Kinetic UV-Vis Spectroscopic and DFT Mechanistic Study of the Redox Reaction of [OsVIIIO4(OH)n]n- (n = 1, 2) and Methanol in a Basic Aqueous Matrix.

This combined experimental and computational study builds on our previous studies to elucidate the reaction mechanism of methanol oxidation by OsVIII oxido/hydroxido species (in basic aqueous media) while accounting for the simultaneous formation of OsVII species via a comproportionation reaction between OsVIII and OsVI. UV-Vis spectroscopy kinetic analyses with either CH3OH or the deuterated analogue CD3OH as a reducing agent revealed that transfer of α-carbon-hydrogen of methanol is the partial rate-limiting step. The resulting relatively large KIE value of approximately 11.82 is a combination of primary and secondary isotope effects. The Eyring plots for the oxidation of these isotopologues of methanol under the same reaction conditions are parallel to each other and hence have the same activation enthalpy [Δ⧧H° = 14.4 ± 1.2 kcal mol-1 (CH3OH) and 14.5 ± 1.3 kcal mol-1 (CD3OH)] but lowered activation entropy (Δ⧧S°) from -12.5 ± 4.1 cal mol-1 K-1 (CH3OH) to -17.1 ± 4.4 cal mol-1 K-1 (CD3OH). DFT computational studies at the PBE-D3 level with QZ4P (Os) and pVQZ (O and H) basis sets provide clear evidence to support the data and interpretations derived from the experimental kinetic work. Comparative DFT mechanistic investigations in a simulated aqueous phase (COSMO) indicate that methanol and OsVIII first associate to form a noncovalent adduct bound together by intermolecular H-bonding interactions. This is followed by spin-forbidden α-carbon-hydrogen transfer (not O-H transfer) from methanol to OsVIII by means of HAT, which is found to be the partial rate-limiting step. Without the organic and inorganic fragments dissociating from each other during the entire stepwise redox reaction (in order to avoid formation of highly energetically unfavorable monomer species), the HAT step is followed by PT and then ET before the final product monomers formaldehyde and OsVI dissociate from each other. DFT-calculated Δ⧧H° is within 5 kcal mol-1 of the experimentally obtained value, while the DFT Δ⧧S° is three times larger than that found from the experiment.

lolal Is an Evolutionarily New Epigenetic Regulator of dpp Transcription during Dorsal-Ventral Axis Formation.

Secreted ligands in the Dpp/BMP family drive dorsal-ventral (D/V) axis formation in all Bilaterian species. However, maternal factors regulating Dpp/BMP transcription in this process are largely unknown. We identified the BTB domain protein longitudinals lacking-like (lolal) as a modifier of decapentaplegic (dpp) mutations. We show that Lolal is evolutionarily related to the Trithorax group of chromatin regulators and that lolal interacts genetically with the epigenetic factor Trithorax-like during Dpp D/V signaling. Maternally driven Lolal(HA) is found in oocytes and translocates to zygotic nuclei prior to the point at which dpp transcription begins. lolal maternal and zygotic mutant embryos display significant reductions in dpp, pMad, and zerknullt expression, but they are never absent. The data suggest that lolal is required to maintain dpp transcription during D/V patterning. Phylogenetic data revealed that lolal is an evolutionarily new gene present only in insects and crustaceans. We conclude that Lolal is the first maternal protein identified with a role in dpp D/V transcriptional maintenance, that Lolal and the epigenetic protein Trithorax-like are essential for Dpp D/V signaling and that the architecture of the Dpp D/V pathway evolved in the arthropod lineage after the separation from vertebrates via the incorporation of new genes such as lolal.

Drosophila Follistatin exhibits unique structural modifications and interacts with several TGF-beta family members.

