Uncharged Compounds Research Articles

Investigations on the hepatic uptake systems for organic cations with a photoaffinity probe of procainamide ethobromide

Azido procainamide methoiodide (APM), a photolabile derivative of the transport model compound procainamide ethobromide (PAEB), shows a close resemblance to PAEB from a physicochemical point of view. Like PAEB it is effectively taken up by the liver and excreted into bile. Kinetics of the uptake of APM in isolated hepatocytes revealed that in addition to a non-saturable process, two saturable uptake systems are involved ( K m1 = 3 μM, V mxl) = 80 pmol/min/10 6 cells K m2 =100 μM, V max2= 130 pmol/min × 10 6 cells). The uptake rate of APM was inhibited markedly in the presence of other organic cations. Organic anions and uncharged compounds generally had no inhibitory effect on the APM uptake. These results support the theory that there is a separate hepatic uptake system for organic cations like APM. Photoaffinity labeling of intact hepatocytes as well as plasma membrane sub-fractions enriched with sinusoidal domains disclosed two major binding polypeptides with apparent M r of 48,000 and 72,000. Such labeling patterns were not observed in membranes from hepatoma cells that are deficient in organic solute uptake. Differential photoaffinity labeling with other cationic compounds such as tributylmethyl ammonium and d-tubocurarine reduced the incorporation of APM in these polypeptides. The 48- and 72-kDa proteins might be involved in carrier-mediated transport of type I organic cations at the hepatic uptake level.

Purification and characterization of diacetyl reductase from chicken liver and Streptococcus lactis and enzymic determination of diacetyl and diketones

Two enzymes which correspond to the Enzyme Commission classification diacetyl reductase (acetoin: NAD oxidoreductase E.C 1.1.1.5) have been isolated and purified from chicken liver and Streptococcus lactis subspecies diacetylactis 18-16. Both enzymes reduced vicinal diketones and uncharged α-dicarbonyl compounds using NADH as cofactor; the liver enzyme also accepted NADPH as cofactor. The bacterial enzyme accepted acetoin as a substrate whereas the liver enzyme did not. The liver enzyme was used to quantify aqueous diacetyl or diketone solutions by enzymic reaction with reduced cofactor. The quantity of reduced cofactor remaining after reaction was inversely proportional to the original concentration of diacetyl or diketones. The relationship between absorbance and concentration was linear up to 50 mg dm −3 diacetyl, with a lower limit of sensitivity of 1 mg dm −3. Greater sensitivity (linearity up to 1.5 mg dm −3, lower limit of 0.05 mg dm −3) could be obtained by coupling the reaction to an enzymic cycling system.

Carrier-mediated transport in the hepatic distribution and elimination of drugs, with special reference to the category of organic cations

Carrier-mediated transport of drugs occurs in various tissues in the body and may largely affect the rate of distribution and elimination. Saturable translocation mechanisms allowing competitive interactions have been identified in the kidneys (tubular secretion), mucosal cells in the gut (intestinal absorption and secretion), choroid plexus (removal of drug from the cerebrospinal fluid), and liver (hepatobiliary excretion). Drugs with quaternary and tertiary amine groups represent the large category of organic cations that can be transported via such mechanisms. The hepatic and to a lesser extent the intestinal cation carrier systems preferentially recognize relatively large molecular weight amphipathic compounds. In the case of multivalent cationic drugs, efficient transport only occurs if large hydrophobic ring structures provide a sufficient lipophilicity-hydrophilicity balance within the drug molecule. At least two separate carrier systems for hepatic uptake of organic cations have been identified through kinetic and photoaffinity labeling studies. In addition absorptive endocytosis may play a role that along with proton-antiport systems and membrane potential driven transport may lead to intracellular sequestration in lysosomes and mitochondria. Concentration gradients of inorganic ions may represent the driving forces for hepatic uptake and biliary excretion of drugs. Recent studies that aim to the identification of potential membrane carrier proteins indicate multiple carriers for organic anions, cations, and uncharged compounds with molecular weights around 50,000 Da. They may represent a family of closely related proteins exhibiting overlapping substrate specificity or, alternatively, an aspecific transport system that mediates translocation of various forms of drugs coupled with inorganic ions. Consequently, extensive pharmacokinetic interactions can be anticipated at the level of uptake and secretion of drugs regardless of their charge.

