OH Bond Research Articles

Imaging surface structure and premelting of ice Ih with atomic resolution.

Ice surfaces are closely relevant to many physical and chemical properties, such as melting, freezing, friction, gas uptake and atmospheric reaction1-8. Despite extensive experimental and theoretical investigations9-17, the exact atomic structures of ice interfaces remain elusive owing to the vulnerable hydrogen-bonding network and the complicated premelting process. Here we realize atomic-resolution imaging of the basal (0001) surface structure of hexagonal water ice (ice Ih) by using qPlus-based cryogenic atomic force microscopy with a carbonmonoxide-functionalized tip. We find that the crystalline ice-Ih surface consists of mixed Ih- and cubic (Ic)-stacking nanodomains, forming periodic superstructures. Density functional theory reveals that this reconstructed surface is stabilized over the ideal ice surface mainly by minimizing the electrostatic repulsion between dangling OH bonds. Moreover, we observe that the ice surface gradually becomes disordered with increasing temperature (above 120 Kelvin), indicating the onset of the premelting process. The surface premelting occurs from the defective boundaries between the Ih and Ic domains and can be promoted by the formation of a planar local structure. These results put an end to the longstanding debate on ice surface structures and shed light on the molecular origin of ice premelting, which may lead to a paradigm shift in the understanding of ice physics and chemistry.

Two-dimensional molybdenum boride coordinating with ruthenium nanoparticles to boost hydrogen generation from hydrolytic dehydrogenation of ammonia borane

The coordination between carrier and active metal is critical to the catalytic efficiency of ammonia borane (AB) hydrolysis reaction. In the present study, we report a new type of catalytic support based on molybdenum boride (MBene) MoAl1-xB and demonstrate that the effective combination of MoAl1-xB with Ru nanoparticles can realize the significantly enhanced performance for hydrogen generation. Owing to the efficient activation and dissociation of reactants, the optimal Ru/MoAl1-xB catalyst achieves the large turnover frequency of 494 molH2 molRu-1 min−1, high hydrogen generation rate of 119817 mL min−1 gRu-1 and favorable apparent activation energy of 39.2 kJ mol−1 for the catalytic hydrolysis of AB under alkaline-free condition. The isotopic test suggests the cleavage of OH bond in H2O is the rate-determining step for hydrolysis reaction, while the fracture of B–H bond in AB is also well revealed by attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy. Significantly, the flexible on-demand hydrogen generation is achieved by using chemical switches for on–off AB hydrolysis. This study provides a new support platform based on two-dimensional MBene to exploit efficient catalysts to boost AB dehydrogenation.

Preparation and thermal conductivity of bimodal diamond particles reinforced phenolic resin composites

AbstractThermal conductive polymer composites have broad application prospects in the field of thermal management. However, due to intrinsically low thermal conductivity of polymers, even if fillers with high mass fraction are filled, the thermal conductivity of polymer composites cannot be significantly improved. In this paper, bimodal diamond particles (70 wt.% 150 μm and 22 wt.% 25 μm) were incorporated into phenolic resin to construct continuous heat transfer pathways by close packing, thereby enhancing its thermal conductivity. The results indicated that diamond particles with smaller particle size can effectively bridge the gaps between larger ones, forming a continuous for heat conduction. As a result, a maximum thermal conductivity value of 12.45 W/(m·K) can be achieved, which is 65.5 times, 9.8 times and 8.4 times higher than pure phenolic resin, 25 μm diamond particles reinforced phenolic resin composite and 150 μm diamond particles reinforced phenolic resin composite, respectively. Furthermore, heat dissipation and water cooling experiments also confirm the superior heat dissipation performance of phenolic resin composites reinforced with bimodal diamond particles. When the heating voltage is 10 V and the water cooling rate is 30 mL/min, the upper surface temperature of bimodal diamond composites is 129.2°C lower than that of pure phenolic resin. This investigation provides a new type of polymer composite with high thermal conductivity, which has promising prospects for application in thermal management. It also provides new insights for preparing polymer composites with high thermal conductivity by close packing of bimodal particles.Highlights Surface modification of the filler enhances its combination with resin. The interfacial bonding will be enhanced by D–OH bond on diamond surface. Bimodal diamond particles lead to the formation of a closely packed structure. This special structure can form a three‐dimensional heat conduction network. The highest TC of the DD/PR composite is 12.45 W/(m·K).

