The AFM observation of linear chain and crystalline conformations of ultrahigh molecular weight polyethylene molecules on mica and graphite

Atomic force microscopy (AFM) has been applied to visualize expanded linear chain and compact crystalline conformations of ultrahigh molecular weight polyethylene (PE) molecules deposited on mica and graphite from diluted solutions at elevated temperatures. Isolated PE chains are visualized on mica with the apparent negative AFM height and the contour length much shorter than the molecular length. The chain conformations have both the kinked random‐coil sites and the sites of the unexpectedly large two‐dimensional expansion. The crystalline conformations on mica are small single‐molecule rod‐like nanocrystallites and the isolated block‐type “edge‐on” nanolamellae comprising several PE molecules. Noticeable fluctuations of the fold length in the range of approximately 10–20 nm around the averaged value of about 15 nm are observed for nanocrystallites and on tips of some nanolamellae. The explanation of the experimentally observed features of chain surface conformations on mica is proposed. It implies the immobilization of PE molecules in the nm‐thickness salt layer formed on mica surface at ambient conditions after PE deposition and the presence along the chain of multiple expanded chain folds. Only isolated lamellae and lamellar domains of a monolayer height are observed on graphite samples. The substrate/polymer epitaxial incommensurability important for the observation of the PE linear chain surface conformations is discussed from the comparison of the results obtained for mica and graphite, the coil‐to‐crystal intramolecular transformation is assumed to be inhibited on mica surface. The slow disintegration of the original gel structure of PE stock‐solution used for the high‐temperature depositions was found to result in the characteristic large‐scale morphological heterogeneity of the samples. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 766–777, 2010     

Near-IR absorption and fluorescence spectra and AFM observation of the light-harvesting 1 complex on a mica substrate refolded from the subunit light-harvesting 1 complexes of photosynthetic bacteria Rhodospirillum rubrum

The subunit light-harvesting 1 (LH 1) complexes isolated from photosynthetic bacteria Rhodospirillum rubrum using n-octyl-beta-glucoside were reassociated and adsorbed on a mica substrate using spin-coat methods with the aim of using this LH complex in a nanodevice. The near-IR absorption and fluorescence spectra of the LH 1 complexes indicated that the LH 1 complex on the mica was stable, and efficient energy transfer from a carotenoid to a bacteriochlorophyll a was observed. Atomic force microscopy of the reassociated LH 1 complexes, under air, showed the expected ringlike structure. The outer and inner diameters of the ringlike structure of the LH 1 complex were approximately 30 and 8 nm, respectively, and the ringlike structure protruded by 0.2-0.6 nm.     

PEI-g-MPEG/白细胞介素-10基因传递系统转染背根神经节细胞的体外性能研究

探索非病毒基因载体聚乙二醇-聚乙烯亚胺共聚物(PEI-g-MPEG)介导白细胞介素-10(Interleukin-10,IL-10)体外转染原代培养背根神经节细胞(dorsal root ganglion cells,DRGs)的效果.采用本实验室设计合成的PEI-g-MPEG,与同时携带增强型绿色荧光蛋白报告基因及IL-10基因的真核表达质粒DNA(pDC316-EGFP/IL-10)形成复合物,以脂质体(lipofectamine)复合体系Lipo/pDNA为对照,通过溴乙啶(ethidiumbromide,EB)排斥实验、凝胶阻滞电泳实验、粒径与电位的测定及扫描电镜等实验方法观察PEI-g-MPEG/pDNA的复合效果.并且检测了复合物对DRGs的毒性、转染效果及IL-10的蛋白表达情况.结果表明,PEI-g-MPEG在N/P(PEI-g-MPEG所含的氮原子和质粒DNA中磷原子的摩尔比)为5时可完全复合pDNA;随着N/P的增大,PEI-g-MPEG/pDNA复合物的粒径逐渐减小,而表面电位逐渐增大;在N/P为15时报告基因转染效果和IL-10蛋白表达情况较好,复合物的形貌呈大小均一的球形.PEI-g-MPEG/IL-10基因传递系统对于神经病理性疼痛的基因治疗具有潜在应用价值.     

