New methods for the preparation of 1-phenyl-trans-cyclohexane-1,2-diol

In contrast with previous reports, it was found that the reaction of 1-phenylcyclohexene with peroxyformic acid is not entirely stereospecific, but gives some trans-1-phenylcyclohexane-1, 2-diol (IV) beside the cis-isomer (III). The reaction of 1-phenylcyclohexene oxide (II) with formic acid yielded a similar mixture of III and IV, while addition of trichloroacetic acid in benzene was entirely cis-stereospecific. Reaction of the epoxide II with potassium hydroxide took place only under very drastic conditions to give a small yield of III, while sodium 2-dimethylaminoethoxide added exclusively in a trans way, leading to the amino ether X, which was easily transformed into the trans-glycol IV. The latter compound was also the main product of the borohydride reduction of 2-hydroxy-2-phenylcyclohexanone (IX). Possible explanations of the observed stereochemical results are discussed.     

Ratios between content of fatty acids as markers for mixture of cow and goat milk

The fat of mixture of goat and cow milk, extracted by di-ethylic ether, was gas chromatographically analysed in order to propose an analytical procedure suitable to reveal small additions of cow milk to goat milk. The obtained results show evident differences in the percentages of some fatty acids. An attempt to apply the peak area ratios, corresponding to the methyl esters of fatty acids, suggested by the literature for cow milk did not yield good results. Other ratios suitable to reveal even the presence of low percentages (up to 5 %) of cow milk in goat milk were found and proposed in this paper. Such ratios are sensitive and can be defined markers towards cow or goat milk and also towards extraneous fat like lard or colza seeds oil.     

Conductometric determination of quaternary ammonium salts by sodium perchlorate and vice versa

A conductometric method is proposed for the determination of quaternary ammonium salts (chloride or bromide), based on the poor solubility of the relative perchlorates. A comparison between expected and found values shows that the method is suitable, rapid, and easy for quantities in the range from 0.2 to 5 g. The error depends on the solubility of the relative perchlorate. The apparent and tentative solubility product of the studied compounds were calculated. The obtained values allowed to propose benzyltributyl ammonium chloride (BTBA Cl) as precipitant for the conductometric titration of perchlorate. This easy, rapid and accurate determination can be used to analyze the perchlorate ion even in concentrated solutions and to determine stability constants for complex formation in aqueous solutions. Received: 11 June 1997 / Revised: 8 October 1997 / Accepted: 11 October 1997     

Conductometric determination of quaternary ammonium salts by sodium perchlorate and vice versa

A conductometric method is proposed for the determination of quaternary ammonium salts (chloride or bromide), based on the poor solubility of the relative perchlorates. A comparison between expected and found values shows that the method is suitable, rapid, and easy for quantities in the range from 0.2 to 5 g. The error depends on the solubility of the relative perchlorate. The apparent and tentative solubility product of the studied compounds were calculated. The obtained values allowed to propose benzyltributyl ammonium chloride (BTBA Cl) as precipitant for the conductometric titration of perchlorate. This easy, rapid and accurate determination can be used to analyze the perchlorate ion even in concentrated solutions and to determine stability constants for complex formation in aqueous solutions.     

An Investigation of Complexation of Cadmium(II) with Arginine

Among amino acids, arginine is important in human physiology because it plays an important role in cardiovascular and depression problems. In this paper the behavior of arginine as a ligand toward cadmium(II) [Cd(II)] in two different ionic media: 1.00 mol·dm^?3 NaCl and NaClO₄, is studied. Knowledge of the species formed between Cd(II) and arginine in a wide concentration range is useful also in biology. This system was investigated using two different methods in two ranges of hydrogen ion concentration. In acidic solutions, electromotive force measurements are performed using glass and Cd amalgam electrodes. In basic solutions, polarography was used and the shift of the half wave potential was measured as a function of the ligand concentration. The experimental data obtained in NaCl solutions are explained by assuming the formation of the species [CdL], [CdHL], [CdL₂], [CdHL₂] and [CdH₂L₂]. The data obtained in NaClO₄ solutions are explained by assuming the formation of the species [CdL], [CdHL], and [CdH₂L₂]. In both cases the stability constants are reported.     

Laser-Induced Azomethine Ylide Formation and Its Covalent Entrapment by Fulleropyrrolidine Derivatives During MALDI Analysis

Two novel monofunctionalized fulleropyrrolidine derivatives (Prato adducts) were prepared and characterized by matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI). MALDI experiments conducted in the positive-ion mode on pure and mixed samples of both monofunctionalized fullerene derivatives revealed the efficient formation of bisadducts (in the case of the pure samples) and mixed bisadducts (in the case of a mixed sample). Bisadducts were not observed in the ESI experiments and thus not present in the sample. A mechanism for the MALDI formation of these bisadduct ions is proposed in which an azomethine ylide fragment is formed in situ from the monofunctionalized fulleropyrrolidine species upon laser irradiation. This fragment, which can survive as an intact moiety in the gas phase in the special environment provided by the MALDI experiment, is then able to attach to a fulleropyrrolidine monoadduct which acts as a dipolarophile, thus leading to the formation of a bisadduct fullerene derivative. The unprecedented re-attachment of the azomethine ylide implies that the establishment of the ligand attainment of Prato adducts based on MALDI analysis alone can lead to wrong assignments.

A Review on Coordination Properties of Al(III) and Fe(III) toward Natural Antioxidant Molecules: Experimental and Theoretical Insights

This review focuses on the ability of some natural antioxidant molecules (i.e., hydroxycinnamic acids, coumarin-3-carboxylic acid, quercetin, luteolin and curcumin) to form Al(III)- and Fe(III)-complexes with the aim of evaluating the coordination properties from a combined experimental and theoretical point of view. Despite the contributions of previous studies on the chemical properties and biological activity of these metal complexes involving such natural antioxidants, further detailed relationships between the structure and properties are still required. In this context, the investigation on the coordination properties of Al(III) and Fe(III) toward these natural antioxidant molecules might deserve high interest to design water soluble molecule-based metal carriers that can improve the metal’s intake and/or its removal in living organisms.     

On‐Surface Synthesis and Characterization of Triply Fused Porphyrin–Graphene Nanoribbon Hybrids

On‐surface synthesis offers a versatile approach to prepare novel carbon‐based nanostructures that cannot be obtained by conventional solution chemistry. Graphene nanoribbons (GNRs) have potential for a variety of applications. A key issue for their application in molecular electronics is in the fine‐tuning of their electronic properties through structural modifications, such as heteroatom doping or the incorporation of non‐benzenoid rings. In this context, the covalent fusion of GNRs and porphyrins (Pors) is a highly appealing strategy. Herein we present the selective on‐surface synthesis of a Por–GNR hybrid, which consists of two Pors connected by a short GNR segment. The atomically precise structure of the Por–GNR hybrid has been characterized by bond‐resolved scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc‐AFM). The electronic properties have been investigated by scanning tunneling spectroscopy (STS), in combination with DFT calculations, which reveals a low electronic gap of 0.4 eV.