CO Moiety Research Articles

Water populations in restricted environments of lipid membrane interphases.

We employ molecular dynamics simulations to study the hydration properties of Dipalmitoylphosphatidylcholine (DPPC) bilayers, both in the gel and the liquid crystalline states. We show that while the tight hydration centers (PO and CO moieties) are significantly hydrated in both phases, the gel-fluid transition involves significant changes at the second hydration shell, particularly at the buried region between the hydrocarbon tails. Thus, while almost no buried water population exists in the gel state below the carbonyls, this hydrophobic region becomes partially water accesible in the liquid crystalline state. We shall also show that such water molecules present a lower H-bond coordination as compared to the molecules at the primary hydration shell. This means that, while the latter are arranged in relatively compact nanoclusters (as already proposed), the buried water molecules tend to organize themselves in less compact structures, typically strings or branched strings, with a scarce population of isolated molecules. This behavior is similar to that observed in other hydration contexts, like water penetrating carbon nanotubes or model hydrophobic channels or pores, and reflects the reluctance of water to sacrifice HB coordination.

Partially fluorinated Scorpionate [HB(3-(CF3),5-(Ph)Pz)3]− as a supporting ligand for silver(I)-benzene, -carbonyl, and -PPh3 complexes

The benzene, CO, and PPh3 adducts [HB(3-(CF3),5-(Ph)Pz)3]AgL (L=C6H6, CO, or PPh3) have been synthesized by a metathesis process using [HB(3-(CF3),5-(Ph)Pz)3]Na(THF), CF3SO3Ag, and the corresponding co-ligands. These silver(I) adducts have been characterized by NMR spectroscopy, and by X-ray crystallography. In all cases the Scorpionate is bound to silver in typical κ3-fashion. The X-ray crystallographic data of [HB(3-(CF3),5-(Ph)Pz)3]Ag(η2-C6H6) show that it has a η2-bound benzene molecule. NMR data point to fluxional behavior in solution. The 13C NMR resonance corresponding to the CO moiety of [HB(3-(CF3),5-(Ph)Pz)3]Ag(CO) appears as a single peak at δ 177.4ppm and the ν¯co is observed at 2148cm−1. These values indicate the presence of a fairly Lewis acidic silver atom in [HB(3-(CF3),5-(Ph)Pz)3]Ag(CO) and significantly diminished Ag→CO π-backbonding. Interesting coupling is observed in the solution 19F and 31P NMR spectra of the Ag(I) adduct [HB(3-(CF3),5-(Ph)Pz)3]Ag(PPh3). A detailed analysis of the spectral and structural features of these complexes has been described herein.

H2 Production Mediated by CO2 via Initial Reduction to Formate

A Ru(NH-NHC) complex with an open coordination site on the metal center adjacent to ligand N–H moieties has been synthesized and characterized. This complex exhibits unique reactivity upon reaction with either CO2 or NaHCO3, yielding a formate-bridged bimetallic complex via a spontaneous deoxygenation reaction and formal reduction at carbon. Dehydrogenation of the formate complex leads to a Ru–carbamate species following carbon–nitrogen bond formation between the CO2 moiety and the NHC ligand. This reactivity opens up new pathways for CO2 reduction and is relevant to H2 storage.

CO2 Activation and Hydrogenation by PtHn (-) Cluster Anions.

Gas phase reactions between PtHn (-) cluster anions and CO2 were investigated by mass spectrometry, anion photoelectron spectroscopy, and computations. Two major products, PtCO2 H(-) and PtCO2 H3 (-) , were observed. The atomic connectivity in PtCO2 H(-) can be depicted as HPtCO2 (-) , where the platinum atom is bonded to a bent CO2 moiety on one side and a hydrogen atom on the other. The atomic connectivity of PtCO2 H3 (-) can be described as H2 Pt(HCO2 )(-) , where the platinum atom is bound to a formate moiety on one side and two hydrogen atoms on the other. Computational studies of the reaction pathway revealed that the hydrogenation of CO2 by PtH3 (-) is highly energetically favorable.

