Electrophoretic Deposition of Layer-by-Layer Unsheathed Carbon Nanotubes-A Step Towards Steerable Surface Roughness and Wettability

It is well known that carbon nanotube (CNT) oxidation (usually with concentrated HNO3) is a major step before the electrophoretic deposition (EPD). However, the recent discovery of the "onion effect" proves that multiwalled carbon nanotubes are not only oxidized, but a simultaneous unsheathing process occurs. We present the first report concerning the influence of unsheathing on the properties of the thus-formed CNT surface layer. In our study we examine how the process of gradual oxidation/unsheathing of a series of multiwalled carbon nanotubes (MWCNTs) influences the morphology of the surface formed via EPD. Taking a series of well-characterized and gradually oxidized/unsheathing Nanocyl MWCNTs and performing EPD on a carbon fiber surface, we analyzed the morphology and wettability of the CNT surfaces. Our results show that the water contact angle could be gradually changed in a wide range (125-163°) and the major property determining its value was the diameter of aggregates formed before the deposition process in the solvent. Based on the obtained results we determined the parameters having a crucial influence on the morphology of created layers. Our results shed new light on the deposition mechanism and enable the preparation of surfaces with steerable roughness and wettability.

The effects of confinement in pores built of folded graphene sheets on the equilibrium of nitrogen monoxide dimerisation reaction

In the current work we have used reactive Monte Carlo simulations to systematically study the effects of graphene folding on equilibria of NO dimerisation occurring at isolated surfaces and in porous networks built of corrugated graphene sheets. It has been demonstrated that the folding of isolated graphene sheets significantly improves the yield of reactions occurring on their surface. Then, it has also been shown that in slit-like pores formed by the folded graphene sheets the reaction yield depends on the corrugation and arrangement of the pore walls. It has been found that the reaction yield increases when the walls' corrugation is high because of the appearance of narrow regions and/or wedge-like regions in the pores. The condensation of reacting fluid in such places, where the bulges at both walls are close one to another, leads to much higher reaction yield than on the surface of isolated sheets. Thus, we recommended the highly corrugated graphene to control the chemical reactions.

Water Nanodroplet on a Hydrocarbon "Carpet"-The Mechanism of Water Contact Angle Stabilization by Airborne Contaminations on Graphene, Au, and PTFE Surfaces

Wetting is very common phenomenon, and it is well documented that the wettability of a solid depends on the surface density of adsorbed airborne hydrocarbons. This "hydrocarbon hypothesis" has been experimentally confirmed for different surfaces, for example, graphene, TiO₂, and SiO₂; however, there are no scientific reports describing the influence of airborne contaminants on the water contact angle (WCA) value measured on the polytetrafluoroethylene (PTFE) surface. Using experimental data showing the influence of airborne hydrocarbons on the wettability of graphene, gold and PTFE by water, together with Molecular Dynamics simulation results we prove that the relation between the WCA and the surface concentration of hydrocarbons ( n-decane, n-tridecane, and n-tetracosane) is more complex than has been assumed up until now. We show, in contrast to commonly approved opinion, that adsorbed hydrocarbons can increase (graphene, Au) or decrease (PTFE) the WCA of a nanodroplet sitting on a surface. Using classical thermodynamics, a simple theoretical approach is developed. It is based on two adsorbed hydrocarbon states, namely, "carpet" and "dimple". In the "carpet" state a uniform layer of alkane molecules covers the entire substrate. In contrast, in the "dimple" state, the preadsorbed layer of alkane molecules covers only the open surface. Simple thermodynamic balance between the two states explains observed experimental and simulation results, forming a good starting point for future studies.

5-Keto-3-cyano-2,4-diaminothiophenes as selective maternal embryonic leucine zipper kinase inhibitors

Maternal embryonic leucine zipper kinase (MELK) is involved in several key cellular processes and displays increased levels of expression in numerous cancer classes (colon, breast, brain, ovary, prostate and lung). Although no selective MELK inhibitors have yet been approved, increasing evidence suggest that inhibition of MELK would constitute a promising approach for cancer therapy. A weak high-throughput screening hit (17, IC₅₀ ≈ 5 μM) with lead-like properties was optimized for MELK inhibition. The early identification of a plausible binding mode by molecular modeling offered guidance in the choice of modifications towards compound 52 which displayed a 98 nM IC₅₀. A good selectivity profile was achieved for a representative member of the series (29) in a 486 protein kinase panel. Future elaboration of 52 has the potential to deliver compounds for further development with chemotherapeutic aims.

