Spectroscopy Of Aqueous Solutions Research Articles

Chemical and biological differences between original and mimetic pentosan polysulfates

Pentosan polysulfate sodium (PPS) is a semi-synthetic, heparin-like polysaccharide with manifold therapeutic actions. It is approved for treatment of bladder pain syndrome / interstitial cystitis in humans and treatment of musculoskeletal diseases in animals.PPS is produced by a complex procedure using beech wood as starting material. It consists of a mixture of sulfated glucuronoxylans, whose structural composition cannot be fully characterized by physicochemical analysis. The question arises whether PPS follow-on products are identical with the original and thus meet the requirement for generic drug application.The aim of this study was to investigate whether commercially available PPS products differ in physicochemical characteristics and biological effects from the original.Ten PPS preparations from different manufactures were analyzed using orthogonal analytical techniques including, inter alia, size exclusion chromatography with triple detection, nuclear magnetic resonance spectroscopy, and high-resolution mid-infrared spectroscopy in aqueous solution with chemometric evaluation. For functional analysis, we measured the plasma kallikrein generation in human plasma and FXII activation.The study revealed significant structural and biological differences between PPS from different sources. Therefore, follow-on products cannot be considered identical but at best similar to original PPS. However, their similar efficacy and safety have still to be proven by comprehensive studies.

New Insights into the Structure‐Function Relationships of G Proteins Containing Disease‐Associated Mutations

G proteins regulate intracellular signaling processes through their interactions with guanine nucleotides, GDP and GTP, and initiate numerous physiological responses. In normal conditions, G protein functions are regulated in a tightly controlled signaling network through complex formation with partner proteins, especially G protein‐coupled receptors (GPCRs). However, loss‐of‐function or gain‐of‐function mutations in the Gα subunit of G proteins disrupt this process, circumventing the usual control mechanisms and causing changes in G protein activity that result in serious illnesses. Our studies focused on the stimulatory class of trimeric G proteins, Gs, and mutations in Gαs associated with multiple cancers1. While the structure of one Gαs variant has been determined and additional Gαs variants have been characterized biochemically, there remains a need for an overall mechanistic framework for relating mutations in Gαs to changes in G protein signaling.To fill in this gap in knowledge, we investigated the interactions of Gαs variants with nucleotides using saturation transfer difference nuclear magnetic resonance (STD‐NMR) spectroscopy in aqueous solutions. In STD‐NMR experiments, we observed interactions between nucleotides and the Gαs variant proteins at atomic resolution, which provided information on nucleotide binding modes. STD‐NMR data of one Gαs variant closely correlated with literature data of the structure and activity of the same variant protein2, establishing a foundation for extending the analysis of NMR data to seven additional disease‐associated Gαs variant proteins for which no structures are available. These NMR data were combined with correlative biophysical data that measured the overall fold of the Gαs‐nucleotide complexes and with functional data reporting on the relative affinities of the Gαs variants for GDP and GTP. Integrating these data together provided a conceptual framework for categorizing variations in Gαs amino acid sequences with changes in signaling activity. Surprisingly, differences in the binding modes of the Gαs variants did not always directly correlate with their different functions, suggesting that mutations in Gαs that impact nucleotide exchange are nuanced and complex. These results imply that strategies for the development of small molecule drugs may need to be specifically tailored for each disease associated Gαs variant.References O’Hayre, M. et. al. The emerging mutational landscape of G proteins and G protein‐coupled receptors in cancer. Nat. Rev. Cancer. 13, 412‐424 (2013). Hu, Q. & Shokat, K. M. Disease‐Causing Mutations in the G Protein Gαs Subvert the Roles of GDP and GTP. Cell. 173, 1254–1264 (2018).

PH-Responsive Emission of Novel Water-Soluble Polymeric Iridium(III) Complexes.

