studied the interacting activities of salt bridges (peptide bonds) of proteins and base pairs (adenine, thymine, cytosine, guanine) of dsDNA on developing nanohydration sphere (NHS) with water and 0.25, 0.50, and 1.00 g% aq-NaCMC. Regression constants of PCPs have elaborated the interacting mechanism of internal linkages of BSA, Hb, and dsDNA for solubilizing them without unfolding assisted by glycosidic bonds of glucopyranose units of NaCMC. Magnitudes of regression constants analyse the inner salt bridges, electrostatic dipoles, and hydrogen bonds (HB) to interact with H₂O dipoles and NaCMC affecting solubilization of biomolecules (biomols) in areas of biochemical, biophysical, bioengineering, tissue, and genetic engineering. PCPs, UV-Vis, fluorescence, CD, and in-silico study analyse their structurally interacting abilities with NaCMC via respective NHS to be extended to pharmaceutical and cosmetic processes by minimizing quantum energy barrier (QEB) as Newtonian behaviour of structural sensors.

Current understanding and insights towards protein stabilization and activation in deep eutectic solvents as sustainable solvent media

Deep eutectic solvents (DESs) have emerged as a new class of green, designer and biocompatible solvents, an alternative to conventional organic solvents and ionic liquids (ILs) which are comparatively toxic and non-biodegradable. DESs are eutectic mixtures that are formed when a hydrogen bond acceptor (HBA) is mixed with a hydrogen bond donor (HBD) at particular molar ratios by mechanical grinding or under mild heating conditions. Very recently, these solvents have been the center of attention for researchers in biotechnology, biomedicine and various scientific applications. These environmentally benign solvents have a close analogy with ILs; however, they offer certain unique merits over traditional ILs. DESs display remarkable properties such as easy preparation, tunable composition, biodegradability, recyclability, inherently low toxicity, sustainability and biocompatibility; these special features validate DESs as new potential solvents/co-solvents for biomolecules. Mechanistically, the biocompatibility and protein friendly nature of DESs depend on various factors, which include the composition of the DES, viscosity and hydration level. Therefore, it becomes an essential task to bring together all the studies related to protein behaviour in DESs to unlock their biomolecular proficiency. This review specifically highlights recent insights into the biomacromolecular functionality in DESs, including outlines of the solubilization and stabilization of proteins, long term protein packaging, different extraction methods and enzyme activation in the presence of DESs. A literature survey reveals that DESs act as green media in which the protein structure and activity are retained. In some cases, proteins refolded and enzymatic activity was enhanced several fold in the presence of DESs. Furthermore, we have reviewed the possible mechanistic behaviour behind protein stabilization, refolding and activation in DESs. Overall, the main objective of this review is to explicate the advantages of the introduction of DESs for biomolecules and to demonstrate the versatility of these eco-friendly solvents for future bio-based applications.

The interaction mechanism between gold nanoparticles and proteins: Lysozyme, trypsin, pepsin, γ-globulin, and hemoglobin

In this study, the interaction between gold nanoparticles (AuNPs) and proteins (including lysozyme, trypsin, pepsin, γ-globulin and hemoglobin) was investigated by UV-visible absorption spectroscopy, fluorescence spectroscopy, circular dichroism (CD) spectroscopy and protein activity assay. AuNPs was synthesized using reduction of HAuCl₄ with sodium citrate. The formation of AuNPs was confirmed from the characteristic surface plasmon resonance band at 521 nm and transmission electron microscopy revealed the average particle size was about 10 nm. The results reveal that AuNPs can interact with proteins to form a "protein corona (PC)", but the protein concentration required to form a relatively stable PC is not the same. The quenching mechanism of proteins by AuNPs is arisen from static quenching. The binding constants of AuNPs with proteins are in the range from 10⁶ to 10¹⁰ L mol^-1, and the order is pepsin > γ-globulin > hemoglobin > trypsin > lysozyme at 298 K. Van der Waals forces and hydrogen bonds are the main forces for the lysozyme-AuNPs system. The interaction between trypsin/pepsin/γ-globulin/hemoglobin and AuNPs is mainly by hydrophobic interaction. The addition of AuNPs has an effect on the secondary structure of proteins as confirmed from CD spectra. The change in secondary structure of different proteins is different and seems to have little relation with the binding constant. The activity of lysozyme/trypsin/pepsin decreases with the addition of AuNPs.

