Air and Environmental Contamination Caused by COVID-19 Patients: a Multi-Center Study.

BACKGROUND: The purpose of this study was to determine the extent of air and surface contamination of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in four health care facilities with hospitalized coronavirus disease 2019 (COVID-19) patients. METHODS: We investigated air and environmental contamination in the rooms of eight COVID-19 patients in four hospitals. Some patients were in negative-pressure rooms, and others were not. None had undergone aerosol-generating procedures. On days 0, 3, 5, and 7 of hospitalization, the surfaces in the rooms and anterooms were swabbed, and air samples were collected 2 m from the patient and from the anterooms. RESULTS: All 52 air samples were negative for SARS-CoV-2 RNA. Widespread surface contamination of SARS-CoV-2 RNA was observed. In total, 89 of 320 (27%) environmental surface samples were positive for SARS-CoV-2 RNA. Surface contamination of SARS-CoV-2 RNA was common in rooms without surface disinfection and in rooms sprayed with disinfectant twice a day. However, SARS-CoV-2 RNA was not detected in a room cleaned with disinfectant wipes on a regular basis. CONCLUSION: Our data suggest that remote (> 2 m) airborne transmission of SARS-CoV-2 from hospitalized COVID-19 patients is uncommon when aerosol-generating procedures have not been performed. Surface contamination was widespread, except in a room routinely cleaned with disinfectant wipes.

Viral Load Kinetics of SARS-CoV-2 Infection in Saliva in Korean Patients: a Prospective Multi-center Comparative Study.

BACKGROUND: This study was performed to compare the viral load and kinetics of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in saliva with those in standard nasopharyngeal/oropharyngeal (NP/OP) swabs. METHODS: Fifteen patients with SARS-CoV-2 infection from four hospitals were prospectively enrolled and matched samples of nasopharyngeal/oropharyngeal swabs and saliva were collected at Day 1 of admission and every other day till consequently negative for two times. Real-time reverse transcription polymerase chain reaction (rRT-PCR) was performed to detect the envelope (E) and RNA-dependent RNA polymerase (RdRP) genes. RESULTS: The cycle threshold values of saliva were comparable to those of NP/OP swabs overall (P = 0.720, Mann-Whitney U test). However, the overall sensitivity of rRT-PCR using saliva was 64% (34/53), which is lower than the 77% (41/53) using NP/OP swabs. The sensitivity of rRT-PCR using saliva was especially lower in early stage of symptom onset (1-5 days; 8/15; 53%) and in patients who did not have sputum (12/22; 55%). CONCLUSION: Saliva sample itself is not appropriate for initial diagnosis of coronavirus disease 2019 (COVID-19) to replace NP/OP swabs, especially for the person who does not produce sputum. COVID-19 cannot be excluded when the test using saliva is negative, and it is necessary to retest using NP/OP swabs.

Influence of π-conjugation structural changes on intramolecular charge transfer and photoinduced electron transfer in donor-π-acceptor dyads.

The influence of π-conjugation structural changes on photoinduced electron transfer (PET) and intramolecular charge transfer (ICT) processes in π-conjugated donor (D)-acceptor (A) dyads (D-π-A) was investigated. Three types of D-π-A dyads were prepared through the modification of the structure of their π-conjugated linker, including D-π-A (1) and D-πtw-A (2) having a twisted π-conjugation, and D-π-Si-π-A (3) with a π-conjugation severed by a Si-atom. In these dyads, carbazole (Cz) and oxadiazole (Oz) moieties act as an electron donor and acceptor, respectively. The emission maxima of dyads 1 and 3 red-shifted with the increase in polarity, which could be attributed to the ICT process. The fluorescence lifetimes of dyads 1 and 3 were 2.64 and 4.29 ns in CH2Cl2, respectively. In contrast, dyad 2 showed dual emission at 350 and 470 nm in CH2Cl2. The emission of dyad 2 at 380 nm corresponded to the monomer fluorescence in the locally excited state. Moreover, the emission at 470 nm increased simultaneously with the diminishing of the fluorescence at 380 nm. This emission band can be assigned as the intramolecular exciplex emission, and showed a strong solvatochromic shift. The low emission quantum yield (<3%) of dyad 2 is due to the PET process. In dyad 2, the cationic and anionic radical species generated by the PET process were confirmed by femtosecond transient absorption (fs-TA) spectroscopy. Upon photoexcitation at 290 or 340 nm, the A or D moieties can be selectively excited. Upon excitation at 290 nm, the acceptor moiety can be excited to the 1A* state, thus the photoinduced hole transfer (PHT) takes place from 1A* to D through the HOMO levels within a few picoseconds. On the other hand, when the donor moiety is excited at 340 nm, the PET process occurs from 1D* to A. Based on the fs-TA studies, it was found that the dynamics and mechanisms for the electron (or charge) transfer were strongly affected by the variation of the π-conjugation of the linker. Herein, we can conclude that the PET and ICT processes are strongly influenced by the π-conjugation properties and their mechanisms are also affected by whether selective excitation of the donor or acceptor moiety occurs. Moreover, unit electron transfers (PET or PHT) were observed dominantly in the dyads having severed/twisted linkers in π-conjugation. However, dyad 1 possessing a well-conjugated linker showed a partial charge transfer character.

