Use of coacervates for the on-site extraction/preservation of polycyclic aromatic hydrocarbons and benzalkonium surfactants

The suitability of coacervates for the preservation of organic pollutants after their extraction from water samples was investigated for the first time. Acid-induced sodium dodecanesulfonic acid (SDSA) micelle-based coacervates were selected for this purpose. Their capacity to preserve benzalkonium homologue (C₁₂, C₁₄ and C₁₆) surfactants (BASs) and different polycyclic aromatic hydrocarbons (PAHs) [benzo(a)pyrene (BaP), benzo(b)fluoranthene (BbF), benzo(k)fluoranthene (BkF), benzo(ghi)perylene (BghiP), benzo(a)anthracene (BaA) and indene(1,2,3-c-d)pyrene (IP)] was investigated. BASs and PAHs were efficiently extracted by the coacervate by formation of mixed aggregates and hydrophobic interactions, respectively. Their stability into the coacervate was investigated under three temperature conditions (room temperature, 4 °C and −20 °C) and two hydrochloric acid concentrations (3.75 M and 4.2 M), which was used to induce coacervation. No losses were observed during at least 3 months at the different experimental conditions tested. The increase of the temperature up to 35 °C for a month did not affect the stability of the target compounds. No influence of the water matrix (distilled, river or wastewater) on the stabilization of BASs and PAHs was observed. The high-stabilizing capacity of the coacervate for the target compounds and its low volume make easy the transport and storage of analytes.     

Complexes of aluminium(III) with picolinic and pipecolinic acids: An27Al-NMR investigation

Summary Aluminium-27 NMR has been employed for the study of the interaction of Al(III) with picolinic (pic-H) and pipecolinic (pip-H) acids in aqueous solution at variablepH. In the reaction with picolinic acid distinct peaks for hydrated Al(III), 1:1 and 1:2 Al-picolinate complexes, as well as a mixed hydroxo-picolinato complex Al(pic)₂OH are observed. An insoluble 1:3 picolinate complex is formed atpH 3. Pipecolinic acid forms 1:1 and 1:2 Al-pipecolinate complexes. No hydroxy-pipecolinate species are formed, however, and the 1:2 complex is deprotonated abovepH 4.5 to colin- (pic-H) und Pipecolinsäure (pip-H) in wäßriger Lösung bei verschiedenenpH angewandt. Bei Al(pip)(H_–1 pip) have been isolated and characterized by elemental analysis, IR and¹H-NMR.

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Komplexe von Aluminium(III) mit Picolin- und Pipecolinsäure: Eine²⁷Al-NMR-Untersuchung

Zusammenfassung ²⁷Al-NMR wurde zur Untersuchung von Wechselwirkungen von Al(III) mit Picolin-(pic-H) und Pipecolinsäure (pip-H) in wäßriger Lösung bei verschiedenenpH angewandt. Bei der Reaktion mit Picolinsäure wurden separate Signale für hydratisiertes Al(III), 1:1 und 1:2 Al-Picolinat-Komplexe und auch für gemischte Hydroxo-picolinat-Komplexe Al(pic)₂OH beobachtet. BeipH3 wird unlöslicher Picolinat-Komplex gebildet. Pipecolinsäure geht 1:1 und 1:2 Al-Pipecolinat-Komplexe ein. Es werden keine Hydroxo-Pipecolinat-Komplexe gebildet. Der 1:2 Komplex wird über einempH von 4.5 deprotoniert und ergibt den unlöslichen Komplex Al(pip)(H_–1 pip). Die [3, 4] as well as those undergoing dialysis treatment for chronic renal failure [5]. taranalyse, IR und¹H-NMR charakterisiert.

     

Coacervation of poly-electrolytes in the presence of lipid bilayers: mutual alteration of structure and morphology

