Photolysis of the ion pair [Pt(NH3)5Cl]S2O8: reduction of platinum(IV) induced by outer-sphere charge transfer excitation

The ion pair [Pt^IV(NH₃)₅Cl]³⁺S₂O₈²⁻ shows a S₂O₈²⁻ → [Pt(NH₃)₅Cl]³⁺ outer-sphere charge transfer (OSCT) absorption at λ_max=267 nm. OSCT excitation leads to the reduction of Pt(IV) by S₂O₈²⁻ to Pt(II) with φ=3×10⁻³ at λ_irr=280 nm.     

Inability of Ehrlich ascites tumor cells to volume regulate following a hyperosmotic challenge

Summary Ehrlich cells shrink when the osmolality of the suspending medium is increased and behave, at least initially, as osmometers. Subsequent behavior depends on the nature of the hyperosmotic solute but in no case did the cells exhibit regulatory volume increase. With hyperosmotic NaCl an osmometric response was found and the resultant volume maintained relatively constant. Continuous shrinkage was observed, however, with sucrose-induced hyperosmolality. In both cases increasing osmolality from 300 to 500 mOsm initiated significant changes in cellular electrolyte content, as well as intracellular pH. This was brought about by activation of the Na⁺/H⁺ exchanger, the Na/K pump, the Na⁺+K⁺+2Cl^– cotransporter and by loss of K⁺ via a Ba-sensitive pathway. The cotransporter in response to elevated [Cl^–] _i (100mm) and/or the increase in the outwardly directed gradient of chemical potential for Na⁺, K⁺ and Cl^–, mediated net loss of ions which accounted for cell shrinkage in the sucrose-containing medium. In hyperosmotic NaCl, however, the net Cl^– flux was almost zero suggesting minimal net cotransport activity.We conclude that volume stability following cell shrinkage depends on the transmembrane gradient of chemical potential for [Na⁺+K⁺+Cl^–], as well as the ratio of intra- to extracellular [Cl^–]. Both factors appear to influence the activity of the cotransport pathway.     

The kinetics of the complex formation between iron(III)-ethylenediaminetetraacetate and hydrogen peroxide in aqueous solution

The kinetics of the formation of the purple complex [Fe^III(EDTA)O₂]³⁻, between Fe^III-EDTA and hydrogen peroxide was studied as a function of pH (8.22-11.44) and temperature (10-40 °C) in aqueous solutions using a stopped-flow method. The reaction was first-order with respect to both reactants. The observed second-order rate constants decrease with an increase in pH and appear to be related to deprotonation of Fe^III-EDTA ([Fe(EDTA)H₂O]⁻ ⇔ Fe(EDTA)OH]²⁻ + H⁺). The rate law for the formation of the complex was found to be d[Fe^IIIEDTAO₂]³⁻/dt=[(k₄[H⁺]/([H⁺] + K₁)][Fe^III-EDTA][H₂O₂], where k₄=8.15±0.05×10⁴ M⁻¹ s⁻¹ and pK₁=7.3. The steps involved in the formation of [Fe(EDTA)O₂]³⁻ are briefly discussed.     

Cell shrinkage triggers the activation of mitogen-activated protein kinases by hypertonicity in the rat kidney medullary thick ascending limb of the Henle's loop. Requirement of p38 kinase for the regulatory volume increase response

The kidney medulla is exposed to very high interstitial osmolarity leading to the activation of mitogen-activated protein kinases (MAPK). However, the respective roles of increased intracellular osmolality and of cell shrinkage in MAPK activation are not known. Similarly, the participation of MAPK in the regulatory volume increase (RVI) following cell shrinkage remains to be investigated. In the rat medullary thick ascending limb of Henle (MTAL), extracellular hypertonicity produced by addition of NaCl or sucrose increased the phosphorylation level of extracellular signal-regulated kinase (ERK) and p38 kinase and to a lesser extent c-Jun NH(2)-terminal kinase with sucrose only. Both hypertonic solutions decreased the MTAL cellular volume in a dose- and time-dependent manner. In contrast, hypertonic urea had no effect. The extent of MAPK activation was correlated with the extent of MTAL cellular volume decrease. Increasing intracellular osmolality without modifying cellular volume did not activate MAPK, whereas cell shrinkage without variation in osmolality activated both ERK and p38. In the presence of 600 mosmol/liter NaCl, the maximal cell shrinkage was observed after 10 min at 37 degrees C and the MTAL cellular volume was reduced to 70% of its initial value. Then, RVI occurred and the cellular volume progressively recovered to reach about 90% of its initial value after 30 min. SB203580, a specific inhibitor of p38, almost completely inhibited the cellular volume recovery, whereas inhibition of ERK did not alter RVI. In conclusion, in rat MTAL: 1) cell shrinkage, but not intracellular hyperosmolality, triggers the activation of both ERK and p38 kinase in response to extracellular hypertonicity; and 2) RVI is dependent on p38 kinase activation.     

