Magic Numbers and Stabilities of Photoionized Water Clusters: Computational and Experimental Characterization of the Nanosolvated Hydronium Ion.

The stability and distributions of small water clusters generated in a supersonic beam expansion are interrogated by tunable vacuum ultraviolet (VUV) radiation generated at a synchrotron. Time-of-flight mass spectrometry reveals enhanced population of various protonated water clusters (H+(H2O)n) based upon ionization energy and photoionization distance from source, suggesting there are "magic" numbers below the traditional n = 21 that predominates in the literature. These intensity distributions suggest that VUV threshold photoionization (11.0-11.5 eV) of neutral water clusters close to the nozzle exit leads to a different nonequilibrium state compared to a skimmed molecular beam. This results in the appearance of a new magic number at 14. Metadynamics conformer searches coupled with modern density functional calculations are used to identify the global minimum energy structures of protonated water clusters between n = 2 and 21, as well as the manifold of low-lying metastable minima. New lowest energy structures are reported for the cases of n = 5, 6, 11, 12, 16, and 18, and special stability is identified by several measures. These theoretical results are in agreement with the experiments performed in this work in that n = 14 is shown to exhibit additional stability, based on the computed second-order stabilization energy relative to most cluster sizes, though not to the extent of the well-known n = 21 cluster. Other cluster sizes that show some additional energetic stability are n = 7, 9, 12, 17, and 19. To gain insight into the balance between ion-water and water-water interactions as a function of the cluster size, an analysis of the effective two-body interactions (which sum exactly to the total interaction energy) was performed. This analysis reveals a crossover as a function of cluster size between a water-hydronium-dominated regime for small clusters and a water-water-dominated regime for larger clusters around n = 17.

Transcatheter closure of ventricular septal defects in children less than 10 kg: experience from a tertiary care referral hospital in Eastern India.

OBJECTIVE: To assess the feasibility of percutaneous transcatheter device closure of ventricular septal defects in children weighing less than 10 kg. BACKGROUND: Although percutaneous transcatheter device closure of ventricular septal defect is a well-established method of treatment in older children and adolescents, there is limited data on device closure in small children weighing less than 10 kg. We present our institutional experience of transcatheter VSD closure in children weighing less than 10 kg. METHOD: Medical records were reviewed for 16 children, who were selected for device closure of ventricular septal defects based on the inclusion criteria. RESULTS: Out of 65 patients with a diagnosis of ventricular septal defect, 16 children less than 10 kg were attempted for percutaneous device closure. In 13 patients, the device was successfully released, and 3 patients needed surgical closure of the defect. Mean age and weight of the patients were 17.3 ± 12.7 months and 6.8 ± 3.2 kg, respectively. Mean defect size was 6 mm (range 3-10). There was no incidence of device embolisation or heart block or death. Five patients had residual left-to-right shunt immediately after the device release, which got closed by the first month's follow-up. We had one accidental perforation of right ventricular free wall at the time of crossing of the defect, which was successfully repaired surgically. CONCLUSION: Percutaneous device closure of ventricular septal defect in small children with weight below 10 kg is feasible with good short-term outcome. Careful patient selection is essential for procedural success and to avoid complications.

Ab initio dynamics and photoionization mass spectrometry reveal ion-molecule pathways from ionized acetylene clusters to benzene cation.

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion-molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (C2H2) n+, just like ionized acetylene clusters. The fragmentation products result from reactive ion-molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C4H4+ and C6H6+ structures solvated with one or more neutral acetylene molecules. Such species contain large amounts (>2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C2H2)n+ isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C6H6+ isomers. These results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM.

Vacuum Ultraviolet Photoionization of Complex Chemical Systems.

