Evaluation of the immobilized artificial membrane phosphatidylcholine: Drug discovery column for high-performance liquid chromatographic screening of drug–membrane interactions

Chromatographic retention factors (k′) of a series of eight β-adrenoceptor antagonist compounds (β-adrenolytic drugs) were determined employing an immobilized artificial membrane column (IAM.PC.DD). The influence of mobile phase pH, ionic strength, and organic modifier composition was studied in order to examine column performance. After the IAM.PC.DD columns were exposed to approximately 7000 column volumes of a 0.01 M PBS mobile phase, five out of six columns tested showed significant peak broadening and decreased k′ values indicative of premature column failure. The data suggested that the immobilized phospholipids stationary phase was removed by the 0.01 M PBS mobile phase. The β-adrenolytic drug's log k′_IAM values obtained with an IAM.PC.DD column were compared to an ^esterIAM.PC.MG column for predicting drug membrane interactions. For the linear regression analysis between log k′_IAM and the logarithm of the n-octanol–water partition coefficients (r_IAM.PC.DD=0.8710 vs. r_IAM.PC.MG=0.9538), the C₁₈ HPLC retention factors (r_IAM.PC.DD=0.8408 vs. r_IAM.PC.MG=0.9380), the liposome partition coefficients (r_IAM.PC.DD=0.8887 vs. r_IAM.PC.MG=0.9187), and various pharmacokinetic parameters, significantly better correlations were obtained with the ^esterIAM.PC.MG column than the IAM.PC.DD column.     

硅胶基质固定相离子对反相液相色谱法测定强离解化合物的正辛醇/水分配系数

反相液相色谱(RPLC)是测定正辛醇/水分配系数(log P)的有效方法,但由于缺少同类型模型化合物,RPLC在测定强离解化合物的log P时遇到挑战。该文在硅胶基质C18色谱柱上,采用离子抑制反相液相色谱(IS-RPLC)和离子对反相液相色谱(IP-RPLC)分别对中性化合物、酚酸、羧酸、磺酸及部分两性化合物的保留行为进行了系统研究。在IS-RPLC模式下,利用中性化合物、弱离解的酚酸和苯羧酸作为模型化合物,建立了表观正辛醇/水分配系数(log D)与纯水相保留因子对数值(log k_w)的定量结构-保留行为关系(QSRR)模型,测定了19种离解化合物的log D值,作为后续IP-RPLC的模型化合物及验证化合物。在IP-RPLC模式下,将中性、弱离解和强离解化合物作为混合模型组,以溶质静电荷n_e、氢键酸碱性参数A和B为桥梁,建立了线性良好的log D-log k_w-IP模型,采用3种不同类型的离解化合物进行了外部验证实验,预测值误差低于10%,证实了模型的可靠性。在此基础上,预测了8种强离解化合物的log D_7.0值(pH 7.0条件下的log D值)。研究表明,利用结构相关参数沟通不同类型的模型化合物,是实现IP-RPLC测定强离解化合物log D值的一种行之有效的方法。与聚乙烯醇基质色谱柱相比,通用型的硅胶基质色谱柱上尽管存在着更多的次级作用,但可以为强离解化合物log D的测定提供更灵活的选择。     

High-performance liquid chromatographic separation of some 2- and 4-hydroxy derivatives of 2'-benzoylbenzoic acid on Florisil and silica gel columns

A series of 2'-benzoylbenzoic acid derivatives including some pairs of positional isomers and other related compounds were chromatographed by HPLC using a normal-phase system with polar adsorbents (Florisil and silica) and 2-propanol, 1,4-dioxane and tetrahydrofuran as modifiers of the eluent. The results obtained were compared as log k′_Florisil vs. log k′_silica relationships to ascertain the differences in distribution and chemical character of surface-active centres of the investifated adsorbents and the mechanism of elution in different eluent systems     

Trace-level determination of polar phenolic compounds in aqueous samples by high-performance liquid chromatography and on-line preconcentration on porous graphitic carbon

The use of porous graphitic carbon (PGC) was investigated for the trace enrichment and the on-line liquid chromatographic separation of polar phenolic compounds (phenol, di- and trihydroxybenzenes, aminophenols, etc.) from aqueous samples. Comparison between retentions obtained with PGC and with the copolymer-based sorbent PRP-1 showed similar variations of the capacity factors with the mobile phase composition, but an inverse retention order. The capacity factor of a very polar analyte, such as 1,3,5-trihydroxybenzene (phloroglucinol), is 1000 in pure water, whereas this analyte is not retained by C₁₈-silica and is poorly retained by PRP-1 (k′ = 3 in water). A precolumn packed with PGC can be coupled to a PGC analytical column for simple separation in the reversed-phase mode. This methodology has been applied to the direct determination of pyrocatechol, resorcinol and phloroglucinol below the 0.1 μg/1 level in a 50-ml sample.     

