Investigation of the origin of selectivity in cavitand-based supramolecular sensors

The sensing properties of functionalized cavitands have been studied by thin-film coating TMSR chemical sensors and by measuring their responses towards model analytes. We studied the relationship between the sensor performance, in terms of sensitivity and selectivity, and the molecular recognition properties of the cavitands. The Langmuir-like shape of the adsorption isotherm, obtained in the case of short-chain alcohols, demonstrated that selective binding can be achieved by the synergistic interactions of the cavity and the bridging PO(in) groups. In the absence of these substituents, the peripheral alkyl chains necessary for the formation of highly permeable thin films attenuate the cavity effect because of nonspecific dispersion interactions. This completely overrides the response originating from molecular recognition. The same effect is observed when the PO groups are oriented outward from the cavity. The use of multivariate chemometrics and the study of the correlations between sensors sensitivity and analyte properties provided further evidence of molecular recognition phenomena, whose intensity is enhanced by the permanent free volume created by the rigid cavity surrounding the PO(in) group.     

Synthesis,spectroscopic and magnetic properties of copper complexes with a ligand containing the pyridoxal moiety

Summary Seven new copper(II)pyridoxal salicyloylhydrazone complexes have been prepared and characterized by vibrational and electronic spectra and magnetic measurements. The u.v. absorption band maxima are compared with those of metal chelates of Schiff bases obtained from condensation of pyridoxal with amines or amino acids.     

New materials: analytical and environmental applications in ion chromatography

This review details ion chromatography developments and related applications, mainly in the field of environmental analysis, gained by the evolution in the science and technology for new stationary phases. Unconventional approaches to ion chromatographic separations are also outlined.     

Liquid-liquid extraction of zirconium with tri-n-butyl-acetohydroxamic acid and spectrophotometric determination in the organic phase with xylenol orange

Zirconium (6–121 μg) is determined with xylenol orange after liquid-liquid extraction by tri-n-butylacetohydroxamic acid (TBAH) from 6 M hydrochloric acid. Under optimal conditions (primarily, 1 1:1.5 ratio of TBAH to xylenol orange, addition of acetic acid, and measurement at 545 nm), the calibration is linear with a molar absorptivity of 34 650 l mol^?1 cm^?1. Ions which are not extracted by TBAH or donot form coloured complexes do not interfere; these include uranium and rare-earth elements. Hafnium interferes; interference from thorium is avoided by a preliminary extraction of zirconium with tri-n-octylamine.     

Molecular mass determination of plasma-derived glycoproteins by ultraviolet matrix-assisted laser desorption/ionization time-of-flight mass spectrometry with internal calibration

Human plasma-derived antithrombin III (AT-III), factor IX (FIX) and vitronectin (VN) were characterized as native glycoproteins and in their de-N-glycosylated form by means of MALDI mass spectrometry. The average molecular masses of the three complex glycoproteins were determined applying internal calibration with high-mass, well-defined protein calibrants. Internal calibration generated for the 47 kDa yeast protein enolase a mass precision in the continuous and delayed extraction mode of +/-0.12 and +/-0.022%, respectively. The achievable mass accuracy for such a high-mass, unmodified protein was in the range of 0.02% in the continuous mode, which turned out to be better than in the delayed extraction mode. Purification of all (glyco) proteins (even the calibration proteins) by means of ZipTip technology and direct elution with a solvent system containing the appropriate MALDI matrix turned out to be a prerequisite to measure the exact molecular masses with an internal calibration. The average molecular masses of the two different forms of AT-III, namely AT-III(alpha) and AT-III(beta), were shown to be 57.26 and 55.04 kDa, respectively. The 2.22 kDa mass difference is attributed to the known difference in carbohydrate content at one specific site (Asn-135). After exhaustive de-N-glycosylation (by means of PNGase F) of the alpha- and beta-form and subsequent MALDI-MS analysis, average molecular masses of 48.96 and 48.97 kDa, respectively, were obtained. These values are in good agreement (-0.15%) with the calculated molecular mass (49.039 kDa) of the protein part based on SwissProt data. The molecular mass of the heavily post-translational modified glycoprotein FIX was found to be 53.75 kDa with a peak width at 10% peak height of 4.5 kDa, because of the presence of many different posttranslational modifications (N- and O-glycosylation at multiple sites, sulfation, phosphorylation, hydroxylation and numerous gamma-carboxyglutamic acids). MALDI-MS molecular mass determination of the native, size-exclusion chromatography-purified, VN sample revealed that the glycoprotein was present as dimer with molecular mass of 117.74 kDa, which could be corroborated by non-reducing SDS-PAGE. After sample treatment with guanidine hydrochloride and mass spectrometric analysis, a single, new main component was detected. The molecular mass turned out to be 59.45 kDa, representing the monomeric form of VN, known as V75. The determined molecular mass value was shown to be on one hand lower than from SDS-PAGE and on the other higher than the calculated amino acid sequence molecular mass (52 277 Da), pointing to the well-known SDS-PAGE bias and to considerable post-translational modifications. Further treatment of the sample with a reducing agent and subsequent MALDI-MS revealed two new components with molecular masses of 49.85 and 9.41 kDa, corresponding to V65 and V10 subunits of VN. PNGase F digest of the V75 and V65 units and MS analysis, exhibiting a molecular mass reduction of 6.37 kDa in both cases, verified the presence of a considerable amount of N-glycans.     

