Determination of standard enthalpy of vaporization and thermal decomposition reactions from derivative thermogravimetric (DTG) curves

The paper proposes the use of the derivative thermogravimetric (DTG) curve for the acquisition of equilibrium vapor pressure and dissociation pressure for the materials and derivation of their standard enthalpy of formation from single DTG curve recorded under optimum experimental conditions, such as heating rate and the sweep rate of the carrier gas passed over the sample. The vapor pressure and the standard enthalpy of sublimation (Δ_subH ° _298.15) of CdI₂ and the dissociation pressure and the standard enthalpy of formation of CaCO₃ derived from their DTG curves are found to be in good agreement with the best assessed values reported in the literature.     

Fluorescence energy transfer efficiency in labeled yeast cytochrome c: a rapid screen for ion biocompatibility in aqueous ionic liquids

A fluorescence energy transfer "de-quenching" assay was implemented to follow the equilibrium unfolding behaviour of site-specific tetramethylrhodamine-labelled yeast cytochrome c in aqueous ionic liquid solutions; additionally, this approach offers the prospect of naked eye screening for biocompatible ion combinations in hydrated ionic liquids.     

Interactions of amines with silicon species in undersaturated solutions leads to dissolution and/or precipitation of silica

The biogeochemical silicon cycle is the focus for many researchers studying the dissolution of silicon species from quartz, amorphous, and biogenic silica. Furthermore, the precipitation of biogenic silica by diatoms, radiolarian, sponges, and plants is also a popular focus for research. The ornate silica structures created by these species has attracted interest from biomaterial scientists and biochemists who have studied mineral formation in an attempt to understand how biogenic silica is formed, often in the presence of proteins and long chain polyamines. This article is at the interface of these seemingly distinct research areas. Here we investigate the effect of a range of amines in globally undersaturated silicon environments. Results are presented on the effect of amine-containing molecules on the formation of silica from undersaturated solutions of orthosilicic acid and globally undersaturated silicon environments. We sought to address two questions: can silica be precipitated/harvested from undersaturated solutions, and can we identify the silicon species that are most active in silica formation? We demonstrate that none of the bioinspired additives investigated here (e.g., poly(allylamine hydrochloride), pentaethylenehexamine, and propylamines) have any influence on orthosilicic acid at undersaturated concentrations. However, under globally undersaturated silicon concentrations, small molecules and polymers containing amine groups were able to interact with oligomers of silicic acid to either generate aggregated materials that can be isolated from solution or increase rates of oligomer dissolution back to orthosilicic acid. Additional outcomes of this study include an extended understanding of how polyelectrolytes and small molecules can promote and/or inhibit silica dissolution and a new method to explore how (bio)organic molecules interact with a forming mineral phase.     

Determination of nickel in finished product alloys by instrumental neutron activation analysis and spectrophotometry

Nickel contents in different finished product alloys were determined using a k ₀-based internal monostandard instrumental neutron activation analysis (IM-INAA) method. Five stainless steels (SS) and three high nickel alloys were analyzed by IM-INAA. BCS CRMs 225/1 (low alloy steel) and 466 (austenitic SS) and NIST SRM 247 (high Ni alloy) were analyzed to evaluate the accuracy of the method. The results of CRMs and SS were found to be in good agreement with certified or specified values. The Ni contents in the high nickel alloys were also determined by relative method of NAA for verification. Nickel contents in BCS CRM 466 and SS 316M were determined by UV–Visible spectrophotometry and the values were found to be in good agreement with IM-INAA results.     

Rare earth elements analysis in archaeological pottery by laser induced breakdown spectroscopy

In the present work, laser induced breakdown spectroscopy has been employed to detect rare earth elements in archaeological potteries and brick sample collected from different locations. Laser Induced breakdown spectroscopy data has been analyzed to investigate the provenance of ancient clay artifacts which is based on the geochemistry of rare earth elements in the artifacts. The qualitative study of spectra shows the presence of a set of rare earth elements such as La, Ce, Pr, Nd, Sm, Gd, Dy, and Er in archaeological potteries which specifies that these potteries were manufactured from the same clay sources.     

Chemistry of aqueous silica nanoparticle surfaces and the mechanism of selective peptide adsorption

Control over selective recognition of biomolecules on inorganic nanoparticles is a major challenge for the synthesis of new catalysts, functional carriers for therapeutics, and assembly of renewable biobased materials. We found low sequence similarity among sequences of peptides strongly attracted to amorphous silica nanoparticles of various size (15-450 nm) using combinatorial phage display methods. Characterization of the surface by acid base titrations and zeta potential measurements revealed that the acidity of the silica particles increased with larger particle size, corresponding to between 5% and 20% ionization of silanol groups at pH 7. The wide range of surface ionization results in the attraction of increasingly basic peptides to increasingly acidic nanoparticles, along with major changes in the aqueous interfacial layer as seen in molecular dynamics simulation. We identified the mechanism of peptide adsorption using binding assays, zeta potential measurements, IR spectra, and molecular simulations of the purified peptides (without phage) in contact with uniformly sized silica particles. Positively charged peptides are strongly attracted to anionic silica surfaces by ion pairing of protonated N-termini, Lys side chains, and Arg side chains with negatively charged siloxide groups. Further, attraction of the peptides to the surface involves hydrogen bonds between polar groups in the peptide with silanol and siloxide groups on the silica surface, as well as ion-dipole, dipole-dipole, and van-der-Waals interactions. Electrostatic attraction between peptides and particle surfaces is supported by neutralization of zeta potentials, an inverse correlation between the required peptide concentration for measurable adsorption and the peptide pI, and proximity of cationic groups to the surface in the computation. The importance of hydrogen bonds and polar interactions is supported by adsorption of noncationic peptides containing Ser, His, and Asp residues, including the formation of multilayers. We also demonstrate tuning of interfacial interactions using mutant peptides with an excellent correlation between adsorption measurements, zeta potentials, computed adsorption energies, and the proposed binding mechanism. Follow-on questions about the relation between peptide adsorption on silica nanoparticles and mineralization of silica from peptide-stabilized precursors are raised.     

