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1.
J Phys Chem A ; 125(1): 366-375, 2021 Jan 14.
Artículo en Inglés | MEDLINE | ID: mdl-33356252

RESUMEN

Metalcyclopentadienyl complexes (MCp)+ (M = Fe, Ru, Os) bound to the large polyaromatic hydrogenated hydrocarbon (PAH) C96H24 used as a model for pristine graphene have been studied using a density functional theory (DFT) generalized gradient approximation (PBE functional) to reveal their structural features and dynamic behavior. The inter-ring haptotropic rearrangements (IRHRs) for these complexes were shown to occur via two transition states and one intermediate. The energy barriers of the η6 ⇌ η6 IRHRs of the (MCp)+ unit were found to be 30, 27, and 29 kcal/mol for M = Fe, Ru, and Os, respectively. These values are significantly lower than the values found previously for smaller PAHs. Both polar and nonpolar solvents were found not to affect significantly the energy barrier heights. Investigated transition metal complexes could be used in general as catalysts in the design of novel derivatives or materials with promising properties. Metalcyclopentadienyl complexes (MCp)+ of PAHs show catalytic properties mainly due to their structural details as well as their important characteristic of inter-ring haptotropic rearrangement. IRHRs take place usually by intramolecular mechanisms. During IRHRs, the MLn organometallic groups (OMGs) undergo shifting along the PAH plane and could coordinate additional reagents, which is important for catalysis. Large PAHs such as graphene, fullerenes, and nanotubes possess intrinsic anticancer activity, and numerous arene complexes of Ru and Os have been proven to have anticancer properties as well. We suppose that coordinating Ru or Os to very large PAHs could synergistically increase the anticancer activity of resulting complexes.

2.
Front Chem ; 11: 1145974, 2023.
Artículo en Inglés | MEDLINE | ID: mdl-37123881

RESUMEN

Computational pharmacology and chemistry of drug-like properties along with pharmacokinetic studies have made it more amenable to decide or predict a potential drug candidate. 4-Hydroxyisoleucine is a pharmacologically active natural product with prominent antidiabetic properties. In this study, ADMETLab 2.0 was used to determine its important drug-related properties. 4-Hydroxyisoleucine is compliant with important drug-like physicochemical properties and pharma giants' drug-ability rules like Lipinski's, Pfizer, and GlaxoSmithKline (GSK) rules. Pharmacokinetically, it has been predicted to have satisfactory cell permeability. Blood-brain barrier permeation may add central nervous system (CNS) effects, while a very slight probability of being CYP2C9 substrate exists. None of the well-known toxicities were predicted in silico, being congruent with wet lab results, except for a "very slight risk" for respiratory toxicity predicted. The molecule is non ecotoxic as analyzed with common indicators such as bioconcentration and LC50 for fathead minnow and daphnia magna. The toxicity parameters identified 4-hydroxyisoleucine as non-toxic to androgen receptors, PPAR-γ, mitochondrial membrane receptor, heat shock element, and p53. However, out of seven parameters, not even a single toxicophore was found. The density functional theory (DFT) study provided support to the findings obtained from drug-like property predictions. Hence, it is a very logical approach to proceed further with a detailed pharmacokinetics and drug development process for 4-hydroxyisoleucine.

