Protonated Amine Groups Research Articles

Carbonaceous materials as catalyst supports for the enantioselective hydrogenation of (E)-α-phenylcinnamic acid: Effect of the support acidity

A systematic comparative study of carbonaceous materials as catalyst supports for the asymmetric heterogeneous hydrogenation of (E)-α-phenylcinnamic acid (PCA) was performed to investigate the influence of the supports on the enantioselectivity. A series of Pd-based catalysts supported on activated carbon (AC), graphene oxide (GO), or carbon nanotubes (CNTs) was prepared using deposition methods. The hydrogenation reactions of PCA were conducted with/without the pretreatment of the prepared catalysts, and the results showed a significant drop of enantiomeric excess (ee) when the Pd/GO catalyst was used (27%) compared to that obtained from the Pd/AC (70%) and Pd/CNTs (66%) catalysts. This drop of ee values was assigned to the abundance of acidic sites present on the Pd/GO catalyst, as revealed by TGA, FT-IR, and TPD–NH3 analyses. The effect of the support acidity on the ee was ascribed to the preferential adsorption mode of cinchonidine (CD) on the GO surface via electrostatic interactions between the negatively charged oxygen functional groups present on the GO surface and the positively protonated amine groups of the CD molecule.

Spectroscopic studies of the equilibrium between complexes of lasalocid acid with propargylamine and metal cations

The molecular structure of 1:1 complex formed between the naturally occurring polyether ionophore, called lasalocid acid (LAS) and propargylamine (PROP) is studied by X-ray, FT-IR, 1H NMR, 13C NMR and ESI-MS methods. The complex formed between deprotonated LAS acid and protonated PROP molecule is stabilized by intra- and inter-molecular hydrogen bonds. The protons of the protonated amine group are hydrogen bonded to etheric and hydroxyl oxygen atoms of the LAS anion. The similarity of the FT-IR spectra of the LAS–PROP complex in solid state and in solution demonstrated that the molecular structures of the complex in both states are comparable. It is shown that LAS in solution can form concurrent complexes with metal cations (M=Li+, Na+, K+) and amine existing in equilibrium. Analysis of the structures of lasalocid complexes is important for a better understanding of the antibacterial and anticancer properties of lasalocid acid.

Study on the coordination structure of pt sorbed on bacterial cells using x-ray absorption fine structure spectroscopy.

Biosorption has been intensively investigated as a promising technology for the recovery of precious metals from solution. However, the detailed mechanism responsible for the biosorption of Pt on a biomass is not fully understood because of a lack of spectroscopic studies. We applied X-ray absorption fine structure spectroscopy to elucidate the coordination structure of Pt sorbed on bacterial cells. We examined the sorption of Pt(II) and Pt(IV) species on bacterial cells of Bacillus subtilis and Shewanella putrefaciens in NaCl solutions. X-ray absorption near-edge structure and extended X-ray absorption fine structure (EXAFS) of Pt-sorbed bacteria suggested that Pt(IV) was reduced to Pt(II) on the cell’s surface, even in the absence of an organic material as an exogenous electron donor. EXAFS spectra demonstrated that Pt sorbed on bacterial cells has a fourfold coordination of chlorine ions, similar to PtCl4 2-, which indicated that sorption on the protonated amine groups of the bacterial cells. This work clearly demonstrated the coordination structure of Pt sorbed on bacterial cells. The findings of this study will contribute to the understanding of Pt biosorption on biomass, and facilitate the development of recovery methods for rare metals using biosorbent materials.

Surface geometry of tryptophan adsorbed on gold colloidal nanoparticles

Two distinct surface-enhanced Raman (SER) spectra of tryptophan depending on the surface adsorption geometry were obtained by using colloidal gold nanoparticles reduced by borohydride and citrate ions. According to the vibrational assignments based on DFT simulations, the SER spectra of tryptamine and 3-indolepropionic acid, and the pH dependence of tryptophan SER spectrum, we found that some indole ring vibrations are very sensitive to the surface adsorption geometry of the molecules. With citrate-reduced gold colloids, tryptophan and related molecules mainly adsorb via the protonated amine group while maintaining a perpendicular geometry of the indole ring to the surface. However, a flat geometry of the indole ring to the surface is preferred on the borohydride-reduced gold colloids where the surface adsorption occurs mainly through the indole ring π electrons. By comparing our results with previous reports on the SER spectra of tryptophan on various silver and gold surfaces, we propose a general adsorption model of tryptophan on metal nanosurfaces.