Sum rule comparison of narrowband and broadband sum frequency generation spectra and comparison with theory

Earlier sum frequency generation (SFG) experiments involve one infrared and one visible laser, and a measurement of the intensity of the response, yielding data on the surface sensitive properties of the sample. Recently, both the real and imaginary components of the susceptibility were measured in two different sets of experiments. In one set, a broadband infrared laser was used, permitting observations at very short times, while in another set the infrared laser was narrowband, permitting higher spectral resolution. The differences in the spectrum obtained by the two will be most evident in studying narrow absorption bands, e.g., the band due to dangling OH bonds at a water interface. The direct comparisons in the integrated amplitude (sum rule) of the imaginary part of the dangling OH bond region differ by a factor of 3. Due to variations in experimental setup and data processing, corrections were made for the quartz reference, Fresnel factors, and the incident visible laser wavelength. After the corrections, the agreement differs now by the factors of 1.1 within broadband and narrowband groups and the two groups now differ by a factor of 1.5. The 1.5 factor may arise from the extra heating of the more powerful broadband laser system on the water surface. The convolution from the narrowband SFG spectrum to the broadband SFG spectrum is also investigated and it does not affect the sum rule. Theory and narrowband experiments are compared using the sum rule and agree to a factor of 1.3 with no adjustable parameters.

Development and Characterization of a Remanufactured Motorcycle Clutch Hub from End-of-Life Aluminium Alloy

This study aims to employ reverse engineering in the development of the Yamaha CY 80 motorcycle clutch hub using end-of-life (EOL) aluminium alloy obtained from automotive vehicle scraps. The remanufactured motorcycle clutch hub underwent characterization and transient thermal analysis by integrating the geometric and structural features of the clutch hub. The EOL aluminium was thoroughly washed with a sodium hydroxide (NaOH) solution, cleaned with running water, and dried under sunlight to remove impurities trapped on the metal surfaces. The EOL aluminium alloy was melted in a gas furnace, and the molten metal was cast into the clutch hub using a permanent mold designed with the geometric features and characteristics of the Yamaha CY 80 motorcycle clutch hub. The EOL aluminium alloy was characterized using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The remanufactured CAD model of the Yamaha CY 80 motorcycle clutch hub was subjected to transient thermal analysis using ANSYS Workbench to predict the thermal behavior of the clutch hub during operation. The FTIR spectra exhibited the following distinctive bands: Al-O stretching modes in octahedral and tetrahedral structures, as well as symmetric bending of Al-O-H, with wavenumbers between 340 and 3131 cm-1 for -OH bonds and between 2109 and 1688 cm-1 for H-O-H bonds. The SEM-EDS micrographs indicated that the two main elements were bromine and silicon. Results from the transient thermal analysis indicated that the minimum and maximum temperatures were 40.109 °C and 250.09 °C within a time frame of 240 seconds. The maximum total heat flux was 30,271,000 W/m2. The compressive yield strength and tensile yield strength obtained in this study were 280 MPa, while the ultimate tensile strength was measured at 310 MPa. The alternating stress levels ranged from 62.05 MPa to 275.8 MPa. This study established that the material is susceptible to fatigue failure, as the alternating stress levels were below the material’s yield strength of 280 MPa.

Degradation induced superlubricity on the rough surface of black phosphorus composite

A rough surface composed of asperities was considered as the obstacle for achieving superlubricity in traditional friction theory. Here, microscale superlubricity with the friction coefficient of 0.0086 was observed on a relatively rougher soft surface of black phosphorus (BP) composite due to the degradation of BP with oxygen and moisture via the atomic force microscopy (AFM) experiment equipped with diamond-like carbon (DLC) microsphere probe. Comparative analyses corroborated that the produced phosphorus oxides (oBP) with abundant P=O and P−OH bonds and the local graphitized amorphous carbon film at the sliding interface decreased the possibility of direct contact between original rough peaks and provided an ultra-low shear strength for achieving superlubricity. Furthermore, a certain nanoscale roughness structure on the composite surface facilitated a more reliable superlubricity state, which supplied the larger contact area and locking capillary force to hold and retain the lubricating liquid film formed by the water absorption of oBP. These findings provided fundamental insights into the nature of tribological mechanisms and suggested a new method to achieve ultra-low friction of polymer composite materials in engineering.

