John Stong - Academia.edu (original) (raw)

Papers by John Stong

Research paper thumbnail of The electronic spectral properties of gallic acid

Spectrochimica Acta Part A: Molecular Spectroscopy, 1982

The electronic spectral properties of gallic acid (3,4,5-trihydroxybenzoic acid), a chemiluminesc... more The electronic spectral properties of gallic acid (3,4,5-trihydroxybenzoic acid), a chemiluminescence reagent which is unstable in oxygenated aqueous solution, have been determined under conditions regulated to retard decomposition. The characteristic blue and red shifts in the u.v. absorption spectra which accompany carboxyi and phenol dissociation, respectively, are in accord with the trends usually observed for these functional groups. The dianionic species exhibits a fluorescence emission band with a peak at 370 nm under 300-nm excitation.

Research paper thumbnail of Determination of ivermectin by fluorescence derivatization

Research paper thumbnail of Differential-pulse polarographic determination of the coccidiostat arprinocid in feed pre-mixes

Research paper thumbnail of Determination of efrotomycin in feeds by high-performance liquid chromatography

Research paper thumbnail of A computer-controlled potentiometric/spectrophotometric titrator

The Journal of Automatic Chemistry, 1988

A laboratory computer controlled potentiometric titrator interfaced to a diode array spectrophoto... more A laboratory computer controlled potentiometric titrator interfaced to a diode array spectrophotometer is described. The titrator consists of widely used, commercially available components; therefore, major attention is given to modes of interconnection and software implementation in data format and system control. Replicate potentiometric titrations of glycines gave a relative standard deviation in titre of 1.035% and a relative standard deviation in pH of 0.745%. Replicate spectrophotometric titrations of bromophenol blue were analysed at three wavelengths toyield pKa 3.898 + 0.075 (1.9% rsd).

Research paper thumbnail of Determination of ivermectin by fluorescence derivatization

Analytical Chemistry, 1987

Research paper thumbnail of Radical-induced oxidation of oxahydrindene (hexahydrobenzofuran) portion of 22,23-dihydroavermectin b1a: Identification of autooxidation products

Journal of Pharmaceutical Sciences, 1992

Abrtract 0 Three products resulting from free-radical-induced oxidation of the oxahydrindene port... more Abrtract 0 Three products resulting from free-radical-induced oxidation of the oxahydrindene portion of 22.23-dihydroavermectin B,, (H2B,a) are 5-oxo-H2Bl,, 8a-oxo-H2Bla, and 5,8a-bisoxo-H,Bla. The last of these compounds has not been reported previously.

Research paper thumbnail of Core Expansion vs. Coming in Porphyrins; Resonance Raman Discrimination Between Five- and Six-Coordinate High-Spin Feiii Hemes

Electrons to Tissues, 1978

Research paper thumbnail of Stabilized Carbapenem Antibiotic Compositions and Method of Making

Research paper thumbnail of Heme models. I. Solution behavior of a water soluble iron porphyrin

Bioinorganic chemistry, 1976

A well-behaved water soluble iron-porphyrin system, meso-tetra-(4-carboxyphenyl) porphinato iron ... more A well-behaved water soluble iron-porphyrin system, meso-tetra-(4-carboxyphenyl) porphinato iron (III) was synthesized. Its solution behavior is described using visable and electron paramagnetic resonance (EPR) spectroscopy. The complex exists in solution as three distinct forms of bridged dimers, oxo, hydroxo and aquo, with the following pK's: oxo + H+ in equilibrium hydroxo, pK = 9.58; hydroxo + H+ in equilibrium aquo, pK = 6.72. In the presence of excess imidazole the second pK is found to be 7.05. Detailed analysis of the interaction of the hydroxo-bridged form with imidazole is presented. It is found that one dimer unit simultaneously binds two imidazole molecules, with an over-all equilibrium constant log Keq = -1.22. EPR spectra are presented for the various forms of iron-porphyrin discussed.

