CH Content Research Articles

Polystyrene-block-poly(2-cinnamoylethyl methacrylate) Tadpole Molecules

In THF/cyclopentane (CP) or THF/cyclohexane (CH) mixtures with sufficiently high CP or CH contents, polystyrene-block-poly(2-cinnamoylethyl metharylate) (PS-b-PCEMA) forms micelles with PCEMA as the core. Coexisting with the micelles are unimer chains. The unimers are expected to have the tadpole conformation with the PS block assuming the normal random-coil conformation and the PCEMA block clustering together like a globule. Photo-cross-linking the PCEMA globule of the unimers enabled our first preparation of permanent tadpole molecules from diblock copolymers. The tadpole conformation has been confirmed by our GPC, light scattering, and NMR study.

Increased NaCl preference of rats fed low-protein diet.

Four studies were conducted to assess the effect of a low-protein diet on NaCl intake. Young rats fed either control (20% casein) or low-protein (5% casein) high-carbohydrate (CHO) diet were allowed to drink either water alone or water and 300 mM NaCl. Relative to rats fed control diet, rats fed the low-protein diet progressively increased NaCl intake so that, despite lower food and water intakes, they drank 180% more NaCl during the last 3 days of the 21-day test. Additional studies found that rats fed low-protein diet always maintained positive sodium balance, were neither sodium depleted nor hypovolemic, and had normal plasma renin activity and aldosterone concentrations. The elevated NaCl intake was not secondary to calcium deficiency and was unaffected by mineral supplementation of the protein-deficient diet. Increases in the diet's CH and/or fat content incidental to decreases in its protein content influenced, but could not completely account for, the effect of protein deficiency on NaCl intake. We conclude that protein deficiency is the primary cause of the elevated NaCl preference produced by being fed a low-protein diet and that a novel physiological mechanism underlies this behavior.

Atmospheric carbon emission from North Asian Lakes: A factor of global significance

Partial pressures of CO 2 and CH 4 were measured directly or calculated from pH and DIC measurements for 20 lakes on the Yakutian Lowland, North Slope of Verkhoyansky Mountain Ridge, the Kolyma Lowland and in the estuary of the Lena River. Most of the northern landscapes were presented in the sample, which are between the High Arctic (Tiksi area) and the Low Arctic/Subarctic (Chersky area). All limnic waters were supersaturated significantly with respect to the atmospheric pressure of CO 2 and CH 4. The content of CH 4 in High Arctic lakes ranged usually between 10 −1 and 10 −2 μM in the surface layer and between 10 0 and 10 −2 μM in the bottom layer. These values are about 10 2 times lower than in Low Arctic/Subarctic lakes. The partial pressure of CO 2 (PCO 2) ranged usually between 400 and 6000 ppm in the Tiksi site and between 4000 and 20,000 ppm in the Chersky site, although extreme values of PCO 2 reached up to 27,000 ppm in the bottom layer of subarctic thaw lakes. The fall-winter shipboard measurements show that the value of PCO 2 varied significantly from the Bering Sea to the Laptevs Sea. The surface waters of the Laptevs Sea were undersaturated by CO 2, whereas other arctic seas east of the Laptevs seas were slightly supersaturated. The shallow coastal waters from the Laptevs Sea to the Bering Sea were usually 1.5-3-fold supersaturated by CO 2. The shipboard measurement of CH 4 in the arctic seas shows that the concentration of CH 4 was usually less than 0.015 μM. It confirms the previous air-flight data that show a 10–15% increase of CH 4 over land. The analysis of up-to-date experimental results and glaciological data concerning air palaeovariations of CH 4 and CO 2 shows that evolution of the northern lakes might be a significant factor in the present and the past.

Is control of distribution of liposomes between tumors and bone marrow possible?

