- Biotechnology, Bioinformatics, Molecular Biology, Biochemistry, Immunology, Weed Science, and 13 morePlant Architecture, Sex steroid hormones, Immunophillins, ABC transporters, Plant Science, Crop improvements, Crop Production, Crop Protection, Sustainable Food Systems, Marker assisted plant breeding, Cultural Weed Management, Climate change and sustainable food production, and Genetics and Plant Breedingedit
The influence of terminal functionalization of oligo(ε-caprolactone)s (OCL) with phenylboronic acid pinacol ester or phenylboronic acid on the enzymatic degradation behavior at the air-water interface is investigated by the Langmuir... more
The influence of terminal functionalization of oligo(ε-caprolactone)s (OCL) with phenylboronic acid pinacol ester or phenylboronic acid on the enzymatic degradation behavior at the air-water interface is investigated by the Langmuir monolayer degradation technique. While the unsubstituted OCL immediately degrades after injection of the enzyme lipase from Pseudomonas cepacia, enzyme molecules are incorporated into the films based on end-capped OCL before degradation. This incorporation of enzymes does not inhibit or suppress the film degradation, but retards it significantly. A specific binding of lipase to the polymer monolayer allows studying the enzymatic activity of bound proteins and the influence on the degradation process. The functionalization of a macromolecule with phenyl boronic acid groups is an approach to investigate their interactions with diol-containing biomolecules like sugars and to monitor their specified impact on the enzymatic degradation behavior at the air-wat...
Research Interests:
Research Interests:
The applicability of nulling-based ellipsometric mapping as a complementary method next to Brewster angle microscopy (BAM) and imaging ellipsometry (IE) is presented for the characterization of ultrathin films at the air-water interface.... more
The applicability of nulling-based ellipsometric mapping as a complementary method next to Brewster angle microscopy (BAM) and imaging ellipsometry (IE) is presented for the characterization of ultrathin films at the air-water interface. First, the methodology is demonstrated for a vertically nonmoving Langmuir layer of star-shaped, 4-arm poly(ω-pentadecalactone) (PPDL-D4). Using nulling-based ellipsometric mapping, PPDL-D4-based inhomogeneously structured morphologies with a vertical dimension in the lower nm range could be mapped. In addition to the identification of these structures, the differentiation between a monolayer and bare water was possible. Second, the potential and limitations of this method were verified by applying it to more versatile Langmuir layers of telechelic poly[(rac-lactide)-co-glycolide]-diol (PLGA). All ellipsometric maps were converted into thickness maps by introduction of the refractive index that was derived from independent ellipsometric experiments, and the result was additionally evaluated in terms of the root mean square roughness, Rq. Thereby, a three-dimensional view into the layers was enabled and morphological inhomogeneity could be quantified.
Research Interests:
Research Interests:
We report on a light-induced isothermal transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the degree of mechanical anisotropy can be controlled by light. Whereas during irradiation by circular... more
We report on a light-induced isothermal transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the degree of mechanical anisotropy can be controlled by light. Whereas during irradiation by circular polarized light the film behaves as an isotropic viscoelastic fluid, it displays considerable fluidity only in the direction parallel to the light field vector under linear polarized light, demonstrating thus extraordinarily anisotropic mechanical properties. The fluidisation phenomenon is related to photoinduced motion of azobenzene-functionalised molecular units, which can be effectively activated only when their transition dipole moments are oriented close to the direction of the light polarization. Along with the phenomenological finding, our work allows us to make a substantial step in understanding the mass transport effect in azobenzene containing systems under conditions of far- and near-field illumination.
Research Interests:
ABSTRACT Poly(2,2-dimethyl-3,4-propylenedioxythiophene) (PProDOT-Me2) thin films have been cyclovoltammetrically coated onto carbon fibre electrode as an active functionalised microelectrode. An electrochemical impedance study on the... more
ABSTRACT Poly(2,2-dimethyl-3,4-propylenedioxythiophene) (PProDOT-Me2) thin films have been cyclovoltammetrically coated onto carbon fibre electrode as an active functionalised microelectrode. An electrochemical impedance study on the prepared electrodes is reported in the present paper under different applied potentials during electrochemical impedance spectroscopic measurements. The capacitive behaviour of the PProDOT-Me2 coated carbon fibre microelectrode was investigated by cyclic voltammetry of polymer in monomer free solution which agreed with the capacitance obtained from electrochemical impedance spectroscopy. The film thickness for the cyclovoltammetrically prepared polymer film was in the range of about 30–50 nm. The electrochemical impedance data fitted two equivalent circuit models were used to find out numerical values of the proposed components. The effect of the deposition charge on the capacitive behaviour of the film was also investigated.
