Dan Scutaru

Synthetic sialic-acid-containing polyvalent antiviral inhibitors

This review gives a brief survey of synthetic inhibitors of influenza virus which have been synthesized to date. It starts with a short introduction which describes the structure and mechanism of action of influenza virus and continues with the main research directions that have been used in order to inhibit the virus. This is followed by discussion of various synthetic materials, including synthesis and antiviral properties, which that have been tested against influenza virus. The most potent inhibitory compounds proved to be polyvalent, because of their high binding affinity and steric stabilization. Finally we conclude with a brief discussion on structural characteristics, a summary, and outlook overview.

The liquid crystalline behaviour of ferrocene derivatives containing azo and imine linking groups

The synthesis and mesogenic properties of some Schiff bases containing ferrocene, azobenzene units and flexible end chains with 17 or 18 carbon atoms are reported. The compounds have been characterized by 1H‐NMR and 13C‐NMR spectroscopy, DSC and optical microscopy in polarized light.

Phase transfer catalysis in polycondensation processes—XI. Liquid crystalline copolyethers based on 4,4′-dihydroxydiphenyl, bisphenol-a, 4,4′-dihydroxyazobenzene and 3,3-bis(chloromethyl)oxetane

Abstract Copolycondensations of 3,3-bis(chloromethyl)oxetane with various diphenols under phase transfer conditions have been performed. The copolyethers show mesomorphism; investigations of their LC properties by optical polarization microscopy and DSC analyses were carried out.

Liquid crystalline polymers: 14. Synthesis and thermal behaviour of some polyethers containing azo-mesogens

Abstract The paper presents a study on the relationship between the structure of macromolecular chain and its capacity to generate a mesophase, when mesogens with an azobenzene structure are implied. The polymers have been synthesized by phase transfer catalysis starting from 1,9-dichlorononane and different bisphenols: diphenyl-4,4 ′ -bis[(azo-4-)phenol], 4,4 ′ -dihydroxyazobenzene, 4,4 ′ -dihydroxydiphenyl, bisphenol A and 4,4 ′ -dihydroxybenzophenone. The polymers have been characterized by 1 H-NMR spectroscopy, DSC calorimetry, optical microscopy in polarized light and thermogravimetrical analysis. Theoretical conformational studies, using molecular simulations have also been performed. Due to their particular geometry, bis-(azobenzene) units are better mesogenic groups as compared with the azobenzene ones. The highly aromatic structure makes impossible the samples isotropisation, as the degradation processes starting advance. For these polymers, under UV irradiation, due to the presence of two azo groups in each mesogen unit, strong conformational modifications are expected. The replacement of the bis-(azobenzene) moieties with azobenzene ones reduces the transition temperatures, making possible the samples isotropisation.

Neuroprotection against ischemic brain injury conferred by a novel nitrate ester

Nitrates exhibit a selectivity of action in different tissue types not fully recognized: in particular, the neuromodulatory and cardiovascular properties can be dissociated. A novel nitrate showed relatively weak systemic effects, but in the middle cerebral artery occlusion rat model of focal ischemia, reduced the cerebral infarct by 60-70% when administered 4 h after the onset of ischemia.

Ferrocene‐containing liquid crystals bearing a cholesteryl unit

The synthesis and characterization of new liquid crystalline compounds containing ferrocene azo or imino aromatic and cholesteryl units is reported. The purpose of this research was to combine the properties of metals (colour, electronic density, magnetism and polarizability) with those of chiral nematics (high birefringence and presence of physical colours) and correlate relationships between chemical structures and properties in the condensed state.

Hockey Stick Liquid Crystals Based on a 2,5-Asymmetric Disubstituted [1,3,4]Oxadiazole Core

The article describes the liquid-crystalline properties of some 2,5-asymmetric disubstituted [1,3,4]oxadiazole derivatives containing an azo and an ester linkage obtained through esterification of 2-(4-methoxyphenyl)-5-(4-hydroxyphenyl)-[1,3,4]oxadiazole with a series of 4-(4-alkoxyphenyl)-benzoic acids containing 6–10 and 18 aliphatic carbon atoms. All reported compounds present liquid-crystalline properties, evidenced by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM), with nematic and smectic C type structures, with very large range of stability of mesophases (between 130°C and 198°C on heating and 134°C and 214°C on cooling).

