Strong correlation between electronic bonding network and critical temperature in hydrogen-based superconductors.

By analyzing structural and electronic properties of more than a hundred predicted hydrogen-based superconductors, we determine that the capacity of creating an electronic bonding network between localized units is key to enhance the critical temperature in hydrogen-based superconductors. We define a magnitude named as the networking value, which correlates with the predicted critical temperature better than any other descriptor analyzed thus far. By classifying the studied compounds according to their bonding nature, we observe that such correlation is bonding-type independent, showing a broad scope and generality. Furthermore, combining the networking value with the hydrogen fraction in the system and the hydrogen contribution to the density of states at the Fermi level, we can predict the critical temperature of hydrogen-based compounds with an accuracy of about 60 K. Such correlation is useful to screen new superconducting compounds and offers a deeper understating of the chemical and physical properties of hydrogen-based superconductors, while setting clear paths for chemically engineering their critical temperatures.

Borates or phosphates? That is the question.

Chemical nomenclature is perceived to be a closed topic. However, this work shows that the identification of polyanionic groups is still ambiguous and so is the nomenclature for some ternary compounds. Two examples, boron phosphate (BPO4) and boron arsenate (BAsO4), which were assigned to the large phosphate and arsenate families, respectively, nearly a century ago, are explored. The analyses show that these two compounds should be renamed phosphorus borate (PBO4) and arsenic borate (AsBO4). Beyond epistemology, this has pleasing consequences at several levels for the predictive character of chemistry. It paves the way for future work on the possible syntheses of SbBO4 and BiBO4, and it also renders previous structure field maps completely predictive, allowing us to foresee the structure and phase transitions of NbBO4 and TaBO4. Overall, this work demonstrates that quantum mechanics calculations can contribute to the improvement of current chemical nomenclature. Such revisitation is necessary to classify compounds and understand their properties, leading to the main final aim of a chemist: predicting new compounds, their structures and their transformations.

On understanding the chemical origin of band gaps.

Conceptual DFT and quantum chemical topology provide two different approaches based on the electron density to grasp chemical concepts. We present a model merging both approaches, in order to obtain physical properties from chemically meaningful fragments (bonds, lone pairs) in the solid. One way to do so is to use an energetic model that includes chemical quantities explicitly, so that the properties provided by conceptual DFT are directly related to the inherent organization of electrons within the regions provided by topological analysis. An example of such energy model is the bond charge model (BCM) by Parr and collaborators. Bonds within an ELF-BCM coupled approach present very stable chemical features, with a bond length of ca. 1 Å and 2[Formula: see text]. Whereas the 2[Formula: see text] corroborate classical views of chemical bonding, the fact that bonds always expand along 1 Å introduces the concept of geometrical transferability and enables estimating crystalline cell parameters. Moreover, combining these results with conceptual DFT enables deriving a model for the band gap where the chemical hardness of a solid is given by the bond properties, charge, length, and a Madelung factor, where the latter plays the major role. In short, the fundamental gap of zinc-blende solids can be understood as given by a 2[Formula: see text] bond particle asymmetrically located on a 1 Å length box and electrostatically interacting with other bonds and with a core matrix. This description is able to provide semi-quantitative insight into the band gap of zinc-blende semiconductors and insulators on equal footing, as well as a relationship between band gap and compressibility. In other words, merging these different approaches to bonding enables to connect measurable macroscopic behavior with microscopic electronic structure properties and to obtain microscopic insight into the chemical origin of band gaps, whose prediction is still nowadays a difficult task. Graphical Abstract Conceptual DFT couples to quatum chemcial topology to explain the band gap of zinc-blende solids.

Understanding the molecular switching properties of octaphyrins.