Dopaminergic drugs in the cationic form interact with D 2 dopamine receptors

Compounds that interact with the dopamine receptor contain a side-chain amino group, which appears to be important for interaction with the dopamine receptor. Interest in structure-activity relationships led Duane Miller, Norman Uretsky and colleagues to alter the structures of dopaminergic drugs through bioisosteric replacement of their side-chain amino groups with either permanently charged or uncharged functional groups. While compounds with a permanent positive charge were able to interact functionally with the D 2 dopaminergic receptor, permanently uncharged compounds were devoid of activity. Although the activity of the permanently charged compounds was qualitatively similar to the parent amines, they were less potent than these amines. On the basis of these observations, the authors propose a hypothesis to explain how the various side-chain groups of dopamine receptor agonists and antagonists may interact with the D 2 receptor .

The relationship between the bilayer to hexagonal phase transition temperature in membranes and protein kinase C activity.

A number of substances affect the activity of protein kinase C. Among uncharged and zwitterionic compounds, those which activate protein kinase C also lower the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine while substances which inhibit protein kinase C raise this transition temperature. Using this criteria, we have identified 3 beta-chloro-5-cholestene, 5 beta-cholan-24-ol and eicosane as new protein kinase C activators and have shown that Z-Ser-Leu-NH2, Z-Gly-Leu-NH2, Z-Tyr-Leu-NH2, cyclosporin A and cholestan-3 beta, 5 alpha, 6 beta-triol are protein kinase C inhibitors.

Transport systems for amphipathic compounds in normal and neoplastic hepatocytes

Photoaffinity labeling of plasma membrane subfractions from liver and of intact liver tissue with a photolabile bile salt derivative, the sodium salt of (7,7-azo-3α,12α-dihydroxy-5β-cholan-24-oyl)-2-aminoethanesulfonic acid, revealed that the hepatobiliary transport of bile salts is accomplished by transport systems different for sinusoidal uptake and canalicular secretion. Polypeptides with apparent M r values 54,000 and 48,000 interact with bile salts at sinusoidal membrane, whereas a polypeptide with an apparent M r of 100,000 is involved in bile salt secretion through the canalicular membrane. Photoaffinity labeling with photolabile derivatives of uncharged and cationic compounds provided evidence that the sinusoidal membrane polypeptides exhibit a broad binding specificity. Photoaffinity labeling studies and kinetic studies suggest that hepatic uptake of different amphipathic anions, uncharged compounds and even of cations is mediated by the sinusoidal transport systems which are involved in the uptake of bile salts. Relatively little is known about the specificity of the canalicular bile salt transport system. The fluorescent bile salt derivative, the sodium salt of { N-[7-(4-nitrobenzo-2-oxa-1,3-diazol)]-3 β-amino-7 α,12 α-dihydroxy-5 β-cholan-24-oyl}-2- aminoethanesulfonic acid, is readily taken up into the hepatocytes of all acinar zones and may be used for the evaluation of the functional state of bile salt transport by fluorescence microscopy. Fluorescent microscopic studies with the fluorescent bile salt derivative showed that ascites hepatoma AS 30D cells do not have the ability to take up bile salts and demonstrated the absence of hepatobiliary bile salt transport in the solid Morris hepatoma 7777. Photoaffinity labeling studies revealed that in both tumor cell models, in hepatoma AS 30D and in Morris hepatoma 7777, the plasma membranes were devoid of the polypeptides having affinities to bile salts and amphipathic cations. A slight labeling of bile salt binding membrane polypeptides in plasma membranes from Morris hepatomas 9618A and TC 5123 opens the possibility to study transport in neoplastic hepatocytes.

