Wheat-gluten-based natural polymer nanoparticle composites

A series of wheat-gluten-based nanocomposites were produced by dispersing Cloisite-30B nanoclay particles into plasticized wheat gluten systems under thermal processing conditions. The exfoliation of the nanoparticles as confirmed by wide-angle X-ray diffraction and transmission electron microscopy has resulted in significant enhancement of the mechanical properties for both deamidated proteins and vital gluten systems under 50% relative humidity (RH). Such strength improvement was also pronounced for wheat gluten (WG) systems under a high humidity condition (RH = 85%). A similar level of further strength enhancement was obtained for the WG systems that had been strengthened by blending with poly(vinyl alcohol) (PVA) and cross-linking with glyoxal. Although the nanoclay modifier, a quaternary ammonium, caused an additional plasticization to the materials, the interactions between the gluten matrix and the nanoparticles were predominant in all of these nanocomposites. A solid-state NMR study indicated that the polymer matrix in all of these nanocomposites displayed a wide distribution of chain mobilities at a molecular level (less than 1 nm). The interactions between the nanoparticles and the natural polymer matrix resulted in motional restriction for all components in the mobile phases including lipid, plasticizers, and plasticized components, although no significant influence from the nanoparticles was obtained in the mobility of the rigid phases (unplasticized components). On a scale of 20-30 nm, the deamidated protein systems tended to be homogeneous. The small domain size of the matrix resulted in modifications of the spin-lattice relaxation of these systems via spin diffusion. The residual starch seemed to remain in a relatively larger domain size in WG systems. The nanoparticles could enhance the miscibility between the starch and the other components in the WG nanocomposite, but such miscibility enhancement did not occur in the WG/PVA blend and the cross-linked system. These polymer matrixes were still heterogeneous on a scale of 20-30 nm.     

pH effect on the mechanical performance and phase mobility of thermally processed wheat gluten-based natural polymer materials

The mechanical properties, phase composition, and molecular motions of thermally processed wheat gluten- (WG-) based natural polymer materials were studied by mechanical testing, dynamic mechanical analysis (DMA), and solid-state NMR spectroscopy. The performance of the materials was mainly determined by the denaturization and cross-linking occurring in the thermal processing and the nature or amount of plasticizers used. The pH effect also played an important role in the materials when water was used as the only plasticizer (WG-w). Alkaline conditions modified the chemical structure of WG, possibly via deamidation; enhanced the thermal cross-linking of WG macromolecules to form a more stable aggregation structure; and promoted intermolecular interactions between water and all components in WG (proteins, starch, and lipid), resulting in a strong adhesion among different components and phases. The saponification of lipid under alkaline conditions also enhanced the hydrophilicity of lipid and the miscibility among lipid, water, and WG components. However, when glycerol was used with water as a plasticizer (WG-wg), the phase mobility and composition of the materials mainly depended on the content of glycerol when the water content was constant. During thermal processing under either acidic or alkaline conditions, glycerol was unlikely to thermally cross-link with WG as suggested previously. The advanced mechanical performance of the WG-wg materials was attributed to the nature of hydrogen-bonding interactions between glycerol and WG components in the materials. This caused the whole material to behave like a strengthened "cross-linked" structure at room temperature due to the low mobility of glycerol. The pH effect on phase mobility and compositions of WG-wg systems was not as significant as that for WG-w materials.     

Chemical modification of wheat-protein-based natural polymers: formation of polymer networks with alkoxysilanes to modify molecular motions and enhance the material performance

The mechanical performance of plasticized wheat gluten (WG) materials was significantly modified through the formation of different chemical and network structures with alkoxysilanes. The epoxy-functionalized alkoxysilanes were grafted to segments of WG, and then the condensation reactions between alkoxysilane segments occurred during thermal processing to form WG-siloxane networks. The mechanical properties and molecular motions of the networks were dependent on the amount and type of alkoxysilanes applied. A lower amount of alkoxysilanes caused the alkoxysilane molecules to predominately graft onto WG chains without forming linkages between WG segments, which produced an additional plasticizing effect on the WG systems with a longer elongation value and weaker tensile strength at relative humidity (RH) = 50% as compared to the WG system. However, such grafting improved the hydrostability of the materials and generated an improvement in tensile strength at RH = 85%. Increasing the amount of alkoxysilanes in the systems led to the formation of cross-linked WG-siloxane networks via linkages between alkoxysilane segments. Remarkable strength improvement was obtained for the networks with elongation values still higher than the original plasticized WG due to the flexible nature of the siloxane components. A more significant strength improvement was obtained for the WG-SiA systems at both RH = 50% and 85%, where SiA could form three-dimensional networks from siloxane condensation and generate highly cross-linked network structures with relatively low mobility. For WG-SiB systems, SiB could only form linear linkages, and the higher mobility of the SiB phase caused the systems to display a lower strength improvement with a longer elongation value.     

