[FeFe]-Hydrogenase Abundance and Diversity along a Vertical Redox Gradient in Great Salt Lake,USA

The use of [FeFe]-hydrogenase enzymes for the biotechnological production of H₂ or other reduced products has been limited by their sensitivity to oxygen (O₂). Here, we apply a PCR-directed approach to determine the distribution, abundance, and diversity of hydA gene fragments along co-varying salinity and O₂ gradients in a vertical water column of Great Salt Lake (GSL), UT. The distribution of hydA was constrained to water column transects that had high salt and relatively low O₂ concentrations. Recovered HydA deduced amino acid sequences were enriched in hydrophilic amino acids relative to HydA from less saline environments. In addition, they harbored interesting variations in the amino acid environment of the complex H-cluster metalloenzyme active site and putative gas transfer channels that may be important for both H₂ transfer and O₂ susceptibility. A phylogenetic framework was created to infer the accessory cluster composition and quaternary structure of recovered HydA protein sequences based on phylogenetic relationships and the gene contexts of known complete HydA sequences. Numerous recovered HydA are predicted to harbor multiple N- and C-terminal accessory iron-sulfur cluster binding domains and are likely to exist as multisubunit complexes. This study indicates an important role for [FeFe]-hydrogenases in the functioning of the GSL ecosystem and provides new target genes and variants for use in identifying O₂ tolerant enzymes for biotechnological applications.     

Superoxide Reductase: Different Interaction Modes with its Two Redox Partners

Anaerobic organisms have molecular systems to detoxify reactive oxygen species when transiently exposed to oxygen. One of these systems is superoxide reductase, which reduces O₂^.? to H₂O₂ without production of molecular oxygen. In order to complete the reduction of superoxide anion, superoxide reductase requires an electron, delivered by its redox partners, which in Desulfovibrio gigas are rubredoxin and/or desulforedoxin. In this work, we characterized the interaction of Desulfovibrio gigas superoxide reductase with both electron donors by using steady‐state kinetics, 2D NMR titrations, and backbone relaxation measurements. The rubredoxin surface involved in the electron transfer complex with superoxide reductase comprises the solvent‐exposed hydrophobic residues in the vicinity of its metal center (Cys9, Gly10, Cys42, Gly43, and Ala44), and a K_d of 3 μM at 59 mM ionic strength was estimated by NMR. The ionic strength dependence of superoxide‐mediated rubredoxin oxidation by superoxide reductase has a maximum k_app of (37±12) min^?1 at 157 mM . Relative to the electron donor desulforedoxin, its complex with superoxide reductase was not detected by chemical shift perturbation, though this protein is able to transfer electrons to superoxide reductase with a maximum k_app of (31±7) min^?1 at an ionic strength of 57 mM . Competition experiments using steady‐state kinetics and NMR spectroscopy (backbone relaxation measurements and use of a paramagnetic relaxation enhancement probe) with Fe‐desulforedoxin in the presence of ¹⁵N‐Zn‐rubredoxin showed that these two electron donors compete for the same site on the enzyme surface, as shown in the model structure of the complex generated by using restrained molecular docking calculations. These combined strategies indicate that the two small electron donors bind in different manners, with the desulforedoxin complex being a short lived electron transfer complex or more dynamic, with many equivalent kinetically competent orientations.     

Gas diffusion electrodes improve hydrogen gas mass transfer for a hydrogen oxidizing bioanode

Background

Bioelectrochemical systems (BESs) are capable of recovery of metals at a cathode through oxidation of organic substrate at an anode. Recently, also hydrogen gas was used as an electron donor for recovery of copper in BESs. Oxidation of hydrogen gas produced a current density of 0.8 A m^‐2 and combined with Cu²⁺ reduction at the cathode, produced 0.25 W m^‐2. The main factor limiting current production was the mass transfer of hydrogen to the biofilm due to the low solubility of hydrogen in the anolyte. Here, the mass transfer of hydrogen gas to the bioanode was improved by use of a gas diffusion electrode (GDE).

