Preventive effect of reduced glutathione on contrast-induced nephropathy in elderly patients undergoing coronary angiography or intervention: a randomized, controlled trial

Coronary angiography can be a high-risk condition for the incidence of contrast-induced nephropathy (CIN) in elderly patients. Reduced glutathione, under a variety of mechanisms, may prevent CIN in this procedure. We prospectively examined whether hydration with reduced glutathione is superior to hydration alone for prevention of CIN in an elderly Han Chinese population. A total of 505 patients (271 males and 234 females) aged 75 years or older who underwent non-emergency coronary angiography or an intervention were randomly divided into two groups. The treatment group received hydration with reduced glutathione (n=262) and the control group received hydration alone (n=243). Serum creatinine and blood urea nitrogen levels were measured prior to coronary angiography and 48 h after this procedure. The primary endpoint was occurrence of CIN, which was defined as 25% or 44.2 µmol/L above baseline serum creatinine levels 48 h after the procedure. The overall incidence of CIN was 6.49% in the treatment group and 7.41% in the control group, with no significant difference between the groups (P=0.68). In subgroup analysis by percutaneous coronary intervention, no significant differences were found between the two groups. In summary, reduced glutathione added to optimal hydration does not further decrease the risk of CIN in elderly patients undergoing coronary angiography or an intervention.

Electrophoretic analisys to detect and quantify additional whey in milk and dairy beverages

Polyacrylamide gel electrophoresis, SDS-PAGE system, was adjusted to detect the presence of additional whey in dairy beverages distributed in a Brazilian Government School Meals Program. Aqueous solutions of samples in 8 M urea were submitted to a polyacrylamide gel gradient (10% to 18%). Gel scans from electrophoresis patterns of previously adulterated milk samples showed that caseins peak areas decreased while peak areas of beta -lactoglobulin plus alpha -lactalbumin increased as the percentage of raw milk powder replaced by whey powder increased. The relative densitometer areas of caseins or beta -lactoglobulin plus alpha -lactalbumin plotted against the percentage of whey added to the raw milk showed a linear correlation coefficient square higher than 0.97. The caseins plot was used to determine the percentage of additional whey in 116 dairy beverages, chocolate or coffee flavor. Considering that the lowest relative caseins concentration found in commercial milk powder samples by the present method was 72%, the dairy beverages containing caseins percentages equal to or higher than this value were considered free of additional whey. Based on this criterion, about 49% of the coffee-flavor dairy beverages and 29% of the chocolate-flavor beverages, among all the samples analyzed were adulterated with whey protein to reach the total protein contents specified on their labels. The present method showed a sensitivity of 5% to additional whey.

Análise físico-química e microbiológica do suco de laranja minimamente processado armazenado em lata de alumínio

Neste trabalho, suco de laranja natural foi pasteurizado em um trocador de calor a placas empregando três diferentes temperaturas de pasteurização: 82,5ºC; 85,0ºC e 87,0ºC e tempos de retenção variando de 11 a 59s, para se obter um produto minimamente processado. Um estudo comparativo foi realizado no suco de laranja armazenado em latas de alumínio em relação ao mesmo produto armazenado em garrafas PEAD, sob refrigeração, por um período de 21 dias. Análises de graus Brix, pH, acidez, sólidos insolúveis e totais e análises microbiológicas foram realizadas em amostras logo após o processamento e durante o período de armazenamento. As propriedades físico-químicas do suco de laranja pasteurizado apresentaram diferenças devido as diferenças detectadas na matéria-prima ao longo do período do estudo. O parâmetro de pasteurização mais apropriado para o suco de laranja natural foi 87,0ºC e com tempo de retenção variando de acordo com o pH do suco. Para pH 4,0 o tempo de retenção requerido foi maior. De acordo com os resultados, uma vida-de-prateleira de 15 dias foi determinada para o suco processado nas condições acima.

