The effect of the nature of the surfactant on the location of 6-R-2,2,4-trimethyl-1,2-dihydroquinolines in micelles

The locus of solubilization of 6-R-2,2,4-trimethyl-1,2-dihydroquinoline molecules (R=Me, OEt) in sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) has been determined by comparing the UV spectra of micellar solutions of the dihydroquinolines and their solutions in solvents of various polarities. The parameterR _pv (defined as the ratio of the absorbance of the long-wave band maximum to that at the adjacent valley) decreases with an increase in the solvent polarity in the order:n-heptane > 2-propanol > ethanol > H₂O. In SDS micellar solutions,R _pv is close to the corresponding value in water and does not depend on [SDS]. In CTAB micellar solutions,R _pv is essentially greater than in water and increases with [CTAB]. Thus, the solubilized dihydroquinoline molecules in SDS micelles reside in the Stern layer, and in CTAB micelles they are located both in the interior of the micelle and in the Stern layer; in this case the micelle packing begins from the core.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 948–950, May, 1994.     

Micellar Catalysis of Composite Reactions II. The Effect of CTAB Micelles on the Alkaline Fading of Malachite Green

The alkaline fading of malachite green, which is interpreted as parallel first order and second order reactions, has been studied in cetyltrimethylammonium bromide (CTAB) micellar solution at 25°C using spectrophotometry. A micellar catalytic model is proposed in this paper for constant concentration of hydroxideion. For this model, the first order and the second order rate constants in CTAB micellar phase,k_1m and k_2m have been obtained.

The experimental results indicate that the first order reaction of malachite green cation with water is catalysed by CTAB micelles while the second order reaction of malachite green cation with hydroxide ion is inhibited by CTAB micelles. The first order rate constant in CTAB micellar phase, k_1m , is 210 times of that in the bulk phase, but the second order rate constant in CTAB micellar phase, k_2m , is 0. 166 time of that in the bulk phase. The results are interpreted mostly in relation to the micellar micropolarity and electrostatic interaction. @Keywords: Micelle, Micellar catalysis, Parallel first order and seond order reactions, Malachite green     

THE EFFECT OF SURFACTANT MICELLES ON THE ALKALINE HYDROLYSIS OF DIMETHYLFORMAMIDE

The alkaline hydrolysis of dimethylformamide has been studied at 40'C in micellar solutions of single surfactant (CTAB. SDS. Brij 35) with the analog thermoanalytical curve method of thermokinetics. A kinetic equation of micellar catalysis under the condition of highter reactant concentration than micellar concentration ([S]>[M]) has been derived from the pseudophase model of micellar catalysis and some relative assumptions, The kinetic parameters. k_m, k_2mand the association constant of reactant with micelle K₁, have been calculated in this way. the results indicate that these surfactant micelles exhibit catalytic effect on the reaction. This is attributed to the micropolarity and local concentration effect of micelles.     

Reactivity and Operational Stability of N‐Tailed TAMLs through Kinetic Studies of the Catalyzed Oxidation of Orange II by H2O2: Synthesis and X‐ray Structure of an N‐Phenyl TAML

