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C Bustamante

Publications and source records attributed to C Bustamante.

At least 109 records · Page 6Linked to original sources
PubMed1988

Statistical effects in the absorption and optical activity of particulate suspensions.

The phenomenon of Duysens flattening of the absorption spectra resulting from the inhomogeneous distribution of the chromophores in the solution is analyzed. These inhomogeneities are treated as localized statistical fluctuations in the concentration of the absorbing species, by using the Gaussian distribution. A law of absorbance is obtained, and the effect of light scattering on the flattening is also characterized. The flattening in the circular dichroism spectra of particulate suspensions is then analyzed. It is shown that the degree of flattening of the circular dichroism of a suspension is, in general, different from the corresponding flattening of its absorption spectrum. A quantitative relationship between the two effects is established.

Circular Dichroism↗
PubMed1987

Differential polarization imaging. I. Theory.

A theory of differential polarization imaging is derived using Mueller calculus. It is shown that, for any arbitrary object, 16 images (in general different) can be obtained by combining different incident polarizations of light and measuring the specific polarization components transmitted or scattered by the object. These are called the Mueller images of the object. Mathematical expressions of these images for an object of arbitrary geometry are derived using classical vector diffraction theory and the paraxial and thin lens approximations. The object is described as a collection of point polarizable groups. The electromagnetic fields are calculated using the first Born-Approximation, but extension of the theory to higher-order approximations is shown to be straightforward. These expressions are obtained for the transmission, or bright-field, geometry, and the scattering, or dark-field, configuration. In both cases, the contributions of scattering, absorption, and background illumination to the Mueller images are characterized. The contributions of linear dichroism, circular dichroism, and linear and circular intensity differential scattering to certain Mueller images are established. It is shown that the Mueller images represent a complete two-dimensional mapping of the molecular anisotropy of the object.

Mathematics↗
PubMed1987

Differential polarization imaging. II. Symmetry properties and calculations.

Various differential polarization images or Mueller images of model objects are generated using the equations derived in the previous paper (paper I of this series). These calculated images include models of the higher-order organization of metaphase chromosomes, and show the applicability of the differential polarization imaging method to the elucidation of complex molecular organizations. Then, the symmetry behavior of the Mueller matrix elements upon infinitesimal rotations of the optical components about the optical axis of the imaging system is presented. It is shown that the rotational properties of the Mueller images can be used to eliminate the linear polarization contributions to the M14 and M44 images, which appear when these images are generated with imperfect circular polarizations. The relationships between the 16 bright-field Mueller images for four different media, i.e., linearly and circularly isotropic, circularly anisotropic, linearly anisotropic, and linearly and circularly anisotropic, are also derived. For the first three cases simple relationships between the Mueller images are found and phenomenological equations in terms of the optical coefficients are derived. In the last case there are no specific relationships between the Mueller images and instead we briefly present Schellman and Jensen's method for treating this type of medium. The criterion of spatial resolution between adjacent domains of different optical anisotropy is then derived. It is found that in transitions between domains of opposite anisotropy the classical Rayleigh limit must be replaced by a magnitude criterion which depends on the limits of the sensitivity of the detection. Finally, the feasibility of optical sectioning in differential polarization imaging is demonstrated.

Mathematics↗
PubMed1987

Differential polarization imaging. III. Theory confirmation. Patterns of polymerization of hemoglobin S in red blood sickle cells.

In this paper we test the predictions of the differential polarization imaging theory developed in the previous two papers. A characterization of the patterns of polymerization of hemoglobin in red blood cells from patients with sickle cell anemia is presented. This system was chosen because it is relatively easy to handle and because previous studies have been done on it. A differential polarization microscope designed and built in our laboratory was used to carry out this study. This microscope uses an image dissector camera, a photoelastic modulator, and a phase-lock amplifier. This design represents a substantial modification with respect to the instrumentation used in the previous results communicated on this system. Therefore, the results presented here also permit us to confirm the validity of our conclusions. On the basis of the differential polarization images obtained, models of the patterns of polymerization of the hemoglobin S inside the sickle cells are proposed and their M12 and regular images are calculated by the theory. Good agreement between those models and the experimental systems is found, as well as with the results previously reported.

Anemia, Sickle Cell↗
PubMed1987

Steady-state pharmacokinetics of imipenem in febrile neutropenic cancer patients.

We ascertained the pharmacokinetics of imipenem in febrile granulocytopenic cancer patients. The values observed were both different from and significantly more variable than those observed in normal volunteers. Free drug concentrations exceeded the MIC for 90% of Escherichia coli, Klebsiella pneumoniae, and Staphylococcus aureus strains for greater than 6 h. The MIC for 90% of Pseudomonas aeruginosa strains was exceeded for 4 h. Because imipenem induces a 2-h postantibiotic effect in P. aeruginosa, it is promising as single-agent empiric therapy in this setting.

