Double-bonded Oxygen Research Articles

Molecular Composition Evolution of Dissolved Organic Matter With Water Depth in Prydz Bay of East Antarctic: Carbon Export Implications

AbstractThis study analyzes the molecular composition of dissolved organic matter (DOM) in Prydz Bay by Fourier Transform Ion Cyclotron Resonance mass spectrometry to probe the carbon sequestration capacity in the continental shelf system. Concentrations of particulate organic carbon (POC), particulate nitrogen and dissolved organic carbon (DOC) with water depth show that POC could be mainly decomposed into DOC and/or microbially degraded. Highly labile DOC is further degraded and remineralized by microorganisms within the upper 200 m, as evidenced by a downward enrichment of 13CPOC and increases in the average molecular weight, oxygen atom number (O) and double bond equivalents of DOM molecules, indicating that biodegradation is the main driver for particulate organic matter and DOM evolution with water depth. Semi‐quantitative calculation demonstrates that ∼83% of POC was transformed to DOC as well as dissolved inorganic carbon (DIC), and ∼30% of DOC further to DIC via microbial degradation within the upper 200 m in summer, resulting in a relatively low total organic carbon content in sediments of Prydz Bay. The newly transformed DIC and residue DOC can be preserved in the deep layer due to the formation of well stratified and stable water body in summer of Prydz Bay, ultimately entering the regional circulation system instead of being released back into the atmosphere. This could be one of the most important processes determining the atmosphere CO2 uptake in the continental shelf system of Southern Ocean.

Molecular dynamics simulations on the anti-memory effect of vinyl lactam-based polymers

Molecular dynamics simulations were carried out to study the microscopic working mechanism of PVCap-co-TBA and PVCap, especially its working mechanism on the memory effect of hydrates. Our simulation results indicate that PVCap-co-TBA could weaken or even eliminate the hydrate memory effect under the higher subcooling conditions compared with PVCap. The hydrogen bonds formed by the double-bond oxygen atoms and nitrogen atoms of the lactam groups in PVCap with water molecules make the hydrate residual structures around PVCap less susceptible to decompose and provide nucleation sites for hydrate reformation at high subcooling conditions. Compared with PVCap, the introduction of strong hydrophobic tertiary butyl functional groups in PVCap-co-TBA accelerates the mass transfer of water and methane molecules, leading to the decomposition of the hydrate residual structures and the aggregation of large nano-bubble, thereby delaying the hydrate re-nucleation even at high subcooling conditions (e.g. 273 K and 30 MPa).

Effect of NaClO disinfectant treatment on the yields, components and combustion characteristics of typical medical waste pyrolysis products

Medical waste with pathogenic bacteria is infectious and toxic, which could cause significant harm to the environment and human health without being adequately disposed of. Pyrolysis-incineration coupled technology can realize the rapid and efficient treatment of medical waste while reducing the generation of pollutants. Whereas, the NaClO disinfection treatment, which is a necessary process prior to transfer and disposal of medical waste, has not been sufficiently described in terms of its effect on the pyrolysis yield and components characteristics of medical waste. This study clarified the influence mechanism of NaClO disinfection treatment on the yields, components, and combustion characteristics of pyrolysis products derived from typical medical waste (cotton swab sticks, masks, and latex gloves). The results showed that NaClO disinfection treatment induced depolymerization of the internal structure of the polymer and increased pyrolysis tar and syngas at 400 °C. In addition, NaClO disinfection treatment reduced syngas quality, which was attributed to generating more CO2 and inhibiting alkynes gas production under medium-low pyrolysis temperatures. Furthermore, the condensation or cyclization of light components into heavy components in the tar increased the average double-bond equivalents and oxygen content, which was detrimental to tar ignition and combustion. Moreover, the combustion performance of char was improved because there was a tendency for the conversion of graphitic carbon to fatty carbon in the char. These findings elucidate the feasibility of pyrolysis-incineration coupled technology for the fast and effective treatment of medical waste.

