Unusual Stabilities Research Articles

Insights into the Heterogeneous Nuclei of an Ultrafast‐Crystallizing Glassy Solid

AbstractCrystallization determines the programming speed of phase‐change memory devices; while, the nucleation phenomenon of many phase‐change materials (PCMs) is not entirely understood, especially concerning the atomic structures and dynamic behaviors of the subcritical nuclei. This is undoubtedly an insurmountable challenge for scandium antimony telluride (ScxSb2Te3) PCM as its subnanosecond‐crystallization nature impedes the real‐time observation of the transient nucleation process. To solve the puzzle, atomic probe tomography and transmission electron microscopy are employed to circumvent the technical difficulties; for the first time, the atomistic information of the heterogeneous nuclei in ScxSb2Te3 is unveiled, such as enriched Sc ≈ 25 at% in core composition, ≈1.0 nm in geometric size, and ≈1023–1024 m−3 in spatial density. The unique nanoscale chemical inhomogeneity ensures the unusual stabilities and dynamics of the early‐stage nuclei, reinforcing them to survive the melt‐quenching action and greatly suppressing the nucleating randomness, thereby facilitating simultaneous and prompt crystal growth throughout the amorphous phase to achieve ultrafast crystallization. The present study offers a new insight into the nonclassical pathways, which will improve understanding and promote better regulation of the nucleation phenomenon in functional materials.

Aluminum hydride cluster cations: A mass spectrometric and computational study

A combined study using mass spectrometry and density functional theory (DFT) was conducted to investigate aluminum hydride cluster cations, AlnHm+ (1⿤n⿤5, 0⿤m⿤12). The mass spectra revealed about 20 previously-unknown aluminum hydride cluster cations. Among these species, several showed high mass spectral intensities, suggesting that they had unusual stabilities. Density functional theory calculations were conducted to investigate the geometric structures of these clusters. Many of these clusters can be viewed as being composed of smaller, stable units, such as Al+, AlH3, Al2+/0, H+ and H2.

Enhancement of Anion Binding in Lanthanide Optical Sensors

In the design of molecular sensors, researchers exploit binding interactions that are usually defined in terms of topology and charge complementarity. The formation of complementary arrays of highly cooperative, noncovalent bonding networks facilitates protein-ligand binding, leading to motifs such as the "lock-and-key". Synthetic molecular sensors often employ metal complexes as key design elements as a way to construct a binding site with the desired shape and charge to achieve target selectivity. In transition metal complexes, coordination number, structure and ligand dynamics are governed primarily by a combination of inner-sphere covalent and outer-sphere noncovalent interactions. These interactions provide a rich variable space that researchers can use to tune structure, stability, and dynamics. In contrast, lanthanide(III)-ligand complex formation and ligand-exchange dynamics are dominated by reversible electrostatic and steric interactions, because the unfilled f shell is shielded by the larger, filled d shell. Luminescent lanthanides such as terbium, europium, dysprosium, and samarium display many photophysical properties that make them excellent candidates for molecular sensor applications. Complexes of lanthanide ions act as receptors that exhibit a detectable change in metal-based luminescence upon binding of an anion. In our work on sensors for detection of dipicolinate, the unique biomarker of bacterial spores, we discovered that the incorporation of an ancillary ligand (AL) can enhance binding constants of target anions to lanthanide ions by as much as two orders of magnitude. In this Account, we show that selected ALs in lanthanide/anion systems greatly improve sensor performance for medical, planetary science, and biodefense applications. We suggest that the observed anion binding enhancement could result from an AL-induced increase in positive charge at the lanthanide ion binding site. This effect depends on lanthanide polarizability, which can be established from the ionization energy of Ln(3+) → Ln(4+). These results account for the order Tb(3+) > Dy(3+) > Eu(3+) ≈ Sm(3+). As with many lanthanide properties, ranging from hydration enthalpy to vaporization energy, this AL-induced enhancement shows a large discrepancy between Tb(3+) and Eu(3+) despite their similarity in size, a phenomenon known as the "gadolinium break". This discrepancy, based on the unusual stabilities of the Eu(2+) and Tb(4+) oxidation states, results from the half-shell effect, as both of these ions have half-filled 4f-shells. The high polarizability of Tb(3+) explains the extraordinarily large increase in the binding affinity of anions for terbium compared to other lanthanides. We recommend that researchers consider this AL-induced enhancement when designing lanthanide-macrocycle optical sensors. Ancillary ligands also can reduce the impact of interfering species such as phosphate commonly found in environmental and physiological samples.