Effect of protonation and deprotonation on oxygen-containing groups functionalized graphene for boron adsorption removal

This study investigated the adsorption mechanisms of boron on protonated and deprotonated graphene with oxygen-containing functional groups. Six representative adsorption conformations of boron predominant species (B(OH)3 (B3) and B(OH)4− (B4)) on graphene were proposed. Protonation and deprotonation of graphene had significant effects on boron adsorption. Deprotonation of hydroxyl-modified (G20-OH) and carboxyl-modified graphene (G20-COOH) with 20 carbon rings decreased B3 and B4 adsorption. Protonation of G20-OH enhanced B3 adsorption. The adsorption interface, mainly around hydrogen atoms associated with protonated groups, exhibited a sharp gradient, due to the increased electron density from OH bond formation. B3 showed stronger electron sharing, emphasizing robust interactions. Hydrogen bonding dominated G20-OH2-B3, while G20-O-B4 exhibited more substantial hydrogen bond interactions. In summary, hydrogen bond strength was crucial in B3 adsorption, while electrostatic repulsion hindered B4 adsorption on deprotonated graphene. These findings highlight the importance of graphene protonated and deprotonated states in effectively removing various pKa contaminants.

A Chemical Sewing Enabled All‐In‐One Control Interface for Robust Zinc Metal Anodes

AbstractDeveloping artificial protective layers is an effective strategy to address the issue of dendrites for aqueous Zn‐metal batteries (ZMBS). However, drawbacks such as rough microscopic morphology, excessive thickness, and single functionality remain, limiting the attainment of a stable zinc anode. Herein, a novel multifunctional organic–inorganic hybrid artificial protective layer is produced by splicing inorganic fragments onto organic materials in situ using a chemical sewing. The protective layer is well‐compatible and also retains the function of organic and inorganic materials, which not only inhibits dendrite production but also alleviates Zn corrosion. The Si─OH bond of the zincophilic group enables planar Zn deposition while forming hydrogen bonds with water, suppressing water activity near the anode and reducing the hydrogen evolution reaction. As expected, the Zn||Zn symmetric cell with a protective layer provides high cycling stability of more than 1960 h at 1 mA cm−2, which is about 28 times higher than that of the symmetric cell assembled without the protective layer. More importantly, a Zn||V2O5 full cell with an ultra‐long lifetime has been achieved with an artificial protective layer. This work provides a potential viable path to achieve long‐lived ZMBS.

Influence of activated protons and acid–base pairs on proton conduction in imino-functionalized MOF-based hybrid membranes

The rich activated protons and effective proton-conducting paths are of importance to improve conductivities of conductors. Herein, a series of Brönsted acids as proton carrier and proton transfer sites is introduced into the highly stable MOF, contributing to create plentiful hydrogen bonds within frameworks. Consequently, the trifluoromethanesulfonic acid-embedded JUC-1000 ([Cu24(BDPO)12(H2O)12]) displays the relatively highest conductivity of 7.04 × 10−4 S cm−1 under ∼98% RH and 328 K, ∼16 times that of JUC-1000 (4.47 × 10−5 S cm−1). When TMSA@JUC-1000 (TMSA = CF3SO3H) blended with chitosan (CS), the proton conductivity of TMSA@JUC-1000/CS-15 is the highest at ∼76% RH and 328 K (1.01×10−2 S cm−1), which is six times higher than that of JUC-1000/CS (1.85×10−3 S cm−1). The CS contains abundant –NH2 and –OH groups as proton jumping sites, which would activate the –NH– or –OH bonds of JUC-1000 and the acidic groups in Brönsted acids. These would result in an increased content of activated protons and effective formation of H-bonding nets by acid-base interactions. The findings provide valuable insights into the potential application of MOFs materials in energy devices.

