Determination of histamine and some other amines by high-performance capillary electrophoresis with on-line mode in-capillary derivatization

We have developed a method for the determination of histamine (His), tyramine (Tyr) and cadaverine (Cad) using high-performance capillary electrophoresis with fluorescence detection and an on-line mode in-capillary derivatization with o-phthalaldehyde (OPA)/N-acetylcysteine (NAC) as derivatization reagent. HPCE separation of His, Tyr, Cad and Spermidine (Spd) was influenced by sodium dodecyl sulfate (SDS) and phosphate–borate buffer (pH 10) concentration. After optimization of the method, a 4-component amine solution containing His, Tyr, Cad and Spd could be separated and detected by using 2 mM OPA/NAC–20 mM SDS–20 mM phosphate–borate buffer (pH 10) as a run buffer at an applied voltage of 25 kV, with detection at 340 nm. Although a practical sensitivity level can be obtained by using fluorescence detection (λ_ex=340 nm, λ_em=450 nm) instead of ultraviolet–visible detection, Spd was not detected at all. The precision (relative standard deviation; n=15) of this method for within- and between-days is less than 2.9% (peak area) and 1.3% (migration time), respectively. Linearity for these analytes, except for Spd, was established over a concentration range of 0.02 to 1.00 μmol/ml and detection limits (S/N=3) range from 1 nmol/ml for His and Tyr to 5 nmol/ml for Cad. The determination of His and some amines in aging raw fish meat samples (room temperature, 48 h) was carried out using the described method with fluorescence detection.     

2-(6,7-Dimethoxy-2,3-Naphthalimido)ethyl Trifluoromethanesulfonate as a Labeling Reagent for Carboxylic Acids in Liquid Chromatography

A new, highly reactive and sensitive labeling reagent, 2-(6,7-dimethoxy-2,3-naphthalimido)ethyl trifluoromethanesulfonate, (6,7-DMNE-OTf), has been synthesized and used to determine several carboxylic acids by high-performance liquid chromatography. Reactions of the reagent with long-chain, saturated monocarboxylic acids proceed to completion within 5 min in acetone at room temperature in the presence of 18-crown-6 as a catalyst. The acid derivatives could be readily eluted with acetonitrile-water (90:10). The detection limits (signal-to-noise RATIO = 3) with ultraviolet and fluorescence detection are 10 fmol (λ_max = 282 nm) and 3 fmol (λ_ex = 282 nm, λ_em = 456 nm), respectively.     

Synthesis of N-Fmoc 3-(4-(di-(tert-butyl)phosphonomethyl)phenyl)pipecolic acid as a conformationally constrained phosphotyrosyl mimetic suitably protected for peptide synthesis

Phosphonomethylphenylalanine (Pmp, 2) has shown wide utility as a hydrolytically stable phosphtyrosyl (pTyr, 1) mimetic, particularly in Src homology 2 (SH2) domain-binding peptides. (2S,3R)-3-(4-(phosphonomethyl)phenyl)pipecolic acid (3) represents a variant of Pmp having φ and χ₁ torsion angles constrained through incorporation into the piperidinyl ring structure contained within pipecolic acid. Reported herein is the enantioselective preparation of 3, in an orthogonally protected form (4) suitable for use in peptide synthesis. Stereochemistries at both the 2- and 3-positions are derived inductively from a single chiral center provided by the commercially available Evans chiral auxiliary, (4S)-4-benzyl-1,3-oxazolidin-2-one. Incorporation of 4 into a Grb2 SH2 domain-directed tripeptide (18) showed that Grb2 SH2 domain-binding affinity was reduced relative to the parent Pmp-containing tripeptide (19). Although conformational constraint did not enhance affinity in this case, novel amino acid analogue 4 may serve as a useful tool for the induction of defined phosphotyrosyl geometry in peptides directed at other signal transduction targets.     

Luminescent properties of carbon-rich starburst gold(I) acetylide complexes. Crystal structure of [TEE][Au(PCy3)]4 ([TEE]H4=tetraethynylethene)

Two carbon-rich starburst gold(I) acetylide complexes [TEE][Au(PCy₃)]₄ (3, [TEE]H₄=tetraethynylethene) and [TEB][Au(PCy₃)]₃ (6, [TEB]H₃=1,3,5-triethynylbenzene) were prepared and their UV–vis absorption, emission and excitation spectra have been recorded. In fluid CH₂Cl₂ solutions, 3 exhibits prompt ¹(ππ*) fluorescence with λ_0–0 and λ_max at 413 and 428 nm, respectively, while 6 displays ³(ππ*) phosphorescence with λ_0–0 and λ_max at 446 and 479 nm, respectively. The crystal structure of 3·CH₂Cl₂ has been determined.     