Research paper thumbnail of Picosecond resonance Raman spectroscopic evidence for excited-state spin conversion in carbonmonoxy-hemoglobin photolysis

Proceedings of the National Academy of Sciences, 1981

The structure of the carbonmonoxy-hemoglobin (COHb) photoproduct has been studied on the picoseco... more The structure of the carbonmonoxy-hemoglobin (COHb) photoproduct has been studied on the picosecond time scale with resonance Raman spectroscopy, by tightly focusing the 30-ps pulses of a synchronously pumped mode-locked cavitydumped dye laser on ajet stream of COHb solution. The spectrum of the photoproduct is similar to that of deoxy Hb, but the frequencies 1603 cm-1 (depolarized), 1552 cm-' (anomalously polarized), and 1542 cm-t (depolarized) are 2-4 cm-' lower than those of deoxy Hb. Similar low frequencies are observed for a species believed to be the bis-tetrahydrofuran adduct of Fei" octaethylporphyrin, containing in-plane high-spin Fe",. These results indicate that in the COHb photoproduct the Fe" is already high-spin but is closer to the heme plane than in deoxy Hb. Photodissociation from a quintet ligand-field excited state of COHb is suggested. The frequency shifts relative to deoxy Hb persist when the laser pulses are lengthened to 20 ns. The apparently slow relaxation to the fully out-of-lane heme conformation of deoxy Hb is suggested to be associate with change of the globin tertiary structure.

Research paper thumbnail of Porphyrin core expansion and doming in heme proteins. New evidence from resonance Raman spectra of six-coordinate high-spin iron(III) hemes

Journal of the American Chemical Society, 1979

Research paper thumbnail of Reactions of superoxide with iron porphyrins in aprotic solvents. A high spin ferric porphyrin peroxo complex

Journal of the American Chemical Society, 1980

Dioxygen complexes of iron porphyrins are of interest because of their proposed involvement in a ... more Dioxygen complexes of iron porphyrins are of interest because of their proposed involvement in a variety of biological processes. Only three types of synthetic iron porphyrin dioxygen complexes have been reported, each of which is prepared by reaction of ferrous ...

Research paper thumbnail of Resonance Raman spectra of nitrosyl heme proteins and of porphyrin analogs

Journal of the American Chemical Society, 1980

stored and averaged by using program DSORTH;32 847 reflections were measured once and 1948 had mo... more stored and averaged by using program DSORTH;32 847 reflections were measured once and 1948 had more than one contributor to average ( R , = E A v l l -A v ( l )~/~A v~l~ = 0.016; R2 = Z l w l wAv(I)l/EwIl = 0.021); 2677 independent reflections with I > 3 0 ( l ) were used to refine the structure.

Research paper thumbnail of Identification of the secondary degradates of L‐648,548 in an animal health formulation

Journal of Pharmaceutical Sciences, 1996

0 L-648,548 is a semisynthetic analog of avermectin. During stability investigations of this comp... more 0 L-648,548 is a semisynthetic analog of avermectin. During stability investigations of this compound in an animal health formulation, two new degradates were discovered. These degradates (L-648,548 phenol and its 8,9-Z isomer) were identified as the reaction products of 5-oxo-L-648,548 formed by oxidation of L-648,548. Addition of base to the reaction medium containing 5-oxo-L-648,548 was found to catalyze the formation of L-648,548 phenol via a postulated dehydration by an E 1cb elimination followed by the rapid tautomerization of the C5 carbonyl. Photolysis of L-648,548 phenol with visible light (including ambient laboratory lighting) was found to readily produce 8,9-Z-L-648,548 phenol. This transformation was confirmed to be exclusively a photoinduced process.

Research paper thumbnail of Meropenem exists in equilibrium with a carbon dioxide adduct in bicarbonate solution

Journal of Pharmaceutical Sciences, 1998

0 Evidence is provided for the existence of a second discrete chemical form of meropenem at clini... more 0 Evidence is provided for the existence of a second discrete chemical form of meropenem at clinically relevant concentrations prepared from the marketed formulation of the drug. Proton and carbon-13 NMR spectra in D 2 O, coupled with tandem mass spectroscopy (MS/MS) and cross polarization/magic angle spinning (CP-MAS) NMR experiments, allow structural assignment of the compound as a covalent carbon dioxide adduct of meropenem. This carbon dioxide adduct exists in equilibrium with the free drug in solution and can be observed in the solid state following lyophilization. The equilibrium constant of formation of the adduct (K eq ) 20 ± 8 M -1 ) was estimated in D 2 O at 25°C.

Research paper thumbnail of Omeprazole determination using HPLC with coulometric detection

Journal of Pharmaceutical and Biomedical Analysis, 2001

A sensitive high performance liquid chromatography (HPLC) method for the determination of omepraz... more A sensitive high performance liquid chromatography (HPLC) method for the determination of omeprazole and three related benzimidazoles is reported. Coulometric detection was carried out at +800 mV using a porous carbon electrode. The linear range is 0.01-10 microg/ml. The method has a high degree of precision; the relative standard deviation of omeprazole at a concentration of 1.06 microg/ml was 0.7% (n=4). The cyclic voltammogram of omeprazole is consistent with the hydrodynamic voltammogram exhibiting a single major irreversible oxidative wave with a peak potential at +1105 mV. The response factors for the four compounds are similar indicating that the oxidative process does not involve the sulfur moiety exclusively. The data are most consistent with oxidation primarily of the benzimidazole groups. The method was applied successfully to the determination of omeprazole in a paste formulation.