Amine, imine, and aminocarbene complexes of platinum(II)

Solutions of the chloride-bridged binuclear platinum complexes [Pt2(µ-Cl)2Cl2L2](L = PMe2Ph or PBu3) readily react with the amines NH2Ph, 4-NO2C6H4NH2, 3-MeOC6H4NH2, NHPh2, or NH2Me to produce trans-[PtCl2(am)L] in the presence or absence of phenylethyne. The imines PhCHNPh, PhCHNMe, 2-MeC6H4CHNPh, or Ph2CNH also react with [Pt2(µ-Cl)2Cl2L2] to produce the analogous N-bonded imine complexes, but reactions of the amines NHEt2 or NH2But with the binuclear compounds lead to additional platinum-containing compounds resulting from ligand redistribution reactions. The complexes of NH2Ph, 4-NO2C6H4NH2, 3-MeOC6H4NH2, and NHPh2 react with phenylethyne over several days at ambient temperature to yield aminocarbene complexes cis-[PtCl2{C(NR1R2)CH2Ph}L](R1R2= H, Ph; H, C6H4NO2-4; H, C6H4OMe-3; or Ph2). Treatment of the imine complexes or any of the other amine complexes with PhCCH, however, led only to decomposition. 2-Aminophenylethyne reacts rapidly with [Pt2(µ-Cl)2Cl2L2] to produce the cyclic carbene complex cis-[PtCl2{[graphic omitted]H}L] in only 1 h, and although the amine-N complexes were observed in solution as transients they were not isolated. Treatment of the carbene complexes with tertiary phosphine, L, leads to cationic complexes trans-[PtCl{C(NR1R2)CH2Ph}L2]Cl. Both the uncharged and cationic aminocarbene compounds are less reactive than their alkoxycarbene analogues, and show no reaction with Cl– and little tendency towards H/D exchange with CD3OD. Hydrogen-1, 13C, and 31P n.m.r. spectroscopic parameters for the complexes are reported and related to the likely solution conformations.

Synthesis and anticholinesterase activity of S-alkynyl diethyl thiophosphates containing hydrophobic or onium groups in the alkylthiol radical

A study has been carried out of the anticholinesterase activity of S-alkynyl dialkyl thiophosphates containing hydrophobic or onium groups in the thioalkyl radical. It has been shown that interaction of the acetylenic bond with the corresponding region of the enzyme is not in accordance with the hydrophobic interaction of the thioalkyl radical. The presence of an acetylenic bond in the onium compounds results in a decrease in their inhibitory activity as compared with the analogous uncharged compounds.

Influence of hydrogen on the magnetic properties of YCo compounds

The effect of hydrogen absorption on the magnetic properties of the Y 2Co 7H x and the YCo 3H x systems was examined in situ. The two systems show similar β and γ phase formation and magnetic behaviour. The β phase exhibits the anomaly that a slight hydrogen enrichment induces a substantial increase in the cobalt moment which varies from a minimum on the low concentration side (0.13 μ B in Y 2Co 7H 2 and 0.15 μ B in YCo 3H) to a maximum on the high concentration side (1.2 μ B in Y 2Co 7H 3 and 0.7 μ B in YCo 3H 2). These maximum values are almost equal to those in the respective uncharged compounds. The cobalt moment in the γ phase decreases with increasing hydrogen concentration in the same way as in ordinary cobalt-based ferromagnets. Both systems tend to lose ferromagnetism in the most hydrogenated compounds Y 2Co 7H 8 and YCo 3H 4. The anomalous dependence of the cobalt moment on composition is discussed.