CO2 Activation and Hydrogenation by PtHn− Cluster Anions

AbstractGas phase reactions between PtHn− cluster anions and CO2 were investigated by mass spectrometry, anion photoelectron spectroscopy, and computations. Two major products, PtCO2H− and PtCO2H3−, were observed. The atomic connectivity in PtCO2H− can be depicted as HPtCO2−, where the platinum atom is bonded to a bent CO2 moiety on one side and a hydrogen atom on the other. The atomic connectivity of PtCO2H3− can be described as H2Pt(HCO2)−, where the platinum atom is bound to a formate moiety on one side and two hydrogen atoms on the other. Computational studies of the reaction pathway revealed that the hydrogenation of CO2 by PtH3− is highly energetically favorable.

An acrylated isocyanonaphthalene based solvatochromic click reagent: Optical and biolabeling properties and quantum chemical modeling

The optical and biolabeling properties of a novel molecule 1-(2-acryloyloxy-3-chloro-prop-1-yl)-amino-5-isocyanonaphthalene (ACAIN) is reported. In addition to being a real solvatochromic fluorophore it reacts quantitatively and rapidly with simple thiols in a thiol-ene click reaction. DFT calculations revealed a dark nonfluorescent state of ACAIN due to a close energy triplet state where electron transition can happen between the acrylic double bond and the aromatic core through an intramolecular hydrogen bond between the NH and CO moieties. The hydrothiolation reaction is accompanied by a 1.5–19 fold increase in fluorescence intensity depending on the solvent used owing to the saturation of the acrylic group. The quantum yield and reactivity of the molecules were found to be largely dependent on the substituent of the acryl moiety.The biolabeling properties were investigated in detail by fluorometry and electrospray ionization (ESI) mass spectrometry using cysteine, KAC as a simple tripeptide and BSA as a model protein.

Solid state drug-polymer miscibility studies using the model drug ABT-102

Amorphous solid dispersions typically suffer storage stability issues due to: their amorphous nature, high drug loading, uneven drug:stabilizer ratio and plasticization effects as a result of hygroscopic excipients. An extensive solid state miscibility study was conducted to aid in understanding the mechanisms involved in drug/stabilizer interactions. ABT-102 (model drug) and nine different polymers with different molecular weights and viscosities were selected to investigate drug/polymer miscibility. Three different polymer:drug ratios (1:3, 1:1 and 3:1, w/w) were analyzed using: DSC, FTIR and PXRD. Three different techniques were used to prepare the amorphous solid dispersions: serial dilution, solvent evaporation and spray drying. Spray drying was the best method to obtain amorphous solid dispersions. However, under certain conditions amorphous formulations could be obtained using solvent evaporation. Melting point depression was used to calculate interaction parameters and free energy of mixing for the various drug polymer mixtures. The spray dried solid dispersions yielded a negative free energy of mixing which indicated strong drug-polymer miscibility compared to the solvent evaporation and serial dilution method. Soluplus was the best stabilizer compared to PVP and HPMC, which is probably a consequence of strong hydrogen bonding between the two CO moieties of soluplus and the drug NH moieities.

The nature of the CO2 (-) radical anion in water.

