Unraveling Hydrogen Bonded Clustering with Water: Density Functional Theory Perspective

Extensive density functional theory (DFT) studies have been compiled and additional investigation has been performed for several energetically favorable conformers of hydrogen bonded water clusters. The focus here is not to merely reviewing the literature on DFT investigations on water clusters but to understand the basic building blocks, structural patterns and trends in the energetics of the clusters during the cluster growth. The successive addition of water molecules to these clusters alters the hydrogen bonding pattern, that leads to modification in overall cluster geometry which is also reflected in the vibrational frequency shifts in simulated vibrational infra-red (IR) spectra

Many-body interaction analysis: Algorithm development and application to large molecular clusters

A completely automated algorithm for performing many-body interaction energy analysis of clusters (MBAC) [M. J. Elrodt and R. J. Saykally, Chem. Rev. 94, 1975 (1994); S. S. Xantheas, J. Chem. Phys. 104, 8821 (1996)] at restricted Hartree-Fock (RHF)/MA Plesset 2nd order perturbation theory (MP2)/density functional theory (DFT) level of theory is reported. Use of superior guess density matrices (DM's) for smaller fragments generated from DM of the parent system and elimination of energetically insignificant higher-body combinations, leads to a more efficient performance (speed-up up to 2) compared to the conventional procedure. MBAC approach has been tested out on several large-sized weakly bound molecular clusters such as (H(2)O)(n), n=8, 12, 16, 20 and hydrated clusters of amides and aldehydes. The MBAC results indicate that the amides interact more strongly with water than aldehydes in these clusters. It also reconfirms minimization of the basis set superposition error for large cluster on using superior quality basis set. In case of larger weakly bound clusters, the contributions higher than four body are found to be repulsive in nature and smaller in magnitude. The reason for this may be attributed to the increased random orientations of the interacting molecules separated from each other by large distances.Financial support from the Council of Scientific and Industrial Research (CSIR), New Delhi, India and the Center for Development of Advanced Computing (C-DAC), Pune, India, is gratefully acknowledged

Stoichiometric control of co-crystal formation by solvent free continuous co-crystallization (SFCC).

yesReproducible control of stoichiometry and difficulties in large scale production have been identified as two of the major challenges to commercial uptake of pharmaceutical co-crystals. The aim of this research was to extend the application of SFCC to control stoichiometry in caffeine: maleic acid co-crystals. Both 1:1 and 2:1 caffeine: maleic acid co-crystals were produced by control of the feedstock composition and process conditions. It was also observed that formation of 2:1 stoichiometry co-crystals involved formation of a 1:1 co-crystal which was subsequently transformed to 2:1 co-crystals. The investigation of stoichiometric transformation revealed that although 1:1 co-crystals could be converted into 2:1 form with addition of excess caffeine, the reverse was not possible in the presence of excess maleic acid. However, conversion from 2:1 into 1:1 was only achieved by melt seeding with the phase pure 1:1 co-crystals. This investigation demonstrates that stoichiometric control can be achieved by SFCC by control of parameters such as extrusion temperature

Global wealth disparities drive adherence to COVID-safe pathways in head and neck cancer surgery

Peer reviewe

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Molecular Hydration of Carbonic Acid: Ab Initio Quantum Chemical and Density Functional Theory Investigation

Molecular hydration of carbonic acid (H2CO3) is investigated in terms of bonding patterns in H2CO3 center dot center dot center dot(H2O)(n) n = 1-4] hydrogen-bonded clusters within ab initio quantum chemical and density functional theory (DFT) frameworks. Successive addition of water molecules to H2CO3 center dot center dot center dot H2O entails elongation of O-H (hydroxyl) bond as well as contraction of specific intermolecular hydrogen bonds signifying hydration of carbonic acid; these structural features get markedly enhanced under the continuum solvation framework. A comparison between the structurally similar clusters H2CO3 center dot center dot center dot(H2O)(n) and HCOOH center dot center dot center dot(H2O)(n) n = 1-3] brings out the structural stability of the former. The present investigation in conjunction with the binding energy behavior of approaching water molecule(s) should serve as a precursor for pathways exploring aqueous dissociation of H2CO3 for larger clusters, as well as development of force-field potentials for acid dissociation process

