The optical rotatory dispersion (ORD, both non-resonant and resonant) and the electronic circular dichroism (CD) of tris-bidentate transition metal complexes of the form [M(L)(3)](n+) (M = Fe, Ru, Os, Co, Rh, Ir; n = 2, 3; L = 1,10-phenanthroline, 2,2'-bipyridine) are calculated using time-dependent density functional theory (TDDFT). The exciton CD band resulting from the coupling of ligand π-to-π* transitions is investigated in detail and analyzed in terms of exciton coupling of long-axis transitions using a dipole coupling model that takes TDDFT data for a single ligand as input. Results of the coupling model agree well with the full TDDFT CD spectra.
View Article and Find Full Text PDFHetero- and homochiral diastereomeric bis(metallahelicene)s have been synthesized. They possess a rare Pt(III)-Pt(III) scaffold bridged by benzoato ligands. It is shown that heterochiral (P,M)-bis(Pt(III)-[6]helicene) can isomerize into the homochiral (P,P)- and (M,M)-bis(Pt(III)-[6]helicene).
View Article and Find Full Text PDFMethodology to calculate electronic chiroptical properties from time-dependent density functional theory (TDDFT) is outlined. Applications of TDDFT to computations of electronic circular dichroism, optical rotation, and optical rotatory dispersion are reviewed. Emphasis is put on publications from 2005 to 2010, but much of the older literature is also cited and discussed.
View Article and Find Full Text PDFAb initio molecular dynamics (MD) and relativistic density functional NMR methods were applied to calculate the one-bond Hg-C NMR indirect nuclear spin-spin coupling constants (J) of [Hg(CN)(2) ] and [CH(3) HgCl] in solution. The MD averages were obtained as J((199) Hg-(13) C)=3200 and 1575 Hz, respectively. The experimental Hg-C spin-spin coupling constants of [Hg(CN)(2) ] in methanol and [CH(3) HgCl] in DMSO are 3143 and 1674 Hz, respectively.
View Article and Find Full Text PDFThe influences of solvent effects and dynamic averaging on the (195)Pt NMR shielding and chemical shifts of cisplatin and three cisplatin derivatives in aqueous solution were computed using explicit and implicit solvation models. Within the density functional theory framework, these simulations were carried out by combining ab initio molecular dynamics (aiMD) simulations for the phase space sampling with all-electron relativistic NMR shielding tensor calculations using the zeroth-order regular approximation. Structural analyses support the presence of a solvent-assisted "inverse" or "anionic" hydration previously observed in similar square-planar transition-metal complexes.
View Article and Find Full Text PDF(14)N solid-state NMR powder patterns have been obtained at high field (21.1 T) using broadband, frequency-swept pulses and a piecewise acquisition method. This approach allowed the electric field gradient (EFG) tensor parameters to be obtained from model organic and inorganic systems featuring spherically asymmetric nitrogen environments (C(Q) values of up to ca.
View Article and Find Full Text PDFA series of silica-based tetracycline (TC)-imprinted xerogel sorbents were prepared by sol-gel processing and were characterized for TC binding. Molecularly imprinted xerogels (MIXs) formed from allyltriethoxysilane (AtEOS) and tetraethoxysilane (TEOS) and end capped with trimethylchlorosilane exhibited the best analytical performance (imprinting factor, IF, of 7.46±0.
View Article and Find Full Text PDFThe creation of tetracycline (TC) responsive molecularly imprinted xerogels (MIXs) was investigated using electronic absorbance, liquid chromatography-ion-trap mass spectrometry (LC-ITMS), and first-principles theory. Experimental results show that the template molecule converts to its epimer, 4-epitetracycline (ETC), during the imprinting process. Additionally, end capping of the MIX surface silanols transforms TC into anhydrotetracycline (ATC) and 4-epianhydrotetracycline (EATC).
View Article and Find Full Text PDFDirhodium tetrakis((S)-N-(dodecylbenzenesulfonyl)prolinate) (Rh2(S-DOSP)4) is an effective catalyst for highly enantioselective cyclopropenation reactions between terminal alkynes and arylvinyldiazoacetates. The resulting vinylcyclopropenes can undergo rhodium-catalyzed regioselective rearrangement to cyclopentadienes. Computational studies indicate that the high enantioselectivity of the process is governed by the specific orientation of the alkyne during its approach to the carbenoid through a relatively late transition state.
View Article and Find Full Text PDFThe optical rotation of natural amino acids becomes more positive when the medium is changed from approximately neutral to strongly acidic (Clough-Lutz-Jirgensons (CLJ) effect). In this work, it is shown by time-dependent density functional computations that the effect can be generalized to other α-substituted chiral carboxylic acids. The physical origin of the generalized CLJ effect is similar to that in amino acids, linking the absolute configuration directly to the sign of CLJ.
View Article and Find Full Text PDFAn implementation of a four-component density corrected approach for calculations of nuclear electric field gradients (EFGs) in molecules based on the two-component relativistic zeroth-order regular approximation (ZORA) is reported. The program module, which is part of the NWChem package, allows for scalar and spin-orbit relativistic computations of EFGs. Benchmark density functional calculations are reported for a large set of main group diatomic molecules, a set of Cu and Au diatomics, several Ru and Nb complexes, the free uranyl ion, and two uranyl carbonate complexes.
