Strong Steric Effect Research Articles

Effects of polycarboxylate superplasticizers with different functional groups on the adsorption behavior and rheology of cement paste containing montmorillonite

The dispersing effectiveness of polycarboxylate superplasticizer (PCE) in cement paste is dramatically reduced as a result of the sorption of PCE by montmorillonite (MMT) clay. To improve the dispersing effectiveness of PCE in MMT-containing cement paste, three PCEswere synthesized by copolymerizing isopentenyl polyoxyethylene ether (TPEG) with trans-2-butenedioic acid (FA) (FA-TPEG), FA and methacryloxyethyltrimethyl ammonium chloride (FA-DMC-TPEG), FA and sodium p-styrene sulfonate (FA-SSS-TPEG), respectively. Their molecular structures were characterized by gel permeation chromatography, specific charge density , Fourier transform infrared spectrum, and 1H nuclear magnetic resonance spectroscopy. X-ray diffraction and adsorption analysis were used to reveal the interactions between PCEs and MMT, and their dispersing performance in cement-MMT paste was evaluated using mini-cone and rheology measurements.. Results indicate that the difference in flowability caused by PCEs is primarily attributed to their different affinity for MMT in cement paste. Among them,, FA-SSS-TPEG showed excellent flowability due to its high affinity for cement particles and strong steric hindrance effect.

Design of 3d transition metal-embedded asymmetric HMo2CF for electrocatalytic conversion of N2 to NH3.

The electrochemical reduction of N2 to NH3 (NRR) is challenging due to the lack of efficient catalysts under mild conditions. We constructed a series of 3d-transition-metal (3d-TM)-embedded asymmetric 2D MXene HMo2CF with one H or F vacancy (Hv or Fv) based on first-principles calculation. Due to the strong steric effect of the surface-covered H or F terminals, N2 is favored to be adsorbed on Hv or Fv through the end-on mode rather than the side-on mode. Compared to NRR on the exposed Mo at F-vacancy (denoted as MoFv) of HMo2CFv, TM-substituted (TM = V, Cr, Mn, and Fe) MoFv improved NRR activities by reducing the barriers to 0.70, 0.59, 0.58, and 0.72 eV, respectively, from the original 0.81 eV. Particularly, Mn- or Cr-embedded HMo2CFv exhibited the best catalytic performances among 3d-TMs (Ti-Ni) undergoing alternating or distal mechanism, where the potential determining step (PDS) occurs at the first hydrogenation of N2 to NNH with a barrier of 0.58 or 0.59 eV. For TM-substituted (TM = Ti to Ni) Mo adjacent to F-vacancy, the catalytic barriers varied slightly in the range of 0.72 to 0.82 eV. The adsorption energy comparison indicated that TM-embedded HMo2CF exhibited higher selectivity toward N2 end-on adsorption than H2 to initialize the following NRR process. Greater electron transfer between TM-N2 was ascribed to the moderate N2 adsorption. Our work is expected to provide an insightful method for designing efficient NRR catalysts.

Construction of Aptamer-Functionalized DNA Hydrogels for Effective Inhibition of Shiga Toxin II Toxicity.

Bacterial infections have been seriously endangering public health and life, making it imperative to explore novel anti-infection strategies for their control. Herein, we constructed a DNA hydrogel encoded with aptamers (Apt-hydrogel) to inhibit Shiga toxin II (Stx2) toxicity, thereby alleviating Escherichia coli (EHEC) infection. The Apt-hydrogel was formed by two Y-shaped DNA scaffolds through rational design, where one end of Y was encoded with an aptamer sequence targeting the B subunit of Shiga toxin II (Stx2B). The Apt-hydrogel not only retained the high affinity of the aptamer but also provided protection for the aptamer, endowing it with better stability and biocompatibility. The results from in vitro and in vivo demonstrated good mediation effects of the Apt-hydrogel on Stx2 toxicity and confirmed its excellent inhibition activity. We hypothesized that the mechanism could be attributed to the high affinity of Apt-hydrogel for Stx2B, which effectively occupies the active site of Stx2B and its receptor Gb3. This interaction enhanced steric hindrance, thereby mediating their interaction and preventing Stx2 from entering the cell to exert toxicity. We anticipate that the novel Apt-hydrogel will expand the usage of aptamers and provide a new dimension for the Apt-hydrogel as a promising blocking assistant to inhibit Shiga toxin infections via a strong steric hindrance effect.

