Geometric view of the thermodynamics of adsorption at a line of three-phase contact

We consider three fluid phases meeting at a line of common contact and study the linear excesses per unit length of the contact line (the linear adsorptions Lambda(i)) of the fluid's components. In any plane perpendicular to the contact line, the locus of choices for the otherwise arbitrary location of that line that makes one of the linear adsorptions, say Lambda(2), vanish, is a rectangular hyperbola. Two of the adsorptions Lambda(2) and Lambda(3) then both vanish when the contact line is chosen to pass through any of the intersections of the two corresponding hyperbolas Lambda(2)=0 and Lambda(3)=0. There may be two or four such real intersections. It is found most surprisingly, and confirmed in a numerical example, that Lambda(1(2,3)), the adsorption of component 1 in a frame of reference in which the adsorptions Lambda(2) and Lambda(3) are both 0, depends on which intersection of the hyperbolas Lambda(2)=0 and Lambda(3)=0 is chosen for the location of the contact line. This implies that what had long been taken to be the line analog of the Gibbs adsorption equation is incomplete; there must be additional, previously unanticipated terms in the relation, consistent with the invariance of the line tension to choice of location of the contact line. It is then not Lambda(1(2,3)) by itself but a related expression containing it that must be invariant, and this invariance is also confirmed in the numerical example. The presence of the additional terms in the adsorption equation is further confirmed and their origin clarified in a mean-field density-functional model. The supplemental terms vanish at a wetting transition, where one of the contact angles goes to 0.     

Bending elasticity of charged surfactant layers: the effect of mixing

Expressions have been derived from which the spontaneous curvature (H(0)), bending rigidity (k(c)), and saddle-splay constant (k(c)) of mixed monolayers and bilayers may be calculated from molecular and solution properties as well as experimentally available quantities such as the macroscopic hydrophobic-hydrophilic interfacial tension. Three different cases of binary surfactant mixtures have been treated in detail: (i) mixtures of an ionic and a nonionic surfactant, (ii) mixtures of two oppositely charged surfactants, and (iii) mixtures of two ionic surfactants with identical headgroups but different tail volumes. It is demonstrated that k(c)H(0), k(c), and k(c) for mixtures of surfactants with flexible tails may be subdivided into one contribution that is due to bending properties of an infinitely thin surface as calculated from the Poisson-Boltzmann mean field theory and one contribution appearing as a result of the surfactant film having a finite thickness with the surface of charge located somewhat outside the hydrophobic-hydrophilic interface. As a matter of fact, the picture becomes completely different as finite layer thickness effects are taken into account, and as a result, the spontaneous curvature is extensively lowered whereas the bending rigidity is raised. Furthermore, an additional contribution to k(c) is present for surfactant mixtures but is absent for k(c)H(0) and k(c). This contribution appears as a consequence of the minimization of the free energy with respect to the composition of a surfactant layer that is open in the thermodynamic sense and must always be negative (i.e., k(c) is generally found to be brought down by the process of mixing two or more surfactants). The magnitude of the reduction of k(c) increases with increasing asymmetry between two surfactants with respect to headgroup charge number and tail volume. As a consequence, the bending rigidity assumes the lowest values for layers formed in mixtures of two oppositely charged surfactants, and k(c) is further reduced in anionic/cationic surfactant mixtures where the surfactant in excess has the smaller tail volume. Likewise, the reduction of k(c) is enhanced in mixtures of an ionic and a nonionic surfactant where the ionic surfactant has the smaller tail. The effective bilayer bending constant (k(bi)) is also found to be reduced by mixing, and as a result, k(bi) is seen to go through a minimum at some intermediate composition. The reduction of k(bi) is expected to be most pronounced in mixtures of two oppositely charged surfactants where the surfactant in excess has the smaller tail in agreement with experimental observations.     

