Influence of Alkali Metal Cations on the Oxygen Reduction Activity of Pt5Y and Pt5Gd Alloys

Electrolyte species can significantly influence the electrocatalytic performance. In this work, we investigate the impact of alkali metal cations on the oxygen reduction reaction (ORR) on active Pt5Gd and Pt5Y polycrystalline electrodes. Due to the strain effects, Pt alloys exhibit a higher kinetic current density of ORR than pure Pt electrodes in acidic media. In alkaline solutions, the kinetic current density of ORR for Pt alloys decreases linearly with the decreasing hydration energy in the order of Li+ > Na+ > K+ > Rb+ > Cs+, whereas Pt shows the opposite trend. To gain further insights into these experimental results, we conduct complementary density functional theory calculations considering the effects of both electrode surface strain and electrolyte chemistry. The computational results reveal that the different trends in the ORR activity in alkaline media can be explained by the change in the adsorption energy of reaction intermediates with applied surface strain in the presence of alkali metal cations. Our findings provide important insights into the effects of the electrolyte and the strain conditions on the electrocatalytic performance and thus offer valuable guidelines for optimizing Pt-based electrocatalysts.

Impact of Pt(hkl) Electrode Surface Structure on the Electrical Double Layer Capacitance

The classical theory of the electrical double layer (EDL) does not consider the effects of the electrode surface structure on the EDL properties. Moreover, the best agreement between the traditional EDL theory and experiments has been achieved so far only for a very limited number of ideal systems, such as liquid metal mercury electrodes, for which it is challenging to operate with specific surface structures. In the case of solid electrodes, the predictive power of classical theory is often not acceptable for electrochemical energy applications, e.g., in supercapacitors, due to the effects of surface structure, electrode composition, and complex electrolyte contributions. In this work, we combine ab initio molecular dynamics (AIMD) simulations and electrochemical experiments to elucidate the relationship between the structure of Pt(hkl) surfaces and the double-layer capacitance as a key property of the EDL. Flat, stepped, and kinked Pt single crystal facets in contact with acidic HClO4 media are selected as our model systems. We demonstrate that introducing specific defects, such as steps, can substantially reduce the EDL capacitances close to the potential of zero charge (PZC). Our AIMD simulations reveal that different Pt facets are characterized by different net orientations of the water dipole moment at the interface. That allows us to rationalize the experimentally measured (inverse) volcano-shaped capacitance as a function of the surface step density.

Molecular-Level Control over Ionic Conduction and Ionic Current Direction by Designing Macrocycle-Based Ionomers

Poor ionic conductivity of the catalyst-binding, sub-micrometer-thick ionomer layers in energy conversion and storage devices is a huge challenge. However, ionomers are rarely designed keeping in mind the specific issues associated with nanoconfinement. Here, we designed nature-inspired ionomers (calix-2) having hollow, macrocyclic, calix[4]arene-based repeat units with precise, sub-nanometer diameter. In ≤100 nm-thick films, the in-plane proton conductivity of calix-2 was up to 8 times higher than the current benchmark ionomer Nafion at 85% relative humidity (RH), while it was 1-2 orders of magnitude higher than Nafion at 20-25% RH. Confocal laser scanning microscopy and other synthetic techniques allowed us to demonstrate the role of macrocyclic cavities in boosting the proton conductivity. The systematic self-assembly of calix-2 chains into ellipsoids in thin films was evidenced from atomic force microscopy and grazing incidence small-angle X-ray scattering measurements. Moreover, the likelihood of alignment and stacking of macrocyclic units, the presence of one-dimensional water wires across this macrocycle stacks, and thus the formation of long-range proton conduction pathways were suggested by atomistic simulations. We not only did see an unprecedented improvement in thin-film proton conductivity but also saw an improvement in proton conductivity of bulk membranes when calix-2 was added to the Nafion matrices. Nafion-calix-2 composite membranes also took advantage of the asymmetric charge distribution across calix[4]arene repeat units collectively and exhibited voltage-gating behavior. The inclusion of molecular macrocyclic cavities into the ionomer chemical structure can thus emerge as a promising design concept for highly efficient ion-conducting and ion-permselective materials for sustainable energy applications.