3.
ACS Omega ; 8(28): 25034-25047, 2023 Jul 18.
Artículo en Inglés | MEDLINE | ID: mdl-37483210

RESUMEN

The effective preparation of two new pyrimidine- and pyridine-based organic crystalline salts with substituted acidic moieties (i.e., (Z)-4-(naphthalen-2-ylamino)-4-oxobut-2-enoic acid (DCNO) and 2-hydroxy-3,5-dinitrobenzoic acid (PCNP)) using methanol as a solvent has been reported. These molecular salts have ionic interactions that are responsible for their structural stabilization in their solid-state assemblies. The crystal structures of DCNO and PCNP were determined by the single-crystal X-ray diffraction (SCXRD) technique. The SCXRD study inferred that cations and anions are strongly packed due to N-H···O, N-H···N, and C-H···O noncovalent interactions in DCNO, whereas in PCNP, N-H···N noncovalent interactions are absent. The noncovalent interactions in both organic crystalline salts were comprehensively investigated by Hirshfeld surface analysis. Further, a detailed density functional theory (DFT) study of both compounds was performed. The optimized structures of both compounds supported the existence of the H-bonding and weak dispersion interactions in the synthesized organic crystalline salt structures. Both compounds were shown to have large and noticeably different HOMO/LUMO energy gaps. The atomic charge analysis results supported the SCXRD and HSA results, showing the formation of intermolecular noncovalent interactions in both organic crystalline salts. The results of the natural bond orbital (NBO) analysis confirmed the existence of (relatively weak) noncovalent interactions between the cation and anion moieties of their organic crystalline salts. The global reactivity parameters (GRPs) analysis showed that both organic crystalline salts' compounds should be quite thermodynamically stable and that DCNO should be less reactive than PCNP. For both compounds, the molecular electrostatic potential (MEP) analysis results support the existence of intermolecular electrostatic interactions in their organic crystalline salts.

4.
J Biomol Struct Dyn ; : 1-11, 2023 Oct 04.
Artículo en Inglés | MEDLINE | ID: mdl-37794772

RESUMEN

Cancer has been recognized as one of the deadliest diseases in the world in recent years. By chemically tailoring specific properties, anticancer agents can be prepared very effectively for the treatment of various cancer types. In this manner, as anticancer agents, a series of soluble metal-free and metallophthalocyanines carrying cinnamyloxy-groups at peripheral ß-positions have been prepared. All synthesized phthalocyanines were characterized by various spectroscopic approaches such as ultraviolet - visible (UV - Vis), Fourier transform infrared (FT-IR), and matrix-assisted laser deionization/ionization time-of-flight mass spectroscopy (MALDI-TOF MS) techniques. These compounds are highly soluble in dimethyl sulfoxide (DMSO) and soluble in common organic solvents. The spectroscopic properties, cytotoxicity, and theoretical calculations of these complexes have been investigated. In cytotoxicity tests, compounds 1, 4, and 7 are the most active against HT-29 cell lines with IC50 values of 36.9 µM, 32.5 µM, and 51.1 µM, respectively. Also, the most and the least cytotoxic compounds against healthy CCD cell line is compounds 5 and 6 with the IC50 value of 13.4 µM and >250 µM, respectively. The PDB ID:4BQG target protein representing the HT-29 cancer cell line and the anti-cancer activities of phthalonitrile and its phthalocyanines were supported by molecular docking studies. Density Functional Theory (DFT) study supported the experimental results, including the spectral data, and implied that the compounds 5-7 are comparable by their characteristics, such as electronic properties, optical properties, electrostatic potentials, reactivity parameters, with the earlier studied compounds 2-4, which were successfully proved to be good candidates for cancer treatment.Communicated by Ramaswamy H. Sarma.

5.
ACS Omega ; 8(32): 29414-29423, 2023 Aug 15.
Artículo en Inglés | MEDLINE | ID: mdl-37599924

RESUMEN

Five new difluorinated biphenyl compounds, 4'-(tert-butyl)-3,4-difluoro-1,1'-biphenyl (TBDFBP), 1-(3',4'-difluoro-[1,1'-biphenyl]-4-yl)ethanone (DFBPE), 3',4'-difluoro-2,5-dimethoxy-1,1'-biphenyl (DFDMBP), 3,4-difluoro-3'-nitro-1,1'-biphenyl (DFNBP), and (3',4'-difluoro-[1,1'-biphenyl]-3-yl)(methyl)sulfane (DFBPMS), have been successfully synthesized by the well-known Suzuki-Miyaura coupling with excellent yields averaging 78%. UV-visible, Fourier transform infrared ,and 13C NMR and 1H NMR spectroscopies along with single-crystal X-ray diffraction (SC-XRD) analysis (for TBDFBP and DFBPE) were used for the structure elucidation of the synthesized compounds. The SC-XRD results demonstrated the crystal systems of the studied compounds, TBDFBP and DFBPE, to be monoclinic, and their space groups were found to be P21/c. Also, a detailed density functional theory study was performed. The calculated structures for TBDFBP and DFBPE were found to agree quite well with the experimental results. The natural bonding orbital charge analysis suggested that molecules of these compounds should interact quite noticeably with each other in the solid phase and with polar solvent molecules. Molecular electrostatic potential analysis suggests that accumulation of positive and negative potential implies possibility of quite significant dipole-dipole intermolecular interactions in crystals of these compounds, as well as quite strong interactions with polar solvent molecules. The global reactivity parameters analysis suggests all compounds to be quite stable in redox reactions, with the compound DFNBP being relatively more reactive and the compounds TBDFBP and DFDMBP being relatively more stable.