Sulfhydryl-modulated CsPbBr3 nanocrystals as a fluorescent tongue for discrimination of formaldehyde releasers and parabens

Adding preservatives to cosmetics have raised many concerns about health issues. Here, we propose a fluorescence sensor array for preservative discrimination based on two types of CsPbBr3 nanocrystals (NCs) modified with two different thiol compounds (i.e., 6-mercapto-1-hexanol (6-MCH) and dithiothreitol (DTT)). The redox reaction between the sulphydryl of 6-MCH and DTT and the carbon oxygen double bonds of preservatives will enhance the fluorescence intensity, which is due to the depletion of superficially decorated DTT and 6-MCH at CsPbBr3. By manipulating this mechanism, different preservatives generate unique fluorescence fingerprint responses through the diverse interactions between targets and two CsPbBr3 NCs. Thus, two types of preservatives, including four formaldehyde releasers and three parabens, were well distinguished at low concentration using linear discriminant analysis (LDA) by this sensor array. Remarkably, preservative identification in hand cream further proves the array’s practical applicability in complex environment.

Unravelling molecular fractionation of dissolved organic matter on ferrihydrite-phosphate complexes

Association of dissolved organic matter (DOM) with iron (Fe) oxyhydroxides leading to significant molecular fractionation, plays a significant role in biogeochemical cycling of carbon in soils. However, the molecular effects of coexisting phosphate, a widely distributed oxyanion in agricultural soils that has a strong affinity with Fe oxyhydroxides on such a process remain poorly understood. Here, using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) with a superiority in deciphering DOM characteristics at the molecular level, this study reveals the DOM molecular fractionation characteristics on ferrihydrite-phosphate (Fh-P) complexes. Results show that the adsorption of DOM on Fh-P complexes can be significantly inhibited by ∼50% compared to that on ferrihydrite. Optical spectroscopy and FT-ICR-MS further indicate that phosphate can greatly change the molecular fractionation of DOM on Fh-P complexes. Phosphate preferentially inhibits the highly aromatic, hydrophobic, and high molecular weight compounds (> 400 Da) of DOM on Fh-P complexes, such as condensed hydrocarbon and tannin; more CHONS compounds preferentially adsorb on the Fh-P complexes than thoseon ferrihydrite. Phosphate inhibits the adsorption of DOM with the characteristics of high oxygen atoms number, aromaticity index (AI), and double bond equivalents (DBE) on ferrihydrite. Our study demonstrates that the inhibitory effects of phosphate on the adsorption of the DOM can significantly influence the fractionation and adsorption of DOM by ferrihydrite. The findings of this work deepen our understanding of biogeochemical cycling of DOM in soil and aquifer environments.

Characterization and Adsorption Capacity of Modified Biochar for Sulfamethylimidine and Methylene Blue in Water.

In this study, a composite of pond mud and lanthanum- and nano-zero valent iron-modified-biochar was investigated for its ability to adsorb methylene blue (MB) and sulfamethazine (SMZ). La-modified attapulgite and nano-zero valent iron (surface area enhanced by 43.7% via Brunauer-Emmett-Teller analysis) were successfully loaded onto the straw-sediment biochar (BC) surface. With the increase in pyrolysis temperature, the biocompatibility yield, the H, O, and N content, and the ratio of carbon elements decreased, while the pH value, surficial micropores, C element, and ash content increased. The biocarbon small molecules were gradually and tightly ordered, and the organic groups such as hydroxyl, carboxyl groups, and carbon oxygen double bonds were gradually lost or disappeared. The original Fe-BC had more phenolic hydroxyl groups forming an intermolecular hydrogen bond than others with a higher adsorption capacity possibly through the Schiff base reaction. The effect of various pH (2-9), temperature (15-35 °C), and initial concentration (1-25 mg L-1) on adsorption was investigated. pH and temperature were the main factors governing the adsorption process. The maximum adsorption capacity was observed at pH 4. The adsorption performances for MB followed the order Fe-BC > La-BC > BC, and the maximum removal rate was over 98.45% with pH = 7. The three types of BC dosages between 0.2 (6.67 g L-1) and 0.4 g showed a removal rate of 99% for MB. The adsorption capacity of Fe-BC, La-BC, and BC for MB was 2.201, 1.905, and 2.401 mg L-1 with pH = 4, while 4.79, 4.58, and 5.55 mg g-1 were observed with BC dosage at 0.025 g. For SMZ, the higher the temperature, the better the adsorption effect, and it reaches saturation at approximately 25 °C. To further evaluate the nature of adsorption, Langmuir/Freundlich/Temkin models were tested and the adsorption capacities were evaluated on the surface of the BC composite. The three modified materials were physisorbed to SMZ, while MB was chemisorbed. For MB, the adsorption performance of BC is the best < 0.2 g (6.67 g L-1) at pH 7.0 at 35 °C. The Elovich model was more suitable for MB, while the Freundlich and Temkin models could better fit the adsorption process of MB. The preparatory secondary dynamics equation and Langmuir equation were more compliant for SMZ, and the saturated adsorption capacities of straw-modified, La-BC, and Fe-BC reached 5.699, 6.088, and 5.678 mg L-1, respectively.

