Temperature effects on the viscosity and the wavelength-dependent refractive index of imidazolium-based ionic liquids with a phosphorus-containing anion.

A systematic study on the viscosity and refractive index of 1-alkyl-3-methylimidazolium based ionic liquids (alkyl = methyl, butyl and hexyl) combined with three phosphorus containing anions, i.e. dimethylphosphate, methyl methylphosphonate and methylphosphonate, is reported. Experimental measurements account for temperature effects, while the refractive index is determined at multiple wavelengths in the visible and near infrared region. Despite the structural similarity of these anions, significant differences in the physical properties of the resulting ILs are identified, along with the clear trend of viscosity increase - and refractive index decrease - with increasing alkyl chain length on the cation. Ab initio theoretical calculations are carried out to support and rationalise the observed behaviour.

Pilot study to determine the association between gut microbiota and fragility hip fracture. / Estudio piloto para determinar la asociación entre la microbiota intestinal y la fractura de cadera por fragilidad.

INTRODUCTION: Hip fractures are the most common cause of hospital admission to orthopaedic departments in Europe and they generate a major health problem. Therefore, it is of great interest to identify additional risk factors that will help us to better understand the pathophysiology of these fractures and improve our preventive capacity. There is sufficient data to support the theory of modulation of bone mass by gut microbiota (osteomicrobiology); however, there is a lack of human clinical studies directly linking microbiota to hip fracture risk. MATERIAL AND METHODS: Observational, analytical, case-control study. The sample consisted of 50 patients and it was distributed as follows: 25 elderly patients with fragility hip fracture and 25 subjects without fracture. The intestinal microbiota was determined by DNA extraction from stool samples and 16S ribosomal DNA sequencing after generation of gene libraries. RESULTS: Alpha diversity revealed an elevation of the estimators for the taxonomic class level in the hip fracture group. The orders Bacteroidales, Oscillospirales, Lachnospirales, Peptostreptococcales-Tissierellales and Enterobacterales were the dominant orders in both groups. In patients with fracture, a significant percentage increase in the orders Bacteroidales (p<.001) and Peptostreptococcales-Tissierellales (p<.005) was observed, as well as a decrease in the orders Lachnospirales (p<.001) compared to controls. CONCLUSIONS: This study has found an association between a specific microbiota in elderly patients with fragility hip fracture. These findings open the door to new strategies to prevent hip fractures. Modification of the microbiota through probiotics may prove to be an effective method to reduce the risk of hip fracture.

[Translated article] Pilot study to determine the association between gut microbiota and fragility hip fracture.

INTRODUCTION: Hip fractures are the most common cause of hospital admission to orthopaedic departments in Europe and they generate a major health problem. Therefore, it is of great interest to identify additional risk factors that will help us to better understand the pathophysiology of these fractures and improve our preventive capacity. There is sufficient data to support the theory of modulation of bone mass by gut microbiota (osteomicrobiology); however, there is a lack of human clinical studies directly linking microbiota to hip fracture risk. MATERIAL AND METHODS: Observational, analytical, case-control study. The sample consisted of 50 patients and it was distributed as follows: 25 elderly patients with fragility hip fracture and 25 subjects without fracture. The intestinal microbiota was determined by DNA extraction from stool samples and 16S ribosomal DNA sequencing after generation of gene libraries. RESULTS: Alpha diversity revealed an elevation of the estimators for the taxonomic class level in the hip fracture group. The orders Bacteroidales, Oscillospirales, Lachnospirales, Peptostreptococcales-Tissierellales and Enterobacterales were the dominant orders in both groups. In patients with fracture, a significant percentage increase in the orders Bacteroidales (p<.001) and Peptostreptococcales-Tissierellales (p<.005) was observed, as well as a decrease in the orders Lachnospirales (p<.001) compared to controls. CONCLUSIONS: This study has found an association between a specific microbiota in elderly patients with fragility hip fracture. These findings open the door to new strategies to prevent hip fractures. Modification of the microbiota through probiotics may prove to be an effective method to reduce the risk of hip fracture.

Solvent effects in ionic liquids: empirical linear energy-density relationships.