Interpretation of light-scattering spectra in terms of particle displacements

Quasielastic light-scattering spectroscopy is regularly used to examine the dynamics of dilute solutions of diffusing mesoscopic probe particles in fluids. For probes in a simple liquid, the light-scattering spectrum is a simple exponential; the field correlation function g(1)(q,tau) of the scattering particles is related to their mean-square displacements X2 identical with [(delta x(tau))2] during tau via g(1)(q,tau) = exp(-1/2 q2X2). However, demonstrations of this expression refer only to identical Brownian particles in simple liquids and show that if the form is correct then it is also true for all tau that g(1)(q,tau) = exp(-gamma tau), a pure exponential in tau. In general, g(1)(q,tau) is not a single exponential in time. A correct general form for g(1)(q,tau) in terms of the X(2n), replacing the incorrect exp(-1/2 q2X2), is obtained. A simple experimental diagnostic determining when the field correlation function gives the mean-square displacement is identified, namely, g(1)(q,tau) only reveals X2 if g(1)(q,tau) is a single exponential in tau. Contrariwise, if g(1)(q,tau) is not a single exponential, then g(1)(q,tau) depends not only on X2 but on all higher moments X(2n). Corrections to the crude approximation g(1)(q,tau) = exp(-1/2 q2X2) closely resemble the higher spectral cumulants from a cumulant expansion of g(1)(q,tau).     

Investigation of some modes of flat-bed chromatography

A comparison of different chromatographic methods is presented: column liquid chromatography (CLC), thin layer chromatography (TLC), and continuous-elution flat-bed chromatography (CEFBC), which is in fact a combination of the first two methods. In CEFBC a sample is applied to a sorbent layer in a steady flow of eluent, and the components are detected directly on the layer, or immediately upon leaving it, during the separation process. It is shown that evaluation of the separation processes in CEFBC is best accomplished in terms of the parameters applicable in CLC. The reproducibility of the analytical results obtained by CEFBC is better than in the case of TLC by a factor of 6 to 10, and approaches that known for CLC.     

Influence of surface interactions on folding and forced unbinding of semiflexible chains

We have investigated the folding and forced unbinding transitions of adsorbed semiflexible polymer chains using theory and simulations. These processes describe, at an elementary level, a number of biologically relevant phenomena that include adhesive interactions between proteins and tethering of receptors to cell walls. The binding interface is modeled as a solid surface, and the wormlike chain (WLC) is used for the semiflexible chain (SC). Using Langevin simulations, in the overdamped limit we examine the ordering kinetics of racquet-like and toroidal structures in the presence of an attractive interaction between the surface and the polymer chain. For a range of interactions, temperature, and the persistence length, l(p), we obtained the monomer density distribution, n(x), (x is the perpendicular distance of a tagged chain end from the surface) for all of the relevant morphologies. There is a single peak in n(x) inside the range of attractive forces, b, for chains in the extended conformations, whereas in racquet and toroidal structures there is an additional peak at x approximately b. The simulated results for n(x) are in good agreement with theory. The formation of toroids on the surface appears to be a first-order transition as evidenced by the bimodal distribution in n(x). The theoretical result underestimates the simulated n(x) for x < b and follows n(x) closely for x >/= b; the calculated density agrees exactly with n(x) in the range x < b. The chain-surface interaction is probed by subjecting the surface structures to a pulling force, f. The average extension, x( f), as a function of f exhibits a sigmoidal profile with sharp all-or-none transition at the unfolding force threshold f = f(c) which increases for more structured states. Simulated x(f) compare well with the theoretical predictions. The critical force, f(c), is a function of l(s)/l(c) for a fixed temperature, where l(c) and l(s) are the length scales that express the strength of the intramolecular and SC-surface attraction, respectively. For a fixed l(s), f(c) increases as l(p) decreases.     

2-取代苯亚胺基噻唑烷类化合物的晶体结构研究

A series of 2-phenyliminothiazolidines has been successfully synthesized; and 2-(2-methylphenyl) iminothiazolidine (I a) and 2-(4-methylphenyl) iminothiazolidine (I b) have been selected to determine their crystal structures by X-ray diffraction technique,from their molecular graph of it is shown that double bond at 2-carbon atom of the heterocycle is all extro-cychc at the crystal state,and there are two main plaines in I a and I b.But in I a ,the angle between the planes is 61.4° and in I b the angle is about 41.4°.And so there is a strong conjugative effect in I b than in I a.So it is thought that the difference in fungicidal activities between 2-substitutedphenyl compounds (I a) and 4-substitutedphenyl compounds(I b) is due to their space factors.     

