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  • 11
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 12
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of elevated hydrostatic pressure on the secondary structure of poly(L-lysine) was studied using Fourier transform ir spectroscopy. According to changes observed in the amide I band, both the β-sheet and the unordered polypeptide undergo a reversible, pressure-induced conformational change to α-helix. The conversion occurs at a much higher pressure from the unordered conformer (∼ 9 kbar) than from the β-sheets (∼ 2 kbar). The structural changes were found to be slower at pH 〉 11, especially at the highest concentration investigated (10 wt%), reflecting the fact that extensive hydrogen-bond networks have to reorganize. This study shows that alterations of polypeptidic conformations induced by elevated hydrostatic pressure are reversible, but that an apparent irreversibility can result from kinetic factors in the case of conformational changes involving extensive rearrangements. The present results also show that the strength of the hydrogen bonds between the backbone amide groups is not the only factor that determines the closest packing of the polypeptide molecules.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 13
    ISSN: 1075-4261
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: The transmission infrared spectra of exfoliated endocervical mucin-producing columnar epithelial cells and the attenuated total reflectance (ATR) infrared spectra of the single-columnar cell layer on the endocervical tissues have been measured and compared with the corresponding infrared spectra of the ectocervical squamous cells and squamous epithelium. The infrared spectra of the exfoliated cervical cells obtained from the present work are comparable with those directly measured from the epithelia on the cervical tissues by ATR technique. The transmission infrared spectra of endocervical columnar epithelial tissue containing some components of the underlying connective tissue have also been measured and compared with the ATR/FTIR (Fourier-transform infrared) spectra of the endocervical columnar epithelial tissue. The effects of the contaminated connective tissue on the infrared spectra of the endocervical columnar epithelial tissue have demonstrated that ATR/FTIR is a more desirable method than the transmission method to obtain meaningful and good-quality infrared spectra of tissue samples, especially samples consisting of thin layers of different types of tissues. Substantial differences in the infrared spectra between the columnar cells and squamous cells on the endocervical and ectocervical tissues, respectively, were evident. The strong glycogen bands in the infrared spectrum of the ectocervical squamous cells are absent in the spectrum of the endocervical columnar cells. This spectral change is similar to that observed in malignant squamous cells. Therefore, if the decrease in the intensity of the glycogen bands is used as the only criterion for the determination of cellular abnormalities in the cervix, the presence of a large number of normal endocervical columnar cells in the cervical specimen would lead to a false result. Consequently, in addition to the glycogen bands, other features in the infrared spectra should be considered for the evaluation of abnormalities in exfoliated cervical epithelial cells. In order to identify the spectral features that are unique to endocervical columnar cells, the infrared spectra of an aqueous solution of glycogen, the mucus from the endocervix, and the connective tissues from both the endocervix and the ectocervix have also been measured and analyzed. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 14
    ISSN: 1075-4261
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Fourier-transform infrared spectra were obtained from the endometrial tissues from 17 females. Thirteen of them had grade I (well differentiated) endometrial adenocarcinoma and four of them had grade III (poorly differentiated) adenocarcinoma. The infrared spectra of the corresponding normal tissues obtained from 1-3 cm away from the tumor were also measured. The spectra of all the normal tissues were essentially identical and differed from those obtained from both the grade I and grade III adenocarcinomas. In order to determine the structural changes at the molecular level, infrared spectra and their pressure dependences of the exfoliated epithelial cells from the normal and grade III adenocarcinoma tissues of the endometrium were studied. Changes in the spectra of malignant samples were observed in the symmetric and asymmetric stretching bands of the phosphodiester backbones of nucleic acids, the CH stretching region, the C(SINGLE BOND)O stretching bands of the C(SINGLE BOND)OH groups of carbohydrates and cellular protein residuals, and the pressure dependence of the CH2 stretching mode. These spectral changes in the malignant endometrium are reproducible and are the result of the structural changes involving an increase in the nuclear size, in the number of hydrogen-bonded phosphodiester groups in DNA, in the intermolecular interaction and packing in nucleic acids, in the conformational and reorientational disorder in the methylene chains of membrane lipids, changes in the membrane fluidity, as well as a decrease in the methyl-to-methylene ratio, and in the number of hydrogen-bonded C(SINGLE BOND)OH groups in carbohydrates and protein residuals. It was also found for the first time from the present work that the epithelium in the normal endometrium exhibits unique structural properties compared with the epithelium of other normal human tissues. © 1996 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 15
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Raman spectrum of aqueous palmitoyl lysolecithin was monitored as a function of pressure between 1 bar and 26.1 kbar. The changes observed in these Raman spectra are discussed in terms of the effect of hydrostatic pressure on the phase state and the molecular structure of lysolecithins. At pressures between 1 and 1900 bar aqueous palmitoyl lysolecithin exists in a micellar state and at pressures above 1.9 kbar it converts into a series of three coagel phases. The critical pressures at 28°C are 1.9 kbar for the micellar to coagel I transition, 4 kbar for the coagel I to coagel II transition and 15 kbar for the coagel II to coagel III transition. The transition from the micellar phase to the coagel I phase has a high pressure hysteresis of 1.1 kbar, while the transitions between the three coagel phases show only negligible pressure hysteresis. The major change in structure occurs at 1.9 kbar where the cylindrical micellar phase converts to an interdigitated lamellar coagel phase; the structural changes at 4 kbar (coagel I/II transition) and at 15 kbar (coagel II/III transition) involve only a modification of the interchain packing.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 16
    ISSN: 1436-5073
    Keywords: infrared ; high pressure ; lipid structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In order to compare the effects ofcis andtrans unsaturation on the structure and packing of phospholipid bilayers, infrared spectra of aqueous dispersions of DOPC and DEPC were measured as a function of pressure up to 36 kbar. Below their respective critical pressures of the liquid crystalline to gel phase transitions, the infrared spectra of DOPC and DEPC are essentially indistinguishable, whereas above these pressures, there are very pronounced differences in the barotropic behavior of these lipids [6]. In particular, the absence of correlation field splittings of the CH2 scissoring and rocking modes of DOPC up to 36 kbar suggests that the bent oleoyl chains are closely packed with all chains parallel to each other.
    Type of Medium: Electronic Resource
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  • 17
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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