Second-Row Transition-Metal Doping of (ZniSi), i = 12, 16 Nanoclusters: Structural and Magnetic Properties

TM@ZniSi nanoclusters have been characterized by means of the Density Functional Theory, in which Transition Metal (TM) stands from Y to Cd, and i = 12 and 16. These two nanoclusters have been chosen owing to their highly spheroidal shape which allow for favored endohedral structures as compared to other nanoclusters. Doping with TM is chosen due to their magnetic properties. In similar cluster-assembled materials, these magnetic properties are related to the Transition Metal-Transition Metal (TM-TM) distances. At this point, endohedral doping presents a clear advantage over substitutional or exohedral doping, since in the cluster-assembled materials, these TM would occupy the well-fixed center of the cluster, providing in this way a better TM-TM distance control to experimentalists. In addition to endohedral compounds, surface structures and the TS’s connecting both isomers have been characterized. In this way the kinetic and thermal stability of endohedral nanoclusters is predicted. We anticipate that silver and cadmium endohedrally doped nanoclusters have the longest life-times. This is due to the weak interaction of these metals with the cage, in contrast to the remaining cases where the TM covalently bond to a region of the cage. The open-shell electronic structure of Ag provides magnetic properties to Ag@ZniSi clusters. Therefore, we have further characterized (Ag@Zn12S12)2 and (Ag@Zn16S16)2 dimers both in the ferromagnetic and antiferromagnetic state, in order to calculate the corresponding magnetic exchange coupling constant, J.This research was funded by Eusko Jaurlaritza (the Basque Government), and the Spanish Office for Scientific Research. The SGI/IZO-SGIker UPV/EHU (supported by Fondo Social Europeo and MCyT) is gratefully acknowledged for generous allocation of computational resources. JMM would like to thank Spanish Ministry of Science and Innovation for funding through a Ramon y Cajal fellow position (RYC 2008-03216). We thanks Elixabete Rezabal for cheerful discussion

Ru-Catalyzed C-H Hydroxylation of Tyrosine-Containing Di- and Tripeptides toward the Assembly of L-DOPA Derivatives

[EN] The development of catalytic tools for the late-stage modification of amino acids within a peptide framework is a challenging task of capital importance. Herein, we report a Ru-catalyzed C(sp(2))-H hydroxylation of a collection of Tyr-containing di- and tripeptides featuring the use of a carbamate as a removable directing group and PhI(OCOCF3)(2) (PIFA) as oxidant. This air-compatible tagging technique is reliable, scalable and provides access to L-DOPA (L-3,4-dihydroxyphenylalanine) peptidomimetics in a racemization-free fashion. Density Functional Theory calculations support a Ru(II)/Ru(IV) catalytic cycle.We are grateful to Ministerio de Ciencia e Innovacion (RTI2018-093721-B-I00, MCI/AEI/FEDER, UE) and Basque Government (IT1033-16 and IT1254-19) for financial support. We thank for technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF). P. A.-S. thanks DIPC for the research contract

Theoretical Characterization of New Frustrated Lewis Pairs for Responsive Materials

In recent years, responsive materials including dynamic bonds have been widely acclaimed due to their expectation to pilot advanced materials. Within these materials, synthetic polymers have shown to be good candidates. Recently, the so-called frustrated Lewis pairs (FLP) have been used to create responsive materials. Concretely, the activation of diethyl azodicarboxylate (DEAD) by a triphenylborane (TPB) and triphenylphosphine (TPP) based FLP has been recently exploited for the production of dynamic cross-links. In this work, we computationally explore the underlying dynamic chemistry in these materials, in order to understand the nature and reversibility of the interaction between the FLP and DEAD. With this goal in mind, we first characterize the acidity and basicity of several TPB and TPP derivatives using different substituents, such as electron-donating and electron-withdrawing groups. Our results show that strong electron-donating groups increase the acidity of TPB and decrease the basicity of TPP. However, the FLP–DEAD interaction is not mainly dominated by the influence of these substituents in the acidity or basicity of the TPB or TPP systems, but by attractive or repulsive forces between substituents such as hydrogen bonds or steric effects. Based on these results, a new material is proposed based on FLP–DEAD complexes.This research was funded by Eusko Jaurlaritza grant number IT1254-19

Combined DFT and MD Simulation Protocol to Characterize Self-Healing Properties in Disulfide-Containing Materials: Polyurethanes and Polymethacrylates as Case Studies

