Acetyl Oxygen Research Articles

Polymerization of isoprene, myrcene, and butadiene catalyzed by cobalt complexes supported with 2‐acetyl‐6‐iminopyridine ligand

Cobalt complexes carrying 2‐acetyl‐6‐iminopyridine ligand are synthesized and characterized. Single‐crystal X‐ray diffraction reveals the cobalt ion is chelated with two nitrogen atoms and an acetyl oxygen atom additionally. A significant prolonged Co–O distance (2.3960(57) Å) is found, indicative of a labile character. Activated by diethylchloroaluminum, all complexes show high conversion rates for isoprene and myrcene polymerizations, affording cis‐1,4/3,4 regulated 1,3‐diene polymers. The polymerization of butadiene, interestingly, gives predominant cis‐1,4 selectivity (>99.2%) with moderate activity. The substituent at ortho‐position of arylimine plays a minor role in controlling activity and selectivity as well as the molecular weight of the resultant polymers. The properties of resultant poly(1,3‐diene)s are stable even in a wide range of operational conditions, such as [Al]/[Co] varied from 20 to 600, temperature spanning from 0°C to 60°C, and monomer–catalyst ratio from 1000 to 4000. These additional benefits of minimum fluctuation in catalytic performances may be suitable for industrial polymerization process.

Enhanced tetracycline abatement by peracetic acid activation with sulfidation of nanoscale zerovalent iron.

Iron-based heterogeneous catalysts due to the environmental friendliness have been widely studied for activation of peracetic acid (PAA) for abatement of organic contaminants in the water and wastewater treatment. However, the slow reduction from Fe(III) to Fe(II) of the iron-based catalysts as the rate-limiting step results in the low PAA activation efficiency. With regard to the excellent electron-donating capability of the reductive sulfur species, sulfidized nanoscale zerovalent iron is proposed for PAA activation (simplified as the S-nZVI/PAA process) and the tetracycline (TC) abatement efficacy and mechanism of this process are elucidated. The optimal sulfidation ratio (S/Fe) of S-nZVI is 0.07, which exhibits superior performance in PAA activation for TC abatement with the efficiency of 80-100% in the pH range of 4.0-10.0. The radical quenching experiments and oxygen release measurements confirm that acetyl(per)oxygen radicals (CH3C(O)OO•) are the main radical contributing to TC abatement. The influence of sulfidation on the crystalline structure, hydrophobicity, corrosion potential, and electron transfer resistance of S-nZVI is evaluated. The main sulfur species on the S-nZVI surface are identified as ferrous sulfide (FeS) and ferrous disulfide (FeS2). The analysis by X-ray photoelectron spectroscopy (XPS) and Fe(II) dissolution suggest that the reductive sulfur species can accelerate the conversion from Fe(III) to Fe(II). In summary, the S-nZVI/PAA process exhibits application prospects for the abatement of antibiotics in the aquatic environments.

Acetyl oxygen benzoate engeletin ester promotes KLF4 degradation leading to the attenuation of pulmonary fibrosis via inhibiting TGFβ1-smad/p38MAPK-lnc865/lnc556-miR-29b-2-5p-STAT3 signal pathway.