The reductive conversion of CO2 into industrial products (e.g., oxalic acid, formic acid, methanol) can occur via aqueous CO2 (-) as a transient intermediate. While the formation, structure, and reaction pathways of this radical anion have been modelled for decades using various spectroscopic and theoretical approaches, we present here, for the first time, a vibrational spectroscopic investigation in liquid water, using pulse radiolysis time-resolved resonance Raman spectroscopy for its preparation and observation. Excitation of the radical in resonance with its 235 nm absorption displays a transient Raman band at 1298 cm(-1), attributed to the symmetric CO stretch, which is at ∼45 cm(-1) higher frequency than in inert matrices. Isotopic substitution at C ((13)CO2 (-)) shifts the frequency downwards by 22 cm(-1), which confirms its origin and the assignment. A Raman band of moderate intensity compared to the stronger 1298 cm(-1) band also appears at 742 cm(-1) and is assignable to the OCO bending mode. A reasonable resonance enhancement of this mode is possible only in a bent CO2 (-)(C2v/Cs) geometry. These resonance Raman features suggest a strong solute-solvent interaction, the water molecules acting as constituents of the radical structure, rather than exerting a minor solvent perturbation. However, there is no evidence of the non-equivalence (Cs) of the two CO bonds. A surprising resonance Raman feature is the lack of overtones of the symmetric CO stretch, which we interpret due to the detachment of the electron from the CO2 (-) moiety towards the solvation shell. Electron detachment occurs at the energies of 0.28 ± 0.03 eV or higher with respect to the zero point energy of the ground electronic state. The issue of acid-base equilibrium of the radical, which has been in contention for decades, as reflected in a wide variation in the reported pKa (-0.2 to 3.9), has been resolved. A value of 3.4 ± 0.2 measured in this work is consistent with the vibrational properties, bond structure, and charge distribution in aqueous CO2 (-).

One‐Pot Deoxygenation of Fructose to Furfuryl Alcohol by Sequential Dehydration and Decarbonylation

AbstractFructose was deoxygenated to furfuryl alcohol (FFA) by tandem dehydration and decarbonylation in one pot over the AlCl3⋅6 H2O/Pd(OAc)2 catalyst combination to give a high FFA yield of 40.6 %. AlCl3⋅6 H2O behaves as an effective Lewis acid to catalyze the dehydration of fructose to 5‐hydroxymethylfurfural (HMF), and subsequently, Pd(OAc)2 catalyzes the removal of a CO moiety from HMF to produce FFA selectively. The hydroxyl group on the HMF intermediate was stabilized by poly(1‐vinyl‐2‐pyrrolidinone) through an intermolecular hydrogen bond, which accelerated the dehydration of fructose and inhibited the hydrogenation of HMF by formic acid. The decarbonylation of HMF was promoted and the unwanted decomposition of fructose was inhibited through the use of 4 Å molecular sieves. This research highlights a “one‐pot” catalytic system to transform renewable carbohydrates into fine chemicals by tandem dehydration and decarbonylation reactions without the separation or purification of HMF.

Substitution and Catalytic Chemistry of Gyroscope‐Like Complexes Derived from Cl–Rh–CO Rotators and Triply trans Spanning Di(trialkylphosphine) Ligands

AbstractReactions of trans‐[Rh(CO)(Cl){P{(CH2)14}3P2(Rh–P2)}] (1) with ZnPh2, MeLi, or NaBH4 give the chloride‐substitution products trans‐[Rh(CO)(Ph){P{(CH2)14}3P2(Rh–P2)}] (3, 89 %), trans‐[Rh(CO)(Me){P{(CH2)14}3P2(Rh–P2)}] (94 %, 92 % purity), and trans‐[Rh(CO)(H2BH2){P{(CH2)14}3P2(Rh–P2)}] (5, 99 %). The crystal structures of 3, 5, and the corresponding (fortuitously obtained) bromide complex are determined, and the ability of the X–Rh–CO moieties to rotate is interpreted in terms of their effective radii and the void space within the dibridgehead diphosphine cage. Reaction of 1 and excess PMe3 gives the diphosphine substitution product trans‐[Rh(CO)(Cl)(PMe3)2] (89 %) and the dibridgehead diphosphine P[(CH2)14]3P (58 %). Complex 5 serves as a catalyst precursor for the hydroformylation of 1‐octene (neat or THF, 60 °C, 75 psig 1:1 CO/H2). The locus of catalysis with respect to the diphosphine cage is discussed.

