Perpendicular Adsorption Research Articles

Unraveling the Fundamentals of Axial Coordination FeN4+1 Sites Regulating the Peroxymonosulfate Activation for Fenton-Like Activity.

Precise modulation of the axial coordination microenvironment in single-atom catalysts (SACs) to enhance peroxymonosulfate (PMS) activation represents a promising yet underexplored approach. This study introduces a pyrolysis-free strategy to fabricate SACs with well-defined axial-FeN4+1 coordination structures. By incorporating additional out-of-plane axial nitrogen into well-defined FeN4 active sites within a planar, fully conjugated polyphthalocyanine framework, FeN4+1 configurations are developed that significantly enhance PMS activation. The axial-FeN4+1 catalyst excelled in activating PMS, with a high bisphenol A (BPA) degradation rate of 2.256 min-1, surpassing planar-FeN4/PMS systems by 6.8 times. Theoretical calculations revealed that the axial coordination between N and the Fe sites forms an optimized axial FeN4+1 structure, disrupting the electron distribution symmetry of Fe and optimizing the electron distribution of the Fe 3d orbital (increasing the d-band center from -1.231 to -0.432eV). Consequently, this led to an enhanced perpendicular adsorption energy of PMS from -1.79 to -1.82eV and reduced energy barriers for the formation of the key reaction intermediate (O*) that generates 1O2. This study provides new insights into PMS activation through the axial coordinated engineering of well-defined SACs in water purification processes.

Structural effects, corrosion inhibition mechanisms and timeliness of three tetrazole derivatives on copper in a 3.5wt.% NaCl solution

The structural effects, corrosion inhibition mechanisms and timeliness of 5-methyltetrazole (MT), 5-aminotetrazole (AT) and 5-mercapto-1-methyltetrazole (MMT) on copper in a 3.5 wt.% NaCl solution were studied by electrochemical experiments, surface characterizations and theoretical calculations. At the initial soaking stage, MT exhibited higher corrosion inhibition efficiency (99.65 %), which might stem from the electron donating effect and hydrophobic interaction of -CH3. While MMT exhibited lower corrosion inhibition efficiency (92.64 %), which might stem from the electron withdrawing effect and hydrophilicity of -SH. As the soaking time prolonged, the corrosion inhibition efficiencies of AT and MMT increased (99.49 % and 99.51 %). This might be because the N and S atoms of -NH2 and -SH could also provide lone pair electrons to coordinate with copper, especially S atom. As the soaking time was further prolonged, the formation of corrosion products weakened the interaction between N and S with copper, reducing the corrosion inhibition performance of AT and MMT. MT, AT and MMT molecules on Cu (111) surface can mainly undergo perpendicular adsorption, simultaneously accompanied by parallel adsorption.

Tandem catalysis of furfural to γ-valerolactone over polyoxometalate-based metal-organic frameworks: Exploring the role of confinement in the catalytic process

Polyoxometalate-based metal-organic frameworks (POMOFs) with bifunctional Lewis-Brønsted acid were designed by confining polyoxometalates (POMs: phosphotungstic acid (PW), phosphomolybdic acid (PMo) or silicotungstic acid (SiW)) within the Zr-MOFs. The confined POMs not only have their own Brønsted acid, but can also regulate the Lewis acid strength of the POMOFs via charge regulation, ultimately allowing the POMOFs to display superior catalytic performance in the tandem catalysis of furfural (FAL) to γ-valerolactone (GVL). Among the three catalysts (POMOF-PW, POMOF-PMo and POMOF-SiW), a complete conversion of FAL was achieved, while POMOF-PW exhibited the highest GVL yield (58.1 %) at 160 °C within 23 h. The leaching experiment and structural characterization of the catalyst before and after recycling confirmed the stability of the catalyst structure. The humin originates from the polymerization of furan ring-containing compounds driven by Brønsted acid. The adsorption configuration of the substrate molecules on the catalyst offers a new explanation for the tandem reaction process, i.e. that perpendicular adsorption performs only the first step of the tandem reaction, while the coexistence of perpendicular and horizontal adsorption permits the entire reaction process. This work gives unique insights into the tandem reaction of FAL and can guide the design of efficient tandem reaction catalysts.

Nanocomposite Films of Silver Nanoparticles and Conjugated Copolymer in Natural and Nano-Form: Structural and Morphological Studies.