Results

With the GDE, hydrogen was oxidized to produce a current density of 2.9 A m^‐2 at an anode potential of –0.2 V. Addition of bicarbonate to the influent led to production of acetate, in addition to current. At a bicarbonate concentration of 50 mmol L^‐1, current density increased to 10.7 A m^‐2 at an anode potential of –0.2 V. This increase in current density could be due to oxidation of formed acetate in addition to oxidation of hydrogen, or enhanced growth of hydrogen oxidizing bacteria due to the availability of acetate as carbon source. The effect of mass transfer was further assessed through enhanced mixing and in combination with the addition of bicarbonate (50 mmol L^‐1) current density increased further to 17.1 A m^‐2.

Conclusion

Hydrogen gas may offer opportunities as electron donor for bioanodes, with acetate as potential intermediate, at locations where excess hydrogen and no organics are available. © 2017 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Photoreduction of Shewanella oneidensis Extracellular Cytochromes by Organic Chromophores and Dye‐Sensitized TiO2

The transfer of photoenergized electrons from extracellular photosensitizers across a bacterial cell envelope to drive intracellular chemical transformations represents an attractive way to harness nature's catalytic machinery for solar‐assisted chemical synthesis. In Shewanella oneidensis MR‐1 (MR‐1), trans‐outer‐membrane electron transfer is performed by the extracellular cytochromes MtrC and OmcA acting together with the outer‐membrane‐spanning porin ? cytochrome complex (MtrAB). Here we demonstrate photoreduction of solutions of MtrC, OmcA, and the MtrCAB complex by soluble photosensitizers: namely, eosin Y, fluorescein, proflavine, flavin, and adenine dinucleotide, as well as by riboflavin and flavin mononucleotide, two compounds secreted by MR‐1. We show photoreduction of MtrC and OmcA adsorbed on Ru^II‐dye‐sensitized TiO₂ nanoparticles and that these protein‐coated particles perform photocatalytic reduction of solutions of MtrC, OmcA, and MtrCAB. These findings provide a framework for informed development of strategies for using the outer‐membrane‐associated cytochromes of MR‐1 for solar‐driven microbial synthesis in natural and engineered bacteria.     

X‐ray Structural Analysis of Tau‐Tubulin Kinase 1 and Its Interactions with Small Molecular Inhibitors

Tau‐tubulin kinase 1 (TTBK1) is a serine/threonine/tyrosine kinase that putatively phosphorylates residues including S422 in tau protein. Hyperphosphorylation of tau protein is the primary cause of tau pathology and neuronal death associated with Alzheimer’s disease. A library of 12 truncation variants comprising the TTBK1 kinase domain was screened for expression in Escherichia coli and insect cells. One variant (residues 14–313) could be purified, but mass spectrometric analysis revealed extensive phosphorylation of the protein. Co‐expression with lambda phosphatase in E. coli resulted in production of homogeneous, nonphosphorylated TTBK1. Binding of ATP and several compounds to TTBK1 was characterized by surface plasmon resonance. Crystal structures of TTBK1 in the unliganded form and in complex with ATP, and two high‐affinity ATP‐competitive inhibitors, 3‐[(6,7‐dimethoxyquinazolin‐4‐yl)amino]phenol ( 1 ) and methyl 2‐bromo‐5‐(7H‐pyrrolo[2,3‐d]pyrimidin‐4‐ylamino)benzoate ( 2 ), were elucidated. The structure revealed two clear basic patches near the ATP pocket providing an explanation of TTBK1 for phosphorylation‐primed substrates. Interestingly, compound 2 displayed slow binding kinetics to TTBK1, the structure of TTBK1 in complex with this compound revealed a reorganization of the L199–D200 peptide backbone conformation together with altered hydrogen bonding with compound 2 . These conformational changes necessary for the binding of compound 2 are likely the basis of the slow kinetics. This first TTBK1 structure can assist the discovery of novel inhibitors for the treatment of Alzheimer’s disease.     