The synthesis and characterization of water-soluble copolymers containing N,N-dimethylacrylamide (DMAM) and a vinylic monomer containing an Iridium(III), Ir(III), complex substituted with the quinoline-based unit 2-(pyridin-2-ylo)-6-styrene-4-phenylquinoline (VQPy) as ligand are reported. These copolymers were prepared through pre- or post-polymerization complexation of Ir(III) with the VQPy units. The first methodology led to copolymer P1 having fully complexed VQPy units, whereas the latter methodology allowed the preparation of terpolymers containing free and Ir(III)-complexed VQPy units (copolymer P2). The optical properties of the copolymers were studied in detail through UV-Vis and photoluminescence spectroscopy in aqueous solution. It is shown that the metal-to-ligand charge transfer (ΜLCT) emission is prevailing in the case of P1, regardless of pH. In contrast, in the case of terpolymer P2 the MLCT emission of the Ir(III) complex is combined with the pH-responsive emission of free VQPy units, leading to characteristic pH-responsive color changes under UV illumination in the acidic pH region.

Variability in the Spatial Structure of the Central Loop in Cobra Cytotoxins Revealed by X-ray Analysis and Molecular Modeling.

Cobra cytotoxins (CTs) belong to the three-fingered protein family and possess membrane activity. Here, we studied cytotoxin 13 from Naja naja cobra venom (CT13Nn). For the first time, a spatial model of CT13Nn with both “water” and “membrane” conformations of the central loop (loop-2) were determined by X-ray crystallography. The “water” conformation of the loop was frequently observed. It was similar to the structure of loop-2 of numerous CTs, determined by either NMR spectroscopy in aqueous solution, or the X-ray method. The “membrane” conformation is rare one and, to date has only been observed by NMR for a single cytotoxin 1 from N. oxiana (CT1No) in detergent micelle. Both CT13Nn and CT1No are S-type CTs. Membrane-binding of these CTs probably involves an additional step—the conformational transformation of the loop-2. To confirm this suggestion, we conducted molecular dynamics simulations of both CT1No and CT13Nn in the Highly Mimetic Membrane Model of palmitoiloleoylphosphatidylglycerol, starting with their “water” NMR models. We found that the both toxins transform their “water” conformation of loop-2 into the “membrane” one during the insertion process. This supports the hypothesis that the S-type CTs, unlike their P-type counterparts, require conformational adaptation of loop-2 during interaction with lipid membranes.

Structural basis for regulation of a human GPCR by membrane lipids investigated by NMR spectroscopy

G protein-coupled receptors (GPCRs) are sensory proteins that comprise the largest class of “druggable” targets. Earlier NMR studies demonstrated that GPCRs exist in a function-related equilibrium of simultaneously populated conformers, the relative populations of which are determined by the efficacy of bound drugs. We now present NMR data that show membrane phospholipids and sterols also control this equilibrium with a magnitude comparable to or greater than the influence of drug efficacy. Using NMR spectroscopy in aqueous solutions, we investigated the structural basis for the regulation of GPCR activity by phospholipids in nanodiscs containing the human A2A adenosine receptor (A2AAR), a representative class A GPCR.

Simple and fast detection of homocysteine by cucurbit[7]uril fluorescent probe based on competitive strategy

This research put forward a simple and rapid fluorescence probe method based on competition strategy to detect homocysteine. The host–guest interaction behavior between cucurbit[7]uril and homocysteine was further studied via UV–vis spectroscopy, Fourier transform infrared spectroscopy, molecular modeling, and 1H NMR spectroscopy in aqueous solution. Under the optimal detection conditions, the fluorescence intensity of the cucurbit[7]uril-berberine complex declined linearly with increasing concentration of homocysteine in the range from 5 to 200 µM, and the limit of detection was 1.76 µM. Meanwhile, it was also successfully employed to detect homocysteine in serum samples with the recovery rate of 85.1% to 102.0%.

Controlling Growth of Poly (Triethylene Glycol Acrylate-Co-Spiropyran Acrylate) Copolymer Liquid Films on a Hydrophilic Surface by Light and Temperature.

