Single Hydroxy Group Research Articles

Rational modification of hydroxy-functionalized covalent organic frameworks for enhanced photocatalytic hydrogen peroxide evolution

Covalent organic frameworks (COFs), a class of flexibly tunable crystalline materials, have fascinating potential in photocatalytic hydrogen peroxide (H2O2) evolution under visible light irradiation. However, achieving efficient catalytic activity by tuning the composition of COFs and the linkages of building blocks is still a challenge. Herein, four imine-linked COFs with different numbers of hydroxy-functionalized are constructed to unveil the latent structure–activity relationship between the reversibility of bonding in supramolecular chemistry and the photocatalytic H2O2 performance. As the optimized material, TAPT-HTA-COF (1H-COF) containing single hydroxy group in aldehyde node exhibits a highest ordered structure and conjugation degree along and across the plane in the extended frameworks originating from the flexibly reversible iminol-to-ketoenamine tautomerism than others, which broadens the visible light absorption and accelerates the dissociation of photogenerated carriers in 1H-COF. These merits ensure that 1H-COF has the highest H2O2 yield (44.5 μmol L−1) and O2 two-electron reduction pathway among the four COFs under visible light irradiation (λ > 420 nm, 10 vol% isopropanol aqueous solution). At the same time, the long-range ordered framework of 1H-COF is well preserved during the photocatalytic H2O2 evolution process assisted by the proton-induced tautomerization. This work facilitates the design and development of COF-based photocatalysts in the evolution of H2O2.

Entropic-Based Separation of Diastereomers: Size-Exclusion Chromatography with Online Viscometry and Refractometry Detection for Analysis of Blends of Mannose and Galactose Methyl-\u03b1-pyranosides at \u201cIdeal\u201d Size-Exclusion Conditions

The separation of carbohydrate diastereomers by an ideal size-exclusion mechanism, i.e., in the absence of enthalpic contributions to the separation, can be considered one of the grand challenges in chromatography: Can a difference in the location of a single axial hydroxy group on a pyranose ring (e.g., the axial OH being located on carbon 2 versus on carbon 4 of the ring) sufficiently affect the solution conformational entropy of a monosaccharide in a manner which allows for members of a diastereomeric pair to be separated from each other by size-exclusion chromatography (SEC)? Previous attempts at answering this question, for aqueous solutions, have been thwarted by the mutarotation of sugars in water. Here, the matter is addressed by employing the non-mutarotating methyl-α-pyranosides of d-mannose and d-galactose. We show for the first time, using SEC columns, the entropically driven separation of members of this diastereomeric pair, at a resolution of 1.2–1.3 and with only a 0.4–1% change in solute distribution coefficient over a 25 °C range, thereby demonstrating the ideality of the separation. It is also shown how the newest generation of online viscometer allows for improved sensitivity, thereby extending the range of this so-called molar-mass-sensitive detector into the monomeric regime. Detector multidimensionality is showcased via the synergism of online viscometry and refractometry, which combine to measure the intrinsic viscosity and viscometric radius of the sugars continually across the elution profiles of each diastereomer, methyl-α-d-mannopyranoside and methyl-α-d-galactopyranoside.

Membrane organization and intracellular transport of a fluorescent analogue of 27-hydroxycholesterol