Nano- and microscale characterization for interfacial transition zone of geopolymer stabilized recycled aggregate of asphalt pavement

Geopolymer technology offers significant advantages in stabilizing recycled asphalt pavement (RAP), allowing its repurposing as road construction materials. This study employs a combination of molecular dynamics simulations and experimental characterization to investigate the properties of the interfacial transition zone (ITZ) in geopolymer-stabilized RAP. A composite model of geopolymer-aged asphalt-aggregate was established using molecular dynamics (MD) to access the effects of aging degrees of RAP on the interfacial bonding. The findings revealed that aging asphalt molecules on the RAP surface exhibit an affinity for Na+ present in geopolymers. Na+ ions migrate to the interfacial region, forming electrostatic interactions with double-bonded oxygen atoms in the aging asphalt molecules. The interfacial interaction energy and nanomechanical performance grow up and then reduced with the aging degree of RAP. SEM-EDS results verified these simulation findings, indicating that C(N)-A-S-H might grow at the interface, leading to a strong affinity and external chemical bonding.

Improved flotation of chalcopyrite from galena and pyrite by employing Cu-affinity phosphate collector

Sulfide minerals have similar flotation behavior using the commonly-used collectors such as xanthate due to its low selectivity to active metal ions on sulfide minerals, which leads to difficulties separating chalcopyrite from galena and pyrite. In this work, dibutyl phosphonate (HDBP) was investigated as a collector for chalcopyrite. Flotation tests confirmed that HDBP can selectively and effectively collect chalcopyrite at low concentrations and at environment-friendly pH. This was supported by the results of X-ray photoelectron spectrometry (XPS), electrochemical tests and Density Functional Theory (DFT) simulations. It can be inferred from the XPS results that single-bonded and double-bonded oxygen atoms in the HDBP structure undergo chemisorption with Cu atoms on the surface of chalcopyrite, while HDBP barely interacts with galena and pyrite. This was supported by the results of DFT simulations which showed that the stable adsorption of HDBP on the surface of chalcopyrite is formed by the four-member chelation ring with the P–O–Cu and P=O–Cu bonds with a higher adsorption energy of −133.01 kcal/mol. Electrochemical tests suggested that the corrosion potential and current of the chalcopyrite electrode increase significantly after using HDBP due to the formation of the new oxides. However, for galena and pyrite, there were no obvious changes, which further indicated that HDBP has a strong and selective reactivity to chalcopyrite. The strong affinity of HDBP for Cu atoms means that it has strong potential as a collector for the selective separation of copper-bearing minerals.

