Maria A. Kalinina

Lateral 2D-3D phase segregation in fatty acid/fatty amine monolayers induced by langmuir-blodgett deposition.

We describe the formation of lateral 2D-3D patterns in mixed multilayer LB films of stearic acid (SA) and octadecylamine (ODA) deposited from aqueous subphases at a basic pH. The 3D particles of SA constituting the micrometer-scale linear assemblies in the LB film are assumed to segregate at the three-phase contact line in the course of film deposition. This 2D-3D phase separation of the two-component system presumably originates from the substrate-induced lowering of the collapse point of SA that leads to spontaneous 3D condensation of an acid on a solid support. The morphology of SA/ODA LB patterns is sensitively influenced by the deposition speed and surface pressure, while the chemistry of the solid support does not affect the resulting structures. The possible mechanism that controls the specific orthogonal arrangement of the 3D phase of SA in the LB film through wettability oscillations is suggested.

Layer-by-layer assembly of porphyrin-based metal–organic frameworks on solids decorated with graphene oxide

Fabrication of metal–organic frameworks (MOFs) as films on surfaces is a challenging and actively developed field in the context of potential applications of surface-integrated MOFs (SURMOFs) in sensing, catalysis and molecular electronics. Herein, we report a method for the preparation of composites of graphene oxide (GO) and zinc tetracarboxyphenyl porphyrin SURMOFs, which are potentially useful as synergetic catalysts on planar solid supports. The SURMOF films were assembled via layer-by-layer coordination of zinc porphyrins with ZnAc2 clusters on the ultrathin surface coatings of GO. We found that non-covalent adsorption of zinc acetate on the GO films is essential for anchoring porphyrin molecules in the growth-initiating template layer. UV-vis spectroscopy provided evidence for a stepwise assembly of the deposited SURMOF films. By using a combination of X-ray diffraction, scanning electron microscopy and atomic force microscopy methods, we show that the resulting GO-associated SURMOFs exhibit a leaflet-like planar morphology with out-of-plane periodicity. Because of the influence of the well-defined surface geometry, the molecular organization in thin SURMOFs is different from that of synthetic bulk materials with a similar composition. The results of BET method measurements suggest that the fabricated SURMOF films have exceptionally large surface areas and adsorption capacities. Our results provide a basis for new types of composite SURMOF structures using GO surface coatings as growth-guiding scaffolds for metal–organic coordination networks integrated with various solid supports.

Decaying of Artemia salina in clay colloids: 14-month experimental formation of subfossils

Abstract. The mechanism that guides the formation of exceptionally preserved fossils with soft tissues variously displayed is a paramount challenge to paleontology. The key question for exceptional preservation is the nature of the slowdown of decay and acceleration of soft tissue mineralization. Here we report the experimental formation of subfossils of the brine shrimp Artemia salina (Crustacea, Branchiopoda), which were produced during 14 months of aging in a kaolinite clay sediment. EDS/SEM elemental analyses showed that the subfossils were preserved as thin clay-organic replicas that displayed fine anatomical details. Decomposition in the clay-colloidal solution established highly heterogeneous acidic conditions, with the lowest pH typically found in the vicinity of the buried organisms, and visually manifested in patchy coloration of the sediment. Elevated acidity is likely what ultimately slowed the decay. An acidic environment increases the rate of clay destruction and, consequently, the diffusion rate decline. As a result, the acidic products quickly accumulate around a buried body; this in turn inhibits bacterial proliferation, accelerates the acidic hydrolysis of clay and, accordingly, the release of tanning and mineralizing agents. The subfossils remained stable under experimental high pressure and temperature. These model subfossils exhibit features that are typical of some Lagerstätten fossils preserved in fine-grained sediments.

Conformational tuning of sensing Langmuir-Blodgett membranes for selective determination of metal ions, anions, and molecular fragments

In this work, we describe a novel approach to prepare ionophore-based Langmuir-Blodgett (LB) sensors with desirable analytical characteristics via fine tuning of macrocycle conformation during the assembly of the membrane. In this context, two related types of LB sensors of dicetyl cyclen and its complex with Zn/sup 2+/ were constructed. The multi-use mass-sensitive and electrochemical LB-multilayer sensors of DCC were used for selective and accurate detection of divalent copper traces (down to 10/sup -9/M) in aqueous solution, containing other similar metal ions (Zn/sup 2+/ and Ni/sup 2+/). The SPR-based imide recognition modeled with uracil binding and the phosphate recognition were investigated with SAM-supported LB monolayers of zinc(II)-dycetyl cyclen complexes. Controlled steric constraints imposed on Zn(II)-DCC structure upon membrane formation resulted in exceptional selectivity toward inorganic HPO/sub 4//sup 2-/ (at least down to 10/sup -8/M of anions).

Highly tunable plasmonic assemblies of gold nanoparticles: in-plane manipulation of plasmon coupling with nanometer precision

A new, highly flexible and operationally simple method was developed for tailoring plasmon coupling in 1D and 2D assemblies of gold nanoparticles with a precision of nanometers in a wide spectral range.