Very Strong Hydrogen Bond in Nitrophthalic Cocrystals.

This work presents the studies of a very strong hydrogen bond (VSHB) in biologically active phthalic acids. Research on VSHB comes topical due to its participation in many biological processes. The studies cover the modelling of intermolecular interactions and phthalic acids with 2,4,6-collidine and N,N-dimethyl-4-pyridinamine complexes with aim to obtain a VSHB. The four synthesized complexes were studied by experimental X-ray, IR, and Raman methods, as well as theoretical Car-Parrinello Molecular Dynamics (CP-MD) and Density Functional Theory (DFT) simulations. By variation of the steric repulsion and basicity of the complex' components, a very short intramolecular hydrogen bond was achieved. The potential energy curves calculated by the DFT method were characterized by a low barrier (0.7 and 0.9 kcal/mol) on proton transfer in the OHN intermolecular hydrogen bond for 3-nitrophthalic acid with either 2,4,6-collidine or N,N-dimethyl-4-pyridinamine cocrystals. Moreover, the CP-MD simulations exposed very strong bridging proton dynamics in the intermolecular hydrogen bonds. The accomplished crystallographic and spectroscopic studies indicate that the OHO intramolecular hydrogen bond in 4-nitrophthalic cocrystals is VSHB. The influence of a strong steric effect on the geometry of the studied cocrystals and the stretching vibration bands of the carboxyl and carboxylate groups was elaborated.

Room Temperature Crystallized Phase-Pure α-FAPbI3 Perovskite with In-Situ Grain-Boundary Passivation.

Energy loss in perovskite grain boundaries (GBs) is a primary limitation toward high-efficiency perovskite solar cells (PSCs). Two critical strategies to address this issue are high-quality crystallization and passivation of GBs. However, the established methods are generally carried out discretely due to the complicated mechanisms of grain growth and defect formation. In this study, a combined method is proposed by introducing 3,4,5-Trifluoroaniline iodide (TFAI) into the perovskite precursor. The TFAI triggers the union of nano-sized colloids into microclusters and facilitates the complete phase transition of α-FAPbI3 at room temperature. The controlled chemical reactivity and strong steric hindrance effect enable the fixed location of TFAI and suppress defects at GBs. This combination of well-crystallized perovskite grains and effectively passivated GBs leads to an improvement in the open circuit voltage (Voc) of PSCs from 1.08V to 1.17V, which is one of the highest recorded Voc without interface modification. The TFAI-incorporated device achieved a champion PCE of 24.81%. The device maintained a steady power output near its maximum power output point, showing almost no decay over 280h testing without pre-processing.

What Happens to a Pyrrole Hemithioindigo Photoswitch Trapped in a Fluorescent Protein?

Artificial molecular photoswitches that can be reversibly controlled into different configurations by external light stimulation have broad application prospects in various fields, such as materials and chemical biology. Among them, the pyrrole hemithioindigo (PHT) photoswitch has a geometric structure similar to that of the fluorescent protein chromophore. What happens when the chromophore is replaced by PHT, and does it achieve similar functions to the original one? To answer these questions, we carried out ONIOM(QM/MM) and classical molecular dynamics studies on the photoisomerization mechanism and spectroscopic properties of PHT in the fluorescent protein. The results showed that in the protein environment, the fate of excited PHT is governed by the competition between fluorescence emission and hula-twist isomerization. Due to the strong steric hindrance effects caused by the interlacing residues in the protein that restrict the PHT conformation transformation, the cis-to-trans isomerization process of PHT needs to overcome a barrier of at least 4.9 kcal/mol; thus, fluorescence emission is more dominant in competition. It is also found that the intermolecular interaction between LYS67 and the carbonyl oxygen of PHT has a significant effect on the fluorescence emission. These results revealed the photochemical reaction mechanism of a light-driven molecular switch in the fluorescent protein and provided further theoretical support for the field of chemical biology.