Pulmonary fibrosis is a common pulmonary interstitial disease of pathogenesis without effective drugs for treatment. Therefore, discovering new and effective drugs is urgently needed. In the present study, we prepared a novel compound named acetyl oxygen benzoate engeletin ester (AOBEE), investigated its effect on experimental pulmonary fibrosis, and proposed a long non-coding RNA (lncRNA)-mediated mechanism of its action. Bleomycin-induced pulmonary fibrosis in mice exhibited that AOBEE improved forced vital capacity (FVC) and alveolar structure and inhibited α-SMA, vimentin, and collagen expression. TGFβ1-stimulated fibroblast L929 cells showed that AOBEE reduced these fibrotic proteins expression and inhibited the activated-fibroblast proliferation and migration. Whole transcriptome sequencing was performed to screen out lncRNA-lnc865 and lnc556 with high expression under bleomycin treatment, but AOBEE caused a considerable decrease in lnc865 and lnc556. Mechanistic study elucidated that AOBEE alleviated pulmonary fibrosis through lnc865- and lnc556-mediated mechanism, in which both lnc865 and lnc556 sponged miR-29b-2-5p to target signal transducer and activator of transcription 3 (STAT3). Further signal pathway inhibitors and the Cignal Finder 45-pathway reporter array illustrated that the up- and downstream pathways were TGFβ1–smad2/3 and p38MAPK, and Krüppel-like factor 4 (KLF4), respectively. In conclusion, AOBEE promoted KLF4 degradation leading to the attenuation of pulmonary fibrosis by inhibiting TGFβ1–smad/p38MAPK–lnc865/lnc556–miR-29b-2-5p–STAT3 signal pathway. We hope this work will provide valuable information to design new drugs and therapeutic targets of lncRNAs for pulmonary fibrosis treatment.

Crystal structures of trans-acetyl-dicarbon-yl(η5-cyclo-penta-dien-yl)(1,3,5-tri-aza-7-phosphaadamantane)molybdenum(II) and trans-acetyl-di-carbon-yl(η5-cyclo-penta-dien-yl)(3,7-diacetyl-1,3,7-tri-aza-5-phosphabi-cyclo-[3.3.1]nona-ne)molyb-den-um(II).

The title compounds, [Mo(C5H5)(COCH3)(C6H12N3P)(CO)2], (1), and [Mo(C5H5)(COCH3)(C9H16N3O2P)(C6H5)2))(CO)2], (2), have been prepared by phosphine-induced migratory insertion from [Mo(C5H5)(CO)3(CH3)]. The mol-ecular structures of these complexes are quite similar, exhibiting a four-legged piano-stool geometry with trans-disposed carbonyl ligands. The extended structures of complexes (1) and (2) differ substanti-ally. For complex (1), the molybdenum acetyl unit plays a dominant role in the organization of the extended structure, joining the mol-ecules into centrosymmetrical dimers through C-H⋯O inter-actions with a cyclo-penta-dienyl ligand of a neighboring mol-ecule, and these dimers are linked into layers parallel to (100) by C-H⋯O inter-actions between the molybdenum acetyl and the cyclo-penta-dienyl ligand of another neighbor. The extended structure of (2) is dominated by C-H⋯O inter-actions involving the carbonyl groups of the acetamide groups of the DAPTA ligand, which join the mol-ecules into centrosymmetrical dimers and link them into chains along [010]. Additional C-H⋯O inter-actions between the molybdenum acetyl oxygen atom and an acetamide methyl group join the chains into layers parallel to (101).

Towards the synthesis of prenylated phloroglucinol derivatives: An X-ray crystallographic and DFT study of unexpected reaction products

Owing to their bioactivity and prevalence in medicinal plant extracts, prenylated phloroglucinols have garnered significant interest. Towards the synthesis of prenylated phloroglucinol derivatives, 2,4,6-trihydroxy-3-(3-methylbut-2-enyl)acetophenone is required as an intermediate. Herein, this was synthesised by a tandem Claisen-Cope rearrangement reaction on 2,4-bis(methoxymethoxy)-6-(3-methylbut-2-enyloxy)acetophenone and a subsequent hydrolysis to remove protecting groups. This reaction yielded the desired product as well as three by-products. Two of these by-products were isomeric chromane derivatives (2 and 3) and the third was a methoxy derivative (4). These compounds have been studied by single crystal X-ray crystallography and DFT methods. Compound (2) crystallised in the P21/c space group with two hydrogen-bonded molecules in the asymmetric unit (Z = 8). Compound (4) crystallised in the Pbca space group with a single molecule in the asymmetric unit (Z = 8). Both compounds formed extensive supramolecular structures supported by hydrogen bonds in the solid state. Compound (2) forms a simple one-dimensional hydrogen-bonded chain co-linear with the a-axis. Compound (4) forms a two-dimensional supramolecular structure comprising “pentameric” hydrogen-bonded motifs linked by additional H-bonds to form the supramolecular structure. Both structures showed intramolecular hydrogen bonds between the acetyl oxygen and adjacent OH group. DFT simulations were used to probe the relative energies of the molecules and hydrogen bonds. These simulations showed that the intramolecular hydrogen bond has a substantial stabilising effect with an interaction strength of 70.64 kJ mol−1. The formation of the hydrogen-bonded dimer of (2) from which the supramolecular structure is formed has a ΔHassoc constant of −42.32 kJ mol−1, illustrating that the formation of the hydrogen-bonded structure is energetically favourable.