Follistatin (FS) is one of several secreted proteins that modulate the activity of TGF-beta family members during development. The structural and functional analysis of Drosophila Follistatin (dFS) reveals important differences between dFS and its vertebrate orthologues: it is larger, more positively charged, and proteolytically processed. dFS primarily inhibits signaling of Drosophila Activin (dACT) but can also inhibit other ligands like Decapentaplegic (DPP). In contrast, the presence of dFS enhances signaling of the Activin-like protein Dawdle (DAW), indicating that dFS exhibits a dual function in promoting and inhibiting signaling of TGF-beta ligands. In addition, FS proteins may also function in facilitating ligand diffusion. We find that mutants of daw are rescued in significant numbers by expression of vertebrate FS proteins. Since two PiggyBac insertions in dfs are not lethal, it appears that the function of dFS is non-essential or functionally redundant.

The Drosophila BMP type II receptor Wishful Thinking regulates neuromuscular synapse morphology and function.

Proper synaptic development is critical for establishing all aspects of neural function including learning, memory, and locomotion. Here, we describe the phenotypic consequences of mutations in the wishful thinking (wit) gene, the Drosophila homolog of the vertebrate BMP type II receptor. Mutations in wit result in pharate lethality that can be rescued by expression of a wit transgene in motor neurons but not in muscles. Mutant larvae exhibit small synapses, severe defects in evoked junctional potentials, a lower frequency of spontaneous vesicle release, and an alteration in the ultrastructure of synaptic active zones. These results reveal a novel role for BMP signaling in regulating Drosophila neuromuscular junction synapse assembly and activity and may indicate that similar pathways could govern vertebrate synapse development.

Absorption of cholesterol from a micellar solution: intestinal perfusion studies in man.

The absorption of cholesterol has been studied in man by perfusing the upper jejunum with a micellar solution of bile salt, 1-monoglyceride, and cholesterol-(14)C, with a triple lumen tube with collection sites 50 cm apart. The absorption of micellar components between the collection sites was calculated from their concentration changes relative to those of the watersoluble marker, polyethylene glycol. Control experiments were performed with cholesterol-free perfusions of saline or bile salt-monoglyceride solutions. Steady state conditions were obtained.Each of the components of the micelle was absorbed to a different extent during passage through the test segment of jejunum. Bile salt was not absorbed (mean, -3%), but micellar monoglyceride was rapidly hydrolyzed and absorbed almost completely (mean, 98%). Cholesterol radioactivity was absorbed to an intermediate extent (mean, 73%), and the absorption of chemically determined cholesterol (mean, 46%) indicated that much of the disappearance of radioactivity represented true absorption and not simple exchange. The specific activity of the perfused cholesterol fell during passage through the loop. This fall was interpreted as signifying the continuous addition of nonradioactive endogenous cholesterol by the test segment. However, the decrease in specific activity may also be considered to signify exchange, in that nonradioactive molecules entered the lumen as radioactive molecules were absorbed. Plant sterols appeared in the intestinal contents during the perfusion and must have been contributed by the perfused segment. The perfusate and samples taken from the upper and lower collection sites were examined by ultracentrifugation to define the physical state of cholesterol. It was found that cholesterol in the perfusate or upper collection site samples did not sediment, but that 23% of the cholesterol in the lower collection site samples was sedimentable (mean of three experiments); bile salt, as control, was not sedimentable. Solubility experiments in model systems showed that cholesterol possessed low solubility in bile salt solution; its solubility increased markedly and in linear proportion to the amount of fatty acid or monoglyceride or both that was added to the bile salt solution. These findings suggest that polar lipid such as fatty acid or monoglyceride as well as bile salt is essential for normal micellar solubilization of cholesterol in intestinal content. They suggest the necessity of considering an insoluble sedimentable phase of particulate sterol in intestinal content as well as an oil and micellar phase for a complete description of sterol absorption. The marked difference in the rates of absorption of individual micellar components suggests that micellar lipid is not absorbed as an intact aggregate and is consistent with the view that polar lipid such as fatty acid is absorbed in molecular form by diffusion from a micellar solution. The experiments confirm previous findings demonstrating that fat absorption without bile salt absorption occurs in the upper small intestine in man.