Identification of potential conserved RNA secondary structure throughout influenza A coding regions

Influenza A is a negative sense RNA virus of significant public health concern. While much is understood about the life cycle of the virus, knowledge of RNA secondary structure in influenza A virus is sparse. Predictions of RNA secondary structure can focus experimental efforts. The present study analyzes coding regions of the eight viral genome segments in both the (+) and (-) sense RNA for conserved secondary structure. The predictions are based on identifying regions of unusual thermodynamic stabilities and are correlated with studies of suppression of synonymous codon usage (SSCU). The results indicate that secondary structure is favored in the (+) sense influenza RNA. Twenty regions with putative conserved RNA structure have been identified, including two previously described structured regions. Of these predictions, eight have high thermodynamic stability and SSCU, with five of these corresponding to current annotations (e.g., splice sites), while the remaining 12 are predicted by the thermodynamics alone. Secondary structures with high conservation of base-pairing are proposed within the five regions having known function. A combination of thermodynamics, amino acid and nucleotide sequence comparisons along with SSCU was essential for revealing potential secondary structures.

Closed-Cage Tungsten Oxide Clusters in the Gas Phase

During the course of a study on the clustering of W-Se and W-S mixtures in the gas phase using laser desorption ionization (LDI) mass spectrometry, we observed several anionic W-O clusters. Three distinct species, W(6)O(19)(-), W(13)O(29)(-), and W(14)O(32)(-), stand out as intense peaks in the regular mass spectral pattern of tungsten oxide clusters suggesting unusual stabilities for them. Moreover, these clusters do not fragment in the postsource decay analysis. While trying to understand the precursor material, which produced these clusters, we found the presence of nanoscale forms of tungsten oxide. The structure and thermodynamic parameters of tungsten clusters have been explored using relativistic quantum chemical methods. Our computed results of atomization energy are consistent with the observed LDI mass spectra. The computational results suggest that the clusters observed have closed-cage structure. These distinct W(13) and W(14) clusters were observed for the first time in the gas phase.

Unusually Stable, Versatile, and Pure Arenediazonium Tosylates: Their Preparation, Structures, and Synthetic Applicability

A new, simple, and effective method for the diazotization of a wide range of arylamines has been developed by using a polymer-supported diazotization agent in the presence of p-toluenesulfonic acid. Various pure arenediazonium tosylates with unusual stabilities can be easily prepared by this method. As a result, these salts are useful and versatile substrates for subsequent transformations, such as halogenation and Heck-type reactions. The unusual stabilities of arenediazonium tosylates are also preliminarily discussed with their X-ray structures.

Multimetallocenes. A Theoretical Study

Quantum chemical calculations using gradient-corrected density functional theory at the BP86 level in conjunction with TZ2P basis sets have been carried out for the multimetallocenes CpMnCp, where M = Be, Mg, Ca, and Zn with n = 2−5. The equilibrium geometries and energetics with respect to loss of one metal atom are theoretically predicted. The nature of the metal−ligand interactions between the Mn2+ and (Cp-)2 moieties was investigated with energy decomposition analysis (EDA). The calculations predict that the CpMnCp species with n > 2 are thermodynamically unstable with respect to loss of one metal atom except for the beryllium compounds. The beryllocenes exhibit unusual stabilities in the gas phase for the whole series CpBenCp up to n = 5. The calculations suggest that the energy for loss of one metal atom from CpBe2Cp is significantly higher than from CpZn2Cp. The energy for the metal extrusion reaction of CpBe3Cp is much less endothermic than for CpBe2Cp but it is still more endothermic than the rea...

Hollow Cages versus Space-Filling Structures for Medium-Sized Gold Clusters: The Spherical Aromaticity of the Au50 Cage

Candidates for the lowest energy structures of medium-sized Au(n), n = 32, 38, 44, 50, and 56, clusters were evaluated using gradient-corrected DFT computations. Both hollow cage and space-filling conformations were considered. The cages were constructed using fullerene-based templates. The space-filling structures were generated by employing a genetic algorithm. We have found that the space-filling isomers were lower in energy except for two notable cases. Like Au(32) [Johansson, M. P.; Sundholm, D.; Vaara, J. Angew. Chem. Int. Ed. 2004, 43, 2678], a hollow cage configuration of Au(50) is more stable than its alternative space-filling isomeric forms. The unusual stabilities of the cage Au(32) and Au(50) can be attributed to spherical aromaticity; both exhibit large negative nucleus-independent chemical shifts and exceptionally large HOMO-LUMO gaps.

