C-H Bond Research Articles

Dual Pt atoms stabilized by an optimized coordination environment for propane dehydrogenation

Tailoring atomically dispersed catalysts by various methods has been the subject of intense current research in heterogeneous catalysis. In this work, the structural stability and propane dehydrogenation performance of Pt-TiO2 catalysts with single, dual, and triple Pt atoms doped on the reduced TiO2 surface have been examined. Experimental results indicate the atomically dispersed Pt is thermally very stable and shows exceptionally high activity (TOFpropane = 4.93 s−1) and selectivity (∼98.5 %) for the dehydrogenation reaction. The recently developed machine-learning-based SSW-NN method is then employed to explore the global potential energy surface of the atomically dispersed Pt atom-doped TiO2, which suggests that the single and dual Pt atoms can be tightly held by the vacancies created on the reduced transition-metal oxide, as confirmed by DFT + U calculated energetics. After that, advanced characterization techniques are used in conjunction with microkinetic analysis to establish the quantitative structure–activity relationships. It is found that the dual-Pt-atom structure with two Pt atoms embedded in adjacent Ti and O vacancies is the only active ensemble that dramatically promotes the CH bond activation and hydrogen recombination, as compared to single Pt atoms accommodated by either Ti or O vacancies. These results provide new and direct evidence in support of the idea that specific function can be imparted to specific active sites by tuning their coordination environments, which makes it possible to tailor the catalytic properties of metal oxides to a particular reaction such as propane dehydrogenation.

Hydration of biologically relevant tetramethylammonium cation by neutron scattering and molecular dynamics.

Neutron scattering and molecular dynamics studies were performed on a concentrated aqueous tetramethylammonium (TMA) chloride solution to gain insight into the hydration shell structure of TMA, which is relevant for understanding its behavior in biological contexts of, e.g., properties of phospholipid membrane headgroups or interactions between DNA and histones. Specifically, neutron diffraction with isotopic substitution experiments were performed on TMA and water hydrogens to extract the specific correlation between hydrogens in TMA (HTMA) and hydrogens in water (HW). Classical molecular dynamics simulations were performed to help interpret the experimental neutron scattering data. Comparison of the hydration structure and simulated neutron signals obtained with various force field flavors (e.g. overall charge, charge distribution, polarity of the CH bonds and geometry) allowed us to gain insight into how sensitive the TMA hydration structure is to such changes and how much the neutron signal can capture them. We show that certain aspects of the hydration, such as the correlation of the hydrogen on TMA to hydrogen on water, showed little dependence on the force field. In contrast, other correlations, such as the ion-ion interactions, showed more marked changes. Strikingly, the neutron scattering signal cannot discriminate between different hydration patterns. Finally, ab initio molecular dynamics was used to examine the three-dimensional hydration structure and thus to benchmark force field simulations. Overall, while neutron scattering has been previously successfully used to improve force fields, in the particular case of TMA we show that it has only limited value to fully determine the hydration structure, with other techniques such as ab initio MD being of a significant help.

An alternative catalytic cycle for selective methane oxidation to methanol with Cu clusters in zeolites.

The partial oxidation of methane to methanol catalyzed by Cu-exchanged zeolites involves at present a three-step procedure that requires changing reaction conditions along the catalytic cycle. In this work we present an alternative catalytic cycle for selective methane conversion to methanol using as active species small Cu5 clusters supported on CHA zeolite. Periodic DFT calculations show that molecular O2 is easily activated on Cu5 clusters producing bi-coordinated O atoms able to dissociate homolytically a CH bond from CH4 and to react with the radical-like non-adsorbed methyl intermediate formed producing methanol, while competitive overoxidation to CO2 is energetically disfavored. The present mechanistic study opens a new avenue to design catalytic materials based on their ability to stabilize radical species.

