effective charge
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In this work, we have generalized the use of capillary isotachophoresis as a universal method for determination of effective charge of anionic and cationic (co)polymers on ordinary capillary electrophoresis instruments. This method is applicable to a broad range of strong or weak polyelectrolytes with good repeatability. Experimental parameters (components and concentrations of leading and terminating electrolytes, capillary diameters, constant electric current intensity) were optimized for implementation in 100 μm i.d. capillaries for both polyanions and polycations. Determined values of polymer effective charge were in a very good agreement with those obtained by capillary electrophoresis with indirect UV detection. Uncertainty of the effective charge measurement using isotachophoresis was addressed and estimated to be ∼5-10% for solutes with mobilities in the 20-50 × 10(-9)m(2)V(-1)s(-1) range.
- MeSH
- anionty chemie MeSH
- elektroforéza kapilární přístrojové vybavení metody MeSH
- elektrolyty MeSH
- izotachoforéza přístrojové vybavení metody MeSH
- kationty chemie MeSH
- koncentrace vodíkových iontů MeSH
- polymery chemie MeSH
- reprodukovatelnost výsledků MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
5th ed. 372 s. : tab., grafy ; 23 cm
Powdery pharmaceuticals are prone to electrostatic charging due to collisions of particles and friction with device walls. The generated electrostatic charge is influenced by particle properties, processing and conditions. The charge of active particles and excipients is often inconvenient being able to cause problems in the production of solid dosage forms. The electrostatic charge of powdery particles affects properties of the materials and all procedures as the charge affects the behaviour and purity of the final dosage form. The problem of electrostatic charging of powders is more complicated when two or more compounds with different physical, chemical and dielectric properties are combined. To better understand the mechanism of electrostatic charging it is necessary to explain all the effects that contribute to charging solid active ingredients and excipients.
- MeSH
- farmaceutická technologie * MeSH
- lékové formy * MeSH
- lidé MeSH
- pevné částice * MeSH
- skladování léků MeSH
- stabilita léku MeSH
- statická elektřina MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- práce podpořená grantem MeSH
Programme international sur la sécurité chimique
XIII, 338 s. : il. ; 24 cm
The conductivity of DNA covalently bonded to a gold surface was studied by means of the STM technique. Various single- and double-stranded 32-nucleotide-long DNA sequences were measured under ambient conditions so as to provide a better understanding of the complex process of charge-carrier transport in natural as well as chemically modified DNA molecules. The investigations focused on the role of several features of DNA structure, namely the role of the negative charge at the backbone phosphate group and the related complex effects of counterions, and of the stacking interactions between the bases in Watson-Crick and other types of base pairs. The measurements have indicated that the best conductor is DNA in its biologically most relevant double-stranded form with Watson-Crick base pairs and charged phosphates equilibrated with counterions and water. All the studied modifications, including DNA with non-Watson-Crick base pairs, the abasic form, and especially the form with phosphate charges eliminated by chemical modifications, lower the conductivity of natural DNA.
- MeSH
- DNA chemie metabolismus MeSH
- elektrická vodivost MeSH
- financování organizované MeSH
- fosfáty chemie metabolismus MeSH
- jednovláknová DNA chemie MeSH
- oligodeoxyribonukleotidy chemie metabolismus MeSH
- párování bází MeSH
- rastrovací tunelová mikroskopie MeSH
- sekvence nukleotidů MeSH
- vodíková vazba MeSH
- zlato chemie MeSH
BACKGROUND: The main goal of this research was to study the interactions of a fully characterized set of silver nanomaterials (Ag ENMs) with cells in vitro, according to the standards of Good Laboratory Practices (GLP), to assure the quality of nanotoxicology research. We were interested in whether Ag ENMs synthesized by the same method, with the same size distribution, shape and specific surface area, but with different charges and surface compositions could give different biological responses. METHODS: A range of methods and toxicity endpoints were applied to study the impacts of interaction of the Ag ENMs with TK6 cells. As tests of viability, relative growth activity and trypan blue exclusion were applied. Genotoxicity was evaluated by the alkaline comet assay for detection of strand breaks and oxidized purines. The mutagenic potential of Ag ENMs was investigated with the in vitro HPRT gene mutation test on V79-4 cells according to the OECD protocol. Ag ENM agglomeration, dissolution as well as uptake and distribution within the cells were investigated as crucial aspects of Ag ENM toxicity. Ag ENM stabilizers were included in addition to positive and negative controls. RESULTS: Different cytotoxic effects were observed including membrane damage, cell cycle arrest and cell death. Ag ENMs also induced various kinds of DNA damage including strand breaks and DNA oxidation, and caused gene mutation. We found that positive Ag ENMs had greater impact on cyto- and genotoxicity than did Ag ENMs with neutral or negative charge, assumed to be related to their greater uptake into cells and to their presence in the nucleus and mitochondria, implying that Ag ENMs might induce toxicity by both direct and indirect mechanisms. CONCLUSION: We showed that Ag ENMs could be cytotoxic, genotoxic and mutagenic. Our experiments with the HPRT gene mutation assay demonstrated that surface chemical composition plays a significant role in Ag ENM toxicity.
