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One of the definitions of hydrophobic interactions is the aggregation of nonpolar particles in a polar solvent, such as water. While this phenomenon appears to be very simple, it is crucial for many complex processes, such as protein folding, to take place. In this work, the hydrophobic association of adamantane and hexane at various temperatures and ionic strengths was studied using molecular dynamics simulations with the AMBER 16.0 program and the GAFF force field. The potentials of mean force of hydrophobic dimer formation, as well as the excess free energy, excess energy, excess entropy, and excess heat capacity corresponding to the formation of the contact minimum, were determined and analyzed. For both systems, the depth of the contact minimum in the potential of mean force was found to increase with both temperature and ionic strength. The excess heat capacity of the association at the contact minimum and T = 298 K was found to be negative and to decrease, while the excess entropy and energy were found to be positive and to increase for both systems, the changes being more pronounced for the hexane dimer. The excess heat capacity is also greater in absolute value for the hexane dimer.

The SARS-CoV-2 virus, commonly known as COVID-19, first occurred in December 2019 in Wuhan, Hubei Province, China. Since then, it has become a tremendous threat to human health. With a pandemic threat, it is in the significant interest of the scientific world to establish its method of infection. In this manuscript, we combine knowledge of the infection mechanism with theoretical methods to answer the question of the virus’s selectivity. We proposed a two-stage infection mechanism. In the first step, the virus interacts with the ACE2 receptor, with the “proper strength”. When the interaction is too strong, the virus will remain in an “improper position”; if the interaction is too weak, the virus will “run away” from the cell. We also indicated three residues (positions 30, 31, and 353) located on the ACE2 protein-binding interface, which seems to be crucial for successful infection. Our results indicate that these residues are necessary for the initiation of the infection process.

Pharmacotherapy for inflammatory bowel disease (IBD) is difficult, and some patients do not respond to currently available treatments. Therefore, the discovery of novel anti-IBD agents is imperative. Our aim was the synthesis of lipidated analogs of sialorphin and the in vitro characterization of their effect on the degradation of Met-enkephalin by neutral endopeptidase (NEP). We also investigated in vivo whether the most active inhibitor (peptide VIII) selected in the in vitro studies could be a potential candidate for the treatment of colitis. Peptides were synthesized by the solid-phase method. Molecular modeling technique was used to explain the effect of fatty acid chain length in sialorphin analogs on the ligand–enzyme interactions. The anti-inflammatory effect was evaluated in the dextran sulphate sodium (DSS)-induced model of colitis in mice. Peptide VIII containing stearic acid turned out to be in vitro the strongest inhibitor of NEP. We have also shown that the length of the chain of stearic acid fits the size of the grove of NEP. Peptides VII and VIII exhibited in vivo similar anti-inflammatory activity. Our results suggest that lipidation of sialorphin molecule is a promising direction in the search for NEP inhibitors that protect enkephalins.

The recent NEWCT-9P version of the coarse-grained UNRES force field for proteins, with scale-consistent formulas for the local and correlation terms, has been tested in the CASP13 experiment of the blind-prediction of protein structure, in the ab initio, contact-assisted, and data-assisted modes. Significant improvement of the performance has been observed with respect to the CASP11 and CASP12 experiments (by over 10 GDT_TS units for the ab initio mode predictions and by over 15 GDT_TS units for the contact-assisted prediction, respectively), which is a result of introducing scale-consistent terms and improved handling of contact-distance restraints. As in previous CASP exercises, UNRES ranked higher in the free modeling category than in the general category that included template based modeling targets. Use of distance restraints from the predicted contacts, albeit many of them were wrong, resulted in the increase of GDT_TS by over 8 units on average and introducing sparse restraints from small-angle X-ray/neutron scattering and chemical cross-link-mass-spectrometry experiments, and ambiguous restraints from nuclear magnetic resonance experiments has also improved the predictions by 8.6, 9.7, and 10.7 GDT_TS units on average, respectively.

Pyrazine and its derivatives are a large group of compounds that exhibit broad biological activity, the changes of which can be easily detected by a substituent effect or a change in the functional group. The present studies combined theoretical research with the density functional theory (DFT) approach (B3LYP/6-311+G**) and experimental (potentiometric and spectrophotometric) analysis for a thorough understanding of the structure of chlorohydrazinopyrazine, its physicochemical and cytotoxic properties, and the site and nature of interaction with DNA. The obtained results indicated that 2-chloro-3-hydrazinopyrazine (2Cl3HP) displayed the highest affinity to DNA. Cytotoxicity studies revealed that the compound did not exhibit toxicity toward human dermal keratinocytes, which supported the potential application of 2Cl3HP in clinical use. The study also attempted to establish the possible equilibria occurring in the aqueous solution and, using both theoretical and experimental methods, clearly showed the hydrophilic nature of the compound. The experimental and theoretical results of the study confirmed the quality of the compound, as well as the appropriateness of the selected set of methods for similar research.

