Optoelectronic and Excitonic Properties of Oligoacenes: Substantial Improvements from Range-Separated Time-Dependent Density Functional Theory

The optoelectronic and excitonic properties in a series of linear acenes (naphthalene up to heptacene) are investigated using range-separated methods within time-dependent density functional theory (TDDFT). In these rather simple systems, it is well-known that TDDFT methods using conventional hybrid functionals surprisingly fail in describing the low-lying La and Lb valence states, resulting in large, growing errors for the La state and an incorrect energetic ordering as a function of molecular size. In this work, we demonstrate that the range-separated formalism largely eliminates both of these errors and also provides a consistent description of excitonic properties in these systems. We further demonstrate that re-optimizing the percentage of Hartree-Fock exchange in conventional hybrids to match wavefunction-based benchmark calculations still yields serious errors, and a full 100% Hartree-Fock range separation is essential for simultaneously describing both of the La and Lb transitions. Based on an analysis of electron-hole transition density matrices, we finally show that conventional hybrid functionals overdelocalize excitons and underestimate quasiparticle energy gaps in the acene systems. The results of our present study emphasize the importance of both a range-separated and asymptotically-correct contribution of exchange in TDDFT for investigating optoelectronic and excitonic properties, even for these simple valence excitations.Comment: Accepted by the Journal of Chemical Theory and Computatio

Title Dinuclear Heterometallic Lanthanide Complexes Exhibiting MRI and Luminescence Response

Heteronuclear lanthanide complexes have gained an increased level of interest recently, due to their high potential for application in various molecular imaging techniques. They appear primarily as the most rational choice for agents to be used in multimodal imaging approaches.[1-2] Namely, due to their versatile physicochemical properties, they are widely used in MRI or luminescence imaging. Several lanthanide complexes have been reported recently with the potential to be used as multimodal agents. Depending on the approach the final ligand structure contained a single chelator for the lanthanide ion, or consisted of two chelating units, consequently bearing same or different Ln3+. Following these principles, we designed and synthesized a ligand containing two different chelators where the antenna acts not only as a linker between these two chelators, but also as an integral component in one of their structures. The macrocyclic, DOTA-type moiety of this ligand forms a stable complex with Eu3+ and Gd3+ which exhibit the expected luminescence emission and relaxometric characteristics, respectively. An aryl-containing acyclic chelator 5A-PADDTA (abbreviated from 5-aminoisophthalamide diethylenediaminetetraacid) of this ligand also forms complexes with lanthanides and their existence is confirmed by the means of luminescence and NMR spectroscopy. Depending on the choice of the metal ion (Gd3+, Tb3+, Eu3+, Nd3+, Yb3+ or Er3+), the system could act as a potential dual-modal (MRI / Vis or NIR luminescence imaging) or dual-emissive (luminescence imaging at various wavelengths in Vis/NIR region) contrast agent

Synthesis and characterization of dinuclear heterometallic lanthanide complexes exhibiting MRI and luminescence response

A molecule bearing a macrocyclic DOTA-type chelator and an acyclic chelator based on the 5-aminoisophthalamide diethylenediaminetetraacid (5A-PADDTA) was synthesized by linking these two moieties via an amide bond. The ligand has the possibility to complex two identical or different lanthanide ions, depending on the desire for its potential application. Luminescence studies involving titrations of the Eu3+ or Gd3+ complex with Tb3+ confirm the formation of heterometallic complexes, as well as the presence of different species in the solution. Comparative 1H NMR spectra of the ligand, its Eu3+ complex, and that containing both Eu3+ and Tb3+ proves the existence of respective monometallic or bimetallic species. NMR diffusion measurements on 5A-PADDTA as a model compound indicate the formation of aggregates upon the addition of Y3+ (chosen as a diamagnetic analogue of lanthanide ions). Hydration values were calculated from the respective luminescence lifetime values. They show the dominance of a q = 1 species for both ions in monometallic complexes, or q = 1 and q = 2 species of ions in aggregated complexes, for DOTA and 5A-PADDTA chelators, respectively