Spinel lithium titanate anode/polyether sulfone nanocomposite synthesized by pulsed laser ablation method for optoelectronic applications

Nowadays, to increase the usage of energy storage applications like electric cars or stationary storage, the cost of these manufacturers must be reduced. Our present study focuses on an alternate electrode production approach to suit the needs of today's lithium ion battery’s cost efficiency by using an eco-friendly method, the pulsed laser ablation method in liquid media technique, which was used for the first time to synthesize spinel lithium titanate anode, Li4Ti5O12 nanoparticles (LTO NPs), and incorporate them with polyether sulfone (PES) in just one step to form a PES/LTO nanocomposite. The evidence from XRD showed that the nanocomposite film is formed as a crystalline phase from a cubic spinel structure corresponding to LTO, with crystalline sizes around 9.4 nm. Furthermore, SEM revealed a semi-spherical distribution of LTO NPs throughout the PES matrix. Also, the elemental analysis provides the elemental peaks for C, S, Ti, and O, and no other elemental peaks do, confirming their purity. Moreover, the FT-IR investigation affirmed the interaction between PES and LTO NPs via the sulfone group with the breakage of the sulfur and oxygen double bond and the formation of a new link between SOLa and SOTi that may be responsible for the emergence of this band. Also, the absorption study confirmed the formation of localized states between occupied and unoccupied molecular orbital bands is made feasible by the chemical linkages between PES chains and LTO NPs. As a result of the dielectric investigation, LTO NPs are a good choice for usage as dopants to enhance the electrical characteristics of PES polymer. Overall, the PES/LTO nanocomposite films' improved dielectric and optical properties make them appropriate for energy storage applications.

Boiling heat transfer of CO2/lubricant on structured surfaces using molecular dynamics simulations

In this paper, the molecular dynamics (MD) simulations are employed to investigate the effects of lubricant (PEC4) on the boiling heat transfer of CO2 on the structured surface. The results show that the structured surfaces can enhance the nucleation boiling of CO2 by providing effective bubble nucleation sites and larger heat transfer areas. However, with the increase of the mass fraction of PEC4, the nucleation boiling heat transfer efficiency decreases on the structured surface. The distribution characteristics of the CO2/PEC4 mixture during the boiling process show that parts of CO2 molecules in the liquid mixture are more likely to be adsorbed by the double-bonded oxygen atoms and carbon atoms of the ester groups of the PEC4 molecules, which hinders the movement and phase transition process of CO2 molecules. Therefore, the PEC4 molecules in the nucleation region first migrate to the top liquid region before bubble nucleation, and then bubble nuclei comes into being. When the mass fraction of PEC4 is higher than 7 wt%, the nucleation temperature is increased by 10 K to 20 K. The decrease of the CO2 nucleation boiling heat transfer performance caused by PEC4 istheconsequenceof thecoaction ofmanyfactors, including that the lubricant leads to a decrease in self-diffusion coefficient of CO2, an increase in liquid phase viscosity, an increase in bubble nucleation temperature of CO2, and a decrease in heat transfer resistance of the solid-liquid interface.

Alkaloid Based Chemical Constituents of Ocimum santum &amp; Cinchona Bark : A Meta Analysis

This article provides a concise summary of the recent developments that have been achieved in our comprehension of the asymmetric addition processes that are catalysed by native Cinchona alkaloids and their derivatives. This class of reactions includes cycloadditions, 1,4-adds, direct nucleophilic additions across carbon–oxygen or carbon–nitrogen double bonds, and direct nucleophilic additions across carbon–oxygen double bonds. Because of their capacity to catalyse the addition of a wide variety of functional groups to C9, many Cinchona alkaloids have been utilised in these processes as catalysts. These functional groups include amino, alkoxy, hydroxyl, amido, urea, and thiourea, among others. The importance of mechanical variables is emphasised in many different contexts. Additionally, the utilisation of adducts in future synthesis is sometimes broken down into its component steps. Ocimum basilicum was discovered to be mostly consisted of estragol (&gt; 35.71 percent), (E)-ocimene (&gt; 1.47 percent), trans-bergamotene (&gt; 0.83 percent), a-cadinol (&gt; 0.41 percent), eucalyptol (&gt; 0.25 percent), and -caryophyllene (&gt; 0.07 percent), whereas Ocimum sanctum is primarily composed of eucaly There is a greater concentration of chemical components in the leaves of Ocimum basilicum and Ocimum sanctum than there is in the actual inflorescence or flowers of the plant. The genetic distance between the two species was analysed in order to better understand the interspecies relationship, and the results showed that it was 2.86. The small difference in genetic makeup that exists between Ocimum basilicum and Ocimum sanctum is evidence that these two species are related to one another and share similar traits.

