Self-Assembly of Supramolecular Double Helix from a Tetrapeptide and Direct Visualization by Scanning Tunneling Microscopy.

This work reports single-crystal X-ray diffraction (XRD), Scanning Tunneling Microscopy (STM), and quantum mechanics calculations of the 3-helical peptide Z-(Aib)-L-Dap(Boc)-Aib-NHiPr (Aib, α-aminoisobutyric acid; Dap, 2,3-diaminopropionic acid; Z, benzyloxycarbonyl; Boc, t-butoxycarbonyl). The peptide forms a double-helical superstructure, studied by XRD and STM. Such architecture is rare in short peptides.

Sandwich d/f Heterometallic Complexes [(Ln(hfac))M(acac)] (Ln = La, Pr, Sm, Dy and M = Co; Ln = La and M = Ru).

Sandwich d/f heterometallic complexes [(Ln(hfac))M(acac)] (Ln = La, Pr, Sm, Dy and M = Co; Ln = La and M = Ru) were prepared in strictly anhydrous conditions reacting the formally unsaturated fragment [Ln(hfac)] and [M(acac)] in a 2-to-1 molar ratio. These heterometallic complexes are highly sensitive to moisture. Spectroscopic observation revealed that on hydrolysis, these compounds yield dinuclear heterometallic compounds [Ln(hfac)M(acac)], prepared here for comparison purposes only.

Understanding Stabilization Factors in Heterodinuclear Ln-Al Complexes from DFT Simulations on Thermochemistry Data: A Counterintuitive Conclusion.

This study validates a computational protocol to predict the stability of heterodinuclear complexes by varying ligands on both moieties and analyzing the reaction Gibbs free energy (Δ) values. To this purpose, a series of Eu-Al complexes with the general formula [Eu()Al()], where is the ligand of europium and is an oxygen donor ligand of aluminum, is used. The nature of the bridging bonds and thermochemical characteristics (Δ, enthalpy, and entropy) of the complexes were evaluated via DFT calculations.

Aluminium 8-Hydroxyquinolinate -Oxide as a Precursor to Heterometallic Aluminium-Lanthanide Complexes.

A reaction in anhydrous toluene between the formally unsaturated fragment [Ln(hfac)] (Ln = Eu, Gd and Er; Hhfac = hexafluoroacetylacetone) and [Al(qNO)] (HqNO = 8-hydroxyquinoline -oxide), here prepared for the first time from [Al(OBu)] and HqNO, affords the dinuclear heterometallic compounds [Ln(hfac)Al(qNO)] (Ln = Eu, Gd and Er) in high yields. The molecular structures of these new compounds revealed a dinuclear species with three phenolic oxygen atoms bridging the two metal atoms. While the europium and gadolinium complexes show the coordination number (CN) 9 for the lanthanide centre, in the complex featuring the smaller erbium ion, only two oxygens bridge the two metal atoms for a resulting CN of 8.

A local point of view of the Cu(100) → NiTPP charge transfer at the NiTPP/Cu(100) interface.

A precise understanding, at the molecular level, of the massive substrate → adsorbate charge transfer at the NiTPP/Cu(100) interface has been gained through the application of elementary symmetry arguments to the structural determination of the NiTPP adsorption site by photoelectron diffraction (PED) measurements and Amsterdam density functional calculations of the free NiTPP electronic structure. In particular, the PED analysis precisely determines that, among the diverse NiTPP chemisorption sites herein considered (fourfold hollow, atop, and bridge), the fourfold hollow one is the most favorable, with the Ni atom located at 1.93 Å from the surface and at an internuclear distance of 2.

Correction: The reaction of acetonitrile with hydrogen peroxide in alkaline medium: a DFT mechanistic study of green production of amides.

Correction for 'The reaction of acetonitrile with hydrogen peroxide in alkaline medium: a DFT mechanistic study of green production of amides' by Girolamo Casella , , 2023, https://doi.org/10.1039/d3cp02024j.

The reaction of acetonitrile with hydrogen peroxide in alkaline medium: a DFT mechanistic study of green production of amides.

