Steric Energy Research Articles

Theoretical and Experimental Study on the Preparation of High-Viscosity Magnetic Nanofluid by Combined Surfactants.

In this study, the mechanism by which combined surfactants affect the dispersion stability of magnetic nanofluids (MNFs) was improved. Two stable lubricating oil-based magnetic nanofluids with high viscosity and one with low viscosity were prepared by chemical coprecipitation. Erucic acid and octanoic acid were used as the combined surfactants to modify the Fe3O4 nanoparticles (MNPs). The size and morphology of the particles were observed using TEM. The rheological properties were tested with a rotational rheometer. The magnetization of the lubricating oil-based magnetic nanofluids was characterized by VSM. The results indicated that the prepared magnetic nanofluids had high viscosity, high magnetism, and good stability. This study provided ideas for the preparation of a high-viscosity magnetic nanofluid. By using combined surfactants, sufficient steric repulsion energy can be provided to counteract the attraction energy of sterically protected nanoparticles, thus achieving a balance of the dispersion stability of MNF.

Transferability of Buckingham Parameters for Short-Range Repulsion between Topological Atoms.

The repulsive part of the Buckingham potential, with parameters A and B, can be used to model deformation energies and steric energies. Both are calculated using the interacting quantum atom energy decomposition scheme where the latter is obtained from the former by a charge-transfer-based energy correction. These energies relate to short-range interactions, specifically the deformation of electron density and steric hindrance, respectively, when topological atoms approach each other. In this work, we calculate and fit the energies of carbonyl carbon, carbonyl oxygen, and, where possible, amine nitrogen atoms to the repulsive part of the Buckingham potential for 26 molecules. We find that while the steric energies of all atom pairs studied display exponential behavior with respect to distance, some deformation energy data do not. The obtained parameters are shown to be transferable by calculating root-mean-square errors of fitted potentials with respect to energy data of the same atom in, as far as possible, all other molecules from our data set. We observed that 36% and 10% of these errors were smaller than 4 kJ mol-1 for steric and deformation energy, respectively. Thus, we find that steric energy parameters are more transferable than deformation energy parameters. Finally, we speculate about the physical meaning of the A and B parameters and the implications of the strong exponential and exponential-linear piecewise relationships that we observe between them.

Intramolecular steric and relaxation analysis of nitrogen clusters

Electron deformation density analysis were performed for ten nitrogen clusters NX (X = 4–12,14), where multiple types of fragmentations were considered for each cluster as interaction between a single isolated nitrogen molecule and the rest of cluster. Two components of electronic deformation density including steric or kinetic energy pressure and orbital relaxation were analyzed to reveal deformation density distributions and the corresponding displaced charges as quantitative description. Results show dominance of relaxation over steric interaction from both qualitative and quantitative displaced charges standpoints. Topological analysis of deformation density is also accomplished and critical points and steric paths were identified.

Enabling C7 Methylation and Arylation of the Indolyl Core via P(III)‐Directed C−H Functionalization

AbstractPeripheral editing of complex molecules via C−H functionalization removes the pervasive retrosynthetic bias toward pre‐functionalization and taps into the innate, often subtle, stereoelectronic differences between C−H linkages. Using this approach, bioactive molecules and residues can be modified without being beholden to lengthy sequences, thus allowing biochemical hypotheses to be interrogated on accelerated timelines. Herein, the C−H functionalization paradigm is leveraged to tackle C7 C−H functionalization of the biologically important tryptophan core. The devised process, which was expanded to indolyl (and related) systems, utilizes an N‐bound unsymmetrical “designer” phosphine to direct C−H functionalization to the desired position while maintaining operational ease of directing group installation/removal. Quantum mechanically calculated steric properties and activation free energies suggest that this phosphine is hindered enough for favoring C−H functionalization over deactivation pathways but is still easily cleaved by nucleophiles. In addition, the process enables the direct C−H methylation, cyclopropanation, and arylation of tryptophan to yield unnatural amino acid (UAA) building blocks. As a testament to the versatility of this method, a solid phase peptide synthesis (SPPS)‐ready phosphinated tryptophan was incorporated into a pentapeptide and the C−H functionalization/dephosphination sequence was executed with ease. The utility of “on‐peptide” editing was exhibited through the late‐stage functionalization of several pentapeptides with a diverse set of C7 substituents on‐ and off‐resin.