Heptanone isomers as biofuel: Reactivity with OH radicals

The reactions of heptanone isomers, namely diisopropyl ketone (DIPK, k1), isopropyl propyl ketone (IPPK, k2), and dipropyl ketone (DPK, k3), with OH radicals play a crucial role in predicting their combustion behavior. We conducted the first high-temperature measurements of these reactions over the temperature range of 876 to 1328 K at pressures near 1 bar. The determined overall rate coefficients may be described as (unit of cm3molecule−1s−1):k1=2.13×10−10e(−2684T)k2=2.42×10−10e(−2733T)k3=2.84×10−10e(−2808T)Over the investigated high temperature range, all three reactions exhibit a positive temperature dependence, with activation energies ranging 5.3 to 5.6 kcal mol−1. We did not observe discernible pressure dependence within the pressure range of 0.66 to 1.66 bar. At 1250 K, DPK reacts with OH radicals 11 % faster than IPPK and 21 % faster than DIPK. Interestingly, compared to heptane, which reacts twice as fast, the presence of the C=O group significantly hinders the reactivity of the normal chain heptanone (DPK) towards OH radicals. Furthermore, the rate coefficients of OH + DIPK reaction in literature models underestimate the measured activation energy and overpredict the overall rate coefficients. To enhance the accuracy of SAR prediction for OH + ketone reactions, a multiplicative factor of 0.6 - 0.75 is suggested. Additionally, this study provides a site-specific expression for the tertiary CH bonds adjacent to the C=O bond in ketone molecules, expanding the applicability of the NNN (next-nearest-neighbor) prediction scheme to encompass larger branched ketones.

Comparative Computational Study on Molecular Structure, Electronic and Vibrational Analysis of Vinyl Bromide based on HF and DFT Approach

In this study, we have used the Hartree-Fock and Density Functional Theory method of calculation and compared the equilibrium configuration, electronic and vibrational mode of Vinyl Bromide molecule. The molecule is geometrically optimized initially by using 6-31G basis set with B3LYP functional and then bond angles, bond lengths, dihedral angles and IR spectra are compared respectively. Various groups of atoms in Vinyl Bromide molecule by DFT has more accurate bond length, bond angle values rather than by HF computation when comparing with the experimental values. The ground state energies are found at angle 10° or 180° or 360° using HF and DFT method of calculation for the H4-C1-C2-Br6 position. Values of the carbon-hydrogen, carbon-carbon and carbon-bromine bond lengths and bond angles for optimization state of C2H3Br molecule using Hartree-Fock and Density Functional Theory methods with respect to the basis set 6-31G have been analyzed. The C−H in-plane bending vibration and C−H out-of-plane bending vibrations occur in the region 1400–1050 cm-1 and 1000–675 cm-1 respectively. The electronic properties, such as Highest Occupied Molecular Orbital and Lowest Unoccupied Molecular Orbital energies are performed by HF and DFT approach and the difference in Highest Occupied Molecular Orbital and Lowest Unoccupied Molecular Orbital energy gap for HF and DFT method are 14.0847 eV and 6.8994 eV respectively

Transition of characteristic explosion limits: From hydrogen to diethyl ether

In this work, the explosion limits of three different fuels: hydrogen (H2), propane (C3H8, C3), and diethyl ether (DEE, C2H5OC2H5, C4), are investigated based on detailed chemical kinetics. The results reveal that the explosion limit of H2O2 exhibits the typical Z-shape, while C3H8O2 exhibits a single-NTC response, and DEE-O2 displays a double-NTC response. Sensitivity analysis indicates that the appearance of the NTC response in both the C3 and DEE fuels is intricately linked to low-temperature reaction paths. Moreover, the extents of the NTC responses are comparable for these two fuels with similar low-temperature reaction paths, but operate under different temperature conditions. Specifically, the double-NTC response observed in DEE is attributed to its primary CH and CO bonds, generating C4 and C2 radicals. The oxygen addition and the subsequent pathways of these radicals dominate in distinct temperature ranges. In contrast, C3H8 only possesses the CH bond, resulting in a single-NTC response, as OH radicals are mainly released by C3 radicals through oxygen addition, isomerization, and decomposition reactions. The results of binary fuel mixtures with H2 addition indicate that the reactivity of H2 controls the low-pressure and high-temperature regime, while the C3 and DEE fuels dominate the high-pressure and low-temperature regime. Additionally, a triangular crossover regime is identified between these two regimes due to the switchover of the reactivity. Sensitivity analysis further reveals the transition of the dominating reactions related to different fuels at various pressure-temperature regimes. Finally, based on the explosion limits of the multi-component mixtures, a detailed explosion regime diagram is proposed for carbon-free fuel (H2), alkane fuel (C3H8), and oxygenated ether fuel (DEE). This new regime diagram provides valuable insights for the investigation and utilization of ether fuels and the mixture of different fuels.