Determination of D-alanine and D-glutamic acid in biological samples by coupled-column chromatography using beta-cyclodextrin as mobile phase additive.

A high-performance liquid chromatographic assay for monitoring traces of D-alanine and D-glutamic acid in peptide and protein hydrolysates is presented, which uses a two-column set-up with column switching. The main advantage of the proposed method is the higher reliability of the results, compared with the analysis by derivatization and single-column chromatography of the diastereomers. A non-chiral alkyl-silica reversed-phase column is combined with a second column, in which beta-cyclodextrin is used as a chiral mobile phase additive. The amino acids of the hydrolysate are dansylated, and the amino acid of interest is separated from the others on the first column and transferred to the second column where chiral resolution is performed. The transfer volume of ca. 200 microliters is small enough not to cause any peak distortion or dilation in the second column.     

Characterization of cysteinylation of pharmaceutical-grade human serum albumin by electrospray ionization mass spectrometry and low-energy collision-induced dissociation tandem mass spectrometry

Three samples of albumin derived from human plasma (pharmaceutical grade, HSA) obtained from different commercial sources were investigated for their micro-heterogeneities by means of electrospray ionization (ESI) ion trap mass spectrometry (ITMS). The study covered MS analyses of the intact proteins as well as on the tryptic peptide level. The intact protein samples were analyzed without any separation step except for simple desalting. With these samples we observed in the positive ion ESI mass spectra that the multiply charged ion signals of HSA consisted of a number of fully or partly resolved peaks with relative intensities depending on the analyzed sample. The non-modified form of HSA was detected in the three HSA preparations at m/z values of 66448 +/- 3.6, 66450 +/- 0.6 and 66451 +/- 3.2 ([MH]+), respectively. The value calculated from the amino acid sequence was 66439. The second compound present with high intensity (in two cases the base peak in the deconvoluted mass spectrum) is interpreted as a modified HSA, and the molecular mass increase in relation to the unmodified HAS was between 116 and 118 Da (m/z of 66 564, 66 567 and 66 569), suggesting the presence of a covalently bound cysteine residue. A further peak in the deconvoluted ESI spectra was found in all three samples with rather low signal/noise ratio at m/z 66 619, 66 621 and 66 613, respectively, which may correspond to a non-enzymatic glycation described in the literature. The verification of the proposed covalent HSA modifications was subsequently done on the peptide level using high-performance liquid chromatography (HPLC)/ESI-MS and HPLC/ESI-MS/MS including low-energy collision-induced dissociation (CID). Prior to the tryptic digestion, the HSA samples were alkylated without a prior reduction step. Following this procedure we detected peptides of the sequence T21-41 that included the Cys-34 residue in both forms: cysteinylated (m/z 639.15 [M+4H]4+) as well as vinylpyridine-alkylated (m/z 635.69 [M+4H]4+, which means in its previously native free SH form). In the next step on-line LC/ESI low-energy CID MS/MS experiments were performed to verify these two proposed structures. By means of MS/MS analysis of the mentioned ions the described modification (cysteinylation) at the Cys-34 residue could be proven. This abundant modification of HSA in pharmaceutical-grade preparations could be unambiguously identified as cysteinylation at the Cys-34 residue. On the other hand, the proposed non-enzymatic glycation was not detectable on the peptide level in the on-line HPLC/ESI-MS mode, maybe due to the low concentration in the three samples under investigation.     

Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 3. A new highly electron-deficient octacationic macrocycle: tetrakis-2,3-[5,6-di{2-(N-methyl)pyridiniumyl}pyrazino]porphyrazine, [(2-Mepy)8TPyzPzH(2)]8+

A new octacationic macrocycle, tetrakis-2,3-[5,6-di{2-(N-methyl)pyridiniumyl}pyrazino]porphyrazine, was obtained in its hydrated form as the water-soluble iodide salt. This compound, abbreviated as [(2-Mepy)(8)TPyzPzH(2)](I(8)).8H(2)O (2-Mepy = 2(N-methyl)pyridiniumyl moiety), was obtained by demetalation of the corresponding Mg(II) complex, [(2-Mepy)(8)TPyzPzMg(H(2)O)](I(8)).5H(2)O, which in turn was prepared from its corresponding neutral hydrated species tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato(monoaquo)magnesium(II), [Py(8)TPyzPzMg(H(2)O)].4H(2)O, by reaction with CH(3)I in N,N-dimethylformamide. The quaternization reactions by using CH(3)I or methyl p-toluenesulfonate were also conducted on the monomeric precursor 2,3-dicyano-5,6-di(2-pyridyl)-1,4-pyrazine, [(CN)(2)Py(2)Pyz], with formation of the monoquaternized ion [(CN)(2)Py(2-Mepy)Pyz](+) neutralized by iodide and p-toluenesulfonate anions. Single-crystal X-ray work allowed elucidation of the structure of the two salt-like species. The diquaternized ion [(CN)(2)(2-Mepy)(2)Pyz](2+) could also be obtained as a p-toluenesulfonate salt, but attempts at direct macrocyclization of this dicationic species were unsuccessful. The iodide salt [(2-Mepy)(8)TPyzPzH(2)](I(8)).8H(2)O is water-soluble, with different solubilities depending on the range of pH explored. It was established that the macrocycle [(2-Mepy)(8)TPyzPzH(2)](8+) undergoes facile deprotonation and behaves as a strong acid. Aggregation phenomena are observed for both the octacation [(2-Mepy)(8)TPyzPzH(2)](8+) and its corresponding centrally deprotonated species [(2-Mepy)(8)TPyzPz](6+). Nevertheless, both cationic moieties exist in their monomeric form under specific experimental conditions. UV-visible monitored titrations with NaOH provide information about the type of protonation/deprotonation equilibria which are complicated by the occurrence of aggregation phenomena.     

Structural researches on metal complexes of polydentate ligands containing carbonyl and α-diimine moieties,part V. Heptacoordination in a manganese(II) complex of 2,6-diacetylpyridinebis(picolinoylhydrazone)

Summary The MnCl₂ (H₂ DIP) · 5H₂O complex [H₂DIP = 2,6-diacetyl-pyridinebis(picolinoylhydrazone)] has been synthesized and examined by i.r.-spectroscopy and x-ray diffractometry. Crystals are triclinic (P ) with unit-cell dimensions: = 15.00(1),b= 13.65(1),c = 7.565(6) Å, = 92.4(1), = 97.5(1), = 117.5(1)°; Z = 2. The structure was solved from 1788 independent diffractometer data by direct methods and refined anisotropically by block-diagonal leastsquares calculations toR = 5.4%. The manganese ion has a distorted pentagonal-bipyramidal geometry, in which the organic molecule acts as a pentadentate ligand. A disordered distribution involving chlorine ions and water molecules is present.Part. IV. Ref. 2.