Significant metabolic acidosis induced by acetazolamide. Not a rare complication.

Blood gas and serum electrolyte levels were measured in 27 elderly patients (mean age +/- SD, 63.3 +/- 13.5 years) who were receiving acetazolamide (250 to 1,000 mg/day) for glaucoma. Eleven glaucomatous patients (mean age, 69.1 +/- 7.4 years) who were not receiving acetazolamide served as a control group. In the acetazolamide-treated group, four patients (14.8%) had mild acidosis (7.29 greater than pH less than or equal to 7.31), ten (37%) had moderate acidosis (7.20 greater than pH less than or equal to 7.29), and one patient (3.7%) had severe acidosis (pH, 7.15). None of the patients in the control group had acidosis. It is concluded that moderate metabolic acidosis of potential clinical significance is common among glaucomatous elderly patients who receive acetazolamide. The exact clinical significance of our observations is yet to be determined.

Double dissociation of error inhibition and correction deficits after basal ganglia or dorsomedial frontal damage in humans.

Effective self-control relies on the rapid adjustment of inappropriate responses. Understanding the brain basis of these processes has the potential to inform neurobiological models of the many neuropsychiatric disorders that are marked by maladaptive responding. Research on error processing in particular has implicated the dorsomedial frontal lobe (DMF) and basal ganglia (BG) in error detection, inhibition and correction. However there is controversy regarding the specific contributions of these regions to each of these component processes. Here we examined the effects of lesions affecting DMF or BG on these error-related processes. A flanker task was used to induce errors that in turn led to spontaneous, online corrections, while response kinematics were measured with high spatiotemporal resolution. The acceleration of errors was initially greater than that of correct responses. Errors then showed slower acceleration compared to correct responses, consistent with engagement of inhibition shortly after error response onset. BG damage disproportionately disrupted this early inhibitory phenomenon, above and beyond effects on baseline motor performance, but did not affect the kinematics of the corrective response. DMF damage showed the opposite pattern, with relatively delayed onset and weaker initial acceleration of the corrective response, but error suppression kinematics similar to that of the control group. This work clarifies the component processes and neural substrates of online post-error control, providing evidence for dissociable contributions of BG to error inhibition, but not correction, and DMF to rapid error correction, but not error suppression.

Isolation of Drosophila activin and follistatin cDNAs using novel MACH amplification protocols.

With the genomic sequence of multicellular organisms such as Caenorhabditis elegans, Drosophila melanogaster, and Homo sapiens completed and others to be finished in the near future, the focus has shifted from accumulating sequence information to the prediction and analysis of genes within the completed genomes. Unfortunately, presently available computer programs do not always accurately predict gene structure such as mRNA and translation start sites or intron/exon boundaries. The only way to be certain about a gene's structure is to isolate and characterize its cDNA. Since the screening of libraries is a time-consuming, labor-intensive process that sometimes fails to yield the desired clone, we searched for faster, more efficient ways to isolate cDNAs. In this study, we describe two methods for amplification and isolation of cDNAs from plasmid libraries that requires no hybridization (MACH). With the polymerase chain reaction-based MACH-2 protocol, we present a strategy that requires little DNA sequence information to selectively isolate the longest cDNA variant from plasmid libraries in about 3 days. Our protocols were used to isolate cDNAs for the Drosophila activin and follistatin genes.

Intermittent administration of furosemide vs continuous infusion preceded by a loading dose for congestive heart failure.