Wheat gluten-based renewable and biodegradable polymer materials with enhanced hydrophobicity by using epoxidized soybean oil as a modifier

Epoxidized soybean oil (ESO) was applied as an additive for wheat gluten (WG) to modify the properties of the renewable and biodegradable natural polymer materials. Optimum intermolecular interactions and crosslinking between ESO chains and the WG matrix were achieved under alkaline conditions. The WGESO materials were heterogeneous on a scale of 20-30 nm, but the homogeneity was improved upon increasing the amount of glycerol as a plasticizer in the materials. The combination of plasticization and crosslinking effects derived from ESO resulted in good retention in mechanical strength for the plasticized WGESO materials as compared to those without 10 wt % of mobile ESO additives. The hydrophobicity of the plasticized WG materials was also enhanced significantly by using the ESO additives.     

Plasticization and crosslinking effects of acetone-formaldehyde and tannin resins on wheat protein-based natural polymers

Efficient plasticization and sufficient crosslinking were achieved by using an acetone-formaldehyde (AF) resin as an additive in the thermal processing of wheat protein-based natural polymers. The mobile AF resin and its strong intermolecular interactions with a wheat protein matrix produced sufficient flexibility for the plastics, while the covalent bonds formed between AF and the protein chains also caused the water-soluble resin to be retained in the materials under wet conditions. The mechanical properties of the materials were also enhanced as an additional benefit due to the formation of crosslinked networks through the polymer matrix. Tensile strength was further enhanced when using AF in conjunction with tannin resin (AFTR) in the systems as rigid aromatic structures were formed in the crosslinking segments. Different components in wheat proteins (WPs) or wheat gluten (WG) (e.g., proteins, residual starch and lipids) displayed different capabilities in interaction and reaction with the AFTR additives, and thus resulted in different performances when the ratio of these components varied in the materials. The application of the AFTR additives provides a feasible methodology to thermally process wheat protein-based natural polymers with improved mechanical performance and water-resistant properties.     

Molecular determinants for ATP-binding in proteins: a data mining and quantum chemical analysis

Adenosine 5'-triphosphate (ATP) plays an essential role in all forms of life. Molecular recognition of ATP in proteins is a subject of great importance for understanding enzymatic mechanism and for drug design. We have carried out a large-scale data mining of the Protein Data Bank (PDB) to analyze molecular determinants for recognition of the adenine moiety of ATP by proteins. Non-bonded intermolecular interactions (hydrogen bonding, pi-pi stacking interactions, and cation-pi interactions) between adenine base and surrounding residues in its binding pockets are systematically analyzed for 68 non-redundant, high-resolution crystal structures of adenylate-binding proteins. In addition to confirming the importance of the widely known hydrogen bonding, we found out that cation-pi interactions between adenine base and positively charged residues (Lys and Arg) and pi-pi stacking interactions between adenine base and surrounding aromatic residues (Phe, Tyr, Trp) are also crucial for adenine binding in proteins. On average, there exist 2.7 hydrogen bonding interactions, 1.0 pi-pi stacking interactions, and 0.8 cation-pi interactions in each adenylate-binding protein complex. Furthermore, a high-level quantum chemical analysis was performed to analyze contributions of each of the three forms of intermolecular interactions (i.e. hydrogen bonding, pi-pi stacking interactions, and cation-pi interactions) to the overall binding force of the adenine moiety of ATP in proteins. Intermolecular interaction energies for representative configurations of intermolecular complexes were analyzed using the supermolecular approach at the MP2/6-311 + G* level, which resulted in substantial interaction strengths for all the three forms of intermolecular interactions. This work represents a timely undertaking at a historical moment when a large number of X-ray crystallographic structures of proteins with bound ATP ligands have become available, and when high-level quantum chemical analysis of intermolecular interactions of large biomolecular systems becomes computationally feasible. The establishment of the molecular basis for recognition of the adenine moiety of ATP in proteins will directly impact molecular design of ATP-binding site targeted enzyme inhibitors such as kinase inhibitors.     

