Indene and pseudoazulene discotic liquid crystals: a synthetic and structural study

Several new liquid-crystalline indene and pseudoazulene systems are reported. These molecules give rise to either columnar hexagonal mesophases and/or columnar plastic phases. The unique nature of these compounds stems from their non-classical discotic structure. Although the molecules have rigid aromatic cores, they lack terminal tails and instead the polarizable atoms (S, halogens) or polar groups (CN, CO) act as unusual soft parts. On the basis of many structurally related materials, we conclude that for this type of compound molecular stacking in the solid state is a prerequisite for the appearance of a columnar mesophase, although other intermolecular interactions within the layers are also important in establishing liquid-crystalline order. The behavior reported for these mesomorphic molecules opens up new possibilities in the search for related molecular interactions that might be useful for the construction of supramolecular architectures with particular properties.     

Reactivity of 2-deoxy-2-iodoglycosyl isothiocyanates with O-, S-, and N-nucleophiles. Synthesis of glycopyranoso-fused thiazoles

The reactivity of 2-deoxy-2-iodoglycosyl isothiocyanates toward O- and S-nucleophiles gives an easy access to 2-deoxy-2-iodoglycopyranosyl thiocarbamates and dithiocarbamates. Internal nucleophilic displacement of the iodine by the sulfur atom in these compounds allows the preparation of glycopyranoso[1,2-d]-1,3-thiazoles and glycopyranoso[1,2-d]-1,3-thiazolidin-2-one or -2-thione. Reaction with amines or polyamines as N-nucleophiles led directly to 2-aminoglycopyranoso[1,2-d]-1,3-thiazoles without isolation of the intermediate thioureas. Methyl 2-deoxy-2-iodoglycopyranosyl thiocarbamates also allow the synthesis of 2-deoxyglycopyranosyl thiocarbamates or 2-deoxy-2-iodoglycopyranosyl carbamates.     

The role of steric and electronic interactions in the stereocontrol of the asymmetric 1,3-dipolar reactions of 5-ethoxy-3-p-(S)-tolylsulfinylfuran-2(5H)-ones with diazoalkanes: theoretical calculations and experimental evidences

The addition of diazomethane and diazoethane to (5S,SS)- and (5R,SS)-5-ethoxy-3-p-tolylsulfinylfuran-2(5H)-ones (1a and 1b) and their 4-methylderivatives (2a and 2b) proceeded in almost quantitative yields and complete regioselectivity. The observed pi-facial selectivity is determined by the configurations at both C-5 and the sulfinyl group, the later being the most important. The syn adducts were almost exclusively obtained from 1a and 2a in apolar solvents but the pi-facial selectivity was strongly decreased in more polar solvents. On the other hand, the major adducts from 1b and 2b were the anti ones and such predominance was slightly increased with solvent polarity. The exo-selectivity was complete in all the cases except for the anti approach to compounds 2a (in polar solvents) and 2b. The role of the sulfinyl group in this behavior was inferred by comparison of these results with those obtained in reactions of diazoalkanes with 5-methoxyfuran-2(5H)-one (3). Steric interactions seem to be the main ones responsible for the observed exo selectivity of reactions with diazoethane, but electronic factors, which can be modulated by the solvent, are also significant in the pi-facial selectivity control. DFT computational methods are able to correctly predict the reactivity, regioselectivity, and pi-facial selectivity exhibited by 5-alkoxyfuranones as well as their changes with the solvent polarity. A C-H.O hydrogen bond, involving the oxygen atom of the 5-alkoxy group at dipolarophiles and the endo-hydrogen atom at dipoles, seems to play a key role in the electronic interactions influencing the stereochemical course of these reactions.     

Carboxylate anions binding and sensing by a novel tetraazamacrocycle containing ferrocene as receptor

A tetraazamacrocycle containing ferrocene moieties has been synthesized and characterized. The tetraprotonated form of this compound was evaluated as a receptor (R) for anion recognition of several substrates (S), Cl(-), PF(6)(-), HSO(4)(-), H(2)PO(4)(-) and carboxylates, such as p-nitrobenzoate (p-nbz(-)), phthalate (ph(2-)), isophthalate (iph(2-)) and dipicolinate (dipic(2-)). (1)H NMR titrations in CD(3)OD indicated that this receptor is not suitable for recognizing HSO(4)(-) and H(2)PO(4)(-), but weakly binds p-nbz(-), and strongly interacts with ph(2-), dipic(2-), and iph(2-) anions forming 1 : 2 assembled species. The largest beta(2) binding constant was determined for ph(2-), followed by dipic(2-) and finally iph(2-). The effect of the anionic substrates on the electron-transfer process of the ferrocene units of R was evaluated using cyclic voltammetry (CV) and square wave voltammetry (SWV) in methanol solution and 0.1 mol dm(-3)(CH(3))(4)NCl as the supporting electrolyte. Titrations of the receptor were undertaken by addition of anion solutions in their tetrabutylammonium or tetramethylammonium forms. The protonated ligand exhibits a reversible voltammogram, which shifts cathodically in the presence of the substrates. The data revealed kinetic constraints in the formation of the receptor/substrate entity for dipic(2-), ph(2-) and iph(2-) anions, but not for p-nbz(-). In spite of the slow kinetics of assembled species formation with the ph(2-) substrate, this anion provides the largest redox-response when the supramolecular entity is formed, followed by dipic(2-), iph(2-) and finally p-nbz(-) anions. This trend is in agreement with the (1)H NMR results and the values of the binding constants. Single crystal X-ray structures of the receptor with PF(6)(-), ph(2-), iph(2-) and p-nbz(-) were carried out and showed that supermolecules with a RS(2) stoichiometry are formed with the first three anions, but RS(4) with p-nbz(-). In all cases the binding occurs outside the macrocyclic cavity via N-H...O=C hydrogen bonds for carboxylate anions and N-H...F hydrogen bonds for the PF(6)(-) anion, which is in agreement with the solution results. The macrocyclic framework adopts different conformations in order to interact with each substrate having Fe...Fe intramolecular distances ranging from 10.125(14) to 12.783(15)A.     