Theoretical study of solvent effect on elimination reactions: Hybrid-DFT study, and NBO analysis

In elimination reactions, the arrangement of leaving groups plays a crucial role in facilitating the reaction. On the other hand, equatorial and axial stereoisomers of a compound have a different share of stability. The presence of a solvent plays a different role in the stability of each stereoisomer. From LC-ωPBE and B3LYP methods and Natural Bond Orbital (NBO) interpretation to investigate 3-chloro-8-methyl-8-azabicyclo [3.2.1] octane (1), 3-bromo-8-methyl-8-azabicyclo [3.2.1] octane (2), and 8-methyl-8-azabicyclo [3.2.1] octan-3-yl 4-methylbenzenesulfonate (3), was used. Investigation of thermodynamic parameters showed that equatorial stereoisomers are more stable than axial stereoisomers, and by changing the gas phase to n-hexane and water, the stability of equatorial stereoisomers increased. The stability of the equatorial stereoisomers is the result of the electrostatic model involving dipole-dipole interactions and the combined effects of hyperconjugation interactions and Total Steric Exchange Energy (TSEE). Therefore, it can be expressed that the equatorial stereoisomers of compounds 1-3 show superior performance in the elimination reaction of 1, 4 in the presence of a solvent, and this performance becomes more evident by changing the polarity of the solvent

Study on dispersion stability of natural brucite in aqueous media

A brucite suspension can absorb sulfur dioxide (SO2). It thereby plays a significant role flue gas desulfurization. However, the dispersion of a natural brucite suspension is low which seriously affects its efficiency for SO2 absorption. The dispersion stability and particle size of the brucite suspension are therefore, particularly important to investigate. The effects of types and dosages of inorganic dispersants on the particle size and dispersion stability of the brucite suspension have been investigated in the present study by performing sedimentation experiments and zeta potential tests. The results showed that the addition of 0.5 wt.% sodium hexametaphosphate (SHMP) had a positive effect on the dispersion stability of brucite in an aqueous medium. The effect of SHMP on the surface properties of the brucite particles was also studied by performing characterizations like scanning electron microscopy (SEM) and infrared spectroscopy (IR), and by using an extended DLVO theory (named after Boris Derjaguin and Lev Landau, Evert Verwey and Theodoor Overbeek). The results showed that SHMP was chemisorbed on the brucite particle surface. It also formed complexes with magnesium ions, and changed the zeta potential of brucite. In addition, calculations based on the extended DLVO theory showed that the sum of the steric hindrance-induced interaction energy, Van-der-Waals energy, and electrostatic energy changed from an unfavorable value to a favorable value with an increase in the particle distance. These results showed that the addition of SHMP could improve the desulphurization effect of the brucite suspension.

Insight into the influence of plant oils on the composition of diacylglycerol fabricated by glycerolysis and esterification

Thirty plant oils are utilized for preparation of value-added DAG by esterification and glycerolysis with glycerol to simultaneously clarify the source-structure-composition relationship in order to increase DAG production and reduce separation process in this investigation. It is found that the dominant DAG components of linoleic acid-rich oils are dilinolein (DL, ECN=28) and linoleoyl-oleoyl glyceride (DOL, ECN=30), and oleic acid-rich oils mainly comprise DOL and diolein (DO ECN=32), whereas DAG from the oils with the close ratio of linoleic/oleic acid dominantly contains the DL, DOL and DO species. The constituents of DAG from the oils rich in unsaturated fatty acid (oleic + linoleic + linolenic acid ≥ 80%) are occupied by the dilinolenin (DLn, ECN=24), dilinoleoyl-linolenoyl glyceride (DLnL, ECN=26) and DL. Visualization and three-dimension structure optimization shows that the DLn, DL, DOL and DO molecules have the lower steric energy. The molecular docking simulation reveals that DAG molecule is mainly interacted with the active pocket (Thr40-Ser105-Asp134-Gln157-His224) of Novozym 435 by O···H bond. This investigation not only provides a deep insight into the source-structure-composition relationship of value-added DAG-rich oils from glycerol as byproduct in biodiesel industries and plant oils derived from agro-industrial residues in food industry, but also discloses the interaction mechanism DAG molecule and Novozym 435.