Bioplastics from feather quill

Poultry feather quills have been extruded in a twin screw extruder with sodium sulfite treatment as a reducing agent. The effect of four different plasticizers (ethylene glycol, propylene glycol, glycerol, and diethyl tartrate) on the thermoplastic properties was then investigated. Conformational changes and plasticizer-protein interactions in the extruded resins were assessed by Fourier transform infrared spectroscopy (FTIR), while viscoelastic behavior of the quill keratin plasticized with different plasticizers was investigated by dynamic mechanical analysis (DMA). Differential scanning calorimetry (DSC) was used to determine the effect of different plasticizers on protein denaturation. Thermal degradation patterns of the extrudates were studied by thermogravimetric analysis (TGA). The effect of plasticizers on the mechanical properties of resins was also assessed by tensile strength measurements. Results indicated that ethylene glycol was able to interact more effectively with quill keratin at the molecular level, exhibiting only one sharp glass transition, better mechanical properties, and higher transparency compared to other plasticized resins. The two phases found in glycerol plasticized material were attributed to glycerol-rich and protein-rich zones. Propylene glycol and diethyl tartrate exhibited lower H-bonding interactions and showed wide transition regions in DMA profiles during heating, suggesting weak and heterogeneous interactions between quill keratin and these plasticizers.     

An orientation-dependent hydrogen bonding potential improves prediction of specificity and structure for proteins and protein-protein complexes

Hydrogen bonding is a key contributor to the specificity of intramolecular and intermolecular interactions in biological systems. Here, we develop an orientation-dependent hydrogen bonding potential based on the geometric characteristics of hydrogen bonds in high-resolution protein crystal structures, and evaluate it using four tests related to the prediction and design of protein structures and protein-protein complexes. The new potential is superior to the widely used Coulomb model of hydrogen bonding in prediction of the sequences of proteins and protein-protein interfaces from their structures, and improves discrimination of correctly docked protein-protein complexes from large sets of alternative structures.     

Preparation and properties of plasticized poly(lactic acid) films

Poly(lactic acid), PLA, was blended with monomeric and oligomeric plasticizers in order to enhance its flexibility and thereby overcome its inherent problem of brittleness. Differential scanning calorimetry, dynamic mechanical analysis, transmission electron microscopy, and tensile testing were used to investigate the properties of the blends. Monomeric plasticizers, such as tributyl citrate, TbC, and diethyl bishydroxymethyl malonate, DBM, drastically decreased the T(g) of PLA, but the blends showed no morphological stability over time since rapid cold crystallization caused a size reduction of the amorphous domains in PLA. Consequently, the ability of PLA to accommodate the plasticizer diminished with the increase in crystallinity and migration of the plasticizer occurred. Increasing the molecular weight of the plasticizers by synthesizing oligoesters and oligoesteramides resulted in blends that displayed T(g) depressions slightly smaller than with the monomeric plasticizers. The compatibility with PLA was dependent on the molecular weight of the oligomers and on the presence or not of polar amide groups that were able to positively interact with the PLA chains. Aging the materials at ambient temperature revealed that the enhanced flexibility as well as the morphological stability of the films plasticized with the oligomers could be maintained as a result of the higher molecular weight and the polar interactions with PLA.     

Viscoelastic properties of wheat gluten in a molecular dynamics study

Wheat (Triticum spp.) gluten consists mainly of intrinsincally disordered storage proteins (glutenins and gliadins) that can form megadalton-sized networks. These networks are responsible for the unique viscoelastic properties of wheat dough and affect the quality of bread. These properties have not yet been studied by molecular level simulations. Here, we use a newly developed α-C-based coarse-grained model to study ∼ 4000-residue systems. The corresponding time-dependent properties are studied through shear and axial deformations. We measure the response force to the deformation, the number of entanglements and cavities, the mobility of residues, the number of the inter-chain bonds, etc. Glutenins are shown to influence the mechanics of gluten much more than gliadins. Our simulations are consistent with the existing ideas about gluten elasticity and emphasize the role of entanglements and hydrogen bonding. We also demonstrate that the storage proteins in maize and rice lead to weaker elasticity which points to the unique properties of wheat gluten.     