Oxysterols are cholesterol metabolites with multiple functions in controlling cellular homeostasis. In particular, 27-hydroxycholesterol (27-OH-Chol) has been shown to regulate a variety of physiological functions, but little is known about its uptake, intracellular trafficking, and efflux from cells. This is largely due to a lack of suitable analogs of 27-OH-Chol, which mimic this oxysterol closely. Here, we present the intrinsically fluorescent 27-hydroxy-cholestatrienol (27-OH-CTL), which differs from 27-OH-Chol only by having two additional double bonds in the steroid ring system. Based on molecular dynamics (MD) simulations, we show that 27-OH-CTL possesses almost identical membrane properties compared to 27-OH-Chol. By comparative imaging of 27-OH-CTL and of the cholesterol analogue cholestatrienol (CTL) in living cells, we assess the impact of a single hydroxy group on sterol trafficking. We find that human fibroblasts take up more CTL than 27-OH-CTL, but efflux the oxysterol analogue more efficiently. For both sterols, efflux includes shedding of vesicles from the plasma membrane. Intracellular, 27-OH-CTL accumulates primarily in lipid droplets (LDs), while CTL is mostly found in endosomes and lysosomes. Using fluorescence recovery after photobleaching (FRAP), we find for both sterols a rapidly exchanging pool, which moves orders of magnitude faster than sterol containing vesicles and LDs. In summary, by applying a new fluorescent derivative of 27-OH-Chol we demonstrate that human cells can distinguish sterols based on a single hydroxy group in the side chain, resulting in different transport itineraries, dynamics, and efflux kinetics. Both intrinsically fluorescent cholesterol and oxysterol analogues show rapid non-vesicular transport in human fibroblasts.

Regioselectivity of Cobalamin-Dependent Methyltransferase Can Be Tuned by Reaction Conditions and Substrate.

Regioselective reactions represent a significant challenge for organic chemistry. Here the regioselective methylation of a single hydroxy group of 4‐substituted catechols was investigated employing the cobalamin‐dependent methyltransferase from Desulfitobacterium hafniense. Catechols substituted in position four were methylated either in meta‐ or para‐position to the substituent depending whether the substituent was polar or apolar. While the biocatalytic cobalamin dependent methylation was meta‐selective with 4‐substituted catechols bearing hydrophilic groups, it was para‐selective for hydrophobic substituents. Furthermore, the presence of water miscible co‐solvents had a clear improving influence, whereby THF turned out to enable the formation of a single regioisomer in selected cases. Finally, it was found that also the pH led to an enhancement of regioselectivity for the cases investigated.

Three-dimensional solvation structure of ethanol on carbonate minerals.

Calcite and magnesite are important mineral constituents of the earth’s crust. In aqueous environments, these carbonates typically expose their most stable cleavage plane, the (10.4) surface. It is known that these surfaces interact with a large variety of organic molecules, which can result in surface restructuring. This process is decisive for the formation of biominerals. With the development of 3D atomic force microscopy (AFM) it is now possible to image solid–liquid interfaces with unprecedented molecular resolution. However, the majority of 3D AFM studies have been focused on the arrangement of water at carbonate surfaces. Here, we present an analysis of the assembly of ethanol – an organic molecule with a single hydroxy group – at the calcite and magnesite (10.4) surfaces by using high-resolution 3D AFM and molecular dynamics (MD) simulations. Within a single AFM data set we are able to resolve both the first laterally ordered solvation layer of ethanol on the calcite surface as well as the following solvation layers that show no lateral order. Our experimental results are in excellent agreement with MD simulations. The qualitative difference in the lateral order can be understood by the differing chemical environment: While the first layer adopts specific binding positions on the ionic carbonate surface, the second layer resides on top of the organic ethyl layer. A comparison of calcite and magnesite reveals a qualitatively similar ethanol arrangement on both carbonates, indicating the general nature of this finding.

Flavonoids, Flavonoid Metabolites, and Phenolic Acids Inhibit Oxidative Stress in the Neuronal Cell Line HT-22 Monitored by ECIS and MTT Assay: A Comparative Study