Revealing Elusive Intermediates of Platinum Cathodic Corrosion through DFT Simulations

Cathodic corrosion of metals discovered more than 120 years ago remains a poorly understood electrochemical process. It is believed that the corrosion intermediates formed during cathodic polarization are extremely short-lived species because of their high reactivity. Together with the concurrent vigorous hydrogen evolution, this makes it challenging to investigate the reaction mechanism and detect the intermediates experimentally. From a computational standpoint, the process also presents a serious challenge as it occurs at rather low negative potentials in concentrated alkaline solutions. Here, we use density-functional-theory calculations to elucidate the identity of reaction intermediates and their reactivity at the Pt(111)/electrolyte interface. By controlling the electrode potential in an experimentally relevant region through constant Fermi-level molecular dynamics, we reveal the formation of alkali cation-stabilized Pt hydrides as intermediates of cathodic corrosion. The results also suggest that the found Pt anions could discharge at the interface to produce H₂ by reacting with either surface-bound hydrogen species or solution water molecules.

Periodicity in the Electrochemical Dissolution of Transition Metals

Extensive research efforts are currently dedicated to the search for new electrocatalyst materials in which expensive and rare noble metals are replaced with cheaper and more abundant transition metals. Recently, numerous alloys, oxides, and composites with such metals have been identified as highly active electrocatalysts through the use of high‐throughput screening methods with the help of activity descriptors. Up to this point, stability has lacked such descriptors. Hence, we elucidate the role of intrinsic metal/oxide properties on the corrosion behavior of representative 3d, 4d, and 5d transition metals. Electrochemical dissolution of nine transition metals is quantified using online inductively coupled plasma mass spectrometry (ICP‐MS). Based on the obtained dissolution data in alkaline and acidic media, we establish clear periodic correlations between the amount of dissolved metal, the cohesive energy of the metal atoms (E_coh), and the energy of oxygen adsorption on the metal (ΔH_O,ads). Such correlations can support the knowledge‐driven search for more stable electrocatalysts.

Mechanistic Study of IrO2 Dissolution during the Electrocatalytic Oxygen Evolution Reaction

Understanding the mechanistic interplay between the activity and stability of water splitting electrocatalysts is crucial for developing efficient and durable water electrolyzers. Ir-based materials are among the best catalysts for the oxygen evolution reaction (OER) in acidic media, but their degradation mechanisms are not completely understood. Here, through first-principles calculations we investigate iridium dissolution at the IrO₂(110)/water interface. Simulations reveal that the surface-bound IrO₂OH species formed upon iridium dissolution should be thermodynamically stable in a relatively wide potential window undergoing transformations into Ir^VI (as IrO₃) at high anodic potentials and Ir^III (as Ir(OH)₃) at low anodic potentials. The identified high-valence surface-bound dissolution intermediates of Ir are determined to display greater OER activities than the pristine IrO₂(110) surface in agreement with the experimentally observed high activity of an amorphous hydrated IrO_x surface layer. Combined with recent experimental results, our simulations illuminate the mechanistic details of the degradation mechanism of IrO₂ and how it couples to electrocatalytic OER.

Abstract A98: Molecular dynamics study of pH-dependent interactions between immune checkpoint receptor PD-1 and PD-L1

Understanding of how small variations in checkpoint protein chemistry (e.g., mutations) and tumor immune microenvironment (e.g., pH) influence receptor-ligand binding and define both the mechanisms and magnitude of immune response is of great importance, but the molecular details are still missing. Here, we employ enhanced free-energy sampling molecular dynamics simulations to unveil pH-dependent binding/unbinding mechanisms and kinetics of PD-1/PD-L1 interactions. By identifying the binding pocket in the PD-1/PD-L1 complex, we show a key role of the His68 protonation state in PD-1 in the complex stabilization at low pH. Specifically, we estimate the unbinding free-energy barrier to be around 15 kJ/mol higher at pH 5.5 than at pH 7.4. The estimated ratio of binding (kon) and unbinding (koff) rate constants is found to agree well with recent experimental data on KD values at different pH. Also, simulations show an important role of solvation state of the binding pocket in mediating polar interactions at the PD-1/PD-L1 binding interface. These initial molecular insights are important for further engineering of binding/unbinding kinetics to formulate more efficient immune checkpoint blockade strategies.