Binding of the ionic liquid cation 1-alkyl-3-methylimidazolium to p-tetranitrocalix[4]arene probed by fluorescent indicator displacement

Acridine orange (AO) was used as a fluorescent probe molecule to study the encapsulation of an alkylimidazolium cation from a water-soluble ionic liquid (IL) within two cavitand species, p-tetranitrocalix[4]arene (1) and calix[4]resorcinarene (2), both in alkaline aqueous media. The addition of IL to the preformed [1·AO] adduct resulted in significantly increased fluorescence due to the expulsion of AO from the inclusion complex to the aqueous phase by competitive recognition of the 1-alkyl-3-methylimidazolium cation ([C(n)mim](+), n = 4 and 6) by 1. Conversely, the fluorescence signal dropped upon the addition of IL to the [2·AO] host-guest complex due to unfavorable binding between [C(n)mim](+) and 2. The formation of these postulated adducts is corroborated using ab initio calculations, which also provide evidence for the location of [bmim](+) at the lower external rim of [2·AO], providing an explanation for the observed luminescence quenching in the latter case. These results point to a number of different paths for exploration, ranging from the fluorescence monitoring of IL contamination in groundwater to the "daisy chaining" of macrocyles toward supramolecular ionic networks. They also broadly encourage the exploration of ILs in host-guest-based optical and mass spectrometric sensory systems.     

Conformational Transitions of the Catalytic Domain of Heme-Regulated Eukaryotic Initiation Factor 2α Kinase, a Key Translational Regulatory Molecule

In mammalian cells, the heme-regulated inhibitor (HRI) plays a critical role in the regulation of protein synthesis at the initiation step through phosphorylation of α-subunit of the eukaryotic initiation factor 2 (eIF2). In this study we have cloned and performed biophysical characterization of the kinase catalytic domain (KD) of rabbit HRI. The KD described here comprises kinase 1, the kinase insertion domain (KI) and kinase 2. We report here the existence of an active and stable monomer of HRI (KD). The HRI (KD) containing three tryptophan residues was examined for its conformational transitions occurring under various denaturing conditions using steady-state and time-resolved tryptophan fluorescence, circular dichroism (CD) and hydrophobic dye binding. The parameter A and phase diagram analysis revealed multi-state unfolding and existence of three stable intermediates during guanidine hydrochloride (Gdn-HCl) induced unfolding of HRI (KD). The protein treated with 6 M Gdn-HCl showed collisional and static mechanism of acrylamide quenching and the constants (K _sv  = 3.08 M⁻¹and K _s   = 5.62 M⁻¹) were resolved using time resolved fluorescence titration. Based on pH, guanidine hydrochloride and temperature mediated transitions, HRI (KD) appears to exemplify a rigid molten globule-like intermediate with compact secondary structure, altered tertiary structure and exposed hydrophobic patches at pH 3.0. The results indicate the inherent structural stability of HRI (KD), a member of the class of stress response proteins.     

Electron inelastic mean free paths in solids: A theoretical approach

In the present paper, the inelastic mean free path (IMFP) of incident electrons is calculated as a function of energy for silicon (Si), oxides of silicon (SiO2 ), SiO, and Al2O3 in bulk form by employing atomic/molecular inelastic cross sections derived by using a semi-empirical quantum mechanical method developed earlier. A general agreement of the present results is found with most of the available data. It is of great importance that we have been able to estimate the minimum IMFP, which corresponds to the peak of inelastic interactions of incident electrons in each solid investigated. New results are presented for SiO, for which no comparison is available. The present work is important in view of the lack of experimental data on the IMFP in solids.     

Micellization behavior of [C16-12-C16], 2Br gemini surfactant in binary aqueous-solvent mixtures

The micellization behavior of bis cationic gemini surfactant, N,N′-dihexadecyl-N,N,N′,N′-tetramethyl-1,12-dodecanediammonium dibromide [C₁₆H₃₃N⁺(CH₃)₂-(CH₂)₁₂-N⁺(CH₃)₂C₁₆H₃₃, 2Br⁻] has been studied in binary aqueous mixtures of dimethyl sulfoxide, methanol, 1,4-dioxane, glycerol and ethylene glycol by conductivity and surface tension measurements at 300 K. The critical micellar concentration, degree of micelle ionization (α), surface excess concentration (Г_max), minimum surface area per molecule of surfactant (A_min), Gibbs free energy of micellization (ΔG_m°), the surface pressure at cmc (π_cmc), and the Gibbs energy of adsorption (ΔG_ad°) of the gemini surfactant have also been determined. The cmc, α, A_min increases where as (ΔG_m°), Г_max, and π_cmc decreases with increasing volume percentage of the solvents in the solvent–water binary mixture. The interfacial properties of the gemini surfactant, solute–solute, solvent–solute interactions and the effectiveness of a surface-active molecule in binary solvent systems have been discussed.