- MeSH
- biologický transport MeSH
- buněčná membrána účinky léků patologie MeSH
- Cricetulus MeSH
- hodnocení rizik MeSH
- hypoxanthinfosforibosyltransferasa genetika MeSH
- kometový test MeSH
- kontrolní body buněčného cyklu účinky léků MeSH
- kovové nanočástice * MeSH
- lidé MeSH
- mutace * MeSH
- mutační analýza DNA MeSH
- nádorové buněčné linie MeSH
- oxidační stres účinky léků MeSH
- poškození DNA * MeSH
- povrchové vlastnosti MeSH
- proliferace buněk účinky léků MeSH
- sloučeniny stříbra chemická syntéza metabolismus toxicita MeSH
- tvar buňky účinky léků MeSH
- velikost částic MeSH
- viabilita buněk účinky léků MeSH
- vztah mezi dávkou a účinkem léčiva MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- srovnávací studie MeSH
In this research, the adsorption of two herbicides, alachlor (ALA) and terbuthylazine (TBA), on granular activated carbon (GAC) in the presence of well-characterized peptide fraction of cellular organic matter (COM) produced by cyanobacterium Microcystis aeruginosa was studied. Two commercially available GACs were characterized using nitrogen gas adsorption and surface charge titrations. The COM peptides of molecular weight (MW) < 10 kDa were isolated and characterized using MW fractionation technique and high-performance size exclusion chromatography (HPSEC). The effect of surface charge on the adsorption of COM peptides was studied by means of equilibrium adsorption experiments at pH 5 and pH 8.5. Electrostatic interactions and hydrogen bonding proved to be important mechanisms of COM peptides adsorption. The adsorption of ALA and TBA on granular activated carbon preloaded with COM peptides was influenced by solution pH. The reduction in adsorption was significantly greater at pH 5 compared to pH 8.5, which corresponded to the increased adsorption of COM peptides at pH 5. The majority of the competition between COM peptides and both herbicides was attributed to low molecular weight COM peptides with MW of 700, 900, 1300 and 1700 Da.
- MeSH
- acetamidy analýza chemie MeSH
- adsorpce MeSH
- chemické látky znečišťující vodu analýza chemie MeSH
- dřevěné a živočišné uhlí chemie MeSH
- herbicidy analýza chemie MeSH
- kinetika MeSH
- Microcystis chemie MeSH
- odpad tekutý - odstraňování metody MeSH
- peptidy chemie MeSH
- povrchové vlastnosti MeSH
- triaziny analýza chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Capillary ITP (CITP) and CZE were applied to the determination of effective charges and ionic mobilities of polycationic antimicrobial peptides (AMPs). Twelve AMPs (deca- to hexadecapeptides) containing three to seven basic amino acid residues (His, Lys, Arg) at variable positions of peptide chain were investigated. Effective charges of the AMPs were determined from the lengths of their ITP zones, ionic mobilities, and molar concentrations, and from the same parameters of the reference compounds. Lengths of the ITP zones of AMPs and reference compounds were obtained from their CITP analyses in cationic mode using leading electrolyte (LE) composed of 10 mM NH4OH, 40 mM AcOH (acetic acid), pH 4.1, and terminating electrolyte (TE) containing 40 mM AcOH, pH 3.2. Ionic mobilities of AMPs and singly charged reference compounds (ammediol or arginine) were determined by their CZE analyses in the BGE of the same composition as the LE. The effective charges numbers of AMPs were found to be in the range 1.65-5.04, i.e. significantly reduced as compared to the theoretical charge numbers (2.86-6.99) calculated from the acidity constants of the analyzed AMPs. This reduction of effective charge due to tightly bound acetate counterions (counterion condensation) was in the range 17-47% depending on the number and type of the basic amino acid residues in the AMPs molecules. Ionic mobilities of AMPs achieved values (26.5-38.6) × 10-9 m2V-1s-1and in most cases were in a good agreement with the ratio of their effective charges and relative molecular masses.
Here, we propose a possible photoactivation mechanism of a 35-kDa blue light-triggered photoreceptor, the Orange Carotenoid Protein (OCP), suggesting that the reaction involves the transient formation of a protonated ketocarotenoid (oxocarbenium cation) state. Taking advantage of engineering an OCP variant carrying the Y201W mutation, which shows superior spectroscopic and structural properties, it is shown that the presence of Trp201 augments the impact of one critical H-bond between the ketocarotenoid and the protein. This confers an unprecedented homogeneity of the dark-adapted OCP state and substantially increases the yield of the excited photoproduct S*, which is important for the productive photocycle to proceed. A 1.37 Å crystal structure of OCP Y201W combined with femtosecond time-resolved absorption spectroscopy, kinetic analysis, and deconvolution of the spectral intermediates, as well as extensive quantum chemical calculations incorporating the effect of the local electric field, highlighted the role of charge-transfer states during OCP photoconversion.