We have investigated using DFT methods the reaction mechanism of the Radzisewski reaction to obtain an amide the reaction of ACN and HO under alkaline conditions. The direct reaction between ACN and HO showed a quite high activation energy (about 45 kcal mol) rendering this path unreliable. Instead, a fast reaction between ACN and HOO forming the deprotonated species (PAIA-) of the peroxyacetimidic acid (PAIA) was observed.

Competing excitation paths in luminescent heterobimetallic Ln-Al complexes: Unraveling interactions via experimental and theoretical investigations.

The interest for heterometallic lanthanide- or- metal (Ln-M) complexes is growing because of a potential cooperative or synergistic effect related to the proximity of two different metals in the same molecular architecture affording special tunable physical properties. To exploit the potentiality of Ln-M complexes, suitable synthetic approaches, and the in-depth understanding of the effect of each building block on their properties are mandatory. Here, we report the study on a family of heterometallic luminescent complexes [Ln(hfac)Al(L)], Ln= Eu and Tb.

Cyclo- and Polyphosphazenes for Biomedical Applications.

Cyclic and polyphosphazenes are extremely interesting and versatile substrates characterized by the presence of -P=N- repeating units. The chlorine atoms on the P atoms in the starting materials can be easily substituted with a variety of organic substituents, thus giving rise to a huge number of new materials for industrial applications. Their properties can be designed considering the number of repetitive units and the nature of the substituent groups, opening up to a number of peculiar properties, including the ability to give rise to supramolecular arrangements.

Helicate versus Mesocate in Quadruple-Stranded Lanthanide Cages: A Computational Insight.

To drive the synthesis of metallo-supramolecular assemblies (MSAs) and to fully exploit their functional properties, robust computational tools are crucial. The capability to model and to rationalize different parameters that can influence the outcome is mandatory. Here, we report a computational insight on the factors that can determine the relative stability of the supramolecular isomers helicate and mesocate in lanthanide-based quadruple-stranded assemblies.

The Magnetic Behaviour of CoTPP Supported on Coinage Metal Surfaces in the Presence of Small Molecules: A Molecular Cluster Study of the Surface -Effect.

Density functional theory, combined with the molecular cluster model, has been used to investigate the surface -effect induced by the coordination of small molecules L (L = CO, NH, NO, NO and O) on the cobalt electronic structure of cobalt tetraphenylporphyrinato (CoTPP) surface-supported on coinage metal surfaces (Cu, Ag, and Au). Regardless of whether L has a closed- or an open-shell electronic structure, its coordination to Co takes out the direct interaction between Co and the substrate eventually present. The CO and NH bonding to CoTPP does not influence the Co local electronic structure, while the NO (NO and O) coordination induces a Co reduction (oxidation), generating a 3d Co (3d Co) magnetically silent closed-shell species.

-[(η-CH)Fe(η-CO)(μ-CO)], the poor relative between and tautomers. A theoretical study of the gas-phase Fe L-edge and C and O K-edge XAS of -/-[(η-CH)Fe(η-CO)(μ-CO)].

The relative stability of -[(η-CH)Fe(η-CO)(μ-CO)] (-I) and -I tautomers in a vacuum and in solvents with different dielectric constants () has been investigated by exploiting density functional theory (DFT). Theoretical results indicate that, in agreement with experimental evidence, -I is more stable than -I in a vacuum (∼1.5 kcal mol; = 1), while the opposite is true in media with > 7.

Nature of the Ligand-Centered Triplet State in Gd β-Diketonate Complexes as Revealed by Time-Resolved EPR Spectroscopy and DFT Calculations.

A series of Gd complexes (-) with the general formula GdL(EtOH), where L is a β-diketone ligand with polycyclic aromatic hydrocarbon substituents of increasing size (-), was studied by combining time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy and DFT calculations to rationalize the anomalous spectroscopic behavior of the bulkiest complex () through the series. Its faint phosphorescence band is observed only at 80 K and it is strongly red-shifted (∼200 nm) from the intense fluorescence band. Moreover, the TR-EPR spectral analysis found that triplet levels of / are effectively populated and have smaller || values than those of the other compounds.

