Spectroscopic and ab initio studies on the conformations and vibrational spectra of selected cyclic and bicyclic molecules

The structure, potential energy functions and vibrational spectra of several cyclic and bicyclic molecules have been investigated using several spectroscopic techniques and high-level ab initio and density functional theory (DFT) calculations. Laser induced fluorescence and Raman spectroscopies were used to study the conformation of 2- indanol in the electronic ground and excited states. These, along with detailed ab initio calculations, confirmed the existence of four different stable conformations with the one undergoing an intermolecular hydrogen bonding being the most stable. A theoretical two-dimensional surface in terms of the ring-puckering and the hydroxyl group internal rotation vibrations was constructed. This work was extended to obtain preliminary insights on the conformations and ring-puckering frequencies of 3-cyclopenten-1-ol using ab initio and DFT calculations. Infrared and Raman spectra were also utilized to study the structures and vibrational spectra of -crotonolactone and 2,3-cyclopentenopyridine (pyrindan). Ab initio results showed that -crotonolactone is rigidly planar in the electronic ground state and has a nearly harmonic ring-puckering potential function. The calculated vibrational levels were shown to be in very good agreement with the experimental ring-puckering frequency from vapor-phase Raman observations. The structures, vibrational spectra, and potential energy functions of several cyclic molecules were reinvestigated using high-level ab initio computations, and detailed vibrational analyses based on DFT-B3LYP calculated frequencies were also carried out. A number of new insights were presented by re-evaluating the available experimental data for several cyclopentenes, silacyclobutanes and silacyclopentenes. It was found that the vibrational spectra of some deuterated cyclopentenes possess extensive coupling between several ring modes and other low-frequency modes. Reassignments of these spectra have been proposed. Frequencies from DFT-B3LYP calculations showed very good agreement with the experimental values for silacyclobutane and its derivatives. The presence of silicon and halogen atoms did not affect the accuracy of the DFT calculations. In addition, the ring-puckering potential energy function for silacyclopent-2-ene was studied and alternative assignments of the far-infrared results were proposed. The new assignments are in good agreement with computational results. Silacyclopent-2-ene and its -1,1-d2 isotopomer were shown to be slightly puckered with barriers of less than 50 cm-1

Temporomandibular Joint Ankylosis as a Complication of Neonatal Septic Arthritis : Report of two cases

Temporomandibular joint (TMJ) ankylosis as a complication of neonatal septic arthritis is rarely reported in the literature. We report two clinical cases of unilateral TMJ ankylosis occurring in paediatric patients subsequent to neonatal septic arthritis. The first case was a 15-month-old male infant who presented to the Sultan Qaboos University Hospital, Muscat, Oman, in May 2010. According to the published English scientific literature, he is the youngest person yet to be diagnosed with this condition. The second case was a five-year-old female who presented to the Al-Nahda Hospital, Muscat, Oman, in October 2011. Both cases presented with facial asymmetry and trismus. They subsequently underwent gap arthroplasty and interpositional temporalis muscle and fascia grafts which resulted in an immediate improvement in mouth opening. Postoperatively, the patients underwent active jaw physiotherapy which was initially successful. Both patients were followed up for a minimum of two years following their surgeries

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Theoretical studies on the mechanism of iridium-catalyzed alkene hydrogenation by the cationic complex [IrH2(NCMe)3(PiPr3)]+

A mechanistic DFT study has been carried out on the ethene hydrogenation catalyzed by the [IrH2(NCMe)3(PiPr3)]+ complex (1). First, the reaction of (1) with ethene has been theoretically characterized, and three mechanistic proposals (A-C) have been made for an identification of the preferred pathways for the alkene hydrogenation catalytic cycle considering Ir(I)/Ir(III) and Ir(III)/Ir(V) intermediate species. Theoretical calculations reveal that the reaction path with the lowest energy starts at an initial ethene migratory insertion into the metal-hydride bond, followed by dihydrogen coordination into the vacancy. Ethane is formed via ?-bond metathesis between the bound H2 and the Ir-ethyl moiety, being the rate-determining step, in agreement with the experimental data available. The calculated energetic span associated with the catalytic cycle is 21.4 kcal mol-1. Although no Ir(V) intermediate has been found along the reaction path, the Ir(V) nature of the transition state for the proposed key σ-bond metathesis step has been determined by electron localization function and geometrical analysis.The authors express their sincere appreciation of the financial support provided by King Abdulaziz City of Science and Technology (KACST) under the funded project (T-K-11-630). Authors also thank KFUPM under the KFUPM-University of Zaragoza research agreement. Financial support of MINECO/FEDER project CTQ2012-35665 and DGA/FSE (group E07) is also acknowledged.Peer Reviewe

