Secondary Salt Research Articles

Luminescence characteristics of individual Beijing haze aerosol particles

The rapid development of industrialization and urbanization has led to haze in Beijing that has garnered world attention. For the first time, we studied the luminescence properties of individual haze aerosol particles by using a scanning electron microscope (SEM) coupled with a cathodoluminescence (CL) spectrometer. CL analysis has rarely been reported for haze particles, however, we found that many haze particles showed varied luminescence characteristics. Many types of mineral dusts showed strong CL emission in the visible light wavelengths. Nitrogen-rich secondary particles had a strong CL emission in the UV wavelengths. Anthropogenic particles such as fly ash and Fe-rich, Ti-rich, and carbonaceous materials had much weaker CL responses. The mixture of mineral dusts and other species showed lower CL intensity and widened CL spectra, which continuously covered the UV-VIS-IR portion of the spectrum and which contrasted with the CL emissions of original mineral dusts and pure secondary salts. The sensitivity of CL spectra with respect to tiny changes in components, impurity, and valences enabled the CL spectroscopy to provide a unique perspective with which to analyze highly complicated mixtures of haze particles.

Comparative Ameliorative Efficiency of Phosphogypsum and Elemental Sulfur in Semi-Terrestrial Soda and Sulfate Moderately Halophytic Solonetz of the Light Gray Earth Subzone

The article presents the data from field tests on determination of the relative ameliorative efficiency of equivalent dosages of phosphogypsum and elemental sulfur on the alkaline saline semi-terrestrialsolonetz. Basing on the analysis data of soil water extract, higher ameliorative efficiency of elemental sulfur compared to phosphogypsum and fast amelioration of alkali-saline soils with the use of sulfur have been detected. Ten month of phosphogypsum and elemental sulfur incubation in soils significantly affected presence and contents of the salts, restructuring their ionic contents and growth of total salts. The latter required carrying out washing of the soils from the starting primary and newly formed secondary salts from root-inhabited soil layer. Washing of the soils ambiguously affected the ionic contents of the soil solution. It created more benefactor conditions on the elemental sulfur variant, to a greater degree reducing contents of all ions compared to phosphogypsum (the exception was НCO3-).

Pedological Characterization of the Soils of Atbara and Gash Rivers Upper Atbara Project Area (Kassala State - Sudan)

The soil study area is composed of wide and nearly flat alluvium plain deposits laid by Atbara and Gash Rivers. The study area makes about 751,290 ha and lies within arid and semi-desert climate zones and experiences rainfall in the order of 100 mm in its northern edge, increasing to some 400mm at its southern boundary close to Kassala and east of New Halfa town. The soil study was based mainly on a semi-detailed level soil surveys and the key specifications are a field density of 1 observation each 150 ha. Previously published soil study information was reviewed and incorporated in the findings [5[; [17]; [14]. The Aridisols and Entisols in eastern region of Sudan have high potential for crop production, but some constraints emerge affecting crop performance and decreasing yields. Those limitations are aspects of climatic conditions, parent materials and topography manifested generally in, 1) soil moisture deficiency and locally in; 2) accumulation of secondary salts 3) clayey topsoil textures. Aridisols are the soils of arid regions that exhibit at least some subsurface horizon development. They are characterized by being dry most of the year and limited leaching. Aridisols contain subsurface horizons in which clays, calcium carbonate, silica, salts, and/or gypsum have accumulated. Aridisols in their natural state are used mainly for range, wildlife, and recreation. Because of the dry climate in which they are found, they are not used for agricultural production unless irrigation water is available. Entisols formed by rapid deposition on floodplains are universally favored for growing food crops in large part because of the influx of fertility in the deposited material, their level topography, and often the proximity to transportation and water afforded by adjacent rivers. In aridic (torric) soil moisture regimes their alluvial deposits close to rivers are more easily irrigated than associated soils on adjacent higher terraces or the far away finer clayey deposits. Many, if not most of these areas are subject to flooding and often have extremely abrupt textural differences (i.e. stratifications) engendered by sedimentation processes. In floodplains the river channels migrate as the watershed characteristics change leaving sandy and silty sediments (levees) near the riverbank and finer textured materials further from the riverbank. In aridic moisture conditions Entisols on depressional areas or at higher terraces close to Aridisols are subject to salt accumulation similar to Aridisols. To minimize the concurrence of hazards in Aridisols and Entisols, management procedures should adhere to land and crop management systems. As well, the fertility status is likely to decline due to intensive farming of some nutrient-depleting crops, but this nutrient deficiency is correctable through implementing a fertilizer programme. In the study area, some parameters are management-factors determining e.g. topsoil textures and flat slope favoring uniform distribution of irrigation water through well designed irrigation and drainage network. Those technical inputs if properly used and practiced are expected to sustain crop production. Key words: Aridisols, Entisols, Atbara and Gash Rivers, Alluvium deposits