Research paper thumbnail of Electronic and resonance Raman spectra of iron(III) complexes of enterobactin, catechol, and N-methyl-2,3-dihydroxybenzamide

Biochemistry, 1978

Resonance Raman electronic absorption and circular dichroism spectra and pH titration curves are ... more Resonance Raman electronic absorption and circular dichroism spectra and pH titration curves are reported for the trianionic ferric complexes of enterobactin, catechol, and N-methyl-2,3-dihydroxybenzamide (MDHB). The spectral signatures of the enterobactin and MDHB complexes are virtually identical and differ from those of the catechol complex in ways that reflect the influence of the amide group on the electronic structure. Excitation in either the visible charge-transfer bands or the near-ultraviolet pi-pi* bands enhances Raman bands associated with benzene ring modes, although the relative enhancements differ markedly in the two regions. The data stronly support a structural model in which iron is bound exclusively to the phenolate oxygen atoms in all three complexes.

Research paper thumbnail of Difference spectrophotometric determination of efrotomycin in feed premixes

Analytical Chemistry, 1984

Research paper thumbnail of Determination and Characterization of Unreacted Hydroxyl Groups in a Cross-Linked Poly(ortho ester)

Analytical Chemistry, 1994

A method is presented for the identification and quantitative determination of unreacted hydroxyl... more A method is presented for the identification and quantitative determination of unreacted hydroxyl groups in a cross-linked poly(ortho ester) derived from the diketene acetal 3,9-bis-(ethylidene-2,4,8,1O-tetraoxaspiro[5.5]undecane), (A)-1,2,6hexanetriol, 1,641exanedio1, and tetraethylene glycol. This method involves exhaustive derivatization of unreacted hydroxyl groups in the intact polymer in advance of mild hydrolysis followed by gradient HPLC analysis. Each of the derivatized polymer components was synthesized and characterized, and evidence is presented demonstrating that exhaustive derivatization has occurred.

Research paper thumbnail of The electronic spectral properties of gallic acid

Spectrochimica Acta Part A: Molecular Spectroscopy, 1982

The electronic spectral properties of gallic acid (3,4,5-trihydroxybenzoic acid), a chemiluminesc... more The electronic spectral properties of gallic acid (3,4,5-trihydroxybenzoic acid), a chemiluminescence reagent which is unstable in oxygenated aqueous solution, have been determined under conditions regulated to retard decomposition. The characteristic blue and red shifts in the u.v. absorption spectra which accompany carboxyi and phenol dissociation, respectively, are in accord with the trends usually observed for these functional groups. The dianionic species exhibits a fluorescence emission band with a peak at 370 nm under 300-nm excitation.

Research paper thumbnail of Determination of ivermectin by fluorescence derivatization

Research paper thumbnail of Differential-pulse polarographic determination of the coccidiostat arprinocid in feed pre-mixes

Research paper thumbnail of Determination of efrotomycin in feeds by high-performance liquid chromatography

Research paper thumbnail of A computer-controlled potentiometric/spectrophotometric titrator

The Journal of Automatic Chemistry, 1988

A laboratory computer controlled potentiometric titrator interfaced to a diode array spectrophoto... more A laboratory computer controlled potentiometric titrator interfaced to a diode array spectrophotometer is described. The titrator consists of widely used, commercially available components; therefore, major attention is given to modes of interconnection and software implementation in data format and system control. Replicate potentiometric titrations of glycines gave a relative standard deviation in titre of 1.035% and a relative standard deviation in pH of 0.745%. Replicate spectrophotometric titrations of bromophenol blue were analysed at three wavelengths toyield pKa 3.898 + 0.075 (1.9% rsd).

Research paper thumbnail of Determination of ivermectin by fluorescence derivatization

Analytical Chemistry, 1987

Research paper thumbnail of Radical-induced oxidation of oxahydrindene (hexahydrobenzofuran) portion of 22,23-dihydroavermectin b1a: Identification of autooxidation products

Journal of Pharmaceutical Sciences, 1992

Abrtract 0 Three products resulting from free-radical-induced oxidation of the oxahydrindene port... more Abrtract 0 Three products resulting from free-radical-induced oxidation of the oxahydrindene portion of 22.23-dihydroavermectin B,, (H2B,a) are 5-oxo-H2Bl,, 8a-oxo-H2Bla, and 5,8a-bisoxo-H,Bla. The last of these compounds has not been reported previously.