Research Interests:
Research Interests:
Octakis(2,3,6-tri-O-methyl)-γ-CD (TRIMEG) cocrystallized at 18 °C with 4.5 water molecules in the orthorhombic space group P212121, unit cell dimensions a=10.7879(3), b=29.0580(9), c=32.2909(11) Å. The TRIMEG macrocycle is in a ‘round’... more
Octakis(2,3,6-tri-O-methyl)-γ-CD (TRIMEG) cocrystallized at 18 °C with 4.5 water molecules in the orthorhombic space group P212121, unit cell dimensions a=10.7879(3), b=29.0580(9), c=32.2909(11) Å. The TRIMEG macrocycle is in a ‘round’ form with all glucose units oriented syn, and one O-6CH3 methoxy group points ‘toward’ the molecular cavity. The TRIMEG·4.5 H2O molecules are stacked to form infinite cylinders with the central cavities aligned into channels filled for each TRIMEG by 4.5 water molecules distributed over 15 partially occupied sites. This structure differs from the two known structures of TRIMEG in which two diametrically opposed glucoses are oriented anti to yield an ‘elliptical’ form, and their O-6CH3 groups are directed ‘toward’ the cavity and close it at this side to form a bowl-shaped molecule.
Research Interests:
ABSTRACT The spectroscopic properties of 1-phenyl-3-benzothiazol-2-yl-5-(4-R-phenyl)-Delta(2)-pyrazolines are strongly dependent on both the electronic nature of the substituent R and solvent polarity. As revealed by spectroscopic studies... more
ABSTRACT The spectroscopic properties of 1-phenyl-3-benzothiazol-2-yl-5-(4-R-phenyl)-Delta(2)-pyrazolines are strongly dependent on both the electronic nature of the substituent R and solvent polarity. As revealed by spectroscopic studies as a function of solvent polarity as well as temperature, for electron-rich amino donor substituents in polar solvents, deactivation of the strongly emissive charge transfer (CT) state of the basic 1-phenyl-3-benzothiazol-2-yl-Delta(2)-pyrazoline chromophore has to compete with a fast intramolecular electron transfer (ET) quenching reaction. In the case of the dimethylamino derivative (R DMA), the rate constant of ET in acetonitrile was determined to k(et) = 3 x 10(10) s(-1). This ET process can be utilized for metal ion sensing by introducing nitrogen containing aza crown ether receptor units to the if-position of the 5-phenyl group. The spectroscopically determined ET rates of the 5-(N-alkyl)amino substituents, a DMA, a tetrathia- (AT(4)15C5), and a tetraoxa-monoaza-15-crown-5 (A15C5) group, correlate with electrochemical data and increase in the order AT(4)15C5 < A15C5 < DMA. The metal ion sensing abilities of the two crowned derivatives are presented, and the different signaling mechanisms include binding to the crown ether in the 4-R position, chelate formation in the 3-benzothiazol-2-yl-Delta(2)-pyrazoline moiety, and electrophotochemical detection. Furthermore, the rigid "pseudo spiro" geometry of the molecules, which holds the three substituents of the central Delta(2)-pyrazoline ring in a fixed prearrangement, was confirmed by X-ray structure analysis.