View Article and Find Full Text PDFHyper-Raman spectra for pyridine and pyridine on the surface of a tetrahedral 20 silver atom cluster are calculated using static hyperpolarizability derivatives obtained from time dependent density functional theory. The stability of the results with respect to choice of exchange-correlation functional and basis set is verified by comparison with experiment and with Raman spectra calculated for the same systems using the same methods. Calculated Raman spectra were found to match well with experiment and previous theoretical calculations.
View Article and Find Full Text PDFPerturbed localized molecular orbitals (LMOs), correct to first order in an applied static perturbation and consistent with a chosen localization functional, are calculated using analytic derivative techniques. The formalism is outlined for a general static perturbation and variational localization functionals. Iterative and (formally) single-step approaches are compared.
View Article and Find Full Text PDFCircularly polarized luminescence (CPL), the differential emission of left- and right-handed circularly polarized light from a molecule, is modeled by using time-dependent density functional theory. Calculations of the CPL spectra for the first electronic excited states of d-camphorquinone and (S,S)-trans-beta-hydrindanone under the Franck-Condon approximation and using various functionals are presented, as well as calculations of absorption, emission, and circular dichroism spectra. The functionals B3LYP, BHLYP, and CAM-B3LYP are employed, along with the TZVP and aug-cc-pVDZ Gaussian-type basis sets.
View Article and Find Full Text PDFHerein, we develop a phenomenological model for microscopic cascading and substantiate it with ab initio calculations. It is shown that the concept of local microscopic cascading of a second-order nonlinearity can lead to a third-order nonlinearity, without introducing any new loss mechanisms that could limit the usefulness of our approach. This approach provides a new molecular design protocol, in which the current great successes achieved in producing molecules with extremely large second-order nonlinearity can be used in a supra molecular organization in a preferred orientation to generate very large third-order response magnitudes.
View Article and Find Full Text PDFWe show that ultrasmall metallic nanoparticles can be combined with large second- and third-order response organic chromophores to enhance the overall third-order response of the system. This approach can be used in combination with microscopic cascading to generate exceptionally large third-order response. Intermolecular charge-transfer coupling between the molecules and the metal clusters enhances the real part of the nonlinearity at telecommunication wavelengths, while avoiding plasmonic enhancement of one- and two-photon absorption, and minimizing optical losses.
View Article and Find Full Text PDFThe NMR nuclear shielding tensors for the series LaX(3), with X = F, Cl, Br and I, have been computed using two-component relativistic density functional theory based on the zeroth-order regular approximation (ZORA). A detailed analysis of the inverse halogen dependence (IHD) of the La shielding was performed via decomposition of the shielding tensor elements into contributions from localized and delocalized molecular orbitals. Both spin-orbit and paramagnetic shielding terms are important, with the paramagnetic terms being dominant.
View Article and Find Full Text PDFAza[n]helicene phosphole derivatives have been prepared from aza[n]helicene diynes by the Fagan-Nugent route. Their photophysical properties (UV/Vis absorption and emission behavior) have been evaluated. Their behavior as P,N chelates towards coordination to Pd(II) and Cu(I) has been investigated: metal-bis(aza[n]helicene phosphole) assemblies are formed by a highly stereoselective coordination process, as demonstrated by X-ray crystallography.
View Article and Find Full Text PDFAb initio molecular dynamics (aiMD) simulations based on density functional theory (DFT) were performed on a set of five anionic platinum complexes in aqueous solution. (195)Pt nuclear magnetic shielding constants were computed with DFT as averages over the aiMD trajectories, using the two-component relativistic zeroth-order regular approximation (ZORA) in order to treat relativistic effects on the Pt shielding tensors. The chemical shifts obtained from the aiMD averages are in good agreement with experimental data.
View Article and Find Full Text PDFTime-dependent density functional theory (TD-DFT) has been employed to calculate the electronic circular dichroism (CD) spectra of tris-bidentate iron group complexes [M(L-L)(3)](2+) (M = Fe, Ru, Os; L-L = 2,2'-bipyridine). The simulated CD spectra are compared with the experiment, and reasonably good agreement is obtained. In this study, much effort has been made to interpret the exciton CD arising from the long-axis-polarized pi --> pi* excitations in the ligands of the complexes.
View Article and Find Full Text PDFA benchmark study for relativistic density functional calculations of NMR spin-spin coupling constants has been performed. The test set contained 47 complexes with heavy metal atoms (W, Pt, Hg, Tl, Pb) with a total of 88 coupling constants involving one or two heavy metal atoms. One-, two-, three-, and four-bond spin-spin couplings have been computed at different levels of theory (nonhybrid vs hybrid DFT, scalar vs two-component relativistic).
View Article and Find Full Text PDFThis "tutorial style" review outlines the theoretical foundation for computations of chiroptical properties for optically active molecules. The formalism covers electronic and vibrational CD, optical rotation, and Raman optical activity. The focus is on first-principles methods.
View Article and Find Full Text PDFThe static dipole polarizabilities of water clusters (2