Magnetic susceptibility of 1,1′,2,2′-tetramethylcobaltocene and 1,1′-diethylcobaltocene: Evidence for the dynamic Jahn-Teller effect

The magnetic susceptibility of 1,1′,2,2′-tetramethylcobaltocene, Co[C₅H₃(CH₃)₂]₂, and 1,1′-diethylcobaltocene, Co(C₅H₄C₂H₅)₂, has been studied between 0.99 and 296 K. The data are well reproduced by a calculation of the dynamic Jahn-Teller effect for the ²E_1g(a_1g²e_2g⁴e_1g) ground state of D_5d symmetry. A suitable set of parameter values is given by ζ = 100 cm⁻¹, δ = 150 cm⁻¹, k_JT = 0.40, κ = 0.70. The magnetism of cobaltocene, Co(C₅H₅)₂, may be described by parameter values of comparable magnitude. The results imply a significantly larger reduction of the spin-orbit coupling parameter ζ due to covalency than of the orbital reduction factor κ.     

Reversed-phase high-performance liquid chromatographic separation of epimeric alkaloid N-oxides from Thalictrum simplex L.

A simple and precise method was developed for the analytical and preparative reversed-phase HPLC separation of a mixture of epimeric pavine N-oxides containing 49.1% of (−)-thalimonine N-oxide A and 50.1% of (−)-thalimonine N-oxide B isolated from Thalictrum simplex L. (Ranunculaceae). A reversed-phase system with Nucleosil C₁₈ analytical and preparative columns and ethanol-1.5% aqueous orthophosphoric acid (15:85) as the mobile phase was used. The epimeric pavine N-oxides were completely separated within 50 min.     

Studies on the long-term thermal stability of stationary phases in subcritical water chromatography

The long-term thermal stability of five commercially available reversed-phase columns has been evaluated under subcritical water conditions (100 and 150 degrees C). The five columns included Zorbax RX-C8, Nucleosil C18 AB, Hypersil BDS C18, PRP-1 (poly(styrene-divinylbenzene)), and ZirChrom-PS (polystyrene) columns. Retention factors, plate numbers, and peak areas were monitored over a prolonged period of time. Comparing the three silica-based columns, the Zorbax RX-C, column was the most stable followed by the Nucleosil C18, AB column. The Hypersil BDS C18 column was the least stable under subcritical water conditions. The ZirChrom-PS column was stable at 100 degrees C for at least 7600 column volumes. Of all five columns, the polymeric PRP-1 column was the most stable under subcritical water conditions.     

Capillary-electrochromatographic separations with copolymeric reversed-stationary phase and ion-exchanger-packed columns

A macroporous, spherical, 7 μm, polystyrene–divinylbenzene (PS–DVB), reversed-phase adsorbent (PRP-1) was evaluated as a stationary phase for the capillary electrochromatographic (CEC) separation of neutral, acidic, and basic analytes of pharmaceutical interest. Electroosmotic flow (EOF) for a PRP-1 packed capillary is nearly constant over the pH 2 to 10 range and is higher than for a silica-based C₁₈ packed capillary on the acidic side. EOF increases with an increase in buffer acetonitrile concentration or as applied potential increases. As analyte hydrophobicity increases, analyte retention and migration time increases. Increasing buffer acetonitrile concentration reduces analyte partitioning with the PS–DVB stationary phase and analyte retention and migration time decreases. When exchange sites are present on the PS–DVB copolymer, EOF (EOF is reversed for the anion-exchanger) increases as the exchange capacity increases. An increased exchange capacity also reduces partitioning of the analyte with the PS–DVB matrix and analyte retention and migration time decrease. Because of excellent stability in an acid environment, the PRP-1 packed capillary can be used in strong acid buffer solution and weak acid and base analytes depending on pK_a values can be separated as neutral species and cations, respectively. CEC separations on a PRP-1 capillary of neutral steroids, weak base pharmaceuticals (separation as cations), purines and pyrimidines (as cations), fatty acids (as undissociated species), and sulfa derivatives (as cations) are described. Efficiency for the PRP-1 packed capillary for acetone or thiourea as the analyte is about 6·10⁴ plates m⁻¹.     

