Hydrocarbon Spacer Research Articles

Investigation in monolayers of double‐chain fluorocarbon amphiphiles Effect of headgroups on molecular packing and interaction between hydrocarbon and fluorocarbon monolayers

AbstractThe surface pressure‐area diagrams of double‐chain fluorocarbon amphiphiles with different headgroup compositions show that the amphiphiles arrange almost perpendicularly to the water subphase and the structure of headgroups exerts significant influence on the amphiphile packing. Strong hydrogen bonding and weak electrostatic interaction favor the formation of stable monolayers. Perfluorooctanoic acid (FOA) cannot form monolayer at water/air interface and can only form liquid monolayer in subphase of calcium nitrate solution. Complete phase separation of palmitic acid and a fluorocarbon amphiphile with shorter hydrocarbon spacer group, 1, could be demonstrated in monolayers by using the phase rule of Crisp. The creation of phase‐separated monolayers is possible when the monolayer is composed of a mixture of palmitic acid and a fluorocarbon amphiphile with longer hydrocarbon spacer group, 2. It can be suggested that the miscibility of hydrocarbon amphiphiles with fluorocarbon amphiphiles is determined by the hydrocarbon fraction of fluorocarbon amphiphiles.

Laser desorption fourier transform mass spectrometric study of porphyrins attached to hydrocarbon spacers

AbstractThe 248 nm laser desorption Fourier transform ion cyclotron resonance positive‐ and negative‐ion mass spectra are presented for two novel porphyrin‐spacer‐quinone bichromophoric systems in which the spacer consists of a polynorbornyl‐type hydrocarbon and also for a model tetraphenylporphyrin compound. The compounds are 1,2,3,4‐tetrahydro‐1.4‐methano‐7,10,13,16‐tetraphenylbenzo [g] quinoxalino [2,3‐b] porphyrin, 5,20‐dihydro‐5,20‐methano‐l,4‐dimethoxy‐8,11,14,17‐tetrapherylnaphtho [2,3‐g]quinoxalino[2,3‐b] porphyrin and 5,10,15,20‐tetraphenyl‐porphyrin. The two‐step laser desorption multiphoton ionization mass spectra recorded at laser powers < 2 MW cm−2 produce only the parent ions M+˙ and M−˙. At increased laser powers of up to 5 MW cm−2 the [M + H]+ and [M  H]− ions are observed to increase significantly in relative abundance. At laser powers >8 MW cm−2 the porphyrins show extensive photodissociation and rearrangement and, in one case, the production of an extensive distribution of carbon cluster fragment ions including the fullerene [C60]+˙.

Incorporation of new amphiphilic perfluoroalkylated bipyridine platinum and palladium complexes into liposomes: stability and structure-incorporation relationships

New perfluoroalkylated side-chain (formed by a perfluoroalkyl tail grafted onto a hydrocarbon spacer) bipyridine complexes of platinum, palladium and their hydrocarbon analogs, when dispersed in aqueous solutions in the presence of egg yolk phospholipids (EYP), are incorporated into EYP vesicles. Most complexes retain their chemical and structural integrity when entrapped into liposomes, thermally sterilized under the FDA norms and stored for 3 months at 25°C. All complex/liposome preparations consist mainly of small unilamellar vesicles (size < 100 nm) together with a population of larger uni- or multilamellar vesicles (100 to 230 nm). These preparations are remarkably stable with respect to particle size and size distribution evolution and complex leakage: no precipitate of drug was detected even after 7 months of storage at 25°C. The impact of the perfluoroalkyl tail and of the other structural features of the complexes on their incorporation efficiency into EYP liposomes is assessed. A high fluorophilic character (long perfluoroalkyl tail), when tempered by an equally lipophilic one (long hydrocarbon spacer) is not detrimental to the incorporation efficiency of a perfluoroalkylated drug into hydrocarbon vesicles. This incorporation efficiency is considerably improved by the introduction of a double bond between the perfluoroalkyl tail and the hydrocarbon spacer, forming the bipyridine side-chains.

