On an intraparticle complex of cationic nanogel with a stoichiometric amount of bound polyanions

A polyelectrolyte nanogel (PENG) particle consisting of lightly cross-linked terpolymer chains of N-isopropylacrylamide, acrylic acid, and 1-vinylimidazole has positive charges in an aqueous medium at pH 3 due to protonation of the imidazole groups, and thereby forms a polyelectrolyte complex with the linear polyanion, potassium poly(vinyl alcohol) sulfate (KPVS). It has been demonstrated that the hydrodynamic radius (Rh), by dynamic light scattering (DLS), and the radius of gyration (Rg), by static light scattering (SLS), of the complex particles are smallest at approximately 1:1 mixing ratio (rm) of anions to cations, in the absence of simple salts such as KCl (Langmuir 2005, 21, 4830). Here, we aimed to study the nature of the complex formed at rm=1 and examined the complex formation process by electrophoretic light scattering (ELS). It was found that the mobility of the cationic PENG with a stoichiometric amount of bound KPVS anions (i.e., the complex formed at rm=1) is positive but not zero at 25 degrees C. This was also the case when the complex was examined by ELS at 45 degrees C, where DLS and SLS show a temperature-driven collapse of the complex. We thus assumed that (a) electroneutrality is maintained in the complex particle with the aid of counterions, but (b) the complex is highly polarizable, and hence (c) during ELS the KPVS anions would dissociate in part from the complex. This hypothesis was supported by the following results: (i) Mixing complexed and uncomplexed PENG particles at different ratios brings about an increase in Rh and a decrease in the light scattering intensity of the complex at the same time, suggesting a polyelectrolyte exchange reaction. (ii) The same phenomenon is seen when poly(diallyldimethylammonium chloride) (PDDA as a polysalt) is added to the complex dispersion, meaning that the PDDA takes out the KPVS from the complex to form a stable PDDA-KPVS complex. (iii) Upon addition of KCl, the complex undergoes little change in Rh (62-67 nm) at a salt concentration (Cs)0.2 M. (iv) The Rh (78 nm) of the soluble complex at Cs from 0.3 to 0.5 M is larger than that at Cs<0.02 M, suggesting dissociation of the KPVS ions. (v) Complexation between KPVS and PDDA as mentioned in (ii) is facilitated in the presence of 0.01 M KCl.     

Polyelectrolyte titration using fluorescent indicator. I. Direct titration of anionic and cationic polyelectrolytes with 10−4N standard solutions

The polyelectrolyte titration, which was originally called colloid titration, is based on the stoichiometric reaction between positively charged colloidal particles and negatively charged ones. In the conventional method, the metachromatic color change of the indicator, toluidine blue, from blue to red-purple has been applied for the determination of the end point in the titration. 2.5 × 10^?3N potassium polyvinylsulfonate (KPVS) is usually used as the standard titrant. In this work, fluorescent indicators such as 6-(p-toluidino)-2-naphthalene sulfonate (TNS), acridine orange, etc., have been introduced. The fluorescence intensity was measured using the spectrophotometer equipped with magnetic stirrer and connected with a vinyl tube attached to the hand piston burette. For example, TNS is practically nonfluorescent, but it exhibits strong fluorescence when it is bound to a cationic polyelectrolyte (CP). The fluorescence of the TNS–CP complex is diminished by titration with KPVS standard solution since TNS is liberated from the complex by substitution with KPVS. After the equivalent point, the fluorescence intensity becomes constant and the end point can thus be detected by that point. It has been elucidated that the very dilute standard solution like 1 × 10^?4N can be used because the sensitivity of fluorescence detection is extremely high. © 1993 John Wiley & Sons, Inc.     

Introduction of pH‐sensitivity into mechanically strong nanoclay composite hydrogels based on N‐isopropylacrylamide