6.
ACS Appl Bio Mater ; 5(3): 1139-1150, 2022 03 21.
Artículo en Inglés | MEDLINE | ID: mdl-35239311

RESUMEN

Photodynamic therapy (PDT) applications carried out with the assistance of ultrasound have attracted significant attention in recent years. The use of phthalocyanines, which are an important component as photosensitizers in PDT, is becoming more important day by day. In therapeutic applications, phthalocyanines can promote the production of reactive oxygen species. Motivated by this fact, the syntheses of metal-free (2), gallium (3), and indium (4) phthalocyanines have been achieved by substituting 4-(cinnamyloxy)phthalonitrile for the first time to evaluate their therapeutic applications. Additionally, photophysicochemical, sonophotochemical, and in vitro evaluations of phthalocyanines have been reported. To the best of our knowledge, this is the first study of the use of phthalocyanines with different metal ions as potential photosensitizers for sonophotodynamic therapy (SPDT) applications in gastric cancer cell lines. The results show that the quantum yield of the generation of singlet oxygen increased in sonophotochemical studies (ΦΔ = 0.55 (2), 0.85 (3), 0.96 (4)), compared to photochemical studies (ΦΔ = 0.22 (2), 0.61 (3), 0.78 (4)). The density functional theory (DFT) results are in good agreement with the experimental results and suggest increased reactivity of phthalocyanines 3 and 4 in various redox processes, thus implying their applicability and usefulness as potential therapeutic agents. These phthalocyanines are effective sensitizers for PDT, sonodynamic therapy (SDT), and SPDT against MKN-28 gastric cancer cell line in vitro. All three treatments decreased cell viability and induced apoptosis in the gastric cancer cell line. However, indium phthalocyanine (4)-mediated SPDT was a more effective treatment modality compared to indium phthalocyanine (4)-mediated PDT and SDT. Also, indium phthalocyanine (4) was found to be a more effective sensitizer to activate apoptosis compared to the other phthalocyanines. To sum up, phthalocyanine-mediated SPDT enhances the cytotoxic effect on gastric cancer cells more than the effect of SDT or PDT alone.


Asunto(s)
Fármacos Fotosensibilizantes , Neoplasias Gástricas , Humanos , Indio , Indoles/farmacología , Isoindoles , Modelos Teóricos , Fármacos Fotosensibilizantes/farmacología , Neoplasias Gástricas/tratamiento farmacológico
7.
Biointerphases ; 17(6): 061001, 2022 11 02.
Artículo en Inglés | MEDLINE | ID: mdl-36323527

RESUMEN

RNA-based therapeutics hold a great promise in treating a variety of diseases. However, double-stranded RNAs (dsRNAs) are inherently unstable, highly charged, and stiff macromolecules that require a delivery vehicle. Cationic ligand functionalized gold nanoparticles (AuNPs) are able to compact nucleic acids and assist in RNA delivery. Here, we use large-scale all-atom molecular dynamics simulations to show that correlations between ligand length, metal core size, and ligand excess free volume control the ability of nanoparticles to bend dsRNA far below its persistence length. The analysis of ammonium binding sites showed that longer ligands that bind deep within the major groove did not cause bending. By limiting ligand length and, thus, excess free volume, we have designed nanoparticles with controlled internal binding to RNA's major groove. NPs that are able to induce RNA bending cause a periodic variation in RNA's major groove width. Density functional theory studies on smaller models support large-scale simulations. Our results are expected to have significant implications in packaging of nucleic acids for their applications in nanotechnology and gene delivery.