Propriedades termofísicas de soluções modelo similares a sucos - Parte I

Propriedades termofísicas, difusividade térmica e calor específico, de soluções modelo similares a sucos, foram determinadas experimentalmente e ajustadas a modelos matemáticos (STATISTICA 6.0), em função da sua composição química. Para definição das soluções modelo foi realizado um planejamento estrela mantendo-se fixa a quantidade de ácido (1,5%) e variando-se a água (82-98,5%), o carboidrato (0-15%) e a gordura (0-1,5%). A determinação do calor específico foi realizada através do método de Hwang & Hayakawa e a difusividade térmica com base no método de Dickerson. Os resultados de cada propriedade foram analisados através de superfícies de respostas. Foram encontrados resultados significativos para as propriedades, mostrando que os modelos encontrados representam significativamente as mudanças das propriedades térmicas dos sucos, com alterações na composição e na temperatura.

Propriedades termofísicas de soluções-modelo similares a sucos: parte II

Propriedades termofísicas, densidade e viscosidade de soluções-modelo similares a sucos foram determinadas experimentalmente. Os resultados foram comparados aos preditos por modelos matemáticos (STATISTICA 6.0) e obtidos da literatura em função da sua composição química. Para definição das soluções-modelo, foi realizado um planejamento estrela, mantendo-se fixa a quanti-dade de ácido (1,5%) e variando-se a água (82-98,5%), o carboidrato (0-15%) e a gordura (0-1,5%). A densidade foi determinada em picnômetro. A viscosidade foi determinada em viscosímetro Brookfield modelo LVF. A condutividade térmica foi calculada com o conhecimento das propriedades difusividade térmica e calor específico (apresentados na Parte I deste trabalho MOURA [7]) e da densidade. Os resultados de cada propriedade foram analisados através de superfícies de respostas. Foram encontrados resultados significativos para as propriedades, mostrando que os modelos encontrados representam as mudanças das propriedades térmicas e físicas dos sucos, com alterações na composição e na temperatura.

Carotenoid production by Rhodotorula rubra cultivated in sugarcane juice, molasses, and syrup

The Rhodotorularubra biomass and carotenoids production was evaluated in sugarcane juice, molasses, and syrup based media. The effects of media supplementation with urea- nitrogen or the commercial nutrient called Nitrofos KL was also verified. The experimental design used was a completely randomized factorial with 3 substrates (juice, molasses, and syrup) and three supplementations (control, urea, and Nitrofos KL). The results were submitted to variance analysis and Tukey test at 5% probability. The highest production of yeast dry mass was obtained with molasses media supplemented with urea or Nitrofos KL (15.09 and 14.87 g/L respectively). The intracellular carotenoid production was high in the media without supplementation (0.329 mg/g). The best growth medium for the volumetric production was molasses (2.74 mg/L), while those supplemented with urea and Nitrofos KL produced 2.55 and 2.32 mg/L, respectively. The major carotenoids produced were torulene, torularhodin, and β-carotene. The lowest carbohydrate consumption was observed in the sugarcane juice medium without supplementation, while the highest consumption was observed in the urea based supplementation medium.

Spirulina platensis: process optimization to obtain biomass

Spirulina platensis is a photoautotrophic mesophilic cyanobacterium. Its main sources of nutrients are nitrate, urea, and ammonium salts. Spirulina cultivation requires temperature, light intensity, and nutrient content control. This microalgae has been studied and used commercially due to its therapeutic and antioxidant potential. In addition, several studies have reported its ability to use CO2, its immune activity, and use as an adjuvant nutritive factor in the treatment of obesity. The objective of this study is the production of biomass of S. platensis using different rates of stirring, nitrogen source, amount of micronutrients, and luminosity. A 2(4) experimental design with the following factors: stirring (120 and 140 RPM), amount of nitrogen (1.5 and 2.5 g/L), amount of micronutrients (0,25 and 0,75 mL/L) (11 and 15 W), and luminosity was used. Fermentation was performed in a 500 mL conical flask with 250 mL of culture medium and 10% inoculum in an incubator with controlled stirring and luminosity. Fermentation was monitored using a spectrophotometer (560 nm), and each fermentation lasted 15 days. Of the parameters studied, luminosity is the one with the highest significance, followed by the amount of nitrogen and the interaction between stirring and micronutrients. Maximum production of biomass for 15 days was 2.70 g/L under the following conditions: luminosity15W; stirring, 120 RPM; source of nitrogen, 1.5 g/L; and micronutrients, 0.75 mL/L.

