The Table of Standard Atomic Weights—An exercise in consensus

The present Table of Standard Atomic Weights (TSAW) of the elements is perhaps one of the most familiar data sets in science. Unlike most parameters in physical science whose values and uncertainties are evaluated using the “Guide to the Expression of Uncertainty in Measurement” (GUM), the majority of standard atomic-weight values and their uncertainties are consensus values, not GUM-evaluated values. The Commission on Isotopic Abundances and Atomic Weights of the International Union of Pure and Applied Chemistry (IUPAC) regularly evaluates the literature for new isotopic-abundance measurements that can lead to revised standard atomic-weight values, A_r°(E) for element E. The Commission strives to provide utmost clarity in products it disseminates, namely the TSAW and the Table of Isotopic Compositions of the Elements (TICE). In 2016, the Commission recognized that a guideline recommending the expression of uncertainty listed in parentheses following the standard atomic-weight value, for example, A_r°(Se) = 78.971(8), did not agree with the GUM, which suggests that this parenthetic notation be reserved to express standard uncertainty, not the expanded uncertainty used in the TSAW and TICE. In 2017, to eliminate this noncompliance with the GUM, a new format was adopted in which the uncertainty value is specified by the “±” symbol, for example, A_r°(Se) = 78.971 ± 0.008. To clarify the definition of uncertainty, a new footnote has been added to the TSAW. This footnote emphasizes that an atomic-weight uncertainty is a consensus (decisional) uncertainty. Not only has the Commission shielded users of the TSAW and TICE from unreliable measurements that appear in the literature as a result of unduly small uncertainties, but the aim of IUPAC has been fulfilled by which any scientist, taking any natural sample from commerce or research, can expect the sample atomic weight to lie within A_r°(E) ± its uncertainty almost all of the time.     

Understanding the Anion-Templated,OSDA-Free,Interzeolite Conversion Synthesis of High Silica Zeolite ZK-5**

High silica zeolite ZK-5 (framework Si/Al=4.8) has been prepared by interzeolite conversion from ultrastable zeolite Y via a co-templating route using alkali metal cations and nitrate anions but without organic structure directing agents. The mechanism, which involves zeolite framework – alkali metal cation – nitrate anion ordering, has been established by a combination of chemical and thermal analyses, Raman spectroscopy, computational modelling, and X-ray powder diffraction. Ammonium exchange gives ZK-5 with occluded ammonium nitrate and subsequent heating gives microporous zeolite ZK-5.     

On the dynamic vibrations of an elastic beam in frictional contact with a rigid obstacle

Existence and uniqueness results are established for weak formulations of initial-boundary value problems which model the dynamic behavior of an Euler-Bernoulli beam that may come into frictional contact with a stationary obstacle. The beam is assumed to be situated horizontally and may move both horizontally and vertically, as a result of applied loads. One end of the beam is clamped, while the other end is free. However, the horizontal motion of the free end is restricted by the presence of a stationary obstacle and when this end contacts the obstacle, the vertical motion of the end is assumed to be affected by friction. The contact and friction at this end is modelled in two different ways. The first involves the classic Signorini unilateral or nonpenetration conditions and Coulomb's law of dry friction; the second uses a normal compliance contact condition and a corresponding generalization of Coulomb's law. In both cases existence and uniqueness are established when the beam is subject to Kelvin-Voigt damping. In the absence of damping, existence of a solution is established for a problem in which the normal contact stress is regularized.The work of the last two authors was supported in part by Oakland University Research Fellowships.     

Explicit green matrices for linear elasticity in the half space

This paper studies traveling-wave solutions of the partial differential equations which model waves in a horizontal water channel traveling in both directions. The existence of solitary-wave solutions for a number of systems is proved. Interesting new multi-pulsed traveling-wave solutions which consist of an arbitrary number of troughs are found numerically. The bifurcation diagrams of N-trough solutions with respect to phase speed and system parameters are presented.     

Quantum-chemical study of the potential anti-cancer drug Ru–NAMI-A in complex with estrogen and the simulated VA and VCD spectra of estrogen, the Ru–NAMI-A drug, and possible/proposed estrogen–Ru–NAMI-A complexes

Following up on an earlier theoretical report by Knapp-Mohammady (Phys Lett A 372:1881–1884, 2008) on the ground state of the neutral Ru complex NAMI-A (trans-imidazoledimethylsulfoxide-tetrachlororuthenate), we first report here a quantum-chemical study of the effect of both oxidation and reduction of the parent molecule to form the anionic and cationic species. The new structures are compared with the equilibrium nuclear structure reported earlier for the neutral complex. We anticipate that one such Ru cluster, with potential as an anti-cancer drug, will interact via an appropriate receptor, rather than directly with DNA. A receptor for NAMI-A binding in here proposed to be the steroid hormone, estrogen, C₁₈H₂₄O₂. The biomolecular structure of the dicomplex is predicted from restricted Hartree–Fock theory and density functional theory (DFT) calculations. The vibrational frequencies of NAMI-A and the dicomplex with estrogen are also reported. Some maps of the ground-state electron-density for the three neutral biomolecular species are finally presented. The use of vibrational spectroscopy, vibrational absorption (VA) and vibrational circular dichorism (VCD) are advocated to be measured, simulated and be used to understand the nature of the interaction of the Ru complex NAMI-A in complex with estrogen. Our aim in presenting these spectral simulations is to motivate the measurement of the VA and VCD spectra of estrogen, the Ru complex NAMI-A and finally of the estrogen–Ru NAMI-A complex. It should also be instructive to measure the VA and VCD spectra of estrogen and the estrogen receptor, both alone, together and finally together in the presence of the Ru NAMI-A complex to substantiate our claim that the Ru complex NAMI-A ties up estrogen, and hence prevents estrogen binding to the estrogen receptor.     

