The Color and Stability of Maya Blue: TDDFT Calculations

Car-Parrinello structural optimizations of realistic models of the Maya Blue (MB) hybrid material are combined with TDDFT calculations of the electronic excitation spectra to identify the nature of the fundamental guest-host interactions leading to the unusual stability of this pigment. The comparison with the features of the experimental visible spectrum reveals that the main mode of interaction between the host solid (the palygorskite clay) and the guest molecule (the organic indigo dye) involves the coordination of the carbonyl group of the dye by Al3+ ions exposed at the edge of the palygorskite tunnels. Analogous Mg2+-dye interactions which do not strongly affect the MB visible spectrum can also be present. Thermal treatment used in the preparation of the pigment appears therefore essential to release some of the structural water molecules tightly bound to the Al3+ ions in the internal clay surface, thus leaving them available to coordinate the organic molecule. Moderate heating also favors the oxidation of indigo to dehydroindigo (DHI): the spectral features of the latter complex with Al3+ are in remarkable agreement with the experimental spectrum, thus confirming the substantial role of DHI in the properties of Maya Blue

Competition between water and hydrogen peroxide at Ti center in Titanium zeolites. An ab initio study

A combined Car 12Parrinello molecular dynamics blue moon sampling approach has been adopted to study the competitive attack of H2O and H2O2 at a tetracoordinated Titanium site in a Ti 12zeolite. The results indicate that, although the attack of water to form a trigonal bipyramidal center is thermodynamically more stable, the attack of hydrogen peroxide to form a similar adduct is kinetically favored. In both cases, solvent cooperation is effective in the formation of the adducts. The relevance of such a result in relation to the catalytic properties of Ti 12zeolites is discussed

Interactions, Behavior, And Stability of Fluorenone inside Zeolite Nanochannels

The development of functional materials based on the supramolecular organization of photoactive species in nanosized porous matrices requires a deep knowledge of host 12guest interactions and of their influence on material properties and stability. Extensive first-principles investigations on the fluorescent dye fluorenone inside zeolite L, both at dry conditions and in the presence of water, have unraveled the molecular origin of the peculiar stability of this composite in humid environments, a fundamental prerequisite for practical applications. Results of first-principles molecular dynamics simulations, structural optimizations, and TDDFT calculations, validated by comparison with experimental data, provide a comprehensive picture of the structure, energetics, electronic excitation properties, and room-temperature behavior of the fluorenone/zeolite L composite and predict a substantial optical anisotropy for this material also maintained upon contact with water. The interaction of the fluorenone carbonyl group with the zeolite extraframework potassium cations is responsible for the dye stabilization in zeolite L nanochannels and features itself as a general leitmotiv regarding important properties of carbonyl functionalized photoactive species in hydrophilic matrices

TS-1 from First Principles

First principles Studies on periodic TS-1 models at Ti content corresponding to 1.35% and 2.7% in weight of TiO2 are presented. The problem of Ti preferential siting is addressed by using realistic models corresponding to the TS-1 unit cell [TiSi95O192] and adopting for the first time a periodic DFT approach, thus providing an energy scale for Ti in the different crystallographic sites in nondefective TS-1. The structure with Ti in site T3 is the most stable, followed by T4 (+0.3 kcal/mol); the less stable structure, corresponding to Ti in T1, is 5.6 kcal/mol higher in energy. The work has been extended to investigate models with two Ti's per unit cell [Ti2Si94O192] (2.7%). The possible existence of Ti-O-Ti bridges, formed by two corner-sharing TiO4 tetrahedra, is discussed. By using Cluster models cut from the optimized periodic DFT structures, both vibrational (DFT) and electronic excitation spectra (TDDFT) have been calculated and favorably compared with the experimental data available on TS-1. Interesting features emerged from excitation spectra: (i) Isolated tetrahedral Ti sites show a Beer-Lambert behavior, with absorption intensity proportional to concentration. Such a behavior is gradually lost when two Ti's occupy sites close to each other. (ii) The UV-vis absorption in the 200-250 nm region can be associated with transitions from Occupied states delocalized on the framework oxygens to empty d states localized on Ti. Such extended-states-to-local-states transitions may help the interpretation of the photovoltaic activity recently detected in Ti zeolites