Abnormal Magnetic Moment and Zero Field Splitting of Some Nickel (II) Complexes

<em>Some complexes of Ni(II) have been prepared with 2-thio-3-acetyl hydantoin (TAHN) and 2-formyl pyridine thiosemicarbazone (FPTS). On the basis of elemental analysis and molar conductivity, the complexes have been formulated as NiL<sub>2</sub>X<sub>2</sub>, where L = TAHN or FPTS and X = Cl<sup>–</sup>, Br<sup>–</sup>, NCS<sup>–</sup>, ClO<sub>4</sub><sup>–</sup>. The infrared spectra of complexes and free ligand reveal that the ligand TAHN is co-ordinated through sulphur and acetyl oxygen, while FPTS ligand co-ordinates through heterocyclic nitrogen and sulphur to Ni(II) metal ion. The magnetic moment of these complexes are found to be 3.20-3.25 B.M. The values are greater than value (2.828 B.M) corresponding to two unpaired electrons of a d<sup>8</sup>-system. The appearance of four absorption bands in their electronic spectra reveal, the tetragonal distortion in the octahedral symmetry of complexes. The zero field splitting parameter(D) and the other crystal field parameters like Dq<sub>(xy)</sub>, Dq<sub>(z)</sub>, Dt have been calculated. The results show that, the tetragonal distortion parameter (Dt) increases in the order of NCS<sup>– </sup>< Cl<sup>–</sup> < Br<sup>–</sup> while the zero field splitting parameter (D) also increases in the same order for both the planer ligands.</em>

Structural diversity in phenyl bismuth(III) bis(carboxylate) complexes

In order to probe the effect of solvent and substituents on the formation of bismuth carboxylates, triphenylbismuth (BiPh3) was treated with salicylic acid, 5-bromosalicylic acid, 3-methoxysalicylic acid, 5-nitrosalicylic acid, 3-methylanthranilic acid, 5-chloroanthranilic acid, and N-acetylanthranilic acid in a 1:2 ratio in a variety of solvents. The following compounds were isolated and structurally characterized: [PhBi(5-Br-2-OH-C6H3CO2)2(Me2CO)], 1; [PhBi(5-Br-2-OH-C6H3CO2)2(EtOH)]·(EtOH) (H2O), 2; [PhBi(5-O2N-2-OH-C6H3CO2)2(4,4′-bipy)]·EtOH (4,4′-bipy = 4,4’-bipyridine), 3; [PhBi(5-Cl-2-NH2-C6H3CO2)2], 4; [Ph2Bi2(3-MeO-2-OH-C6H3CO2)4(EtOH)], 5; [Ph2Bi2(3-MeO-2-OH-C6H3CO2)4(i-PrOH)], 6; [PhBi(2-MeC(O)NH–C6H3CO2)2]·EtOH, 7; [PhBi(3-MeO-2-OH-C6H3CO2)2]∞·PhCH3, 8; [PhBi(3-Me-2-NH2-C6H3CO2)2(2,2′-bipy)]·0.42MeCN; (2,2′-bipy = 2,2′-bipyridine), 9; cis-[PhBi(5-Br-2-OH-C6H3CO2)2]2, 10; trans-[PhBi(5-Br-2-OH-C6H3CO2))2]2·2MeCN, 11; [PhBi(5-Br-2-OH-C6H3CO2))2]2·2MeOH, 12, trans- [PhBi(2-OH-C6H4CO2)2]2, 13. Compounds 1 and 2 are monomeric possessing a coordinated solvent molecule in an equatorial coordination site of a pentagonal pyramidal bismuth(III) center. The same coordination geometry is found in 3 where two such units are tethered together via the 4,4’-bipyridine ligand. Compounds 5 and 6 form dimers in which one Bi atom attains a pentagonal pyramidal geometry via coordination of the solvent and the other via binding to the phenol group of a 3-methoxysalicylate ligand attached to the other Bi atom. Compounds 7 and 8 are polymeric. In 7, a coordination polymer is created by the donation of the acetyl oxygen atom of the [PhBi(2-MeC(O)NHC6H3CO2)2] unit to an adjacent [PhBi(2-MeC(O)NHC6H3CO2)2] center, while in 8 a similar situation arises but through the phenolic and methoxy oxygen atoms of a 3-methoxysalicylate ligand, giving rise to the first observed hexagonal pyramidal coordination complex of a bismuth carboxylate. In 9, one of the carboxylate ligands is bidentate while the other remains monodentate, displaying the same structural geometry as previously reported for [PhBi(2-MeO-C6H4CO2)2(2,2′-bipy)]·0.5EtOH and [PhBi(4-Me-2-OH-C6H3CO2)2(2,2′-bipy)]. Compounds 10–13 are dimeric structures arising from shared carboxylate oxygen atoms that bridge the two bismuth atoms.