Several expanded porphyrins switch between Hückel, Möbius and twisted-Hückel topologies, encoding different aromaticity and NLO properties. Since the topological switch can be induced by different external stimuli, expanded porphyrins represent a promising platform to develop molecular switches for molecular electronic devices. In order to determine the optimum conditions for efficient molecular switches from octaphyrins, we have carried out a comprehensive quantum chemical study focusing on the conformational preferences and aromaticity of [36]octaphyrins. Different external stimuli for triggering the topological switch have been considered in our work, such as protonation and redox reactions. Importantly, the structure-property relationships between the molecular conformation, the number of π-electrons and aromaticity in octaphyrins have been established by using energetic, magnetic, structural and reactivity descriptors. Remarkably, we found that the aromaticity of octaphyrins is highly dependent on the π-conjugation topology and the number of π-electrons and it can be modulated by protonation and redox reactions. A non-aromatic figure-eight conformation is strongly preferred by neutral [36]octaphyrins that switches to a Möbius aromatic conformation upon protonation. Such a change of topology involves an aromaticity switch in a single molecule and is accompanied by a drastic change in the NLO properties. In contrast, the twisted-Hückel topology remains the most stable one in the oxidized and reduced species, but the aromaticity is totally reversed upon redox reactions. Aromaticity is shown to be a key concept in expanded porphyrins, determining the electronic, magnetic and NLO properties of these macrocycles.

Understanding conductivity in molecular switches: a real space approach in octaphyrins.

In recent years, expanded porphyrins have emerged as a promising class of π-conjugated molecules that display unique electronic, optical and conformational properties. Several expanded porphyrins can switch between planar and twisted conformations, which have different photophysical properties. Such a change of topology involves a Hückel-Möbius aromaticity switch in a single molecule and it can be induced by solvent, pH and metallation. These features make expanded porphyrins suitable for the development of a novel type of molecular switches for molecular electronic devices. Octaphyrins consisting of eight pyrrole rings, exhibit twisted-Hückel, Möbius and Hückel π-conjugation topologies depending on the oxidation and protonation state, with distinct electronic structures and aromaticity. Our working hypothesis is that a significant change in the conductance of expanded porphyrins will be observed after the topology switching. Despite the potential of Hückel-Möbius systems as conductance switches, the relationship between the conductance and the molecular topology is not yet understood. We have explored the performance of local descriptors of conductivity in simple molecules, as well as the relationship with conductance. Since these indexes provide a qualitative measure of delocalization and conductance in the probe molecules, we have carried out a local analysis of electrical conductance changes as a function of the π-conjugation in two examples. In one of them, the locality of the electronic changes ensures the ability of these indexes to describe the conductance as local. Moreover, it enables to identify which conformational switch would be more efficient from an electronic device perspective. However, we also show that it is not always possible to reduce conductance changes to one bond, and in those molecules where a deep rearrangement occurs far from the structural perturbation, local measures show a limited efficiency. This is a first step for the description of the connection between the molecular structure and conductance in molecular switches.

Unravelling Protein-DNA Interactions at Molecular Level: A DFT and NCI Study.

Histone-DNA interactions were probed computationally at a molecular level, by characterizing the bimolecular clusters constituted by selected amino acid derivatives with polar (asparagine and glutamine), nonpolar (alanine, valine, and isoleucine), and charged (arginine) side chains and methylated pyrimidinic (1-methylcytosine and 1-methylthymine) and puric (9-methyladenine and 9-methylguanine) DNA bases. The computational approach combined different methodologies: a molecular mechanics (MMFFs forced field) conformational search and structural and vibrational density-functional calculations (M06-2X with double and triple-ζ Pople's basis sets). To dissect the interactions, intermolecular forces were analyzed with the Non-Covalent Interactions (NCI) analysis. The results for the 24 different clusters studied show a noticeable correlation between the calculated binding energies and the propensities for protein-DNA base interactions found in the literature. Such correlation holded even for the interaction of the selected amino acid derivatives with Watson and Crick pairs. Therefore, the balance between hydrogen bonds and van der Waals interactions (specially stacking) in the control of the final shape of the investigated amino acid-DNA base pairs seems to be well reproduced in dispersion-corrected DFT molecular models, reinforcing the idea that the specificity between the amino acids and the DNA bases play an important role in the regulation of DNA.