Citation Format: Vitaly Alexandrov, Konstantin Klyukin. Molecular dynamics study of pH-dependent interactions between immune checkpoint receptor PD-1 and PD-L1 [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr A98.

Kinetics of pH-dependent interactions between PD-1 and PD-L1 immune checkpoint proteins from molecular dynamics

Immune checkpoint blockade of signaling pathways such as PD-1/PD-L1 has recently opened up a new avenue for highly efficient immunotherapeutic strategies to treat cancer. Since tumor microenvironments are characterized by lower pH (5.5-7.0), pH-dependent protein-ligand interactions can be exploited as efficient means to regulate drug affinity and specificity for a variety of malignancies. In this article, we investigate the mechanism and kinetics of pH-dependent binding and unbinding processes for the PD-1/PD-L1 checkpoint pair employing classical molecular dynamics simulations. Two representative pH levels corresponding to circumneutral physiological conditions of blood (pH 7.4) and acidic tumor microenvironment (pH 5.5) are considered. Our calculations demonstrate that pH plays a key role in protein-ligand interactions with small pH changes leading to several orders of magnitude increase in binding affinity. By identifying the binding pocket in the PD-1/PD-L1 complex, we show a pivotal role of the His68 protonation state of PD-1in the complex stabilization at low pH. The results on the reaction rate constants are in qualitative agreement with available experimental data. The obtained molecular details are important for further engineering of binding/unbinding kinetics to formulate more efficient immune checkpoint blockade strategies.

Ferroelectric Tunnel Junctions Enhanced by a Polar Oxide Barrier Layer

Ferroelectric tunnel junctions (FTJs) have recently aroused significant interest due to the interesting physics controlling their properties and potential application in nonvolatile memory devices. In this work, we propose a new concept to design high-performance FTJs based on ferroelectric/polar-oxide composite barriers. Using density functional theory calculations, we model electronic and transport properties of LaNiO₃/PbTiO₃/LaAlO₃/LaNiO₃ tunnel junctions and demonstrate that an ultrathin polar LaAlO₃(001) layer strongly enhances their performance. We predict a tunneling electroresistance (TER) effect in these FTJs with an OFF/ON resistance ratio exceeding a factor of 10⁴ and ON state resistance as low as about 1 kΩμm². Such an enhanced performance is driven by the ionic charge at the PbTiO₃/LaAlO₃ interface, which significantly increases transmission across the FTJ when the ferroelectric polarization of PbTiO₃ is pointing against the intrinsic electric field produced by this ionic charge. This is due to the formation of a two-dimensional (2D) electron or hole gas, depending on the LaAlO₃ termination being (LaO)⁺ or (AlO₂)^-, respectively, which is formed to screen the polarization charge of the nonuniform polarization state. This 2D electron (hole) gas can be switched ON and OFF by the reversal of ferroelectric polarization, resulting in the giant TER effect. The proposed design suggests a new direction for creating FTJs with a stable and reversible ferroelectric polarization, a sizable TER effect, and a low-resistance-area product, as required for memory applications.

Ab Initio Modeling of Transition Metal Dissolution from the LiNi0.5Mn1.5O4 Cathode

Irreversible dissolution of transition metals (TMs) from cathode materials in lithium-ion batteries (LIBs) represents a serious challenge for the application of high-energy-density LIBs. Despite substantial improvements achieved by Ni doping of the LiMn₂O₄ spinel, the promising high-voltage LiNi_0.5Mn_1.5O₄ (LNMO) cathode material still suffers from the loss of electro-active materials (Mn and Ni). This process contributes to the formation of solid-electrolyte interfaces and capacity loss severely limiting the battery life cycle. Here, we combine static and ab initio molecular dynamics free energy calculations based on the density functional theory to investigate the mechanism and kinetics of TM dissolution from LNMO into the liquid organic electrolyte. Our calculations help deconvolute the impact of various factors on TM dissolution rates such as the presence of surface protons and oxygen vacancies and the nature of TMs and electrolyte species. The present study also reveals a linear relationship between adsorption strength of the electrolyte species and TM dissolution barriers that should help design electrode/electrolyte interfaces less vulnerable to TM dissolution.