Several reports have suggested that continuous intravenous administration of loop diuretics may be superior to intermittent administration. We performed a prospective randomized crossover study comparing intermittent intravenous administration (IA) of furosemide with continuous infusion following a single loading dose (LDCI) in nine patients with severe congestive heart failure. At the time of hospital admission, patients were randomly assigned to one of two treatment groups. One group (four patients) received an IV bolus injection of furosemide followed immediately by a continuous infusion for 48 h. The second group (five patients) was treated with three IV bolus injections a day for 48 h. Total doses of furosemide were equivalent in the two groups. After 48 h, each patient was crossed over to the other method and treated for an additional 48 h. LDCI produced significantly greater diuresis and natriuresis than IA (total urine output increased by 12 to 26 percent, total sodium excretion increased by 11 to 33 percent) (p less than 0.01). There were no significant differences in side effects between the two methods. These results indicate that LDCI may be a preferred method for administration of furosemide in patients with congestive heart failure.

Anti-Rnp antibodies in chronic liver diseases.

Antinuclear antibodies are commonly observed in chronic liver disorders. Sera from 87 patients with various chronic liver diseases were tested for the presence of antibodies against two extractable nuclear antigens (ENA) - RNP and Sm. Using an enzyme-linked immunosorbent assay (ELISA) anti-RNP antibodies were detected in 13 patients (15%) most of whom had cryptogenic or primary biliary cirrhosis. When the sera were further tested by ELISA for the presence of anti-Sm antibodies no antibody binding could be detected. These findings support the notion that anti-RNP (but not anti-Sm) antibodies are included among the autoantibodies shared by systemic lupus erythematosus and chronic liver diseases.

Antinuclear autoantibodies in chronic liver diseases.

Circulating autoantibodies are often observed in liver disorders, especially in those thought to have an autoimmune etiology-such as primary biliary cirrhosis (PBC) and chronic active hepatitis (CAH). The pathophysiologic role of these antibodies, however, remains obscure. The present study was performed to evaluate the incidence and diagnostic value of different antinuclear antibodies in chronic liver diseases, and to assess whether the antibodies are a non-specific expression of the hypergammaglobulinemia observed in these disorders. We measured six different antinuclear and closely related antibodies (against ssDNA, dsDNA, Poly (I), Poly (dT), RNA and cardiolipin) and their IgG, IgA and IgM isotypes in the sera of 86 patients with autoimmune, as well as other chronic liver diseases--namely, PBC, CAH, alcoholic (AC) and cryptogenic cirrhosis (CC). Antibodies against all the various nuclear antigens were detected in all diseases studied. The incidence ranged from 4% (anti-cardiolipin-IgG in CC) to 74% (anti-Poly (dT)-IgM in PBC). Although the antibody profiles differed among the various disease entities, they were not distinct enough to be of any clinical diagnostic value. In alcoholic cirrhosis antibody levels correlated with corresponding immunoglobulin isotype levels (notably IgA), suggesting a non-specific expression of hypergammaglobulinemia. In the other liver diseases such a correlation was lacking, favoring the existence of an underlying specific antigenic stimulation, or some other more specific immune dysfunction.

Pregnancy and primary biliary cirrhosis.

Pregnancy is rarely encountered in patients with primary biliary cirrhosis. Ten pregnancies in nine patients have been reported in the literature. All five pregnancies that continued beyond the 31st week had increasing jaundice during late pregnancy. We describe a case of primary biliary cirrhosis with symptomatic onset at age 19, pregnancy a year later, with subsequent resolution of jaundice and pruritus. This course is different than most described by others.

[Trimethoprim-sulphamethoxazole-induced meningitis].

Drug-induced meningitis is rarely included in the differential diagnosis of aseptic (usually recurrent) meningitis. A 74-year-old man who suffered from recurrent aseptic meningitis following re-exposures to trimethoprim-sulphamethoxazole (Resprim) is presented. The clinical and laboratory findings resembled those found in bacterial meningitis, excluding normal glycorrachia. Extensive microbiological, serologic and imaging studies did not disclose any relevant findings. All symptoms and signs resolved rapidly following drug withdrawal, and findings on follow-up lumbar puncture were normal.

