The temperature of maximum in density of aqueous solutions of nitrate and ammonium salts: Testing the Madrid-2019 force field.

The shift in the temperature of maximum in density (TMD) at room pressure of aqueous solutions of a set of five salts containing NO3- and/or NH4+ groups is studied both through experiments and through molecular dynamics simulations using the Madrid-2019 force field for ions and the TIP4P/2005 model for water. The experiments demonstrate the potential transferability and limitations of the Madrid-2019 force field for nitrate and ammonium ions recently developed by our group at different temperatures and add updated information to the reported datasets of TMDs for strong electrolytes. By using the Despretz law, individual ion contributions are extracted for predictive purposes from the experimental values of the shift in the TMD. Interesting findings for the behavior of the shift in the TMD in nitrate salts expose that this property might be particularly challenging for modelization approaches when dealing with polyatomic species.

Vibrational signatures of dynamic excess proton storage between primary amine and carboxylic acid groups.

Ammonium and carboxylic moieties play a central role in proton-mediated processes of molecular recognition, charge transfer or chemical change in (bio)materials. Whereas both chemical groups constitute acid-base pairs in organic salt-bridge structures, they may as well host excess protons in acidic environments. The binding of excess protons often precedes proton transfer reactions and it is therefore of fundamental interest, though challenging from a quantum chemical perspective. As a benchmark for this process, we investigate proton storage in the amphoteric compound 5-aminovaleric acid (AV), within an intramolecular proton bond shared by its primary amine and carboxylic acid terminal groups. Infrared ion spectroscopy is combined with ab initio Molecular Dynamics (AIMD) calculations to expose and rationalize the spectral signatures of protonated AV and its deuterated isotopologues. The dynamic character of the proton bond confers a fluxional structure to the molecular framework, leading to wide-ranging bands in the vibrational spectrum. These features are reproduced with remarkable accuracy by AIMD computations, which serves to lay out microscopic insights into the excess proton binding scenario.

Inelastic Collisions of O2 with He at Low Temperatures.

Rotationally inelastic collisions of O2 with He in the 10-34 K thermal range are investigated by means of an experimental procedure based on supersonic gas jets probed by Raman spectroscopy. The procedure employs a kinetic master equation (MEQ) that describes the time evolution of the rotational populations of O2 along supersonic jets of O2 and He mixtures. The MEQ is expressed in terms of experimental quantities (number density and rotational populations) measured here, and state-to-state rate coefficients for the O2:He inelastic collisions calculated here, plus those for O2:O2 collisions from the literature. An agreement with the experiments is accomplished for temperatures between 10 and 34 K. Within this thermal range, the role of the fine structure due to electron spin in the collision dynamics of O2 is discussed.

Second-trimester fetal aberrant right subclavian artery: original study, systematic review and meta-analysis of performance in detection of Down syndrome.

OBJECTIVES: First, to estimate the prevalence of fetal aberrant right subclavian artery (ARSA) in our population and its association with Down syndrome. Second, to determine the feasibility of ultrasound to visualize ARSA in the three planes. Finally, to carry out a systematic review of the literature on the performance of second-trimester ARSA to identify fetuses with Down syndrome. METHODS: ARSA was assessed by ultrasound in the axial plane and confirmed in the longitudinal and coronal planes during the second half of pregnancy in women attending our unit (from February 2011 to December 2012). A search of diagnostic tests for the assessment of ARSA was carried out in international databases. Relevant studies were subjected to a critical reading, and meta-analysis was performed with Meta-DiSc. RESULTS: Of the 8781 fetuses in our population (mean gestational age: 24 ± 5.4 weeks), 22 had Down syndrome. ARSA was detected in the axial view in 60 cases (0.7%) and confirmed in the coronal view in 96.7% and in the longitudinal view in 6.7% (P < 0.001). Seven cases with ARSA had Down syndrome and all were in the non-isolated-ARSA group. The estimates of positive likelihood ratio (LR) were 0 for isolated ARSA and 199 (95% CI, 88.9-445.2) for non-isolated ARSA. In the systematic review, six studies were selected for quantitative synthesis. The pooled estimates of positive and negative LRs for global ARSA were, respectively, 35.3 (95% CI, 24.4-51.1) and 0.75 (95% CI, 0.64-0.87). For isolated ARSA, the positive and negative LRs were 0 (95% CI, 0.0-14.7) and 0.98 (95% CI, 0.94-1.02), respectively. CONCLUSIONS: The prevalence of ARSA seems close to 1%. The coronal plane is the most suitable for its confirmation after detection in the axial plane. Detection of isolated or non-isolated ARSA should guide decisions about karyotyping given that isolated ARSA shows a weak association with Down syndrome.