Impact of landuse on the groundwater quality along coastal aquifer of Thiruvallur district, South India

The present study was carried out to understand the impact of landuse pattern that includes agricultural and urban development on coastal aquifers of the SE coast of India. Regional geology includes marine sediments, alluvium, sandstone and laterite formations. Groundwater samples were collected from 50 dug wells and bore wells during pre-monsoon 2013 (May) and post-monsoon 2014 (January). Water samples were analyzed for physical and chemical parameters such as electrical conductivity (EC), pH, TDS, Na+, K+, Ca2+, Mg2+, Cl−, HCO3 −, SO4 2−, NO3 − and Total Hardness, using standard procedures. Results indicate the following order of concentration of ions: Na+ > Ca2+ > Mg2+ > K+, and Cl− > HCO3 − > SO4 2− > NO3 −. Further, total hardness (TH) was evaluated to understand the suitability of groundwater for drinking purpose. Na–Cl, Mixed Ca–Mg–Cl and Ca–HCO3 facies were the dominant groundwater types in the study area. Study findings gives a detail understanding of interrelations between geology and landuse practices with water quality. Statistical results indicate that leaching of secondary salts, sea water intrusion, infiltration of contaminated water and ion exchange processes are responsible for the groundwater chemistry variation.

Hydrological cycle and water balance estimates for the megadune–lake region of the Badain Jaran Desert, China

AbstractThe hydrology and water balance of megadunes and lakes have been investigated in the Badain Jaran Desert of China. Field observations and analyses of sand layer water content, field capacity, secondary salt content, and grain size reveal 3 types of important natural phenomenon: (a) vegetation bands on the leeward slope of the megadunes reflect the hydrological regime within the sandy vadose zone; (b) seepage, wet sand deposits, and secondary salt deposits indicate the pattern of water movement within the sandy vadose zone; (c) zones of groundwater seeps and descending springs around the lakes reflect the influence of the local topography on the hydrological regime of the megadunes. The seepage exposed on the sloping surface of the megadunes and gravity water contained within the sand layer confirm the occurrence of preferential flow within the vadose zone of the megadunes. Alternating layers of coarse and fine sand create the conditions for the formation of preferential flows. The preferential flows promote movement of water within the sand layer water that leads to deep penetration of water within the megadunes and ultimately to the recharging of groundwater and lake water. Our results indicate that a positive water balance promotes recharge of the megadunes, which depends on the high permeability of the megadune material, the shallow depth of the surface sand layer affected by evaporation, the occurrence of rainfall events exceeding 15 mm, and the sparse vegetation cover. Water balance estimates indicate that the annual water storage of the megadunes is about 7.5 mm, accounting for only 8% of annual precipitation; however, the shallow groundwater per unit area under the megadunes receives only 3.6% of annual precipitation, but it is still able to maintain a dynamic balance of the lake water. From a water budget perspective, the annual water storage in the megadunes is sufficient to serve as a recharge source for lake water, thereby enabling the long‐term persistence of the lakes. Overall, our findings demonstrate that precipitation is a significant component of the hydrological cycle in arid deserts.

Structural setting and evolution of the Mensa and Thunder Horse intraslope basins, northern deep-water Gulf of Mexico: A case study

