Structures, Bonding, and Energetics of N2O2 Isomers

The structures and energetics of the N202 isomers are predicted at several levels of theory. Both single reference and multireference based correlated methods were used to determine the structures and relative energies. Five high-energy minima were located above 2NO with QCISD(T)/6-311 +G(2df)//MP2/6-311 +G( d) (PT2F/6-311+G(2df)//MCSCF/6-31G(d)) relative energies of ca. 38 (51), 46 (51), 61 (74), 69 (74), and 68 (80) kcallmol for 1 ,2-diaza-3,4-dioxacyclobutene (1), bond stretch 1 ,3-diaza-2,4-dioxa[l.l.O]bicyclobutane (2), a-N202 (3), 4, and 1 ,3-diaza-2,4-dioxa[l.l.O]bicyclobutane (5), respectively. The effect of basis sets on structures is small within a given level of theory. The MCSCF structures agree reasonably with those of MP2

Theoretical studies of spin‐forbidden radiationless decay in polyatomic systems. II. Radiationless decay of a‐N2O2

The stability with respect to spin‐forbidden radiationless decay of the previously reported [J. Chem. Phys. 88, 7248 (1988)] asymmetric dimer of NO, N–N–O–O (a‐N2O2) is considered. The spin‐allowed decay channel a‐N2O2(1 A’)→N2O(X  1Σ+)+O(1 D) is endoergic. However, the spin‐forbidden decay channel a‐N2O2(1 A’)→N2O(X  1Σ+)+O(3 P) is exoergic. Large scale multireference configuration interactionwave functions, approximately 300 000–1 400 000 configuration state functions, based on double zeta polarization and triplet zeta polarization bases are used to study this process. The minimum energy crossing of the ground singlet 1 A’ state and the lowest excited triplet 3 A‘ state was determined as was the interstate spin–orbit coupling. This electronic structure data was used in the context of a simple one‐dimensional model to show that a‐N2O2 is rapidly predissociated to N2O(X  1Σ+) and O(3 P)

Long-range three-body atom-diatom potential for doublet Li3{}_3

An accurate long-range {\em ab initio} potential energy surface has been calculated for the ground state ${}^2A'$ lithium trimer in the frozen diatom approximation using all electron RCCSD(T). The {\em ab initio} energies are corrected for basis set superposition error and extrapolated to the complete basis limit. Molecular van der Waals dispersion coefficients and three-body dispersion damping terms for the atom-diatomic dissociation limit are presented from a linear least squares fit and shown to be an essentially exact representation of the {\em ab initio} surface at large range

Intravenous alteplase for stroke with unknown time of onset guided by advanced imaging: systematic review and meta-analysis of individual patient data

Background: Patients who have had a stroke with unknown time of onset have been previously excluded from thrombolysis. We aimed to establish whether intravenous alteplase is safe and effective in such patients when salvageable tissue has been identified with imaging biomarkers. Methods: We did a systematic review and meta-analysis of individual patient data for trials published before Sept 21, 2020. Randomised trials of intravenous alteplase versus standard of care or placebo in adults with stroke with unknown time of onset with perfusion-diffusion MRI, perfusion CT, or MRI with diffusion weighted imaging-fluid attenuated inversion recovery (DWI-FLAIR) mismatch were eligible. The primary outcome was favourable functional outcome (score of 0–1 on the modified Rankin Scale [mRS]) at 90 days indicating no disability using an unconditional mixed-effect logistic-regression model fitted to estimate the treatment effect. Secondary outcomes were mRS shift towards a better functional outcome and independent outcome (mRS 0–2) at 90 days. Safety outcomes included death, severe disability or death (mRS score 4–6), and symptomatic intracranial haemorrhage. This study is registered with PROSPERO, CRD42020166903. Findings: Of 249 identified abstracts, four trials met our eligibility criteria for inclusion: WAKE-UP, EXTEND, THAWS, and ECASS-4. The four trials provided individual patient data for 843 individuals, of whom 429 (51%) were assigned to alteplase and 414 (49%) to placebo or standard care. A favourable outcome occurred in 199 (47%) of 420 patients with alteplase and in 160 (39%) of 409 patients among controls (adjusted odds ratio [OR] 1·49 [95% CI 1·10–2·03]; p=0·011), with low heterogeneity across studies (I2=27%). Alteplase was associated with a significant shift towards better functional outcome (adjusted common OR 1·38 [95% CI 1·05–1·80]; p=0·019), and a higher odds of independent outcome (adjusted OR 1·50 [1·06–2·12]; p=0·022). In the alteplase group, 90 (21%) patients were severely disabled or died (mRS score 4–6), compared with 102 (25%) patients in the control group (adjusted OR 0·76 [0·52–1·11]; p=0·15). 27 (6%) patients died in the alteplase group and 14 (3%) patients died among controls (adjusted OR 2·06 [1·03–4·09]; p=0·040). The prevalence of symptomatic intracranial haemorrhage was higher in the alteplase group than among controls (11 [3%] vs two [<1%], adjusted OR 5·58 [1·22–25·50]; p=0·024). Interpretation: In patients who have had a stroke with unknown time of onset with a DWI-FLAIR or perfusion mismatch, intravenous alteplase resulted in better functional outcome at 90 days than placebo or standard care. A net benefit was observed for all functional outcomes despite an increased risk of symptomatic intracranial haemorrhage. Although there were more deaths with alteplase than placebo, there were fewer cases of severe disability or death. Funding: None

Structures, Bonding, and Energetics of N2O2 Isomers

The structures and energetics of the N202 isomers are predicted at several levels of theory. Both single reference and multireference based correlated methods were used to determine the structures and relative energies. Five high-energy minima were located above 2NO with QCISD(T)/6-311 +G(2df)//MP2/6-311 +G( d) (PT2F/6-311+G(2df)//MCSCF/6-31G(d)) relative energies of ca. 38 (51), 46 (51), 61 (74), 69 (74), and 68 (80) kcallmol for 1 ,2-diaza-3,4-dioxacyclobutene (1), bond stretch 1 ,3-diaza-2,4-dioxa[l.l.O]bicyclobutane (2), a-N202 (3), 4, and 1 ,3-diaza-2,4-dioxa[l.l.O]bicyclobutane (5), respectively. The effect of basis sets on structures is small within a given level of theory. The MCSCF structures agree reasonably with those of MP2.Reprinted (adapted) with permission from Journal of Physical Chemistry 96 (1994): 10072, doi:10.1021/j100091a021. Copyright 1994 American Chemical Society.</p