1-Thioglycopyranosyl Esters of N-Acylamino Acids

Abstract

Fully protected 1-thioglycopyranosyl esters of N-acylamino acids (5, 6, and 7) were prepared by condensation of methyl 2, 3, 4-tri-O-acetyl-1-thio-β-d–glucopyranuronate (1), 2, 3, 4-tri-O-acetyl-1-thio-l–arabinopyranose (2), and 2, 3, 4-tri-O-acetyl-1-thio-D-arabinopyranose (3) with pentachlorophenyl esters of N-acylamino acids in the presence of imidazole. The ¹³C NMR chemical shifts of the starting 1-thio sugars and the 1-thiol ester products are reported.     

Peptide Formation by Aminolysis of 1-Thio-β-D-glucopyranosyl Esters of N-Acylaminoacids

Abstract

The susceptibility of the fully acetylated 1-thio–β-D-glucopyranosyl esters of N-protected amino acids toward the amino group of an external amino acid-or peptide-ester was examined in dichloromethane at room temperature and at 40°, respectively. In each case, the aminolysis reaction led to rupture of the C-1 thiolester bond and formation of the corresponding N-acylpeptide ester; the reaction proceeded without racemization of the aglycon chiral centre. Evidence for a remarkably high acylating efficiency of the sugar—amino acid C-1 thiolester bond is presented.     

Validation of methodology for determination of the mercury methylation potential in sediments using radiotracers

Experiments to determine the mercury methylation potential were performed on sediments from two locations on the river Idrijca (Slovenia), differing in ambient mercury concentrations. The tracer used was the radioactive isotope ¹⁹⁷Hg. The benefit of using this tracer is its high specific activity, which enables spikes as low as 0.02 ng Hg²⁺ g⁻¹ of sample to be used. It was therefore possible to compare the efficiency of the methylation potential experiments over a range of spike concentrations from picogram to microgram levels. The first part of the work aimed to validate the experimental blanks and the second part consisted of several series of incubation experiments on two different river sediments using a range of tracer additions. The results showed high variability in the obtained methylation potentials. Increasing Hg²⁺ additions gave a decrease in the percentage of the tracer methylated during incubation; in absolute terms, the spikes that spanned four orders of magnitude (0.019–190 pg g⁻¹ of sediment slurry) resulted in MeHg formation between 0.01 and 0.1 ng MeHg g⁻¹ in Podroteja and Kozarska Grapa. Higher spikes resulted in slightly elevated MeHg production (up to a maximum of 0.27 ng g⁻¹). The values of methylation potential were similar in both sediments. The results imply that the experimental determination of mercury methylation potential strongly depends on the experimental setup itself and the amount of tracer added to the system under study. It is therefore recommended to use different concentrations of tracer and perform the experiments in several replicates. The amount of mercury available for methylation in nature is usually very small. Therefore, adding very low amounts of tracer in the methylation potential studies probably gives results that have a higher environmental relevance. It is also suggested to express the results obtained in absolute amounts of MeHg produced and not just as the percentage of the added tracer.     

Novel 2,4-methanoadamantane-benzazepine by domino photochemistry of N-(1-adamantyl)phthalimide

The photochemical reaction of N-(1-adamantyl)phthalimide (1) gives cleanly one product, the novel hexacyclic benzazepine derivative of 2,4-methanoadamantane 2. Its structure was characterized by spectroscopic methods and X-ray analysis and represent the first example of the 2-azahexacyclo[8.7.1.1 (1,4).0 (4,9).0 (11,16).0 (12,18)]nonadeca-4,6,8-triene skeleton. The product is formed by a domino process of two consecutive excited-state intramolecular gamma-hydrogen-transfer reactions. Base hydrolysis of the benzazepine 2 gives in high yield the keto derivative of the 1,2-substituted adamantane epsilon-amino acid 3.     

