Physiological pH Environment Research Articles

Infrared Structural Biology: How to Detect Protonation States of Histidine Side Chains in Proteins

The imidazole group of histidine residues are found functionally important in a vast number of catalytic proteins. The remarkable catalytic power of histidine side chains originates from its ionizable imidazole ring armed with a pair of different tertiary amines and the ability of adopting three protonation states near physiological pH environment. Knowledge on the protonation states of key histidine side chains in enzymes at rest and during catalytic actions is indispensable to elucidation of the structure-function relationship underlying enzymatic catalysis. We report a rigorous method on how to detect the three protonation states of functionally important histidine imidazole rings in the static and dynamic states of enzymes using infrared structural biology. First principle computational methods based on density functional theory were employed to develop two vibrational structural markers (VSM) of the imidazole group: VSMq for the charged states of the imidazole group, while VSMt for distinguishing the D and E tautomers of charge neutral histidine. The accuracy of the VSMs is assessed by comparison of calculated VSMs with experimental FT-IR data of the 4-ethyl-imidazole model compound. We will discuss how these VSMs may be employed in structure-function studies on functionally important histidine residues in enzymes.

Solubility and in vitro drug permeation behavior of ethenzamide cocrystals regulated in physiological pH environments

Drug release behavior of few ethenzamide cocrystals was investigated at different pH buffers. Change in lipophilic behavior and conformational adjustment of drug along with supramolecular synthons were probed for their improved drug efficacy.

Synthesis of doxorubicin-PLGA loaded chitosan stabilized (Mn, Zn)Fe2O4 nanoparticles: Biological activity and pH-responsive drug release

We have synthesized Mn1−xZnxFe2O4 ((Mn, Zn) ferrite) magnetic nanoparticles (MNPs) having radius of 25nm to act as platforms for delivering drugs. The Mn0.9Zn0.1Fe2O4 MNPs exhibit superparamagnetic behavior with large saturation magnetization (MS). They were encapsulated in polymer so that they can be developed into PLGA-coated chitosan stabilized (Mn, Zn) MNPs, i.e., DOX-PLGA@CS@Mn0.9Zn0.1Fe2O4 which can serve as an effective carrier of the anti-cancer drug doxorubicin (DOX) whose release would be controlled by the pH in the environment surrounding the cancer tumor. The structure of the as-prepared particles is of a magnetic core-encapsulated by polymer shell layer of around 50nm thick. At a pH of 4.0, the DOX release within the first 5h is fast (around 57%). It becomes slower (around 46% over the next 25h) when the pH is increased to 7.4. The DOX-PLGA@CS@Mn0.9Zn0.1Fe2O4 (for concentrations lower than 125μgmL−1) shows lower toxicity against HeLa cells using DOX only. When the DOX-PLGA@CS@Mn0.9Zn0.1Fe2O4 is increased to 250μgmL−1, the DOX-PLGA@CS@Mn0.9Zn0.1Fe2O4 shows greater anti-cancer activity and has satisfactory therapeutic effect. The slow sustained release of the DOX by the drug loaded particles when they are in the physiological pH environment (7.4) of normal tissues and mild toxicity of DOX against cancer cell at low concentration point to the DOX loaded PLGA@CS@Mn0.9Zn0.1Fe2O4 being safely used for treating cancer. The higher dosage of DOX needed to kill the cancer cells will be released when the synthesized carriers are subject to the pH stimuli surrounding these cells.

A copper(II) complex with pyridine-2,6-dicarboxylic acid: Synthesis, characterization, thermal decomposition, bioactivity and interactions with herring sperm DNA

The copper(II) complex of pyridine-2,6-dicarboxylic acid was synthesized and characterized by elemental analyses, single crystal X-ray diffraction, FTIR and UV–Vis spectra, and thermogravimetric analysis coupled with infrared spectrometry (TGA-FTIR). The results show that the crystal structure of the complex belongs to the triclinic system, and the Cu(II) ion is five-coordinated by one pyridine N atom, two carboxylate O atoms from the ligand anion and two O atoms from two water molecules, forming a distorted triangular bipyramidal geometry. Under the conditions of a physiological pH environment, the interaction of the complex with herring sperm DNA was studied by means of spectral methods using acridine orange as a fluorescence probe. The bonding mode between the complex and DNA is evidenced to be intercalative binding, and the binding of the complex to DNA is driven by entropy.

Spectroscopic studies on the interaction mechanisms of safranin T with herring sperm DNA using acridine orange as a fluorescence probe

Under the condition of physiological pH environment (pH = 7.40), the interactions of safranin T (ST) with herring sperm DNA were studied by means of spectral methods using acridine orange (AO) as a fluorescence probe. The spectroscopic characteristics of DNA-AO in the case of ST (along with the increase of concentration) were observed in an aqueous medium. The binding constants for ST stranded DNA and competitive bindings of ST interacting with DNA-AO systems were examined by fluorescence spectra, and the binding mechanism of ST with DNA was researched via viscosity measurements. All the testimony manifested that bonding modes between ST and DNA were evidenced to be intercalative binding and electrostatic binding, and the combining constant of ST with DNA was obtained. The binding of ST to DNA was driven by entropy and enthalpy through the calculated thermodynamic parameters (Δr Hm (Ө), Δr Sm and Δr Gm (Ө)).