Research Interests:
Dedicated to Dr Gerhard Herzberg on the occasion of his 90th birthday Recent large-scale ab initio calculations for small negative molecular ions are reviewed. Accurate equilibrium geometries are established for several species like NH2-,... more
Dedicated to Dr Gerhard Herzberg on the occasion of his 90th birthday Recent large-scale ab initio calculations for small negative molecular ions are reviewed. Accurate equilibrium geometries are established for several species like NH2-, HCC-, NO2-, CH2N- C5- and C6-. Predictions are made for various spectroscopic properties like vibrational frequencies, rotational constants and infrared intensities. The effects of a shallow energy minimum in the T-shaped configuration on the rovibrational term energies of HCC - are investigated. The calculated vibrational structures of the photoelectron spectra of SiH3- and CH2N - are in very good agreement with the experiment. The present calculations support the assignment of an absorption observed at 608 nm in a neon matrix to the
Research Interests:
We describe experimental studies of cubic nonlinear optical properties performed in reflection mode on thin films of polyaniline. It is shown that pump-probe and degenerate four-wave mixing reflection techniques are sensitive enough to... more
We describe experimental studies of cubic nonlinear optical properties performed in reflection mode on thin films of polyaniline. It is shown that pump-probe and degenerate four-wave mixing reflection techniques are sensitive enough to obtain readily detectable nonlinear optical signals from polyaniline with femtosecond pulses at light intensities on the order of 100 GW/cm. The results are compared with previous studies indicating that nonlinear coefficients of polyaniline are in the range of |n2| = 10–10 cm/W and that the relaxation of the nonlinear effects involves picosecond range processes.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
The new 3,4-propylenedioxythiophenes (ProDOT) bearing hydroxy- or chloro-functionalized side chains of varying length and polarity were synthesized and electropolymerized on single carbon fiber microelectrode (SCFME) using... more
The new 3,4-propylenedioxythiophenes (ProDOT) bearing hydroxy- or chloro-functionalized side chains of varying length and polarity were synthesized and electropolymerized on single carbon fiber microelectrode (SCFME) using cyclo-voltammetry. Electrochemical impedance spectroscopy (EIS) revealed highest capacitance values for the hydroxy-functionalized Poly 5 carrying a side chain of medium length. The EIS data were fitted with an equivalent electrical circuit giving a good correlation. AFM analysis of the topography showed higher roughness values for Poly 5 than for the two other polymers bearing longer side chains. Due to their reactive end groups the polymers should be useful for post-polymerization functionalization of the electrode surface.
Research Interests:
Research Interests:
Electrochemical doping processes of aromatic poly(1,3,4-oxadiazole)s in acetonitrile/Bu4NBF4 have been studied to characterize the charge and discharge properties of these polymers. Cyclic voltammograms were measured of thin... more
Electrochemical doping processes of aromatic poly(1,3,4-oxadiazole)s in acetonitrile/Bu4NBF4 have been studied to characterize the charge and discharge properties of these polymers. Cyclic voltammograms were measured of thin poly(arylene-1,3,4-oxadiazole) films on glassy carbon, Pt and ITO glasses. The reduction potential values Ered as well as the reoxidation peaks Ereox were shifted to lower potentials if the phenylene unit in the main
Research Interests:
ABSTRACT A negative solubility coefficient is displayed by the title compound (DIMEB) in water: at 50 °C it is sparingly soluble and crystallizes as anhydrate, and at 18 °C it is highly soluble and crystallizes as DIMEB⋅15 H2O. The 15 H2O... more
ABSTRACT A negative solubility coefficient is displayed by the title compound (DIMEB) in water: at 50 °C it is sparingly soluble and crystallizes as anhydrate, and at 18 °C it is highly soluble and crystallizes as DIMEB⋅15 H2O. The 15 H2O molecules form a clathrate hydrate channel structure with 416281 polygons (see picture) as a repeating motif accommodating DIMEB. Owing to the 15 host – guest hydrogen bonds, DIMEB⋅15 H2O is thermally stable until decomposition at 280 °C, in stark contrast to commonly known clathrate hydrates.
Research Interests:
The molecular structure of poly(p-phenylene-1,3,4-oxadiazole) (POD) is investigated using i.r. and Raman spectroscopy. Both methods reveal characteristic differences for the α- and β-POD forms that are most obvious in the spectral region... more
The molecular structure of poly(p-phenylene-1,3,4-oxadiazole) (POD) is investigated using i.r. and Raman spectroscopy. Both methods reveal characteristic differences for the α- and β-POD forms that are most obvious in the spectral region between 1500 and 1650 cm−1. The spectra for dimer and tetramer compounds already show the same features as found for longer chains. Based on molecular modelling calculations these differences are assigned to cis and trans conformations of the main chain segments. High pressure measurements show a linear shift of the Raman lines and support the result of the thermodynamic stability of the trans conformation.
Research Interests:
We report on a nearly isothermal, reversible transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the degree of mechanical anisotropy can be controlled by light. The phase transition phenomenon and... more
We report on a nearly isothermal, reversible transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the degree of mechanical anisotropy can be controlled by light. The phase transition phenomenon and the related unidirectional mass-transport effect are caused by optically driven molecular motion of azobenzene-functionalised molecular units, which can be effectively activated only when their transition dipole moments are oriented close to the direction of the light polarization. We also show that the selective excitation of chromophores by linear polarized light induces an anisotropic expanding force, which can be used for polarization-selective opto-mechanical actuators and sensors. Moreover, since the molecular motions can be induced also by spatially confined non-propagating optical fields, we are able to manipulate the state and position of nanoscopic elements of matter using optical near-field approaches.