Effect of para substituents on the rate of bond shift in arylcyclooctatetraenes

The rate constants for bond shift (k(BS)) in phenylcyclooctatetraene (1b) and its p-nitro and p-methoxy analogues (1a and 1c, respectively) in THF-d(8) were determined by dynamic NMR spectrometry to be identical, but k(BS) is eight times greater at 280 K relative to 1b when the para substituent is cyclooctatetraenyldipotassium (2(2-)/2K(+)). These results are discussed in the context of (a) possible intrinsically small substituent effects (as determined by (13)C chemical shifts in the ground state (GS)) for 1a-c and (b) differences in steric interactions and resonance stabilization between the ground and BS transition state (TS). The latter factor was modeled by employing HF/3-21G(*) ab initio molecular orbital calculations of the GS and ring inversion TS. It is concluded that k(BS) is unchanged in 1a-c because the potentially greater pi interaction in the BS TS is counterbalanced by a greater degree of twist between the aryl and COT rings resulting from increased steric hindrance relative to the GS. However, pi interaction assumes a greater importance in the TS of 2(2-)/2K(+) owing to a decreased HOMO-LUMO energy gap compared to 1a-c, particularly when the counterions are solvated. This causes a decrease in the inter-ring twist angle and, together, these changes are responsible for the observed increase in k(BS) in 2(2-)/2K(+). The effect of substituents on a possible contribution of heavy atom tunneling to the reaction mechanism is also discussed.     

Revision of the dissociation energies of mercury chalcogenides--unusual types of mercury bonding.

Mercury chalcogenides HgE (E=O, S, Se, etc.) are described in the literature to possess rather stable bonds with bond dissociation energies between 53 and 30 kcal mol(-1), which is actually difficult to understand in view of the closed-shell electron configuration of the Hg atom in its ground state (...4f(14)5d(10)6s(2)). Based on relativistically corrected many body perturbation theory and coupled-cluster theory [IORAmm/MP4, Feenberg-scaled IORAmm/MP4, IORAmm/CCSD(T)] in connection with IORAmm/B3LYP theory and a [17s14p9d5f]/aug-cc-pVTZ basis set, it is shown that the covalent HgE bond is rather weak (2-7 kcal mol(-1)), the ground state of HgE is a triplet rather than a singlet state, and that the experimental bond dissociation energies have been obtained for dimers (or mixtures of monomers, dimers, and even trimers) Hg2E2 rather than true monomers. The dimers possess association energies of more than 100 kcal mol(-1) due to electrostatic forces between the monomer units. The covalent bond between Hg and E is in so far peculiar as it requires a charge transfer from Hg to E (depending on the electronegativity of E) for the creation of a single bond, which is supported by electrostatic forces. However, a bonding between Hg and E is reduced by strong lone pair-lone pair repulsion to a couple of kcal mol(-1). Since a triplet configuration possesses somewhat lower destabilizing lone pair energies, the triplet state is more stable. In the dimer, there is a Hg-Hg pi bond of bond order 0.66 without any a support. Weak covalent Hg-O interactions are supported by electrostatic bonding. The results for the mercury chalcogenides suggests that all experimental dissociation energies for group-12 chalcogenides have to be revised because of erroneous measurements.     

Decay of the peroxide intermediate in laccase: reductive cleavage of the O-O bond.

Laccase is a multicopper oxidase that contains four Cu ions, one type 1, one type 2, and a coupled binuclear type 3 Cu pair. The type 2 and type 3 centers form a trinuclear Cu cluster that is the active site for O(2) reduction to H(2)O. To examine the reaction between the type 2/type 3 trinuclear cluster and dioxygen, the type 1 Cu was removed and replaced with Hg(2+), producing the T1Hg derivative. When reduced T1Hg laccase is reacted with dioxygen, a peroxide intermediate (P) is formed. The present study examines the kinetics and mechanism of formation and decay of P in T1HgLc. The formation of P was found to be independent of pH and did not involve a kinetic solvent isotope effect, indicating that no proton is involved in the rate-determining step of formation of P. Alternatively, pH and isotope studies on the decay of P revealed that a proton enhances the rate of decay by 10-fold at low pH. This process shows an inverse k(H)/k(D) kinetic solvent isotope effect and involves protonation of a nearby residue that assists in catalysis, rather than direct protonation of the peroxide. Decay of P also involves a significant oxygen isotope effect (k(16)O(2)/k(18)O(2)) of 1.11 +/- 0.05, indicating that reductive cleavage of the O-O bond is the rate-determining step in the decay of P. The activation energy for this process was found to be approximately 9.0 kcal/mol. The exceptionally slow rate of decay of P is explained by the fact that this process involves a 1e(-) reductive cleavage of the O-O bond and there is a large Franck-Condon barrier associated with this process. Alternatively, the 2e(-) reductive cleavage of the O-O bond has a much larger driving force which minimizes this barrier and accelerates the rate of this reaction by approximately 10(7) in the native enzyme. This large difference in rate for the 2e(-) versus 1e(-) process supports a molecular mechanism for multicopper oxidases in which O(2) is reduced to H(2)O in two 2e(-) steps.     

