Glycerol absorption

Glycerol absorption in H. diminuta occurs by passive diffusion at high concentrations (>0.5mM) and by a carrier-mediated process at lower concentrations. At lower concentrations, absorption of this lipid precursor is non-linear, dependent on temperature and pH, and competitively inhibited by glycerol and a-glycerophosphate. The existence of two distinct carriers for this molecule is suggested by studies which show that only about half the saturable component in H. diminuta is Na -sensitive and inhibitable by 1,2-propandiol (2). 

Crocin is a yellow-orange glycoside that is freely soluble in hot water, slightly soluble in absolute alcohol, glycerol, and propylene glycol, and insoluble in vegetable oils. Crocin melts with decomposition at about 186°C and has absorption maxima in methanol at about 464 nm and 434 nm. 

Fig. 9. Comparison of Eqs. (144) (solid line) and (145) (dashed line) with the experimental data of Calderbank and Moo-Young (C4) for the absorption of C02 at 25°C in water containing the following percentages by weight of glycerol [after Gal-Or and Walatka (G9)]...

Fig. 10 Spectra of absorption (1-5) and fluorescence (6-10) for DMABN in different solvents 1,6-cyclohexan 2,7-dioxan 3,9-tetrahydrofuran 5,8-glycerol 4,10-acetonitrile...

A 500-ml. three-necked round-bottomed flask is fitted with an efficient reflux condenser, a glycerol-sealed mechanical stirrer,1 a dropping funnel, and a gas inlet tube extending nearly to the blades of the stirrer (Note 1). An absorption train,2 with the addition in / of a safety tube which extends nearly to the bottom, is connected to the upper end of the reflux condenser (Note 2). A 2-cm. layer of water in J allows it to serve as a bubble counter K is one-third filled with a 50% potassium hydroxide solution. The entire apparatus is set up in subdued light in a hood and swept with dry hydrogen (Notes 3 and 4). Phenyl-magnesium bromide is prepared in the flask by the usual procedure 3 from 78.5 g. (0.5 mole) of bromobenzene, 12 g. (0.5 gram... 

The pA a shift can be directly measured by the solvatochromic shift of the ultraviolet absorption spectra. For PCP, the p%lir is 5.97 in phosphatidyl choline membranes, and increases up to 6.78 in the negatively charged phosphatidyl glycerol membranes [123], The addition of cholesterol decreases the pATam again slightly in both types of membranes. 

Fast librational motions of the fluorophore within the solvation shell should also be consideredd). The estimated characteristic time for perylene in paraffin is about 1 ps, which is not detectable by time-resolved anisotropy decay measurement. An apparent value of the emission anisotropy is thus measured, which is smaller than in the absence of libration. Such an explanation is consistent with the fact that fluorescein bound to a large molecule (e.g. polyacrylamide or monoglucoronide) exhibits a larger limiting anisotropy than free fluorescein in aqueous glycerolic solutions. However, the absorption and fluorescence spectra are different for free and bound fluorescein the question then arises as to whether r0 could be an intrinsic property of the fluorophore. 

Some polyalcohols, particularly glycerol and ethyleneglycol, also form a similar complex although the absorption maxima do vary slightly from those... 

An alternative method uses glycerol dehydrogenase (EC 1.1.1.6) to produce NADH. This is measured either by its absorbance at 340 nm or by using a diaphorase (EC 1.6.4.3), which catalyses the reduction of a dye, p-iodonitro-tetrazolium violet (INT) to produce a coloured complex with an absorption maximum at 540 nm ... 

Goodridge and Robb(14) used a laminar jet to study the rate of absorption of carbon dioxide into sodium carbonate solutions containing a number of additives including glycerol, sucrose, glucose, and arsenites. For the short times of exposure used, absorption rates into sodium carbonate solution or aqueous glycerol corresponded to those predicted on the basis of pure physical absorption. In the presence of the additives, however, the process was accelerated as the result of chemical reaction. 

Figure 2.11. The dependence of the position of the fluorescence spectrum maximum on excitation wavelength for tryptophan in a model medium (glycerol) at different temperatures (a) and singletryptophan proteins (b). 1, Whiting parvalbumin, pH 6.S in the presence of Ca2+ ions 2, ribonuclease Th pH 6.5 3, ribonuclease C2, pH 6.5 4, human serum albumin, pH 7.0, +10"4 M sodium dodecyl sulfate 5, human serum albumin, pH 3.2 6, melittin, pH 7.5, +0.15 M NaCl 7, protease inhibitor IT-AJ from Actinomyces janthinus, pH 2.9 8, human serum albumin, pH 7.0 9, -casein, pH 7.5 10, protease inhibitor IT-AJ, pH 7.0 11, basic myelin protein, pH 7.0 12, melittin in water. The dashed line is the absorption spectrum of tryptophan.

Thus, the apparent membrane permeability characteristics of hydrophilic compounds listed in Table 3.4 indicate that colonic epithelium is different from small intestinal epithelium in selectivity, or size or density distribution of the paracellular pathway. This is further complicated because of the possible involvement of unidentified carriers or channels for some compounds, as suggested for glycerol and D-xylose. However, the colon-to-SI ratios of the apparent membrane permeability are generally comparable with (or lower than) those calculated considering the morphological surface area, suggesting that such factors are not in favor for colonic absorption in most cases. Matching... 

Note Data represent the mean S.E. (n = 3). MW, molecular weight P0/w, octanol-to-water partition coefficient CLapp, apparent membrane permeability clearance SI, midgut area of the small intestine NA, not available or applicable. Absorption was evaluated in our laboratory using the closed loop of the rat intestine in situ (urethane anesthesia, 1.125 g/4.5 ml/kg, i.p.) in 60 min for riboflavin and L-camitine and 30 min for the others. For those that are transported by carriers in part (riboflavin and glycerol in both colon and SI, and L-carnitine, 5-fluorouracil, and cephradine in SI), absorption was evaluated at higher concentrations where the contribution of carrier-mediated transport is negligible. Values of P0/w were obtained from a report by Leo et al. [30] except for that of D-xylose, which was determined in our laboratory. a Data by single-pass perfusion experiments. b Unpublished data from our laboratory. 

Yuasa H, Hamamoto K, Dogu S, Marutani T, Nakajima A, Kato T, Hayashi Y, Inoue K, Watanabe J (2003) Saturable absorption of glycerol in the rat intestine. Biol Pharm Bull 26 1633-1636... 

---