Dolomitic Lime Mortars: Carbonation Complications and Susceptibility to Acidic Sulfates

Dolomitic lime mortars, widely used in historic construction and as repair mortars today, are distinguished by their high magnesium content as well as their high plasticity, water retention, and workability. However, the dolomitic lime creates a more complicated chemistry in the resulting mortar in which the magnesium and calcium compounds carbonate at different rates. Although portlandite readily carbonates to calcite, the carbonation of brucite is delayed and could result in a variety compounds in the cured mortar. The reaction of these magnesium compounds with acidic sulfates in the environment could lead to the formation of magnesium sulfate salts, which have the potential to deteriorate the mortar itself and surrounding materials. Mortar deterioration could also occur due to the dissolution of the magnesium compounds in the mortar and subsequent material losses. A series of experiments have been conducted that examine the carbonation of dolomitic lime mortars as well as the extent to which these mortars interact with acidic sulfates. First the production of dolomitic lime was simulated in a laboratory setting, using XRD and SEM to determine the chemical and physical changes that occur during the calcining process. The same analytical techniques were used to examine the level of carbonation in dolomitic lime model mortars. The fundamental reactivity of acidic sulfate solutions with certain compounds in dolomitic mortars was explored using AA. Acidic sulfate attack via acid rain was also simulated on model mortars, and the effects of that exposure analyzed by AA and XRD. Laboratory work for this thesis was conducted at Columbia University GSAPP's Architecture Conservation Laboratory, the Department of Scientific Research at the Metropolitan Museum of Art, and Highbridge Materials Consulting, Inc

Adsorption of CO on Supported Gold Nanoparticle Catalysts: A Comparative Study

The adsorption of CO on three different gold nanoparticle catalysts supported on high surface area TiO2 was studied using infrared transmission spectroscopy at room temperature and CO pressures typically used in CO oxidation reactions. The three, real-world catalysts were Au catalysts synthesized in our laboratory from thiol monolayer protected clusters (MPCs) and two commercial catalysts from the World Gold Council (WGC and AuTEK). Within experimental reproducibility, the adsorption data for the three catalysts are indistinguishable. While showing approximately Langmuir behavior, the adsorption data also show coverage dependence, as others have observed for many catalyst systems. Two approaches were used to fit the data, a two-site model and a variable binding constant model. The two-site Langmuir model yielded strong (36%) and weak (64%) binding constants of 2740 and 146 atm-1, respectively. Alternatively, using a sliding-tangent Langmuir fit gave a variable binding constant of 2670-120 atm-1 at room temperature for coverage θ ) 0-0.8. The heat of adsorption was then extracted from the binding constants using a literature value for -TΔS. These values were determined as ΔH)-64 and -56 kJ/mol for strong and weak binding according to the two-site model and ΔH)-63 to -56 kJ/mol for coverage θ ) 0-0.8 for the variable binding constant model. These values agree well with literature values obtained (i) using supported catalysts under higher pressures and (ii) using model catalysts under higher pressures and ultrahigh vacuum conditions

CSAR Benchmark Exercise of 2010: Selection of the Protein–Ligand Complexes

ABSTRACT: A major goal in drug design is the improvement of computational methods for docking and scoring. The Community Structure Activity Resource (CSAR) aims to collect available data from industry and academia which may be used for this purpose (www.csardock.org). Also, CSAR is charged with organizing community-wide exercises based on the collected data. The first of these exercises was aimed to gauge the overall state of docking and scoring, using a large and diverse data set of protein ligand complexes. Participants were asked to calculate the affinity of the complexes as provided and then recalculate with changes which may improve their specific method. This first data set was selected from existing PDB entries which had binding data (Kd or Ki) in Binding MOAD, augmented with entries from PDBbind. The final data set contains 343 diverse protein ligand complexes and spans 14 pKd. Sixteen proteins have three or more complexes in the data set, from which a user could start an inspection of congeneric series. Inherent experimental error limits the possible correlation between scores and measured affinity; R 2 is limited to ∼0.9 when fitting to the data set without over parametrizing. R 2 is limited to ∼0.8 when scoring the data set with a method trained on outside data. The details of how the data set was initially selected, and the process by which it matured t

Genomic investigations of unexplained acute hepatitis in children

Since its first identification in Scotland, over 1,000 cases of unexplained paediatric hepatitis in children have been reported worldwide, including 278 cases in the UK1. Here we report an investigation of 38 cases, 66 age-matched immunocompetent controls and 21 immunocompromised comparator participants, using a combination of genomic, transcriptomic, proteomic and immunohistochemical methods. We detected high levels of adeno-associated virus 2 (AAV2) DNA in the liver, blood, plasma or stool from 27 of 28 cases. We found low levels of adenovirus (HAdV) and human herpesvirus 6B (HHV-6B) in 23 of 31 and 16 of 23, respectively, of the cases tested. By contrast, AAV2 was infrequently detected and at low titre in the blood or the liver from control children with HAdV, even when profoundly immunosuppressed. AAV2, HAdV and HHV-6 phylogeny excluded the emergence of novel strains in cases. Histological analyses of explanted livers showed enrichment for T cells and B lineage cells. Proteomic comparison of liver tissue from cases and healthy controls identified increased expression of HLA class 2, immunoglobulin variable regions and complement proteins. HAdV and AAV2 proteins were not detected in the livers. Instead, we identified AAV2 DNA complexes reflecting both HAdV-mediated and HHV-6B-mediated replication. We hypothesize that high levels of abnormal AAV2 replication products aided by HAdV and, in severe cases, HHV-6B may have triggered immune-mediated hepatic disease in genetically and immunologically predisposed children