A Theoretical Study of the Occupied and Unoccupied Electronic Structure of High- and Intermediate-Spin Transition Metal Phthalocyaninato (Pc) Complexes: VPc, CrPc, MnPc, and FePc.

The structural, electronic, and spectroscopic properties of high- and intermediate-spin transition metal phthalocyaninato complexes (MPc; M = V, Cr, Mn and Fe) have been theoretically investigated to look into the origin, symmetry and strength of the M-Pc bonding. DFT calculations coupled to the Ziegler's extended transition state method and to an advanced charge density and bond order analysis allowed us to assess that the M-Pc bonding is dominated by interactions, with FePc having the strongest and most covalent M-Pc bond. According to experimental evidence, the lightest MPcs (VPc and CrPc) have a high-spin ground state (GS), while the MnPc and FePc GS spin is intermediate.

Multireference Investigation on Ground and Low-Lying Excited States: Systematic Evaluation of - Mixing in a Eu Luminescent Complex.

A theoretical protocol combining density functional theory (DFT) and multireference (CAS) calculations is proposed for a Eu complex. In the complex, electronic levels of the central Eu ion are correctly calculated at the CASPT2 level of theory, and the effect of introducing different numbers of states in the configuration interaction matrices is highlighted as well as the shortcomings of DFT methods in the treatment of systems with high spin multiplicity and strong spin-orbit coupling effects. For the D state energy calculation, the inclusion of states with different multiplicity and the number of states considered for each multiplicity are crucial parameters, even if their relative weight is different.

Ferrous to Ferric Transition in Fe-Phthalocyanine Driven by NO Exposure.

Due to its unique magnetic properties offered by the open-shell electronic structure of the central metal ion, and for being an effective catalyst in a wide variety of reactions, iron phthalocyanine has drawn significant interest from the scientific community. Nevertheless, upon surface deposition, the magnetic properties of the molecular layer can be significantly affected by the coupling occurring at the interface, and the more reactive the surface, the stronger is the impact on the spin state. Here, we show that on Cu(100), indeed, the strong hybridization between the Fe d-states of FePc and the sp-band of the copper substrate modifies the charge distribution in the molecule, significantly influencing the magnetic properties of the iron ion.

Antenna triplet DFT calculations to drive the design of luminescent Ln complexes.

Density functional theory-based methods have been exploited to look into the structural, vibrational and electronic properties of antenna ligands, all of them being crucial factors for the reliable design of customized luminescent lanthanide (Ln3+) complexes. The X-ray structures, UV-Vis absorption spectra and triplet (T1) energies of three novel β-diketone ligands with a thienyl group and naphthyl (L1), phenanthryl (L2), and pyrenyl (L3) polycyclic aromatic hydrocarbons as substituents have been modelled. Vibronic progressions provide a strong contribution to the L1 and L2 absorption spectra, while the L3 absorption spectrum needs the assumption of different conformational isomers in solution.

On-surface synthesis of extended linear graphyne molecular wires by protecting the alkynyl group.

In this paper we report on the use of an Ullmann-like aryl halide homocoupling reaction to obtain long Graphyne Molecular Wires (GY MWs) organized in dense, ordered arrays. Instead of using highly reactive terminal alkynes, we resort to a precursor wherein the acetylenic functional group is internal, namely protected by two phenyl rings, each bearing a Br atom in the para position to allow for linear homocoupling. In addition, two further factors concur with the production of dense and highly ordered arrays of very long GY MWs, namely the geometric compatibility between the substrate and both the organometallic intermediates and the final polymeric products of the synthesis, coupled with the presence of surface-adsorbed bromine atoms separating the MWs, which minimize inter-wire cross-linking secondary reactions.

Comparative Experimental and Theoretical Study of the C and O K-Edge X-ray Absorption Spectroscopy in Three Highly Popular, Low Spin Organoiron Complexes: [Fe(CO)], [(η-CH)Fe(CO)(μ-CO)], and [(η-CH)Fe].

