Cristian Morari

Evidence of a Bimodal Binding between Diclofenac-Na and β-Cyclodextrin in Solution

The complexation between diclofenac sodium and β-cyclodextrin was investigatedin solution by 1D and 2D proton NMR. The continuous variation method was usedto establish the stoichiometry. The obtained results indicate that simultaneous inclusionof both rings occur giving rise to two isomeric 1:1 complexes. The view of abimodal binding between diclofenac sodium and β-cyclodextrin was also supportedby ROESY experiments. The association constants for the two 1:1 complexeswere calculated by non-linear least-squares regression analysis, applying an iterationprocedure. The geometry of the two 1:1 complexes, according to the obtainedNMR data is given.

Adsorption of cysteine clusters on Au(110)−(1 × 1) surface: a DFT study

Cysteine clusters of various sizes are investigated, as free structures and adsorbed on the Au(110)−(1 × 1) surface, by using density-functional theory. We analyse the adsorption of clusters in protonized and deprotonized forms. The presence of a trend for the values of bonding energy per adsorbed cysteine molecule as a function of cluster size is pointed out. To explain these findings we analyse the electronic density of states of the clusters and the charge transfer occurring between the surface and cysteine molecules. We emphasize the broadening of the molecular density of states as a function of cluster size. Details of the geometrical structure of the adsorbed clusters in protonized and deprotonized forms are compared and discussed from the perspective provided by the electronic structure calculation. By investigating the redistribution of the electron density upon the adsorption we point out the significant features of the molecule–surface charge transfer. In particular we show that the charge redistribution occurs only at the thiol end while the electronic density of the carboxylic group is not affected in the adsorbed state.

Localization and anharmonicity of the vibrational modes for GC Watson–Crick and Hoogsteen base pairs

We present an ab initio study of the vibrational properties of cytosine and guanine in the Watson–Crick and Hoogsteen base pair configurations. The results are obtained by using two different implementations of the DFT method. We assign the vibrational frequencies to cytosine or to guanine using the vibrational density of states. Next, we investigate the importance of anharmonic corrections for the vibrational modes. In particular, the unusual anharmonic effect of the H+ vibration in the case of the Hoogsteen base pair configuration is discussed.

NMR study and computational assays of meclofenamic Na salt and β-cyclodextrin inclusion complex

Complexation in solution between meclofenamate sodium (MCF) and β-cyclodextrin was studied using one- and two-dimensional 1H NMR spectroscopy and molecular docking coupled with ab initio calculations. The large variation of chemical shifts from protons located inside the hydrophobic cavity of β-cyclodextrin, provided clear evidence of inclusion complexation. The stoichiometry of the inclusion complex was determined to be 1:1, using the method of continuous variation. To ascertain the solution geometry of the host–guest complex a ROESY experiment was carried out. The results suggested a preferential binding of the dichlorophenyl moiety of the guest molecule within the β-cyclodextrin cavity, conformation which also sustained by the theoretical computational investigations. The association constant of the inclusion complex was determined using 1H NMR titration method in solution followed by a non-linear least-square regression implemented in CONSTEQ, a software developed in our group. After a preliminary molecular docking investigation, the most probable conformation was subjected to ab initio calculations using SIESTA software package, to characterize more precisely the stabilization energy of the 1:1 inclusion complex.

Combined molecular and periodic DFT analysis of the adsorption of co macrocycles on graphene

The molecular doping of graphene with π‐stacked conjugated molecules has been widely studied during the last 10 years, both experimentally or using first‐principle calculations, mainly with strongly acceptor or donor molecules. Macrocyclic metal complexes have been far less studied and their behavior on graphene is less clear‐cut. The present density functional theory study of cobalt porphyrin and phthalocyanine adsorbed on monolayer or bilayer graphene allows to compare the outcomes of two models, either a finite‐sized flake of graphene or an infinite 2D material using periodic calculations. The electronic structures yielded by both models are compared, with a focus on the density of states around the Fermi level. Apart from the crucial choice of calculation conditions, this investigation also shows that unlike strongly donating or accepting organic dopants, these macrocycles do not induce a significant doping of the graphene sheet and that a finite size model of graphene flake may be confidently used for most modeling purposes.

Numerical algorithm for optimization of positive electrode in lead-acid batteries

The positive electrode in lead-acid batteries is one of the most sensitive parts of the whole battery, since it is affected by various aggresive chemical processes during its life. Therefore, an optimal design of the positive electrode of the battery may have as efect a dramatic improvement of the properties of the battery - such as total capacity or endurance during its life. Our efforts dedicated to this goal cover a range of rather complex tasks, from the design based on numerical analysis to statistic analysis. We present the structure of the software implementation and the results obtained for three types of positive electrodes.

A first-principles study of π-conjugated thiol phenothiazine derivatives adsorbed on Au(111) surface

We present an extensive theoretical study of a series of phenothiazine derivatives adsorbed on Au(111). A series of experimentally accessible quantities are calculated (ultra-violet photoemission spectra, scanning tunneling microscopy images). All simulations were performed by using DFT techniques and LCAO expansion of the molecular orbitals. The microscopic picture established in this work provides a deeper understanding of the interfacial processes that govern the working principle of single-molecule electronics and organic electronic devices.

Theoretical investigation of the normal modes for the ground and first excited states of a realistic retinal chromophore model

Ab initio and DFT computations are used to investigate the vibrational normal coordinates of the protonated Schiff base (PSB) 4-cis-γ, η-dimethyl-C9H9 NH2+. The ground and the first excited states are investigated. Our results suggests that the torsional motion involving the central C=C bonds that plays a significant role in the isomerization process involves mostly the central part of the carbon skeleton of the PSB. Together with the information coming from the simulated IR spectra these results offer a qualitative description of the dynamics of the system on its first excited state.