Asunto(s)
Nanopartículas del Metal , Ácidos Nucleicos , Oro/química , ARN , Nanopartículas del Metal/química , Ligandos , Ácidos Nucleicos/metabolismo
8.
Inorg Chem ; 49(5): 2557-67, 2010 Mar 01.
Artículo en Inglés | MEDLINE | ID: mdl-20128599

RESUMEN

Reactions of the "naked" and MgO(100) supported Zr(2)Pd(2) cluster with nitrogen and four hydrogen molecules were studied at the density functional level using the periodic slab approach (VASP). It was shown that adsorption of the Zr(2)Pd(2) cluster on the MgO(100) surface does not change its gas-phase geometry and electronic structure significantly. In spite of this the N(2) coordination to the MgO(100)-supported Zr(2)Pd(2) cluster, I/MgO, is found to be almost 30 kcal/mol less favorable than for the "naked" one. The addition of the first H(2) molecule to the resulting II/MgO, that is, II/MgO + H(2) --> IV/MgO reaction, proceeds with a relatively small, 9.0 kcal/mol, barrier and is exothermic by 8.3 kcal/mol. The same reaction for the "naked" Zr(2)Pd(2) cluster requires a slightly larger barrier (10.1 kcal/mol) and is highly exothermic (by 23.3 kcal/mol). The interaction of the H(2) molecule with the intermediate IV/MgO (i.e., the second H(2) molecule addition to II/MgO) requires larger energy barrier, 23.3 kcal/mol vs 8.8 kcal/mol for the "naked" cluster, and is exothermic by 20.5 kcal/mol (vs 18.2 kcal/mol reported for the "naked" Zr(2)Pd(2) cluster). The addition of the H(2) molecule to VI/MgO and VI (i.e., the third H(2) molecule addition to II/MgO and II, respectively) requires similar barriers, 12.0 versus 16.8 kcal/mol, respectively, but is highly exothermic for the supported cluster compared to the "naked" one, 13.6 versus 0.1 kcal/mol. The addition of the fourth H(2) molecule occurs with almost twice larger barrier for the "naked" cluster compared to the adsorbed species, 30.7 versus 15.9 kcal/mol. Furthermore, this reaction step is endothermic (by 11.4 kcal/mol) for the gas-phase cluster but exothermic by 7.8 kcal/mol for the adsorbed cluster. Dissociation of the formed hydrazine molecule from the on-surface complex X/MgO and the "naked" complex X requires 19.1 and 26.3 kcal/mol, respectively. Thus, the Zr(2)Pd(2) adsorption on the MgO(100) surface facilitates its reaction with N(2) and four H(2) molecules, as well as formation of hydrazine from the hydrogen and nitrogen molecules. The reported differences in the reactivity of the "naked" and MgO adsorbed Zr(2)Pd(2) clusters were explained by analyzing the nature of the H(2) addition steps in these systems.


Asunto(s)
Hidrógeno/química , Óxido de Magnesio/química , Nitrógeno/química , Paladio/química , Teoría Cuántica , Circonio/química , Catálisis , Hidrogenación , Modelos Moleculares , Conformación Molecular , Propiedades de Superficie
9.
J Phys Chem A ; 114(43): 11417-24, 2010 Nov 04.
Artículo en Inglés | MEDLINE | ID: mdl-20925417

RESUMEN

To probe photoinduced water oxidation catalyzed by the Mn4O4L6 cubane clusters, we have computationally studied the mechanism and controlling factors of the O2 formation from the [Mn4O4L6] catalyst, 6. It was demonstrated that dissociation of an L = H2PO2⁻ ligand from 6 facilitates the direct O-O bond formation that proceeds with a 28.3 (33.4) kcal/mol rate-determining energy barrier at the transition state TS1. This step (the O-O single bond formation) of the reaction is a two-electron oxidation/reduction process, during which two oxo ligands are transformed into to µ²:η²-O2²â» unit, and two ("distal") Mn centers are reduced from the 4+ to the 3+ oxidation state. Next two-electron oxidation/reduction occurs by "dancing" of the resulted O2²â» fragment between the Mn¹ and Mn²/Mn(2')-centers, keeping its strong coordination to the Mn(1')-center. As a result of this four-electron oxidation/reduction process Mn centers of the Mn4-core of I transform from {Mn¹(III)-Mn(1')(III)-Mn²(IV)-Mn(2')(IV)} to {Mn¹(II)-Mn(1')(II)-Mn²(III)-Mn(2')(III)} in IV. In other words, upon O2 formation in cationic complex [Mn4O4L5](+), I, all four Mn-centers are reduced by one electron each. The overall reaction I → TS1 → II → III → TS2 → IV → TS3 → V → VI + O2 is found to be exothermic by 15.4 (10.5) kcal/mol. We analyze the lowest spin states and geometries of all reactants, intermediates, transition states, and products of the targeted reaction.

