bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fast photovoltage measurements in photosynthesis. I. Theory and data evaluation
Authors: Wulf Karsten , Trissl Hans‐Wilhelm 
Published: May 2005

AbstractFast photovoltage measurements are a valuable tool for the study of trapping of excitation energy, kinetics of charge separation, and relative distances of intermediary acceptors in the photosynthetic reaction center. Recent advances of both, the technique and the data analysis have not been described before. Here, in a first article of this sequence, we describe a theoretical model of the primary photosynthetic reactions and the computer analysis of transient photovoltage as well as of fluorescence data. The model assumes free energy migration between photosynthetic units and takes into account specific effects of high energy excitation like the acceleration of the trapping kinetics, the quenching of the excited state by oxidized reaction centers, and the nonlinear process of exciton‐exciton annihilation. Furthermore, the finite duration of the picosecond flashes is considered. The approximations involved in this model are discussed with respect to different functional antenna organizations. In a second article of this sequence we describe the experimental set‐up, calibration procedures and the application of the present theory to experimental data. © 1995 John Wiley & Sons, Inc.
Fast photovoltage measurements in photosynthesis. II. Experimental methods
Authors: Trissl Hans‐Wilhelm , Wulf Karsten 
Published: May 2005

AbstractFast photovoltage measurements in the pico‐ and nanosecond time range represent a valuable tool for the study of excitation energy trapping, kinetics of charge separation, and the location of intermediary acceptors in the photosynthetic reaction center. However, data recording and data analysis are complex. In a preceding article (Wulf and Trissl,Biospectroscopy,1(1995), pp. xx–xx) we have described the theoretical fundamentals of data analysis. Here we describe the experimental set‐up, calibration procedures, and strategies for the determination of the parameters involved. Limitations of the method will be discussed. © 1995 John Wiley & Sons, Inc.
Kinetics of decomposition of UV‐absorbing intermediate generated during electrochemical oxidation of 6‐mercaptopurine at stationary pyrolytic graphite electrode
Authors: Goyal R. N. , Verma Madhu Shri 
Published: May 2005

AbstractSpectroscopic technique coupled with electrochemical oxidation has been used to study the redox‐mechanism of 6‐mercaptopurine. Electrochemical oxidation of 6‐mercaptopurine has been studied in the pH range 2.0–10.0 by linear and cyclic sweep voltammetry, coulometry and constant potential electrolysis. Spectroscopic technique has been used to monitor the clevage of the SS bond in the UV‐absorbing intermediate generated during electrooxidation. The decay has been observed in a pseudo first order reaction. The ultimate products of oxidation in controlled potential electrolysis have been found as 6‐mercaptopurine and purine‐6‐sulfinic acid. Tentative mechanisms for the formation of the products have also been suggested. It is concluded that spectroscopic studies coupled with electrochemical studies provide a uniquely invaluable insight into the redox mechanism of biologically significant molecules. © 1995 John Wiley & Sons, Inc.
FTIR spectra of deoxyoligonucleotide‐nogalamycin complexes
Authors: Missailidis S. , Hester R. E. 
Published: May 2005

AbstractFTIR spectroscopy has been used to study the three self‐complementary oligonucleotides TGATCA, CGATCG, and TGTACA in the form of complexes with the anthracycline drug nogalamycin. These complexes were prepared under conditions that enable the bulky nogalamycin to intercalate into the double helixes of the oligonucleotide duplexes. Changes in the FTIR spectra on complexation are indicative of strong perturbation of the AT base pairs, in contrast with the effect of the structurally related drugs adriamycin and daunamycin, which show affinity for GC base pairs. These differences are attributed to binding interactions with the functional groups attached to the aglycone chromophore rather than to the specific site of drug intercalation in the double helix. © 1995 John Wiley & Sons, Inc.
Infrared spectroscopic data favor a global mode hydration in determining DNA conformation by water activity
Authors: Phole Walter , Bohl Martin 
Published: May 2005