Wheat gluten-thiolated poly(vinyl alcohol) blends with improved mechanical properties

A multifunctional macromolecular thiol (TPVA) obtained by esterification of poly(vinyl alcohol) (PVA) with 3-mercaptopropionic acid was characterized by a combination of NMR, IR, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC), and was used as a wheat gluten (WG) reactive modifier. The effect of TPVA molecular weight (M(w) = 2000, 9500, 50 000, and 205 000) and blend composition (5, 20, and 40% w/w TPVA/WG) on the mechanical properties of compression-molded bars indicates that TPVA/WG blends increase the fracture strength by up to 76%, the elongation by 80%, and the modulus by 25% above WG. In contrast, typical WG additives such as glycerol and sorbitol improve flexibility but decrease modulus and strength. Preliminary investigations of suspension rheology, water uptake, molecular weight distribution and electron microscopy of TPVA/WG and PVA/WG blends illustrate the different protein interactions with PVA and TPVA. Further work is underway to determine whether TPVA and WG form protein conjugates or microphase-separated morphologies.     

Lipid intermolecular hydrogen bonding: influence on structural organization and membrane function

The great variety of different lipids in membranes, with modifications to the hydrocarbon chains, polar groups and backbone structure suggests that many of these lipids may have unique roles in membrane structure and function. Acidic groups on lipids are clearly important, since they allow interaction with basic groups on proteins and with divalent cations. Another important property of certain lipids is their ability to interact intermolecularly with other lipids via hydrogen bonds. This interaction occurs through acidic and basic moieties in the polar head groups of phospholipids, and the amide moiety and hydroxyl groups on the acyl chain, sphingosine base and sugar groups of sphingo- and glycolipids. The putative ability of different classes of lipids to interact by intermolecular hydrogen bonding, the molecular groups which may participate and the effect of these interactions on some of their physical properties are summarized in Table IX. It is frequently questioned whether intermolecular hydrogen bonding could occur between lipids in the presence of water. Correlations of their properties with their molecular structures, however, suggest that it can. Participation in intermolecular hydrogen bonding increases the lipid phase transition temperature by approx. 8-16 Cdeg relative to the electrostatically shielded state and by 20-30 Cdeg relative to the repulsively charged state, while having variable effects on the enthalpy. It increases the packing density in monolayers, possibly also in the liquid-crystalline phase in bilayers, and decreases the lipid hydration. These effects can probably be accounted for by transient, fluctuating hydrogen bonds involving only a small percentage of the lipid at any one time. Thus, rotational and lateral diffusion of the lipids may take place but at a slower rate, and the lateral expansion is limited. Intermolecular hydrogen bonding between lipids in bilayers may be significantly stabilized, despite the presence of water, by the fact that the lipids are already intermolecularly associated as a result of the hydrophobic effect and the Van der Waals' interactions between their chains. The tendency of certain lipids to self-associate, their asymmetric distribution in SUVs, their preferential association with cholesterol in non-cocrystallizing mixtures, their temperature-induced transitions to the hexagonal phase and their inhibitory effect on penetration of hydrophobic residues of proteins partway into the bilayer can all be explained by their participation in intermolecular hydrogen bonding interactions.(ABSTRACT TRUNCATED AT 400 WORDS)     

Designed chain architecture for enhanced migration resistance and property preservation in poly(vinyl chloride)/polyester blends

Blends of poly(vinyl chloride) (PVC) and poly(butylene adipate) (PBA) with varying degrees of branching were analyzed with respect to migration resistance during aging in water, preservation of material properties, and thermal stability. Gas chromatography-mass spectrometry, water absorption, weight loss, thermogravimetric analysis, Fourier transform infrared spectroscopy, contact angle, tensile testing, and differential scanning calorimetry were used to analyze the blends before and after aging in water for 6 weeks. Films plasticized with slightly branched polyester maintained their material and mechanical properties best during aging. High degree of branching was accompanied by poor miscibility, increased hydrophilicity, and polydispersity, and highly branched PBA was not favorable as a plasticizer. Strong intermolecular interactions reduced the water absorption and increased the migration resistance of the blends. Polymeric plasticizers with no, low, or moderate degree of branching improved the thermal stability of films compared to films plasticized with a traditional phthalate plasticizer. Proper design of plasticizer architecture led, thus, to improved migration resistance, long-term properties, and thermal stability in PVC/polyester blends.     