Adult↗
PubMed1985

Circular dichroism studies on single Chinese hamster cells.

The circular dichroism (CD) and circular intensity differential scattering (CIDS) contributions to the CD of single Chinese hamster (CHO) cells have been measured as a function of the position in the cell cycle. The data are analyzed in three main spectral regions: (1) the region above 290 nm (scattering region), (2) the 250-290-nm regions (nucleic acid absorption region), and (3) the region below 240 nm (protein absorption region). The results show that CD/CIDS microspectrophotometry is a good indicator of the cell cycle phase. The results are consistent with the view that chromatin is organized in chiral superstructures which differentially scatter circularly polarized light. These structures appear highly specific and repeatable as the cell passes through its cycle.

Animals↗
PubMed1985

Imaging of optically active biological structures by use of circularly polarized light.

If an optically active (chiral) sample is placed in a microscope and illuminated with circularly polarized light, an image can be formed that is related to the circular dichroism of each feature of the sample. A theoretical investigation has been done for the circular differential image obtained by subtracting the images formed under right- and left-circularly polarized light. Two types of differential images are possible: (i) dark-field images formed from light reflected or scattered by the sample and (ii) bright-field images formed from light transmitted through the sample. The sign and magnitude of each feature in a circular differential image strongly depend on the structure of the sample. The dark-field circular differential images are most sensitive to large features with dimensions similar to the wavelength of illumination whereas the bright-field images are most sensitive to the short-range molecular order. Applications of circular differential imaging may include clinical fingerprinting of normal and transformed cells and structural analysis of individual cellular components.

Circular Dichroism↗
PubMed1984

Multiple-dose pharmacokinetics of imipenem-cilastatin.

We characterized the pharmacokinetic profile of imipenem-cilastatin administered intravenously to six normal volunteers in a dose of 1,000 mg of each drug every 6 h for 40 doses. The plasma concentrations of imipenem and cilastatin 1 h after the end of a 30-min infusion were 18.7 (+/- 2.1) and 19.1 (+/- 4.6), 20.0 (+/- 3.2) and 17.8 (+/- 4.8), and 23.4 (+/- 2.3) and 19.1 (+/- 3.5) micrograms/ml in the 1st, 17th, and 37th dosing intervals, respectively. The central compartment volumes of distribution for imipenem and cilastatin were 0.16 (+/- 0.05) and 0.14 (+/- 0.03) liter/kg, respectively. Elimination half-lives were short: 0.93 (+/- 0.09) h for imipenem and 0.84 (+/- 0.11) h for cilastatin. Plasma clearances were 12.1 (+/- 0.06) liters/h per 1.73 m2 for imipenem and 12.4 (+/- 1.1) liters/h per 1.73 m2 for cilastatin. Renal clearance accounted for 54% of the plasma clearance of imipenem and 69% of the plasma clearance of cilastatin. The concentrations of imipenem in plasma and urine remained above the MICs of the vast majority of pathogens throughout the dosing interval.

Adult↗
PubMed1984

Contribution of differential scattering of circularly polarized light to the optical rotatory dispersion of a sample.

A chiral scattering molecule has the ability to interact differently with circularly polarized light of opposite polarization. This phenomenon has been termed circular intensity differential scattering. It is shown that the differential-scattering phenomenon contributes to the total optical rotatory dispersion (ORD) of the sample. This contribution is independent of the presence of chromophores in the sample. From two general relations, the Kronig-Kramers transforms, obeyed by linear, causal systems, and the optical theorem, a result of energy conservation and power flow, the contribution of the preferential scattering of circularly polarized light to the ORD of the sample is formally obtained. It is seen that this contribution takes place through the circular preferential removal of the coherent part of the wave, i.e., the extinction (by means of scattering) of the transmitted radiation. It is shown that the use of approximations in the description of the internal field in the scattering equations can equivocally predict the absence of a scattering-dependent ORD contribution.

Circular Dichroism↗
PubMed1983

Circular differential scattering can be an important part of the circular dichroism of macromolecules.

Differential scattering of incident left and right circularly polarized light can be an important contribution to the circular dichroism of macromolecules. In principle both differential absorption and differential scattering of circularly polarized light contribute to circular dichroism, but differential scattering is increasingly important for particles whose dimensions are greater than 1/20th the wavelength of light. The scattering contribution is probably not important for unaggregated proteins and nucleic acids in solution. It can be very important for viruses, membranes, and other protein-nucleic acid complexes. Outside the absorption bands of the scattering, chiral particle, only differential scattering contributes to the circular dichroism. The sign and magnitude of the differential scattering is quantitatively related to the relative orientations and the distances between the scattering units of the particle. The interpretation of the circular differential scattering depends on a simple, classical method. Thus, in understanding a measured circular dichroism, it often will be easier to relate the differential scattering to the structure of a particle (such as a virus) than it is to relate the differential absorption to the structure.

Biopolymers↗