Coupling of narrow-bore liquid chromatography to thin-layer chromatography : Part I. Interfacing

The coupling of liquid chromatography (l.c.) on narrow-bore columns to thin-layer chromatography (t.l.c.) is described. The effluent from a l.c. column can be deposited on a t.l.c. plate after a normal-phase or reversed-phase separation without serious loss of chromatographic information. Both silica and alkyl-modified silica plates can be used for storage. The interface is a fused silica capillary which connects the column outlet to the spray jet assembly of a Linomat applicator for t.l.c. The stored chromatogram can serve as starting point for a new separation, but also allows the use of detection principles which are normally not compatible with l.c. The chromatography of some polynuclear aromatic hydrocarbons is used to illustrate the possibilities of the combinations.     

A novel synthesis of vinyl esters from vinylversatate-10

Vinylversatate-10 (VV10)¹ has successfully been used to synthesise a large number of lower vinyl esters by transvinylation in presence of mercuric acetate and sulfuric acid. The synthesis of vinylhalo esters proceeds with more difficulty. It has been observed that neither Hg(OAc)₂ nor H₂SO₄ alone is capable of initiating the transvinylation. Furthermore, it has been found that a molar ratio 2:1 of VV10 to carboxylic acid is sufficient to drive the reaction to the right by continuous distillation of the vinyl ester formed, and as a result a high yield of vinyl ester is obtained. A mechanism for this reaction and for the formation of side products has been proposed.     

Chemical ionization mass spectrometry of bifunctional cyclopentanes and cyclohexanes. A correlation between stereochemistry and chemical ionization spectra

A correlation has been fround between the stereochemistry of 3-methoxyeyclopentyl and 3-methoxyccyelohexyl acetic acid esters and their methane or isobutane themical ionizaion spectra: only the cis compounds yield quasimolecular ions and the [MH? CH₃OH]⁺ ions are more abundant for the trans isomers. A similar situation occurs in the iow temperature methane chemical ionization spectra of the coresponding trimethylsilylethers.     

Synthesis of Pyranthiones

A general method for the preparations of pyranthiones is particularly useful for preparing substituted xanthiones which are unavailable by established procedures. Reaction of a xanthone with p-tosyl isocyanate or with trichloroacetyl isocyanate produces the corresponding imino derivatives, which upon treatment with n-butylamine followed by hydrogen sulfide gives the desired xanthione in good yield.     

Substituent effects in π-(tricarbonylchromium)arenes: V. Thermodynamic dissociation constants of some substituted π-(tricarbonylchromium)benzoic acids

The thermodynamic dissociation constants of a series of 38 substituted π-(tricarbonylchromium)benzoic acids in 50% aqueous ethanol at 25°C have been determined. The results require revision of some literature values.The pK_a^*-values of the π-(tricarbonylchromium)benzoic acids were correlated with the electronic substituent parameters in terms of the Yukawa-Tsuno equation. The reaction constant (ρ) decreases from 1.4 for the benzoic acids to 0.8 for the π-(tricarbonylchromium)benzoic acids, reflecting the decreased ability of the complexed aromatic system to transmit electronic substituent effects. For the alkylsubstituted π-(tricarbonylchromium)benzoic acids, conformational effects of the Cr(CO)₃ group can account for some of the anomalies observed. The substituent parameters, σ_meta and σ_para, of the π-(Cr(CO)₃)phenyl group as a substituent were derived from the dissociation constants of the complexed phenylbenzoic acids.     

Covalent amination of 1-alkyl- and 1-aryl-3-carbamoylpyridinium chlorides as “model” for enzymic activity of rabbit liver aldehyde oxidase

The site of animation for 1-alkyl-3-carbamoylpyridinium chlorides in liquid ammonia is dependent on the identity of the 1-alkyl substituent. For the methyl, ethyl and n-propyl derivatives exclusively 6-adducts are found. Adduct formation takes place at C-6 and C-4, when the 1-substituent is an i-propyl or t-butyl group. The adduct ratio for the latter compounds is determined by the size of the substituent. 1-Aryl derivatives exhibit amination at C-2 and C-6 and the adduct ratios are dependent on the temperature. When the aryl substituent is a 2,4,6-trimethylphenyl group the 4-adduct is detected as well. A comparison is made between the sites of oxidation of these compounds by rabbit liver aldehyde oxidase and the covalent amination pattern in liquid ammonia. It is shown that covalent animation as a “model” for the enzymic activity of aldehyde oxide1 is particularly valuable in cases where the enzyme reaction is controlled by steric factors.     

Detection of a biomarker for Alzheimer's disease from synthetic and clinical samples using a nanoscale optical biosensor

A nanoscale optical biosensor based on localized surface plasmon resonance (LSPR) spectroscopy has been developed to monitor the interaction between the antigen, amyloid-beta derived diffusible ligands (ADDLs), and specific anti-ADDL antibodies. Using the sandwich assay format, this nanosensor provides quantitative binding information for both antigen and second antibody detection that permits the determination of ADDL concentration and offers the unique analysis of the aggregation mechanisms of this putative Alzheimer's disease pathogen at physiologically relevant monomer concentrations. Monitoring the LSPR-induced shifts from both ADDLs and a second polyclonal anti-ADDL antibody as a function of ADDL concentration reveals two ADDL epitopes that have binding constants to the specific anti-ADDL antibodies of 7.3 x 10(12) M(-1) and 9.5 x 10(8) M(-1). The analysis of human brain extract and cerebrospinal fluid samples from control and Alzheimer's disease patients reveals that the LSPR nanosensor provides new information relevant to the understanding and possible diagnosis of Alzheimer's disease.     

Reduction of Aldehydes and Ketones by Transition Metal Hydrides. Part 2. Reaction of trans,trans-[WH(CO)2(NO)(PMe3)2] with pyridine,functionalized aldehydes,and ketones

The reaction of trans,trans-[WH(CO)₂(NO)(PMe₃)₂] ( 1 ) with (pyridin-2-yl)-substituted aldehydes and ketones, (pyridin-2-yl)C(O)R where R = H, Me, Ph, pyridin-2-yl, and with 6-methylpyridine-2-carbaldehyde was studied. In all cases, facile insertion of the C?O bond into the W? H bond was observed, with rapid subsequent extrusionof a coordinated CO ligand affording O,N-bidentate coordinated tungsten alkoxides. Only in case of pyridine-2-carbaldehyde and di(pyridin-2-yl) ketone, the initial n¹ O-bonded insertion product could be observed as unstable intemediates by low-temperature NMR.     

Recovering a frame from its sheaves of algebras

Let

be a frame, α an element of

and T a finitary algebraic theory. In this paper we compare the category

of sheaves of T-algebras on

with the category Sh(α↓,T) of sheaves of T-algebras on α↓ (where α↓ is the initial segment {β|β<α}). This comparison suggests the definition of formal initial segments of the category

. For a large class of theories to be called ‘integral’ (examples of which are sets, monoids, groups, rings, modules on a integral domain, boolean algebras,hellip;) the formal initial segments of

coincide with the usual initial segments of

: this means that we are able to recover

axiomatically from

.When

is the initial frame {0, 1}, the frame of formal initial segments of

is the frame of open subsets of a compact space Spec T, called the spectrum of the theory T. When T is the theory of modules on some ring R, we recover in this way various well known notions of spectra and their corresponding sheaf-representation of the ring.