Evaluation of select variables in the ion chromatographic determination of F-, Cl-, Br-, NO(-)3, SO(-2)4, and PO(-3)4 in serum samples

A full experimental design at two levels is applied for the estimation of the significance of select factors that may influence the ion chromatography (IC) determination of F-, Cl-, Br-, NO(-)3, SO(-2)4, and PO(-3)4 in serum samples. The factors studied are various sample deproteinization procedures, eluent composition, and flow rates. Deproteinization using either acetonitrile-NaOH or ultrafiltration can be used in order to obtain a significant protein removal before IC analysis; however, the former is recommended because it is less time-consuming and cheaper. Better resolution is obtained when a sodium hydroxide solution is used as the eluent. There is no influence of the sample's deproteinization procedures on the chromatographic resolution.     

Exceptionally active yttrium-salen complexes for the catalyzed ring opening of epoxides by TMSCN and TMSN(3)

Halide or alkoxide free yttrium-salen complexes are excellent catalysts for the ring opening of epoxides mediated by TMSCN and TMSN3. Substrate to catalyst ratios up to 10000 have been realized in these potentially useful reactions, which can be run under solvent-free conditions. Even though the enantioselectivities for the TMSCN-mediated reaction remains modest (best 77% ee), these studies with a highly tunable ligand system may provide further impetus for work in this important area of catalysis. Even though attempts to isolate a Y-cyanide complex, which was detected by in situ IR spectroscopy, failed, a related dimeric hydroxide complex was isolated. A kinetic study using in situ IR spectroscopy did not provide conclusive data to assign an order with respect to Y in this reaction.     

Rapid and efficient ring opening of epoxides catalyzed by a new electron deficient tin(IV) porphyrin

The new electron deficient tin(IV) tetraphenylporphyrinato trifluoromethanesulfonate, [Sn^IV(tpp)(OTf)₂], was used as an efficient catalyst for the alcoholysis, hydrolysis and acetolysis of epoxides. Conversion of epoxides to thiiranes and acetonides were also performed efficiently in the presence of this catalyst.     

Asymmetric ring opening of meso epoxides with TMSCN catalyzed by (pybox)lanthanide complexes

The asymmetric ring opening of meso epoxides with TMSCN is catalyzed by (pybox)YbCl3 complexes, yielding the beta-trimethylsilyloxy nitrile ring-opened products with good enantioselectivities (83-92% ee). The reaction exhibits a second-order kinetic dependence on catalyst concentration and a first-order dependence on epoxide concentration, consistent with a bimetallic pathway involving simultaneous activation of epoxide and cyanide.     

Efficient ring opening of epoxides with trimethylsilyl azide and cyanide catalyzed by erbium(III) triflate

Epoxides can be opened under neutral conditions with TMSN₃ and TMSCN in the presence of catalytic amounts of Lewis acid, affording the corresponding ring-opened compounds in high yields.     

Zn(OAc)2/podand catalyzed ring opening of epoxides by aromatic amines under solvent-free conditions

A highly regioselective ring opening of epoxides with aromatic amines in the presence of a catalytic amount of Zn(OAc)₂ and a recently synthesized podand under solvent-free conditions is described. The yields of the amino alcohols are uniformly good and the recovered catalyst could be used in new attempts without any purification.     

Multiple hydrogen-bonding interactions between macrocyclic triurea and F-, Cl-, Br-, I- and NO3(-): a theoretical investigation

The binding behaviors of the 27-membered macrocyclic triurea 1 towards the five anions, F(-), Cl(-), Br(-), I(-) and NO(3)(-), through multiple hydrogen-bonding interactions, were investigated at the B3LYP/6-311++G(d,p)//B3LYP/6-31(1)++G(d,p) (6-31(1)++G(d,p) is a hybrid basis set; for more details see computational methods) level. Three binding modes (I, II, and III) were found for all the five anions in the gas phase, and seven structural parameters have been used to describe these binding modes. Binding mode I and II have similar binding geometries and their coordination number of anions is six. Binding mode III exhibits completely different binding characteristics and the coordination number is three except for NO(3)(-). Our calculation revealed that the binding strength of binding modes follows the trend, mode II > I > III, with the exception of F(-) complex. The binding affinity of anions in the gas phase goes in this order: F(-) > Cl(-) > NO(3)(-) > Br(-) > I(-). The changes in the binding affinity for all 15 urea-anion complexes under the influence of solvent environment were examined using the IEF-PCM continuum solvation model. Although the binding affinities are weakened substantially because of solvent effect, these drastic changes do not affect the affinity order in the gas phase. The experimentally observed affinity strength in chloroform, Cl(-) > NO(3)(-) > Br(-), was confirmed by this work. Moreover, we found a high correlation between ΔE(bind) (1) and ΔE(In) (1,3-dimethylurea) for all three binding modes, implying that the affinity strength of 1 to these five anions is determined mainly by the proton-accepting ability of anions, not by steric effect.     