Virus-sized DNA nanoparticles for gene delivery based on micelles of cationic calixarenes

Macrocyclic amphiphilic molecules based on calix[4]arenes are highly attractive for controlled supramolecular assembly of DNA into small nanoparticles, since they present a unique conical architecture and can bear multiple charged groups. In the present work, we synthesized new amphiphilic calixarenes bearing cationic groups at the upper rim and alkyl chains at the lower rim. Their self-assembly in aqueous solution was characterized by fluorescent probes, fluorescence correlation spectroscopy, dynamic light scattering, gel electrophoresis and atomic force microscopy. We found that calixarenes bearing long alkyl chains (octyl) self-assemble into micelles of 6 nm diameter at low critical micellar concentration and present the unique ability to condense DNA into small nanoparticles of about 50 nm diameter. In contrast, the short-chain (propyl) analogues that cannot form micelles at low concentrations failed to condense DNA, giving large polydisperse DNA complexes. Thus, formation of small DNA nanoparticles is hierarchical, requiring assembly of calixarenes into micellar building blocks that further co-assemble with DNA into small virus-sized particles. The latter showed much better gene transfection efficiency in cell cultures relative to the large DNA complexes with the short-chain analogues, which indicates that gene delivery of calixarene/DNA complexes depends strongly on their structure. Moreover, all cationic calixarenes studied showed low cytotoxicity. Thus, this work presents a two-step hierarchical assembly of small DNA nanoparticles for gene delivery based on amphiphilic cone-shaped cationic calixarenes.     

Fluoride-assisted synthesis of mullite (Al5.65Si0.35O9.175) nanowires

Novel silicon-deficient mullite (Al5.65Si0.35O9.175) single crystal nanowires were synthesized in large quantities on mica substrates assisted by the intermediate fluoride species. The nanowires have diameters in the range 50-100 nm and typical lengths of several microm. Aligned nanowires were observed at the substrate edge. The nanowires have strong photoluminescence (PL) emission bands at 310, 397, 452 and 468 nm.     

Characterization of aliphatic and aromatic polyester hyperbranched dendrimers by AFM imaging

The aggregates of aliphatic (AL-PE) and aromatic polyester (AR-PE) hyperbranched dendrimers were imaged by tapping mode atomic force microscopy (AFM). The second and third generations of AL-PE dendrimers were adsorbed on mica in large aggregates of 150- and 166-nm diameters with little heights (ca. 1–2 nm). The origin of such flattened aggregates is attributed to their favorable adsorption on mica in view of the presence of –OH surface groups. AR-PE did not show such flattened aggregates instead small aggregates of 63 nm were observed in an organized manner beaving a cavity in the center of each aggregate. The organized aggregates of AR-PE with smaller dimension than AL-PE are ascribed to less favorable adsorption of the latter on mica in view of its stronger hydrophobicity.     

Comparison of different commercially available cationic liposome-DNA lipoplexes: Parameters influencing toxicity and transfection efficiency

Lipid–DNA complexes (lipoplexes) are widely used, since several years, as gene carriers. However, their transfection efficiency, both in vitro and in vivo, depends, in a rather complex way, on different interconnected parameters, ranging from the chemical composition of the lipid components to the size and size distribution of the complexes and, moreover, to the composition of the suspending medium. In this paper, we have investigated the behavior of nine different commercially available transfection agents (liposomal and non-liposomal) and their lipoplexes, at different molar charge ratios and in different experimental conditions. The size and the time stability of the resulting lipoplexes were investigated by means of dynamic light scattering methods and their toxicity and transfection efficiency were assayed in vitro in a model tumor cell line (C6 rat glioma cell line). An attempt to correlate the different parameters governing the complex phenomenology observed has been made. Whereas all the formulations investigated display a low toxicity, that increases with the increase of the lipid–DNA molar charge ratio, the transfection efficiency markedly depends, besides the molar charge ratio, on the lipid composition and on the lipoplex size, in a rather correlated way. The aim of this work is to present, in a wide scenario, an example of the inter-correlation among the different parameters that influence the transfection efficiency of lipoplexes and to suggest the role exerted by the average size of the resulting aggregates in their overall effectiveness as carriers in gene therapy.     