Langmuir–Blodgett Monolayers and Films of Alkylated Tetraazacrowns Containing Metal Ions and Nanoparticles

The behavior of individual 1,7-dicetyltetraaza-12-crown-4 and its mixture with 1,4,7,10-tetracetyltetraaza-12-crown-4 in the Langmuir monolayers at the subphases containing Cu(II) ions or colloidal gold particles is studied. Based on the compression isotherms, the complexing ability of these amphiphilic cyclenes in a monolayer at the surface of aqueous dilute solutions of copper salt is established. It was shown that the fraction of complexes in a monolayer is proportional to the copper ion concentration in the subphase. Using surface balance, atomic force microscopy, and electron microscopy methods, it was revealed that the monolayer of dicetylcyclene at the surface of gold hydrosol binds nanoparticles from the subphase; the number of particles bound by the monolayer is proportional to their content in the hydrosol. The Langmuir–Blodgett films (LBF) of dicetylcyclene are prepared; their ability to bind copper ions from solution was disclosed by quartz crystal microbalance. The LBFs of dicetylcyclene containing gold nanoparticles in each layer are assembled.

Molecular recognition of uracil and adenine nucleobases by Langmuir monolayers of metal complexes of amphiphilic cyclen

The molecular recognition of purine and pyrimidine nucleobases (adenine and uracil) by the Langmuir monolayers of amphiphilic macrocyclic tetraamine (dicetylcyclen) is studied using independent methods of quartz microbalance and FTIR spectroscopy. Data show that the specific binding of pyrimidine base occurs in the presence of zinc ions and results from the formation of macrocyclic complex with metal ion followed by the coordination of uracil imide group to the metal complex. Experimental conditions that favor an increase in the efficiency of the recognition of uracil by the monolayer of metal complexes are determined. The inhibition effect of trace amounts of copper ions in the subphase containing zinc chloride-uracil mixture on the uracil recognition by the monolayer of dicetylcyclen is revealed. It is also established that the monolayer of Zn2+-dicetylcyclen complexes is inactive with respect to purine base (adenine). Therefore, the results suggest that monolayers of amphiphilic cyclen can be used as planar biomimetic modeling the function of active sites of transcription metalloproteins.

Langmuir-Blodgett composite films for the selective determination of calcium in aqueous solutions

A sensitive membrane of a new type was suggested for the determination of calcium ions in aqueous solutions. Polylayer membranes were formed by the Langmuir-Blodgett method from octadecylamine and 1,2-bis-(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid. When brought in contact with an aqueous solution of a calcium salt, the ultrathin film sorbs metal ions. The chelator then transports metal ions over the whole membrane volume, and the ions are accumulated in the form of calcium hydroxide crystallites in regions enriched in the diphilic base. The main analytic parameters were determined by piezoquartz weighing, electrochemical impedance spectroscopy, and surface plasmon resonance spectroscopy. The response of sensor elements of this type was shown to be a linear function of the logarithm of the concentration of calcium ions over the concentration range 10−8–10−1 mol/l at the contact time between the film and the solution under study no more than 10 s. The conclusion was drawn that the membranes obtained remained highly sensitive with respect to calcium ions in 0.1 M solutions of NaCl and were selective with respect to other biologically relevant cations.

Kinetics of Complexation in the Monolayers of Amphiphilic Dicetylcyclene on the Surface of Aqueous Copper(II) Chloride Solutions

The kinetics of complexation in monolayers of dicetycyclene at the surface of aqueous copper(II) chloride solutions was studied. It was shown that the changes in the phase state of monolayer related to the conformational transitions of macrocycle are responsible for the differences in the rate and binding mechanism of copper ions. It was concluded that the sterically more advantageous (for the coordination with the metal ion) conformation of macrocyclic polyamine is ensured in a monolayer. In addition, it was established that the rate and mechanism of complexation in such monolayers greatly depend on the degree of protonation of ligands, the latter being dependent on the subphase pH. It was also demonstrated that an increase in subphase pH to 7 and higher results in an almost total suppression of metal ion binding due to strong conformational distortion of dicetylcyclene macrocycles in a monolayer and the hydrogen bonding between macrocycles.

PERSISTENCE OF EXTERNAL ANATOMY OF SMALL CRUSTACEANS IN A LONG TERM TAPHONOMIC EXPERIMENT

Abstract:  Although studied for more than a century, the preservation mechanisms of soft-bodied organisms in Lagerstätten remain disputable. One aspect of this phenomenon, the role of sediments in the decay and preservation of soft tissues, is understudied. We present the results of an 18-month decay experiment that shows the difference between the preservation of the crustacean Artemia salina buried in marine water and inside clay sediment. We found that the decay of the external tissues of A. salina is slower in the sediment than in marine water, while the internal anatomy decays rapidly in both settings. This results in the formation of exuviae-like structures, accounted for not by the recalcitrance of external tissues, but by the burying conditions in the thick marine sediment. The experiment indicates the importance of organic-mineral interactions in the understanding of the taphonomic retarding of soft-tissue decay and the persistence of fine external anatomical features.