Unusual thermal stabilities of some proteins and enzymes bound in the galleries of layered α-Zr(IV)phosphate/phosphonates

Significant improvements in the thermal stabilities of proteins and enzymes (increase in denaturation temperatures as large as 33 °C) bound in the galleries of crystalline α-Zr(IV) phosphate (α-Zr(PO 4) 2·H 2O, abbreviated as α-ZrP) and α-Zr(IV) phosphonates (α-Zr(RPO 3) 2·H 2O, RCH 2COOH, CH 2CH 2COOH, abbreviated as ZrCMP, and ZrCEP, respectively) are demonstrated, in specific cases. The thermal stabilities are monitored using attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR), powder X-ray diffraction, absorption, and fluorescence methods. The amide I and amide II vibrational bands of the protein/inorganic materials are monitored in ATR FTIR studies, as a function of temperature, and these indicated sharp shifts in the band positions at specific temperatures. These shifts served as markers for protein denaturation. The denaturation temperatures of met hemoglobin/α-ZrP, glucose oxidase/α-ZrRP (ROH, CH 2CH 2COOH), and Cytochrome c/α-ZrRP (ROH, CH 2CH 2COOH), for example, are >95, 55, 65, 100, and 75 °C, respectively. These values are greater than the denaturation temperatures of the corresponding free proteins in the solid state (70, 50, and 67 °C, respectively). Proteins bound to α-ZrP, and α-ZrCEP, in general, indicated stabilities that are greater than or comparable to those of the free proteins, while binding to α-ZrCMP resulted in diminished stabilities except in case of Hb. The interactions of the surface functions of the solid matrix with the bound protein, therefore, are crucial in determining the bound protein stability. The improved stabilities observed in specific cases are welcome changes for applications of these materials in biocatalysis, biosensors, and biomedical devices.

SDS-resistant Active and Thermostable Dimers Are Obtained from the Dissociation of Homotetrameric β-Glycosidase from Hyperthermophilic Sulfolobus solfataricus in SDS: STABILIZING ROLE OF THE A-C INTERMONOMERIC INTERFACE

beta-Glycosidases are fundamental, widely conserved enzymes. Those from hyperthermophiles exhibit unusual stabilities toward various perturbants. Previous work with homotetrameric beta-glycosidase from hyperthermophilic Sulfolobus solfataricus (M(r) 226,760) has shown that addition of 0.05-0.1% SDS was associated with minimal secondary structure perturbations and increased activity. This work addresses the effects of SDS on beta-glycosidase quaternary structure. In 0.1-1% SDS, the enzyme was dimeric, as determined by Ferguson analysis of transverse-gradient polyacrylamide gels. The catalytic activity of the beta-glycosidase dimer in SDS was determined by in-gel assay. A minor decrease of thermal stability in SDS was observed after exposure to temperatures up to 80 degrees C for 1 h. An analysis of beta-glycosidase crystal structure showed different changes in solvent-accessible surface area on going from the tetramer to the two possible dimers (A-C and A-D). Energy minimization and molecular dynamics calculations showed that the A-C dimer, exhibiting the lowest exposed surface area, was more stabilized by a network of polar interactions. The charge distribution around the A-C interface was characterized by a local short range anisotropy, resulting in an unfavorable interaction with SDS. This paper provides a detailed description of an SDS-resistant inter-monomeric interface, which may help understand similar interfaces involved in important biological processes.

ChemInform Abstract: Unusual Stabilities and Reactivities of Tris‐ and Bis(2,4,6‐trimethoxyphenyl)carbenium Salts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Unusual Stabilities and Reactivities of Tris- and Bis(2,4,6-trimethoxyphenyl)carbenium Salts