Hemoglobin coated oxygen storage metal-organic framework as a promising artificial oxygen carrier

Hemoglobin-functionalized HKUST-1 as an artificial oxygen carrier has been developed. The new oxygen carrier has excellent oxygen loading capacity and good chemical durability. The sustained electrochemical responses toward H2O2 and O2 make this new material an ideal candidate as a promising artificial blood substitute.

Effect of local anesthetic drug procaine hydrochloride on the conformational stability of bovine hemoglobin: Multi-spectroscopic and computational approaches

The interaction between bovine hemoglobin (BHb) and local anesthetic drug procaine hydrochloride (PCH) was examined by spectroscopic and computational studies. Intrinsic fluorescence analysis explored the ground-state complex formation in the binding of PCH with BHb through static quenching mechanism. The binding constants (K_b) are 29.38 × 10³, 22.54 × 10³ and 17.99 × 10³ M^-1 at 288, 298 and 308 K, respectively, and the ratio of BHb:PCH was 1:1 in the interaction mechanism of PCH and BHb. The acquired thermodynamic parameters (ΔH⁰, ΔG⁰ and ΔS⁰) demonstrated that interaction mechanism is spontaneous and enthalpy driven. The van der Waals forces and hydrogen bonding have been played a predominant role in the binding mechanism. The UV-vis spectroscopy validates the ground-state complexation between PCH and BHb and the binding constant (K_b) has been evaluated utilizing Benesi-Hildebrand equation. Fluorescence resonance energy transfer (FRET) results have demonstrated that the distance between donor (BHb) and acceptor (PCH) is very short (2.34 nm) suggesting a significant probability to energy transfer from BHb to PCH. Synchronous fluorescence results revealed that the alteration in the micro-environment of Tyrosine (Tyr) is more than tryptophan (Trp) residues suggesting that PCH molecule is close to Tyr residue. The secondary structure alterations were confirmed by CD, 3-D fluorescence and FT-IR spectroscopic measurements. Moreover, computational analyses further corroborated that PCH molecules are closer to Tyr residues as compared to Trp residues of BHb during the interaction process. The BHb-PCH complexes may contribute to a deeper understanding of the metabolism of drug, blood circulation process and may help to illustrate the relationship between functions and structure of BHb.Communicated by Ramaswamy H. Sarma.

The study on the interactions of two 1,2,3-triazoles with several biological macromolecules by multiple spectroscopic methodologies and molecular docking

1-(4-chlorophenyl)-5-phenyl-1H-1,2,3-triazole (CPTC) and 5-(3-chlorophenyl) -1-phenyl-1H-1,2,3-triazole (PCTA) are two new derivatives of 1,2,3-triazole. Their structural and spectral properties were characterized by density functional theory calculations (DFT). The binding properties of CPTC or PCTA with several typical biomacromolecules such as human serum albumin (HSA), bovine hemoglobin (BHb), human immunoglobulin (HIgG) or DNA were investigated by molecular docking and multiple spectroscopic methodologies. The different parameters including binding constants and thermodynamic parameters for CPTC/PCTA-HSA/BHb/HIgG/DNA systems were obtained based on various fluorescence enhancement or quenching mechanisms. The results of binding constants indicated that there were the strong interactions between two triazoles and four biological macromolecules due to the higher order of magnitude between 10³ and 10⁵. The values of thermodynamic parameters revealed that the binding forces for these systems are mainly hydrophobic interactions, electrostatic force, or hydrogen bond, respectively, which are in agreement with the results of molecular docking to a certain extent. Moreover, the information from synchronous, 3D fluorescence and UV-Vis spectroscopies proved that two compounds CPTC and PCTA could affect the microenvironment of amino acids residues of three kinds of proteins. Based on the above experimental results, a comparison of the interaction mechanisms for CPTC/PCTA-proteins/DNA systems have been performed in view of their different molecular structures, which is beneficial for the further research in order to design them as the novel drugs.