Unraveling non-covalent interactions within flexible biomolecules: from electron density topology to gas phase spectroscopy.

The NCI (Non-Covalent Interactions) method, a recently-developed theoretical strategy to visualize weak non-covalent interactions from the topological analysis of the electron density and of its reduced gradient, is applied in the present paper to document intra- and inter-molecular interactions in flexible molecules and systems of biological interest in combination with IR spectroscopy. We first describe the conditions of application of the NCI method to the specific case of intramolecular interactions. Then we apply it to a series of stable conformations of isolated molecules as an interpretative technique to decipher the different physical interactions at play in these systems. Examples are chosen among neutral molecular systems exhibiting a large diversity of interactions, for which an extensive spectroscopic characterization under gas-phase isolation conditions has been obtained using state-of-the-art conformer-specific experimental techniques. The interactions presently documented range from weak intra-molecular H-bonds in simple amino-alcohols, to more complex patterns, with interactions of various strengths in model peptides, as well as in chiral bimolecular systems, where invaluable hints for the understanding of chiral recognition are revealed. We also provide a detailed technical appendix, which discusses the choices of cut-offs as well as the applicability of the NCI analysis to specific constrained systems, where local effects require attention. Finally, the NCI technique provides IR spectroscopists with an elegant visualization of the interactions that potentially impact their vibrational probes, namely the OH and NH stretching motions. This contribution illustrates the power and the conditions of use of the NCI technique, with the aim of providing an easy tool for all chemists, experimentalists and theoreticians, for the visualization and characterization of the interactions shaping complex molecular systems.

Potassium under pressure: a pseudobinary ionic compound.

Experimentally, we have found that among the "complicated" phases of potassium at intermediate pressures is one which has the same space group as the double hexagonal-close-packed structure, although its atomic coordination is completely different. Calculations on this P6(3)/mmc (hP4) structure as a function of pressure show three isostructural transitions and three distinctive types of chemical bonding: free electron, ionic, and metallic. Interestingly, relationships between localized metallic structures and ionic compounds are found.

Bases for Understanding Polymerization under Pressure: The Practical Case of CO2.

We present a novel quantitative strategy for monitoring chemical bonding transformations in solids from the topology of their electronic structure. Developed in the context of the electron localization function formalism, it provides an unambiguous characterization of long-range interactions and bond formation. Charge flux between electron localization regions is found to hold the key for identifying the nature of the interaction between the chemically meaningful entities in the solid (valence shells, lone pairs, molecules, etc.). Because of the wide range of interesting properties that high pressure induces in molecular solids, we illustrate the potentialities of our strategy to unveil controversial questions involved in the bond reorganization along the polymerization of CO2. Our study confirms that the topology of the bonding network in the pseudopolymeric phases points toward the incipient formation of the new bonds in the higher pressure polymers. This transformation is identified as a synchronic weakening of the intramolecular (C==O) double bond and the birth of a new intermolecular C--O bond controlled by the oxygen lone pairs. Overall, the relationship that this type of analysis establishes between different polymorphs of the phase diagram could be further exploited for the prediction of the coordination of high pressure phases, opening new avenues for experimental synthesis and structure indexation.

Computation of Local and Global Properties of the Electron Localization Function Topology in Crystals.

We present a novel computational procedure, general, automated, and robust, for the analysis of local and global properties of the electron localization function (ELF) in crystalline solids. Our algorithm successfully faces the two main shortcomings of the ELF analysis in crystals: (i) the automated identification and characterization of the ELF induced topology in periodic systems, which is impeded by the great number and concentration of critical points in crystalline cells, and (ii) the localization of the zero flux surfaces and subsequent integration of basins, whose difficulty is due to the diverse (in many occasions very flat or very steep) ELF profiles connecting the set of critical points. Application of the new code to representative crystals exhibiting different bonding patterns is carried out in order to show the performance of the algorithm and the conceptual possibilities offered by the complete characterization of the ELF topology in solids.

A Quantum Chemical Interpretation of Compressibility in Solids.