A real-time and label-free in vitro assay based on electric cell-substrate impedance sensing (ECIS) was established, validated, and compared to an end-point MTT assay within an experimental trial addressing the cytoprotective effects of 19 different flavonoids, flavonoid metabolites, and phenolic acids and their methyl esters on the HT-22 neuronal cell line, after induction of oxidative stress with tert-butyl hydroperoxide. Among the flavonoids under study, only those with a catechol unit and an additional 4-keto group provided cytoprotection. The presence of a 2,3-double bond was not a structural prerequisite for a neuroprotective effect. In the case of the phenolics, catechol substitution was the only structural requirement for activity. The flavonoids and other phenolics with a ferulic acid substitution or a single hydroxy group showed no activity. Electrochemical characterization of all compounds via square-wave voltammetry provided a rather specific correlation between cytoprotective activity and redox potential for the active flavonoids, but not for the active phenolics with a low molecular weight. Moreover this study was used to compare label-free ECIS recordings with results of the established MTT assay. Whereas the former provides time-resolved and thus entirely unbiased information on changes of cell morphology that are unequivocally associated with cell death, the latter requires predefined exposure times and a strict causality between metabolic activity and cell death. However, MTT assays are based on standard lab equipment and provide a more economic way to higher throughput.

Switching on a Signaling Pathway with an Organoruthenium Complex

Altering cellular function with small synthetic molecules is a general approach for the design of drugs (medicinal chemistry) and molecular probes (chemical genetics). Medicinal chemistry and chemical genetics are focused predominately on the design of organic molecules, whereas inorganic compounds find applications mainly for their reactivity (e.g., cisplatin as DNA-reactive therapeutic) or imaging properties (e.g., gadolinium complexes as MRI diagnostics). 2] We are exploring a new direction that aims at utilizing the unique structural opportunities of metal complexes for the design of “organiclike” small-molecule probes and drugs. 4] We recently described an organoruthenium compound to be a low-nanomolar inhibitor for the protein kinase glycogen synthase kinase 3 (GSK-3). Here we disclose our success in developing this compound into a molecular probe for cellular signal transduction pathways involving GSK-3. Our strategy for the design of metal complexes as protein kinase inhibitors uses the class of indolocarbazole alkaloids (e.g., staurosporine) as a lead structure. Accordingly, these metal complexes bear a bidentate ligand which retains the structural features of the indolocarbazole heterocycle. This targets the metal complexes to the ATP-binding site by enabling two hydrogen bonds to the backbone of the hinge between the N-terminal and C-terminal kinase domains, analogous to ATP and conventional organic indolocarbazole inhibitors (Scheme 1). The remaining ligand sphere of the ruthenium atom gives the opportunity to create interactions with other parts of the ATP-binding site. Following this strategy, we recently described ruthenium compound 1-H as a selective low-nanomolar and ATP-competitive inhibitor of GSK-3. The key component of the design was the novel pyridocarbazole ligand 2-H, derived from arcyriaflavin A by just replacing one indole moiety with a pyridine residue. Here we introduce the ruthenium complex 1-OH (Scheme 1), derived from 1-H by adding a single hydroxy group to the indole moiety. Molecular modeling suggests that this OH group can occupy a small hydrophilic cavity within the ATP-binding site of GSK-3. Indeed, this modification not only increases the affinity for GSK-3 by an order of magnitude, but at the same time increases water solubility considerably, and thus makes it a promising molecular probe for GSK-3. GSK-3 is a component and negative regulator of the wnt signaling pathway, and we demonstrate in the following that 1-OH can switch on the wnt signaling pathway by inhibiting GSK-3 inside living cells and in Xenopus embryos. We devised a short and economic synthetic route to this class of metalated pyridocarbazoles (Scheme 2). Starting with aryl hydrazine hydrochloride 3, Fischer indole synthesis and protecting-group exchange lead to pyridoindole 4, which is deprotonated and treated with the TBS-protected dibromomaleimide 5 to yield monosubstitution product 6. The key step of the synthetic scheme is the following smooth anaerobic photocyclization to the TBS-protected pyridocarbazole 7 in 78% yield. Compound 7 can be deprotected with TBAF to give 2-OH or treated with [Ru(Cp)(CO)(CH3CN)2]PF6 in the presence of K2CO3 to yield cyclometalated ruthenium complex 8. Subsequent TBS deprotection with TBAF gives 1-OH. Complex 1-OH is stable in aqueous solution, in cell culture medium, under air, and can even withstand a 5 mm solution of 2-mercaptoethanol for 12 h without any sign of decomposition, as determined by 1H NMR spectroscopy. Furthermore, 1-OH also has favorable solubility in water. For example, it can be dissolved in 3% DMSO/water at a concentration of 1 mm. We next examined the potency of 1-OH by determining the concentration required for 50% inhibition (IC50) of GSK3a (the a isoform) and GSK-3b (the b isoform). The IC50 of 1OH is 300 pm and 500 pm for GSK-3a and GSK-3b, respectively, approximately an order of magnitude lower than that [*] D. S. Williams, G. E. Atilla, H. Bregman, Prof. Dr. E. Meggers Department of Chemistry University of Pennsylvania 231 South 34th Street, Philadelphia, PA 19104 (USA) Fax: (+1)215-746-0348 E-mail: meggers@sas.upenn.edu