The UNited RESidue (UNRES) force field was tested in the 14th Community Wide Experiment on the Critical Assessment of Techniques for Protein Structure Prediction (CASP14), in which larger oligomeric and multimeric targets were present compared to previous editions. Three prediction modes were tested (i) ab initio (the UNRES group), (ii) contact-assisted (the UNRES-contact group), and (iii) template-assisted (the UNRES-template group). For most of the targets, the contact restraints were derived from the server models top-ranked by the DeepQA method, while the DNCON2 method was used for 11 targets. Our consensus-fragment procedure was used to run template-assisted predictions. Each group also processed the Nuclear Magnetic Resonance (NMR)- and Small Angle X-Ray Scattering (SAXS)-data assisted targets. The average Global Distance Test Total Score (GDT_TS) of the ‘Model 1’ predictions were 29.17, 39.32, and 56.37 for the UNRES, UNRES-contact, and UNRES-template predictions, respectively, increasing by 0.53, 2.24, and 3.76, respectively, compared to CASP13. It was also found that the GDT_TS of the UNRES models obtained in ab initio mode and in the contact-assisted mode decreases with the square root of chain length, while the exponent in this relationship is 0.20 for the UNRES-template group models and 0.11 for the best performing AlphaFold2 models, which suggests that incorporation of database information, which stems from protein evolution, brings in long-range correlations, thus enabling the correction of force-field inaccuracies.

This work describes the chemical synthesis, combinatorial selection, and enzymatic evaluation of peptidomimetic fluorescent substrates specific for the trypsin-like (&beta, 2) subunit of the 20S human proteasome. After deconvolution of a library comprising nearly 6000 compounds composed of peg substituted diaminopropionic acid DAPEG building blocks, the sequence ABZ&ndash, Dap(O2(Cbz))&ndash, Dap(GO1)&ndash, Arg&ndash, ANB&ndash, NH2, where ABZ is 2-aminobenzoic acid, and ANB- 5 amino 2- nitro benzoic acid was selected. Its cleavage followed sigmoidal kinetics, characteristic for allosteric enzymes, with Km = 3.22 &plusmn, 0.02 &mu, M, kcat = 245 s&minus, 1, and kcat/Km = 7.61 &times, 107 M&minus, 1 s&minus, 1. This process was practically halted when a selective inhibitor of the &beta, 2 subunit of the 20S human proteasome was supplemented to the reaction system. Titration of the substrate resulting in decreased amounts of proteasome 20S produced a linear signal up to 10&minus, 11 M. Using this substrate, we detected human proteasome 20S in human urine samples taken from the bladders of cancer patients. This observation could be useful for the noninvasive diagnosis of this severe disease.

One of the possible applications of ionic liquids is to produce electricity from heat. The iron oxide nanoparticle is a potent electrical particle, which is expected to improve the heat's efficiency to electricity conversion, however, it is prone to aggregation and sedimentation, which hamper its application. One of the methods to enhance the nanoparticle's solubility and electrical properties is the use of a stabilizing component in the production and application process. In this research, we studied, how the nanoparticle affects the properties of the 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI) ionic liquid. The citric acid was used as a nanoparticle stabilizing agent and led to decrease of the diffusion coefficient of the ionic liquid's components. Our results indicated, that with the addition of the citric acid, strong solvation sphere around nanoparticle was formed. The presence of nanoparticles significantly reduced the diffusion of ionic liquid components. Finally, the citric acid was found to be the strongest nanoparticle binding component of the studied system, and therefore it was able to stabilize the nanoparticle in solution.

Experimental methods of investigations of nanoparticle (NP)–protein interactions are limited, because they require a high amount of samples and the NPs tend to interfere with spectral results. Therefore, molecular modeling is a commonly accepted tool in such kind of investigations. Examining the molecule toxicity on the molecular level, we usually want to know, mainly, the location of the ligand on the protein surface and what is an influence of such a contact on the biological functions of the protein. In the presented work, we demonstrate that multiple-docking of the ligand from a random start and with large grid volume, to let the ligand search the whole protein surface, allows to find the best binding sites and gives reliable results considering ligand–protein interactions. In the present work, we have constructed six models of bronchoalveolar lavage fluids proteins: α1-antitripsin, albumin, ceruloplasmin, lactoferrin, lysozyme, and transferrin with fullerene, C60 utilizing molecular docking methods. The most probable results were examined with steered molecular dynamics (SMD) to see, if the simple docking method is able to predict the fullerene binding affinity. Albumin and lysozyme were already widely investigated and literature data is available for their complexes with fullerene C60 and/or its derivatives. Thus, we used these two models as a reference set to validate the used molecular modeling methods. With our best knowledge, interactions of the remaining four proteins with NPs have never been investigated in detail before. Our results indicate that fullerene C60 readily interacts with all studied proteins and may have a large impact on their biological functions.