The ability of the electron localization function to perform a partition of the unit cell volume of crystalline solids into well-defined, disjoint, and space-filling regions enables us to decompose the bulk compressibility into local contributions with a full chemical meaning. This partition has been applied to a set of prototype crystals of the chemical elements of the first three periods of the periodic table, and the equations of state for core, valence, bond, and lone electron pairs have been obtained. Solids are unequivocally classified into two groups according to their response to hydrostatic pressure. Those with sharing electrons (metals and covalent crystals) obey a simple relationship between the average valence electron density and the zero pressure bulk modulus. The stiffness of the closed-shell systems (molecular and ionic solids) is rationalized resorting to the Pauli principle. Overall, the results clearly correlate with chemical intuition: periodic trends are revealed, cores are almost incompressible and do not contribute appreciably to the macroscopic compressibility, and lone pair basins are rather easier to compress than bond basins.

How electron localization function quantifies and pictures chemical changes in a solid: the B3-->B1 pressure induced phase transition in BeO.

Advantages of the analysis of the topology of the electron localization function (ELF) in the characterization of the chemical bonding in solids are illustrated in the study of the zinc blende --> rock salt transformation in BeO. The 4-fold to 6-fold coordination change is described as a two-step process: first, a catastrophic-like emergence of two new Be-O bonds reveals the onset of the rock salt structure, and second, the new interactions gradationally evolve to achieve the bonding network of the high-pressure phase. The increase in coordination, the volume collapse and the enhancement in the bulk modulus across the transition pathway are qualitatively and quantitatively traced back to the oxygen's valence shell. Although several ELF indexes point toward the expected greater bond polarity in the B3 than in the B1 structure, it can be concluded that there is no substantial modification in the nature of the crystal interactions induced by the phase transformation.

[Treatment of lithiasis in horseshoe kidney with extracorporeal shock-wave lithotripsy]. / Tratamiento de la litiasis en el riñón en herradura mediante litotricia extracorpórea por ondas de choque.

UNLABELLED: The horseshoe kidney is the most frequent renal anomaly. As a consequence of impaired urinary drainage, urolithiasis is present in 20% of the cases. Indications for extracorporeal shock wave lithotripsy (ESWL) in the treatment of patients with anomalous kidneys is still the subject of controversy. OBJECTIVE: To evaluate ESWL efficacy in the treatment for lithiasis in horseshoe kidney. MATERIAL AND METHODS: Between april 1988 and december 1999 a total of 32 symptomatic lithiasis in 30 patients with horseshoe kidneys were managed by 65 sessions with ESWL. Until march 1999 a Dornier HM-4 electrohydraulic lithotripter was used. Posteriorly, two treatments was performed with an electromagnetic Dornier Lithotripter S. These procedures have been performed without anaesthesia or sedation for the Dornier HM-4 equipment. Analgesia with Meperidine was used for the Dornier Lithotripter S. Diuresis was not forced during or after treatment with diuretics or serotherapy. Treatments was conducted in an outpatient clinic in all cases. RESULTS: Treatment/lithiasis rate was 2.03. Following treatment 16 patients (54%) were stone-free by X-ray, 9 patients (30%) had residual fragments and in 5 patients (16%) no sign of stone disintegration was observed. Open surgery was performed in three of this patients. Better results was achieved in stones located in the renal pelvis and stone size is 10 mm or less. Clinical evolution: free of symptoms in 20 patients; chronic vague flank pain in 5 patients and acute renal colic with or without hematuria in 5 patients. No major complication was observed in our compilation. CONCLUSIONS: These results suggest that ESWL is the method of primary choice in the treatment for small lithiasis (10 mm or less) in horseshoe kidney.