Synthesis and photochromic behavior of some azo-polysiloxanes modified with nucleobases or donor-acceptor groups

This paper presents the syntheses, characterization and photochromic behavior of some new azo-polysiloxanes modified with uracil, cytosine or nitro-phenolic groups. Taking into consideration the possibility of generating H-bonds or donor/acceptor interactions, this class of materials present a potential applicability in the immobilization of biomolecules and their nano-manipulations. Also, such compounds are capable of producing a fluid phase, with directional flowing capacity. For all these polymers, the molecular modeling simulations have shown disordered structures, which would generate amorphous phases, a very important aspect for molecules’ nano-manipulation. The photochromic behavior in the presence of UV irradiation was also evaluated.

Liquid crystalline polymers, 9. Synthesis and thermal behavior of some oligomers containing a diethyletheric spacer

Polyethers based on bis(2-chloroethyl) ether and various bisphenols were obtained using a phase transfer catalysis technique in a liquid/liquid system. 4,4′-Dihydroxyazobenzene, 4,4′-dihydroxybiphenyl, bisphenol A, 2,7-dihydroxynaphthalene and 4,4′-dihydroxydiphenyl) sulfide were used. Only the polymers with azobenzene and biphenyl units exhibited mesophases, since the others have semi-crystalline or amorphous structures. The polymers were characterized by 1H NMR, DSC and optical microscopy in polarized light. The molecular weights of the samples were low, situated in the oligomeric domain. The various transfer rates of the bisphenols from the aqueous to the organic phase, in some cases, led to very different copolymerization ratios as compared to the feed ratios. The LC polymers exhibited monotropic mesophases, probably for conformational reasons. A comparison between similar polyether structures containing the diethyletheric spacer and an oxetanic one was effectuated. Polyether aus Bis(2-chlorethyl)ether und verschiedenen Diphenolen wurden durch Phasentransferkatalyse in einem zweiphasigen flussigen System hergestellt. Als Diphenol-Verbindungen wurden 4,4′-Dihydroxyazobenzol, 4,4′-Dihydroxybiphenyl, Bisphenol A, 2,7-Dihydroxynaphthalin und 4,4′-Dihydroxydiphenylsulfid eingesetzt. Lediglich die Polymeren mit Azobenzol- und Diphenyleinheiten bildeten Mesophasen, wohingegen die anderen Produkte semikristalline oder amorphe Strukturen ausbildeten. Die Polymeren wurden durch 1H NMR, DSC und Polarisationsmikroskopie charakterisiert. Die Proben besasen niedrige Molekulargewichte im Bereich von Oligomeren. Die unterschiedlichen Transfergeschwindigeiten der Diphenole von der wasrigen in die organische Phase fuhrten in einigen Fallen zu vom Ausgangsmonomerverhaltnis sehr verschiedenen Copolymerzusammensetzungen. Die flussigkristallinen Polymeren bildeten, vermutlich aufgrund der Molekulkonformation, monotrope Mesophasen. Die Ergebnisse wurden mit denen von Polyethern ahnlicher Struktur mit Diethylether- und Oxetan-Spacern verglichen.

Liquid Crystalline Polymers. 15. Synthesis and Thermal Behavior of Some Aromatic Polyethers Containing Different Spacers

A series of aromatic homo- and copolyethers containing 6, 7 or 8 methylenic groups as spacers are presented. The polymers were synthesized by phase-transfer catalysis and they were characterized by using 1H-NMR, polarized light microscopy, differential scanning calorimetry and thermogravimetric analyses. All copolymers have low molecular weight, situated within the oligomer domain. They have high transition temperatures except for the case when bent or semi-flexible bisphenols were used as comonomers. Only 4,4 -dihydroxyazobenzene-based polymers showed liquid crystalline properties with a mesophase range over 50° C, and with the clearing temperatures situated near their thermal decomposition limit. The insertion of kink or flexible bisphenols was not favorable to mesophase formation (it induced too high a disorder in the system), but it lowered the transition temperatures, as expected. Few exceptions occurred in the case of bisphenol A and 4,4 -dihydroxybenzophenone. The biphasic nature of these copolyethers is most probably due to both the polydispersity and the chemical heterogeneity of the samples. Some of the semi-crystalline copolymers may exhibit virtual mesophase that can be uncovered by increasing their molecular weight or by raising the free energy of the isotropic liquid state.