The substitution pattern of anthocyanidins affects different cellular signaling cascades regulating cell proliferation

The aglycons of the most abundant anthocyanins in food, cyanidin (cy) and delphinidin (del), represent potent inhibitors of the epidermal growth factor receptor (EGFR). Structure-activity studies show that the presence of vicinal hydroxy substituents at the phenyl ring at the 2-position (B-ring) is crucial for target interaction. The presence of a single hydroxy group or introduction of methoxy substituents at the B-ring results in a substantial loss of inhibitory properties. However, biological activity is not exclusively limited to compounds bearing vicinal hydroxy groups. A contradictory structure-activity relationship is observed for the inhibition of cAMP-specific phosphodiesterases (PDEs). Of the anthocyanidins tested, malvidin, bearing methoxy substituents in the 3'- and 5'-positions, most effectively inhibited cAMP hydrolysis. The absence of methoxy groups and/or replacement by hydroxy substituents was found to strongly diminish PDE-inhibitory properties. We found that either effective EGFR inhibition or effective PDE inhibition is required to achieve a shut-down of the central mitogen-activated protein kinase (MAPK) pathway, a signaling cascade crucial for the regulation of cell growth. This is consistent with the finding that efficient reduction of cell growth is limited to anthocyanidins that are potent EGFR- or PDE-inhibitors including cy and del or malvidin (mv), respectively. In summary, depending on the substitution pattern at the B-ring, anthocyanidins interfere with different signaling cascades involved in the regulation of cell growth.

Cyclodextrins and Stilbenes as Components of Supramolecular Structures

Background Cyclodextrin-based supramolecules have assumed importance since such assemblies may be either prototypes for, or components of, molecular devices with potential uses in nanotechnology. Cyclodextrins (cyclic oligomers comprising α-1,4-linked D-(+)-glucopyranose units) form host guest complexes with a wide range of hydrophobic molecules in an aqueous environment. [ 1 ] Stilbenes are known to form stable complexes with cydodextrins. [ 2 , 3 ] Their ability to interconvert between the cis and trans forms has made them the focus of our research. Mechanically interlocked structures called rotaxanes are formed when bulky end-capping groups are introduced on the stilbene so that the complex can no longer dissociate (Fig. 1). [ 3 ] The guest stilbene is free to rotate within the cyclodextrin; however, this free motion may be restricted by introduction of substituents on the stilbene and the cyclodextrin (Fig. 2a). [ 4 ] Fig. 2 also shows other examples of cyclodextrin- and stilbene-based structures being investigated. Cyclodextrins where a single hydroxy group is substituted with a stilbene are called hermaphrodites as they have both host and guest components (Fig. 2b). In concentrated solutions, trans-stilbene hermaphrodites form dimeric complexes, which can be characterized when end-capping groups are introduced to form rotaxanes. [ 5 a ] Alternatively, the hermaphrodites may assemble into linear daisy chain type structures. In molecular shuttles (Fig. 2c), the cyclodextrin moves from one binding site to another upon application of an external stimulus. [ 6 ] .