Insight into the medium-long-medium structured lipids made from Camellia oil: Composition-structure relationship.

Medium-long-medium (MLM) structured lipid (SL) as a new SL is a potential functional ingredient in food and nutraceutical products, but its composition-structure-physicochemical properties relationship has not been revealed in food industry. MLM type of medium-long chain triacylglycerol (MLCT) was synthesized from Camellia oil by combi-lipase; its physicochemical properties and composition-structure relationship were investigated in this research. The higher MLCT (67.24%±0.09) and MLM (52.71%±0.53) productivities were achieved after parameter optimization. The physicochemical characterization of SLs exhibited mild thermal property, intermediate Fourier transform infrared spectroscopy absorption intensity, and better crystal morphology. Joint characterizations identified that MLM and long-medium-long type SL were rich in 1,3-dioctanoyl-2-linoleoyl glyceride (CaLCa), 1,3-dioctanoyl-2-oleoyl glyceride (CaOCa), 1,3-dilinoleoyl-2-octanoyl glyceride (LCaL), and 1,3-dilinoleoyl-2-decanoyl glyceride (LCL) components, respectively. This is ascribed to the higher proportion of caprylic and linoleic acid in 1,3-specific enzyme. The 3D structural analysis further demonstrated that the CaLCa, CaOCa, LCaL, and LCL molecules had lower steric energy to form symmetrical structure at 1,3-position. This research provides a practical method to produce MLM-type SL from edible oils and fats in food industry.

A comparison between steepest descent and non-linear conjugate gradient algorithms for binding energy minimization of organic molecules

The main intention of optimization is to bring about the “best” of any model by prioritizing the needs along with a given set of constraints. There is a wide range of optimization problems, among which, unfortunately, the problems that are formulated from nature are not convex in nature. Solving non-convex optimization problems are quite trickier than the conventional method of derivatives. One such problem is Computing the minimum value of binding free energy of various molecules. Minimization of free energy of a molecule is highly significant in the field of Molecular mechanics which is the foundation of computational biology. For any molecule, free energy refers to the amount of energy needed to separate an individual particle from a system of particles or to disseminate all particles in a system. The significance of free energy is that it can be used to compute the lowest energy conformation, which corresponds to the least Steric energy. Hence, this paper aims at computing the minimum value of binding free energy of various organic molecules in isolated conditions using the steepest descent algorithm and conjugate gradient algorithm and comparing them.

Benzoquinoline Chemical Space: A Helpful Approach in Antibacterial and Anticancer Drug Design.

Benzoquinolines are used in many drug design projects as starting molecules subject to derivatization. This computational study aims to characterize e benzoquinone drug space to ease future drug design processes based on these molecules. The drug space is composed of all benzoquinones, which are active on topoisomerase II and ATP synthase. Topological, chemical, and bioactivity spaces are explored using computational methodologies based on virtual screening and scaffold hopping and molecular docking, respectively. Topological space is a geometrical space in which the elements composing it can be defined as a set of neighbors (which satisfy a particular axiom). In such space, a chemical space can be defined as the property space spanned by all possible molecules and chemical compounds adhering to a given set of construction principles and boundary conditions. In this chemical space, the potentially pharmacologically active molecules form the bioactivity space. Results show a poly-morphological chemical space that suggests distinct characteristics. The chemical space is correlated with properties such as steric energy, the number of hydrogen bonds, the presence of halogen atoms, and membrane permeability-related properties. Lastly, novel chemical compounds (such as oxadiazole methybenzamide and floro methylcyclohexane diene) with drug-like potential, active on TOPO II and ATP synthase have been identified.