The objective of this study is to clarify to what extent the accumulation of liposomes from the blood into the tumor and bone marrow can be controlled by liposome size and membrane fluidity. Liposomes with different diameters (50–400 nm) and different membrane fluidity were prepared from hydrogenated egg phosphatidylcholine (HEPC) or egg phosphatidylcholine (EPC), cholesterol (Ch) and dicetylphosphate in various molar ratios. These liposomes were injected intravenously into rats bearing Yoshida sarcoma, and the ratios of the accumulation of liposomes in the tumor to those in the bone marrow, liver and spleen were compared. The tumor-to-bone marrow accumulation ratio increased with the decrease in liposome size from 400 to 50 nm. This ratio was greater than those for the liver and spleen at all sizes. Although tumor-to-liver accumulation ratios of 50- and 100-nm HEPC-containing liposomes were higher than those of EPC-containing liposomes, no obvious difference in tumor-to-bone marrow or tumor-to-spleen accumulation ratios was found between these liposomes. Tumor-to-bone marrow accumulation ratio of HEPC-containing liposomes increased remarkably with the decrease in Ch content from 40 to 30 or 20 mol% compared with ratios for the liver and spleen. Interestingly, the tumor uptake clearance of liposomes of the same size was constant regardless of their membrane fluidity. These findings show that the increases in these accumulation ratios are due to their decreased uptake clearance by the bone marrow. Furthermore, the uptake of 50-nm HEPC-containing liposomes by the bone marrow was specifically inhibited by preinjection of other liposomes, but not when they were exposed in advance to in vivo components. These observations suggest the involvement of in vivo component(s) in the uptake of these liposomes by the bone marrow. We conclude that small HEPC-liposomes with low Ch content show their significantly decreased uptake by the bone marrow due to their decreased recognition by this tissue.

Environmental impact of demolition waste — An overview on 10 years of research and experience

Demolition waste is a major part of industrial waste. In general, demolition waste is heterogeneous and consists to a large extent of building materials but includes even small amounts of hazardous substances. Since the early 1980s the processing of building rubble has become more and more common in most industrialised countries. After appropriate processing the major part of these materials meet the technical properties for reuse. Increasing emphasis is being placed on the environment-related properties due to composition and origin. The results of standard leaching tests are discussed both regarding treatment technologies and different secondary building materials obtained. Generally, the effect of wet or dry processing is considered to be of subordinate importance to the environment-related properties of the main fraction. A comparison of more than 10 different treatment plants proves this statement. Only some 3–50% of this fraction is subjected to wet and dry processing. Even a significant difference between portable and stationary plants could not be ascertained. Inorganic compounds dominate the leachate composition due mainly to the mineral matter in demolition wastes. However, organics, e.g. phenols, PAH, PCB and halogenated compounds, are detected in some cases. The leachability of sulphate, heavy metals (Ni, Pb), and phenols as well as the solid content of EOX, PAH and CH might restrict an unlimited application. Compared to the research carried out earlier, the environment-related properties of leachate from demolition waste are now less important. In fact, the influence of waste treatment is of minor significance whereas the pre-treatment or pre-selection is more important to the operators of demolition recycling plants. According to the change in waste composition and tighter specifications the treatment process and demolition techniques must be optimised.

Compositional and sequential analysis of poly(ethylene-tetrafluoroethylene) by pyrolysis-gas chromatography

Compositional and sequential analysis of PETFE (poly(ethylene (E)-tetrafluoro-ethylene (TFE)-perfluoroalkylethylene (RfCHCH 2))) are carried out after optimization of pyrolysis-gas chromatography (Py-GC) experimental conditions. The content of RfCHCH 2 is readily obtained by Py-GC using standard samples whose compositions are known by conventional techniques ( 19F NMR and total fluorine content analysis). Reproducibility of the determination of each composition by Py-GC stands up to comparison with the conventional techniques. The amount of TFE-TFE sequence in the terpolymer is estimated from seven selected peaks on the pyrogram, so that a rough indication of the TFE E ratio is obtained. Consequently, a quick and easy determination method by Py-GC is established. Furthermore, it is found that crystallinity due to the decrease in the alternating character of the TFE-E sequence may cause the decrease in melting point of the terpolymer.

