Polar Self-Organization of Ferroelectric Nematic-Liquid-Crystal Molecules on Atomically Flat Au(111) Surface.

Understanding nanoscale mechanisms responsible for the recently discovered ferroelectric nematics can be helped by direct visualization of self-assembly of strongly polar molecules. Here, we report on scanning tunneling microscopy studies of monomolecular layers of a ferroelectric nematic liquid crystal on a reconstructed Au(111) surface. The monolayers are obtained by deposition from a solution at ambient conditions. The adsorbed ferroelectric nematic molecules self-assemble into regular rows with tilted orientation, resembling a layered structure of a smectic C. Remarkably, each molecular dipole in this architecture is oriented along the same direction giving rise to polar ferroelectric ordering.

Salvia dumetorum essential oil: GC-MS analysis, antibacterial activity and effect on the formation of Streptococcus mutans biofilms.

Salvia dumetorum essential oil (SDEO) was obtained using a Clevenger apparatus by hydrodistillation approach. The chemical composition of the essential oil was determined by GC-MS analysis. In this study SDEO was screened for its antibacterial activity against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Candida albicans and the amount of biofilm formed by Streptococcus mutans bacteria. For the first time the chemical composition of SDEO growing in Central Kazakhstan was established. The results obtained from GC-MS showed the predominance of sesquiterpenoids (54.15%). The antibacterial study results showed that SDEO exhibited strong antibacterial activity against B. subtilis and S. aureus in vitro and also demonstrated an inhibitory effect on S. mutans biofilm formation on 1% sucrose medium. During the study, no antibacterial activity was detected against E. coli and C. albicans. These results demonstrated that SDEO can be used in the development of new antibacterial and anti-caries therapeutic dental products.

Level of FABP3, FABP4, Nt-proBNP and Total Cardiovascular Risk in the Population of Central Kazakhstan.

AIM: The study analyzed the level of cytokines playing the significant role in the diagnosis of circulatory system diseases and total cardiovascular risk. MATERIAL AND METHODS: The study involved 1,244 residents of Karaganda region. We had studied baseline participant characteristics, in addition to calculating the total cardiovascular risk and assessment of Fatty Acid Binding Proteins 3 (FABP3), Fatty Acid Binding Proteins 4 (FABP4) and N-Terminal Prohormone of Brain Natriuretic Peptide (NT-proBNP) level. RESULTS: The results showed the combination of high cardiovascular risk (CVR) with increased titers of cardiac markers, reflecting common pathogenic mechanisms in its development, among residents of Karaganda region. CONCLUSION: The combination of high CVR with the increased titers of cardiac markers showed common pathogenic mechanisms in its development, and support the diagnostic and prognostic value of these parameters among residents of Karaganda region, and also reflects the possibility to include these cardiac markers in the program of screening survey of population for early prevention of cardiovascular disease and its complications.

Emergence of chirality in hexagonally packed monolayers of hexapentyloxytriphenylene on Au(111): a joint experimental and theoretical study.

We investigate the expression of chirality in a monolayer formed spontaneously by 2,3,6,7,10,11-pentyloxytriphenylene (H5T) on Au(111). We resolve its interface morphology by combining scanning tunneling microscopy (STM) with theoretical calculations of intermolecular and interfacial interaction potentials. We observe two commensurate structures. While both of them belong to a hexagonal space group, analogical to the triangular symmetry of the molecule and the hexagonal symmetry of the substrate surface, they surprisingly reveal a 2D chiral character. The corresponding breaking of symmetry arises for two reasons. First it is due to the establishment of a large molecular density on the substrate, which leads to a rotation of the molecules with respect to the molecular network crystallographic axes to avoid steric repulsion between neighboring alkoxy chains. Second it is due to the molecule-substrate interactions, leading to commensurable large crystallographic cells associated with the large size of the molecule. As a consequence, molecular networks disoriented with respect to the high symmetry directions of the substrate are induced. The high simplicity of the intermolecular and molecule-substrate van der Waals interactions leading to these observations suggests a generic character for this kind of symmetry breaking. We demonstrate that, for similar molecular densities, only two kinds of molecular networks are stabilized by the molecule-substrate interactions. The most stable network favors the interfacial interactions between terminal alkoxy tails and Au(111). The metastable one favors a specific orientation of the triphenylene core with its symmetry axes collinear to the Au⟨110⟩. This specific orientation of the triphenylene cores with respect to Au(111) appears associated with an energy advantage larger by at least 0.26 eV with respect to the disoriented core.

Switching at the nanoscale: light- and STM-tip-induced switch of a thiolated diarylethene self-assembly on Au(111).

The light-induced and STM-tip-induced switching of photochromic thiol functionalized terphenylthiazole-based diarylethene self-assembly on Au(111) has been investigated in ambient conditions. For such a purpose, we took advantage of the formation of highly ordered domains of opened-ring (1o) or closed-ring (1c) diarylethene isomers. We evidenced a STM-tip-induced switching for the 1o isomer characterized by a tip bias threshold of 1000 mV above which switching of all molecules of the ordered 1o domains occurs into the 1c isomer. In contrast, switching from 1c form into 1o form is not observed at the same tunnelling conditions within a domain formed by ordered 1c molecules. We compared tip-induced switching of ordered 1o domains and switching of single 1o isomers embedded in 1c domains. This led to the demonstration that the process of switching of the 1o isomer is determined by geometry of the molecules but also that the stability of the switched 1c isomer depends on the nature of the surrounding isomers. We also compare tip-induced switching and switching under the action of external UV light irradiation of ordered 1o domains. In contrast with STM tip-induced switching, the UV light induces switching of 1o domains into their stable 1c form, in agreement with a collective switching under irradiation, which cannot occur under the action of STM tip.

