Numerical Study of Jet–Target Interaction: Influence of Dielectric Permittivity on the Electric Field Experienced by the Target

Plasma Chemistry and Plasma Processing - This work presents a study of the influence of dielectric permittivity on the interaction between a positive pulsed He plasma jet and a 0.5 mm-thick...     

Study on the Interaction between Strychnine and Bovine Serum Albumin by Capillary Electrophoretic Frontal Analysis

Most drugs are usually bound to proteins such as serum albumin,α1-acid glycoprotein,lipoprotein,and other blood constituents.The plasma concentration of an unbound drug shows better correlation to the pharmaceutical activity1.It is therefore necessary to know the extent of drug-protein binding in order to adjust the optimal therapeutic dose of the drug.Strychnos nux-vomica L.(Loganiaceae)is an evergreen tree native to southeast Asia.Its dried seeds are used for treatment of nervous diseases…     

Use of Capillary Electrophoresis in the Study of Interaction between dsDNA and Drug Molecules

The advantages of berberine such as the anticancer1, antiinflammatory2 and no side effects of camptothecin1, have promoted the research in the mechanism of berberine with macrobiomolecules. In general, three different points of view have been presented on…     

Interaction of Amino Acid and Dipeptide β-Naphthylamide Derivatives with Hyaluronic Acid and Human Serum Albumin Studied by Capillary Electrophoresis Frontal Analysis

Interactions of drug candidates with the biomacromolecules of the synovial fluid affect drug targeting to the articular cartilage as well as clearance from the synovial space upon intra-articular administration. Hyaluronic acid (HA) and human serum albumin (HSA) are two main components existing in the synovial fluid. To this end, we investigated the affinity of seven cationic amino acid and dipeptide β-naphthylamide derivatives towards HA and HSA in order to shed light on possible relationships between physicochemical properties, in particular charge state, and biomacromolecular interactions to increase the joint residence time. Capillary electrophoresis frontal analysis was used for characterization of the binding of the derivatives to hyaluronic acid and HSA at 25 °C in acetate buffer (pH 4.65) and phosphate buffer (pH 7.40), respectively. Linear binding isotherms were observed for the ligand–hyaluronic acid interactions and the obtained binding constants ranged from 43 to 133 M^?1. The average fraction of bound ligand towards hyaluronic acid increased with increasing the net charge of the ligands but was less than 67 % for all investigated ligands. The obtained binding constants of the ligands with HSA varied in the range of 10³–10⁶ M^?1. The interactions of low-molecular weight derivatives with hyaluronic acid were highly dependent on the ligand charge state. This trend was not observed for the interactions with HSA. The obtained affinity data may provide useful information in the design of cartilage adhesive prodrugs with extended residence time in the synovial cavity.     

Study of Interaction between Red-tide Toxin, Domoic Acid and Double ——stranded DNA by Capillary Zone Electrophoresis

The interactions between amnesic red-tide toxin, domoic acid (DA) and 14mer double-stranded DNA (dsDNA with three kinds of sequences) were studied by capillary zone electrophoresis (CZE). For the dsDNA with a sequence of 5‘-CCCCCTATACCCGC-3‘, the amount of free dsDNA decreases with the increase of added DA, and the signal of DA-dsDNA complex was observed. Meanwhile, the other two dsDNAs, 5‘-(C)12GC-3‘ and 5‘-(AT)7-3‘, the existence of DA could not lead to the change of dsDNA signal and indicated that there is no interaction between DA and these two dsDNAs.     

A Novel Method for Quantification of Circulating DNA in Serum by Capillary Zone Electrophoresis

In this paper, we first presented a novel method for quantification of circulating DNA in human serum based on capillary zone electrophoresis with laser-induced fluorescence detection (CZE-LIF). The serum was digested by proteinase to release free DNA, and then CZE-LIF system was used for the quantification of total circulating DNA. This method was successfully used to quantify the circulating DNA levels in sera from healthy individuals and certain cancer patients.We found the significantly elevated circulating DNA levels in certain prostate cancer patients. Our results demonstrated that CZE-LIF system has good linearity, excellent sensitivity (0.5 ng/mL DNA),satisfactory reproducibility (RSDs in one day and between days were both less than 5%) and reliability, and is well suitable to the quantification of the circulating DNA in human serum or plasma.     