Experimental and computational study of the thermal degradation of primary amines used in CO2 capture

CO2 loaded amine polymerizes during solvent regeneration at temperatures above 100 °C, resulting in the deterioration of solvent performance. Herein, five primary amines were heated to 120, 135 and 150 °C with CO2 loading of 0.4C/N to study thermal degradation. It was found that 2-amine-1-butanol showed the greatest amine loss of 38.5 % after heating to 135 °C for 672 hrs while 2-amino-2-methyl-1-propanol was most stable with amine loss of 17.4 % under the same conditions. The degradation products were identified and the reaction pathway was studied through density functional theory (DFT) calculation. Furthermore, the transition state for ring closure and opening reactions was analyzed. The ring closure reaction to form oxazolidinones had a higher energy barrier, showing that it was the limiting step. This is further supported by the good agreement with experimental results. The structure–activity relationship showed the strong steric hindrance effect and the methyl group at β-carbon improved the amine stability.

Bispecific Nanobody-Aptamer Conjugates for Enhanced Cancer Therapy in Solid Tumors.

Bispecific antibodies possess exceptional potential as therapeutic agents due to their capacity to bind to two different antigens simultaneously. However, challenges pertain to unsatisfactory stability, manufacturing complexity, and limited tumor penetration hinder their broad applicability. In this study, a versatile technology is presented for the rapid generation of bispecific nanobody-aptamer conjugates with efficient tumor penetration. The approach utilizes microbial transglutaminase (MTGase) and click chemistry to achieve site-specific conjugation of nanobodies and aptamers, which are termed nanotamers. The nanotamers recognize and bind to two types of molecular targets expressed on cancer cells. As a prototype, a bispecific nanotamer is developed that binds both clusters of differentiation 47 (CD47) and mesenchymal epithelial transition receptor (Met) expressed on the tumor cell membrane. This CD47-Met nanotamer demonstrates high affinity and specificity toward tumor cells expressing both targets, exhibits improved receptor functional inhibition through a strong steric hindrance effect. Moreover, its capacity for deep tumor penetration greatly enhances the impact of conventional chemotherapy on antitumor efficacy. The as-developed nanotamer synthesis approach shows promise to customize bispecific molecular probes targeting different cancer types and different therapeutic goals.

The impact of imidazolium with steric hindrance on the dissociation of phosphoric acid and the performance of high-temperature proton exchange membranes

This study proposes a strategy of blending polyimidazolium with strong steric effect in HT-PEMs in order to promote phosphoric acid dissociation and enhance proton conduction efficiency.

Aggregation Behavior of Ethoxylated Phytosterol Surfactants in Different Protic Solvents: An Insight from Dielectric Relaxation Studies.

The micellar aggregation behavior of biocompatible surfactants, phytosterol ethoxylates (BPS-n, n is the oxyethylene (EO) chain length), containing polyoxyethylene chains in four organic solvents (glycerol (G), ethylene glycol (EG), formamide (FA), and N,N-dimethylformamide (DMF)) was studied by dielectric spectroscopy in the frequency range of 40 Hz to 110 MHz. Only the BPS-n/EG and BPS-n/G systems show distinct dielectric loss peaks near 104 Hz, indicating that BPS-n forms micellar aggregates in EG and G solvents, and the interfacial polarization (IP) between the aggregates and solvents leads to this relaxation. The dielectric spectra were analyzed based on the IP theory and a columnar dispersion model. The dielectric parameters of micelles, the permittivity and conductivity of micelles and solvents, and the volume fraction of the aggregates in solvents were calculated. On this basis, the binding numbers of each EO group on the hydrophobic chain to the solvent molecules EG and G were calculated to be 0.42 and 0.22, respectively. It was suggested that the aggregation appears to be related to the magnitude of the hydrogen bonding interactions. The lower number of EO group-binding solvents is because of the strong steric effect of alcohol solvents and the magnitude of the hydrogen bonding force.