Phenol Molecular Sheets Woven by Water Cavities in Hydrophobic Slit Nanospaces

Despite extensive research over the last several decades, the microscopic characterization of topological phases of adsorbed phenol from aqueous solutions in carbon micropores (pore size < 2.0 nm), which are believed to exhibit a solid and quasi-solid character, has not been reported. Here, we present a combined experimental and molecular level study of phenol adsorption from neutral water solutions in graphitic carbon micropores. Theoretical and experimental results show high adsorption of phenol and negligible coadsorption of water in hydrophobic graphitic micropores (super-sieving effect). Graphic processing unit-accelerated molecular dynamics simulation of phenol adsorption from water solutions in a realistic model of carbon micropores reveal the formation of two-dimensional phenol crystals with a peculiar pattern of hydrophilic-hydrophobic stripes in 0.8 nm supermicropores. In wider micropores, disordered phenol assemblies with water clusters, linear chains, and cavities of various sizes are found. The highest surface density of phenol is computed in 1.8 nm supermicropores. The percolating water cluster spanning the entire pore space is found in 2.0 nm supermicropores. Our findings open the door for the design of better materials for purification of aqueous solutions from nonelectrolyte micropollution.

Abstract 3516: Discovery of novel SHMT small molecule inhibitors for cancer treatment

Over-activation of the serine synthesis pathway, upregulation of SHMT2 has been described in over 20% of solid tumors (e.g. breast, lung, colorectal cancers). Such cancer cells are highly dependent on serine. Serine hydroxymethyltransferase (SHMT) plays a key role in a so-called one-carbon pathway, a group of biochemical reactions involved in amino acid metabolism. SHMT catalyzes the conversion of serine to glycine and also plays a role in the folate (vitamin B9) cycle. Antagonists of folate metabolism or antifolates are an established chemotherapy in certain cancers. Folate antagonism disrupts cell division, DNA/RNA synthesis and protein synthesis. Pemetrexed (for non-small cell lung carcinoma, mesothelioma) and methotreaxate (for autoimmune conditions like rheumatoid arthritis and certain cancers) are two well established and effective antifolates. The main drawback with antifolates in cancer treatment, however, is the development of resistance. In this study we report development of a series of small molecule SHMT1/2 inhibitors. Synthetized compounds exert potency in SHMT1/2 biochemical assay as well as in cellular assay (measured by the C13 serine to glycine conversion) with the low nanomolar range. Therapeutic effect of the compounds was investigated in the panel of cancer cell lines with different genetic background as well as with different SHMT2 levels. We identified several cell lines in which tested compounds inhibited cancer cell grow with nM GI50 values. Taken together, presented data supports our rationale for using SHMT1/2 inhibitors as a novel and interesting approach for the cancer therapy.

Citation Format: Anna Bartosik, Pawel Guzik, Marta Sowinska, Karolina Gluza, Marcin Krol, Anna Wrobel, Agnieszka Dreas, Faustyna Iwanska, Magdalena Zastawna, Urszula Kulesza, Nicolas Boutard, David Schultz, Justyna Wujkowska, Karolina Pyziak, Agnieszka Sroka-Porada, Agnieszka Przybylowicz, Agnieszka Adamus, Magdalena Sieprawska-Lupa, Przemyslaw Golik, Piotr Kowalczyk, Krzysztof Brzozka, Tomasz Rzymski, Mateusz Nowak. Discovery of novel SHMT small molecule inhibitors for cancer treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3516.

Nanoscale Water Contact Angle on Polytetrafluoroethylene Surfaces Characterized by Molecular Dynamics-Atomic Force Microscopy Imaging

The aim of this study is to link polytetrafluoroethylene (PTFE) surface characteristics with its wetting properties in the nanoscale. To do this using molecular dynamics (MD) simulation, three series of rough PTFE surfaces were generated by annealing and compressing and next characterized by the application of the MD version of the atomic force microscopy (AFM) method. The values of specific surface areas were additionally calculated. The TIP4P/2005 water model was used to study the wetting properties of obtained PTFE samples. The simulated water contact angle (WCA) value for the most flat (but slightly rough) sample having PTFE density is equal to 106.94°, and it is close to the value suggested for a perfect PTFE surface on the basis of experimental results. Also, the changes in the WCA with PTFE compression are in the same range as experimentally reported. The obtained MD simulation results make it possible to link, for the first time, the WCA values with the surface MD-AFM root-mean-square roughness and with the PTFE density. Finally, we show that for PTFE wetting in the nanoscale, the line tension is negligible and the Bormashenko's equation reduces to the Cassie-Baxter (CB) model. In fact, our simulation results are close to the CB mechanism.