Anaerobic CO2 fixation by the acetogenic bacterium Moorella thermoacetica

Anaerobic bacteria such as Moorella thermoacetica have the capacity of fixing carbon dioxide with carbon monoxide and hydrogen for the production of ethanol, acetic acid, and other useful chemicals. In this study, we evaluated the fixation of CO₂ for the production of acetic acid, as a product in its own right but also as precursor for lipid synthesis by oleaginous organisms. We achieved maximum cell optical density of 11.3, acetic acid titer of 31 g/L, and productivity of 0.55 g/L‐h at CO mass‐transfer rate of 83 mM/h. We also showed electron availability by CO mass transfer limited the process at CO mass transfer rates lower than 30 mM/h. Further enhancement of mass‐transfer rate removed such limitations in favor of biological kinetics as main limitation. This work underlines the potential of microbial processes for converting syngas to fuel and chemical products in processes suitable for distributed feedstock utilization. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3176–3183, 2013     

A Caged,Destabilized, Free Radical Intermediate in the Q‐Cycle

The Rieske/cytochrome b complexes, also known as cytochrome bc complexes, catalyze a unique oxidant‐induced reduction reaction at their quinol oxidase (Q_o) sites, in which substrate hydroquinone reduces two distinct electron transfer chains, one through a series of high‐potential electron carriers, the second through low‐potential cytochrome b. This reaction is a critical step in energy storage by the Q‐cycle. The semiquinone intermediate in this reaction can reduce O₂ to produce deleterious superoxide. It is yet unknown how the enzyme controls this reaction, though numerous models have been proposed. In previous work, we trapped a Q‐cycle semiquinone anion intermediate, termed SQ_o, in bacterial cytochrome bc₁ by rapid freeze‐quenching. In this work, we apply pulsed‐EPR techniques to determine the location and properties of SQ_o in the mitochondrial complex. In contrast to semiquinone intermediates in other enzymes, SQ_o is not thermodynamically stabilized, and can even be destabilized with respect to solution. It is trapped in Q_o at a site that is distinct from previously described inhibitor‐binding sites, yet sufficiently close to cytochrome b_L to allow rapid electron transfer. The binding site and EPR analyses show that SQ_o is not stabilized by hydrogen bonds to proteins. The formation of SQ_o involves “stripping” of both substrate ‐OH protons during the initial oxidation step, as well as conformational changes of the semiquinone and Q_o proteins. The resulting charged radical is kinetically trapped, rather than thermodynamically stabilized (as in most enzymatic semiquinone species), conserving redox energy to drive electron transfer to cytochrome b_L while minimizing certain Q‐cycle bypass reactions, including oxidation of prereduced cytochrome b and reduction of O₂.     

Mass‐Spectrometric and Kinetic Studies on the Mechanism and Degradation Pathways of Titanium Salalen Catalysts for Asymmetric Epoxidation with Aqueous Hydrogen Peroxide

The composition and degradation of a highly active and enantioselective titanium salalen in situ catalyst for the asymmetric epoxidation of olefins with aqueous hydrogen peroxide was investigated. Kinetic data and ESI‐MS studies point to a mononuclear titanium salalen as the catalytically active species. By means of ESI‐MS and selective monodeuteration of the salalen ligand, the oxidative degradation was studied. Upon exposure to aqueous hydrogen peroxide, the amine functionality of the salalen ligand is converted to the hydroxylamine, followed by loss of water and generation of the inactive titanium‐salen complex. This transformation limits the activity of the catalyst in the epoxidation of less electron‐rich olefins, such as 1‐octene.     

Synthesis,characterization, and antitumor activity of poly(maleic anhydride‐co‐vinyl acetate‐co‐acrylic acid)

The ternary copolymerization of maleic anhydride (MA), vinyl acetate (VA), and acrylic acid (AA) [P(MA‐co‐VA‐co‐AA)], which is considered to be an acceptor–donor–acceptor system, was carried out in 1,4‐dioxane with benzoyl peroxide as an initiator at 70°C under a nitrogen atmosphere. Constants of complex formation for the monomer systems in the study were determined by UV–visible (hydrogen‐bonding complex) and ¹H‐NMR (charge transfer complex) methods, respectively. The results show that polymerization of the P(MA‐co‐VA‐co‐AA) system proceeds by an alternating terpolymerization mechanism. It is shown that the synthesized copolymers have typical polyelectrolyte behavior, ability for reversible hydrolysis–anhydrization reactions, and semicrystalline structures. In these cases, including radical polymerization, and formation of semicrystalline structures, the hydrogen‐bonding effect plays a significant role. The in vitro cytotoxicities of the synthesized terpolymer and alternating copolymer were evaluated using Raji cells (human Burkitt lymphoma cell line). The antitumor activities of prepared anion‐active copolymers were studied using methyl–thiazol–tetrazolium colorimetric assay and 50% of the cytotoxic dose of each copolymer and terpolymer were calculated. Hydrolyzed P(MA‐co‐VA‐co‐AA) and P(MA‐alt‐AA) copolymers have sufficiently high antitumor activity, which depends on the amount of hydrogen‐bonding carboxylic groups and their regular distribution in the side chain of functional macromolecules. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3425–3432, 2006     