Multiparameter linear energy-density relationships to model solvent effects in room temperature ionic liquids (RTILs) are introduced and tested. The model incorporates two solvent dependent and two specific solute-solvent parameters represented by a set of electronic indexes derived from the conceptual density functional theory. The specific solute-solvent interactions are described in terms of the electronic chemical potential for proton migration between the anion or cation and the transition state structure of a specific reaction. These indexes provide a quantitative estimation of the hydrogen bond (HB) acceptor basicity and the hydrogen bond donor acidity of the ionic solvent, respectively. A sound quantitative scale of HB strength is thereby obtained. The solvent dependent contributions are described by the global electrophilicity of the cation and nucleophilicity of the anion forming the ionic liquid. The model is illustrated for the kinetics of cycloaddition of cyclopentadiene towards acrolein. In general, cation HB acidity outweighs the remaining parameters for this reaction.

Publisher Correction: Fe-functionalized paramagnetic sporopollenin from pollen grains: one-pot synthesis using ionic liquids.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Fe-functionalized paramagnetic sporopollenin from pollen grains: one-pot synthesis using ionic liquids.

The preparation of Fe-decorated sporopollenins was achieved using pollen grains and an ionic liquid as solvent and functionalizing agent. The integrity of the organic capsules was ascertained through scanning electron microscopy studies. The presence of Fe in the capsule was investigated using FT-IR, X-ray photoemission spectroscopy and energy-dispersive X-ray spectroscopy. Electron paramagnetic resonance and magnetization measurements allowed us to demonstrate the paramagnetic behavior of our Fe-functionalized sporopollenin. A few potential applications of pollen-based systems functionalized with magnetic metal ions via ionic liquids are discussed.

Estudio piloto para determinar la asociación entre la microbiota intestinal y la fractura de cadera por fragilidad / Pilot study to determine the association between gut microbiota and fragility hip fracture

Introducción: Las fracturas de cadera son la causa más frecuente de ingreso hospitalario en los servicios de ortopedia de Europa y suponen un importante problema sanitario. Por ello, es de gran interés identificar factores de riesgo adicionales que nos ayuden a comprender mejor la fisiopatología de estas fracturas y a mejorar nuestra capacidad preventiva. Existen datos suficientes para apoyar la teoría de la modulación de la masa ósea por la microbiota intestinal (osteomicrobiología); sin embargo, faltan estudios clínicos en humanos que relacionen directamente la microbiota con el riesgo de fractura de cadera. Material y métodos: Estudio observacional, analítico, de casos y controles. La muestra consta de 50 pacientes y se distribuye de la siguiente manera: 25 pacientes ancianos con fractura de cadera por fragilidad y 25 controles sanos sin fractura. Se analizó la microbiota intestinal mediante extracción de ADN de muestras de heces y secuenciación del ADN ribosómico 16S tras la generación de bibliotecas de genes. Resultados: La diversidad alfa reveló una elevación de los estimadores para el nivel taxonómico de clase en el grupo de fracturas de cadera. Los órdenes Bacteroidales, Oscillospirales, Lachnospirales, Peptostreptococcales-Tissierellales y Enterobacterales fueron los órdenes dominantes en ambos grupos. En los pacientes con fractura, se observó un aumento porcentual significativo del orden de Bacteroidales (p<0,001) y Peptostreptococcales-Tissierellales (p<0,005), así como una disminución de las del orden Lachnospirales (p<0,001) respecto a los controles. Conclusiones:Este estudio ha encontrado una asociación entre una microbiota específica en pacientes ancianos con fractura de cadera por fragilidad. Estos hallazgos abren la puerta a nuevas estrategias para prevenir las fracturas de cadera. Es posible que la modificación de la microbiota mediante probióticos se revele como un método eficaz para reducir el riesgo de fractura de cadera.(AU)

Introduction: Hip fractures are the most common cause of hospital admission to orthopaedic departments in Europe and they generate a major health problem. Therefore, it is of great interest to identify additional risk factors that will help us to better understand the pathophysiology of these fractures and improve our preventive capacity. There is sufficient data to support the theory of modulation of bone mass by gut microbiota (osteomicrobiology); however, there is a lack of human clinical studies directly linking microbiota to hip fracture risk. Material and methods: Observational, analytical, case–control study. The sample consisted of 50 patients and it was distributed as follows: 25 elderly patients with fragility hip fracture and 25 subjects without fracture. The intestinal microbiota was determined by DNA extraction from stool samples and 16S ribosomal DNA sequencing after generation of gene libraries. Results: Alpha diversity revealed an elevation of the estimators for the taxonomic class level in the hip fracture group. The orders Bacteroidales, Oscillospirales, Lachnospirales, Peptostreptococcales-Tissierellales and Enterobacterales were the dominant orders in both groups. In patients with fracture, a significant percentage increase in the orders Bacteroidales (p<.001) and Peptostreptococcales-Tissierellales (p<.005) was observed, as well as a decrease in the orders Lachnospirales (p<.001) compared to controls. Conclusions: This study has found an association between a specific microbiota in elderly patients with fragility hip fracture. These findings open the door to new strategies to prevent hip fractures. Modification of the microbiota through probiotics may prove to be an effective method to reduce the risk of hip fracture.(AU)