10.
J Phys Chem A ; 114(1): 535-42, 2010 Jan 14.
Artículo en Inglés | MEDLINE | ID: mdl-19957979

RESUMEN

Geometry and electronic structure of five species [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](10-) (1), [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](9-) (2), [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](8-) (3), [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](7-) (4), and [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](6-) (5) with different oxidation states of Ru centers were studied at the density functional and COSMO levels of theory. These species are expected to be among the possible intermediates of the recently reported 1-catalyzed water oxidation (Geletii, Y. V.; Botar, B.; Kogerler, P.; Hillesheim, D. A.; Musaev, D. G.; Hill, C. L. Angew. Chem. Int. Ed. 2008, 47, 3896-3899 and Sartorel, A.; Carraro, M.; Scorrano, G.; Zorzi, R. D.; Geremia, S.; McDaniel, N. D.; Bernhard, S.; Bonchio, M. J. Am. Chem. Soc. 2008, 130, 5006-5007). It was shown that RI-BP86 correctly describes the geometry and energy of the low-lying electronic states of compound 1, whereas the widely used B3LYP approach overestimates the energy of its high-spin states. Including the solvent and/or countercation effects into calculations improves the agreement between the calculated and experimental data. It was found that the several HOMOs and LUMOs of the studied complexes are bonding and antibonding orbitals of the [Ru(4)O(4)(OH)(2)(H(2)O)(4)](6+) core, and four subsequent one-electron oxidations of 1, leading to formation of 2, 3, 4, and 5, respectively, involve only {Ru(4)} core orbitals. In other words, catalyst instability due to ligand oxidation in the widely studied Ru-blue dimer, [(bpy)(2)(O)Ru(V)-(mu-O)-Ru(V)(O)(bpy)(2)](4+), is not operable for 1: the latter all-inorganic catalyst is predicted to be stable under water oxidation turnover conditions. The calculated HOMOs and LUMOs of all the studied species are very close in energy and exhibit a "quasi-continuum" or "nanoparticle-type" electronic structure similar to that of nanosized transition metal clusters. This conclusion closely correlates with the experimentally reported oxidation and reduction features of 1 and explains the unusual linear dependence of oxidation potential versus charges for these compounds. The decrease in total negative charge of the system via 1 > 2 > 3 > 4 > 5, on average, decreases the {Ru(4)}-{SiW(10)} distance. It is predicted that at higher pH compound 1 will, initially, release protons from the mu-O(Ru) oxygen centers.