In(OTf)3 catalyzed reductive etherification of 2-aryloxybenzaldehydes and 2-(arylthio)benzaldehydes

2-Aryloxybenzaldehydes and 2-(arylthio)benzaldehydes undergo reductive etherification in presence of 5 mol% In(OTf)₃ and stoichiometric amount of Et₃SiH under solvent free conditions to generate novel symmetrical dibenzyl ethers and thioethers in excellent yields. In(OTf)₃ is found to be superior in terms of catalytic activity over the other metal triflates tested for the reaction. Xanthenes and thioxanthenes, as anticipated, could not be obtained under these conditions.     

Micellar induced regioselectivity in the two-step consecutive reaction of SO3(2-) with Br-(CH2CH2)n-Br (n=2-5)

High field (800 MHz) (1)H NMR was used to monitor the two-step consecutive reaction of excess SO(3)(2-) with symmetrical bifunctional alpha,omega-dibromoalkanes with butane (DBB), hexane (DBH), octane (DBO), and decane (DBD) chains in CTAB micelles at 25 degrees C. The first-order rate constant for the first substitution step for DBB and DBH is about 5 times faster than for the second, but the kinetics for DBO and DBD were not cleanly first-order. After 40 min, the solution contained about 80% of the intermediate bromoalkanesulfonate from DBB and DBH and the remainder is alkanedisulfonate and unreacted starting material. The same reactions were carried out in homogeneous MeOH/D(2)O solutions at 50 degrees C. The rate constants for all four alpha,omega-dibromoalkanes were first-order throughout the time course of the reaction and the same within +/-10%. However, because micellar solutions are organized on the nanoscale and bring together lipophilic and hydrophilic reactants into a small reaction volume at the micellar interface, they speed this substitution reaction considerably compared to reaction in MeOH/D(2)O. The CTAB micelles also induce a significant regioselectivity in product formation by speeding the first step of the consecutive reaction more than the second. The results are consistent with the bromoalkanesulfonate intermediates having a radial orientation within the micelles with the -CH(2)SO(3)(-) group in the interfacial region and the -CH(2)Br group directed into the micellar core such that the concentration of -CH(2)Br groups in the reactive zone, i.e., the micellar interface, is significantly reduced. These results provide the first example of self-assembled surfactant system altering the relative rates of the reaction steps of a consecutive reaction and, in doing so, enhancing monosubstitution of a symmetrically disubstituted species.     

Stereoselective synthesis of (3S,4R)- and (3R,4S)-4-(N-substituted-amino)-2,2-dimethyl-6-nitrochroman-3-ols via the microwave assisted regioselective ring opening of epoxides in the presence of neutral alumina

With the aim of discovering new molecules with potassium channel activating properties, we have designed and synthesized derivatives with structural similarity to cromakalim, an important molecule which shows specific affinity toward potassium channels, based on previous structure–activity investigations by applying different C-4 substitutions. This has been accomplished by using a stereoselective Jacobsen epoxidation and microwave assisted regioselective epoxide opening with neutral alumina as the key reactions.     

Change in Volume Properties of and Complex Formation in the System Hg(NO3)2-KX-H2O (X- = Cl-, Br-, I-)

The chemical nature of the anions in step complex formation in Hg(NO₃)₂-KX-H₂O systems (X^- = Cl^-, Br^-, I^-) manifests itself in different trends in variation of the molar volumes of the solutions.     

