Chromatographic investigation of the hydrophobic properties of isomeric naphthalene derivatives

Summary Selected isomeric α and β derivatives of naphthalene were semi-quantitatively compared in respect of their hydrophobic properties. Investigations were carried out by both adsorption and partition TLC chromatography; the solubilities of the individual substances in water were also determined. The results were explained of electronic and steric effects. Permanent dipole moments in terms (literature data) are also utilized to explain the comparatively weak hydrophobic properties of the β isomers as compared to the α isomers.     

Application of semi-permeable membrane dialysis/ion trap mass spectrometry technique to determine polybrominated diphenyl ethers and polychlorinated biphenyls in milk fat

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are hazardous food contaminants, their maximum legally allowable levels in food and environment are in the low pg g⁻¹ range. Therefore some highly selective and sensitive analytical methods must be used to determine them. The 96/23/EC Directive implemented by EC Decision of 12 August 2002 requires recovery rate of an analyte at a concentration below 1 ng g⁻¹ within the 50–120% range at relative standard deviation (RSD) as low as possible.     

Temperature dependence of Kováts indices in gas chromatography revisited

The performance of Fourier transform infrared spectroscopy (FT-IR) detection coupled to high-performance liquid chromatography for the analysis of C₆₀ and C₇₀ fullerenes was investigated. The isocratic separation method involved an octadecylsilane (ODS) column and an acetonitrile–toluene (1:1) mobile phase. The hyphenated system was designed with a split valve to control eluent volume leading to the FT-IR detector; this allowed for additional coupling of the liquid chromatograph to ultraviolet–visible detection. On-line FT-IR spectra of C₆₀ and C₇₀ were matched with standard off-line FT-IR spectra from the literature. In addition, with band chromatograms individual fullerenes can be identified using FT-IR active modes known specifically for each fullerene. Few changes to a pre-existing HPLC–UV method were necessary for the HPLC–FT-IR method, and there was no need for fraction collection to identify the fullerenes C₆₀ and C₇₀.     

Application of organolithium and related reagents in synthesis XVI: Synthetic strategies based on aromatic metallation. A concise regiospecific conversion of chlorobenzoic acids into their benzylated derivatives

Summary The reaction of benzyl bromide withbis-(N- and C-ortho)-lithiated chloroanilides4,5, and6 has been examined. It has been found that in the case where the lithiated compound was derived frommeta-methoxyanilides, pre-addition of LiBr orTMEDA was required to achieve C-benzylation. These results were accounted for by the conversion of the usually formed dimer into a mixed dimer with the LiBr orTMEDA complex in which the C-lithium bond appears to be more accessible towards electrophiles. The practical synthesis of -benzylchlorobenzoic acids10,11, and12 was accomplishedvia ionic reductive cleavage (Et₃SiH/TiCl₄) of the corresponding phthalides18,19, and20. The acids10,11b, and11c afforded the corresponding anthrones, upon treatment with trifluoroacetic anhydride which were oxidized by chromium trioxide to the new chloroantraquinones21,22, and23.

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Anwendung von Organolithium und verwandten Reagenzien in organischen Synthesen, 16. Mitt.: Synthesen mittels aromatischer Metallierung. Eine bequeme regiospezifische Umwandlung von Chlorbenzoesäuren in ihre Benzylderivate

Zusammenfassung Die Reaktion von Benzylbromid mit denbis-(N- und C-ortho)-lithiierten Chloraniliden4,5 und6 wurde untersucht. Im Falle lithiierter Verbindungen ausmeta-Methoxyaniliden ist die Zugabe von LiBr oderTMEDA während des Lithiierungsprozesses für die C-Benzylierung erforderlich. Diese Ergebnisse werden durch Umwandlung des gewöhnlich enstehenden Dimers in ein gemischtes Dimer mit dem LiBr- oderTMEDA-Komplex erklärt, in welchem die C-Li-Bindung für Elektrophile leichter zugänglich ist. Diese praktische Synthese dero-Benzylchlorbenzoesäuren10,11 und12 wird durch reduktive Spaltung der entsprechenden Phthalide18,19 und20 mit Et₃SiH/TiCl₄ ergänzt. Bei der Reaktion der Säuren10,11b und11c mit Trifluoressigsäureanhydrid entstehen die erwarteten Anthrone, die durch Oxidation mit Chromtrioxid in die neuen Chloranthrachinone21,22 und23 umgewandelt wurden.