Bisphosphonates enhance bacterial adhesion and biofilm formation on bone hydroxyapatite

BackgroundBecause of the suspicion that bisphosphonates enhance bacterial colonization, this study evaluated adhesion and biofilm formation by Streptococcus mutans 25175, Staphylococcus aureus 6538, and Pseudomonas aeruginosa 14454 reference strains on hydroxyapatite coated with clodronate, pamidronate, or zoledronate. Material and methodsBacterial strains were cultured on bisphosphonate-coated and noncoated hydroxyapatite discs. After incubation, nonadhered bacteria were removed by centrifugation. Biofilm formation was confirmed by scanning electron microscopy. Bacterial colonization was estimated using quantitative cultures compared by means with Kruskal–Wallis and post-hoc Student-Newman-Keuls tests. Modeling of the interactions between bisphosphonates and hydroxyapatite was performed using the Density Functional Theory method. ResultsBacterial colonization of the hydroxyapatite discs was significantly higher for all tested strains in the presence of bisphosphonates vs. controls. Adherence in the presence of pamidronate was higher than with other bisphosphonates. Density Functional Theory analysis showed that the protonated amine group of pamidronate, which are not present in clodronate or zoledronate, forms two additional hydrogen bonds with hydroxyapatite. Moreover, the reactive cationic amino group of pamidronate may attract bacteria by direct electrostatic interaction. ConclusionIncreased bacterial adhesion and biofilm formation can promote osteomyelitis, cause failure of dental implants or bisphosphonate-coated joint prostheses, and complicate bone surgery in patients on bisphosphonates.

Electrocatalytic Hydrogen Production by [Ni(7PPh2NH)2]2+: Removing the Distinction Between Endo- and Exo-Protonation Sites

A new Ni(II) complex, [Ni(7PPh2NH)2H]3+ (7PPh2NH = 3,6-diphenyl-1-aza-3,6-diphosphacycloheptane), has been synthesized, and its electrochemical properties have been reported. The 7PPh2NH ligand features an NH, ensuring properly positioned protonated amine groups (N–H+) for electrocatalysis, regardless of whether protonation occurs exo or endo to the metal center. The compound is an electrocatalyst for H2 production in the presence of organic acids (pKa range 10–13 in CH3CN), with turnover frequencies ranging from 160 to 780 s–1 at overpotentials between 320 and 470 mV, as measured at the potential of the catalytic wave. In stark contrast to [Ni(PPh2NR′2)2]2+ (PPh2NR′2 = 3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) and other [Ni(7PPh2NR′)2]2+ complexes, catalytic turnover frequencies for H2 production by [Ni(7PPh2NH)2]2+ do not show catalytic rate enhancement upon the addition of H2O. This finding supports the assertion that [Ni(7PPh2NH)2]2+ eliminates the distinction between the endo- and exo-protonation isomers.

Large-Area, Highly Ordered Array of Graphitic Carbon Materials Using Surface Active Chitosan Prepatterns.

We demonstrate that chitosan prepatterns can generate not only highly periodic DNA pattern but also various types of graphitic carbon materials such as single-walled carbon nanotubes (SWNTs), graphene oxide (GO) and reduced graphene oxide (RGO). Scanning electron microscopy (SEM), fluorescence imaging and Raman spectroscopic results revealed that the graphitic carbon materials were selectively deposited on the surface of the periodic chitosan patterns by the electrostatic interaction between protonated amine groups of chitosan and the negative charged carbon materials. One proof-of-concept application of the system to the fabrication of electrical devices based on the micropatterns of SWNTs and RGO was also demonstrated. The strategy to use highly surface active chitosan pattern that can easily fabricate highly periodic pattern via a variety of lithographic tools may pave the way for the production of periodic arrays of graphitic carbon materials for large area device integration.

