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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Probiotic bacteria are sold mainly in fermented foods, and dairy products play a predominant role as carriers of probiotics. These foods are well suited to promoting the positive health image of probiotics for several reasons: 1) fermented foods, and dairy products in particular, already have a positive health image; 2) consumers are familiar with the fact that fermented foods contain living microorganisms (bacteria); and 3) probiotics used as starter organisms combine the positive images of fermentation and probiotic cultures. When probiotics are added to fermented foods, several factors must be considered that may influence the ability of the probiotics to survive in the product and become active when entering the consumer's gastrointestinal tract. These factors include 1) the physiologic state of the probiotic organisms added (whether the cells are from the logarithmic or the stationary growth phase), 2) the physical conditions of product storage (eg, temperature), 3) the chemical composition of the product to which the probiotics are added (eg, acidity, available carbohydrate content, nitrogen sources, mineral content, water activity, and oxygen content), and 4) possible interactions of the probiotics with the starter cultures (eg, bacteriocin production, antagonism, and synergism). The interactions of probiotics with either the food matrix or the starter culture may be even more intensive when probiotics are used as a component of the starter culture. Some of these aspects are discussed in this article, with an emphasis on dairy products such as milk, yogurt, and cheese.
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PMID:Probiotic bacteria in fermented foods: product characteristics and starter organisms. 1115 44

Reactions of chloramine, NH2Cl, with HO-, RO- (R = CH3, CH3CH2, CH3CH2CH2, C6H5CH2, CF3CH2), F- , HS- , and Cl- have been studied in the gas phase using the selected ion flow tube technique. Nucleophilic substitution (S(N)2) at nitrogen to form Cl- has been observed for all the nucleophiles. The reactions are faster than the corresponding S(N)2 reactions of methyl chloride; the chloramine reactions take place at nearly every collision when the reaction is exothermic. The thermoneutral identity S(N)2 reaction of NH2Cl with Cl-, which occurs approximately once in every 100 collisions, is more than two orders of magnitude faster than the analogous reaction of CH3Cl. The significantly enhanced S(N)2 reactivity of NH2Cl is consistent with a previous theoretical prediction that the barrier height for the S(N)2 identity reaction at nitrogen is negative relative to the energy of the reactants, whereas this barrier height for reaction at carbon is positive. Competitive proton abstraction to form NHCl- has also been observed with more highly basic anions (HO-, CH3O-, and CH3CH2O-), and this is the major reaction channel for HO- and CH3O-. Acidity bracketing determines the heat of deprotonation of NH2Cl as 374.4 +/- 3.0 kcal mol(-1).
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PMID:Gas phase reactions of NH2Cl with anionic nucleophiles: nucleophilic substitution at neutral nitrogen. 1121 98

A flow-batch system allowing in-line individual sample matrix matching is proposed for analysis of sample lots with high variability in acidity. The feasibility of the approach is demonstrated in the spectrophotometric determination of total nitrogen in Kjeldahl digests, using a column with a slightly soluble reagent (AgCl). The solutions are sequentially injected by means of an 8-port selecting valve and processed in a mixing chamber that is also used as a monitoring unit. The system yields reproducible results (r.s.d. usually < 2.5%) and the sampling rate is 14 samples/h. The analytical curve is linear within 1.00 and 6.00% N (dry basis), and the regression coefficient is > 0.999 (n = 6). Results are in agreement with certified values of standard reference materials and with results obtained by conductometry.
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PMID:Individual sample conditioning in flow analysis. Determination of N-total in plant materials. 1122 32