[Translated article] Pilot study to determine the association between gut microbiota and fragility hip fracture / Estudio piloto para determinar la asociación entre la microbiota intestinal y la fractura de cadera por fragilidad

Introducción: Las fracturas de cadera son la causa más frecuente de ingreso hospitalario en los servicios de ortopedia de Europa y suponen un importante problema sanitario. Por ello, es de gran interés identificar factores de riesgo adicionales que nos ayuden a comprender mejor la fisiopatología de estas fracturas y a mejorar nuestra capacidad preventiva. Existen datos suficientes para apoyar la teoría de la modulación de la masa ósea por la microbiota intestinal (osteomicrobiología); sin embargo, faltan estudios clínicos en humanos que relacionen directamente la microbiota con el riesgo de fractura de cadera. Material y métodos: Estudio observacional, analítico, de casos y controles. La muestra consta de 50 pacientes y se distribuye de la siguiente manera: 25 pacientes ancianos con fractura de cadera por fragilidad y 25 controles sanos sin fractura. Se analizó la microbiota intestinal mediante extracción de ADN de muestras de heces y secuenciación del ADN ribosómico 16S tras la generación de bibliotecas de genes. Resultados: La diversidad alfa reveló una elevación de los estimadores para el nivel taxonómico de clase en el grupo de fracturas de cadera. Los órdenes Bacteroidales, Oscillospirales, Lachnospirales, Peptostreptococcales-Tissierellales y Enterobacterales fueron los órdenes dominantes en ambos grupos. En los pacientes con fractura, se observó un aumento porcentual significativo del orden de Bacteroidales (p<0,001) y Peptostreptococcales-Tissierellales (p<0,005), así como una disminución de las del orden Lachnospirales (p<0,001) respecto a los controles. Conclusiones:Este estudio ha encontrado una asociación entre una microbiota específica en pacientes ancianos con fractura de cadera por fragilidad. Estos hallazgos abren la puerta a nuevas estrategias para prevenir las fracturas de cadera. Es posible que la modificación de la microbiota mediante probióticos se revele como un método eficaz para reducir el riesgo de fractura de cadera.(AU)

Introduction: Hip fractures are the most common cause of hospital admission to orthopaedic departments in Europe and they generate a major health problem. Therefore, it is of great interest to identify additional risk factors that will help us to better understand the pathophysiology of these fractures and improve our preventive capacity. There is sufficient data to support the theory of modulation of bone mass by gut microbiota (osteomicrobiology); however, there is a lack of human clinical studies directly linking microbiota to hip fracture risk. Material and methods: Observational, analytical, case–control study. The sample consisted of 50 patients and it was distributed as follows: 25 elderly patients with fragility hip fracture and 25 subjects without fracture. The intestinal microbiota was determined by DNA extraction from stool samples and 16S ribosomal DNA sequencing after generation of gene libraries. Results: Alpha diversity revealed an elevation of the estimators for the taxonomic class level in the hip fracture group. The orders Bacteroidales, Oscillospirales, Lachnospirales, Peptostreptococcales-Tissierellales and Enterobacterales were the dominant orders in both groups. In patients with fracture, a significant percentage increase in the orders Bacteroidales (p<.001) and Peptostreptococcales-Tissierellales (p<.005) was observed, as well as a decrease in the orders Lachnospirales (p<.001) compared to controls. Conclusions: This study has found an association between a specific microbiota in elderly patients with fragility hip fracture. These findings open the door to new strategies to prevent hip fractures. Modification of the microbiota through probiotics may prove to be an effective method to reduce the risk of hip fracture.(AU)

The metabolism of carbamazepine in humans: steric course of the enzymatic hydrolysis of the 10,11-epoxide.