Ethylene oligomerization by diimine iron(II) complexes/EAO

The catalytic properties of a series of Fe(II) diimine complexes (diimine=N,N′-o-phenylenebis(salicylideneaminato), N,N′-ethylenebis(salicylideneaminato), N,N′-o-phenylenebisbenzal, N,N′-ethylenebisbenzal) in combination with ethylaluminoxane (EAO) for ethylene oligomerization have been investigated. Treatment of the iron(II) complexes with EAO in toluene generates active catalytic systems in situ that oligomerize ethylene to low-carbon olefins. The effects of reaction temperature, ratios of Al/Fe and reaction periods on catalytic activity and product distribution have been studied. The activity of complex FeCl₂(PhCH=o-NC₆H₄N=CHPh) with EAO at 200°C is 1.35×10⁵ g oligomers/mol Fe·h, and the selectivity of C_4–10 olefins is 84.8%.     

Structural evolutions of the n-heneicosane and n-tricosane molecular alloys at 293 K

A structural study of odd-numbered n-alkane (C_n) binary mixtures (C₂₁ : C₂₃) was carried out on powder samples using a Guinier-de Wolff camera with increasing concentration of n-C₂₃ at 293 K.

Despite the reports in the literature, these molecular alloys do not form an orthorhombic continuous homogeneous solid solution to C₂₁ from C₂₃ at “low temperature”. Instead, as already observed in two even-numbered C_n systems, X-ray diffraction results show the existence of seven solid solutions as the molar concentration of C₂₃ increases: four terminal solid solutions, denoted β₀(C₂₁)β₀(C₂₃), isostructural with the “low temperature” phase of pure C₂₁ and C₂₃ (Pbcm), β′₀(C₂₁) and β′₀(C₂₃), identical to the phase β′₀ which appears in pure C₂₃ above the δ transition, and three orthorhombic intermediate solid solutions, designated β″₁, β′₁ and β″₂.

On the basis of powder X-ray photographs, the phases β″₁ and β″₂ (C₂₁ : C₂₃) are indistinguishable, and they are isostructural with the intermediate solid solution β″ of the even-numbered C_n binary systems (C₂₂ : C₂₄) and (C₂₄ : C₂₆). The phase β′₁(C₂₁ : C₂₃) is also isostructural with the two indistinguishable intermediate solid solutions β′₁ and β′₂ of the molecular alloys (C₂₂ : C₂₄) and (₂₄ : C₂₆).

From this study and our other laboratory results, the sequences of appearance of the solid solutions and the structural identities between these phases are established at “low temperature” for all the binary molecular alloys of consecutive C_n (odd-odd, even-even or odd-even: 19 < n < 27) when increasing the solute concentration.     

Exchange reactions of distibines

Distibines of the type R₂SbSbR′₂ with R = CH₃, R′ = C₂H₅ (1), R = CH₃, R′= n-C₃H₇ (2), R = CH₃, R′= C₆H₅ (3), R = C₂H₅, R′= C₆H₅ (4), R = n-C₃H₇, R′ = C₆H₅ (5), and R = CH₃, R′ = 2,4,6-(CH₃)₂C₆H₂ (6) are formed in equilibria by exchange reactions of the respective distibines of the type R₄Sb₂ and R′₄Sb₂.     

Conformational and structural analysis of N-N′-bis(4-methoxybenzylidene)ethylenediamine

The Schiff base compound, N-N′-bis(4-methoxybenzylidene)ethylenediamine (C₁₈H₂₀N₂O₂) has been synthesized and its crystal structure has been investigated by X-ray analysis and PM3 method. The compound crystallizes in monoclinic space group P2₁/n with a=10.190(1), b=7.954(1), c=10.636(1) Å, β=111.68(1)°, V=801.1(1) ų, Z=2 and D_cal=1.229 Mgm⁻³. The title structure was solved by direct methods and refined to R=0.056 for 2414 reflections [I>3.0σ(I)] by full-matrix anisotropic least-squares methods. The energy profile of the compound was calculated by PM3 method as a function of θ[N1′–C9′–C9–N1]. The most stable molecular structure of the title compound is the anti conformation, which is different in energy by 5.0 and 1.0 kcal mol⁻¹ from the eclipsed conformation I and gauche conformations, (III and V), respectively.     