A simple method for predicting the frequency of the infrared inactive carbonyl stretching mode in LM(CO)5 molecules with C4V symmetry

The paper presents a new method for predicting the frequency of the b₁ mode, which is infrared-inactive, in complexes of the type LM(CO)₅ belonging to C_4V point group. The method was based on the relation λ₃=λ₄+[(1−δ/δ)](λ₁−λ₂), where δ=(λ₁−λ₂)/(λ₁−λ₂+λ₃−λ₄), λ₁, λ₂, λ₃ and λ₄ are the λ parameters of the , , b₁ and e modes, respectively. For a large numbers of complexes of the type LM(CO)₅ the average value of δ was found to be 0.80, with a standard deviation of 0.02. With the use of average value of δ, the frequencies of b₁ mode were estimated. The result obtained indicated that there exists a rather good fit between observed and calculated frequencies, with a mean error of 2.7 cm⁻¹. In addition, it was shown that the δ parameter can be used as a criterion of the correct band assignment for the complexes understudy.     

Determination of rhodamine 123 by sequential injection technique for pharmacokinetic studies in the rat placenta

The sequential injection (SIA) technique was applied in pharmacokinetic studies of the transporter-mediated passage of a model substrate, rhodamine 123 (Rho123), through the dually perfused rat term placenta. The method described was used for real-time monitoring of Rho123 concentrations in both the maternal and fetal compartments. Determination was processed by fluorescence detection (λ_ex=480 nm, λ_em580 nm); calibration curve was linear over the range 0.01–50 μmol l⁻¹ (r=0.99965), detection limit was 10 nmol l⁻¹ (3σ) and RSD2% (10 readings). Transport of Rho123 was scanned under various conditions (ATP-synthesis inhibition) and several inhibitors of P-glycoprotein transporter were tested (e.g. quinidine). The advantages of the modern SIA method—an automated analytical tool providing both fast and precise analysis—were successfully demonstrated for examination of transport profiles to investigate the effect of P-glycoprotein on the placental transfer of Rho123.     

cis,cis-Spiro[4.4]nonane-1,6-diol: A new chiral auxiliary for the asymmetric Diels-Alder reaction

The use of a mono-pivalate mono-acrylate bis-ester of (+)-1S,5S,6S-spiro[4.4]nonane-1,6-diol in an asymmetric Diels-Alder reaction with cyclopentadiene (2 equiv. BCl₃, −85°C, CH₂Cl₂) provided the expected endo bicyclo adduct in >97% de. Iodolactonization of the bicyclo adduct provided the (+)-lactone (5) with a 1S,4S,6S,8R,9S configuration (97% ee). The de's obtained from using various types and amounts of Lewis acids, and both chiral and racemic bis-esters in the Diels-Alder reaction with cyclopentadiene are also reported.     

Novel glassy nematic and chiral nematic oligomers derived from 1,3,5-cyclohexanetricarboxylic and (1R,3S)-( )-camphoric acids

Novel nematic and chiral nematic liquid crystals capable of vitrification have been synthesized using 1,3,5-cyclohexanetricarboxylic and (1R,3S)-(+)-camphoric acids as the base structures to which cyanotolan, cyanobiphenyl, methoxybiphenylbenzoate nematogenic groups, (S)-(-)-1-phenylethylamine and (S)-(+)-1,3-butanediol chiral moieties are attached. Once the glassy state is induced by quenching or controlled cooling from the isotropic state, these liquid crystals showed no detectable tendency towards crystallization upon heating through the glass transition temperature. In all cases, the ΔC_p and ΔH_c values resulting from the DSC heating scans are comparable to those previously reported for polymer analogues and other low molar mass glassy liquid crystals. In the nematic series with varying spacer lengths, both T_g and T_c are consistently lower than the linear polymer counterparts, in contrast to the siloxane-based systems. It was also demonstrated that cholesteric mesomorphism can be induced following one of the three approaches: chiral nematic mixture, chiral nematic cyclic cooligomer, and pendant nematogenic groups attached to a chiral ring.     