Microwave spectroscopy and quantum chemical investigation of nine low energy conformers of the 15-crown-5 ether.

Crown ether macrocyles constitute a central class of selective substrates in Supramolecular Chemistry. The backbone of crown ethers is particularly flexible which makes the spectroscopic and computational investigations challenging. In this work, we present a systematic investigation of the low energy conformational landscape of the benchmark macrocycle 15-crown-5 ether (15c5) under isolated conditions. Molecular beam Fourier transform microwave spectroscopy is employed to measure a broad ensemble of rotational transitions within the range of 4-11 GHz. The recorded spectra allow us to determine the rotational constants of eight individual 15c5 rotamers which are identified among the nine lowest energy conformers predicted by ab initio MP2 computations. The study illustrates well the variety of conformers of prolate and oblate character that the 15c5 molecule displays within a narrow range of energies. Implications for the supramolecular behavior of 15c5 are discussed.

Crown ether complexes with H3O⁺ and NH4⁺: proton localization and proton bridge formation.

The complexes formed by crown ethers with hydronium and ammonium cations are of key relevance for the understanding of their supramolecular behavior in protic solvents. In this work, the complexes of the 15-crown-5 (15c5) and 18-crown-6 (18c6) ethers with H3O⁺ and NH4⁺ and their deuterated variants are investigated under isolated conditions. The study employs infrared multiple photon dissociation (IRMPD) vibrational spectroscopy and DFT B3LYP/6-31++G(d,p) calculations for conformational assignment. The 18c6 ether provides two energetically nearby C(3v) conformations with commensurate linear O-H···O and N-H···O bonds. The 15c5 ether ring adopts partially folded asymmetric pyramidal geometries, yielding one shorter linear H bond and two longer non-linear H bonds. Remarkably, an appreciable broadening of the IRMPD vibrational bands is observed for the 15c5-H3O⁺/D3O⁺ complexes. This can be interpreted as a signature for partial sharing of the proton (or deuteron) between the water and the crown ether along the linear O-H···O intermolecular H bond, which is indeed particularly short for this complex.

Fetal thymus size in uncomplicated twin and singleton pregnancies.

OBJECTIVES: The main objective of this study was to determine whether fetal thymic measurements could be obtained in twins, with a secondary goal to determine whether thymic measurements from uncomplicated singleton and twin pregnancies are comparable. METHODS: The transverse diameter and perimeter of the fetal thymus were measured prospectively in 678 singleton and 56 twin pregnancies, and their relationships with gestational age were determined and compared between groups. RESULTS: Thymic measurements were possible in 757 (95.8%) of the 790 fetuses. Measurements were not possible in 19 of 678 singletons (2.8%) and in 14 of the 112 (12.5%) twins (P < 0.001). After construction of nomograms for the transverse diameter and perimeter of the fetal thymus, similar measurements were noted for singletons and twins. CONCLUSIONS: These results suggest that sonographic measurements of the thymus are feasible in twin pregnancies and that, in uncomplicated pregnancies, these measurements are similar to those noted for singletons. These findings pave the way for future studies aimed at determining the clinical utility of thymic measurements in complicated singleton and twin pregnancies.