Combination of cathodic reduction with adsorption for accelerated removal of Cr(VI) through reticulated vitreous carbon electrodes modified with sulfuric acid–glycine co-doped polyaniline

Improving the reduction kinetics is crucial in the electroreduction process of Cr(VI). In this study, we developed a novel adsorption–electroreduction system for accelerated removal of Cr(VI) by employing reticulated vitreous carbon electrode modified with sulfuric acid–glycine co-doped polyaniline (RVC/PANI-SA-GLY). Firstly, response surface methodology confirmed the optimum polymerization condition of co-doped polyaniline for modifying electrodes (Aniline, sulfuric acid and glycine, respectively, of 0.2mol/L, 0.85mol/L, 0.93mol/L) when untraditional dopant glycine was added. Subsequently, RVC/PANI-SA-GLY showed higher Cr(VI) removal percentages in electroreduction experiments over RVC electrode modified with sulfuric acid doped polyaniline (RVC/PANI-SA) and bare RVC electrode. In contrast to RVC/PANI-SA, the improvement by RVC/PANI-SA-GLY was more significant and especially obvious at more negative potential, lower initial Cr(VI) concentration, relatively less acidic solution and higher current densities, best achieving 7.84% higher removal efficiency with entire Cr(VI) eliminated after 900s. Current efficiencies were likewise enhanced by RVC/PANI-SA-GLY under quite negative potentials. Fourier transform infrared (FTIR) and energy dispersive spectrometer (EDS) analysis revealed a possible adsorption–reduction mechanism of RVC/PANI-SA-GLY, which greatly contributed to the faster reduction kinetics and was probably relative to the absorption between protonated amine groups of glycine and HCrO4−. Eventually, the stability of RVC/PANI-SA-GLY was proven relatively satisfactory.

亜鉛めっき上に形成したアミノシラン－リン酸皮膜の電気化学的挙動

The effects of phosphoric acid in a 3-amino-propyltriethoxy silane (3-APS) coating system on electro-galvanized steel were examined in terms of the phosphoric acid effect on corrosion resistance. Acetic acid and 3-glycidoxy-propyltriethoxy silane (3-GPS) were also used for comparison of corrosion protection performance to that of phosphoric acid and 3-APS. The corrosion resistance mechanism was analyzed using electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS).Adding phosphoric acid to the solution of 3-APS improved corrosion protection when the coating was immersed in 0.6 mol/dm3 NaCl. Results show that the addition of phosphoric acid had the greatest anti-corrosion effect and that it suppressed electrolyte uptake effectively. The roles of phosphoric acid were explained by the formation of protonated amine group (-NH3+) and Si-O-Si bonds in the coating. These coating changes are expected to produce the superior corrosion resistance. Acetic acid had no effect on the corrosion resistance compared to phosphoric acid. Results show that 3-GPS mixed with phosphoric acid, which has no amine group in the molecule, was inferior to the 3-APS and phosphoric acid composite coating.

Stability and Solution Structure of Binary and Ternary Cu(II) Complexes with l-Glutamic Acid and Diamines as Well as Adducts in Metal-Free Systems in Aqueous Solution.

Binary and ternary complexes of copper(II) with l-glutamic acid (Glu) and diamines 1,3-diaminopropane and 1,4-diaminobutane, putrescine (tn, Put), as well as adducts formed in the metal-free systems, have been investigated in aqueous solutions. The types of complexes formed and their overall stability constants were established on the basis of computer analysis of potentiometric results. The reaction centers and the modes of interaction were identified on the basis of spectroscopic studies (NMR, Vis and EPR). In the ligands studied the interaction centers are the oxygen atoms from carboxyl groups, nitrogen atom from the amine group of glutamic acid and the nitrogen atoms from amine groups of the diamines. The centers of noncovalent interaction in the adducts that formed in the metal-free systems are also potential sites of metal ion coordination, which is important in biological systems. In the Glu–diamine systems, molecular complexes of the (Glu)Hx(diamine) type are formed. In the (Glu)H2(tn) adduct, in contrast to the corresponding complex with Put, an inversion effect was observed in which the first deprotonated amine group of tn became a negative reaction center and interacted with the protonated amine groups from Glu. Depending on the pH, the amine groups from the diamine can be either a positive or a negative center of interaction. In the Cu(Glu)2 species the first molecule of Glu takes part in metallation through all functional groups, whereas the second molecule makes a “glycine-like” coordination with the Cu(II) ions that is only through two functional groups. According to the results, introduction of Cu(II) ions into metal-free systems (Glu–diamine) changes the character of interactions between the bioligands in the complexes that form in Cu(II)–Glu–diamine systems and no ML…L′ type complexes are formed. However, in the ternary systems only the heteroligand complexes Cu(Glu)(diamine) and Cu(Glu)(diamine)(OH) are observed.

