Sol-Gel-based SPME and GC–MS for Trace Determination of Geosmin in Water and Apple Juice Samples

A headspace solid-phase microextraction (HS-SPME) method was developed for the trace determination of geosmin in water and apple juice samples. A poly(dimethylsiloxane) (PDMS) fiber was synthesized as coated fiber using sol-gel methodology. After performing the extraction in the headspace, the fiber was introduced directly into the injection port of a gas chromatography-mass spectrometry (GC–MS) using electron impact (EI) ionization mode. One-at-the-time optimization strategy was applied to investigate and optimize important extraction parameters such as extraction temperature and time, ionic strength, headspace volume, and desorption temperature and time. The analytical data exhibited an RSD of 2–15%, a linear calibration range of 1–1,000 ng L^?1, and a detection limit of 0.30 ng L^?1 using selected ion monitoring (SIM) mode. The proposed method was successfully applied to the extraction and determination of geosmin in the spiked real water and apple juice samples and a relative recovery of 95–102% were achieved. The developed method offers the advantage of being simple to use, with shorter analysis times, lower cost of equipment, very little matrix effect, and high relative recovery in comparison to conventional methods of analysis.     

A compilation of X- and gamma-ray sensitivities from isotopes produced by the (n, γ) reaction for utilization in instrumental neutron activation analysis

A comprehensive compilation of X- and γ-ray emitting isotopes produced by the (n, γ) reaction is reported in this paper for application to instrumental neutron activation analysis (INAA). The X- and γ-ray sensitivities are computed theoretically by a computer code. Interfering photons from isotopes of neighbouring elements are identified by the code and the percentage interference is computed. Additionally an advantage factor (X-ray: γ-ray sensitivity) is computed, which is a figure of merit for X-ray spectroscopy in INAA. Further, mathematical representation of background continua for typical matrices encountered in INAA allow the calculation of elemental detection limits for the X-ray and γ-ray photons.     

A simple, efficient, and highly selective method for the iodination of alcohols using ZrCl4/NaI

Iodination of primary, secondary, allylic, and benzylic alcohols giving their corresponding iodides was achieved with ZrCl₄/NaI in anhydrous CH₃CN with excellent yields and selectivities.     

Magnesium triflate [Mg(OTf)2] a highly stable, non-hygroscopic and a recyclable catalyst for the high yielding preparation of diethyl α-trimethylsilyloxyphosphonates from diethyl α-hydroxyphosphonates by HMDS under solventless conditions

A broad, adaptable, high yielding and convenient procedure for the easy conversion of various α-hydroxyphosphonates to α-trimethylsilyloxyphosphonates under mild conditions with HMDS in the presence of a catalytic amount of magnesium triflate as a highly stable and a non-hygroscopic recyclable catalyst in neat conditions is described. In order to show the general applicability of this method, we have also applied this procedure successfully for the silylation of ordinary alcohols and phenols.     

Synthesis of novel exocyclic amino nucleosides by parallel solid-phase combinatorial strategy

A versatile parallel solid-phase combinatorial strategy was developed for the synthesis of large nucleoside libraries. Twelve libraries L1-12 of 1152 novel exocyclic triazinylamino nucleosides and one library L13 of 82 new substituted clitocine derivatives were synthesized in high quality as natural product mimic nucleosides on the semi-automated synthesizer. The polystyrene MMT-Cl resin was selected and utilized. The key intermediate resins 5 and 9 loaded with the corresponding scaffolds were prepared and validated with various amines before parallel synthesis. After a variety of amino building blocks were validated, 56 primary amines in 12 groups (building block set A) and 24 secondary amines in 3 groups (building block set B) were selected and utilized to combinatorialize the first and the second reactive sites on scaffold 5 for the synthesis of libraries L1-12. Eighty-two amines (building block set C) were utilized for the synthesis of clitocine library L13. Thirteen libraries of 1234 novel exocyclic amino nucleosides were all analyzed and characterized by high throughput LC-MS. 81.3-100% of the library members in 13 libraries show more than 60% purity, and 65.7-92.7% of the library members in these libraries show 80-100% purity. The strategy can be widely used for the synthesis of other diverse nucleoside libraries.     

ZrCl4 dispersed on dry silica gel provides a useful reagent for S-alkylation of thiols with alcohols under solvent-free conditions

ZrCl₄ which is commercially available and not a costly compound, is a relatively safe chemical [LD₅₀ [ZrCl₄, oral rat] = 1688 mg Kg]. In this report we describe the use of ZrCl₄ dispersed on dry silica gel as an efficient reagent for the efficient preparation of thioethers from thiols with alcohols under solvent-free conditions.     

Silicaphosphine (Silphos): a filterable reagent for the conversion of alcohols and thiols to alkyl bromides and iodides

Silicaphosphine (Silphos), [P(Cl)_3−n(SiO₂)_n], as a new heterogeneous reagent is introduced. This reagent converts alcohols and thiols to their corresponding bromides and iodides in the presence of X₂ (X=Br, I) in refluxing CH₃CN in high to quantitative yields. Use of Silphos provides a highly practical method for the easy separation of the Silphos oxide byproduct by a simple filtration.     

Solvent excess entropy at the electrode—solution interface

A model for water molecules in the double layer based upon information from gas-phase adsorption measurements has been used to calculate the configurational entropy of water in the double layer as a function of electric charge. The calculations agree well experimentally both in respect to dependence on charge and particularly in the position of the maximum entropy. The model can also be made consistent with the rest of the solvent excess entropy. The consistency between model and experiment favours models of capacitance humps which are not dependent upon water molecule orientation.     

Conversion of alcohols, thiols, and trimethysilyl ethers to alkyl cyanides using triphenylphosphine/2,3-dichloro-5,6-dicyanobenzoquinone/n-Bu(4)NCN

Triphenylphosphine and 2,3-dichloro-5,6-dicyanobenzoquinone afford an adduct, which in the presence of n-Bu(4)NCN converts alcohols, thiols, and trimethylsilyl ethers into their corresponding alkyl cyanides in good to excellent yields at room temperature. This method is highly selective for the conversion of 1 degrees alcohols in the presence of 2 degrees and 3 degrees ones, thiols and silyl ethers.     

Catalytic and chemoselective deprotection of S,S- and S,O-acetals and ketals in the presence of their O,O-analogs with electrophilic halogens under neutral conditions

A novel and catalytic method is described for the selective deprotection of S,S- and S,O-acetals and ketals in the presence of their O,O-analogs to their corresponding carbonyl compounds based on the use of N-bromosuccinimide (NBS), N-chlorosuccinimide (NCS), 2,4,4,6-tetrabromo-2,5-cyclohexadiene-1-one (TABCO), trichlorocyanuric acid (TCCA) or molecular bromine as sources of electrophilic halogens in the presence of DMSO as the source of oxygen in CHCl₃.