Tunable vacuum ultraviolet (VUV) radiation coupled to mass spectrometry is applied to the study of complex chemical systems. The identification of novel reactive intermediates and radicals is revealed in flame, pulsed photolysis, and pyrolysis reactors, leading to the elucidation of spectroscopy, reaction mechanisms, and kinetics. Mass-resolved threshold photoelectron photoion coincidence measurements provide unprecedented access to vibrationally resolved spectra of free radicals present in high-temperature reactors. Photoionization measurements in water clusters, nucleic acid base dimers, and their complexes with water provide signatures of proton transfer in hydrogen-bonded and π-stacked systems. Experimental and theoretical methods to track ion-molecule reactions and fragmentation pathways in intermolecular and intramolecular hydrogen-bonded systems in sugars and alcohols are described. Photoionization of laser-ablated molecules, clusters, and their reaction products inform thermodynamics and spectroscopy that are relevant to astrochemistry and catalysis. New directions in coupling VUV radiation to interrogate complex chemical systems are discussed.

Proton transfer in acetaldehyde-water clusters mediated by a single water molecule.

Proton transfer in aqueous media is a ubiquitous process, occurring in acid-base chemistry, biology, and in atmospheric photochemistry. Photoionization mass spectrometry coupled with theoretical calculations demonstrate that a relay-type proton transfer mechanism is operational for single-water-molecule-assisted proton transfer between two acetaldehyde molecules in the gas phase. Threshold photoionization of acetaldehyde-water clusters leads to proton transfer between the formyl groups (-CH[double bond, length as m-dash]O) of one acetaldehyde molecule to another, and the subsequent formation of cationic moieties. Density functional theory computations reveal several plausible pathways of proton transfer in mixed cluster cations. Among these pathways, water-mediated proton transfer is energetically favored. Mass spectra and photoionization efficiency curves confirm these theoretical findings and also demonstrate the increased stability of cluster cations where acetaldehyde molecules are symmetrically bonded to the hydronium ion.

Probing Ionic Complexes of Ethylene and Acetylene with Vacuum-Ultraviolet Radiation.

Mixed complexes of acetylene-ethylene are studied using vacuum-ultraviolet (VUV) photoionization mass spectrometry and theoretical calculations. These complexes are produced and ionized at different distances from the exit of a continuous nozzle followed by reflectron time-of-flight mass spectrometry detection. Acetylene, with a higher ionization energy (11.4 eV) than ethylene (10.6 eV), allows for tuning the VUV energy and initializing reactions either from a C2H2(+) or a C2H4(+) cation. Pure acetylene and ethylene expansions are separately carried out to compare, contrast, and hence identify products from the mixed expansion: these are C3H3(+) (m/z = 39), C4H5(+) (m/z = 53), and C5H5(+) (m/z = 65). Intensity distributions of C2H2, C2H4, their dimers and reactions products are plotted as a function of ionization distance. These distributions suggest that association mechanisms play a crucial role in product formation closer to the nozzle. Photoionization efficiency (PIE) curves of the mixed complexes demonstrate rising edges closer to both ethylene and acetylene ionization energies. We use density functional theory (ωB97X-V/aug-cc-pVTZ) to study the structures of the neutral and ionized dimers, calculate their adiabatic and vertical ionization energies, as well as the energetics of different isomers on the potential energy surface (PES). Upon ionization, vibrationally excited clusters can use the extra energy to access different isomers on the PES. At farther ionization distances from the nozzle, where the number densities are lower, unimolecular decay is expected to be the dominant mechanism. We discuss the possible decay pathways from the different isomers on the PES and examine the ones that are energetically accessible.

Probing methanol cluster growth by vacuum ultraviolet ionization.