The Mensa and Thunder Horse intraslope minibasins in southcentralMississippi Canyon, northern deep-water Gulf ofMexico, had a linked structural evolution from the Early Cretaceous through the late Miocene. Analysis of the two minibasins illustrates the complexities of deep-water sedimentation and salt tectonics in intraslope minibasins. This study is based on the integration of a 378-mi2 (979-km2) three-dimensional seismic data set,wire-line logs, and biostratigraphic data. These two minibasins comprise several structural features that affected their geologic evolution: basement faults, autochthonous salt, three allochthonous salt systems (top Barremian, top Cretaceous, and Neogene), a growth fault and raft system, three major turtle structures with associated extensive crestal faults, and strike-slip faults. Remnant allochthonous salt pillows are present above the 125 Ma horizon (approximate top Barremian system) and on the 66 Ma horizon (top Cretaceous system) throughout the Mensa minibasin, whereas the top Cretaceous allochthonous salt system is identified regionally by a salt weld in the Thunder Horse area. These allochthonous salt systems formed weld surfaces beneath the Mensa and Thunder Horse turtle structures. Structural features and associated minibasins evolved during several discrete intervals. From the Early Cretaceous through the latest Oligocene (125 to 24 Ma), an extensive allochthonous salt canopy was present within the Mensa and Thunder Horse minibasins. During this interval, sediments loaded the salt, forming thinwedge-and sheet-formdeposits in theMensa area and a thick, northwest-Trending trough in the ThunderHorse area. A secondary allochthonous salt system extruded at the Top Cretaceous level, as seen by remnant salt bodies. Salt withdrawal from these allochthonous salt systems provided accommodation for bowl-and trough-shaped external stratigraphic forms to develop during the Miocene. High sedimentation rates produced salt evacuation from these allochthonous salt systems and initiated diapirism that formed the Neogene allochthonous salt level. The prominent turtle structures in the two minibasins, critical to the formation of traps to the two major fields, developed at slightly different times: Thunder Horse at 14.35 and Mensa at 11.4 Ma. Copyright © 2017 The American Association of Petroleum Geologists. All rights reserved.

Halokinetic sequences and diapiric structural kinematics in the field: Two-day excursion to La Popa Basin, northeastern Mexico

Exposures of salt diapirs and flanking strata in La Popa basin, in the Mexican states of Nuevo Leon and Coahuila, contain world-class examples of salt–sediment interaction that provided the basis for the concept of halokinetic sequences. The basin also contains one of the first secondary salt welds described in outcrop. The two-day field trip described here provides an easily accessible overview of salt–sediment relations within a short distance of Monterrey, the capital city of Nuevo Leon. The first day constitutes an introduction to basin stratigraphy, a traverse through halokinetic sequences at El Papalote diapir, and visits to the Cretaceous–Paleogene boundary bed and a salt-cored detachment fold near the town of Hidalgo, north of Monterrey. The second day is a visit to La Popa salt weld, where stops at several parts of the weld permit comparison of different structural styles developed along the weld. The trip begins and ends at the Marriott Courtyard Hotel, near the Monterrey airport.

Synthesis of Cadmium Selenide Quantum Dots, Using 2,2‐Bipyridine as a Capping and Phase Transfer Agent

AbstractCadmium selenide quantum dots (CdSe QDs), were synthesized by one‐pot or water‐to‐organic phase transfer and capped with molten 2,2′‐bipyridine (bipy). The obtained CdSe QDs by the two‐step procedure, reveal average sizes of 2 nm while the one‐pot are mixed with secondary salt products and bipy and are undetectable by TEM. However the absorption peak of both CdSe QDs was at 425 nm and the emission band is centered at 535 nm, with a band width at half height of 77 nm, when excited with 425 nm light. The two‐step CdSe QDs synthesis has the great advantage of capping the CdSe QDs with bipy, forming a solid phase, which is easily stored and dispersed in most of the organic solvents. On the other hand, the one‐pot procedure requires an extra step to remove the secondary products.

Aeolian Carbon Salts in the Taklamakan and Badanjilin Deserts in Northwestern China and Their Potential Role in Global Carbon Cycle

Previous studies have suggested that a significant loop in the carbon cycle may be hidden in the global desert areas (both low latitude and middle latitude). Due to the complexity of salt formation involved in atmosphere-landscape relation, there are few study involved into the pool of secondary carbonates in world desert soils, particularly in arid areas in northern China. Large sandy deserts in the middle latitudes of northwestern China were investigated in this study. The physical and geochemical examinations are carried out into soluble carbon salts in modern and ancient dune sediments from the inland deserts in northwestern China, with the aim to explore the composition of carbon salts in aeolian sediments and their possible environmental implications for global carbon cycle. The results show that the aeolian salt has high alkalinities, which are mainly determined by evaporitic alkaline earth carbonates. The carbonates are secondary salt in origin and are possibly introduced from the atmosphere into the pedosphere by a carbon-fixation process. Owing to the high capability to neutralize atmospheric carbonic acid, large desert area, and the strong potential of carbonate preservation in soil under arid climate, the middle-latitude Chinese deserts can be potentially qualified as a significant contributor to the global carbon cycle. But the low-latitude deserts in tropic areas may be not able to provide such a contribution.