Redox-induced reversible intramolecular carbon–nitrogen bond formation of an azopyridylruthenium complex: Control of carbonyl ligand photoreactivity caused by structural change of the complex

Intramolecular carbon–nitrogen bond formation between a carbonyl and proximal azopyridine ligand by ligand-based reduction led to the formation of a novel ruthenium complex containing a bidentate carbamoyl ligand. Reversible C–N bond formation and cleavage reactions were confirmed by chemical and electrochemical redox reactions. The change in character of the CO moiety based on intramolecular structural change affects the CO ligand photoreactivity. The molecular structures of the carbamoyl compound and photoreaction products were determined by X-ray crystallography to confirm the present photoreaction process.

ChemInform Abstract: Accessible Protocol for Asymmetric Hydroformylation of Vinylarenes Using Formaldehyde.

AbstractBoth the decarbonylative degradation of formaldehyde (II) to a CO moiety and hydrogen and the subsequent hydroformylation of vinylarenes are promoted by a chiral single‐loaded Rh(I)‐catalyst.

α‐Carbonylimine to α‐Carbonylamide: An Efficient Oxidative Amidation Approach

AbstractOur interest in generating amide bonds by employing the activated C=N system has led to the development of an efficient oxidative amidation reaction between 2‐oxoaldehyde and weak nucleophilic amines (anilines, benzamides and sulfonamides). Mechanistic studies support the involvement of α‐carbonylimine (–CO–C=N–) based compounds or intermediates as a central feature of the reaction, in which an adjacent CO moiety enhances the electrophilicity of the C=N system, which favors attack of the oxidant (TBHP or SeO2), thereby resulting in the generation of the desired products in good yields. The direct oxidative coupling of 2‐oxoaldehydes and weak nucleophilic amines has been accomplished through either MgSO4–TBHP–pyridine/CuBr, or SeO2·pyridine promoted methods. In the current study, SeO2·pyridine emerged as a versatile reagent with which to promote initial α‐carbonylimine formation between 2‐oxoaldehyde and weak nucleophilic amine, and subsequent oxidation to the corresponding α‐carbonylamide. The reported methodology constitutes one of the few reports of the synthesis of α‐ketoamides from anilines, perhaps the second report for the generation of α‐ketoimides, and the first report of the generation of 2‐oxoamides with sulfonamides.

Revisiting the Kolbe–Schmitt reaction of sodium 2-naphthoxide

The mechanism of the carboxylation reaction of sodium 2-naphthoxide (NaphONa) was investigated in the positions 1, 3, and 6 by means of three methods: B3LYP, B3LYP-D2, and M06-2X. While B3LYP failed to describe reaction pathways 3 and 6, B3LYP-D2 (owing to the empirical correction term) and M06-2X (owing to the way it has been parameterised) produced relatively consistent results which create completely new picture of the reaction mechanism. It was found that the reactants can build two NaphONa–CO2 complexes, of which only one can be further transformed to the reaction products. In this new NaphONa–CO2 complex, the CO2 moiety is perfectly positioned to perform electrophilic attacks on all three nucleophilic carbons of the naphthalene ring. Each reaction pathway occurs via two transition states and one intermediate. The mechanism involves a bimolecular reaction step for proton transfer, which requires notably smaller activation barrier than previously considered intramolecular rearrangement. It was shown that reaction pathway 6 is unfavourable from both kinetic and thermodynamic points of view. On the other hand, pathways 1 and 3 are competitive: pathway 1 requires lower activation barriers, but pathway 3 yields the most stable reaction product. These thermochemical results are in good agreement with the experimentally determined products ratio.