Deciphering the GPER/GPR30-agonist and antagonists interactions using molecular modeling studies, molecular dynamics, and docking simulations

The G-protein coupled estrogen receptor 1 GPER/GPR30 is a transmembrane seven-helix (7TM) receptor involved in the growth and proliferation of breast cancer. Due to the absence of a crystal structure of GPER/GPR30, in this work, molecular modeling studies have been carried out to build a three-dimensional structure, which was subsequently refined by molecular dynamics (MD) simulations (up to 120 ns). Furthermore, we explored GPER/GPR30’s molecular recognition properties by using reported agonist ligands (G1, estradiol (E2), tamoxifen, and fulvestrant) and the antagonist ligands (G15 and G36) in subsequent docking studies. Our results identified the E2 binding site on GPER/GPR30, as well as other receptor cavities for accepting large volume ligands, through GPER/GPR30 π–π, hydrophobic, and hydrogen bond interactions. Snapshots of the MD trajectory at 14 and 70 ns showed almost identical binding motifs for G1 and G15. It was also observed that C107 interacts with the acetyl oxygen of G1 (at 14 ns) and that at 70 ns the residue E275 interacts with the acetyl group and with the oxygen from the other agonist whereas the isopropyl group of G36 is oriented toward Met141, suggesting that both C107 and E275 could be involved in the protein activation. This contribution suggest that GPER1 has great structural changes which explain its great capacity to accept diverse ligands, and also, the same ligand could be recognized in different binding pose according to GPER structural conformations.

Research Communications - over 100 papers and counting!

Research Communications - over 100 papers and counting!

Anti-estrogenic activity of mansonone G and mansorin A derivatives

Context: Mansonone G and mansorin A are major bioactive constituents from Mansonia gagei Drumm (Sterculiaceae) wood, and their mild anti-estrogenic activity was reported previously by the authors.Objective: In order to increase the potency of their anti-estrogenic effect and to clarify their binding way to estrogen receptor on a molecular level, several derivatives of both compounds will be prepared and a docking study of the original compounds and their derivatives on estrogen receptor alpha (ERα) was carried out.Materials and methods: The original compounds were isolated from the heartwood of M. gagei. Nine alkyl derivatives were prepared by acetylation, methylation, or adding a basic side chain to the free hydroxyl group of both compounds. The estrogenic/anti-estrogenic activities of the derivatives compared to the original compounds were carried out using ERα competitive binding screen and yeast two-hybrid assay expressing ERα and ERβ using concentrations ranging from 10 to 100 μM.Results: Acetyl mansonone G showed a 10-fold increase in its binding ability to ERα compared to mansonone G with an IC50 630 μM. Similarly, methyl mansonone G and acetyl mansonone G showed 50% and 35% inhibition of 17β-estradiol-induced β-galactosidase activity at 10 μM in the yeast expressing ERα, and 42% and 30%, respectively, at 10 μM in the yeast expressing ERβ. Virtual docking of acetyl mansonone G to ERα showed that it binds, with its acetyl oxygen, in a similar way to the 17β-OH of estradiol.Discussion and conclusion: The phenolic hydroxyl group in mansonones and mansorins was not essential for binding to estrogen receptors. In addition, acetyl mansonone G could represent a promising starting material for the synthesis of anti-estrogenic agents.