Antimicrobial Activity of Chitosan Derivatives Containing N-Quaternized Moieties in Its Backbone: A Review

Chitosan, which is derived from a deacetylation reaction of chitin, has attractive antimicrobial activity. However, chitosan applications as a biocide are only effective in acidic medium due to its low solubility in neutral and basic conditions. Also, the positive charges carried by the protonated amine groups of chitosan (in acidic conditions) that are the driving force for its solubilization are also associated with its antimicrobial activity. Therefore, chemical modifications of chitosan are required to enhance its solubility and broaden the spectrum of its applications, including as biocide. Quaternization on the nitrogen atom of chitosan is the most used route to render water-soluble chitosan-derivatives, especially at physiological pH conditions. Recent reports in the literature demonstrate that such chitosan-derivatives present excellent antimicrobial activity due to permanent positive charge on nitrogen atoms side-bonded to the polymer backbone. This review presents some relevant work regarding the use of quaternized chitosan-derivatives obtained by different synthetic paths in applications as antimicrobial agents.

Green synthesis and antimicrobial activity of silver chloride nanoparticles stabilized with chitosan oligomer.

Nanocrystalline silver (Ag) and Ag containing nanostructure synthesized using various methods have been studied for their antimicrobial, wound healing, and anti-inflammatory efficacy. Among these, crystalline silver chloride (AgCl) nanostructures exhibit desirable properties for biological and biomedical applications. However, most of them are synthesized using hazardous agents and organic solvents, which has been limited for application in the biological field. A simple and environmentally friendly method was demonstrated for AgCl nanoparticles stabilized with chitosan oligomer (CHI-AgCl NPs) as both a resource of Cl ions and stabilizing agent with expectations of synergistic effects. The CHI-AgCl NPs stabilized by the chitosan oligomer had spherical morphology with a mean diameter of 42±15nm. Ag ions precipitated as AgCl in presence of Cl ions, which remained in the protonated amine group after HCl hydrolysis of the chitosan. Moreover, much of the amine and hydroxyl group bound to the AgCl NPs for growth and stabilization. These nanoparticles were characterized via various spectroscopic techniques, including UV-Vis spectrophotometry, X-ray photoelectron spectrometry, X-ray diffractometry, and transmission electron microscopy.

A Metal-Ion Adsorbent Based on Composite of Graphene Oxide/Poly (1-(3-aminopropyl) Pyrrole)

A novel metal-ion adsorbent was developed based on graphene oxide (GO) and poly (1-(3-aminopropyl) pyrrole. Firstly, GO was covalently functionalized by 1-(3-aminopropyl) pyrrole (APP) monomer by an esterification reaction between the carboxyl groups of GO and the amine groups of APP. Subsequently, a GO/poly (1-(3-aminopropyl) pyrrole) (poly (GO-APP)) composite was prepared by in situ crosslinking polymerization.The chemical structure of poly (GO-APP) composite was determined by a series of characterization methods, such as Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) and Thermogravimetric analysis (TGA).The poly (GO-APP) was a hard solid material like a coal (Figure a), which is due to the crosslinked polymerization between GO and polymer. In this composite system, the GO is a crosslinking agent like a polyfunctional monomer, which can turn the linear polymer into crosslinked network polymer to increase the stiffness, strength and stability of poly (GO-APP).This poly (GO-APP) composite is used for the adsorption of metal ions. As shown in Figure b, the absorption capacity of poly (GO-APP) was much larger than that of GO. The sorption of metal ions is based on both nitrogen and oxygen functional groups. The oxygen-containing functional groups in GO and the protonated amine groups in APP can bind to cations easily. Moreover, the chemical affinity of metal ions for amine groups is stronger than that for oxygen-containing functional groups. Therefore, the absorption capacity increases with the content of APP monomer.Besides, the poly (GO-APP) showed a conducting property due to the conjugated π-π system in the main chain of copolymer, which will greatly expand the application fields of poly (GO-APP) composite.