Defect-Assisted Tunneling Electroresistance in Ferroelectric Tunnel Junctions

Recent experimental results have demonstrated ferroelectricity in thin films of SrTiO_{3} induced by antisite Ti_{Sr} defects. This opens a possibility to use SrTiO_{3} as a barrier layer in ferroelectric tunnel junctions (FTJs)-emerging electronic devices promising for applications in nanoelectronics. Here using density functional theory combined with quantum-transport calculations applied to a prototypical Pt/SrTiO_{3}/Pt FTJ, we demonstrate that the localized in-gap energy states produced by the antisite Ti_{Sr} defects are responsible for the enhanced electron tunneling conductance which can be controlled by ferroelectric polarization. Our tight-binding modeling, which takes into account multiple defects, shows that the predicted defect-assisted tunneling electroresistance effect is greatly amplified when the defect energy levels are brought to the Fermi energy by one of the polarization states. Our results have implications for FTJs based on conventional ferroelectric barriers with defects and can be employed for the design of new types of FTJs with enhanced performance.

Ab Initio Metadynamics Study of the VO2+/VO2+ Redox Reaction Mechanism at the Graphite Edge/Water Interface

Redox flow batteries (RFBs) are promising electrochemical energy storage systems, for which development is impeded by a poor understanding of redox reactions occurring at electrode/electrolyte interfaces. Even for the conventional all-vanadium RFB chemistry employing V²⁺/V³⁺ and VO₂⁺/VO²⁺ couples, there is still no consensus about the reaction mechanism, electrode active sites, and rate-determining step. Herein, we perform Car-Parrinello molecular dynamics-based metadynamics simulations to unravel the mechanism of the VO₂⁺/VO²⁺ redox reaction in water at the oxygen-functionalized graphite (112̅0) edge surface serving as a representative carbon-based electrode. Our results suggest that during the battery discharge aqueous VO₂⁺/VO²⁺ species adsorb at the surface C-O groups as inner-sphere complexes, exhibiting faster adsorption/desorption kinetics than V²⁺/V³⁺, at least at low vanadium concentrations considered in our study. We find that this is because (i) VO₂⁺/VO²⁺ conversion does not involve the slow transfer of an oxygen atom, (ii) protonation of VO₂⁺ is spontaneous and coupled to interfacial electron transfer in acidic conditions to enable VO²⁺ formation, and (iii) V³⁺ found to be strongly bound to oxygen groups of the graphite surface features unfavorable desorption kinetics. In contrast, the reverse process taking place upon charging is expected to be more sluggish for the VO₂⁺/VO²⁺ redox couple because of both unfavorable deprotonation of the VO²⁺ water ligands and adsorption/desorption kinetics.

Tunneling Hot Spots in Ferroelectric SrTiO3

Strontium titanate (SrTiO₃) is the "silicon" in the emerging field of oxide electronics. While bulk properties of this material have been studied for decades, new unexpected phenomena have recently been discovered at the nanoscale, when SrTiO₃ forms an ultrathin film or an atomically sharp interface with other materials. One of the striking discoveries is room-temperature ferroelectricity in strain-free ultrathin films of SrTiO₃ driven by the Ti_Sr antisite defects, which generate a local dipole moment polarizing the surrounding nanoregion. Here, we demonstrate that these polar defects are not only responsible for ferroelectricity, but also propel the appearance of highly conductive channels, "hot spots", in the ultrathin SrTiO₃ films. Using a combination of scanning probe microscopy experimental studies and theoretical modeling, we show that the hot spots emerge due to resonant tunneling through localized electronic states created by the polar defects and that the tunneling conductance of the hot spots is controlled by ferroelectric polarization. Our finding of the polarization-controlled defect-assisted tunneling reveals a new mechanism of resistive switching in oxide heterostructures and may have technological implications for ferroelectric tunnel junctions. It is also shown that the conductivity of the hot spots can be modulated by mechanical stress, opening a possibility for development of conceptually new electronic devices with mechanically tunable resistive states.