Ionic liquids (ILs) have attracted much attention for their unique physicochemical properties, which can be designed as needed by altering the ion combinations. Besides experimental work, numerous computational studies have been concerned with prediction of physical properties of ILs. The results of molecular dynamics simulations of ILs depend strongly on the proper force field parameterization. Classical force fields and the force fields designed specifically for ILs have been found to yield diffusion coefficients, that are too low for the liquid state. This has been attributed to the lack of electronic polarizability in the most force fields. One simple solution to this problem has been uniform by scaling down of the partial charges of all ions. In this work we investigated the influence of the charge scaling, the size of the simulated system and the temperature factor on calculated density, radial distribution function and the diffusion coefficients of the cation and anion of two methylpyridinium based ionic liquids: 1-butyl-4-methylpyridinium tetrafluoroborate ([b4mpy][BF 4 ]) and 1-butyl-4-methylpyridinium chloride ([b4mpy][Cl]). We show that the parameterization is the key for a proper reproduction of the diffusion coefficient and as a consequence the melting temperature and ionic conductivity. We were also able to get some structural informations on the cation-anion relationships in the investigated ILs.

Phosphorylated proteins take part in many signaling pathways and play a key role in homeostasis regulation. The all-atom force fields enable us to study the systems containing phosphorylated proteins, but they are limited to short time scales. In this paper, we report the extension of the physics-based coarse-grained UNRES force field to treat systems with phosphorylated amino-acid residues. To derive the respective potentials, appropriate physics-based analytical expressions were fitted to the potentials of mean force of systems modeling phosphorylated amino-acid residues computed in our previous work and implemented in UNRES. The extended UNRES performed well in ab initio simulations of two miniproteins containing phosphorylated residues, strongly suggesting that realistic large-scale simulations of processes involving phosphorylated proteins, especially signaling processes, are now possible.

In this paper we present the methodology for assessing the ionic liquids’ viscosity at six temperature points (25, 35, 45, 50, 60 and 70 [°C]), which utilizes only the in silico approach. The main idea of such assessment is based on the “correction equation” describing the correlation between experimentally measured viscosity and theoretically derived density (calculated with use of molecular mechanics), given at 6 different temperature points. The equation allows for recalculating the viscosity of ILs at 25 °C to determine the viscosity of ILs at other, higher temperature. Since the equation needs the basic viscosity value (at 25 °C) we additionally developed QSPR model that allows predicting it. According to our model, the viscosity of ILs is dependent to the size and branching of the cation and size, shape, symmetry and the vertical electron binding energy of IL’s anion. With those novel tools, it is possible to predict the viscosity of new ionic liquids at different temperatures without the need of experimental measurements.

Knowledge-based methods are, at present, the most effective ones for the prediction of protein structures; however, their results heavily depend on the similarity of a target sequence to those of proteins with known structures. On the other hand, the physics-based methods, although still less accurate and more expensive to execute, are independent of databases and give reasonable results where the knowledge-based methods fail because of weak sequence similarity. Therefore, a plausible approach seems to be the use of knowledge-based methods to determine the sections of the structures that correspond to sufficient sequence similarity and physics-based methods to determine the remaining structure. By participating in the 12th Community Wide Experiment on the Critical Assessment of Techniques for Protein Structure Prediction (CASP12) as the KIAS-Gdansk group, we tested our recently developed hybrid approach, in which protein-structure prediction is carried out by using the physics-based UNRES coarse-grained energy function, with restraints derived from the server models. Best predictions among all groups were obtained for 2 targets and 80% of our models were in the upper 50% of the models submitted to CASP. Our method was also able to exclude, with about 70% confidence, the information from the servers that performed poorly on a given target. Moreover, the method resulted in the best models of 2 refinement targets and performed remarkably well on oligomeric targets.

