On the cation sensibility of the vitamin B12-dependent methionine synthetase (5-methyltetrahydrofolate-homocysteine-methyltransferase from Escherichia coli).
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Ammonia↗
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Results for “Lithium Compounds”
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The use of epidemiological concepts and techniques to discern factors associated with the nitrate concentration of well water on swine farms in the USA.
This epidemiological study investigates the relationship between various factors associated with swine farms and the nitrate concentration of well water in the USA. Through a random sampling procedure, 605 swine farms located in 18 states were selected for inclusion in this study. A total of 631 well water samples were collected from these farms and tested for a variety of elements and compounds. The concentrations of nitrate, nitrite, sulfate, chloride, sodium, potassium, ammonia, fluoride, bromide and lithium were determined by an ion chromatograph while an inductively coupled argon plasma emission spectrophotometer was used to determine the concentrations of calcium, magnesium, barium, zinc, iron and phosphate. Data concerning various farm factors were gathered via a personally administered questionnaire. The data were examined using both multiple linear regression and logistic regression. Results indicate that 53.6% (338/631) of the wells contained detectable levels of nitrate, 11.7% (74/631) had nitrate levels exceeding 45 ppm and 4.3% (27/631) exceeded 100 ppm. Logistic models demonstrated an association between nitrate concentrations > 45 ppm, increasing water potassium levels and wells < 100 ft deep. Nitrate levels > 100 ppm were related to increasing water concentrations of potassium, magnesium, barium and zinc, wells 6-10 years old, increasing distance from the study farm to the nearest cattle farm and a greater distance to the nearest waterway located off the study farm. A negative association was seen between nitrate concentrations > 100 ppm, the water level of sulfate, and the use of the same well to supply both the household and livestock. Multiple linear regression models revealed a positive association between increasing nitrate concentration and the water levels of chloride, calcium, zinc and the greater number of miles from the study farm to the nearest farm with cattle or sheep. A negative association was noted between the concentration of well water nitrate and the water levels of sulfate and ammonia, the use of water treatment, the number of miles to the nearest farm with poultry, the employment of water treatment and the use of the same well to supply water to both livestock and the household.
Agriculture↗
Localization and functional significance of the Na+/Ca2+ exchanger in presynaptic boutons of hippocampal cells in culture.
Immunocytochemical evidence for localized distribution of the Na+/Ca2+ exchange protein in nerve terminals of cultured hippocampal cells is presented together with results on the functional relevance of the exchanger in the control of [Ca2+]i and of synaptic vesicle recycling. The monoclonal antibody R3F1, directed against an epitope on the intracellular loop of the protein, revealed higher densities of expression in synaptic regions than in other parts of the neurons. Removal of extracellular Na+ produced enhanced and prolonged elevation of [Ca2+]i in nerve terminals during and after electrical stimulation of the cells. Correspondingly, initial rates of exocytosis, measured by fluorescence changes of FM 1-43 during stimulation, were faster in LiCl-containing solution than in NaCl-containing solution. By contrast, endocytosis at 20 s was the same in both solutions.
Animals↗
Transport processes at the brain cell membrane.
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Acetates↗
Spectroscopic and DFT studies to understand the liquid formation mechanism in the LiTFSI/acetamide complex system.
It is interesting that although both lithium bis(trifluoromethane sulfone) imide (LiN(SO2CF3)2, LiTFSI) and acetamide (CH3CONH2) are solid, their mixture is a liquid in an appropriate molar ratio range at room temperature. The liquid formation mechanism of the LiTFSI/acetamide complex has been investigated by FT-IR and FT-Raman spectroscopy. The spectroscopic studies show that the Li+ ions coordinate with the C=O group of acetamide whereas the SO2 group in TFSI- anions interacts with the NH2 group of acetamide via hydrogen bonding. These interactions lead to the breakage of the hydrogen bonds between acetamide molecules and to the dissociation of LiTFSI, resulting in the formation of this molten salt. Furthermore, it has been found that moderate interaction between LiX and RCONH2 (R = -NH2, -CH3 and -CF3) is favorable for forming a LiX/RCONH2 molten salt system with low eutectic temperature and high conductivity based on density functional theory (DFT) calculational and experimental comparison for different R groups in RCONH2 and different lithium salts.
Acetamides↗
Epoxidation and reduction of cholesterol, 1,4,6-cholestatrien-3-one and 4,6-cholestadien-3beta-ol.
