Search

We present a computational protocol for the fast and automated screening of excited-state hybrid quantum mechanics/molecular mechanics (QM/MM) models of rhodopsins to be used as fluorescent probes based on the automatic rhodopsin modeling protocol (

Molecules where the energy of the lowest excited singlet state is found below the energy of the lowest triplet state (inverted singlet-triplet molecules) are extremely rare. It is particularly challenging to discover new ones through virtual screening because the required wavefunction-based methods are expensive and unsuitable for high-throughput calculations. Here, we devised a virtual screening approach where the molecules to be considered with advanced methods are pre-selected with increasingly more sophisticated filters that include the evaluation of the HOMO-LUMO exchange integral and approximate CASSCF calculations. A final set of 7 candidates (0.05\% of the initial 15000) were verified to possess inversion between singlet and triplet states with state-of-the-art multireference methods (MS--CASPT2). One of them is deemed of particular interest because it is unrelated to other proposals made in the literature.

We introduce a rigorous computational protocol based on multiobjective optimisation leading to the systematic identification of the conformations showing the best compromise among all the properties relevant to TADF applications.

Source code of the PyARM package, Access to the developer's repository can be obtained by contacting the corresponding author. L.P.G, L.B., D.P., L.D.V. and M.O. acknowledge partial support provided by MUR (Ministero dell'Università e della Ricerca) grant "Dipartimento di Eccellenza 2018 - 2022". M.M. acknowledges for ERASMUS+ Internship 2019-2020 from Wrocław University of Science and Technology. D.P. acknowledges the Italian Ministry of University and Research (MUR) for a Rita Levi Montalcini grant (PGR18PJMBW). M.O. acknowledges partial support provided by grants NSF CHE-CLP-1710191, NIH 1R15GM126627 01, and Banca d'Italia.

The wide range of time/length scales covered by self-assembly in soft matter makes molecular dynamics (MD) the ideal candidate for simulating such a supramolecular phenomenon at an atomistic level. However, the reliability of MD outcomes heavily relies on the accuracy of the adopted force-field (FF). The spontaneous re-ordering in liquid crystalline materials stands as a clear example of such collective self-assembling processes, driven by a subtle and delicate balance between supramolecular interactions and single-molecule flexibility. General-purpose transferable FFs often dramatically fail to reproduce such complex phenomena, for example, the error on the transition temperatures being larger than 100 K. Conversely, quantum-mechanically derived force-fields (QMD-FFs), specifically tailored for the target system, were recently shown (

Non-fullerene acceptors led to outstanding improvements in the efficiency of organic photovoltaic devices, with high promises of further advancements. Several studies have been performed to rationalise their exceptional performances, with the final goal of developing a reliable protocol for the identification of new materials with better properties. In this respect, we here combine molecular dynamics, density functional theory and Fermi's Golden Rule (FGR) to model two recent all-small-molecule bulk heterojunctions with high power conversion efficiencies, namely ZR1:IDIC-4Cl and ZR1:Y6 (Nat. Commun. 2019, 10, 5393). We evaluate the FGR rates for photoinduced hole and electron transfer, excitation energy transfer, and charge recombination on a statistical ensemble of donor/acceptor pairs extracted from molecular dynamics simulations. Our results provide a simple rationalisation of the great performance of Y6: aside from a slower charge recombination rate, we found that the charge transfer state for ZR1:Y6 can be accessed both via electron and hole transfer, while the latter pathway is significantly slower for IDIC-4Cl, indicating that its first excited state behaves as a trap, as confirmed by a simple kinetic model. In light of the recently reported possibility of developing donors and acceptors with complementary absorption spectra, multiple photoexcited charge transfer pathways represent a key property to efficiently harvest the whole solar spectrum.

