# New Paper at The Journal of Physical Chemistry B

**Explicit Aqueous Solvation Treatment of Epinephrine from Car–Parrinello Molecular Dynamics: Effect of Hydrogen Bonding on the Electronic Absorption Spectrum**

Arsênio P. Vasconcelos, Daniel F. S. Machado, Thiago O. Lopes, Ademir J. Camargo and Heibbe C. B. de Oliveira

The electronic absorption spectrum of the neurotransmitter epinephrine (EPN) in water solution is studied, combining ab initio Car–Parrinello molecular dynamics (CPMD) with a quantum mechanical approach within the framework of the time-dependent density functional theory (TDDFT) scheme. By selecting 52 uncorrelated snapshots, the excitation modes were calculated at the LC-ωPBE/6-31+G(d) level of theory, using an optimal range-separation parameter ω, determined by means of the gap-tuning scheme in the presence of the solvent molecules. By comparing with static approaches (vacuum and implicit solvation), we show here that explicit solvation treatment dramatically enhances the photophysical properties of the EPN, especially because of the more realistic dynamic description of the molecular geometry. The agreement between the simulated and experimental spectra is demonstrated when TDDFT calculations are performed with the optimally tuned version of the DFT hybrid, not only improving the relative intensities of the absorption bands but also the λmax position. These results highlight that accounting for the nuclear motions, that is, thermal effects (of both chromophore and solvent molecules), is imperative to predict experimental absorption spectra. In this paper, we have addressed the critical importance of explicit solvation effects on the photophysics of the EPN, raking in performance when the simulation is performed based on first-principles molecular dynamics such as CPMD.

# New Paper at Journal of Physical-Chemical Letters

*Bond Ellipticity Alternation: An Accurate Descriptor of the Nonlinear Optical Properties of pi-Conjugated Chromophores*Thiago O. Lopes, Daniel F. Scalabrini Machado, Chad Risko, Jean-Luc Brédas, and Heibbe C. B. de Oliveira

Well-defined structure–property relationships offer a conceptual basis to afford a priori design principles to develop novel π-conjugated molecular and polymer materials for nonlinear optical (NLO) applications. Here, we introduce the bond ellipticity alternation (BEA) as a robust parameter to assess the NLO characteristics of organic chromophores and illustrate its effectiveness in the case of streptocyanines. BEA is based on the symmetry of the electron density, a physical observable that can be determined from experimental X-ray electron densities or from quantum-chemical calculations. Through comparisons to the well-established bond-length alternation and π-bond order alternation parameters, we demonstrate the generality of BEA to foreshadow NLO characteristics and underline that, in the case of large electric fields, BEA is a more reliable descriptor. Hence, this study introduces BEA as a prominent descriptor of organic chromophores of interest for NLO applications.

# New Paper at Journal of The American Society for Mass Spectrometry

*Charge-tagged N-heterocyclic carbenes (NHC): Direct transfer from ionic liquid solutions and long-lived nature in the gas phase*Thyago S. Rodrigues, Denis Lesage, Wender A. da Silva, Richard B. Cole, Günter Ebeling, Jaïrton Dupont, Heibbe C. B. de Oliveira, Marcos N. Eberlin, Brenno A. D. Neto

Negatively charge-tagged N-heterocyclic carbenes have been formed in solution via deprotonation of imidazolium ions bearing acid side groups and transferred to the gas phase via ESI(–)-MS. The structure of the putative and apparently stable gaseous carbenes formed in such conditions were then probed via reactions with carbon dioxide using a triple quadrupole mass spectrometer particularly optimized for ion/molecule reactions of ESI-generated ions. Complete conversion to imidazolium carboxylates was achieved, which seems to demonstrate the efficiency of the transfer, the gas-phase stability, and the long-lived nature of these unprecedented charge-tagged carbenes and their predominance in the ionic population. Comprehensive studies on the intrinsic reactivity of N-heterocyclic carbenes with silent charge tags are therefore possible.