Many naturally occurring polyhydroxylated sterols and oxysterols exhibit potent biologic activities. This paper describes reagent and position selectivity of epoxidation and reduction of cholesterol derivatives. Cholesterol was reacted with m-chloroperoxybenzoic acid (m-CPBA) to form 5alpha,6alpha-epoxycholestan-3beta-ol, but in reaction with 30% H(2)O(2), it did not reacted. 1,4,6-cholestatrien-3-one was obtained from cholesterol and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in dioxane. 1,4,6-cholestatrien-3-one was reacted with 30% H(2)O(2) and 5% NaOH in methanol to give 1alpha,2alpha-epoxy-4,6-cholestadien-3-one, which was stereoselectively reduced with NaBH(4) to form 1alpha,2alpha-epoxy-4,6-cholestadien-3beta-ol and reduced with Li metal in absolute ethanol to give 2-ethoxy-1,4,6-cholestatrien-3-one. And 1,4,6-cholestatrien-3-one was epoxidized with m-CPBA in dichloromethane to afford 6alpha,7alpha-epoxy-1,4-cholestadien-3-one, which was reacted with NaBH(4) to synthesize 6alpha-hydroxy-4-cholesten-3-one and reduced Li metal in absolute ethanol to form 2-ethoxy-1,4,6-cholestatrien-3-one, respectively. 1,4,6-cholestatrien-3-one was reduced with NaBH(4) in absolute ethanol to form 4,6-cholestadien-3beta-ol, which was reacted with 30% H(2)O(2) to leave original compound, but was reacted with m-CPBA to give 4beta,5beta-epoxy-6-cholesten-3beta-ol as the major product and 4beta,5beta-epoxy-6alpha,7alpha-epoxycholestan-3beta-ol as the minor product.
Boron Compounds↗
Use of LiCl in phospholipase C assays masks the impaired functionality of a mutant angiotensin II receptor.
We recently reported that replacement of Tyr302 for Ala in the human angiotensin II type 1 receptor (hAT1) severely impaired its ability to activate phospholipase C (PLC). Another study demonstrated that the same mutation in the rat AT1 receptor only slightly impaired its ability to activate PLC. The most striking difference between the two studies was the use of LiCl in the experimental conditions. Thus, in the present report we evaluated the effect of LiCl on the rate of accumulation of inositol trisphosphate (IP3) in transfected cells stimulated with angiotension II (Ang II). In the presence of LiCl, Ang II caused a significant accumulation of IP3 in COS-7 cells transfected with the hAT1Y302A mutant receptor. In stably expressing CHO cells, stimulation of hAT1Y302A did not induce any IP3 elevation even in the presence of LiCl whereas the hAT1 wild-type receptor increased the production of IP3 exclusively in the presence of LiCl. These results show that LiCl is a convenient tool to enhance the sensitivity of PLC assays. However, in structure-activity relationship studies, it may underestimate or mask the debilitating effect of some mutations.
Amino Acid Substitution↗
(K+)-dependent acyl phosphatase as part of the (na+ + K+)-dependent ATPase of cell membranes.
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Adenosine Triphosphatases↗
Infrared intensity in dielectric media by an electrostatic model.
A change in an infrared intensity in dielectric media is treated by an electrostatic model. The basic model is originally formalized for a dipolar liquid. The model is satisfactorily applied to the infrared intensity of the C-H stretching of chloroform, which changes 22 times large in the liquid state at -43 degrees C as in the gaseous state. A change in the infrared intensity in lithium ammonium tartrate, where a ferroelectric phase transition takes place, is analyzed on the basis of a local polarization above T(c) or a spontaneous polarization below T(c), deducing important quantities on a phase transition. A difference in the infrared intensity of the C-Br stretching of 1,10-dibromodecane between the urea clathrate and the crystalline state is analyzed by evaluating electric fields due to bond moments and oscillating dipoles. These analyses confirm the mechanism of the change in the absolute infrared intensity, which originates from an electrostatic interaction with an electric field applied to a molecule or a functional group closely related to a normal mode.
Carbon↗
Preferential uptake of D-glucose by isolated human erythrocyte membranes.
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Ammonium Chloride↗
Relative role of anions and cations in the stabilization of halophilic malate dehydrogenase.