Efficient and Green Route to γ‐Lactams by Copper‐Catalysed Reversed Atom Transfer Radical Cyclisation of α‐Polychloro‐N‐allylamides,using a Low Load of Metal (0.5 mol%)

The cyclisation of N‐allyl‐N‐substituted‐α‐polychloroamides is efficiently obtained through a copper‐catalysed activators regenerated by electron transfer–atom transfer radical cyclisation process, with a metal load of only 0.5 mol%. The redox catalyst is introduced in its inactive form as copper(II) chloride/[nitrogen ligand] complex, and continuously regenerated to the active copper(I) chloride/[nitrogen ligand] species by ascorbic acid. To preserve the catalyst integrity, the hydrochloric acid, released after each regeneration cycle, has been quenched by carbonate. The choice of the solvent is critical, the best performance being observed in ethyl acetate‐ethanol (3:1).     

Photophysics of Structurally Modified Flavin Derivatives in the Blue‐Light Photoreceptor YtvA: A Combined Experimental and Theoretical Study

The light‐induced processes of two flavin mononucleotide derivatives (1‐ and 5‐deaza flavin mononucleotide, 1DFMN and 5DFMN), incorporated into the LOV domain of YtvA protein from Bacillus subtilis, were studied by a combination of experimental and computational methods. Quantum mechanics/molecular mechanics (QM/MM) calculations were carried out in which the QM part was treated by density functional theory (DFT) using the B3LYP functional for geometry optimizations and the DFT/MRCI method for spectroscopic properties, whereas the MM part was described by the CHARMM force field. 1DFMN is incorporated into the protein binding site, yielding a red‐shifted absorption band (λ_max=530 nm compared to YtvA wild‐type λ_max=445 nm), but does not undergo any LOV‐typical photoreactions such as triplet and photoadduct formation. QM/MM computations confirmed the absence of a channel for triplet formation and located a radiation‐free channel (through an S₁/S₀ conical intersection) along a hydrogen transfer path that might allow for fast deactivation. By contrast, 5DFMN‐YtvA‐LOV shows a blue‐shifted absorption (λ_max=410 nm) and undergoes similar photochemical processes to FMN in the wild‐type protein, both with regard to the photophysics and the formation of a photoadduct with a flavin‐cysteinyl covalent bond. The QM/MM calculations predict a mechanism that involves hydrogen transfer in the T₁ state, followed by intersystem crossing and adduct formation in the S₀ state for the forward reaction. Experimentally, in contrast to wild‐type YtvA, dark‐state recovery in 5DFMN‐YtvA‐LOV is not thermally driven but can only be accomplished after absorption of a second photon by the photoadduct, again via the triplet state. The QM/MM calculations suggest a photochemical mechanism for dark‐state recovery that is accessible only for the adduct with a C4a? S bond but not for alternative adducts with a C5? S bond.     

Iridium‐Catalyzed Transfer Hydrogenation of 1,10‐Phenanthrolines using Formic Acid as the Hydrogen Source

The iridium‐catalyzed highly regioselective transfer hydrogenation of a variety of 2‐substituted and 2,9‐disubstituted 1,10‐phenanthrolines under mild conditions with formic acid as the hydrogen source is described. In the presence of a catalytic amount of the iridium complex [Cp*IrCl₂]₂, the transfer hydrogenation proceeded smoothly in 1,4‐dioxane under ligand‐free conditions, exclusively leading to a range of 1,2,3,4‐tetrahydro‐1,10‐phenanthroline products in high yields. The catalyst generated in situ from [Cp*IrCl₂]₂ and (R,R)‐(CF₃)₂C₆H₃SO₂‐dpen [N‐(2‐amino‐1,2‐diphenylethyl)‐3,5‐bis(trifluoromethyl)benzenesulfonamide] could efficiently catalyze the asymmetric transfer hydrogenation of these 1,10‐phenanthrolines in isopropyl alcohol (i‐PrOH) to afford chiral 1,2,3,4‐tetrahydro‐1,10‐phenanthrolines in high yields with up to >99% ee. The key to the success of the reduction is the choice of solvent and hydrogen source.