[Disappointing response of chronic C hepatitis to interferon].

From February 1990 to August 1995 we treated 58 patients with chronic hepatitis C alfa-interferon, 3 million units 3 times weekly for 6 months. Of the 48 patients with adequate follow-up, 34 did not respond to treatment at all. 10 patients responded, but within a few months hepatic enzymes again increased. These 2 groups can be considered failures of interferon treatment. In 4 patients enzymes remained normal for the duration of follow-up, (10-34 months). Even in this small group, 1 patient had a positive test for HCV RNA after completion of treatment. A partial explanation of our disappointing results may be the high prevalence of a subtype of C hepatitis-subtype 1b, which has recently been reported in Israel. This strain is particularly resistant to interferon. The means to define subtypes were not, and as far as we know are not yet available in Israel. Various groups have attempted to improve the outcome of treatment of hepatitis C, which in other hands too was still far from satisfactory. Thus, regimens of interferon utilizing higher doses and longer periods of treatment are being evaluated, as well as the addition of Ribavirin, which hopefully will improve results.

[Acute recurrent suppurative thyroiditis in childhood].

Acute suppurative thyroiditis in children is very rare and has been reported in only six cases. We describe a 4 1/2 year old girl who presented with acute suppurative thyroiditis of the left lobe. All thyroid function tests were normal but the radioisotope scan showed decreased activity over the upper pole of the left lobe. The child was treated with massive doses of antibiotics and gradually recovered. Three years later she presented with exactly the same findings in the left lobe of the thyroid. Thyroid function tests were again normal but repeated radioisotopic scan showed decreased activity over the left upper pole. Again she recovered gradually under massive antibiotic treatment. A follow up scan showed great improvement with almost complete recovery of activity in the left lobe.

35Cl/37Cl isotope effects in 103Rh NMR of [RhCl(n)(H2O)(6-n)](3-n) complex anions in hydrochloric acid solution as a unique 'NMR finger-print' for unambiguous speciation.

A detailed analysis of the (35)Cl/(37)Cl isotope effects observed in the 19.11 MHz (103)Rh NMR resonances of [RhCl(n)(H(2)O)(6-n)](3-n) complexes (n=3-6) in acidic solution at 292.1K, shows that the 'fine structure' of each (103)Rh resonance can be understood in terms of the unique isotopologue and in certain instances the isotopomer distribution in each complex. These (35)Cl/(37)Cl isotope effects in the (103)Rh NMR resonance of the [Rh(35/37)Cl(6)](3-) species manifest only as a result of the statistically expected (35)Cl/(37)Cl isotopologues, whereas for the aquated species such as for example [Rh(35/37)Cl(5)(H(2)O)](2-), cis-[Rh(35/37)Cl(4)(H(2)O)(2)](-) as well as the mer-[Rh(35/37)Cl(3)(H(2)O)(3)] complexes, additional fine-structure due to the various possible isotopomers within each class of isotopologues, is visible. Of interest is the possibility of the direct identification of stereoisomers cis-[RhCl(4)(H(2)O)(2)](-), trans-[RhCl(4)(H(2)O)(2)](-), fac-[RhCl(3)(H(2)O)(3)] and mer-[RhCl(3)(H(2)O)(3)] based on the (103)Rh NMR line shape, other than on the basis of their very similar δ((103)Rh) chemical shift. The (103)Rh NMR resonance structure thus serves as a novel and unique 'NMR-fingerprint' leading to the unambiguous assignment of [RhCl(n)(H(2)O)(6-n)](3-n) complexes (n=3-6), without reliance on accurate δ((103)Rh) chemical shifts.

The Drosophila mitochondrial translation elongation factor G1 contains a nuclear localization signal and inhibits growth and DPP signaling.