The catalytic activity of the N‐tailed (“biuret”) TAML (tetraamido macrocyclic ligand) activators [Fe{4‐XC₆H₃‐1,2‐( N COCMe₂ N CO)₂NR}Cl]^2? ( 3 ; N atoms in boldface are coordinated to the central iron atom; the same nomenclature is used in for compounds 1 and 2 below), [X, R=H, Me ( a ); NO₂, Me ( b ); H, Ph ( c )] in the oxidative bleaching of Orange II dye by H₂O₂ in aqueous solution is mechanistically compared with the previously investigated activator [Fe{4‐XC₆H₃‐1,2‐( N COCMe₂ N CO)₂CMe₂}OH₂]^? ( 1 ) and the more aggressive analogue [Fe(Me₂C{CON(1,2‐C₆H₃‐4‐X) N CO}₂)OH₂]^? ( 2 ). Catalysis by 3 of the reaction between H₂O₂ and Orange II (S) occurs according to the rate law found generally for TAML activators (v=k_Ik_II[Fe^III][S][H₂O₂]/(k_I[H₂O₂]+k_II[S]) and the rate constants k_I and k_II at pH 7 both decrease within the series 3 b > 3 a > 3 c . The pH dependency of k_I and k_II was investigated for 3 a . As with all TAML activators studied to‐date, bell‐shaped profiles were found for both rate constants. For k_I, the maximal activity was found at pH 10.7 marking it as having similar reactivity to 1 a . For k_II, the broad bell pH profile exhibits a maximum at pH about 10.5. The condition k_I?k_II holds across the entire pH range studied. Activator 3 b exhibits pronounced activity in neutral to slightly basic aqueous solutions making it worthy of consideration on a technical performance basis for water treatment. The rate constants k_i for suicidal inactivation of the active forms of complexes 3 a – c were calculated using the general formula ln([S₀]/[S_∞])=(k_II/k_i)[Fe^III]; here [Fe^III], [S₀], and [S_∞] are the total catalyst concentration and substrate concentration at time zero and infinity, respectively. The synthesis and X‐ray characterization of 3 c are also described.     

Hydrophobic N‐Diazeniumdiolates and the Aqueous Interface of Sodium Dodecyl Sulfate (SDS) Micelles

Zwitterionic diazeniumdiolates of the form RN[N(O)NO^?](CH₂)₂NH₂⁺R, where R=CH₃ ( 1 ), (CH₂)₃CH₃ ( 2 ), (CH₂)₅CH₃ ( 3 ), and (CH₂)₇CH₃ ( 4 ) were synthesized by reaction of the corresponding diamines with nitric oxide. Spectrophotometrically determined pK_a(O) values, attributed to protonation at the terminal oxygen of the diazeniumdiolate group, show shifts to higher values in dependence of the chain lengths of R. The pH dependence of the decomposition of NO donors 1 – 3 was studied in buffered solution between pH 5 and 8 at 22 °C, from which pK_a(N) values for protonation at the amino nitrogen, leading to release of NO, were estimated. It is shown that the decomposition of these diazeniumdiolates is markedly catalyzed by anionic SDS micelles. First‐order rate constants for the decay of 1 – 4 were determined in phosphate buffer pH 7.4 at 22 °C as a function of SDS concentration. Micellar binding constants, K_SM, for the association of diazeniumdiolates 1 – 3 with the SDS micelles were also determined, again showing a significant increase with increasing length of the alkyl side chains. The decomposition of 1 – 3 in micellar solution is quantitatively described by using the pseudo‐phase ion‐exchange (PIE) model, in which the degree of micellar catalysis is taken into account through the ratio of the second‐order rate constants (k_2m/k_2w) for decay in the micelles and in the bulk aqueous phase. The decay kinetics of 1 – 3 were further studied in the presence of cosolvents and nonionic surfactants, but no effect on the rate of NO release was observed. The kinetic data are discussed in terms of association to the micelle–aqueous phase interface of the negatively charged micelles. The apparent interfacial pH value of SDS micelles was evaluated from comparison of the pH dependence of the first‐order decay rate constants of 2 and 3 in neat buffer and the rate data obtained for the surfactant‐mediated decay. For a bulk phase of pH 7.4, an interfacial pH of 5.7–5.8 was determined, consistent with the distribution of H⁺ in the vicinity of the negatively charged micelles. The data demonstrate the utility of 2 and 3 as probes for the determination of the apparent pH value in the Stern region of anionic micelles.     

Kinetics of interaction of Histidine and Histidine Methyl Ester with Ninhydrin in micellar media

Kinetics of the interaction of histidine and histidine methyl ester with ninhydrin under varying concentrations of reactants, anionic (sodium dodecyl sulphate, SDS), cationic (cetyltrimethylammonium bromide, CTAB) and non‐ionic (Triton X‐100, TX‐100) micelles have been carried out. Rate of the reaction was found to be independent of the initial concentration of histidine (and histidine methyl ester) but was dependent on [Ninhydrin]. The SDS micelles had no effect on the rate of the reaction. In the presence of the CTAB micelles a small enhancement in the rate was observed. The rate − [CTAB] profile showed that the increase in [CTAB] increased the rate up to a maximum value and a further increase had a decreasing effect on the rate. The rate was enhanced by TX‐100 also but, unlike CTAB micelles, TX‐100 possessed a curve without peak for the rate − [TX‐100] profile. The following rate equation was obeyed by the reaction in CTAB and TX‐100 micelles: Values of k_w, k_m, and K_S were evaluated and are reported herein. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 103–111, 1999     