Homogeneous oxidative coupling catalysts. Mechanism of catalysts formation by oxidation of [(Pip)nCuX]4 (n = 1 or 2, Pip = piperidine, X = Cl, Br or I) by dioxygen in aprotic media

This paper reports the mechanism of formation of oxidative coupling catalysts [(Pip)_nCuX]₄O₂, n = 1 or 2 and X = Cl, Br or I, which represent half of the catalytical cycle, Scheme 1. The mechanism has been described as a pre-equilibrium between [(Pip)_nCuX]₄ and O₂. K values are very sensitive to how strong the hydrogen-bonding between copper (I) tetranuclear and incoming dioxygen is, such association is also sensitive to the variation of X. The pronounced pre-equilibrium is the reason behind the oxidation of [(Pip)_nCuI]₄, which is not the case for pyridine type of ligands. The pre-equilibrium followed by rate determining step k₂, which is responsible to the formation of the oxidative coupling catalysts [(Pip)_nCuX]₄O₂. The overall reaction is a second-order process, first order in each [[(Pip)_nCuX]₄] and [O₂], with rate constant k_on (k_on = Kk₂) and exothermic ΔH^≠ varying from −3 to −12 kcal mol⁻¹ and ΔS^≠ varying from −87 to −65 cal deg⁻¹ mol⁻¹. k_on were found to be very sensitive to n value 1 or 2 and to the type of X (Cl, Br or I).     

Effect of CO2 concentration on the PIC/POC ratio in the coccolithophore Emiliania huxleyi grown under light-limiting conditions and different daylengths

We compared the effect of CO₂ concentration ([CO₂], ranging from ∼5 to ∼34 μmol l⁻¹) at four different photon flux densities (PFD=15, 30, 80 and 150 μmol m⁻² s⁻¹) and two light/dark (L/D) cycles (16/8 and 24/0 h) on the coccolithophore Emiliania huxleyi. With increasing [CO₂], a decrease in the particulate inorganic carbon to particulate organic carbon (PIC/POC) ratio was observed at all light intensities and L/D cycles tested. The individual response in cellular PIC and POC to [CO₂] depended strongly on the PFD. POC production increased with rising [CO₂], irrespective of the light intensity, and PIC production decreased with increasing [CO₂] at a PFD of 150 μmol m⁻² s⁻¹, whereas below this light level it was unaffected by [CO₂]. Cell growth rate decreased with decreasing PFD, but was largely independent of ambient [CO₂]. The diurnal variation in PIC and POC content, monitored over a 38-h period (16/8 h L/D, PFD=150 μmol m⁻² s⁻¹), exceeded the difference in carbon content between cells grown at high (∼29 μmol l⁻¹) and low (∼4 μmol l⁻¹) [CO₂]. However, consistent with the results described above, cellular POC content was higher and PIC content lower at high [CO₂], compared to the values at low [CO₂], and the offset was observed throughout the day. It is suggested that the observed sensitivity of POC production for ambient [CO₂] may be of importance in regulating species-specific primary production and species composition.     

Kinetic Studies on Enzyme-Catalyzed Reactions: Oxidation of Glucose, Decomposition of Hydrogen Peroxide and Their Combination

The kinetics of the glucose oxidase-catalyzed reaction of glucose with O₂, which produces gluconic acid and hydrogen peroxide, and the catalase-assisted breakdown of hydrogen peroxide to generate oxygen, have been measured via the rate of O₂ depletion or production. The O₂ concentrations in air-saturated phosphate-buffered salt solutions were monitored by measuring the decay of phosphorescence from a Pd phosphor in solution; the decay rate was obtained by fitting the tail of the phosphorescence intensity profile to an exponential. For glucose oxidation in the presence of glucose oxidase, the rate constant determined for the rate-limiting step was k = (3.0 ± 0.7) ×10⁴ M⁻¹s⁻¹ at 37°C. For catalase-catalyzed H₂O₂ breakdown, the reaction order in [H₂O₂] was somewhat greater than unity at 37°C and well above unity at 25°C, suggesting different temperature dependences of the rate constants for various steps in the reaction. The two reactions were combined in a single experiment: addition of glucose oxidase to glucose-rich cell-free media caused a rapid drop in [O₂], and subsequent addition of catalase caused [O₂] to rise and then decrease to zero. The best fit of [O₂] to a kinetic model is obtained with the rate constants for glucose oxidation and peroxide decomposition equal to 0.116 s⁻¹ and 0.090 s⁻¹ respectively. Cellular respiration in the presence of glucose was found to be three times as rapid as that in glucose-deprived cells. Added NaCN inhibited O₂ consumption completely, confirming that oxidation occurred in the cellular mitochondrial respiratory chain.     

