We have spectroscopically determined breath ammonia levels in seven patients with end-stage renal disease while they were undergoing hemodialysis at the University of California, Los Angeles, dialysis center. We correlated these measurements against simultaneously taken blood samples that were analyzed for blood urea nitrogen (BUN) and creatinine, which are the accepted standards indicating the level of nitrogenous waste loading in a patient's bloodstream. Initial levels of breath ammonia, i.e., at the beginning of dialysis, are between 1,500 ppb and 2,000 ppb (parts per billion). These levels drop very sharply in the first 15-30 min as the dialysis proceeds. We found the reduction in breath ammonia concentration to be relatively slow from this point on to the end of dialysis treatment, at which point the levels tapered off at 150 to 200 ppb. For each breath ammonia measurement, taken at 15-30 min intervals during the dialysis, we also sampled the patient's blood for BUN and creatinine. The breath ammonia data were available in real time, whereas the BUN and creatinine data were available generally 24 h later from the laboratory. We found a good correlation between breath ammonia concentration and BUN and creatinine. For one of the patients, the correlation gave an R 2 of 0.95 for breath ammonia and BUN correlation and an R 2 of 0.83 for breath ammonia and creatinine correlation. These preliminary data indicate the possibility of using the real-time breath ammonia measurements for determining efficacy and endpoint of hemodialysis.end-stage renal disease ͉ breath analysis E xpired human breath has been analyzed extensively by mass spectrometric techniques for the existence of a variety of trace amounts of volatile organic compounds and several small inorganic molecules such as ammonia, nitric oxide, carbon disulfide, and carbon dioxide (1). Of these, several gases exhaled in human breath, e.g., ammonia, nitric oxide, aldehydes, and ketones, have been linked to kidney and liver malfunction, asthma, diabetes, cancer, and ulcers (2-4). Others, such as carbon disulfide, ethane, butane, and pentane have been linked to neurological disorders, including schizophrenia (5, 6). A few nascent technologies promise the ability to detect some of these compounds at the required parts-per-million (ppm) or parts-per-billion (ppb) concentration levels while in the presence of other interfering species. Recently, a chemiluminescence detector is being deployed for quantifying nitric oxide in human breath (7-9). Of the above aff lictions, endstage renal failure forces over 197,000 patients who require hemodialysis in the United States to undergo lengthy, threetimes-per-week, often painful, in-clinic treatment (paid by Medicare) to compensate for the loss of their kidney functions. Another 28,000 patients undergo peritoneal-or hemodialysis in their homes. Improper, insufficient, and͞or delayed treatment leads quickly to secondary organ failures and a rapid death.Our study indicates that a breath ammonia measurement may be capable of p...

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Temperature dependent photon echo (PE) and nonphotochemical hole burning (NPHB) measurements are reported on resorufin in three organic glasses: ethanol (1.5–11 K), glycerol (1.1–25 K), and d-ethanol (1.5–11 K). In all cases, the NPHB results are broadened considerably from the PE results at low temperatures, but the two measurements coalesce at high temperatures. The temperature dependences are found to deviate from the power law dependence expected for two-level system dephasing, and the deviation is attributed to dephasing by a pseudolocal mode. The appropriate correlation functions for PE and hole burning experiments are shown to be different from each other. They also differ from the correlation function for the optical absorption (OA) experiment, which has been the basis for most calculations of optical dephasing in glasses. The broadening of hole widths beyond the PE result is shown to be a measure of the slow spectral diffusion processes in the glass. Other types of dephasing measurement are also analyzed and each measurement is shown to be sensitive to spectral diffusion to a different degree. By making standard assumptions about glass dynamics, the main experimental results can be accounted for. A long range chromophore–glass interaction and a 1/R distribution of relaxation rates R at short times are indicated.