Many intrinsically disordered peptides have been shown to undergo liquid–liquid phase separation and form complex coacervates, which play various regulatory roles in the cell. Recent experimental studies found that such phase separation processes may also occur at the lipid membrane surface and help organize biomolecules during signaling events; in some cases, phase separation of proteins at the membrane surface was also observed to lead to significant remodeling of the membrane morphology. The molecular mechanisms that govern the interactions between complex coacervates and lipid membranes and the impacts of such interactions on their structure and morphology, however, remain unclear. Here we study the coacervation of poly-glutamate (E₃₀) and poly-lysine (K₃₀) in the presence of lipid bilayers of different compositions. We carry out explicit-solvent coarse-grained molecular dynamics simulations by using the MARTINI (v3.0) force-field. We find that more than 20% anionic lipids are required for the coacervate to form stable contact with the bilayer. Upon wetting, the coacervate induces negative curvature to the bilayer and facilitates local lipid demixing, without any peptide insertion. The magnitude of negative curvature, extent of lipid demixing, and asphericity of the coacervate increase with the concentration of anionic lipids. Overall, we observe a decrease in the number of contacts among the polyelectrolytes as the droplet spreads over the bilayer. Therefore, unlike previous suggestions, interactions among polyelectrolytes do not constitute a driving force for the membrane bending upon wetting by the coacervate. Rather, analysis of interaction energy components suggests that bending of the membrane is favored by enhanced interactions between polyelectrolytes with lipids as well as with counterions. Kinetic studies reveal that, at the studied polyelectrolyte concentrations, the coacervate formation precedes bilayer wetting.

Intrinsically disordered polyelectrolytes undergoing liquid–liquid phase separation to form complex coacervates on a membrane, which profoundly alters the membrane morphology.     

Effects of biopolymer ratio and heat treatment on the complex formation between whey protein isolate and soluble fraction of Persian gum

Proteins and polysaccharides are the two most important natural ingredients with unique functional properties. Their interactions can be considered as a route to produce new materials of various technological applications. In this study, the effect of pH (3–7) as well as the mixing ratio of whey protein isolate (WPI)/soluble part of Persian gum (PG) (1:3, 1:1, 3:1, 6:1, and 9:1% w/w WPI/PG) on the complex formation behavior of the two polymers were studied using spectrophotometric and dynamic light scattering techniques, soluble protein measurement, and microscopic observations. Investigating the curves of turbidity versus pH showed that pHc and pH_?1, which are associated with the formation of soluble and insoluble complexes, moved toward higher pH values by increasing WPI:PG ratio. Increased solubility was observed at pHc?>?pH?>?pH_?1 for all biopolymers mixtures. In addition, lowering the pH toward pH_?1 resulted in a decrease in the size of complexes, while further decrease of pH beyond this point led to larger particles. No significant difference was noticed between pH_c and pH_?1 of heated and unheated WPI/PG mixtures, although the turbidity of heated samples increased due to the formation of larger aggregates.     

Preparation of zinc sodium polyphosphates glasses from coacervates precursors. Characterisation of the obtained glasses, and their applications

A soft chemistry route is described to obtain glasses in the P₂O₅–Na₂O–ZnO–H₂O. It is based on the addition of zinc salts to coacervates prepared from sodium polyphosphate. The processing of these coacervates leads to polyphosphate glasses with the same properties as those of glasses prepared in the classical way. So far, little work has been implemented in this system using ‘coacervate route’. However, it makes an attractive method for coating and joining processes on the industrial scale. As the anion associated to zinc may take part in the adhesion mechanism, coacervate formation has been studied using zinc chloride, nitrate and sulphate as starting materials. The physical properties of the glasses obtained by this method are reported and potential applications of zinc and silver coacervate are described.     

Rigorous nonlinear regression analysis of phase solubility diagrams to obtain complex stoichiometry and true thermodynamic drug-cyclodextrin complexation parameters

This work reports rigorous nonlinear regression procedures aimed at analyzing various types of phase solubility diagrams (PSDs) corresponding to the different soluble and insoluble complex stoichiometries, which are generally encountered in drug-cyclodextrin (CD) complexation studies. These are depicted in final equations that can be modeled to fit experimental data of measured drug solubility against CD concentration utilizing simple spreadsheet software available for all PCs (i.e., the Solver Add-in in Microsoft Excel). They cover all types of guest/host phase solubility diagrams (A-, B_S-and B_I-types) allowing accurate estimation of soluble and insoluble complex stoichiometries generally encountered in drug/CD complexes (1:1, 2:1, 1:2, 2:2, 2:3, 3:2), the corresponding thermodynamic complex formation constants (K₁₁, K₂₁, K₁₂, K₂₂, K₂₃, K₃₂) and solubility product constants (K_sp) of saturated complexes.     