AbstractThe conformational A–B transition of natural random‐sequence NaDNA can be evoked simply by increasing the water activity in the specimen. Infrared spectroscopic data create a basis for the idea that the relevant solvent action proceeds in a global sense comprising a collective influence of the water molecules belonging to DNA hydration shell rather than by directly bound water molecules. This conclusion is consistent with the results of Molecular Dynamics simulations applied to various DNA fragment‐water systems. © 1995 John Wiley & Sons, Inc.
Interaction between drugs and water‐soluble polymers: VIII. Binding position of naproxen to bovine serum albumin
Authors: Tanaka Masami , Asahi Yutaka , Masuda Seizo 
Published: May 2005

AbstractThe interaction between naproxen (NP) and bovine serum albumin (BSA) was investigated by equilibrium dialysis. Since the binding constant of NP to BSA was independent of ionic strength and decreased with increase of alkyl chain length of fatty acid added, the interaction between NP and BSA was considered to be due to hydrophobic mechanism. Chemical shifts in 1H‐NMR spectra of NP were independent of the concentration of NP and addition of BSA. Spin‐lattice relaxation time (T1) and spin‐spin relaxation time (T2) of respective protons of NP were independent of the concentration, but depended on the concentration of BSA added. The binding position of NP to BSA was considered to involve the hydrophobic aromatic moiety of NP from the ratio of spin‐spin relaxation rates (1/T2) of NP bound to BSA and free NP. © 1995 John Wiley & Sons, Inc.
Peroxidation of erythrocytes: FTIR spectroscopy studies of extracted lipids, isolated membranes, and intact cells
Authors: Moore David J. , Sills Richard H. , Mendelsohn Richard 
Published: May 2005

AbstractFourier transform infrared (FTIR) spectroscopy was used to directly monitor peroxidative damage to membrane phospholipid acyl chains in erythrocyte membranes. Samples were suspended in a mixed 2H2O/H2O buffer system, thereby producing a “spectral window” in the C‐H stretching region of the infrared spectrum. A decrease in the number of acyl chain CC bonds upon erythrocyte peroxidation was quantitated directly from the spectra of isolated membranes. Second‐derivative spectroscopy permitted the conformationally sensitive membrane acyl chain methylene stretching modes to be separated from the protein (mostly hemoglobin) vibrations that dominate the spectra of intact cells. The sensitivity of these modes in erythrocytes was then determined in a series of thermotropic experiments. The effect of peroxidation upon the membrane acyl chain conformational order was monitored in isolated membranes and intact cells. No change in conformational order was detected upon peroxidation in intact cell and ghost spectra. In contrast, experiments with pure unsaturated phospholipids demonstrated that decreasing the CC bond population results in increased conformational order. The finding of identical results for peroxidation versus control samples in isolated membranes (“ghosts”) validates the results observed for intact cells. FTIR technology permits the direct monitoring of conformational order in the acyl chains of intact cells. © 1995 John Wiley & Sons, Inc.
Infrared spectra of human central nervous system tissue: Diagnosis of alzheimer's disease by multivariate analyses
Authors: Choo L.‐P. , Mansfield J. R. , Pizzi N. , Somorjai R. L. , Jackson M. , Halliday W. C. , Mantsch H. H. 
Published: May 2005

AbstractWe present an infrared (IR) spectroscopic view of the pathological features of Alzheimer's disease (AD), along with a means of classifying the spectroscopic data nonsubjectively using several multivariate methods. The results demonstrate that IR spectroscopy can potentially be used in the diagnosis of AD from autopsy tissue. Although several spectral features that appear to be related to the disease process can be detected by a visual inspection of the IR spectra of AD grey matter, the appearance of these features was inconsistent. A more successful (consistent) diagnosis is achieved using multivariate analysis of the spectroscopic data. It is shown that correct classification of white and grey matter from brains identified by standard pathological methods as heavily, moderately, and minimally involved can be achieved with success rates of greater than 90% using appropriate methods. Classification of tissue as either control or AD was achieved with a success rate of 100%. © 1995 John Wiley & Sons, Inc.
Copper bilirubinate and black pigment gallstone
Authors: Li W.‐H. , Shen G.‐R. , Soloway R. D. , Yang Z.‐L. , Tong X.‐B. , Wu E. , Xu D.‐F. , Wu J.‐G. , Xu G.‐X. 
Published: May 2005