Sizes and Conformation of the Molecules of DNA–Surfactant Complexes in Dilute Solutions and on the Atomic Smooth Substrates

The conformations of the molecules of DNA–surfactant complexes in dilute solutions and on the atomic smooth surfaces of mica and highly oriented pyrolytic graphite were comparatively studied by the methods of isothermal diffusion, electric birefringence, and atomic force microscopy. The DNA–surfactant complexes were deposited onto the substrates from a chloroform solution. The number of particles of the DNA–surfactant complex on the substrate was changed by varying the concentration of the initial solution within three orders of magnitude. The particles of a shape close to ellipsoidal, 25–70 nm in diameter and 2–4 nm high, were observed at the lowest concentration of DNA–surfactant solution on the mica substrate. The shape and size of these particles correspond to those of a single DNA–surfactant complex, calculated from its translational diffusion coefficient and the time of orientational relaxation in dilute solutions. An increase in the number of molecules deposited onto the substrate leads to an increase in the characteristic sizes of DNA–surfactant complex particles observed by the atomic force microscopy. This may be associated with the aggregation of DNA–surfactant complexes.     

Size-tuneable and micro-patterned iron nanoparticles derived from biomolecules via microcontact printing SAM-modified substrates and controlled-potential electrolyses

Site-selected and size-controlled iron nanoparticles were prepared on coplanar surfaces via microcontact printing of SAM-modified Au/mica electrodes and controlled-potential electrolytic reactions using ferritin biomolecules. Ferritin molecules packed like a full monolayer on 6-amino-1-hexanethiol (AHT)- and 11-amino-1-undecanethiol (AUT)-modified Au/mica surface via electrostatic interactions, which did not depend on the chain length of the amino terminal alkane thiols. After heat-treatment at 400 degrees C for 60 min, iron oxide nanoparticles (ca. 5 nm in diameter) derived from ferritin cores were observed at the Au/mica surface by atomic force microscopy (AFM). On the study on the electrochemistry of ferritin immobilized onto AHT- and AUT-modified Au/mica electrodes, the redox response of the ferritin immobilized AHT-modified electrode was clearly observed. On the other hand, no redox peak for ferritin was obtained at the AUT-modified electrode. The electron transfer between ferritin and the electrode through the AUT membrane could not take place. The difference in the electrochemical response of ferritin immobilized onto AHT- and AUT-modified Au/mica was caused by the chain length of the amino terminal alkane thiols. Uniform patterns of AHT and AUT on the Au/mica electrode surface were performed by use of a poly(dimethylsiloxane) (PDMS) stamp. After the immobilization of ferritin onto both AHT- and AUT-modified electrode surfaces, the modified electrode was applied to a -0.5 V potential for 30 min in a phosphate buffer solution. After this procedure, the PDMS stamp patterning image appeared by scanning electron microscopy (SEM) image. The SEM results induced by the size change of the ferritin core consisting of iron(III) by electrolysis.     

Time-dependent conformational changes in fibrinogen measured by atomic force microscopy

