Magnetic circular dichroism spectra from resonant and damped coupled cluster response theory

A computational expression for the Faraday A term of magnetic circular dichroism (MCD) is derived within coupled cluster response theory and alternative computational expressions for the B term are discussed. Moreover, an approach to compute the (temperature-independent) MCD ellipticity in the context of coupled cluster damped response is presented, and its equivalence with the stick-spectrum approach in the limit of infinite lifetimes is demonstrated. The damped response approach has advantages for molecular systems or spectral ranges with a high density of states. Illustrative results are reported at the coupled cluster singles and doubles level and compared to time-dependent density functional theory results.Comment: Submitted to J. Chem. Phys. on May 10, 202

Insights into the Structures of Bilirubin and Biliverdin from Vibrational and Electronic Circular Dichroism: History and Perspectives

: In this work we review research activities on a few of the most relevant structural aspects of bilirubin (BR) and biliverdin (BV). Special attention is paid to the exocyclic C=C bonds being in mostly Z rather than E configurations, and to the overall conformation being essentially different for BR and BV due to the presence or absence of the double C=C bond at C-10. In both cases, racemic mixtures of each compound of either M or P configuration are present in achiral solutions; however, imbalance between the two configurations may be easily achieved. In particular, results based on chiroptical spectroscopies, both electronic and vibrational circular dichroism (ECD and VCD) methods, are presented for chirally derivatized BR and BV molecules. Finally, we review deracemization experiments monitored with ECD data from our lab for BR in the presence of serum albumin and anesthetic compounds

Characterization of "Free Base" and Metal Complex Thioalkyl Porphyrazines by Magnetic Circular Dichroism and TDDFT Calculations

UV-vis absorption and magnetic circular dichroism (MCD) spectra of octakis thioethyl "free base" porphyrazine H2OESPz and its metal complexes MOESPz (M = Mg, Zn, Ni, Pd, Cu), as well as of [MnOESPz(SH)] were recorded. In the last case, MCD proved to have quite good sensitivity to the coordination of this complex with 1-methylimidazole (1-mim) in benzene. Time-dependent density functional theory (TDDFT) calculations were carried out for the considered porphyrazine complexes and showed good performance on comparing with MCD and UV-vis experimental spectra, even in the open-shell Cu and Mn cases. Calculations accounted for the red shift observed in the thioalkyl compounds and allowed us to reveal the role of sulfur atoms in spectroscopically relevant molecular orbitals and to highlight the importance of the conformations of the thioethyl external groups. Calculated MCD spectra of [MnOESPz(SH)] confirm the Mn(III) → Mn(II) redox process, which leads to the [Mn(OESPz)(1-mim)2] species, and the relevance of the spin state for MCD is revealed

MCD and MCPL Characterization of Luminescent Si(IV) and P(V) Tritolylcorroles: The Role of Coordination Number

Two triarylcorrole complexes, (hydroxy)[5,10,15- tritolylcorrolato]silicon-(TTC)Si(OH) and (dihydroxy)[5,10,15- tritolylcorrolato]phosphorous-(TTC)P(OH)2, have been investigated by magnetic circular dichroism (MCD) and magnetic circularly polarized luminescence (MCPL). The spectroscopic investigations have been combined with explicit calculation of MCD response through time-dependent density functional theory (TD-DFT) formal- ism. This has allowed us to better define the role of molecular orbitals in the transitions associated with the Soret and Q bands. Besides and more importantly, MCD has made it possible to follow the titration process of (TTC)Si(OH) in dimethyl sulfoxide (DMSO) solution with NaF and of (TTC)P(OH)2 in dichloromethane solution with alcohols in a complementary and, we dare say, more sensitive way with respect to absorption and fluorescence data. Finally, the MCPL spectra and the ancillary TD-DFT calculations have allowed us to characterize the excited state of (TTC)Si(OH)

L-Stercobilin-HCl and d-Urobilin-HCl. Analysis of Their Chiroptical and Conformational Properties by VCD, ECD, and CPL Experiments and MD and DFT Calculations