A comparison of ferroelectric liquid crystals containing diastereomeric propionic acids derived from natural ethyl lactate

Two diastereomeric carboxylic acids, 2(S)-[2(R)-methylhexyloxy]propionic acid and 2(S)[2(S)-methylhexyloxy]propionic acid, were prepared from ethyl (S)-lactate and (R)-1-iodo2-methylhexane or (S)-1-iodo-2-methylhexane in the presence of Ag₂O. From these acids two liquid crystals, 2 and 3 , whose configurations are (S , R ) and (S, S) were synthesized and their liquid crystal properties investigated. Although both LCs have the same phase sequence Cr-SmC*-N*-I as well as a wide SmC* phase range, the influence of the relative stereochemistry on their physical properties is clear. The liquid crystal with (S, S)-configuration possesses better properties: lower SmC* phase transition temperature, wider SmC* phase range and higher P_s value. The P_s value difference between the ferroelectric LCs 2 and 3 (97 and 131nCcm^-2, respectively, at T_c - T = 10°C) is unexpectedly large. The consideration, alone, of a zigzag conformation at the chiral molecular part of 2 and 3 is insufficient to explain such a difference.     

Enantioselective organic syntheses using chiral transition metal complexes V. (2S,3S)-Bis(dibenzophospholyl)butane, a rigid (S,S)-CHIRAPHOS analog

The P–Ph cleavage of phenyldibenzophosphole (1) with lithium in THF gives lithium dibenzophospholide (2). Reaction of 2 with ethyleneglycol ditosylate produces the known chelate ligand 1,2-bis(dibenzophospholyl)ethane (3) in good yield. Similarly, 2 and (2R,3R)-butanediol ditosylate give the new chiral chelate ligand (2S,3S)-bis(dibenzophospholyl)butane (4). Ligand exchange of [CpRu(PPh₃)₂Cl] with 3 or 4 yields the halfsandwich complexes [CpRu(C₁₂H₈PC₂H₄PC₁₂H₈)Cl] (5) and [CpRu((S,S)-C₁₂H₈PCHMeCHMePC₁₂H₈)Cl] (6). Complex 6 was characterized crystallographically (monoclinic, space group P2₁ (no. 4), a=820.6(4), b=1501.0(3), c=1172.8(6) pm, β=108.87(2)°, V=1.367(1)×10⁹ pm³, Z=2). The most conspicuous feature of the structure of 6 is the perfect coplanarity of the two dibenzophosphole moieties imposed by their steric interaction with the Cp ligand. Complex 6 and the thiophene complex [CpRu((S,S)-C₁₂H₈PCHMeCHMePC₁₂H₈)(SC₄H₄)]BF₄ (7) derived therefrom are remarkably unreactive with regard to ligand substitutions. A possible explanation is the lack of intramolecular

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–C stabilization en route to the transition state of ligand substitution. The enantiomeric purity of 6 and 7 could nevertheless be demonstrated by conversion to diastereomerically pure [CpRu((S,S)-C₁₂H₈PCHMeCHMePC₁₂H₈)((S)-CNCHMePh)]BF₄ (8).     

Structural and spectroscopic properties of Hexamethylenetetramine cobalt(II) complex: [Co(NCS)2(hmt)2(H2O)2][Co(NCS)2(H2O)4] (H2O)

Synthesis, structure, spectroscopy and thermal properties of complex [Co(NCS)₂(hmt)₂(H₂O)₂][Co(NCS)₂(H₂O)₄] (H₂O) (I), assembled by hexamethylenetetramine and octahedral Co(II) metal ions, are reported. Crystal data for I: F_w 387.34, a=9.020(8), b=12.887(9), c=7.95(1) Å, =96.73(4), β=115.36(5), γ=94.16(4)°, V=820(1) Å³, Z=2, space group=P−1, T=173 K, λ(Mo-K)=0.71070 Å, ρ_calc=1.718567 g cm⁻³, μ=17.44 cm⁻¹, R=0.088, R_w=0.148. An interesting two-dimensional network is assembled via hydrogen bonds through coordinated and free water molecules. The d–d transition energy levels of Co(II) ion are determined by UV–vis spectroscopy and calculated by ligand field theory. The calculated results agree well with experiment ones.     

Ferroelectric liquid crystal materials synthesized from 2(S)-[2(S)-methylbutyloxy]propanol

A new chiral alcohol, 2(S)-[2(S)-methylbutyloxy]propanol (3), containing two chiral centres has been synthesized from ethyl lactate and (S)-1-iodo-2-methylbutane. It was used as a chiral building block for the preparation of ferroelectric liquid crystal materials. Several of the new materials exhibit an enantiotropic S*_c phase with a wide temperature range. The results indicate that the molecular structure of 3 is useful for synthesizing ferroelectric liquid crystal materials.     