Surface characterization of 1-butyl-3-methylimidazolium Br-, I-, PF6-, BF4-, (CF3SO2)2N-, SCN-, CH3SO3-, CH3SO4-, and (CN)2N- ionic liquids by sum frequency generation

Sum frequency generation spectroscopy, SFG, was used for the surface characterization at the gas-liquid interface of the 1-butyl-3-methylimidazolium cation combined with the following anions: Br-, I-, PF6-, BF4-, (CF3SO2)2N- (imide), SCN-, CH3SO3- (MeSO3), CH3SO4- (MS), and (CN)2N- (DCN). The SFG spectra obtained for the different ionic liquids were similar independent of the anion selected; therefore, a comprehensive analysis for the surface characterization of the ionic liquids' cation was focused only on the PF6- and Br- anion combinations. For an accurate identification of the vibrational modes observed, FT-IR and Raman spectroscopy in combination with isotopic labeling with deuterium and polarized Raman spectroscopy was used. The cation orientation was determined by analysis of polarization-dependent SFG spectra. For a compound dried in a vacuum to < or = 2 x 10(-5) Torr, the cation appears to be oriented with the ring laying flat along the surface plane and the butyl chain projecting into the gas phase independent of the anion identity.     

Efficient regio- and stereoselective ring opening of epoxides with alcohols, acetic acid and water catalyzed by ammonium decatungstocerate(IV)

Epoxides can be cleaved in a regio- and stereoselective manner under neutral conditions with alcohols and acetic acid in the presence of catalytic amounts of decatungstocerate(IV) ion, ([CeW₁₀O₃₆]⁸⁻), affording the corresponding β-alkoxy and β-acetoxy alcohols in high yields. In water, ring opening of epoxides occurs with this catalyst to produce the corresponding diols in good yields.     

Regioselective ring opening of amino epoxides with nitriles: an easy synthesis of (2R,3S)- and (2S,3S)-1,3-diaminoalkan-2-ols with differently protected amine functions

[reaction: see text] Transformation of enantiopure (2R,1'S)- or (2S,1'S)-2-(1-aminoalkyl)epoxides 1 or 2 into the corresponding (2R,3S)- and (2S,3S)-1,3-diaminoalkan-2-ols 3 or 4 is described. The opening of the epoxide ring with different nitriles (Ritter reaction) takes place with total selectivity and in high yields in the presence of BF3.Et2O. Interestingly, the two amine groups are differently protected. A mechanism to explain this transformation is proposed.     

Asymmetric Friedel-Crafts alkylation of indoles with methyl (E)-2-oxo-4-aryl-3-butenoates catalyzed by Sc(OTf)3/pybox

The asymmetric Friedel–Crafts reaction between a series of substituted indoles 2 a – l and methyl (E)‐2‐oxo‐4‐aryl‐3‐butenoates 3 a – c has been efficiently catalyzed by the scandium(III) triflate complex of (4′S,5′S)‐2,6‐bis[4′‐(triisopropylsilyl)oxymethyl‐5′‐phenyl‐1′,3′‐oxazolin‐2′‐yl]pyridine (pybox; 1 ). Substituted 4‐(indol‐3‐yl)‐2‐oxo‐4‐arylbutyric acid methyl esters 4 a – n were usually formed in excellent yields and the enantioselectivity was up to 99 % ee, irrespective of the electronic character of the substituent and its location on the indole ring, albeit with the exclusion of position 2. The adducts could be obtained as stable enol tautomers and the equilibrium with the keto structure is discussed. The X‐ray crystal structure determination of 4 m indicated the 4R absolute configuration, thus confirming the proposal of Jørgensen for 4 i . The sense of the stereoinduction can be rationalized by the same octahedral complex 5 between 3 , pybox 1 , and scandium triflate already proposed for the Diels–Alder/hetero‐Diels–Alder and the Mukaiyama–aldol reactions of pyruvates.     

Zirconyl triflate, [ZrO(OTf)2], as a new and highly efficient catalyst for ring-opening of epoxides

A highly efficient method for the ring opening of epoxides catalyzed by ZrO(OTf)₂ was adopted. This catalyst efficiently catalyzed alcoholysis, acetolysis and hydrolysis of epoxides and the corresponding alkoxy alcohols, acetoxy alcohols and 1,2- diols were obtained in excellent yields. Conversion of epoxides to 1,2-diacetetes, thiiranes and 1,3-dioxolanes was also performed in the presence of catalytic amounts of ZrO(OTf)₂, and the corresponding products were obtained in high to excellent yields. The high catalytic activity of ZrO(OTf)₂ is due to the replacement of Cl with OTf, which makes the ZrO(OTf)₂ as efficient Lewis acid.     

Regioselectivity in the ring opening of epoxides for the synthesis of aminocyclitols from D-(-)-quinic acid

Efficient syntheses of four aminocyclitols are reported. Each synthesis is accomplished in eight steps starting from D-(-)-quinic acid. The key step involves a highly regioselective ring opening of epoxides by sodium azide.