Effect of additives on the cloud point of polyethylene glycols

Polyethylene glycol 20, 000 and 6, 000 were found to have an upper consolute temperature, called “cloud point”, and the effects of various additives on the polyethylene glycols were investigated in this study. Electrolytes lowered the cloud point in proportion to their concentrations through dehydration and electrostriction. It was found that anions played a more important role than cations and the effects of both the cations and the anions clearly followed the classical Hofmeister series. However, the Schultze-Hardy rule holds for the effect of anions, and fails for the effect of cations. Salts of large polarizable anions such as iodide and thiocynate rather raised the cloud point, and their effects were ascribed to the fact that they break the water structure and weaken hydrophobic bonding of the polyoxyethylene moiety. Nitrates of polyvalent cations also raised the cloud point. This was ascribed to the complex formation between the polyvalent cations and ether oxygens of the polyoxyethylenes. This explained the failure ‘of the Schultze-Hardy rule for cations. Uncharged aromatic compounds drastically lowered the cloud point, while aliphatic alcohols slightly lowered the cloud point, This result suggests that there might be some interaction between ether oxygens and aromatic nucleus.

Polyfunctional Radiosensitizers: VI. Dexamethasone Inhibits Shoulder Modification by Uncharged Nitroxyl Biradicals in Mammalian Cells Irradiated in Vitro

Overnight exposure of Chinese hamster cells (V. 79-753B) in vitro to 1 micrograms/ml dexamethasone increases the radiation resistance of the cells by about 20% both in air and in hypoxia, while having no appreciable effect on the oxygen enhancement ratio (OER). This is accompanied by substantially higher levels of glutathione. When dexamethasone-treated hypoxic cells are irradiated in the presence of nitroxyl biradicals there is no effect on the slope ratio of of the exponential portion of the survival curves. In the case of uncharged biradicals, Ro.03-6061 and RSU-4072. which have been shown to modify the shoulder region of the hypoxic cell survival curve, there is an increase in extrapolation number in dexamethasone-treated cells. When hypoxic cells are exposed to the charged biradical RSU-4073, which does not exhibit shoulder modification, there is no change in extrapolation number. Experiments to examine the effect of concentration of these compounds on radiosensitization show that lower concentrations of both RSU-4072 and RSU-4073 are required to mediate changes in the slope of the hypoxic cell survival curve than to mediate shoulder modification, in the case of RSU-4072. Quantitative ESR data comparing the uptake of RSU-4072 and RSU-4073 with the monoradical TMPN into cells suggest that the cell membrane may act as a barrier to the incorporation of biradicals, and that this is greater for charged than for uncharged compounds. Treatment of cells with dexamethasone does not affect the uptake of the compounds. The data suggest, however, that the cell membrane may be an important site for localization of uncharged biradicals and that this may be important in determining shoulder modification.

Nuclear magnetic resonance and electron absorption studies of acenaphthylene dianion. Ion-pair structure and charge distribution

The 1H and 13C n.m.r. chemical shifts of acenaphthylene dianion are studied by variation of cation, solvent, and temperature. For the description of the charge distribution, comparisons are also made with the neutral hydrocarbon, acenaphthylene. In the contact ion pair structure, the cations occupy nonequivalent positions relative to the dianion. The ability to undergo solvation also differs for the two cations. The Na and K salts exist solely as contact ion pairs under the investigated conditions. 7Li N.m.r. and u.v.–visible spectroscopic characterization provide further evidence for the proposed ion pair structures. The comparatively small and variable 13C chemical shift–charge correlation factor of the dinegative–uncharged compounds is discussed in view of a varying degree of diatropicity. The electronic structure of the dianion is best described in terms of a partly localized π-electronic system.

Detection by ion-pairing probes in reversed-phase liquid chromatography

Compounds without own detector response can be detected and quantified by a UV-absorbing or fluorescent, ion-pairing probe in reversed-phase liquid-solid systems. Charged as well as uncharged samples give response by affecting the distribution of the probe between the phases. The probe is usually a hydrophobic organic ion. It is included in the mobile phase, which also contains a counter ion and an ion of the same charge as the probe, both fairly hydrophilic. The choice of properties and concentrations of the hydrophilic ions is essential for the response since too low and too high distribution of the mobile phase ions to the adsorbent will make the system insensitive. It is with UV-absorbing probes possible to get a response corresponding to a molar absorptivity of more than 3000 for ionic samples. Fluorescent probes have given 3–5 times higher sensitivity. Uncharged compounds give as a rule lower response. A combination of two UV-absorbing probes with different charge gives a considerable improvement of the response for samples with low retention. A simplified theoretical model for the detector response is suggested on the basis of detailed studies of the concentration changes in the eluted mobile phase.

