Carbonyl Molecules Research Articles

Intramolecular Vibrational Dynamics in Free Polyatomic Molecules with C═O Chromophore Bond Excited by Resonant Femtosecond IR Laser Radiation

In nine polyatomic molecules, we have studied the intramolecular redistribution of vibrational energy from chromophore C═O group excited by a resonant femtosecond IR laser radiation at a wavelength of ∼5 μm. All experiments have been performed in the gas phase using the IR-IR pump-probe technique in combination with the spectral analysis of the probe radiation. For molecules with one C═O end group, characteristic times of intramolecular vibrational redistribution (IVR) lie in the range between 2.4 and 20 ps and correlate with the density of four-frequency Fermi resonances. The IVR times in metal carbonyl molecules are anomalously long, being ∼1.0 ns for Fe(CO)5 and ∼1.5 ns for Cr(CO)6. In the CH3(C═O)OC2H5 and H2CCH(C═O)OC2H5 molecules, it has been observed that there are two characteristic IVR times, which differ by an order of magnitude from each other; this was interpreted in terms of the developed model of "accumulating states". For the ICF2COF molecule, it has been revealed that the IVR time decreases with increasing level of the vibrational excitation of the C═O bond of the molecule.

Mechanisms on electrical breakdown strength increment of polyethylene by aromatic carbonyl compounds addition: a theoretical study

A theoretical investigation is accomplished on the mechanisms of electrical breakdown strength increment of polyethylene at the atomic and molecular levels. It is found that the addition of aromatic carbonyl compounds as voltage stabilizers is one of the important factors for increasing electrical breakdown strength of polyethylene, as the additives can trap hot electrons, obtain energy of hot electrons, and transform the aliphatic cation to relatively stable aromatic cation to prevent the degradation of the polyethylene matrix. The HOMO-LUMO energy gaps (E(g)), the ionization potentials (IPs), and electron affinities (EAs) at the ground states of a series of aromatic carbonyl compounds are obtained at the B3LYP/6-311+G(d,p) level. The theoretical results are in good agreement with the available experimental findings, show that 2,4-dioctyloxybenzophenone (Bzo) and 4,4'-didodecyloxybenzil (Bd) molecules can effectively increase the electrical breakdown strength when they are doped into polyethylene because of their much smaller E g values than all the other studied aromatic carbonyl molecules and excellent compatibility with polymers matrix.

Impacts of medium, substituents, and specific interactions with water on hydration of carbonyl compounds

Theoretical study on hydration of carbonyl compounds has been done at B3LYP/6-31++G** and MP2/6-31++G** levels. The variations in ΔGhyd and hydration constants are explored in terms of medium effect, substituent effect, and hydrogen bonding abilities of carbonyl compounds and their hydrated products. The dielectric of medium decreases the ΔGhyd values thereby favoring the process. The presence of electron-releasing substituents at the carbonyl carbon disfavors the hydration process, while that of electron-withdrawing substituents favor the process. Hydrogen bonding interactions stabilize the product to a larger extent than the carbonyl molecules, thereby favoring the hydration process. Linear correlation between the calculated log Khyd values and the experimental values is seen in case of specific interactions with water (R = 0.976) than in the case without those interactions (R = 0.955).

Theoretical study of association of acetylene, benzene, and carbonyl molecules “squeezed” inside fullerene cages

The equilibrium geometries, normal mode frequencies, magnetic shielding constants, and energetic characteristics of model endohedral 2(C2H2)@C70, (C4H4)@C70, 2(C6H6)C84, (C12H12)@C84, 6(CO)@C84, and (C6O6)@C84 clusters, mimicking the structure and properties of the guest molecules under “ultrahigh” pressures inside the fullerene cages, were calculated at the density functional theory B3LYP/6-31G and B3LYP/6-31G* levels. According to the calculations, all the structures under consideration correspond to local minima of the corresponding potential energy surfaces. The 2(C2H2)@C70 isomer with two separated endohedral acetylene molecules turns out to be considerably less favorable than the (C4H4)@C70 isomer with endohedral cyclobutadiene. The 2(C6H6)C84 isomer with two separated endohedral benzene rings is almost 30 kcal/mol less favorable than the (C12H12)@C84) isomer with distorted endohedral prismane. The 6(CO)@C84 isomer with six separated carbonyl molecules is almost 45 kcal/mol less favorable than the (C6O6)@C84 isomer in which the carbonyls are associated to form a more compact cyclic hexamer C6O6. The barriers separating the “associated” and “dissociated” (consisting of monomers) isomers are estimated at 10–15 kcal/mol. Calculations show that, in extremely tight endoclusters, the increase in compression and strain energy caused by the repulsion of the electronic shells of guest molecules and wall atoms is accompanied by a sharp energetic stabilization of compact associated isomers (including those poorly stable or unstable in the free state) as compared with the dissociated isomers, on the one hand, and by a sharp decrease in activation barriers, on the other hand. Both factors should favor the realization of association processes unlikely or impossible under common conditions.