A quartz crystal microbalance with dissipation monitoring (QCM-D) was employed for in situ investigations of the effect of temperature and light on the conformational changes of a poly (triethylene glycol acrylate-co-spiropyran acrylate) (P (TEGA-co-SPA)) copolymer containing 12–14% of spiropyran at the silica–water interface. By monitoring shifts in resonance frequency and in acoustic dissipation as a function of temperature and illumination conditions, we investigated the evolution of viscoelastic properties of the P (TEGA-co-SPA)-rich wetting layer growing on the sensor, from which we deduced the characteristic coil-to-globule transition temperature, corresponding to the lower critical solution temperature (LCST) of the PTEGA part. We show that the coil-to-globule transition of the adsorbed copolymer being exposed to visible or UV light shifts to lower LCST as compared to the bulk solution: the transition temperature determined acoustically on the surface is 4 to 8 K lower than the cloud point temperature reported by UV/VIS spectroscopy in aqueous solution. We attribute our findings to non-equilibrium effects caused by confinement of the copolymer chains on the surface. Thermal stimuli and light can be used to manipulate the film formation process and the film’s conformational state, which affects its subsequent response behavior.

Structural Insights into Activation of a Human G Protein‐Coupled Receptor by Membrane Phospholipids

The 826 human G protein-coupled receptors (GPCRs) are involved in nearly every physiological process and comprise the largest class of “druggable” proteins. For over the past decade, crystal and cryo-EM structures have focused on revealing molecular details of GPCR interactions with small molecules and intracellular partner proteins, which are well-established regulators of GPCR function. More recently, literature data from biological and biophysical studies have demonstrated that phospholipids found in the endogenous membrane environment also control GPCR function and act as allosteric modulators. In particular, phospholipids with charged headgroups have been reported to be especially important regulators of GPCR function and facilitate the formation of signaling complexes. Using nuclear magnetic resonance (NMR) spectroscopy in aqueous solutions, we investigated the structural basis for the regulation of GPCR activity by phospholipids in nanodiscs containing the human A2A adenosine receptor (A2AAR), a representative class A GPCR. Lipid nanodiscs containing mixtures of uncharged and charged phospholipids were produced, yielding homogeneous preparations over a wide range of lipid compositions. NMR data of uniformly stable-isotope labeled A2AAR showed the receptor was properly folded in lipid nanodiscs and shared a similar global conformation to detergent micelle preparations of A2AAR. Using 19F NMR with conformationally-sensitive probes located at the A2AAR intracellular surface, we systematically investigated the influence of lipid composition over a wide range of mixtures of charged and uncharged phospholipids. A2AAR complexes with antagonists showed almost no response to variation in lipid composition. In striking contrast to this, A2AAR complexes with agonists showed a clear response to changes in the relative proportion of charged phospholipids. NMR data of agonist complexes in nanodiscs containing lower proportions of charged lipids were highly similar to data of antagonist complexes, showing a higher proportion of neutral lipids negated the efficacy of bound agonists. As the proportion of charged phospholipids increased, the relative population of an A2AAR active conformation also increased. The dependence of the receptor response to bound agonists on lipid composition suggested specific interactions between lipid headgroups and charged amino acids at the A2AAR intracellular surface underlie the regulation of activity. Results from this study indicate that lipid composition must be carefully selected in studies of GPCRs in nanodiscs. Our data also provide a potential molecular mechanism for how changes in membrane composition, due to disease for example, can directly impact the efficacy of drugs.

Resonance IR spectroscopy in aqueous solution by combining IR super-resolution with TFD-IR method

We have developed a novel method to measure an IR spectrum of solute molecules in aqueous solution that should be called resonance IR spectroscopy. We applied this method to flavin mononucleotide (FMN) and succeeded in measuring the IR spectrum in aqueous solution. When compared with the Raman spectra of FMN, it is found that not only do peak positions in the IR spectrum match well those in the Raman spectra, but the spectral feature in intensity is quite similar to that in the resonance Raman spectrum too. This similarity is discussed based on the Franck-Condon factor.

Thermodynamic, spectroscopic and biological investigation of interaction of anionic surfactants with [Cu(im)6]F2·4H2O complex in aqueous solution

Present study describes the physicochemical behavior of the coordination complex of copper i.e. [Cu(im)6]F2.4H2O (Hexakis(imidazole)copper(II) fluoride tetrahydrate) and its solubilization by anionic surfactants sodium dodecyl sulphate (SDS) and sodium stearate (SS). The detailed investigation was accomplished by electrical conductivity measurements and UV–visible spectroscopy in aqueous solutions of anionic surfactants in the sub micellar and micellar concentration ranges. Furthermore, thermodynamic parameters of complex-surfactant interaction and CMC of both surfactants in the presence of copper imidazole complex were evaluated by electrical conductivity and experimental results revealed an increase in CMC of both surfactants in the presence of complex. CMC increases with rise in temperature and the trend of variation in thermodynamic parameters indicates that the solubilization of copper imidazole complex in micelles of both surfactants is spontaneous and enthalpy as well as entropy driven. Spectroscopic investigation indicates high degree of solubilization and strong interaction in case of complex and SDS than for SS.