Research Interests:
Research Interests:
Electrospinning is known as a fabrication technique for electrode architectures that serve as immobilization matrices for biomolecules. The current work demonstrates a novel approach to construct a conductive polymeric platform, capable... more
Electrospinning is known as a fabrication technique for electrode architectures that serve as immobilization matrices for biomolecules. The current work demonstrates a novel approach to construct a conductive polymeric platform, capable not only of immobilization, but also of electrical connection of the biomolecule with the electrode. It is produced upon electrospinning from mixtures of three different highly conductive sulfonated polyanilines and polyacrylonitrile on ITO electrodes. The resulting fiber mats are with a well-retained conductivity. After coupling the enzyme pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) to polymeric structures and addition of the substrate glucose an efficient bioelectrocatalysis is demonstrated. Depending on the choice of the sulfonated polyanilline mediatorless bioelectrocatalysis starts at low potentials; no large overpotential is needed to drive the reaction. Thus, the electrospun conductive immobilization matrix acts here as a transducing element, representing a promising strategy to use 3D polymeric scaffolds as wiring agents for active enzymes. In addition, the mild and well reproducible fabrication process and the active role of the polymer film in withdrawing electrons from the reduced PQQ-GDH lead to a system with high stability. This could provide access to a larger group of enzymes for bioelectrochemical applications including biosensors and biofuel cells.
Research Interests:
Research Interests:
Research Interests:
The paper shows that the conductivity properties of a composite regarded as a two- or multiphase material do not obey the rule of mixtures. The discussion concerns the conductivity of a quasihomogeneous composite defined as a composite... more
The paper shows that the conductivity properties of a composite regarded as a two- or multiphase material do not obey the rule of mixtures. The discussion concerns the conductivity of a quasihomogeneous composite defined as a composite material in which the distribution of stereometric parameters (volume fraction, shape factor, and orientation of constituent particles) is constant in a representative volume which is large compared to the size of the single particles involved. The theory of the conductivity of quasihomogeneous composites is examined relative to the type of structure (dispersion type and interconnecting-phases type) shape factor, and orientation. The concept of quasihomogeneous material does not consider transport mechanisms for the thermal conductivity, so that consideration of particle size limits the application of the concept of quasihomogeneity to the thermal conductivity of composites. Also discussed are an analysis of the microstructure of a composite, experimental evidence in support of the theory, and the special case of porous materials.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
ABSTRACT
Research Interests:
Thin films in the range of 50 nm to 10 &mgr;m thickness have been prepared from NMP solutions of silicon-containing polyphenylquinoxaline-amides which had been synthesized by the polycondensation reaction of aromatic... more
Thin films in the range of 50 nm to 10 &mgr;m thickness have been prepared from NMP solutions of silicon-containing polyphenylquinoxaline-amides which had been synthesized by the polycondensation reaction of aromatic diaminophenylquinoxalines with bis(p-chlorocarbonylphenyl)diphenylsilane. A spin-coating technique onto glass plates or onto silicon wafers was used to make the films, followed by gradual heating to remove the solvent. The resulting films were very smooth and free of pinholes when studied by atomic force microscopy (AFM). They showed a strong adhesion to silicon wafers, were thermally stable in air to above 400 °C and their dielectric constant was in the range of 3.5–3.7. Thermal treatment of the films was performed in order to induce crosslinking. Such treated films became completely insoluble in organic solvents, maintained their smoothness and strong adhesion to the silicon substrate, and did not show any Tg in DSC experiments. Their FTIR spectra in reflection mode d...
Research Interests:
Three oligo[(rac-lactide)-co-glycolide] based polyesterurethanes (OLGA-PUs) containing different diurethane linkers are investigated by the Langmuir monolayer technique and compared to poly[(rac-lactide)-co-glycolide] (PLGA) to elucidate... more
Three oligo[(rac-lactide)-co-glycolide] based polyesterurethanes (OLGA-PUs) containing different diurethane linkers are investigated by the Langmuir monolayer technique and compared to poly[(rac-lactide)-co-glycolide] (PLGA) to elucidate the influence of the diurethane junction units on hydrophilicity and packing motifs of these polymers at the air-water interface. The presence of diurethane linkers does not manifest itself in the Langmuir layer behavior both in compression and expansion experiments when monomolecular films of OLGA-PUs are spread on the water surface. However, the linker retard the evolution of morphological structures at intermediate compression level under isobaric conditions (with a surface pressure greater than 11 mN m(-1) ) compared to the PLGA, independent on the chemical structure of the diurethane moiety. The layer thicknesses of both OLGA-PU and PLGA films decrease in the high compression state with decreasing surface pressure, as deduced from ellipsometric data. All films must be described with the effective medium approximation as water swollen layers.