Carbamazepine 10,11-oxide (1a,10b-dihydro-6H-dibenzo[b,f]oxireno[d]azepine-6-carboxamide), a key intermediate in carbamazepine metabolism, was found to be unusually resistant to enzymatic hydrolysis when incubated with microsomal and cytosolic fractions from rabbit, rat, and guinea pig livers. However, its hydrolysis product, trans-10,11-dihydro-10,11-dihydroxy-5H-dibenzo[b,f]azepine-5-carboxamide , was excreted, as previously reported, both in the free and in conjugated forms, as the main metabolite in the urine of humans under carbamazepine treatment. The free diol and that obtained after treatment with beta-glucuronidase/arylsulfatase were both found by Mosher's method to be formed in an enantiomeric excess of 80%, the prevalent enantiomer having the (-)-10S,11S absolute configuration, as determined by applying the CD exciton coupling method to its bis[p-(dimethylamino)benzoyl] ester. This finding confirms the pronounced enantioselectivity of the microsomal epoxide hydrolase toward meso and racemic substrates, but is in contrast with the prevalent formation of (R,R)-diols in most other known cases of enzymatic hydrolysis of epoxides. Preparatively useful syntheses of the racemic trans-10,11-dihydro-10,11-diol and of 9-(hydroxymethyl)-10-carbamoylacridan, another carbamazepine metabolite, are reported for the first time.

Stereoselective halogenations of alkenes and alkynes in ionic liquids.

[reaction: see text]. Room-temperature ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bromide, and 1-butyl-3-methylimidazolium chloride, are used as "green" recyclable alternative to chlorinated solvents for the stereoselective halogenation of alkenes and alkynes.

Genetic effects of methylmercury in human chromosomes: I. A cytogenetic study of people exposed through eating contaminated fish.

An analysis of chromosomal aberrations (structural and numerical) and sister chromatid exchange (SCE) was carried out on 16 people exposed to methylmercury through eating fish caught in Cartagena Bay (Columbia), an area of known methylmercury contamination. Fourteen people whose diet consisted mainly of fish caught in another, noncontaminated area of the Atlantic acted as controls. The results showed a significant difference between the experimental and control groups in methylmercury (MM) concentrations measured in hair and peripheral blood. Subsequently, significant differences between levels of organic mercury in blood and hair were found when all the individuals studied were classified in two groups according to their blood mercury levels. When achromatic lesions were included, the frequency of structural chromosome aberrations differed significantly between the exposed and control groups. Furthermore, a significant correlation (p less than 0.05) was found between structural chromosome aberrations and groups (exposed and control). When achromatic lesions were excluded from the analyses, these differences were not found. There was a significant correlation between SCE and age. This is the first report of a study on the frequency of SCE in a population exposed to methylmercury.

Steric strain and reactivity: electrophilic bromination of trans-(1-methyl-2-adamantylidene)-1-methyladamantane

trans-(1-Methyl-2-adamantylidene)-1-methyladamantane (DMAD, 1b) reacts with Br(2) in chlorinated hydrocarbon solvents to give either a bromonium polybromide ion pair or a substitution product, depending on bromine concentration. The first intermediate is a 1:1 pi-complex having K(f) = 1.85(0.19) x 10(3) M(-)(1) at 25 degrees C, which rapidly evolves to the bromonium tribromide ion pair. At high bromine concentration, which shifts all equilibria involving the counteranion of the ion pair intermediate toward the pentabromide species, this bromonium ion is stable and unable to further evolve into products. Temperature-dependent NMR spectra indicate chemical exchange of Br(+) between the sides of the plane containing the two carbons of the bromonium ion. At very low bromine concentration, no ionic intermediate is detected and the reaction rapidly yields a rearranged substitution product, identified as 10. Under these conditions the disappearance of the pi-complex follows a first-order rate law, and the observed rate constant increases with increasing olefin concentration, showing that product formation implies Br(-) as counteranion of the ionic intermediate, whose formation is a reversible process. A comparison of the results reported here for the bromination of 1b with those previously found for the parent olefin, adamantylideneadamantane (1a), shows that steric strain markedly affects the reactivity of the double bond.

Population genetics in the American tropics : XI. Seasonal and temporal variations in relative frequencies of species belonging to the Willistoni group in Colombia.

The authors examined seasonal and plant food preferences of members of Drosophila willistoni group in three different ecosystems in Colombia. The results show that there are seasonal preferences as well as food preferences. Furthermore, there exist clear cut temporal (hours of the day) selection which would make possible the sympatric exploitation of equal ecological niches. Comparisons with melanogaster species and with obscura species group are also made.