In Vitro Evaluation of HPMA-Copolymers Targeted to HER2 Expressing Pancreatic Tumor Cells for Image Guided Drug Delivery

Personalized medicine for the treatment of pancreatic cancer is one potential avenue which can prevent the dire outcome of this difficult to treat disease. Image guided drug delivery (IGDD) is a method allowing real-time imaging of drug therapy in order to predict the potential efficacy and safety of a given treatment. Water soluble macromolecular drug carriers such as N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers provide multifunctional platforms for the construction of such IGDD systems. HPMA copolymer conjugates containing gemcitabine, a targeting ligand for HER2 receptors overexpressed in some pancreatic cancers, and an (111) In(3+) chelating agent are synthesized, characterized, and evaluated in vitro for their potential use as an IGDD system for pancreatic tumors. The conjugates are capable of binding to pancreatic tumor cell lines which express HER2. In vitro drug release is achieved under physiological and acidic pH environments. The chelated radioisotopes are stable in the presence of mouse serum. The conjugates are effective in killing pancreatic tumor cell lines in vitro. These copolymers have potential for further preclinical evaluation in pancreatic tumor models.

Trivalent Ultrashort Lipopeptides are Potent pH Dependent Antifungal Agents

The activity of antimicrobial peptides (AMPs) that contain a large proportion of histidine residues (pK(a) ∼ 6) depends on the physiological pH environment. Advantages of these AMPs include high activity in slightly acidic areas of the human body and relatively low toxicity in other areas. Also, many AMPs are highly active in a multivalent form, but this often increases toxicity. Here we designed pH dependent amphiphilic compounds consisting of multiple ultrashort histidine lipopeptides on a triazacyclophane scaffold, which showed high activity toward Aspergillus fumigatus and Cryptococcus neoformans at acidic pH, yet remained nontoxic. In vivo, treatment with a myristic acid conjugated trivalent histidine-histidine dipeptide resulted in 55% survival of mice (n = 9) in an otherwise lethal murine lung Aspergillus infection model. Fungal burden was assessed and showed completely sterile lungs in 80% of the mice (n = 5). At pH 5.5 and 7.5, differing peptide-membrane interactions and peptide nanostructures were observed. This study underscores the potential of unique AMPs to become the next generation of clinical antimicrobial therapy.

Interaction Mode Between Methylene Blue-Pr(III) Complex and Herring-Sperm DNA

ABSTRACT By spectroscopic method, the binding ratios between methylene blue-Pr(III) and DNA in physiological pH environment (pH = 7.40) were determined as n Pr:n MB(III) = 1:3 and n Pr(III)(MB)3:n DNA = 8:1. The binding constants at different temperatures = 7.14 × 105 L · mol−1 and = 2.43 × 105 L · mol−1 were obtained by double reciprocal method. Thermodynamic function computation demonstrates that is the primary driving power of the interaction between Pr(III)(MB)3 and herring-sperm DNA. According to the analysis, we have evidenced that the interaction mode between Pr(III)(MB)3 complex and herring-sperm DNA is partial intercalation binding.

Synthesis and DNA Binding Studies of Mg(II) Complex of Schiff Base Derived from Vanillin and L-Tryptophan

The Mg(II) complex of Schiff base (K[HL]) derived from vanillin and L-tryptophan could bind with herring sperm DNA. The binding behaviors between them in physiological pH environment (pH 7.40) have been studied by spectroscopy, cyclic voltammetry and viscosity methods. Binding ratios of nMg(II): nK[HL] = 1:1 and nMg(II)L: nDNA = 5:1 were confirmed. The obtained thermodynamic parameters suggest that the interaction between Mg(II)L and DNA is driven mainly by entropy. Combined with fluorimeteric studies, cyclic voltammetry, CD spectroscopy and viscosity methods, the results indicate the interaction modes between Mg(II)L and DNA are mainly with intercalation and involving some electrostatic interaction.

Autonomous folding in the membrane proximal HIV peptide gp41659–671: pH tuneability at micelle interfaces

The flexibility of the Membrane Proximal Region (MPR) of the HIV-1 gp41 envelope glycoprotein is believed to be relevant to its biological function. Its conformational bias is potentially influenced by the various environmental conditions experienced during viral fusion. Using a combination of Circular Dichroism and Molecular Dynamics simulations, we show that a very short MPR fragment gp41(659-671) spanning the 2F5 monoclonal antibody epitope, exhibits autonomous helical folding in the presence of membrane mimicking SDS micelles and the extent of which can be tuned by pH variation: Specifically, the peptide shows no defined fold type at basic pH but is helical at physiological and lower pH environments. By contrast, no such control of helical folding by pH is observed in aqueous solutions in the absence of SDS. Instead, the experimental data imply that unfolded structures persist and that pH has negligible influence on conformational bias. We also explore the pronounced sensitivity to standard empirical potentials and conclude that AMBER-ff03 provides a reasonably accurate description of the solution state structure and is therefore a good choice for future exploration of membrane-induced phenomena.