Halophilic malate dehydrogenase unfolds at low salt, and increasing the salt concentration stabilizes, first, the folded form and then, in some cases, destabilizes it. From inactivation and fluorescence measurements performed on the protein after its incubation in the presence of various salts in a large range of concentrations, the apparent effects of anions and cations were found to superimpose. A large range of ions was examined, including conditions that are in general not of physiological relevance, to explore the physical chemistry driving adaptation to extreme environments. The order of efficiency of cations and anions to maintain the folded form is, for the low-salt transition, Ca(2+) approximately Mg(2+) > Li(+) approximately NH(4)(+) approximately Na(+) > K(+) > Rb(+) > Cs(+), and SO(4)(2)(-) approximately OAc(-) approximately F(-) > Cl(-), and for the high-salt transition, NH(4)(+) approximately Na(+) approximately K(+) approximately Cs(+) > Li(+) > Mg(2+) > Ca(2+), and SO(4)(2)(-) approximately OAc(-) approximately F(-) > Cl(-) > Br(-) > I(-). If a cation or anion is very stabilizing, the effect of the salt ion of opposite charge is limited. Anions of high charge density are always the most efficient to stabilize the folded form, in accordance with the order found in the Hofmeister series, while cations of high charge density are the most efficient only at the lower salt concentrations and tend to denature the protein at higher salt concentrations. The stabilizing efficiency of cations and anions can be related in a minor way to their effect on the surface tension of the solution, but the interaction of ions with sites only present in the folded protein has also to be taken into account. Unfolding at high salt concentrations corresponds to interactions of anions of low charge density and cations of high charge density with the peptide bond, as found for nonhalophilic proteins.
Acetates↗
Exploring the scope of poly(ethylene glycol) (PEG) as a soluble polymer matrix for the Stille cross-coupling reaction.
The optimization and efficient parallel synthesis and purification of a library of biaryl, heterobiaryl, and styryl derivatives, via the first reported poly(ethylene glycol)-supported palladium-catalyzed Stille procedure, are described. Preliminary investigations into the reaction between monomethoxy poly(ethylene glycol)5000-supported iodide 1a with tributylphenyltin 2 revealed that the optimal "liquid-phase" conditions employ PdCl2(PPh3)2 (0.1 equiv) catalysis with LiCl (10 equiv) in DMF at 80 degrees C for either 48 h (at 20 mM concentration of 1a) or 24 h (at 10 mM concentration of 1a). The soluble polymer-supported reaction is superior to its solution-phase counterpart because the tributyltin side products and excess reagents are easily separated from the product intermediate 3a by precipitation of 3a into diethyl ether followed by recovery of the polymer by filtration in > 99%. In addition, the homocoupled byproduct 6 is also removed during this precipitation step. Under these conditions the transesterified biaryl adduct 4a can be isolated in 97-98% yield. The scope of this reaction was probed in a parallel format with the PEG-supported electrophiles 1a-b and a range of tributyl stannanes 2 and 7-13 under the optimized conditions vide supra. Subsequent cleavage of the polymer-supported adducts, by transesterification, and short column chromatography yielded a library of substituted methyl benzoates 4a-b and 14a-b to 20a-b in high yield (69-99%) and purity (> 95%).
Catalysis↗
The reduction of indoles and related compounds.
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Acids↗
Synthesis of titanium(IV) guanidinate complexes and the formation of titanium carbonitride via low-pressure chemical vapor deposition.
The mono(guanidinato) complex [Ti(NMe2)2Cl{i-PrNC[N(SiMe3)2]N-i-Pr}] (1) was prepared by reaction of [Ti(NMe2)2Cl2] with 1 or 2 equiv of the lithium guanidinate salt [Li{i-PrNC[N(SiMe3)2]N-i-Pr}]. Compound 1 has been characterized by X-ray crystallography. Treatment of TiCl4 with 2 equiv of [Li{i-PrNC[N(SiMe3)2]N-i-Pr}] resulted in the formation of dark red crystals. X-ray crystallography showed that these crystals consist of a 70:30 mixture of two bis(guanidinato) complexes, namely, [TiCl2{i-PrNC[N(SiMe3)2]N-i-Pr}{i-PrNC(N=CMe2)N-i-Pr}] (2) and [TiCl2{i-PrNC[N(SiMe3)2]N-i-Pr}{i-PrNC[N(H)-i-Pr]N-i-Pr}] (3). Both compounds 2 and 3 possess a transformed guanidinate ligand. Low-pressure chemical vapor deposition of either compound 1 or [TiCl2{i-PrNC(NMe2)N-i-Pr}] (4) at 600 degrees C results in thin films of titanium carbonitride.
Journal Article↗
Novel rhenium(V) oxo complexes containing bis(pyrazol-1-yl)acetate and bis(pyrazol-1-yl) sulfonate as tripodal N,N,O-heteroscorpionate ligands.