An insight into the mechanism of the aerobic oxidation of aldehydes catalyzed by N-heterocyclic carbenes.

N-Heterocyclic carbene catalysis for the aerobic oxidation and esterification of aromatic aldehydes was monitored by ESI-MS (MS/MS) and the key intermediates were intercepted and characterized using the charge-tag strategy.

Kinetics and stereochemistry of the microsomal epoxide hydrolase-catalyzed hydrolysis of cis-stilbene oxides.

The microsomal epoxide hydrolase (mEH)-catalyzed hydrolysis of cis-4,4'-dimethylstilbene oxide (1a), cis-4,4'-diethylstilbene oxide (1b), cis-4,4'-diisopropylstilbene oxide (1c), and cis-4,4'-dichlorostilbene oxide (1d) have been investigated using rabbit liver microsomal preparations. The kinetic parameters, Km and Vmax, and the absolute stereochemistry of the reactions have been determined and compared with those of cis-stilbene oxide (1e). All epoxides 1a-d are hydrolyzed by mEH with high product enantioselectivity to give (R,R)-(+)-diols with ee > or = 90%. The presence of the substituents on the phenyl rings markedly reduces the rates of mEH catalyzed hydrolysis with respect to cis-stilbene oxide, by increasing Km and reducing Vmax in the cases of 1a, 1b, and 1d, or reducing only the Vmax in the case of 1c. The very low Vmax, together with a persistent ability to fit into the mEH active site, make all these epoxides, and particularly 1c, inhibitors of cis-stilbene oxide hydrolysis. The kinetic and stereochemical results are interpreted on the basis of the proposed topology of the mEH active site.

The rabbit liver microsomal biotransformation of 1,1-dialkylethylenes: enantioface selection of epoxidation and enantioselectivity of epoxide hydrolysis.

The rabbit liver microsomal biotransformation of alpha-methylstyrene (1a), 2-methyl-1-hexene (1b), 2,4,4-trimethyl-1-pentene (1c), and 1,3,3-trimethyl-1-butene (1d) has been investigated with the aim at establishing the enantioface selection of the cytochrome P-450-promoted epoxidation of the double bond and the enantioselectivity of microsomal epoxide hydrolase(mEH)-catalyzed hydrolysis of the resulting epoxides. GLC on a Chiraldex G-TA (ASTEC) column was used to determine the enantiomeric composition of the products. The epoxides 2 first produced in incubations carried out in the presence of an NADPH regenerating system were not detected, being rapidly hydrolyzed by mEH to diols 3. The enantiomeric composition of the latter showed that no enantioface selection occurred in the epoxidation of 1c and 1d, and a very low (8%) ee of the (R)-epoxide was formed from 1b. Incubation of racemic epoxides 2b-d with the microsomal fraction showed that the mEH-catalyzed hydrolysis of 2c and 2d was practically nonenantioselective, while that of 2b exhibited a selectivity E = 4.9 favoring the hydrolysis of the (S)-enantiomer. A comparison of these results with those previously obtained for linear and branched chain alkyl monosubstituted oxiranes shows that the introduction of the second alkyl substituent suppresses the selectivity of the mEH reaction of the latter and reverses that of the former substrates.

The low reactivity of 5H-dibenzo[a, d]cycloheptene 10,11-oxide in microsomal epoxide hydrolase catalysed hydration.

1. The rate of hydration of 5H-dibenzo[a, d]cycloheptene 10,11-oxide catalysed by rabbit liver microsomal epoxide hydrolase has been compared with that of the acyclic analogue cis-stilbene oxide. The latter was shown to be a much better substrate for the enzyme than the former epoxide. 2. The kinetic parameters for the hydration of 5H-dibenzo[a,d]cycloheptene 10,11-oxide and cis-stilbene oxide have been determined using a rabbit liver microsomal preparation at 37 degrees C and pH 7.4. The much slower hydration of the former is due to a much lower Vs and not to a higher Km relative to the latter epoxide. 3. 5H-Dibenzo[a,d]cycloheptene 10,11-oxide inhibited the hydration of cis-stilbene oxide by rabbit liver microsomal epoxide hydrolase.

The mechanism of oxidation of allylic alcohols to alpha,beta-unsaturated ketones by cytochrome P450.