# New Paper at Journal of Molecular Modeling

*A novel analytical potential function for dicationic diatomic molecular systems based on deformed exponential function*Daniel F. S. Machado, Rodrigo A. L. Silva, Ana Paula de Oliveira, Valter H. Carvalho-Silvam Ricardo Garganom Luciano Ribeiro, Heibbe C. B. de Oliveira

In this paper, we propose a new alternative analytical function aiming to better describe the potential energy curves of the doubly charged diatomic molecules. To achieve this goal, we modified an existing potential function in the literature to describe dicationic diatomic molecules using the deformed exponential function. We generated the potential energy curve of the testing group of dicationic diatomic molecules Be2+2Be22+ , BH2+, He2+2He22+ and NH2+ by means of the CCSD(T)/aug-cc-pVQZ level of theory. To validate this new function, we also calculated the spectroscopic constants and the rovibrational spectra for the electronic state X1Σ+gX1Σg+ of the Be2+2Be22+ and He2+2He22+ systems using the Dunham and discrete variable representation methods. For BH2+ and NH2+ molecules, despite exhibiting a local minimum in the potential energy curve, no vibrational levels are supported, so the spectroscopic constants for these poorly bound systems are invalidated. The fitting accuracy had a better performance over the original potential for describing dicationic diatomic systems, considering that the discrete variable representation method resulted in a similar vibrational structure described in the literature. This fact can be explained due to the deformed function’s flexibility.

# New Paper at Journal of Molecular Modeling

*Effect of the crystalline environment on the third-order nonlinear optical properties of L-arginine phosphate monohydrate: a theoretical study*Clodoaldo Valverde, Rosemberg F. N. Rodrigues, Daniel F. S. MachadoBasílio Baseia, Heibbe C. B. de Oliveira

A supermolecular approach combined with an iterative electrostatic scheme was employed to investigate the nonlinear optical properties of the hybrid L-arginine phosphate monohydrate crystal, the procedure being aided by DFT calculations. The supermolecular scheme basically treated the molecules surrounding the unit cell as point charges; this approximation results in rapid convergence, making it a feasible method. DFT functionals of different flavors were considered: B3LYP, B2PLYP, CAM-B3LYP, ωB97, and M06HF, utilizing the 6-311 + G(d) basis set. All functionals gave sufficiently accurate values for the dipole moment (μ) with respect to the experimental value 32(2) D. For the average linear polarizability ( α⎯⎯⎯α¯ ) and the total first hyperpolarizability (βtot), good agreement was observed between the DFT-calculated values and MP2-derived results reported in the literature. For the second hyperpolarizability, both static and dynamic regimes were considered. The point-charge embedding approach led to an attenuation of the second hyperpolarizability γ for all frequencies considered. Excitations of γ were not observed for frequencies smaller than 0.1 a.u. For the second hyperpolarizability (both static and dynamic), computational results showed that L-arginine phosphate monohydrate exhibits a large nonlinear optical effect, which implies the occurrence of microscopic third-order NLO behavior.

# Back Cover of Physical Chemistry Chemical Physics

*Rovibrational spectroscopic constants of the interaction between ammonia and metallo-phthalocyanines: a theoretical protocol for ammonia sensor design*Alan R. Baggio, Daniel F. S. Machado, Valter H. Carvalho-Silva, Leonardo G. Paterno and Heibbe Cristhian B. de Oliveira

In the present contribution, we develop an adapted theoretical approach based on DFT calculations (B3LYP functional) and solution of the nuclear Schrödinger equation by using the Discrete Variable Representation method to model the interaction of ammonia with metallo-phthalocyanines (MPcs, where M = Fe2+, Co2+, Ni2+, Cu2+ or Zn2+). This approach is intended to be a general protocol for the rational design of chemical sensors. The as-obtained binding energy curves, obtained from ab initio points, permitted us to calculate rovibrational energies and spectroscopic constants, as well as to establish the relative population of rovibrational states in different types of MPc–NH3 thermodynamic systems. Simulated binding energy curves show that the binding energy in MPc–NH3 systems is dependent on the type of M central ion, decreasing in the order FePc > ZnPc > CoPc > CuPc > NiPc, with values spanning from −170 to −16 kJ mol−1. Also, MPc–NH3 systems have at least 16 rovibrational levels, which confirms that they are all bound systems (chemically or physically). Despite that, only the interaction between ammonia and FePc, CoPc or ZnPc is spontaneous within the studied temperature range (200–700 K). NiPc and CuPc show a change between spontaneous and non-spontaneous behaviours at ∼400 K and ∼500 K, respectively. Less bound systems should more efficiently guarantee the sensors' signal reset, while they are also less specific than sensors built with medium to strongly bound systems. Moreover, the intermediate energy and spontaneous binding of ammonia to NiPc and CuPc at operation temperatures, as determined with our theoretical approach, suggests that these MPcs are most promising for ammonia sensors.