Early initiation of dialysis: mortality and renal function recovery in acute kidney injury patients

INTRODUCTION: The decision of when to start dialysis in Acute Kidney Injury (AKI) patients with overt uremia is strongly established, however, when blood urea nitrogen (BUN) levels is < 100 mg/dL the timing of initiation of dialysis remains uncertain. Purpose: The aim of this study was to assess mortality and renal function recovery AKI patients started on dialysis at different BUN levels. METHODS: This was a retrospective study performed at Medical School Hospital, São Paulo, Brazil, enrolling 86 patients underwent to dialysis. RESULTS: Dialysis was started when BUN < 75 mg/dl in 23 patients (Group I) and BUN > 75 mg/dl in 63 patients (Group II). Hypervolemia and mortality were higher in Group I than in Group II (65.2% vs. 14.3% - p < 0.05, 39.1% vs. 68.9%- p < 0.05, respectively). Among survivors, the rate of renal function recovery was higher in Group I (71.4% and 36.8%, respectively - p < 0.05). Multivariate analysis showed that sepsis, age > 60 years, peritoneal dialysis and BUN > 75 mg/dl at dialysis initiation were independently related with mortality. CONCLUSIONS: Lower mortality and higher renal function recovery rates were associated with early dialysis initiated at lower BUN leves in AKI patients.

Inverse association between serum creatinine and mortality in acute kidney injury

Introduction: Sepsis is a leading precipitant of Acute Kidney Injury (AKI) in intensive care unit (ICU) patients, and is associated with a high mortality rate. Objective: We aimed to evaluate the risk factors for dialysis and mortality in a cohort of AKI patients of predominantly septic etiology. Methods: Adult patients from an ICU for whom nephrology consultation was requested were included. End-stage chronic renal failure and kidney transplant patients were excluded. Results: 114 patients were followed. Most had sepsis (84%), AKIN stage 3 (69%) and oliguria (62%) at first consultation. Dialysis was performed in 66% and overall mortality was 70%. Median serum creatinine in survivors and non-survivors was 3.95 mg/dl (2.63 - 5.28) and 2.75 mg/dl (1.81 - 3.69), respectively. In the multivariable models, oliguria and serum urea were positively associated with dialysis; otherwise, a lower serum creatinine at first consultation was independently associated with higher mortality. Conclusion: In a cohort of septic AKI, oliguria and serum urea were the main indications for dialysis. We also described an inverse association between serum creatinine and mortality. Potential explanations for this finding include: delay in diagnosis, fluid overload with hemodilution of serum creatinine or poor nutritional status. This finding may also help to explain the low discriminative power of general severity scores - that assign higher risks to higher creatinine levels - in septic AKI patients.

Influence of temperate grass seed rotation systems on weed seed soil bank composition

Due to changing cropping practices in perennial grass seed crops in western Oregon, USA, alternative rotation systems are being considered to reduce weed infestations. Information is generally lacking regarding the effects of alternative agronomic operations and herbicide inputs on soil weed seed bank composition during this transition. Six crop rotation systems were imposed in 1992 on a field that had historically produced monoculture perennial ryegrass (Lolium perenne L.) seeds. Each system plot was 20 x 30 m, arranged in a randomized complete block design, replicated four times. Twenty to thirty soil cores were sampled in June 1997 from each plot. The weed species composition of the cores was determined by successive greenhouse grow-out assays. In addition to seed density, heterogeneity indices for species evenness, richness, and diversity were determined. The most abundant species were Juncus bufonius L. and Poa annua L. Changes in seed bank composition were due to the different herbicides used for the rotation crop components. Compared to the other rotation systems, no-tillage, spring-planted wheat (Triticum aestivum L.) and oat (Avena sativa L.) reduced overall weed seed density and richness, but did not affect weed species evenness or diversity. When meadowfoam (Limnanthes alba Hartweg ex Benth.) succeeded wheat in rotation, weed species richness was unaffected, but evenness and diversity were reduced, compared to the other rotation systems. For meadowfoam in sequence after white clover (Trifolium repens L.), crop establishment method (no-tillage and conventional tillage) had no effect on weed seed species density, evenness, or diversity.