The Self-Association and Mixed Micellization of an Anionic Surfactant,Sodium Dodecyl Sulfate,and a Cationic Surfactant,Cetyltrimethylammonium Bromide: Conductometric,Dye Solubilization,and Surface Tension Studies

In the present study, we investigate the self-association and mixed micellization of an anionic surfactant, sodium dodecyl sulfate (SDS), and a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The critical micelle concentration (CMC) of SDS, CTAB, and mixed (SDS + CTAB) surfactants was measured by electrical conductivity, dye solubilization, and surface tension measurements. The surface properties (viz., C₂₀ (the surfactant concentration required to reduce the surface tension by 20 mN/m), Π_CMC (the surface pressure at the CMC), Γ_max (maximum surface excess concentration at the air/water interface), and A_min (the minimum area per surfactant molecule at the air/water interface)) of SDS, CTAB, and (SDS + CTAB) micellar/mixed micellar systems were evaluated. The thermodynamic parameters of the micellar (SDS and CTAB), and mixed micellar (SDS + CTAB) systems were evaluated.

A schematic representation of micelles and mixed micelles.     

Effect of dicationic gemini surfactants 16–s‐16 (s = 4, 5, 6) on the ninhydrin‐dipeptide (glycyl‐tyrosine) reaction

The effect of dicationic gemini surfactants H₃₃C₁₆(CH₃)₂N⁺‐(CH₂)_s‐N⁺(CH₃)₂ C₁₆H₃₃, 2Br^? (s= 4, 5, 6) on the reaction of a dipeptide glycyl–tyrosine (Gly–Tyr) with ninhydrin has been studied spectrophotometrically at 70°C and pH 5.0. The reaction follows first‐ and fractional‐order kinetics, respectively, in [Gly–Tyr] and [ninhydrin]. The gemini surfactant micellar media are comparatively more effective than their single chain–single head counterpart cetyltrimethylammonium bromide (CTAB) micelles. Whereas typical rate constant (k_Ψ) increase and leveling‐off regions, just like CTAB, are observed with geminis, the latter produces a third region of increasing k_Ψ at higher concentrations. This subsequent increase is ascribed to the change in the micellar morphology of the geminis. The pseudophase model of micelles was used to quantitatively analyze the k_Ψ ? [gemini] data, wherein the micellar‐binding constants K_S for [Gly–Tyr] and K_N for ninhydrin were evaluated. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 800–809, 2012     

Stabilization of a Silaaldehyde by its η2 Coordination to Tungsten

Treatment of pyridine‐stabilized silylene complexes [(η⁵‐C₅Me₄R)(CO)₂(H)W?SiH(py)(Tsi)] (R=Me, Et; py=pyridine; Tsi=C(SiMe₃)₃) with an N‐heterocyclic carbene ^MeIⁱPr (1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene) caused deprotonation to afford anionic silylene complexes [(η⁵‐C₅Me₄R)(CO)₂W?SiH(Tsi)][H^MeIⁱPr] (R=Me ( 1‐Me ); R=Et ( 1‐Et )). Subsequent oxidation of 1‐Me and 1‐Et with pyridine‐N‐oxide (1 equiv) gave anionic η²‐silaaldehydetungsten complexes [(η⁵‐C₅Me₄R)(CO)₂W{η²‐O?SiH(Tsi)}][H^MeIⁱPr] (R=Me ( 2‐Me ); R=Et ( 2‐Et )). The formation of an unprecedented W‐Si‐O three‐membered ring was confirmed by X‐ray crystal structure analysis.     