Exploring weak, transient protein--protein interactions in crowded in vivo environments by in-cell nuclear magnetic resonance spectroscopy

Biology relies on functional interplay of proteins in the crowded and heterogeneous environment inside cells, and functional protein interactions are often weak and transient. Thus, methods that preserve these interactions and provide information about them are needed. In-cell nuclear magnetic resonance (NMR) spectroscopy is an attractive method for studying a protein's behavior in cells because it may provide residue-level structural and dynamic information, yet several factors limit the feasibility of protein NMR spectroscopy in cells; among them, slow rotational diffusion has emerged as the most important. In this paper, we seek to elucidate the causes of the dramatically slow protein tumbling in cells and in so doing to gain insight into how the intracellular viscosity and weak, transient interactions modulate protein mobility. To address these questions, we characterized the rotational diffusion of three model globular proteins in Escherichia coli cells using two-dimensional heteronuclear NMR spectroscopy. These proteins have a similar molecular size and globular fold but very different surface properties, and indeed, they show very different rotational diffusion in the E. coli intracellular environment. Our data are consistent with an intracellular viscosity approximately 8 times that of water, too low to be a limiting factor for observation of small globular proteins by in-cell NMR spectroscopy. Thus, we conclude that transient interactions with cytoplasmic components significantly and differentially affect the mobility of proteins and therefore their NMR detectability. Moreover, we suggest that an intricate interplay of total protein charge and hydrophobic interactions plays a key role in regulating these weak intermolecular interactions in cells.     

Inversion of the balance between hydrophobic and hydrogen bonding interactions in protein folding and aggregation

Identifying the forces that drive proteins to misfold and aggregate, rather than to fold into their functional states, is fundamental to our understanding of living systems and to our ability to combat protein deposition disorders such as Alzheimer's disease and the spongiform encephalopathies. We report here the finding that the balance between hydrophobic and hydrogen bonding interactions is different for proteins in the processes of folding to their native states and misfolding to the alternative amyloid structures. We find that the minima of the protein free energy landscape for folding and misfolding tend to be respectively dominated by hydrophobic and by hydrogen bonding interactions. These results characterise the nature of the interactions that determine the competition between folding and misfolding of proteins by revealing that the stability of native proteins is primarily determined by hydrophobic interactions between side-chains, while the stability of amyloid fibrils depends more on backbone intermolecular hydrogen bonding interactions.     

Easy methods to study the smart energetic TNT/CL-20 co-crystal

2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is a high-energy nitramine explosive with high mechanical sensitivity. 2,4,6-trinitrotoluene (TNT) is insensitive but by no means a high performance explosive. To reveal the significant importance and smart-material functionality of the energetic-energetic co-crystals, the stability, mechanical and explosive properties TNT/CL-20 co-crystal, TNT crystal and CL-20 crystal were studied. Non-hydrogen bonded non-covalent interactions govern the structures of energetic-energetic co-crystals. However, it is very difficult to accurately calculate the non-covalent intermolecular interaction energies. In this paper, the local conformation and the intricate non-covalent interactions were effectively mapped and analyzed from the electron density (ρ) and its derivatives. The results show that the two components TNT and CL-20 are connected mainly by nitro–aromatic interactions, and nitro–nitro interactions. The steric interactions in TNT/CL-20 could not be confronted with the attractive interactions. Moreover, the scatter graph of TNT crystal reveals the reason why TNT is brittle. The detailed electrostatic potential analysis predicted that the detonation velocities (D) and impact sensitivity for the compounds both increase in the sequence of CL-20 > TNT/CL-20 co-crystal > TNT. Additionally, TNT/CL-20 co-crystal has better malleability than its pure components. This demonstrates the capacity and the feasibility of realizing explosive smart materials by co-crystallization, even if strong hydrogen bonding schemes are generally lacking in energetic materials.

