Characterising latex particles and fractal aggregates using image analysis

The fractal nature of latex particles and their aggregates was characterised by image analysis in terms of fractal dimensions. The one- and two-dimensional fractal dimensions, D ₁ and D ₂, were estimated for polystyrene latex aggregates formed by flocculation in citric acid/phosphate buffer solutions. The dimensional analysis method was used, which is based on power law correlations between aggregate perimeter, projected area and maximum length. These aggregate characteristics were measured by image analysis. A two-slopes method using cumulative size distributions of aggregate length and solid volume has been developed to determine the three-dimensional fractal dimension (D ₃) for the latex aggregates. The fractal dimensions D ₁, D ₂ and D ₃ measured for single latex particles in distilled water agreed well with D ₁ = 1, D ₂ = 2 and D ₃ = 3 expected for Euclidean spherical objects. For the aggregates, the fractal dimension D ₂ of about 1.67 ± 0.04 (±standard deviation) was comparable to the fractal dimension D ₃ of approximately 1.72 ± 0.13 (±standard deviation), taking the standard deviations into account. The measured three-dimensional fractal dimension for latex aggregates is within the fractal dimension range 1.6–2.2 expected for aggregates formed through a cluster-cluster mechanism, and is close to the D ₃ value of about 1.8 indicated for cluster formation via diffusion-limited colloidal aggregation. Received: 28 September 1998 Accepted: 29 October 1998     

Chiral imines and amines based on 2-hydroxypinan-3-one

The new chiral derivatives of benzylamine and 2α-hydroxypinan-3-one (1R,2R,5R)-3-[(1S)-α-methylbenzylamino]-2,6,6-trimethylbicyclo[3.1.1]heptan-2-ol (2), (1S,2S,3S,5S)-3-(benzylamino)-2,6,6-trimethylbicyclo[3.1.1]heptan-2-ol (3), and (1R,2R,3R,5R)-3-[(1S)-α-methylbenzylamino]-2,6,6-trimethylbicyclo[3.1.1]heptan-2-ol (4) were synthesized and characterized. It was shown that reduction of the benzylimines by sodium triacetoxyborohydride formed stereoselectively 3β-substituted pinanamines.     

Interaction of blockcopolymer micelles as probed by small-angle neutron and by small-angle X-ray scattering

 The analysis of the interaction of micelles formed by a blockcopolymer is given by means of small-angle X-ray (SAXS) and small-angle neutron scattering (SANS). The blockcopolymer consists of poly(styrene) and poly(ethylene oxide) (molecular weight of each block: 1000 g/mol) and forms well-defined micelles (weight-association number: 400, weight-average diameter: 15.4 nm) in water. The internal structure has been studied previously (Macromolecules 29:4006 (1996)) by SAXS. There it has been shown that the micelles are spherical objects. The structure factor S(q) as a function of the scattering vector q (q=(4π/λ) sin (θ/2); λ: wavelength of the radiation in the medium; θ: scattering angle) can be extracted from both sets of small-angle scattering data (SANS: q≤0.4 nm^-1; SAXS: q≤0.6 nm^-1). It is shown that particle interaction in the present system can be described by assuming soft interaction which is modeled by a square-step potential. Received: 12 May 1997 Accepted: 9 July 1997     

Enantiospecific synthesis of (S)-(+)-3-methylheneicosan-2-one, an analog of the sex pheromone of the German cockroach (Blatella germanica L.) from (−)-(1R,4S)-menthone

An enantiospecific synthesis of (S)-(+)-3-methylheneicosan-2-one, an analog of the sex pheromone of the German cockroach (Blatella germanica L.), was carried out through selective transformations of (3R,6S)-3,7-dimethyloctane-6-olide obtained from (−)-menthonevia the Baeyer—Villiger reaction. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1071–1073, May, 1997.     

Synthesis of chiral benzoacridinone derivatives by three-component condensation of [(1<Emphasis Type="Italic">S</Emphasis>,4<Emphasis Type="Italic">S</Emphasis>)-1,7,7-trimethylbicyclo[2.2.1]hept-2-ylidene]acetaldehyde with naphthalen-1-amine and cyclic β-diketones

Three-component condensation of [(1S,4S)-1,7,7-trimethylbicyclo[2.2.1]hept-2-ylidene]acetaldehyde with naphthalen-1-amine and cyclic β-diketones gave 7-[(1S,4S)-1,7,7-trimethylbicyclo[2.2.1]hept-2-ylidenemethyl]-7,8,9,10,11,12-hexahydro-7H-benzo[c]acridin-8-one derivatives possessing three or more asymmetric carbon atoms. Steric factors were found to be responsible for the predominant formation of the (7R)-isomers (R/S ≈ 7: 5) and orientation of substituents in the cyclohexenone fragment. The same factors determined complete regioselectivity of the reaction with methyl 2,4-dioxocyclohexane-1-carboxylates as dicarbonyl component, which led to exclusive formation of methyl 8-oxobenzoacridine-11-carboxylates. In the reaction of [(1S,4S)-1,7,7-trimethylbicyclo[2.2.1]hept-2-ylidene]acetaldehyde with naphthalen-1-amine and barbituric acid as dicarbonyl component, the only product was that formed by two-component condensation of barbituric acid with bicyclic aldehyde.     