Four-coordinate trispyrazolylboratomanganese and -iron complexes with a pyrazolato co-ligand: syntheses and properties as oxidation catalysts

A series of complexes of the type [(Tp^R1,R2)M(X)] (Tp=trispyrazolylborato) with R¹/R² combinations Me/tBu, Ph/Me, iPr/iPr, Me/Me and for M=Mn or Fe coordinating [Pz^Me,tBu]^? (Pz=pyrazolato) or Cl^? as co‐ligand X has been synthesised. Although the chloride complexes were very unreactive and stable in air, the pyrazolato series was far more reactive in contact with oxidants like O₂ and tBuOOH. The [(Tp^R1,R2)M(Pz^Me,tBu)] complexes proved to be active pre‐catalysts for the oxidation of cyclohexene with tBuOOH, reaching turnover frequencies (TOFs) ranging between moderate and good in comparison to other manganese catalysts. Cyclohexene‐3‐one and cyclohexene‐3‐ol were always found to represent the main products, with cyclohexene oxide occasionally formed as a side product. The ratios of the different oxidation products varied with the reaction conditions: in the case of a peroxide/alkene ratio of 4:1, considerably more ketone than alcohol was obtained and cyclohexene oxide formation was almost negligible, whereas a ratio of 1:10 led to a significant increase of the alcohol proportion and to the formation of at least small amounts of the epoxide. Pre‐treatment of the dissolved [(Tp^R1,R2)M(Pz^Me,tBu)] pre‐catalysts with O₂ led to product distributions and TOFs that were very similar to those found in the absence of O₂, so that it may be argued that tBuOOH and O₂ both lead to the same active species. The results of EPR spectroscopy and ESI‐MS suggest that the initial product of the reaction of [(Tp^Me,Me)Mn(Pz^Me,tBu)] with O₂ contains a Mn^III(O)₂Mn^IV core. Prolonged exposure to O₂ leads to a different dinuclear complex containing three O‐bridges and resulting in different TOFs/product distributions. Analogous findings were made for other complexes and formation of these overoxidised products may explain the deviation of the catalytic performances if the reactions are carried out in an O₂ atmosphere.     

Kinetics and mechanism of interaction of dipeptide (glycyl–glycine) with ninhydrin in aqueous micellar media

The rates of reaction between ninhydrin and dipeptide glycyl–glycine (Gly–Gly) have been determined by studying the reaction spectrophotometrically at 70°C and pH 5.0 in aqueous and in aqueous cationic micelles of cetyltrimethylammonium bromide (CTAB). The reaction follows first‐ and fractional‐order kinetics, respectively, in [Gly–Gly] and [ninhydrin]. The observed rate constant is affected by [CTAB] changes and the maximum rate enhancement is ca. three‐fold. As the k_ψ ? [CTAB] profile shape is characteristic of bimolecular reactions catalyzed by micelles, the catalysis is explained in terms of the pseudo‐phase model of the micelles (proposed by Menger and Portnoy and developed by Bunton and Romsted). The presence of inorganic salts (NaCl, NaBr, Na₂SO₄) does not reveal any regular effect but the data with organic salts (NaBenz, NaSal) show an increase in the rate followed by a decrease. The kinetic data have been used to calculate the micellar binding constants K_S for Gly–Gly and K_N for ninhydrin and the respective values are 317 and 69 mol^?1 dm³. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 643–650, 2006     

Effect of cationic and anionic surfactants on the addition–elimination-type interaction between o-toluidine and d-glucose

The kinetics of the o-toluidine–d-glucose reaction has been studied as a function of [o-toluidine], [d-glucose], [acetic acid], and temperature by UV–visible spectrophotometry at 630 nm in the absence and presence of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). The reaction follows second-order kinetics, being unity in each of the reactants in both media. The effect of added surfactants has also been investigated. The model of micellar catalysis, such as the Menger–Portony model modified by Bunton, is applied to explain the catalytic role of CTAB and SDS micelles. The association/incorporation constants (K _s and K _n), the rate constant in micellar media (k _m), and the activation parameters of this system have been calculated and discussed. The value of the rate constant is found to be higher in SDS than in CTAB. Hydrophobic and electrostatic interactions are responsible for higher reaction rates in SDS. From all observed facts, a reaction mechanism involving a nucleophilic addition–elimination path has been suggested.     