Interactions of Vitamin K3 with Herring-Sperm DNA Using Spectroscopy and Electrochemistry

By means of ultraviolet-visible (UV-Vis) and fluorescence spectra, the binding ratio between vitamin K(3) and herring-sperm DNA in a physiological pH environment (pH = 7.40) was determined as n(K3):n(DNA) = 2:1, and the binding constants of vitamin K(3) binding to DNA at different temperatures were determined as K(θ)(298K) = 1.28 × 10(5) L·mol(-1) and K(θ)(310K) = 7.19 × 10(4) L·mol(-1), which were confirmed using the double reciprocal method are Δ(r)H(m)(θ) = -3.57 × 10(4) J·mol(-1), Δ(r)G(m)(θ) = -2.92 × 10(4) J·mol(-1), and Δ(r)S(m)(θ) = 217.67 J·mol(-1)K(-1). The driving power of this process was enthalpy. An intercalation binding of the vitamin K(3) with DNA was supported by a competitive experiment using acridine orange (AO) as a spectral probe. By combination analysis of the Scatchard method and cyclic voltammetry, we suggested that the interaction mode between vitamin K(3) and herring-sperm DNA would be a mixed mode. The quinonoid, duality fused-ring of vitamin K(3) can intercalate into the base pairs of DNA, and there is an electrostatic binding along with intercalation binding.

Water-soluble polyaniline with strong photoluminescence in physiological pH environment

Polyaniline (PANI) can show strong photoluminescence (PL) and well dispersed ability in water after simple refluxing with H 2SO 4 (sulfonated polyaniline, SPANI). This kind of fluorescent SPANI exhibits pH sensitive PL properties, especially, the strongest PL intensity is obtained in physiological pH environment (pH 7–8). The pH sensitive PL properties of SPANI are mainly attributed to the structure transition under different pH conditions.

Spectroscopic studies on the interaction between tryptophan–erbium(III) complex and herring sperm DNA

By means of UV and fluorescence spectra, the binding ratios between Er(III)–Trp and DNA in physiological pH environment (pH 7.40) were determined as n Trp: n Er(III) = 3:1 and n ER ( III ) ( Trp ) 3 : n DNA = 2 : 1 , and the apparent molar absorptivity of ɛ Er(III)–Trp–DNA is 4.33 × 10 5 L mol −1 cm −1 which was confirmed by molar ratio method. The binding constants at different temperatures K B 25 ° C θ = 1.93 × 10 4 L mo l − 1 and K B 37 ° C θ = 5.28 × 10 3 L mo l − 1 were obtained by double reciprocal method. Thermodynamic function computation demonstrates that Δ r H m θ is the primary driving power of the interaction between Er(III)(Trp) 3 and DNA. By combination analysis of the Scatchard method and CD spectrometry, we suggested that the interaction mode between Er(III)(Trp) 3 complex and herring sperm DNA is groove and intercalation bindings.

Interaction between tryptophan-vanillin Schiff base and herring sperm DNA

The interaction of the Schiff base (K[HL]) with herring sperm DNA was studied by UV-vis absorption, fluorescence and viscosity methods in a physiological pH environment (pH 7.40), where the Schiff base was derived from vanillin and L-tryptophan. A binding ratio of nK[HL]:nDNA = 5:1 and an apparent molar absorption coefficient of ?K[HL]-DNA = 4.98 ? 105 L?mol-1?cm-1 were confirmed by the mole ratio method. The binding constants of KB ? 28?C = 1.94 ? 105 L?mol-1 and KB ? 37?C = 1.09 ? 105 L?mol-1 were obtained by the double reciprocal method. Thermodynamic parameters suggest that the interaction between K[HL] and DNA is driven mainly by enthalpy. Combined with Scatchard methods and viscosity methods, the results indicate the presence of intercalation and groove binding between K[HL] and DNA.

Layer-by-layer assembled DNA functionalized single-walled carbon nanotube hybrids for arsenic(III) detection

Based on layer-by-layer assembled DNA functionalized single-walled carbon nanotube hybrids, a DNA biosensor for the detection of arsenic(III) in a nearly physiological pH environment was developed. The redox process between arsenic(III) and arsenic(0) on the biosensor was proved. The growth of those hybrids on glassy carbon electrode was monitored by detecting arsenic(III). The arsenic(III) current on the biosensor was similar over a broad pH range (3.0–8.0) and the limit of detection ( S/ N = 3) was 0.05 μg L −1 at pH 7.0. The biosensor can be reused up to 16 times.