Spacer-modified, photolabile tetrasaccharides as analogues of maltopentaose are versatile probes for porcine pancreatic alpha-amylase

The syntheses are described of methyl 4′-O-[4-S-(3-azi-4-α-d-glucopyranosyloxybutyl)-6-deoxy-4-thio-α-d-xylo-hex-5-enopyranosyl]-α-maltoside (28), methyl 4-O-[4-S-(3-azi-4-α-maltosyloxybutyl)-6-deoxy-4-thio-α-d-xylo-hex-5-enopyranosyl]-α-d-glucopyranoside (29), and methyl 4-S-(3-azi-4-α-maltotriosyloxybutyl)-6-deoxy-4-thio-α-d-xylo-hex-5-enopyranoside (30), which are analogues of maltopentaose in which a central glucosyl unit is replaced by an acyclic, four-membered hydrocarbon spacer carrying a photolabile azi group. Only 30 was slowly cleaved by high concentrations of pancreatic alpha-amylase. The Ki values (mm) were 0.15 (28), 2.1 (29), and 2.5 (30). Deactivation of the enzyme by irradiation in the presence severally of 28–30 was 96.4%, 98.1%, and 40%, respectively. There is an indication for regiospecific photoaffinity labelling of the binding subsites of the enzyme.

Design and Synthesis of High Refractive Index Polymers. II

Abstract The synthesis, physical and optical properties of a series of high molecular weight, colorless, nonbirefringent, amorphous polymethacrylates (and acrylates) comprising brominated and iodinated carbazole rings that are connected to the backbone by short hydrocarbon spacers are described. The refractive indices exhibited by these homopolymers are in the range of 1.67 to 1.77. A ternary mixture of brominated monomers has a low melting point (<50°C); the refractive index of the corresponding polymer = 1.72.

Localization and correlation corrections in electronic interactions through single bonded hydrocarbon spacers

The electronic interaction between non-conjugated π electrons is studied for a series of oligonorbornyls, synthesized and previously studied by Paddon-Row and co-workers. Polarization around the electron hole state as well as correlation effects are taken into account. CASSCF calculations, performed for the localized π hole states, are followed by configuration interaction between the localized wavefunctions using a procedure designed by Roos and Malmqvist. We obtain an energy splitting |Δ| between odd and even states, closely corresponding to the electronic factor in electron transfer reactions. The decrease of the electronic factor with distance is slightly steeper than at the Hartree-Fock SCF level.

Time-Resolved Microwave Conductivity Studies of Long-Distance Electron Tunnelling in Molecular Systems

Abstract Recent results on charge recombination via electron tunnelling through intervening saturated hydrocarbon media, obtained using the time-resolved microwave conductivity (TRMC) technique, are presented. The systems studied are a) isolated donor-insulator-acceptor molecules (DIADs) with rigid, saturated hydrocarbon spacers of variable length and b) columnar aggregates of octa-n-alkoxy substituted phthalocyanines. In both cases the rate of recombination of charge is found to depend exponentially on the dimension of the intervening saturated hydrocarbon medium i.e. kR = V exp(-aR), with a = 0.88 and 0.64 Å−1respectively.

New nitrophenyl‐ and nitromethoxyphenyl‐substituted methylpolysiloxane stationary phases for capillary column gas chromatography

AbstractNitrophenyl‐, nitrophenylethyl‐, dinitrophenylethyl‐, and methoxynitrophen‐ ylethyl‐substituted polysiloxanes (25‐50% substitution) have been synthesized and evaluated as stationary phases in capillary column gas chromatography. Phases with 25% substitution and with ethylene spacers between the phenyl substituents and the polysiloxane backbone were found to provide high efficiencies, moderate thermal stabilities, and useful selectivities. Without flexible hydrocarbon spacers, the station‐ ary phases exhibited poor efficiencies. The 50% substituted phases generally provided narrower operational temperature ranges and lower efficiencies, and they were more difficult to immobilize by free radical crosslinking. Several methods of immobilization were evaluated, and a dynamic procedure with dicumylperoxide (DCP) was found to produce the best results for these nitrophenyl‐containing phases. The enhancements in polarity resulting from the resonances of the nitrophenyl substituent groups pro‐ vided unique selectivities for specific applications involving aromatic compounds. The dinitrophenyl‐containing phases showed, in addition, selectivity based on charge transfer complex formation.