The use of conjugated polymers (CPs) and metallic nanoparticles is an interesting way to form nanocomposites with improved optical properties. For instance, a nanocomposite with high sensitivity can be produced. However, the hydrophobicity of CPs may hamper applications due to their low bioavailability and low operability in aqueous media. This problem can be overcome by forming thin solid films from an aqueous dispersion containing small CP nanoparticles. So, in this work we developed the formation of thin films of poly(9,9-dioctylfluorene-co-3,4-ethylenedioxythiophene) (PDOF-co-PEDOT) from its natural and nano form (NCP) from aqueous solution. These copolymers were then blended in films with triangular and spherical silver nanoparticles (AgNP) for future applicability as a SERS sensor of pesticides. TEM characterization showed that the AgNP were adsorbed on the NCP surface, forming a nanostructure with an average diameter of 90 nm (value according to that obtained by DLS) and with a negative potential zeta. These nanostructures were transferred to a solid substrate, forming thin and homogeneous films with different morphology of PDOF-co-PEDOT films, as observed by atomic force microscopy (AFM). XPS data demonstrated the presence of the AgNP in the thin films, as well as evidence that films with NCP are more resistant to the photo-oxidation process. Raman spectra showed characteristic peaks of the copolymer in the films prepared with NCP. It should also be noted the enhancement effect of Raman bands observed on films containing AgNP, a strong indication of the SERS effect induced by the metallic nanoparticles. Furthermore, the different geometry of the AgNP influences the way in which the adsorption between the NCP and the metal surface occurs, with a perpendicular adsorption between the NCP chains and the surface of the triangular AgNP.

Constructing hierarchical structures of Pd catalysts to realize reaction pathway regulation of furfural hydroconversion

The technique of controlling nanoscale features precisely has been exploited to develop and improve bifunctional catalysts, which are important in the hydroconversion of furfural to high-value chemicals. Such bifunctional hydroconversion catalysts consist of metal sites and acid sites, and the intimacy extent of both active sites dictates the catalytic performance. In-depth exploration of the intimacy extent has been long limited by the lack of material synthesis and characterization method with nanometer precision. Herein, hierarchical catalytic structures with the spatial separation of Pd and acid sites were constructed by the multistep deposition strategy, wherein Pd was confined on defective CeO2 nanoclusters, which were dispersed on high-surface-area SiO2 with the strong acidity. The intimacy extent of Pd and acid sites in hierarchical catalytic structures of Pd/CeO2/SiO2 can be modulated by adjusting the CeO2 content, which leads to the aqueous-phase hydrogenation of furfural following a unique treble-site mechanism. The perpendicular adsorption of furfural on enriched oxygen vacancies of Pd/CeO2 contributes to the selective hydrogenation of the carbonyl group, and then the formed furfuryl alcohol undergoes the acid-catalyzed rearrangement of furan rings on SiO2 through the cooperative effect of acid sites and hydrogen spillover to give cyclopentanone. Meanwhile, the asynchronous catalysis effectively hinders the furan ring hydrogenation to tetrahydrofurfuryl alcohol by spatially separating Pd from the SiO2 surface. The superior catalytic performance is obtained on Pd/CeO2/SiO2-10 with a furfural conversion of 93% and cyclopentanone selectivity of 84%. We anticipate that the strategy of constructing hierarchical catalytic structures demonstrated here to spatially organize different active sites at the nanoscale will boost the further development of multifunctional catalysts.

Advanced prediction of organic–metal interactions through DFT study and electrochemical displacement approach