A Study of Water Interaction with γ-Al2O3Surface by Adsorption Calorimetry

The steps at 70, 62, and 56 kJ/mol were specified on the dependences of differential heats of adsorption on the values of adsorption aon the hydroxylated -Al₂O₃surface resulted from the interaction of adsorbed water molecules with the surface-coordinated water molecules, acid and basic hydroxyl groups, respectively; effective charges qwere estimated for the protons of coordinated water molecules and acid and basic OH groups. The hydration numbers were calculated in the region of monolayer coverage for the three aforementioned adsorption sites. The texture changes discovered in -Al₂O₃particles were attributed to the interlamellar swelling of the secondary sorbent packets formed from its primary particles.     

Determination of Memantine in Human Plasma by LC–MS–MS: Application to a Pharmacokinetic Study

A sensitive and selective liquid chromatography–tandem mass spectrometry method for the determination of memantine was developed and validated over the linearity range 0.1–25 ng mL^?1 with 0.5 mL of plasma using procainamide as the internal standard. This analysis was carried out on a Cosmosil 5C₁₈-MS column and the mobile phase was composed of methanol: 0.5% formic acid (50:50, v/v). Detection was performed on a triple–quadrupole tandem mass spectrometer using positive ion mode electrospray ionization and quantification was performed by multiple reaction monitoring mode. The MS–MS ion transitions monitored were m/z 180 → 107 and 236 → 163 for memantine and procainamide, respectively. The between- and within-day precision was less than 10.9% and accuracy was less than 2.5%. The lower limit of quantification (LLOQ) was 0.1 ng mL^?1. The method proved to be accurate and specific, and was applied to the pharmacokinetic study of memantine in healthy Chinese volunteers.     

Study on the Interaction of Pentachlorophenol with Urease in Aqueous Solution by Multiple Spectroscopic Techniques

The interactions between pentachlorophenol (PCP) and jack bean urease were studied using UV/vis absorption, CD, fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectroscopic techniques. The fluorescence data showed that the fluorescence quenching of urease by PCP the results of the formation of a PCP–urease complex involving a hydrophobic interaction. The distance r between the donor (urease) and acceptor (PCP) was obtained from the fluorescence resonance energy transfer. The effect of PCP on the conformation of urease was analyzed using UV/vis absorption, synchronous fluorescence and three-dimensional fluorescence spectroscopic techniques. The result showed that PCP can enter into the hydrophobic pocket at the interface of urease and that the micro environments around the tyrosine and tryptophan residues were changed.     

Insights into the Activation Mode of α-Carbonyl Sulfoxonium Ylides in Rhodium-Catalyzed C−H Activation: A Theoretical Study

A computational study has been performed to investigate the mechanism of Rh^III-catalyzed C−H bond activation using sulfoxonium ylides as a carbene precursor. The stepwise and concerted activation modes for sulfoxonium ylides were investigated. Detailed theoretical results showed that the favored stepwise pathway involves C−H bond activation, carbonization, carbene insertion, and protonation. The free energy profiles for dialkylation of 2-phenylpyridine were also calculated to account for the low yield of this reaction. Furthermore, the substituent effect was elucidated by comparing the energy barriers for the protonation of meta- and para-substituted sulfoxonium ylides calculated by density functional theory.     

Study on Interactions of Several Psychopharmaceutical Drugs with β-Cyclodextrin by Affinity Capillary Electrophoresis and their Application in Separation

The binding of psychopharmaceutical drugs by -cyclodextrin (-CD) changed their effective electrophoretic mobilities. Based on this phenomenon the interactions between some psychopharmaceutical drugs and -cyclodextrin were studied and the binding constants of -CD with tiapride, imipramine, clomipramine, amitriptyline, trifluoperazine, perphenazine and carbamazepine were determined by affinity capillary electrophoresis. The presence of -CD improved the separation of these psychopharmaceutical drugs. Organic modifier was used as another kind of additive to be added in the running buffer to improve further the separation. 70 mM pH 7.2 phosphate buffer solution containing 12 mM -cyclodextrin and 15% (v/v) acetone was selected as optimal running buffer for separation by capillary electrophoresis.     

