Me2SO Solutions Research Articles

Cryopreservation with reduced ME2so and cold storage solutions for cells based therapies

Cryopreservation with reduced ME2so and cold storage solutions for cells based therapies

Noncovalent Sulfoxide–Nitrile Coupling Involving Four-Center Heteroleptic Dipole–Dipole Interactions between the Sulfinyl and Nitrile Groups

The 4-X-5-nitro substituted phthalodinitriles (X = Br 1, I 2) were crystallized from Me2SO solutions affording crystalline adducts (1–2)•Me2SO, which were characterized by X-ray crystallography at ...

Effects of ultrasound on permeation of cryoprotectants into Japanese whiting Sillago japonica embryos

Cryopreservation of fish embryos requires the swift uptake of considerable amounts of cryoprotectant (CPA) but this process is hampered by the low permeability of the egg chorion. This study examined the relative efficiency of ultrasound to promote the incorporation of CPAs in two different embryonic developmental stages (somites and tail elongation) of Japanese whiting Sillago japonica and performed a preliminary cryopreservation trial using the best conditions determined during the study. Embryos tolerated ultrasound densities up to 37.5 W/cm2 well for up to 3 min but had significant mortality at 50 W/cm2. Hatching rates of somites embryos sonicated at 37.5 W/cm2 for 1–3 min in 10 and 20% Me2SO solutions were comparable (61–72%) to that of sonication in artificial seawater (65–86%) but decreased sharply at the concentration of 30% (0–55%); at similar conditions, tail elongation embryos had comparatively lower survival. Me2SO content of sonicated embryos at the somites and tail elongation stages increased significantly by 58–191% and 27–123%, respectively, compared to controls exposed to Me2SO without ultrasound. Pre-exposure to Me2SO before sonication increased the CPA uptake further by 36% without impairing survival. A preliminary cryopreservation trial after ultrasound-mediated impregnation of somites embryos with a CPA solution containing 20% PG and 10% MeOH did not yield live embryos after freeze-thawing but resulted in a significant decrease of nucleation temperature and increase of the proportion of morphologically intact embryos after freeze-thawing. These results suggest that sonication might be useful for fish embryo cryopreservation although it may require combination with other techniques to enhance CPA permeation.

C-2022: Monitoring of the residual cryoprotectant concentration with electrical conductivity measurements during cryoprotectant removal

Cryoprotective agents (CPA) should be added to cell suspension before freezing and removed after thawing. Nowadays people mainly apply centrifugation for CPA removal. This method may cause many problems. Meanwhile, a fast, easy and cheap method to monitor the residual CPA concentration remains an unfilled need. In this work, real-time monitoring of residual CPA concentration with electrical conductivity (EC) measurements was proposed and tested. It was found that CPA concentration is correlated with the EC of the solution. The standard data of “CPA concentration—EC of the solution” for a few widely used CPA solutions were obtained. A “dilution–filtration” system based on a hollow fiber dialyzer, three peristaltic pumps and some well-designed tubing connections was applied to remove CPA. Me2SO solutions (Me2SO–NaCl–H2O solutions with or without 5% BSA) were selected as representative examples. The results showed that CPA can be removed effectively by the “dilution–filtration” system. The ECs of waste solution (filtration product) and “cell suspension” were almost identical after a short period of processing, which were validated by osmolality measurements with an osmometer. EC readings of waste solution can convey the instant residual CPA concentrations in cell suspension. This validates the feasibility of a safe (no contamination), easy and cheap way to real-time monitoring of CPA concentration in cell suspension by measuring the EC of the waste solution. Compared to other CPA removal methods that are applied traditionally (centrifugation) or proposed recently (microfluidic device), the “dilution–filtration” method may offer advantages of low time and labor consumption, low injury to the cells, high effectiveness, ease of controlling the final suspension volume and low risk of contamination. The configuration of the “dilution–filtration” system can also be modified easily to achieve CPA addition and volume control of cell suspension (concentration or dilution of the cell suspension).