Bis-axial cyanide coordination induces high nucleophilicity of the in-plane thiolato ligands bound to a Co(III) center: model complexes related to the Co-containing nitrile hydratases

In situ cyanide bis-axial coordination of a square planar complex [Co^IIIN₂S₂]⁻, containing a di-N-carboxamido and dithiolato tetradentate ligand, generates the highly nucleophilic species [Co^IIIN₂S₂(CN)₂]³⁻. Its di-S-chloromethylation and di-S-oxygenation products were isolated and structurally characterized.     

Effect of anisotonic media on cell volume and electrolyte fluxes in slices of the dogfish (Squalus acanthias) rectal gland

Summary Osmotic responses of slices of dogfish rectal gland to hypotonic (urea-free) and hypertonic media were studied. Transfer of tissue from isotonic (890 mosM) to hypotonic (550 mosM) saline produced an osmotic swelling associated with a slow net uptake of cell K⁺ (and Cl^–) and a slow, two-component efflux of urea. Media made hypertonic (1180 mosM) by addition of urea or mannitol produced osmotic shrinkage with a net loss of KCl. The cell osmotic responses in hypotonic media were lower than predicted for an ideal osmometer. No volume regulatory responses were seen subsequent to the initial osmotic effects. The cation influx in hypotonic media lacked specificity: in the presence of 0.5 mM ouabain or in K⁺-free media a net influx of Na⁺ was found. At steady state, the cell membrane potential evaluated from the Nernst potentials of K⁺ and triphenylmethyl phosphonium⁺, was independent of medium tonicity, suggesting the membrane potential as a determinant in the cellular osmotic response. Zero-time⁸⁶Rb⁺ fluxes were measured:⁸⁶Rb⁺ influx was not affected by hypotonicity, implying an unchanged operation of the Na⁺–K⁺-ATPase. On the other hand,⁸⁶Rb⁺ efflux was significantly reduced at hypotonicity; this effect was transient, the efflux returning to the control value once the new steady state of cell volume had been reached. A controlled efflux system is therefore involved in the cell osmotic response. The absence of the volume regulatory phenomenon suggests that the cells are not equipped with a volume-sensing mechanism.Abbreviations and symbols DW dry weight - E extracellular (polyethylene glycol) space - E Nernst potential - H₂O_e H₂O_i tissue water, extra- and intracellular - TPMP ⁺ triphenyl methyl phosphonium salt - WW wet weight     

Complexation of Group IIIA metals with asymmetric tridentate ligands: Synthesis, characterization, formation constants and cytotoxicity

A series of new aluminum(III), gallium(III) and indium(III) complexes with some tridentate Schiff base, viz., N-{pyridine-2-ylmethyl}-2-hydroxy-5-methoxy-benzylideneamine [HL¹], N-{pyridine-2-ylmethyl}-2-hydroxy-benzylideneamine [HL²], N-{pyridine-2-ylmethyl}-2-hydroxy-5-nitro-benzylideneamine [HL³], N-{pyridine-2-ylmethyl}-2-hydroxy-5-bromo-benzylideneamine [HL⁴], N-{pyridine-2-ylethyl}-2-hydroxy-5-methoxy-benzylideneamine [HL⁵], N-{pyridine-2-ylethyl}-2-hydroxy-benzylideneamine [HL⁶], N-{pyridine-2-ylethyl}-2-hydroxy-5-nitro-benzylideneamine [HL⁷], N-{pyridine-2-ylethyl}-2-hydroxy-5-bromo-benzylideneamine [HL⁸], with the general formula [ML₂][Y] (M = Al³⁺, Ga³⁺, In³⁺; Y = NO₃⁻, ClO₄⁻) were synthesised and characterized by elemental analysis, ¹H NMR, FT-IR, UV-Vis spectrophotometry and mass spectrometry. The thermodynamic formation constants of the complexes were determined spectrophotometrically at constant ionic strength (I = 0.10 M NaClO₄) and at 25 °C in methanol. The trend of formation constants of the complexes are as follow:

Al<Ga<In     

Silver(I) derivatives with new functionalised acylpyrazolonates

Silver(I) acylpyrazolonate derivatives of formula [Ag(Q)(R₃P)]₂ and [Ag(Q)(R₃P)₂], (QH=1-phenyl-3-methyl-4-R′(CO)-pyrazol-5-one; Q^OH, R′=furane; Q^SH, R′=thiophene; R=Ph, Cy, o-tol), have been synthesised and characterised, both in the solid state and in solution. The derivatives [Ag(Q)(R₃P)]₂ contain dinuclear AgO₂NP units with the acylpyrazolonate coordinating in a bridging O,O′-Q-N fashion. The [Ag(Q)(R₃P)₂] are tetrahedral species, with the distortion from ideal geometry increasing with the bulk of the phosphine. The [Ag(Q)(R₃P)₂] derivatives are fluxional in chloroform solution when R₃P is sterically hindered (R=Cy or o-tol), dissociating partially to the [Ag(Q)(R₃P)] fragment and free R₃P. [Ag(Q^S)(Ph₃P)]₂ reacts with 1-methyl-2-mercaptoimidazole (Hmimt) affording the compound [Ag(Hmimt)(Ph₃P)(Q^S)] and [Ag(Q^O)(Ph₃P)]₂ reacts with 1-methyl-imidazole (Meim) affording the compound [Ag(Meim)(Ph₃P)(Q^O)], whereas [Ag(Q^S)(Ph₃P)]₂ reacts with 1,10-phenanthroline (phen), affording the compound [Ag(phen)(Ph₃P)](Q^S). Finally [Ag(Q^S)(Ph₃P)₂] reacts with phen producing the ionic species [Ag(phen)(Ph₃P)₂](Q^S).     

Effect of fluorine position on the coordinating ability of fluorosalicylic acids--an experimental study complemented with computations

The complexation of 3-, 4-, and 6-fluorosalicylic acids (HL) with copper(II) was investigated in aqueous solution by pH-potentiometry combined with UV-visible spectrophotometry, and in 50 v/v % water-methanol mixture by the two-dimensional ESR simulation method. Both methods showed the formation of [CuLH₋₁] and [CuL₂H₋₂]²⁻ of high stabilities, and, at low excess of ligand, the ESR-silent mixed hydroxido complex [Cu₂L₂H₋₃]⁻. Further species were also identified by the two-dimensional ESR simulation method: [CuL]⁺ in the acidic region, the minor dimer [Cu₂L₂H₋₂], and the cis and the trans isomers for [CuL₂H₋₂]²⁻. The position of the fluorine atom in the aromatic ring had significant effect on the coordination abilities of the ligands, in good correlation with their reported biological activities. It was 3-fluorosalicylic acid, which formed the most stable complexes [CuLH₋₁] and [CuL₂H₋₂]²⁻, while the mononuclear complexes with 6-fluorosalicylic acid were found to be the least stable. For the other ligands (including 5-fluorosalicylic acid studied recently), complexes of medium stabilities were formed. For the interpretation of these findings, ab initio and semi-empirical quantum chemical calculations were carried out for the ligand molecules, isolated and surrounded by water molecules, respectively.     

An antiferromagnetically coupled trinuclear Cu(II) complex containing μ(O,O′), μ(O) carboxylates and μ(O) phenoxide bridges

The trinuclear complex [L₂Cu₃(CF₃CO₂)₄] (1) has been synthesized and its crystal structure determined. It consists of a linear arrangement of Cu(II) centers. The central copper atom is bonded to six oxygen atoms and has a tetragonally distorted octahedral geometry, while the terminal copper atoms are bonded to three oxygen and two nitrogen atoms and show a distorted square pyramidal geometry. The complex shows di-μ(O,O′) syn-syn carboxylate bridging as well as monoatomic (μ-O) bridging, along with phenolate (μ-O) oxygen bridging. Cryomagnetic investigations in the range 2-300 K revealed an antiferromagnetic spin exchange interaction with J = −95.7 cm⁻¹, based on the isotropic exchange model H_ex = −2J[S₁ · S₂ + S₂ · S₃].     