Neuronal damage and decrease of central acetylcholine level following permanent occlusion of bilateral common carotid arteries in rat

The neuronal damages and the changes in central acetylcholine (ACh) and choline (Ch) contents following permanent occlusion of bilateral common carotid arteries (2VO) of rats were investigated 1 and 4 months after the operation. Two types of neuronal damages were observed in the rats with permanent 2VO. The first type was the infarctions observed in the cerebral cortex and striatum. The infarction in the cortex and striatum was observed in 28.6 and 42.9% of the animals examined 1 month after permanent 2VO, respectively. These ratios did not change even when examined 4 months after permanent 2VO, suggesting that this type of neuronal damage is due to acute ischemic attacks. The second type was progressive neuronal damages observed in the hippocampus and white matter: the neuronal loss in the CA1 subfield appeared 4 months but not 1 month after permanent 2VO and the rarefaction of white matter which was observed 1 months after permanent 2VO and markedly increased 4 months after the operation. Moreover, ACh level significantly decreased in the striatum but not in the cortex, hippocampus or hypothalamus 1 month after permanent 2VO, while the ACh levels in the cortex, striatum and hypothalamus, and Ch levels in all the regions tested significantly decreased when tested 4 months after the operation. These changes did not accompany necrosis. These results suggest that the progressive neuronal degeneration and cholinergic dysfunction following the permanent 2VO are in part involved in chronic cerebral hypoperfusion-induced long-lasting cognition deficits in rats.

95/02112 Current status of FTIR in the analysis of coal structure

Infrared spectroscopy has been a basic {open_quotes}workhorse{close_quotes} technique for coal characterization since the pioneering work of Brown nearly 40 years ago. The optical and data handling advantages of MR have allowed various advances, such as the introduction of {open_quotes}hyphenated{close_quotes} techniques (GC-FTIR, IR-Microscopy, etc.) and novel sampling methods (diffuse reflection, photo-acoustic measurement, etc.), but most of the problems in coal structural analysis remain the same; the quantitative determination of various functional groups in coal and how the concentration of these groups varies with, for example, oxidation or liquefaction. In a short article of this type justice cannot be done to the range and scope of work reported by various groups. Accordingly, we will concentrate our attention on just one problem, but a problem that is of central importance in the analysis of coal structure; the determination of the aliphatic and aromatic CH content of coal and coal derived material.

Brain fixation for acetylcholine measurements

Brain fixation using a commercially available microwave oven (power output: 750 W) has been investigated as a means for enzyme inactivation preventing post-mortem changes in brain acetylcholine (ACh) and choline (Ch) levels. Rats and mice were decapitated, and the severed heads immediately irradiated for 5.5 and 3 s, respectively, resulting in a complete inactivation of brain acetylcholine esterase (AChE) and choline acetyltransferase (ChAT). The ACh and Ch contents measured in various brain regions of rat and mouse were: (in rat) striatum 60.5 and 32.4 nmol/g, hippocampus 20.4 and 30.9 nmol/g, cortex 24.2 and 19.6 nmol/g; (in mouse) striatum 70 and 47.2 nmol/g, hippocampus 22. 1 and 30.2 nmol/g, cortex 22.9 and 27.9 nmol/g. These values were found in accordance with those reported in the literature by irradiating whole animals in instruments of higher power capabilities. Thus, the procedure described in the present work may be a simple and valuable means of brain fixation for neurochemical studies of brain ACh in small animal species.