Abstract 2,4,6-Trimethoxyphenyllithium, Φ′Li[Φ′ = 2,4,6-(MeO)3C6H2], reacted with diphenyl carbonate and with ethyl formate to give tris(2,4,6-trimethoxyphenyl)methanol, Φ′3COH (1), and bis(2,4,6-trimethoxyphenyl)methanol, Φ′2CHOH (2), respectively. Compound 1 reacted with a slight excess of perchloric acid in 2-propanol to give very dark-purple crystals of the triarylcarbenium salt, [Φ′3C]X (3, X = ClO4), which were inert even in hot ethanol. However, a treatment of 3 (X = Cl), prepared in situ in 1 M (1 M = 1 mol dm−3) hydrochloric acid, with 1 M sodium hydroxide resulted to give 4-bis(2,4,6-trimethoxyphenyl)methylene-3,5-dimethoxy-2,5-cyclohexadienone. Compound 2 also reacted with a slight excess of perchloric acid in methanol to give dark-red crystals of the diarylcarbenium salt, [Φ′2CH]X (5, X = ClO4). Compound 5 was considerably inert even in hot methanol, but was easily reduced in primary and secondary alcohols to give bis(2,4,6-trimethoxyphenyl)methane, Φ′2CH2. Measurements of the half-lives of 5 in these alcohols showed that 5 was more labile in secondary alcohols, such as 2-propanol and 2-butanol, than in primary alcohols. When a suspension of 5 (X = Cl), prepared in situ in 1 M hydrochloric acid, was heated, tris(2,4,6-trimethoxyphenyl)methane, Φ′3CH (7), was obtained. Analogous reactions to give 7 were observed in methanol containing a slight excess of hydrochloric acid or nitric acid in place of perchloric acid. The possible paths of these reactions are discussed.

Stability Studies of Nucleic Acid-Binding Fab Isolated from Combinatorial Bacteriophage Display Libraries

This study examined the global stability and activity properties of recombinant DNA-binding antibody fragments that were obtained from a bacteriophage combinatorial display library. The goal of this study was to determine whether the combinatorial approach of heavy and light chain assembly inE. coliand subsequent affinity selection preferentially selects for antibody fragments with unusual structural stabilities. Specifically, the binding properties and stability of recombinant antibody fragments with or without a C-terminal His tag to temperature, pH, and guanidine–HCl were examined. Both Fab exhibited almost identicalKd(120–130, 140–170, and 450–560 nm) and maximal fluorescence quenching (20–25%) values for binding to (dT)20, (dT)15, and (dT)10, respectively. Thermal denaturation data obtained by CD spectroscopy demonstrated that both Fab possessed structural properties comparable to well-folded proteins with defined tertiary structures which were stable below 70°C (Tm73°C). These results were confirmed by differential scanning calorimetry. Both Fab exhibited the same rate of irreversible thermal inactivation (0.061–0.069 min−1) at 75°C and could be reversibly renatured from guanidine–HCl and pH extremes. Crystallization trials with one recombinant DNA-binding Fab yielded diffraction quality crystals also suggesting a well-defined tertiary structure.

Unusual stabilities of 6,6′-bis(aminomethyl)-2,2′-bipyridyl chelates of transition-metal ions and crystal structures of the ligand and its copper(II) and nickel(II) complexes

An improved four-step synthesis of the tetradentate compound 6,6′-bis(aminomethyl)-2,2′-bipyridyl (badp) has been developed and the crystal structure of its dihydrochloride monohydrate determined: space group C2/c, a= 11.991(2), b= 5.703(1), c= 22.109(3)A, β= 97.17(1)° and Z= 4. The complexes of copper(II) and nickel(II) with badp have also been synthesized and structurally characterized. The metal ion in [Cu(badp)(H2O)]Br2 is five-co-ordinated and the complex crystallizes in the monoclinic P21/c space group with a= 11.508(3), b= 9.584(3), c= 14.362(3)A, β= 107.93(2)° and Z= 4. The complex [Ni(badp)(H2O)Br]Br contains six-co-ordinated NiII and crystallizes in the monoclinic P21/c space group with a= 11.387(3), b= 9.417(2), c= 14.317(5)A, β= 106.21(2)° and Z= 4. The stepwise stability constants of the 1 : 1 ligand to metal complexes of badp with divalent transition-metal ions have been determined in KCl as supporting electrolyte (0.100 mol dm–3) at 25.0 °C: log KML=[ML]/[M][L] for the FeII, CoII, NiII, CuII and ZnII complexes is 8.94, 10.16, 11.87, 15.05 and 10.02 respectively. Iron(II) and cobalt(II) also formed 2:1 complexes with badp. The unusually low stabilities of the transition-metal complexes are considered due to the low basicity of the ligand and to the unfavourable spacing of its donor groups as indicated by the structures of the complexes of NiII and CuII.

ChemInform Abstract: Precursors to the Cyclo(n)carbons: (4n + 2)‐ and (4n)Annulenes with Unusual Stabilities.