AbstractA series of copper bilirubinate complexes (CuBR) was synthesized in solution and in solid state to mimic the black color of the black‐pigment gallstone and to explore the formation mechanism of the gallstonein vitro. The variation of the copper contents of these samples indicated that CuBR also exhibits nonstoichiometric characteristics from the FTIR study, i.e., both the so‐called acid and neutral copper complex moieties exist in CuBR. The NH groups in pyrrole and lactam groups of bilirubin (H2BR) are binding to the copper ions. An EPR study demonstrates the generation of free radicals and the variation of its electronic structure and conjugation system in the skeleton of H2BR molecule during complex formation. A polymer of CuBR may form through the reaction of H2BR with copper ions. © 1995 John Wiley & Sons, Inc.
Surface‐enhanced Raman spectroscopy of bilirubin‐metal ion complexes
Authors: He Jiping , Lu Xian Dan , Zhou Xingyao , Yu Nai‐teng , Chen Zhenhua 
Published: May 2005

AbstractSurface‐Enhanced Raman Scattering (SERS) spectra of bilirubin–metal ion (Cu2+, Co2+, Zn2+, Cd2+) complexes (MBR) are reported. These spectra reveal significant differences between MBR and bilirubin (BR) itself. But SERS spectra of bilirubin–Cu2+, Co2+, Zn2+, Cd2+ complexes are similar to each other. The mole ratio of bilirubin‐metal in the complexes M2+ : BR = 1 : 1 was measured. Empirical assignments of the major SERS bands are given. The spectrum of CuBR in solution is consistent with a square planar structure. It should be noted, however, that H2O or COOH of another BR molecule occupy the positions above and below the plane in solutions of complexes of this type and forms CuO bond.By comparing the SERS spectra of bilirubin‐copper (or zinc) and biliverdin‐copper (or zinc) complexes, the similar Raman frequencies and relative intensities were attributed to the oxidation of the bilirubin‐copper (or zinc) complex to the green biliverdin‐copper (Zn) complexes. It is shown that . © 1995 John Wiley & Sons, Inc.
DNA dynamics observed with long lifetime metal‐ligand complexes
Authors: Lakowicz Joseph R. , Malak Henryk , Gryczynski Ignacy , Castellano Felix N. , Meyer Gerald J. 
Published: May 2005

AbstractMeasurements of DNA dynamics are typically limited to the nanosecond timescale because of the nanosecond decay times of commonly used fluorophores such as ethidium bromide and acridine derivatives. We show that the time‐resolved anisotropy measurements can be extended to the submicrosecond timescale using metal‐ligand complexes. The ruthenium complex [Ru(2,2′,‐bipyridine)2(dipyrido[3,2‐a : 2′,3′‐c]phenazine)]2+, or [Ru(bpy)2(dppz)]2+, was found to display high anisotropy near 0.2, at −60°C in 100% glycerol, when excited in its long‐wavelength absorption bands. The decay time of [Ru(bpy)2(dppz)]2+ when bound to DNA is over 100 ns, allowing intensity to be measured to over 400 ns. Other Ru complexes display still longer lifetimes to 750 ns when bound to DNA. This class of fluorophores should enable measurement of DNA dynamics over a wide range of times (from 1 ns to several μs), which were previously inaccessible using time‐resolved fluorescence. © 1995 John Wiley & Sons, Inc.
Role of amino‐acid sidechains in electron‐transfer reactions in reaction center of rhodopseudomonas viridis as revealed by extended hückel molecular orbital calculations
Authors: Nakagawa Hiroyuki , Okada Takashi , Koyama Yasushi 
Published: May 2005