黄豆黄素与黄豆黄苷吸收光谱和荧光光谱的比较研究

研究了黄豆黄素和黄豆黄苷在不同pH条件下的吸收光谱和荧光光谱, 从分子结构的角度解释了二者呈现不同光谱特征的原因. 黄豆黄素分子基本无荧光. 在弱碱性时, 黄豆黄素分子发生7-OH质子的电离, 导致吸收光谱中320 nm的吸收峰红移至348 nm. 采用pH-光度法测得7-OH质子的电离常数pK_a1=7.08±0.04. 黄豆黄素一价阴离子呈现较强荧光, 最大激发和发射波长λ_ex/λ_em分别为334 nm/464 nm, 荧光量子产率为0.049. 在碱性溶液中, 黄豆黄素4'-OH质子电离, 导致吸收光谱中254 nm的吸收峰红移至260 nm, 电离常数pK_a2=9.96±0.01. 黄豆黄苷分子基本无荧光. 在碱性条件下, 黄豆黄苷分子的4'-OH质子发生电离, 导致吸收光谱中256 nm的吸收峰红移至 280 nm, 电离常数pK_a=9.81±0.03. 黄豆黄苷阴离子基本无荧光, 但在热碱性条件下发生γ-吡喃酮环裂解反应而产生较强荧光, λ_ex/λ_em为288 nm/388 nm, 裂解产物的荧光量子产率为0.056. 虽然, 黄豆黄苷与黄豆黄素是苷与苷元的关系, 但黄豆黄苷不能在热碱性条件下通过糖苷水解转变为黄豆黄素, 二者的荧光增强机理存在本质不同.     

A triple helical calcium-based coordination polymer with strong blue fluorescent emission

A hydrothermal reaction of 1,3-dicyanobenzene and Ca(OH)₂ yielded a triple helical calcium-based coordination polymer of the formula, C₂₀H₂₅Ca_2.50O_18.50 (1). The 1,3-benzenecarboxylate anion, found in the final product was generated in situ during the synthesis by the hydrolysis of 1,3-dicyanobenzene. X-ray diffraction study shows that the complex 1 crystallizes in the monoclinic system, C2/c space group, a=15.5701(5), b=21.4445(7), c=17.1601(6) Å, β=111.7400(7)°, V=5322.1(3) Å³, Z=8, D_c=1.651 Mg/m³. The calcium atoms show differences in the coordination environments. Complex 1 emits strong blue fluorescent light (λ_em(max)=419 nm) when it is excited by UV light (λ_ex(max)=316 nm) in the solid state at room temperature.     

Synthesis, characterization and reactivity of tetracyclopentadienylniobium(IV), a precursor to organometallic derivatives of niobium(IV)

In toluene as medium, tetra(cyclopentadienyl)niobium(IV), NbCp₄, has been prepared in satisfactory yields from the reaction of NaCp with: (a) Nb₂C1₁₀, (b) NbCl₄(THF)₂, or (c) NbCp₂Cl₂. Tetracyclopentadienylniobium(IV) has been characterized by X-ray diffraction. Crystal data: C₂₀H₂₀Nb, M=353.29 g mol⁻¹, hexagonal, space group P6₅ (no. 170), a=b=9.396(2), c=31.23(3) Å, V=2388(2) ų, Z=6, d_calc=1.48 g cm⁻³, λ(Cu–K)=1.54184 Å, T=291 K, μ=62.04 cm⁻¹, F(000)=1686. Two of the four cyclopentadienyl ligands are bonded to niobium in a pentahapto fashion, the other two being monohapto. NbCp₄ undergoes cyclopentadiene elimination in the presence of species containing active protons such as Ph₃SiOH or strong acids, the products being tris- or biscyclopentadienyl compounds depending on the molar ratio of the reagents.     

Synthesis of a novel copper(II) complex and its crystal structure

One novel chiral copper(II) complex was successfully synthesized from the reaction of chiral 1,3-thiazolidine-2-thione ligand with CuCl₂ in dichloromethane in the presence of Et₃N and DMAP at room temperature. Its unique crystal structure was unambiguously disclosed by X-ray analysis. The crystal is tetragonal, space group I4(1), space group a=15.0875(11), b=15.0875(11), c=19.362(3) Å, =90, β=90, γ=90°, V=4407.4(8) ų, Z=8, ρ_calc=1.639 mg cm⁻³.     

