Fast-response system for signal acquisition and processing in electrothermal atomic absorption spectrometry

An electrothermal atomic absorption (a.a.) spectrometer is modified to allow accurate correlation of absorbance and pyrometrically measured temperature with time. To by-pass the slow electronics of the spectrometer, the signal is fed from the preamplifier immediately after the photomultipier tube to a 12-bit A/D converter mounted in a 320K IBM-PC microcomputer. The wall temperature of the graphite furnace, measured with an automatic optical pyrometer, is recorded simultaneously with absorbance by feeding the pyrometer output to a second channel of the A/D board. Fast deuterium-arac background correction is also done. Background-corrected absorbance, background absorbance and temperature are recorded at 60 Hz. A simple algorithm allowed experimental activation energies to be calculated automatically. All programming was in BASIC or PASCAL.     

On the uniqueness of a local martingale with a given absolute value

Summary D. Gilat has shown that any non-negative submartingale (X, .) is equal in law to the absolute value of a martingale (M, .). This result may be strenthened so that the pairs (X,.) and (¦M¦,.) are synonomous. In this paper the question of uniqueness of M is considered. Conditions on a local martingale (M, .) are found that lead to an explicit formula for the finite-dimensional distributions of M in terms of the Doob-Meyer decomposition of the local martingale X. In many cases of interest the conditions on M are unnecessary. For example, if X is the pth power of an Itô integral it is shown that (M) is unique if p> 1 but not in general if p=1.     

Comprehensive two-dimensional gas chromatography with isotope dilution time-of-flight mass spectrometry for the measurement of dioxins and polychlorinated biphenyls in foodstuffs. Comparison with other methods

A comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC x GC-TOF-MS) experimental setup was tested for the measurement of seven 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs), ten 2,3,7,8-substituted polychlorinated dibenzofurans (PCDFs), four non-ortho-polychlorinated biphenyls (PCBs), eight mono-ortho-PCBs, and six indicator PCBs (Aroclor 1260) in foodstuff samples. A 40m RTX-500 (0.18mm I.D., 0.10 microm df) was used as the first dimension (1D) and a 1.5 m BPX-50 (0.10mm I.D., 0.10 microm df) as the second dimension (2D). The GC x GC chromatographic separation was completed in 45 min. Quantification was performed using 13C-label isotope dilution (ID). Isotope ratios of the selected quantification ions were checked against theoretical values prior to peak assignment and quantification. The dynamic working range spanned three orders of magnitude. The lowest detectable amount of 2,3,7,8-TCDD was 0.2 pg. Fish, pork, and milk samples were considered. On a congener basis, the GC x GC-ID-TOF-MS method was compared to the reference GC-ID high resolution mass spectrometry (HRMS) method and to the alternative GC-ID tandem-in-time quadrupole ion storage mass spectrometry (QIST-MS/MS). PCB levels ranged from low picogram (pg) to low nanogram (ng) per gram of sample and data compared very well between the different methods. For all matrices, PCDD/Fs were at a low pg level (0.05-3 pg) on a fresh weight basis. Although congener profiles were accurately described, RSDs of GC x GC-ID-TOF-MS and GC-QIST-MS/MS were much higher than for GC-ID-HRMS, especially for low level pork and milk. On a toxic equivalent (TEQ) basis, all methods, including the dioxin-responsive chemically activated luciferase gene expression (DR-CALUX) assay, produced similar responses. A cost comparison is also presented.     

Formation of a [2 + 2]-heterotetranuclear macrocycle from reaction of a platina-homoditopic ligand with iron(II)

Reaction of 4'-(2-propyn-1-oxy)-2,2':6',2'-terpyridine (HC triple bond CCH2Oterpy) with trans-[PtI2(PEt3)2] regioselectively metallates the alkyne to give trans-[Pt(C triple bond CCH2Oterpy)2(PEt3)2] which, when treated with Fe(II), gives a [2 + 2]-metallocycle.     