Functionalization of CPO-27-Ni through metal hexacarbonyls: The role of open Ni2+ sites

Cr(CO)6 and Mo(CO)6 have been used as precursors to obtain grafted (η6-arene) M(CO)3 species inside the CPO-27-Ni material. The presence of open Ni(II) sites in the MOF scaffold promotes distinctive reactivities with respect to that observed previously on other MOFs (MOF-5 and UiO-66). The formation of two organometallic M(CO)3(η6-arene) conformers (staggered and eclipsed) has been considered, also taking into account data obtained by a recent theoretical work. IR spectroscopy shows how open metal sites in a MOF structure can destabilize metal carbonyl molecules, favoring CO elimination and acting as CO scavenger, which fastens the decomposition and frustrate the reverse reaction. The work can open new studies on precursors of catalytic species stabilized inside MOFs cages.

Final state distributions of methyl radical desorption from ketone photooxidation on TiO2(110)

In this work, we report on product energy distributions for methyl radicals produced by UV photooxidation of a set of structurally related carbonyl molecules, R(CO)CH(3) (R = H, CH(3), C(2)H(5), C(6)H(5)), adsorbed on a TiO(2)(110) surface. Specifically, laser pump-probe techniques were used to measure the translational energy distributions of methyl radicals resulting from α-carbon bond cleavage induced by photoexcited charge carriers at the TiO(2) surface. Photoreaction requires the presence of co-adsorbed oxygen and/or background oxygen during UV laser (pump) exposure, which is consistent with the formation of a photoactive oxygen complex, i.e., η(2)-bonded diolate species (R(COO)CH(3)). The methyl translational energy distributions were found to be bimodal for all molecules studied, with "slow" and "fast" dissociation channels. The "fast" methyl channel is attributed to prompt fragmentation of the diolate species following charge transfer at the TiO(2) surface. The average translational energies of the "fast" methyl channels are found to vary with R-substituent and correlate with the mass of the remaining surface fragments, RCO(x) (x =1 or 2). By comparison, the average energies of the "slow" methyl channels do not show any obvious correlation with R-substituent. The apparent correlation of the "fast" methyl translation energies with surface fragment mass is consistent with a simple two-body fragmentation event isolated on the diolate molecule with little coupling to the surface. These results also suggest that the total available energy for methyl fragmentation does not vary significantly with changes in R-substituent and is representative of exit barriers leading to "fast" methyl fragments.

Enhanced reactivity of carbonyl compounds on MgO surface: A computational study

The paper analyzes the activation of carbonyl derivatives on regular MgO(0 0 1) surface based on appropriate reactivity descriptors derived from density functional theory computations. The carbonyl molecules adsorbed on the surface were found activated for nucleophilic addition reaction due to polarization of the C O bond and increased electrophilicity, in particular of the carbon atom. The influence of the support was discussed in terms of electrostatic field and polarization of the electron density in the adsorbate. The substituent effect on reactivity for isolated and adsorbed molecules was also characterized.

Generation of organic radicals during photocatalytic reactions on TiO2

Using a variety of organic carbonyl molecules (R1C(O)R2) and the rutile TiO2(110) surface as a model photocatalyst, we demonstrate both experimentally and theoretically that ejection of organic radicals from TiO2 surfaces is likely a prevalent reaction process occurring during heterogeneous photooxidation of organic molecules. Organic carbonyls react with coadsorbed oxygen species to form organic diolates which are more strongly bound to TiO2 than are the parent carbonyls. The parent carbonyls, when bound to TiO2(110) in an η1 configuration, are photo-inactive toward valence band holes. However, the diolates are shown to photodecompose by ejection of one of the two R substituents from the surface into the gas phase, leaving behind the carboxylate of the other R group. Theoretical calculations using DFT show that in most cases the choice of which R group is ejected can be predicted based on the C–R bond energies and, to a lesser extent, the stability of the ejected R group.