Self-programmed enzyme phase separation and multiphase coacervate droplet organization

Membraneless organelles are phase-separated droplets that are dynamically assembled and dissolved in response to biochemical reactions in cells. Complex coacervate droplets produced by associative liquid–liquid phase separation offer a promising approach to mimic such dynamic compartmentalization. Here, we present a model for membraneless organelles based on enzyme/polyelectrolyte complex coacervates able to induce their own condensation and dissolution. We show that glucose oxidase forms coacervate droplets with a cationic polysaccharide on a narrow pH range, so that enzyme-driven monotonic pH changes regulate the emergence, growth, decay and dissolution of the droplets depending on the substrate concentration. Significantly, we demonstrate that time-programmed coacervate assembly and dissolution can be achieved in a single-enzyme system. We further exploit this self-driven enzyme phase separation to produce multiphase droplets via dynamic polyion self-sorting in the presence of a secondary coacervate phase. Taken together, our results open perspectives for the realization of programmable synthetic membraneless organelles based on self-regulated enzyme/polyelectrolyte complex coacervation.

Self-programmed enzyme phase separation is exploited to assemble dynamic multiphase coacervate droplets via spontaneous polyion self-sorting under non-equilibrium conditions.     

Interfacial energy of polypeptide complex coacervates measured via capillary adhesion

A systematic study of the interfacial energy (γ) of polypeptide complex coacervates in aqueous solution was performed using a surface forces apparatus (SFA). Poly(L-lysine hydrochloride) (PLys) and poly(L-glutamic acid sodium salt) (PGA) were investigated as a model pair of oppositely charged weak polyelectrolytes. These two synthetic polypeptides of natural amino acids have identical backbones and differ only in their charged side groups. All experiments were conducted using equal chain lengths of PLys and PGA in order to isolate and highlight effects of the interactions of the charged groups during complexation. Complex coacervates resulted from mixing very dilute aqueous salt solutions of PLys and PGA. Two phases in equilibrium evolved under the conditions used: a dense polymer-rich coacervate phase and a dilute polymer-deficient aqueous phase. Capillary adhesion, associated with a coacervate meniscus bridge between two mica surfaces, was measured upon the separation of the two surfaces. This adhesion enabled the determination of the γ at the aqueous/coacervate phase interface. Important experimental factors affecting these measurements were varied and are discussed, including the compression force (1.3-35.9 mN/m) and separation speed (2.4-33.2 nm/s). Physical parameters of the system, such as the salt concentration (100-600 mM) and polypeptide chain length (N = 30, 200, and 400) were also studied. The γ of these polypeptide coacervates was separately found to decrease with both increasing salt concentration and decreasing polypeptide chain length. In most of the above cases, γ measurements were found to be very low, <1 mJ/m(2). Biocompatible complex coacervates with low γ have a strong potential for applications in surface coatings, adhesives, and the encapsulation of a wide range of materials.     

Microstructure of beta-lactoglobulin/pectin coacervates studied by small-angle neutron scattering

Small-angle neutron scattering (SANS) has been used to investigate the microstructure of beta-lactoglobulin/pectin coacervates prepared by different initial protein/polysaccharide weight ratio (r), sodium chloride concentration (C(NaCl)), and pectin charge density. The higher r and higher pectin charge density lead to higher scattering intensity at small q range (0.007 Angstrom(-1) < q < 0.02 Angstrom(-1)), suggesting that the charges of pectin chains are screened significantly by the binding of oppositely charged protein molecules, leading to a tighter aggregation of pectin chains. On the other hand, the appearance of a shoulder peak at intermediate q range (0.04 Angstrom(-1) < q < 0.2 Angstrom(-1)) is used to interpret the formation of protein domains in beta-lactoglobulin/pectin coacervates. At C(NaCl) = 0.1 M, the coacervate of beta-lactoglobulin and pectin A does not show a shoulder peak at intermediate q range at r = 10:1, suggesting that protein molecules are separately bound on pectin chains. However, a shoulder peak appears at intermediate q range at r = 20:1 and 30:1, and the average protein domain size estimated from the shoulder peak position is 7.2 and 8.5 nm, respectively, for these two coacervates. When C(NaCl) increases from 0.05 to 0.2 M, the shoulder peak shifts toward smaller q and becomes broader, indicating that the addition of a higher amount of salt leads to a more heterogeneous coacervate structure. Pectin B with a lower linear charge density favors the formation of larger protein domains. The formation of protein domains in beta-lactoglobulin/pectin coacervates is partially ascribed to the self-aggregation of beta-lactoglobulin molecules. Two kinds of microstructures of beta-lactoglobulin/pectin coacervates with and without observable protein domains have been proposed.     

