Internal Methylene Transfer Reactions Employing Sulfur Ylides: Stereospecific Epoxide formation 1 2 3

The synthetic utility of sulfur ylides in orgnic chemistry has been successfully explored over the past several years and has provided an easily accessible route to a number of functional groups,⁴ including cyclopropanes,⁵ and optically active epoxides⁶.     

Order sequencing on a unidirectional cyclical picking line

A real life order-picking configuration that requires multiple pickers to cyclically move around fixed locations in a single direction is considered. This configuration is not the same, but shows similarities to, unidirectional carousel systems described in literature. The problem of minimising the pickers’ travel distance to pick all orders on this system is a variant of the clustered travelling salesman problem. An integer programming (IP) formulation of this problem cannot be solved in a realistic time frame for real life instances of the problem. A relaxation of this IP formulation is proposed that can be used to determine a lower bound on an optimal solution. It is shown that the solution obtained from this relaxation can always be transformed to a feasible solution for the IP formulation that is, at most, within one pick cycle of the lower bound. The computational results and performance of the proposed methods as well as adapted order sequencing approaches for bidirectional carousel systems from literature are compared to one another by means of real life historical data instances obtained from a retail distribution centre.     

Structural characteristics and residual stresses in oxide films produced on Ti by pulsed unipolar plasma electrolytic oxidation

Oxide films, 7–10 µm thick, were produced on commercially pure titanium by plasma electrolytic oxidation in a sodium orthophosphate electrolyte using a pulsed unipolar current with frequency (f) and duty cycle (δ) varying within f = 0.1–10 kHz and δ = 0.8–0.2, respectively. The coatings comprised a mixture of an amorphous phase with nanocrystalline anatase and rutile phases, where the relative rutile content range was 17–25 wt%. Incorporation of phosphorus from the electrolyte into the coating in the form of PO₂ ^–, PO₃ ^2– and PO₄ ^3–, as demonstrated by EDX and FT-IR analyses, contributed to the formation of the amorphous phase. Residual stresses associated with the crystalline coating phase constituents were evaluated using the X-ray diffraction sin² ψ method. It was found that, depending on the treatment parameters, internal direct and shear stresses in anatase ranged from–205 (±17) to–431 (±27) MPa and from–98 (±6) to–145 (±10) MPa, respectively, whereas the rutile structure is comparatively stress-free.     

The Effect of Silver Perchlorate of the Reaction of Trialkyl Phosphite with α-Halogenoketones

Abstract

Trialkyl phosphites are known to react with α-halogenoketones to yield β-ketophosphonates (Arbuzov product) or vinyl phosphates (Perkow product) according to coniiitions.¹ α-Hydroxyphosphonate may be formed in addition, in prcltic media.² We have now shown that none of these products is formed in the presence of silver perchlorate (in benzene sclutim); nor could we detect the ketophosphonium perchlorate reported previously. Phosphorus-31 nmr showed the formation of trimethyl phosphate and tetramethyl pyrophosphate as the exclusive phosphorus-containing products. The sequence of possible reaction is complex and the overall stoichiometry may vary somewhat according to the rate and order of rixing. Trialkyl phosphate could be formed by elimination of alkyne from vinyloxyphosphonium intermediate produced together with silver iodine in first stage of the interaction. Pyrophosphate formation would then result from nucleophilic attack of trimethyl phosphate on the trimethoxy(1-nethylvinyloxy)phosphoniun ion, which may be formed as a reactive intermediate. Evidence for formation of methyl perchlorate in the final dealkylation of the quasiphosphonium intermediate is provided by proton nmr spectroscopy and by the formation of the N-methylquino-linium salt on addition of quinoline. No change in the ³¹P nmr spectrum occurs at this stage. Other by-products of the main reactions include the dehalogenated ketone (acetone from iodoacetone or acetnphenone from α-iodoacetophenone).     

Advances towards using finger/toenail dosimetry to triage a large population after potential exposure to ionizing radiation

Rapid and accurate retrospective dosimetry is of critical importance and strategic value for the emergency medical response to a large-scale radiological/nuclear event. One technique that has the potential for rapid and accurate dosimetry measurements is electron paramagnetic resonance (EPR) spectroscopy of relatively stable radiation-induced signals (RIS) in fingernails and toenails. Two approaches are being developed for EPR nail dosimetry. In the approach using ex vivo measurements on nail clippings, accurate estimation of the dose-dependent amplitude of the RIS is complicated by the presence of mechanically-induced signals (MIS) that are generated during the nail clipping. Recent developments in ex vivo nail dosimetry, including a thorough characterization of the MIS and an appreciation of the role of hydration and the development of effective analytic techniques, have led to improvements in the accuracy and precision of this approach. An in vivo nail dosimetry approach is also very promising, as it eliminates the problems of MIS from the clipping and it has the potential to be an effective and efficient approach for field deployment. Two types of EPR resonators are being developed for in vivo measurements of fingernails and toenails.     