Interaction between 2-pyrrolidine-1-hydroxymethane-1,1-diphosphonic acid and palladium(II) in aqueous solutions

The structure of the 2-pyrrolidine-l-hydroxymethane-l,l-diphosphonic acid (PyrHMDP, H4L) has been determined by X-ray crystallography. Formation of the complexes between K2[PdCl4] and PyrHMDP was studied by pH-potentiometry, UV–Vis spectrophotometry and 31P, 13C and 1H NMR spectroscopy in aqueous solutions containing CKCl = 0.15 mol L−1, which corresponds to the concentration of chloride ions in intercellular fluid. The formation constants were calculated for the protonated forms of the PyrHMDP and for the [PdHLCl2]3− and [PdLCl2]4− complexes. The equilibrium concentration distribution diagram for the complexes of different composition was drawn using the formation constants of the Pd chloro-aqua complexes and the chloride concentration. In equimolar palladium complexes with PyrHMDP the ligand was coordinated in a bidentate manner via the nitrogen atom of the pyrrolidine ring and the oxygen atom of the phosphonic group forming a six-membered chelate ring.

Spectroscopic studies on the potassium 1-fluorobenzoyltrifluoroborate salt by using the FT-IR, Raman and UV–Visible spectra and DFT calculations

Potassium 1-fluorobenzoyltrifluoroborate (FBTFB) salt was characterized using Fourier Transformed Infrared (FT-IR) and Raman solid-state spectroscopies as well as ultraviolet–visible spectroscopy in aqueous solution. The functional hybrid B3LYP with the 6-311++G** basis set have optimized the structures of salt in gas phase and in aqueous solution with CS symmetries. In solution, the influence of solvent was studied at the same level of theory with the integral equation formalism variant polarised continuum method (IEFPCM) and the universal solvation model. FBTFB has evidenced the lower solvation energy (−81.54 kJ/mol), as compared with other trifluoroborate salts probably due to the presence of F in the 1st position of phenyl ring that decreases the solubility of this salt. NBO studies clearly support the ionic characteristics of K+F− and K+O− bonds and the high energy values of LPF17→ LP*B14 transitions (ΔΕn→n*) while AIM analyses suggest a high stability of salt in both media due to three ionic and one C–H⋅⋅⋅F interactions. Analyses of frontier orbitals have suggested that the FBTFB salt is more reactive in solution than in gas phase and, than 2-phenylacetyl-trifluoroborate (PTFB) in the two media possibly because FBTFB presents higher global electrophilicity (ω) and nucleophilicity indexes (E) in both media than PTFB. Here, the calculated harmonic force fields, scaled force constants and complete assignments of all vibration normal modes expected for FBTFB in both media are reported. Predicted IR, Raman and UV–Visible spectra have shown good concordance when they are compared with the corresponding experimental ones.

Toward time-resolved laser T-jump/X-ray probe spectroscopy in aqueous solutions

Most chemical and biochemical reactions in nature and in industrial processes are driven by thermal effects that bring the reactants above the energy barrier for reaction. In aqueous solutions, this process can also be triggered by the laser driven temperature jump (T-jump) method, in which the water vibrational (stretch, bend, or combination) modes are excited by a short laser pulse, leading to a temperature increase in the irradiated volume within a few picoseconds. The combination of the laser T-jump with X-ray spectroscopic probes would add element-specificity as well as sensitivity to the structure, the oxidation state, and the spin state of the intermediates of reactions. Here, we present preliminary results of a near infrared pump/X-ray absorption spectroscopy probe to study the ligand exchange of an octahedral aqueous Cobalt complex, which is known to pass through intermediate steps yielding tetrahedral chlorinated as final species. The structural changes of the chemical reaction are monitored with great sensitivity, even in the presence of a mild local increase in temperature. This work opens perspectives for the study of non-light-driven reactions using time-resolved X-ray spectroscopic methods.