Research paper thumbnail of Core Expansion vs. Coming in Porphyrins; Resonance Raman Discrimination Between Five- and Six-Coordinate High-Spin Feiii Hemes

Electrons to Tissues, 1978

Research paper thumbnail of Stabilized Carbapenem Antibiotic Compositions and Method of Making

Research paper thumbnail of Heme models. I. Solution behavior of a water soluble iron porphyrin

Bioinorganic chemistry, 1976

A well-behaved water soluble iron-porphyrin system, meso-tetra-(4-carboxyphenyl) porphinato iron ... more A well-behaved water soluble iron-porphyrin system, meso-tetra-(4-carboxyphenyl) porphinato iron (III) was synthesized. Its solution behavior is described using visable and electron paramagnetic resonance (EPR) spectroscopy. The complex exists in solution as three distinct forms of bridged dimers, oxo, hydroxo and aquo, with the following pK's: oxo + H+ in equilibrium hydroxo, pK = 9.58; hydroxo + H+ in equilibrium aquo, pK = 6.72. In the presence of excess imidazole the second pK is found to be 7.05. Detailed analysis of the interaction of the hydroxo-bridged form with imidazole is presented. It is found that one dimer unit simultaneously binds two imidazole molecules, with an over-all equilibrium constant log Keq = -1.22. EPR spectra are presented for the various forms of iron-porphyrin discussed.

Research paper thumbnail of Picosecond resonance Raman spectroscopic evidence for excited-state spin conversion in carbonmonoxy-hemoglobin photolysis

Proceedings of the National Academy of Sciences, 1981

The structure of the carbonmonoxy-hemoglobin (COHb) photoproduct has been studied on the picoseco... more The structure of the carbonmonoxy-hemoglobin (COHb) photoproduct has been studied on the picosecond time scale with resonance Raman spectroscopy, by tightly focusing the 30-ps pulses of a synchronously pumped mode-locked cavitydumped dye laser on ajet stream of COHb solution. The spectrum of the photoproduct is similar to that of deoxy Hb, but the frequencies 1603 cm-1 (depolarized), 1552 cm-' (anomalously polarized), and 1542 cm-t (depolarized) are 2-4 cm-' lower than those of deoxy Hb. Similar low frequencies are observed for a species believed to be the bis-tetrahydrofuran adduct of Fei" octaethylporphyrin, containing in-plane high-spin Fe",. These results indicate that in the COHb photoproduct the Fe" is already high-spin but is closer to the heme plane than in deoxy Hb. Photodissociation from a quintet ligand-field excited state of COHb is suggested. The frequency shifts relative to deoxy Hb persist when the laser pulses are lengthened to 20 ns. The apparently slow relaxation to the fully out-of-lane heme conformation of deoxy Hb is suggested to be associate with change of the globin tertiary structure.

Research paper thumbnail of Porphyrin core expansion and doming in heme proteins. New evidence from resonance Raman spectra of six-coordinate high-spin iron(III) hemes

Journal of the American Chemical Society, 1979

Research paper thumbnail of Reactions of superoxide with iron porphyrins in aprotic solvents. A high spin ferric porphyrin peroxo complex

Journal of the American Chemical Society, 1980

Dioxygen complexes of iron porphyrins are of interest because of their proposed involvement in a ... more Dioxygen complexes of iron porphyrins are of interest because of their proposed involvement in a variety of biological processes. Only three types of synthetic iron porphyrin dioxygen complexes have been reported, each of which is prepared by reaction of ferrous ...

Research paper thumbnail of Resonance Raman spectra of nitrosyl heme proteins and of porphyrin analogs

Journal of the American Chemical Society, 1980

stored and averaged by using program DSORTH;32 847 reflections were measured once and 1948 had mo... more stored and averaged by using program DSORTH;32 847 reflections were measured once and 1948 had more than one contributor to average ( R , = E A v l l -A v ( l )~/~A v~l~ = 0.016; R2 = Z l w l wAv(I)l/EwIl = 0.021); 2677 independent reflections with I > 3 0 ( l ) were used to refine the structure.