Electrochemistry and Electrocatalysis of Hemoglobin Based on Graphene Quantum Dots Modified Electrode

Background:

Graphene quantum dots (GQD) is a new member of carbon nanomaterial that has attracted increasing attention owing to its better chemical inertness, low cytotoxicity, large specific surface area, cheap cost, suitable conductivity and excellent biocompatibility.

Methods:

Electrochemical behaviors of this modified electrode were studied by cyclic voltammetry and electrochemical impedance spectroscopy. Electrochemical investigations of Nafion/Hb/GQD/ CILE were carried out with electrochemical parameters calculated.

Results:

In the phosphate buffer solution with a pH value of 5.0, good linear relationships between the catalytic reduction current and the concentration of substrate were got for TCA (6.0~100.0 mmol·L-1), NaNO2 (2.0~12.0 mmol·L-1) and H2O2 (6.0~30.0 mmol·L-1). The proposed method was applied to NaNO2 concentration detection in soak water from picked vegetables with satisfactory results.

Conclusion:

This Nafion/Hb/GQD/CILE had a good bioelectrocatalytic activity to different substrates such as trichloroacetic acid, NaNO2 and H2O2 reduction with the advantages including wide detection range, low detection limit and good stability. Therefore, the application of GQD in electrochemical sensor was extended in this paper.

Effects of Eucommia ulmoides leaf extracts on growth performance, antioxidant capacity and intestinal function in weaned piglets

Eucommia ulmoides is traditional Chinese medicine, and it possesses several potential bioactivities, such as anti-inflammatory, antioxidant and immune regulatory activities. This study was conducted to determine the effects of dietary Eucommia ulmoides leaf extracts (ELE) on growth performance, antioxidant capacity and intestinal function of weaned piglets. Two hundred crossbred (Duroc × Landrace × Yorkshire) piglets with an average initial weight of 12.96 ± 0.28 kg were randomly allotted to five treatments: C0 (basal diet), C1 (basal diet + antibiotics) and basal diet supplemented with increasing levels of ELE (0.2, 0.3 or 0.4 g/kg of feed). The results showed that ELE or antibiotics supplementation remarkably decreased diarrhoea rate and 0.3 g/kg ELE increased average daily gain compared with C0 (p < .05). 0.3 g/kg ELE increased alkaline phosphatase (AKP) levels and total antioxidant capacity (T-AOC) in serum and liver, as well as increased the content of serum albumin and total protein (TP) compared with the C0 (p < .05). The lipase activity of duodenum content and trypsin activity of jejunum content were improved fed diets containing 0.3 g/kg ELE compared with C0 (p < .05). The 0.3 g/kg ELE treatments have a higher villus height of the duodenum and jejunum compared with the C0 (p < .05). These results suggested that ELE supplementation had beneficial effects on antioxidant and intestinal function in weaned piglets, which also could increase growth performance and decreased diarrhoea rate. Accordingly, ELE is a potential alternative to antibiotics.

Revisiting the nitrite reductase activity of hemoglobin with differential pulse voltammetry

Nitric oxide (NO) is an omnipresent signalling molecule in all vertebrates. NO modulates blood flow and neural activity. Nitrite anion is one of the most important sources of NO. Nitrite is reduced to NO by various physiological mechanisms including reduction by hemoglobin in vascular system. In this study, nitrite reductase activity (NRA) of hemoglobin is reported using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in a wide potential window from +0.3 V to -1.3 V (vs. Ag/AgCl). To the best of our knowledge, a detailed look into NRA of hemoglobin is proposed here for the first time. Our results indicated two different regimes for reduction of nitrite by hemoglobin in its Fe(II) and Fe(I) states. Both reactions showed a reversible behaviour in the time scale of the experiments. The first reduction displayed a normal redox behaviour, while the latter one had the characteristics of a catalytic electro-reduction/oxidation. The reduction in Fe(II) state was selected as a tool for comparing the NRA of hemoglobin (Hb) and hemoglobin-S (Hb-S) under native-like conditions in a didodecyldimethyl ammonium bromide (DDAB) liquid crystal film. These investigations lay the prospects and guidelines for understanding the direct electrochemistry of hemoglobin utilizing a simplified mediator-free platform.