"Hot" Surface Activation of Molecular Complexes: Insight from Modeling Studies

Rock-and-roll over hot floors: Theoretical modeling of the first activation stages of a Cu complex on top of a heated surface (750 K) revealed two mobility regimes, a slow bump-and-rock diffusion over the surface and a fast roll-and-go motion accompanied by significant temperature-induced bond oscillations. This study enables a deeper insight into "hot" surface molecular activation processes.Tanz auf dem Vulkan: Das Modellieren der ersten Aktivierungsstufen eines Cu-Komplexes auf einer beheizten Oberfl\ue4che (750\u2005K) enth\ufcllte zwei Bewegungsarten: eine langsame Diffusion durch \u201eAnsto fen und Taumeln\u201c und eine schnelle Rollbewegung, die mit deutlichen temperaturinduzierten Bindungsoszillationen einhergeht. Diese Befunde geben einen Einblick in die Prozesse bei der Aktivierung durch \u201ehei fe\u201c Oberfl\ue4chen

Water in acid boralites: Hydration effects on framework B sites

Properties and behavior of protonated boron-containing zeolites at different hydration degree have been investigated by means of periodic DFT approaches. Geometry optimization and room-temperature Car-Parrinello molecular dynamics results, in line with experimental findings, indicate that the BO3-bound silanolic acid site typical of dry boralites should convert to a solvated H3O+ hydrogen bonded to tetrahedral BO4 at moderate water content. By increasing the water loading, the tetrahedral structure of the B site is stabilized and the physicochemical properties of the water molecules solvating the acid proton gradually approach the liquid-phase ones. A relevant role of structural and vibrational properties of the zeolite framework in the water-induced trigonal-to-tetrahedral transition at the B site is highlighted by simulation results

Potential for Detection of Safety Signals for Over-the-Counter Medicines Using National ADR Spontaneous Reporting Data: The Example of OTC NSAID-Associated Gastrointestinal Bleeding.

One post-marketing surveillance challenge for many regulatory authorities is access to information regarding the safety of over-the-counter (OTC) medicines. National spontaneous adverse drug reaction (ADR) report data represent a rich potential data source for the detection of safety signals associated with OTC medicines, yet little is known regarding the possibility of detecting safety signals for OTC medicines within these datasets. The aim of this study was to evaluate the potential for detecting safety signals for OTC medicines in National ADR spontaneous reporting data, using OTC non-steroidal anti-inflammatory drugs (NSAIDs) and gastrointestinal bleeding as an example. Data from the Australian Adverse Drug Reactions System (ADRS) dataset (1971-2008) and the Canadian Vigilance Adverse Reaction Online Database (VAROD) (1965-2013) were used to explore the feasibility of using spontaneous reporting data, exploring the association between gastrointestinal bleeding and the use of OTC NSAIDs. Safety signals were examined using disproportionality analyses and reporting odds ratios calculated. After adjusting for age, gender, medications known to increase the risk of bleeding, and medications used for the management of conditions associated with an increased risk of bleeding, a two-fold increase in the risk of gastrointestinal (GI) bleeding with OTC NSAID was observed within each dataset. This study demonstrates that spontaneous ADR reporting data can be used in pharmacovigilance to monitor the safety of OTC medicines

Prescribing Hemodialysis or Hemodiafiltration: When One Size Does Not Fit All the Proposal of a Personalized Approach Based on Comorbidity and Nutritional Status