Mutations in the human mitochondrial elongation factor G1 (EF-G1) are recessive lethal and cause death shortly after birth. We have isolated mutations in iconoclast (ico), which encodes the highly conserved Drosophila orthologue of EF-G1. We find that EF-G1 is essential during fly development, but its function is not required in every tissue. In contrast to null mutations, missense mutations exhibit stronger, possibly neomorphic phenotypes that lead to premature death during embryogenesis. Our experiments show that EF-G1 contains a secondary C-terminal nuclear localization signal. Expression of missense mutant forms of EF-G1 can accumulate in the nucleus and cause growth and patterning defects and animal lethality. We find that transgenes that encode mutant human EF-G1 proteins can rescue ico mutants, indicating that the underlying problem of the human disease is not just the loss of enzymatic activity. Our results are consistent with a model where EF-G1 acts as a retrograde signal from mitochondria to the nucleus to slow down cell proliferation if mitochondrial energy output is low.

A kinetic and thermodynamic study of the unexpected comproportionation reaction between cis-[Os(VIII)O4(OH)2](2-) and trans-[Os(VI)O2(OH)4](2-) to form a postulated [Os(VII)O3(OH)3](2-) complex anion.

A kinetic study of [OsO(4)] reduction by aliphatic alcohols (MeOH and EtOH) was performed in a 2.0 M NaOH matrix at 298.1 K. The rate model that best fitted the UV-VIS data supports a one-step, two electron reduction of Os(VIII) (present as both the [Os(VIII)O(4)(OH)](-) and cis-[Os(VIII)O(4)(OH)(2)](2-) species in a ratio of 0.34:0.66) to form the trans-[Os(VI)O(2)(OH)(4)](2-) species. The formed trans-[Os(VI)O(2)(OH)(4)](2-) species subsequently reacts relatively rapidly with the cis-[Os(VIII)O(4)(OH)(2)](2-) complex anion to form a postulated [Os(VII)O(3)(OH)(3)](2-) species according to: cis-[Os(VIII)O(4)(OH)(2)](2-) + trans-[Os(VI)O(2)(OH)(4)](2-) (k+2) <−> (k-2) 2[Os(VII)O(3)(OH)(3)](2-). The calculated forward, k(+2), and reverse, k(-2), reaction rate constants of this comproportionation reaction are 620.9 ± 14.6 M(-1) s(-1) and 65.7 ± 1.2 M(-1) s(-1) respectively. Interestingly, it was found that the postulated [Os(VII)O(3)(OH)(3)](2-) complex anion does not oxidize MeOH or EtOH. Furthermore, the reduction of Os(VIII) with MeOH or EtOH is first order with respect to the aliphatic alcohol concentration. In order to corroborate the formation of the [Os(VII)O(3)(OH)(3)](2-) species predicted with the rate model simulations, several Os(VIII)/Os(VI) mole fraction and mole ratio titrations were conducted in a 2.0 M NaOH matrix at 298.1 K under equilibrium conditions. These titrations confirmed that the cis-[Os(VIII)O(4)(OH)(2)](2-) and trans-[Os(VI)O(2)(OH)(4)](2-) species react in a 1:1 ratio with a calculated equilibrium constant, K(COM), of 9.3 ± 0.4. The ratio of rate constants k(+2) and k(-2) agrees quantitatively with K(COM), satisfying the principle of detailed balance. In addition, for the first time, the molar extinction coefficient spectrum of the postulated [Os(VII)O(3)(OH)(3)](2-) complex anion is reported.

The interaction between two TGF-beta type I receptors plays important roles in ligand binding, SMAD activation, and gradient formation.