Reactions of [NBu4][Re(O)Cl4] with bis(pyrazol-1-yl)methane (bpzm) and bis(pyrazol-1-yl)acetate (Hbpza) and with the lithium salts lithium [bis(3,5-dimethylpyrazol-1-yl)acetate] (Libdmpza) and lithium [bis(3,5-dimethylpyrazol-1-yl)methanesulfonate] (Libdmpzs) produce a series of new compounds containing either a kappa2-N,N bidentate pyrazolyl ligand [Re(O)(bpzm)Cl3 (1), Re(O)(bpzm)(OMe)Cl2 (2), Re(O)(bpzaOMe)(OMe)Cl2 (4)] or a kappa3-N,N,O heteroscorpionate [Re(O)(bpza)Cl2 (3), Re(O)(bdmpza)Cl2 isomers 5 and 6, Re(O)(bdmpza)(OMe)Cl (7), Re(O)(bdmpza)(OEt)Cl (8), Re(O)(bdmpzs)(OMe)Cl (9), Re(O)(bdmpzs)(OEt)Cl (10)]. X-ray analyses of 1 and 3 show in both cases a distorted octahedral environment around the rhenium atom. The nature and the geometry of the products are strongly determined by the reaction solvent and by the heteroscorpionate ligand itself. When scorpionates bear methylated pyrazolyl rings mixed heterocomplexes Re(O)(bdmpza)(glycol) (11) and Re(O)(bdmpzs)(glycol) (12) are obtained (H2glycol = ethylene glycol). Also 11 shows an octahedral geometry as assessed by X-ray study.
Journal Article↗
Diastereoselective alkylation of beta-amino esters: structural and rate studies reveal alkylations of hexameric lithium enolates.
Alkylation of beta-amino ester enolates proceeds with high diastereoselectivity. Single crystal, powder, and solution X-ray diffraction studies of the enolate show that the racemic enolate forms prismatic hexamers. 6Li NMR spectroscopic studies on partially racemic enolates reveal complex mixtures of homo- and heterochiral hexamers. An implicit fit of the aggregate populations to the Boltzmann distribution provides the free energy differences and equilibrium constants for the ensemble. Rate studies show that enolate alkylation occurs directly from the hexamer with participation by THF. A mechanism based on the alkylation of a ladder-like aggregate is proposed.
Alkylation↗
On the mechanism of THF catalyzed vinylic lithiation of allylamine derivatives: structural studies using 2-D and diffusion-ordered NMR spectroscopy.
N-Lithio-N-(trialkylsilyl)allylamines can be deprotonated in the presence of ethereal solvents exclusively at the cis-vinylic position to yield 3,N-dilithio-N-(trialkylsilyl)allylamines under mild conditions. Low temperature (1)H and (7)Li NMR ((1)H NOESY, TOCSY, (1)H/(7)Li HSQC, and DO-NMR) studies on the solution structure of 3,N-dilithio-N-(tert-butyldimethylsilyl)allylamine identified three major aggregates in THF (monomer, dimer and tetramer), but the aggregate structures failed to explain the solvent dependence and regiochemical outcome of the reaction. Low temperature (1)H NMR (NOESY, TOCSY, DO-NMR) studies on the solution structure of N-lithio-N-(tert-butyldimethylsilyl)allylamine in the presence of nBuLi identified amide/nBuLi mixed aggregates in both the ethereal solvent THF (1:1 dimer) and the hydrocarbon solvent toluene (1:3 tetramer). Addition of 2 equiv of THF to toluene solutions induces the formation of the same THF solvated 1:1 dimer as observed in neat THF. NMR evidence suggests that in THF the mixed aggregate has close contact between the olefin and the beta-CH(2) of nBuLi, while in the absence of THF, the allyl chain appears to be pointed away from the nearest nBuLi residues.
Allylamine↗
Formation of phosphorus-nitrogen bonds by reduction of a titanium phosphine complex under molecular nitrogen.
The reduction of high oxidation state metal complexes in the presence of molecular nitrogen is one of the most common methods to synthesize a dinitrogen complex. However, the presence of strong reducing agents combined with the poor binding ability of N2 can lead to unanticipated outcomes. For example, the reduction of [NPN]ZrCl2(THF) (where NPN = PhP(CH2SiMe2NPh)2) with KC8 under N2 leads to the formation of the side-on bridged dinuclear dinitrogen complex ([NPN]Zr(THF))2(mu-eta2:eta2-N2) with an N-N bond distance of 1.503(3) A; however, reduction of the corresponding titanium precursor, [NPN]TiCl2, under N2 does not generate a dinitrogen complex, rather the bis(phosphinimide) derivative, ([N(PN)N]Ti)2, is isolated in which the added N2 is incorporated between the titanium and phosphine centers. Performing the reaction under 15N2 results in the 15N label being incorporated in the phosphinimide unit. A suggested mechanism for this process involves an initially formed dinitrogen complex being over reduced to generate a species with bridging nitrides that undergoes nucleophilic attack by the coordinated phosphine ligands and formation of the P=N bond of the phosphinimide.
Crystallography, X-Ray↗