     

Novel divinyl monomer for preparation of unsaturated polymers

To simplify the preparation of unsaturated polymers, a new type of divinyl monomer was designed in this article. The double bonds of the divinyl monomer are different not only in reactivity but also in electron density. Based on quantum chemistry calculation, (z)‐4‐(2‐(acryloyloxy)ethoxy)‐4‐oxobut‐2‐enoic acid (cis‐AEOEA) was selected as the nonelectron‐donating divinyl monomer in which inactive double bond was electron deficient and can be activated by electron‐donating comonomers by forming charge transfer complex (CTC) copolymerization system. So, cis‐AEOEA can be used to simplify the preparation of unsaturated polymers and the content of inactive double bonds left in the polymer is controlled by electron‐donating ability of comonomers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Considerations on film reactivity in the aqueous biphasic hydroformylation

In experiments and kinetic models it was shown that the reaction rate of the biphasic aqueous hydroformylation of 1‐octene is linear dependent on the created interfacial area. This phenomenon is directly linked to the question whether the reaction takes place in the bulk phase and is mass transfer limitation or at the surface which would mean an increase of reaction space. To evaluate the place of reaction a mass transfer analysis has been carried out. No mass transfer limitation for the gaseous components carbon monoxide and hydrogen as well as the olefin 1‐octene was determined for the aqueous catalyst phase by calculating the Hatta numbers. With this observation it is possible to exclude the mass transfer as a potential influence and hence the aqueous bulk as the place of reaction. Thus the reaction is most probably surface active. This can be either explained the increase in film volume fraction where non‐polar substrate as well as polar catalyst complex is present or through an increased catalyst concentration at the surface through dipole moment fluctuations. © 2017 American Institute of Chemical Engineers AIChE J, 63: 161–171, 2018     

Non‐Racemic Halohydrins via Biocatalytic Hydrogen‐Transfer Reduction of Halo‐Ketones and One‐Pot Cascade Reaction to Enantiopure Epoxides

Biocatalytic hydrogen‐transfer reduction of α‐chloro‐ketones furnished non‐racemic chlorohydrins by employing either Rhodococcus ruber as lyophilized cell catalyst or an alcohol dehydrogenase preparation from Pseudomonas fluorescens DSM 50106 (PF‐ADH). For all substrates investigated, Rhodococcus ruber gave strictly the “Prelog” product, whereas PF‐ADH showed scattered stereopreference. One possibility for a follow‐up reaction of halohydrins is the ring closure to the corresponding epoxide. A novel “one pot‐one step strategy” was employed to obtain the enantiopure epoxide from the α‐chloro‐ketone in a cascade like fashion at pH>12 involving biocatalytic hydrogen transfer reduction and in situ chemo‐catalyzed ring closure.     

Blends of high density polyethylene with branched poly(styrene‐co‐dodecyl acrylate): Rheological,mechanical, and thermal properties

Branched poly(styrene‐co‐dodecyl acrylate) (BPSDA) was prepared by the atom transfer radical copolymerization of styrene with dodecyl acrylate using p‐cholomethyl styrene as initiator‐monomer (inimer) and CuCl/Bpy (2,2′‐bipyridine) complex as catalyst. The remarkable discrepancies between the molecular weight determined by gel permeation chmotagraphy and multiangel laser light scattering reveals the highly branched structure of the resulting copolymer. Furthermore, the composition was analyzed by hydrogen nuclear magnetic resonance (¹H NMR), which is consistent with the feed ratio of monomers. Blending of the branched product with high density polyethylene (HDPE) was attempted in haake mixer. The rheological, mechanical, and thermal stability properties of the resulting blends were studied. Compared with pure HDPE, the complex viscosity of blend with addition of 4 wt % BPSDA decreased by 15.9%. While the elongation at break decreased by 5.5% and tensile strength decreased by 4.2%. SEM (scanning electron microscopy) revealed that the average particle size of disperse phase in HDPE/4% BPSDA blend is 0.45 μm in diameter. Differential scanning calorimetry characterization showed that the addition of BPSDA accelerated the relative crystallization rate but decreased the final absolute degree of crystallinity. No obvious change of thermal stability of the blends was observed relative to pure HDPE. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The AT2 Domain of KirCI Loads Malonyl Extender Units to the ACPs of the Kirromycin PKS