The concerned azo ligands are 2-(phenylazo)pyridine (HL) and 2-((p-chlorophenyl)azo)pyridine (ClL). The reaction of KReO4 with HL in hot concentrated HCl is attended with metal reduction and ligand chlorination affording the oxo complex ReVOCl3(ClL), 2, which furnishes ReIII(OPPh3)Cl3(ClL), 3, upon treatment with PPh3. Aromatic amines, ArNH2, convert 2 to the imido complex ReV(NAr)Cl3(ClL), 5, and the unusual oxo-imido dimer (ClL)-Cl2(O)ReVOReV(NAr)Cl2(ClL), 7. The complex ReIII(OPPh3)Cl3(HL), 4, has been generated from ReVOCl3(PPh3)2 and HL. Reaction of 4 with HL has yielded ReV(NPh)Cl3(HL), 6, via azo splitting. The complexes have been characterized with the help spectral, magnetic, and X-ray structural data (2, 3, 5c (Ar = pClC6H4) and 7.CH2Cl2 (Ar = pMeC6H4)). In 2, 3, and 5c the ReCl3 fragment is meridionally disposed, and in 7 the ReCl2 fragments have a trans configuration. The Re-O(oxo) bond, 1.663(6) A, in 2 and Re-N(imido) bond, 1.719(5) A, in 5c are triple bonds. The corresponding bonds are slightly longer in 7 wherein the (O)Re(1)-O(2)-Re(2)(NAr) bridge is angular (151.0(5) degrees) and unsymmetrical, the Re(1)-O(2) bond, 1.849(7) A, having a large double-bond character (Re(2)-O(2), 1.954(7) A). In effect, cis-ReVO2 acts as a monodentate oxygen ligand toward ReVNAr in 7. In all cases the pyridine nitrogen binds trans to the oxo, OPPh3, or NAr donor. Bond length data are consistent with the presence of substantial d(Re)-pi*(azo) back-bonding. In acetonitrile solution the complexes display electrochemical one-electron metal (ReVI/ReV or ReIV/ReIII) and azo redox. The imido ligand in 5 stabilizes the ReVI state (E1/2 approximately 1.4 V) better than the oxo ligand in 2 (approximately 1.9 V). Parallely it is more difficult to reduce the azo group in 5 (approximately -0.4 V) than in 2 (approximately 0.0 V). In 7 the metal (approximately 1.0 V) and azo (approximately -0.4 V) couples correspond to the imido and oxo halves, respectively. The significantly higher (by 0.2-0.6 V) metal reduction potentials of the azopyridine compared to pyridine-2-aldimine complexes is ascribed to the superior pi-acidity and electron-withdrawing character of the azo function relative to the aldimine function. This also makes the transfer of the ReVO oxygen function much more facile under azopyridine chelation as in 2. For the same reason, ReOCl3(PPh3)2 reacts with HL affording only 4 while it reacts with pyridine-2-aldimines furnishing oxo species. Crystal data for the complexes are as follows: 2, empirical formula C11H8Cl4N3ORe, crystal system triclinic, space group P1, a = 7.118(4) A, b = 8.537(4) A, c = 13.231(9) A, alpha = 79.16(5) degrees, beta = 78.03(5) degrees, gamma = 70.96(4) degrees, V = 737.2(7) A3, Z = 2; 3, empirical formula C29H23Cl4N3OPRe, crystal system monoclinic, space group P2(1)/n, a = 11.264(2) A, b = 15.221(3) A, c = 17.628(4) A, beta = 94.21(3) degrees, V = 3014(1) A3, Z = 4; 5c, empirical formula C17H12Cl5N4Re, crystal system triclinic, space group P1, a = 9.683(3) A, b = 10.898(3) A, c = 11.522(3) A, alpha = 63.67(2) degrees, beta = 71.24(2) degrees, gamma = 86.79(2) degrees, V = 1026(1) A3, Z = 2; 7.CH2Cl2, empirical formula C30H25Cl8N7O2Re2, crystal system triclinic, space group P1, a = 12.522(6) A, b = 12.857(8) A, c = 13.182(7) A, alpha = 67.75(4) degrees, beta = 88.30(4) degrees, gamma = 82.09(4) degrees, V = 1945(2) A3, Z = 2.
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PMID:Chemistry of the rhenium-azopyridine family: an oxo parent and derivatives thereof including a novel oxo-imido dimer. 1122 35

