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  • 1995-1999  (5)
  • Analytical Chemistry and Spectroscopy  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Fast atom bombardment tandem mass spectrometry of the anti-parasitic agent pentamidine and its oxygenated metabolites (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 549-556 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Although pentamidine (1,5-bis(4′-amidinophenoxy)pentane) is currently in use for the treatment of a variety of parasitic infections, including acquired immune deficiency syndrome-related Pneumocystis carinii pneumonia, its metabolism is still under investigation. Positive-ion fast atom bombardment mass spectrometry was used with high-energy collision-activated dissociation (CAD) and linked scanning at constant B/E to obtain tandem mass spectra of protonated molecules of pentamindine and seven synthetic oxygenated derivatives, which are known metabolites of pentamidine. Charge-initiated fragmentation produced abundant fragment ions of m/z 120 and 137 and loss of neutral ammonia from the protonated analyte that characterized the amidinophenoxy group. The structures of isomeric 2-hydroxypentamidine, 3-hydroxypentamidine and N-hydroxypentamidine could be distinguished based on charge-remote fragmentation that produced a series of fragment ions of the pentyl chain and permitted the exact location of the hydroxyl group in each molecule to be determined. Next, tandem mass spectra were obtained and the charge-initiated and charge-remote fragmentation discussed for four other metabolites of pentamidine, including N,N′-dihydroxypentamidine, 5-(4′-amidinophenoxy)pentanoic acid, 5-(4′-amidinophenoxy) pentan-1-ol, and p-hydroxybenzamidine. Finally, tandem mass spectrometry was used to identify pentamidine and three pentamidine metabolites contained in high-performance liquid chromatographic (HPLC) fractions from rat liver perfusate and rat urine following treatment with pentamidine. Pentamidine metabolites identified in rat urine and liver perfusate using mass spectrometry and HPLC retention times included 2-hydroxypentamidine, 3-hydroxypentamidine and 5-(4′-amidinophenoxy)pentanoic acid.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190300405
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  • 2
    Electronic Resource
    Electronic Resource
    Modeling the heme vibrational spectrum: Normal-mode analysis of nickel (II) etioporphyrin-I from resonance raman, ft-raman, and infrared spectra of multiple isotopomers (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biospectroscopy 1 (1995), S. 395-412 
    Details
    ISSN: 1075-4261
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Nearly complete vibrational assignments have been obtained for a heme model, nickel etioporphyrin-I (NiEPI), using variable-wavelength resonance Raman (RR), and FT-Raman (FT-R), as well as infrared (IR) spectroscopy, on a series of isotopomers labeled at positions in the skeleton (15N, β-13C, meso-d4, 15N-meso-d4) and in the peripheral substituents (methyl-d12, ethyl-d8, and ethyl-d12). The vibrational bands are assigned to the porphyrin skeletal and substituent modes on the basis of the mode description scheme developed for nickel octaethylporphyrin (NiOEP) with the aid of a normal-mode analysis of NiEPI, explicitly including the peripheral substituents, i.e., the methyl and ethyl groups. The previously reported NiOEP force field was refined to account for the observed isotope shifts of NiEPI isotopomers. An important result is the requirement of relatively large, long-range force constants for methine bridge bonds on opposite sides of the porphyrin ring. These 1-8 and 1-9 interaction force constants are required to reproduce the frequencies and isotope shifts of six Cα-Cm stretching modes and especially to predict the relative order of the two highest-frequency Eu modes, v(Cα-Cm) (v38, ∼ 1570 cm-1) and v(Cβ-Cβ) (v37, ∼ 1600 cm-1). Most of the substituent (methyl and ethyl) vibrations are located in the RR and IR spectra. Strong RR enhancement of some substituent modes can be attributed to hyperconjugative interaction of the aliphatic groups with the porphyrin a1u orbital, as well as vibrational mixing of substituent modes with the nearby skeletal modes. © 1995 John Wiley & Sons, Inc.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bspy.350010605
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  • 3
    Electronic Resource
    Electronic Resource
    Structural evolution of the heme group during the allosteric transition in hemoglobin: Insights from resonance raman spectra of isotopically labeled heme (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biospectroscopy 2 (1996), S. 311-316 
    Details
    ISSN: 1075-4261