[EN] The introduction of dynamic bonds in polymeric materials facilitates the emergence of new functionalities, such as self-healing capacity. Understanding the role of the molecular structure in the efficiency of the self-healing process is fundamental to design new materials with improved features. Computational chemistry has emerged as a valuable tool for the characterization of polymeric materials. In this work, computational chemistry is used to analyze the observed self-healing capacity of a set of disulfide-containing polyurethanes and polymethacrylates, including different hard segments and dynamic bonds. For this purpose, a recently developed theoretical protocol has been used. This protocol is based on three parameters: the probability of generating radicals by cleavage of the disulfide bond, the energetic barrier of the exchange reaction among disulfides and the dynamics of the polymeric chains. This protocol is able to qualitatively explain the experimental self-healing properties of these materials. In particular, it explains both the great performance of two materials and the lack of self-healing capacity of another two. Besides, it can also describe the improvement of the self-healing capacity with increasing temperature. These results demonstrate the robustness and usefulness of this approach for the analysis and prediction of self-healing properties in polymeric materials. Therefore, this protocol allows to predict new materials with improved properties and will help the experimental community in the development of these improved materials.This research was funded by Eusko Jaurlaritza grant number IT1254-19

On the Mechanism of Cross-Dehydrogenative Couplings between N-Aryl Glycinates and Indoles: A Computational Study

Despite the widespread use of cross-dehydrogenative couplings in modern organic synthesis, mechanistic studies are still rare in the literature and those applied to α-amino carbonyl compounds remain virtually unexplored. Herein, the mechanism of Co-catalyzed cross-dehydrogenative couplings of N-aryl glycinates with indoles is described. Density functional theory studies supported the formation of an imine-type intermediate as the more plausible transient electrophilic species. Likewise, key information regarding the role of the N-aryl group and free NH motif within the reaction outcome has been gained, which may set the stage for further developments in this field of expertise.Ministerio de Ciencia e Innovación (RTI2018-093721-B-I00) Eusko Jaurlaritza (IT1033-16; IT1254-19

Role of dispersion interactions in Endohedral TM@(ZnS)12 structures

Role of dispersion interactions in Endohedral TM@(ZnS)(12) structures[EN] II−VI semiconducting materials are gaining attention due to their optoelectronic properties. Moreover, the addition of transition metals, TMs, might give them magnetic properties. The location and distance of the TM are crucial in determining such magnetic properties. In this work, we focus on small hollow (ZnS)12 nanoclusters doped with TMs. Because (ZnS)12 is a cage-like spheroid, the cavity inside the structure allows for the design of endohedral compounds resembling those of C60. Previous studies theoretically predicted that the first-row TM(ZnS)12 endohedral compounds were thermodynamically unstable compared to the surface compounds, where the TM atom is located at the surface of the cluster. The transition states connecting both structure families were calculated, and the estimated lifetimes of these compounds were predicted to be markedly small. However, in such works dispersion effects were not taken into account. Here, in order to check for the influence of dispersion on the possible stabilization of the desired TM(ZnS)12 endohedrally doped clusters, several functionals are tested and compare to MP2. It is found that the dispersion effects play a very important role in determining the location of the metals, especially in those TMs with the 4s3d shell half-filled or completely filled. In addition, a complete family of TM doped (ZnS)12 nanoclusters is explored using ab initio molecular dynamics simulations and local minima optimizations that could guide the experimental synthesis of such compounds. From the magnetic point of view, the Cr(7S)@(ZnS)12 compound is the most interesting case, since the endohedral isomer is predicted to be the global minimum. Moreover, molecular dynamics simulations show that when the Cr atom is located at the surface of the cluster, it spontaneously migrates toward the center of the cavity at room temperature.Financial support comes from Eusko Jaurlaritza through project IT1254-19. The authors are thankful for technical and human support provided by SGIker (UPV/EHU, ERDF, EU). E.J.I. acknowledges the support of the Ikerbasque Fellowship. E.R.C. acknowledges funding from the Juan de la Cierva program IJCI-2017-34658

Building machine learning assisted phase diagrams: Three chemically relevant examples

In this work, we present a systematic procedure to build phase diagrams for chemically relevant properties by the use of a semi-supervised machine learning technique called uncertainty sampling. Concretely, we focus on ground state spin multiplicity and chemical bonding properties. As a first step, we have obtained single-eutectic-point-containing solid–liquid systems that have been suitable for contrasting the validity of this approach. Once this was settled, on the one hand, we built magnetic phase diagrams for several Hooke atoms containing a few electrons (4 and 6) trapped in spheroidal harmonic potentials. Changing the parameters of the confinement potential, such as curvature and anisotropy, and interelectronic interaction strength, we have been able to obtain and rationalize magnetic phase transitions flipping the ground state spin multiplicity from singlet (nonmagnetic) to triplet (magnetic) states. On the other hand, Bader’s analysis is performed upon helium dimers confined by spherical harmonic potentials. Covalency is studied using descriptors as the sign for Δρ(rC) and H(rC), and the dependency on the degrees of freedom of the system is studied, i.e., potential curvature ω2 and interatomic distance R. As a result, we have observed that there may exist a covalent bond between He atoms for short enough distances and strong enough confinement. This machine learning procedure could, in principle, be applied to the study of other chemically relevant properties involving phase diagrams, saving a lot of computational resources.This work has been carried out in the Theoretical Chemistry Group http://www.ehu.eus/chemistry/theory/category/1_group/ in the Faculty for Chemical Sciences of the University of the Basque Country and the Donostia International Physics Center (DIPC) in the frame of the project from the Basque Government GV IT1254-19 (October 07, 2019). The SGI/IZO-SGIker UPV/EHU is gratefully acknowledged for generous allocation of computational resources