Synthesis of 1,11,11-trimethyl-3,6-diazotricyclo [6.2.1.0<Superscript>2,7</Superscript>]undeca-2,6-diene and 1,15,15-trimethyl-3,10-diazotetracyclo[10.2.1.0<Superscript>2,11</Superscript>.0<Superscript>4,9</Superscript>]pentadeca-2,4(9),5,7,10-pentaene from camphoroquinone enantiomers

Optically active camphordihydro-2,3-pyrazine and camphorquinoxaline were prepared from camphoroquinone enantiomers. It was shown that (1S,4R)-(+)-camphoroquinone was formed by oxidation of (1S,3R, 4R)-(−)-3-bromocamphor and (1R,4S)-(−)-camphoroquinone from (1R,3S, 4S)-(+)-3-bromocamphor, respectively. Camphor anhydride was a side product (6–10%) of the reaction. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 50–52, January–February, 2007.     

Asymmetric trimethylsilylcyanation of aldehydes catalyzed by chiral salen TiIV complexes with theC 1 symmetry

Asymmetric trimethylsilylcyanation of a number of aromatic and aliphatic aldehydes catalyzed by chiral Ti^IV complexes preparedin situ from Ti(OPrⁱ)₄ and (1S)-[N,N′-bis(2′-hydroxy-3′-tert-butylbenzylidene)]-1,2-diaminoalkanes gives products with (S)-absolute configurations. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2040–2042, November, 1997.     

Asymmetric synthesis of β-N-substituted α,β-diamino acidsvia a chiral complex of NiII with a dehydroalanine derivative

Asymmetric synthesis of β-N-substituted (S)-α,β-diamino acids was accomplished by Michael addition of amines to the Ni^II complex of the Schiff base derived from (S)-2-[N-(N′-benzylprolyl)amino]benzophenone (BPB) and dehydroalamine. Diastereoselectivity of the reaction is kinetically and thermodynamically controlled. The chiral auxiliary reagent, BPB, can be recovered and reused. Translated fromIzvestiya Akademii Nauk. Serya Khimicheskaya, No. 3, pp. 504–507, March, 1997.     

正离子Gemini表面活性剂/负离子聚电解质相互作用的研究

摘要 采用荧光探针法和电导法研究了正离子偶联表面活性剂(C₁₂H₂₅(CH₃)₂N-(CH₂)₆-N(CH₃)₂C₁₂H₂₅•2Br) (12-6-12• 2Br^－)和带相反电荷聚电解质聚丙烯酸钠(NaPA)的相互作用, 结果表明: 由于静电相互作用, 12-6-12•2Br^－和NaPA之间可以形成类胶束或复合物. 对比十二烷基三甲基溴化铵(DTMAB)与NaPA复配体系的荧光光谱, 发现偶联表面活性剂与NaPA的相互作用强于传统表面活性剂. 此外, 还研究了盐和醇对偶联表面活性剂/聚丙烯酸钠的复配体系微极性的影响, 发现盐和醇对表面活性剂在聚电解质上形成类胶束和复合物的溶解都有一定的促进作用.     

Enantioselectivity of enzymatic acylation of some structurally various racemic alcohols in anhydrous aprotic media

Partial acylation of (R,S)-3,7-dimethyloctan-1-ol (1) and (R,S)-7-methoxy-3,7-dimethyloctan-1-ol (2) with vinyl acetate catalyzed by the lipase fromCandida cylindracea affords in good yields the correspondingS-configured acetates with 92–98% enantiomeric excess (ee). Under similar conditions, racemic α-cyclogeraniol (3), drim-7-en-11-ol, methyl 4-(3-hydroxy-2-methylpropyl)benzoate, and its η⁶-chromium(tricarbonyl) complex (6) are acylated with rather poor (and, for the two latter, opposite) enantioselectivity, whereas (R,S)-2,4∶3,5-di-O-benzylidenexylitol remains unaffected. Racemic isoborneol (8) and 2-nitro-1-phenylethanol also remain almost or completely unconverted. Attempts to perform enantioselective acylation of alcohols 3 and 8 with Ac₂O in the presence of porcine pancreatic lipase (PPL) proved equally unsuccessful. By contrast, the PPL-catalyzed acylation of alcohol 6 with vinyl acetate at 17% conversion affords the levorotatory acetate (S)-6a withca. 100%ee. PPL-Mediated partial acylation of (R,S)-pantolactone with Ac₂O, followed by mild deacylation of the resultingR acetate, gives (R)-(-)-pantolactone of 97% enantiomeric purity in 60% overall yield. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 175–186, January, 1997.     