The unoccupied electronic structures of three closed-shell, highly popular organoiron complexes ([Fe(CO)], [(η-CH)Fe(CO)(μ-CO)], and [(η-CH)Fe]; , , and , respectively) have been investigated both experimentally and theoretically by combining original gas-phase X-ray absorption spectroscopy (XAS) outcomes recorded at the C and O K-edge with results of scalar relativistic time-dependent density functional calculations carried out within the zeroth order regular approximation. Experimental evidence herein discussed complement the Fe L-edges XAS ones we recently recorded, modeled, and assigned for the same complexes (Carlotto et al. 2019, 58, 5844).

Coordinative unsaturated Cu entities are crucial intermediates governing cell internalization of copper. A combined experimental ESI-MS and DFT study.

Model peptides relevant to hCtr1 transchelate CuI from the anti-tumour [CuI(PTA)] complex before metal internalization into tumor cells. ESI(+)MS experiments corroborated by DFT calculations indicate that tetracoordinated-Cu and linear-Cu arrangements of in situ generated copper-peptide products play a crucial role in promoting the transfer of copper from the terminal MDH portion into adjacent HSH peptide sequence.

Correction: New light on an old debate: does the RCN-PtCl bond include any back-donation? RCN ← PtCl backbonding vs. the IR ν blue-shift dichotomy in organonitriles-platinum(ii) complexes. A thorough density functional theory - energy decomposition analysis study.

Correction for 'New light on an old debate: does the RCN-PtCl bond include any back-donation? RCN ← PtCl backbonding vs. the IR ν blue-shift dichotomy in organonitriles-platinum(ii) complexes. A thorough density functional theory - energy decomposition analysis study' by Girolamo Casella et al.

New light on an old debate: does the RCN-PtCl bond include any back-donation? RCN←PtCl backbonding vs. the IR ν blue-shift dichotomy in organonitriles-platinum(ii) complexes. A thorough density functional theory - energy decomposition analysis study.

For a series of organonitrile [RCN (R = Me, CF, Ph, CHPh, CFPh)] ligands, the nature of the N-Pt bond in the related cis-/trans-(RCN)PtCl complexes has been computationally investigated by Density Functional Theory. A fragment based bond analysis has been performed in the canonical Kohn-Sham molecular orbitals framework, and it has been ultimately assessed that this bond is characterized both by N→Pt σ and by N←Pt π contributions. Voronoi Deformation Density charges further confirms the occurrence of N←Pt π interactions.

Comparative Experimental and Theoretical Study of the Fe L-Edges X-ray Absorption Spectroscopy in Three Highly Popular, Low-Spin Organoiron Complexes: [Fe(CO)], [(η-CH)Fe(CO)(μ-CO)], and [(η-CH)Fe].

The occupied and unoccupied electronic structures of three highly popular, closed shell organoiron complexes ([Fe(CO)], [(η-CH)Fe(CO)(μ-CO)], and [(η-CH)Fe]) have been theoretically investigated by taking advantage of density functional theory (DFT) calculations coupled to the isolobal analogy ( Elian et al. Inorg. Chem.

Substrate involvement in dioxygen bond dissociation catalysed by iron phthalocyanine supported on Ag(100).

Dioxygen adsorbs in the end-on configuration on-top of the Fe atoms of an iron phthalocyanine monolayer supported on Ag(100) and is partly cleaved at room temperature to produce O/FePc/Ag(100). Scanning tunnelling microscopy coupled to density functional theory calculations gives the first experimental evidence of the substrate involvement in the O2 bond dissociation.

Theoretical Investigation of the Electronic Properties of Three Vanadium Phthalocyaninato (Pc) Based Complexes: PcV, PcVO, and PcVI.

The electronic properties of three vanadium phthalocyaninato (Pc) based complexes (PcV, PcVO, and PcVI; I-III, respectively) were theoretically investigated and corresponding L-edge XAS spectra modeled. Ground state (GS) DFT outcomes indicated that II is more stable than III by 141 kcal/mol; moreover, the Ziegler transition state method allowed us to estimate the PcV-X bond dissociation energy and to quantify σ/π contributions to the V-X interaction. As such, the Nalewajski-Mrozek V-X and V-N bond multiplicity indexes (V-O/V-I = 2.