11.
J Am Chem Soc ; 131(19): 6844-54, 2009 May 20.
Artículo en Inglés | MEDLINE | ID: mdl-19388697

RESUMEN

Dioxygen and water activation on multi-Ru-substituted polyoxometalates were studied using the B3LYP density functional method. It was shown that the reaction of the Ru(2)-substituted gamma-Keggin polyoxotungstate {gamma-[(H(2)O)Ru(III)-(mu-OH)(2)-Ru(III)(H(2)O)][SiW(10)O(36)]}(4-), I(H(2)O), with O(2) is a 4-electron highly exothermic [DeltaE(gas) = 62.5 (DeltaE(gas) + DeltaG(solv(water)) = 24.6) kcal/mol] process and leads to formation of (H(2)O){gamma-[(O)Ru-(mu-OH)(2)-Ru(O)](H(2)O)[SiW(10)O(36)]}(4-), IV(H(2)O). Both the stepwise (or dissociative) and the concerted (or associative) pathways of this reaction occurring with and without water dissociation, respectively, were examined, and the latter has been found to be kinetically more favorable. It was shown that the first 1e-oxidation is achieved by the H(2)O-to-O(2) substitution, which might occur with a maximum of 23.1 (10.5) kcal/mol barrier and leads to the formation of {gamma-[(OO)Ru-(mu-OH)(2)-Ru(H(2)O)](H(2)O)[SiW(10)O(36)]}(4-), II(H(2)O). The second 1e-oxidation is initiated by the proton transfer from the coordinated water molecule to the superoxide (OO(-)) ligand in II(H(2)O) and is completed upon formation of hydroperoxo-hydroxo intermediate {gamma-[(OOH)Ru-(mu-OH)(2)-Ru(OH)](H(2)O)[SiW(10)O(36)]}(4-), III-1(H(2)O). The final 2e-oxidation occurs upon the proton transfer from the terminal OH-ligand to the Ru-coordinated OOH fragment and is completed at the formation of (H(2)O)...{gamma-[(O)Ru-(mu-OH)(2)-Ru(O)](H(2)O)[SiW(10)O(36)]}(4-), IV(H(2)O), with two Ru=O bonds. Each step in the associative pathway is exothermic and occurs with small energy barriers. During the process, the oxidation state of Ru centers increases from +3 to +4. The resulting IV(H(2)O) with a {Ru(O)-(mu-OH)(2)-Ru(O)} core should be formulated to have the Ru(IV)=O(*) units, rather than the Ru(V)=O groups. The reverse reaction, water oxidation by IV(H(2)O), is found to be highly endothermic and cannot occur; this finding is different from that reported for the "blue-dimer" intermediate, {(bpy)(2)[(O(*))Ru-(mu-O)-Ru(O(*))](bpy)(2)}(4+), which readily oxidized an incoming water molecule to produce O(2). The main reason for this difference in reactivity of IV(H(2)O) (i.e., Ru(2)-POM) and the "blue-dimer" intermediates toward the water molecule is found to be a high stability of IV(H(2)O) as compared to the analogous "blue-dimer" intermediate relative to O(2) formation. This, in turn, derives from the electron-rich nature of [SiW(10)O(36)](4-) as compared to bpy ligands.

12.
Inorg Chem ; 48(5): 1871-8, 2009 Mar 02.
Artículo en Inglés | MEDLINE | ID: mdl-19235950

RESUMEN

The mechanisms of olefin epoxidation by hydrogen peroxide catalyzed by [gamma-1,2-H(2)SiV(2)W(10)O(40)](4-), 1, were studied using the density functional (B3LYP) approach in conjunction with large basis sets. The role of solvent is taken into account via both including an explicit water molecule into the calculations and using the polarizable continuum model (PCM) with acetonitrile as a solvent (numbers given in parentheses). The countercation effect (using one molecule of Me(4)N(+) as a countercation (1CC)) is also taken into account (numbers given in brackets). It was shown that the formation of the vanadium-hydroperoxo species 2(H(2)O) with an {OV-(mu-OOH)(mu-OH)-VO}(H(2)O) core from 1 and H(2)O(2) is a very facile process. The resulting complex 2(H(2)O) may eliminate a water molecule and form complex 2. From the intermediates 2 and 2(H(2)O), reaction may proceed via two distinct pathways: "hydroperoxo" and "peroxo". The water-assisted "hydroperoxo" pathway starts with coordination of olefin (C(2)H(4)) to 2(H(2)O) and proceeds with a 36.8(25.5)[31.7][(21.6)] kcal/mol rate-determining barrier at the O-atom transfer transition state TS2[TS2(1CC)]. The "water-free peroxo" and "water-assisted peroxo" pathways start with rearrangement of 2 and 2(H(2)O) to vanadium-peroxo species 3 and 3(H(2)O), respectively, with an {OV-(eta(2)-O(2))-VO} core, and follow the O-atom transfer from catalyst to olefin. The 2 --> 3 and 2(H(2)O) --> 3(H(2)O) hydroperoxo --> peroxo rearrangement processes require 16.8(13.0)[13.0][(11.1)] and 14.2(9.0)[1.3][(7.2)] kcal/mol of energy, respectively. The calculated overall energy barriers are 28.1(19.1)[23.8][(17.2)] and 25.4(11.0)[10.6][(13.0)] kcal/mol for "water-free peroxo" and "water-assisted peroxo" pathways, respectively. On the basis of these data we predict that the [gamma-1,2-H(2)SiV(2)W(10)O(40)](4-)-catalyzed olefin epoxidation by H(2)O(2) most likely occurs via a "water-assisted peroxo" pathway.