Tapping-mode atomic force microscopy was used to study the time-dependent changes in the structure of fibrinogen under aqueous conditions following adsorption on two model surfaces: hydrophobic graphite and hydrophilic mica. Fibrinogen was observed in the characteristic trinodular form, and the dimensions of the adsorbed molecules were consistent with previously reported values for these surfaces. On the basis of the differences in the relative heights of the D and the E domains, four orientation states were observed for fibrinogen adsorbed on both the surfaces. On graphite, the initial asymmetric orientation states disappeared with spreading over time. Some small lateral movements of the adsorbed proteins were observed on mica during repeated scanning, whereas no such movement was observed on graphite, indicating strong adhesion of fibrinogen to a hydrophobic surface. Spreading kinetics of fibrinogen on the two surfaces was determined by measuring the heights of the D and E domains over a time period of approximately 2 h. On graphite, the heights of both the D and E domains decreased with time to a lower plateau value of 1.0 nm. On mica, the heights of both the D and E domains showed an increase, rising to an upper plateau value of approximately 2.1 nm. The spreading of the D and E domains on graphite was analyzed using an 'exponential-decay-of-height' model. A spreading rate constant of approximately 4.7 x 10(-4) s(-1) was observed for the whole fibrinogen molecule adsorbed on graphite, corresponding to a free energy of unfolding of approximately 37 kT. Extrapolation of the exponential curve in the model to t = 0 yielded values of 2.3 and 2.2 nm for the heights of the D and the E domains at the time of contact with the hydrophobic graphite substrate, significantly less than their free solution diameters. A two-step spreading model is proposed to explain this observation.     

From clusters to fibers: parameters for discontinuous para-hexaphenylene thin film growth

All relevant steps of discontinuous thin film growth of para-hexaphenylene on muscovite mica (0 0 1) from wetting layer over small and large clusters to nanofibers are observed and investigated in detail by a combined polarized fluorescence and atomic force microscopy study. From a variation of film thickness and surface temperature, we determine effective activation energies for cluster growth of 0.17 eV, for nanofiber length growth of 0.46 eV, for width growth of 0.19 eV, and for height growth of 0.07 eV. The corresponding exponential prefactors for the nanofiber growth are 1 x 10(9), 6 x 10(4), and 3 x 10(2) nm. Polarized fluorescence studies reveal that nanofibers grow along the grooves of the mica surface and that they do not change direction if they cross an even number of mica surface steps, while they change direction by 120 degrees for an odd number of steps. These results are taken as an input for a model of the unidirectional growth process on mica. Absolute parameters allowing one to grow nanofibers of predetermined morphology via organic molecular beam epitaxy are also given.     

Studies of poly-<Emphasis Type="Italic">L</Emphasis>-lysine-starch nanoparticle preparation and its application as gene carrier

Anion starch nanoparticle (StNP) with a diameter of 50 nm was prepared in water-in-oil microemulsion, with soluble starch as raw materials and POCl₃ as crosslinking agent. PLL-StNP was prepared by linking poly-L-lysine (PLL) on the surface of StNP. At the same time, the size of PLL-StNP and its stability in aqueous solution were checked by AFM. The analysis of plasmid DNA binding, DNase I enzymatic degradation, toxicity and transfection were done. We discovered that PLL-StNP may be used as non-virus nanoparticle gene carrier. And we developed the method of preparing PLL-StNP gene carrier and used it in cell transfection. As non-virus gene carrier, PLL-StNP has some advantages, such as large load of DNA, high transfection efficiency, low cell toxicity and biodegradability.     

Protonation of Lysozymes and Its Consequences for the Adsorption onto a Mica Surface

Several physicochemical properties of chicken egg white lysozyme (LSZ) in electrolyte solutions were determined. The hydrodynamic diameter of LSZ at an ionic strength of 0.15 M was found to be 4.0 nm. Using the determined parameters, the number of uncompensated (electrokinetic) charges, N(c), on the molecule surface was calculated from the electrophoretic mobility data. It was found that the N(c) = 2.8 at pH = 3.0 and an ionic strength of I = 0.15 M. At the lower ionic strength, I = 1 × 10(-3) M, this positive charge increased to N(c) = 5.6 at a pH = 3.0 The physicochemical characteristics were supplemented by the dynamic viscosity measurements. The intrinsic viscosity and the hydrodynamic diameter results were compared with theoretical predictions from Brenner's model. Using this approach, it was found that the effective molecule length of LSZ is equal to L(ef) = 5.6 nm. Additional information on the LSZ adsorbed films was obtained by the contact angle measurements. The notably large contact angles were measured on LSZ films formed under the conditions where both the LSZ and the mica were oppositely charged. The higher the positive zeta potential of LSZ, the greater the contact angle measured, which indicates that LSZ affinity for the adsorption on mica increases with its uncompensated charge. The adsorption dependence on the zeta potential of LSZ was explained, assuming a roughly uniform distribution of the net charge on the molecule surface. This assumption is supported by the results of depositing negatively charged, fluorescent latex particles onto the mica surface, which had been modified by LSZ adsorption. The highest latex coverage was formed on mica surfaces that had first been coated with LSZ solutions of lower pH, as a result of the increasing charge of LSZ monolayers in this condition.     