Disruption of polystyrene latex aggregates in capillary flow

 Disruption of polystyrene latex aggregates, formed in 1 M citric acid/phosphate buffer solution at pH 3.8 through diffusion-limited colloid aggregation (DLCA) and in 0.2 M NaCl solution at pH 5.5 through reaction-limited colloid aggregation (RLCA), was studied with respect to aggregate size and fractal nature. This was achieved using small-angle laser scattering in conjunction with a specially designed sampling method, which brought about the elimination of the disruption of the aggregates caused by a commercial stirrer sample unit. Aggregations were carried out in a mixture of deuterium oxide and water instead of water alone as a solvent to minimise sedimentation resulting from the differences in density between the latex particles and the electrolytes. An initial “steady state” in terms of aggregate size and fractal dimension was found to occur after around 20 min and 2 days for DLCA and RLCA aggregates, respectively, at 25 °C. No aggregate disruption was detected for DLCA and RLCA aggregates after their passing through a capillary tube for shear rates up to 1584 and 2694 s⁻¹, respectively. At higher shear rates, significant decreases in the aggregate volume-mean diameter, D[4, 3], occurred after shearing. The degree of reduction in D[4, 3] was larger for DLCA aggregates in comparison to RLCA aggregates. The results would suggest that DLCA aggregates were more subject to disruption during shearing. A high degree of disruption was observed in turbulent flow for both aggregates. Received: 30 June 1999 Accepted in revised form: 11 November 1999     

Structure,Stability, and Fragmentation of Sodium bis(2-ethylhexyl)Sulfosuccinate Negatively Charged Aggregates In Vacuo by MD Simulations

Negatively charged supramolecular aggregates formed in vacuo by n bis(2-ethylhexyl)sulfosuccinate (AOT^–) anions and n + n _c sodium counterions (i.e., [AOT _n Na _n+nc ] ^nc ) have been investigated by molecular dynamics (MD) simulations for n = 1 to 20 and n _c = –1 to –5. By comparing the maximum excess charge values of negatively and positively charged AOTNa aggregates, it is found that the charge storage capability is higher for the latter systems, the difference decreasing as the aggregation number increases. Statistical analysis of physical properties like gyration radii and moment of inertia tensors of aggregates provides detailed information on their structural properties. Even for n _c = –5, all stable aggregates show a reverse micelle-like structure with an internal core, including sodium counterions and surfactant polar heads, surrounded by an external layer consisting of the surfactant alkyl chains. Interestingly, the reverse micelle-like structure is retained also in proximity of fragmentation. Moreover, the aggregate shapes may be approximated by elongated ellipsoids whose longer axis increases with n and |n _c |. The fragmentation patterns of a number of these aggregates have also been examined and have been found to markedly depend on the aggregate charge state. The simulated fragmentation patterns of a representative aggregate show good agreement with experimental data obtained using low collision voltages. Figure

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Synthesis of isomeric 2-oxazolidinones from (1<Emphasis Type="Italic">R</Emphasis>,2<Emphasis Type="Italic">R</Emphasis>)-and (1<Emphasis Type="Italic">S</Emphasis>,2<Emphasis Type="Italic">S</Emphasis>)-2-amino-1-(4-nitrophenyl)-1,3-propanediols

A synthesis is reported for (4R,5R)-and (4S,5S)-4-hydroxymethyl-5-(4-nitrophenyl)oxazolidin-2-ones and (1′R,4R)-and (1′S,4S)-4-[hydroxy(4-nitrophenyl)methyl]oxazolidin-2-ones from (1R,2R)-and (1S,2S)-2-amino-1-(4-nitrophenyl)-1,3-propanediols. The effect of the experimental conditions on the formation of these compounds was studied. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1562–1570, October, 2007.     

pH-Dependent Aggregation Behavior and Emulsion Stability of Comb-Like Surfactant Containing PEO Grafts