Indices of atmospheric particulate matter (PM) have been reported to be associated with daily mortality and morbidity in a large number of recent time-series studies. However, the question remains as to which components of PM are responsible for the reported associations. Multiple PM components rarely are measured simultaneously. To investigate PM effects on mortality and morbidity, we used the multiple PM components measured in Windsor, Ontario, at a site only a few miles from downtown Detroit, Michigan. This study focused primarily on two study periods in which multiple PM components were measured in Windsor: 1985 to 1990, when levels of total suspended particles (TSP), sulfate from TSP (TSP-SO4(2-)), PM less than 10 microns in diameter (PM10), and nonthoracic TSP (TSP-PM10) were measured throughout the year; and 1992 to 1994, when data on PM10, PM2.5 (PM less than 2.5 microns in diameter), PM10-2.5 (PM10 minus PM2.5), particle acidity (H+), and artifact-free sulfates (SO4(2-)) were available for mostly summer months. Mortality data were analyzed for the 1985 to 1990 study period, and data on both mortality and hospital admissions of elderly patients were analyzed for the 1992 through 1994 period. Poisson regressions were used to estimate the effects of these PM components and gaseous criteria pollutants on mortality (nonaccidental, circulatory, respiratory, and nonaccidental without circulatory and respiratory) and on hospital admissions of elderly patients (for pneumonia, chronic obstructive pulmonary disease [COPD], ischemic heart disease, dysrhythmias, heart failure, and stroke), adjusting for temperature and humidity, trends and seasonal cycles, and day of the week. Both PM10 and TSP were associated significantly with respiratory mortality for the 1985 to 1990 period, with similar relative risk (RR) estimates for PM10 (RR = 1.123; 95% confidence interval [CI] 1.0361-1.218) and TSP (RR = 1.109; 95% CI 1.028-1.197), per 5th to 95th percentile increment. The effect-size estimates for TSP-SO4(2-) and TSP-PM10 were smaller and less significant. In two-pollutant models, simultaneous inclusion of gaseous pollutants with PM10 or TSP reduced PM coefficients by 0 to 34%. The effect-size estimates for total mortality, circulatory mortality, and total minus circulatory and respiratory mortality were less than those for respiratory mortality. Ozone (O3) and nitrogen dioxide (NO2) also were associated significantly with total and circulatory mortality, but a simultaneous consideration of these pollutants with PM10 reduced PM10 coefficients only slightly, or even increased them. In these results, pollution coefficients often were positive at multiple lag days (0-day through 3-day lags were examined), but for PM indices, 1-day lag coefficients were most significant. However, when all combinations of multiple-day average exposures were examined, for cases in which multiple lag days were positive, the choice of single-day or multiple-day average exposure did not appreciably change the estimated effect sizes. An examination of temporal correlation showed that the order of spatial uniformity as expressed by the median site-to-site correlation was O3 (0.83), PM10 (0.78), TSP (0.71), NO2 (0.70), carbon monoxide (CO) (0.50), and sulfur dioxide (SO2) (0.49), which suggests less exposure error for O3 and PM10 than for the other measured pollutants. Thus, these results suggest that spatially homogeneous pollution indices show higher associations with measured health outcomes.
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PMID:Association of particulate matter components with daily mortality and morbidity in urban populations. 1124 87

The formation and structure of gold (III)-L-histidine complex was investigated with the use of carbon (13C) and proton (1H) nuclear magnetic resonance (NMR), infrared (IR) spectroscopy, capillary electrophoresis (CE), capillary electrophoresis-inductively coupled plasma-mass spectroscopy (CE-ICP-MS), X-ray fluorescence spectroscopy (XRF), matrix-assisted laser desorption/ionization (MALDI), and laser desorption mass spectroscopy (LDMS). It was found that two L-histidine molecules and one gold ion slowly form a complex in acidic solution. Each L-histidine molecule provided two nitrogen ligands; one was the alpha-amino group and the other from the imidazole ring. The Au(III)-bis-L-histidine complex precipitates after deprotonation of the free carboxylic group, resulting in an increase in the solution acidity. Determination of the exact sequence of events and the identity of the complex was a comprehensive instrumental analysis problem involving the above techniques.
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PMID:Speciation of gold(III)-L-histidine complex: a multi-instrumental approach. 1124 92

The preparation is described of two modified derivatives of the tripodal tetraamine tren, 2-hydroxy-N,N-bis(2-aminoethyl)ethylamine, NN(2)O222, and 2-amino-N,N-bis(2-hydroxyethyl)ethylamine, NNO(2)222, in which one and two primary amines, respectively, have been replaced with hydroxyl groups. The aqueous acid-base and metal ion (Ni2+, Cu2+, Zn2+) coordination properties of these two compounds were studied by potentiometric, spectrophotometric, and NMR titrations. Two and three acidity constants, respectively, were determined for NNO(2)222 and NN(2)O222 by potentiometry. NMR titrations proved that deprotonation of the two OH residues in NNO(2)222, and of the one in NN(2)O222, corresponded to pK(a) > 14. Acidity constants related to deprotonation of the terminal primary amine functions were similar in both NNO(2)222 and NN(2)O222 (and to those in the parent compound tren), whereas deprotonation of the tertiary ammonium N atom had a very different acidity constant in each of these three compounds. Charge repulsion, polar effects, and intramolecular hydrogen bond formation are responsible for the discrepancy. Chelated diamine metal complexes for each ligand studied depended only on the basicity of the corresponding two amines, suggesting that the hydroxyl group interacted with the metal ion very weakly in acidic or neutral solutions. The ML2+ species further deprotonated to form M(L - H)+ and M(L - 2H) complexes, in which the protons are released from the coordinated OH group. A pM vs pH correlation showed that replacing an NH2 group with a OH group in tren or NN(2)O222 makes the resulting metal complex less stable. Electronic spectra showed that the Cu(II) complexes of both NNO(2)222 and NN(2)O222 adopted a square pyramidal geometry rather than a trigonal bipyramidal geometry. The X-ray crystal structure analysis of the zinc complex [Zn(OH)(mu-NNO(2)222 - H)Zn(NNO(2)222)]2+, as its [BF4]- salt, shows a dinuclear molecule containing two zinc ions, each coordinated in a distorted trigonal bipyramid. The coordination environment at one zinc atom is composed of the four donor groups of a mono-O-deprotonated ligand NNO(2)222 and a hydroxyl ion with the central nitrogen atom of the ligand and the hydroxyl ion in equatorial positions. The oxygen atom of the deprotonated alkoxo group bridges to the second zinc atom, which is coordinated by this atom and one undeprotonated ligand NNO(2)222.
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PMID:Effects of sequential replacement of -NH2 by -OH in the tripodal tetraamine tren on its acidity and metal ion coordinating properties. 1126 60