Promote the activation and ring opening of intermediates for stable photocatalytic toluene degradation over Zn-Ti-LDH

Improving the selectivity of photocatalysis and reducing the generation of toxic by-products are the two key challenges for the development of highly efficient and stable photocatalysts. In this work, it was revealed that Zn-Ti-layered double hydroxide (ZT-LDH) photocatalyst, which generated less intermediates, showed better toluene degradation efficiency (removal ratio, 75.2%) and stability, compared with P25 (removal ratio, 10.9%). During the photocatalytic toluene degradation, benzaldehyde and benzoic acid were the main intermediates existed in the gas phase and on the surface of the catalyst, respectively. By combining experiments with theoretical calculation, it was found that the hydrogen atoms on the hydroxyl groups in the LDH would selectively attract the oxygen atoms in the carbon–oxygen double bond of the two major intermediates, facilitating their adsorption and activation on ZT-LDH. Besides, the surface electronic structure of ZT-LDH was demonstrated to facilitate the ring-opening reaction of the two major intermediates, eventually maintaining high activity and stability. This work could provide new molecular perspectives for understanding the photocatalytic reactions in VOCs degradation and developing efficient and stable photocatalysts.

Titanium infiltration into ultrathin PMMA brushes

Vapor phase infiltration (VPI) is a bottom-up process that involves the infiltration of polymers, often using atomic layer deposition compatible precursors. By exposing a polymer to an organo-metallic precursor, area selective material formation is achieved where the precursor reacts with regions covered by an infiltration-receptive polymer brush. Combining receptive and rejecting polymers that have the capability of forming complex nanopatterns could potentially allow for the creation of nanofeatures, offering a route to area selective deposition. This work is concerned with the creation and characterization of titanium-infiltrated films with a VPI process. Thin films of poly(methyl methacrylate) (PMMA) were infused with titanium isopropoxide and subsequently analyzed with angular resolved x-ray photoelectron spectroscopy. All XPS analysis and VPI treatments were completed without breaking vacuum in an integrated ultrahigh vacuum setup, with O 1s, C 1s, Ti 2p, and Si 2p core levels revealing the successful incorporation of titanium into the polymer. Grazing angle Fourier-transform infrared spectroscopy demonstrates the breaking of carbon–oxygen double bonds within the PMMA structure due to titanium incorporation.

Probing key organic substances driving new particle growth initiated by iodine nucleation in coastal atmosphere

Abstract. Unlike the deep understanding of highly oxygenated organic molecules (HOMs) driving continental new particle formation (NPF), little is known about the organic compounds involved in coastal and open-ocean NPF. On the coastline of China we observed intense coastal NPF events initiated by iodine nucleation, but particle growth to cloud condensation nuclei (CCN) sizes was dominated by organic compounds. This article reveals a new group of C18,30HhOoNn and C20,24,28,33HhOo compounds with specific double-bond equivalents and oxygen atom numbers in new sub 20 nm coastal iodine particles by using ultrahigh-resolution Fourier transform–ion cyclotron resonance mass spectrometry (FT-ICR-MS). We proposed these compounds are oxygenated or nitrated products of long-chain unsaturated fatty acids, fatty alcohols, nonprotein amino acids or amino alcohols emitted mutually with iodine from coastal biota or biologically active sea surface. Group contribution method estimated that the addition of –ONO2, –OH and –C=O groups to the precursors reduced their volatility by 2–7 orders of magnitude and thus made their products condensable onto new iodine particles in the coastal atmosphere. Nontarget MS analysis also provided a list of 440 formulas of iodinated organic compounds in size-resolved aerosol samples during the iodine NPF days, which facilitates the understanding of unknown aerosol chemistry of iodine.