# New Paper at New Journal of Chemistry

*Synthesis, structural characterization and computational study of a novel amino chalcone: a potential nonlinear optical material*Leonardo R. Almeida, Murilo M. Anjos, Gabriela C. Ribeiro, Clodoaldo Valverde, Daniel F. S. Machado, Guilherme R. Oliveira, Hamilton B. Napolitano and Heibbe C. B. de Oliveira

The interest for novel chalcone-based materials in nonlinear optics is dependent on strong second harmonic generation in organic systems. Chalcones are α,β-unsaturated ketones that can be easily obtained by Claisen–Schmidt condensation between ketones and aromatic aldehydes. A new 2-amino-chalcone was synthesized and its crystal molecular structure was elucidated using the single crystal X-ray diffraction technique. This compound, C15H12BrNO2, crystallizes in monoclinic centrosymmetric space group C2/c with cell parameters a= 29.47(7) Å; b = 6.97(5) Å, c = 13.59(1) Å, β = 112.52(6)° and V = 2581.2(2) Å3. In addition to the crystal structure, the analysis of Hirshfeld surfaces indicates the presence of hydrogen bonds of types N–H⋯O and O–H⋯O that stabilize two independent centrosymmetric dimers, and also indicates the presence of π–π stacking interactions that stabilize a supramolecular trimeric system. Being a push–pull chromophore we investigated the NLO properties of the 2-amino-chalcone asymmetric unit using the supermolecule approach in combination with an iterative electrostatic polarization scheme. The calculations were performed using the CAM-B3LYP/6-311+G(d) level of theory for both dynamic and static situations. In the presence of the embedding charges, the γ value is increased by 20% for the dynamic calculation but only 8% for the static limit. In contrast to the crystal form, when in solution the 2-amino-chalcone lacks an inversion center so that second order NLO properties do not vanish. Following this idea we computed the NLO properties using the implicit solvation approach IEF-PCM. The solvent effect on the NLO properties was to augment its values as the solvent polarity increases. We obtained for the in-crystal and in DMSO 2-amino-chalcone, γ(−2ω;ω,ω,0) = 144.12 × 10−36 esu and 260.163 × 10−36 esu, respectively, and therefore interesting materials for third order NLO applications.

# Cover of Journal of Computacional Chemistry

*Deformed transition-state theory: Deviation from Arrhenius behavior and application to bimolecular hydrogen transfer reaction rates in the tunneling regime*Valter H. Carvalho-Silva, Vincenzo Aquilanti, Heibbe C. B. de Oliveira, Kleber C. Mundim

A formulation is presented for the application of tools from quantum chemistry and transition-state theory to phenomenologically cover cases where reaction rates deviate from Arrhenius law at low temperatures. A parameter d is introduced to describe the deviation for the systems from reaching the thermodynamic limit and is identified as the linearizing coefficient in the dependence of the inverse activation energy with inverse temperature. Its physical meaning is given and when deviation can be ascribed to quantum mechanical tunneling its value is calculated explicitly. Here, a new derivation is given of the previously established relationship of the parameter d with features of the barrier in the potential energy surface. The proposed variant of transition state theory permits comparison with experiments and tests against alternative formulations. Prescriptions are provided and implemented to three hydrogen transfer reactions: CH4 + OH → CH3 + H2O, CH3Cl + OH → CH2Cl + H2O and H2 + CN → H + HCN, widely investigated both experimentally and theoretically. © 2016 Wiley Periodicals, Inc.

# New Paper at The Journal of Physical Chemistry C

**Strong Solvent Effects on the Nonlinear Optical Properties of Z and E Isomers from Azo-Enaminone Derivatives**

Daniel F. S. Machado, Thiago O. Lopes, Igo T. Lima, Demétrio A. da Silva Filho, and Heibbe C. B. de Oliveire

We calculated the nonlinear optical properties of 24 azo-enaminone derivatives, incorporating solvent effects on their geometric and electronic structure, to assess the impact of the environment on these properties. Namely, we incorporated chloroform, tetrahydrofuran, acetone, ethanol, methanol, and dimethyl sulfoxide in our calculations and compared our results incorporating solvent effects with our gas-phase calculations. To account for the electron correlation effects on NLO properties, we performed the calculations at MP2/6-31G(p)//MP2/6-31G(d) level set. The polarizable continuum model was used to simulate the presence of the solvent. The exponents of p extra functions added to heavy atoms were obtained, imposing the maximization of the first hyperpolarizability. Two structural configurations (Z and E) of azo-enaminones were investigated to assess the isomeric effects of the electric properties. Our results show that both solvent polarity and relative strength of the donor groups have a significant impact on the electric properties but more strikingly on the first hyperpolarizability β.