Probing the interaction between levamlodipine and hemoglobin based on spectroscopic and molecular docking methods

In recent years, levamlodipine (LAML) has been widely used as a common drug for the treatment of hypertension. However, no reports exist that focus on the binding process of LAML with the transport proteins present in blood circulation. Here, several spectroscopy techniques, molecular docking and a molecular dynamics simulation were employed to comprehensively analyze the mechanism underlying the interaction between bovine hemoglobin (BHb) and LAML, as well as the effect of other drugs on the BHb-LAML system. The results indicated that a stable BHb-LAML complex was formed and that the binding site for LAML was located at β-37 tryptophan in the central cavity of BHb. Van der Waals force and hydrogen bonds played major roles in this binding process, and the number of binding sites (n) in the binary system was approximately equal to 1. Multiple spectroscopy experiments (FT-IR and three-dimensional fluorescence spectrometry) and a dynamics simulation revealed that LAML could induce a conformational in BHb and that the microenvironment of Trp/Tyr changed. Interestingly, the values of the binding constant between LAML and BHb significantly increased due to the effect of rofecoxib, propranolol and enalapril. Meanwhile, these drugs did not produce synergistic or negative synergistic effects on the LAML binding with BHb. These results provide new insight into the transport mechanisms for LAML in the human body.

Green fluorescent carbon quantum dots as a label-free probe for rapid and sensitive detection of hematin

Hematin is an oxidized form of heme, and the abnormal levels of hematin in the human body can lead to various inflammatory lesions. Hence, there is still a need to establish a rapid, sensitive and efficient method for hematin detection. Herein, the green fluorescent carbon quantum dots (CQDs) are synthesized by using L-cysteine and hydrogen peroxide as precursors. The synthesized CQDs exhibit some fascinating characters including excellent water solubility, high fluorescence quantum yield, and good stability in a broad pH range of 7.0-11.0 and high ionic strength solution. Excitingly, the fluorescence of CQDs can be rapidly and selectively quenched by hematin via the inner filter effect. Moreover, the detection of hematin by the CQDs fluorescent probe shows a good linearity in the concentration range of 0.5-30 μM with a minimum detection limit of 0.1 μM. Finally, the proposed approach is successfully applied to detect hematin in human blood samples.

Interaction of bisphenol A 3, 4-quinone metabolite with human hemoglobin, human serum albumin and cytochrome c in vitro

Since covalent protein-bisphenol A adducts generated by the interaction of protein nucleophiles with bisphenol A quinone affect the physicochemical properties of proteins in functional foods and biological tissues, it has become a hot topic nowadays. Therefore, we investigated the interaction of several different biomacromolecules such as hemoglobin, human serum albumin and cytochrome c with bisphenol A 3, 4-quinone (BPAQ). The effects of binding on changes in biomolecular structure were determined by various spectroscopic methods. BPAQ effects were investigated by using the UV-Vis spectroscopy and the quenching phenomenon from fluorescence emission. It proved that the formation of bio-complex and their aromatic micro-environment was likely to be disturbed with as well. Changes observed in circular dichroism (CD) spectroscopy confirmed the quantitative loss of the alpha-helical structure. Further studies with matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOFMS) and molecular docking indicated combining ratio and binding sites between proteins and BPAQ. The in vitro data of BPAQ-proteins adducts may provide a valuable theoretical basis for the elucidation of the toxicological mechanisms of BPAQ adducts in biological systems and environments.