The ionization process of chemical warfare agent simulants in low temperature plasma ionization.

The application of low-temperature plasma ionization technology in the chemical warfare agent detection was mostly focused on the research of rapid detection methods. Limited studies are available on the ionization process of chemical warfare agents in low temperature plasma. Through the intensity of protonated molecules of dimethyl methylphosphonate (DMMP) in different solvents including methanol, deuterated methanol (methanol-D4), pure water, and deuterium oxide (water-D2), it was concluded that the water molecule in the air provides the hydrogen ion (H+) needed for ionization. The product ion spectra and the collision-induced dissociation processes of protonated molecules of nerve agent simulants, including DMMP, diethyl methanephosphonate (DEMP), trimethyl phosphate (TMP), triethyl phosphate (TEP), tripropyl phosphate (TPP), and tributyl phosphate (TBP) were analyzed. Results revealed that H+ mostly combined with phosphorus oxygen double bond (P = O) in the low-temperature plasma ionization. By analyzing the peak intensity distribution of product ions of protonated molecules, the presence of proton and charge migration in the low temperature plasma ionization and collision-induced dissociation were researched. This study could provide technical guidance for the rapid and accurate detection of chemical warfare agents through low temperature plasma ionization-mass spectrometry.

Structural characterization of thermal bitumen extracted from Fushun oil shale semi-coke with ionic liquid/N-methyl pyrrolidone

Thermal bitumen is an organic intermediate during the pyrolysis of oil shale kerogen. In this work, semi-cokes were prepared for obtaining thermal bitumen by pyrolyzing Fushun oil shale to 400–500 °C, followed by extraction with a mixture of an ionic liquid (1-butyl-3-methylimidazolium chloride) and a polar solvent (N-methyl pyrrolidone). The critical thermal bitumen with the highest yield of the 450 °C semi-coke extraction was carefully performed by gas chromatography–mass spectrometry, Fourier transform infrared spectrophotometry, liquid-state 13C nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. The thermal bitumen was mainly composed of aliphatic structures, especially methylene chains. The dominant aliphatic hydrocarbons were between C13 and C27, and the alkanes and corresponding alkenes from C14 to C22 were continuously identified in pairs. A small quantity of benzenes and naphthalenes was identified as well as phenols, carboxylic acids, and nitrogen compounds. The oxygen functional groups were mainly carbon and oxygen double bonds, and the nitrogen and sulfur functional groups were characterized as pyrrole and thiophene. Ultimately, a structural formula (C370H570O29N4S) and its atomic distribution were proposed, based on the final analysis of experimental data.

Electron paramagnetic resonance study of the paramagnetic center in gamma-irradiated tetrahydrophthalic anhydride single crystal

Electron Paramagnetic Resonance (EPR) analysis of gamma-irradiated tetrahydrophthalic anhydride (C8H8O3) single crystals was performed at 120 K. The single crystals were exposed to 60Co-gamma source at room temperature. The EPR spectra of gamma-irradiated single crystals of tetrahydrophthalic anhydride (THPA) were recorded at 10-degree intervals for different orientations of crystals in a magnetic field. Detailed examination of THPA single crystals by EPR spectroscopy method showed the presence of two carbon-centered THPA anion radicals. Both radicals were determined to have the same structure. The anion radicals observed in gamma-irradiated THPA single crystal were created by the scission of the carbon–oxygen double bond. The g values of the radiation damage centers observed in the THPA single crystal and the hyperfine structure constants of the free electron with nearby protons were obtained. Highlights Single crystals of tetrahydrophthalic anhydride were exposed to gamma radiation. Radiation damage centers in single crystals of tetrahydrophthalic anhydride were determined by EPR spectroscopy method. The presence of two anion radicals in single crystals of tetrahydrophthalic anhydride was determined. The formation mechanism of the paramagnetic centers in the tetrahydrophthalic anhydride is similar to that of succinic anhydride.