Molecular electrostatics for exploring hydration patterns of molecules: 2 - Formamide

50-59Hydration of various molecular species is of great importance in chemical and biological sciences. Several studies dealing with hydration of molecules by ab initio methods, density functional formalism as well as molecular dynamics/molecular mechanics calculations have been reported in the literature. This article reports an attempt to explore the stepwise hydration patterns of molecules with formamide as a test case using the molecular electrostatic potential (MESP) as a tool for probing weak interactions. The present work is based on mapping of MESP topography followed by the application of an electrostatics-based model, viz., electrostatic potential for intermolecular complexation (EPIC), for obtaining the structures and trends in energetics in different hydrated species, viz., HCONH2 . . . n(H2O), 1≤ n ≤ 8. These EPIC calculations are followed up by RHF/6-31G * * investigations. The structures predicted by EPIC are generally found to be qualitatively similar to those obtained by ab initio optimization. Also, the EPIC structures when subjected to ab initio optimization are found to converge faster. This highlights the utility of MESP for investigating the hydration patterns at molecular level by understanding lock-and-key mechanism in such processes. The patterns found in the present study could be gainfully employed further for probing the complete first and second hydration shells of small- and medium-sized molecules

Quantum chemical and electrostatic studies of anionic water clusters, (H<SUB>2</SUB>O)<SUB>n</SUB><SUP>-</SUP>

Quantum chemical investigations are carried out to determine the structure and energetics of anionic water clusters, (H<SUB>2</SUB>O)<SUB>n</SUB><SUP>-</SUP> for n = 8, 10, 12 and 15. Quantum chemical computations performed herein employing a density functional theory (DFT) prescription reveal that these open-shell anionic clusters are metastable in comparison with their neutral analogues. Electron localization of the excess electron in these clusters, traced through molecular electrostatic potential (MESP) and singly occupied molecular orbital (SOMO) density maps, brings out the fact that the excess electron in these clusters is essentially a 'surface' electron i.e. binds externally to the cluster

Exploring hydration patterns of aldehydes and amides: ab initio investigations

Results of an extensive ab initio level investigation of the hydration patterns and energetics of some carbonyl compounds, viz., formaldehyde, acetaldehyde, formamide, and acetamide, are reported. This study employs restricted Hartree-Fock and density functional theory with the 6-31G(d,p) and 6-31++G(d,p) basis sets for exploring explicit hydration of these substrates with 8, 12, and 16 water molecules. Hydrated structures are seen to be dominated by four- and five-membered rings of water molecules as also exhibited by the (H<SUB>2</SUB>O)<SUB>n</SUB> clusters. Electrostatic guidelines are found to be useful for predicting the growth of the smaller hydrated clusters. Hydration of these molecules leads to the weakening of C=O and N-H bonds as revealed by the corresponding internuclear distances and vibrational frequencies

Structure and stability of water clusters (H<SUB>2</SUB>O)<SUB>n</SUB>, n = 8-20: an ab initio investigation

Extensive ab initio calculations have been performed using the 6-31G(d,p) and 6-311++G(2d,2p) basis sets for several possible structures of water clusters (H2O)n, n = 8-20. It is found that the most stable geometries arise from a fusion of tetrameric or pentameric rings. As a result, (H2O)n, n = 8, 12, 16, and 20, are found to be cuboids, while (H2O)10 and (H2O)15 are fused pentameric structures. For the other water clusters (n = 9, 11, 13, 14, and 17-19) under investigation, the most stable geometries can be thought of as arising from either the cuboid or the fused pentamers or a combination thereof. The stability of some of the clusters, namely, n = 8-16, has also been studied using density functional theory. An attempt has been made to estimate the basis set superposition error and zero-point energy correction for such clusters at the Hartree-Fock (HF) level using the 6-311++G(2d,2p) basis set. To ensure that a minimum on the potential-energy surface has been located, frequency calculations have been carried out at the HF level using the 6-31G(d,p) and 6-311++G(2d,2p) basis sets for some of the clusters. Molecular electrostatic potential topography mapping has been employed for understanding the reactivity as well as the binding patterns of some of the structurally interesting clusters