Simple method for determining the amount of ion-exchange groups on chromatographic supports

The objective of this study was to develop a fast, simple, non-destructive, non-toxic and low-priced method for determining the amount of ionic groups on resins, since the conventional titration method fails to give proper results on methacrylate monoliths. After the column had been pre-saturated with a high concentration buffer solution, a low concentration buffer solution of the same pH value was pumped through the column. Measuring pH and absorbance, the profiles with a shape of typical break-through curve were obtained. It was shown that the time of the pH transient, which appeared under such conditions, could be used as a measure of the total ionic capacity of ion-exchange monolithic columns. The effect of the column length, linear velocity and varying concentrations of buffer solutions on the time of the pH transient was examined. The method was shown to be suitable for determining the amount of ionic groups on both anion and cation monolithic columns. In addition, it could also be applied to particle bed columns. The time of the pH transient and the protein dynamic binding capacity were also compared and it was concluded that for a given monolith the protein capacity can be derived from the data obtained by the new method.     

Bridged Polysilsesquioxane Xerogels Functionalizated by Amine- and Thiol- Groups: Synthesis, Structure, Adsorption Properties

Bridged polysilsesquioxane xerogels containing amine (–NH₂; –NH(CH₂)₂NH₂; —NH) and thiol (–SH) groups were synthesized by hydrolytic polycondensation of 1,2-bis(triethoxysilyl)ethane, 1,4-bis(triethoxysilyl)benzene and appropriate trifunctionalized silanes in the presence of a fluoride-ion catalyst in an ethanol solution. ²⁹Si CP/MAS NMR give indication of the molecular framework of these materials formed by structural T¹, T² and T³ units. 3-aminopropyl or 3-mercaptopropyl groups accessible to proton or metal ions are fixed to the xerogel surface by the siloxane bonds. IR and ¹³C CP/MAS NMR data clearly show that 3-aminopropyl groups form hydrogen bonds. The same data testify that all xerogels contain non-condensed silanol groups and some fraction of non-hydrolyzed ethoxygroups. Functionalized polysilsesquioxane xerogels obtained by means of organic spacers have a porous structure (500–1000 m²/g) and a high content of functional groups (1.0–2.7 mmol/g). AFM data indicate that xerogels are formed by aggregating primary particles—the size of such aggregates is in the range 30–65 nm. It was established that the main factors influencing the structure and adsorption properties considered hybrid materials are: the nature and geometrical size of the functional groups, spacer flexibility and, in some cases, the ratio of the reacting alkoxysilanes and the ageing time of the gel.     

Solid-phase enolate chemistry investigated using HR-MAS NMR spectroscopy.

Supported P4-t-Bu enolate chemistry of phenylacetyloxymethyl polystyrene (PS) resin was investigated using high-resolution magic angle spinning (HR-MAS) NMR spectroscopy. Direct analysis of the crude reaction suspensions through the use of a diffusion filter (DF) allowed a rapid selection of the optimal experimental conditions, but also the characterization of the enolate on the solid phase. Comparison with solution experiments and literature data allowed us to address partially the structure of the enolate. HR-MAS NMR spectra of the enolate revealed also a tight interaction of P4-t-Bu base with the polymer matrix.     

Selten‐Erd‐Metall‐Koordinationspolymere: Synthese und Kristallstrukturen von fünf neuen Adipinaten, [M2(Adi)3(H2O)4](AdiH2)(H2O)4 (M = La,Nd), [Er(Adi)(H2O)5]Cl(H2O) und [M(Adi)(H2O)5](NO3)(H2O) (M = Gd,Er)

Rare‐Earth‐Metal Coordination Polymers: Synthesis and Crystal Structures of Five New Adipinates, [M₂(Adi)₃(H₂O)₄](AdiH₂)(H₂O)₄ (M = La, Nd), [Er(Adi)(H₂O)₅]Cl(H₂O) and [M(Adi)(H₂O)₅](NO₃)(H₂O) (M = Gd, Er) The new rare‐earth compounds [M₂(Adi)₃(H₂O)₄](AdiH₂)(H₂O)₄ (M = La ( 1 ), Nd ( 2 )), [Er(Adi)(H₂O)₅]Cl(H₂O) ( 3 ) and [M(Adi)(H₂O)₅](NO₃)(H₂O) (M = Gd ( 4 ), Er ( 5 )) were obtained from the reaction of adipinic acid with La(OH)₃·xH₂O, Nd₂O₃, ErCl₃·6H₂O, Gd(NO)₃·xH₂O and Er₂O₃, respectively. Their crystal structures were determined by single‐crystal X‐ray diffraction. The coordination polymers [M₂(Adi)₃(H₂O)₄](AdiH₂)(H₂O)₄ crystallize in the triclinic space group (no. 2) with a = 875.4(1), b = 1000.4(2), c = 1179.0(2) pm, α = 74.70(1), β = 69.85(1), γ = 86.18(2)° and Z = 1 (crystal data for M = La, ( 1 )). The quasi‐isostructural compounds [Er(Adi)(H₂O)₅]Cl(H₂O) ( 3 ) and [M(Adi)(H₂O)₅](NO₃)(H₂O) (M = Gd ( 4 ), Er ( 5 )) crystallize with monoclinic symmetry, space group C2/c (no. 15) with lattice parameters of a = 1231.5(1), b = 1532.6(1), c = 895.4(1) pm, β = 123.44(1)° and Z = 4 (crystal data for ( 3 )). The rare‐earth cations have the coordination numbers 10 ( 1 , 2 ) and 9 ( 3 , 4 and 5 ), respectively. The compounds [M₂(Adi)₃(H₂O)₄](AdiH₂)(H₂O)₄ are constructed of infinite chains of edge‐sharig [MO₈(H₂O)₂] polyhedra that are cross‐linked by adipinic acid molecules to form framework structures. In [Er(Adi)(H₂O)₅]Cl(H₂O) ( 3 ) and [M(Adi)(H₂O)₅](NO₃)(H₂O) (M = Gd ( 4 ), Er ( 5 )) the central cations are bridged by adipinic acid molecules in a bidentate‐chelating manner to positively charged zigzag chains. Between these the counter ions and crystal water molecules are incorporated.     