pH‐sensitive nanoclay composite hydrogels based on N‐isopropylacrylamide (NIPA) were synthesized by copolymerization with cationic and anionic comonomers. Laponite nanoclay particles served as multifunctional crosslinkers, producing hydrogels with exceptionally high mechanical strengths, as measured by elongation at break. Cationic copolymer gels based on NIPA and dimethylaminoethylmethacrylate were prepared by aqueous free radical polymerization, adopting a procedure reported by Haraguchi (Adv Mater 2002, 14, 1120–1124). Without modification, this technique failed to produce anionic copolymer gels of NIPA and methacrylic acid (MAA), due to flocculation of clay particles. Three methods were conceived to incorporate acidic MAA into nanoclay hydrogels. First, NIPA was copolymerized with sodium methacrylate under dilute conditions, producing hydrogels with good pH‐sensitivity but weak mechanical characteristics. Second, NIPA was copolymerized with methyl methacrylate, which was then hydrolyzed to generate acid sidegroups, yielding hydrogels that were much stronger but less pH sensitive. Third, NIPA was copolymerized with MAA following modification of the nanoclay surface with pyrophosphate ions. The resulting hydrogels exhibited both strong pH‐sensitivities at 37 °C and excellent tensile properties. Optical transparency changed during polymerization, depending on hydrophobicity of the components. This work increases the diversity and functionality of nanoclay hydrogels, which display certain mechanical advantages over conventionally crosslinked hydrogels. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6630–6640, 2008     

Thermoresponsive nanostructured poly(N-isopropylacrylamide) hydrogels made via inverse microemulsion polymerization

The synthesis of nanostructured poly(N-isopropylacrylamide) (polyNIPA) hydrogels by a two-stage polymerization process is reported here. The process involves the synthesis of slightly crosslinked polyNIPA nanoparticles by inverse (w/o) microemulsion polymerization; then, these particles are dried, cleaned and dispersed in an aqueous solution of NIPA and a crosslinking agent (N,N-methylene-bis-acrylamide or NMBA) and polymerized to produce the nanostructured hydrogels. Their swelling and de-swelling kinetics, volume phase transition temperatures (T _VPT) and mechanical properties at the equilibrium swollen state are investigated as a function of the weight ratio of polyNIPA particles to monomer (NIPA). The nanostructured gels exhibit larger equilibrium water uptake, faster swelling and de-swelling rates and similar T _VPT than those of the conventional ones; moreover, the elastic and Young moduli are larger than those of the conventional hydrogels at similar swelling ratios. The fast swelling and de-swelling kinetics are explained in terms of the controlled inhomogeneities introduced by the method of synthesis.     

Polyampholyte gels of a cross-linked polyanion or polycation network into which an oppositely charged polyion was immobilized

Three polyampholyte gels (G1 to G3) composed of acrylic acid (AA), 1-vinylimidazole (VI) and N-isopropylacrylamide (NIPA) were prepared: G1 with a pre-gel solution (pH?≈?12) containing NIPA (700 mM), AA (150 mM), VI (150 mM) and N,N′-methylenebis(acrylamide) (10 mM); G2 with the same pre-gel, except for containing poly(acrylic acid) (PAA) (150 unit mM) instead of AA; and G3 with the same pre-gel, except for containing poly(1-vinylimidazole) (PVI) (150 unit mM) instead of VI. The immobilization of PAA ( $ {\overline M_{\text{w}}} = {2}0{5},000 $ ) and PVI ( $$ {\overline M_{\text{w}}} = <$> <$>35,900 $$ ) resulted in transparent G2 and G3, respectively, while G3 with another PVI ( $ {\overline M_{\text{w}}} = {193},000 $ ) was opaque. Potentiometric titrations and swelling measurements of an anionic and a cationic copolymer gel (as a control sample) suggested that each polyampholyte gel exhibits an isoelectric point (pI) at pH?≈?5.6, at which the electrostatic attraction between the carboxylate and imidazole ions leads to gel collapse. Indeed, all the ampholyte gels underwent a collapse transition at pH around the pI upon cyclic pH changes (first increased and then decreased). The pH region where gel collapse was observed, however, was broader for G2 and G3 (with immobilized polyions) than for G1 (random terpolymer gel). The swelling/deswelling characteristics of transparent and opaque G3 gels were different from each other, and also from those of G1 and G2. These results were discussed in terms of the role of hydrogen bonding of the amide with the carboxyl or imidazole groups in the collapse transition of the ampholyte gels.     