A Deployable In Vivo EPR Tooth Dosimeter for Triage After a Radiation Event Involving Large Populations

In order to meet the potential need for emergency large-scale retrospective radiation biodosimetry following an accident or attack, we have developed instrumentation and methodology for in vivo electron paramagnetic resonance spectroscopy to quantify concentrations of radiation-induced radicals within intact teeth. This technique has several very desirable characteristics for triage, including independence from confounding biologic factors, a non-invasive measurement procedure, the capability to make measurements at any time after the event, suitability for use by non-expert operators at the site of an event, and the ability to provide immediate estimates of individual doses. Throughout development there has been a particular focus on the need for a deployable system, including instrumental requirements for transport and field use, the need for high throughput, and use by minimally trained operators.Numerous measurements have been performed using this system in clinical and other non-laboratory settings, including in vivo measurements with unexposed populations as well as patients undergoing radiation therapies. The collection and analyses of sets of three serially-acquired spectra with independent placements of the resonator, in a data collection process lasting approximately five minutes, provides dose estimates with standard errors of prediction of approximately 1 Gy. As an example, measurements were performed on incisor teeth of subjects who had either received no irradiation or 2 Gy total body irradiation for prior bone marrow transplantation; this exercise provided a direct and challenging test of our capability to identify subjects who would be in need of acute medical care.     

Characterisation of martian soil simulants for the ExoMars rover testbed

The European Space Agency (ESA) ExoMars mission involves landing a rover on the surface of Mars on an exobiology mission to extend the search for life. The locomotion capabilities of the ExoMars rover will enable it to use its scientific instruments in a wide variety of locations. Before it is sent to Mars, this locomotion system must be tested and its performance limitations understood. To test the locomotion performance of the ExoMars rover, three martian regolith simulants were selected: a fine dust analogue, a fine Aeolian sand analogue, and a coarse sand analogue. To predict the performance of the ExoMars rover locomotion system in these three regolith simulants, it is necessary to measure some fundamental macroscopic properties of the materials: cohesion, friction angle, and various bearing capacity constants. This paper presents the tests conducted to determine these properties. During these tests, emphasis was placed on preparing the regolith simulants at different levels of density in order to evaluate its impact on the value of the parameters in particular. It was shown that compaction can influence the Bekker coefficients of pressure-sinkage. The shear properties are consistent with the critical state model at normal stresses similar to those of the ExoMars rover in all but one of the simulants, which showed behaviour more consistent with transitional soil behaviour. It is necessary to give due consideration to these variations to ensure a robust test regime is developed when testing the tractive ability of the ExoMars mobility system.     

Surface activity and self-aggregation ability of three cationic quaternized aminocalix[4]arenes

The self-aggregation ability of three amphiphilic cationic calix[4]arenes possessing four quaternary amino groups (aminoCAs) was investigated using a variety of methods. All of the studied compounds possess high aggregation ability. Their critical aggregation concentration (CAC) values in water are in the 0.0009–0.04 % (w/v) concentration range. Several size populations of aggregates were detected by DLS for all three CAs, and restructuring of aggregates was observed to be dependent on concentration. Particles formed above CAC were attributed to formation of vesicular structures (vesicles). The coexistence of other type of aggregates (presumably micelles) with vesicles was observed in the aqueous solution of CAs 2 and 3 from concentrations of 0.5 and 0.8 % (w/v), respectively. The filtration procedure was found to be a significant factor since the obtained data from filtered and unfiltered samples was different. The particle sizes obtained by TEM measurements were somewhat correlated with the DLS data for unfiltered CAs solutions. An analysis of the aggregate composition was undertaken by a size-exclusion method using semi-permeable cellophane membranes with different MWCO. A negative deviation from linearity of permeability flux profile starting from 0.8 % (w/v) concentration of donor phase indicated that the fraction of large aggregates at this point is significant enough that the molecules could not easily permeate through the membranes.     

Products in the Reactions of Trialkyl Phosphites with α-Halogeno-acetophenones in Alcoholic Media

Abstract

α-Hydroxyphosphonates are formed, in addition to vinyl phosphates and dehalogenated ketones, in the reactions of trimethyl phosphite (in methanol) or triethyl phosphite (in ethanol) with variously substituted α-chloro, α-bromo, and α,α,-dichloro-acetophenones. Tri-isopropyl phosphite in propan-2-ol gives only the vinyl phosphate. Ketophosphonates are not detectable amongst the reaction products under the conditions used. Trends in product composition can be correlated with the leaving ability of halogen, substituent effects, structure of the phosphite, and reaction temperature. Reactant ratios may also influence the product composition. The reactions of trimethyl phosphite in methanol with 4-nitro-α-chloroacetophenone, or α,α-dichloroacetophenones yield the dehalogenated α-hydrogxyphosphonates in addition. In the case of the 4-nitro derivative, this product cannot be accounted for by reaction of the phosphite with dehalogenated ketone (4-nitroacetophenone). Dehalogenation of the first-formed α-hydroxyphosphonate was, however, shown to occur under reaction conditions and appears to require the removal of positive chlorine, followed by protonation. Reactions of the α,α-dichloroacetophenones were similar to those of the α-chloroacetophenones, giving the corresponding chlorovinyl phosphate, α,α-dichloro-α-hydroxyphosphonate, and monodehalogenated ketone(i.e. α-chloroacetophenone); the latter was not however detected as it reacted further with excess phosphite to give the expected products as described above. Possible mechanisms for the various reactions are discussed. The ¹H and ¹³C nmr spectra of the α-hydroxy-phosphonates show magnetic non-equivalence of the two alkoxy groups, attributed to restricted rotation about the P-C bond as a result of intramolecular hydrogen-bonding.