Evidence for Li-rich brines and early magmatic fluid-rock interactionin the Larderello geothermal system

The geochemical features of fluids accompanying the first stages of geothermal activity linked to magmatic intrusions have been documented for the Larderello geothermal system (Italy). Deep drilling has provided samples which preserve evidence of this early geothermal activity. Four wells (San Pompeo 2, Monteverdi 7, Sasso 22, and Serrazzano, VC 11) penetrated the deeper parts of the Larderello system, located in a metamorphic basement underlying the Tertiary nappe complex which constitutes the main aquifer at Larderello. The drill holes terminated close to the inferred roof of a granitic complex thought to be responsible for geothermal activity. Fluid inclusion data were obtained from recrystallized quartz lenses and quartz veins in samples displaying high temperature assemblages (plagioclase-actinolite-biotite-tourmaline; clinopyroxene ± andradite-wollastonite) and also from magmatic quartz in a leucogranite dike. The inclusions are mainly secondary in origin, oriented in fluid inclusion planes (FIP) related to hydrothermal circulation in the Larderello system. Several generations of high temperature fluids were trapped and include: 1. (1) H 2OCO 2 dominated vapors displaying variable but significant contents of CH 4 and N 2; 2. (2) aqueous vapors containing LiCl, with variable salinity; 3. (3) aqueous LiCl brine, often oversaturated with respect to halite at room temperature; 4. (4) complex brine, always oversaturated at room temperature with respect to two (halite and sylvite) or more ( n ≤ 4) salts. The presence of LiCl was confirmed by identification of the salt hydrate (LiCl5H 2O) at very low temperature using Raman spectroscopy. Bulk salinities could be roughly estimated at around 30 wt% eq. LiCl for the LiCl brine. Geometric and chronologic relationships between FIP reveal close relationships and mutual contamination between the H 2OCO 2 vapors and LiCl brine, indicating synchronism in their trapping. These fluids were generated and trapped at pressures of 100–130 MPa, nearly 23 MPa above the estimated present-day lithostatic pressure. This implies a denudation rate between 0.2 and 0.5 mrn· a −1 since the onset of hydrothermal activity, compatible with the setting of Larderello in a young (Tortonian) collision belt. Fluid inclusion trapping temperatures (425–650°C) show a monotonous increase towards the inferred granite, and are around 100–200°C higher than the highest present-day temperatures. The results are interpreted as recording the interaction between magmatic and contact metamorphic fluids in the early Larderello system. The H 2OCO 2 vapors resulted from the reheating of the basement metamorphic series (often C-rich) under relatively high temperatures during contact metamorphism. Lirich fluids expelled from an underlying Li-rich leucogranite migrated through the metamorphic series and the already cooled granite dikes and experienced local boiling. The fluid inclusion data demonstrate the involvement of magmatic fluids during the initial development of this high energy geothermal field.

Effect of dexamethasone on the expression of binding sites for high-density lipoproteins in cultured rat hepatocytes (Independence of the hormone effect on the intracellular cholesterol pool)

It is shown that glucocorticoids play a key regulatory role directed toward the maintenance of an optimal level of binding and internalization of HDL3 in hepatocytes. Their stimulatory effect on the expression of HDL receptors proves to be independent of changes in the CH content in parenchymal cells.

Acute neurochemical changes in mouse brain following cerebral ischemia

Acute changes in neurochemical levels induced by ischemia were studied in the mouse brain. Contents of neurochemicals in the frontal, parietal and occipital cortices and hippocampus were determined immediately after 15 min of ischemia (0), and then at 15, 30, 90 and 180 min after recirculation following ischemia. These data were compared with those for sham-operated control mice. Choline (Ch) contents in ischemic animals increased by 530–630% from control levels immediately after ischemia, and returned to control levels by 90 min. Decreases in levels of norepinephrine (NE) and serotonin (5-HT) were observed during 30 min after recirculation. There were no significant changes in levels of acetylcholine (ACh) or dopamine (DA), throughout recirculation. On the other hand, DA and 5-HT metabolites (3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid) significantly increased. Thus, comprehensively investigating the various neurotransmitters will provide meaningful information regarding the disturbance of central nervous system induced by cerebrovascular disease.