Placenta–heart axis: abnormal cardiovascular development and VEGF expression after perigestational alcohol intake at mid-gestation in mouse.

Potassium 1-fluorobenzoyltrifluoroborate (FBTFB) salt was characterized using Fourier Transformed Infrared (FT-IR) and Raman solid-state spectroscopies as well as ultraviolet–visible spectroscopy in aqueous solution. The functional hybrid B3LYP with the 6-311++G** basis set have optimized the structures of salt in gas phase and in aqueous solution with CS symmetries. In solution, the influence of solvent was studied at the same level of theory with the integral equation formalism variant polarised continuum method (IEFPCM) and the universal solvation model. FBTFB has evidenced the lower solvation energy (−81.54 kJ/mol), as compared with other trifluoroborate salts probably due to the presence of F in the 1st position of phenyl ring that decreases the solubility of this salt. NBO studies clearly support the ionic characteristics of K+F− and K+O− bonds and the high energy values of LPF17→ LP*B14 transitions (ΔΕn→n*) while AIM analyses suggest a high stability of salt in both media due to three ionic and one C–H⋅⋅⋅F interactions. Analyses of frontier orbitals have suggested that the FBTFB salt is more reactive in solution than in gas phase and, than 2-phenylacetyl-trifluoroborate (PTFB) in the two media possibly because FBTFB presents higher global electrophilicity (ω) and nucleophilicity indexes (E) in both media than PTFB. Here, the calculated harmonic force fields, scaled force constants and complete assignments of all vibration normal modes expected for FBTFB in both media are reported. Predicted IR, Raman and UV–Visible spectra have shown good concordance when they are compared with the corresponding experimental ones.

Synthesis and characterization of silver nanoparticles using as a reducing agent plant extract of Dandelion (Taraxacun officianale)

The objective of this work was to synthesize the synthesis of silver nanoparticles using as a reducing agent of ionic silver the plant extract of Dandelion (Taraxacun officianale), vegetable of high availability and low cost, as an alternative to the processes conventional, based on the antioxidant capacity of plant extracts that reduce metals in solution. The nanoparticles prepared by this method were characterized by the golden yellow color characteristic of silver nanoparticle solutions. Measurements with UV-Vis spectroscopy of aqueous solutions of Ag1 + ions after coming into contact with plant extracts of Dandelion at different pHs showed an intense absorption band around 400-450 nm, characteristic of the resonance of the Plasmon of silver nanoparticles. Through the scanning of the samples by means of AFM (atomic force microscopy), morphological information of the nanoparticles is obtained, from 3D topographic images of them, such as distribution, size and shape of the silver nanoparticles. Finally, its antibacterial activity was tested against the Escherichia coli strain.

A spectroscopic study of a cyclodextrin-based polymer and the “molecular accordion” effect

The formation of host–guest complexes was studied for two hosts: β-cyclodextrin (β-CD) and a cross-linked polymer containing an equimolar ratio of β-CD and hexamethylene diisocyanate (HDI), denoted as HDI-1. The thermodynamics of host–guest binding were studied with 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS) using steady-state fluorescence spectroscopy in aqueous solution at variable temperature and ambient pH. The association of 1,8-ANS with β-CD and HDI-1 showed a fluorescence enhancement of ∼4 and 12 units, respectively. Greater fluorescence enhancement for the polymer/dye system indicates the presence of multiple binding sites (inclusion and interstitial). By contrast, the β-CD/dye system adopts trends that indicate the formation of well-defined inclusion complexes. HDI-1 has inclusion sites (β-CD) and interstitial domains (HDI) that afford dual binding with variable binding affinity. Simplified binding models employed herein address the role of inclusion binding without an explicit account for higher order or secondary binding equilibria. The approximate 1:1 binding constant (K1:1) for CD/1,8-ANS is about two-fold greater over the HDI-1/1,8-ANS system. HDI-1 displays cooperative effects among the polymer subunits, according to changes in relative fluorescence intensity due to structural transitions and binding site loci. The relative fluorescence intensities of the HDI-1/1,8-ANS system relate to a reversible temperature-driven structural transition (globular ⇌ extended) of the polymer between 5 °C and 60 °C, in contrast to the β-CD/1,8-ANS complex. The temperature- and guest-driven structural transition, described as the “molecular accordion” effect, is supported by new insight provided by complementary fluorescence and1H NMR spectral results in aqueous solution.