A series of candidates of thermally activated delayed fluorescence (TADF) materials, which have important applications in organic light emitting diodes devices, are identified by a high-throughput virtual screening of a database of known molecular materials. The first step of the screening identifies nearly 700 molecules that, in the X-ray geometry, have a sufficiently small gap between excitation energy of the lowest singlet and triplet states and acceptable oscillator strength of the singlet. After geometry optimization, 125 molecules continue to satisfy the energy criteria for potential TADF. Furthermore, the parameters of excited state dynamics including the reorganization energy, adiabatic excitation energy and spin–orbital coupling are calculated for a sample of molecules based on the optimized excited state geometries. The majority of the candidates are not known as TADF materials and could be considered promising lead compounds for the exploration of this materials class. Interestingly, it is found that some novel chromophores deviate from the current design rule for TADF materials, which are invariably based on a donor–acceptor molecular architecture. We also illustrate how to design completely new types of TADF materials using the results of this screening.

he diradical and multiradical characters of a large and diverse set of 241 predicted singlet fission candidates are determined by multiconfigurational wavefunction methods, specifically natural orbital occupation number (NOON) analysis using the CASSCF method. The ascertained multiradical character strongly supports the current prediction that a good singlet fission candidate, independent of its structure, will tend to be of the weak biradicaloid class as well as having very little tetraradical character. Although the rule remains robust, it is not absolute as a small portion of our potential candidates are predicted to be closed shell. Additionally, a smaller handful of outliers with apparent tetraradical characters are identified, suggesting there may be the possibility, albeit rare, of singlet fission amongst weak tetraradicaloids.

The stereoselective transformation of chiral UV-transparent amines and alcohols to phthalimides has proved to be a simple and efficient method to enhance the chiroptical response of these substrates allowing their reliable absolute configuration determination by computational analysis of ECD spectra. Such a transformation also leads to a significant reduction in the molecular conformational flexibility thus simplifying the conformational analysis required by the computational treatment. The method described herein thus allows the absolute configuration assignment to these challenging substrates to be much easier and reliable.

In recent years, photoactive proteins such as rhodopsins have become a common target for cutting-edge research in the field of optogenetics. Alongside wet-lab research, computational methods are also developing rapidly to provide the necessary tools to analyze and rationalize experimental results and, most of all, drive the design of novel systems. The Automatic Rhodopsin Modeling (ARM) protocol is focused on providing exactly the necessary computational tools to study rhodopsins, those being either natural or resulting from mutations. The code has evolved along the years to finally provide results that are reproducible by any user, accurate and reliable so as to replicate experimental trends. Furthermore, the code is efficient in terms of necessary computing resources and time, and scalable in terms of both number of concurrent calculations as well as features. In this review, we will show how the code underlying ARM achieved each of these properties.

In recent years, photoactive proteins such as rhodopsins have become a common target for cutting-edge research in the field of optogenetics. Alongside wet-lab research, computational methods are also developing rapidly to provide the necessary tools to analyze and rationalize experimental results and, most of all, drive the design of novel systems. The Automatic Rhodopsin Modeling (ARM) protocol is focused on providing exactly the necessary computational tools to study rhodopsins, those being either natural or resulting from mutations. The code has evolved along the years to finally provide results that are reproducible by any user, accurate and reliable so as to replicate experimental trends. Furthermore, the code is efficient in terms of necessary computing resources and time, and scalable in terms of both number of concurrent calculations as well as features. In this review, we will show how the code underlying ARM achieved each of these properties.

We present a data set of 48182 organic semiconductors, constituted of molecules that were prepared with a documented synthetic pathway and are stable in solid state. We based our search on the Cambridge Structural Database, from which we selected semiconductors with a computational funnel procedure. For each entry we provide a set of electronic properties relevant for organic materials research, and the electronic wavefunction for further calculations and/or analyses. This data set has low bias because it was not built from a set of materials designed for organic electronics, and thus it provides an excellent starting point in the search of new applications for known materials, with a great potential for novel physical insight. The data set contains molecules used as benchmarks in many fields of organic materials research, allowing to test the reliability of computational screenings for the desired application, “rediscovering” well-known molecules. This is demonstrated by a series of different applications in the field of organic materials, confirming the potential for the repurposing of known organic molecules.