Study of femtosecond dynamics in vibrationally excited free bis(trifluoromethyl)ketene and metal carbonyl molecules induced by CO bond resonant excitation

The dynamics of relaxation processes in free bis(trifluoromethyl)ketene (CF3)2CCO and Fe(CO)5 and Cr(CO)6 metal carbonyl molecules after multiphonon excitation of the C=C=O and C=O vibrations by femtosecond laser infrared radiation was studied. The temporal and spectral dependences of the relaxation of the excited vibrational states were measured. Kinetics with a characteristic decay time of about 5 ps was obtained for (CF3)2CCO molecules. Its behavior is interpreted as a manifestation of the intramolecular relaxation of the excited vibration states of the resonance mode. Kinetic curves with characteristic times of about 250–500 fs were observed for Fe(CO)5 and Cr(CO)6. The behavior of these curves depends on the mutual orientation of the polarizations of the pump and probe pulses.

Effect of Salt on the Adsorption Affinity of an Aromatic Carbonyl Molecule to the Air−Aqueous Interface: Insight for Aqueous Environmental Interfaces

The interface-selective second harmonic generation (SHG) nonlinear optical spectroscopy and the surface tension method have been used to measure the effect of electrolyte on the adsorption isotherm of 4-hydroxyacetophenone (4-HA) at the air−solution interface. It was observed that high NaCl concentration favors adsorption of organic molecules to the air−solution interface. Measurements of the polarization of the SHG field showed that the orientation of the organic molecule at the air−solution interface is close to that in the neat air−water interface and does not vary with organic concentration. The free energy of adsorption of the molecule to the air−solution interface becomes significantly more negative with an increase in salt concentration, and good agreement was found between the results from the two different techniques. We conclude that the increased affinity of 4-HA for the air−water interface in the presence of NaCl is due to the salting-out effect.

The role of spin state on the local atomic and electronic structures of some metalloporphyrin complexes

The Porphyrin molecule is an archetypal metalloorganic complex, which shows up in many biochemical molecules like chlorophyll, haemoglobin and cytochrome. The prospect of switching the spin in the metalloporphyrin ring is a particularly interesting one, as this could be used, for example, for spin-dependent electric transport through biomolecular devices. These molecules can be used in various applications like optical switches, information storage and non linear optics. Here, we study the molecular spin state of chloro-hemin, hemin cyanide and hemin carbonyl molecules by ADF code. Chloro-hemin has been studied by analyzing the Fe K-edge X-Ray Absorption Near Edge Structure (XANES) spectra. At first stage of investigation we assume an approximate initial geometry, then we perform the geometry optimization with different molecular spin states and search for configuration with minimal total energy with the use of Density Functional Theory (ADF 2008). The results of geometry optimization of chloro-hemin molecule performed with the GGA OPBE functional showed that configuration with total spin S = 5/2 has minimal total energy. This configuration corresponds well with the geometry structure obtained via X-Ray diffraction method (Fe-N-N angle is 13.3°). The similar calculations that were carried out for hemin carbonyl and hemin cyanide molecules showed that for these structures minimal energy is found to be for S = 1/2. The experimental Fe K-XANES spectra of the investigated compound have been collected. The theoretical analysis of the experimental data has been performed on the basis of finite difference method (FDMnes2007 program code).

Condensation and desorption of nickel tetra-carbonyl on Cu(1 1 0)

The condensation and desorption of nickel tetra-carbonyl (Ni(CO) 4) on Cu(1 1 0) has been studied by thermal desorption spectroscopy. A quite unusual evolution of the desorption spectra is observed. First a desorption peak appears at around 140 K, which disappears with increasing coverage and merges into a clearly separated new desorption peak at around 150 K. This transformation takes place at a coverage of about 10% of a monolayer. It is suggested that the low temperature peak is due to desorption of monomers. With increasing coverage nucleation and growth of multilayer islands starts, from which the desorption energy is higher due to the higher coordination of the carbonyl molecules, compared to that of the monomers. Evaluation of the multilayer desorption spectra yields a desorption energy of 57.9 kJ/mol (0.60 eV) and an unusually high frequency factor of 1.6 × 10 19 s −1.

A new hybrid DFT approach to electronic excitation and first hyperpolarizabilities of transition metal complexes

The electronic excitations and the static first hyperpolarizability of three typical transition metal (TM) aromatic carbonyl complexes, two tungsten pentacarbonyl derivatives (W(CO)5L, L = Py and PyCHO) and one chromium tricarbonyl arene derivative (Cr(CO)3Bz, Bz = benzene), have been theoretically studied by a variety of density functional methods. The assessments reveal that most of the conventional DFT methods including local density approximation, generalized gradient approximation (GGA), and the various kinds of hybrid exchange-correlation (xc) methods present the first hyperpolarizabilities of these TM-containing molecules with large deviations from the experiments. A one-parameter hybrid xc functional is introduced by using the Perdew-Wang 1991 gradient-corrected correlation functional (PW91) and the Barone's-modified PW91 exchange functional (mPW). The ratio between the exact and the density functional exchange is determined to be 0.40 by the adiabatic connection method. The application of the new hybrid functional to the three organometallic carbonyl molecules results in the satisfactory agreement between the calculated first hyperpolarizabilities and the experimental ones. The second-order nonlinear optical properties of the three organometallic complexes are addressed to the metal-to-ligand charge transfers, and the extended pi-delocalization ligands benefit the enhancement of the first hyperpolarizability.