Noncanonical Amino Acids to Improve the pH Response of pHLIP Insertion at Tumor Acidity

The pH low insertion peptide (pHLIP) offers the potential to deliver drugs selectively to the cytoplasm of cancer cells based on tumor acidosis. The WT pHLIP inserts into membranes with a pH₅₀ of 6.1, while most solid tumors have extracellular pH (pH_e) of 6.5–7.0. To close this gap, a SAR study was carried out to search for pHLIP variants with improved pH response. Replacing Asp25 with α‐aminoadipic acid (Aad) adjusts the pH₅₀ to 6.74, matching average tumor acidity, and replacing Asp14 with γ‐carboxyglutamic acid (Gla) increases the sharpness of pH response (transition over 0.5 instead of 1 pH unit). These effects are additive: the Asp14Gla/Asp25Aad double variant shows a pH₅₀ of 6.79, with sharper transition than Asp25Aad. Furthermore, the advantage of the double variant over WT pHLIP in terms of cargo delivery was demonstrated in turn‐on fluorescence assays and anti‐proliferation studies (using paclitaxel as cargo) in A549 lung cancer cells at pH 6.6.     

Inclusion complexation of naproxen with cyclosophoraoses and succinylated cyclosophoraoses in different pH environments

Cyclosophoraoses [cyclic β-(1,2)-glucan, Cys] isolated from Rhizobium leguminosarum biovar trifolii TA-1 have unique structures and high solubility, which make it a potent solubilizer for host–guest inclusion complexation. Succinylated cyclosophorasoses (S-Cys) were also synthesized by chemically modifying isolated cyclosophoraoses. In ultraviolet-visible studies using naproxen (NAP), Cys was shown to form the most stable complexes with NAP (K _1:1?=?2457.9?M^?1), which was followed by the negatively charged S-Cys (K _1:1?=?357.1?M^?1) at pH 3.4. A further strong reduction in the complex stability constant was observed at pH 7.5. When the reduction in the stability constant was compared with other cyclic oligosaccharides (Cys; 119.2?M^?1, CD; 14.48?M^?1 and HP-CD; 6.75?M^?1), S-Cys (K _1:1?=?5.6?M^?1) was shown to have the highest decrease in stability constant. These results suggest that the S-Cys could regulate the efficiency of inclusion complexation at external pH values. NMR studies of complex formation between NAP and Cys also showed a different correlation pattern at pH 3.4 and 7.5. This difference in correlation demonstrates that the inclusion complexes between Cys and NAP formed as a result of the differential charge distribution of the carboxyl groups of NAP. The pH-dependent inclusion behavior of Cys for NAP was also evaluated using molecular docking simulations.     

The extraction of Yb(III) and Lu(III) with chloroform from aqueous solutions in the presence of cupferron

The equilibrium of distribution of Yb(III) and Lu(III) between chloroform and the aqueous phase in the presence of cupferron (the ammonium salt of N-nitrosophenylhydroxylamine) were studied as apH function of the aqueous phase and the concentration of N-nitrosophenylhydroxylamine (HL). The stability constants for theLnL _n ^3–n ) complexes (n=1÷3) being formed in the aqueous phase were established, as well as the equilibrium constants of the extraction reaction $$Ln(H_2 O)_m^{3 + } + 3HL_{(O)} \mathop \rightleftharpoons \limits^{K_{ex} } LnL_{3(O)} + 3H^ + + mH_2 O(Ln^{3 + } = Yb,Lu),$$ two-phase stability constants for theLnL ₃ complexes,pH _0.5 and the separation factor Lu(III) from Yb(III).     

Coacervation of copolymer of diallyldimethylammonium chloride and sodium styrenesulfonate aqueous solution

Coacervate behavior of polyelectrolyte complexes has been studied by many papers. Few studies have focused on the coacervate behavior of amphoteric polymer. In this study, amphoteric copolymer of diallyldimethylammonium chloride (DM) and sodium styrenesulfonate (SS) (the copolymer was noted as DMS) was synthesized with the mole content of SS to DM ranged from 0 to 10%. Firstly, DMS was characterized by static light scattering, FTIR, ¹H-NMR, TGA and DSC. Then, its phase and coacervate behaviors were studied. Turbidity was utilized as an indicator for the coacervate formation. It was found that when the SS content was more than 4 mol%, DMS coacervate would be formed in deionized water at a certain concentration. Temperature and pH have no effect on the formation of DMS coacervate. Meanwhile, salts has a great influence on the DMS coacervation. Unlike the results of the other polyelectrolyte complexes, Na₂SO₄, Na₂HPO₄, NaCOOCH₃, sodium citrate and NaI cannot prevent the DMS coacervate formation. However, the addition of NaCl, NaNO₃, NaBr and NaSCN can prevent the coacervate formation. The influence cannot be described by Hofmeister-like behavior. Results of surface tension and fluorescence spectrum presented that the driving forces to formation of DMS coacervate are the electrostatic interaction and the intermolecular hydrophobic interaction.     