Comprehensive analysis of two Shank3 and the Cacna1c mouse models of autism spectrum disorder

To expand, analyze and extend published behavioral phenotypes relevant to autism spectrum disorder (ASD), we present a study of three ASD genetic mouse models: Feng's Shank3^tm2Gfng model, hereafter Shank3/F, Jiang's Shank3^tm1Yhj model, hereafter Shank3/J and the Cacna1c deletion model. The Shank3 models mimick gene mutations associated with Phelan-McDermid Syndrome and the Cacna1c model recapitulates the deletion underlying Timothy syndrome. This study utilizes both standard and novel behavioral tests with the same methodology used in our previously published companion report on the Cntnap2 null and 16p11.2 deletion models. We found that some but not all behaviors replicated published findings and those that did replicate, such as social behavior and overgrooming in Shank3 models, tended to be milder than reported elsewhere. The Shank3/F model, and to a much lesser extent, the Shank3/J and Cacna1c models, showed hypoactivity and a general anxiety-like behavior triggered by external stimuli which pervaded social interactions. We did not detect deficits in a cognitive procedural learning test nor did we observe perseverative behavior in these models. We did, however, find differences in exploratory patterns of Cacna1c mutant mice suggestive of a behavioral effect in a social setting. In addition, only Shank3/F showed differences in sensory-gating. Both positive and negative results from this study will be useful in identifying the most robust and replicable behavioral signatures within and across mouse models of autism. Understanding these phenotypes may shed light of which features to study when screening compounds for potential therapeutic interventions.

First-principles study of adsorption–desorption kinetics of aqueous V2+/V3+ redox species on graphite in a vanadium redox flow battery

Vanadium redox flow batteries (VRFBs) represent a promising solution to grid-scale energy storage, and understanding the reactivity of electrode materials is crucial for improving the power density of VRFBs.

Ab Initio Modeling of Bulk and Intragranular Diffusion in Ni Alloys

Knowledge of solid-state and interfacial species diffusion kinetics is of paramount importance for understanding mechanisms of grain boundary (GB) oxidation causing environmental degradation and cracking of Ni-base structural alloys. In this study, first-principles calculations of vacancy-mediated diffusion are performed across a wide series of alloying elements commonly used in Ni-based superalloys, as well as interstitial diffusion of atomic oxygen and sulfur in the bulk, at the (111) surface, ⟨110⟩ symmetric tilt GBs of Ni corresponding to model low- (Σ = 3/(111)) and high-energy (Σ = 9/(221)) GBs. A substantial enhancement of diffusion is found for all species at the high-energy GB as compared with the bulk and the low-energy GB, with Cr, Mn, and Ti exhibiting remarkably small activation barriers (<0.1 eV; ~10 times lower than in the bulk). Calculations also show that the bulk diffusion mechanism and kinetics differ for oxygen and sulfur, with oxygen having a faster mobility and preferentially diffusing through the tetrahedral interstitial sites in Ni matrix, where it can be trapped in a local minimum.

Electron transport in pure and substituted iron oxyhydroxides by small-polaron migration

Iron oxyhydroxides (FeOOH) are common crystalline forms of iron that play a critical role in technology and the natural environment via a variety of important reduction-oxidation reactions, including electrical semiconduction as an aspect. However, a basic understanding of the electron transport properties of these systems is still lacking. We examine the electron mobility in goethite (α-FeOOH), akaganéite (β-FeOOH), and lepidocrocite (γ-FeOOH) polymorphs by means of density functional theory based (DFT+U) calculations. We show that room temperature charge transport should be dominated by the small-polaron hopping type, and that the attendant mobility should be highest for pure goethite and akaganéite. Hopping pathways through the various lattices are discussed in terms of individual electron exchange steps and rates for each. Given the usual occurrence of compositional impurities in natural iron oxyhydroxides, we also investigate the effect of common stoichiometric defects on the electron hopping activation energies such as Al and Cr substitutional cations in goethite, and Cl anions in the channels of akaganéite.