Dominant changes in centre Fe atom of decamethyl-ferrocene from ferrocene in methylation

Staggered decamethyl-ferrocene (*Fc) becomes the lower energy conformer at low temperature, whereas the eclipsed conformer of ferrocene (Fc) is more stable. The powerful infrared (IR) spectroscopy which has remarkably provided signatures of ferrocene (Fc) in eclipsed and staggered conformers recently is employed to investigate methylation of Fc. The most significant consequences of the full methylation of Fc in the IR spectra are the blue shift of the band at ~ 800 cm−1 in Fc to ~ 1500 cm−1 in *Fc, and the enhancement of the C–H stretch band at ~ 3200 cm−1 region in *Fc. Further analysis reveals large impact of Fc methylation on core electron energies of the centre Fe atom (1s22s22p63s23p6). The Fe core electron energy changes can be as large as ~ 10 kcal mol−1 and are directional—the Fe 2pz and 3pz orbitals along the *Cp–Fe–*Cp axis (Cp centroids, vertical) change more strongly than other Fe core electrons in px and py orbitals. The directional inner shell energy changes are evidenced by larger inner shell reorganization energy. Energy decomposition analysis (EDA) indicates that methyl groups in *Fc apparently change the physical energy components with respect to Fc. The large steric energy of *Fc evidences that the closest hydrogens on adjacent methyl groups of the same *Cp ring in crystal structure are 0.2–0.4 Å closer than the hydrogens on nearest-neighbour methyl groups on opposing rings in *Fc. A significant increase in Pauli repulsive energy contributes to the large repulsive steric energy in *Fc.

Bimodal brush-functionalized nanoparticles selective to receptor surface density

Nanoparticles or drug carriers which can selectively bind to cells expressing receptors above a certain threshold surface density are very promising for targeting cells overexpressing specific receptors under pathological conditions. Simulations and theoretical studies have suggested that such selectivity can be enhanced by functionalizing nanoparticles with a bimodal polymer monolayer (BM) containing shorter ligated chains and longer inert protective chains. However, a systematic study of the effect of these parameters under tightly controlled conditions is still missing. Here, we develop well-defined and highly specific platforms mimicking particle-cell interface using surface chemistry to provide a experimental proof of such selectivity. Using surface plasmon resonance and atomic force microscopy, we report the selective adsorption of BM-functionalized nanoparticles, and especially, a significant enhanced selective behavior by using a BM with longer protective chains. Furthermore, a model is also developed to describe the repulsive contribution of the protective brush to nanoparticle adsorption. This model is combined with super-selectivity theory to support experimental findings and shows that the observed selectivity is due to the steric energy barrier which requires a high number of ligand-receptor bonds to allow nanoparticle adsorption. Finally, the results show how the relative length and molar ratio of two chains can be tuned to target a threshold surface density of receptors and thus lay the foundation for the rational design of BM-functionalized nanoparticles for selective targeting.

Unraveling the origin of the cooperative adsorption of carbon monoxide in an Fe(II) metal-organic framework.

Using periodic DFT calculations, we have established the mechanism of the unusual cooperative adsorption of CO gas in an Fe-bistriazolate MOF observed previously. The binding of one CO molecule to FeII triggers structural alteration of the neighbouring Fe centres, reducing the steric energy penalty and aiding cooperative adsorption. This is similar to the entatic state concept proposed for metalloenzymes, and offers novel strategies for selective gas adsorption.

A novel insight into the binding behavior between soy protein and homologous ketones: Perspective from steric effect

The binding behavior between soy protein isolate (SPI) and homologous ketones was examined in this study. Three ketones (2-hexanone, 2-heptanone, and 2-octanone) with different carbon chain lengths were selected to investigate the interaction mechanism between SPI and ketones, and three ketones with positional isomers, namely 2-nonanone, 3-nonanone, and 4-nonanone, were used to construct different steric effect. Ultraviolet, fluorescence, and circular dichroism results showed that ketones induced the conformational perturbations of SPI, weakening the polarity of the environment in which the chromogenic group was located and triggering the quenching of SPI intrinsic fluorescence. Hydrophobic site competition experiments revealed that the presence of steric hindrance hindered the collision of compounds with SPI active site. The optimal binding locus for ketones within the SPI structure was determined by molecular docking, and two key amino acids, LYS412 and ASN484, were found. The calculated binding energy (-25.682 ∼ -17.952 kcal mol−1) and steric energy (7.883 ∼ 14.894 kcal mol−1) of ketones showed that steric effects played a negative role in the binding of SPI to flavor compounds, but this role was weaker than hydrophobic interactions and hydrogen bonding. The improved understanding of the role of carbon chain lengths and steric hindrance on ketone retention could support the flavor product designer or scientists to optimize flavor retention and delivery.