Inhibition of mild steel corrosion in CO2 and H2S-saturated acidic media by a new polyurea-based material

Oil well acidizing is a common practice used to boost oil well productivity in the industry. This practice, however, exposes the mild steel components of the wells to extremely harsh corrosive environments. Under such conditions, highly efficient inhibitors are used to minimize corrosion attack. In the present study, corrosion inhibition of mild steel in simulated acidic medium saturated with CO2 and H2S gases by a newly synthesized polyurea-based material (PUCorr-1) was investigated. Electrochemical studies supported with quantum chemical density-functional theory calculations and surface characterization revealed that PUCorr-1 adsorbs onto mild steel through a chemisorption mechanism yielding a stable protective film. The polyurea exhibited an excellent efficiency of 99.9% at a temperature of 50 C and a low concentration of 100 ppm, yielding a corrosion current density of 0.3 A/cm2. In the presence of CO2 and H2S gases, PuCorr-1 exhibited a remarkable performance (>93% efficiency) making it a potential corrosion inhibitor in industrial processes that involve the use of acid solutions in the presence of CO2 and H2S gases.The authors would like to acknowledge the financial support provided by the Deanship of Scientific Research (DSR) at the King Fahd University of Petroleum and Minerals (KFUPM) through project no. NUS15107/8.Scopu

Intermolecular hydroamination versus stereoregular polymerization of phenylacetylene by rhodium catalysts based on N-O bidentate ligands

N-O bidentate ligands, such as 8-quinolinol and aminoacids, in combination with the dinuclear precursor [{Rh(μ-OMe)(COD)}2] are versatile catalytic systems. Thus, stereoregular polymerization of phenylacetylene (PA) is observed in the presence of secondary amines. Interestingly, the outcome of the catalysis changes drastically on addition of strong coordinating phosphines, giving the product of the intermolecular anti-Markovnikov hydroamination of phenylacetylene. © 2013 Elsevier B.V. All rights reserved.The authors would like to acknowledge the support from the Ministry of Higher Education, Saudi Arabia, in establishment of the Center of Research Excellence in Petroleum Refining & Petrochemicals at King Fahd University of Petroleum and Minerals (KFUPM). The support of the KFUPM under the KACST funded project (T-K-11-630) and the KFUPM-University of Zaragoza research agreement are also highly appreciated. The author (MAC) thankfully acknowledges the support from the project CTQ2012-35665.Peer Reviewe

Experimental and Theoretical Studies of the Vibrational and Electronic Properties of (2E)-2-[3-(1H-imidazol-1-yl)-1-phenyl-propylidene]-N-phenylhydrazinecarboxamide: An Anticonvulsant Agent

In the current investigation, the molecular structure of the anticonvulsant agent (2E)-2-[3-(1H-imidazol-1-yl)-1-phenylpropylidene]-N-phenylhydrazinecarboxamide ((2E)-HIPC) was theoretically modelled using ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) calculations. The Fourier transform (FT) infrared and FT-Raman spectra of (2E)-HIPC were also recorded, and the observed bands were assigned to the vibrational normal modes. The main functional groups were identified via vibrational analysis, and their absorption bands were assigned. A comparative analysis was performed for the computed and experimental results. Subtle differences were observed between the calculated and experimental UV-Vis spectra. Time-dependent density functional theory (TD-DFT) excitation energies were calculated for five excited electronic states. The calculations were applied to simulate the spectra of (2E)-HIPC, and these simulated spectra exhibited excellent agreement with the experimental spectra. The DFT/B3LYP/6-311++G(d,p) method, after scaling, exhibited better agreement with the experimental values than the results obtained by the HF method. The energy, oscillator strength, and wavelength computed by TD-DFT (IEFPCM) are consistent with the experimental results. The molecular electrostatic potential (MEP) and frontier molecular orbitals (HOMO-LUMO) were also determined to enable prediction of the structural changes and reactive sites. Mulliken population charges of the title molecule were also calculated in the gas phase. The NMR chemical shifts (13C and 1H) were calculated using the gauge-including atomic orbital method and the B3LYP/6-311++G(d,p) approach and were compared with the experimental values