Magnetic properties and155Gd Mossbauer effect in GdCu2and its ternary hydride

The magnetic and crystallographic properties of GdCu2 and its ternary hydride GdCu2Hx have been investigated. Upon hydrogen absorption the crystal structure of GdCu2 changes from orthorhombic (CeCu2-type) to tetragonal (MoSi2-type), accompanied by a lattice expansion of 29%. The uncharged intermetallic compound GdCu2 orders antiferromagnetically (TN=37K). After H2 absorption it becomes ferromagnetic (TC=45K). There is a strong increase in the asymptotic Curie temperature (from theta p=7K to theta p=57K). Studies of the 155Gd Mossbauer effect in the uncharged and charged compounds show that the H2 absorption leads to an increase in isomer shift and in the absolute value of the hyperfine field at 4.2K. Both changes have been discussed in terms of a changing conduction electron concentration.

The action of organic mercurials on the erythrocyte membrane

The solubilisation of proteins from erythrocyte membranes by treatment with organic mercurials has been studied with different species. The marked solubilisation previously reported for human membranes does not seem to be a general phenomenon. All of the other species examined showed less than 50% of the solubilisation shown by human membranes. The protein-solubilising effect seems to be dependent on hydrophobic mercury derivatives carrying a net negative charge. Uncharged compounds like phenylmercuric acetate blocked the effect, although N- ethylmaleimide and iodoacetamide did not. With the aid of radioactively labelled compounds, and of atomic absorption spectrophotometry, the proteins reactive towards the mercurials were identified. The major integral protein, band 3, was the major protein capable of binding the mercurial. Reaction with the mercurial appears to disrupt interaction of band 3 with bands 2.1 and 4.2, allowing dissociation of the cytoskeleton from the membrane. In addition, band 4.9 was also found to react with the mercurials, possibly resulting in disruption of the cytoskeleton.

Magnetic properties of the ternary hydrides of Nd 6Mn 23 and Sm 6Mn 23

The intermetallic compounds Nd 6Mn 23 and Sm 6Mn 23 and their ternary hydrides were studied by X-ray diffraction. The crystal structure (Th 6Mn 23 type) is preserved after hydrogen absorption. From the change in lattice constants a volume increase of about 14% was deduced. The temperature dependence of the magnetization of Nd 6Mn 23, Sm 6Mn 23 and their hydrides was studied in the range 4–500 K. The uncharged compounds have magnetic ordering temperatures above 400 K while in the hydrides magnetic ordering occurs close to 200 K. Indications were obtained of a substantial weakening of the magnetic coupling between the rare earth and manganese sublattice magnetization.

Cationic and uncharged substrates and reversible inhibitors in hydrolysis by acetylcholinesterase (EC 3.1.1.7). The trimethyl subsite.