Ab initio modeling of Fe(ii) adsorption and interfacial electron transfer at goethite (α-FeOOH) surfaces

First-principles study of the mechanism of aqueous Fe(ii) adsorption and Fe(ii)–Fe(iii) interfacial electron transfer at goethite surfaces.

Adaptation of vulnerable regional agricultural systems in Europe to climate change – results from the ADAGIO project

Abstract. During 2007-2009 the ADAGIO project (http://www.adagio-eu.org) is carried out to evaluate regional adaptation options in agriculture in most vulnerable European regions (mediterranean, central and eastern European regions). In this context a bottom-up approach is used beside the top-down approach of using scientific studies, involving regional experts and farmers in the evaluation of potential regional vulnerabilities and adaptation options. Preliminary results of the regional studies and gathered feedback from experts and farmers show in general that (increasing) drought and heat are the main factors having impact on agricultural vulnerability not only in the Mediterranean region, but also in the Central and southern Eastern European regions. Another important aspect is that the increasing risk of pest and diseases may play a more important role for agricultural vulnerability than assumed before, however, till now this field is only rarely investigated in Europe. Although dominating risks such as increasing drought and heat are similar in most regions, the vulnerabilities in the different regions are very much influenced by characteristics of the dominating agroecosystems and prevailing socio-economic conditions. This will be even be more significant for potential adaptation measures at the different levels, which have to reflect the regional conditions.

[Combined surgical treatment of patients with huge aortic abdominal aneurysms associated with coronary artery lesions]

The objective of this study was to define the perioperative risk of simultaneous operations in patients with abdominal aortic aneurysm (AAA) associated with coronary artery disease (CAD). The hospital data of 30 patients with coexistent severe symptomatic AAA and significant CAD, who underwent one stage surgery of the abdominal aorta and the coronary arteries was retrospectively analysed. Most of the pts.--28 were male and only 2 female. The average age consisted 57.7 years. Infrarenal AAA (diameter over 5 cm) was presented in 25 patients and suprarenal extension was in presented in 5 pts, while all patients with coexisting CAD had three vessels disease and significant impairment of left ventricular function (23 pts with ejection fraction (EF) < 50% and 10 pts < 30% EF). The resections of AAA in pts. undergoing simultaneous coronary artery procedure were performed on cardiopulmonary bypass (CPB) and moderate hypothermia. There were 2 early postoperative deaths (6.66%) and 5 major nonfatal postoperative complications (16.6%). Our experience with simultaneous surgery of coexistent huge AAA and CAD demonstrated that: a) Combined procedure can be performed safely in patients with significant AAA and CAD. b) The overall early operative mortality and morbidity after combined surgery compare favourably with the results after CABG of patients with impaired left ventricular function. c) Simultaneous operation seems to be more favourable in patients with coexistent AAA and CAD regarding the high risk of aneurysmal rupture, saving them also the potential morbidity and eventually fatal complications associated with the second procedure. d) Even the management of suprarenal and huge infrarenal AAA can be carried out easier and with less risk of complications under the protection of CPB.

PartsList: a web-based system for dynamically ranking protein folds based on disparate attributes, including whole-genome expression and interaction information