The antibiotic kirromycin is assembled by a hybrid modular polyketide synthases (PKSs)/nonribosomal peptide synthetases (NRPSs). Five of six PKSs of this complex assembly line do not have acyltransferase (AT) and have to recruit this activity from discrete AT enzymes. Here, we show that KirCI is a discrete AT which is involved in kirromycin production and displays a rarely found three‐domain architecture (AT₁‐AT₂‐ER). We demonstrate that the second AT domain, KirCI‐AT₂, but not KirCI‐AT₁, is the malonyl‐CoA‐specific AT which utilizes this precursor for loading the acyl carrier proteins (ACPs) of the trans‐AT PKS in vitro. In the kirromycin biosynthetic pathway, ACP5 is exclusively loaded with ethylmalonate by the enzyme KirCII and is not recognized as a substrate by KirCI. Interestingly, the excised KirCI‐AT₂ can also transfer malonate to ACP5 and thus has a relaxed ACP‐specificity compared to the entire KirCI protein. The ability of KirCI‐AT₂ to load different ACPs provides opportunities for AT engineering as a potential strategy for polyketide diversification.     

Kinetic Model of Gas‐Liquid‐Liquid Reactive Extraction for Production of Hydrogen Peroxide

The kinetic aspects of the gas‐liquid‐liquid reactive extraction process for the production of hydrogen peroxide were investigated in a batch reactor. It was observed that the gas‐liquid reaction rate is strongly affected by mass transfer of oxygen across the liquid film and the reaction can be simplified to pseudo‐first order. The extraction rate is governed by both reaction and liquid‐liquid mass transfer, and is slightly lower than the reaction rate. In addition, a kinetic model of the reactive extraction process for the production of hydrogen peroxide was developed. Kinetic parameters under different conditions were determined by experiments. The data calculated from the kinetic model match experimental data well under different conditions for hydrogen peroxide production in gas‐liquid‐liquid reactive extraction.     

Synthesis and application of dyes derived from benz[cd]indol‐2(1H)‐one as visible‐light‐absorbing polymerisation photoinitiators

Several potential initiators based on benz[cd]indol‐2(1H)‐one dye have been synthesised and evaluated in the radical polymerisation of a system containing trimethylolpropane triacrylate under visible light. Absorption, fluorescence, and phosphorescence spectra and the electrochemical properties of these novel dyes were determined. Owing to the presence of an appropriate hydrogen donor group in their structure, these photoinitiators do not need an extra coinitiator to initiate the polymerisation process. During photopolymerisation they act both as a triplet sensitiser and as a hydrogen donor. The relationship between the polymerisation rate and the triplet‐excited‐state reduction potential suggests that initiating radicals are formed from the triplet state via hydrogen transfer. This mechanism is supported by density functional theory calculations. 8‐Bromo‐6‐[(2‐sulphanylethyl)sulphanyl]benzo[cd]indol‐2(1H)‐one and 8‐bromo‐6‐sulphanylbenz[cd]indol‐2(1H)‐one may be applied as visible‐light initiators of free radical polymerisation to obtain a low‐molecular‐weight polymer.     

Hydrogen‐bonding interaction of an alternating maleic acid–vinyl acetate copolymer with poly(ethylene glycol), polyacrylamide and poly(N‐isopropylacrylamide): a comparative study

The hydrogen‐bonding interaction and interpolymer complex formation between an alternating maleic acid–vinyl acetate copolymer, (MAc‐alt‐VA) and poly(ethylene glycol) (PEG), polyacrylamide (PAM) or poly(N‐isopropylacrylamide) (PNIPAM) in aqueous solution was potentiometrically and viscometrically investigated. MAc‐alt‐VA formed with PEG a strong hydrogen‐bonding interpolymer complex with a compact structure, and while its interaction with PAM seems to be very weak, if any, the complex formed with PNIPAM is even stronger than that with PEG. This indicates a very important contribution of hydrophobic interaction to the formation of such hydrogen‐bonding interpolymer complexes. Copyright © 2003 Society of Chemical Industry