Synthesis of a thermoresponsive shell‐crosslinked 3‐layer onion‐like polymer particle with a hyperbranched polyglycerol core

A novel thermoresponsive shell crosslinked three‐layer onion‐like polymer particles were prepared using hyperbranched polyglycerol (PG) as parents compound, the periphery hydroxyl groups of PG were transformed into trithiocarbonates (? SC(S)S? ) first; then, it was used as chain transfer agent to prepare star‐like block copolymer of N‐isopropyl acrylamide (NIPA) and N,N‐dimethylaminoethyl acrylate (DMA) in sequence via reversible addition fragmentation chain transfer (RAFT) process. Thus, a three‐layer polymer, PG? [SC(S)S? (DMA)? b? (NIPA)]_n, was obtained. The middle layer of poly(DMA) was then crosslinked with 1,8‐diiodoctane, and the resulting onion‐like three‐layer polymer showed a lower critical solution temperature (LCST) in water because of the outer layer of poly(NIPA). The LCST value only slightly depended on the crosslinking degree. Finally, the ? SC(S)S? were transformed into thiols by sequential treating with sodium borohydride and formic acid; thus, the core molecule was chemically detached from the crosslinked shell and a novel shell crosslinked polymer particle was obtained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5652–5660, 2005     

Conductometric and light scattering studies on the complexation between cationic polyelectrolyte nanogel and anionic polyion

This work aims to provide a basic understanding of the water dispersibility of a 1:1 stoichiometric polyelectrolyte complex (SPEC) in water in the absence of low-molecular-weight salts. We studied the complexation of a linear polyanion, potassium poly(vinyl alcohol sulfate) (KPVS), with a cationic polyelectrolyte nanogel (CPENG) composed of a lightly cross-linked copolymer of N-isopropylacrylamide and 1-vinylimidazole, in an aqueous salt-free solution (pH 3 and 25 °C), as a function of the molar mixing ratio (Mmr) of anionic to cationic groups. Also studied for comparison was the complexation of KPVS with poly(diallyldimethylammonium chloride) (PDDA), which is a standard reaction in colloid titration. Turbidimetric and conductometric measurements were used in combination of dynamic light scattering (DLS). An abrupt increase of turbidity curve and a break of conductivity curve were observed at Mmr =1 when KPVS was added to the CPENG or PDDA solution, indicating the formation of SPEC. All the complexes formed at Mmr ≤ 1 were water-dispersible and hence characterized by DLS. The CONTIN analysis of DLS data showed that (i) an increase of Mmr causes a decrease of the hydrodynamic radius (R(h)) of the nanogel complex particle but (ii) the R(h) of the PDDA complex remains unchanged at Mmr < 0.8. Taking these into account, we discussed the conductometric results in terms of the random model (RM) and all-or-none model (AONM) in polyelectrolyte complex formations. It was found that KPVS and PDDA yield a water-dispersible SPEC particle at each Mmr, accompanying the uptake of counterions (K(+) and Cl(-)) by the complex. This uptake amount was about 7% of the stoichiometric release of the counterions. In the nanogel system, a complete release of the counterions was observed at Mmr < 0.2 at which one or two KPVS chains were bound to a CPENG particle, but further KPVS binding led to about 20% of the counterion uptake to maintain electroneutrality. Thus, we suggest that the counterion uptake becomes a key factor to understand the water dispersibility of SPEC particles.     

Studies on the Synthesis and Properties of Temperature Responsive and Biodegradable Hydrogels

Novel linear poly(NIPA‐co‐CL) copolymers have been synthesized by radical copolymerization of N‐isopropylacrylamide (NIPA) and 2‐methylene‐1,3‐dioxepane (MDO). The structure of copolymers was confirmed by ¹H NMR and IR spectroscopy. Cross‐linked poly(NIPA‐co‐CL) hydrogels have also been prepared in toluene using N,N′‐methylenebisacrylamide as cross‐linking agent. The hydrogels thus obtained exhibit good temperature response and are biodegradable in the presence of proteinase K.

Temperature influence on the enzymatic degradation by proteinase K of poly(NIPA‐co‐CL) hydrogel (G‐60).     

Speciation,separation and enrichment of Cr(III) and Cr(VI) in environmental samples by ion-pair solvent extraction using a β-diketone ligand

A simple speciation, separation and enrichment method has been developed for the determination of Cr(III) and Cr(VI) ions in different samples by ion-pair solvent extraction with a β-diketone ligand, 2-(4-methoxybenzoyl)-N′-benzylidene-3-(4-methoxyphenyl)-3-oxo-N-phenyl-propono hydrazide (MBMP). Cr(III) was separated from Cr(VI) as Cr(III)-(MBMP)-perchlorate ternary ion-pair complex. The influences of various analytical parameters including pH, amount of reagent, shaking time, sample volume and ionic strength on the recovery of Cr(III) and/or Cr(VI) were investigated. Total chromium was obtained after reducing Cr(VI) to Cr(III) with NH₂OH?·?HCl. Recoveries were found to be higher than 95% and the relative standard deviation (RSD) was less than 2%. The method detection limit based on 3σ criterion for Cr(III) was found to be 0.32?µg?L^?1. The formed ternary ion-pair complex, Cr(III)?:?MBMP?:?2ClO₄, has a molar ratio of 1?:?1?:?2. The developed method has been applied successfully to the speciation of chromium in various natural water, soil, sediment and hair samples with satisfactory results.     