The p-xylylene monomers of parylene N, C and D have similar high polymerization reactivity. For effective copolymerization processes this fact is basically a drawback and for instance the copolymerization with styrene doesn’t go at all (Corley et al. J Pol Sc 13(68):137–156, [15]). Substitution of terminal hydrogen atoms by chlorine atoms reduces reactivity dramatically. 7,7,8,8-tetrachloro-p-xylylene and 2,5,7,7,8,8-hexachloro-p-xylylene can be isolated as yellow crystals. These crystals can be kept without any change in temperature below 0 ∘C, but they polymerize slowly at room temperature. Perchloro-p-xylylene is stable even at elevated temperatures and does not polymerize under any conditions. Both 7,7,8,8-tetrachloro-p-xylylene and 2,5,7,7,8,8-hexachloro-p-xylylene copolymerize with various vinyl monomers, such as styrene and others. In this work the polymerization reactions of different chloro-derivatives of p-xylylene were modeled by means of the DFT method with hybrid correlation functionals (B3LYP and PBE0) and, for comparison, by means of the Hartree Fock methods. We inquired both initiation as well as elongation polymeric reactions for each of the reactants. We survied their reactivity analytically examining energetics and configurations in Szwarc-like process. The quantitative influence of chlorine atoms on the reactivity in polymerization steps, their location in the reactants’ structure (aromatic and/or aliphatic) as well as their number, were reviewed. The polymerizations of p-xylylenes with chlorine atoms as terminal aliphatic substituents yet revealed one more access path for parylenes’ in situ functionalization. Electronic supplementary material The online version of this article (doi:10.1007/s00894-016-3179-6) contains supplementary material, which is available to authorized users.

The folding of the N-terminal part of the B-domain of staphylococcal protein A (PDB ID: 1BDD, a 46-residue three-α-helix bundle) and the formin-binding protein 28 WW domain (PDB ID: 1E0L, a 37-residue three-stranded anti-parallel β protein) was studied by means of Langevin dynamics with the coarse-grained UNRES force field to assess the influence of hydrodynamic interactions on protein-folding pathways and kinetics. The unfolded, intermediate, and native-like structures were identified by cluster analysis, and multi-exponential functions were fitted to the time dependence of the fractions of native and intermediate structures, respectively, to determine bulk kinetics. It was found that introducing hydrodynamic interactions slows down both the formation of an intermediate state and the transition from the collapsed structures to the final native-like structures by creating multiple kinetic traps. Therefore, introducing hydrodynamic interactions considerably slows the folding, as opposed to the results obtained from earlier studies with the use of Gō-like models.

S100B protein is one of the factors involved in the down-regulation of tumor suppressor protein p53, a transcription activator that signals for cycle arrest and apoptosis. As the inactivation of normal p53 functions is found in over half of human cancers, restoration of normal p53 functions through the destruction or prevention of S100B - p53 complexes represents a possible approach for the development of anti-cancer drugs. The aim of this work was to propose the S100B binding interface through an examination of the literature and use of molecular modeling (MM) techniques with AutoDock program and the AMBER force field. We propose two residues in the S100B binding pocket (Val56, Phe76) and two residues on the protein surface (Val52, Ala83) are essential for ligand binding. The data presented here indicate that interactions with these four residues are necessary for a reduction in the incidence of the S100B - p53 complex. Additionally, we have tried to explain a mechanism for the action of pentamidine, the best-known S100B ligand, and have proposed two S100B - pentamidine structures. The results presented here may be useful for the efficient design of new S100B ligands.

The potentials of mean force (PMFs) were determined for systems forming molecular and ionic heterocomplexes (in which the proton is transferred from a neutral acid to a neutral base molecule) composed of acetic acid and phenol with amines in three solvents with different polarities and hydrogen-bonding propensities: acetonitrile (AN), dimethyl sulfoxide (DMSO), and water. For each pair and each solvent, a series of umbrella-sampling molecular dynamics simulations with the AMBER force field and explicit solvent molecules were carried out and the PMF was calculated by using the weighted histogram analysis method (WHAM). Subsequently, heteroconjugation equilibrium constants were calculated by numerical integration of the respective PMF profiles. All complexes except those involving acetic acid as a proton donor in water were found to form in solution, which was manifested by the presence of contact minima corresponding to hydrogen-bonded species in the PMF curves. The calculated heteroconjugation constants were found to be greater for complexes with proton transfer than for those without proton transfer for the acetic acid-n-butylamine system in all solvents and for the phenol-imidazole and phenol-n-butylamine systems in DMSO when the same reference state (molecular acid and molecular base) was considered. For the acetic acid-n-butylamine system in acetonitrile and dimethyl sulfoxide, the calculated constants of ionic heterocomplex formation are greater than the values determined by potentiometric titration, while the calculated constants of molecular heterocomplex formation, as well as the calculated constants of heterocomplex formation from acetic acid and 4(5)-methylimidazole, are in good agreement with the experimental data, which suggests that the force field applied overestimates the energy of the interactions of oppositely charged ions or the energy of the interactions of hydrogen-bonding species with solvent molecules. The constants were found to decrease with an increasing polarity and hydrogen-bonding propensity of the solvent (i.e., in the series AN > DMSO > H 2 O), this being in agreement with the available experimental data.