Multinuclear magnetic resonance study of Pt(II) compounds with sulfoxide ligands and crystal structures of complexes of the types [Pt(R2SO)X3] and Pt(R2SO)2Cl2

Pt(II) complexes of the types K[Pt(R₂SO)X₃], NR₄[Pt(R₂SO)X₃] and Pt(R₂SO)₂Cl₂ (where X = Cl or Br) were characterized by multinuclear magnetic resonance spectroscopy (¹⁹⁵Pt, ¹H and ¹³C). In ¹⁹⁵Pt NMR, the chloro ionic compounds have shown signals between −2979 and −3106 ppm, while the cis disubstituted complexes were observed at higher fields, between −3450 and −3546 ppm. The signal of the compound trans-Pt(DPrSO)₂Cl₂ was found at higher field (−3666 ppm) than its cis analogue (−3517 ppm), since π-back-donation is considerably less effective in the trans geometry. In ¹H NMR, a single signal was observed for the sulfoxide in [Pt(DMSO)Cl₃]⁻, but for the other more sterically hindered ligands, two series of resonances were observed for the protons in α and β positions. The coupling constant ³J(¹⁹⁵Pt-¹H) are between 15 and 33 Hz. The ¹³C NMR results were interpreted in relation to the concept of inversed polarization of the π sulfoxide bond. The ²J(¹⁹⁵Pt-¹³C) values vary between 35 and 66 Hz, while a few ³J(¹⁹⁵Pt-¹³C) couplings were observed (13-26 Hz). The crystal structures of five monosubstituted ionic compounds N(n-Bu)₄[Pt(TMSO)Cl₃], N(Me)₄[Pt(DPrSO)Cl₃], K[Pt(EMSO)Cl₃], K[Pt(TMSO)Br₃] · H₂O and N(Et)₄[Pt(DPrSO)Br₃] and one disubstituted complex cis-Pt(DBuSO)₂Cl₂ were determined. The trans influence of the different ligands is discussed.     

An aluminoborate cluster [AlB12O14(OH)12]: Synthesis and structure of [C5H6N][AlB12O14(OH)12]

A new aluminoborate, [C₅H₆N][AlB₁₂O₁₄(OH)₁₂], has been hydrothermally synthesized at 200 °C. The single-crystal diffraction study reveals that it crystallizes in space group C2/c. It consists of aluminoborate clusters [AlB₁₂O₁₄(OH)₁₂]⁻ and counterions [C₅H₆N]⁺. The aluminoborate cluster contains an Al(OH)₆ octahedron as a core that is capped by two raft-like polyborate units [B₆O₇(OH)₆]. These clusters are further interlinked by extensive hydrogen bonding to form a three-dimensional (3D) network, containing large channels along the b-axis, in which the [C₅H₆N]⁺ cations are located.     

Structure and magnetic properties of a tetranuclear Cu4O4 open-cubane in [Cu(L)]4·4H2O with L = (E)-N′-(2-oxy-3-methoxybenzylidene)benzohydrazide

The in-situ formed hydrazone Schiff base ligand (E)-N′-(2-oxy-3-methoxybenzylidene)benzohydrazide (L²⁻) reacts with copper(II) acetate to a tetranuclear open cubane [Cu(L)]₄ complex which crystallizes as two symmetry-independent (Z′ = 2) S₄-symmetrical molecules in different twofold special positions with a homodromic water tetramer. The two independent (A and B) open- or pseudo-cubanes with Cu₄O₄ cores of 4 + 2 class (Ruiz classification) each have three different magnetic exchange pathways leading to an overall antiferromagnetic coupling with J_1B = J_2B = −17.2 cm⁻¹, J_1A = −36.7 cm⁻¹, J_2A = −159 cm⁻¹, J_3A = J_3B = 33.5 cm⁻¹, g = 2.40 and ρ = 0.0687. The magnetic properties have been analysed using the H = −Σ_i,jJ_ij(S_iS_j) spin Hamiltonian.     

Synthesis, characterization and structural analysis of isostructural dinuclear molybdenum and tungsten oxo-bis-μ-sulfido-benzenedithiolene complexes

Reactions of the molybdenum and tungsten precursors [MO₂S₂]²⁻ with equimolar amounts of benzenedithiol in acetonitrile give the title compounds [M₂O₂(μ-S)₂(bdt)₂]²⁻ with M = Mo, W and bdt = benzene-dithiolate. In case a tungsten to ligand ratio of 1:2 is used the dimer forms as well but only as a minor species whereas the monomer [WO(bdt)₂]²⁻ is the main product. In both dimeric compounds the syn-isomers are formed referring to the position of the apical oxo ligands with respect to the M₂S₂ plane. For the molybdenum compound this contrasts with a published crystal structure of the anti-isomer. Both complexes give highly symmetric isomorphous crystals but still show subtle differences in their bond lengths and angles around the central metal. The X-ray crystal structures of both are analyzed in detail and compared with each other and with the isomeric molybdenum compound. Differences and similarities between tungsten and both isomers of molybdenum complexes are shown to be more influenced by the conformation than by the central metal and a reason for the formation of syn- and anti-isomers based on the respective synthetic procedures is proposed.     