Solubilization of triglycerides in liquid crystals of nonionic surfactant

The solubilization of triglycerides [1,2,3-tributanoylglycerol (TBG) and 1,2,3-trihexanoylglycerol (THG)] in water/octa(oxyethylene) dodecyl ether (C(12)EO(8)) systems has been investigated. Oil-induced changes in the structure of liquid crystals in water/C(12)EO(8) system have been studied by optical observation and small-angle X-ray scattering (SAXS) measurements. In the water/C(12)EO(8)/oil systems, solubilization of THG and TBG induces a transition between H(1) (hexagonal) and L(alpha) (lamellar) liquid crystals at high C(12)EO(8) concentrations, whereas at low surfactant concentrations a H(1)-I(1) (discontinuous micellar cubic phase) transition occurs. This anomalous behavior is attributed to the partitioning of solubilized oil in the micelles. At low surfactant concentrations THG is mainly solubilized into the hydrophobic cores of the surfactant micelles, indicating high swelling or low penetration tendency, resulting in a steep increase in the radius of the aggregates (r(H)), thereby inducing a rod-sphere transition. At high surfactant concentrations, THG is not mainly solubilized into the core but distributed between the palisade layer and the core of the aggregates. The TBG is considerably solubilized into the surfactant palisade layer, indicating a high penetration tendency, resulting in an increase in the effective cross-sectional area per surfactant molecule, a(s). The thermal stability of the I(1) phase increases with the solubilization of THG into the aggregate cores. The percentage deviation of the experimental interlayer spacings (P(d)) from complete swelling was also evaluated for different triglycerides in the H(1) and L(alpha) phases or different surfactant concentrations. It is found that the penetration tendency of triglycerides could be used as a tuning parameter for I(1) phase formation depending on the surfactant concentration and the molecular weight of the oil.     

Donnan Dialysis of Bromocomplexes of Some Platinum Group Metal Ions

Abstract

The separation of bromocomplexes of platinum group metals by Donnan dialysis is demonstrated with both anion and cation exchange membranes. the inclusion of ethylenediamine (en) in the sample improves the separation of Pd(II) from Pt(IV) with experiments performed with an anion exchange membrane and decreases the amount of metal retained on the membrane phase. With a cation exchange membrane, the addition of a ligand such as en is required for transport. With 5.6 mM en in the sample at pH 10, 74% of Pd(II) is transported across an anion exchange membrane into 0.5 M NH4Br after 6 hours while only 8% of the Pt(IV) is dialyzed. Rhodium(III) and iridium(III) behave like Pt(IV). Using a cation exchange membrane under the same conditions except with a 1 hour dialysis results in a 30-fold preferential preconcentration of Pd(II) relative to Pt(IV), and, based on the amount retained in the membrane, a preconcentration of Ir(III) which exceeds that of Pd(ll) and Pt(IV) by factors of 40 and 20, respectively.     

Dual fluorescence of syringaldazine

The absorption and fluorescence spectra of syringaldazine (SYAZ) has been recorded in solvents of different polarity, pH and beta-cyclodextrin (beta-CD) and compared with syringaldehyde (SYAL). The inclusion complex of SYAZ with beta-CD is investigated by UV-vis, fluorimetry, AM 1, FT-IR, (1)H NMR and scanning electron microscope (SEM). DeltaG value suggests the inclusion process is an exothermic and spontaneous. In all solvents a dual fluorescence is observed for SYAZ, whereas, SYAL shows a dual luminescence only in polar solvents. The excitation spectra for the 410 nm is different from 340 nm indicate two different species present in this molecule. In pH solutions: (i) a large red shifted maxima is observed in the dianion and is due to large interactions between the aromatic ring and (ii) the large blue shift at pH approximately 4.5, is due to dissociation of azine group and formation of aldehyde. beta-CD studies reveal that, SYAZ forms a 1:2 complex from 1:1 complex with beta-CD.     