High yield synthesis and reactivity of a phosphinidene bridged dimolybdenum complex

Protonation of [Mo2Cp2(mu-H)(mu-PHR*)(CO)4] (Cp = eta5-C5H5, R* = 2,4,6-C6H2tBu3) with HBF4.OEt2 gives the hydridophosphinidene complex [Mo2Cp2(mu-H)(mu-PR*)(CO)4]BF4, which is easily deprotonated with H2O to give the known phosphinidene complex [Mo2Cp2(mu-PR*)(CO)4] in 95% yield. Reaction of the latter with I2 gives the unsaturated phosphinidene complex [Mo2Cp2I2(mu-PR*)(CO)2], which exhibits an intermetallic distance of 2.960(2) A. Irradiation of solutions of [Mo2Cp2(mu-PR*)(CO)4] with UV light gives a mixture of the triply bonded [Mo2Cp2(mu-PR*)(mu-CO)2] and the hydridophosphido derivative [Mo2Cp2(mu-H){mu-P(CH2CMe2)C6H2tBu2}(CO)4] as major species. The latter complex results from an intramolecular C-H bond cleavage from a tBu group and has been characterized by spectroscopy and an X-ray study. Irradiation in the presence of HCC(p-tol) results in the insertion of the alkyne into the Mo-P bond to give [Mo2Cp2{mu-eta1:eta2,kappa-C(p-tol)CHPR*}(CO)4] structurally characterized through an X-ray study.     

Setting up of recovery profiles: A tool to perform the compliance with recovery requirements for residue analysis

The use of the recovery term has presented some confusion in Analytical Chemistry. Recent IUPAC recommendations propose to distinguish between two terms: recovery or recovery factor, ℜ, and apparent recovery, ℜ*. Apparent recovery includes recovery factor and a new recovery term proposed in this paper, named calibration recovery, ℜ^C, which depends of the type of systematic error due to the matrix effect (constant and/or proportional) and is related to the applied calibration methodology. This paper highlights the dependence of the calibration recovery on the sample analyte concentration and, for extension, of the apparent recovery, defines the recovery profile, and makes evident the need to determine a “fit for purpose” analyte concentration interval to comply with a regulated recovery requirements. An approach to estimate the calibration recovery and its associated uncertainty in relation to the above-mentioned dependence is presented. The usefulness of the proposed methodology has been shown in the quantification of a pesticide by GC-ECD for assessing dermal exposure.     

Structure of Low Temperature Phase b-Ba_3Y(BO_3)_3 Crystal

1 INTRODUCTION Recently the series of compounds M3Ln(BO3)3 (M = Sr, Ba and Ln = LaLu, Sc, Y) with space group P63cm or -3R have been reported[1～5], and some of them exhibit interesting optical properties when doped with the active Cr3+ or Yb3+ ions as laser materials. For example, Yb3+-doped Sr3Y- (BO3)3 crystal is a promising laser material for both tunable and femtosecond laser applications[6～8]. The Ba3Y(BO3)3 crystal melts congruently at 1256 ℃ and has a phase transitio…     

Synthesis of 4″-benzyloxyimino-4″-deoxyavermectin Bla derivatives

Six new 4″-benzyloxyimino-4″-deoxyavermectin Bla derivatives were synthesized from avermectin Bla by the selective protection of C-5-hydroxy group,oxidation of C-4″-hydroxy group,and deprotection followed by reaction with O-substituted hydroxylamine hydrochlorides.Their structures were confirmed by IR,~1H NMR,~(13)C NMR and MS.Insecticidal activities of the derivatives against Phopalosiphum pseudobrassicae,Spodoptera exigua and Pluteua xylosteua were evaluated.     

High performance liquid chromatography post-column chemiluminescence determination of sulfonamide residues in milk at low concentration levels using bis[4-nitro-2-(3,6,9-trioxadecyloxycarbonyl)phenyl] oxalate as chemiluminescent reagent

The determination of seven sulfonamides by means of HPLC with chemiluminescence detection is proposed for the first time. The analytes are derivatized with fluorescamine, separated and subsequently they participate in the post-column chemiluminescence (CL) peroxyoxalate system using imidazole as a catalyst. Among the different peroxyoxalates tested, bis[4-nitro-2-(3,6,9-trioxadecyloxycarbonyl)phenyl] oxalate provides higher sensitivities and stabilities, avoiding precipitation problems. A rigorous optimization of the significant variables by means of experimental designs has been developed in order to reconcile the chromatographic conditions with the CL reaction. The method provides detection limits in the low microgl(-1) range and has been satisfactorily applied to the analysis of spiked raw milk samples.     

Synthesis and Crystal Structure of 3,3,6,6-Tetramethyl-N-hydroxy-9-ethyl-1,8-dioxo-1,2,3,4,5,6,7,8,9,10-decahydroacridine

1 INTRODUCTION 1,4-Dihydropyridines (1,4-DHPs) are well-knowncompounds because of their pharmacological pro-perty as calcium channel modulators[1, . The che- 2]mical modifications, such as the introduction of dif-ferent substituents[3, or heteroatoms[5], of the DHP 4]ring have allowed the expansion of researches onthe structure-activity relationship to gain new in-sights into the molecular interactions at the receptorlevel. In fact, it is well established th…