• 8-AN, 8-MQ, and 8-QSA chimisorbed on Mg(0001) surface via covalent bonds formation. • Upon the formation of coordination complexes between 8-AN and Mg 2+ , energy gap underwent change about ∆ E = 5.7 eV. • 8-AN, 8-MQ, and 8-QSA in their parallel configurations are found to interact strongly with the Mg atoms. • Electron donor effect of 8-AN compound strongly increases its coordination to Mg(0001) surface. • Interaction energies of all geometries follow the electrochemical performance trends. Heterocyclic compounds are the promising biological compounds as nature-friendly for the corrosion protection of metallic surface. In this work, three heterocyclic compounds such as 1-azanaphthalene-8-ol (8-AN), 2-methylquinoline-8-ol (8-MQ), and 8-quinolinol-5-sulfonic acid (8-QSA) were used as green compounds, and their anti-corrosion performance for AZ31 Mg in saline water was discussed on the basis of impedance interpretation and surface analysis. Findings found that the electrochemical performance was improved in the order of 8-AN > 8-MQ > 8-QSA, demonstrating the electron donor effect of N-heterocycles to form coordination complexes on the magnesium surface. From the electrochemical performance, the protective layer constructed at the optimal concentration reinforces the barrier against aggressive environments, with potential inhibition efficiency of 87.4%, 99.0%, and 99.9% for 8-QSA, 8-MQ, and 8-AN, respectively. Quantum chemical parameters and electron density distribution for free organic species in the absence and presence of Mg 2+ cation were evaluated using density functional theory (DFT). Upon the formation of coordination complexes between organic compound and Mg 2+ , energy gap underwent change about ∆ E = 5.7 eV in the 8-AN/Mg 2+ system. Furthermore, the adsorption of heterocyclic compounds on Mg surface reveals the formation of strong covalent bonds with Mg atoms, which further confirmed by the electron density difference and projected density of states analyses. Based on theoretical calculations, three inhibitors can adsorb on the metal surface in both parallel and perpendicular orientations via C, O and N atoms. In the parallel configuration, the C-Mg, N-Mg and O-Mg bond distances are between 2.11 and 2.25 Å, whereas the distances in the case of perpendicular adsorption are between 2.20 and 2.40 Å (covalent bonds via O and N atoms). The results indicated that parallel configurations are energetically more stable, in which the adsorption energies are -4.48 eV (8-AN), -4.28 eV (8-MQ) and -3.82 eV (8-QSA) compared to that of perpendicular adsorption (-3.65, -3.40, and -2.63 eV). As a result, experimental and theoretical studies were in well agreement and confirm that the nitrogen and oxygen atoms will be the main adsorption sites.

Molecular Adsorption of H2 on Small Neutral Silver-Copper Bimetallic Nanoparticles: A Search for Novel Hydrogen Storage Materials.

In the search for novel hydrogen storage materials, neutral silver–copper bimetallic nanoparticles up to the size of eight atoms (CumAgn: m + n ≤ 8) have been computationally studied. Density functional theory with the B3LYP exchange–correlation functional and the combined basis sets of LanL2DZ and aug-cc-pVQZ were used in all of the calculations. H2 adsorption studies on the most stable cluster geometries of all of the neat and heterogeneous entities found that 12 potential candidates, CuAg4, Cu6, Cu5Ag, Cu4Ag2, Cu3Ag3, Cu2Ag4, CuAg6, Cu5Ag3, Cu4Ag4, Cu3Ag5, Cu2Ag6, and CuAg7, fall within the recommended physisorption range of −18 to −6 kJ mol–1. A correlation in the behavior of binding energy, vibrational frequency, average bond distance, highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap, and chemical hardness with H2 adsorption was observed. This analysis further revealed that the H2 adsorption to the cluster was either a parallel or a perpendicular alignment. The analysis of the electron configuration of each atom in the cluster and the H2 molecule and the charge transfer analysis of these 12 clusters also showed that the physisorption in the perpendicular mechanism is due to an induced dipole interaction, while that in the parallel mechanism is due to a weak ionic interaction. The clusters identified with perpendicular adsorption, CuAg4H2, Cu6H2, Cu3Ag3H2, and Cu2Ag4H2, polarized the H2 molecule but had no charge transfer with the H2 molecule and those identified with parallel adsorption, Cu5AgH2, Cu4Ag2H2, CuAg6H2, Cu5Ag3H2, Cu4Ag4H2, Cu3Ag5H2, Cu2Ag6H2, and CuAg7H2, pulled the electrons from the H2 molecule and had charge transfer with the H2 molecule. The shapes of the frontier molecular orbital diagrams of the HOMO and LUMO also followed this observation.

First‐principles based theoretical investigation of the adsorption of alkanethiols on the iron surface: A DFT-D3 study

The search for novel corrosion inhibitors is a never-ending and challenging task. Computational studies are fundamental to assessing the interaction of inhibitor molecules with metals, thus opening the way to design new inhibitors with specific characteristics. Herein, first-principles DFT-D3 calculations were performed to simulate the bonding of three alkanethiols, namely 11-mercaptoundecanoic acid (MDA), decanethiol (DT), hexanethiol (HT) with the iron surface Fe(110). The interaction energies obtained from different adsorption systems predicted this adsorption strength: MDA > DT > HT. The perpendicular adsorption geometries were found to be more stable than other adsorption modes. However, all adsorption configurations showed covalent interactions between sulfur atom and iron surface. Electron density difference (EDD) plots and projected density of states (PDOS) further confirmed the electron-donation and back-donation synergic interactions between interactive systems. This study showed that alkanethiols with a long carbon chain and an end-functional group had increased charge transfer and bonding with the bare iron surface, i.e., Fe(110).