Kinetic and thermodynamic evaluation of phosphate ions binding onto sevelamer hydrochloride

Sevelamer hydrochloride is the first non-aluminium, non-calcium-based phosphate binder developed for the management of hyperphosphatemia in end stage renal diseases. It is a synthetic ion-exchange polymer which binds and removes phosphate ions due to the high content of cationic charge associated with protonated amine groups on the polymer matrix. This is the first in-depth study investigating phosphate removal in vitro from aqueous solutions using commercially available sevelamer hydrochloride at physiological conditions of phosphate level, pH and temperature. The kinetic and thermodynamic parameters of phosphate binding onto the sevelamer hydrochloride particles were evaluated in order to define the binding process. A series of kinetic studies were carried out in order to delineate the effect of initial phosphate concentration, absorbent dose and temperature on the rate of binding. The results were analysed using three kinetic models with the best-fit of the experimental data obtained using a pseudo-second order model. Thermodynamic parameters provide in-depth information on inherent energetic changes that are associated with binding. Free energy ΔG°, enthalpy ΔH°, and entropy ΔS° changes were calculated in this study in order to assess the relationship of these parameters to polymer morphology. The binding reaction was found to be a spontaneous endothermic process with increasing entropy at the solid–liquid interface.

Protonation Pattern, Tautomerism, Conformerism, and Physicochemical Analysis in New Crystal Forms of the Antibiotic Doxycycline

Doxycycline (DOX) is a tetracycline class drug that is used worldwide as a broad-spectrum antibiotic. Although its clinical importance and use have been known since the 1960s, only four crystal forms have been reported until now. These are doxycycline hyclate (DOX.HYC), which is a hydrochloride salt hemiethanolate-hemihydrate; its isomorphous hydrobromide, hydrochloride salt dihydrate (DOX·HCl·2H2O); and doxycycline monohydrate (DOX·H2O). Here we report the preparation of two new multicomponent molecular crystal forms of doxycycline and their crystal structure determination along with their melting temperature, aqueous solubility, and time-dependent dissolution profile. These crystal forms are a hydronitrate salt hemihydrate (DOX·HNO3·0.5H2O) and an acetic acid solvate dihydrate (DOX·HAc·2H2O). The two new doxycycline crystal forms were compared with known forms, including DOX·HCl·2H2O, the structure of which was redetermined in this work. The structural variability of the protonation patterns, tautomerism of the keto–enolate moieties, and conformation of the amide groups was observed for these compounds. While intramolecular rings assembled through resonance-assisted hydrogen bond (RAHB) were observed in both fused keto–enol moieties of all structures, DOX·HCl·2H2O and DOX·HNO3·0.5H2O have another RAHB encompassing the protonated amide carbonyl oxygen and the enolate oxygen. These two crystal forms have a net positive charge on their drug molecule as DOX·HYC. They crystallize with the N,N-dimethylamine and amide carbonyl groups protonated and the neighboring hydroxyl group deprotonated. DOX, by contrast, crystallizes as a zwitterion in DOX·HAc·2H2O similarly to DOX·H2O. Their amide carbonyl oxygens are not protonated, which differs from the salt forms. DOX·HNO3·0.5H2O presents as two tautomers that are similar to those of DOX·HYC, namely, T1, in which the enolate oxygen is next to the protonated amine group, and T2, with the carbonyl oxygen close to the protonated amine group. These tautomers also differ in their amide conformations due to a rotation of ca. 180° on the C–C bond axis of the amide group, which directs the protonated carbonyl oxygen toward the enolate oxygen. DOX·HCl·2H2O has only one T1-like tautomer and therefore only one amide conformation similar to that of T1. A T1-like keto–enolate tautomer is present in DOX·HAc·2H2O, which exhibits an amide conformation similar to that of T2. Thermal (DSC and TG) and infrared analysis and equilibrium solubility, dissolution profiles, and forced degradation studies were performed to both new and known DOX forms. The results were correlated with their structural features. DOX·HNO3·0.5H2O was the most soluble form. This new form was also more stable than the commercial DOX·HYC in the oxidation test and more stable than commercial DOX·H2O against acid and basic hydrolysis and in the photostability study. DOX·HNO3·0.5H2O and DOX·HYC (commercial form) were observed to have similar drug release behaviors from capsules (F2 > 50) and therefore they could be interchangeable.

On the Mechanism of Bifunctional Squaramide‐Catalyzed Organocatalytic Michael Addition: A Protonated Catalyst as an Oxyanion Hole

A joint experimental-theoretical study of a bifunctional squaramide-amine-catalyzed Michael addition reaction between 1,3-dioxo nucleophiles and nitrostyrene has been undertaken to gain insight into the nature of bifunctional organocatalytic activation. For this highly stereoselective reaction, three previously proposed mechanistic scenarios for the critical CC bond-formation step were examined. Accordingly, the formation of the major stereoisomeric products is most plausible by one of the bifunctional pathways that involve electrophile activation by the protonated amine group of the catalyst. However, some of the minor product isomers are also accessible through alternative reaction routes. Structural analysis of transition states points to the structural invariance of certain fragments of the transition state, such as the protonated catalyst and the anionic fragment of approaching reactants. Our topological analysis provides deeper insight and a more general understanding of bifunctional noncovalent organocatalysis.