Insight into the structural features of Zhaotong lignite using multiple techniques

The chemical structures of Zhaotong lignite (ZL) were characterized with multiple direct tools, including solid-state 13C nuclear magnetic resonance (NMR), X-ray photoelectron spectrometer (XPS), Fourier transform infrared (FTIR) spectrometer, and thermogravimetric (TG) analyzer, combined with ZL ethanolysis and subsequent electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (ESI FT-ICR MS) analysis of the resulting ethanol-soluble portion (ESP). According to 13C NMR analysis, ZL mainly consists of aliphatic (52.3%) and aromatic (42.2%) carbons. Methylene is the most abundant among the aliphatic carbons. Each aromatic cluster contains 2 rings on average and the number of substituents on each aromatic ring is 3 or 4. XPS analysis suggests that oxygen atoms mainly exist in CO moieties, which is consistent with 13C NMR and FTIR analyses, and pyrrolic nitrogen species are the main nitrogen form in ZL. Based on TG analysis, cleavage of CalO and CalCal bonds should be the major reactions during ZL ethanolysis. A series of neutral nitrogen compounds (NNCs, i.e., pyrrolic nitrogen) in the ESP were detected by negative-ion ESI FT-ICR MS analysis. The identified NNCs are N1Ox (x = 0–5) class species with 3–13 double bond equivalent (DBE) values and 10–31 carbon numbers, in which N1O2 class species are predominant NNCs. According to DBE distributions of NNCs, pyrroles, indoles, and carbazoles account for most of the neutral nitrogen occurrences in ZL. Such multiple characterizations proved to be an effective method for fully understanding the chemical structures of coals, especially lignites.

Carboxylation of sodium 2-naphthoxide. Reinvestigation of the mechanism by means of a hybrid meta density functional theory method

Aromatic hydroxy acids, the compounds of large industrial importance, can be prepared in the Kolbe-Schmitt reaction, i.e. a carboxylation reaction of alkali metal phenoxides (MOPh) and naphthoxides (MONaph). On the basis of the experimental results two contradictory reaction mechanisms have been proposed: the one of direct carboxylation, and the other involving initial formation of the MOPh-CO2 or MONaph-CO2 complex. Previous theoretical investigations of the carboxylation reaction of sodium 2-naphthoxide, performed by means of the B3LYP method, confirmed the initial formation of the NaONaph-CO2 complex, and showed that the carbon of the CO2 moiety performs an electrophilic attack at C1 of the ring, leading to the formation of sodium 2-hydroxy-1-naphthoate (E1). Surprisingly, transition states for possible electrophilic attacks at C3 and C6 were not revealed, and the formation of other two products (E3 and E6) was explained by a number of consecutive rearrangements. In addition, this mechanism includes a reaction step with rather high activation energy. Since more sophisticated functionals are today available, the aim of this work is to reinvestigate the mechanism of the Kolbe-Schmitt reaction of NaONaph in all three positions (1, 3, and 6). Our investigations with the M062X method demonstrated that CO2 and NaONaph can spontaneously build two complexes: B (the one previously reported) and C. While B cannot be further transformed to yield the reaction products, the CO2 moiety in C takes perfect position for electrophilic attacks at all three sites of the ring. These attacks are realized via the transition states TS1, which lead to the formation of the new C-C bonds, and corresponding intermediates D. In the next, bimolecular reaction step two D intermediates exchange the protons adjacent to the CO2 groups. These intermolecular reaction steps require significantly lower activation energies in comparison to the intramolecular proton shift from C to O. The carboxylation reaction in the position 6 is both kinetically and thermodynamically unfavourable, whereas the pathways in the positions 1 and 3 are competitive. Pathway 1 requires the lowest activation energies, but E3 is significantly more stable than other two products. In accord with these findings are the experimental results which show that, at very low temperature (293 K) only E1 is formed at low yield, whereas the yields of E3 and E6 increase with the increasing temperature. Since the Kolbe-Schmitt reaction is experimentally performed at relatively high temperatures (around 500 K), the main product is thermodynamically most stable E6.