The goal of this report is to elucidate the contributions of the Drosophila TGF-beta type I receptors TKV and SAX to the activity gradient formed by the two BMP family members DPP and GBB that play important roles in growth and patterning of imaginal discs. Binding studies display preferential interactions of DPP and GBB with homodimers of TKV or SAX, respectively, but also low affinities of both ligands to heterodimers. Inside the cell, constitutively activated forms of both TKV and SAX can ectopically phosphorylate the SMAD transcription factor MAD. However, MAD phosphorylated by homodimers of activated SAX or certain mutant forms of TKV localizes to the nucleus without changing the expression of downstream genes. Differences in signaling between SAX and TKV can be localized to amino acid residues within an area that has been shown to influence complexes formation between type I and type II receptors. The finding that the type II receptor PUT but not activated forms of SAX can enhance signaling of a pseudo-activated MAD-SDVD, which cannot be phosphorylated at the C-terminus, suggests a model, where activation of SMADs requires the presence of type II receptors and a second activation step in addition to C-terminal phosphorylation. Complete activation of MAD can only occur in tetrameric complexes of type II receptors in combination with SAX-TKV heterodimers or TKV homodimers but not SAX homodimers. Since TKV is not distributed equally in wing discs, heterodimers of SAX and TKV play an important role in extending the BMP activity gradient by facilitating DPP diffusion and assisting GBB signaling through functional complexes with type II receptors.

Separation and quantification of [RhCln(H2O)(6-n)](3-n) (n=0-6) complexes, including stereoisomers, by means of ion-pair HPLC-ICP-MS.

A hyphenated ion-pair (tetrabutylammonium chloride-TBACl) reversed phase (C(18)) HPLC-ICP-MS method (High Performance Liquid Chromatography Inductively Coupled Plasma Mass Spectroscopy) for anionic Rh(III) aqua chlorido-complexes present in an HCl matrix has been developed. Under optimum chromatographic conditions it was possible to separate and quantify cationic Rh(III) complexes (eluted as a single band), [RhCl(3)(H(2)O)(3)], cis-[RhCl(4)(H(2)O)(2)](-), trans-[RhCl(4)(H(2)O)(2)](-) and [RhCl(n)(H(2)O)(6-n)](3-n) (n=5, 6) species. The [RhCl(n)(H(2)O)(6-n)](3-n) (n=5, 6) complex anions eluted as a single band due to the relatively fast aquation of [RhCl(6)](3-) in a 0.1 mol L(-1) TBACl ionic strength mobile phase matrix. Moreover, the calculated t(1/2) of 1.3 min for [RhCl(6)](3-) aquation at 0.1 mol kg(-1) HCl ionic strength is significantly lower than the reported t(1/2) of 6.3 min at 4.0 mol kg(-1) HClO(4) ionic strength. Ionic strength or the activity of water in this context is a key parameter that determines whether [RhCl(n)(H(2)O)(6-n)](3-n) (n=5, 6) species can be chromatographically separated. In addition, aquation/anation rate constants were determined for [RhCl(n)(H(2)O)(6-n)](3-n) (n=3-6) complexes at low ionic strength (0.1 mol kg(-1) HCl) by means of spectrophotometry and independently with the developed ion-pair HPLC-ICP-MS technique for species assignment validation. The Rh(III) samples that was equilibrated in differing HCl concentrations for 2.8 years at 298K was analyzed with the ion-pair HPLC method. This analysis yielded a partial Rh(III) aqua chlorido-complex species distribution diagram as a function of HCl concentration. For the first time the distribution of the cis- and trans-[RhCl(4)(H(2)O)(2)](-) stereoisomers have been obtained. Furthermore, it was found that relatively large amounts of 'highly' aquated [RhCl(n)(H(2)O)(6-n)](3-n) (n=0-4) species persist in up to 2.8 mol L(-1) HCl and in 1.0 mol L(-1) HCl the abundance of the [RhCl(5)(H(2)O)](2-) species is only 8-10% of the total, far from the 70-80% as previously proposed. A 95% abundance of the [RhCl(6)](3-) complex anion occurs only when the HCl concentration is above 6 mol L(-1). The detection limit for a Rh(III) species eluted from the column is below 0.147 mg L(-1).