Environmental Contamination by SARS-CoV-2 During Noninvasive Ventilation in COVID-19.

BACKGROUND: Environmental contamination by SARS-CoV-2 from patients with COVID-19 undergoing noninvasive ventilation (NIV) in the ICU is still under investigation. This study set out to investigate the presence of SARS-CoV-2 on surfaces near subjects receiving NIV in the ICU under controlled conditions (ie, use of dual-limb circuits, filters, adequate room ventilation). METHODS: This was a single-center, prospective, observational study in the ICU of a tertiary teaching hospital. Four surface sampling areas, at increasing distance from subject's face, were identified; and each one was sampled at fixed intervals: 6, 12, and 24 h. The presence of SARS-CoV-2 was detected with real-time reverse transcriptase-polymerase-chain-reaction (RT-PCR) test on environmental swabs; the RT-PCR assay targeted the SARS-CoV-2 virus nucleocapsid N1 and N2 genes and the human RNase P gene as internal control. RESULTS: In a total of 256 collected samples, none were positive for SARS-CoV-2 genetic material, whereas 21 samples (8.2%) tested positive for RNase P, thus demonstrating the presence of genetic material unrelated to SARS-CoV-2. CONCLUSIONS: Our data show that application of NIV in an appropriate environment and with correct precautions leads to no sign of surface environmental contamination. Accordingly, our data support the idea that use of NIV in the ICU is safe both for health care workers and for other patients.

Fine Tuning of Retinal Photoinduced Decay in Solution.

Single methylation at position C10 of the all-trans retinal protonated Schiff base switches its excited-state decay in methanol from a slower picosecond into an ultrafast, protein-like subpicosecond process. QM/MM modeling in conjunction with on-the-fly excited-state dynamics provides fundamental understanding of the fine-tuning mechanics that "catalyzes" the photoinduced decay of solvated retinals. Methylation alters the interplay between the ionic S1 and covalent S2 states, reducing the excited-state lifetime by favoring the formation of a S1 transient fluorescent state with fully inverted bond lengths that accounts for the recorded transient spectroscopy and from which a space-saving conical intersection seam is quickly (<1 ps) reached. Minimal and apparently innocent chemical modifications thus affect the characteristic intramolecular charge-transfer of the S1 state as well as the interaction with the covalent S2 excited state, eventually providing the high tunability of retinal photophysics and photochemistry and delivering a new concept for the rational design of retinal-based photoactive molecular devices.

Deciphering the photochemical mechanisms describing the UV-induced processes occurring in solvated guanine monophosphate.

The photophysics and photochemistry of water-solvated guanine monophosphate (GMP) are here characterized by means of a multireference quantum-chemical/molecular mechanics theoretical approach (CASPT2//CASSCF/AMBER) in order to elucidate the main photo-processes occurring upon UV-light irradiation. The effect of the solvent and of the phosphate group on the energetics and structural features of this system are evaluated for the first time employing high-level ab initio methods and thoroughly compared to those in vacuo previously reported in the literature and to the experimental evidence to assess to which extent they influence the photoinduced mechanisms. Solvated electronic excitation energies of solvated GMP at the Franck-Condon (FC) region show a red shift for the ππ(*) La and Lb states, whereas the energy of the oxygen lone-pair nπ(*) state is blue-shifted. The main photoinduced decay route is promoted through a ring-puckering motion along the bright lowest-lying La state toward a conical intersection (CI) with the ground state, involving a very shallow stationary point along the minimum energy pathway in contrast to the barrierless profile found in gas-phase, the point being placed at the end of the minimum energy path (MEP) thus endorsing its ultrafast deactivation in accordance with time-resolved transient and photoelectron spectroscopy experiments. The role of the nπ(*) state in the solvated system is severely diminished as the crossings with the initially populated La state and also with the Lb state are placed too high energetically to partake prominently in the deactivation photo-process. The proposed mechanism present in solvated and in vacuo DNA/RNA chromophores validates the intrinsic photostability mechanism through CI-mediated non-radiative processes accompanying the bright excited-state population toward the ground state and subsequent relaxation back to the FC region.

Excited state evolution of DNA stacked adenines resolved at the CASPT2//CASSCF/Amber level: from the bright to the excimer state and back.

Deactivation routes of bright ππ* (La) and excimer charge transfer (CT) states have been mapped for two stacked quantum mechanical (CASPT2//CASSCF) adenines inside a solvated DNA double strand decamer (poly(dA)·poly(dT)) described at the molecular mechanics level. Calculations show that one carbon (C2) puckering is a common relaxation coordinate for both the La and CT paths. By mapping the lowest crossing regions between La and CT states, together with the paths connecting the two states, we conclude that at least one CT state can be easily accessible. The lowest-lying conical intersections between ground state (GS) and CT states have been fully characterized in a realistic DNA environment for the first time. We show that the path to reach this crossing region from the CT minima involves high barriers that are not consistent with experimental data lifetimes. Instead, the multiexponential decay recorded in DNA, including the longest (ca. 100 picoseconds) lifetime component detected in oligomeric single- and double-stranded systems, is compatible with both intra-monomer relaxation processes along the La deactivation path (involving small barriers) and the population of the excimer (CT) state that behaves as a trap. In the latter case, deactivation is feasible only going back to the La state by following its preferred decay coordinate.

Probing deactivation pathways of DNA nucleobases by two-dimensional electronic spectroscopy: first principles simulations.

The SOS//QM/MM [Rivalta et al., Int. J. Quant. Chem., 2014, 114, 85] method consists of an arsenal of computational tools allowing accurate simulation of one-dimensional (1D) and bi-dimensional (2D) electronic spectra of monomeric and dimeric systems with unprecedented details and accuracy. Prominent features like doubly excited local and excimer states, accessible in multi-photon processes, as well as charge-transfer states arise naturally through the fully quantum-mechanical description of the aggregates. In this contribution the SOS//QM/MM approach is extended to simulate time-resolved 2D spectra that can be used to characterize ultrafast excited state relaxation dynamics with atomistic details. We demonstrate how critical structures on the excited state potential energy surface, obtained through state-of-the-art quantum chemical computations, can be used as snapshots of the excited state relaxation dynamics to generate spectral fingerprints for different de-excitation channels. The approach is based on high-level multi-configurational wavefunction methods combined with non-linear response theory and incorporates the effects of the solvent/environment through hybrid quantum mechanics/molecular mechanics (QM/MM) techniques. Specifically, the protocol makes use of the second-order Perturbation Theory (CASPT2) on top of Complete Active Space Self Consistent Field (CASSCF) strategy to compute the high-lying excited states that can be accessed in different 2D experimental setups. As an example, the photophysics of the stacked adenine-adenine dimer in a double-stranded DNA is modeled through 2D near-ultraviolet (NUV) spectroscopy.