Understanding the Reducibility of CeO2 Surfaces by Proton-Electron Transfer from CpCr(CO)3H.

CeO2 is a popular material in heterogeneous catalysis, molecular sensors, and electronics and owes many of its special properties to the redox activity of Ce, present as both Ce3+ and Ce4+. However, the reduction of CeO2 with H2 (thought to occur through proton-electron transfer (PET) giving Ce3+ and new OH bonds) is poorly understood due to the high reduction temperatures necessary and the ill-defined nature of the hydrogen atom sources typically used. We have previously shown that transition-metal hydrides with weak M-H bonds react with reducible metal oxides at room temperature by PET. Here, we show that CpCr(CO)3H (1) transfers protons and electrons to CeO2 due to its weak Cr-H bond. We can titrate CeO2 with 1 and measure not only the number of surface Ce3+ sites formed (in agreement with X-ray absorption spectroscopy) but also the lower limit of the hydrogen atom adsorption free energy (HAFE). The results match the extent of reduction achieved from H2 treatment and hydrogen spillover on CeO2 in a wide range of applications.

In situ temperature synthesis and characterization of ferroelectric PZN-4.5PT nanoparticles’ thin films using synchrotron light source

ABSTRACT Despite the excellent properties of Pb(Zn1/3Nb2/3)O3-4.5PbTiO3 (PZN-4.5PT) single crystals, the greatest difficulty for their application on electronic devices is to make them to thin layers related to the difficulty to make them as ceramic materials. In this paper, we use the combined USAXS/SAXS/WAXS instrument at 9ID beamline at APS-ANL for in situ characterization of PZN-4.5PT inorganic perovskite nanoparticles thin films deposited on nanotextured silicon to understand the phase transitions and determine the observed microcrystals' structure. The sample was annealed from ambient to 1000°C. The results revealed structure changes in the nanoparticles' thin films which could be explained by the new phase that can be assigned to the Pb3(PO4)2-based component. The peak at 31° indicates the presence of the rhombohedral phase perovskites assigned to the nanoparticles. WAXS characterization permitted to identification of many transitions during thermal annealing like dehydration or dihydroxylation of phosphorus gel –OH bonds and internal water.

Investigation of the effect of amine and thiol as functional groups on gold Nanobipyramids properties

Metal nanoparticles are increasingly popular due to their unique properties, such as their vast surface area, tiny size, strong reactivity in live cells, and high-temperature stability. Gold nanoparticles, as one of the metal nanoparticle types, are frequently utilized in biosensor applications because of their adjustable Localized Surface Plasmon Resonance (LSPR) characteristics, less cytotoxic nature, and increased sensitivity to changes in the surrounding medium. The anisotropic metal nanoparticle of gold nanobipyramids (GNBPs) provides for higher Refractive Index Sensitivity (RIS) and Figure of Merit (FOM) value than others, allowing for higher sensitivity. This work lies in the comprehensive investigation of GNBPs functionalized with amine and thiol groups over varying shorter time durations (0.5 – 12 h) through the immediate change in optical, structural, morphological, electrical surfaces, and molecular properties. The findings show amine groups enable the red-shifted spectrum, whereas thiol groups impact the blue-shifted spectrum. By employing amine groups, it is able to produce side peaks in the XRD pattern made up of amine atoms. The use of thiol groups, meanwhile, has an impact on the growth increase in the (111) direction. Then, the highest surface density is obtained in 3 h, 59.78 % for amine-functionalized GNBPs (a-GNBPs) and 75.49 % for thiol-functionalized GNBPs (t-GNBPs). Next, a-GNBPs generate the highest angle slope compared to t-GNBPs, i.e., 140.422⁰. In addition, for the electrical surface effect, amine functionalization increases the zeta potential value from 0.3 to 2.5 mV, indicating the inhibition of nanoparticle agglomeration. On the other hand, thiol functionalization affects the decreasing of zeta potential value from 0.3 to -0.5 mV, allowing for nanoparticle agglomeration. Subsequent FTIR characterization analysis obtained shifts in the wave numbers, with the -OH bond exhibiting changes within the range of 3306.75 – 3269.95 cm-1, C=-CH bond providing for 2138.48 – 2136.56 cm-1 range, and the C = O bond showing alterations between 1637.59 – 1637.33 cm-1 following amine and thiol functionalization. Extended observation reveals that both a-GNBPs and t-GNBPs exhibit significant signal responses in glucose detection applications utilizing LSPR-based sensors, suggesting the feasibility of functionalizing GNBPs with amine and thiol groups for potential biosensor development.