Revealing the microscopic formation mechanism and stability characteristics of anionic surfactant microemulsions using coarse-grained simulations

Microemulsion is thermodynamically stable dispersion system formed by emulsifiers such as surfactants adsorbed at the oil-water interface. However, the evolution mechanism of surfactant-stabilized microemulsions and its stability are not adequately understood. Motivated by these issues, the underlying formation mechanism and the complex interplay on the microemulsion stability were systematically investigated by dissipative particle dynamics simulations. Coarse-grained models of oil/water/surfactants were developed to demonstrate a clear Ostwald ripening mechanism for W/O microemulsion, whereas a collisional fusion mechanism for O/W microemulsion. Mutual transformation between O/W and W/O microemulsions was dominated by the change of interfacial water/oil area. As the surfactant concentration increased, smaller microemulsion formed with a higher stability. Compared to sodium lauryl sulfonate, sodium dodecylbenzene sulfonate with benzene structure could form a thicker interfacial film, thereby improving the microemulsion stability. Internal olefin sulfonate with a branched structure was able to form an interfacial film with greater strength, enduring a higher shear rate of 0.033/ps. Furthermore, longer molecular chains of surfactant could result in a stronger steric effect, leading to a higher salinity tolerance of microemulsion with aHH is 17. The obtained results are expected to provide a solid theoretical foundation for the rational design of efficient microemulsions and pave the way for the applications such as oil recovery, pollution control, and dispersion of drugs.

Multifunctional titanium surface coating for oral implants with strong resistance to bacteria and mineralization ability

Titanium (Ti) has good mechanical properties, corrosion resistance, and biocompatibility. Biomaterials for the oral cavity have special requirements, such as the ability to resist bacterial adhesion and promote mineralization. Therefore, the modified Ti surface must have good antibacterial adhesion properties and mineralization activity. The material surface with zwitteric ionic polymer modification has a strong hydration and steric resistance effect, providing excellent bacteria resistance. In our previous work, zwitterionic poly[2-(methacryloyloxy)ethyl choline phosphate] (Ti-PMCP) was used to modify Ti surface via surface-initiated atom transfer radical polymerization, which can promote cell adhesion and prevent nonspecific protein adsorption. In this work, we further studied the antibacterial and mineralization properties of Ti-PMCP and its the application potential in oral implant materials.

Probing strong steric hindrance effects in aqueous alkanolamines for CO2 capture from first principles

Carbon dioxide (CO2) absorption into aqueous amine solvents is known to be governed by two competing reactions leading to carbamate or bicarbonate formation. Sterically hindered alkanolamines with different degrees of methylation are experimentally known to cause different favorability in forming carbamate or bicarbonate. However, the fundamental mechanisms responsible for the preferential formation of carbamate or bicarbonate still remain unclear. Herein, we present CO2 absorption behavior with several different sterically hindered amines, especially the effects of methylation and temperature. Our ab initio metadynamics simulations clearly demonstrate that free-energy barriers for the carbamate and bicarbonate formation reactions strongly depend on the degree of steric hindrance of hydrophobic methyl groups. This in turn directly impacts on the kinetic favorability of the two competing reaction pathways. Our analysis shows that various degrees of steric effects cause considerably different temperature-dependent degrees of solvation of the nitrogen atom of hindered amines, which may directly affect CO2 accessibility to form carbamate. Moreover, the enhanced solvation as a result of increased steric effects particularly at low absorption temperatures lead to kinetically facile protonation of the nitrogen atom of amines, initiating and promoting bicarbonate formation. Our work sheds light on the effects of various degrees of steric hindrance, with different temperature-dependent solvation degrees governing reaction mechanisms and rates during CO2 capture.