Effect of pore solution calcium and substrate calcium on PMMA/cement paste interface during early stages of hydration

AbstractThe interfacial shear strength of polymer thin film coating on calcium–silicate–hydrate (C–S–H) or cement paste significantly depends on the time‐point, from addition of water, when the polymer is coated. This is because the physico‐chemical properties of C–S–H surface evolve over time as hydration progresses. The instant of coating thus determines the interfacial performance of a thin film coating in an organic‐inorganic material system. In this work, we provide molecular insights into the interactions of poly(methyl methacrylate) (PMMA) functional groups with the pore solution calcium and bound substrate calcium present in hydrating C–S–H. The experimental observation reveals that PMMA thin film coated on second day of hydration exhibits larger interfacial shear strength than when coated on the 28th day. The possible reasons for this observations are: a) chemical crosslinking of two oxygen atoms from two different PMMA polymer chains by pore solution calcium ions and b) the physical interaction between double bond oxygen (O1) present in –COO functional group of PMMA with pore solution calcium. In this work, physical interaction between double bond oxygen (O1) present in –COO functional group of PMMA with pore solution calcium and substrate calcium in C–S–H is addressed.

An atomic resolution description of folic acid using solid state NMR measurements.

The chemical shift anisotropy tensor and site-specific spin-lattice relaxation time of folic acid were determined by a 13C 2DPASS CP-MAS NMR experiment and Torchia CP experiment respectively. The molecular correlation time at various carbon nuclei sites of folic acid was evaluated by assuming that the 13C spin-lattice relaxation mechanism is mainly governed by chemical shift anisotropy interaction and hetero-nuclear dipole–dipole coupling. CSA parameters are larger for the carbon nuclei residing at the heteroaromatic ring and aromatic ring, and those attached to double-bonded electronegative oxygen atoms. It is comparatively low for C9, C19, C21, and C22. The molecular correlation time is of the order of 10−4/10−5 s for C9, C19, C21 and C22 carbon nuclei, whereas it is of the order of 10−3 s for the rest of the carbon nuclei sites. Spin lattice relaxation time varies from 416 s to 816 s. For C23 and C14, the value is 816 s, and it is 416 s for C7 nuclei. The correlation between structure and dynamics on an atomic scale of such an important drug as folic acid can be visualized by these types of extensive spectroscopic measurements, which will help to develop an advanced drug for DNA replication.

Bottom-Up Fabrication of a Metal-Supported Oxo–Metal Porphyrin

In situ preparation of oxotitanium tetraphenylporphyrin (TiO-TPP) on Ag(111) under ultrahigh vacuum conditions was achieved in a multistep procedure starting from adsorbed free-base tetraphenylporphyrin (2H-TPP). The final product as well as the intermediate titanium tetraphenylporphyrin (Ti-TPP) was characterized by a suite of surface-sensitive spectroscopic tools combined with scanning tunneling microscopy and density functional theory (DFT), and compared against the parent 2H-TPP species. Facile oxidation of Ti-TPP with molecular oxygen was observed at 300 K, with X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) from the Ti 2p core levels supporting a change in the oxidation state from Ti2+ to Ti4+. N K-edge and Ti L-edge NEXAFS suggest that the tetrapyrrole macrocycle conformation is modified upon binding to oxygen, in agreement with DFT calculations that predict a marked change of the local environment of the Ti centers upon oxygen attachment. O K-edge NEXAFS and O 1s energy-scanned photoelectron diffraction from the resulting TiO-TPP monolayer provide strong evidence for the presence of a titanium–oxygen double bond, with the latter technique yielding a bond length of 1.56 ± 0.02 Å. The majority of adsorbed TiO-TPP species have the oxo group pointing away from the surface rather than toward it, and thus the oxygen atom can potentially interact with external species. Both the highly reactive, intermediate Ti-TPP species and the final product TiO-TPP are of great interest for catalytic applications.