There is no simple way to prescribe hemodialysis. Changes in the dialysis population, improvements in dialysis techniques, and different attitudes towards the initiation of dialysis have influenced treatment goals and, consequently, dialysis prescription. However, in clinical practice prescription of dialysis still often follows a “one size fits all” rule, and there is no agreed distinction between treatment goals for the younger, lower-risk population, and for older, high comorbidity patients. In the younger dialysis population, efficiency is our main goal, as assessed by the demonstrated close relationship between depuration (tested by kinetic adequacy) and survival. In the ageing dialysis population, tolerance is probably a better objective: “good dialysis” should allow the patient to attain a stable metabolic balance with minimal dialysis-related morbidity. We would like therefore to open the discussion on a personalized approach to dialysis prescription, focused on efficiency in younger patients and on tolerance in older ones, based on life expectancy, comorbidity, residual kidney function, and nutritional status, with particular attention placed on elderly, high-comorbidity populations, such as the ones presently treated in most European centers. Prescription of dialysis includes reaching decisions on the following elements: dialysis modality (hemodialysis (HD) or hemodiafiltration (HDF)); type of membrane (permeability, surface); and the frequency and duration of sessions. Blood and dialysate flow, anticoagulation, and reinfusion (in HDF) are also briefly discussed. The approach described in this concept paper was developed considering the following items: nutritional markers and integrated scores (albumin, pre-albumin, cholesterol; body size, Body Mass Index (BMI), Malnutrition Inflammation Score (MIS), and Subjective Global Assessment (SGA)); life expectancy (age, comorbidity (Charlson Index), and dialysis vintage); kinetic goals (Kt/V, normalized protein catabolic rate (n-PCR), calcium phosphate, parathyroid hormone (PTH), beta-2 microglobulin); technical aspects including vascular access (fistula versus catheter, degree of functionality); residual kidney function and weight gain; and dialysis tolerance (intradialytic hypotension, post-dialysis fatigue, and subjective evaluation of the effect of dialysis on quality of life). In the era of personalized medicine, we hope the approach described in this concept paper, which requires validation but has the merit of providing innovation, may be a first step towards raising attention on this issue and will be of help in guiding dialysis choices that exploit the extraordinary potential of the present dialysis “menu”

Energy Transfer from Magnetic Iron Oxide Nanoparticles: Implications for Magnetic Hyperthermia

Magnetic iron oxide nanoparticles (IONPs) have gained momentum in the field of biomedical applications. They can be remotely heated via alternating magnetic fields, and such heat can be transferred from the IONPs to the local environment. However, the microscopic mechanism of heat transfer is still debated. By X-ray total scattering experiments and first-principles simulations, we show how such heat transfer can occur. After establishing structural and microstructural properties of the maghemite phase of the IONPs, we built a maghemite model functionalized with aminoalkoxysilane, a molecule used to anchor (bio)molecules to oxide surfaces. By a linear response theory approach, we reveal that a resonance mechanism is responsible for the heat transfer from the IONPs to the surroundings. Heat transfer occurs not only via covalent linkages with the IONP but also through the solvent hydrogen-bond network. This result may pave the way to exploit the directional control of the heat flow from the IONPs to the anchored molecules─i.e., antibiotics, therapeutics, and enzymes─for their activation or release in a broader range of medical and industrial applications

Constraint methods for determining pathways and free energy of activated processes

Activated processes from chemical reactions up to conformational transitions of large biomolecules are hampered by barriers which are overcome only by the input of some free energy of activation. Hence, the characteristic and rate-determining barrier regions are not sufficiently sampled by usual simulation techniques. Constraints on a reaction coordinate r have turned out to be a suitable means to explore difficult pathways without changing potential function, energy or temperature. For a dense sequence of values of r, the corresponding sequence of simulations provides a pathway for the process. As only one coordinate among thousands is fixed during each simulation, the pathway essentially reflects the system's internal dynamics. From mean forces the free energy profile can be calculated to obtain reaction rates and insight in the reaction mechanism. In the last decade, theoretical tools and computing capacity have been developed to a degree where simulations give impressive qualitative insight in the processes at quantitative agreement with experiments. Here, we give an introduction to reaction pathways and coordinates, and develop the theory of free energy as the potential of mean force. We clarify the connection between mean force and constraint force which is the central quantity evaluated, and discuss the mass metric tensor correction. Well-behaved coordinates without tensor correction are considered. We discuss the theoretical background and practical implementation on the example of the reaction coordinate of targeted molecular dynamics simulation. Finally, we compare applications of constraint methods and other techniques developed for the same purpose, and discuss the limits of the approach