A new example of a tetranuclear iron(III) cluster containing the [Fe4O2] core: preparation, X-ray crystal structure, magnetochemistry and Mössbauer study of [Fe4O2(O2CMe)6(N3)2(phen)2]

Two synthetic procedures have been employed that allow access to the new tetranuclear cluster [Fe₄O₂(O₂CMe)₆(N₃)₂(phen)₂] (1), where phen is 1,10-phenanthroline. Complex 1 · 3MeCN displays an unusual structural asymmetry (observed for the second time) in its [Fe₄O₂]⁸⁺ core that can be considered as a hybrid of the bent (butterfly) and planar dispositions of four metal ions seen previously in such compounds with transition metals. Complex 1 has been characterized by variable-temperature magnetic susceptibility studies, and by IR and variable-temperature ⁵⁷Fe Mössbauer spectroscopies. Magnetochemical data reveal a diamagnetic ground state (S=0) with antiferromagnetic body-body and body-wingtip interactions between the iron(III) ions of the butterfly core (J_bb=−11 cm⁻¹, J_wb=−70 cm⁻¹). Magnetochemical and Mössbauer studies on 1 show that its structural asymmetry has practically no influence on these properties compared with the more symmetric types.     

BEDT-TTF salts of the unsymmetrical [M(tfadt)2] dithiolene complexes (M = Ni, Au; tfadt = S2C2(CN)(CF3))

Two closely related 1:1 salts are obtained upon electrocrystallization of BEDT-TTF (BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene) in the presence of the isosteric [M(tfadt)₂]⁻ dithiolene complexes (tfadt: 1-trifluoromethyl-2-cyano-1,2-dithiolato), which essentially differ by their spin state, S = 0 in [Au(tfadt)₂]⁻, S = 1/2 in [Ni(tfadt)₂]⁻. In both [BEDT-TTF][M(tfadt)₂] salts, the BEDT-TTF radical cations form chains with a strong lateral overlap and strong antiferromagnetic interactions while the paramagnetic anions in the nickel-containing salt [BEDT-TTF][Ni(tfadt)₂] are essentially non-interacting. The structural differences between the nickel and gold complexes are analyzed and discussed.     

Oxygen transfer properties and dimensions of red blood cells in high-altitude camelids,dromedary camel and goat

Summary To estimate the advantage of the small red blood cells (RBC) of high-altitude camelids for O₂ transfer, the kinetics of O₂ uptake into and release from the RBC obtained from llama, vicuña and alpaca were investigated at 37°C with a stopped-flow technique. O₂ transfer conductance of RBC (G) was estimated from the rate of O₂ saturation change and the corresponding O₂ pressure difference between medium and hemoglobin. For comparison, O₂ kinetics for the RBC of a lowaltitude camelid (dromedary camel) and the pygmy goat were determined and previously measured values for human RBC were used. O₂ transfer of RBC was found to be strongly influenced by extracellular diffusion, except with O₂ release into dithionite solutions of sufficiently high concentration (>30 mM). TheG values measured in these standard conditions,G _st (in mmol · min^–1 · Torr^–1 · (ml RBC)^–1) were: high-altitude camelids, 0.58 (averaged for llama, alpaca and vicuña since there were no significant interspecific differences); camel 0.42; goat, 0.42; man, 0.39. The differences can in part be attributed to expected effects of the size and shape of the RBC (volume, surface area, mean thickness), as well as to the intracellular O₂ diffusivity which depends on the concentration of cellular hemoglobin. The highG _st of RBC of highaltitude camelids may be considered to enhance O₂ transfer in lungs and tissues. But the O₂ transfer conductance of blood, , equal toG _st multiplied by hematocrit (in mmol · min^–1 · Torr^–1 · (ml blood)^–1), was only slightly higher as compared to other species: 0.20 (llama, alpaca, vicuña), 0.14 (camel), 0.18 (goat), 0.17 (man).Abbreviations DPG 2,3-diphosphoglycerate - G conductance - Hb hemoglobin - RBC red blood cells - percent saturation of hemoglobin