The Alkylidenphthalan–1-Alkylisobenzofuran Equilibrium: A Computational Study

Semiempirical (AM1, PM3) and density functional theoretical studies (B3LYP/6-31G*) are reported for the tautomerism of 2-methylidene-2,5-dihydrofurans (3a–e) and the corresponding 2-methylfurans (4a–e) and of benzannulated derivatives (5a–e, 6a–e, 7–14).     

Study of tungstate–protein interaction in human serum by LC–ICP-MS and MALDI-TOF

Oral administration of sodium tungstate is an effective treatment for type 1 and 2 diabetes in animal models; it does not incur significant side effects, and it may constitute an alternative to insulin. However, the mechanism by which tungstate exerts its observed metabolic effects in vivo is still not completely understood. In this work, serum-containing proteins which bind tungstate have been characterized. Size exclusion chromatography (SEC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) with a Phenomenex Bio-Sep-S 2000 column and 20 mM HEPES and 150 mM NaCl at pH 7.4 as the mobile phase was chosen as the most appropriate methodology to screen for tungsten–protein complexes. When human serum was incubated with tungstate, three analytical peaks were observed, one related to tungstate–albumin binding, one to free tungstate, and one to an unknown protein binding (MW higher than 300 kDa). Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometric analysis of the tungsten-containing fractions collected from SEC–ICP-MS chromatograms, after desalting and preconcentration processes, confirmed the association of tungstate with albumin and the other unknown protein. Figure SEC-ICP-MS // MALDI-TOF     

A Study on the Interaction of the DAS-K with Bovine Serum Albumin by On-line Ultrafiltration and Chemiluminescence

Potassium dehydroandrographolide succinate （DAS-K） has antibacterial and antiviral effects. It has been used widely for the treatment of virus pneumonia, malaria and respiratory infections. In this work, a novel flow-injection chemiluminescence （CL） method for the determination of DAS-K was proposed. The method is based on the reaction between DAS-K and hexacyanoferrate（III） in alkaline solution to give weak CL signal, which is enhanced by rhodamine B. The experimental conditions for the CL reaction were optimized and the possible reaction mechanism was discussed. Under the optimum conditions, the concentration of DAS-K is proportional to the CL intensity in the range of 0.1-80 μmol·L^-1 with a detection limit of 0.05 μmol·L^-1. The interaction of the DAS-K with bovine serum albumin by on-line ultrafiltration and flow-injection chemiluminescence was studied. The concentrations of unbound DAS-K from ultra filter tube were determined by the flow-injection CL method. The binding parameters were estimated by the Scatchard plot and Klotz plot. The proposed system proved that FIA-CL coupled with on-line ultrafiltration sampling was a fast and simple technique for the study of drug-protein interaction.     

Mixed Micelles in the Presence of Macrocyclic Additives: A Host–Guest Conductometric Study

The conductances of sodium dodecylsulphate (SDS) + sodium decylsulfate (SDeS) and decyltrimethylammonium bromide (DeTAB) + tetradecyltrimethylammonium bromide (TTAB) over the entire mole fraction range of SDS (_SDS) or DeTAB (_DeTAB) were measured in water, 18-crown-6 ether + water (CR + W) and -cyclodextrin + water (CYC + W) mixtures at fixed 4 mM and 8 mM of CR or CYC in their respective binary mixtures at 30 °C. The conductivity plots for SDS + SDeS mixtures show a single break whereas two breaks are observed at most of the _DeTAB for DeTAB + TTAB mixtures. From the break in the conductivity data, the mixed critical micellar concentration (cmc) and degree of counter-ion association () were computed. The first break corresponds to the classical cmc of TTAB is termed as the first cmc (C₁) and the second break which is observed at concentrations about 4 times the first one, corresponding to the classical cmc of DeTAB and is considered to be the second cmc (C₂). The non-ideality in SDS + SDeS mixtures has been evaluated by using the regular solution theory and it has been observed that the mixture is close to ideal in the absence and presence of additives. The variation in C₁, C₂ and ₁, ₂ for DeTAB + TTAB has been discussed in terms of the mixed micelle formation which are predominantly rich in the TTAB and DeTAB monomers respectively.     