Design of Liquid Crystalline Block Molecules with Nonconventional Mesophase Morphologies: Calamitic Bolaamphiphiles with Lateral Alkyl Chains

Novel bolaamphiphiles, consisting of a biphenyl rigid core, polar 2,3-dihydroxypropoxy groups at each terminal end, and an additional long alkyl chain in a lateral position have been synthesized. The structures of these ternary block molecules were systematically changed by variation of the length and position of the alkyl chain, by introduction of additional spacer units between one of the 2,3-dihydroxypropyl groups and the rigid core, and by replacement of one of the 2,3-dihydroxypropoxy groups by a single hydroxy group. The influence of these structural variations on the liquid crystalline properties of these new materials was investigated by polarized-light microscopy, differential scanning calorimetry, and X-ray diffraction. These investigation have shown that, by elongation of the lateral chain, a transition from a smectic monolayer structure (SmA1) via a strongly distorted layer structure (SmA+), a centered rectangular columnar phase (Colr/c2mm) and a noncentered rectangular columnar phase (Colr/p2...

Novel hydroxycarotenoids with improved antioxidative properties produced by gene combination in Escherichia coli.

We have used combinatorial biosynthesis to synthesize novel lipophilic carotenoids that are powerful cellular antioxidants. By co-expressing three different carotenoid desaturases in combination with a carotenoid hydratase, a cyclase, and a hydroxylase on compatible plasmids in Escherichia coli, we synthesized four novel carotenoids not previously detected in biological material or chemically synthesized. Their identification was based on their relative retention times on HPLC, spectroscopic properties, molecular weights, number of hydroxy groups, and 1H-NMR spectra. The carotenoids were designated as 1-HO-3', 4'-didehydrolycopene, 3, 1'-(HO)2-gamma-carotene, 1,1'-(HO)2-3, 4, 3', 4'-tetradehydrolycopene, and 1, 1'-(HO)2-3, 4-didehydrolycopene. These novel acyclic derivatives differ from structurally related compounds by extension of the conjugated polyene chain as well as additional hydroxy groups at position C-1'. We determined their antioxidative activity in a liposome-membrane model system, which showed that their ability to protect against photooxidation and radical-mediated peroxidation reactions was linked to the length of the conjugated double-bond system and the presence of a single hydroxy group. The protection of membrane degradation was superior to the related 1-HO and 1, 1'-(HO)2 lycopene derivatives, making them interesting pharmaceutical candidates.

Total Synthesis of the Marine Natural Product 7‐Deoxy‐okadaic Acid: A Potent Inhibitor of Serine/Threonine‐Specific Protein Phosphatases

A small change to the structure of okadaic acid (1), the omission of the single hydroxy group at C7, facilitated substantially the first total synthesis of the derivative 7-deoxyokadaic acid (2). The conformation of 2 is in agreement with that of 1 and this minimal structural variation has been reported previously to have little effect on the inhibitory activity towards the serine/threonine-specific protein phosphatases PP-1 and PP-2A.

Comparison of azacyclic urea A-98881 as HIV-1 protease inhibitor with cage dimeric N-benzyl 4-(4-methoxyphenyl)-1,4-dihydropyridine as representative of a novel class of HIV-1 protease inhibitors: a molecular modeling study.