We considered a database of tens of thousands of known organic semiconductors and identified those compounds with computed electronic properties (orbital energies, excited state energies, and oscillator strengths) that would make them suitable as nonfullerene electron acceptors in organic solar cells. The range of parameters for the desirable acceptors is determined from a set of experimentally characterized high-efficiency nonfullerene acceptors. This search leads to ∼30 lead compounds never considered before for organic photovoltaic applications. We then proceed to modify these compounds to bring their computed solubility in line with that of the best small-molecule nonfullerene acceptors. A further refinement of the search can be based on additional properties like the reorganization energy for chemical reduction. This simple strategy, which relies on a few easily computable parameters and can be expanded to a larger set of molecules, enables the identification of completely new chemical families to be explored experimentally.

We investigate the role of the local protein environment on the energy transfer processes in biological molecules, excluding from the analysis the effect of intra-chromophore nuclear motions, and focussing on the exciton-phonon coupling. We studied three different proteins (FMO and two variants of the WSCP protein) with different biological functions but similar chromophores, to understand whether a classification of chromophores based on the details of the environment would be possible, and whether specific environments enhance or suppress the coupling between exciton and protein dynamics. Our results show that despite the different biological role, there is no significant difference in the influence of the environment on the properties of the chromophores. Additionally, we show that the main role in influencing molecular properties is played by solvent molecules: the interaction occurs on a medium-range scale, and the solvent is kept in place by a strong H-bond network being free to rotate, suggesting a dipole-dipole interaction mechanism. Steric hindrance exerted by other moieties can help modulating the interactions and tuning the energy transfer process. Overall, considering also the relatively greater importance of intra-molecular nuclear motions, the protein environment around biological chromophores does not appear fine-tuned for a specific function.

We used a homogeneous computational approach to derive the excitonic Hamiltonian for five light harvesting complexes containing only one type of chromophore and compare them in terms of statistical descriptors. We then studied the approximate exciton dynamics for the five complexes introducing a measure, the (averaged and time-dependent) inverse participation ratio, that enables the comparison between very diverse complexes on the same ground. We find that the global dynamics are very similar across the set of systems despite the variety of geometric structures of the complexes. In particular, the dynamics of four out of five light harvesting complexes are barely distinguishable with a small variation from the norm seen only for the Fenna-Matthews-Olson complex. We use the information from the realistic Hamiltonians to build a reduced model system that shows how the global dynamics are ultimately dominated by a single parameter, the degree of localization of the excitonic Hamiltonian eigenstates. Considering the physically plausible range of system parameters, the reduced model explains why the dynamics are so similar across most light harvesting complexes containing a single type of chromophore regardless of the detailed pattern of the inter-chromophore excitonic coupling.

A large set of candidates for singlet fission, one of the most promising processes able to improve the efficiency of solar cells, are identified by screening a database of known molecular materials. The screening was carried out through a procedure exploiting quantum chemical calculations of excited state energies, carefully calibrated against a substantial set of experimental data. We identified ∼200 potential singlet fission molecules, the vast majority of which were not known as singlet fission materials. The molecules identified could be grouped into chemical families, enabling the design of further singlet fission materials using the hits as lead compounds for further exploration. Many of the discovered materials do not follow the current design rules used to develop singlet fission materials, illustrating at the same time the power of the screening approach and the need for developing new design principles.

We present a translation of the chemical intuition in materials discovery, in terms of chemical similarity of efficient materials, into a rigorous framework exploiting machine learning. We computed equilibrium geometries and electronic properties (DFT) for a database of 249 Organic donor–acceptor pairs. We obtain similarity metrics between pairs of donors in terms of electronic and structural parameters, and we use such metrics to predict photovoltaic efficiency through linear and non-linear machine learning models. We observe that using only electronic or structural parameters leads to similar results, while considering both parameters at the same time improves the predictive capability of the models up to correlations of r ≈ 0.7. Such correlation allows for reliable predictions of efficient materials, and lends to be coupled with combinatorial of evolutionary approaches for a more reliable virtual screening of candidate materials.

