Estimation of uncertainty in routine pH measurement

A procedure for estimation of measurement uncertainty of routine pH measurement (pH meter with two-point calibration, with or without automatic temperature compensation, combination glass electrode) based on the ISO method is presented. It is based on a mathematical model of pH measurement that involves nine input parameters. Altogether 14 components of uncertainty are identified and quantified. No single uncertainty estimate can be ascribed to a pH measurement procedure: the uncertainty of pH strongly depends on changes in experimental details and on the pH value itself. The uncertainty is the lowest near the isopotential point and in the center of the calibration line and can increase by a factor of 2 (depending on the details of the measurement procedure) when moving from around pH 7 to around pH 2 or 11. Therefore it is necessary to estimate the uncertainty separately for each measurement. For routine pH measurement the uncertainty cannot be significantly reduced by using more accurate standard solutions than ±0.02 pH units – the uncertainty improvement is small. A major problem in estimating the uncertainty of pH is the residual junction potential, which is almost impossible to take rigorously into account in the framework of a routine pH measurement.¹ Received: 11 August 2001 Accepted: 22 February 2002     

Solvent-mediated self-association of a Horning-crown macrocycle

A member of a new class of novel macrocycles possessing both polyether and phenolic functionalities, forms dimers in both the solid-state and in solution when exposed to chloroform, dichloromethane or toluene, but does not self-associate in the presence of dimethyl sulfoxide.     

Short and stereoselective synthesis of C-glycosylated glycine derivatives from glycals by radical addition and reduction

Only three steps are required for the convenient synthesis of 2-C-branched glyco-amino acids from glycals with good yields and stereoselectivities.     

Haplotype studies support slippage as the mechanism of germline mutations in short tandem repeats

Germline mutations of human short tandem repeat (STR) loci are expansions or contractions of repeat arrays which are not well understood in terms of the mechanism(s) underlying such mutations. Although polymerase slippage is generally accepted as a mechanism capable to explain most features of such mutations, it is still possible that unequal crossing over plays some role in those events, as most studies in humans could not exclude unequal crossing over (UCO). Crossing over can be studied by analyzing haplotypes using flanking markers. To check for UCO in mutations, we have analyzed 150 paternity cases for which more than the usual trio (mother, child, and father) were available for testing by analyzing 16 STR loci. In a total of 4900 parent-child allele transfers four mutations were observed at different loci (D8S1179, D18S51, D21S11, and SE33/ACTBP2). To identify the mutated allele and to check for UCO, we typed at least four informative loci flanking the mutated locus and used the pedigree data to establish haplotypes. By doing so we were able to exclude UCO in each case. Moreover, we were able to identify the mutations as one-repeat contractions/expansions. Our data thus support slippage as the mechanism of germline mutations in STRs.     

Incremental Tuning Up of Fluorous Phenazine Acceptors

In a simple, one‐step direct trifluoromethylation of phenazine with CF₃I we prepared and characterized nine (poly)trifluoromethyl derivatives with up to six CF₃ groups. The electrochemical reduction potentials and gas‐phase electron affinities show a direct, strict linear relation to the number of CF₃ groups, with phenazine(CF₃)₆ reaching a record‐high electron affinity of 3.24 eV among perfluoroalkylated polyaromatics.     

Copper Causes Regiospecific Formation of C4F8‐Containing Six‐Membered Rings and their Defluorination/Aromatization to C4F4‐Containing Rings in Triphenylene/1,4‐C4F8I2 Reactions

The presence of Cu in reactions of triphenylene (TRPH) and 1,4‐C₄F₈I₂ at 360 °C led to regiospecific substitution of TRPH ortho C(β) atoms to form C₄F₈‐containing rings, completely suppressing substitution on C(α) atoms. In addition, Cu caused selective reductive‐defluorination/aromatization (RD/A) to form C₄F₄‐containing aromatic rings. Without Cu, the reactions of TRPH and 1,4‐C₄F₈I₂ were not regiospecific and no RD/A was observed. These results, supported by DFT calculations, are the first examples of Cu‐promoted 1) regiospecific perfluoroannulation, 2) preparative C?F activation, and 3) RD/A. HPLC‐purified products were characterized by X‐ray diffraction, low‐temperature PES, and ¹H/¹⁹F NMR.     

Activity of AC electrokinetically immobilized horseradish peroxidase

Dielectrophoresis (DEP) is an AC electrokinetic effect mainly used to manipulate cells. Smaller particles, like virions, antibodies, enzymes, and even dye molecules can be immobilized by DEP as well. In principle, it was shown that enzymes are active after immobilization by DEP, but no quantification of the retained activity was reported so far. In this study, the activity of the enzyme horseradish peroxidase (HRP) is quantified after immobilization by DEP. For this, HRP is immobilized on regular arrays of titanium nitride ring electrodes of 500 nm diameter and 20 nm widths. The activity of HRP on the electrode chip is measured with a limit of detection of 60 fg HRP by observing the enzymatic turnover of Amplex Red and H₂O₂ to fluorescent resorufin by fluorescence microscopy. The initial activity of the permanently immobilized HRP equals up to 45% of the activity that can be expected for an ideal monolayer of HRP molecules on all electrodes of the array. Localization of the immobilizate on the electrodes is accomplished by staining with the fluorescent product of the enzyme reaction. The high residual activity of enzymes after AC field induced immobilization shows the method's suitability for biosensing and research applications.     

High-Entropy Lithium Argyrodite Solid Electrolytes Enabling Stable All-Solid-State Batteries

Superionic solid electrolytes (SEs) are essential for bulk-type solid-state battery (SSB) applications. Multicomponent SEs are recently attracting attention for their favorable charge-transport properties, however a thorough understanding of how configurational entropy (ΔS_conf) affects ionic conductivity is lacking. Here, we successfully synthesized a series of halogen-rich lithium argyrodites with the general formula Li_5.5PS_4.5Cl_xBr_1.5-x (0≤x≤1.5). Using neutron powder diffraction and ³¹P magic-angle spinning nuclear magnetic resonance spectroscopy, the S²⁻/Cl⁻/Br⁻ occupancy on the anion sublattice was quantitatively analyzed. We show that disorder positively affects Li-ion dynamics, leading to a room-temperature ionic conductivity of 22.7 mS cm⁻¹ (9.6 mS cm⁻¹ in cold-pressed state) for Li_5.5PS_4.5Cl_0.8Br_0.7 (ΔS_conf=1.98R). To the best of our knowledge, this is the first experimental evidence that configurational entropy of the anion sublattice correlates with ion mobility. Our results indicate the possibility of improving ionic conductivity in ceramic ion conductors by tailoring the degree of compositional complexity. Moreover, the Li_5.5PS_4.5Cl_0.8Br_0.7 SE allowed for stable cycling of single-crystal LiNi_0.9Co_0.06Mn_0.04O₂ (s-NCM90) composite cathodes in SSB cells, emphasizing that dual-substituted lithium argyrodites hold great promise in enabling high-performance electrochemical energy storage.