Spectroscopic characterization, calorimetric study and molecular docking to evaluate the bioconjugation of maltol with hemoglobin

Maltol, a food additive, is extensively used in our daily life. To date, its biological safety is still debated. In this article, binding interaction of maltol with bovine hemoglobin (BHb), an important functional protein, was studied by molecular docking research and spectroscopic and calorimetric measurements. We found that maltol could cause structural changes of BHb. By interacting with Glu 101 (1.27 Å) and Lys 104 (2.49 Å) residues, maltol changed the cavity structure and induced a microenvironment change around tryptophan (Trp) residue. Thermodynamic parameters obtained from isothermal titration calorimetry (ITC) measurement showed that hydrophobic forces were the main forces existing in this system. The association constant of K (8.0 ± 3.4 × 10⁴  M^-1 ) shows the mild ligand-protein binding for maltol with BHb. The α-helix amount in BHb increased (59.6-62.6%) with different concentrations of maltol and the intrinsic fluorescence intensity was quenched by maltol, indicating the conformation changes and denaturation of BHb. This work presents the interactions of maltol with BHb at the molecular level and obtains evidence that maltol induces adverse effects to proteins in vitro.

Mechanisms of Enhanced Hemoglobin Electroactivity on Carbon Electrodes upon Exposure to a Water-Miscible Primary Alcohol

Exposing a carbon electrode to hemoglobin (Hb) and alcoholic solvents, such as methanol, ethanol or 1-propanol, drastically changes Hb electroactivity, but until this work, the important underlying mechanisms were unclear. For the first time, we show that these alcohols impact Hb electroactivity via three mechanisms: modification of the carbon surface oxides on the glassy carbon (GC) electrode, Hb film formation, and structural changes to Hb. C_1s X-ray photoelectron spectroscopy provided evidence for significant alcohol-induced modification of the carbon surface oxides, and differential pulse voltammetry showed links between these modifications and Hb electroactivity. Spectroscopic ellipsometry showed that Hb films formed during exposure to Hb- and alcohol-containing electrolytes increased in thickness with increasing alcohol content, although film thickness played only a minor role in Hb electroactivity. Alcohol-induced structural changes in Hb are confirmed with UV-visible absorption and fluorescence data, showing that Hb denaturation also was a significant factor in increasing Hb electroactivity. Carbon-surface-oxide modification and Hb denaturation worked in tandem to maximally increase the Hb electroactivity in 60% methanol. While in ethanol and 1-propanol, the significant increases in Hb electroactivity caused by Hb denaturation were offset by an increase in Hb-inhibiting carbon surface oxides. Knowledge of these mechanisms shows the impact of alcohols on both Hb and carbon electrodes, allows for thoughtful design of the Hb-sensing system, is vital for proper analysis of Hb electroactivity in the presence of these alcohols (e.g., when used as binder solvents for immobilizing Hb into films), and provides fundamental understanding of the Hb-carbon interactions.

Protein bioelectronics: a review of what we do and do not know

We review the status of protein-based molecular electronics. First, we define and discuss fundamental concepts of electron transfer and transport in and across proteins and proposed mechanisms for these processes. We then describe the immobilization of proteins to solid-state surfaces in both nanoscale and macroscopic approaches, and highlight how different methodologies can alter protein electronic properties. Because immobilizing proteins while retaining biological activity is crucial to the successful development of bioelectronic devices, we discuss this process at length. We briefly discuss computational predictions and their connection to experimental results. We then summarize how the biological activity of immobilized proteins is beneficial for bioelectronic devices, and how conductance measurements can shed light on protein properties. Finally, we consider how the research to date could influence the development of future bioelectronic devices.

Hemoglobin becomes electroactive upon interaction with surface-protected Au nanoparticles

In this work, we report on the electrochemical behavior of bioconjugates prepared with gold nanoparticles (AuNP) capped with three different molecular layers (citrate anions, 6-mercaptopurine and ω-mercaptoundecanoic acid) and the protein hemoglobin (Hb). Freshly formed bioconjugates are deposited on a glassy carbon electrode and assayed for electroactivity. A pair of redox peaks with formal potential at -0.37V is obtained, in contrast with the free Hb protein that is inactive on the glassy carbon substrate. The redox response is typical for quasi-reversible processes allowing the determination of the electron transfer rate constant for the three bioconjugates. Additional evidence of the structural integrity of protein upon forming the bioconjugate is obtained by monitoring the electrochemical response of the Hb heme Fe(III)/Fe(II) redox couple as a function of solution pH. Moreover, the Hb forming the protein corona around the AuNPs show good electrocatalytic activity for the reduction of hydrogen peroxide and oxygen. It has been found that only the first layer of Hb surrounding the AuNPs are electroactive, although some part of the second layer also contribute, pointing to the role of the AuNP in the electrochemical response.