Structure of the complex monolayer of gemini surfactant and DNA at the air/water interface

The properties of the complex monolayers composed of cationic gemini surfactants, [C(18)H(37)(CH(3))(2)N(+)-(CH(2))(s)-N(+)(CH(3))(2)C(18)H(37)],2Br(-) (18-s-18 with s = 3, 4, 6, 8, 10 and 12), and ds-DNA or ss-DNA at the air/water interface were in situ studied by the surface pressure-area per molecule (π-A) isotherm measurement and the infrared reflection absorption spectroscopy (IRRAS). The corresponding Langmuir-Blodgett (LB) films were also investigated by the atomic force microscopy (AFM), the Fourier transform infrared spectroscopy (FT-IR), and the circular dichroism spectroscopy (CD). The π-A isotherms and AFM images reveal that the spacer of gemini surfactant has a significant effect on the surface properties of the complex monolayers. As s ≤ 6, the gemini/ds-DNA complex monolayers can both laterally and normally aggregate to form fibril structures with heights of 2.0-7.0 nm and widths of from several tens to ~300 nm. As s > 6, they can laterally condense to form the platform structure with about 1.4 nm height. Nevertheless, FT-IR, IRRAS, and CD spectra, as well as AFM images, suggest that DNA retains its double-stranded character when complexed. This is very important and meaningful for gene therapy because it is crucial to maintain the extracellular genes undamaged to obtain a high transfection efficiency. In addition, when s ≤ 6, the gemini/ds-DNA complex monolayers can experience a transition of DNA molecule from the double-stranded helical structure to a typical ψ-phase with a supramolecular chiral order.     

Nanoscale morphology of melt crystallized polyethylene/graphite (HOPG) interphase

High density polyethylene (PE) was crystallised from the melt on freshly cleaved surface of highly oriented pyrolitic graphite (HOPG) or mica. Atomic force microscopy (AFM) studies of structure of the polymer surface adjacent to the graphite or mica were performed after peeling of from the substrate. Significant differences of crystalline structure on the interface were found between PE crystallised on graphite and mica. The surface of polyethylene crystallised on graphite shows large areas with regularly arranged rectangular structures. These objects (ca 20‐80 nm big) probably represent the nucleation centres of the lamellar growth. The surface of polyethylene crystallised at mica surface shows some dot‐like structures showing no particular arrangement.     

Ternary dinuclear copper(II) complexes of a hydroxybenzamide ligand with diimine coligands: the 5,6-dmp ligand enhances DNA binding and cleavage and induces apoptosis