C-2030 : Investigation of anti-freeze proteins effect on vitrification–devitrificartion processes in a micro-scale view

Ice crystals can greatly damage biological matter which is kept at low temperature for preservation. This problem can be avoided using vitrification, a process by which a liquid is solidified into a non-crystalline (glassy) state by lowering the temperature in the presence of solutes and greatly increasing the viscosity. This process is also beneficiary since it avoids the formation of concentration gradients introduced during crystallization and thereby avoids osmotic injuries resulting in loss of sample viability. Since the late thirties, when Luyet raised the idea of cells cryopreservation by vitrification, a lot of progress has been made in understanding this process and developing this technique to suit biological needs. However, there is still the main difficulty which has not come into a successful solution – the phenomena called ’devitrification’, when ice crystals form during the rewarming step of partially vitrified biological material. We suggest a natural alternative to face this challenge by using antifreeze proteins (AFPs) found in cold-adapted organisms. These proteins are known to inhibit ice growth in slightly supercooled conditions, and inhibit recrystalization of ice in frozen tissues. In this study we investigate the influence of AFPs on the vitrification and de-vitrification processes under a microscope equipped with controlled cold stage and by differential scanning calorimetry (DSC). Observation on vitrification and de-vitrification of Me2SO solutions at different volumes, temperatures and cooling and warming rates have demonstrated these processes in a micro scale. Preliminary results show that addition of the hyperactive AFP fromTenibrio molitor in various concentrations appear to have less ice nucleation centers during warming. Moreover, ice crystals, at post vitrification temperatures (i.e ∼−105 °C), display slower growth in solutions containing AFPs. These novel effects of TmAFP will be further characterized and developed in a course of utilizing these findings into biological matter cryopreservation applications.

005 Integration of polarized light into scanning cryomacroscopy

This study presents the integration of polarized light into the scanning cryomacroscope—a recently developed device to visualize physical effects in large-scale cryopreservation [Y. Rabin, J.S.G. Feig, A.C. Williams, C.C. Lin, C. Thaokar, Cryomacroscopy in 3D: a device prototype for the study of cryopreservation, ASME-SBC 2012, Fajardo, Puerto Rico]. The cryomacroscope is the only means available for visualization and recording physical events along the path-dependent process of cryopreservation in large samples. The application of polarized light enhances the ability to trace ice nucleation, thermo-mechanical stress formation, fracturing, and contamination in the cryopreserved material. Several versions of the cryomacroscope have been presented in recent years, all of which share the same key features: (i) a cryogenic setup to cool a specimen along cryopreservation protocols of interest, (ii) a data acquisition system to monitor and record the thermal history of the specimen, (iii) a borescope to transfer sample images from the cryogenic environment to, (iv) a camera held at room temperature, and (v) image post-processing capabilities. The scanning cryomacroscope was recently developed to analyze samples bigger than the field of view of the borescope. The current study is focused on enhancing visualization capabilities by integrating, for the first time, polarized light with cryomacroscopy. The implementation of polarized light uses two parallel and concentric polarizing filters, rotated 90° to one another around their common axis. As a result, only refracted light refracted by an object placed intermediate to the first filter (polarizer) and second filter (analyzer) may pass the analyzer and be captured by the cryomacroscope camera. The filters used in the new setup are 0.3-mm thick dichroic polarizing film sheets sandwiched (epoxied) between protective glass windows. These glass windows are coated by an antireflective film, which is optimized for the visible light spectrum that in the range from 400 to 700 nm. The analyzer is secured to the borescope tip with a 3D-printed housing. The polarizer is secured in a housing attached to a beam-rotating mirror. Light is directed from a halogen source (150 W at 3200 K) via fiber optics to the mirror. Alternating diffuse light is directed from an independent LED source (5 W at 6000 K) to the sample by a second set of fiber optic bundles. Vitrification experiments on Me2SO solutions at various concentrations and subject to varying cooling protocols have been conducted. The following effects are demonstrated with the new polarized light setup: (1) display of contaminants otherwise unobservable with diffuse light, some of which are longer than 5 mm; (2) observation of ice nuclei larger than 15 μm in characteristic diameter within a 4.5 ml domain; (3) improved contrast in fractured sites; and, (4) visualization of mechanically strained vitrified material (cryoprotective agent and container), where the strained material is coded with the visible light spectrum. Source of funding: This project has been supported by Award Number 5R21RR026210 from the National Center for Research Resources, and Award Number 8R21GM103407 from the National Institute of General Medical Sciences. Conflict of interest: None declared. rabin@cmu.edu