O cinema e a escola: formas imagéticas da violência

Este artigo pretende analisar as relações entre mito, violência e cinema. Queremos saber que suportes a narrativa fílmica oferece para que o público, ao ver um filme, possa criar e recriar sentidos, indo além dos valores reiterados pela estrutura fílmica. A escola seria um dos espaços para que a literatura, as artes em geral, e o cinema em particular, germinassem as possibilidades de alunos e professores transformarem-se em "sujeitos imaginantes", produtores e não apenas reprodutores de sentidos.

Recueil de lettres et de pièces originales, et de copies de pièces indiquées comme telles dans le dépouillement qui suit.

Contient : 1 Lettre d'« ELIZABET », reine d'Espagne, à la reine Catherine de Médicis, sa mère ; 2 Lettre, en espagnol, de « el duque DE ALVA,... a la reyna de Francia madre... De Madrid, a XIIII° de junio 1562 » ; 3 Lettre d'« ELIZABET [reine d'Espagne]... à la royne, madame ma bonne mere... De Toledo, le IIe jour de may 1561 » ; 4 Lettre, en espagnol, de « el duque DE ALVA,... a la reyna, madre del rey... De Toledo, a XXIII de enero 1561 » ; 5 Lettre, en espagnol, de « la condesa DE UREÑA,... a... la reina, [madre del] rey de Francia... De Toledo, diez y siete de mayo de 1561 » ; 6 Lettre de « S[EBASTIEN] DE LAUBESPINE, evesque de Lymoges... à la royne... De Madril, ce IIIe jour de janvier 1561 » ; 7 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... au roy de Navarre... De Madril, ce XXIIe de janvier 1561 » ; 8 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... à la royne... De Madril en Castille, ce IXe de mars 1562, avant Pasques » ; 9 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... à la royne... De Toledo, ce XXVIIe d'avril 1561 » ; 10 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... à monsieur de Fresne, conseiller du roy, secretaire d'Estat et de ses finances... De Tolledo, se VIII de may » ; 11 « Memoyre de Mr Lymoges [S. DE LAUBESPINE], du IXe de may » 156 sur les affaires politiques de l'Europe en général et de l'Espagne en particulier ; 12 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... au roy de Navarre... De Toledo, ce IXe de may 1561 » ; 13 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... au roy... De Toledo, ce Xe de may 1561 » ; 14 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... à la royne... De Toledo, ce Xe de may 1561 » ; 15 Lettre de « FRANÇOYS DE CLEVES,... conte D'EU,... à la royne... De Toledo, ce XIe de may 1561 » ; 16 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... à la royne... De Toledo, ce XIIe de may 1561 » ; 17 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... à la royne... De Toledo, ce XIIIe de may 1561 » ; 18 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... au roy... De Toledo, ce XXe de may 1561 » ; 19 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... à la royne... De Toledo, ce XXme de may 1561 » ; 20 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... à la royne... De Toledo, ce XXe de may 1561 » ; 21 « Memoire de Mr DE LYMOGES, du XXme de may 1561 », sur l'arrivée du « conte d'Heu,... en Hespaigne » ; 22 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... à la royne... De Toledo, ce XXIXe de may 1561 » ; 23 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... à la royne... De Illesques, ce premier de juing 1561 » ; 24 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... au roy de Navarre... De Illesques, ce XIIIIe juing 1561 » ; 25 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... à la royne... De Illesques, ce XIIIIe de juing 1561 » ; 26 Lettre de « S. DE LAUBESPINE, evesque de Lymoges... à monsieur de Fresque,... De Illesques, ce XIIIe de juing » ; 27 Lettre, en espagnol, du roi PHILIPPE II « a Don Garcia de Toledo, viserey de Cataluña... De Toledo, a dos de mayo 1561 ». Copie ; 28 Lettre, en espagnol, du roi PHILIPPE II à « don Juan de Mendoça,... capitan