Structural and spectral studies of N-2-(pyridyl)-, N-2-(3-, 4-, 5-, and 6-picolyl)- and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenylthioureas

Structures of the following compounds have been obtained: N-(2-pyridyl)-N′-2-thiomethoxyphenylthiourea, PyTu2SMe, monoclinic, P2₁/c, a=11.905(3), b=4.7660(8), c=23,532(6) Å, β=95.993(8)°, V=1327.9(5) ų and Z=4; N-2-(3-picolyl)-N′-2-thiomethoxyphenyl-thiourea, 3PicTu2SeMe, monoclinic, C2/c, a=22.870(5), b=7.564(1), c=16.941(4) Å, β=98.300(6)°, V=2899.9(9) ų and Z=8; N-2-(4-picolyl)-N′-2-thiomethoxyphenylthiourea, 4PicTu2SMe, monoclinic P2₁/a, a=9.44(5), b=18.18(7), c=8.376(12) Å, β=91.62(5)°, V=1437(1) ų and Z=4; N-2-(5-picolyl)-N′-2-thiomethoxyphenylthiourea, 5PicTu2SMe, monoclinic, C2/c, a=21.807(2), b=7.5940(9), c=17.500(2) Å, β=93.267(6)°, V=2893.3(5) ų and Z=8; N-2-(6-picolyl)-N′-2-thiomethoxyphenylthiourea, 6PicTu2SMe, monoclinic, P2₁/c, a=8.499(4), b=7.819(2), c=22.291(8) Å, β=90.73(3)°, V=1481.2(9) ų and Z=4 and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenyl-thiourea, 4,6LutTu2SMe, monoclinic, P2₁/c, a=11.621(1), b=9.324(1), c=14.604(1) Å, β=96.378(4)°, V=1572.4(2) ų and Z=4. Comparisons with other N-2-pyridyl-N′-arylthioureas having substituents in the 2-position of the aryl ring are included.     

胆固醇基键合相-反相高效液相色谱法测定正辛醇/水分配系数

通过反相高效液相色谱法系统地考察了中性和弱酸性化合物在新型胆固醇基键合相色谱柱（Cholester柱）上的保留行为。以甲醇和乙腈为有机调节剂,建立了保留因子（k）与有机调节剂比例（φ）间的关系,并外推获取100%水相为流动相时的log k_w;同时进一步建立并验证了不同流动相下正辛醇/水分配系数的对数（log K_ow）和log k_φ（log k_w）间的模型,并预测了部分化合物的log K_ow。结果表明,使用Cholester柱测定log K_ow时,甲醇比乙腈更适合作为有机调节剂;对中性化合物和中性状态的酸性化合物,可以用任意甲醇比例下获取的log k_φ预测log K_ow;对存在离解的酸性化合物,依然用外推方式获取的log k_w预测log K_ow。将采用Cholester柱与文献中采用C₁₈柱、C₈柱建立的log K_ow-log k_φ模型进行对比,结果表明化合物与胆固醇基键合相存在特别的作用。     

Spectroscopic and theoretical investigations on effective and selective complexation between porphyrins and fullerenes

We have tailored some interesting mono- and diporphyrins, viz., 5, 10, 15, 20-tetrakis(octadecyloxyphenyl)-21H,23H-porphyrin (TP), 5, 15-bis(3, 5-dioctylphenyl)-2, 8, 12, 18-tetramethyl-3, 7, 13, 17-tetradodecyl-21H,23H-porphyrin (AP) and 1, 3-bis(10′,20′-diundecyl-21′H,23′H-porphyrin-5′-yl)benzene (DP) as host molecules to study their complexation behavior with C₆₀ and C₇₀. Fluorescence spectroscopic measurements showed that emission of TP, AP and DP in toluene was quenched in the presence of C₆₀ or C₇₀. Large binding constants (K) in the magnitude of 1.5 × 10⁴ dm³ mol⁻¹ have been obtained for the 1:1 complexes of C₇₀ with TP, AP and DP. However, the C₆₀ complexes have exhibited 8.5 times smaller K compared to C₇₀ complexes. Ab initio theoretical calculations give a good support in favor of strong complexation between C₇₀ and porphyrins.     

Regioselective addition of protic acids to tricarbonyliron complexes of 2,3,5,6-tetrakis(methylene)-7-oxabicyclo[2.2.1]heptane. Crystal structure of (C10H10O)Fe2(CO)6

The main product of the thermal reaction between the title oxatetraene (I) and Fe₂(CO)₉ in ether/pentane is the bimetallic complex (C₁₀H₁₀O)Fe₂(CO)₆-diexo (II), which has C_2υ symmetry both in the solid state (X-ray analysis) and in solution. Whereas the protonation of the free ligand leads usually to polymerisation, the addition of a protic acid such as CF₃CO₂H to II proceeds cleanly at 0°C giving first a (η 3-allyl)Fe(CO)₃O₂CCF₃ complex (III). The intermediate III adds a second equivalent of acid in a slower step (k₂/k₁ = 0.1, CF₃CO₂D/CHCl₃, 0°C) giving the trans-bis(η³-allyl) isomer IV with high regioselectivity. The addition of CF₃CO₂D yields the corresponding deuteriomethylallyliron tricarbonyl trifluoroacetates III′ and IV′. No further deuterium incorporation is observed at 0°C, thus confirming the kinetic control of the regioselective double addition of protic acid to II.     