Investigation and drug design for novel molecules from natural products as inhibitors for controlling multiple myeloma disease using in-silico tools

Multiple myeloma (MM) is a disease that causes plasma cell growth in the bone marrow and immune globulin buildup in blood and urine. Despite recent advances in MM therapy, many still die due to its high mortality rate. A study using computational simulations analyzed 100 natural ingredients from the SANC database to determine if they inhibited the IgH domain, a known cause of multiple myeloma. Natural component Diospyrin inhibited the IgH enzyme with the best binding energy of −10.3 kcal/mol and three carbon-hydrogen bonds, followed by Parviflorone F complex with a binding energy of −10.1 kcal/mol and two conventional-hydrogen bonds. As a result, the Molecular Dynamic simulation was used to test the stability of the two complexes. During the simulation, the Diospyrin molecule dissociated from the protein at roughly 67.5 ns, whereas the Parviflorone F molecule stayed attached to the protein throughout. The latter was the subject of the investigation. The analysis of the production run data revealed that the Parviflorone F molecule exhibits a variety of conformations within the binding pocket while keeping a relatively constant distance from the protein’s center of mass. The analysis of the production run data revealed that the Parviflorone F molecule exhibited a variety of conformations within the binding pocket while keeping a relatively constant distance from the protein’s center of mass. The root mean square deviation (RMSD) plots for both the protein and complex showed a stable and steady average value of 4.4 Å for the first 82 nanoseconds of manufacture. As a result, the average value increased to 8.3 Å. Furthermore, the components of the binding free energy, as computed by MM-GBSA, revealed that the mean binding energy of the Parviflorone F molecule was −23.88 kcal/mol. Finally, after analyzing all of the examination data, Parviflorone F was identified as a powerful inhibitor of the IgH domain and hence of the MM disease, which requires further in-vivo conformation. Communicated by Ramaswamy H. Sarma

Aliphatic C[sbnd]H azidation by Mn based mimics of α-ketoglutarate dependent enzymes

α-Ketoglutarate dependent nonheme halogenases catalyze regioselective functionalization of aliphatic CH bonds via H abstraction by the ferryl site of the [X−FeIV=O] intermediate, followed by radical rebound to an adjacent halogen ligand X at the same Fe center. Herein we report biomimetic nonheme Mn complexes, possessing two labile cis-α coordination sites and capable of catalyzing the enantioselective azidation of C(sp3)−H groups. Proper ligand environment of the active sites imposes steric constraints on HO−Mn rebound, thus accounting for preferential C-radical rebound to the adjacent N3−Mn ligand. Such mechanism of selectivity control is analogous to that operating in the prototypical α-ketoglutarate-dependent nonheme iron halogenases.

Evaluation of in silico anticancer activity of some striazine derivatives as VEGFR2 inhibitors

The s-triazine derivatives have been shown to have diverse biological activities, especially anticancer activity. Fifty s-triazine derivatives were screened for anticancer activity through inhibition of VEGFR2 (vascular endothelial growth factor receptor-2) by molecular docking method using AutoDock Vina software. Compounds 20 and 40 showed the strongest interactions among all tested compounds with the binding affinity values of -10.8 and -10.5 Kcal/mol, respectively compared to reference drugs Gedatolisib (-9.1 Kcal/mol) and Paclitaxel (-7.8 Kcal/mol) at the active site of VEGFR2. These compounds established one carbon-hydrogen bond at amino acid HIS1026, specifically exhibiting better electrostatic and hydrophobic interactions than the reference drugs Gedatolisib and Paclitaxel. Moreover, compounds 20 and 40 also showed interactions with the VEGFR2 receptor that resemble the reference drug Gedatolisib at amino acids such as ARG1027, ASP1046, and HIS1026. Therefore, these compounds could be a potential lead molecule for anticancer activity.