Formation of intra- and interparticle polyelectrolyte complexes between cationic nanogel and strong polyanion

Polyelectrolyte complex formation of a strong polyanion, potassium poly(vinyl alcohol) sulfate (KPVS), with positively charged nanogels was studied at 25 degrees C in aqueous solutions with different KCl concentrations (C(s)) as a function of the polyion-nanogel mixing ratio based on moles of anions versus cations. Used as the gel sample was a polyampholytic nanogel consisting of lightly cross-linked terpolymer chains of N-isopropylacrylamide, acrylic acid, and 1-vinylimidazole; thus, the complexation was performed at pH 3 at which the imidazole groups are fully protonated to generate positive charges. Turbidimetric titration was employed to vary the mixing ratio. Also employed for studies of the resulting complexes at different stages of the titration were dynamic light scattering (DLS) and static light scattering (SLS) techniques. It was found from the titration as well as DLS and SLS that there is a critical mixing ratio (cmr) at which both the size and molar mass of the complexed gel particles abruptly increase. The value of the cmr at C(s) = 0 or 0.01 M (mol/L) was observed at approximately 1:1 mixing ratio of anions versus cations but at lower mixing ratios than the 1:1 ratio under conditions of C(s) = 0.05 and 0.1 M. At the mixing ratios less than the cmr, the molar mass of the complex agrees with that of one gel particle with the calculated amount of the bound KPVS ions, indicating the formation of an "intraparticle" KPVS-nanogel complex, by the aggregation of which an "interparticle" complex is formed at the cmr. During the process of the intraparticle complex formation, both the hydrodynamic radius by DLS and the radius gyration by SLS decreased with increasing mixing ratio, demonstrating the gel collapse due to the complexation. At C(s) = 0 or 0.01 M and under conditions where the amount of KPVS bindings was less than half of the nanogel cations, however, the decrease of the hydrodynamic radius was very small, while the radius gyration fell monotonically. These results were discussed in connection with a collapse of dangling chains attached to the nanogel surface by the binding of KPVS.     

Light scattering study of complex formation between protein and polyelectrolyte at various ionic strengths

Formation of protein-polyelectrolyte complexes (PPCs) between bovine serum albumin (BSA) and potassium poly (vinyl alcohol) sulfate (KPVS) was studied at pH 3 as a function of ionic strength. Turbidimetric titration was employed by a combination of dynamic light scattering (DLS) and electrophoretic light scattering (ELS). The formal charge (Z(PPC)) of the resulting PPCs at different ionic strengths were estimated from ELS data by assuming the free draining and the non-free draining model. The radius of a BSA molecule in the complex was used in the former model for calculation of Z(PPC) with the Henry's equation, while in the latter case the hydrodynamic radius of a PPC particle determined from DLS was employed. The results obtained were compared with the Z(PPC) values calculated using a relation of Z(PPC)=n(b)Z(BSA)+alphaZ(KPVS), where Z(BSA) (> or =0) and Z(KPVS) (< or =0) denote the formal charge of BSA and KPVS, respectively. Moreover, n(b) is the number of bound proteins per complex composed of alpha polymer chains. It was suggested that the PPC between BSA and KPVS behaves as a free draining molecule during the electrophoresis, at least at a high ionic strength. Also suggested is that the PPC formation at low ionic strength follows a 1:1 stoichiometry in the charge neutralization.     

Modification of Poly‐ and Oligosaccharides with Os(VI)pyridine. Voltammetry of the Os(VI) Adducts Obtained by Ligand Exchange

Polysaccharides and oligosaccharides were modified with Os(VI)pyridine complex followed by ligand exchange with different ligands such as 2,2′‐bipyridine or N,N,N′,N′‐tetramethylethylenediamine. The time of the modification was much shorter (taking about 15 min) then direct modification with the given Os(VI) complex. The resulting saccharide adducts were analyzed by voltammetric methods at carbon and mercury electrodes. The results showed that the proposed technique gives promise for a new approach to analysis of glycoproteins.     