Effects of Micellar Aggregates on the Kinetics and Mechanism of the Reaction between 4‐Nitrobenzenediazonium Ions and Some Amino Acids

We have explored the kinetics and mechanism of the reaction between 4‐nitrobenzenediazonium ions (4NBD), and the hydrophilic amino acids (AA) glycine and serine in the presence and absence of sodium dodecyl sulfate (SDS) micellar aggregates by means of UV/VIS spectroscopy. The observed rate constants k_obs were obtained by monitoring the disappearance of 4NBD with time at a suitable wavelength under pseudo‐first‐order conditions. In aqueous acid (buffer‐controlled) solution, in the absence of SDS, the dependence of k_obs on [AA] was obtained from the linear relationship found between the experimental rate constant and [AA]. At a fixed amino acid concentration, k_obs values show an inverse dependence on acidity in the range of pH 5–6, suggesting that the reaction takes place through the nonprotonated amino group of the amino acid. All kinetic evidence is consistent with an irreversible bimolecular reaction with k=2390±16 and 376±7 M ^?1 s^?1 for glycine and serine, respectively. Addition of SDS inhibits the reaction because of the micellar‐induced separation of reactants originated by the electrical barrier imposed by the SDS micelles; k_obs values are depressed by factors of 10 (glycine) and 6 (serine) on going from [SDS]=0 up to [SDS]=0.05M . The hypothesis of a micellar‐induced separation of the reactants was confirmed by ¹H‐NMR spectroscopy, which was employed to investigate the location of 4NBD in the micellar aggregate: the results showed that the aromatic ring of the arenediazonium ion is predominantly located in the vicinity of the C(β) atom of the surfactant chain, and hence the reactive ? N group is located in the Stern layer of the micellar aggregate. The kinetic results can be quantitatively interpreted in terms of the pseudophase kinetic model, allowing estimations of the association constant of 4NBD to the SDS micelles.     

Micellar and salt effects on the interaction of [Cu(II)‐Gly‐Gly]+ with ninhydrin

The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the kinetics of interaction of copper dipeptide complex [Cu(II)‐Gly‐Gly]⁺ with ninhydrin has been studied spectrophotometrically at 70°C and pH 5.0. The reaction follows first‐ and fractional‐order kinetics, respectively, in complex and ninhydrin. The reaction is catalyzed by CTAB micelles, and the maximum rate enhancement is about twofold. The results obtained in the micellar medium are treated quantitatively in terms of the kinetic pseudophase and Piszkiewicz models. The rate constants (k_obs or k_Ψ), micellar‐binding constants (k_S for [Cu(II)‐Gly‐Gly]⁺, k_N for ninhydrin), and index of cooperativity (n) have been evaluated. A mechanism is proposed in accordance with the experimental results. The influence of different inorganic (NaCl, NaBr, Na₂SO₄) and organic (NaBenz, NaSal) salts on the reaction rate has also been seen, and it is found that tightly bound/incorporated counterions are the most effective. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 556–564, 2007     

The α‐effect in micelles: Nucleophilic substitution reaction of p‐nitrophenyl acetate with N‐phenylbenzohydroxamate ion

Pseudo‐first‐order rate constants have been determined for the nucleophilic substitution reactions of p‐nitrophenyl acetate with p‐chlorophenoxide (4‐ClC₆H₄O^?) and N‐phenylbenzohydroxamate (C₆H₅CON(C₆H₅)O^?) ions in phosphate buffer (pH 7.7) at 27°C. The effect of cationic, (CTAB, TTAB, DTAB), anionic (SDS), and nonionic (Brij‐35) surfactants has been studied. The k_obs value increases upon addition of CTAB and TTAB. The effect of DTAB and other surfactants on the reaction is not very significant. The micellar catalysis and α‐effect shown by hydroxamate ion have been explained. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 26–31, 2006     

Interaction of Sulfonated Ruthenium(II) Polypyridine Complexes with Surfactants Probed by Luminescence Spectroscopy