The influence of π-conjugation on competitive pathways: charge transfer or electron transfer in new D-π-A and D-π-Si-π-A dyads.

In order to elucidate the influence of π-conjugation on photoinduced electron transfer (PET) and intramolecular charge transfer processes, donor-π-acceptor dyads (D-π-A (1) and D-π-Si-π-A (2)) were newly synthesized. In these dyads, carbazole and triazine moieties acted as the electron donor and acceptor, respectively. The fluorescence of dyad 1 red-shifted as the solvent polarity was increased. The electron charge distribution of the excited state of dyad 1 was delocalized in the acceptor moiety, forming the charge transfer D(δ+)-π-A(δ-) dyad in the excited state. In the excited state of dyad 1, the π-conjugation acted as the linker for charge transfer between the donor and acceptor moieties. A large dipole moment change (Δµ = 45.6 D) between the ground and excited states was determined using the Lippert-Mataga plot. Furthermore, the fluorescence of dyad 1 was observed upon two-photon excitation. In contrast, dyad 2, in which the π-conjugation is disconnected by a Si-atom in the linker, displayed weak dual-emission: a short-wavelength emission at around 350 nm arising from the monomeric species and a long-wavelength one assigned to the emission from an intramolecular exciplex between the donor and acceptor moieties. The weak emission of dyad 2 indicates that the D(+)˙-π-Si-π-A(-)˙ species was generated through a PET process in the excited state. The cationic radical species of the carbazole and the anionic radical species of the triazine, which show transient absorption (TA) bands at around 780 and 530 nm, respectively, were characterized using the femtosecond TA method.

Electronic Alteration on Oligothiophenes by o-Carborane: Electron Acceptor Character of o-Carborane in Oligothiophene Frameworks with Dicyano-Vinyl End-On Group.

We studied electronic change in oligothiophenes by employing o-carborane into a molecular array in which one or both end(s) were substituted by electron-withdrawing dicyano-vinyl group(s). Depending on mono- or bis-substitution at the o-carborane, a series of linear A1-D-A2 (1a-1c) or V-shaped A1-D-A2-D-A1 (2a-2c) oligothiophene chain structures of variable length were prepared; A1, D, and A2, represent dicyano-vinyl, oligothiophenyl, and o-carboranyl groups, respectively. Among this series, 2a shows strong electron-acceptor capability of o-carborane comparable to that of the dicyano-vinyl substituent, which can be elaborated by a conformational effect driven by cage σ*-π* interaction. As a result, electronic communications between o-carborane and dicyano-vinyl groups are successfully achieved in 2a.

Incorporating two different chromophores onto a silicon atom: the crystal structure and photophysical properties of 9-{4-[(9,9-dimethyl-9H-fluoren-2-yl)dimethylsilyl]phenyl}-9H-carbazole.

The crystal structure of the title bifunctional silicon-bridged compound, C(35)H(31)NSi, (I), has been determined. The compound crystallizes in the centrosymmetric space group P2(1)/c. In the crystal structure, the pairs of aryl rings in the two different chromophores, i.e. 9-phenyl-9H-carbazole and 9,9-dimethyl-9H-fluorene, are positioned orthogonally. In the crystal packing, no classical hydrogen bonding is observed. UV-Vis absorption and fluorescence emission spectra show that the central Si atom successfully breaks the electronic conjugation between the two different chromophores, and this was further analysed by density functional theory (DFT) calculations.