Characterization of invertase entrapped into calcium alginate beads

A solution of 10 g/L of sodium alginate (Satialgine® types used [Sanofi trademark]: SG800® and S1100® with manuronic/guluronic ratio of 0.5 and 1.2, respectively) containing invertase (0.08 g of protein/L) was dropped into 0.1 M CaCl₂ solution buffered at pH 4.0, 7.0, or 8.0. The beads were left to harden in CaCl₂ solution for 24 h. The high immobilization yield of 60% occurred with SG800 at pH8.0. The activity of soluble and insoluble invertase was measured against pH (2.8–8.0), sucrose concentration (4.5–45 mM), and temperature (30–60°C). Both forms presented an optimum pH of 4.6. However, the soluble invertase was stable at the overall pH interval studied, whereas insoluble invertase lost 30% of its original activity at pH > 5.0. At temperatures above 40°C, the insoluble form was more stable than the soluble one. The kinetic constants and activation energies (E _a ) for free invertase were K _M =41.2 mM, V _max=0.10 mg of TRS/(min · mL), and E _a 28 kJ/mol for entrapped invertase they were (K _M ) _ap =7.2 mM, (V _max) _ap =0.060 mg of TRS/(min · mL), and (E _a )_ap=24 kJ/mol.     

The structure of 1-chloro-1-silabicyclo(2.2.2)octane as determined by gas-phase electron diffraction

The structure of 1 -chloro-1 -si labicyclo( 2.2.2 )octane is determined by gas-phase electron diffraction. The molecule is found to have a large amplitude twisting motion with a double minimum quartic potential function of the form V(φ) = V_o[1 + (φ/φ_o)⁴ - 2(φ/φ_o)²]. Least-squares analysis of the experimental data gives values of 1.4(0.8) kcal mole^? for V_o and 17.5(2.5)° for φ_o. Other structural parameters for the “quasi-C_3v” cage-like molecule include: r_g(Si-Cl) = 2.061(3) Å, r_g(Si-C) = 1.863(3) Å, r_g(C-C_av) = 1.559(2) Å, and r_g(C-H_av) = 1.098(7) Å. Several valence angles exhibit large deviations from tetrahedral values, e.g. ∠Cl-Si-C₂ = 114.6(0.2)°, ∠Si-C₂-C₃ = 105.8(0.4)°, ∠C₂-C₃-C₄ = 114.2(1.2)°, ∠C-₃-C₄-C₅ = 111.4(0.8)° and ∠C₂-Si-C₆= 103.9(0.2)°. Many of the structural features in this strained polycyclic compound. Including the nature of the quartic potential function, can be rationalized in terms of a simple molecular mechanics model. A new method for the calculation of an analytical Jacobian of the intensity function with respect to parameters of the potential function is also discussed.     

Acid soap formation of oleic acid and catanionic complex formation in the alkyldimethylamine oxide/sodium oleate equimolar mixtures

The influence of adding alkyldimethylamine oxide (CnDMAO) with varying alkyl chain lengths (n_c) on the acid soap formation of oleic acid was investigated. The solutions of equimolar mixtures of CnDMAO and sodium oleate (Na⁺Ol^–), each 25 mmol kg^–1, became turbid at a certain critical pH (pH_c) on decreasing pH. Values of the pH_c depended on n_c and showed the minimum at C10DMAO/NaOl mixture. The presence of the minimum was interpreted in terms of two different kinds of the complex formed in the micelles depending on n_c: the catanionic complex (CnDMAOH⁺/Ol^–) in the mixed micelles of n_c=16, 14, 12 and 10, and the acid soap of oleic acid for C6DMAO/NaOl and C8DMAO/NaOl mixtures. At pH_c where the amounts of these complexes of double-chain nature reached certain critical values in the mixed micelles, a phase separation (most probably lamella formation) took place. It was expected that the critical amount of the catanionic complex was smaller for the mixtures of higher n_c values and hence pH_c increased with n_c for the mixtures n_c10. For the mixtures of n_c<10, it was expected that the amount of the acid soap in the mixed micelles increased with decreasing n_c at a given pH and the pH_c increased with decreasing n_c. Micelle compositions at cmc were evaluated on the basis of the regular solution theory coupled with the pseudo phase approximation. The micelle compositions at 100 mmol kg^–1 were examined with ¹³C-NMR. The results showed the mixed micelle formation for n_c=16–10, while the micelles mostly consisting of oleic acid for the mixtures of n_c=8 and 6. The assumption of two different complexes for the two groups of the mixture was thus supported. The cmc range of mixed micelles was evaluated and it was well correlated with the observed concentration range of pyrene fluorescence change.     