Vibrational circular dichroism (CD) and IR spectra of dichloromethane solutions of l-stercobilin and d-urobilin hydrochlorides have been recorded in the mid-IR region. The spectra are best interpreted by combining molecular dynamics calculations and density functional theory (DFT) calculations within the quantum mechanics/molecular mechanics ONIOM-type framework, and the combined predicted results are better and more informative than the more standard analysis provided by DFT calculations. The same approach also sheds light on the Cotton effect sign inversion of room temperature versus low-temperature electronic CD spectra of the same compounds in methanol–glycerol solution. Finally, circularly polarized luminescence spectra for l-stercobilin in chloroform solution provide information on the excited-state geometry of this molecule

Experimental and theoretical aspects of magnetic circular dichroism and magnetic circularly polarized luminescence in the UV, visible and IR ranges: A review

A historical sketch of the MCD (magnetic circular dichroism) spectroscopy is reported in its experimental and theoretical aspects. MCPL (magnetic circularly polarized luminescence) is also considered. The main studies are presented encompassing porphyrinoid systems, aggregates and materials, as well as simple organic molecules useful for the advancement of the interpretation. The MCD of chiral systems is discussed with special attention to new studies of natural products with potential pharmaceutical valence, including Amaryllidaceae alkaloids and related isocarbostyrils. Finally, the vibrational form of MCD, called MVCD, which is recorded in the IR part of the spectrum is also discussed. A final brief note on perspectives is given

Bilirubin and its congeners: conformational analysis and chirality from metadynamics and related computational methods

The conformational properties of natural bilirubin, bisbutyricmesobilirubin-XIIIα, and their chiral derivatives (βS,β′S)- dimethylmesobilirubin-XIIIα and 8,12-(γR,γ′R)- dimethylbisbutyricmesobilirubin-XIIIα were investigated by metadynamics, an improved molecular dynamics computational methodology useful for conformational analysis. Applied to linear tetrapyrroles, which may be treated as two blade molecular propellers, our results are represented by conformational energy hypersurface maps built as functions of the two central dihedral torsion angles (φ1 and φ2) following rotations of two dipyrrinone units about the connecting CH2, and are compared successfully with maps previously obtained from molecular mechanics. With an emphasis on the conformationally more flexible 8,12-(γR,γ′R)-dimethylbisbutyricmesobilirubin-XIIIα, a conformationally mobile optically active bilirubinoid with butyric acid replacing propionic, metadynamics reveals global and nearby minima. Its electronic circular dichroism and UV–Vis spectra predicted by DFT calculations correlate well with the experimental spectra and are explained on the basis of equilibrium between the predicted conformational energy minima

Carotid artery aneurysm associated with Marfan Syndrome: A case report

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The Antitumor Didox Acts as an Iron Chelator in Hepatocellular Carcinoma Cells

Ribonucleotide reductase (RR) is the rate-limiting enzyme that controls the deoxynucleotide triphosphate synthesis and it is an important target of cancer treatment, since it is expressed in tumor cells in proportion to their proliferation rate, their invasiveness and poor prognosis. Didox, a derivative of hydroxyurea (HU), is one of the most potent pharmaceutical inhibitors of this enzyme, with low in vivo side effects. It inhibits the activity of the subunit RRM2 and deoxyribonucleotides (dNTPs) synthesis, and it seems to show iron-chelating activity. In the present work, we mainly investigated the iron-chelating properties of didox using the HA22T/VGH cell line, as a model of hepatocellular carcinoma (HCC). We confirmed that didox induced cell death and that this effect was suppressed by iron supplementation. Interestingly, cell treatments with didox caused changes of cellular iron content, TfR1 and ferritin levels comparable to those caused by the iron chelators, deferoxamine (DFO) and deferiprone (DFP). Chemical studies showed that didox has an affinity binding to Fe3+ comparable to that of DFO and DFP, although with slower kinetic. Structural modeling indicated that didox is a bidentated iron chelator with two theoretical possible positions for the binding and among them that with the two hydroxyls of the catechol group acting as ligands is the more likely one. The iron chelating property of didox may contribute to its antitumor activity not only blocking the formation of the tyrosil radical on Tyr122 (such as HU) on RRM2 (essential for its activity) but also sequestering the iron needed by this enzyme and to the cell proliferation