Burkhard Schulz | University of Maryland (original) (raw)
Papers by Burkhard Schulz
Macromolecular rapid communications, 2016
The influence of terminal functionalization of oligo(ε-caprolactone)s (OCL) with phenylboronic ac... 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...
Macromolecular rapid communications, 2016
Beilstein Journal of Nanotechnology, 2016
The applicability of nulling-based ellipsometric mapping as a complementary method next to Brewst... 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.
High Performance Polymers, Sep 1, 1996
J Incl Phenom Macrocycl Chem, 2003
Proceedings of Spie the International Society For Optical Engineering, 2006
We report on a light-induced isothermal transition of a polymer film from an isotropic solid to a... 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.
Surface Engineering, Aug 31, 2008
ABSTRACT Poly(2,2-dimethyl-3,4-propylenedioxythiophene) (PProDOT-Me2) thin films have been cyclov... 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.
Mendeleev Communications, 1999
In 7- (1,2,3,4,5,6,7-heptaphenylcycloheptatrienyl) isothiocyanate and isoselenocyanate, migration... more In 7- (1,2,3,4,5,6,7-heptaphenylcycloheptatrienyl) isothiocyanate and isoselenocyanate, migration of isothiocyanate and isoselenocyanate groups along the perimeter of the seven-membered ring occurs via an intramolecular dissociation-recombination mechanism with high free energy barriers (DG ¹ 298 ) of 24.3 and 22.4 kcal mol -1 , respectively.
Carbohyd Res, 2000
Octakis(2,3,6-tri-O-methyl)-γ-CD (TRIMEG) cocrystallized at 18 °C with 4.5 water molecules in the... 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.
J Phys Chem a, 2000
ABSTRACT The spectroscopic properties of 1-phenyl-3-benzothiazol-2-yl-5-(4-R-phenyl)-Delta(2)-pyr... 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.
International Reviews in Physical Chemistry, 1995
Dedicated to Dr Gerhard Herzberg on the occasion of his 90th birthday Recent large-scale ab initi... 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
Mol Cryst Liquid Cryst, 2006
We describe experimental studies of cubic nonlinear optical properties performed in reflection mo... 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.
Colloid Polym Sci, 2004
A comprehensive study gives experimental evidence that a complex made from pyrrole and bnaphthale... more A comprehensive study gives experimental evidence that a complex made from pyrrole and bnaphthalenesulfonic acid in a molar composition of 3:1 acts as morphological precursor in the subsequent oxidative polymerization of pyrrole initiated with ammonium peroxodisulfate. The precursor complex itself is unable to polymerize but its outer parallelepipedal shape with a high aspect ratio is templated in the inner surface of the formed conducting polypyrrole tubes.
Acta Crystallogr E Struct Rep, 2003
High Performance Polymers, 1994
Journal of Nanoscience and Nanotechnology, Oct 1, 2012
The new 3,4-propylenedioxythiophenes (ProDOT) bearing hydroxy- or chloro-functionalized side chai... 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.
Fusion Engineering and Design, Apr 1, 1991
This paper describes a part of the work performed on the determination of the thermophysical prop... more This paper describes a part of the work performed on the determination of the thermophysical properties of alloys in the binary system Li-Pb. The preparation of the eutectic alloy from the pure elements and its characterization using chemical analysis, metallography, thermal and thermal differential analysis is described. Results of the measurements of the following properties are presented: latent heat of fusion, specific heat, density, thermal expansion, thermal and electric conductivity and viscosity. The wetting behaviour of Li(17)Pb(83) against SS 316 is discussed in terms showing the influence of especially of oxygen on the wetting angle in this system.
Proceedings Imcs 2012, May 21, 2012
Differently substituted polyaniline copolymes are shown to provide interfaces for the communicati... more Differently substituted polyaniline copolymes are shown to provide interfaces for the communication with biosystems. The various substitutions of the aromatic ring are influencing the conductivity properties of the polymer immobilized on electrode surfaces, and lead to a modified interaction with proteins and/or enzyme molecules. It is shown that an analytical signal chain starting from the substrate sulfite in solution via the enzyme sulfite oxidase and the redox protein cyt c to the polymer can be constructed. The electron transfer is also shown without the use of an electric field. The enzymatic system induces redox switching between oxidized and reduced states of polymer, which can be visualized not only in solution, but also with a thin polymer film on electrodes.