As the number of protein folds is quite limited, a mode of analysis that will be increasingly common in the future, especially with the advent of structural genomics, is to survey and re-survey the finite parts list of folds from an expanding number of perspectives. We have developed a new resource, called PartsList, that lets one dynamically perform these comparative fold surveys. It is available on the web at http://bioinfo.mbb.yale.edu/partslist and http://www.partslist.org. The system is based on the existing fold classifications and functions as a form of companion annotation for them, providing 'global views' of many already completed fold surveys. The central idea in the system is that of comparison through ranking; PartsList will rank the approximately 420 folds based on more than 180 attributes. These include: (i) occurrence in a number of completely sequenced genomes (e.g. it will show the most common folds in the worm versus yeast); (ii) occurrence in the structure databank (e.g. most common folds in the PDB); (iii) both absolute and relative gene expression information (e.g. most changing folds in expression over the cell cycle); (iv) protein-protein interactions, based on experimental data in yeast and comprehensive PDB surveys (e.g. most interacting fold); (v) sensitivity to inserted transposons; (vi) the number of functions associated with the fold (e.g. most multi-functional folds); (vii) amino acid composition (e.g. most Cys-rich folds); (viii) protein motions (e.g. most mobile folds); and (ix) the level of similarity based on a comprehensive set of structural alignments (e.g. most structurally variable folds). The integration of whole-genome expression and protein-protein interaction data with structural information is a particularly novel feature of our system. We provide three ways of visualizing the rankings: a profiler emphasizing the progression of high and low ranks across many pre-selected attributes, a dynamic comparer for custom comparisons and a numerical rankings correlator. These allow one to directly compare very different attributes of a fold (e.g. expression level, genome occurrence and maximum motion) in the uniform numerical format of ranks. This uniform framework, in turn, highlights the way that the frequency of many of the attributes falls off with approximate power-law behavior (i.e. according to V(-b), for attribute value V and constant exponent b), with a few folds having large values and most having small values.

Perioperative myocardial protection with the calcium antagonist diltiazem

The effect of the calcium channel blocker, diltiazem, on cardiac performance was examined in 90 patients who underwent isolated aortic valve replacement for aortic valve diseases with marked left ventricular hypertrophy. The patients were randomly assigned to one of five groups dependent on the treatment plan with diltiazem: group 1, 5-day preoperative treatment with oral administration of 60 mg diltiazem 3 times daily, 10 mg diltiazem intravenously as a bolus dose before the beginning of the cardiopulmonary bypass, and 5 mg diltiazem intravenously 10 min before removal of aortic clamp; group 2, 5-day preoperative treatment with oral administration of 60 mg diltiazem 3 times daily; group 3, 10 mg diltiazem intravenously as a bolus dose before the beginning of CPB and 5 mg 10 min before removal of the aortic clamp; group 4, 15 mg diltiazem in 1000 ml cardioplegic solution, given as additive; group 5, control group not receiving diltiazem. All operative procedures were performed in an identical manner with an average cross-clamping time of 57.7 min and cooling the heart down to 16 degrees-17 degrees septal temperature by perfusion of the coronary arteries with 4 degrees C cold cardioplegic solution. In each patient the heart rate (HR), cardiac output and cardiac index (CO, CI), stroke volume index (SVI), left ventricular stroke work index (LVSWI) and systemic vascular resistance index (SVRI) were recorded and calculated before and after the ischemic period. Transmural samples were obtained three times by needle biopsy technique from the anterior free wall of the heart. Analysis of the variables revealed that: (1) complete cessation of electromechanical activity was achieved significantly more rapidly in groups 1 and 3 than in the other groups; (2) recovery of sinus rhythm and function of the conductive system required significantly longer in groups 1 and 3; (3) the time-related values of the important hemodynamic factors (CO, CI, LWSVI and SVRI) showed a significantly more effective postperfusion cardiac performance in groups 1 and 3 than in groups 2, 4 and 5. An oral dose of 180 mg diltiazem for 5 to 7 days preoperatively in combination with intravenous administration of 10 mg before the beginning of CPB and 5-10 mg during reperfusion can be recommended in patients undergoing open-heart surgery for isolated aortic valve diseases and left ventricular hypertrophy.

Modifying factors in prenatal carcinogenesis (review)

A description of the experimental approaches devised to control the growth of tumors induced by transplacental exposure to carcinogens is given. Due to the massive cell proliferation and differentiation taking place during embryogenesis, fetal tissues are believed to be privileged targets of neoplastic changes. As a consequence, trace amounts of environmental carcinogens capable of accumulating into the conceptuses may determine the appearance of tumors in the offspring, a possibility documented in several animal species including humans. Endogenous and exogenous factors counteracting this process have potential application as regulators of developmental carcinogenesis. Their identification is regarded as a means to chemoprevent pediatric tumors and can be instrumental in the analysis of the aetiopathogenesis of neoplastic phenotypes.