Facile synthesis of N‐vinylimidazole‐based hydrogels via frontal polymerization and investigation of their performance on adsorption of copper ions

We report a new facile strategy for quickly synthesizing pH sensitive poly(VI‐co‐HEA) hydrogels (VI = N‐vinylimidazole; HEA = 2‐hydroxyethyl acrylate) by frontal polymerization. The appropriate amounts of VI, HEA, and ammonium persulfate (APS)/N,N,N′,N′‐tetramethylethylenediamine (TMEDA) couple redox initiator were mixed together at ambient temperature in the presence of glycerol as the solvent medium. Frontal polymerization (FP) was initiated by heating the upper side of the mixture with a soldering iron. Once initiated, no further energy was required for the polymerization to occur. The dependence of the front velocity and front temperature on the VI/HEA weight ratios were investigated. The pH sensitive behavior, morphology, and heavy metal removal study of poly(VI‐co‐HEA) hydrogels prepared via FP were comparatively investigated on the basis of swelling measurements, scanning electron microscopy, and inductively coupling plasma spectrometer. Results show that the poly(VI‐co‐HEA) hydrogels prepared via FP exhibit good pH sensitivity and adsorption capacity. The FP can be exploited as an alternative means for synthesis of pH sensitive hydrogels in a fast and efficient way. The as‐prepared hydrogels can be applied to remove heavy metals. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4005–4012, 2010     

Solvent extraction and spectrophotometric determination of uranium(VI) with pyridine-2-carboxaldehyde 2-hydroxybenzoylhydrazone

Pyridine-2-carboxaldehyde 2-hydroxybenzoylhydrazone (PAHB) is proposed as an extractant for the separation and spectrophotometric determination of uranium(VI). The optimum extraction conditions have been evaluated by studying various parameters such as pH, diluents, equilibration time and reagent concentration. PAHB forms yellow colored complex with uranium(VI) in the pH range of 3.5-4.6 which can be extracted by isobutyl methyl ketone. The extracted complex exhibits an absorption maximum at 375 nm. Beer's law was obeyed in the concentration range 1.0-5.6 ppm of uranium(VI). The nature of the extracted species (1:2) was determined by log D-log c plot. The proposed method permits selective separation of uranium(VI) from its binary mixtures. The method is also applied for the estimation of uranium in multicomponent mixtures and monazite sand.     

Radical copolymerization of N-isopropylacrylamide with anhydrides of maleic and citraconic acids

Radical-initiated copolymerization of N-isopropylacrylamide (NIPA) with maleic (MA) and citraconic (CA) anhydrides was carried out in the presence of 2,2^′-azobisisobutyronitrile (AIBN) as an initiator in 1,4-dioxane at 65 °C under nitrogen atmosphere. Structure and monomer unit compositon of the copolymers obtained from a wide range of monomer feed were determined by elemental analysis (content of N for NIPA units), Fourier transform infrared and ¹H NMR spectroscopy. Monomer reactivity ratios for NIPA (M₁)-MA (M₂) and NIPA (M₁)-CA (M₂) pairs were determined by Kelen-Tüdõs (KT) and non-linear regression (NLR) methods using elemental and ¹H NMR spectroscopy analyses data. They are r₁=0.45 and r₂=0.08 (KT, N analysis), r₁=0.44 and r₂=0.10 (KT, ¹H NMR), r₁=0.45 and r₂=0.078 (NLR) for NIPA-MA monomer pair and r₁=0.52 and r₂=0.02, r₁=0.44 and r₂=0.04, r₁=0.51 and r₂=0.014 for NIPA-CA monomer pair, respectively. Observed tendency towards alternating copolymerization at ?50 mol% NIPA concentration in monomer feed and relatively high activity of NIPA growing radical was explained by H-bond formation between CO (anhydride) and NH (amide) fragments during chain growth reactions. Intrinsic viscosity, molecular weight and thermal behaviour of the synthesized copolymers were found to depend on the type of comonomer and the amount of NIPA units in the copolymers. These functional amphiphilic copolymers containing anion- and cation-active groups show both temperature and pH sensitivity and can be used for biological purposes as physiologically active macromolecular systems.     