Structurally related cationic and uncharged compounds have been studied as inhibitors of hydrolysis by acetylcholinesterase of acetylcholine and its uncharged carbon analog, 3,3-dimethylbutyl acetate. Similar effects of the inhibitors on hydrolysis of the two substrates indicate that the quaternary ammonium group of acetylcholine and the neopentyl group of 3,3-dimethylbutyl acetate bind at the same subsite. Comparison of (CH3)3+NCH2CH2CH2COCH3 (Compound I), Ki = 0.02 mM, and its tertiary homologue, (CH3)2-+NHCH2CH2CH2COCH3 (Compound V), Ki = 0.75 mM, with a secondary isomer of Compound I, 3-oxo-(N-tert-butyl)-butanaminium, (CH3)3C+NH2CH2CH2COCH3 (Compound II), Ki = 0.15 mM, and its lower homologue, (CH3)2CH+NH2CH2CH2COCH3 (Compound IX), Ki = 2 mM, attests to the importance of the branched trimethyl structure and the smaller effect of hydrophobicity of the quaternary ammonium structure. This is supported by competitive inhibition by tert-butyl ammonium, (CH3)3C+NH3 (Compound IV), Ki = 0.45 mM, compared with mixed inhibition by its quarternary isomer, (CH3)4+N (Compound VII), Ki = 1.5 mM, and choline (Compound VI), Ki = 1.0 mM. Uncharged analogues of Compound II, 4-tert-butylthio-2-butanone, (CH3)3CSCH2CH2COCH3 (Compound III), Ki = 0.4 mM, and 4-tert-butoxy-2-butanone, (CH3)3COCH2CH2COCH3 (Compound VIII), Ki = 1.6 mM, and of Compound VI, 3,3-dimethylbutanol (Compound XI), Ki = 7.5 mM, indicate that positive charge contributes factors of 3 to 10 to binding. This may be attributed to peripheral negative charges, present at pH 7-8 in the enzyme of isoelectric point approximately 5, indicating that the binding subsite may be explored more specifically by tert-butyl than by charged reagents.

Current concepts of the mechanism of action of local anesthetics.

Recent experiments are reviewed to present a current view of the mechanisms of conduction block by local anesthetics. Local anesthetics block the sodium channels whose opening causes the rising phase of the action potential. Both charged and neutral forms of local anesthetics are able to block channels. Charged anesthetics interfere with a "gating" mechanism after gaining access to a "receptor" site in the aqueous pore of the channel from the axoplasmic surface of the membrane. This site is only available to charged compounds when the gate of the channel is open. In contrast, uncharged compounds (including the free base form of local anesthetics) appear to reach the site through the membrane's lipid interior, bypassing the channel "gates." Anesthetics blocking the gate of the channel can either enhance or inhibit the normal inactivation mechanism of the sodium channel, depending on the particular anesthetic.

Problems Involved in the Elucidation of the Donor-Acceptor Nature of Substituents in Aromatic Sulfur-Containing Radical Anions

Abstract A review of data in the literature indicates that the subdivision of substituents into donors and acceptors is of value for uncharged sulfur-containing aromatic compounds but appears somewhat useless for radical anions of the same molecules. A novel general approach is suggested for the characterization of the substituent effects in radical anions. The method employs correlation diagrams to evaluate the difference between the orbital energies of the aromatic moiety and the substituent. The approach is combined with a variety of experimental data and presented here.

Changes in membrane potential and membrane fluidity in Tetrahymena pyriformis in association with chemoreception of hydrophobic stimuli: fluorescence studies.

The fluorescence intensity of rhodamine 6G (Rh6G) and 1,6-diphenyl-1,3,5-hexatriene (DPH) in the presence of Tetrahymena pyriformis was measured to monitor changes in the membrane potential and in the gross structure of the surface membrane in response to chemical stimuli. So-called "odorants" for higher vertebrates, which are usually uncharged and hydrophobic compounds, were chosen as chemical stimuli for a model study of the olfactory response. The fluorescence intensity of Rh6G started to increase at the chemotactic thresholds of the stimuli, indicating that negative chemotaxis of T. pyriformis to the hydrophobic stimuli is induced by depolarization of the cell. The fluorescence intensity of DPH increased in close association with chemoreception of the hydrophobic stimuli. The increase in the fluorescence intensity was ascribed mainly to uptake of DPH, suggesting that gross structural changes of the surface membrane occur with the reception of hydrophobic stimuli. The membrane fluidity determined by fluorescence polarization of DPH increased in close association with the chemoreception of the hydrophobic stimuli. Inorganic salts such as NcCl, KCl, and CaCl2 did not change the DPH fluorescence intensity or the fluorescence polarization, although these stimuli induced depolarization and negative chemotaxis in T. pyriformis.