Calculation of cancellous bone elastic properties with the polarization-based FFT iterative scheme

The Fast Fourier Transform-based method, originally introduced by Moulinec and Suquet in 1994 has gained popularity for computing homogenized properties of composites. In this work, the method is used for the computational homogenization of the elastic properties of cancellous bone. To the authors' knowledge, this is the first study where the Fast Fourier Transform scheme is applied to bone mechanics. The performance of the method is analyzed for artificial and natural bone samples of 2 species: bovine femoral heads and implanted femurs of Hokkaido rats. Model geometries are constructed using data from X-ray tomographies, and the bone tissue elastic properties are measured using microindentation and nanoindentation tests. Computed results are in excellent agreement with those available in the literature. The study shows the suitability of the method to accurately estimate the fully anisotropic elastic response of cancellous bone. Guidelines are provided for the construction of the models and the setting of the algorithm.

Water Adsorption Property of Hierarchically Nanoporous Detonation Nanodiamonds

The detonation nanodiamonds form the aggregate having interparticle voids, giving a marked hygroscopic property. As the relationship between pore structure and water adsorption of aggregated nanodiamonds is not well understood yet, adsorption isotherms of N₂ at 77 K and of water vapor at 298 K of the well-characterized aggregated nanodiamonds were measured. HR-TEM and X-ray diffraction showed that the nanodiamonds were highly crystalline and their average crystallite size was 4.5 nm. The presence of the graphitic layers on the nanodiamond particle surface was confirmed by the EELS examination. The pore size distribution analysis showed that nanodiamonds had a few ultramicropores with predominant mesopores of 4.5 nm in average size. The water vapor adsorption isotherm of IUPAC Type V indicates the hydrophobicity of the nanodiamond aggregates, with the presence of hydrophilic sites. Then the hygroscopic nature of nanodiamonds should be associated with the surface functionalities of the graphitic shell and the ultramicropores on the mesopore walls.

Nanoscale Insight into the Mechanism of a Highly Oriented Pyrolytic Graphite Edge Surface Wetting by "Interferencing" Water

The new molecular dynamics simulation results showing the influence of the edge carbon surface atoms on the wettability of a highly oriented pyrolytic graphite (HOPG) surface with water nanodroplets are reported. The conditions for the occurrence of the Wenzel effect are discussed, and the Cassie-to-Wenzel transition (CTWT) mechanism in the nanoscale is explored. This transition is detected by the application of a new procedure showing that the CTWT point shifts toward larger values of carbon-oxygen potential well depth with the decrease in the HOPG side angle. It is concluded that the Wenzel effect significantly contributes to the contact angles (CAs) measured for the HOPG surfaces. The Wenzel effect is also very important for the "HOPG" structures possessing the disturbed C-C interlayer distance, and its influence on the water nanodroplet CAs is strongly pronounced. The structure of water confined inside slits and on a HOPG surface is studied using the analysis of the density profiles, the number of hydrogen bonds, and, modified for the purpose of this study, structure factor. The detailed analysis of all parameters describing confined water leads to the conclusion about the presence of characteristic interference patterns revealed as a result of long-term simulation. A simple model describing this effect is proposed as the starting point for further considerations.

Determination of Isosteric Heat of Adsorption by Quenched Solid Density Functional Theory

The heat of adsorption is one of the most important parameters characterizing energetic heterogeneity of the adsorbent surface. Heats of adsorption are either determined directly by calorimetry or calculated from adsorption isotherms measured at different temperatures using the thermodynamic Clausius-Clapeyron equation. Here, we present a method for calculating the isosteric heat of adsorption that requires as input only a single adsorption isotherm measured at one temperature. The proposed method is implemented with either nonlocal (NLDFT) or quenched solid (QSDFT) density functional theory models of adsorption that are currently widely used for calculating pore size distributions in various micro- and mesoporous solids. The pore size distribution determined from the same experimental isotherm is used for predicting the isosteric heat. The QSDFT method has advantages of taking into account two factors contributing to the structural heterogeneity of adsorbents: the molecular level roughness of the surface and the pore size distribution. The method is illustrated with examples of low temperature nitrogen and argon adsorption on selected samples of carbons of different degree of graphitization and MCM-41 mesoporous silicas of different pore size. The isosteric heat predictions from the NLDFT and QSDFT methods are compared against relevant experiments and the results of Monte Carlo (MC) simulations, with good agreement found in the cases where the surface model adequately reflects the pore surface roughness. Analyses with the QSDFT method show that the isosteric heat of adsorption significantly depends of the molecular level roughness of the adsorbent surface, which is ignored in NLDFT and MC models. The proposed QSDFT method with further verification can be used for calculating the isosteric heat as an additional parameter characterizing the adsorbent surface in parallel with routine calculations of the pore size distribution from a single adsorption isotherm.