Theoretical Studies on the Mechanism of Iridium-Catalyzed Alkene Hydrogenation by the Cationic Complex [IrH₂(NCMe)₃(P^<i>i</i>Pr₃)]⁺

A mechanistic DFT study has been carried out on the ethene hydrogenation catalyzed by the [IrH₂­(NCMe)₃­(P^<i>i</i>Pr₃)]⁺ complex (<b>1</b>). First, the reaction of (<b>1</b>) with ethene has been theoretically characterized, and three mechanistic proposals (<b>A</b>–<b>C</b>) have been made for an identification of the preferred pathways for the alkene hydrogenation catalytic cycle considering Ir­(I)/Ir­(III) and Ir­(III)/Ir­(V) intermediate species. Theoretical calculations reveal that the reaction path with the lowest energy starts at an initial ethene migratory insertion into the metal–hydride bond, followed by dihydrogen coordination into the vacancy. Ethane is formed via σ-bond metathesis between the bound H₂ and the Ir-ethyl moiety, being the rate-determining step, in agreement with the experimental data available. The calculated energetic span associated with the catalytic cycle is 21.4 kcal mol^–1. Although no Ir­(V) intermediate has been found along the reaction path, the Ir­(V) nature of the transition state for the proposed key σ-bond metathesis step has been determined by electron localization function and geometrical analysis

Evaluation of the inhibition performance of piperazine-based polyurea towards mild steel corrosion: The role of keto-enol tautomerization

The lack of solubility of polyurea materials impedes their application as effective inhibitors against metallic corrosion in aqueous media. Herein, we have synthesized a new piperazine-based polyurea inhibitor (PUCorr) which is readily soluble in water through dispersion in N-methyl-2-pyrrolidone for mild steel corrosion. The inhibitor exhibits a sufficient protection of the surface of mild steel via an intra-molecular keto-enol proton transfer mechanism leading to the formation of the Fe-PUCorr complex. First-principles calculations proposed that the keto-enol tautomerism enhances the adsorption with an increase of adsorption energies of 510, 221, 171 and 211 kJ/mol on {100}, {110}, {111} and {112} surfaces of iron, respectively. The presence of PUCorr at 100 ppm decreases the corrosion current density from 30.3 to 3.05 μA/cm2 in 0.5 M NaCl at room temperature, exhibiting a remarkable inhibition efficiency of 94.5%. Electrochemical measurements revealed that PUCorr functions as a mixed-type inhibitor, suppressing both anodic and cathodic processes. The use of synthetic polyurea materials with a low dosage shall provide a promising approach to reduce mild steel corrosion in harsh environments

Iridium complexes as catalysts in the hydrogen transfer of isopropanol to acetophenone: Ligand effects and DFT studies

Methoxo-bridged diiridium complexes of the type [{Ir(μ-OMe)(diolefin)}2] (diolefin = 1,5-cyclooctadiene, tetrafluorobenzobarrelene), in the presence on P- or N-donor ligands, are active catalyst precursors in the catalytic hydrogen transfer of iPrOH to acetophenone. Both the nature of the diolefin and that of additional P- and N-donor ligands have a marked effect in the catalytic outcome of the reactions. DFT theoretical studies have been carried out on the binary catalytic systems composed of the iridium complexes and mono phosphanes (Ir/P = 1/1), which indicated that the operative mechanism in these transformations follows the classic “hydrido” route.The authors express their sincere appreciation of the financial support provided by King Abdulaziz City of Science and Technology (KACST) under the funded project (T-K-11-630). The support of KFUPM and the KFUPM-University of Zaragoza research agreement are highly appreciated. The author (MAC) thankfully acknowledges the support from the project CTQ2012-35665.Peer Reviewe