The functional groups of cage dimeric N-alkyl substituted 3,5-bis(hydroxymethyl)-4-(4-methoxyphenyl)-1,4-dihydropyridines are similar to those of cyclic and azacyclic ureas that are potent inhibitors of HIV-1 protease of the dihydroxyethylene- and hydroxyethylene type, respectively. In the following study the conformity of common functional groups is investigated concerning their orientation in space as well as in the enzyme HIV-1 protease. Starting from X-ray crystal data of the centrosymmetric cage dimeric N-benzyl derivative with ester groups, the derivative with hydroxymethylene groups was built and a systematic conformational search was performed for the conformationally important torsion angles considering electrostatic and van der Waals interactions. From the huge number of conformations those comprising centrosymmetrical and C2-symmetrical energy minima were selected and minimized. The three remaining conformers were fitted to the azacyclic urea A-98881 selected from the HIV-1 protease enzyme-inhibitor complex using the centroids of the corresponding aromatic residues and additionally by the field fit option of the Advanced CoMFA module of SYBYL. Interestingly, the energetically most favourable one, which, additionally, possesses C2-symmetry like the active site cavity of HIV-1 protease, showed the best fit. Comparing the electrostatic potential (EP) of the latter with the EP of A-98881 the aromatic residues show excellent accordance. Slight differences in the extent of the EP were found in the areas of the hydroxymethylene groups of the cage dimer and the single hydroxy group as well as the urea carbonyl group of A-98881, respectively. In order to compare the binding possibilities to the enzyme HIV-1 protease for the cage dimer and A-98881, their interaction fields with certain probes (CH3 for alkyl, NHamide, and carbonyl, O- of COO-), representing the decisive functional groups of the active site, have been calculated using GRID and projected into the enzyme placing the structures according to the position of A-98881 in the enzyme-inhibitor complex. The strongest calculated fields of the O- probe were found near Asp 25 for both structures. Another respective conformity consists in the overlap of the fields for the NHamide probe near Ile 50 and 50' for the investigated cage dimer and A-98881.

Differential behavior of (25 R)-5,6-epoxyspirostan-22α- O-3β-ol and (25 R)-5,6-epoxyspirostan-22α- O-3β,4β-diol toward Dowex

The acid-catalyzed hydrolytic cleavage of the 5,6-epoxyspirostane derivatives by the cation exchange resin Dowex 50W X8 has been exploited with the goal of developing synthetic protocols toward 3,4,5,6-polyhydroxyspirostane analogs that can serve as intermediates to potential biologically active compounds. Whereas the diastereomers (25 R)-5α,6α-epoxyspirostan-22α- O-3β-ol and and (25 R)-5β,6β-epoxyspirostan-22α- O-3β-ol yield two products, (25 R)-6β- methoxyspirostan-22α- O-3β,5α-diol and (25 R)-spirostan-22α- O-3β,5α,6β-triol on Dowex treatment in water-methanol, the α- and β-diastereomers of the 5,6-epoxy derivative of 3β,4β-diol provide a single product, (25 R)-3β,6β-dihydroxy-5α-spirostan-4-one, in good yields. The structures of these products have been confirmed using 1H NMR, 13C NMR, and 1H- 1H J-correlated spectroscopies. Multifunctional product formation suggests tremendous utility of Dowex in steroid synthesis. The product formation has been rationalized on the basis of differential conformational constraints of the A/B rings of the different epoxides in directing the reaction course. The reaction shows an interesting example of stereoelectronic effect of a single hydroxy group in discriminating solvent participation.

Molecular design of amphotropic materials: influence of oligooxyethylene groups on the mesogenic properties of calamitic liquid crystals