Monte Carlo study of chemical reaction equilibria in pores of activated carbons

Systematic Monte Carlo studies concerning relationships between the porous structure of activated carbons and the equilibria of reactions under confinement are presented.

Water nanodroplet on a graphene surface-a new old system

The major subject of our study is the accuracy of contact angle calculations. Reporting new simulation data for graphene-water systems, we show that the majority of previously reported data should be treated with caution, since the proper contact angle can be recorded only after a sufficiently long simulation time. It has been proven that-if one wants to gain accuracy greater than 0.1°-long calculations (exceeding 50 ns) are required. Finally, we also show, using both a Groningen Machine for Chemical Simulations (GROMACS) package and our new molecular dynamics (MD) code, that the changes in the contact angle, caused by graphene bottom layer rotation, are within the range of calculation error. We also propose a novel definition of the bottom of the droplet as the height where the density is half the density of liquid water. This new definition is applied in the method of the contact angle calculation from the MD simulation data.

Numerical Analysis of the Horvath–Kawazoe Equation — The Adsorption of Nitrogen, Argon, Benzene, Carbon Tetrachloride and Sulphur Hexafluoride

A previously proposed numerical procedure based on the Horvath–Kawazoe (HK) model for estimating the MPSD (micropore size distribution) from a single nitrogen adsorption isotherm was developed. The results of the calculation of MSPD for two synthetic carbons obtained from numerical studies using the modified procedure are presented and discussed. These allowed the evaluation of the distribution from a single adsorption isotherm of nitrogen, argon, benzene, carbon tetrachloride and sulphur hexafluoride. In addition, the nitrogen and argon adsorption potential distributions were calculated for the same carbons applying the HK and condensation approximation (CA) methods. Agreement between these two independent approaches was observed. Differences between the MSPD obtained from HK and from the Dubinin micropore filling model (using the CONTIN package) were observed and discussed. It was shown that the structural parameter of the Dubinin–Astakov equation had no significant influence on the MSPD curves obtained.

Inflammation increases oxidative DNA damage repair and stimulates preneoplastic changes in colons of newborn rats

Oxidative DNA damage may be a risk factor for development of various pathologies, including malignancy. We studied inflammation triggered modulation of repair activity in the intestines of three weeks old rats injected i.p. with E.coli or S. typhimurium lipopolysaccharides (LPS) at doses of 1, 5 or 10 mg/kg. Subsequent formation in these animals of colonic preneoplastic lesions, aberrant crypt foci (ACF) was also investigated. Five days after LPS administration no differences were observed in repair rate of 1,N(6)-ethenoadenine (εA), 3,N(4)-ethenocytosine (εC) and 8-oxoguanine (8-oxoG) in intestines of these rats, as measured by the nicking assay. However a significant increase in all three repair activities was found within one and two months after S. typhimurium LPS treatment. E. coli LPS significantly increased only the 8-oxoG repair. S. typhimurium LPS stimulated mRNA transcription of pro-inflammatory proteins, lipooxygenase-12 and cyclooxygenase-2, as well as some DNA repair enzymes like AP-endonuclease (Ape1) and εC-glycosylase (Tdg). mRNA level of DNA glycosylases excising εA (MPG) and 8-oxoG (OGG1) was also increased by LPS treatment, but only at the highest dose. Transcription of all enzymes increased for up to 30 days after LPS, and subsequently decreased to the level observed before treatment, with the exception of APE1, which remained elevated even two months after LPS administration. Thus, the repair efficiency of εA, εC and 8-oxoG depends on the availability of APE1, which increases OGG1 and TDG turnover on damaged DNA, and presumably stimulates MPG. One and two months after administration of E. coli or S. typhimurium LPS, the number of aberrant crypt foci in rat colons increased in a dose and time dependent manner. Thus, inflammation stimulates the repair capacity for εA, εC and 8-oxoG, but simultaneously triggers the appearance of preneoplastic changes in the colons. This may be due to increased oxidative stress and imbalance in DNA repair.