Chemical Mimics of Aspartate-Directed Proteases: Predictive and Strictly Specific Hydrolysis of a Globular Protein at Asp-X Sequence Promoted by Polyoxometalate Complexes Rationalized by a Combined Experimental and Theoretical Approach

Creating efficient and residue-directed artificial proteases is a challenging task due to the extreme inertness of the peptide bond, combined with the difficulty of achieving specific interactions between the catalysts and the protein side chains. Herein we report strictly site-selective hydrolysis of a multi-subunit globular protein, hemoglobin (Hb) from bovine blood, by a range of ZrIV -substituted polyoxometalates (Zr-POMs) in mildly acidic and physiological pH solutions. Among 570 peptide bonds in Hb, selective cleavage was observed at only eleven sites, each occurring at Asp-X peptide bonds located in the positive patches on the protein surface. The molecular origins of the observed Asp-X selectivity were rationalized by means of molecular docking, DFT-based binding, and mechanistic studies on model peptides. The proposed mechanism of hydrolysis involves coordination of the amide oxygen to ZrIV followed by a direct nucleophilic attack of the side chain carboxylate group on the C-terminal amide carbon atom with formation of a cyclic anhydride, which is further hydrolyzed to give the reaction products. The activation energy for the cleavage of the structurally related Glu-X sequence compared to Asp-X was calculated to be higher by 1.4 kcal mol-1 , which corresponds to a difference of about one order of magnitude in the rates of hydrolysis. The higher activation energy is attributed to the higher strain present in the six-membered ring of glutaric anhydride (Glu-X), as compared to the five-membered ring of the succinic anhydride (Asp-X) intermediate. Similarly, the cleavage at X-Asp and X-Glu bonds are predicted to be kinetically less likely as the corresponding activation energies were 6 kcal mol-1 higher, explaining the experimentally observed selectivity. The synergy between the negatively charged polyoxometalate cluster, which binds at positive patches on protein surfaces, and selective activation of Asp-X peptide bonds located in these regions by ZrIV ions, results in a novel class of artificial proteases with aspartate-directed reactivity, which is very rare among naturally occurring proteases.status: publishe

Polyoxometalates as a Novel Class of Artificial Proteases: Selective Hydrolysis of Lysozyme under Physiological pH and Temperature Promoted by a Cerium(IV) Keggin-Type Polyoxometalate

Hen-egg-white lysozyme (HEWL) is specifically cleaved at the Trp28-Val29 and Asn44-Arg45 peptide bonds in the presence of a Keggin-type [Ce(α-PW11O39)2]10- polyoxometalate (POM; 1) at pH 7.4 and 37 °C. The reactivity of 1 towards a range of dipeptides was also examined and the calculated reaction rates were comparable to those observed for the hydrolysis of HEWL. Experiments with α-lactalbumin (α-LA), a protein that is structurally highly homologous to HEWL but has a different surface potential, showed no evidence of hydrolysis, which indicates the importance of electrostatic interactions between 1 and the protein surface for the hydrolytic reaction to occur. A combination of spectroscopic techniques was used to reveal the molecular interactions between HEWL and 1 that lead to hydrolysis. NMR spectroscopy titration experiments showed that on protein addition the intensity of the 31P NMR signal of 1 gradually decreased due to the formation of a large protein/polyoxometalate complex and completely disappeared when the HEWL/1 ratio reached 1:2. Circular dichroism (CD) measurements of HEWL indicate that addition of 1 results in a clear decrease in the signal at λ=208 nm, which is attributed to changes in the α-helical content of the protein. 15N-1H heteronuclear single quantum coherence (HSQC) NMR measurements of HEWL in the presence of 1 reveal that the interaction is mainly observed for residues that are located in close proximity to the first site in the α-helical part of the structure (Trp28-Val29). The less pronounced NMR spectroscopic shifts around the second cleavage site (Asn44-Arg45), which is found in the β-strand region of the protein, might be caused by weaker metal-directed binding, compared with strong POM-directed binding at the first site. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.SCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe

Nanozymatic Activity of UiO-66 Metal-Organic Frameworks: Tuning the Nanopore Environment Enhances Hydrolytic Activity toward Peptide Bonds

status: publishe