The nonapeptide hormones arginine vasopressin (CYFQNCPRG-NH2, AVP) and oxytocin (CYIQNCPLG-NH2, OT), control many essential functions in mammals. Their main activities include the urine concentration (via stimulation of AVP V2 receptors, V2R, in the kidneys), blood pressure regulation (via stimulation of vascular V1a AVP receptors, V1aR), ACTH control (via stimulation of V1b receptors, V1bR, in the pituitary) and labor and lactation control (via stimulation of OT receptors, OTR, in the uterus and nipples, respectively). All four receptor subtypes belong to the GTP-binding (G) protein-coupled receptor (GPCR) family. This work consists of docking of YM087, a potent non-peptide V1aR and V2R - but not OTR - antagonist, into the receptor models based on relatively new theoretical templates of rhodopsin (RD) and opiate receptors, proposed by Mosberg et al. (Univ. of Michigan, Ann Arbor, USA). It is simultaneously demonstrated that this RD template satisfactorily compares with the first historical GPCR structure of bovine rhodopsin (Palczewski et al., 2000) and that homology-modeling of V2R, V1aR and OTR using opiate receptors as templates is rational, based on relatively high (20-60%) sequence homology among the set of 4 neurophyseal and 4 opiate receptors. YM087 was computer-docked to V1aR, V2R and OTR using the AutoDock (Olson et al., Scripps Research Institute, La Jolla, USA) and subsequently relaxed using restrained simulated annealing and molecular dynamics, as implemented in AMBER program (Kollman et al., University of California, San Francisco, USA). From about 80 diverse configurations, sampled for each of the three ligand/receptor systems, 3 best energy-relaxed complexes were selected for mutual comparisons. Similar docking modes were found for the YM087/V1aR and YM087/V2R complexes, diverse from those of the YM087/OTR complexes, in agreement with the molecular affinity data.

The mechanism of polymerization of p-xylylene and its derivatives is analyzed at the theoretical level. The polymerization reaction takes place in vacuo without any catalyst. The first step is a pyrolytic decomposition of starting material for polymerization, p-cyclophane, a cyclic dimer of p-xylylene, into biradical linear dimer and finally into two quinonoid monomeric molecules of p-xylylene. The quinonoid monomer is diamagnetic; i.e., it has a singlet ground state. The monomers after pyrolysis, when the temperature is lowered, do not re-form cyclic dimers but instead polymerize into long chain molecules. The initiation of polymerization requires dimerization of two monomers leading to formation of a genuine noncoupled biradical dimer. The chain molecules grow through the propagation reaction only one unit at a time, by the attachment of a monomer to a radical chain end. In this work the pyrolysis reaction, the initiation reaction and the first propagation steps of parylene polymerization (up to pentamer) are studied in details using different quantum chemical methods: AM1 and PM6 semiempirical methods and density functional theory (DFT) approach using B3LYP functional with two basis sets of different size (SVP and TZVP).

G protein-coupled receptors relay diverse extracellular signals into cells via a common mechanism, involving activation of cytosol G proteins. The mechanism underlies the actions of approximately 50% of all drugs. In this work, we focus on simulating three protein-ligand complexes of the neurohypophyseal hormone analog 4-OH-phenylacetyl- D-Y(Me)FQNRPR-NH2 (I) with the human V1a, V2 and oxytocin receptors. The peptideI is a potent selective V1a receptor antagonist. To obtain relaxed models of the complexes, the following techniques were used: docking ofI into the vasopressin V1a, V2 and oxytocin receptor models, optimization of the geometry of the resulting complexes and molecular dynamics in a fully hydrated 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphatidylcholine lipid bilayer. The results of the simulations allow us to draw some conclusions about the ligand selectivity to V1aR.

Parylene C, poly(chloro-para-xylylene) is the most widely used member of the parylene family due to its excellent chemical and physical properties. In this work we analyzed the formation of the parylene C film using molecular mechanics and molecular dynamics methods. A five unit chain is necessary to create a stable hydrophobic cluster and to adhere to a covered surface. Two scenarios were deemed to take place. The obtained results are consistent with a polymer film scaling growth mechanism and contribute to the description of the dynamic growth of the parylene C polymer. Electronic supplementary material The online version of this article (doi:10.1007/s00894-011-1050-3) contains supplementary material, which is available to authorized users.