13. Peripheral blood derived hematopoietic progenitor cells (HPC): An overview of a successful application of cryobiology

Hematopoietic progenitor cells (HPC) are primitive pluripotent cells capable of self renewal as well as of differentiation and maturation into all hematopoietic lineages. They can be found in bone marrow, in fetal liver, in umbilical cord blood, and in the mononuclear cell fraction of circulating blood. They are characterized by their colony-forming capacities in different in vitro cell culture assays and by the surface antigen marker CD34. Today, HPC are successfully cryopreserved using methods based on a dimethyl sulphoxide (Me2SO) method proposed by Ashwood-Smith (1961) for bone marrow. Cryopreserved peripheral HPC (in combination with patient high-dose chemotherapy or irradiation) have become a “standard” blood component for the treatment of several malignant diseases in more than 10,000 patients in Europe per year, e.g. lymphoma, myeloma, leukemia, and germ cell tumors. Nowadays HPC are usually obtained by apheresis from peripheral blood after stimulation with a cytokine named G-CSF (granulocyte colony stimulating factor). During cooling, heat is removed either by computer-controlled and liquid nitrogen (LN2) operated machines or in mechanical (−80 °C) refrigerators. Stiff et al. (1983) have demonstrated that the addition of 6% hydroxyethyl starch (HES) reduced the “original” concentration of Me2SO (10%) by half. A serious problem regarding frozen peripheral HPC is the danger of clotting after thawing. Although it is highly advisable to use as little anticoagulant – mostly ACD-A (acid–citrate–dextrose, formula A) or heparin – as possible during the apheresis procedure from the patient’s point of view, this may lead to problems during the following processing and after thawing. So if low anticoagulant concentrations have been used during the apheresis procedure, we recommend adding additional ACD-A to the final apheresis product. There are reports in the literature (e.g., Douay et al., 1982; Goldman et al., 1978) on Me2SO toxicity at room temperature. As a consequence of these and other reports, in clinical protocols diluted and precooled Me2SO solutions are usually added at 0–4 °C. In an investigation with highly pure Me2SO (pharmaceutical grade), however, no impairment (colony assay) within the first hour was found when 5% or 10% of Me2SO were added at either 4 or 37 °C (Rowley and Anderson, 1993). Cool-down kinetics depend on several parameters: geometry (“undefined,” cylindrical, or plate shaped), sample thickness, composition (type and concentration of cryoprotectants), and thermal properties (heat capacity, heat conductivity) of the freezing bag and (if used) the surrounding metal envelope. Therefore, temperature time-histories measured in small reference samples (e.g., tubes) may differ significantly from those measured in the corresponding product bags. With regard to cryoprotectant concentration and cooling rates, we did not find significant differences in cell recovery and clonogenicity (Sputtek et al., 1997), provided at least 5% Me2SO was present and cooling rates did not exceed 5 °C/min. Our most recent data supports the conclusion that a reliable −150 °C freezer is as suitable for long-term storage of HPC as is storage in the vapor phase over LN2. There was no systematic decline in viability measured in terms of six different parameters after more than 16 months storage in a −150 °C freezer (Sputtek et al. 2011). In our hands cell counts dropped significantly within 5 h after thawing compared to a high recovery when post thaw storage was performed at 20 °C and 0 °C, respectively. Therefore, we recommend to continue the common practice of thawing the frozen HPC units at the patient’s bedside.