Novel anionic [RuL₂L′]²⁻ complexes, where L stands for (1,10‐phenanthroline‐4,7‐diyl)bis(benzenesulfonate) (pbbs; 3a ) or (2,2′‐bipyridine)‐4,4′‐disulfonate (bpds; 3b ), and L′ is N‐(1,10‐phenanthrolin‐5‐yl)tetradecanamide (pta; 2a ) or N‐(1,10‐phenanthrolin‐5‐yl)acetamide (paa; 2b ), were synthesized, and their interaction with the prototypical surfactants sodium dodecylsulfate (SDS), cetyl trimethyl ammonium bromide (CTAB), and Triton X‐100 (TX‐100) was investigated by electronic absorption, luminescence spectroscopy, emission‐lifetime determinations, and O₂‐quenching measurements. [Ru(pbbs)₂(pta)]²⁻ ( 5a ) displayed cooperative self‐aggregation in aqueous medium at concentrations above 1.3 μM ; the observed association was enhanced in the presence of either β‐cyclodextrin or NaCl. This amphiphilic Ru^II compound showed the strongest interaction with all the detergents tested: nucleation of surfactant molecules around the luminescent probe was observed below their respective critical micellar concentrations. As much as a 12‐fold increase of the emission intensity and a 3‐fold rise in the lifetime were measured for 5a bound to TX‐100 micelles; the other complexes showed smaller variations. The O₂‐quenching rate constants decreased up to 1/8 of their original value in H₂O (e.g., for [Ru(bpds)₂(pta)]²⁻ ( 6a ) bound to CTAB micelles). Luminescence‐lifetime experiments in H₂O/D₂O allowed the determination of the metal‐complex fraction exposed to solvent after binding to surfactant micelles. For instance, such exposure was as low as 25% for pta complexes⋅CTAB aggregates. The different behaviors observed were rationalized in terms of the Ru^II complex structure, the electrostatic/hydrophobic interactions, and the probe environment.     

Micellae catalysis of the oxidation of 1,4-dihydro-nicotinamides by methylene blue part 2

The oxidation of 1-R-1,4-dihydronicotinamides (1a: R = benzyl, 1b:R = octyl, 1c:R = cetyl) by methylene blue has been studied in the presence of micelles of cetyltrimethylammonium bromide (CTAB), polyoxyethylene[23]lauryl ether (Brij^® 35) and sodium dodecylbenzenesulfonate (SDBS). In CTAB, a small rate enhancement was observed below the cmc, followed by a gradual decrease above the cmc. Brij 35 has little effect on the reaction rate. The rate vs. concentration profile in SDBS shows a very sharp maximum near the cmc for 1b and 1c, whereas a more moderate increase in rate is observed for 1a. The effects are analyzed in terms of the pseudophase model for micellar catalysis, and it appears that the observed rate enhancements can be completely ascribed to increments of the reactant concentration in the micellar pseudophase. Comparison with rate effects in sodium dodecylsulfate (SDS) micelles reveals that the reaction in SDBS micelles proceeds in a more polar environment. This provides kinetic evidence that the aryl moiety in SDBS allows a deeper penetration of water molecules into the micelle, thus giving rise to a more open surface for SDBS micelles than for SDS micelles.     

Synthesis and Structures of Homoleptic Methyl‐ and Phenylthiomethylaluminium Complexes [Al(CH2SR)3](R = Me,Ph)

