Twin-to-Twin Transfusion Syndrome: Diagnostic Imaging and Its Role in Staving Off Malpractice Charges and Litigation.

The study aims to expound upon the imaging-based diagnostic methodologies aimed at identifying twin-to-twin transfusion syndrome (TTTS), a serious, somewhat rare prenatal condition that takes place in pregnancies where identical twins, or other multiples, share a placenta (monochorionic placenta), highlighting how medico-legal outcomes can be affected by provable compliance with consolidated diagnostic guidelines or best practices. It is of utmost importance to produce a prompt identification of TTTS instances; an early diagnosis is in fact critical in order to effectively treat and manage TTTS. By virtue of TTTS being a highly progressive condition, a delay in diagnosis can result in disastrous outcomes; just a few weeks delay in the diagnosis of TTTS can turn out fatal for one or both twins.

Coupling to Charge Transfer States is the Key to Modulate the Optical Bands for Efficient Light Harvesting in Purple Bacteria.

The photosynthetic apparatus of purple bacteria uses exciton delocalization and static disorder to modulate the position and broadening of its absorption bands, leading to efficient light harvesting. Its main antenna complex, LH2, contains two rings of identical bacteriochlorophyll pigments, B800 and B850, absorbing at 800 and 850 nm, respectively. It has been an unsolved problem why static disorder of the strongly coupled B850 ring is several times larger than that of the B800 ring.

Shaping excitons in light-harvesting proteins through nanoplasmonics.

Nanoplasmonics has been used to enhance molecular spectroscopic signals, with exquisite spatial resolution down to the sub-molecular scale. By means of a rigorous, state-of-the-art multiscale model based on a quantum chemical description, here we show that optimally tuned tip-shaped metal nanoparticles can selectively excite localized regions of typically coherent systems, eventually narrowing down to probing one single pigment. The well-known major light-harvesting complex LH2 of purple bacteria has been investigated because of its unique properties, as it presents both high and weak delocalization among subclusters of pigments.

Coupling Real-Time Time-Dependent Density Functional Theory with Polarizable Force Field.

Real-time time-dependent density functional theory (RT-TDDFT) is a powerful tool for obtaining spectroscopic observables and understanding complex, time-dependent properties. Currently, performing RT-TDDFT calculations on large, fully quantum mechanical systems is not computationally feasible. Previously, polarizable mixed quantum mechanical and molecular mechanical (QM/MMPol) models have been successful in providing accurate, yet efficient, approximations to a fully quantum mechanical system.

Hybrid QM/MM Molecular Dynamics with AMOEBA Polarizable Embedding.

We present the implementation of a Born-Oppenheimer (BO) hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) strategy using density functional theory (DFT) and the polarizable AMOEBA force field. This approach couples the Gaussian and Tinker suite of programs through a variational formalism allowing for a full self-consistent relaxation of both the AMOEBA induced dipoles and the DFT electron density at each MD step. As the DFT SCF cycles are the limiting factor in terms of computational efforts and MD stability, we focus on the latter aspect and compare the time-reversible BO (TR-BO) and the extended BO Lagrangian approaches (XL-BO) to the MD propagation.

Excited-State Gradients in Polarizable QM/MM Models: An Induced Dipole Formulation.

Charge and structural relaxation of electronically excited states in embedded systems are strongly affected by the environment. It is known that the largest part of environment effects comes from electrostatics. However, polarization can also play a role by tuning the electronic and geometrical properties of the states, finally modifying the fluorescence.

Theoretical description of protein field effects on electronic excitations of biological chromophores.

Photoinitiated phenomena play a crucial role in many living organisms. Plants, algae, and bacteria absorb sunlight to perform photosynthesis, and convert water and carbon dioxide into molecular oxygen and carbohydrates, thus forming the basis for life on Earth. The vision of vertebrates is accomplished in the eye by a protein called rhodopsin, which upon photon absorption performs an ultrafast isomerisation of the retinal chromophore, triggering the signal cascade.

An Ab Initio Description of the Excitonic Properties of LH2 and Their Temperature Dependence.

The spectroscopic properties of light-harvesting (LH) antennae in photosyntehtic organisms represent a fingerprint that is unique for each specific pigment-protein complex. Because of that, spectroscopic observations are generally combined with structural data from X-ray crystallography to obtain an indirect representation of the excitonic properties of the system. Here, an alternative strategy is presented which goes beyond this empirical approach and introduces an ab initio computational description of both structural and electronic properties and their dependence on the temperature.

A QM/MM Approach Using the AMOEBA Polarizable Embedding: From Ground State Energies to Electronic Excitations.

A fully polarizable implementation of the hybrid quantum mechanics/molecular mechanics approach is presented, where the classical environment is described through the AMOEBA polarizable force field. A variational formalism, offering a self-consistent relaxation of both the MM induced dipoles and the QM electronic density, is used for ground state energies and extended to electronic excitations in the framework of time-dependent density functional theory combined with a state specific response of the classical part. An application to the calculation of the solvatochromism of the pyridinium N-phenolate betaine dye used to define the solvent ET(30) scale is presented.