Investigation of the binding affinity in vitamin B12-Bovine serum albumin system using various spectroscopic methods

The binding affinity between vitamin B12 (VitB12) and bovine serum albumin (BSA) has been investigated in aqueous solution at pH=7.4, employing UV-vis absorption and steady-state, synchronous and three-dimensional fluorescence spectra techniques. Representative effects noted for BSA intrinsic fluorescence resulting from the interactions with VitB12 confirm the formation of π-π stacked non-covalent and non-fluorescent complexes in the system VitB12-BSA. All the determined parameters, the binding, fluorescence quenching and bimolecular quenching rate constants (of the order of 10⁴Lmol^-1, 10³Lmol^-1 and 10¹¹Lmol^-1s^-1, respectively), as well as Förster resonance energy transfer parameters validate the mechanism of static quenching. The interaction with VitB12 induces folding of the polypeptide chains around Trp residues of BSA, resulting in a more hydrophobic surrounding. Presented outcomes suggest that the addition of VitB12 can lead to the more organized BSA conformation and its more folded tertiary structure, what could influence the physiological functions of bovine serum albumin, notably in case of its overuse or abnormal metabolism.

Phytosterols improve immunity and exert anti-inflammatory activity in weaned piglets

BACKGROUND

Phytosterols (PS), plant-derived natural steroid compounds, are novel feed additives to regulate immune function and promote pig growth. This study was conducted to determine the effects of PS on the immune response of weaned piglets.

RESULTS

One hundred and twenty crossbred (Duroc × Landrace × Yorkshire) piglets with an average initial weight of 9.58 ± 0.26 kg were randomly allotted to three treatments. Treatments consisted of a control, PS (0.2 g kg^-1 ) and polymyxin E (0.04 g kg^-1 , antibiotic control) treatment. The results showed that PS or polymyxin E supplementation remarkably decreased diarrhea rate and elevated CD3⁺ CD4⁺ /CD3⁺ CD8⁺ ratio in piglets compared with the control (P < 0.05). PS increased basophil and serum interleukin-4, and caused a shift towards Th2 profile by decreasing Th1/Th2 ratios in piglets compared with control (P < 0.05). Polymyxin E contributed to an increase in interleukin-10 compared with the control (P < 0.05). No significant difference was observed in the amount of Lactobacillus, Bifidobacterium or Escherichia coli of jejunum among the three treatments (P > 0.05).

CONCLUSION

These results suggest that PS supplementation has no significant effect on growth but could remarkably decrease diarrhea rate, and improve immunity and anti-inflammatory activity in weaned piglets. In addition, PS supplementation had similar effects on growth, anti-inflammation and intestinal microorganisms as supplementation with polymyxin E in piglets. © 2017 Society of Chemical Industry.

Inner filter with carbon quantum dots: A selective sensing platform for detection of hematin in human red cells

Hematin plays a crucial role in various physiological functions, and the determination of hematin in complex biological matrixes is a significant but difficult issue. Considering the unique photophysical/photochemical properties of carbon quantum dots (CQDs) prepared with p-aminobenzoic acid (PABA) and ethanol, a new strategy for the design of fluorescent probes for hematin has been achieved. The proposed sensor array is fabricated based on the inner filter effect (IFE) between hematin and CQDs with phenomenon of selective fluorescence quenching of CQDs which results from the strong absorption of the excitation and emission spectrum of CQDs by hematin. The fluorescence quenching of CQDs is closely related to the amount of hematin and there is a good linear relationship over the range of 0.5-10μM with a detection limit of 0.25μM. What's more, the fluorescence assay has been successfully applied for hematin sensing in healthy human red cells showing this sensing assay has a great potential prospect for detection of hematin in the complex matrixes.