The ability to probe the formation and growth of clusters is key to answering fundamental questions in solvation and nucleation phenomena. Here, we present a mass spectrometric study of methanol cluster dynamics to investigate these two major processes. The clusters are produced in a molecular beam and ionized by vacuum ultraviolet (VUV) radiation at intermediate distances between the nozzle and the skimmer sampling different regimes of the supersonic expansion. The resulting cluster distribution is studied by time-of-flight mass spectrometry. Experimental conditions are optimized to produce intermediate size protonated methanol and methanol-water clusters and mass spectra and photoionization onsets and obtained. These results demonstrate that intensity distributions vary significantly at various nozzle to ionization distances. Ion-molecule reactions closer to the nozzle tend to dominate leading to the formation of protonated species. The protonated trimer is found to be the most abundant ion at shorter distances because of a closed solvation shell, a larger photoionization cross section compared to the dimer, and an enhanced neutral tetramer precursor. On the other hand, the protonated dimer becomes the most abundant ion at farther distances because of low neutral density and an enhanced charged protonated monomer-neutral methanol interaction. Thomson's liquid drop model is used to qualitatively explain the observed distributions.

Unexpected chemistry from the reaction of naphthyl and acetylene at combustion-like temperatures.

The hydrogen abstraction/acetylene addition (HACA) mechanism has long been viewed as a key route to aromatic ring growth of polycyclic aromatic hydrocarbons (PAHs) in combustion systems. However, doubt has been drawn on the ubiquity of the mechanism by recent electronic structure calculations which predict that the HACA mechanism starting from the naphthyl radical preferentially forms acenaphthylene, thereby blocking cyclization to a third six-membered ring. Here, by probing the products formed in the reaction of 1- and 2-naphthyl radicals in excess acetylene under combustion-like conditions with the help of photoionization mass spectrometry, we provide experimental evidence that this reaction produces 1- and 2-ethynylnaphthalenes (C12 H8 ), acenaphthylene (C12 H8 ) and diethynylnaphthalenes (C14 H8 ). Importantly, neither phenanthrene nor anthracene (C14 H10 ) was found, which indicates that the HACA mechanism does not lead to cyclization of the third aromatic ring as expected but rather undergoes ethynyl substitution reactions instead.

Infrared spectroscopy of solvation in small Zn+ (H2O)n complexes.

Singly charged zinc-water cations are produced in a pulsed supersonic expansion source using laser vaporization. Zn(+)(H2O)n (n = 1-4) complexes are mass selected and studied with infrared laser photodissociation spectroscopy, employing the method of argon tagging. Density functional theory (DFT) computations are used to obtain the structures and vibrational frequencies of these complexes and their isomers. Spectra in the O-H stretching region show sharp bands corresponding to the symmetric and asymmetric stretches, whose frequencies are lower than those in the isolated water molecule. Zn(+)(H2O)nAr complexes with n = 1-3 have O-H stretches only in the higher frequency region, indicating direct coordination to the metal. The Zn(+)(H2O)2-4Ar complexes have multiple bands here, indicating the presence of multiple low energy isomers differing in the attachment position of argon. The Zn(+)(H2O)4Ar cluster uniquely exhibits a broad band in the hydrogen bonded stretch region, indicating the presence of a second sphere water molecule. The coordination of the Zn(+)(H2O)n complexes is therefore completed with three water molecules.

Communication: photoelectron angular distributions of CH(-) reveal a temporary anion state.

Photoelectron imaging has broadened the scope of traditional photoelectron spectroscopy by combining a simultaneous photoelectron angular distribution, PAD, measurement with kinetic energy analysis. A fundamental understanding of PADs has been largely limited to simple atomic systems. However, a new model has recently been developed that predicts PADs as a function of electron kinetic energy for a simple linear combination of s and p atomic orbitals. We used CH(-) to test this model by acquiring PADs in a photoelectron imaging spectrometer at wavelengths from 600 to 355 nm. The PADs for electron detachment from the HOMO (1π) of CH(-) fit model predictions. However, the PADs associated with detachment from the HOMO-1 (3σ) orbital exhibit anomalous behavior at low electron kinetic energies because of a resonant process that arises from a previously undetected excited state of CH(-).

IR spectroscopy of protonation in benzene-water nanoclusters: hydronium, zundel, and eigen at a hydrophobic interface.