Preparation, crystal structure, absolute configuration, and conformational analysis of (−)436-(S)-(−)-diphenyl-1-phenylethylaminophosphine(η-pentamethylcyclopentadienyl)-dimethylphosphonato)cobalt(III)

Reaction of CpCoI₂(P(OMe)₃) 8 with the chiral aminophosphine (S)-(−)-diphenyl-phenylethylaminophosphine affords the diastereomeric phosphonate complexes (R,S)_Co,S_C-CpCoI(P(0)(OMe)₂)(PPh₂NHCH(Me)Ph) (10a,10b) via Arbuzov dealkylation. 10a,10b are separable and configurationally stable in solution for extended periods. The structure and absolute configuration of the lower R_f diastereomer (−)-₄₃₆-10b were determined via single-crystal X-ray diffraction. It crystallizes as a toluene solvate in space group P2₁ with a 13.194(6), b 9.062(4), c 17.023(5) Å, β 108.78(3)°, Z = 2, and was refined to R = 0.067 for 6318 reflections. Spectroscopic and structural evidence demonstrate a strong 1,6 intramolecular NH O=P hydrogen bond between the aminophosphine NH and the basic phosphoryl oxygen, which establishes a quasi-boat conformation. Proton nuclear Overhauser difference spectra show that the conformation in solution is the same as that observed in the solid state.     

Fluorescence properties of domperidone and its determination in pharmaceutical preparations

The native fluorescence characteristics of domperidone in various solvents and at different pH values are reported. The fluorophore is the benzo-1,3-diazolin-2-one group which is also present in the analogous benperidol, droperidol and pimozide molecules from which domperidone is derived; the substituent may therefore be considered as a relatively strong fluorophore; its excitation and emission maxima are little influenced by pH variation. Domperidone can be determined in pharmaceutical preparations by its native fluorescence in ethanol (λ_ex = 283 nm ;λ_em = 324 nm) and in 0.01 M HCl (λ_ex = 284 nm;λ_em = 329 mn) with a detection limit of 0.01 μg ml^-1.     

Synthesis of Pt compounds containing chiral (2S,4S) -pentane-2,4-diyl-bis(5H-dibenzo[b]phosphindole) as ligand and their use in asymmetric hydroformylation of styrene derivatives

Unlike bis(diphenyl)phosphine derivatives in general, (2S,4S)-pentane-2,4-diyl-bis(5H-dibenzo[b]phosphindole), S,S-BDBPP, gives a trans oligomeric compound [PtCl₂(S,S-BDBPP)]_n, 1, in reaction with dichloro-Pt precursors such as PtCl₂(PhCN)₂, PtCl₂(CH₃CN)₂ and PtCl₂(COD) at room temperature. Compound 1, which could be readily isolated, slowly rearranges in solutions at room temperature to the expected cis-monomer PtCl₂(S,S-BDBPP), 3. Heating or the presence of PtCl₂(COD) accelerates the transformation of compound 1 to 3. SnCl₂ adducts of both compounds, trans-[PtCl(SnCl₃)(S,S-BDBPP)]_n, 2, and cis-PtCl(SnCl₃)(S,S-BDBPP), 4, as well as the known cis-PtCl(SnCl₃)(S,S-BDPP), 5, (S,S-BDPP = (2S,4S)-2,4-bis(diphenylphosphino)pentane) have been tested as catalysts in the asymmetric hydroformylation of p-isobutylstyrene. The phenyl analog 5 provides up to 75% e.e. but moderate yields to chiral 2-(4-isobutylphenyl)-2-propanal. Compared to this, the regioselectivity to the branched aldehyde is remarkably increased; however, the enantioselectivity is drastically decreased by the use of both dibenzophosphole derivatives 2 and 4. The similarities in the selectivities provided by 2 and 4 indicate that the trans oligomer 2 transforms to the cis-monomer 4 during the catalytic process. X-ray crystal structure determination of compound 3 shows a half-chair conformation for the chelate ring with a symmetric arrangement of dibenzophosphole groups. Besides a preference for the latter achiral conformation, the planar structure of the dibenzophosphole groups can also be considered as reason for the moderate enantioselectivities provided by 4.     

Structure of liquid 1-chloronaphthalene at 293 K

The structure of 1-chloronaphthalene, C₁₀H₇–Cl, at 293 K was investigated using the X-ray diffraction method. Monochromatic radiation MoK (λ=0.71069 Å) enabled the determination of the scattered radiation intensity between S₀=4πsin ₀/λ=0.430 Å⁻¹ and S_max=14.311 Å⁻¹. The interpretation of the results was carried out using the reduction method of Blum and Narten. Experimental distributions of X-ray scattered intensity were compared with theoretical results predicted for a proposed model of 1-chloronaphthalene molecule. The electron-density radial-distribution function was calculated and some intra- and intermolecular distances in liquid 1-chloronaphthalene were determined. X-ray structural analysis was applied to determine the packing coefficient of 1-chloronaphthalene molecules.