European Polymer Journal, Apr 1, 1996
Electrochemical doping processes of aromatic poly(1,3,4-oxadiazole)s in acetonitrile/Bu4NBF4 have... 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
Macromolecular rapid communications, 2016
The influence of terminal functionalization of oligo(ε-caprolactone)s (OCL) with phenylboronic ac... 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...
Macromolecular rapid communications, 2016
Beilstein Journal of Nanotechnology, 2016
The applicability of nulling-based ellipsometric mapping as a complementary method next to Brewst... 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.
High Performance Polymers, Sep 1, 1996
J Incl Phenom Macrocycl Chem, 2003
Proceedings of Spie the International Society For Optical Engineering, 2006
We report on a light-induced isothermal transition of a polymer film from an isotropic solid to a... 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.
Surface Engineering, Aug 31, 2008
ABSTRACT Poly(2,2-dimethyl-3,4-propylenedioxythiophene) (PProDOT-Me2) thin films have been cyclov... 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.
Mendeleev Communications, 1999
In 7- (1,2,3,4,5,6,7-heptaphenylcycloheptatrienyl) isothiocyanate and isoselenocyanate, migration... more In 7- (1,2,3,4,5,6,7-heptaphenylcycloheptatrienyl) isothiocyanate and isoselenocyanate, migration of isothiocyanate and isoselenocyanate groups along the perimeter of the seven-membered ring occurs via an intramolecular dissociation-recombination mechanism with high free energy barriers (DG ¹ 298 ) of 24.3 and 22.4 kcal mol -1 , respectively.
Carbohyd Res, 2000
Octakis(2,3,6-tri-O-methyl)-γ-CD (TRIMEG) cocrystallized at 18 °C with 4.5 water molecules in the... 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.
J Phys Chem a, 2000
ABSTRACT The spectroscopic properties of 1-phenyl-3-benzothiazol-2-yl-5-(4-R-phenyl)-Delta(2)-pyr... 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.
International Reviews in Physical Chemistry, 1995
Dedicated to Dr Gerhard Herzberg on the occasion of his 90th birthday Recent large-scale ab initi... 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
Mol Cryst Liquid Cryst, 2006
We describe experimental studies of cubic nonlinear optical properties performed in reflection mo... 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.
Colloid Polym Sci, 2004
A comprehensive study gives experimental evidence that a complex made from pyrrole and bnaphthale... more A comprehensive study gives experimental evidence that a complex made from pyrrole and bnaphthalenesulfonic acid in a molar composition of 3:1 acts as morphological precursor in the subsequent oxidative polymerization of pyrrole initiated with ammonium peroxodisulfate. The precursor complex itself is unable to polymerize but its outer parallelepipedal shape with a high aspect ratio is templated in the inner surface of the formed conducting polypyrrole tubes.
Acta Crystallogr E Struct Rep, 2003
High Performance Polymers, 1994
Journal of Nanoscience and Nanotechnology, Oct 1, 2012
The new 3,4-propylenedioxythiophenes (ProDOT) bearing hydroxy- or chloro-functionalized side chai... 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.
Fusion Engineering and Design, Apr 1, 1991
This paper describes a part of the work performed on the determination of the thermophysical prop... more This paper describes a part of the work performed on the determination of the thermophysical properties of alloys in the binary system Li-Pb. The preparation of the eutectic alloy from the pure elements and its characterization using chemical analysis, metallography, thermal and thermal differential analysis is described. Results of the measurements of the following properties are presented: latent heat of fusion, specific heat, density, thermal expansion, thermal and electric conductivity and viscosity. The wetting behaviour of Li(17)Pb(83) against SS 316 is discussed in terms showing the influence of especially of oxygen on the wetting angle in this system.
Proceedings Imcs 2012, May 21, 2012
Differently substituted polyaniline copolymes are shown to provide interfaces for the communicati... more Differently substituted polyaniline copolymes are shown to provide interfaces for the communication with biosystems. The various substitutions of the aromatic ring are influencing the conductivity properties of the polymer immobilized on electrode surfaces, and lead to a modified interaction with proteins and/or enzyme molecules. It is shown that an analytical signal chain starting from the substrate sulfite in solution via the enzyme sulfite oxidase and the redox protein cyt c to the polymer can be constructed. The electron transfer is also shown without the use of an electric field. The enzymatic system induces redox switching between oxidized and reduced states of polymer, which can be visualized not only in solution, but also with a thin polymer film on electrodes.
European Polymer Journal, Apr 1, 1996
Electrochemical doping processes of aromatic poly(1,3,4-oxadiazole)s in acetonitrile/Bu4NBF4 have... 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