Biocatalytic hydroxylation tertiary C-H bonds for synthesis of chiral tertiary alcohols by cytochrome P450

In view of the importance and beneficial characteristics of enantioenriched tertiary alcohols in pharmaceutical chemistry, efficient and green strategies for their synthesis are highly sought after. Here, we report a simple synthesis of the elusive chiral tertiary alcohols. A cytochrome P450 monooxygenase called P450PL2 was developed to enable chiral tertiary alcohols by the benzylic CH bonds asymmetric hydroxylation of the racemic tertiary carbon substrates. This P450-catalyzed protocol provides various chiral tertiary alcohols with unexpectedly functional group tolerance and excellent enantioselectivities (up to >99 % ee). The method features mild reaction and employs molecular oxygen as an oxidant, avoids the use of pre-oxygen functionalized substrates. Preliminary molecular dynamics simulation studies were carried out to reveal the possible reasons for the exceptional selective hydroxylation of substrate during P450PL2 catalysis.

Peptidomics Screening and Molecular Docking with Umami Receptors T1R1/T1R3 of Novel Umami Peptides from Oyster (Crassostrea gigas) Hydrolysates.

In this study, novel umami peptides were prepared from oyster (Crassostrea gigas) hydrolysates, and their umami mechanisms were investigated. Umami fractions G2 and G3 were isolated by gel filtration chromatography (GFC) and sensory evaluation. The umami scores of the G2 and G3 fractions were 7.8 ± 0.12 and 7.5 ± 0.18, respectively. 36 potential umami peptides with molecular weights below 1500 Da, E and D accounting for >30% of the peptides and iUmami-SCM > 588 were screened by peptidomics. Peptide source analysis revealed that myosin, paramyosin, and sarcoplasmic were the major precursor proteins for these peptides. The electronic tongue results demonstrated that the synthetic peptides DPNDPDMKY and NARIEELEEE possessed an umami characteristic, whereas SIEDVEESRNK and ISIEDVEESRNK possessed a saltiness characteristic. Additionally, molecular docking results indicated that the umami peptide (DPNDPDMKY, NARIEELEEE, SIEDVEESRNK, and ISIEDVEESRNK) binds to H145, S276, H388, T305, Y218, D216, and Q389 residues in the T1R3 taste receptor via a conventional hydrogen bond and a carbon-hydrogen bond. This research provides a new strategy for the screening of umami peptides.

Pyrolysis and combustion reaction mechanisms of methyl palmitate with ReaxFF-MD method

As a substitute for fossil fuel, methyl palmitate (C17H34O2) has important scientific and practical significance to study its pyrolysis and combustion mechanism. In this paper, the ReaxFF-MD method is used to research the reaction mechanism and main products of C17H34O2. The effects of temperature and O2 on the decomposition, main products and reaction paths of C17H34O2 are analyzed to determine its reaction mechanism. The results show that the reaction activation energies of C17H34O2 in pyrolysis and combustion are 201.76 kJ/mol and 139.07 kJ/mol, respectively. The effect of temperature on C17H34O2 is greater than O2 on C17H34O2 at higher temperature. The basic reaction paths for the initial decomposition of C17H34O2 is that the CC, CO, and CH bonds are broken into smaller intermediates. In addition, the detailed distribution and generation paths of the main products C2H4, H2, H2O, CH2O, and so on are depicted to construct the reaction mechanism of C17H34O2.

Intramolecular C-H bond amination catalyzed by myoglobin reconstituted with iron porphycene

C−H bond amination is an effective way to obtain nitrogen-containing products. In this work, we demonstrate that myoglobin reconstituted with iron porphycene (rMb(FePc)) catalyzes intramolecular C(sp3)−H bond amination of arylsulfonyl azides to yield corresponding sultam analogs. The total turnover number of rMb(FePc) is up to 5.7 × 104 for the C−H bond amination of 2,4,6-triisopropylbenzenesulfonyl azide. Moreover, rMb(FePc) exhibits higher selectivity for the desired C-H bond amination than the competing azide reduction compared to native myoglobin. Kinetic studies reveal that the kcat value of rMb(FePc) is 4-fold higher than that of native myoglobin. Furthermore, H64A, H64V and H64I mutants of rMb(FePc) enhance the turnover number (TON) and enantioselectivity for the C−H bond amination of 2,4,6-triethylbenzenesulfonyl azide. The present findings indicate that iron porphycene is an attractive artificial cofactor for myoglobin toward the C−H bond amination reaction.