Efficient extraction of rhenium through demulsification of imidazolium ionic liquid-based microemulsions from aqueous solution

Rhenium has important applications in metallurgy, military, aviation, chemical, and petrochemical industries and related fields. Because the average concentration of rhenium in the Earth’s crust is just one part per billion (ppb), it is necessary to research the separation and extraction of rhenium from its associated minerals or related solutions. In this study, rhenium extraction through demulsification of an alkyl imidazolium ionic liquid-based microemulsion was explored. Alkyl chain length, components of microemulsion, temperature, acid concentration, and competitive ions affecting rhenium extraction were thoroughly considered. The components of the microemulsion had a significant effect on the extraction process. Extraction efficiency improved with the increase in the alkyl chain length, but it decreased with the rising concentration of nitric acid. The concentration of alkyl imidazole cations in the continuous phase had obvious effects on extraction efficiency. Thermodynamic studies showed the process was endothermic and spontaneous. The extraction mechanisms were an anion exchange and electrostatic attraction between the two N atoms of the imidazole ring and water (H2O) or perthenate (ReO4−) forming the complex ([Omim]ReO4)•(HReO4). Thus, the extraction efficiency of the microemulsion system was about 1.6 times greater than that of the performance of ionic liquids alone. A microemulsion system can be damaged by a strong electrostatic repulsion and steric hindrance effect between the adjacent imidazole rings on the interface of the microemulsion droplet after rhenium extraction. The extraction system is a potential application for the selective separation and extraction of rhenium from simulated radionuclide liquid waste through adjustments to the acidity concentration. Findings of this study provide some basic data regarding the technology for separating and extracting rhenium in future.

Intermolecular Hydrogen-Bond-Assisted Solid-State Dual-Emission Molecules with Mechanical Force-Induced Enhanced Emission.

Hydrogen bonds not only play a crucial role in the life sciences but also endow molecules with fantastic physical and chemical properties, which help in the realization of their high-tech applications. This work presents an efficient strategy for achieving highly efficient solid-state dual-emission blue emitters with mechanical force-induced enhanced emission properties via intermolecular hydrogen bonds via novel pyrene-based intermediates, namely, 1,3,6,8-tetrabromo-2,7-dihydroxypyrene (1) and 1,3,6,8-tetrabromo-2-hydroxypyrene (2), prepared via hydroxylation and bromination of pyrene in high yields. Moreover, further use of a classical Pd-catalyzed coupling reaction affords new pyrene-based luminescent materials 3-5, which display high thermal stability (in range of 336-447 °C), blue emission (<463 nm), and high quantum yields in solution. Interestingly, with the monosubstituted hydroxyl (OH) or methoxy (OMe) group located at position 2 of pyrene, compounds 4a and 5 display exciting dual emission with mechanical force-induced enhanced emission properties, due to the presence of several hydrogen-bond interactions. Moreover, this series of compounds exhibits numerous advantages, for example, deeper blue emission with a narrower full width at half-maximum, a stronger steric effect, and higher hydrophilicity. Thus, these novel bromopyrene intermediates and related pyrene-based luminescent materials will pave the way for further exploration of novel organic solid-state luminescent materials for potential application in organic electronics, bioimaging, chemosensors, etc.

Effect of glycosylation with apple pectin, citrus pectin, mango pectin and sugar beet pectin on the physicochemical, interfacial and emulsifying properties of coconut protein isolate

The present study aimed to investigate the effect of glycosylation with four different sources of pectin on the structural, interfacial and emulsifying properties of coconut protein isolate (CPI). The conjugates achieved the degree of graft of 59.11%, 52.80%, 41.39% and 39.26% for apple pectin, citrus pectin, mango pectin and sugar beet pectin, respectively. The covalent bonding of the conjugates was further confirmed by SDS-PAGE gel electrophoresis and FT-IR spectra. In addition, CD spectra exhibited that the conjugates had less α-helix and β-sheet, and more random coil, resulting in more flexible and loose protein structure. Attributed to glycosylation and the strong steric hindrance effects of pectin, fluorescence intensity of the conjugates decreased significantly. Moreover, the solubility, soluble free sulfhydryl content, surface hydrophobicity, emulsifying activity and emulsifying stability of the conjugates improved significantly after glycosylation. The results of adsorption kinetics showed that glycosylation could increase interfacial pressure, adsorption and rearrangement rates of CPI at the oil–water interface. In summary, the glycosylation between CPI and the four different sources of pectin can significantly improve their emulsifying properties, in particular, citrus pectin and sugar beet pectin have more significant effects.