Cholesterol level in peripheral blood lymphocytes: Relationship with ischemic heart disease in patients with various forms of hyperlipidemia

Even though a correlation between the incidence of ischemic heart disease(IHD) and the plasma level of "atherogenic" cholesterol has been demostrated in a number of extensive population studies [1-3], the mechanism underlying this phenomenon remains unclear. It is generally accepted that a rise of plasma cholesterol (Ch) level above 6.5 mmol/ l i ter increases the risk of atherosclerotic plaque formation [4]. Cholesterol accumulation in the vascular intima is due to the transformation of macrophages and smooth muscle cells into foam cells [5,6], which does not reflect the Ch content of other cells in the body. Cholesterol accumulat ion in tissues may occur without pronounced hypercholesterolemia. Yu. M. Lopukhin has described "cholesterosis" of red blood cells in patients with hypercholesterolemia [7]. However, these non-nucleated cells do not have their system for own controlling Ch balance, and the Ch concentration in their plasma membrane simply reflects the intensity of the concentration gradient transport. The mechanism responsible for the coupling

Biphasic Striatal Acetylcholine Release during and after Transient Cerebral Ischemia in Gerbils

Acetylcholine (ACh) release into the extracellular space was measured by HPLC with electrochemical detection after in vivo intracerebral microdialysis in the striatum of gerbils subjected to 15 min of bilateral carotid artery occlusion followed by 5 h of recirculation. Tissue ACh and choline (Ch) contents were also determined during ischemia and after 5, 30, 60, and 120 min of reflow. Fifteen minutes of ischemia led to a significant transient increase in extracellular ACh concentration (threefold after 7.5 min of ischemia) concomitant with a reduced endogenous ACh level (-62%) and increased tissue Ch content (ninefold). Recirculation significantly reduced the ACh release during the early period of reflow (-50% vs. basal level), followed by a significant increase in ACh release between 1 and 3 h of reflow (45-55% vs. basal level) and subsequent normalization. Simultaneously, a "rebound" of tissue ACh level occurred in the early period of reflow (fourfold vs. ischemic value), followed by gradual normalization after 2 h of reperfusion, whereas a rapid decrease in tissue Ch levels was found after 30 min of reflow. These findings represent the first demonstration of a biphasic release of ACh during ischemia and reperfusion, as assessed by intracerebral microdialysis in gerbils.

Determination of the aliphatic and aromatic CH contents of coals by FT-i.r.: studies of coal extracts

The pyridine-soluble extracts of 44 US coals and 17 Polish coals were characterized by FT-i.r. and proton n.m.r., allowing the determination of absorption coefficients for aliphatic and aromatic vibrational modes. Various aspects of methodology are discussed and it is demonstrated that the absorption coefficients of the stretching modes vary not only with rank — lignite and subbituminous coals being different from bituminous coals — but also with the origin of the parent coal. It is also demonstrated that the use of the out-of-plane bending modes to determine aromatic CH content introduces a systematic error into the results; although the size of this error remains undefined at this point, it is probably small.

The effects of coalification and paleoenvironment on aliphatic and aromatic CH contents in the Lower Kittanning coal seam

Absorption spectra for 33 whole-seam channel samples and 24 vitrinite concentrates of the Lower Kittanning coal seam in western Pennsylvania and eastern Ohio were obtained by Fourier transform infrared (FTIR) analysis. Absorption areas for aliphatic and aromatic functional groups were calculated and compared to selected parameters of coalification in bivariate and multivariate statistical analyses. The aliphatic CH 3 and lone CH contents show weak correlations with coalification, whereas the correlations for aliphatic CH 2 and all aromatic CH groups are stronger. A secondary paleoenvironmental control over the concentrations of aliphatic CH 3, CH 2 and CH is suggested by trends on isopleth maps which show lateral variability of these components. These maps suggest that paleotopography, which influenced the distribution of marine and fresh-water sediments and their associated flora, was an important control in aliphatic concentrations. Statistical analysis indicates that the variability of aromatic CH may be entirely rank-controlled.

