Acid-base and lipophilic properties of peptide nucleic acid derivatives

The first combined experimental and theoretical study on the ionization and lipophilic properties of peptide nucleic acid(PNA)derivatives,including eleven PNA monomers and two PNA decamers,is described.The acidity constants(pKa)of individual acidic and basic centers of PNA monomers were measured by automated potentiometric pH titrations in water/methanol solution,and these values were found to be in agreement with those obtained by MoKa software.These results indicate that single nucleobases do not change their pKa values when included in PNA monomers and oligomers.In addition,immobilized artificial membrane chromatography was employed to evaluate the lipophilic properties of PNA monomers and oligomers,which showed the PNA derivatives had poor affinity towards membrane phospholipids,and confirmed their scarce cell penetrating ability.Overall,our study not only is of potential relevance to evaluate the pharmacokinetic properties of PNA,but also constitutes a reliable basis to properly modify PNA to obtain mimics with enhanced cell penetration properties.

A New Approach to Carbonate Alkalinity

The article provides experimental data applied to the determination of carbonate alkalinity (CAM) according to modified Gran II functions. CAM is related to the mixtures NaHCO3 + Na2CO3 and Na2CO3 + NaOH. In addition to the determination of equivalence volumes, one of the main novelties of the proposed method is the possibility of determining the activity coefficient of hydrogen ions (γ). Moreover, CAM can be used to calculate the dissociation constants (K1, K2) for carbonic acid and the ionic product of water (KW) from a single pH titration curve. The parameters of the related functions are calculated according to the least squares method.

Inflection Points on Some S-Shaped Curves

This paper refers to inflection point—the fundamental property of S-shaped curves. In this paper, the inflection points are related to pH titration curve pH = pH(V), and to the curve s = s(pH) involved with surface tension, s.

Formulation of the System of Isohydric Solutions

The isohydricity (pH constancy) as the property referred to mixtures of acids or bases, is illustrated on a simple example of the solutions: HL (C0, mol/L) and HL (C mol/L) mixed according to titrimetric mode (pH titration). A new derivation of the Michalowski formula C0=C+C2·10PK1 expressing this property is presented, and its applicability for determination of pK1 = – logK1 value is indicated. The principle of the isohydric method of pK1 determination is also outlined.

Determining short chain fatty acids in sewage sludge hydrolysate: A comparison of three analytical methods and investigation of sample storage effects

In anaerobic digestion, the production of short-chain fatty acids （SCFAs） can be beneficial or harmful to the overall process, depending on the concentration of accumulated acids. Therefore, the accurate determination of the SCFA concentration in both fresh and stored sludge hydrolysates is important. To select a suitable method for monitoring SCFAs during the anaerobic digestion of sewage sludge, the accuracy of three available analytical methods, including 5 pH point acid titration （TITRA5）, gas chromatography （GC）, and spectrophotometry, were compared in the present study. The results revealed that TITRA5 and GC displayed better agreement in the achieved measurements and higher precision and accuracy than the spectrophotometric assay, as supported by the application of different statistical models. TITRA5 excelled in titrating unfiltered hydrolysate while simultaneously measuring the alkalinity, whereas the GC method provided detailed information on the contribution of different fatty acids to the total acidity. In contrast, the spectrophotometric assay suffered from many forms of interference, depending on the sample＇s matrix. SCFA production followed the pattern of enzymatic reactions and fitted the Michaelis-Menten model. In addition to promoting TITRA5 as an accurate and robust analytical tool for routine SCFA analyses, this comparative study also demonstrated the possibility of storing hydrolysate samples at different temperatures and durations without altering the SCFA measurements.