Percarbonate activation by N-doped polyethylene terephthalate (PET)-derived carbon: The role of vacancy and insights into the mechanism

Percarbonate-based advanced oxidation processes catalyzed by carbon materials from plastic waste are rarely reported and lack clarity in their mechanisms. We synthesized N-doped polyethylene terephthalate (PET)-derived carbon materials with surface areas of up to 2190.9 m2/g and nitrogen/oxygen vacancies via urea-assisted pyrolysis. These materials exhibited exceptional adsorption and catalytic activities in a Fenton-like reaction for tetracycline degradation. The N-doped PET-derived catalyst (NPETK-800) achieved a 95 % removal efficiency for tetracycline at 50 mg/L, attributed to synergistic adsorption and oxidation effects via sodium percarbonate activation. NPETK-800 underwent surface hydroxylation through the electrostatic adsorption of OH− from CO32− hydrolysis on N and O vacancies, and its hydroxylated surface converted the adsorption mode of H2O2 to a H-bonded structure. This mode favored cleaving the OH bond over the OO bond in H2O2, generating 1O2 and O2−, crucial for tetracycline degradation. This study unveils the pivotal role of vacancies in tuning the generation of reactive oxygen species in Fenton-like reactions.

Encapsulation of quercetin fraction from Musa balbisiana banana blossom in chitosan alginate solution, its optimization and characterizations

This study comprises the isolation of quercetin from the bhimkol banana (Musa balbisiana) blossom, encapsulation, and its characterizations. An isolated quercetin rich fraction was obtained from HPLC followed by column chromatography and subsequently encapsulated with chitosan-alginate polyelectrolyte complex at optimum encapsulation conditions obtained by ant colony optimization. Quercetin fraction and encapsulated quercetin were characterized for their physicochemical properties (by HPLC, FTIR, NMR, XRD, Dynamic Light Scattering, and release study). The yield and purity of isolated quercetin rich fractions were 2.35 ± 0.08 μg/ml and 83.12 ± 0.31 %, respectively. After the optimization of encapsulation, quercetin 0.2 %, sodium alginate 4 %, chitosan 0.5 %, and agitation at 300 rpm were found to be the optimal conditions resulting in higher encapsulation efficiency (EE, 84.54 %). EE was significantly improved by a slight increase in sodium alginate, and agitation. Encapsulated quercetin revealed good pH resistance by releasing 68.27 mg QE/g quercetin in simulated gastric fluid at 60 min. Microbeads of encapsulated quercetin showed the structural bond stretching of encapsulating materials and quercetin in FTIR spectra (stretching at 1511 cm−1, 1380 cm−1, and 1241 cm−1 are attributed to the stretching vibration of CO in aromatic rings, and bending vibration of OH bond in phenols). An average particle size of 2.71 μm exhibited the microgel behavior of microbeads (by XRD). The present study on the underutilized variety of banana blossoms has diverse applications in the food and pharmaceutical industries that will productively exhibit effective drug delivery properties.

Dysprosium hydroxide nanoparticle-embedded photoluminescent composite films

Dy(NO3)3 was dissolved in water–ethanol complex solvent, and the obtained solution was used to fabricate composite films wherein Dy compound particles were embedded in a transparent urethane resin. All the resulting composite films exhibited photoluminescence properties attributed to the Dy-based compounds. When the composite films were prepared by varying the water/ethanol ratio of the raw material solution, the PL intensity was stronger when the water content of the composites was higher. Further ultraviolet irradiation of the resulting films caused the disappearance of the Dy–OH bonds and decrease in the PL intensity of the films. The increase in the PL intensity with increasing water content was attributed to the presence of Dy–OH bonds in the films. In addition, we investigated the presence and PL properties of Dy–OH bonds in Dy-based particle composite films.