AbstractThe amino‐acid sequences of the L‐ and M‐subunits of the reaction centers (RC) from four purple photosynthetic bacteria were compared by the use of CLUSMOL/S (Clustering System for Molecules/Sequences), and conserved and character‐conserved amino acids were extracted. Extended Hückel molecular orbital (MO) calculations were made, based on the three‐dimensional structure of the Rhodopseudomonas viridis RC, for eleven composites of pigments, in which the sidechains (except for aliphatic sidechains) of the above amino acids within a distance of 6 Å from both of each pair of electron donor and acceptor were included. Calculations of the electronic coupling between each pair of donor and acceptor as well as evaluations of mixing of the lowest unoccupied molecular orbital (LUMO) of one chromophore with the orbitals of another chromophore and amino‐acid sidechains elucidated the roles of the sidechains in the electron transfer reactions: (1) L181‐Phe and M208‐Tyr function as a pair of bridges in the electronic coupling among pigments bacteriopheophytin in the M‐branch (HM), accessory bacteriochlorophyll in the M‐branch (BM), one of the special‐pair bacteriochlorophylls in the M‐branch (PM), one of the special‐pair bacteriochlorophylls in the L‐branch (PL), accessory bacteriochlorophyll in the L‐branch (BL), and bacteriopheophytin in the L‐branch (HL), and can affect the special‐pair bacteriochlorophylls (P) → HL electron transfer; (2) M250‐Trp plays a crucial role in the HL → primary quinone (QA) electron transfer, but L216‐Phe does not facilitate the HM → secondary quinone (QB) electron transfer; (3) the Fe2+ ion and the ligating histidines facilitate the QA → QB electron transfer; (4) L162‐Tyr plays a key role in the third heme in the cytochrome subunit (Heme) → P (PM plus PL) electron transfer. © 1995 John Wiley & Sons, Inc.
FTIR and EPR study of radicals of aromatic amino acids 4‐methylimidazole and phenol generated by UV irradiation
Authors: Berthomieu Catherine , Boussac Alain 
Published: May 2005

AbstractThe oxidized radicals of aromatic amino acids, 4‐methylimidazole and phenol were generated by UV irradiation at low temperature. The radicals were monitored by EPR spectroscopy. For the first time, infrared (IR) modes characteristic of the tyrosine, tryptophan, phenylalanine, and histidine radicals were obtained by FTIR difference spectroscopy between the ground state and the radical state. The effects of D‐ (on Tyr and phenol) or 15N‐ (on His) labeling on the IR modes of the radicals were studied, as were the influence of hydrogen bonding and of pH. These parameters were studied to model the possible radical structures and environments in proteins. The radicals obtained with tyrosine, phenol, and 4‐ethylphenol present six main IR modes: a combination mode at ∼ 2110–2106 cm−1; the v8b(CC) mode at 1550–1556 cm−1, the v7a(CO) and v19b(CC) modes both at 1515–1500 cm−1, which are distinctly affected by D‐labeling of the phenol ring; the 14(vCC + δCH) mode at 1290–1288 cm−1, which is strongly modified when the radical is hydrogen bonded; and the 9a(CC) mode at 1163–1159 cm−1. These IR modes partly confirm the assignments made by resonance Raman (RR) spectroscopy and should help to obtain precise structure and force field calculations for the radicals. The deprotonated 4‐methylimidazole radical (4‐MeIm·) is obtained at pH 12. It has characteristic IR modes at 1593 v(CC), 1425 δCH3, 1376 δCH3, 1315 cm−1, 1213 cm−1 and 1098 cm−1 δ(CH). The methyl modes seem strongly downshifted upon radical formation, while the ring modes appear less affected. In particular, the C4C5 double‐bond character is conserved. The protonated 4‐methylimidazole radical formed at pH ≤ 6 is characterized by signals at 1433 cm−1, 1380 cm−1, 1310 cm−1, 1227 cm−1, and 1172 cm−1. The histidine and tyrosine radicals present similar IR modes as the corresponding model of their sidechain. For all the amino acids, the vas(COO−) and vs(COO−) modes of the terminal carboxylate were respectively up‐ and downshifted by ∼ 20 cm−1 upon the radical formation. This effect suggests that, in a protein, the amide bond of the amino acid could also be influenced by the radical formation. © 1995 John Wiley & Sons, Inc.
Pressure‐induced secondary structure changes of ribonuclease A and ribonuclease S studied by FTIR spectroscopy
Authors: Takeda Naohiro , Kato Minoru , Taniguchi Yoshihiro 
Published: May 2005