Comparative solution studies and cytotoxicity of gallium(III) and iron(III) complexes of 3-hydroxy-2(1H)-pyridinones

The stoichiometry and stability constants of the gallium(III) and iron(III) complexes of two alkoxycarbonylmethyl-3-hydroxy-2(1H)-pyridinone ligands were determined by means of pH-potentiometry, UV–Vis spectrophotometry and 1H and 71Ga NMR spectroscopy in aqueous solution. The cytotoxicity of one of the gallium(III) complexes was also measured in multidrug resistant/non-resistant human colon adenocarcinoma cell lines. Iron(III) forms complexes with the studied 3-hydroxy-2-pyridinones of higher stability than gallium(III), while the obtained pFe values are significantly lower (pFe: 14.95, 15.06; pH 7.4, cM = 1 µM, cL = 10 µM) compared to those of typical iron binders such as deferiprone or transferrin. The moderate gallium(III) and iron(III) binding ability of the compounds stands for lower solution complex stability compared to that of analogous bidentate non-substituted 3-hydroxy-2-pyridinone or 3-hydroxy-4-pyridinone (O,O) donor ligands. Tris-ligand complexes of the general formula [ML3] (M = Ga, Fe) predominate at physiological pH for both ligands. No interaction with cell culture medium components was observed in the millimolar concentration range of gallium(III) complexes, however they can suffer significant decomposition at biologically relevant low concentrations leading to negligible cytotoxic activity. The redox potential of the studied iron–3-hydroxy-2-pyridinone complex (E1/2 = −597 mV at pH 7.4) falls into the range that is typical of iron(III) complexes with conventional bidentate (O,O) donor-containing chelators.

Interaction of Dyes with Cationic Surfactants in Solutions: Determination of Critical Micelle Concentration

Interactions of sulforhodamine B or ethyl eosin (as the anionic dye) with cetylpyridinium bromide (as a cationic surfactant) have been investigated by visible spectroscopy in aqueous solution. The object of research is the association between an anion of dye and of cationic surfactant in aqueous solutions and its features. Computer simulation of these interactions was carried out with the use of AM1 and PM3 semi-empirical methods. A new spectrophotometric method was developed for determination of critical micelle concentration of cationic surfactants.

Interaction of Dyes with Cationic Surfactants in Solutions: Determination of Critical Micelle Concentration

Interactions of sulforhodamine B or ethyl eosin (as the anionic dye) with cetylpyridinium bromide (as a cationic surfactant) have been investigated by visible spectroscopy in aqueous solution. The object of research is the association between an anion of dye and of cationic surfactant in aqueous solutions and its features. Computer simulation of these interactions was carried out with the use of AM1 and PM3 semi-empirical methods. A new spectrophotometric method was developed for determination of critical micelle concentration of cationic surfactants.

Complexation of dichloro(ethylenediamine)palladium(II) with 1-hydroxyethylidene-1,1-diphosphonic acid

Abstract Formation of the complex between [Pd(en)Cl2] (en = ethylenediamine) and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP, H4L) was studied by pH-potentiometry, UV–Vis spectrophotometry and 31P NMR spectroscopy in aqueous solutions containing CKCl = 0.15 mol L−1 and 0.004 mol L−1, which corresponds to the concentration of chloride ions in intercellular and intracellular fluids. The formation constants were calculated for [Pd(en)HL]−, [Pd(en)L]2− and {[Pd(en)]2L} complexes. In combination with data reported in the literature, they were used for deriving distribution curves for the corresponding aqua-, hydroxo- and chloro-substituted complexes of the [Pd(en)]2+ moiety. The binuclear complex {[Pd(en)]2L} was synthesized and characterized by elemental analysis and NMR spectroscopy. The structure of this complex in which the HEDP bridges two [Pd(en)]2+ moieties has been determined by X-ray crystallography.