Reversible, voluminous and tunable patterning of multiwalled carbon nanotubes in ferrofluid: Partial or complete?

A new kind of hybrid fluids showing multiwalled carbon nanotubes (MWCNTs) coupled with magnetic nanoparticles have been synthesized and investigated for their structural, magnetic, and magneto-viscoelastic properties. The experimental results confirmed the cooperative coupling between MWCNTs and Fe3O4 nanoparticles forming the basis of magnetorheological mechanism which narrates the rheological properties. The molecular dynamics (MD) simulation and interaction calculations for particle-particle, particle-tube and tube-tube have been described and explained comprehensively in view of the interface properties of nanoparticles and nanotubes. The whole of the experimental and theoretical investigations confirms the bulk alignment of bent MWCNTs in ferrofluidic system which can be tuned with an applied magnetic field. The MD simulation predicts a weak and short-range molecular ordering mediated via free oleic acid molecules between MWCNTs and coated nanoparticles of ferrofluid. The interparticle interaction calculations (van der Waals, steric and magnetic energies) showed that the surface coated magnetic nanoparticles are kinetically stable in the fluid while the MWCNTs form chain-like aggregates. Moreover, by application of classical beam theory, a thermodynamic energy barrier comparison was made for the unbending of particle impregnated MWCNTs. Thus, considering the dimensional compatibility of nanotubes and nanoparticles, a field-induced partial alignment of MWNCTs by virtue of their bent form in ferrofluidic system is proposed. A partial or complete accomplishment of the reversibility and tunability of the patterning of MWCNTs on a large scale in ferrofluid has been investigated in detail.

Eco-friendly utilization of oilfield fracturing flow-back fluid and coal pitch for preparing slurry: Experiments and extended DLVO study

The fracturing flow-back fluid (FF), as the primary pollutant in oilfield exploitation, is challenging to handle because of the large output and complex components. In addition, large amounts of coal pitch (CP) are insufficiently utilized. In this study, based on the principle of clean production, three dispersants were employed to prepare CP-water slurry (CPWS) and CP-FF slurry (CPFS), which had the characteristics of high efficiency and low pollution. The feasibility of CPWS and CPFS and the influences of dispersants on their performance were systematically studied by measuring the viscosity, rheology and stability. Furthermore, the dispersion mechanisms of dispersants were investigated via adsorption, Zeta potential, and extended DLVO (EDLVO) theory. Results showed that replacing water with FF reduced the slurryability, while the stability was improved. The CPFS exhibited the shear-thinning characteristics, and the components in FF strengthened the pseudoplastic of slurry. Among the three dispersants, the adsorption capacity of AC-1215 was higher than that of PS and MF. And the inorganic salts in FF promoted the adsorption of dispersants. The calculation of interaction energies demonstrated that for CPFS without dispersant, the polar interaction energy played a dominant role, resulting in the aggregation of CP particles. The addition of AC-1215 maximized the total interaction energies (greater than zero) by introducing the steric hindrance energy, which was 1–4 orders of magnitude higher than other interaction energies.

2,2‐Bistrifluoromethyl‐4,5‐difluoro‐1,3‐dioxole‐co‐tetrafluoroethylene copolymers with different compositions: Synthesis, chain and condensed matter structures and optical properties

AbstractSynthesis of 2,2‐bistrifluoromethyl‐4,5‐difluoro‐1,3‐dioxole‐co‐tetrafluoroethylene (PDD‐TFE) copolymers with precise chemical structures and understanding effects of the structures on properties are essential for their application. Herein, PDD‐TFE copolymers with different average compositions and narrow composition distributions (NCDs) were synthesized and applied to study the influences of chemical structures on condensed matter structures and optical properties of copolymers. The average length of (PTFE)n sequences were decreased from 7.62 to 1.63, and percentage of TFE in long (PTFE)n sequences (n > 5) decreased from approximately 50% to less than 1%, as PDD molar fraction in the copolymer (FPDD) increased from 13.24% to 52.22%. Consequently, the copolymer with FPDD = 13.24% was semi‐crystalline with a crystallinity degree of 11.57% (determined by WAXD), while the copolymer with FPDD = 52.22% was completely amorphous. The steric energies, glass transition temperatures and transparency of PDD‐TFE copolymers were increased as more cyclic and non‐coplanar structure PDD monomer was incorporated into the copolymers. Refractive indexes of PDD‐TFE copolymers were low and linearly decreased with the increase of FPDD. PDD‐TFE copolymers with high transparencies, low refractive indexes and other excellent properties can be successfully used in the optical fibers and semiconductor fields.