Influence of operating parameters on the yield of micro-plastics from plastics incineration

Plastics account for a large proportion of domestic waste. However, micro-plastics will be produced after the plastic is incinerated. The purpose of this study is to find out the change rule of micro-plastics produced during incineration under different conditions. Combining micro-FTIR and PCA algorithm is a good tool to identify the micro-plastics. The PE, PP and PVC micro-plastics are distinguished using PCA-FTIR spectra. The results show different incineration conditions significantly affect the output of micro-plastics. The yield of micro-plastics increases with increasing temperature for both PP and PVC. And the yield of micro-plastics decreases with the increase in flow rate. The maximum amount of micro-plastics is produced by PE, which is 6.62 × 103 after 1 g PE incineration. The yield of micro-plastics in the co-incineration of PE and PP, as well as PE and PVC, significantly increased to 1.42 and 1.89 times of the calculated values, respectively. The nano-particles are also observed. The FTIR and EDS results show that the nano-particles are the products of incineration of plastics, including partly CH bond and unburned carbon, tar and ash.

Trinuclear ruthenium clusters supported by piconol ligands: Application in catalytic C(sp3)-H bond oxidation in CH3CN/H2O

Trinuclear ruthenium clusters supported by piconol ligands [6-C8H6N-PyCR1R2O](μ2H)Ru3(CO)9 (R1 = R2 = CH3 (1); R1 = R2 = CH2CH3 (2); R1, R2 = -(CH2)4- (3); R1 = CH3, R2 = Ph (4)) have been proved to be efficient catalysts for the oxidation of saturated CH bonds. Cluster 1 was found to be the most active of the four, which can catalyze the oxidation of various hydrocarbons, with tert‑butyl hydroperoxide as the oxidant in CH3CN/H2O at room temperature, to afford the corresponding ketones in excellent yields.

Physico-chemical surface modification of the natural leather using gliding arc discharge: An in-depth analysis of improving surface and mechanical properties

Leather, a widely used material in various industries, presents challenges in terms of dye uptake, hydrophilicity, and environmental concerns associated with chemical wet processing. In this context, non-thermal plasma technology offers a promising alternative for leather surface modification. In this study, the gliding arc, with air and water vapor plasmas, was used for the surface modification of natural leather for the first time. The influence of the treatment time and also the plasma gas chemistry on the surface chemical bonding, surface morphology, wettability, water absorption time and absorption capacity, color, and mechanical properties of the leather were investigated. The results showed that in the water vapor gliding arc discharge, the produced active oxygen and hydroxyl species can effectively react with the functional groups and break the relatively weak hydrocarbon CH bonds in the chemical composition of the natural leather. SEM images showed increased pore depth and diameter on the leather surface after air and water vapor plasma treatment with mean diameters of 76 μm and 92 μm, respectively. The tensile stress-strain curves illustrated that despite small cracks were created on the plasma treated samples, the elongation at break (ultimate strain) increased from 83.7 % to 88.5 % and 91.8 % for the samples treated with the air and the water vapor plasmas for 5 min, respectively. The water contact angle decreased from 96° to 55° and 48° after only 5-second treatment with the air and the water vapor plasmas, respectively. The same trend was also observed for the water absorption time and the absorption capacity of the treated samples. Also, the color analysis showed that the color change in the plasma treated samples was not detected by the unaided eye. It was also found that water vapor plasma has a better influence on the physico-chemical properties of the leather.