13.
J Phys Chem B ; 123(47): 10044-10060, 2019 11 27.
Artículo en Inglés | MEDLINE | ID: mdl-31687817

RESUMEN

Numerous metalloporphyrin stacks have been synthesized and studied. Electronic interactions between constituent metalloporphyrins are able to determine the structures and properties of porphyrin arrays. In 2016, Co(II)-, Cu(II)-, Pt(II)-, and Zn(II)-porphyrins were shown to pack to form dimers as well as trimers. Porphyrin rings were found to strongly overlap with lateral shifts between ring centers. However, no binding energies and electronic structures of these stacks have been reported. We have performed first computational study of the dimers of Co(II)-, Cu(II)-, and Zn(II)-porphyrins, both in vacuum and in two implicit solvents. For all three stacks the configurations with strong overlap of the metalloporphyrin rings with lateral shifts between ring centers were found to be the global minimum structures, 1A for [ZnP]2 and 3A for [CuP]2 and [CoP]2. Also, open-shell singlets with the same energy or close-lying in energy were found for [CuP]2 and [CoP]2. The binding energies were calculated to be significant, from ca. -13 to -39 kcal/mol (gas phase, depending on the computational approach). The computational results showed quite good agreement with the experimental data. The dimers were found to be bound by strong bonding combinations of the monomer MOs which explained significant binding energies computed for the dimers. The shifted dimer configurations could be explained by the way how the monomer MOs preferably overlap.

14.
RSC Adv ; 9(9): 5091-5099, 2019 Feb 05.
Artículo en Inglés | MEDLINE | ID: mdl-35514619

RESUMEN

Size-tunability of the electronic and optical properties of semiconductor quantum dots and nanoclusters is due to the quantum size effect, which causes variations in the electronic excitations as the particle boundaries are changed. Recently, CdSe and CdTe quantum dots have been used in energy harvesting devices. Despite these promising practical applications, a complete understanding of the electronic transitions associated with the surfaces of the nanoparticles is currently lacking and is difficult to achieve experimentally. Computational methods could provide valuable insights and allow us to understand the electronic and optical properties of quantum dots and nanoclusters. Hollow cage and endohedral or core-shell cage structures for Cd n Te n clusters have been reported before. We have performed systematic density functional theory (DFT) studies on the structure and electronic properties of the Cd n Te n (n = 1-17) clusters. As the number of atoms increases in the Cd n Te n clusters, the predicted geometries change from simple planar structures to more complicated 3D-structures. Two classes of the most stable structures were elucidated for clusters with n = 10-17: (i) hollow cage structures with an empty center; and (ii) endohedral or core-shell cage structures with one or more atoms inside the cage. Noticeably higher highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps were observed for the hollow cage isomers as compared to the core-shell structures. The highest occupied molecular orbitals of all of the clusters studied were shown to be localized on the surface of the cage for the hollow cage structures, while in the case of the core-shell structures, the HOMO electron densities were found to be distributed both on surface and the interior of the structures. Most of the small size clusters Cd n Te n (n = 2-9) showed minimal values for the dipole moments (close to zero) owing to the highly ordered and symmetric configurations of these structures. For isomers of the larger clusters (n = 10-17), it was observed that the core-shell structures have higher values for the dipole moments than the hollow cage species because of the highly symmetric structures of the hollow cages. Core-shell cage structures exhibited lower polarizability than the respective hollow cage structures.