EVIDENCE FOR A MAGNESIUM DEPENDENT ATPase IN BOVINE ROD OUTER SEGMENT DISK MEMBRANES*†

Abstract—In the presence of Mg²⁺ and adenosine triphosphate (ATP), a rapid. light-induced, light-scattering transient is observed from bovine rod outer segments (ROS). This light-scattering transient we have labelled 'A'. Ca²⁺ cannot replace Mg²⁺. nor can guanosine triphosphate (GTP) replace ATP. 'A' is observed at ATP concentrations as low as a few μM.
The half-time of 'A', 60 ms at 20° and 20 ms at 37°, is consistent with a process possibly involved in visual transduction.
'A' has the action spectrum of rhodopsin bleaching and its amplitude is strictly proportional to the fraction of rhodopsin bleached per flash. 'A' can be regenerated by 11- cis retinal.
Inhibition studics with ATP analogues, which cannot be hydrolysed and fail to evoke an 'A' response, reveal that an ATP hydrolysis process has to precede illumination in order for 'A' to occur.
On the basis of the above findings. it is proposed that there is a Mg²⁺ dependent ATPase in ROS that allows the disk membrane to assume a new membrane state which, upon illumination, is altered. giving rise to the structural phenomenon monitored as light-scattering transient 'A'.     

Water confined in two-dimensions: Fundamentals and applications

The behavior of water in close proximity to other materials under ambient conditions is of great significance due to its importance in a broad range of daily applications and scientific research. The structure and dynamics of water at an interface or in a nanopore are often significantly different from those of its bulk counterpart. Until recently, experimental access to these interfacial water structures was difficult to realize. The advent of two-dimensional materials, especially graphene, and the availability of various scanning probe microscopies were instrumental to visualize, characterize and provide fundamental knowledge of confined water. This review article summarizes the recent experimental and theoretical progress in a better understanding of water confined between layered Van der Waals materials. These results reveal that the structure and stability of the hydrogen bonded networks are determined by the elegant balance between water-surface and water-water interactions. The water-surface interactions often lead to structures that differ significantly from the conventional bilayer model of natural ice. Here, we review the current knowledge of water adsorption in different environments and intercalation within various confinements. In addition, we extend this review to cover the influence of interfacial water on the two-dimensional material cover and summarize the use of these systems in potential novel applications. Finally, we discuss emerged issues and identify some flaws in the present understanding.     

Influence of Equilibration Time in Solution on the Inclusion/Exclusion Topology Ratio of Host–Guest Complexes Probed by Ion Mobility and Collision‐Induced Dissociation

Host–guest complexes are formed by the creation of multiple noncovalent bonds between a large molecule (the host) and smaller molecule(s) or ion(s) (the guest(s)). Ion‐mobility separation coupled with mass spectrometry nowadays represents an ideal tool to assess whether the host–guest complexes, when transferred to the gas phase upon electrospray ionization, possess an exclusion or inclusion nature. Nevertheless, the influence of the solution conditions on the nature of the observed gas‐phase ions is often not considered. In the specific case of inclusion complexes, kinetic considerations must be taken into account beside thermodynamics; the guest ingression within the host cavity can be characterized by slow kinetics, which makes the complexation reaction kinetically driven on the timescale of the experiment. This is particularly the case for the cucurbituril family of macrocyclic host molecules. Herein, we selected para‐phenylenediamine and cucurbit[6]uril as a model system to demonstrate, by means of ion mobility and collision‐induced dissociation measurements, that the inclusion/exclusion topology ratio varies as a function of the equilibration time in solution prior to the electrospray process.     

Irreversible Structural Changes of Copper Hexacyanoferrate Used as a Cathode in Zn-Ion Batteries

The structural changes of copper hexacyanoferrate (CuHCF), a Prussian blue analogue, which occur when used as a cathode in an aqueous Zn-ion battery, are investigated using electron microscopy techniques. The evolution of Zn_xCu_1−xHCF phases possessing wire and cubic morphologies from initial CuHCF nanoparticles are monitored after hundreds of cycles. Irreversible introduction of Zn ions to CuHCF is revealed locally using scanning transmission electron microscopy. A substitution mechanism is proposed to explain the increasing Zn content within the cathode material while simultaneously the Cu content is lowered during Zn-ion battery cycling. The present study demonstrates that the irreversible introduction of Zn ions is responsible for the decreasing Zn ion capacity of the CuHCF cathode in high electrolyte concentration.