Discovery of Small Molecule Inhibitors of the Interaction of the Thyroid Hormone Receptor with Transcriptional Coregulators

Thyroid hormone (3,5,3'-triiodo-L-thyronine, T3) is an endocrine hormone that exerts homeostatic regulation of basal metabolic rate, heart rate and contractility, fat deposition, and other phenomena (1, 2). T3 binds to the thyroid hormone receptors (TRs) and controls their regulation of transcription of target genes. The binding of TRs to thyroid hormone induces a conformational change in TRs that regulates the composition of the transcriptional regulatory complex. Recruitment of the correct coregulators (CoR) is important for successful gene regulation. In principle, inhibition of the TR-CoR interaction can have a direct influence on gene transcription in the presence of thyroid hormones. Herein we report a high throughput screen for small molecules capable of inhibiting TR coactivator interactions. One class of inhibitors identified in this screen was aromatic beta-aminoketones, which exhibited IC50 values of approximately 2 microm. These compounds can undergo a deamination, generating unsaturated ketones capable of reacting with nucleophilic amino acids. Several experiments confirm the hypothesis that these inhibitors are covalently bound to TR. Optimization of these compounds produced leads that inhibited the TR-CoR interaction in vitro with potency of approximately 0.6 microm and thyroid signaling in cellular systems. These are the first small molecules irreversibly inhibiting the coactivator binding of a nuclear receptor and suppressing its transcriptional activity.

Extracellular pH Modifies Mitochondrial Control of Capacitative Calcium Entry in Jurkat Cells

It was found that a collapse of the mitochondrial calcium buffering caused by the protonophoric uncoupler CCCP, antimycin A plus oligomycin, or the inhibitor of the mitochondrial Ca2+/Na+ exchanger led to a strong inhibition of thapsigargin-induced capacitative Ca2+ entry (CCE) into Jurkat cells suspended in a medium at pH 7.2. The effect of these inhibitors was markedly less significant at higher extracellular pH. Moreover, dysfunction of the mitochondrial calcium handling greatly decreased CCE sensitivity to extracellular Ca2+ when the pH of extracellular solution was 7.2 (apparent Kd toward extracellular Ca2+ rose from 2.3 +/- 0.6 mm in control cells to 11.0 +/- 1.7 mM in CCCP-treated cells) as compared with pH 7.8 (apparent Kd toward extracellular Ca2+ increased from 1.3 +/- 0.4 mM in control cells to 2.4 +/- 0.4 mM in uncoupler-treated cells). Changes in intracellular pH triggered by methylamine did not influence Ca2+ influx. This suggests that, in Jurkat cells, store-operated calcium channels sense extracellular pH change as a parameter that modifies their sensitivity to intracellular Ca2+. In contrast, in human osteosarcoma cells, changes in extracellular pH as well as mitochondrial uncoupling did not exert any inhibitory effects on CCE.

Glass-Forming Tendency in the System Water–Dimethyl Sulfoxide

The glass-forming tendency on cooling and the stability of the wholly amorphous state on warming have been previously reported for many cryoprotective solutions. However, unlike the other solutions, those of dimethyl sulfoxide (Me2SO) have not been studied on cooling. In this paper, the glass-forming tendency of Me2SO aqueous solutions has been measured for solutions containing 40, 43, 45, and 47.5% (w/w) Me2SO. At a concentration of 45% (w/w), the glass-forming tendency decreases in the following order: levo-2,3-butanediol, 1,3-butanediol, 1,2-propanediol, 1,2,3-butanetriol, dimethyl sulfoxide, dimethylformamide, diethylformamide, 1,4-butanediol, ethylene glycol, glycerol, 1,3-propanediol. New measurements have also been made on warming the Me2SO solutions.

Rapid MR Imaging of Cryoprotectant Permeation in an Engineered Dermal Replacement

Magnetic resonance (MR) imaging is a powerful technique for monitoring the permeation of cryoprotective agents (CPAs) inside tissues. However, the techniques published until now suffer from inherently long imaging times, limiting the application of these techniques to slow diffusion processes and large CPA concentrations. In this study, we present a rapid MR imaging technique based on a CHESS-FLASH scheme combined with Keyhole image acquisition. This technique can image the fast permeation of Me2SO solutions into freeze-dried artificial dermal replacements for concentrations down to 10% v/v. Special attention is given to evaluating the technique for quantitative analysis.