Source-sink relationships in maize grown in a cool-temperate area

lationships. The experiment was conducted at Balcarce over a 2-year period with 2 hybrids (short season: SPS 240, long season: D2F11). The treatments consisted of 2 levels of source reduction (45 and 55% shading during the grain filling period, GFS), 2 levels of reproductive sink reduction (45 and 55% shading aroung flowering, FS) and an unshaded control. The different shading treatments had a constant reduction of radiation with variable shading duration (30-38 days). The results indicate the existence of a colimitation by source of assimilates and reproductive sinks because grain yield dropped similarly in response to shading during the flowering and the grain filling periods. FS reduced grain number/unit area and slightly increased 1 000 kernel weight. GFS reduced 1 000 kernel weight, and to a lesser extent grain number/unit area. The study of dry matter and CH accumulation or remobilization in response to shading at the R3-R5 period, relative to those of the control treatment, was useful to indicate trends toward sink or source limitations. Relative to the control, shading at any period produced a decrease in stem CH content during the treatment period. During the post-shading period, the FS treatments presented a greater CH accumulation in stems than the control. This is explained by the decrease in reproductive sink number that produced a drop in their demand of CH and by the increased importance of the stem as an alternative sink for assimilates. GFS treatments produced a strong increase in CH remobilization rate from stem during the treatment period. The 2 hybrids did not show statistically significant differences in their source-sink relationship. Nevertheless, a tendency toward a source limitation was evident in the long season hybrid.

Effect of oxotremorine, physostigmine, and scopolamine on brain acetylcholine synthesis: A study using HPLC

The synthesis rate of brain acetylcholine (ACh) was estimated in mice following i.v. administration of [3H]choline (Ch). The measurements were performed 1 min after the tracer injection, using the [3H]ACh/[3H]Ch specific radioactivity ratio as an index of ACh synthesis rate. Endogenous and labeled Ch and ACh were quantified using HPLC methodology. Oxotremorine and physostigmine (0.5 mg/kg, i.p.) increased the steady state concentration of brain ACh by + 130% and 84%, respectively and of Ch by + 60% (oxotremorine); they decreased ACh synthesis by 62 and 55%, respectively. By contrast, scopolamine (0.7 mg/kg, i.p.) decreased the cerebral content of Ch by - 26% and of ACh by - 23% without enhancing the synthesis of ACh. The results show the utility of HPLC methodology in the investigation of ACh turnover.

Physical-chemical behavior of dietary and biliary lipids during intestinal digestion and absorption. 1. Phase behavior and aggregation states of model lipid systems patterned after aqueous duodenal contents of healthy adult human beings

We developed equilibrium phase diagrams corresponding to aqueous lipid compositions of upper small intestinal contents during lipid digestion and absorption in adult human beings. Ternary lipid systems were composed of a physiological mixture of bile salts (BS), mixed intestinal lipids (MIL), principally partially ionized fatty (oleic) acid (FA) plus racemic monooleylglycerol (MG), and cholesterol (Ch), all at fixed aqueous-electrolyte concentrations, pH, temperature, and pressure. The condensed phase diagram for typical physiological conditions (1 g/dL total lipids, FA:MG molar ratio of 5:1, pH 6.5, 0.15 M Na+ at 37 degrees C) was similar to that of a dilute model bile [BS/lecithin (PL)/Ch] system [Carey, M. C., & Small, D. M. (1978) J. Clin. Invest. 61, 998-1026]. We identified two one-phase zones composed of mixed micelles and lamellar liquid crystals, respectively, and two two-phase zones, one composed of Ch monohydrate crystals and Ch-saturated micelles and the other of physiologic relevance composed of Ch- and MIL-saturated mixed micelles and unilamellar vesicles. A single large three-phase zone in the system was composed of Ch-saturated micelles, Ch monohydrate crystals, and liquid crystals. Micellar phase boundaries for otherwise typical physiological conditions were expanded by increases in total lipid concentration (0.25-5 g/dL), pH (5.5-7.5), and FA:MG molar ratio (5-20:1), resulting in a reduction of the size of the physiological two-phase zone. Mean particle hydrodynamic radii (Rh), measured by quasielastic light scattering (QLS), demonstrated an abrupt increase from micellar (less than 40 A) to micelle plus vesicle sizes (400-700 A) as this two-phase zone was entered. With relative lipid compositions within this zone, unilamellar vesicles formed spontaneously following coprecipitation, and their sizes changed markedly as functions of time, reaching equilibrium values only after 4 days. Further, vesicle Rh values were influenced appreciably by MIL:mixed bile salt (MBS) ratio, pH, total lipid concentration, and FA:MG ratio, but not by Ch content. In comparison, micellar systems equilibrated rapidly, and their Rh values only slightly influenced by physical-chemical variables of physiological importance. In contrast to the BS-PL-Ch system [Mazer, N. A., & Carey, M. C. (1983) Biochemistry 22, 426-442], no divergence in micellar sizes occurred as the micellar phase boundary was approached. The ionization state of FA at simulated "intestinal" pH values (5.5-7.5) in the micellar and physiologic two-phase zones was principally that of 1:1 sodium hydrogen dioleate, an insoluble swelling "acid soap" compound. By phase separation and analysis, tie-lines for the constituent phase in the two-phase zone demonstrated that the mixed micelles were saturated with MIL and Ch and the coexisting vesicles were saturated with MBS, but not with Ch.(ABSTRACT TRUNCATED AT 400 WORDS)