Two-dimensional self-assembly and complementary base-pairing between amphiphile nucleotides on graphite.

2D supramolecular structures on HOPG by self-assembly of physisorbed amphiphile nucleotides have been successfully imaged by high resolution STM. The organization of the systems depends on the nature of nucleic bases. In the case of the thymidine derivative a head-to-tail self-assembly is observed, whereas the amphiphile adenosine affords head-to-head nanostructures. The co-adsorption of complementary A+T amphiphile molecules induces the formation of a third head-to-head 2D supramolecular structure stabilized via base pairing. Molecular modelling calculations including the graphite surface provide models for all the 2D supramolecular systems observed.

Rotational polymorphism in 2-naphthalenethiol SAMs on Au(111).

We evidence by STM that 2-naphthalenethiol self-assembled monolayers formed at the n-tetradecane/Au(111) interface coexist as two structural phases which both possess molecules into two different orientations (standing and lying). Such a rotational polymorphism is observed and understood at the molecular level for the first time.

Structural evolution of hexa-peri-hexabenzocoronene adlayers in heteroepitaxy on n-pentacontane template monolayers.

The growth and structure of self-assembled adlayers of hexakis(n-dodecyl)-peri-hexabenzocoronene (HBC-C12) adsorbed on highly ordered pyrolitic graphite (HOPG) decorated by an n-pentacontane (n-C50H102) monolayer have been investigated by scanning tunneling microscopy (STM). Whereas on HOPG the HBC-C12 molecules readily self-assemble into a unique stable 2D structure, on the [n-C50H102 monolayer/graphite] system we observe morphological phase transitions with formation of time dependent alpha, beta, and gamma phases (alpha-->beta-->gamma). The initial alpha-phase is similar to that obtained on bare graphite, while intermediate beta- and final gamma-structures present molecular dimers and rows, respectively. The observed two-dimensional polymorphism is due to weak interaction between HBC-C12 molecules and n-C50H102-modified graphite substrate. Our results constitute an important step toward the control of the growth and structure of highly ordered monolayers of functional conjugated molecules by modifying the graphite surface with an n-alkane monolayer of appropriate chain length.

Substrate-induced pairing in 2,3,6,7,10,11-hexakis-undecalkoxy-triphenylene self-assembled monolayers on Au111.

We present an STM study of self-assembled monolayers of 2,3,6,7,10,11-undecalkoxy-substituted triphenylene (T11) at the n-tetradecane/Au(111) interface under ambient conditions. T11 molecules self-organize as paired rows with molecules lying flat on the surface in an antiparallel position. Three alkyl chains of each T11 molecule align along the 110 direction of the underlying Au(111) substrate. The association of T11 in molecular pairs appears to result from a substrate-induced mechanism governed by the strong anisotropic interaction between T11 alkyl chains and Au(111).

A molecular approach to self-assembly of trimethylsilylacetylene derivatives on gold.

We recently discovered that a linear multifunctional trimethylsilylacetylene (TMSA) compound forms long-range and highly stable self-assembled monolayers (SAMs) on reconstructed Au(111). To better understand the interactions governing self-assembly in this new system, we synthesized a series of homologue organosilanes and performed scanning tunneling microscopy (STM) measurements at the Au(111)/n-tetradecane interface. The four TMSA-terminated linear silanes that we synthesized self-assemble in similar ways on gold, with the molecules standing upright on the surface. In contrast, compounds with a slightly modified terminal group but the same polyunsaturated linear chain above the TMSA head do not self-assemble. In particular, substituting a methyl group of TMSA with a more bulky one prevents self-assembly. Removing the C triple bond C triple bond of TMSA or substituting the Si atom by a C atom also hinders self-assembly. Finally, substituting one methyl group of TMSA by a hydrogen atom induces self-assembly but in a different geometry, with the molecules lying flat on the gold surface in a quasi-epitaxy mode. Our molecular approach demonstrates the key role played by the TMSA head in self-assembly, its origin being twofold: 1) the TMSA layers are commensurate to the Au(111) adlattice along the <112> direction, and 2) the C triple bond C triple bond of TMSA activates the Si atom and induces the creation of a surface Si-Au chemical bond. The highly stable TMSA-based SAMs appear then as promising materials for applications in surface modification.

Long-range self-assembly of a polyunsaturated linear organosilane at the n-tetradecane/Au(111) interface studied by STM.

We report on the formation of self-assembled monolayers of 13-(trimethylsilyl)-1-tridecene-6,12-diyne [C13H17-Si(CH3)3], an organosilane derivative with a linear polyunsaturated chain, on Au(111) substrates. Molecular resolution STM images recorded at the liquid-solid interface between gold and tetradecane reveal a long-range and densely packed hexagonal lattice with a ( radical3 x radical3)R30 degrees -like structure commensurate against gold adlattice.