Hydrogenation of substituted nitroaromatics on non-noble metal catalysts: mechanistic insights to improve selectivity.

The mechanism of nitrobenzene hydrogenation on non-noble metals such as Ni is different from that previously reported for noble metals like Pt. The newly proposed pathway involves the initial dissociation of the two N-O bonds of nitrobenzene (Ph-NO2→ Ph-NO → Ph-N), leading to partial oxidation of the catalyst surface, followed by two successive hydrogenation steps (Ph-N → Ph-NH → Ph-NH2) that finally produce the functionalized aniline. Due to the oxophilic nature of non-noble metals like Ni, Co or Cu, the hydrogenation of the Ph-N intermediate and the removal of O in the form of water become the most energy demanding steps of the process. The strength of the interaction of O, H and N with different metals, and the preferential mode of adsorption of nitroarenes on clean and partially oxidized systems obtained from DFT calculations, are now used to propose an efficient non-noble metal catalyst that optimizes activity and selectivity.

On the adsorption affinity of graphene and white graphene sheets by dioxin‐like pollutants

AbstractThe affinity of graphene and white graphene sheets by dioxin‐like pollutants was compared by means of high‐level quantum chemical calculations. 2,3,7,8‐tetrachloro‐p‐dibenzodioxin (TCDD) and 2,3,7,8‐tetrachlorodibenzofuran (TCDF) were chosen as prototypes of dioxin‐like pollutants with high toxicological activity. Large interaction energies were obtained both in graphene and white graphene surfaces, contrary to other previous works using the graphene surface only. The interactions clearly differed in the relative weight of inductive and dispersion forces, being the former more important in white graphene. Leaving thermal effects out, the stacking adsorption was energetically favored over the perpendicular in graphene whereas no difference was found in white graphene. Due to the low water solubility of dioxin‐like pollutants very small differences were obtained between gas phase and solution adsorption enthalpies. Including thermal effects, perpendicular adsorption was found to be both energetically and entropically favored over stacking at 298 K. The adsorption free energies reflected a larger affinity by white graphene than graphene by around 2–5 kcal·mol−1. Therefore, boron nitride 2D surfaces are expected to perform better than carbon 2D surfaces as adsorbents for dioxin‐like pollutants in line with recent experimental works on water contaminants.

Recyclable Raman chip for detection of trace Mercury ions

Due to enrichment effect of Mercury ions (Hg2+), even if the concentration of Hg2+ is very low, it will do harm to human health. Precise detection of trace Hg2+ is important for environment protection and human health monitoring. In this work, gold nanoparticles (AuNPs) are immobilized on the surface of ITO with aid of inositol-hexaphosphate as linker agent and then 4-pyridinethiol (4-MPy) is decorated to form a 4-MPy/AuNPs/ITO chip. 4-MPy in the chip acts two roles involving the capture agent for Hg2+ and Raman signal reporter. With the adding of Hg2+, the linear increase of SERS response of 4-MPy is in the range from 1.0 ppt to 100 ppb (R2 = 0.9896) and the limit of detection could be down to 1 ppt. The mechanism of the Raman chip was also explored by molecular simulation. It is found that the interaction between Hg2+ and the nitrogen atoms changes the electron distribution of pyridine ring and induces reorientation of the 4-MPy molecules tending to more perpendicular adsorption fashion with respect to AuNPs surface, which leads to enhancement of the intensity of the pyridine breathing vibration peak at 1093 cm−1. The as-prepared SERS sensor chip features excellent stability and reproducibility as well as could be reused. The rapid 4-MPy/AuNPs/ITO-chip-based Raman protocol with capability against interference is competent for monitoring trace Hg2+ in river water samples.

Adsorption and photocatalytic degradation of benzene compounds on acidic F-TiO2/SiO2 catalyst.

The adsorption and photocatalytic degradation performance of F-TiO2/SiO2 catalyst towards a series of benzene compounds were studied. The results revealed that the F-TiO2/SiO2 catalyst is superior to TiO2 P25 in adsorption capacity and photocatalytic degradation under simulant sunlight irradiation. The adsorptive capacity for chlorobenzene is the highest and the degradation rate is the greatest among these target pollutants. The increase of absorptive organic molecules on acidic F-TiO2/SiO2 catalyst benefits photocatalytic degradation. The photocatalytic reaction accords to Langmuir-Hinshelwood mechanism. The FTIR results indicated that the promoting effect of acidic centers on adsorption of benzene compounds depends on electron property of the functional groups. The electron-donating groups (-OH and -NH2) of benzene compounds are weakly adsorbed on acidic centers of the catalyst due to the competitive adsorption with H2O, while the electron-withdrawing groups (-Cl and -NO2) are adsorbed more strongly at acidic sites. The monosubstituted chlorobenzene prefers to perpendicular adsorption on acidic surface, while the disubstituted benzenes prefer to horizontal adsorption, which decreases the adsorbed amounts. A photocatalytic rate mainly depends on electron donating property of the functional group and amount of adsorptive organic molecules, but not on electron density of benzene ring.