Thermal mobility of β-O-4-type artificial lignin

Several lignin model polymers and their derivatives comprised exclusively of β-O-4 or 8-O-4' interunitary linkages were synthesized to better understand the relation between the thermal mobility of lignin, in particular, thermal fusibility and its chemical structure; an area of critical importance with respect to the biorefining of woody biomass and the future forest products industry. The phenylethane (C6-C2)-type lignin model (polymer 1) exhibited thermal fusibility, transforming into the rubbery/liquid phase upon exposure to increasing temperature, whereas the phenylpropane (C6-C3)-type model (polymer 2) did not, forming a char at higher temperature. However, modifying the Cγ or 9-carbon in polymer 2 to the corresponding ethyl ester or acetate derivative imparted thermal fusibility into this previously infusible polymer. FT-IR analyses confirmed differences in hydrogen bonding between the two model lignins. Both polymers had weak intramolecular hydrogen bonds, but polymer 2 exhibited stronger intermolecular hydrogen bonding involving the Cγ-hydroxyl group. This intermolecular interaction is responsible for suppressing the thermal mobility of the C6-C3-type model, resulting in the observed infusibility and charring at high temperatures. In fact, the Cγ-hydroxyl group and the corresponding intermolecular hydrogen bonding interactions likely play a dominant role in the infusibility of most native lignins.     

Conformational changes and molecular mobility in plasticized proteins

Most biopolymers exist in a plasticized state, whether it is naturally with water or unnaturally with glycerol or other suitable polyol, to make a flexible material. We have found that the extent to which a biopolymer can be plasticized is dependent on its molecular and higher order structures outside of simply molecular weight. Lactalbumin, ovalbumin, corn zein, wheat gluten, and feather keratin were plasticized with glycerol from very low to very high amounts. The conformation of the proteins was monitored with Fourier transform-infrared (FT-IR) spectroscopy and X-ray powder diffraction (XRD) and correlated with the tensile modulus. Protein conformational changes were pronounced for polar proteins with a low amount of cysteine. FT-IR showed that the conformational changes resulted in ordering of the protein at low to moderate plasticization levels. For proteins with little resistance to conformational changes, additional small-scale ordering occurred around the glass transition, as observed in XRD. Accurate comparison of plasticized proteins was dependent on knowing whether or not the protein was glassy or rubbery at room temperature as no differences arose in the glassy state. The transition from glassy to rubbery behavior with plasticization level can be found from modulus, FT-IR, and XRD data.     

Proline and glycine control protein self-organization into elastomeric or amyloid fibrils

Elastin provides extensible tissues, including arteries and skin, with the propensity for elastic recoil, whereas amyloid fibrils are associated with tissue-degenerative diseases, such as Alzheimer's. Although both elastin-like and amyloid-like materials result from the self-organization of proteins into fibrils, the molecular basis of their differing physical properties is poorly understood. Using molecular simulations of monomeric and aggregated states, we demonstrate that elastin-like and amyloid-like peptides are separable on the basis of backbone hydration and peptide-peptide hydrogen bonding. The analysis of diverse sequences, including those of elastin, amyloids, spider silks, wheat gluten, and insect resilin, reveals a threshold in proline and glycine composition above which amyloid formation is impeded and elastomeric properties become apparent. The predictive capacity of this threshold is confirmed by the self-assembly of recombinant peptides into either amyloid or elastin-like fibrils. Our findings support a unified model of protein aggregation in which hydration and conformational disorder are fundamental requirements for elastomeric function.     

Quantum mechanical electronic structure calculation reveals orientation dependence of hydrogen bond energy in proteins

Hydrogen bond plays a unique role in governing macromolecular interactions with exquisite specificity. These interactions govern the fundamental biological processes like protein folding, enzymatic catalysis, molecular recognition. Despite extensive research work, till date there is no proper report available about the hydrogen bond's energy surface with respect to its geometric parameters, directly derived from proteins. Herein, we have deciphered the potential energy landscape of hydrogen bond directly from the macromolecular coordinates obtained from Protein Data Bank using quantum mechanical electronic structure calculations. The findings unravel the hydrogen bonding energies of proteins in parametric space. These data can be used to understand the energies of such directional interactions involved in biological molecules. Quantitative characterization has also been performed using Shannon entropic calculations for atoms participating in hydrogen bond. Collectively, our results constitute an improved way of understanding hydrogen bond energies in case of proteins and complement the knowledge‐based potential. Proteins 2017; 85:1046–1055. © 2017 Wiley Periodicals, Inc.