Regiospecific growth of Au on a concave PtZn nanocube forming an Au–PtZn surface mosaic nanocube and an Au–PtZn octapod

Regioselective growth of a heterophase on facet-controlled nanocrystals is an indispensable step towards generation of geometrically well-defined heteronanoarchitectures. The growth of a heterophase usually occurs on the most unstable surface features of a nanoparticle, such as vertices and edges, and therefore the ability to control the surface energy of facet-controlled nanocrystals is crucial for the rational synthesis of nanoarchitectures. It is, however, not easy to attain the ability to regioselectively grow a heterophase on a facet-controlled nanocrystal. Herein we introduce a simple strategy to pinpoint the site of heterophase growth on the surface of a faceted nanocrystal by controlling the concentration of surface-stabilizing moieties. Specifically, we show the regioselective growth of Au on a PtZn concave nanocube, covered with surface-bound CO moieties, forming two completely different Au–PtZn heteronanostructures of a filled-concave Au–PtZn surface mosaic nanocube and a vertex-covered Au–PtZn octapod. We also show their application in surface-enhanced Raman scattering (SERS)-based detection of small molecules.

Spectroscopic Identification of a Bidentate Binding Motif in the Anionic Magnesium–CO2 Complex ([ClMgCO2]−)

AbstractA magnesium complex incorporating a novel metal–CO2 binding motif is spectroscopically identified. Here we show with the help of infrared photodissociation spectroscopy that the complex exists solely in the [ClMg(η2‐O2C)]− form. This bidentate double oxygen metal–CO2 coordination has previously not been observed in neutral nor in charged unimetallic complexes. The antisymmetric CO2 stretching mode in [ClMg(η2‐O2C)]− is found at 1128 cm−1, which is considerably redshifted from the corresponding mode in bare CO2 at 2349 cm−1, suggesting that the CO2 moiety has a considerable negative charge (∼1.8 e−). We also employed electronic structure calculations and kinetic analysis to support the interpretation of the experimental results.

Spectroscopic identification of a bidentate binding motif in the anionic magnesium-CO2 complex ([ClMgCO2 ](-)).

A magnesium complex incorporating a novel metal-CO2 binding motif is spectroscopically identified. Here we show with the help of infrared photodissociation spectroscopy that the complex exists solely in the [ClMg(η(2) -O2 C)](-) form. This bidentate double oxygen metal-CO2 coordination has previously not been observed in neutral nor in charged unimetallic complexes. The antisymmetric CO2 stretching mode in [ClMg(η(2) -O2 C)](-) is found at 1128 cm(-1) , which is considerably redshifted from the corresponding mode in bare CO2 at 2349 cm(-1) , suggesting that the CO2 moiety has a considerable negative charge (∼1.8 e(-) ). We also employed electronic structure calculations and kinetic analysis to support the interpretation of the experimental results.

Synthesis and spectroscopic and structural studies of ruthenium carbonyl derivatives of N-salicylidene-2-hydroxyaniline Schiff base

The mononuclear ruthenium tricarbonyl derivative mer-[Ru(CO)3(sha)], 1, was synthesized from the reaction of [Ru3(CO)12] with N-salicylidene-2-hydroxyaniline (shaH2) Schiff base. The corresponding reactions of the ruthenium cluster with shaH2 in the presence of a secondary ligand L, L=2-aminobenzimidazole, thiourea, pyridine, and triphenylphosphine, resulted in formation of the dicarbonyl derivatives [Ru(CO)2(sha)(L)], 2–5. The two carbonyl groups in these complexes were attached to the metal in a cis arrangement. In case of bipyridine (bpy) as a secondary ligand the [Ru(CO)2(shaH)(bpy)], 6, where the two CO moieties in a trans position. All the complexes were characterized by elemental analysis, mass, infrared and 1H nuclear magnetic resonance spectra. The ultraviolet–vis spectra of the complexes showed broad visible bands due to metal-to-ligand charge transfer. The stereochemistry and theoretical optimization of the three-dimensional geometry of the ligand and the complexes were determined.