Interplay of Magnetic Exchange Interactions and Ni?S?Ni Bond Angles in Polynuclear Nickel(II) Complexes

The ability of bridging thiophenolate groups (RS^?) to transmit magnetic exchange interactions between paramagnetic Ni^II ions is examined. Specific attention is paid to complexes with large Ni? SR? Ni angles. For this purpose, dinuclear [Ni₂L¹(μ‐OAc)?I₂][I₅] ( 2 ) and trinuclear [Ni₃L²(OAc)₂][BPh₄]₂ ( 3 ), where H₂L¹ and H₂L² represent 24‐membered macrocyclic amino‐thiophenol ligands, are prepared and fully characterized by IR‐ and UV/Vis spectroscopy, X‐ray crystallography, static magnetization M measurements and high‐field electron spin resonance (HF‐ESR). The dinuclear complex 2 has a central N₃Ni₂(μ‐S)₂(μ‐OAc)Ni₂N₃ core with a mean Ni? S? Ni angle of 92°. The macrocycle L² supports a trinuclear complex 3 , with distorted octahedral N₂O₂S₂ and N₂O₃S coordination environments for one central and two terminal Ni^II ions, respectively. The Ni? S? Ni angles are at 132.8° and 133.5°. We find that the variation of the bond angles has a very strong impact on the magnetic properties of the Ni complexes. In the case of the Ni₂‐complex, temperature T and magnetic field B dependencies of M reveal a ferromagnetic coupling J=?29 cm^?1 between two Ni^II ions (H=JS₁S₂). HF‐ESR measurements yield a negative axial magnetic anisotropy (D<0) which implies a bistable (easy axis) magnetic ground state. In contrast, for the Ni₃‐complex we find an appreciable antiferromagnetic coupling J′=97 cm^?1 between the Ni^II ions and a positive axial magnetic anisotropy (D>0) which implies an easy plane situation.     

A novel rearrangement of fluorescent human thymidylate synthase inhibitor analogues in ESI tandem mass spectrometry

Cu(I) catalyzed alkyne-azide cycloaddition reaction was employed to synthesize a series of anthracene-based human thymidylate synthase (hTS) inhibitor analogues. The triazolo-anthracene derivatives were characterized by ESI-MS/MS and a novel rearrangement reaction in ESI-MS/MS was observed. The mechanism is proposed whereby the protonated triazolo-anthracene derivative forms a carbocation, and then the carbocation electrophilically attacks an anthracene moiety resulting in formation of a rearrangement ion. Moreover, the carbocation prefers to attack the γ position rather than the α or β position of the anthracene moiety by an electrophilic substitution mechanism.     

Power loss of an energetic charged particle moving parallel to a graphene sheet

In this work we analyze the energy loss of a fast charged particle moving parallel to a two-dimensional (2D) graphene sheet. The response dynamics of the 2D graphene sheet are modeled using the random phase approximation in the degenerate limit (zero temperature). We determine the energy loss and stopping power for motion parallel to the graphene sheet as a function of the distance of the charged particle from the 2D sheet and of its velocity.     

Metallic Free Carbon Nanotube Cluster Modified Screen Printed Electrodes for the Sensing of Nicotine in Artificial Saliva

We demonstrate that metallic free carbon nanotube cluster modified screen printed electrodes provide an advantageous sensing methodology for nicotine. The electrochemical oxidation of nicotine is possible at low potentials compared to other commercially available carbon electrodes. Using the carbon nanotube cluster modified screen printed electrodes a detection range of 10 to 1000 μM is possible with a limit of detection of 2 μM. The sensing protocol is shown to be viable in artificial saliva and is promising as a portable and rapid sensor for nicotine in oral fluid (saliva) in areas such as health/life insurance, instances where smoking is banned and also as a point of care test to help improve smoking quit rates.     

Highlighting the role of the chlorine substituents in the glycopeptide antibiotic balhimycin for chiral recognition in capillary electrophoresis

The vancomycin-type glycopeptide antibiotic balhimycin (I) and its dehaloanalogue dechlorobalhimycin (III), which is characterized by the total substitution of the two chlorine atoms of I by hydrogen, were employed as chiral selectors for the enantioresolution of 11 racemic dansyl amino acids and six 2-arylpropionic acid nonsteroidal anti-inflammatory racemic drugs by CE. The observed enantioresolution capability of I for all test analytes is clearly higher than that observed for III. This result suggests that chlorine substituents of I played a major role in the enantioresolution of these test analytes. A dimerization-based mechanism is proposed in order to explain this phenomenon. The two chlorine substituents of each monomer, which mutually penetrate into the cavity of the adjacent molecule of the dimer, are assumed to promote dimerization and as a consequence also enantioresolution.