Bidentate enantiopure Schiff base ligands, (R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldiminate (R- or S-N^O), diastereoselectively provide Λ- or Δ-chiral-at-metal four-coordinated Zn(R- or S-N^O)2 {Ar = C6H5; Zn-1R or Zn-1S and p-C6H4OMe; Zn-2R or Zn-2S}. Two R- or S-N^O-chelate ligands coordinate to the zinc(II) in a tetrahedral mode and induce Λ- or Δ-configuration at the zinc metal center. In the solid state, the R- or S-ligand diastereoselectively gives Λ- or Δ-Zn configuration, respectively, and forms enantiopure crystals. Single crystal structure determinations show two symmetry-independent molecules (A and B) in each asymmetric unit to give Z' = 2 structures. Electronic circular dichroism (ECD) spectra show the expected mirror image relationship resulting from diastereomeric excess toward the Λ-Zn for R-ligands and Δ-Zn for S-ligands in solution. ECD spectra are well reproduced by TDDFT calculations, while the application of the exciton chirality method, in the common point-dipole approximation, predicts the wrong sign for the long-wavelength couplet. A dynamic diastereomeric equilibrium (Λ vs Δ) prevails for both R- and S-ligand-metal complexes in solution, respectively, evidenced by (1)H NMR spectroscopy. Variable temperature (1)H NMR spectra show a temperature-dependent shift of the diastereomeric equilibrium and confirm Δ-Zn configuration (for S-ligand) to be the most stable one and favored at low temperature. DSC analyses provide quantitative diastereomeric excess in the solid state for Zn-2R and Zn-2S, which is comparable to the results of solution studies.

Chiroptical spectra such as electronic circular dichroism (ECD) are said to be much more sensitive to conformation than their non-chiroptical counterparts, however, it is difficult to demonstrate such a common notion in a clear-cut way. We run DFT and TDDFT calculations on two closely related 1,1-diarylmethanols which show mirror-image ECD spectra for the same absolute configuration. We demonstrate that the main reason for the different chiroptical response of the two compounds lies in different conformational ensembles, caused by a single hydrogen-to-methyl substitution. We conclude that two compounds, having the same configuration but different conformation, may exhibit mirror-image ECD signals, stressing the importance and impact of conformational factors on ECD spectra.

In this paper, we adopt an approach suitable for monitoring the time evolution of the intramolecular contribution to the spectral density of a set of identical chromophores embedded in their respective environments. We apply the proposed method to the Fenna-Matthews-Olson (FMO) complex, with the objective to quantify the differences among site-dependent spectral densities and the impact of such differences on the exciton dynamics of the system. Our approach takes advantage of the vertical gradient approximation to reduce the computational demands of the normal modes analysis. We show that the region of the spectral density that is believed to strongly influence the exciton dynamics changes significantly in the timescale of tens of nanoseconds. We then studied the impact of the intramolecular vibrations on the exciton dynamics by considering a model of FMO in a vibronic basis and neglecting the interaction with the environment to isolate the role of the intramolecular exciton-vibration coupling. In agreement with the assumptions in the literature, we demonstrate that high frequency modes at energy much larger than the excitonic energy splitting have negligible influence on exciton dynamics despite the large exciton-vibration coupling. We also find that the impact of including the site-dependent spectral densities on exciton dynamics is not very significant, indicating that it may be acceptable to apply the same spectral density on all sites. However, care needs to be taken for the description of the exciton-vibrational coupling in the low frequency part of intramolecular modes because exciton dynamics is more susceptible to low frequency modes despite their small Huang-Rhys factors.

We constructed a database of 80 high performing non-fullerene electron acceptors and studied the common electronic and geometric properties in search of unifying design rules. We discovered that, without exception, all high performing materials are characterized by very low gap between LUMO and LUMO+1 orbitals, a feature that is consistent with microscopic models and seems to be true for all classes of compounds considered. We also confirmed that non-planarity of the acceptor is beneficial but not for all classes of acceptors. We suggested that by building similar databases and keeping it up to date it will be possible to identify statistically meaningful structure–property relations.