Ligand deprotonation significance in the formation of the molybdate ion-malic acid complexes

Using the temperature jump technique, the study of the kinetics of the complexing of oxomolybdate anion with malic acid has been carried out in aqueous solutions of pH 7.15–8.5 at ionic strength 0.1 M (KNO₃) and 25°'C. A reaction scheme for the formation of 1 : 1 complexes is proposed which accounts for the observed relaxation rates.

The significance of the ligand deprotonation on the complexation reaction of MoO₄²⁻ by a single protonated ligand, i.e. MoO₄²⁻+LH^nk→MoO₃(OH)Lⁿ⁻², (where n = 1 -, 2 -, etc), is analysed on the basis of a simple model. A linear correlation between the log k and the pK of the monoprotonated ligand (LH) is found for this reaction when the global process is controlled by the proton transfer from the ligand to an oxogroup, i.e. log k = a - 0.5xpK. It is found that this correlation is satisfied by MoO₄²⁻ and WO₄²⁻. The experimental slopes for these oxyanions are −0.503 and −0.543 respectively, in agreement with the predictions.     

High-performance liquid chromatographic analysis of hexosamines, hexosaminitols, N-acetylhexosamines and Nacetylhexosaminitols by ultraviolet and fluorescence detection at picomole levels

A simple and rapid method for the preparation of 9-fluorenylmethoxycarbonyl (Fmoc) derivatives of hexosamines (glucosamine, galactosamine), hexosaminitols (glucosaminitol, galactosaminitol), N-acetylhexosamines (N-acetylglucosamine, N-acetylgalactosamine) and N-acetylhexosaminitols (N-acetylglucosaminitol, N-acetylgalactosaminitol), is described. The derivatization was performed at room temperature for 5–10 min under neutral and slightly alkaline conditions. The separation of Fmoc-amino sugar and amino sugar alcohol derivatives on various reversed-phase columns (Cosmosil C₁₈, Sinopak-S C₈ and Develosil C₁₈) with isocratic elution was examined. The determination limits of hexosaminitol, N-acetylhexosamine, and N-acetylhexosaminitol derivatives were 0.4, 1.4 and 1.6 pmol with fluorescence detection and 4.6, 16 and 20 pmol with ultraviolet detection, respectively.     

Structural, spectral and thermal studies of N-2-(4-picolyl)- and N-2-(6-picolyl)-N′-(2-chlorophenyl)thioureas and N-2-(6-picolyl)-N′-(2-bromophenyl)thiourea

N-2-(4-picolyl)-N′-2-chlorophenylthiourea, 4PicTu2Cl, monoclinic, P2₁/c, a=10.068(5), b=11.715(2), β=96.88(4)°, and Z=4; N-2-(6-picolyl)-N′-2-chlorophenylthiourea, 6PicTu2Cl, triclinic, P-1, a=7.4250(8), b=7.5690(16), c=12.664(3) Å, =105.706(17), β=103.181(13), γ=90.063(13)°, V=665.6(2) ų and Z=2 and N-2-(6-picolyl)-N′-2-bromophenylthiourea, 6PicTu2Br, triclinic, P-1, a=7.512(4), b=7.535(6), c=12.575(4) Å, a=103.14(3), β=105.67(3), γ=90.28(4)°, V=665.7(2) ų and Z=2. The intramolecular hydrogen bonding between N′H and the pyridine nitrogen and intermolecular hydrogen bonding involving the thione sulfur and the NH hydrogen, as well as the planarity of the molecules, are affected by the position of the methyl substituent on the pyridine ring. The enthalpies of fusion and melting points of these thioureas are also affected. ¹H NMR studies in CDCl₃ show the NH′ hydrogen resonance considerably downfield from other resonances in their spectra.     

Bibracchial diazatetralactams. Structure and molecular modeling of calcium complexes

Doubly-armed diazatetralactams constitute a new series of easily synthesized tetralactams. The structural study of the calcium complexes of their N,N′-dimethyl acetamido and (2-pyridylmethyl) derivatives was performed by IR, ¹H, ¹³C NMR spectroscopies and molecular modeling. These complexes showed a C₂ symmetry and a high number (8–9) of coordination around the calcium atom.