general de las galeras d'España... En Toledo, a primero de mayo de myll y quinientos y sesenta y un años ». Copie ; 29 « O que Sua Alteza [JEAN III] responde ao que o sennor de Sam Sulpice Ihe dise da parte do... rey de França, sobre o acontecido no forte que o cavaleiro de Vilaganham [Villegaignon] fez na provintia do Brasyl he ». Copie, en portugais ; 30 « Extraict des informations faictes en Toledo, le second jour du moys de may mil cinq cens soixante et ung, par le docteur Suares de Toledo, alcade de court, sur quelques rapportz faictz à Sa Majesté catholique qu'aucuns François avoient mené, porté et deschargé en Arger grandes munitions de guerre contre les traictés de paix » ; 31 Extrait « de la despeche de monsieur de Lymoges, du XXIXe may 1561, à Toledo », sur la capture du « navire le Chien », faite « par don Jouan de Mendosse en Catalougne » ; 32 Lettre, en portugais, de « donna CATHERINNA, rainha de Portugual... a donna Catherina, rainha de França... De Lixbôa, a V de mayo de 1561 » ; 33 Lettre, en portugais, « de CATHERINNA, rainha de Portugual... a Dom Carlos, rey de França... Lixbôa, a V de mayo de 1561 » ; 34 Lettre, en portugais, du cardinal HENRI DE PORTUGAL au roi de France Charles IX. « De Lisbôa, a 3 de janeiro de 1561 » ; 35 Lettre, en portugais, de « Dom SEBASTIAM, rey de Portugual,... a donna Catherina, rainha de França... A Lixbôa, a VI de janeiro de 1561 » ; 36 Lettre, en portugais, de « CATHERINA, rainha de Portugual, a Dom Charles, rey de França... Lixbôa, a VI de janeiro de 1561 » ; 37 Lettre, en portugais, de « CATHERINA, rainha de Portugual, a donna Catherina, raynha de França... Lixbôa, a VI de janeiro de 1561 » ; 38 Lettre, en portugais, de l'infante « Dona MARIA », datée de « Lixbôa, a VIII de janeiro de M.D.LXI » ; 39 Lettre, en portugais, de l'infante « Dona MARIA », datée de « Lixbôa, a VIII de janeiro de M.D.LXI » ; 40 Lettre, en portugais, de l'infante « Dona MARIA » au « rey de França... Em Lixbôa, a cinco de maio de 1561 » ; 41 Lettre, en portugais, du cardinal HENRI au « rei de França » Charles IX, datée de « Lisbôa, 5 de maio de 1561 » ; 42 Lettre, en portugais, de l'infante « dona MARIA » à la « raynha de França... De Lixbôa, a cingo de mayo de M.D.LXI » ; 43 Lettre de l'ambassadeur en Portugal « J. NICOT,... au roy [Charles IX]... De Lisbonne, ce XIIe jour d'apvril 1561 » ; 44 Lettre de « J. NICOT,... à la royne... De Lisbonne, ce XIIe jour d'avril M.D.LXI » ; 45 Lettre de « J. NICOT,... à la royne... De Lisbonne, ce XVI avril M.D.LXI » ; 46 Lettre de « J. NICOT,... au roy... De Lisbonne, ce sixiesme jour de may 1561 » ; 47 Lettre de « J. NICOT,... à la royne... De Lisbonne, ce VIe jour de may 1561 » ; 48 Lettre de « J. NICOT,... à la royne... De Lisbonne, ce VIe jour de may 1561 » ; 49 « Information » sur la saisie faite par J. NICOT d'un « navire françoys... Lisbonne, ce vingt deuxiesme jour... de may, mil cinq cens soixante ung ». Signé : « J. NICOT », et autres ; 50 Lettre de « J. NICOT,... au roy... De Lisbonne, ce XXVIIIe jour du mois de may 1561 » ; 51 Lettre de « J. NICOT,... à la royne... De Lisbonne, ce XXVIIIe jour de may M.V.C.LXI » ; 52 Lettre de « S[EBASTIEN] DE LAUBESPINE, evesque de Limoges... au roy... D'Illesques, ce XIIIIe de juing 1561 » ; 53 Lettre de « J. NICOT,... au roy... De Lisbonne, ce XXme jour du moys de juing 1561 » ; 54 Lettre de « J. NICOT,... à la royne... De Lisbonne, ce XXe jour de juing M.D.LXI » ; 55 « Double du memoyre baillé au roy Charles pour a marchandize sequestrée à Barselonne » ; 56 Lettre, en portugais, de « JULIAN ROMERO,... al... obispo de Limoja [Sébastien de Laubespine], enbaxador por el rey de Françia... De Malaga, y de abril 17 de 1561 » ; 57 « Information, en espaignol, contre ceulx qui de Provence portent des munitions aux Turcqs d'Argeies » ; 58 Lettre du « cappitaine BOILLEAU,... à monseigneur l'anbassadeur de France... De St Jacques, ce XIIIe avril 1561 »