Co-Gasification of Pistachio Shells with Wood Pellets in a Semi-Industrial Hybrid Cross/Updraft Reactor for Producer Gas and Biochar Production

The possibilities of pistachio shell biochar production on laboratory-scale gasification and pyrolysis devices have been described by several previous studies. Nevertheless, the broader results of the pistachio shell co-gasification process on pilot-scale units have not yet been properly investigated or reported, especially regarding the detailed description of the biochar acquired during the routine operation. The biochar was analysed using several analytical techniques, such as ultimate and proximate analysis (62%wt of C), acid–base properties analysis (pH 9.52), Fourier-transform infrared spectroscopy (the presence of –OH bonds and identification of cellulose, hemicellulose and lignin), Raman spectroscopy (no determination of Id/Ig ratio due to high fluorescence), and nitrogen physisorption (specific surface 50.895 m2·g−1). X-ray fluorescence analysis exhibited the composition of the main compounds in the biochar ash (32.5%wt of Cl and 40.02%wt of Na2O). From the energy generation point of view, the lower heating value of the producer gas achieved 6.53 MJ·m−3 during the co-gasification. The relatively high lower heating value of the producer gas was mainly due to the significant volume fractions of CO (6.5%vol.), CH4 (14.2%vol.), and H2 (4.8 %vol.), while hot gas efficiency accomplished 89.6%.

Uniform redistribution of Zn2+ flux induced by remodeling the solvated structure to form zincophilic interfaces via sodium alginate electrolyte additive

Irregular dendrites produced by zinc anodes and self-corrosion phenomena hinder the large-scale application of aqueous zinc-ion batteries. In this work, a natural polysaccharide sodium alginate molecule (SG) was introduced into the ZnSO4 electrolyte. Relying on the polar groups contained in the SG molecule, the coordination structure of anions and cations in the system is reshaped, and the hydrogen bonding is enhanced by a significant shift of the –OH bond, the reduction of H2 is reduced and the corrosion inhibition efficiency is 16 %. Moreover, the strong chelation between SG molecules and Zn anode prompted the formation of new interfaces, which limited the disordered two-dimensional diffusion of Zn2+, thus achieving the effect of inducing preferential transport and uniform redistribution deposition of Zn2+. Specifically, the Zn||Zn symmetric batteries survived for more than 2500 h for 2 mA cm−2 at 1 mAh cm−2, and survived for more than 1100 h under more severe conditions (10 mA cm−2, 2 mAh cm−2). The Zn||Cu half-cells still have high average Coulombic Efficiency (99.67 %) after 800 cycles, and the Zn||Na3VO4 (NVO) full-cells can stably run for 600 cycles with a remaining specific capacity above 150 mAh g−1. This strategy provides a new idea for the construction of aqueous batteries.

High-electrophilic (SiO)2Nb(OH)(=O) sites confined in silanol defects over Nb-Beta zeolite for efficient cyclic alkene epoxidation reactions

Dealuminated Beta zeolite has a large amount of silanol defects on its interface, which provides an ideal place for embedding metal species and creating metal active sites in a confined microenvironment. The confined metal sites as well as their surroundings are closely related to the reactant activation and transient state achievement. Hence, unraveling the confined metal sites is of great significance for the catalytic reaction process. Herein, niobium species were incorporated into the silanol defects over dealuminated Beta zeolite with a facile dry impregnation method, co-grinding the niobium precursor with dealuminated Beta zeolite support. The successful incorporation of niobium into the silanol defects for 30Nb-Beta zeolite was verified by DRIFT, 1H MAS NMR, UV–Vis and UV-Raman characterizations. XAS characterization and DFT calculations further disclosed that the confined Nb species existed as (SiO)2Nb(OH)(=O), containing two Si−O−Nb bonds, one Nb=O bond as well as one Nb−OH bond. The synthesized 30Nb-Beta zeolite catalyst displayed a superior cyclohexene conversion of 51.1%, cyclohexene oxide selectivity of 83.1% as well as TOF value of 188.2 h−1 ascribed to the inherent electrophilicity of Nb(V) for confined (SiO)2Nb(OH)(=O) species as well as the low oxygen transfer energy barrier for NbV−OOH species. Furthermore, the prepared 30Nb-Beta zeolite can be effectively employed to other cyclic alkene epoxidation reactions.