Unusual pathways for the reaction between [MCl2(Me2SO)4] (M = Os, Ru) and hydrazine dihydrochloride: deoxygenation of sulfoxides vs. coordination of hydrazinium

Reaction of trans-[OsCl2(Me2SO)4] 1 with excess N2H4·2HCl leads to the osmium(III) compound mer-[OsCl3(NH3)2(Me2S)] 2 in the course of concerted reactions, i.e. oxidation of the metal, deoxygenation of the sulfoxide, disproportionation of hydrazine and substitution by NH3. In contrast, interaction of cis-[RuCl2(Me2SO)4] cis-3 with hydrazine dihydrochloride brings about easy substitution (without redox conversion) leading to mer-[RuCl3(N2H5)(Me2SO)2] 4 which is a rare example of a hydrazinium complex. X-Ray single-crystal diffraction analyses were performed on 1, 2 and 4. In 4, one Ru–S bond is unusually short due to the enhanced π bonding contribution as a result of an intramolecular H-bond between the Me2SO and the cis N2H5+ group. The complexes show anodic oxidations and 4, that in aqueous medium undergoes spontaneous dehydrochlorination, exhibits by controlled potential electrolysis a multi-electron oxidation process with anodically-induced H+ loss, oxidation of the hydrazine ligand to N2 and N-oxides, and of Me2SO to SO2. The anodic waves of Me2SO or H2O solutions of cis-3 were assigned to trans-[RuCl2(Me2SO-S)4] trans-3 and [RuCl(H2O)2(Me2SO-S)3]+, respectively. The oxidation potential values were interpreted on the basis of redox potential–structure relationships and the Lever electrochemical parameter EL was tentatively estimated for both S- and O-coordinated Me2SO and for the hydrazinium ligand, showing that Me2SO-S in our complexes behaves as a significant π-electron acceptor and N2H5+ as a rather weak net electron donor, and applied to predict the oxidation potential of some Ru and Os complexes.

Membrane Permeability Characteristics of Metaphase II Mouse Oocytes at Various Temperatures in the Presence of Me2SO

In this study, the hydraulic conductivity (Lp), Me2SO permeability (pMe2SO), and the reflection coefficients (ς) and their activation energies were determined for Metaphase II (MII) mouse oocytes by exposing them to 1.5 M Me2SO at temperatures of 30, 20, 10, 3, 0, and −3°C. These data were then used to calculate the intracellular concentration of Me2SO at given temperatures. Individual oocytes were immobilized using a holding pipette in 5 μl of an isosmotic PBS solution and perfused with precooled or prewarmed 1.5 M Me2SO solutions. Oocyte images were video recorded. The cell volume changes were calculated from the measurement of the diameter of the oocytes, assuming a spherical shape. The initial volume of the oocytes in the isoosmotic solution was considered 100%, and relative changes in the volume of the oocytes after exposure to the Me2SO were plotted against time. Mean (means ± SEM) Lpvalues in the presence of Me2SO (lMe2SOp) at 30, 20, 10, 3, 0, and −3°C were determined to be 1.07 ± 0.03, 0.40 ± 0.02, 0.18 ± 0.01, 7.60 × 10−2± 0.60 × 10−2, 5.29 × 10−2± 0.40 × 10−2, and 3.69 × 10−2± 0.30 × 10−2μm/min/atm, respectively. ThepMe2SOvalues were 3.69 × 10−3± 0.3 × 10−3, 1.07 × 10−3± 0.1 × 10−3, 2.75 × 10−4± 0.15 × 10−4, 7.83 × 10−5± 0.50 × 10−5, 5.24 × 10−5± 0.50 × 10−5, and 3.69 × 10−5± 0.40 × 10−5cm/min, respectively. The ς values were 0.70 ± 0.03, 0.77 ± 0.04, 0.81 ± 0.06, 0.91 ± 0.05, 0.97 ± 0.03, and 1 ± 0.04, respectively. The estimated activation energies (Ea) forlMe2SOp,pMe2SO, and ς were 16.39, 23.24, and −1.75 Kcal/mol, respectively. These data may provide the fundamental basis for the development of more optimal cryopreservation protocols for MII mouse oocytes.