Influence of the displacement out of the center of mass and nonaxiality of the dipole on the thermodynamics of liquids composed of linear dipole molecules.

We present results for organic liquids modeled as linear rods with an embedded point dipole shifted from the geometrical center. Previously, we have obtained results for the vapor-liquid equilibrium (VLE) of similar systems with centered point dipoles. Our results included both models and applications to real systems. Results presented here are based on a previous work ( Phys. Rev. E 2003, 68, 021201) on the structural properties of these systems where relevant results about the appearance of dimers were found. Now, we have also performed systematic simulations on these systems to calculate the VLE of models with different aspect ratios, dipole shifts, and dipole strengths using the Gibbs ensemble Monte Carlo (GEMC) to calculate equilibrium densities and vapor pressure at each temperature. The applications considered here include some important substances such as 1-amines, acetonitrile, and 1-alcohols whose intermolecular parameters were fitted from our model simulations. Furthermore, we have used quantum chemistry calculations to obtain a reliable charge distribution, and we have applied our model to predict the vapor pressure of alpha,omega-diols where experimental results are rather scarce. Our results show a general improvement of the agreement between experiment and models compared to centered dipole models previously used. Results for amines are particularly remarkable.

Prenatal diagnosis of Potocki-Lupski syndrome in a fetus with hypoplastic left heart and aberrant right subclavian artery.

Potocki-Lupski syndrome (PTLS) is a rare genetic disorder associated with neurodevelopmental delay and heart defects. We report the first case of prenatal diagnosis of PTLS in a fetus with hypoplastic left heart and aberrant right subclavian artery. Detection of a fetal heart defect should be followed by chromosomal and genetic studies in order to rule out fetal aneuploidy and/or associated genetic syndromes with significant implications for the treatment of children with PTLS.

High-Resolution Rotational Spectroscopy of a Cyclic Ether.

The conformational landscape of crown ethers has constituted a central topic in the development of host-guest supramolecular chemistry. We report a high-resolution rotational study of a crown ether, 1,4,7,10,13-pentaoxacyclopentadecane (15-crown-5), by means of molecular beam Fourier transform microwave spectroscopy. The considerable size and the broad range of conformations allowed by the flexibility of the cyclic backbone of this ether pose important challenges to spectroscopy approaches. In this investigation, three stable rotamers of the 15-crown-5 ether have been identified and characterized through their rotational constants and centrifugal distortion coefficients. Ab initio quantum calculations at the MP2 level predict these conformers as the most stable ones for the title system and reproduce accurately their distinct structural features. The results pave the ground for an extensive survey of the conformational landscape of the 15-crown-5 and related cyclic ethers in the near term.

Ultrasonographic measurement of fetal nasal bone in a low-risk population at 19-22 gestational weeks.

OBJECTIVE: To determine the potential value of sonographic measurement of fetal nasal bone at 19-22 weeks' gestation in screening for trisomy 21 in a low-risk population. METHODS: The fetal nasal bone was measured in a mid-sagittal view in 2035 fetuses at 19-22 weeks' gestation. A reference range was constructed and the measurements in fetuses with trisomy 21 were compared to the normal group. RESULTS: The fetal profile was successfully examined in 1913/2035 (94%) fetuses. The mean nasal bone length increased linearly with gestation from 6.2 mm at 19 weeks to 6.8 mm at 22 weeks. Nasal bone hypoplasia, defined by absence of the bone or a measurement below the 2.5th centile, was observed in 34/1899 (1.8%) chromosomally normal fetuses (1.8%), in 5/5 fetuses with trisomy 21 and in 0/9 fetuses with other chromosomal defects. CONCLUSION: At 19-22 weeks' gestation, nasal bone hypoplasia is observed in a high proportion of trisomy 21 fetuses and in less than 2% of chromosomally normal fetuses.