Mesomorphism — structure relationships in polyesters based on twin p‐oxybenzoate mesogens

AbstractThree homologous series of semiflexible polyesters constituted by twin spaced p‐oxybenzoyl diads were studied with respect to their mesomorphic behaviour as a function of the relative length of the two different spacers [oligo(oxyethylene) and polymethylene] connected in an alternating fashion in the repeating unit. Within each series the oligo(oxyethylene) segment was maintained constant (n = 2, 3, 4), whereas the polymethylene segment varied in steps of one methylene unit from pentamethylene to decamethylene (m = 5 to 10). Indications are gained of how the parity of both ether and hydrocarbon spacers may affect the phase diagrams of the samples. The parity of the oligo(oxyethylene) segments appears in particular very effective in maximizing the orientational correlation between the mesogenic p‐oxybenzoyl diads.

Distance dependence of intramolecular hole and electron transfer in organic radical ions

An experimental study of the distance dependence of intramolecular, long-distance hole transfer in organic radical cations has been performed. The aromatic donor and acceptor groups, biphenyl and naphthalene (D and A), were held at fixed distances by five rigid saturated hydrocarbon spacer groups. The kinetics of the transfer reactions (D{sup +}SA {yields} DSA{sup +}) were monitored by transient absorption of the hole donor, 4-biphenylyl radical cation. Intramolecular hole-transfer rate constants were determined for this process and compared with previous results for electron transfer in radical anions of the identical molecules. A comparison of the hole- and electron-transfer results reveals that the attenuation of the rate constants, and therefore the electronic coupling, as a function of distance is the same for both within the limits of error of the experiment.

High‐performance ligand‐exchange chromatography of amino acids on chiral stationary phases

AbstractThree chiral stationary phases, obtained by grafting silica gel with (‐)‐trans‐1,2‐cyclohexanediamine, were studied for the resolution of α‐amino acids by ligand‐exchange chromatography. The packings were prepared by bonding the chiral ligand to silica gel via different hydrocarbon spacers. Separation of the optical isomers was accomplished by eluents containing a constant concentration of copper(II) acetate (0.05mM). The elution sequence of amino acids was found to be dependent on the grafting reaction selected to prepare the chiral packings.

ChemInform Abstract: Transmembrane Electron Transfer as Catalyzed by Poly(ethyleneimine)‐Linked Manganese Porphyrins.

AbstractPoly(ethyleneimine)‐linked Mn porphyrins such as (I) associate with phospholipid bilayers in a manner that allows the porphyrin to penetrate the membrane to a depth limited by the hydrocarbon spacer (number of CH2 units between the amide bonds) linking it to the extremely hydrophilic polymer.

The penems, a new class of beta-lactam antibiotics. 7. Synthesis and antimicrobial activity of 2-heterocyclylmercaptoalkyl derivatives.

2-Heterocyclylmercaptoalkyl penems were synthesized and their in vitro potency was established. The compounds exhibit moderate to strong antibacterial activity against various Gram-positive and Gram-negative bacteria. Their antimicrobial activity is related to the nature of the heterocycle, the length of the hydrocarbon spacer between the 2-position of the penem nucleus and the mercapto group, and the substitution pattern of the C-6 position of the penem skeleton.

Evaluation of smectic biphenylcarboxylate ester liquid‐crystalline polysiloxane stationary phases for capillary column gas chromatography

AbstractMesomorphic biphenylcarboxylate esters were coupled via flexible aliphatic hydrocarbon spacers to a polysiloxane backbone. The influence of spacer length, percent mesomorphic substitution, and crosslinking of the stationary phase on liquid‐crystalline transition temperatures and on chromatographic performance was investigated. Unique selectivity and good efficiency over a wide temperature range for gum and cross‐linked liquid‐crystalline phases were demonstrated by the separation of various isomeric polycyclic aromatic compounds.

Stable, high capacity and non charged agarose derivatives for immobilization of biologically active compounds and for affinity chromatography.

Methods are described for the preparation of hydrazido-alkyl agarose derivatives useful for purification of biologically active compounds by affinity chromatography. The hydrazido-agarose permits the attachment of different functional groups through non-charged extended hydrocarbon spacers. These spacers place the functional groups at varying distances from the gel matrix. The different functional groups introduced, enable the coupling of ligands to agarose through their amino, carboxyl, imidazole, phenol and thiol groups.