Interaction of Ruthenium(II) with Terminal Alkynes: Benchmarking DFT Methods with Spectroscopic Data

Synthesis, Cytotoxic Activity and In Silico Study of Novel Dihydropyridine Carboxylic Acids Derivatives

To aid the possible prevention of multidrug resistance in tumors and cause lower toxicity, a set of sixteen novel dihydropyridine carboxylic acids derivatives 3a-p were produced; thus, the activation of various ynones with triflic anhydride was performed, involving a nucleophilic addition of several bis(trimethylsilyl) ketene acetals, achieving good yields requiring easy workup. The target molecules were unequivocally characterized by common spectroscopic methods. In addition, two of the tested compounds (3a, and 3b) were selected to perform in silico studies due to the highest cytotoxic activity towards the HCT-15 cell line (7.94 ± 1.6 μM and 9.24 ± 0.9 μM, respectively). Employing theoretical calculations with density functional theory (DFT) using the B3LYP/6-311++G(d,p) showed that the molecular parameters correlate adequately with the experimental results. In contrast, predictions employing Osiris Property Explorer showed that compounds 3a and 3b present physicochemical characteristics that would likely make it an orally active drug. Moreover, the performance of Docking studies with proteins related to the apoptosis pathway allowed a proposal of which compounds could interact with PARP-1 protein. Pondering the obtained results (synthesis, in silico, and cytotoxic activity) of the target compounds, they can be judged as suitable antineoplastic agent candidates.

Structures and Bonding in Hexacarbonyl Diiron Polyenes: Cycloheptatriene and 1,3,5-Cyclooctatriene

Structural preferences of (1,3,5-cyclooctatriene) hexacarbonyl diiron [(C8H10)Fe2(CO)6] and cycloheptatriene hexacarbonyl diiron [(C7H8)Fe2(CO)6] were explored using density functional theory (DFT) computations. DFT computations together with experimental results demonstrated that structure with the [η3, (η1, η2)] mode is the preferred structure in (C8H10)Fe2(CO)6, and the [η3,η3] mode is preferred in (C7H8)Fe2(CO)6. For (C8H10)Fe2(CO)6, the conversion between the structures with [η3, (η1, η2)] mode and the [η3, η3] mode is prevented by the relatively high activation barrier. (C8H10)Fe2(CO)6 is indicated as a fluxional molecule with a Gibbs free energy of activation of 8.5 kcal/mol for its ring flicking process, and an excellent linear correlation (R2 = 0.9909) for the DFT simulated 1H-NMR spectra was obtained. Results provided here will develop the understanding on the structures of other polyene analogs.

Gold(I) and Silver(I) π-Complexes with Unsaturated Hydrocarbons

Gold π-complexes have been studied largely in the past 2 decades because of their role in gold-catalyzed reactions. We report an experimental and theoretical investigation of the interaction between a wide range of unsaturated hydrocarbons (alkanes, alkynes, alkadienes, and allenes) and triphenylphosphine-gold(I), triphenylphosphine-silver(I), and acetonitrile-silver(I) cations. The bond dissociation energies of these complexes were determined by mass spectrometry collision-induced dissociations and their structures were studied by density functional theory calculations and infrared photodissociation spectroscopy. The results show that with the same phosphine ligand, gold binds stronger to the π-ligands than silver and thereby activates the unsaturated bond more effectively. Ligand exchange of phosphine by acetonitrile at the silver complexes increases the binding energy as well as the activation of the π-ligands. We also show that the substitution of an unsaturated bond is more important than the bond type.

Anti-cancer organoruthenium(ii) complexes and their interactions with cysteine and its analogues. A mass-spectrometric study

The ruthenium complexes [Ru(CYM)(p-Cl-dkt)(Cl)] (1), [Ru(CYM)(pta)(p-Cl-dkt)]PF₆ (2), and [Ru(CYM)(pta)Cl₂] (3, RAPTA-C) (CYM = para-cymene, p-Cl-dkt = 1-(4-chlorophenyl)-4,4,4-trifluorobutane-1,3-dione, pta = 1,3,5-triaza-7-phosphaadamantane) are biologically active and show anti-cancer activities, albeit with different mechanisms. To further understand these mechanisms, we compared their speciation in aqueous solutions with an amino acid (cysteine), with an amino acid derivative (N-acetylcysteine) and with a tripeptide (glutathione) by Mass Spectrometry (MS). Here, we show that all ruthenium complexes have high selectivity for cysteine and cysteine-derived molecules. On one hand, [Ru(CYM)(p-Cl-dkt)(Cl)] undergoes solvolysis in water and forms [Ru₂(CYM)₂(OH)₃]⁺. Subsequently, all hydroxyl anions are exchanged by deprotonated cysteine. Infrared Photodissociation Spectroscopy (IRPD) showed that cysteine binds to the ruthenium atoms via the deprotonated thiol group and that sulfur bridges the ruthenium centers. On the other hand, the pta-bearing complexes remain monometallic and undergo only slow Cl or p-Cl-dkt exchange by deprotonated cysteine. Therefore, the pta ligand protects the ruthenium complexes from ligand exchange with water and from the formation of biruthenium clusters, possibly explaining why the mechanism of pta-bearing ruthenium complexes is not based on ROS production but on their reactivity as monometallic complexes.

