model substances
Recently Published Documents


TOTAL DOCUMENTS

165
(FIVE YEARS 19)

H-INDEX

22
(FIVE YEARS 2)

2021 ◽  
Vol 903 ◽  
pp. 22-27
Author(s):  
Aina Semjonova ◽  
Agris Bērziņš

The possibility to modify the morphology by crystallization additives of model substances was studied using molecular dynamics simulations. For this 2,6-dimethoxybenzoic acid and 3-hydroxybenzoic acid, each having two polymorphic forms, including a form without carboxylic acid homodimers in their crystal structure were selected. For each polymorph 2-3 largest crystal faces were selected for the study and the crystal was cut along these planes by preparing a simulation box with these planes facing towards solution containing additives. In the performed study it was evaluated which additives potentially can influence the crystal morphology and possibly also polymorph obtained in the crystallization by significantly changing the growth rate of crystal by adsorbing on the surface. For the study 4-5 additives providing different intermolecular interaction possibilities were selected. Among the studied additives urea showed the most complete adsorption and the longest residence time on surfaces of both substances, with the exceptions of few specific planes.


Author(s):  
Agnieszka Piegat ◽  
◽  
Agata Niemczyk ◽  
Agata Goszczyńska ◽  

A series of N,O-acylated chitosan derivatives were emulsified with different fatty acids. Hydrophobically modified chitosan derivatives were expected to exhibit self-assembly behaviour resulting in micelle formation. Several parameters of the oil-in-water emulsification process were investigated: mixing method, speed and duration, volume oil phase and addition of modifiers. Their influence on micellar Z-average diameter, size distribution and Zeta potential was analysed based on dynamic light scattering measurements. There were various relations between the hydrodynamic behaviour of chitosan derivatives, their chemical structure and the process parameters. Additionally, the obtained micelles could serve as active compound carriers because they encapsulated two model substances, namely ibuprofen and α-tocopherol.


2021 ◽  
Author(s):  
Philip Rohland ◽  
Kristin Schreyer ◽  
Rene Burges ◽  
Nicole Fritz ◽  
Martin D. Hager ◽  
...  

AbstractThis study presents the first liquid chromatography method for the quantitative and qualitative analysis of highly reactive oxoammonium cations based on a simple derivatization reaction. Rapid 1,2-electrophilic addition reactions with olefins were used to transform these reactive species into analyzable derivates. Three model substances were chosen to represent each of the main application fields of oxoammonium cations and to demonstrate the versatility of the method. The measuring protocol was validated according to the ICH and USP guidelines. The method revealed an excellent linearity (R2 = 0.9980–0.9990) with a low limit of detection (0.16–0.14 mmol L−1) and a low limit of quantification (0.55–0.43 mmol L−1). The protocol was finally used to determine the oxoammonium cations in the presence of their corresponding radical, showing a robustness against impurity concentration of up to approx. 30%.


Membranes ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 509
Author(s):  
Lisa Wiedenhöft ◽  
Mohamed M. A. Elleithy ◽  
Mathias Ulbricht ◽  
Felix H. Schacher

Porous adsorber membranes are promising materials for the removal of charged pollutants, such as heavy metal ions or organic dyes as model substances for pharmaceuticals from water. Here, we present the surface grafting of polyethylene terephthalate (PET) track-etched membranes having well defined cylindrical pores of 0.2 or 1 µm diameter with two polyelectrolytes, poly(2-acrylamido glycolic acid) (PAGA) and poly(N-acetyl dehydroalanine) (PNADha). The polyelectrolyte functionalised membranes were characterised by changes in wettability and hydraulic permeability in response to the external stimuli pH and the presence of Cu2+ ions. The response of the membranes proved to be consistent with functionalisation inside the pores, and the change of grafted polyelectrolyte macro-conformation was due to the reversible protonation or binding of Cu2+ ions. Moreover, the adsorption of the model dye methylene blue was studied and quantified. PAGA-grafted membranes showed an adsorption behavior following the Langmuir model for methylene blue.


Soil Systems ◽  
2021 ◽  
Vol 5 (2) ◽  
pp. 33
Author(s):  
Stella Gypser ◽  
Elisabeth Schütze ◽  
Dirk Freese

Phosphorus (P) fixation is a global problem for soil fertility and negatively impacts agricultural productivity. This study characterizes P desorption of already fixed P by using KCl, KNO3, histidine, and malic acid as inorganic and organic compounds, which are quite common in soil. Goethite, gibbsite, and ferrihydrite, as well as hydroxide mixtures with varying Fe- and Al-ratio were selected as model substances of crystalline and amorphous Fe- and Al-hydroxides. Especially two- and multi-component hydroxide systems are common in soils, but they have barely been included in desorption studies. Goethite showed the highest desorption in the range from 70.4 to 81.0%, followed by gibbsite with values in the range from 50.7 to 42.6%. Ferrihydrite had distinctive lower desorption in the range from 11.8 to 1.9%. Within the group of the amorphous Fe-Al-hydroxide mixtures, P desorption was lowest at the balanced mixture ratio for 1 Fe: 1 Al, increased either with increasing Fe or Al amount. Precipitation and steric effects were concluded to be important influencing factors. More P was released by crystalline Fe-hydroxides, and Al-hydroxides of varying crystallinity, but desorption using histidine and malic acid did not substantially influence P desorption compared to inorganic constituents.