AbstractFourier transform infrared (FTIR) spectroscopy combined with a resolution‐enhancement technique has been used to characterize pressure‐induced changes in the secondary structure of ribonuclease A (RNase A) and ribonuclease S (RNase S) in D2O solution at 30°C. According to the observed changes in the amide I' band, both RNase A and RNase S are reversibly unfolded by application of high pressure. The pressure‐unfolded state of the two proteins does not have any secondary structure elements characteristic of their native state, such as α‐helix, β‐sheet, and reverse turn. However, there is a slight difference in the structural features between pressure‐unfolded RNase A and RNase S, which is distinguished by the formation of nonnative turns only for RNase S. The dramatic structural transition of RNase A occurs over the pressure range between 570 and 1030 MPa. The pressure stability of RNase S is decreased by about 300 MPa compared with RNase A, despite little difference in the two native secondary structural features identified by FTIR spectroscopy. The structural features upon the pressure‐induced unfolding are additionally characterized by the interesting behavior of hydrogen‐deuterium exchange at high pressure. Most of the backbone amide protons protected at atmospheric pressure, which are involved in the α‐helices and β‐sheet of both RNase A and RNase S, are exchanged with solvent deuterons in the pressure range where the two secondary structure elements are virtually identified as intact. It is suggested that the solvent accessibility to the internal regions is strongly correlated to the pressure stability. © 1995 John Wiley & Sons, Inc.
Structure characterization of strontium (II) bilirubinate complexes
Authors: Liu Huizhou , Lu Kunquan , Soloway Roger D. , Yang Zhanlan , Zhao Yaqin , Wu Jinguang , Xu Guangxian 
Published: May 2005

AbstractCalcium bilirubinate (CaBR) is the main component of pigment gallstones. At present no crystal structure of CaBR is available. Extended x‐ray absorption fine structure (EXAFS) is a powerful tool for local atomic structure determination, but it is difficult to measure the EXAFS spectra of calcium in compounds. Strontium bilirubinate (SrBR) was used instead of calcium, because of the similarity of IR spectra between CaBR and SrBR complexes. In this investigation a series of SrBR was synthesized. FTIR and EXAFS spectroscopic techniques were adapted to characterization. The results provide evidence of SrBR formation. It follows that the first shell about Sr (II) of the neutral BR compound consists of oxygen and nitrogen atoms with Sr‐O and Sr‐N distances of 2.61 Å and 2.69 Å, respectively. The coordination number of Sr is eight, consisting of four O atoms and four N atoms. It can lead to the unfolding of the coordination structure of CaBR. © 1995 John Wiley & Sons, Inc.
Determination of the hydrogen‐bonded structure of CGG trimers in chloroform solution by vibrational spectroscopy
Authors: Carmona P. , Molina M. , Lasagabaster A. , Escobar R. 
Published: May 2005