The singlet excitonic coupling between many pairs of chromophores is evaluated in three different light harvesting complexes (LHCs) and two organic semiconductors (amorphous and crystalline). This large database of structures is used to assess the relative importance of short-range (exchange, overlap, orbital) and long-range (Coulombic) excitonic coupling. We find that Mulliken atomic transition charges can introduce systematic errors in the Coulombic coupling and that the dipole–dipole interaction fails to capture the true Coulombic coupling even at intermolecular distances of up to 50 Å. The non-Coulombic short-range contribution to the excitonic coupling is found to represent up to ∼70% of the total value for molecules in close contact, while, as expected, it is found to be negligible for dimers not in close contact. For the face-to-face dimers considered here, the sign of the short-range interaction is found to correlate with the sign of the Coulombic coupling, i.e. reinforcing it when it is already strong. We conclude that for molecules in van der Waals contact the inclusion of short-range effects is essential for a quantitative description of the exciton dynamics.

Lanthanide complexes exhibit interesting spectroscopic properties yielding many applications as imaging probes, natural chirality amplifiers, and therapeutic agents. However, many properties are not fully understood yet. Therefore, we applied magnetic circular dichroism (MCD) spectroscopy, which provides enhanced information about the underlying electronic structure to a series of lanthanide compounds. The metals in the M(3+) state included Y, La, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu; the spectra were collected for selected tetraphenylporphin (TPP) and octaethylporphin (OEP) complexes in chloroform. While the MCD and UV-VIS absorption spectra were dominated by the porphyrin signal, metal binding significantly modulated them. MCD spectroscopy was found to be better suited to discriminate between various species than absorption spectroscopy alone. The main features and trends in the lanthanide series observed in MCD and absorption spectra of the complexes could be interpreted at the Density Functional Theory (DFT) level, with effective core potentials on metal nuclei. The sum over state (SOS) method was used for simulation of the MCD intensities. The combination of the spectroscopy and quantum-chemical computations is important for understanding the interactions of the metals with the organic compounds.

A series of 13 enantiopure aryl benzyl sulfoxides (1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i, 1j, 1k, 1l, 1m) with different substituents on the two aromatic rings has been previously analyzed by means of electronic circular dichroism (CD) spectroscopy. Most of these compounds are crystalline and their X-ray structure is established. For almost one-half of the series, CD spectra measured in the solid state were quite different from those in acetonitrile solution. We demonstrate that the difference is due to strong exciton couplings between molecules packed closely together in the crystal. The computational approach consists of time-dependent density functional theory (TDDFT) calculations run on “dimers” composed of nearest neighbors found in the lattice. Solid-state CD spectra are well reproduced by the average of all possible pairwise terms. The relation between the crystal space group and conformation, and the appearance of solid-state CD spectra, is also discussed. Chirality 26:462–470, 2013. © 2013 Wiley Periodicals, Inc.

Three forms of chiroptical spectroscopies, electronic circular dichroism (ECD), vibrational circular dichroism (VCD), and optical rotatory dispersion (ORD) have been employed to study the configuration and conformational properties of the three molecules: (S)-3-phenylcyclopentanone, (S)-3-phenylcyclohexanone, and (S)-3-phenylcycloheptanone (including (S)-3-phenylcyclopentanone-2,2,5,5-d4 and (S)-3-phenylcyclohexanone-2,2,6,6-d4). ECD and VCD spectra in the mid-IR for the three molecular systems are marginally dependent on fine conformational details, as interpreted in terms of standard DFT computational methods, with common spectroscopic features to the three systems clearly identified. Accounting for vibronic coupling mechanisms reproduces the structuring of ECD n→π∗ band. The ORD curves are quite similar for the three types of molecules, but their interpretation highlights a crucial role played by conformations of the cycloalkanone ring in the case of (S)-3-phenylcycloheptanone. The same conclusions are reached by considering the VCD spectra in the CH-stretching region.