     

TLC-Densitometric Analysis of p-Sitosterol in Pumpkin Seed Oil

JPC – Journal of Planar Chromatography – Modern TLC - A densitometric thin-layer chromatographic method has been established for quantitative determination of P-sitosterol in pumpkin...     

Phenolic acids in Peucedanum verticillare L. Koch ex Dc

JPC – Journal of Planar Chromatography – Modern TLC - Phenolic acids in the leaves, roots, and fruits of Peucedanum verticillare L. Koch ex Dc have been qualitatively determined for the...     

The comparison of hydrogen-bond dissociation of cis-9-octadecenoic acid and trans-9-octadecenoic acid in the inactive solvents by means of IR absorption spectroscopy

The comparison was made of the dissociation degree values for the hydrogen-bond multimers of two geometrical isomers: cis- and trans-9-octadecenoic acids. The measurements were performed for the series of solutions of the discussed substances in the inactive solvents: carbon tetrachloride and n-hexane. The applied technique was ir absorption spectroscopy. The general statement is that trans-9-octadecenoic acid in both carbon tetrachloride and n-hexane shows greater tendency towards dissociation of multimers than cis-9-octadeconoic acid.     

Friction force microscopy as an alternative method to probe molecular interactions

Friction force microscopy was applied to study protein-carbohydrate interactions that are important in many cellular recognition processes. The expression and structure of carbohydrates can be investigated using lectins as molecular probes since they recognize different types of sugar molecules. Lectins (concanavalin A and lentil lectin, recognizing mannose-type carbohydrates) were attached to the probing tip and carboxypeptidase Y (possessing complementary carbohydrates) was immobilized on a modified glass surface using microcontact printing. The results obtained from friction force maps and dependencies on the loading rate (measured in a physiological buffer) were divided in two distinct groups. The first group of results obtained for lectin-protein complexes was assigned to molecular recognition events, whereas the other including all control measurements was attributed to nonspecific interaction. All results presented here indicate that friction force microscopy can be successfully employed to study recognition processes.     

The difference in reactivity of (−)-mono and dimenthyl vs. diethyl alkylphosphonates in the α-lithiation reaction: Carbanionic synthesis of unknown (−)-dimenthyl 1-iodoalkylphosphonates and their first use in the radical iodine atom transfer addition (I-ATRA) and cyclisation (I-ATRC) reactions

Unknown (−)-dimenthyl and ethyl (−)-menthyl 1-iodoethylphosphonates were synthesized via 1-lithio derivatives in 85-87% yields. Starting (−)-dimenthyl alkylphosphonates (R = Me, Et, i-Pr) were obtained in the Michaelis-Becker reaction (75-81% yields) and/or in the methylation reaction of the corresponding 1-lithio-alkylphosphonates (78-92% yields). An interesting concentration and time correlations, never observed for diethyl alkylphosphonates, were found for the metalation of bulky (−)-menthyl alkylphosphonates with n-BuLi and general reaction conditions for the carbanion generation were elaborated. The first example of the I-ATRA reaction of (−)-dimenthyl 1-iodoethylphosphonate with 1-hexene (AIBN) gave four diastereomers (1.6:1:1:0.4), separated into two pairs. The I-ATRC reaction was not effective due to a steric hindrance around the reactive center. The X-ray analysis of (−)-dimenthyl methylphosphonate confirmed a considerable steric hindrance in higher (−)-dimenthyl alkylphosphonate esters in comparison to their diethyl analogs.