The structure of ions in water at a hydrophobic interface influences important processes throughout chemistry and biology. However, experiments to measure these structures are limited by the distribution of configurations present and the inability to selectively probe the interfacial region. Here, protonated nanoclusters containing benzene and water are produced in the gas phase, size-selected, and investigated with infrared laser spectroscopy. Proton stretch, free OH, and hydrogen-bonding vibrations uniquely define protonation sites and hydrogen-bonding networks. The structures consist of protonated water clusters binding to the hydrophobic interface of neutral benzene via one or more π-hydrogen bonds. Comparison to the spectra of isolated hydronium, zundel, or eigen ions reveals the inductive effects and local ordering induced by the interface. The structures and interactions revealed here represent key features expected for aqueous hydrophobic interfaces.

Polymorphic haplotypes of CRELD1 differentially predispose Down syndrome and euploids individuals to atrioventricular septal defect.

To explore the role of CRELD1 variants on congenital heart defects, we sequenced the entire reading frame of CRELD1 in the samples from Kolkata and adjoining areas. Nearly, 400 participants were included in the genetic association study and they were stratified as Down syndrome (DS) with atrioventricular septal defect (AVSD), DS without AVSD, euploid with AVSD, and euploid without AVSD. A significant association was found between AVSD and three polymorphisms, namely rs9878047 (c.1049-129T > C), rs3774207 (c.1119C > T), and rs73118372 (c.1136T > C) among the Down syndrome and euploid individuals. The polymorphism rs73118372, involves a transition (c.1136T > C) that leads to change in amino acid methionine to threonine which alters protein secondary structure as confirmed by the bioinformatics software SOPMA. In addition, two haplotypes, C-T-C and C-T-T, in the order of loci rs9878047-rs3774207-rs73118372 were associated with incidence of AVSD among euploid and Down syndrome, with a slightly higher odds ratio in the later group. We hypothesize that these haplotypes increase the risk of AVSD, and the susceptibility is exacerbated in DS, possibly due to the trisomy 21 genetic background. Moreover, we report for the first time on an interaction between the mutant alleles of rs3774207 and rs73118372 which could disrupt the delicate balance between different CRELD1 isoforms.

Transcatheter management of combined patent ductus arteriosus and left pulmonary artery stenosis in congenital rubella syndrome: A series of three patients and an insight into case selection for intervention.

Transcatheter closure of patent ductus arteriosus (PDA) is now the standard of care with some exceptions. Best treatment for peripheral pulmonary artery (PA) stenosis in small children is still debatable. Surgical augmentation, balloon dilatation, and stenting are the available options with each having its own risks and limitations. Here, we are reporting complete transcatheter management of three cases of congenital rubella syndrome who had PDA and left branch PA stenosis by device closure and stent placement, with successful outcome in two cases and complication, leading to surgery in one. We also share our understanding of case selection for a better outcome.

Structure of the phenylacetylene-water complex as revealed by infrared-ultraviolet double resonance spectroscopy.

The structure of the phenylacetylene-water complex has been elucidated based on spectral shifts in electronic and vibrational transitions. Phenylacetylene forms a cyclic complex with water incorporating C-H...O and O-H...pi hydrogen bonds, which is different from both the benzene-water and acetylene-water complexes, even though phenylacetylene combines the features of both benzene and acetylene. Formation of such a complex can be rationalized on the basis of cooperativity between the two sets of hydrogen bonds.

Extrinsic obstruction of the main coronary arteries in a child with hypertrophic cardiomyopathy.

Phasic narrowing of the coronary arteries on angiography is a well-known entity in both children and adults and has been described in relation to all epicardial arteries. There is a high incidence of myocardial bridges in hypertrophic cardiomyopathy. We report the case of a 6-year-old girl with hypertrophic obstructive cardiomyopathy who had extrinsic obstruction of the left main and right coronary arteries.

