A comparative study of several HPLC methods for determining free amino acid profiles in honey

A study of the viability of three derivatizing reagents for obtaining amino acid profiles in honey through high performance liquid chromatography (HPLC) is presented. A method using diode array detection based on a reaction with diethyl ethoxymethylene malonate (DEMM) and two other methods using fluorescence detection based on derivatization with fluorenylmethyl chloroformate (FMOC-Cl) and 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) have been developed. The three methods yield detection limits close to the ppb level, but vary in relation to other analytical characteristics. The use of methyl chloroformate derivatives allows the profile to be obtained with the greatest sensitivity within a short time frame. On applying such methods to honey samples of diverse botanical origin, we observe that the proline values obtained are always lower than those found using the official spectrophotometric method, thereby underlining the advisability of using HPLC methods to reduce uncertainty in these results.     

Transition metal methylene complexes : III. Methylene (CH2), a carbonyl analogous ligand; crystal structure of μ-methylenebis(carbonyl-η5-cyclopentadienylrhodium)(Rh—Rh

μ-Carbonylbis(carbonyl-ν⁵-cycopentadienylrhodium)(Rh—Rh) reacts with N-methyl-and N-ethyl-N-nitrosourea in boiling benzene to yield the dinuclear, diamagnetic, neutral rhodium complexes μ-methylene- (A) and μ-ethylidenebis(carbonyl-η⁵-cyclopentadienylrhodium)(Rh—Rh) (B), respectively. Deuterium labelled experiments prove the origin of the metal-stabilized methylene ligand to be the alkyl group of the organic precursor. This new method of preparation of transition metal—methylene complexes may be used as an alternative to the commonly used diazo method; the latter method was shown to work with diazodiethylmalonate and dicarbonyl-η⁵-cyclopentadienylrhodium, the reaction yielding μ-bis(ethoxycarbonyl)methylenebis(carbonyl-η⁵-cyclopentadienylrhodium)(Rh—Rh).Compound A crystallizes in the triclinic system, P$\text{1}$, and with cell constants of a 803.42(5), b 909.98(6), c 938.81(2) pm, α 74.402(3), β81.923(3), and γ 83.685(6)°. The unit cell volume and the calculated density are 651.6 ų and 2.069 g cm^-3, for one molecule in the asymmetric unit. The molecular geometry of μ-CH₂[η⁵-C₅H₅Rh(CO)]₂ was established from 2718 unique reflections collected with a computer-controlled diffractometer and refined to a final R(F) = 0.0379. The molecular parameters derived from the single-crystal X-ray study conform to a remarkable degree with those found for μ-CO[η⁵-C₅H₅Rh(CO)]₂. Thus, the bridging ligands CH₂ and CO seem to be analogous in their effects on the structural characteristics of the molecular framework of the two molecules.     

Structural studies on a novel reaction product of malononitrile with aβb,δ-unsaturated allene aldehyde

Condensation of 2,5,5-trimethylhexa-2,3-dien-6-a1 with malononitrile affords an unexpected product, C₁₅H₁₆N_4X, ($\text{3}$), the structure of which was partially characterized by spectral (infrared, ultraviolet, ¹H, and ¹³C nmr) methods and fully elucidated by single crystal X-ray analysis. $\text{3}$ is l-cyano-2-amino-3-(2-propenyl)-5,5-dimethy-6- dicyanomethycycohexa-l,3-diene in a half-chair conformation. Conjugation of the $\text{cis}$-aminocyanoethenyl moiety leads to intermolecular

hydrogen bonding in the crystal. A reaction sequence and its mechanistic implications are proposed.     

The stereochemistry of organosulfur compounds. XIX. The crystal and molecular structure of 10-(1,3-dithiolan-2-ylidene)-10H-indeno[1,2-f]-1,2,3,4,5-pentathiepin

The molecular structure of 10-(1,3-Dithiolan-2-ylidene)-10H-indeno[1,2-f] -1,2,3,4,5-pentathiepin S₇C₁₂H₈₉ has been determined by single crystal X-ray diffraction. The crystals are triclinic, space group PI, with two molecules in a unit cell of dimensions α = 8.931(2), b = 9.387(2), c = 10.175(2) Å, α = 75.73(2), β = 73.35(1), γ = 64.37(2)°. The structure was solved by direct methods, and refined to a final R value of 3.3% for 1925 independent reflections. The molecule consists of an indene core with a nearly co-planar dithiolane and a fused pentasulfide chain. The S₅C₂ ring is in the chair configuration, with an average S? S distance of 2.052 Å. There is no variation of bond lengths as is frequently seen in multi-sulfur chains. The indenone ring shows no evidence of any delocalization, while the dithiolane ring is disordered at the two methylene positions. No attempt was made to resolve the disorder, since it is frequently seen and has been thoroughly investigated previously.     

Determination of rotenone residues in raw honey by solid-phase extraction and high-performance liquid chromatography

A method for determining residues of the insecticide rotenone in raw-honey by high-performance liquid chromatography (HPLC) is described. To extract the residues, organic solvents such as ethyl acetate, n-hexane/dichloromethane and solid-phase extraction with octadecylsilane cartridges or Florisil packed columns were tested. Determination was carried out by reversed-phase HPLC using acetonitrile-buffer phosphate (pH 7) (60:40, v/v) as mobile phase and detection at 210 nm. Although the data showed that the two extraction methods were able to isolate the pesticide residues, the extraction on octadecylsilane cartridges was preferred due to its simplicity and higher recovery. Recoveries depended strongly on the fortification level for the two extraction procedures. Practical determination limits of 0.015 mg/kg were obtained. In the analysis of honeys, from beehives treated with rotenone at therapeutical doses for 1 month, residual amounts below 0.2 mg/kg were found.