In 1997, Sandström and co-workers reported the case of two chiral spiro compounds with very similar skeletons but showing almost mirror-image electronic circular dichroism (ECD) spectra for the corresponding absolute configuration. The paper has been often cited as a proof and good educational example of the pronounced sensitivity of ECD toward molecular conformation, and a clear warning against the use of ECD spectral correlations to assign absolute configurations. Although both concepts remain valid, they are not exemplified by the quoted paper. We demonstrate that the original configurational assignment of one compound was wrong and revise it by using TDDFT calculations. The main reason for the observed failure is the use of the matrix method, a popular approach to predict ECD spectra of compounds which can be treated with an independent system approximation (ISA), including proteins. Using a modern version of the matrix method, we demonstrate that the ISA is not valid for the title compound. Even in the absence of apparent conjugation between the component chromophores, the validity of the ISA should never be taken for granted and the effective extent of orbital overlap should always be verified.

Aggregates of chiral polythiophenes (PTs) show strong electronic circular dichroism (ECD) spectra with a unique vibronic structure. A computationally fast procedure, exploiting the quantum dynamics of the exciton-coupled electronic states of simple oligothiophene dimers as models of PT aggregates, is able to reproduce experimental vibronic ECD spectra of aggregated phases.

We present a quantum mechanical (QM) simulation of the electronic circular dichroism (ECD) of nucleic acids (NAs). The simulation combines classical molecular dynamics, to obtain the structure and its temperature-dependent fluctuations, with a QM excitonic model to determine the ECD. The excitonic model takes into account environmental effects through a polarizable embedding and uses a refined approach to calculate the electronic couplings in terms of full transition densities. Three NAs with either similar conformations but different base sequences or similar base sequences but different conformations have been investigated and the results were compared with experimental observations; a good agreement was seen in all cases. A detailed analysis of the nature of the ECD bands in terms of their excitonic composition was also carried out. Finally, a comparison between the QM and the DeVoe models clearly revealed the importance of including fluctuations of the excitonic parameters and of accurately determining the electronic couplings. This study demonstrates the feasibility of the ab initio simulation of the ECD spectra of NAs, that is, without the need of experimental structural or electronic data.

The results of a combined experimental and theoretical study of the electronic circular dichroism spectrum of (−)–[9] (2,5)Pyridinophane are presented. The features observed in the measured spectrum in the 180–350 nm wavelength region are reproduced by a series of calculations carried out within a density functional time-dependent approach, coupled with a vibronic analysis allowing rationalizing unambiguously the chiral response of the molecule. Chirality 24:994–1004, 2012. © 2012 Wiley Periodicals, Inc.

By reacting flexible and optically transparent in UV-vis molecules such as 1,2-, syn- and anti-1,3-diols, 1,3-sulfanylalcohols of known absolute configuration (AC) with fluorenone dimethyl acetal, the corresponding ketals are obtained. They are conformationally well-defined (only one conformer in most cases) compounds exhibiting medium-high optical rotation (OR) values, which are independent of the solvent, and electronic circular dichroism (ECD) spectra, which show several (up to five) Cotton effects in the 350-200 nm range due to valence shell pi--pi* transitions. These features allow simulation of the chiroptical properties of these compounds at the TDDFT/B3LYP/6-31G* level of theory to obtain, using the known ACs of these compounds, a satisfactory reproduction of the OR values (sign and order of magnitude; quantitatively, the predicted values are twice the experimental ones), and a more than satisfactory reproduction of the ECD spectra (sign, intensity, and position of the lowest-energy four Cotton effects) for all the compounds studied. Therefore, this approach can be used to assign the AC of such flexible molecules, in particular, syn-1,3-diols, which are important substrates in organic synthesis and for which nonempirical methods of AC assignment have not been devised so far. Furthermore, since the fluorene chromophore leads to the presence of several Cotton effects from, say, 350 to 200 nm, their correct simulation of sign, intensity, and position is a guarantee of the correct assignment of AC: in this way, ECD spectroscopy gains the same advantages of VCD spectroscopy, that is, the need of reproducing many ECD bands and then a solid guarantee of a correct AC assignment.