Splendid symmetry: crystallization of an unbridged isomer of Co2(CO)8 in Co2(CO)8·C60

Cocrystallization of Co2(CO)8 with C60 traps the cobalt carbonyl molecule as the D(3d) isomer that otherwise is not available for crystallographic analysis.

Molecular parameters of tetraatomic carbonyls X2CO and XYCO (X, Y = H, F, Cl) in the ground and lowest excited electronic states, part 1: A test ofab initiomethods

AbstractGeometrical parameters of tetraatomic carbonyl molecules X2CO and XYCO (X, Y = H, F, Cl) in the ground (S0) and lowest excited singlet (S1) and triplet (T1) electronic states as well as values of barriers to inversion inS1andT1states andS1←S0andT1←S0adiabatic transition energies were systematically investigated by means of various quantum‐chemical techniques. The following methods were tested: HF, MP2, CIS, CISD, CCSD, EOM‐CCSD, CCSD(T), CR‐EOM‐CCSD(T), CASSCF, MR‐MP2, CASPT2, CASPT3, NEVPT2, MR‐CISD, and MR‐AQCC within cc‐pVTZ and cc‐pVQZ basis sets. The accuracy of quantum‐chemical methods was estimated in comparison with experimental data and rather accurate structures of excited electronic states were obtained. MP2 and CASPT2 methods appeared to be the most efficient and CCSD(T), CR‐EOM‐CCSD(T), and MR‐AQCC the most accurate. It was found that at equilibrium all the molecules under study are nonplanar inS1andT1electronic states with CO out‐of‐plane angle ranging from 34° (H2CO,S1) to 52° (F2CO,T1), and height of barrier to inversion varying from 300 (H2CO,S1) to 11,000 (F2CO,T1) cm−1. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Crystal Structure of Ca 2 + -Free S100A2 at 1.6-Å Resolution

S100A2 is an EF hand-containing Ca 2 + -binding protein of the family of S100 proteins. The protein is localized exclusively in the nucleus and is involved in cell cycle regulation. It attracted most interest by its function as a tumor suppressor via p53 interaction. We determined the crystal structure of homodimeric S100A2 in the Ca 2 + -free state at 1.6-Å resolution. The structure revealed structural differences between subunits A and B, especially in the conformation of a loop that connects the N- and C-terminal EF hands and represents a part of the target-binding site in S100 proteins. Analysis of the hydrogen bonding network and molecular dynamics calculations indicate that one of the two observed conformations is more stable. The structure revealed Na + bound to each N-terminal EF hand of both subunits coordinated by oxygen atoms of the backbone carbonyl and water molecules. Comparison with the structures of Ca 2 + -free S100A3 and S100A6 suggests that Na + might occupy the S100-specific EF hand in the Ca 2 + -free state.

Rat Plasma Oxidation Status After Nigella Sativa L. Botanical Treatment in CCL4-Treated Rats

ABSTRACTNigella sativa Linn. (family Ranunculaceae), commonly known as black cumin, is native to the Mediterranean area and has been used for thousands of years as a health and beauty aid. The present study investigated the protective effects of Nigella sativa (NS) extract (NSE) and oil (NSO) on CCl4-induced nitrosative stress and protein oxidation in rat. CCl4 (0.8 mg/kg) was used as an aid for induction of nitrosative stress. In vitro antioxidant potential was tested in the presence of 2,4-dinitrophenylhyrdazine (DPPH) as an organic nitrogen radical. Doses of 0.2, 0.3, and 1 mg/kg of the NS extract and oil were administered to CCL4-treated rats for 10 days. At the end of treatment, blood was taken from rats under anesthesia and plasma was separated. The concentration of nitric oxide (NO), total antioxidant power (TAP), carbonyl molecules (CM) as measure of protein oxidation (PO), tumor necrosis factor-alpha (TNF-α), and total thiol molecules (TTM) were measured in plasma. In vitro evaluation of antioxidant effects of NSE and NSO showed that the highest antioxidant activity (80%) was observed with the concentration of 10 and 20 mg/ml, respectively, that were equal to vitamin E (200 mg/ml). Administration of CCL4 increased plasma PO, NO, TNF-α and decreased TAP and TTM. Both NSE and NSO showed significant protection against CCl4-induced changes in biochemical parameters, but not dose-dependently. Doses of 0.3 and 1 mg/kg were more effective than doses of 0.2 mg/kg for both NSE and NSO, but dose of 1 mg/kg was the most effective one. The results indicate the potential of NS in preventing CCL4-induced toxic nitrosative stress. It is concluded that NS has marked antioxidant potentials that may be beneficial in alleviating complications of many illnesses related to oxidative/nitrosative stress in humans, but preclinical safety measures should be completed before clinical trials.