The aggregation behavior of the comb-like surfactant, poly(styrene-co-maleic anhydride)-g-(poly(ethylene glycol) monomethyl ether) (SMA-M), prepared via the one-pot method, at surface and in solution, was investigated by equilibrium surface tension, rheological technology, and transmission electron microscopy (TEM). The emulsion prepared from n-decane/water/C₁₃E₇ was used as a model system to determine the influence of SMA-M on the stability of the emulsion. The equilibrium surface tensions of SMA-M solution with various pH were measured. The adsorption data, that is, the saturation surface excess concentration (Γ_max) and the minimum area (A _min) were evaluated using the average monomeric molecular weight (M _nA ). The results showed that Γ_max decreased with the increase of pH, but the A _min enlarged with the increase of pH. The results of the steady-state shear experiment indicated that the aggregate structure of the as-prepared comb-like surfactant SMA-M in aqueous solution evolved from interlinked micelle-like aggregates to isolated inflated micelle-like aggregates, then to rod-like aggregates with the increasing pH, which were confirmed by the TEM images. The investigation of the stabilization of n-decane/water/C₁₃E₇/SMA-M emulsion system indicated that SMA-M obviously slows down the phase separation, and the most effectively stabilized sample was obtained at pH 5.0. Supplemental materials are available for this article. Go to the publisher's online edition of the Journal of Dispersion Science and Technology to view the free supplemental file.     

Chitosan structure in aqueous solution

Chitosans having three different degrees of acetylation (DA) were studied in acid solution using the uranyl staining technique and electron microscopy. Strings of approximately spherical aggregates were seen. The aggregates were interpreted as micelle-like agglomerates formed by almost fully acetylated polysaccharide, interconnected by blocks of almost fully deacetylated polysaccharide stretched by electrostatic repulsion. These agglomerates include NH₃⁺ groups which produce electrostatic swelling of the agglomerates, giving a radius proportional to the degree of deacetylation. The length of the strings are also proportional to the deacetylation degree. These strings are extended because of the electrostatic repulsion between charged ammonium groups.     

Small-angle neutron-scattering study and micellar model of the gemini (phenylenedimethylene)bis(n-octylammonium)dibromide surfactant micelles in water

The microstructure of the micelles formed in aqueous solution by gemini surfactants with aromatic spacers, [Br(CH₃)₂N⁺(C _m H_{2 m +1})-(Ph)-(C _m H_{2 m +1})N⁺(CH₃)₂Br, m=8 and Ph = o-, m- or p-phenylenedimethylene] has been examined by small-angle neutron scattering. Aggregation of the gemini surfactants with an o-phenylenedimethylene spacer brings about formation of premicelles and small micelles at concentrations below the second critical micelle concentration, while above this concentration marked micellar growth and variation in shape occurs. It is suggested that the minimum aggregate formed at this critical micelle concentration may be the trimer or tetramer and that this result supports the mechanism of “gemini → submicelle → assembly” for micellar growth. Received: 8 September 1998 Accepted in revised form: 27 November 1998     

Chiral differentiation of some cyclopentane and cyclohexane β-amino acid enantiomers through ion/molecule reactions

Chiral differentiation of four enantiomeric pairs of β-amino acids, cis-(1R,2S)-, cis-(1S,2R)-, trans-(1R,2R)-, and trans-(1S,2S)-2-aminocyclopentanecarboxylic acids (cyclopentane β-amino acids), and cis-(1R,2S)-, cis-(1S,2R)-, trans-(1R,2R)-, and trans-(1S,2S)-2-aminocyclohexanecarboxylic acids (cyclohexane β-amino acids) was performed successfully by using host-guest complexes and ion/molecule reactions. The experiments were conducted by using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The effect of a chiral host molecule was tested by using three different host compounds; (+)-(18-Crown-6)-2,3,11,12-tetracarboxylic acid, (−)-(18-Crown-6)-2,3,11,12-tetracarboxylic acid, and β-cyclodextrin. This is the first time that small enantiomeric pairs with two chiral centers have been differentiated using ion/molecule reactions and host-guest complexes.     

Different coordination modes of the dimethyldisulfide ligand in trimethylplatinum(IV) complexes