A combined experimental-computational analysis of the one- and two-photon absorption (OPA, TPA) and the electronic circular dichroism (ECD) of complex chiral shape-persistent (2,6)-pyrido[14(2)]allenoacetylenic cyclophane, (P,P,P,P)-MC[14(2)] enantiomers, sheds light on the origin of their peculiar spectral signatures. The study on MC[14(2)], which is represented in solution by three possible conformers, indicates that two of them (chair and twist) are the prevalent conformers at room temperature; the population ratio depending on the solvent. The complex shape of the red-edge of the UV and ECD spectra is qualitatively reproduced by using vibronic calculations and assigned to progressions on the ethynyl stretchings observable only in the chair and twist conformers. The picture arising from the analysis of the linear spectra is confirmed by two-photon spectroscopies, showing that they constitute valuable tools for the exploration of high-energy electronic transitions in pyridoallenoacetylenic cyclophanes. Discrepancies among computed and experimental spectra point out that an accurate description of such complex systems with a large delocalized framework and a dense manifold of electronic excited state remains a challenge for theoretical models.

International audience; Enantiopure hemicryptophanes designed from the cyclotriveratrylene (CTV) unit display remarkable properties in selective host–guest recognition or as supramolecular catalysts. The unprecedented control of the helical chirality of the CTV unit by remote stereogenic centers of a tren moiety is reported, providing an original access to this highly promising class of host molecules. Although the chiral centers and the CTV unit are separated by more than 10 Å, one single diastereomer is formed; the nature of the diastereoselective process is discussed and the procedure is exemplified using different enantiopure tren derivatives. This work also highlights the influence of the chirality of the CTV unit on the whole cage structure.

International audience; Four new enantiopure hemicryptophanes were synthesized and their absolute configuration was determined from experimental and calculated ECD spectra. Complexation properties of these receptors were studied toward six carbohydrate stereoisomers derived from glucose, galactose and mannose. All the receptors showed a better affinity for α-mannoside with association constants up to 2.5 × 103 M−1. One of the receptor can complex almost exclusively α-mannoside facing to α-galactoside.

International audience; Four new enantiomerically and diastereomerically pure hemicryptophane hosts (M-SSS-2/P-SSS-2 and M-RRR-2/P-RRR-2 pairs) were designed for the recognition of sugar derivatives. Their absolute configuration was determined from the circular dichroism spectra and DFT calculations. The host molecules were then used for the stereoselective recognition of glucopyranosides. Binding constants were obtained from 1H NMR titration experiments showing an increase of affinity for this class of receptors, associated with an improved diastereo- and enantio-differentiation.

A series of 13 enantiopure aryl benzyl sulfoxides (1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i, 1j, 1k, 1l, 1m) with different substituents on the two aromatic rings has been previously analyzed by means of electronic circular dichroism (CD) spectroscopy. Most of these compounds are crystalline and their X-ray structure is established. For almost one-half of the series, CD spectra measured in the solid state were quite different from those in acetonitrile solution. We demonstrate that the difference is due to strong exciton couplings between molecules packed closely together in the crystal. The computational approach consists of time-dependent density functional theory (TDDFT) calculations run on "dimers" composed of nearest neighbors found in the lattice. Solid-state CD spectra are well reproduced by the average of all possible pairwise terms. The relation between the crystal space group and conformation, and the appearance of solid-state CD spectra, is also discussed. Chirality 26:102-110, 2013. © 2013 Wiley Periodicals, Inc. © 2013 Wiley Periodicals, Inc.

A new dibenzocyclooctene-type lignan, named schisandrin A1 (1), together with nine known lignans (2-10), was isolated from the stems of Schisandra sphenathera. The structure of schisandrin A1, which contains a spirocyclic epoxy unit, was established by means of spectroscopic methods. The absolute configurations of schisandrin A1 (1) and schisantherin A (2) were determined by electronic circular dichroism (CD) and TDDFT calculations, with 2 further confirmed by X-ray crystallographic data. Ten new schisantherin A derivatives (11-20) and 6,7-secoschisantherol A (2b) were synthesized. In addition, natural lignans and semisynthetic schisantherin A derivatives showed the antiproliferative activity on four human cancer cell lines and Id1 (an inhibitor of DNA binding protein) and estrogenic potency. Compounds 5, 7, and 8 exhibited very potent estrogenic activity.