The dinuclear copper(II) complexes [Cu(2)(LH)(2)(diimine)(2)(ClO(4))(2)](ClO(4))(2) (1-4), where LH = 2-hydroxy-N-[2-(methylamino)ethyl]benzamide and diimine = 2,2'-bipyridine (bpy; 1), 1,10-phenanthroline (phen; 2), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp; 3), and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq; 4), have been isolated and characterized. The X-ray crystal structure of complex 1 contains two copper(II) centers bridged by the phenolate moiety of the amide ligand. All of the complexes display a ligand-field band (630-655 nm) and the PhO(-)-to-Cu(II) ligand-to-metal charge-transfer band (405-420 nm) in solution. Absorption and emission spectral studies and viscosity measurements indicate that complex 4 interacts with calf thymus DNA more strongly than all of the other complexes through strong partial intercalation of the extended planar ring (dpq) with a DNA base stack. Interestingly, 3 exhibits a DNA binding affinity higher than 2, suggesting the involvement in hydrophobic interaction of coordinated 5,6-dmp with the DNA surface. In contrast to the increase in relative viscosities of DNA bound to 2-4, a decrease in viscosity of DNA bound to 1 is observed, indicating a shortening of the DNA chain length through formation of kinks or bends. All of the complexes exhibit an ability to cleave DNA (pUC19 DNA) in a 5% DMF/5 mM Tris-HCl/50 mM NaCl buffer at pH 7.1 in the absence of an oxidant at 100 μM complex concentration, which varies as 4 > 2 > 1 > 3. The order of DNA the cleavage ability at 30 μM concentration in the presence ascorbic acid is 4 > 2 > 1 > 3, and, interestingly, 4 alone shows an ability to convert supercoiled DNA into nicked-coiled DNA even at 6 μM concentration, beyond which complete degradation is observed and the pathway of oxidative DNA cleavage involves hydroxyl radicals. In the presence of distamycin, all of the complexes, except 3, show decreased DNA cleavage activity, suggesting that the complexes prefer to bind in the DNA minor groove. All of the complexes exhibit prominent DNA cleavage even at very low concentrations (nM) in the presence of H(2)O(2) as an activator, with the order of cleavage efficiency being 3 > 2 > 4 > 1. Studies on the anticancer activity toward HEp-2 human larynx cell lines reveal that the ability of the complexes to kill the cancer cell lines varies as 3 > 4 > 2 > 1. Also, interestingly, the IC(50) value of 3 is lower than that of cisplatin, suggesting that the hydrophobicity of methyl groups on the 5 and 6 positions of the complex enhances the anticancer activity. The mode of cell death effected by the complex has been explored by using various biochemical techniques like comet assay, mitochondrial membrane potency, and Western blotting. The complex has been found to induce nuclear condensation and fragmentation in cell lines. Also, it triggers activation of caspases by releasing cytochrome c from mitochondria to cytosol, suggesting that it induces apoptosis in cells via the mitochondrial pathway.     

Probing colloidal forces between a Si3N4 AFM tip and single nanoparticles of silica and alumina

The atomic force microscope (AFM) has been used to measure surface forces between silicon nitride AFM tips and individual nanoparticles deposited on substrates in 10(-4) and 10(-2) M KCl solutions. Silica nanoparticles (10 nm diameter) were deposited on an alumina substrate and alumina particles (5 to 80 nm diameter) were deposited on a mica substrate using aqueous suspensions. Ionic concentrations and pH were used to manage attractive substrate-particle electrostatic forces. The AFM tip was located on deposited nanoparticles using an operator controlled offset to achieve stepwise tip movements. Nanoparticles were found to have a negligible effect on long-range tip-substrate interactions, however, the forces between the tip and nanoparticle were detectable at small separations. Exponentially increasing short-range repulsive forces, attributed to the hydration forces, were observed for silica nanoparticles. The effective range of hydration forces was found to be 2-3 nm with the decay length of 0.8-1.3 nm. These parameters are in a good agreement with the results reported for macroscopic surfaces of silica obtained using the surface force apparatus suggesting that hydration forces for the silica nanoparticles are similar to those for flat silica surfaces. Hydration forces were not observed for either alumina substrates or alumina nanoparticles in both 10(-4) M KCl solution at pH 6.5 and 10(-2) M KCl at pH 10.2. Instead, strong attractive forces between the silicon nitride tip and the alumina (nanoparticles and substrate) were observed.     