ESI-MS study of ruthenium complexes shows their high selectivity toward thiol containing molecules and formation of larger thiolate-bound clusters in absence of a protecting ligand such as pta.

Ribeiro FW, Cervi G, C. Correra T. Evaluation of Common Theoretical Methods for Predicting Infrared Multiphotonic Dissociation Vibrational Spectra of Intramolecular Hydrogen-Bonded Ions

Infrared photodissociation analyses are supported by theoretical calculations that allow a trustworthy interpretation of experimental spectra of gaseous ions. B3LYP calculations are the most prominent method used to model IR spectra, as detailed in our bibliographic survey. However, this and other commonly used methods are known to provide inaccurate energy values and geometries, especially when it comes to long-range interactions, such as intramolecular H-bonds, which show increased anharmonicity. Therefore, we evaluated some of the most commonly used density functional theory methods (B3LYP, CAM-B3LYP, and M06-2X) and basis sets (6-31+G(d,p), 6-311++G(d,p), 6-311++G(3df,2pd), aug-cc-pVDZ, and aug-cc-pVTZ), including anharmonicity and dispersion corrections. The results were compared to MP2 calculations and to experimental high-frequency (2000-4000 cm-1) IR multiphotonic dissociation (IRMPD) spectra of two protonated model molecules containing intramolecular hydrogen bonds: biotin and tryptophan. M06-2X/6-31+G(d,p) was shown to be the most cost-effective level of theory, whereas CAM-B3LYP was the most efficient method to describe the van der Waals interactions. The use of the dispersion correction D3, proposed by Grimme, improved the description of O-H vibrations involved in H-bonding but worsened the description of N-H stretches. Anharmonic calculations were shown to be extremely expensive when compared to other approaches. The efficiencies of well-established scaling factors (SFs) in opposition to sample-dependent SFs were also discussed and the use of fitted SFs were shown to be the most cost-effective approach to predict IRMPD spectra. M06-2X/6-31+G(d,p) and CAM-B3LYP/aug-cc-pVDZ were also tested against the fingerprint region. Our results suggest that these methods can also be used for analysis in this lower frequency range and should be regarded as the methods of choice for cost-effective IRMPD simulations rather than the ubiquitous B3LYP method, especially when further molecular properties are needed.

Transforming hemithioindigo from a two-way to a one-way molecular photoswitch by isolation in the gas phase

Photoswitching of a permanently charged hemithioindigo switch was probed by two photon experiments in the gas phase at 3 K.

Exploring the Gas-Phase Activation and Reactivity of a Ruthenium Transfer Hydrogenation Catalyst by Experiment and Theory in Concert

This study elucidates structures, activation barriers, and the gas-phase reactivity of cationic ruthenium transfer hydrogenation catalysts of the structural type [(η⁶-cym)RuX(pympyr)]⁺. In these complexes, the central ruthenium(+II) ion is coordinated to an η⁶-bound p-cymene (η⁶-cym), a bidentate 2-R-4-(2-pyridinyl)pyrimidine ligand (pympyr) with R = NH₂ or N(CH₃)₂, and an anion X = I^-, Br^-, Cl^-, or CF₃SO₃^-. We present infrared multiple-photon dissociation (IR-MPD) spectra of precursors (before HCl loss) and of activated complexes (after HCl loss), which elucidates C-H activation as the key step in the activation mechanism. A resonant two-color IR-MPD scheme serves to record several otherwise "dark" bands and enhances the validity of spectral assignments. We show that collision-induced dissociation (CID)-derived activation energies of the [(η⁶-cym)RuX(pympyr)]⁺ (R = N(CH₃)₂) complexes depend crucially on the anion X. The obtained activation energies for the HX loss correlate well with quantum chemical activation barriers and are in line with the HSAB concept. We further elucidate the reaction of the activated complexes with D₂ under single-collision conditions. Quantum mechanical simulations substantiate that the resulting species represent analogues for hydrido intermediates formed after abstraction of H⁺ and H^- from isopropanol, as postulated for the catalytic cycle of transfer hydrogenation by us before.

Chasing the Evasive Fe═O Stretch and the Spin State of the Iron(IV)-Oxo Complexes by Photodissociation Spectroscopy

We demonstrate the application of infrared photodissocation spectroscopy for determination of the Fe═O stretching frequencies of high-valent iron(IV)-oxo complexes [(L)Fe(O)(X)]^2+/+ (L = TMC, N4Py, PyTACN, and X = CH₃CN, CF₃SO₃, ClO₄, CF₃COO, NO₃, N₃). We show that the values determined by resonance Raman spectroscopy in acetonitrile solutions are on average 9 cm^-1 red-shifted with respect to unbiased gas-phase values. Furthermore, we show the assignment of the spin state of the complexes based on the vibrational modes of a coordinated anion and compare reactivities of various iron(IV)-oxo complexes generated as dications or monocations (bearing an anionic ligand). The coordinated anions can drastically affect the reactivity of the complex and should be taken into account when comparing reactivities of complexes bearing different ligands. Comparison of reactivities of [(PyTACN)Fe(O)(X)]⁺ generated in different spin states and bearing different anionic ligands X revealed that the nature of anion influences the reactivity more than the spin state. The triflate and perchlorate ligands tend to stabilize the quintet state of [(PyTACN)Fe(O)(X)]⁺, whereas trifluoroacetate and nitrate stabilize the triplet state of the complex.