Identification of secondary salts and their sources in deteriorated stone monuments using micro‐Raman spectroscopy, SEM‐EDS and XRD

Salts crystallisation is a cause of deterioration of stone monuments. Very small sizes of salt crystals, often a multiphase composition and usually low concentrations hamper their identification. Therefore, micro‐Raman spectroscopy, scanning electron microscopy and, in some cases, X‐ray diffraction have been used to identify the salts that crystallised within and on the weathered limestone and sandstone architectonic details of the Blessed Salomea sculpture and its arch in the cloister of the Poor Clares in Kraków, Poland. Possible sources of salts, i.e. regarding the plaster around the details, the mortar of joints of the arch and previous conservation procedures, have been discussed. The limestone sculpture reveals the presence of black crusts and the sandstone arch of white efflorescences, both stones crumble and exfoliate. Gypsum and barite were the only salts in the black crust and subflorescences of the limestone. The salts in the pore space of the sandstone include mainly aphthitalite, niter, nitratine and burkeite, while efflorescences consist of thenardite and syngenite. Such differences probably result from various precipitation conditions in narrow pore spaces and on the unconfined sandstone surface. The deterioration products have been mainly assigned to air pollution, stone itself in the case of the limestone, and migration of ions from structural elements of the arch in the case of the sandstone. The impact of the chemicals utilised for stone conservation also seems to be possible. Characterisation of the salts present in deteriorated stones can help in selecting the methods of stone desalination and conservation. Copyright © 2016 John Wiley & Sons, Ltd.

Investigation of Electrolytes for Sio/Graphite Anode Based High Energy Cells

High energy cells with SiO/graphite composite anode tend to demonstrate fast capacity fade and gas generation during long term cycling test, due primarily to large volume expansion of Si particles and continuous SEI formation which consumes electrolyte components quickly. As a result, loss of accessible anode material and depletion of electrolyte are common failure mechanisms. Overcoming those challenges requires careful electrolyte formulation to create a stable anode SEI layer with the goal of extending cycle life and reducing cell gas generation. In this study, a commercial grade small-format pouch cell with SiO/graphite and NCM 523 was selected as an electrochemical test vehicle to screen various electrolyte formulations. A baseline was obtained with commercial electrolytes, which revealed fluoroethylene carbonate (FEC) as a key enabling additive for cycle life. Unfortunately severe cell gassing is often observed with cells that exhibited superior cycle life. A rigorous electrolyte formation matrix was then constructed by varying FEC content, solvent type and ratio, introducing anti-gassing additives and mixed salts. Subsequent testing of these formulations demonstrated that up to 2% 1,3-propane sultone (PS) could effectively reduce cell gassing, but the associated higher cell impedance also adversely impacted cycle life. Formulations with lithium bis(oxalato)borate (LiBOB) as a secondary salt had little influence on cell cyclability but significantly increased cell gassing. The culpability of the additive was confirmed via gas composition analysis. Other variables such as solvent ratio and additives commonly used in graphite based cells appeared to be much less effective for Si containing anodes. Through composition modification, an optimal electrolyte formulation was identified with long cycle life and low gas generation.

Characteristics of dry deposited mineral particles associated with weather conditions in the adjacent sea areas of East China during a cruise in spring 2011

Dry deposited particles, larger than 1.3μm, were collected under clear, cloudy, and foggy conditions during a cruise, traversing the Yellow Sea and the East China Sea from 23 March to 8 April 2011. In these areas, air masses are influenced by pollution outflows from the Asian continent. The size and elemental composition of dry deposited particles were investigated using a scanning electron microscope. Number–size distributions of these particles were approximately lognormal. Under clear conditions, the mode size was about 5.0μm, with a mean diameter of 6.9μm. Under cloudy and foggy conditions, the mean diameters were 5.7 and 6.0μm, respectively, but the mode sizes were vague. Non-mixed mineral particles, sea salt, and mixed mineral–sea salt particles were the major particle types. Correspondingly, Al and Si were the most frequently detected elements. Frequencies of K-, Ca-, and S-containing particles were highest under foggy conditions, while the frequency of Na-containing particles was lowest. These results indicate that fog favored sulfate production on the particles and led to the deposited mineral particles more abundant in secondary salt, suggesting the importance to consider the dependence of the composition of deposited mineral particles on weather as well as particle size.