Isomeric acetoxy analogs of celecoxib and their evaluation as cyclooxygenase inhibitors

A group of celecoxib analogs having a SO(2)NH(2) (9a-f), or SO(2)Me (12a-f), COX-2 pharmacophore at the para-position of the N-1 phenyl ring in conjunction with a C-5 phenyl ring having a variety of substituents (4-, 3-, 2-OAc; 4-Me,2-OAc, 4-Me,3-OAc, 4-F,2-OAc) was synthesized for evaluation as cyclooxygenase (COX) inhibitors of the COX-1/COX-2 isozymes. Within this group of compounds, 1-(4-aminosulfonylphenyl)-3-trifluoromethyl-5-(2-acetoxy-4-fluorophenyl)pyrazole (9f) emerged as the most potent (COX-1 IC(50)=0.7 μM; COX-2 IC(50)=0.015 μM) and selective (COX-2 selectivity index=47) inhibitor agent that exhibited good anti-inflammatory activity (ED(50)=42.3mg/kg) which was lower than the reference drug celecoxib (ED(50)=10.8 mg/kg), but greater than ibuprofen (ED(50)=67.4 mg/kg) and aspirin (ED(50)=128.7 mg/kg). Molecular modeling studies for 9f showed that the SO(2)NH(2) group assumes a position within the secondary pocket of the COX-2 active site wherein the SO(2)NH(2) oxygen atom is hydrogen bonded to the H90 residue (2.90Å), the SO(2)NH(2) nitrogen atom forms a hydrogen bond with L352 (N⋯O=2.80Å), and the acetyl group is positioned in the vicinity of the S530 residue where the acetyl oxygen atom undergoes hydrogen bonding to L531 (2.99Å).

Exploring a Reaction Mechanism for Acetato Ligand Replacement in Paddlewheel Tetrakisacetatodirhodium (II,II) Complex by Ammonia: Computational Density Functional Theory Study

This study focuses on the first step of interaction between DNA and the paddle-wheel dirhodium complex. The ammonia molecule was used to model the oligonucleotide sequence. The reaction was considered in neutral and acidic conditions, in gas phase, and in solvent, using the COSMO model. Molecular structures of the complexes were optimized in both models at the B3PW91/6-31G(d) level. The B3LYP functional and aug-cc-pvdz basis set were employed for single-point energy determination and electron distribution analyses. It was shown that in neutral solution the replacement of axial aqua ligand is mildly exoergic. The reaction is characterized by a relatively low activation barrier (10-12 kcal/mol), and, according to Eyring transition state theory, it proceeds very quickly. The breaking of the Rh-O(ac) bond in neutral solution is mildly endoergic (less than 1 kcal/mol) with an activation barrier of about 21 kcal/mol. However, this process can occur much more spontaneously (ΔG of -14 kcal/mol) when the dirhodium complex is protonated at the acetyl oxygen in remote position.