Analysis of the binding interaction in uric acid - Human hemoglobin system by spectroscopic techniques

The binding interaction between human hemoglobin and uric acid has been studied for the first time, by UV-vis absorption and steady-state, synchronous and three-dimensional fluorescence techniques. Characteristic effects observed for human hemoglobin intrinsic fluorescence during interaction with uric acid at neutral pH point at the formation of stacking non-covalent and non-fluorescent complexes. All the calculated parameters, the binding, fluorescence quenching and bimolecular quenching rate constants, as well as Förster resonance energy transfer parameters confirm the existence of static quenching. The results of synchronous fluorescence measurements indicate that the fluorescence quenching of human hemoglobin originates both from Trp and Tyr residues and that the addition of uric acid could significantly hinder the physiological functions of human hemoglobin.

Aza-heterocyclic Receptors for Direct Electron Transfer Hemoglobin Biosensor

Direct Electron Transfer biosensors, facilitating direct communication between the biomolecule of interest and electrode surface, are preferable compared to enzymatic and mediator based sensors. Although hemoglobin (Hb) contains four redox active iron centres, direct detection is not possible due to inaccessibility of iron centres and formation of dimers, blocking electron transfer. Through the coordination of iron with aza-heterocyclic receptors - pyridine and imidazole - we report a cost effective, highly sensitive and simple electrochemical Hb sensor using cyclic voltammetry and chronoamperometry. The receptor can be either in the form of liquid micro-droplet mixed with blood or dry chemistry embedded in paper membrane on top of screen printed carbon electrodes. We demonstrate excellent linearity and robustness against interference using clinical samples. A truly point of care technology is demonstrated by integrating disposable test strips with handheld reader, enabling finger prick to result in less than a minute.

Electrochemical Evidence for Neuroglobin Activity on NO at Physiological Concentrations

The true function of neuroglobin (Ngb) and, particularly, human Ngb (NGB) has been under debate since its discovery 15 years ago. It has been expected to play a role in oxygen binding/supply, but a variety of other functions have been put forward, including NO dioxygenase activity. However, in vitro studies that could unravel these potential roles have been hampered by the lack of an Ngb-specific reductase. In this work, we used electrochemical measurements to investigate the role of an intermittent internal disulfide bridge in determining NO oxidation kinetics at physiological NO concentrations. The use of a polarized electrode to efficiently interconvert the ferric (Fe(3+)) and ferrous (Fe(2+)) forms of an immobilized NGB showed that the disulfide bridge both defines the kinetics of NO dioxygenase activity and regulates appearance of the free ferrous deoxy-NGB, which is the redox active form of the protein in contrast to oxy-NGB. Our studies further identified a role for the distal histidine, interacting with the hexacoordinated iron atom of the heme, in oxidation kinetics. These findings may be relevant in vivo, for example, in blocking apoptosis by reduction of ferric cytochrome c, and gentle tuning of NO concentration in the tissues.

Hydrogen bonding-assisted interaction between amitriptyline hydrochloride and hemoglobin: spectroscopic and molecular dynamics studies

Herein, we have explored the interaction between amitriptyline hydrochloride (AMT) and hemoglobin (Hb), using steady-state and time-resolved fluorescence spectroscopy, UV-visible spectroscopy, and circular dichroism spectroscopy, in combination with molecular docking and molecular dynamic (MD) simulation methods. The steady-state fluorescence reveals the static quenching mechanism in the interaction system, which was further confirmed by UV-visible and time-resolved fluorescence spectroscopy. The binding constant, number of binding sites, and thermodynamic parameters viz. ΔG, ΔH, ΔS are also considered; result confirms that the binding of the AMT with Hb is a spontaneous process, involving hydrogen bonding and van der Waals interactions with a single binding site, as also confirmed by molecular docking study. Synchronous fluorescence, CD data, and MD simulation results contribute toward understanding the effect of AMT on Hb to interpret the conformational change in Hb upon binding in aqueous solution.