Stable isotopic evidence for anaerobic maintained sulphate discharge in a polythermal glacier

To understand the sources and sinks of sulphate and associated biogeochemical processes in a High Arctic environment, late winter snowpacks, the summer melt-waters and rock samples were collected and analysed for major ions and stable isotope tracers (δ18O, δ34S). The SO42¯/Cl¯ ratio reveal that more than 87% of sulphate (frequently > 95%) of total sulphate carried by the subglacial runoff and proglacial streams was derived from non-snowpack sources. The proximity of non-snowpack sulphate δ34S (∼8–19‰) to the δ34S of the major rocks in the vicinity (∼−6 to +18‰) suggest that the non-snowpack sulphate was principally derived from rock weathering. Furthermore, Ca2++Mg2+/SO42ˉ molar shows that sulphate acquisition in the meltwaters was controlled by two major processes: 1) coupled-sulphide carbonate weathering (molar ratio ∼ 2) and, 2) re-dissolution of secondary salts (molar ratio ∼ 1). The δ34S–SO4 = +19.4‰ > δ34S–S of rock, accompanied by increased sulphate concentration also indicates an input from re-dissolution of secondary salts. Overall, δ18O composition of these non-snowpack sulphate (−11.9 to −2.2‰) mostly stayed below the threshold δ18O value (−6.7 to −3.3‰) for minimum O2 condition, suggesting that certain proportion of sulphate was regularly supplied from anaerobic sulphide oxidation.

Mineralogy and heavy metal content of secondary mineral salts: A case study from the Witwatersrand Gold Basin, South Africa.

Secondary minerals associated with acid mine drainage play an important role in metal cycling and may pose a geochemical hazard. The occurrence of secondary minerals indicates prevailing and past geochemical conditions. Detecting and characterising secondary minerals is necessary to the planning of remediation programmes. This paper investigates the mineralogical and heavy metal contents of mineral salts associated with acid mine drainage in the East Rand area of the Witwatersrand Basin. Powdered X-ray diffraction was used to identify and quantify mineralogical phases and a scanning electron microscope was used to determine the morphology of the identified minerals. Major cations and anions were determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Ion Chromatography (IC). Geochemical modelling was used to predict the saturation of the minerals. Efflorescent crusts contained high levels of trace metals. Enrichment of trace metals, electrical conductivity and sulphate were highest in white salts. A high metal content was associated with low pH values in mineral salts. The salts were dominated by quartz and clay minerals of the smectite group. Tamarugite, apjohnite and jarosite were the predominant sulphate minerals in the salts. These minerals are very acidic and will accelerate weathering in the surrounding soils. Geochemical modelling yielded precipitated hydrated sulphate, halite and goethite. The information gathered during this study will be useful in managing salinity and high metal contents in receiving waters and soils associated with gold mining activities.

Новые данные по геохимии газов калийных месторождений

Рассмотрен состав газовой фазы соляных пород из ряда европейских (Верхнекамское, Старобинское, польский цехштейн) и азиатских (Тюбегатанское, Жилянское, Сатимолинское) месторождений, что позволило разделить их на две группы. В азиатских объектах происходило формирование только аутигенных сухих газов за счет диагенетического разложения органики. Структурная открытость этих залежей привела к окислению метана и водорода и обогащению углекислым газом. Верхнекамское и Старобинское месторождения в структурном отношении были закрыты для процессов окисления, но открыты во время соленакопления, когда в бассейн седиментации происходил подток тяжелых углеводородов с нижних горизонтов. В истории формирования газового режима Верхнекамского месторождения могут быть выделены три этапа: 1) сингенетичный захват глубинных газов и аутигенной органики, преобразованной при диагенезе до метана, доля которого постепенно возрастает за счет увеличения мощности флюидоупорной соляной залежи; 2) «прорыв» глубинных газов в бассейн при накоплении верхов карналлитовой зоны и покровной каменной соли; 3) соскладчатая мобилизация флюидов, рассеянных в газово-жидких включениях и, вероятно, подток тяжелых углеводородов с углекислым газом, способствующий формированию зон вторичных солей. «Замещение» карналлитовых пластов приводит к высвобождению изоморфного иона аммония и образованию водорода.

2]Pseudorotaxanes Based on Naphtho‐21‐crown‐7 and Secondary Dialkylammonium Salts: Remarkably Improved Association Constants Among Four Threaded Structures

AbstractThis research article is focused on the recognition interaction of a new host naphtho‐21‐crown‐7 and four secondary dialkylammonium salts. In acetone, they can form 1:1 host‐guest complexes which belong to slow‐exchange systems. We also found the differences of binding affinity and binding selectivity between the host and its complementary guest moieties, which could be ascribed to the aromatic π‐π stacking effect and the acidity increase of N‐methylene and ammonium hydrogens due to the increasing electron withdrawing ability from butyl to methoxyphenyl to phenyl to p‐cyanophenyl substituents in the recognition motif.