Tratamiento de la litiasis en el riñón en herradura mediante litotricia extracorpórea por ondas de choque / Extracorporeal shock wave lithotripsy in the treatment for lithiasis in horseshoe kidney

El riñón en herradura constituye la anomalía congénita más frecuente del riñón. La dificultad en el drenaje urinario influye en que un 20 por ciento de los mismos desarrollan litiasis renal. El papel de la litotricia extracorpórea por ondas de choque (LEOC) en el tratamiento de la litiasis en pacientes afectos de malformaciones congénitas renales es todavía motivo de controversia. OBJETIVO: Evaluar la eficacia de la LEOC en el tratamiento de la litiasis en el riñón en herradura. MATERIAL Y MÉTODOS: Entre abril de 1988 y diciembre de 1999 hemos tratado a 30 pacientes con riñón en herradura portadores de 32 litiasis sintomáticas que han requerido de 65 sesiones de LEOC para su resolución. Hasta marzo de 1999 hemos utilizado un equipo Litotriptor Dornier HM-4 de energía electrohidráulica. Posteriormente dos tratamientos se han realizado con equipo Dornier Lithotripter S de energía electromagnética. Todos los tratamientos han sido realizados sin anestesia ni sedación con el equipo Dornier HM-4 y utilizamos analgesia con meperidina con el Dornier Lithotripter S. En ningún caso se ha forzado diuresis con diuréticos ni sueroterapia. Todos los tratamientos se han realizado de forma ambulatoria. RESULTADOS: El índice tratamiento/litiasis ha sido de 2.03. El número de pacientes libres de litiasis tras el tratamiento es de 16 lo que supone un 54 por ciento. En 9 pacientes (30 por ciento) se consiguió fragmentación de la litiasis y en 5 pacientes (16 por ciento) no se produjeron cambios tras el tratamiento. En tres de los casos se recurrió a la cirugía convencional para la resolución de su litiasis. Se ha producido recidiva en 2 pacientes lo que supone un 6 por ciento. Obtenemos mejor o total eliminación de la litiasis cuando ésta está alojada a nivel piélico y es de un tamaño igual o inferior a 10 mm. Evolución clínica: asintomáticos 20 pacientes; lumbalgia 5 pacientes; cólico nefrítico con o sin hematuria: 5 pacientes. No hemos asistido a ninguna complicación mayor en esta serie. CONCLUSIONES: Estos resultados sugieren que la LEOC es la primera opción terapéutica a utilizar ante una litiasis renal de pequeño tamaño (=10 mm) alojada en un riñón en herradura (AU)

[Current treatment of lithiasis in congenital renoureteral malformations]. / Tratamiento actual de la litiasis en malformaciones congénitas renoureterales.

OBJECTIVE: To evaluate the treatment of urinary calculi in renoureteral malformations. METHODS: From April 1988 to December 2000, we have treated 158 patients with renoureteral malformations (36 horseshoe kidneys, 32 caliceal diverticula, 2 megacaliosis, 2 crossed renal ectopy, 3 polycystosis, 7 hydrocalyx, 24 complete duplex ureter, 18 incomplete duplex ureter, 22 ureterocele, 2 segmental megaureter). RESULTS: Renoureteral malformations were diagnosed in 158 of 19,000 patients that were treated in our stone unit from April 1988 and December 2000. Horseshoe kidney: 54% of the patients treated by ESWL are stone-free; PNL was performed in 2 patients and conventional surgery in another 2 patients. Caliceal diverticulum: 42% of the patients treated by ESWL are stone-free; 3 patients underwent conventional surgery. Other renal malformations: 62% of the patients treated by ESWL are stone-free. Ureteral malformations: duplex ureter and megaureter: 82% of the patients treated by ESWL are stone-free. Ureterocele: due to the poor results achieved by ESWL, we performed endoscopic transurethral meatotomy. CONCLUSIONS: These results indicate that ESWL alone can be considered to be the treatment of choice for small calculi in patients with renal malformations, although we consider it to be mandatory to perform individual assessment of the urinary tract and stone size in these patients in order to choose the best therapeutic option. The same criteria for the normal urinary tract can be applied in ureteral malformations except ureteroceles, for which we advocate performing endoscopic surgery for stone removal.