Preparation and Characterization of Gold Nanoparticles in Chitosan Suspension by One-Pot Chemical Reduction Method

Gold nanoparticles were synthesized in chitosan suspension by one-pot chemical reduction method without any chemical reducing reagent. In aqueous acidic medium, chitosan exhibits polycationic nature due to protonation of amine groups of each glucosamine repeating units. The adsorption of AuCl4- ions occurs on chitosan through electrostatic attraction and further reduction of Au3+ to Au0 proceeds through a three electron transfer mechanism by oxidation of protonated amine groups of chitosan chain. The change of color from dirty yellow to intense red indicates the formation of gold nanoparticles in chitosan suspension which acts as both reducing and stabilizing agent. Characterization techniques such as UV-VIS, FTIR, Zeta potential measurement, FESEM and TEM were carried out in order to examine the reduction and stabilization phenomena rendered by chitosan.

2-Methyl-benzene-1,3-di-ammonium dinitrate.

In the crystal structure of the title salt, C7H12N2 2+·2NO3 −, the nitrate ions are located in the vicinity of the protonated amine groups, accepting strong N—H⋯O hydrogen bonds. Each ammonium group is involved in a total of three such inter­actions with neighbouring nitrate ions, generating a three-dimensional network. In addition, there are π–π inter­actions between the aromatic rings of centrosymmetrically related di­ammonium moieties, with a centroid–centroid distance of 3.682 (1) Å.

Biofouling resistance of reverse osmosis membrane modified with polydopamine

It has been reported that surface modification with polydopamine (PDA) increases the hydrophilicity and the negative charge density of membrane surfaces, which improves their antifouling potential against organic foulants. Thus, in this paper, we attempted to modify a reverse osmosis (RO) membrane with PDA to improve antibiofouling potential. The deposition of PDA was confirmed by several methods, including X-ray photoelectron and Fourier-transform infrared spectroscopy. However, increases in hydrophilicity and negative charge density were not clearly observed. Nevertheless, the improvement of antibiofouling properties was confirmed by cross-flow filtration of a bacterial (Pseudomonas putida) suspension. The high antiadhesion property of the PDA-modified membrane was confirmed by scanning electron microscope surface images after 1200minute continuous filtration of the bacterial suspension. In addition, it was confirmed by using a shake flask test with Escherichia coli that the PDA-modified membrane had a bactericidal property. Using shake flask tests in the different pH solutions, it was concluded that the antibiofouling property of PDA-modified membranes could be attributed to the bactericidal property of protonated amine groups of PDA deposited on the membrane surface.

Introducing small cationic groups into 4-armed PLLA–PEG copolymers leads to preferred micellization over thermo-reversible gelation

Starting from bis-MPA, PEG–PLLA triblock copolymers (bis-MPA-(PLLA–PEG)2), comprising a central N-hydroxysuccinimide active ester, were synthesized. Reacting the corresponding active ester with α,ω-diamines afforded four-armed (PEG–PLLA)2–R–(PLLA–PEG)2 copolymers with central α,ω-diamide groups (R). Applying the α,ω-diamines, hexamethylene-diamine, spermine or norspermidine none, one or two secondary amine groups, respectively, were introduced into the linking moiety R. Whereas a copolymer containing no secondary amine groups showed fully thermo-reversible gelation behavior, copolymers comprising a central moiety containing one or two secondary amine groups retained the ‘sol’ state after a few heating and cooling cycles. Dynamic light scattering revealed that the copolymer containing no secondary amine groups showed a thermo-reversible shift in micellar size and small aggregates (57 and 877 nm at 25 °C and 40 and 152 nm at 50 °C). Conversely, copolymers comprising a central moiety containing secondary amine groups show a temperature independent distribution mainly consisting of micelles. It is proposed that the protonated amine groups preferably are located at the corona of the micelles and micellar aggregates and/or shielded by the PEG blocks, hindering the formation of hydrogels by PEG entanglements upon a change in temperature.