The structure of lactose permease from Escherichia coli in its lipid environment was studied by attenuated total ref lection Fourier transform infrared spectroscopy. The protein exhibits an ␣-helical content of about 65% and about 25% ␤-sheet. Unusually fast hydrogen͞deuterium (H͞D) exchange to 90-95% completion suggests a structure that is highly accessible to the aqueous phase. An average tilt angle of 33°for the helices was found with respect to the bilayer normal at a lipid-to-protein ratio of Ϸ800:1 (mol͞mol), and the permease exhibits optimal activity under these conditions. However, upon decreasing the lipid-to-protein ratio, activity decreases continuously in a manner that correlates with the decrease in the lipid order parameter and the increase in the average helical tilt angle. Taken together, the data indicate that the structure and function of the permease are strongly dependent on the order and integrity of the lipid bilayer.Understanding of structure-function relationships in membrane proteins is limited for two major reasons: (i) most membrane proteins are difficult to crystallize and therefore their x-ray structures have not been determined, and (ii) the physicochemical influence of the surrounding lipid bilayer on the protein is poorly understood on a molecular level. The lactose permease of Escherichia coli is a paradigm for secondary membrane transport proteins and a suitable candidate to approach these problems. The permease has been overexpressed, purified, reconstituted, and shown to catalyze ␤-galactoside: H ϩ symport as a monomer (for recent reviews, see refs. 1 and 2). All available evidence indicates that the protein spans the bilayer with 12 transmembrane ␣-helices. In addition, freeze-fracture electron microscopy reveals a cleft in the protein that might be related to substrate transport, thereby making the protein highly accessible to the surrounding aqueous phase (3).Employing site-directed and Cys-scanning mutagenesis, as few as four residues in the permease [Glu-269 (helix VIII), Arg-302 (helix IX), His-322 (helix X), and Glu-325 (helix X)] have been shown to be irreplaceable for H ϩ -coupled sugar translocation. Most recently, a molecular mechanism for coupling between H ϩ and lactose translocation has been presented which assigns roles to the four essential residues and their functional relationship to the substrate translocation pathway (4). A central aspect of the proposed mechanism is substrateinduced movement and protonation of Glu-325 from an ionic interaction with Arg-302 into the lipid environment. In the low dielectric environment, the pK a of Glu-325 increases dramatically, and when substrate is released, the ionic interaction between Glu-325 and Arg-302 is reestablished, resulting in deprotonation of Glu-325. Numerous additional effects of the lipid environment on the functional integrity of the permease have been observed. Phosphatidylethanolamine (PE; 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine) has been shown to act as a chaperone for the in vivo ...

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Results of picosecond photon echo and optical hole burning experiments are reported for four ionic dyes in ethanol glass. At low temperatures, the dephasing times deduced from the hole widths are as much as nine times shorter than those measured by the two-pulse echo because of the effect of spectral diffusion. The temperature dependences found are of the form aTα+b exp (−ΔE/kT) due to glass two level system dynamics (T<4 K) and a process that activates exponentially at higher temperatures, possibly from a pseudolocal mode or glass optical phonon. Comparing the ratios of echo to hole burning measured dephasing times for the four dyes suggests that the dephasing is influenced by the existence of distinct local ethanol solvation shells in addition to the dynamics of the bulk solvent. A theoretical description of solvent shell effects is achieved through the use of a two spatial domain model of the glass dynamics. Calculations of dynamic perturbations from distinct solvation shell and bulk solvent regions show that the observed differences between the dyes’ dephasing ratios can be explained if the ionic chromophores alter glass dynamics locally.

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Infrared-absorption studies of thin fullerene films as a function of temperature reveal a splitting of an absorption line at 245+3 K. Another absorption line narrows and its frequency shifts without splitting.These observations support earlier neutronand x-ray-di6raction findings of an orientational phase transformation at 250 K in bulk samples. We provide an explanation based on an accepted crystal structure of C60.The recent discovery of the eScient synthesis of C6p (Ref. 1) has resulted in a fiurry of experimental and theoretical investigations of this highly symmetric cage structure. In addition, observations of photoconductivity and superconductivity ' in doped C6p have focused our attention on the electronic structure and temperature dependence of structural properties of this unusual material. In this paper we report temperature-dependent infrared (IR) spectra of thin films of C6o from room temperature to 10 K. We have studied two of the four IR-active modes. One of the IR absorptions at 1183 cm ' narrows and shifts slightly toward higher energies while the other mode at 1429 cm ' splits at approximately 245 K, and becomes better resolved as the temperature is further lowered to 10 K. We offer an explanation based on a model of the vibrational modes of C60 (Ref. 5) and proposed crystal structures.' These observations are consistent with the recently reported orientational ordering in bulk C60 studied using ' C NMR (Ref. 11 and 12) andx-ray and neutron diffraction.C6p was prepared in an arc and purified chromatographically to remove impurities including C7p