AbstractNeither (III) can be deprotected without complete destruction; so the bis(ketal) of (IIIa) is deprotected to give (IV).

Precursors to the cyclo[n]carbons: [4n + 2]- and [4n]annulenes with unusual stabilities

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPrecursors to the cyclo[n]carbons: [4n + 2]- and [4n]annulenes with unusual stabilitiesYves Rubin and Francois DiederichCite this: J. Am. Chem. Soc. 1989, 111, 17, 6870–6871Publication Date (Print):August 1, 1989Publication History Published online1 May 2002Published inissue 1 August 1989https://doi.org/10.1021/ja00199a073RIGHTS & PERMISSIONSArticle Views296Altmetric-Citations23LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (272 KB) Get e-Alerts Get e-Alerts

The ionization potentials of Ag n and Au n and binding energies of Ag n, Au n, Ag n+ and Au n+ ( n = 1–4)

The ionization potentials and binding energies of gold and silver clusters and their positive ions containing up to four atoms are investigated using a complete active space MCSCF followed by multi-reference singles + doubles CI which included up to 1.9 million configurations. The ionization potentials for both Au n and Ag n as a function of cluster size n exhibit an interesting “saw-tooth” behavior. The total binding energies of both the clusters and ions as a function of size reveal that the tetramers of gold and silver exhibit unusual stabilities. The gold clusters in general have larger AEs and IPs in comparison to silver clusters due to relativistic effects.

Complex formation of phenolphthalein and some related compounds with β-cyclodextrin

The complex formation of phenolphthalein and β-cyclodextrin (cyclohepta-amylose) has been investigated by spectrophotometric, c.d., and potentiometric methods. It has been shown that complexes are formed with the protonated and dissociated forms of phenolphthalein as well; the dianion is complexed in alkaline solution in a colourless form. The complexes formed have the largest stability constants among cyclodextrin complexes known up to now. The unusual stabilities and colour change can be explained by the combined effect of the accessibility of the phenolic-phenolate moiety and presence of the carboxy–carboxylate group simultaneously, providing optimal space filling and the possibility for the cyclodextrin molecule to interact with three functional groups of phenolphthalein at the same time.

Physiology of Acidophilic and Alkalophilic Bacteria

Publisher Summary This chapter reviews the physiology of acidophilic and alkalophilic bacteria. The greatest problem with respect to life at low pH values is the maintenance of a cytoplasmic environment far less acidic than the external milieu. Acidophiles could accomplish this in two ways, firstly, by pumping protons outward effectively and/or secondly, by possession of a cell-surface barrier extremely impermeable to protons. If the cytoplasmic pH value of acidophiles is maintained near neutrality, then no problems would be expected in connection with cytoplasmic enzymes or synthetic processes. However, extracellular enzymes, flagella, and all processes associated with the external membrane surface would have to function at extremely acid pH values. Unusual properties of the cell wall and membrane layer would be anticipated. Many bacteria are able to grow at pH values as low as 4.0, but the vast majority of such organisms can also grow at neutral pH values. More unusual are those bacteria that thrive at pH values below 3.0 and cannot grow at neutral pH. For extreme, obligately alkalophilic bacteria, the optimal external pH value for growth on most substrates is between pH 10.0 and 11.0. Growth at even higher pH values is also observed. The most obvious and pressing physiological problem is regulation of cytoplasmic pH value. Maintenance of a relatively acidic cytoplasm— that is, nearer to neutral pH value than the highly alkaline pH value of the medium, might bypass any need for unusual pH optima or stabilities for cytoplasmic enzymes or macromolecules.

Structure‐Resonance Valence Bond Theory for Ferrocenes and Ferrocenylalkyl Cations

AbstractStructure‐resonance theory can be used to derive charge distributions and bond orders in ferrocenes, open ferrocenes and α‐ferrocenylalkyl cations. These species are of interest because they are unusually accessible and stable and understanding the electronic origin of this stabilization would aid in developing bonding models for organometallic systems. The methods for carrying out the calculations will be outlined. They involve shortcuts and algorithms for counting structures. The choice of structure basis, limited to conventional principal resonance structures, will be discussed. Charges and bond orders will be compared with NMR chemical shift and X‐ray data. The unusual stabilities of the ions and the role of the metal in stabilizing positive charge will be understandable within the conventional ideas of structural organic chemistry and resonance theory. These metal‐organic systems are highly delocalized and consequently resonance stabilized to a significant degree. They can be characterized as three‐dimensional aromatic compounds.