Chitosan grafted alginate and polyvinylpyrrolidone as the binder for porous silicon nanoparticles from coal fly ash in lithium-ion batteries

Polymer binders are also important to overcome silicon as an anode in lithium-ion batteries (LIBs). Binder polymers with carboxylate or hydroxyl groups are used because they can bond with silicon through covalent or hydrogen bonding and reduce the formation of large volume changes during charging and discharging. The 1H NMR spectra show a new peak at 2.19 ppm, indicating the formation of cyclic compounds derived from PVP. FTIR spectra show peak adsorption at 3297 cm−1, indicating hydroxyl and amino group stretching. Adsorption at 1413 cm−1 shows COO symmetric stretching vibration. Adsorption at 1323 cm−1 shows stretching vibration in the C-N group. The adsorption at 1024 cm−1 shows C-O stretching. Adsorption at 443 cm−1 shows CH2 bond and also N-CO bending. The electrochemical performance of lithium-ion shows high capacity. The CV curve shows that the reduction peak is around 0.16 V, and the oxidation peak is around 0.38 V and 0.56 V. Nyquist plots show a small half circle indicating that the solid-electrolyte interphase layer is low on the electrode. The cycling performance shows a high initial capacity of 2912 mAh/g. It can maintain a high and good capacity until 400 cycles at 1374 mAh/g.

Kinetic and thermodynamic control of C(sp2)-H activation enables site-selective borylation.

Catalysts that distinguish between electronically distinct carbon-hydrogen (C-H) bonds without relying on steric effects or directing groups are challenging to design. In this work, cobalt precatalysts supported by N-alkyl-imidazole-substituted pyridine dicarbene (ACNC) pincer ligands are described that enable undirected, remote borylation of fluoroaromatics and expansion of scope to include electron-rich arenes, pyridines, and tri- and difluoromethoxylated arenes, thereby addressing one of the major limitations of first-row transition metal C-H functionalization catalysts. Mechanistic studies established a kinetic preference for C-H bond activation at the meta-position despite cobalt-aryl complexes resulting from ortho C-H activation being thermodynamically preferred. Switchable site selectivity in C-H borylation as a function of the boron reagent was thereby preliminarily demonstrated using a single precatalyst.

On the Mechanism Underlying the Distinct Activities of Rutile-Type Metal Oxides Toward Methane Activation

We report herein a density functional theory study on the C–H bond activation of CH4 over several rutile-type metal oxide catalysts, namely IrO2(110), TiO2(110), and β-MnO2(110) surfaces. We find that CH4 is strongly chemisorbed on the IrO2(110) surface, which distorts the CH4 geometry. Together with a strong thermodynamic driving force derived from the formation of Ir–CH3 bond, the H–CH3 bond activation proceeds with a negative barrier. In contrast, a weakly chemisorbed CH4 molecule on the TiO2(110) surface cannot proceed to the C–H bond cleavage due to a high activation barrier and a low thermodynamic driving force. The reaction on the β-MnO2(110) surface, on the other hand, is found to begin with a weak CH4 physisorption, followed by the C–H bond scission with a low activation barrier. However, here, the formation of •CH3 radical is more preferred than the Mn–CH3 bond formation, most possibly due to the electrophilic nature of MnO that suitably renders the catalyst as a perfect electron acceptor for the H-atom abstraction of CH4. With such low barrier and stability of the •CH3 formation, we suggest β-MnO2(110) as a potential catalyst that is good not only for the H–CH3 bond activation but also for the methanol formation.

Photo-induced versatile aliphatic C–H functionalization via electron donor–acceptor complex

The ability to selectively introduce diverse functionality onto hydrocarbons is of substantial value in the synthesis of both small molecules and pharmaceuticals. In this endeavour, as a photocatalyst- and metal-free process, the electron donor–acceptor (EDA) strategy has not been well explored. Here we report an approach to aliphatic carbon-hydrogen bond diversification through an EDA complex constituted by HCl and SIV=O groups. As an efficient hydrogen atom transfer (HAT) reagent, chlorine radical can be produced via a proton-coupled electron transfer process in this system. Based on this unusual path, a photo-promoted versatile aliphatic C–H functionalization is developed without photo- and metal-catalysts, including thiolation, arylation, alkynylation, and allylation. This conversion has concise and ambient reaction conditions, good functional group tolerance, and substrate diversity, and provides an alternative solution for the high value-added utilization of bulk light alkanes.