Dielectrophoretic field‐flow fractionation of electroporated cells

We describe the development and testing of a setup that allows for DEP field‐flow fractionation (DEP‐FFF) of irreversibly electroporated, reversibly electroporated, and nonelectroporated cells based on their different polarizabilities. We first optimized the channel and electrode dimensions, flow rate, and electric field parameters for efficient DEP‐FFF separation of moderately heat‐treated CHO cells (50°C for 15 min) from untreated ones, with the former used as a uniform and stable model of electroporated cells. We then used CHO cells exposed to electric field pulses with amplitudes from 1200 to 2800 V/cm, yielding six groups containing various fractions of nonporated, reversibly porated, and irreversibly porated cells, testing their fractionation in the chamber. DEP‐FFF at 65 kHz resulted in distinctive flow rates for nonporated and each of the porated cell groups. At lower frequencies, the efficiency of fractionation deteriorated, while at higher frequencies the separation of individual elution profiles was further improved, but at the cost of cell flow rate slowdown in all the cell groups, implying undesired transition from negative into positive DEP, where the cells are pulled toward the electrodes. Our results demonstrate that fractionation of irreversibly electroporated, reversibly electroporated, and nonelectroporated cells is feasible at a properly selected frequency.     

Intermolecular central to axial chirality transfer in the self-assembled biphenyl containing amino acid-oxalamide gelators

Chiral amino acid and biphenyl incorporating oxalamide gelators 4-7 with large, 9 bond distance between chiral centres and biphenyl units have been studied. CD investigation of 4-octanol gel and the crystal structure of rac-4 reveal that efficient central to axial chirality transfer occurs by intermolecular interactions in gel and solid state assemblies.     

Optimising organic ionic plastic crystal electrolyte for all solid-state and higher than ambient temperature lithium batteries

Organic ionic plastic crystal (OIPC) electrolytes are among the key enabling materials for solid-state and higher than ambient temperature lithium batteries. This work overviews some of the parameter studies on the Li|OIPC interface using lithium symmetrical cells as well as the optimisation and performance of Li|OIPC|LiFePO₄ cells. The effects of temperature and electrolyte thickness on the cycle performance of the lithium symmetrical cell, particularly with respect to the interfacial and bulk resistances, are demonstrated. Whilst temperature change substantially alters both the interfacial and bulk resistance, changing the electrolyte thickness predominantly changes the bulk resistance only. In addition, an upper limit of the current density is demonstrated, above which irreversible processes related to electrolyte decomposition take place. Here, we demonstrate an excellent discharge capacity attained on LiFePO₄|10 mol% LiNTf₂-doped [C₂mpyr][NTf₂]|Li cell, reaching 126 mAh g^-1 at 50 °C (when the electrolyte is in its solid form) and 153 mAh g^-1 at 80 °C (when the electrolyte is in its liquid form). Most remarkably, at high temperature operation, the capacity retention at long cycles and high current is excellent with only a slight (3%) drop in discharge capacity upon increasing the current from 0.2 C to 0.5 C. These results highlight the real prospects for developing a lithium battery with high temperature performance that easily surpasses that achievable with even the best contemporary lithium-ion technology.     

New mathematical models of the generalized vehicle routing problem and extensions

The generalized vehicle routing problem (GVRP) is an extension of the vehicle routing problem (VRP) and was introduced by Ghiani and Improta [1]. The GVRP is the problem of designing optimal delivery or collection routes from a given depot to a number of predefined, mutually exclusive and exhaustive node-sets (clusters) which includes exactly one node from each cluster, subject to capacity restrictions. The aim of this paper is to provide two new models of the GVRP based on integer programming. The first model, called the node formulation is similar to the Kara-Bekta? formulation [2], but produces a stronger lower bound. The second one, called the flow formulation, is completely new. We show as well that under specific circumstances the proposed models of the GVRP reduces to the well known routing problems. Finally, the GVRP is extended for the case in which the vertices of any cluster of each tour are contiguous. This case is defined as the clustered generalized vehicle routing problem and both of the proposed formulations of GVRP are adapted to clustered case.