The free heme concentration in healthy human erythrocytes

Heme, the prosthetic group of hemoglobin, may be released from its host due to an intrinsic instability of hemoglobin and accumulate in the erythrocytes. Free heme is in the form of hematin (Fe(3+) protoporphyrin IX OH) and follows several pathways of biochemical toxicity to tissues, cells, and organelles since it catalyzes the production of reactive oxygen species. To determine concentration of soluble free heme in human erythrocytes, we develop a new method. We lyse the red blood cells and isolate free heme from hemoglobin by dialysis. We use the heme to reconstitute horseradish peroxidase (HRP) from an excess of the apoenzyme and determine the HRP reaction rate from the evolution of the emitted luminescence. We find that in a population of five healthy adults the average free heme concentration in the erythrocytes is 21±2μM, ca. 100× higher than previously determined. Tests suggest that the lower previous value was due to the use of elevated concentrations of NaCl, which drive hematin precipitation and re-association with apoglobin. We show that the found hematin concentration is significantly higher than estimates based on equilibrium release and the known hematin dimerization. The factors that lead to enhanced heme release remain an open question.

TiO2 nanoparticle modified organ-like Ti3C2 MXene nanocomposite encapsulating hemoglobin for a mediator-free biosensor with excellent performances

TiO2 nanoparticle modified organ-like Ti3C2 MXene (TiO2-Ti3C2) nanocomposite has been synthesized and then used to immobilize hemoglobin (Hb) to fabricate a mediator-free biosensor. The morphology and structure of TiO2-Ti3C2 nanocomposite were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Spectroscopic and electrochemical results revealed that TiO2-Ti3C2 nanocomposite is an excellent immobilization matrix with biocompatibility for redox protein, affording good protein bioactivity and stability. Due to the special organ-like hybrid structure of TiO2-Ti3C2, the direct electron transfer of Hb is facilitated and the prepared biosensors displayed good performance for the detection of H2O2 with a wide linear range of 0.1-380 μM for H2O2 (sensitivity of 447.3 μA mM(-1) cm(-2)), an extremely low detection limit of 14 nM for H2O2. Especially, numerous TiO2 nanoparticles with excellent biocompatibility on the surface of the nanocomposite may provide a protective microenvironment for Hb to make the prepared biosensor improve long-term stability. The TiO2-Ti3C2 based biosensor retains 94.6% of the initial response to H2O2 after 60-day storage. TiO2-Ti3C2 nanocomposite could be a promising matrix for the fabrication of mediator-free biosensors, and might find wide potential applications in environmental analysis and biomedical detection.

Unraveling the binding interaction of Toluidine blue O with bovine hemoglobin – a multi spectroscopic and molecular modeling approach

Toluidine blue O (TBO) is a cationic photosensitizer that belongs to the class of phenothiazinium dyes.

Bioreceptor multi-walled carbon nanotubes@Fe3O4@SiO2–surface molecular imprinted polymer in an ultrasensitive chemiluminescent biosensor for bovine hemoglobin

A highly selective and ultrasensitive chemiluminescent biosensor, based on a bioreceptor surface molecular imprinted polymer using core–shell Fe₃O₄@SiO₂–multi-walled carbon nanotube nanostructures as the backbone material, for bovine hemoglobin (BHb) detection was proposed.

Protein-coated pH-responsive gold nanoparticles: Microwave-assisted synthesis and surface charge-dependent anticancer activity

The biocompatibility and ease of functionalization of gold nanoparticles underlie significant potential in biotechnology and biomedicine. Eight different proteins were examined in the preparation of gold nanoparticles (AuNPs) in aqueous medium under microwave irradiation. Six of the proteins resulted in the formation of AuNPs. The intrinsic pH of the proteins played an important role in AuNPs with strong surface plasmon bands. The hydrodynamic size of the nanoparticles was larger than the values observed by TEM and ImageJ. The formation of a protein layer on the AuNPs accounts for this difference. The AuNPs exhibited sensitivity towards varying pH conditions, which was confirmed by determining the difference in the isoelectric points studied by using pH-dependent zeta potential titration. Cytotoxicity studies revealed anticancerous effects of the AuNPs at a certain micromolar concentration by constraining the growth of cancer cells with different efficacies due to the use of different proteins as capping agents. The positively charged AuNPs are internalized by the cells to a greater level than the negatively charged AuNPs. These AuNPs synthesized with protein coating holds promise as anticancer agents and would help in providing a new paradigm in area of nanoparticles.