Frequency response of the glucose sensor based on immobilized glucose oxidase membrane

Frequency response of the glucose sensor based on the immobilized glucose oxidase membrane was investigated experimentally by giving the sinusoidal change of glucose concentration to the glucose sensor and observing its output signal. Observed values of gains and phase lags of the frequency response of the glucose sensor followed the frequency response model of the first-order with dead time; The time constant and also the dead time were estimated and found to decrease as the amount of enzyme immobilized in the membrane increased and the thickness of the membrane decreased.

     

Self-assembly of programmed building blocks into structurally uniform dendrimers

Selective and independent dimerization of tri- and tetraurea derivatives was used to build up dendritic assemblies which are uniform in size and structure. Dendrimers with the total molecular masses of about 25 000 g/mol were obtained. The existence of uniform assemblies was proved by 1H and 1H DOSY NMR experiments and also by dynamic light scattering.     

The Sol-Gel Chemistry of Ferroelectric SrBi2Ta2O9 Thin Layers

A characterization of sol-gel precursors of SrBi₂Ta₂O₉ (SBT) has been carried out. Each molecular precursor, [SrBi_2+x Ta₂(OCH₂CH₂OCH₃)₁₈] _n (1) (x = 0.0, 0.2, and 0.4) and [SrTa₂(OEt)(O ⁱ Pr)₁₁( ⁱ PrOH)₂] (2) was prepared from the mixtures of Bi(OR)₃, Sr(OR)₂, and Ta(OR)₅ (R = Et, ⁱ Pr, and CH₂CH₂OCH₃), respectively. ¹H and ¹³C NMR spectroscopy and powder X-ray diffractometry have been used to characterize precursor molecules and their oxides, respectively. Especially, X-ray single crystal studies of complex 2 show that the molecule is made up of three octahedra; the central [SrO₆] octahedron is sharing two neighboring edges with the peripheral [TaO₆] ones. The SBT film derived from the precursor 1 presents outstanding ferroelectric properties (P _r = 9 C/cm²; E _c = 0.8 V).     

Self-assembled dendrimers with uniform structure

Calix[4]arenes substituted at their wide rim by four aryl urea residues (1) form hydrogen-bonded dimers in apolar solvents. Replacement of one urea residue by an acetamido moiety leads to calix[4]arene derivatives (5) which form hydrogen-bonded tetramers under the same conditions. Both self-assembly processes occur independently. Therefore, molecules have been prepared in which a tetra-urea calix[4]arene and a tri-urea mono acetamide derivative are covalently connected between their narrow rims by a long, mainly aliphatic chain [-O-(CH(2))(n)-C(O)-NH-(CH(2))(m)-O-] (7). In the presence of an equimolar amount of tetra-tosyl urea calix[4]arene () they form dendritic assemblies since the well known heterodimerization of tetra-tosyl and tetra-aryl urea calix[4]arenes prevents the formation of a cross-linked structure. Covalent connection of adjacent urea residues leads to tetra-loop derivatives (3) that cannot form homodimers, but instead form heterodimers with tetra-aryl or tetra-tosylureas. Therefore, similar dendrimers should be available using the selective dimerization observed for 3. The formation of a single, structurally uniform dendrimer from eight building blocks is confirmed by (1)H NMR spectra, showing only peaks that are also found for respective model assemblies. Translational diffusion coefficients of the assemblies have been determined using (1)H DOSY NMR.     

Probing molecular recognition in the solid-state by use of an enolizable chromophoric barbituric acid

Complex formation of the enolizable chromophor 1-n-butyl-5-(4-nitrophenyl)barbituric acid 1 with multiple binding sites for supramolecular assemblies and its corresponding adducts produced with the Proton Sponge (1,8-bis(dimethylamino)naphthalene), PS) and the adenine-mimetic 2,6-diacetamidopyridine (DAC) have been studied by means of solid-state proton NMR spectroscopy under fast magic-angle spinning, X-ray analysis, and UV/vis spectroscopy. Both NMR data and X-ray results reveal that the enolic chromophor undergoes self-aggregation to hydrogen-bonded dimers which are involved in stacked arrangements. Depending on the nature of the added base, this dimeric assembly is preserved in the formed enolate anion but can be broken in the presence of complementary hydrogen-bonding pattern leading to supramolecular complexes. Molecular recognition of these structural different bases significantly influences the chromophoric pi-system of 1.     

Synthesis of highly phenylene substituted p-phenylene oligomers from pyrylium salts

A transition metal free route to phenyl substituted oligophenylenes that tolerates halogens is described.