Control of Coherences and Optical Responses of Pigment-Protein Complexes by Plasmonic Nanoantennae.

The key for light-harvesting in pigment-protein complexes are molecular excitons, delocalized excited states comprising a superposition of excitations at different molecular sites. There is experimental evidence that the optical response due to such excitons can be largely affected by plasmonic nanoantennae. Here we employ a multiscale approach combining time-dependent density functional theory and polarizable classical models to study the optical behavior of the LH2 complex present in bacteria when interacting with a gold nanorod.

Photoprotection and triplet energy transfer in higher plants: the role of electronic and nuclear fluctuations.

Photosynthetic organisms employ several photoprotection strategies to avoid damage due to the excess energy in high light conditions. Among these, quenching of triplet chlorophylls by neighboring carotenoids (Cars) is fundamental in preventing the formation of singlet oxygen. Cars are able to accept the triplets from chlorophylls by triplet energy transfer (TET).

Achieving linear scaling in computational cost for a fully polarizable MM/continuum embedding.

In this paper, we present a new, efficient implementation of a fully polarizable QM/MM/continuum model based on an induced-dipoles polarizable force field and on the Conductor-like Screening Model as a polarizable continuum in combination with a self-consistent field QM method. The paper focuses on the implementation of the MM/continuum embedding, where the two polarizable methods are fully coupled to take into account their mutual polarization. With respect to previous implementations, we achieve for the first time a linear scaling with respect to both the computational cost and the memory requirements without limitations on the molecular cavity shape.

Plasmon enhanced light harvesting: multiscale modeling of the FMO protein coupled with gold nanoparticles.

Plasmonic systems, such as metal nanoparticles, are becoming increasingly important in spectroscopies and devices because of their ability to enhance, even by several orders of magnitude, the photophysical properties of neighboring systems. In particular, it has been shown both theoretically and experimentally that combining nanoplasmonic devices with natural light-harvesting proteins substantially increases the fluorescence and absorption properties of the system. This kind of biohybrid device can have important applications in the characterization and design of efficient light-harvesting systems.

Excitation energy transfer in donor-bridge-acceptor systems: a combined quantum-mechanical/classical analysis of the role of the bridge and the solvent.

The technical application of excitation energy transfer requires a fine control of the geometry of the system. This can be achieved by introducing a chemical bridge between the donor and acceptor moieties that can be tuned in its chemical properties and its length. In such donor-bridge-acceptor systems, however, the role of the bridge in enhancing or depleting the energy transfer efficiency is not easy to predict.

Geometry Optimization in Polarizable QM/MM Models: The Induced Dipole Formulation.

We present the mathematical derivation and the computational implementation of the analytical geometry derivatives for a polarizable QM/MM model (QM/MMPol). In the adopted QM/MMPol model, the focused part is treated at QM level of theory, while the remaining part (the environment) is described classically as a set of fixed charges and induced dipoles. The implementation is performed within the ONIOM procedure, resulting in a polarizable embedding scheme, which can be applied to solvated and embedded systems and combined with different polarizable force fields available in the literature.

Toward a Unified Modeling of Environment and Bridge-Mediated Contributions to Electronic Energy Transfer: A Fully Polarizable QM/MM/PCM Approach.

Recent studies have unveiled the similar nature of solvent (screening) effects and bridge-mediated contributions to electronic energy transfer, both related to the bridge/solvent polarizability properties. Here, we exploit the similarity of such contributions to develop a fully polarizable mixed QM/discrete/continuum model aimed at studying electronic energy transfer processes in supramolecular systems. In the model, the definition of the three regions is completely flexible and allows us to explore the possibility to describe bridge-mediated contributions by using a polarizable MM description of the linker.

Quantum mechanical study of the solvent-dependence of electronic energy transfer rates in a Bodipy closely-spaced dyad.

The ability of Förster theory to describe electronic energy transfer rates, and their solvent-dependence, have been studied theoretically in a series of 15 solvents of varying degrees of polarity for a rigid closely-spaced dyad, constituted by two boron dipyrromethene dyes, which was recently studied experimentally by Harriman & Ziessel, Photochem. Photobiol. Sci.

Theoretical investigation of the mechanism and dynamics of intramolecular coherent resonance energy transfer in soft molecules: a case study of dithia-anthracenophane.

A computational study is conducted on dithia-anthracenophane (DTA), for which there is experimental evidence for coherent resonance energy transfer dynamics, and on dimethylanthracene (DMA), a molecule representing the energy donor and the acceptor in DTA. Electronic excitation energies are calculated by configuration interaction singles (CIS) and time-dependent density functional theory (TD-DFT) methods and are compared to experimental ones. Electronic coupling constants are calculated between two DMAs embedded into the ground-state structure of DTA employing methods based on transition densities.