Structural and energetic aspects of the protonation of phenol,catechol, resorcinol,and hydroquinone

The various protonated forms of phenol (1), catechol (2), resorcinol (3), and hydroquinone (4) were explored by ab initio quantum chemical calculations at the MP2/6-31G(d) and B3LYP/6-31G(d) levels. Proton affinities (PA) of 1-4 were calculated by the combined G2(MP2,SVP) method, and their gas-phase basicities were estimated after calculation of the change in entropy on protonation. These theoretical data were compared with the corresponding experimental values determined in a high-pressure mass spectrometer. This comparison confirmed that phenols are essentially carbon bases and that protonation generally occurs in a position para to the hydroxyl group. Resorcinol is the most effective base (PA = 856 kJ mol-1) due to the participation of both oxygen atoms in the stabilization of the protonated form. Since protonation is accompanied by a freezing of the two internal rotations, a significant decrease in entropy is observed. The basicity of catechol (PA = 823 kJ mol-1) is due to the existence of an intramolecular hydrogen bond, which is strengthened upon protonation. The lower basicity of hydroquinone (PA = 808 kJ mol-1) is a consequence of the fact that protonation necessarily occurs in a position ortho to the hydroxyl group. When the previously published data are reconsidered and a corrected protonation entropy is used, a proton affinity value of 820 kJ mol-1 is obtained for phenol.     

Control of the photocatalytic activity of bimetallic complexes of pyropheophorbide-a by nucleic acids

Photocatalytic activity of a photosensitizer (PS) in an oligodeoxyribonucleotide duplex 5'-PS~ODN1/ODN2~Q-3' is inhibited because of close proximity of a quencher Q. The ODN2 in this duplex is selected to be longer than the ODN1. Therefore, in the presence of a nucleic acid (analyte), which is fully complementary to the ODN2 strand, the duplex is decomposed with formation of an analyte/ODN2~Q duplex and a catalytically active, single stranded PS~ODN1. In this way the catalytic activity of the PS can be controlled by the specific nucleic acids. We applied this reaction earlier for the amplified detection of ribonucleic acids in live cells (Arian, D.; Cló, E.; Gothelf, K.; Mokhir, A. Chem.-Eur. J.2010, 16(1), 288). As a photosensitizer (PS) we used In(3+)(pyropheophorbide-a)chloride and as a quencher (Q)--Black-Hole-Quencher-3 (BHQ-3). The In(3+) complex is a highly active photocatalyst in aqueous solution. However, it can coordinate additional ligands containing thiols (e.g., proteins, peptides, and aminoacids), that modulate properties of the complex itself and of the corresponding bio- molecules. These possible interactions can lead to undesired side effects of nucleic acid controlled photocatalysts (PS~ODN1/ODN2～Q) in live cells. In this work we explored the possibility to substitute the In(3+) complex for those ones of divalent metal ions, Zn(2+) and Pd(2+), which exhibit lower or no tendency to coordinate the fifth ligand. We found that one of the compounds tested (Pd(pyropheophorbide-a) is as potent and as stable photosensitizer as its In(3+) analogue, but does not coordinate additional ligands that makes it more suitable for cellular applications. When the Pd complex was introduced in the duplex PS~ODN1/ODN2~Q as a PS, its photocatalytic activity could be controlled by nucleic acids as efficiently as that of the corresponding In(3+) complex.     

Generation of singlet oxygen from fragmentation of monoactivated 1,1-dihydroperoxides

The first singlet excited state of molecular oxygen ((1)O(2)) is an important oxidant in chemistry, biology, and medicine. (1)O(2) is most often generated through photosensitized excitation of ground-state oxygen. (1)O(2) can also be generated chemically through the decomposition of hydrogen peroxide and other peroxides. However, most of these "dark oxygenations" require water-rich media associated with short (1)O(2) lifetimes, and there is a need for oxygenations able to be conducted in organic solvents. We now report that monoactivated derivatives of 1,1-dihydroperoxides undergo a previously unobserved fragmentation to generate high yields of singlet molecular oxygen ((1)O(2)). The fragmentations, which can be conducted in a variety of organic solvents, require a geminal relationship between a peroxyanion and a peroxide activated toward heterolytic cleavage. The reaction is general for a range of skeletal frameworks and activating groups and, via in situ activation, can be applied directly to 1,1-dihydroperoxides. Our investigation suggests the fragmentation involves rate-limiting formation of a peroxyanion that decomposes via a Grob-like process.     