Thermal and photochemical olefin isomerizations with complex [(C5Me4H)2Ti(CH3)2] as initiator

Irradiation of the complex [(C₅Me₄H)₂Ti(Ci(CH₃)₂] in an olefin as a solvent promotes stereospecific photoassisted isomerizations: olefins with terminal double bonds are rapidly isomerized into 2-alkenes with an E-configuration. Kinetic studies of hydrogen migration and of Z-E isomerizations of disubstituted olefins have demonstrated the influence of substitution and of branching of the hydrocarbon chain on the course of the reaction. Formation of paramagnetic complexes of Ti^III that are probably intermediates in these reactions has been confirmed by ESR. The same reactions, but with a lower stereoselectivity, are initiated thermally by the [(C₅Me₄H)₂Ti(CH₃)₂] complex.     

Equilibrium Studies of Binary and Mixed-Ligand Complexes of Zinc(II) Involving 2-(Aminomethyl)-Benzimidazole and Some Bio-Relevant Ligands

Binary and mixed-ligand complexes of zinc(II) involving 2-(aminomethyl)-benzimidazole (AMBI) and amino acids, peptides (HL) or DNA constituents have been investigated. Ternary complexes of amino acids or peptides are formed simultaneously. Amino acids form the complex Zn(AMBI)L, whereas amides form two complex species Zn(AMBI)L and Zn(AMBI)(LH_?1). The ternary complexes of zinc(II) with AMBI and DNA are formed in a stepwise process, whereby binding of zinc(II) to AMBI is followed by ligation of the DNA constituents. The stability of ternary complexes is quantitatively compared with their corresponding binary complexes in terms of the parameters ??log₁₀ K, log₁₀ ??_stat and log₁₀ X. The effect of the side chains of amino acid ligands (??_R) on complex formation is discussed. The values of ??log₁₀ K indicated that the ternary complexes containing aromatic amino acids are significantly more stable than the complexes containing alkyl- and hydroxyalkyl-substituted amino acids. This may be taken as evidence for a stacking interaction between the aromatic moiety of AMBI and the aromatic side chains of the bio-active ligands. The concentration distributions of various species formed in solution were also evaluated as a function of the pH.     

Formation of mixed-ligand complexes in the complexing polymer sorbent-Pb<Superscript>2+</Superscript>-dinitrophenol systems

The complexation of lead(II) with a group of synthesized sorbents based on aminopolystyrene and substituted phenols having structurally different substituents of various electronic natures in the para position with respect to phenolic hydroxyl was studied. As third components, α-dinitrophenol and γ-dinitrophenol were examined. The following most important parameters of sorption were determined: the optimum pH value of quantitative sorption (pH_opt), the recovery (R, %), the sorption capacity of the sorbent (SCS_Pb, mg/g), the half-sorption pH value (pH₅₀), and the temperature and time (τ) of sorption in the presence of a third component. The structure of the mixed-ligand complex was determined.     

Time-programmable pH: decarboxylation of nitroacetic acid allows the time-controlled rising of pH to a definite value

In this report it is shown that nitroacetic acid 1 (O₂NCH₂CO₂H) can be conveniently used to control the pH of a water solution over time. Time-programmable sequences of the kind pH_1(high)–pH_2(low)–pH_3(high) can be achieved, where both the extent of the initial pH jump (pH_1(high)–pH_2(low)) and the time required for the subsequent pH rising (pH_2(low)–pH_3(high)) can be predictably controlled by a judicious choice of the absolute and relative concentrations of the reagents (acid 1 and NaOH). Successive pH_1(high)–pH_2(low)–pH_3(high) sequences can be obtained by subsequent additions of acid 1. As a proof of concept, the method is applied to control over time the pH-dependent host–guest interaction between alpha-cyclodextrin and p-aminobenzoic acid.

Predictable and time-programmable sequences of the kind pH_1(high)–pH_2(low)–pH_3(high) in water solution are obtained by a judicious choice of the concentration of nitroacetic acid undergoing decarboxylation.