The syntheses and liquid-crystalline properties of novel oligoethylene glycol derivatives are described. These are amphiphiles and podand-like trimesogens. The hydrophobic sections of the amphiphiles consist of calamitic 4-(5-pentadecyl-l,3,4-thiadiazol-2-yl)-phenyl, 4′-dodecyloxybiphenyl-4-yl or 4-decylphenyl units, which are connected by a hydrophilic 12,13-dihydroxy-l,4,7,10-tetraoxatridecyloxy, 9,10-dihydroxy-l,4,7-trioxadecyloxy, 6,7-dihydroxy-l,4-dioxaheptyloxy or 2,3-dihydroxypropoxy groups. All these amphiphiles contain a 1,2-diol unit. In addition the 12-hydroxy-l,4,7,10-tetraoxadodecyl-, 9-hydroxy-l,4,7-trioxanonyl, 6-hydroxy-l,4-dioxahexyl and 2-hydroxyethoxy derivatives of 4′-dodecyloxybiphenyl are described. These compounds have only a single hydroxy group at their hydrophilic termini. The podand-like trimers consist of three 4′-dodecyloxybiphenyl units which are connected via oligooxyethylene chains with an α, α′,α″-mesitylenetriyl unit. The thermotropic liquid-crystalline properties of these compounds were investigated by polarising microscopy, differential scanning calorimetry and, in some cases by X-ray scattering. Most diol derivatives exhibited an SA–SC dimorphism. However, one of the biphenyl derivatives [4-dodecyloxy-4′-(6,7-dihydroxy-l,4-dioxaheptyl)biphenyl] displays another phase instead of the SC phase, probably a phase with a ribbon structure. The liquid-crystalline phases of these diol derivatives were influenced by the addition of protic solvents. Only lamellar phases were found for the biphenyl derivatives. Some thiadiazole derivatives additionally formed lyomesophases consisting of curved aggregates. No thermotropic liquid crystalline properties could be detected for the oligoethylene glycol monoethers without the 1,2-diol group. However, lyotropic liquid-crystalline phases could be induced by the addition of ethylene glycol or formamide. Only those podands with a medium spacer length were thermotropic liquid crystals and no lyotropic mesophases were detected for the podands.

Synthesis and Solid-State Structure of the Unsymmetrical Squaraine Dye 2-[4-(Dibutylamino)-2-hydroxyphenyl]-4-[4-(dibutylamino)phenyl]-cyclobutenebis(ylium)-1,3-diolate

The synthesis of an unsymmetrical squaraine dye, 2-[4-( dibutylamino )-2-hydroxyphenyl]-4-[4-( dibutylamino )phenyl] cyclobutenebis ( ylium )-1,3-diolate, has been achieved via a cross condensation reaction. In the solid state the compound is isomorphous with the known symmetrical dye bis [4-( dibutylamino )phenyl] squaraine. The single hydroxy group is found to be disordered equally over the centrosymmetrically trans-related ortho and ortho' phenyl ring sites.

Preparation and characterisation of C70Ph9OH; the first fullerene with a single hydroxy group attached to the cage

The fullerenol C70Ph9OH is obtained as a minor product from the reaction of C70Cl10 with benzene/FeCl3and is chiral due to the attachment of a hydroxy group and a phenyl group across the 7,8-bond; this adjacency inhibits free rotation of the 8-phenyl group.

Molecular design of amphotropic materials: double-headed diol-based mesogens incorporating rigid structural units

The syntheses of novel bolaamphiphilic triol and tetraol compounds incorporating rigid structural units are described. Their liquid-crystalline properties were investigated by polarizing microscopy, differential scanning calorimetry and in some cases also by means of X-ray diffraction. Most 4,4-disubstituted biphenyl derivatives exhibit one or more smectic phases (predominantly SA but also Sc, SB, SG and Sk) and extraordinarily high clearing temperatures. No thermotropic liquid-crystalline properties could be detected for bolaamphiphiles incorporating a single 1,4-disubstituted phenyl ring or a 2,6-disubstituted naphthalene ring system, but for naphthalene derivatives a lyotropic smectic A phase was induced by addition of water. If one of the diol groups of the biphenyl-derived bolaamphiphiles is replaced by a single hydroxy group or by a carboxylic acid group the mesophase stability is decreased. Mesomorphic properties are lost if the hydrogen-bonding density is further diminished by the replacement of one diol group by an ethyl carboxylate group. However, in these cases lyotropic liquid-crystalline phases can be induced by the addition of water.

ChemInform Abstract: Synthesis of a Branched High Molecular Weight Hydrocarbon with a Single Hydroxy Group as Polar Stationary Phase for Gas Chromatography.

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Synthesis of a Branched High Molecular Weight Hydrocarbon with a Single Hydroxy Group as Polar Stationary Phase for Gas Chromatography

The synthesis of 18,23-dioctadecyl-1-hentetracontanol (12), a high molecular weight solvent employed as a polar stationary phase for gas chromatography, having only one functional group, is described. This stationary phase allows the study of polar forces in the separation process