Macromol. Theory Simul. 3/2007

Cover: The picture shows that diprotonation of carbonyl compounds does not occur in triflic acid. The triflic acid mediated reaction of polyhydroxyalkylation of aromatic hydrocarbons involves only monoprotonated species. The reactivity of carbonyl molecules is governed by electronic effects of the groups linked directly to the carbonyl. Strong donor and strong electron withdrawing groups reduce the reactivity of carbonyl group as electrophile; in the first case the protonation leads to the formation of excessively stable cation, in the second one monoprotonation is impossible thermodynamically. Further details can be found in the article by A. L. Lira, M. G. Zolotukhin, L. Fomina, and S. Fomine* on page 227.

Reactions of the Small Tin Clusters with Carbon Monoxide: Infrared Spectra and DFT Calculations of the SnnCO (n = 2–5) and Sn2(CO)2 Molecules in Solid Argon

Abstract Laser-ablated Sn atoms have been co-deposited with CO molecules in solid argon to produce tin carbonyls. In addition to the previously reported Sn(CO)n (n = 1 and 2) molecules, small tin cluster carbonyls SnnCO (n = 2–5) and Sn2(CO)2 are formed on sample annealing, and are characterized using infrared spectroscopy on the basis of the results of the isotopic substitution, the CO concentration change, and the comparison with theoretical predictions. It is found that Sn2CO, Sn3CO, and Sn5CO are bridge-bonded carbonyl compounds, whereas Sn2(CO)2 and Sn4CO are terminal-bonded carbonyl molecules. The Sn2(CO)2 species observably undergoes photo-induced decomposition to Sn(CO)2. Another interesting finding is that the absorption of Sn4CO shifts from 1994.0 to 1989.8 cm−1 by UV light irradiation, probably due to the change of the electronic state or the matrix effect. The density functional theory calculations have been performed on these molecules and the corresponding small naked tin clusters. Furthermore, energetic analysis for the possible reactions of lead atoms with CO molecules is also given.

The Uptake of Methyl Vinyl Ketone, Methacrolein, and 2-Methyl-3-butene-2-ol onto Sulfuric Acid Solutions

To investigate the link between molecular structure, reactivity, and partitioning of oxygenated organic compounds in acidic aerosols, the uptake of three compounds found in the atmosphere, methyl vinyl ketone (MVK), methacrolein (MACR), and 2-methyl-3-butene-2-ol (MBO), by sulfuric acid solutions has been measured using a rotated wetted-wall reactor (RWW) coupled to a chemical ionization mass spectrometer (CIMS). MVK was found to partition reversibly into 20-75 wt % H(2)SO(4) solutions, and we report Henry's law coefficients between 20 and 7000 M atm(-1) over this range. A chemical reaction for MVK was likely responsible for the uptake observed for 80-96 wt % H(2)SO(4) solutions. We derive an upper limit to the aldol self-reaction rate coefficient for MVK in 80 wt % solution of approximately 3 M(-1) s(-1). MACR partitioned reversibly over most of the acidity range, and in contrast to that for MVK, the Henry's law coefficient was relatively independent of H(2)SO(4) content. These differences indicate that the increase of the coefficient with acidity is likely due to the ability of the carbonyl molecule to form an enol. These results indicate that aldol condensation can be facile in concentrated sulfuric acid solutions, but it should be negligibly slow in dilute acid solutions such as tropospheric aerosols. MBO uptake could be explained by a Henry's law coefficient that decreases slightly as acid content varies from 20 to 55 wt % H(2)SO(4); we also measured the value in water, 70 M atm(-1) at 298 K. A steady-state uptake of MBO was observed onto 40-80 wt % H(2)SO(4) solutions, a reaction product was observed, and the reaction was tentatively identified as Pinacol rearrangement. Similar rearrangements could be at the origin of some substituted oxygenated species found in atmospheric aerosols.