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Visible resonance Raman spectra in the low-frequency region (200-500 cm-1) are reported for hemoglobin (Hb) reconstituted with heme that is deuterated at the meso carbon atoms (meso-d4). Spectra were obtained in the deoxy form and in the immediate photoproduct of the carbonmonoxide adduct, HbCO. The isotope shifts permit assignment of two out-of-plane modes, γ6 and γ7, and the in-plane skeletal mode ν8, as well as the well-known iron-histidine [Fe-His] stretching vibration. Important differences between deoxyHb and the immediate photoproduct include 1) a large upshift in the Fe-His frequency, from 216 to 228 cm-1, 2) an upshift in γ6 (349 to 353 cm-1) together with substantial diminution of the ν8 (341 cm-1) intensity, and 3) collapse of two γ7 bands (305 and 296 cm-1) to a single band at 304 cm-1. This last observation implies subunit heterogeneity in deoxyHb but not in the photoproduct. When these bands are monitored in the time-resolved RR spectra following HbCO photolysis, it is seen that subunit heterogeneity is first detectable in the 0.5-μs transient [intermediate S], which has been associated with the initial rearrangement of the subunits to form the T-state contacts, on the basis of ultraviolet RR spectroscopy.1 However the intensification of ν8 does not occur until the 17-μs transient (intermediate T′), in which the T-state contacts are locked in and the Fe-His bond is strained. Implications for the mechanism of Hb allostery are discussed. © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    Heme-protein interactions in cytochrome c peroxidase revealed by site-directed mutagenesis and resonance Raman spectra of isotopically labeled hemes (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biospectroscopy 2 (1996), S. 365-376 
    Details
    ISSN: 1075-4261
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Isotope labeling has been used to assign the resonance Raman spectra of cytochrome c peroxidase, expressed in Escherichia coli [CCP (MKT)], and of the D235N site mutant. 54Fe labeling establishes the coexistence of two separate bands (233 and 246 cm-1), arising from the stretching of the bond between the Fe atom and the proximal histidine ligand, His175. These are assigned to tautomers of the H-bond between the His175 imidazole NΓH proton and the Asp235 carboxylate side chain: In one tautomer the proton resides on the imidazole while in the other the proton is transferred to the carboxylate. When Asp235 is replaced by Asn, the H-bond is lost, and the Fe-His stretching frequency is markedly lowered. Two new RR bands are produced, at 205 and 185 cm-1, as a result of coupling between the shifted Fe-His vibration and a nearby porphyrin mode; the two bands share the 54Fe sensitivity expected for Fe-His stretching. C=C stretching and CβC=C bending vibrations have been separately assigned to the 2- and 4-vinyl groups of the protoheme prosthetic group via selective vinyl deuteration. In the acid form of the enzyme, the frequencies coincide for the two vinyl groups, at 1618 cm-1 for the C=C stretch, and at 406 cm-1 for the CβC=C bend. However, the 2-vinyl frequencies are elevated in the alkaline form of the enzyme, to 1628 cm-1 for C=C stretching, and to 418 cm-1 for CβC=C bending, while the 4-vinyl frequencies remain unshifted. Thus, the acid-alkaline transition involves a protein conformation change that specifically perturbs the 2-vinyl substituent. This perturbation might be a reorientation of the vinyl group, or an alteration of the porphyrin geometry that affects the porphyrin-vinyl coupling. The perturbation is attenuated when CO is bound to the enzyme; the C=C frequency is then unaffected in the alkaline form, while the CβC=C bending frequency is shifted to a smaller extent (412 cm-1). This attenuation is probably linked to inhibition of distal histidine binding to the heme Fe in the alkaline form when the CO is bound. © 1996 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    UV resonance Raman spectroscopy of cis - -amidesThis paper is dedicated to Professor D. A. Long on the occasion of his 70th birthday. (1995)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 26 (1995), S. 867-876 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: UV resonance Raman (UVRR) spectroscopy with 210 nm excitation was used to study the cis-amide bonds of caprolactam (CAP) and cis-N-methylacetamide (NMA) in aqueous solution. The UVRR spectrum of CAP is dominated by an intense stretching mode at 1492 cm-1, designated amide cII, which is assigned to a localized CN stretching vibration. The amide cI mode, described as a C=O stretch, can be located at 1621 cm-1 using Fourier transform IR spectroscopy. Photoisomerization of NMA with high laser power, followed by subtraction of the trans-NMA spectrum, is used to generate the isolated UVRR spectrum of cis-NMA and its (C)CD3, (N)CD3 and (C,N)CD3 methyl isotopomers. The spectrum of cis-NMA is also dominated by an intense amide cII band at 1495 cm-1, and a weak band at 1623 + 3 cm-1 can be assigned to amide cI. The amide cII mode is strongly mixed with vibrations of the (N)CH3 group, as revealed by its 24 cm-1 downshift upon (N)CD3 substitution, but no isotopic sensitivity is observed for (C)CD3 substitution. Studies of CAP in various solvents show linear correlations between amide cI and cII wavenumbers and the solvent acceptor number, where amide cI downshifts and amide cII upshifts in hydrogen bonding solvents. However, the slope of the wavenumber dependence for the cis-amide modes of CAP is smaller than for the corresponding trans-amide modes of NMA and cannot be attributed to the differences in mode composition. This behavior is ascribed to different orientations of the ground-state dipole for amides in trans and cis configurations. Finally, the selective enhancement of cis-amide modes at 210 nm excitation was applied to monitor the increase in equilibrium population of cis-NMA with increasing temperature. A Van't Hoff plot of the spectral data to calculate ΔH for cis-trans isomerization yielded values of 1.9 + 0.2 kcal mol-1 from peak heights and 1.7 + 0.2 kcal mol-1 from peak areas (1 kcal = 4.180 kJ), which are in good agreement with previously published theoretical and experimental results.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250260838
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