15.
Comput Theor Chem ; 981: 73-85, 2012 Feb 01.
Artículo en Inglés | MEDLINE | ID: mdl-23560251

RESUMEN

Using density functional theory, we have studied the effects on structural and electronic consequences (including HOMO-LUMO energy gaps, vertical ionization potentials (IPv), and vertical electron affinities (EAv)) of the following two factors: (a) meso- and ß-substituents acting as inductive donors (CH3), inductive acceptors that are electron-donating through resonance (Br), inductive electron acceptors (CF3), and resonance enabled acceptors (NO2); and (b) complete replacement of pyrrole nitrogens with P-atoms. The principal results of the study are: (1) For the bare Ni-porphyrin, the solvents were found not to affect the HOMO-LUMO gaps but to change the IPv and EAv noticeably. (2) In the series CH3 → Br → CF3 → NO2 the HOMO-LUMO energy gaps, IPv, and EAv increase for both meso- and ß-substituents. The ruffling distortion of the porphyrin core is retained, and becomes stronger for the two acceptor groups. In general, effects of meso-substituents on the ruffling distortion of the porphyrin core is more pronounced. (3) Most significantly, complete replacement of pyrrole nitrogens in the NiP with phosphorus atoms produces the species, NiP(P)4, with the structural and electronic features drastically different from the original NiP. This implies that NiP(P)4 can possess interesting and unusual novel properties, including aromaticity and reactivity, leading to its various beneficial potential applications. Furthermore, NiP(P)4 high stability both in the gas phase and different solvents was shown, implying the feasibility of its synthesis.

16.
Science ; 328(5976): 342-5, 2010 Apr 16.
Artículo en Inglés | MEDLINE | ID: mdl-20223949

RESUMEN

Traditional homogeneous water oxidation catalysts are plagued by instability under the reaction conditions. We report that the complex [Co4(H2O)2(PW9O34)2]10-, comprising a Co4O4 core stabilized by oxidatively resistant polytungstate ligands, is a hydrolytically and oxidatively stable homogeneous water oxidation catalyst that self-assembles in water from salts of earth-abundant elements (Co, W, and P). With [Ru(bpy)3]3+ (bpy is 2,2'-bipyridine) as the oxidant, we observe catalytic turnover frequencies for O2 production > or = 5 s(-1) at pH = 8. The rate's pH sensitivity reflects the pH dependence of the four-electron O2-H2O couple. Extensive spectroscopic, electrochemical, and inhibition studies firmly indicate that [Co4(H2O)2(PW9O34)2]10- is stable under catalytic turnover conditions: Neither hydrated cobalt ions nor cobalt hydroxide/oxide particles form in situ.

19.
Inorg Chem ; 41(3): 532-7, 2002 Feb 11.
Artículo en Inglés | MEDLINE | ID: mdl-11825080

RESUMEN

We have recently advanced the aromaticity concept into all-metal molecules containing Al(4)(2-), XAl(3)(-), Ga(4)(2-), In(4)(2-), Hg(4)(6-), Al(3)(-), and Ga(3)(-) aromatic units. All these systems are electron deficient species compared to the corresponding aromatic hydrocarbons. The electron deficiency results in an interesting new feature in all-metal aromatic systems, which should be considered as having both pi- and sigma-aromaticity, and that should result in their additional stability. In this work, we obtain crude evaluations of the resonance energies for Na(2)Al(4) and Na(2)Ga(4) all-metal aromatic molecules. The resonance energies were found to be unusually high: 30 kcal/mol (B3LYP/6-311+G*) and 48 kcal/mol (CCSD(T)/6-311+G(2df)) for Na(2)Al(4) and 21 kcal/mol (B3LYP/6-311+G*) for Na(2)Ga(4) compared to 20 kcal/mol in benzene. We believe that the high resonance energies in Na(2)Al(4) and in Na(2)Ga(4) are due to the presence of three completely delocalized bonds, one pi-bond and two sigma-bonds, thus confirming the presence of pi- and sigma-aromaticity.

20.
Inorg Chem ; 41(14): 3596-8, 2002 Jul 15.
Artículo en Inglés | MEDLINE | ID: mdl-12099859

RESUMEN

We analyzed the molecular orbitals for a Al(4)Cl(4)(NH(3))(4) compound, which is a model of the (AlBr x NEt(3))(4) crystal structure recently reported by Schnöckel and co-workers. We found that even though Al(4)Cl(4)(NH(3))(4) contains a planar square Al(4) cluster it is not an aromatic compound. However, the addition of two sodium atoms to Al(4)Cl(4)(NH(3))(4) yields a new Na(2)Al(4)Cl(4)(NH(3))(4) compound which is a pi-aromatic molecule. We hope that prediction of this new compound will facilitate a synthesis of aluminum aromatic solids.

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