Structural alterations in lecithin-cholesterol vesicles following interactions with monomeric and micellar bile salts: physical-chemical basis for subselection of biliary lecithin species and aggregative states of biliary lipids during bile formation.

Using complementary physical-chemical methods including turbidimetry, quasielastic light scattering, gel filtration, and phase analysis, we examined the interactions between dilute concentrations of the common bile salt, taurochenodeoxycholate (TCDC), and uni- and multilamellar vesicles (MLVs) composed of defined molecular species of lecithin (L) and varying contents of cholesterol (Ch). Dissolution rates of MLVs with micellar TCDC, as assessed by turbidimetry, were more rapid with vesicles composed of sn-1 palmitoyl species, typical of biliary L, compared with those composed of the more hydrophobic sn-1 stearoyl species. Incorporation of Ch retarded MLV dissolution rates in proportion to the Ch content, and only at high Ch contents were dissolution rates appreciably influenced by the sn-2 fatty acid composition of L. When MLVs contained Ch in amounts characteristic of intracellular membranes (Ch/L approximately 0.1), the dissolution rates of the individual L species by TCDC accurately predicted the steady state L composition of human bile. TCDC interacted with small unilamellar L/Ch vesicles (SUVs) at concentrations well below, as well as appreciably above, its critical micellar concentration. In accordance with the TCDC-egg yolk L-H2O phase diagram, perimicellar concentrations of TCDC interacted with SUVs to form aggregates that were approximately twice the size of the SUVs. These were consistent with the formation of a dispersed hexagonal (rod-like) phase, which co-existed with aqueous bile salt (BS) monomers and either micellar or unilamellar SUV phases. Micellar TCDC completely solubilized SUVs as mixed micelles, putatively via this transient hexagonal phase. With modest Ch-supersaturation, dissolution was followed by the reemergence of a new vesicle population that coexisted metastably with mixed micelles. With high Ch supersaturation, TCDC extracted L and Ch molecules from SUVs in different proportions to form Ch-supersaturated mixed micelles and Ch-enriched SUVs, in accordance with the metastable phase diagram. These experiments are consistent with the hypothesis that sn-1 palmitoyl L species are subselected for bile, in part, by physical-chemical interactions of intracellular BS concentrations with Ch-poor membranes and that the subsequent evolution of Ch-rich vesicles and Ch-saturated mixed micelles occurs via a transitional hexagonal (rod) phase. These liquid-crystalline states are likely to be transient in Ch-unsaturated biles, but may persist in Ch-supersaturated human biles because of their high Ch contents which retard or inhibit these phase transitions.