Computational insights into the reaction mechanism of the synthesis of quinazoline derivatives via the cyclocondensation reaction between methyl 2-amino-4-(2-diethylaminoethoxy)-5-methoxybenzoate and formamide

In this work, the cyclocondensation reaction mechanism between methyl 2-amino-4-(2-diethylaminoethoxy)-5-methoxybenzoate (MAD, 1) and formamide (FME, 2) was theoretically explored at the DFT level using the B3LYP/6-311++G(d,p) computational method. The two paths (a and b) involved in this reaction take place through four steps. CDFT results show the most favourable electrophilic/nucleophilic interaction between the C3 electrophilic center of MAD (1) and the N4 nucleophilic center of FME (2). Activation energy analysis predicts the formation of quinazoline derivative as the main product, in reasonable agreement with experimental results. BET allowed a deeper understanding of the reaction mechanism by revealing the existence of four structural stability domains (SSD) during the processes of CN and OH bond formation. The bond process is as follows: depopulation of V(N) basin with the formation of first CN bond (appearance of V(C,N) basin), cleavage of NH bond with the creation of V(N) and V(H) monosynaptic basins, and finally the appearance of V(H,O) disynaptic basin related to the OH bond. In the case of dehydration, the transition from SSD-I to SSD-II corresponds to the cleavage of the CO bond, whose electron population is transferred to the V(O3) basin. The cleavage of N7-H9 bond with the formation of V(N) and V(H) basins is the first stage, followed by the formation of the OH bond as the second stage.

Stable hydrogen and oxygen isotope geochemistry of Fe3+-rich, interstratified clay minerals from seafloor hydrothermal sites

Chemical and structural complexities in interstratified clay minerals arising from mineral transformations and evolving formation conditions should be recorded in their stable isotope signatures. This paper examines the controls on the stable hydrogen and oxygen isotope compositions of Fe3+-rich, glauconite-nontronite, talc-nontronite and talc-saponite from submarine hydrothermal sites, with a focus on the Red Sea Atlantis II Deep. Values of δ18O became less positive in the order nontronite > glauconite-nontronite > talc-nontronite > talc-saponite, yielding oxygen isotope temperatures ranging from ∼40 °C for nontronite to ∼135–300 °C for talc-saponite. These clay minerals have low δ2H, ranging from −145 to −127‰ for talc-nontronite, −135‰ for nontronite, −129 to −85‰ for glauconite-nontronite, and −95 to −59‰ for talc-saponite. The clay mineral-water hydrogen isotope fractionation is strongly affected by Fe3+ content, with increasing structural Fe3+ causing progressive weakening of O-H bonds. The large ionic radius and high charge of Fe3+ cause it to be more poorly shielded by surrounding oxygen from hydroxyl hydrogen relative to other octahedral or tetrahedral cations. The resulting lengthening of O-H bonds favours 1H over 2H. Our results confirm that Fe-rich phases, such as nontronite-glauconite, are produced at the lowest temperatures and Mg-rich phases, such as talc-saponite, are formed at the highest temperatures in seafloor hydrothermal environments. Evolving fluid chemistry and fluid pathways during clay mineral formation are also important. Glauconite layer formation from precursor nontronite likely occurred during diagenesis; redox changes causing Fe-reduction and an increase in layer charge facilitated interlayer K-fixation. Talc-saponite compositions vary with temperature and fluid chemistry, forming at variable sediment depths depending on access to the hottest hydrothermal fluids.