(η2-Allyl­ammonium)­aqua­bis­(sulfam­ato-N)copper(I)

The Cu^I atom in the title complex, [Cu(NH₂SO₃)₂(C₃H₈N)(H₂O)], is coordinated by the C=C bond of the allyl­ammonium cation, two N atoms of the sulfamate anions and the O atom of the H₂O mol­ecule in the apical position. Thus, the central atom is in a distorted trigonal–pyramidal environment. Strong N—H⃛O and O—H⃛O contacts connect separate moieties of the complex into a three-dimensional framework. The title compound is representative of hitherto unknown copper(I)–sulfamate π-complexes.     

The ozonation of silanes and germanes: an experimental and theoretical investigation

Ozonation of various silanes and germanes produced the corresponding hydrotrioxides, R3SiOOOH and R3GeOOOH, which were characterized by 1H, 13C, 17O, and 29Si NMR, and by infrared spectroscopy in a two-pronged approach based on measured and calculated data. Ozone reacts with the E-H (E = Si, Ge) bond via a concerted 1,3-dipolar insertion mechanism, where, depending on the substituents and the environment (e.g., acetone-d6 solution), the H atom transfer precedes more and more E-O bond formation. The hydrotrioxides decompose in various solvents into the corresponding silanols/germanols, disiloxanes/digermoxanes, singlet oxygen (O2(1delta(g))), and dihydrogen trioxide (HOOOH), where catalytic amounts of water play an important role as is indicated by quantum chemical calculations. The formation of HOOOH as a decomposition product of organometallic hydrotrioxides in acetone-d6 represents a new and convenient method for the preparation of this simple, biochemically important polyoxide. By solvent variation, singlet oxygen (O2(1delta(g))) can be generated in high yield.     

Refinement of hydrogen positions in (NH4)2SeO4

The crystal structure of ammonium selenate has been studied by means of single crystal x-ray and neutron diffraction with the purpose of the refinement of hydrogen positions. The refined hydrogen positions obtained by single crystal neutron diffraction show that N-H bond lengths form a regular tetrahedron in an ammonium ion. The single crystal x-ray diffraction data show that N-H bond lengths are shorter than those obtained by neutron diffraction and are not equal between themselves. Thus, the comparison of the results of x-ray and neutron diffraction allows one to suggest that the shorter N-H bond lengths obtained by x-ray diffraction reflect the distribution of the electron charge density of ammonium ions within the (NH₄)₂SeO₄ crystal lattice. The text was submitted by the authors in English.     

Chemical and chromatographic stability of methacrylate-based monolithic columns

Chemical and chromatographic stability of methacrylate-based monolithic columns bearing 3-N,N-diethylamino-2-hydroxypropyl (DEAE) and quarternary amine (QA) groups was studied. The leakage products from both monolithic columns were determined and the leakage of amines has been quantified in alkali solutions. Monolithic columns bearing QA functional groups being exposed to 1M sodium hydroxide solution for up to 3 months caused reduction of ion-exchange groups for approximately 12%, while for DEAE monolithic columns was only around 3% in 1 year. In 0.1M NaOH and 20% ethanol degradation was significantly lower. The main leaking compound from DEAE monolith was found to be 3-(diethylamino)-1,2-propanediol and 2,3-dihydroxypropyltrimethylammonium salt for QA monolith. During repeated 50 cleaning-in-place (CIP) cycles, no changes in chromatographic properties were detected.     

Synthesis of thiazolidine thioester peptides and acceleration of native chemical ligation

Thiazolidine thioester peptides were synthesized by reacting bis(2-sulfanylethyl)amido peptides with glyoxylic acid at pH 1. A significant increase in Native Chemical Ligation (NCL) rate was observed with thiazolidine thioesters compared to 3-mercaptopropionic acid-thioester analogues. The method is of particular interest for accelerating valine-cysteine peptide bond formation.