Experimental Electron Density Study of Tetrakis-μ-(acetylsalicylate)dicopper(II): a Polymeric Structure with Cu···Cu Short Contacts

The electron density, its topological features, and the electrostatic potential of tetrakis-mu-(acetylsalicylate)dicopper(II), Cu[C(9)H(7)O(4)](2), have been derived from an accurate high-resolution diffraction experiment at 100 K. This complex exhibits a polymeric structure involving one acetyl oxygen atom as a bridge in the solid state. Only van der Waals interactions between the polymeric chains are observed. The copper cation is octahedrally coordinated with five oxygen atoms of the aspirinate ligands and one adjacent Cu with short Cu...Cu contact distances in the range of 2.6054(1) A. The Cu-O bond lengths are equal to 1.96 A except the apical one which is 2.2183(7) A. The multipole refinements were carried out using the Hansen-Coppens model coded in the MOPRO computer program. Starting from the 3d(10)4s(1) copper electron configuration, the electron density analysis and Cu d-orbital populations reveal that the observed configuration is close to being [Ar]3d(9)4s(1). As expected from the ligand field theory, the most depopulated 3d-orbital is the d(x(2)-y(2)) (1.17 e) one with lobes pointing toward the carboxylic oxygen atoms. Conversely, the d(z(2)) is the most populated orbital for a z-axis directed along the Cu...Cu bond. The atomic charges were derived from a kappa-refinement and yielded a metal net charge of +1.20(3) e. Deficits of +0.72(6) and +0.59(7) e are obtained for the acetyl carbon atoms of the aspirinate ligands, those involved in the drug activity of aspirin. Comparisons are made to the results of our previous work on the zinc-aspirinate complex.

Sir2 Deacetylases Exhibit Nucleophilic Participation of Acetyl-Lysine in NAD+ Cleavage

Sir2 Deacetylases Exhibit Nucleophilic Participation of Acetyl-Lysine in NAD⁺ Cleavage

Conformational and tautomeric eccentricities of 2‐acetyl‐1,8‐dihydroxynaphthalenes

Tautomerism in aromatic systems with oxygen substitutents is rare. This is investigated in 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (1) and in 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (2). The tautomeric nature of 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene is supported by long-range hydrogen-hydrogen coupling between the OH-1 and the OH-8 and by the isotope effects on 13C caused by deuteration at the CH3C==O methyl group. Compound 2 participates in a degenerate equilibrium between two equivalent nonsymmetrical rotamers (2A and 2B), each having two intramolecular O...HO hydrogen bonds: one involving an acetyl oxygen and the neighboring hydroxyl group, and the other between the oxygen centers at positions 1 and 8. In addition, each rotamer is involved in a tautomeric equilibrium, with a structure having an OH-substituted exocyclic double bond (2AT or 2BT).DFT calculations for a large set of compounds highlight the factors controlling the unusual rotational and tautomeric behaviors. A very important factor seems to be the repulsive interaction between the O-1 and O-8 centers, which is modulated by formation of an OH-1...O-8 or OH-8...O1 hydrogen bond. Steric interactions, mesomeric release of electrons from the oxygen at position 8, and a strong OH...O...C hydrogen bond are other factors.Solid-state 13C NMR spectra of 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene at different temperatures demonstrated no averaging in the solid, whereas partially deuterated 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene showed an isotope effect at C-1 of 1.5 ppm, indicating tautomerism in the solid state.

Insights into the Sirtuin Mechanism from Ternary Complexes Containing NAD+ and Acetylated Peptide

Sirtuin proteins comprise a unique class of NAD+-dependent protein deacetylases. Although several structures of sirtuins have been determined, the mechanism by which NAD+ cleavage occurs has remained unclear. We report the structures of ternary complexes containing NAD+ and acetylated peptide bound to the bacterial sirtuin Sir2Tm and to a catalytic mutant (Sir2Tm(H116Y)). NAD+ in these structures binds in a conformation different from that seen in previous structures, exposing the alpha face of the nicotinamide ribose to the carbonyl oxygen of the acetyl lysine substrate. The NAD+ conformation is identical in both structures, suggesting that proper coenzyme orientation is not dependent on contacts with the catalytic histidine. We also present the structure of Sir2Tm(H116A) bound to deacteylated peptide and 3'-O-acetyl ADP ribose. Taken together, these structures suggest a mechanism for nicotinamide cleavage in which an invariant phenylalanine plays a central role in promoting formation of the O-alkylamidate reaction intermediate and preventing nicotinamide exchange.