Research paper thumbnail of Identification of the secondary degradates of L‐648,548 in an animal health formulation

Journal of Pharmaceutical Sciences, 1996

0 L-648,548 is a semisynthetic analog of avermectin. During stability investigations of this comp... more 0 L-648,548 is a semisynthetic analog of avermectin. During stability investigations of this compound in an animal health formulation, two new degradates were discovered. These degradates (L-648,548 phenol and its 8,9-Z isomer) were identified as the reaction products of 5-oxo-L-648,548 formed by oxidation of L-648,548. Addition of base to the reaction medium containing 5-oxo-L-648,548 was found to catalyze the formation of L-648,548 phenol via a postulated dehydration by an E 1cb elimination followed by the rapid tautomerization of the C5 carbonyl. Photolysis of L-648,548 phenol with visible light (including ambient laboratory lighting) was found to readily produce 8,9-Z-L-648,548 phenol. This transformation was confirmed to be exclusively a photoinduced process.

Research paper thumbnail of Meropenem exists in equilibrium with a carbon dioxide adduct in bicarbonate solution

Journal of Pharmaceutical Sciences, 1998

0 Evidence is provided for the existence of a second discrete chemical form of meropenem at clini... more 0 Evidence is provided for the existence of a second discrete chemical form of meropenem at clinically relevant concentrations prepared from the marketed formulation of the drug. Proton and carbon-13 NMR spectra in D 2 O, coupled with tandem mass spectroscopy (MS/MS) and cross polarization/magic angle spinning (CP-MAS) NMR experiments, allow structural assignment of the compound as a covalent carbon dioxide adduct of meropenem. This carbon dioxide adduct exists in equilibrium with the free drug in solution and can be observed in the solid state following lyophilization. The equilibrium constant of formation of the adduct (K eq ) 20 ± 8 M -1 ) was estimated in D 2 O at 25°C.

Research paper thumbnail of Omeprazole determination using HPLC with coulometric detection

Journal of Pharmaceutical and Biomedical Analysis, 2001

A sensitive high performance liquid chromatography (HPLC) method for the determination of omepraz... more A sensitive high performance liquid chromatography (HPLC) method for the determination of omeprazole and three related benzimidazoles is reported. Coulometric detection was carried out at +800 mV using a porous carbon electrode. The linear range is 0.01-10 microg/ml. The method has a high degree of precision; the relative standard deviation of omeprazole at a concentration of 1.06 microg/ml was 0.7% (n=4). The cyclic voltammogram of omeprazole is consistent with the hydrodynamic voltammogram exhibiting a single major irreversible oxidative wave with a peak potential at +1105 mV. The response factors for the four compounds are similar indicating that the oxidative process does not involve the sulfur moiety exclusively. The data are most consistent with oxidation primarily of the benzimidazole groups. The method was applied successfully to the determination of omeprazole in a paste formulation.

Research paper thumbnail of Electronic and resonance Raman spectra of iron(III) complexes of enterobactin, catechol, and N-methyl-2,3-dihydroxybenzamide

Biochemistry, 1978

Resonance Raman electronic absorption and circular dichroism spectra and pH titration curves are ... more Resonance Raman electronic absorption and circular dichroism spectra and pH titration curves are reported for the trianionic ferric complexes of enterobactin, catechol, and N-methyl-2,3-dihydroxybenzamide (MDHB). The spectral signatures of the enterobactin and MDHB complexes are virtually identical and differ from those of the catechol complex in ways that reflect the influence of the amide group on the electronic structure. Excitation in either the visible charge-transfer bands or the near-ultraviolet pi-pi* bands enhances Raman bands associated with benzene ring modes, although the relative enhancements differ markedly in the two regions. The data stronly support a structural model in which iron is bound exclusively to the phenolate oxygen atoms in all three complexes.

Research paper thumbnail of Difference spectrophotometric determination of efrotomycin in feed premixes

Analytical Chemistry, 1984

Research paper thumbnail of Determination and Characterization of Unreacted Hydroxyl Groups in a Cross-Linked Poly(ortho ester)

Analytical Chemistry, 1994

A method is presented for the identification and quantitative determination of unreacted hydroxyl... more A method is presented for the identification and quantitative determination of unreacted hydroxyl groups in a cross-linked poly(ortho ester) derived from the diketene acetal 3,9-bis-(ethylidene-2,4,8,1O-tetraoxaspiro[5.5]undecane), (A)-1,2,6hexanetriol, 1,641exanedio1, and tetraethylene glycol. This method involves exhaustive derivatization of unreacted hydroxyl groups in the intact polymer in advance of mild hydrolysis followed by gradient HPLC analysis. Each of the derivatized polymer components was synthesized and characterized, and evidence is presented demonstrating that exhaustive derivatization has occurred.