Author(s):  
Egbert Müller ◽  
Djuro Josic ◽  
Marija Begic ◽  
Suzana Pecenkovic ◽  
Uros Andjelkovic

Difference between two strong cation-exchange resins, namely sulfonium type and sulfate type regarding both their salt tolerance and hydrophobicity were investigated. There is only tiny variation between sulfate and sulfonic group and at the first glance it seems unlikely that it could be the reason for changed selectivity and salt tolerance that was detected in our preliminary experiments. For that reason salt tolerance and hydrophobicity of both ligands was investigated by using two representative polymethacrylate-based ion exchangers as for the sulfonium type TOYOPEARL GigaCap S-650M and for the sulfate type TOYOPEARL Sulfate-650F. In addition some in-silico calculations were performed for model substances representing the sulfonium and sulfate group, and significant differences were calculated regarding their hydrophobicity. These experiments confirmed the working hypothesis that salt tolerance and higher affinity and selectivity for some human plasma derived vitamin K dependent clotting factors and inhibitors are interrelated and dependent from the presence of the sulfate group. The affinity for these proteins was experimentally verified by separation of clotting factor IX from the prothrombin complex concentrate. Presented results show that a simple and fast separation between clotting factor IX and other vitamin K dependent clotting factors II, VII and X is possible, only if the resin with the sulfate, and not with sulfonic acid ligand was applied. Consequently, an immediate application of undiluted feedstock or the eluate from previous isolation step to sulfate resin is possible, and a significant optimization of downstream process can be achieved.


ADMET & DMPK ◽  
2020 ◽  
Vol 9 (1) ◽  
pp. 57-68
Author(s):  
Alisa Elezović ◽  
Amina Marić ◽  
Amila Biščević ◽  
Jasmina Hadžiabdić ◽  
Selma Škrbo ◽  
...  

The kinetics of passive transport of ketoprofen and metformin, as model substances for high and low permeability, respectively, across the artificial membrane under the influence of the pH of donor solution was investigated. There was an upward trend in the apparent permeation coefficient (Papp) of ketoprofen with the decrease in pH to a value close to pKa. At the pH value below pKa the permeation coefficient had lower value, due to the higher retention of ketoprofen in the artificial membrane. Metformin is a low permeable compound, and the highest permeation values were recorded at pH 7.4. Two dissociation constants determine that metformin at physiological pH exists as a hydrophilic cationic molecule, i.e. predominantly in ionized form. At pH values below 2.8, metformin mainly exists in diprotonated form, and it was, thus, very poorly permeable. The highest retention, i.e. affinity of both ketoprofen and metformin to the membrane, was at the lowest pH values, which is explained by different mechanisms. At higher pH values of the donor compartment, the substances showed significantly less affinity to the membrane. The obtained values of apparent permeation coefficients at studied pH values showed a good correlation with the obtained experimental values by other in vitro methods.    


Fuel ◽  
2020 ◽  
Vol 279 ◽  
pp. 118038 ◽  
Author(s):  
Peng Liu ◽  
Xiaofeng Wang ◽  
Xiaofu Li ◽  
Ting Zhang ◽  
Guichao Du ◽  
...  

2020 ◽  
Vol 1 (2) ◽  
pp. 247-259
Author(s):  
Alexey Krushelnitsky ◽  
Kay Saalwächter

Abstract. Chemical shift anisotropy (CSA) and dipolar CODEX (Cenralband Only Detection of EXchange) experiments enable abundant quantitative information on the reorientation of the CSA and dipolar tensors to be obtained on millisecond–second timescales. At the same time, proper performance of the experiments and data analysis can often be a challenge since CODEX is prone to some interfering effects that may lead to incorrect interpretation of the experimental results. One of the most important such effects is RIDER (relaxation-induced dipolar exchange with recoupling). It appears due to the dipolar interaction of the observed X nuclei with some other nuclei, which causes an apparent decay in the mixing time dependence of the signal intensity reflecting not molecular motion, but spin flips of the adjacent nuclei. This may hamper obtaining correct values of the parameters of molecular mobility. In this contribution we consider in detail the reasons why the RIDER distortions remain even under decoupling conditions and propose measures to eliminate them. That is, we suggest (1) using an additional Z filter between the cross-polarization (CP) section and the CODEX recoupling blocks that suppresses the interfering anti-phase coherence responsible for the X-H RIDER and (2) recording only the cosine component of the CODEX signal since it is less prone to the RIDER distortions in comparison to the sine component. The experiments were conducted on rigid model substances as well as microcrystalline 2H ∕ 15N-enriched proteins (GB1 and SH3) with a partial back-exchange of labile protons. Standard CSA and dipolar CODEX experiments reveal a fast-decaying component in the mixing time dependence of 15N nuclei in proteins, which can be misinterpreted as a slow overall protein rocking motion. However, the RIDER-free experimental setup provides flat mixing time dependences, meaning that the studied proteins do not undergo global motions on the millisecond timescale.


Sign in / Sign up

Export Citation Format

Share Document