Structural effect of imidazolium salts on electrochemical conversion of carbon dioxide to imidazolium carboxylate

Imidazolium salts with various alkyl side chains and counter anions were synthesized. The conversion of CO2 to N-heterocyclic carbene-CO2 adducts (NHC-CO2) were achieved by in situ electroreduction of the imidazolium salts under CO2 atmosphere. The yield of NHC-CO2 decreases with the increase of steric effect of alkyl side chains, which is attributed to the decrease of reactivity of NHCs in the case of strong steric effect. The hydrogen bond accepting ability of anion has a substantial effect on the conversion of CO2. The high ability of anion to establish hydrogen bond favors the conversion of CO2. A good correlation between hydrogen bond accepting abilities of anions and yields of NHC-CO2 was demonstrated.

Spectroscopic analyses on an azatricycloderivative by DFT with different solvents, reactivity analysis and MD simulations

The solvent effects, spectroscopic, wavefunction reactivity analysis and molecular dynamics simulation of a biologically active azatricycloderivative is reported. Vibrational spectra are discussed in detail. The solvation energy values are lowest and highest for chloroform and DMSO and chemical descriptors show variations in solvent phases. The thermochemical quantities are increasing as the dielectric constant of solvents increases. Strong steric effect is seen at the center of six member and pyrazine rings. SASA values changed very little in all of the complexes according to MD simulations.

Metal-ligand bonding in bispidine chelate complexes for radiopharmaceutical applications

The complexes of selected radionuclides relevant for nuclear medicine (InIII, BiIII, LuIII, AcIII and in addition LaIII for comparative purposes) with the octadentate (6,6′-((9-hydroxy-1,5-bis(methoxycarbonyl)-2,4-di(pyridin-2-yl)-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(methylene))dipicolinic acid) ligand, H2bispa2, have been studied by density functional theory calculations modelling both isolated and aqueous solution conditions. The properties in focus are the encapsulation efficiency of the ligand for the different-size metals (M), the differences in bonding with the various MIII ions analysed using Bader’s atoms in molecules theory and the possibility and characteristics of nona- and decacoordination by H2O ligands. The computed results confirmed strong steric effects in the case of the In complex excluding higher than octacoordination. The studied properties depend strongly on the interplay of the sizes and electronic structures of the MIII ions. The computations support high stability of the complexes in aqueous solution, where also the solvation energies of the MIII ions (as dissociation products) play a significant role.

Complexation of pea protein isolate with dextran sulphate and interfacial adsorption behaviour and O/W emulsion stability at acidic conditions

SummaryThis study was aimed at improving the emulsifying property and physical stability of pea protein isolate (PPI) stabilised emulsions at acidic conditions by complexation with dextran sulphate (DS). Soluble and insoluble complexes with different charge and particle size were formed depending on the phase separation behaviour. The surface adsorption of PPI became slower after complexation with DS, but the percentage of adsorbed proteins at the oil–water interface was not affected. The formation of PPI–DS soluble complexes at high content of DS (≥0.4%) significantly improved the negative net charges of PPI, prevented the aggregation of protein, which further improved the emulsifying property of PPI at acidic conditions through the strong electrostatic repulsion and steric hindrance effects. Insoluble complexes with relatively weak net charge and large particles were formed at low DS content (≤0.2%), resulting in the bridging flocculation of oil droplets at pH 5 and 4. Thus, the emulsifying ability of PPI under acidic conditions could be significantly improved by formation of soluble complexes with DS.