Few electron systems confined in Gaussian potential wells and connection to Hooke atoms

In this work, we have computed and implemented one-body integrals concerning Gaussian confinement potentials over Gaussian basis functions. Then, we have set an equivalence between Gaussian and Hooke atoms and we have observed that, according to singlet and triplet state energies, both systems are equivalent for large confinement depth for a series of even number of electrons n = 2, 4, 6, 8 and 10. Unlike with harmonic potentials, Gaussian confinement potentials are dissociative for small enough depth parameter; this feature is crucial in order to model phenomena such as ionization. In this case, in addition to corresponding Taylor-series expansions, the first diagonal and sub-diagonal Pade approximant were also obtained, useful to compute the upper and lower limits for the dissociation depth. Hence, this method introduces new advantages compared to others.This research was funded by Eusko Jaurlaritza (the Basque Government), through Consolidated Group Project No. IT1254-19 and IT1584-22. Technical and human support provided by IZO-SGI, SGIker (UPV/EHU, MICINN, GV/EJ, ERDF and ESF) is gratefully acknowledged

Hydrogen Tunneling in Catalytic Hydrolysis and Alcoholysis of Silanes

[EN] An unprecedented quantum tunneling effect has been observed in catalytic Si-H bond activations at room temperature. The cationic hydrido-silyl-iridium(III) complex, {Ir[SiMe(o-C6H4SMe)(2)](H)(PPh3)(THF)}[BAr4F], has proven to be a highly efficient catalyst for the hydrolysis and the alcoholysis of organosilanes. When triethylsilane was used as a substrate, the system revealed the largest kinetic isotopic effect (KIESi-H/Si-D=346 +/- 4) ever reported for this type of reaction. This unexpectedly high KIE, measured at room temperature, together with the calculated Arrhenius preexponential factor ratio (A(H)/A(D)=0.0004) and difference in the observed activation energy [(EaD -EaH )=34.07 kJ mol(-1)] are consistent with the participation of quantum tunneling in the catalytic process. DFT calculations have been used to unravel the reaction pathway and identify the rate-determining step. Aditionally, isotopic effects were considered by different methods, and tunneling effects have been calculated to be crucial in the process.This research was supported by the Universidad del Pais Vasco (UPV/EHU) (GIU13/06), Ministerio de Economia y Competitividad (PID2019-111281GB-00), Gobierno Vasco (IT1880-19 and IT1254-19). Technical and human support provided by IZO-SGI, SGIKER (UPV/EHU, MICINN, GV/EJERDF and ESF), is gratefully acknowledged for assistance and generous allocation of computational resources. N.A. is grateful to Diputacion Foral de Gipuzkoa (OF215/2016), and M.A.H. and Z.F. to IKERBASQUE for funding. We would like to thank Dr. Eugene E. Kwan for his support and fruitful discussion using PyQuiver program

Metal–Polymer Heterojunction in Colloidal-Phase Plasmonic Catalysis

[EN] Plasmonic catalysis in the colloidal phase requires robust surface ligands that prevent particles from aggregation in adverse chemical environments and allow carrier flow from reagents to nanoparticles. This work describes the use of a water-soluble conjugated polymer comprising a thiophene moiety as a surface ligand for gold nanoparticles to create a hybrid system that, under the action of visible light, drives the conversion of the biorelevant NAD+ to its highly energetic reduced form NADH. A combination of advanced microscopy techniques and numerical simulations revealed that the robust metal-polymer heterojunction, rich in sulfonate functional groups, directs the interaction of electron-donor molecules with the plasmonic photocatalyst. The tight binding of polymer to the gold surface precludes the need for conventional transition-metal surface cocatalysts, which were previously shown to be essential for photocatalytic NAD+ reduction but are known to hinder the optical properties of plasmonic nanocrystals. Moreover, computational studies indicated that the coating polymer fosters a closer interaction between the sacrificial electron-donor triethanolamine and the nanoparticles, thus enhancing the reactivity.This work was supported by grant PID2019-111772RB-I00 funded by MCIN/AEI/10.13039/501100011033 and grant IT 1254-19 funded by Basque Government. The authors acknowl- edge the financial support of the European Commission (EUSMI, Grant 731019). S.B. is grateful to the European Research Council (ERC-CoG-2019 815128). The authors acknowledge the contributions by Dr. Adrian Pedrazo Tardajos related to sample support and electron microscopy experiments