Research Interests:
New silicon-containing aromatic polyhydrazides were synthesized by low-temperature solution polycondensation reaction of bis(p-chlorocarbonylphenyl)diphenylsilane with various aromatic dihydrazides, or of... more
New silicon-containing aromatic polyhydrazides were synthesized by low-temperature solution polycondensation reaction of bis(p-chlorocarbonylphenyl)diphenylsilane with various aromatic dihydrazides, or of bis(p-carbohydrazidophenyl)diphenylsilane with diacid chlorides. The corresponding poly(arylene-1,3,4-oxadiazole)s wvere prepared by thermal cyclodehydration in the solid state. The cyclization process takes place at temperatures in the range of 250-300 IC. The resulting silicon-containing poly(arylene-1,3,4-oxadiazole)s are soluble in common organic solvents and have good film-forming abilities. They are stable up to 420-480 'C and their glass transition temperature is in the range of 262-278C.
Research Interests:
ABSTRACT
Surface relief gratings (SRG) made from azobenzene polymer films by holographic exposure with actinic light show remarkable density modifications in addition to the surface relief. The origin of the huge material transport is attributed... more
Surface relief gratings (SRG) made from azobenzene polymer films by holographic exposure with actinic light show remarkable density modifications in addition to the surface relief. The origin of the huge material transport is attributed to cooperative phenomena associated with the light induced trans-cis and cis-trans isomerization of azobenzene moieties and the subsequent changing of viscoelastic properties during illumination. In case of polydisperse red 1 methacrylate (pDR1m) films and using particular illumination conditions the amplitude of the density grating (DG) can be maximized whereas the amplitude of surface undulations keeps small. The capability of DG formation makes it possible to induce grating formation in the azobenzene polymer film through a thick polymer cover layer which is not affected by the actinic light. Using PMMA as cover layer the grating is located at the PMMA - pDR1m interface (interface grating) while the sample surface stayed almost flat. This concept ...
ABSTRACT
Research Interests: Fluorescence and Polymer
Research Interests:
ABSTRACT For the fluorescent ligand 1-(9-anthrylcarbonyl)-3,3-tetramethylenethiourea with Cu(ClO(4))(2) or strong acids an unusual rearrangement reaction occurred yielding a highly emissive S-(9-anthryl)isothiouronium salt. This... more
ABSTRACT For the fluorescent ligand 1-(9-anthrylcarbonyl)-3,3-tetramethylenethiourea with Cu(ClO(4))(2) or strong acids an unusual rearrangement reaction occurred yielding a highly emissive S-(9-anthryl)isothiouronium salt. This rearrangement product was characterised by NMR spectroscopy and X-ray analysis as well as absorption and fluorescence spectroscopy. Additionally, the chemical and complexation behaviour of the N-anthrylcarbonylthiourea derivative is compared to that of its naphthyl and phenyl analogues.
The study of plant mutants with twisting growth in axial organs, which normally grow straight in the wild-type, is expected to improve our understanding of the interplay among microtubules, cellulose biosynthesis, cell wall structure, and... more
The study of plant mutants with twisting growth in axial organs, which normally grow straight in the wild-type, is expected to improve our understanding of the interplay among microtubules, cellulose biosynthesis, cell wall structure, and organ biomechanics that control organ growth and morphogenesis. However, geometric constraints based on symplastic growth and the consequences of these geometric constraints concerning interpretations of twisted-organ phenotypes are currently underestimated. Symplastic growth, a fundamental concept in plant developmental biology, is characterized by coordinated growth of adjacent cells based on their connectivity through cell walls. This growth behavior implies that in twisting axial organs, all cell files rotate in phase around the organ axis, as has been illustrated for the Arabidopsisspr1 and twd1 mutants in this work. Evaluating the geometry of such organs, we demonstrate that a radial gradient in cell elongation and changes in cellular growth ...
The title compound [systematic name: dimethyl 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylenedicarboxylate], C(18)H(14)N(2)O(5), crystallizes under similar conditions in two different orthorhombic crystalline forms. In both forms, the... more
The title compound [systematic name: dimethyl 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylenedicarboxylate], C(18)H(14)N(2)O(5), crystallizes under similar conditions in two different orthorhombic crystalline forms. In both forms, the molecule consists of two equivalent parts. In form 1, these parts are related by a twofold axis of space group Pbcn, and in form 2, by a mirror plane of space group Cmc2(1). The O atom of the oxadiazole ring occupies a special position on the twofold axis and on the mirror plane in forms 1 and 2, respectively.