The oxidation of cyclohex-2-en-1-ol, a simple model substrate for allylic alcohols, is catalyzed by several P450 isoenzymes and leads exclusively to cyclohex-2-en-1-one. No double bond epoxidation or C(4) hydroxylation have been observed. The large primary kinetic isotope effect measured using [2H]-1-cyclohex-2-en-1-ol is consistent with an at least partially rate limiting breaking of the C(1)-H bond. The mass spectrometric analysis of cyclohex-2-en-1-one obtained from [18O]cyclohex-2-en-1-ol has established that a gem-diol intermediate is involved, even if a dual hydrogen abstraction pathway may contribute to the reaction.

Stereochemical course of the biotransformation of isoprene monoepoxides and of the corresponding diols with liver microsomes from control and induced rats.

The stereochemical course of the biotransformation of isoprene by liver enzymes from control and induced rats has been determined. Between the two primarily formed metabolites, 2-methyl-2-vinyloxirane (2) and isopropenyloxirane (3), epoxide 2 is rapidly transformed into the corresponding vicinal racemic diol 4, predominantly through a nonenzymatic hydrolysis reaction. At variance, epoxide 3 is mainly biotransformed into the diol 5 by microsomal epoxide hydrolase (mEH) to give, before 50% conversion, selectively (R)-3-methyl-3-butene-1,2-diol, 5. The hydrolysis competes with the oxidation of the monoepoxide 3 to the corresponding diepoxides 6. Epoxidation of 3 catalyzed by P450 is characterized by a moderate stereoselectivity which, however, was strongly dependent on P450 induction. Treatment of rats with phenobarbital (PB) (an inducer of P450 2B1 and 3A) leads to threo-(2R,2'R)-6 with a high selectivity, while with pyrazole (Pyr) (an inducer of P450 2E1), the formation of both erythro-(2S,2'R)- and threo-(2R,2'R)-6 is favored. The mEH-catalyzed hydrolysis of diepoxides 6 proceeds, although with a moderate turnover rate, with substrate and product diastereo- and enantioselection by nucleophilic attack on the more substituted oxirane ring to give selectively (2R,3S)-3,4-epoxy-2-methyl-1,2-diol (7). Both diols 4 and 5 may be further oxidized on their double bond by P450. These reactions, which occur at a slow rate and are dependent on P450 induction with PB and Pyr, may be negligible in the overall isoprene biotransformation. On the other hand, the epoxydiol 7, which is formed by hydrolysis of diepoxides 6 but it is itself not hydrolyzable, may play an important role in the isoprene toxicity.

Substituent dependence of the diastereofacial selectivity in iodination and bromination of glycals and related cyclic enol ethers.

The stereochemical course of the electrophilic iodination and bromination of tri-O-benzyl-D-glucal under various conditions has been compared to that of substituted dihydropyrans 2-5. IN(3) addition in acetonitrile affords trans-alpha-iodoazides (80-87%), besides small amounts of trans-beta-adducts, in the presence or the absence of benzyloxy substituents at C-3 or C-4, and in agreement with bridged iodonium ion intermediates. In contrast, the diastereofacial selectivity of bromine addition in dichloroethane going through open bromo oxocarbenium ions depends strongly on the substituents. Whereas the trans-alpha-dibromides are the main (85-95%) adducts in the absence of C-4 and C-5 substituents, in their presence a moderate to exclusive selectivity for cis-alpha-addition (60-99%) is observed. The predominance of trans-alpha-addition is again observed whatever the substituents when the bromination is carried out in the same solvent but with a tribromide ion salt, supporting a concerted addition of the two bromine atoms under these conditions. Finally, bromine addition in methanol exhibits a completely different behavior with the nonselective formation of trans-alpha- and trans-beta-methoxybromides and a small dependence on the substituents. In agreement with the absence of azide trapping of any cationic intermediate, it is concluded that these brominations which do not go through an ionic intermediate are concerted additions of bromine and methanol with very loose rate- and product-determining transition states. Finally, the substituent conformation at C-4 influences drastically the stereoselectivity in all these brominations. Evidence for alpha-anomeric control of the nucleophile approach at C-1 is given by the highly predominant formation of alpha-adducts, except in the methanolic bromination. The factors determining the versatile selectivity of the electrophile approach are discussed in terms of PPFMO theory and of the special mechanisms of glycal reactions.