Crystallization of Ice in Aqueous Solutions of Glycerol and Dimethyl Sulfoxide. 1. A Comparison of Mechanisms

The crystallization of ice from aqueous solutions of glycerol and dimethyl sulfoxide (Me2SO) has been studied using differential scanning calorimetry. In particular, the ice crystallization behavior of glycerol and Me2SO solutions containing approximately the same mole percent solute concentration (i.e., approximately 16 mol%) has been compared. These solutions (45 w/w% Me2SO (15.9 mol%) and 50 w/w% glycerol (16.4 mol%)) were shown to exhibit markedly different ice crystallization properties. For example, the peak homogeneous nucleation temperature of the Me2SO solution was observed to be 3°C aboveTg, whereas the peak homogeneous nucleation temperature of the glycerol solution was shown to be 20°C aboveTg. Further, the 50 w/w% glycerol solution was shown to devitrify at temperatures close to those of the peak nucleation rate, whereas the Me2SO solution was found to devitrify at temperatures much higher than the peak nucleation temperature. This, along with evidence from emulsion-based calorimetry experiments, indicates that the nucleation leading to devitrification in 45 w/w% Me2SO solutions is largely heterogeneous in nature.

Intramolecular hydrogen bonds in monosaccharides in dimethyl sulfoxide solution

By the use of the SIMPLE NMR method, strong intramolecular hydrogen bonds were found in the Me2SO solutions of sugars having two syn-axial hydroxy groups, like the talopyranoses. Weaker hydrogen bonds were detected between hydroxy groups in a 1,3-arrangement when one was outside the ring but only weak, although numerous, hydrogen bonds were detected in solutions of other sugars and inositols.

Cyclic Voltammetric and E.P.R. Spectroscopic Studies on Apical Substituent Effects in Radical Anions of 9-Substituted and 9,10-Disubstituted Nitroethanoanthracenes

Cyclic voltammetry and electron paramagnetic resonance spectroscopy were used to examine apical substituent effects on the properties of Me2SO solutions of the radical anions from 9-substituted and 9,10-disubstituted 2- and 3-nitro-9,10-dihydro-9,10-ethanoanthracenes (1)-(24). The reductions of the nitro group are, in general, reversible at 100 mV s-1 and at 20°, except where there are coupled intra-or inter-molecular electron or proton transfer reactions with aliphatic bridgehead substituents, such as a carboxylic acid or iodine. The substituent effects for the meta- and para-nitroethanoanthracene systems are both similar and additive. This similarity in the meta and para polar substituent effects is attributed to the orthogonality of the π*(ArNO2/ArNO2-) orbital with the σ* orbital of the carbon substituent (C-X) groups at the bridgehead positions. Overall, the meta substituent effect was slightly lower than that for corresponding simple meta-nitrobenzyl systems, but the para-nitro systems showed substituent effects that are a factor of 2 smaller than that for corresponding simple para-nitrobenzyl systems. These linear correlations between the substituent effects and redox potentials have been used to estimate the redox potentials of irreversible systems, which are required for digital simulations of reactions involving nitroaryl radical anions. Only small substituent effects are present in hyperfine coupling with the aliphatic and aromatic protons of the nitroaromatic radical anions of ethanoanthracenes (1)-(13), but a clear trend to lower nitrogen hyperfine values was observed with increasing electron-withdrawing ability of the apical substituent. In addition, no spin density was transferred to the benzylic bridgehead substituent in any of the nitro radical anions studied, clearly demonstrating that the bond between the bridgehead substituent and the carbon at a benzylic position is orthogonal to the π-system of the nitroaromatic ring bearing the odd electron.

A multinuclear NMR study of some mesoionic 1,3-dimethyltetrazoles, 1- and 2-methyltetrazoles and related compounds

Mesoionic 1,3-dimethyltetrazoles of the type A with sulfur, oxygen and nitrogen exocyclic groups, and related mono- and di-methylated tetrazoles have been investigated by means 1H, 13C, 14N and 15N NMR spectroscopy. The measurements were carried out in Me2SO and/or CF3CO2H solutions. The location of the protonation sites of the tetrazoles has been determined. The hydrogen atom is located on the exocyclic group of the mesoionic aminotetrazole 1, whereas the monomethylated and unsubstituted tetrazoles are protonated at the N-4 position (compounds 4,6, 8, 11–13). The monomethylated and non-ring substituted tetrazoles (compounds 4–8, 11–14 and 16) exist as non-mesoionic compounds, but compounds 1, 2, 9, 10 and 15 have a mesoionic structure.