Sulfur‐substituted methylmercury compounds [Hg(CH₂SR)₂]( 1a, R = Me; 1b, R = Ph ) react with aluminium amalgam in refluxing toluene with transmetallation to give homoleptic tris(thiomethyl)aluminium complexes [Al(CH₂SR)₃]( 2a, R = Me; 2b, R = Ph ) (degree of conversion: >80%, isolated yields: 2a 63%, 2b 41%). Their identities were confirmed by NMR spectros‐copy (¹H, ¹³C) and X‐ray crystal structure analyses. In crystals of compound 2a the aluminium atoms possess a trigonal‐bipyramidal arrangement with the coordination polyhedron defined by three carbon and two sulfur atoms. Two of the three CH₂SMe ligands are bridging ligands (μ‐η²; 1kC:2kS), the third one is terminal bound (η¹; kC). The structure is polymeric. Crystals are threaded by helical chains built up of six‐membered Al₂C₂S₂ rings. Crystals of 2b are built up of centrosymmetrical dimers with six‐membered Al₂C₂S₂ rings having bridging CH₂SPh ligands (μ‐η²; 1kC:2kS). On each Al atom two terminal (η¹; kC)CH₂SPh ligands are bound. They exhibit quite different Al‐C‐S angles (116.7(4) and 106.5(3)?). Similar values (114.32115.7? and 109.52109.9?) were found in ab initio calculations of model compounds [{Al(CH₂SR)₃}₂]( 3a, R=H; 3b, R=Me; 3c, R=CH=CH₂ ). A conformational energy diagram for rotation of one of the terminal CH₂SH ligand in the parent compound 3a around the Al‐C bond is discussed in terms of repulsive interactions of lone electron pairs of sulfur atoms.     

PNPP Cleavage Catalyzed by Schiff Base Mn(III) Complexes Containing Polyether Side Chains in CTAB Micellar Solutions

Two Schiff base Mn(III) complexes containing polyether side chain were synthesized and characterized. The catalytic hydrolysis of p‐nitrophenyl picolinate (PNPP) by the two complexes in the buffered CTAB micellar solution in the pH range of 6.60–8.20 was investigated kinetically in this study. The influences of acidity, temperature, and structure of complex on the catalytic cleavage of PNPP were also studied. The mechanism of PNPP hydrolysis catalyzed by Schiff base manganese(III) complexes in CTAB micellar solution was proposed. The relative kinetic and thermodynamic parameters were determined. Comparied with the pseudo‐first‐order rate constant (k ₀) of PNPP spontaneous hydrolysis in water, the pseudo‐first‐order rate constants (k _obsd) of PNPP catalytic hydrolysis are 1.93×10³ fold for MnL¹ ₂Cl and 1.06×10³ fold for MnL² ₂Cl in CTAB micellar solution at pH=7.00, T=25°C, and [S]=2.0×10^?4mol · dm^?3, respectively. Furthermore, comparing the k _obsd of PNPP catalytic hydrolysis by metallomicelles with that of PNPP hydrolysis catalyzed only by metal complexes or CTAB micelle at the above‐mentioned condition, metallomicelles of MnL₂(L=L¹, L²) Cl/CTAB exhibit notable catalytic activities for promoting PNPP hydrolysis, and MnL¹ ₂Cl/CTAB system is superior in promoting cleavage of PNPP relative to MnL² ₂Cl/CTAB system under the same experimental conditions. The results indicate that the rate of PNPP catalytic cleavage is influenced by the structures of the two complexes, the acidity of reaction systems, and the solubilization of PNPP in CTAB micelles.     

Syntheses,Crystal Structures,and Properties of Lead(II), ­Zinc(II), and Manganese(II) Complexes Constructed from 2, 3, 5, 6‐Tetraiodo‐1, 4‐benzenedicarboxylic Acid

Three new coordination compounds, [Pb(HBDC‐I₄)₂(DMF)₄]( 1 ) and [M(BDC‐I₄)(MeOH)₂(DMF)₂]_n (M = Zn^II for 2 and Mn^II for ( 3 ) (H₂BDC‐I₄ = 2, 3, 5, 6‐tetraiodo‐1, 4‐benzenedicarboxylic acid), were synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric (TG) analysis, and X‐ray single crystal structure analysis. Single‐crystal X‐ray diffraction reveals that 1 crystallizes in the monoclinic space group C2/c and has a discrete mononuclear structure, which is further assembled to form a two‐dimensional (2D) layer through intermolecular O–H ··· O and C–H ··· O hydrogen bonding interactions. The isostructural compounds 2 and 3 crystallize in the space group P2₁/c and have similar one‐dimensional (1D) chain structures that are extended into three‐dimensional (3D) supramolecular networks by interchain C–H ··· π interactions. The Pb^II and Zn^II complexes 1 and 2 display similar emissions at 472 nm in the solid state, which essentially are intraligand transitions.