Two new 1D cadmium(II) azido complexes: catina-Poly[di-μ1,1-azido(2,2′-bipyridyl)cadmium(II)] and a new polymorph of catina-Poly[di-μ1,1-azido (2-acetylpyridine)cadmium(II)

Two new cadmium(II) azido complexes, [Cd(2,2′-bipy)(N3)2]n (1) and [Cd(2-acpy)(N3)2]n (2) (2,2′-bipy = 2,2′-bipyridyl and 2-acpy = 2-acetylpyridine), have been synthesized and structurally characterized by single-crystal X-ray diffraction methods. The coordination environment of the central cadmium atom is distorted octahedral (MN6) in 1 and (MN5O) in 2, with one-dimensional chains formed through Cd2N2 units and alternatively chelating N,N′-bipyridyl or N,O-2-acetylpyridine groups. The central Cd(II) ion is coordinated to two nitrogen atoms of a chelating bipyridyl group or one nitrogen atom and one acetyl oxygen of 2-acetylpyridine and four nitrogen atoms of four different end-on bridging (μ1,1-N3) groups. Chains in the c direction in 1 are stabilized in b direction by π–π interactions involving the aromatic rings of bipyridyl ligands. IR and NMR spectra of the two complexes are reported.

On the use of the MNDO-d semiempirical method for the structural study of chlorophyll b and anhydrous chlorophyll b dimer

Semiempirical MNDO-d molecular orbital calculations have been used for the structural study of chlorophyll b and anhydrous chlorophyll b dimer systems in their respective ground states. A model of chlorophyll b dimer has been considered whereby the magnesium atom is five-coordinate with an oxygen atom in the fifth coordination site. Total energies, net electric charges, and electronic dipole moments have been determined for the ground states of the above-mentioned molecules. The proposed models allow for the examination of distortions within the pyrroles and porphyrin macrocycles of these magnesium complexes. They also permit the estimate of changes in bond lengths, bond angles and dihedrals produced by dimerization via the acetyl oxygen of the carbometoxy group and the central magnesium atom, and changes in the π-electronic system of the chlorin systems. The results obtained are in good agreement with the experimental findings, and they reproduce many of the observed trends. In particular, neutron diffraction crystal structure, NMR and infrared spectra, provide experimental evidence in support of these theoretical predictions. Comparison with other theoretical results, shows that there is a good correlation between the DFT/B3LYP(6-31G*) and the MNDO-d, and also that the MNDO-d performs better than the HF/6-31G* and the PM5 in general.

Infrared multiphoton dissociation spectroscopy of protonated N-acetyl-alanine and alanyl-histidine

Using Fourier transform ion cyclotron resonance mass-spectrometry (FT-ICR-MS) in combination with infrared multiphoton dissociation (IRMPD) spectroscopy, at the free electron laser (FEL) facility CLIO in Orsay (France), we obtain the IR spectra, in the 900–1900 cm −1 range, of two model protonated dipeptides: N-acetyl-alanine (AcNH-Ala) and alanyl-histidine (Ala-His). By comparison with simulated spectra, calculated at the B3LYP/6-31++G ** level for many low-lying possible conformers of these two species, we are able to assign the position of the protonation site, on the acetyl oxygen for AcNH-Ala and on the side-chain imidazole nitrogen for Ala-His, and to obtain some more information on the low-lying equilibrium structures of these two species in the gas phase.

Selective addition to iridium of aryl C-H bonds ortho to coordinating groups. Not chelation-assisted.

Precursors of the pincer-ligated iridium species, (PCP)Ir, react with nitrobenzene or acetophenone at ambient temperature to give O,C-chelated complexes resulting from addition of an aryl C-H bond and coordination of a nitro or acetyl oxygen. The C-H additions appear to be completely regioselective for the position ortho to the functional group; however, structural characterization and low-temperature NMR studies demonstrate that the reaction does not proceed via coordination of the functional group followed by C-H addition. In the case of nitrobenzene, kinetic preference for the para and meta positions is demonstrated at low temperature. Addition occurs more slowly at the ortho position, without assistance by the functional group; the ortho-C-H addition product is then trapped by chelation.