Insights into the inhibition mechanism of three 5-phenyltetrazole derivatives for copper corrosion in sulfuric acid medium via experimental and DFT methods

Abstract 5-Phenyltetrazole (PT), 5-(2-Bromophenyl)-1H-Tetrazole (5-2-BPT), 5-(4-Bromophenyl)-2H-Tetrazole (5-4-BPT) as inhibitors for Cu corrosion in 0.5 M H 2 SO 4 were evaluated via experimental and DFT methods. Electrochemical test data show that they are all mixed-type inhibitors and exhibit remarkable corrosion inhibition ability. The order of corrosion inhibition efficiency is 5-4-BPT > 5-2-BPT > PT. The morphology tests also convincingly prove this sequence of inhibition efficiency. The adsorption of 5-4-BPT, 5-2-BPT and PT on the copper surface is consistent with Langmuir isotherm model. DFT calculation results show that their adsorbed on the Cu surface by N Cu bond perpendicular adsorption to obtain the most stable adsorption configuration.

A combined computational and experimental study of the adsorption of sulfur containing molecules on molybdenum disulfide nanoparticles

Abstract

Polarization-Dependent SFG Spectroscopy of Near Ambient Pressure CO Adsorption on Pt(111) and Pd(111) Revisited

Polarization-dependent sum frequency generation (SFG) vibrational spectroscopy was employed to examine CO overlayers on Pt(111) and Pd(111) single crystal surfaces at room temperature. Utilizing different polarization combinations (SSP and PPP) of the visible and SFG light allows to determine the molecular orientation (tilt angle) of interface molecules but the analysis of the measured I_{text{ppp}}/I_{text{ssp}} is involved and requires a proper optical interface model. For CO/Pt(111), the hyperpolarizability ratio left( {R={beta _{aac}}/{beta _{ccc}}={beta _{bbc}}/{beta _{ccc}}} right) is not exactly known and varying R in the range 0.1–0.5 yields tilt angles of 40°–0°, respectively. Based on the known perpendicular adsorption of CO on Pt, an exact R-value of 0.49 was determined. Polarization-dependent SFG spectra in the pressure range 10−4 to 36 mbar did not indicate any change of the tilt angle of adsorbed CO. Modeling also indicated a strong dependence of {I_{{text{ppp}}}}/{I_{{text{ssp}}}} on the incidence angles of visible and IR laser beams. Complementing previous low temperature/low pressure data, room temperature CO adsorption on Pd(111) was examined from 10−6 to 250 mbar. The absolute PPP and SSP spectral intensities on Pt and Pd were simulated, as well as the expected {I_{{text{ppp}}}}/{I_{{text{ssp}}}} ratios. Although CO on Pt and Pd should exhibit similar intensities (at high CO coverage), the higher {I_{{text{ppp}}}}/{I_{{text{ssp}}}} ratio for Pd (48 vs. 27 on Pt) renders the detection of adsorbed CO in SSP spectra difficult. The presence or absence of CO species in SSP spectra can thus not simply be correlated to tilted or perpendicular CO molecules, respectively. Careful modeling, including not only molecular and interface properties, but also the experimental configuration (incidence angles), is certainly required even for seemingly simple adsorbate–substrate systems.

Adsorption of naphthenic acids to the nitrogen-coordinated transition-metal embedded graphene: A DFT study

The adsorption properties of two types of naphthenic acids (NAs), benzoic acid and cyclohexane carboxylic acid on four-nitrogen coordinated transition-metal (Mn, Fe, Co, Ni, Cu, and Zn) embedded graphene (TMN4-G) were investigated in detail by means of density functional theory method. The calculation results indicate that NAs prefer the perpendicular adsorption configuration by bonding interactions between their carbonyl oxygen atom and TMN4 active site, and could be chemisorbed on FeN4-G, MnN4-G, and ZnN4-G. The FeN4-G gives the strongest adsorption to the NAs, indicating it is the best adsorbent among them. Electron density maps further confirm that NAs are chemically adsorbed on the FeN4-G surface, accompanied by electron transfer in the adsorption systems. The calculations indicate that benzoic acid has relatively stronger adsorption energy than that of cyclohexane carboxylic acid for the perpendicular adsorption on TMN4-G surface.