AbstractInfrared and Raman spectra of 2′‐deoxy‐3′,5′‐bis (triisopropylsilyl) guanosine (G) and its 2 : 1 mixture with 2′‐deoxy‐3′,5′‐bis (triisopropylsilyl) cytidine (C) have been studied in chloroform solution. Strong interactions occur between CG base pair and a second G whose association constant was first determined. CGG trimer is stabilized by two hydrogen bonds between a G which is in a Watson‐Crick base pair and a second G. These interguanine hydrogen bonds involve the N(7) and O(6) guanine acceptors and N(1)H and N(2)H guanine donors. The 1570 cm−1 band of guanine is sensitive to hydrogen bonding at the N(3) position. Since this band is unchanged upon CGG formation, it is concluded that no binding at the guanine N(3) position occurs in the trimer. The pattern of hydrogen bonding in CGG trimer in chloroform solution here appears to correspond with patterns of hydrogen bonding in nucleic acid triplexes. These spectroscopic measurements constitute the first application of vibrational spectroscopy to the structural study of CGG trimer and self‐associated G in a nonaqueous solvent, and these nucleosides can be used as molecular models to know the hydrogen bonding in the hydrophobic interior of nucleic acid double and triple helices. © 1995 John Wiley & Sons, Inc.
Comparison of base inclinations for left‐handed DNA and RNA
Authors: Krittanai Chartchai , Kang Hunseung , Jin Xiaokui , Riazance‐Lawrence Jeannine H. , Curtis W. Johnson 
Published: May 2005

AbstractThe Z'‐form of poly(dG‐m5dC) · poly(dG‐m5dC) in 85% ethanol/MOPS and the Z‐form poly(rG‐rC) · poly(rG‐rC) in 4.8 M NaClO4, 20% ethanol are studied by flow linear dichroism. Simulataneous analysis of the isotropic absorption and linear dichroism data yields the angle of inclination of the base normal relative to the helix axis, and the orientation of the axis around which the bases incline. For the Z'‐form of poly(dG‐m5dC) · poly(dG‐m5dC) the inclination angles are 31.3° for guanine, and 27.9° for cytosine; for the Z‐form of poly(rG‐rC) · poly(rG‐rC) they are 25.0° for guanine, and 23.3° for cytosine. The inclination angles for the Z'‐form DNA are similar to those for the Z‐form, and the angles for Z‐form RNA are somewhat smaller. The axes of inclination for guanine and cytosine are similar in all three left‐handed forms. © 1995 John Wiley & Sons, Inc.
Raman depolarization ratios in RNA and DNA are sensitive for sugar‐base coupling
Authors: Terpstra P. A. , Otto C. , Segers‐Nolten G. M. J. , Kanger J. S. , Greve J. 
Published: May 2005

AbstractPolarized and depolarized Raman spectra are obtained for a number of synthetic polynucleotides containing adenine, uracil, and thymine bases. The depolarization ratios are determined by two methods: (1) by dividing the ⟂‐spectrum by the ∥‐spectrum and (2) after curve fitting. Overlapping bands, isotope splitting, reorientational broadening, and noncoincidence splitting affect the magnitude of the depolarization ratios over the band‐width. For both Lorentz and Gauss curves these influences are simulated. A comparison of the Raman spectra of RNA and DNA molecules shows that the depolarization ratios for a number of similar base vibrations are different. The vibrational modes and the depolarization ratios of sugar vibrations are most sensitive to the structure of the polynucleotide. Base vibrations that have their potential energy distributed over base and sugar atoms also seem to be more sensitive to the structure. For instance the adenine vibrations at 1332 cm−1 and 1344 cm−1 in poly(dA), poly(dA) · poly(dT) and poly(dA‐dT) · poly(dA‐dT) have different depolarization ratios of, respectively, 0.36 and 0.28. This supports a previous assignment of the 1332 cm−1 band to a different sugar pucker (O4,‐endo) than the C2,‐endo corresponding with the 1344 cm−1 vibration. Assuming equal Raman scattering coefficients for this vibration, irrespective of the sugar pucker gives rise to the following ratio of the O4,‐endo/C2,‐endo in poly(dA) of 0.41, in poly(dA) · poly(dT) of 0.37, and in poly(dA‐dT) · poly(dA‐dT) of 0.41. © 1995 John Wiley & Sons, Inc.