Aza-Michael Addition in Explicit Solvent: A Relative Energy Gradient–Interacting Quantum Atoms Study

Aza-Michael additions are key reactions in organic synthesis. We investigate, from a theoretical and computational point of view, several examples ranging from weak to strong electrophiles in dimethylsulfoxide treated as explicit solvent. We use the REG-IQA method, which is a quantum topological energy decomposition (Interacting Quantum Atoms, IQA) coupled to a chemical-interpretation calculator (Relative Energy Gradient, REG). We focus on the rate-limiting addition step in order to unravel the different events taking place in this step, and understand the influence of solvent on the reaction, with an eye on predicting the Mayr electrophilicity. For the first time, a link is established between an REG-IQA analysis and experimental values.     

Herb—Drug Interaction of Quercetin on the Pharmacokinetics of Losartan in Rats: A High-Performance Thin-L ayer Chromatography Study

JPC – Journal of Planar Chromatography – Modern TLC - Losartan potassium (LOS), used in the treatment of hypertension, is metabolized primarily by cytochrome P450. This study...     

Protonation Sites in Gaseous Pyrrole and Imidazole: A Neutralization–Reionization and ab initio Study

Mild gas-phase acids C₄H₉⁺ and NH₄⁺ protonate pyrrole at C-2 and C-3 but not at the nitrogen atom, as determined by deuterium labeling and neutralization–reionization mass spectrometry. Proton affinities in pyrrole are calculated by MP2/6–311G(2d, p) as 866, 845 and 786 kJ mol^-1 for protonation at C-2, C-3 and N, respectively. Vertical neutralization of protonated pyrrole generates bound radicals that in part dissociate by loss of hydrogen atoms. Unimolecular loss of hydrogen atom from C-2-and C-3-protonated pyrrole cations is preceded by proton migration in the ring. Protonation of gaseous imidazole is predicted to occur exclusively at the N-3 imine nitrogen to yield a stable aromatic cation. Proton affinities in imidazole are calculated as 941, 804, 791, 791 and 724 for the N-3, C-4, C-2, C-5 and N-1 positions, respectively. Radicals derived from protonated imidazole are only weakly bound. Vertical neutralization of N-3-protonated imidazole is accompanied by large Franck–Condon effects which deposit on average 183 kJ mol^-1 vibrational energy in the radicals formed. The radicals dissociate unimolecularly by loss of hydrogen atom, which involves both direct N-H bond cleavage and isomerization to the more stable C-2 H-isomer. Potential energy barriers to isomerizations and dissociations in protonated pyrrole and imidazole isomers and their radicals were investigated by ab initio calculations.     

Kinetic Study of Radical Polymerization VIII. A Comprehensive Study of Solution Copolymerization of Vinyl Acetate and Methyl Acrylate by 1H‐NMR Spectroscopy

Radical copolymerization reaction of vinyl acetate (VA) and methyl acrylate (MA) was performed in a solution of benzene‐d₆ using benzoyl peroxide (BPO) as the initiator at 60°C. Kinetic studies of this copolymerization reaction were investigated by on‐line ¹H‐NMR spectroscopy. Individual monomer conversions vs. reaction time, which was followed by this technique, were used to calculate the overall monomer conversion, as well as the monomer mixture and the copolymer compositions as a function of time. Monomer reactivity ratios were calculated by various linear and nonlinear terminal models and also by simplified penultimate model with r _2(VA)=0 at low and medium/high conversions. Overall rate coefficient of copolymerization was calculated from the overall monomer conversion vs. time data and k _p  . k _t ^?0.5 was then estimated. It was observed that k _p  . k _t ^?0.5 increases with increasing the mole fraction of MA in the initial feed, indicating the increase in the polymerization rate with increasing MA concentration in the initial monomer mixture. The effect of mole fraction of MA in the initial monomer mixture on the drifts in the monomer mixture and copolymer compositions with reaction progress was also evaluated experimentally and theoretically.