Timing of di-ammonium phosphate addition to fermenting chardonnay must : effect on nitrogen utilization, ethyl-carbamate formation, and CAR1 expression by yeast /

The maximum amount of ethyl carbamate (EC), a known animal carcinogen produced by the reaction of urea and ethanol, allowed in alcoholic beverages is regulated by legislation in many countries. Wine yeast produce urea by the metabolism of arginine, the predominant assimilable amino acid in must. This action is due to arginase (encoded by CARl). Regulation of CARl, and other genes in this pathway, is often attributed to a well-documented phenomenon known as nitrogen catabolite repression. The effect of the timing of di-ammonium phosphate (DAP) additions on the nitrogen utilization, regulation of CARl, and EC production was investigated. A correlation was found between the timing of DAP addition and the utilization of nitrogen. When DAP was added earlier in the fermentations, less amino nitrogen and more ammonia nitrogen was sequestered from the media by the cells. It was also seen that early DAP addition led to more total nitrogen being used, with a maximal difference of ~25% between fermentations where no DAP was added versus addition at the start of the fermentation. The effect of the timing ofDAP addition on the expression of CARJ during fermentation was analyzed via northern transfer and the relative levels of CARl expression were determined. The trends in expression can be correlated to the nitrogen data and be used to partially explain differences in EC formation between the treatments. EC was quantified at the end of fermentation by GC/MS. In Montrachet yeast, a significant positive correlation was found between the timing of DAP addition, from early to late, and the final EC concentration m the wine (r = 0.9226). In one of the fermentations, EC levels of 30.5 ppb was foimd when DAP was added at the onset of fermentation. A twofold increase (69.5 ppb) was observed when DAP was added after 75% of the sugars were metabolized. When no DAP was added, the ethyl carbamate levels are comparable at a value of 38 ppb. In contrast, the timing of DAP additions do not affect the level EC produced by the yeast ECU 18 in this manner. The study of additional yeast strains shows that the effect of DAP addition to fermentations is strain dependent. Our results reveal the potential importance of the timing of DAP addition to grape must with respect to EC production, and the regulatory effect of DAP additions on the expression of genes in the pathway for arginine metabolism in certain wine yeast strains.

NMR studies of mixed tetrahaloborates and some related boron trihalide complexes /|nGary John Schrobilgen. -- 260 St. Catharines, Ont. : [s. n.],

Nuclear magnetic resonance spectroscopy has been used to study donor-acceptor complexes of boron trifluoride with several ureas, tetramethylthiourea, tetramethylselenourea, and tetramethylquanidine as well as adducts of tetramethyl- -urea with BF2Cl, BFC1 2 , and BC1 3 - A large number of mixed tetrahaloborate ions, including some of the ternary ones such as BF2CIBr-,have been obtained by ligand exchange reactions and studied by NMR techniques. The bonding in these ions is of the same inherent interest as the bonding in the isoelectronic tetrahalomethanes which have been the subject of many detailed studies and have been involved in a controversy concerning the existence of and the nature of "fluorine hyperconjugation" or C-F P1T- Pn bonding_ Ligand exchange reactions also gave rise to the difluoroboron cation, (TMU)20BF2+o The difluoroboron cation has been observed in solutions of TMU-BF3 , and has been proposed as a possible intermediate for fluorine exchange reactions in BF3 adducts.