Functional capacity following univentricular repair--midterm outcome.

OBJECTIVE: Previous studies have seldom compared functional capacity in children following Fontan procedure alongside those with Glenn operation as destination therapy. We hypothesized that Fontan circulation enables better midterm submaximal exercise capacity as compared to Glenn physiology and evaluated this using the 6-minute walk test. DESIGN AND PATIENTS: Fifty-seven children aged 5-18 years with Glenn (44) or Fontan (13) operations were evaluated with standard 6-minute walk protocols. RESULTS: Baseline SpO(2) was significantly lower in Glenn patients younger than 10 years compared to Fontan counterparts and similar in the two groups in older children. Postexercise SpO(2) fell significantly in Glenn patients compared to the Fontan group. There was no statistically significant difference in baseline, postexercise, or postrecovery heart rates (HRs), or 6-minute walk distances in the two groups. Multiple regression analysis revealed lower resting HR, higher resting SpO(2) , and younger age at latest operation to be significant determinants of longer 6-minute walk distance. Multiple regression analysis also established that younger age at operation, higher resting SpO(2) , Fontan operation, lower resting HR, and lower postexercise HR were significant determinants of higher postexercise SpO(2) . Younger age at operation and exercise, lower resting HR and postexercise HR, higher resting SpO(2) and postexercise SpO(2) , and dominant ventricular morphology being left ventricular or indeterminate/mixed had significant association with better 6-minute work on multiple regression analysis. Lower resting HR had linear association with longer 6-minute walk distances in the Glenn patients. CONCLUSIONS: Compared to Glenn physiology, Fontan operation did not have better submaximal exercise capacity assessed by walk distance or work on multiple regression analysis. Lower resting HR, higher resting SpO(2) , and younger age at operation were factors uniformly associated with better submaximal exercise capacity.

Device occlusion of pseudoaneurysm of ascending aorta.

Pseudoaneurysm of ascending aorta is an infrequent but well-recognized and potentially fatal complication after cardiac surgeries. The complication can develop early, delayed or late, and the presentation is also varied. We are presenting here two cases of pseudoaneurysm of ascending aorta following cardiac surgery that were successfully managed by the transcatheter method. The first one occurred following coronary artery bypass surgery and the second one occurred following double-valve replacement surgery. The aortic openings of these aneurysms were occluded with 12 mm and 10 mm atrial septal occluders, respectively, with a good outcome. An immediate postprocedure angiogram showed no residual flow into the sac. Six months of follow-up of both cases also showed excellent results.

Anomalous left coronary artery from pulmonary artery with mitral stenosis.

The usual presentation of anomalous left coronary artery from pulmonary artery is severe left-sided heart failure and mitral valve insufficiency presenting during the first months of life. The manifestations of left heart failure may be masked if pulmonary artery pressure remains high. We believe this is a rarest of rare case of anomalous left coronary artery from pulmonary artery with severe mitral stenosis and pulmonary hypertension in which pulmonary hypertension, along with good collateral circulation helped to preserve left ventricular function.

Transcatheter device closure of ruptured sinus of Valsalva: Immediate results and short term follow up.

This is a retrospective, observational study comprising of eight patients with isolated rupture of the sinus of Valsalva (RSOV) who underwent transcatheter device closure. The mean age of presentation was 32.8 +/- 10.0 years. New York Heart Association (NYHA) class at the time of presentation was II (six patients) and III (two patients). The RSOVs were all closed using a patent ductus arteriosus device. The mean procedural time was 42.3 +/- 5.4 minutes, while the fluoroscopic time was 24.5 +/- 6.9 minutes. All had complete closure of the shunt. The average hospital stay was 2.9 +/- 1.1 days. There were no major complications. The patients were followed up for a mean of 11.3 +/- 4.1 months. At the time of the last follow up all the patients were in NYHA class I. We conclude that in the short term, transcatheter closure of isolated RSOV is a viable alternative to surgical repair.