Structural studies of self-assembled monolayers of 4-mercaptopyridine on gold electrodes with surface-enhanced Raman spectroscopy

Self-assembled monolayers of 4-mercaptopyridine adsorbed on polycrystalline gold electrodes were investigated with cyclic voltammetry and surface-enhanced Raman spectroscopy (SERS). Within the electrode potential window given by the onset of hydrogen and oxygen evolution results from both methods suggest a perpendicular adsorption geometry with a Au-S bond being the anchoring function. pH effects typical of unbuffered electrolyte solutions related to the adsorbate tautomerism are observed spectroelectrochemically.

Topological and Electronic Structure of Heterocyclic Compounds Adsorbed on Hydrotreating Catalysts

We studied the electronic structure of the adsorption of S- and N-containing aromatic compounds present in crude oils on MoS2 and WS2 clusters by means of all-electron DFT methods. The aim of this work is to understand results related to the hydrotreating catalyst poisoning by quinoline. We studied the adsorption of the organic compounds by flat (π) and perpendicular (σ) adsorption on each cluster catalyst. The calculated adsorption energies indicated that π-adsorption was more favorable over σ-adsorption. In the σ mode, quinoline presented the largest adsorption energy, which led to understand the poisoning of the catalysts. We performed electron localization function (ELF) studies on the molecules adsorbed on a perpendicular orientation. We showed methyl-substituted compounds had a weaker S-{Mo,W} bond due to steric hindrance. Furthermore, atoms-in-molecules (AIM) calculations at the critical points (i.e. {S,N}-{Mo,W} interfaces) revealed a correlation between electron density and Laplacian of the electron density at this region and the adsorption energy. Ellipticity (e) studies revealed structural information of binding at these sites, as well as the competition between S- and N-containing compounds. Similarly, e showed that methyl-containing compounds had a very distinct character than non-substituted ones, thus revealing the importance of steric effects. Analytic tools such as ELF and AIM provide correlations between the experimental observations and properties. We find these studies can be further used to understand other catalytic phenomena. .

Theoretical Investigation of the Adsorption and C–C Bond Scission of CCH3 on the (111) and (100) Surfaces of Pd: Comparison with Pt

Understanding the mechanism of C–C bond cleavage on the surface of a catalyst is central to the optimization of several reactions in the petrochemical industry. In this study, first-principles density functional theory calculations were performed to examine the adsorption properties, electronic structures, and energies of C–C bond scission in ethylidyne (CCH3) adsorbed on the (111) and (100) surfaces of Pd, and the results were compared with those of Pt. On the basis of the analyses of the electron density of states (DOS), partial charge density, and wave functions, it appears that on the adsorption of C–C, two types of bonding orbitals, namely, σC–C and πC–C, are formed. On both the low-index surfaces of Pd, the perpendicular adsorption of CCH3 was found to be the most stable configuration. Compared with the adsorption on the Pd(111) surface, the adsorption on the Pd(100) surface was less stable. On the contrary, the adsorption energies on the (111) and (100) surfaces of Pt were almost the same. Neverthe...

Concentration dependent conformation of inosine on colloidal silver nanoparticles: A study by Raman, SERS and DFT calculation

Surface enhanced Raman spectroscopic (SERS) study of biologically important inosine molecules adsorbed in Ag-sol is reported for the first time. Possible adsorption mechanism is discussed. The enhancement is significantly influenced by the concentration of inosine in Ag-sols. The in plane base ring breathing mode appears at 715cm−1 in solid phase and is shifted to 724cm−1 in aqueous solution. Appearance of this band at 736cm−1 in the adsorbed state suggests C(2′) endo-anti conformation at concentrations up to 5×10−7M at which monomolecular layer is formed on the silver surface. However, C(3′) endo-syn conformation is suggested at a concentration of 5×10−11M. Inosine molecule, possibly, interact with the silver nano-particles through C5′ atom at higher concentration. The π system of electrons of the hypoxanthine ring may be involved in the adsorption process at lower concentration. Monomolecular layer is formed at concentrations of 5×10−7M and 5×10−11M indicating perpendicular and parallel adsorption respectively. Density functional calculations are performed for the explanation of the experimental results.