Forces between hydrophilic surfaces adsorbed with apolipoprotein AII alpha helices

To provide better understanding of how a protein secondary structure affects protein-protein and protein-surface interactions, forces between amphiphilic alpha-helical proteins (human apolipoprotein AII) adsorbed on a hydrophilic surface (mica) were measured using an interferometric surface force apparatus (SFA). Forces between surfaces with adsorbed layers of this protein are mainly composed of electrostatic double layer forces at large surface distances and of steric repulsive forces at small distances. We suggest that the amphiphilicity of the alpha-helix structure facilitates the formation of protein multilayers next to the mica surfaces. We found that protein-surface interaction is stronger than protein-protein interaction, probably due to the high negative charge density of the mica surface and the high positive charge of the protein at our experimental conditions. Ellipsometry was used to follow the adsorption kinetics of this protein on hydrophilic silica, and we observed that the adsorption rate is not only controlled by diffusion, but rather by the protein-surface interaction. Our results for dimeric apolipoprotein AII are similar to those we have reported for the monomeric apolipoprotein CI, which has a similar secondary structure but a different peptide sequence and net charge. Therefore, the observed force curves seem to be a consequence of the particular features of the amphiphilic alpha-helices.     

Assemblies of poly(styrene/⇌-tert-butoxy-ω-vinyl-benzyl-poryglycidol) Microspheres with different diameters deposited on mica plates

Formation of poly(styrene/α-tert-butoxy-ω-vinyl-benzyl-polyglycidol) microsphere assemblies on mica plates modified with 3-aminopropyltriethoxysilane was investigated. Microsphere assemblies contained two types of particles similar with respect of their chemical structure but with different diameters (D _n = 1000 and 350 nm). Methods of particle deposition included: deposition from water suspension of a mixture of small and large particles on mica plates placed at the bottom of suspension container, deposition of particles from a drop of ethanol suspension (containing large and small microspheres) placed on the mica substrate, deposition of microspheres on modified mica plates crossing the liquid-air interface-sequential deposition of large and small particles, and one-batch deposition from a mixed water suspension of large and small microspheres. Deposition from water suspension containing large and small microspheres on plates placed on the bottom of suspension container yielded assemblies with large particles randomly distributed among the small ones. Fraction of large particles in adsorbed particle assembly was smaller than fraction of large particles in suspension. Particle assemblies prepared by placement of ethanol suspension of large and small microspheres on mica were composed of quite regularly distributed large particles among the small ones. A two step process consisting of withdrawal of mica plate from water suspension of large particles and then on using this plate as substrate in a second step during which the plate was withdrawn from suspension of small particles yielded particle assemblies containing aggregates of large particles randomly distributed among the small ones. Withdrawal of mica plates from water suspension of large and small microspheres resulted in particle assemblies composed of regularly distributed stripes of large and small microspheres. Formation of the described above microsphere assemblies is possible only in case of reversible adsorption of particles.     

Absorption spectroscopic and FTIR studies on EDA complexes between TNT (2,4,6-trinitrotoluene) with amines in DMSO and determination of the vertical electron affinity of TNT

TNT (2,4,6-trinitrotoluene) formed deep red 1:1 CT complexes with chromogenic agents like isopropylamine, ethylenediamine, bis(3-aminopropyl)amine and tetraethylenepentamine in DMSO. The complexes were also observed in solvents like methanol, acetone, etc. when the amines were present in large excess. The isopropylamine, complex showed three absorption peaks (at 378, 532 and 629 nm) whereas higher amines showed four peaks (at 370, 463, 532 and 629 nm). The peak at 463 nm vanished rapidly. The peak of the complexes near 530 nm required about 8-10 min to develop and the complexes were stable for about an hour but the peak slowly shifted towards 500 nm and the complexes were found to be stable for more than 24 h. The evidence of complex formation was obtained from distinct spots in HPTLC plates and from the shifts in frequencies and formation of new peaks in FTIR spectra. The peaks near 460 nm (transient) and 530 nm may be due to Janovsky reaction but could not be established. The extinction coefficients of the complexes were determined directly which enabled the accurate determination of the association constants KDA with TNT and amines in stoichiometric ratios. The results were verified using iterative method. The quantification of TNT was made using epsilon value of the complex with ethylenediamine. The vertical electron affinity (EA) of TNT was calculated using the method suggested by Mulliken.