[Ambulatory treatment of ureteral lithiasis using shock wave extracorporeal lithotripsy]. / Tratamiento ambulatorio de la litiasis ureteral mediante litotricia extracorpórea por ondas de choque.

Presentation of the results obtained with extracorporeal shock wave lithotripsy (ESWL) applied to 3173 ureteral lithiasis with a Dornier HM-4 equipment. Location of lithiasis was pyeloureteral junction (329), lumbar ureter (1068), sacral ureter (238), iliopelvic ureter (1474) and "lithiasic path" (64). All lithiasis were treated in situ. Treatments were carried out ambulatory with no anaesthesia. Treatment/lithiasis rate was 1.3. Percentage of stone-free patients with ESWL alone was 79.2% after the first session, and reached 86.14% with retreatment. Percentage of success for lithiasis in pyeloureteral junction was 81.8%, 79.7% for lumbar ureter lithiasis, 80.09% sacral lithiasis, 90.10% iliopelvic ureter lithiasis and 79.9% for those in the "lithiasic path". 12.6% lithiasis required post-ESWL auxiliary manoeuvres. Post-ESWL minor complications (pain, vegetations) occurred in 5.6% cases and major complications (obstruction, fever, sepsis) in 2.9%. The factors influencing lithiasis fragmentation were the number of shock waves and the lithiasis duration. Size of lithiasis and presence or absence of ureteral catheter had no influence. These results suggest that ESWL is an effective method for managing ureteral lithiasis.

[Role of electrohydraulic extracorporeal shockwave lithotripsy (Dornier HM 4) in the treatment of caliceal diverticulum lithiasis]. / Papel de la litotricia extracorpórea por ondas de choque electrohidráulicas (Dornier HM 4) en el tratamiento de las litiasis en divertículos caliciales.

UNLABELLED: Caliceal diverticula may be congenital or acquired malformations of the collecting system, normally asymptomatic and discovered during an IVP. Indications for treatment included chronic vague flank pain, acute renal colic, urinary tract infection and hematuria. We present the results of 29 patients with symptomatic calculi in caliceal diverticula who were managed by ESWL monotherapy. All treatments were performed with electrohydraulic machine (Dornier HM 4) in ambulatory form. RESULTS: The average followup was 42 months. 12 patients (40%) had passed successfully all of the stone fragments, while 2 patients (7%) had passed more than half and 4 (13.5%) had passed less than half of the fragments. 66 per cent of patients had been rendered free of symptoms. The possibility of producing a satisfactory result (66% free of symptoms and 40% stone free by X ray) and the low morbidity of ESWL suggest that this treatment may be appropriate for majority of calculi in calicea diverticula.

[Renal hematoma after shockwave extracorporeal lithotripsy]. / Hematomas renales tras litotricia extracorpórea por ondas de choque.

OBJECTIVE: Renal haematomas after shock wave extracorporeal lithotripsy (SWEL) represent a potentially serious complication. This paper examines those cases of post-SWEL renal haematoma seen in our Centre, analyzing the likely risk factors. PATIENTS AND METHODS: Between May 1988 and June 1996, 12,800 patients were treated with 15100 lithiasis at some level of the urinary tract requiring 16,000 SWEL sessions. All treatments were done with a Dornier HM-4 lithotripter. Voltage applied ranged from 18 to 26 Kv, averaging 2500 waves/session. Complementary testing (ultrasound/computerised tomography) was requested immediately after treatment if clinical complications were suspected. RESULTS: A total of 10 renal haematomas (0.078%) were diagnosed. Six cases were mild, but 4 presented extensive haematoma with significant haemodynamic consequence. Although in one case nephrectomy was undertaken to control haemorrhage, death finally occurred by disseminated intravascular coagulation. Four patients who developed haematoma were hypertensive and 3 had a previously corrected haemostasis alteration. CONCLUSIONS: The possibility of renal haematoma should be taken into account in the face of persistent and unjustified pain after SWEL treatment. Normalization of blood pressure values, correction of urinary infection as well as adequate correction of haemostatic disorders is advisable.