The reaction of [PtMe₃(bpy)(Me₂CO)](BF₄) (2) (prepared from [PtMe₃I(bpy)] (1) plus Ag(BF₄)) with MeSSMe resulted in the formation of [PtMe₃(bpy)(MeSSMe-κS)](BF₄) (3). A single-crystal X-ray diffraction analysis revealed in the octahedral Pt(IV) complex (configuration index: OC-6-33), a conformation of the monodentately κS bound MeSSMe ligand (C–S–S–C 92.7(4)°) being very close to that in non-coordinated MeSSMe, thus allowing some hyperconjugative interaction stabilizing the S–S bond. The reaction of [K(18C6)][(PtMe₃)₂(μ-I)(μ-pz)₂] (4; 18C6 = 18-crown-6, Hpz = pyrazole) with Ag(BF₄) and MeSSMe resulted in the formation of dinuclear complexes [(PtMe₃)₂(μ-pz)₂(μ-MeSSMe)] existing at room temperature in acetone solution as different fast interconverting isomers. At –40 °C, two isomers with a μ-1κS:2κS (5a) and a μ-1κS:2κS′ (5b) coordinated MeSSMe ligand in the ratio 2:1 could be identified ¹H NMR spectroscopically. DFT calculations of type 5 complexes revealed the existence of two conformers with a μ-MeSSMe-1κS:2κS ligand, which differ mainly in the C–S–S–C dihedral angle (66.4 vs. 180.0° 6a/6a′). They have essentially the same energy and a very low activation barrier in acetone as solvent (1.3 kcal/mol) for their mutual interconversion. A further equilibrium structure was identified to be an isomer having a μ-MeSSMe-1κS:2κS′ ligand (6b) that proved to be only 1.9 kcal/mol higher in energy than 6a/6a′.     

α‐Propargyl amino acid‐derived optically active novel substituted polyacetylenes: Synthesis,secondary structures,and responsiveness to ions

Novel optically active substituted acetylenes HC? CCH₂CR¹(CO₂CH₃)NHR² [(S)‐/(R)‐ 1 : R¹ = H, R² = Boc, (S)‐ 2 : R¹ = CH₃, R² = Boc, (S)‐ 3 : R¹ = H, R² = Fmoc, (S)‐ 4 : R¹ = CH₃, R² = Fmoc (Boc = tert‐butoxycarbonyl, Fmoc = 9‐fluorenylmethoxycarbonyl)] were synthesized from α‐propargylglycine and α‐propargylalanine, and polymerized with a rhodium catalyst to provide the polymers with number‐average molecular weights of 2400–38,900 in good yields. Polarimetric, circular dichroism (CD), and UV–vis spectroscopic analyses indicated that poly[(S)‐ 1 ], poly[(R)‐ 1 ], and poly[(S)‐ 4 ] formed predominantly one‐handed helical structures both in polar and nonpolar solvents. Poly[(S)‐ 1a ] carrying unprotected carboxy groups was obtained by alkaline hydrolysis of poly[(S)‐ 1 ], and poly[(S)‐ 4b ] carrying unprotected amino groups was obtained by removal of Fmoc groups of poly[(S)‐ 4 ] using piperidine. Poly[(S)‐ 1a ] and poly[(S)‐ 4b ] also exhibited clear CD signals, which were different from those of the precursors, poly[(S)‐ 1 ] and poly[(S)‐ 4 ]. The solution‐state IR measurement revealed the presence of intramolecular hydrogen bonding between the carbamate groups of poly[(S)‐ 1 ] and poly[(S)‐ 1a ]. The plus CD signal of poly[(S)‐ 1a ] turned into minus one on addition of alkali hydroxides and tetrabutylammonium fluoride, accompanying the red‐shift of λ_max. The degree of λ_max shift became large as the size of cation of the additive. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Physicochemical characterization of a novel surfactant peptide containing an arginine cation and laurate anion

 A novel surfactant peptide consisting of an arginine cation with laurate anion has been synthesized, purified and characterized. The critical micellar concentration (cmc) of peptide in aqueous solutions has been determined using spectroscopic techniques and is found to increase from 0.06 to 0.11 mM with increasing temperature (15–45 °C). Cmc is also determined in the presence of salts like NaCl, KCl and sodium acetate and it is found that these electrolytes hinder aggregation with a significant increase in the case of sodium acetate. The aggregation number of the surfactant peptide has been determined using fluorescence quenching measurements and is observed to decrease from 14 to 6 with increasing temperature (15–45 °C). The standard free energy change (ΔG ⁰ _m) and standard enthalpy change (ΔH ⁰ _m) of the peptide aggregate are found to be negative with a small positive value for standard entropy change (ΔS ⁰ _m). The peptide aggregate seems to undergo phase transition above 50 °C as observed from UV–vis and fluorescence spectroscopy. From pyrene binding studies, it is shown that the interior dielectric constant increases from 5.08 at 34 °C to 8.77 at 50 °C and further decreases with increase in temperature indicating a phase change at 50 °C. Also, the ratio of excimer intensity to monomer intensity, which is a measure of microviscosity of the aggregate, decreases with increase in temperature with a change at 50 °C indicating a phase change. Received: 14 February 1997 Accepted: 13 August 1997