Protonation of the Os(IV) amido complex TpOs(NHPh)Cl(2) (1) to give the aniline complex [TpOs(NH(2)Ph)Cl(2)]OTf (2) requires excess triflic acid (HOTf). Complex 1 is unreactive with HCl and other moderately strong acids. Consistent with the low basicity of 1, the aniline complex 2 is extremely acidic and is deprotonated by stoichiometric addition of weak bases such as Cl(-) or H(2)O. No reaction is observed between 1 and methyl triflate (CH(3)OTf) at ambient temperatures. Upon heating, CH(3)OTf removes the chloride ligands from 1 to give CH(3)Cl and the amidobis(triflate) complex TpOs(NHPh)(OTf)(2) (3). Attack at the amido nitrogen is not observed. Complex 1 is thus very inert to protonation and electrophilic attack at nitrogen. A deprotonated form of 1, TpOs[NPh(MgBr)]Cl(2) (4), is generated on reaction of PhMgBr with TpOs(N)Cl(2). Complex 4 is extremely basic and will protonate to 1 with weak acids such as CH(3)CN, DMSO, and acetic anhydride. Thus, 1 has a low acidity as well as a low basicity; it is both less acidic and less basic than aniline. The inertness of 1 is ascribed to partial Os-N pi bonding and to the oxidizing nature of the Os(IV) center.
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PMID:Protonation and deprotonation of TpOs(NHPh)Cl(2): an unusually inert amido ligand. 1131 46

Changes in pH, titratable acidity, total soluble solids and proteins of Dabar sorghum (Sorghum bicolor (Linn) Moench.) during natural fermentation at 37 degreesC for up to 36 h were monitored. The pH of the fermenting material decreased sharply with a concomitant increase in the titratable acidity. Total soluble solids increased with progressive fermentation time. The crude protein and non-protein nitrogen slightly increased during the last stages of fermentation. The in vitro protein digestibility markedly increased as a result of fermentation. The globulin plus albumin fractions increased significantly (p < or = 0.05) during the first 8 h of fermentation. Kaffirin fraction decreased during the first 8 h of fermentation but increased sharply as fermentation progressed. Cross-linked kaffirins fluctuated during the fermentation process. Glutelin like protein, which was the minor fraction, true glutelins, the second most abundant fraction, together with non-extractable proteins fluctuated during the fermentation process.
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PMID:Effect of fermentation on sorghum protein fractions and in vitro protein digestibility. 1131 6

A general synthetic route to novel nitrogen-bridged heterocyclic carbenium ions of the acridinium and triangulenium type has been developed and investigated. The synthetic method is based on nucleophilic aromatic substitution (SNAr) on the tris(2,6-dimethoxyphenyl)carbenium ion (1) with primary amines and, by virtue of its stepwise and irreversible nature, provides a powerful tool for the preparation of a wide variety of new heterocyclic carbenium salts. Several derivatives of the three new oxygen- and/or nitrogen-bridged triangulenium salts, azadioxa- (6), diazaoxa- (7), and triazatriangulenium (4), have been synthesized and their physicochemical properties have been investigated. Crystal structures for compounds 2 b-PF6, 2 d-PF6, 4b-BF4, 4c-BF4, 6e-BF4, and 8 are reported. The different packing modes found for the triazatriagulenium salts are discussed in relation to the electrostatic and space-filling requirements of the ions. The stabilities of the cations 6a, 7b, and 4a, as expressed by their pKR+ values, have been determined in strongly basic nonaqueous solution by use of the C_ acidity function; the values obtained were 14.5, 19.4, and 23.7, respectively. This study further implied that the C_ scale in its present form is unsuitable for the precise determination of pKR+ values beyond 22.
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PMID:Synthesis, structure, and properties of azatriangulenlenium salts. 1134 20


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