City sewer collectors biocorrosion

AbstractThis paper presents the biocorrosion of city sewer collectors impregnated with special polymer sulphur binders, polymerized sulphur, which is applied as the industrial waste material. The city sewer collectors are settled with a colony of soil bacteria which have corrosive effects on its structure. Chemoautotrophic nitrifying bacteria utilize the residues of halites (carbamide) which migrate in the city sewer collectors, due to the damaged dampproofing of the roadway and produce nitrogen salts. Chemoorganotrophic bacteria utilize the traces of organic substrates and produce a number of organic acids (formic, acetic, propionic, citric, oxalic and other). The activity of microorganisms so enables the origination of primary and secondary salts which affect physical properties of concretes in city sewer collectors unfavourably.

Energy Recovery in Parallel Capacitive Deionization Operations

The integration of capacitive deionization cells is shown to deionize a secondary salt stream using solely the energy stored in a charged CDI cell. A primary cell was charged at 1.2 and 1.5 V resulting in electrosorption capacities of 3.3 and 3.7 mg NaCl (g carbon)-1, respectively. The cell charged at 1.2 and 1.5 V was used to directly deionize a parallel secondary stream resulting in electrosorption capacities of 0.5 and 1.0 mg NaCl (g carbon)-1, respectively. Integration of CDI cells can drastically lower the energy cost for the production of fresh water.

Stabilization of diketo tautomer of curcumin by premicellar cationic surfactants: A spectroscopic, tensiometric and TD-DFT study

The interaction of aqueous curcumin with cationic surfactants of varying chain lengths and head group, stabilizing its β-diketo tautomer and exhibiting an UV band around 355nm, has been studied in buffered aqueous solutions in the pH range of 2.00–7.00 by UV–visible and fluorescence spectroscopy, and surface tensiometry under optimal experimental conditions of submicellar concentration of the surfactants. Time Dependent Density Functional Theory (TD-DFT) has also been used to predict the molecular structure and excitation energies of the interaction product in the ground state and the nature of the interaction. As the surfactant concentration increases, the curcumin–cationic complex forms premicellar aggregates where the curcumin exists in a highly polar microenvironment before shifting its location to the nonpolar core of the surfactant micelles. The strength of the interaction increases with the chain length of the surfactant and also changes on changing the head group of the surfactant. An observed secondary salt effect on the interaction indicates an unusual involvement of a proton in the interaction. Based on the experimental and theoretical evidences the following mechanism has been proposed for the stabilization of the β-diketo form: on the approach of the cationic surfactant, a protonation of the methylenic central carbon atom of curcumin takes place simultaneously breaking the π-conjugation and facilitating the detachment of the enolic proton paving the way for an ion dipole binding between the cationic head group and the electron-rich β-diketo oxygen atoms. Hydrophobic interaction between the tail of the surfactant and the nonionic curcumin molecule assists the electrostatic interaction.

Fe(III)-Heme Complexes with the Amyloid Beta Peptide of Alzheimer's Disease: QM/MM Investigations of Binding and Redox Properties of Heme Bound to the His Residues of Aβ(1-42).

Pursuant to our previous paper [J. Chem. Theory Comput. 2012, 8, 5150-5158], the structures of complexes between Aβ(1-42) and ferriheme (Fe(III)-heme-H2O) were determined by application of Amber and ONIOM(B3LYP/6-31G(d):Amber) methodology. Attachment at each of the three His residues was investigated. As well as direct bonding of the iron to the His residue, bonding is augmented by formation of secondary salt bridges between the carboxylate groups of the heme and positively charged residues of Aβ (at His13, by Lys16 and the N-terminus; at His14, by Lys16; at His6, by Arg5). The results indicate a slight preference for His13 followed by His6 and His14, with the lowest 10 structures lying within 30 kJ mol(-1) of each other. The absolute binding affinities are predicted to be approximately 30-40 kJ mol(-1). Standard reduction potentials (E°) are calculated for various Fe(III)/Fe(II) couples. Regardless of the point of attachment of the heme, E° values are approximately -0.6 V relative to the standard hydrogen electrode.