Density functional theory study of redox pairs: 2. Influence of solvation and ion-pair formation on the redox behavior of cyclooctatetraene and nitrobenzene

A study of the electrochemical behavior of cyclooctatetraene (COT) and nitrobenzene with Density Functional Theory and the conductor like solvation model (COSMO) is reported. The two-electron reduction of the tub-shaped COT molecule is accompanied by a structural change to a planar structure of D(4)(h)() symmetry in the first electron addition step, and to a fully aromatic structure of D(8)(h)() symmetry in the second electron addition step. Theoretical models are examined that are aimed at understanding the electrolyte- and solvent-dependent redox behavior of COT, in which a single 2e(-) redox wave is observed with KI electrolyte in liquid ammonia solution (DeltaDeltaE(disp) = [E(-2) - E(-1)] - [E(-1) - E(0)] < 0, inverted potential), while two 1e(-) redox waves are observed (DeltaDeltaE(disp) > 0) with NR(4)(+)X(-) (R = butyl, propyl; X(-) = perchlorate) electrolyte in dimethylformamide solution. In all cases, the computed reaction energy profiles are in fair agreement with the experimental reduction potentials. A chemically intuitive theoretical square scheme method of energy partitioning is introduced to analyze in detail the effects of structural changes and ion-pair formation on the relative energies of the redox species. The structural relaxation energy for conversion of tub-COT to planar-COT is mainly apportioned to the first reduction step, and is therefore a positive contribution to DeltaDeltaE(disp). The effect of the structural change on the disproportionation energy for COT is counteracted by the substantially more positive reduction potential for planar-(COT)(-1) in comparison to tub-(COT)(-1). Ion pairing of alkali metal counterions with the anionic reduction products gives rise to a negative contribution to DeltaDeltaE(disp) because the second ion-pairing step is more exothermic than the first, and the reduction of [KA] (A = COT, NB) is more exothermic than the reduction of A(-1). For COT, this negative energy differential term as a result of ion pairing predicts the experimentally observed inversion in the two 1e(-) potentials (DeltaDeltaE(disp) < 0). Nitrobenzene is treated with the same computational protocol to provide a system for comparison that is not complicated by the major structural change that influences the COT energy profile.     

Separation of actinides by means of HPLC

A procedure is described separating, identifying and determining the actinides (An) U, Np, Pu, Am and Cm in the presence of the lanthanides (Ln) La, Ce, Pr, Nd, Pm, Sm, Eu and Ho on an analytical scale. It is based on high-pressure liquid chromatography (HPLC) combined with a dual on-line detection system and is accomplished within a short time, in one step and under isocratic conditions (for An). The separation was carried out on a strongly acidic and highly capacitive cationic exchange resin on a polystyrene divinylbenzene copolymer (Aminex A9, co. BioRad) basis. Radionuclides emitting α- and β-particles are detected on-line using a custom-made solid scintillation flow-through cell. Inactive components are monitored by colour reagent complex detection (Arsenazo III, λ-648 nm) with a VIS detector placed in series.     

2-芳亚胺基噻唑烷类化合物的晶体结构研究

2-芳亚胺基噻唑烷类化合物具有良好的农用杀菌活性 [1] ,对于其双键异构问题 ,文献观点不一 [2 ,3] .另外 ,芳环上取代基的位置对化合物的杀菌活性影响较大 ,如苯环邻位甲基取代 ( a)及对位甲基取代 ( b)的化合物在 50 mg/L浓度时对某些致病菌的活性有较大差异 (见表 1 ) .本文以苯环上甲基取代的化合物为代表 ,测定了该类化合物的晶体结构 .Table1　Fungicidal activity( % ) of a and b( Dose:50 mg/L)Com pd. Gibberella zeae Phoma asparagi Cercospora beticola Alternaria solani Physalospora piricola a 6 0 .0 6 3.6 5 3.3 2 …     

A novel spectrophotometric method for the determination of aminophylline in pharmaceutical samples in the presence of methanol

A rapid, simple and sensitive method for the determination of aminophylline (Ami) using sodium 1, 2-naphthoquine-4-sulfonate (NQS) and methanol is established in this paper. It is based on the fact that a russety product can be formed by the reaction between aminophylline (Ami) and sodium 1, 2-naphthoquine-4-sulfonate (NQS) in pH 13.00 buffer solution. When methanol is added to the solution, the sensitivity of the color development reaction between Ami and NQS is improved, and the color of the system of NQS-Ami becomes a salmon pink. Beer's law is obeyed in a range of 4.97-69.5 microg ml(-1) of Ami at the maximum absorption of 453 nm (epsilon=4.87 x 10(3) l mol(-1) cm(-1)). The linear regression equation of the calibration curve is A=0.14458+0.00832C (microg ml(-1)), with a linear regression correlation coefficient of 0.9944. The detection limit is 0.7 microg ml(-1) (3sigma/k), R.S.D. is 1.1% and the recovery rate is in range of 92.5-105%. Furthermore, this method has been successfully applied to the determination of Ami in pharmaceutical samples.