Dolomitic Lime Mortars: Carbonation Complications and Susceptibility to Acidic Sulfates

Dolomitic lime mortars, widely used in historic construction and as repair mortars today, are distinguished by their high magnesium content as well as their high plasticity, water retention, and workability. However, the dolomitic lime creates a more complicated chemistry in the resulting mortar in which the magnesium and calcium compounds carbonate at different rates. Although portlandite readily carbonates to calcite, the carbonation of brucite is delayed and could result in a variety compounds in the cured mortar. The reaction of these magnesium compounds with acidic sulfates in the environment could lead to the formation of magnesium sulfate salts, which have the potential to deteriorate the mortar itself and surrounding materials. Mortar deterioration could also occur due to the dissolution of the magnesium compounds in the mortar and subsequent material losses. A series of experiments have been conducted that examine the carbonation of dolomitic lime mortars as well as the extent to which these mortars interact with acidic sulfates. First the production of dolomitic lime was simulated in a laboratory setting, using XRD and SEM to determine the chemical and physical changes that occur during the calcining process. The same analytical techniques were used to examine the level of carbonation in dolomitic lime model mortars. The fundamental reactivity of acidic sulfate solutions with certain compounds in dolomitic mortars was explored using AA. Acidic sulfate attack via acid rain was also simulated on model mortars, and the effects of that exposure analyzed by AA and XRD. Laboratory work for this thesis was conducted at Columbia University GSAPP's Architecture Conservation Laboratory, the Department of Scientific Research at the Metropolitan Museum of Art, and Highbridge Materials Consulting, Inc

Application of the Temkin Model to the Adsorption of CO on Gold

A treatment of the Temkin model was developed for describing the adsorption of CO on gold. In this presentation, it is made clear that the Temkin thermodynamic model is an extension of the Langmuir model that incorporates a linear variation of the adsorption enthalpy. It is also stressed that the Temkin model can be interpreted in terms of two distinct physical situations: the first assumes equivalent binding sites and an adsorption enthalpy that varies with coverage due adsorbate interactions, while the second assumes a uniform distribution of heterogeneous binding sites and an adsorption enthalpy that varies due to the heterogeneity of sites. In addition, a midrange approximation, where the surface is roughly half covered with adsorbates, is commonly employed. While each of these situations is similar, they are not equivalent and yield slightly different analytical expressions that describe the adsorption coverage as a function of pressure and temperature. Fitting data with the different analytical expressions therefore produces slightly different thermodynamic values for the adsorption enthalpy and entropy. These different cases are explicitly defined and developed. For the adsorption of CO on gold, the adsorbate interaction case is shown to be most consistent with the current body of experimental and theoretical evidence. The various analytical expressions are used to apply the Temkin model to data for CO adsorption on 1% Au/TiO2 real-world catalysts (from the World Gold Council) studied under catalytically relevant isothermal (T = 275–325 K) and isobaric (PCO = 0–10 Torr) experimental conditions. Infrared transmission spectroscopy was the analytical technique used for quantitatively measuring the adsorption coverage. The coverage as a function of pressure (θ,P) and as a function of temperature (θ,T) was fit with the Temkin adsorption models. The models yield the thermodynamic adsorption enthalpy at zero and full coverage as well as the adsorption entropy. The values of these thermodynamic parameters differ slightly depending upon the particular Temkin situation considered (cf. adsorbate interaction, heterogeneous surface, and midrange approximation cases). While all three Temkin cases produced excellent fits to both the isothermal and isobaric data sets, the adsorbate interaction case is most consistent with experimental and theoretical evidence describing the adsorption of CO on gold. The average enthalpy values from fitting the isothermal and isobaric data sets using the adsorbate interaction model are −ΔH0 = 59.2 kJ/mol and −ΔH1 = 54.6 kJ/mol for zero and full coverage, respectively. The adsorption entropy, −ΔS = 142 J/(K mol), was determined by fitting the data sets from multiple isothermal experiments with the adsorbate interaction case. These thermodynamic adsorption values are in excellent agreement with previously reported values. The validity of the Temkin adsorbate interaction model was further supported by fitting isothermal and isobaric data for the adsorption of CO on a well-defined gold surface, as reported previously by Gottfried et al. This new treatment of the Temkin adsorption model is theoretically and experimentally straightforward and applicable to both isothermal and isobaric data sets. It provides meaningful thermodynamic values of adsorption enthalpy and entropy, which can be used to characterize and explain differences between various catalysts. The model should also be applicable to the adsorption of other small molecules on metal surfaces and particles that show coverage-dependent adsorption properties