Ultrafast Responsive Poly‐ (N‐isopropylacrylamide) Gel Produced by Cryostructuring of Self‐crosslinkable Polymer Microgels

A macroporous material composed of closely aggregated particles was prepared by cryo‐structuration of N‐isopropylacrylamide‐co‐N‐hydroxymethylacrylamide (NIPA‐co‐HMAm) particle suspensions. The formed structure was maintained by the formation of covalent bonds through self‐crosslinking between the particles while the system was in a semi‐frozen state thus avoiding the need to freeze‐dry the sample. This resulted in macroporous structure composed of closely aggregated thermoresponsive particles which exhibit an ultrafast temperature response. The response rate can be attributed both to the macroporous structure as well as the fast responsive properties of the individual particles.

     

Potentiometric titration behavior of poly(acrylic acid) within a cross-linked polymer network having amide groups

This study aimed to investigate the effect of COOH group distribution within a polymer network having amide groups, with which the COOH could form hydrogen bonds. We employed here two polyelectrolyte gels composed of N-isopropylacrylamide (NIPA) networks, either copolymerized with acrylic acid (AA) or within which poly(acrylic acid) (PAA) was entrapped. Both gels (AA–NIPA ∼ 1:4 mol/mol) were prepared by aqueous red-ox polymerization with N,N’-methylenebisacrylamide as the cross-linker. Finely divided gels in NaCl solutions (0.025 and 0.1 M) were titrated with NaOH and back-titrated with HCl at 25 °C. The results of the copolymer gel (CG) agreed well with those of a linear copolymer and a nanoscale gel which had a similar AA content to CG. However, marked differences were observed in the titration behaviors of the AA-copolymerized and PAA-entrapped gels, mainly due to the hydrogen bonding between the entrapped PAA chain and its surrounding NIPA network.     

A facile fabrication of MOF for selective removal of chromium (III) from aqueous solution

A simple method for fabricating a metal organic framework (MOF: HKUST-1) as sorbent for selective removal of chromium (III) from aqueous solution is discussed. The structure and morphology of HKUST-1 was identified by fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), the powder X-ray diffraction (XRD) and N₂ adsorption-desorption (BET) analysis. Its removal process of chromium (III) and chromium (VI) on HKUST-1 was assessed systematically under various conditions such as pH value, shaking time and initial concentration of chromium (III). At pH 6.0–8.0, HKUST-1 were selective towards chromium (III) but hardly chromium (VI). Kinetic parameters fitted well with pseudo-second-order model and adsorption progress was described by Langmuir isotherm equations and spontaneous and endothermic according to the results of thermodynamics studies (?G?<?0, ?H?>?0, ?S?>?0).     

Spectroscopic study of the complexes of poly(N-methacryloyl-L-asparagine) with palladium (II)

The complexes formed between palladium (II) and a polymeric ligand derived from L -asparagine, poly(N-methacryloyl-L -asparagine) (PNMAsn) have been investigated by electronic absorption and circular dichroism. N-isobutyroyl-L -asparagine (NIBAsn) was also synthesized and studied with the purpose of comparison with its polymeric analog. NIBAsn gives two complexes: at low pH, an optically active complex between one carboxylate and one secondary amide nitrogen (so-called 1N complex), and at higher pH, a 2N complex involving the primary and secondary amide group. This complex is also optically active. PNMAsn gives at low pH a 1N complex similar to that of NIBAsn, but at higher pH the 2N complex is formed between two carboxylate groups and two secondary amide groups of two different side chains of the polymer. At very high pH this 2N complex is hydrolyzed, i.e., the carboxylate-palladium bonds are replaced by hydroxyle-palladium bonds, and the complex becomes optically inactive.     

Determination of the acid dissociation constants of N-carboxymethyl-N-(p-hydroxy phenyl carbamoylmethyl)-2,3-dihydroxy-5-carbomethoxy benzylamine and the stability constants of its metal complexes

The acid dissociation constants of N-carboxymethyl-N-(p-hydroxy phenyl carbamoyl-methyl)-2,3-dihydroxy-5-carbomethoxy benzylamine (CHDCB) and the stability constants of its 1:1 complexes with alkaline earth, Cd(II), Co(II), Ni(II), Cu(II), Zn(II), Fe(III), Th(IV) and U(VI) ions have been determined at 25.0 ± 0.1 °C and at an ionic strength of 0.1 (KNO₃) by pH titration method. The probable coordination sites have also been discussed.