Electrochemical Characteristics of the Copper(II)-Copper(I) Redox Couple in Dimethyl Sulfoxide Solutions

A study of the electrochemical characteristics of the copper(II)/copper(I) redox couple has been made in chloride and bromide media in dimethyl sulfoxide (Me2SO) and their aqueous analogues. The formal potentials of the CuII/CuI couple in the Me2SO media are approximately 0.15 V less positive than in their aqueous counterparts probably due to a combination of solvation and complexation effects. Diffusion coefficients for both CuI and CuII are 5-10 times lower in Me2SO than in H2O as a result of the higher viscosity of Me2SO solutions. Heterogeneous electron-transfer rate constants for the CuII/CuI system on platinum are also an order of magnitude smaller than in aqueous solution. In general the electrochemical characteristics of the CuII/CuI system parallel those reported elsewhere for the FeIII/FeII couple. However, a detailed investigation of the CuII/CuI system by cyclic voltammetry indicates that the overall electrode process is complex, probably involving a quasi-reversible electron-transfer step coupled to a rate-determining loss of Cl - from CuII.

13C NMR studies on the structure of aminosulfonic acids in dimethyl sulfoxide and water

AbstractThe 13C NMR spectra of three aminosulfonic acids (HA) [p‐aminobenzenesulfonic acid (sulfanilic acid), amino‐methanesulfonic acid and 2‐aminoethanesulfonic acid (taurine)] and their anions (A−) and cations (H2A+) were obtained using aqueous H2SO4, fuming H2SO4 and Me2SO solutions of trifluoromethanesulfonic acid. The chemical shifts of HA, A− and H2A+ and the protonation and deprotonation shifts of HA are compared with corresponding data for related amines and sulfonic acids in Me2SO and water. Our results indicate that the three aminosulfonic acids are essentially zwitterionic in Me2SO.

The small cage 12,17-dimethyl-5-oxa-1,9,12,17-tetra-azabicyclo[7.5.5]nonadecane (L): its synthesis, characterization, and ‘proton sponge’ behaviour. The crystal structure of the dipicrate salt [H2(L)](picrate)2

The synthesis and characterization of the new oxa-azamacrobicycloalkane 12,17-dimethyl-5-oxa-1,9,12,17-tetra-azabicyclo[7.5.5]nonadecane (L) are described. Its basicity behaviour in both aqueous and water–Me2SO (50:50 mol/mol) solutions has been investigated by potentiometric and spectroscopic (1H and 13C n.m.r.) techniques. In aqueous solution it behaves as a very strong base (proton sponge) in the first protonation step, and as a relatively strong base in the second step (log k2= 11.21). In the mixed water–Me2SO solvent both protonation constants have been measured: log k1= 14.0 and log k2= 8.2. 1H N.m.r. experiments indicate that in the monoprotonated species H(L)+ the proton is rapidly exchanged with acidic hydrogens on the n.m.r. timescale. 1H–1H and 1H–13C two-dimensional n.m.r. experiments allowed the unequivocal assignment for all the 1H proton and 13C resonances of both species H(L)+ and H2(L)2+. Crystals of [H2(L)](picrate)2 are monoclinic, space group P21/n, with a= 12.868(8), b= 17.201(2), c= 16.614(2)A, β= 110.18(1)°, and Z= 4; final R values of 0.090 (Rw= 0.090) for 3 801 observed reflections. The four basal nitrogen atoms and the apical oxygen atom are located at the apices of a slightly distorted square pyramid. X-Ray analysis shows that protonation occurs on the NCH3, groups. Each hydrogen atom of the NH+CH3 interacts with the oxygen atom, the 0 ⋯ H distances 2.328(16) and 2.112(18)A, and with both bridgehead nitrogen atoms, the H ⋯ N distances ranging from 2.32 to 2.34 A. This arrangement makes the overall structure very stable from the thermodynamic point of view and explains the unusually high basicity of (L) in both first- and second-protonation step.