The impact of steric repulsion on the total free energy of electric double layer capacitors

We present an analysis of the total free energy of a supercapacitor modelled with a composite diffuse layer (CDL) formed by a steric repulsive potential. The steric potential is modelled with a simple approximation to the Bikerman steric potential, enabling derivation of an analytical expression for the total free energy of the supercapacitor in terms of the size and valency of the electrolyte counterions and electrode potentials. The analytical expression for the total free energy of the supercapacitor matches the exact numerical Bikerman calculation at high potential with relative error close to 1%. This provides an upper bound over the more accurate Carnahan-Starling model. A maximum upper bound for the energy is also provided in the limit where bulk concentrations approach the ion concentration cap. We analyze the relative contribution of the steric interaction to the total free energy. At large voltages, the steric free energy is comparable in magnitude to that of the electrostatic free energy, and introduces ion-size effects in the energy of the supercapacitor. Consequently at high potentials the total free energy exceeds (doubles) the classical energy 12CV2, indicating that this formula does not correctly describe the available stored energy from the experimentally measured capacitance.

Spectroscopic and theoretical studies of some 2-(2′-ethylsulfanyl)acetyl-5-substituted furans and thiophenes

The conformational equilibrium of 2-(2′-ethylsulfanyl)acetyl-5-substituted furans and thiophenes [EtSCH2C(O)(C4H2X)Y] (1–5; Scheme 1) was determined through the infrared analysis of the carbonyl stretching band (νCO) supported by DFT (B3LYP/aug-cc-pVTZ) and molecular dynamics simulations (OPLS-AA). Six stable conformations, syn(1–3) and anti(1–3), were obtained through the optimisation of the isolated systems, where the syn/anti nomenclature refers to the dihedral angle between the carbonyl and the aromatic heteroatom (O=C–C–X; X = O, S) and 1, 2, and 3 refer to the ethyl rotation (Scheme 2) (torsion around the γ dihedral angle). The three ethyl conformers resemble six- (1 and 2) or seven-(3) member pseudo-rings with an electrostatic intramolecular hydrogen bond (Oδ-···Hδ+). The IR spectra in solution show νCO doublets for all compounds in all solvents (n-C6H14, CCl4, CHCl3, CH2Cl2 and CH3CN). The polarisable continuum model and molecular dynamics data allow the lowest wavenumber and more intense νCO IR component to be ascribed to the three anti conformers of the furan derivatives and to the three syn ones of the thiophene compounds. The conformational preferences of all compounds are governed by a balance between orbital and coulombic interactions, as estimated by means of natural bond orbital, natural coulomb electrostatic, pairwise steric exchange energy, quantum theory of atoms in molecules, non-covalent interaction and short-contact analyses. While the conformational isomerism of the ethylthioacetyl moiety is determined by both quantum and columbic effects, the equilibrium involving the carbonyl and heterocyclic moiety is controlled largely by electrostatic interactions.

Does Steric Hindrance Actually Govern the Competition between Bimolecular Substitution and Elimination Reactions?

Bimolecular nucleophilic substitution (SN2) and elimination (E2) reactions are prototypical examples of competing reaction mechanisms, with fundamental implications in modern chemical synthesis. Steric hindrance (SH) is often considered to be one of the dominant factors determining the most favorable reaction out of the SN2 and E2 pathways. However, the picture provided by classical chemical intuition is inevitably grounded on poorly defined bases. In this work, we try to shed light on the aforementioned problem through the analysis and comparison of the evolution of the steric energy (EST), settled within the IQA scheme and experienced along both reaction mechanisms. For such a purpose, the substitution and elimination reactions of a collection of alkyl bromides (R-Br) with the hydroxide anion (OH–) were studied in the gas phase at the M06-2X/aug-cc-pVDZ level of theory. The results show that, generally, EST recovers the appealing trends already anticipated by chemical intuition and organic chemistry, supporting the role that SH is classically claimed to play in the competition between SN2 and E2 reactions.