A re-examination of the use of 7,7,8,8-tetracyanoquinodimethane (TCNQ) in determining the critical micelle concentrations

Summary A detailed re-examination of the use of TCNQ in ] determining the critical micelle concentration (c. m. c.'s) of aqueous and reversed micelles was carried out. The mechanism of the interaction of TCNQ with ionic and non-ionic detergents was investigated in order to delineate the origin of the production of the dye anion-radical. In several cases, the formation of the latter species can be eliminated, or kept to a minimum, if highly purified detergents and solvents were used. Under these conditions, the neutral TCNQ visible absorption band should be used in the c.m.c. determination. The origin of the formation of the TCNQ anion-radical has been traced to the presence of difficulty removable impurities in the anionic and/or non-ionic surfactants, and to the reaction of the dye with the counter-ion of the positive micelles.     

Solid-phase synthesis of 89 polyamine-based cationic lipids for DNA delivery to mammalian cells

The ability of non-viral gene delivery systems to overcome extracellular and intracellular barriers is a critical issue for future clinical applications of gene therapy. In recent years much effort has been focused on the development of a variety of DNA carriers, and cationic liposomes have become the most common non-viral gene delivery system. Solid-phase synthesis was used to produce three libraries of polyamine-based cationic lipids with diverse hydrophobic tails. These were characterised, and structure-activity relationships were determined for DNA binding and transfection ability of these compounds when formulated as cationic liposomes. Two of the cationic lipids produced high-efficiency transfection of human cells. Surprisingly, these two compounds were from the library with two headgroups and one aliphatic tail, a compound class regarded as detergent-like and little investigated for transfection. These cationic lipids are promising reagents for gene delivery and illustrate the potential of solid-phase synthesis methods for lipoplex discovery.     

Synthesis and polymerization of tail-type cationic polymerizable surfactants and hydrophobic counter-anion induced association of polyelectrolytes

A series of tail-type cationic surface-active monomers with the cationic charge at the -end (1; ST-C_m-AB, m=5, 7, and 9, where ST is a styrenic group, C_m the alkylene chain at the 4-position of styrene, and AB is alkyltrimethylammonium bromide) have been synthesized as a novel cationic polymerizable surfactant. Their fundamental physicochemical properties such as critical micelle concentration (cmc) and weight-average aggregation number of the micelle (N_w(agg)) have been characterized in water at 25 °C by static light-scattering measurements. The cmc values determined for the tail-type surfactant monomers are two-orders of magnitude smaller than those of the corresponding head-type cationic surfactant monomers (2; ST-C₁-AC-C_m). The N_w(agg) of ST-C_m-AB is 68 for m=5, 156 for m=7, and 413 for m=9. Free-radical homopolymerization of ST-C₇-AB proceeds very rapidly in water as a result of organization in the micelle to afford the corresponding amphiphilic cationic polyelectrolyte with M_w=3.63×10⁶ and 23 nm hydrodynamic radius at 25 °C. Emulsion copolymerization of styrene with ST-C_m-AB also proceeds rapidly to afford very stable cationic polystyrene latex particles of 30–60 nm diameter. The amphiphilic cationic polyelectrolyte of poly(ST-C₇-AB) is likely to assume a compact conformation with high segment density in 0.1 mol L^–1 NaCl in water. Addition of hydrophobic aromatic counter-anions with an weak acid group, for example potassium hydrogen phthalate (PHK) and sodium salicylate, to a salt-free aqueous solution of poly(ST-C₇-AB) induces intermolecular aggregation and increases the solution viscosity substantially, often producing gels and precipitation at high polymer concentration.     

A convenient method for the synthesis of cationic glycerolipids with potential biological activity

Cationic ether lipids containing nitrogenous heterocyclic bases as the positively charged groups were synthesized. Treatment of methylthiomethyl ethers of dialkylglycerols with bromine afforded highly reactive -bromo ethers. These products reacted with various nucleophilic reagents giving rise to a series of cationic alkylglycerols.     

Ionic rectification properties of a bipolar interface consisting of a cationic surfactant and cation-exchange membrane

A novel bipolar interface that consists of cationic surfactant and cation-exchange membrane was successfully prepared in an aqueous electrolyte system. This bipolar interface shows a ionic rectification behavior similar to that observed in bipolar membranes. However, different from bipolar membranes, this system has a total rectification behavior, where we cannot observe the occurrence of a water-splitting phenomenon, which always occurs in the bipolar membrane process under reverse bias conditions.     

Interactions with Charged Cyclodextrins and Chiral Recognition

Anionic N-acetylated -aminoacids (AcTrp^-, AcPhe^-, AcLeu^- and AcVal^-) are bound to protonatedheptakis(6-amino-6-deoxy)--cyclodextrin(per-NH₃ ⁺--CD) by a cooperative work of inclusion and Coulomb interactions.Such complexation occurs enantioselectively ((S)-selective)and is accompanied bypositive entropy changes. Similar (S)-selectivecomplexation occurs in the oppositelycharged system. Namely, cationic -aminoacid methyl esters are enantioselectivelybound to dissociatedheptakis(6-carboxymethylthio-6-deoxy)--cyclodextrin(per-COO^---CD). In order to obtain thegeneral mechanism for complexationof a charged host with an oppositely charged guest,we examined the ¹H NMR spectra oncomplexation of simple carboxylate anions suchas p-methylbenzoate anion andalkanoate anions with per-NH₃ ⁺--CD.Both Coulomb interactions andinclusion are essential to form stable complexesof these carboxylate anions. In allcases, positive entropy changes promote thecomplexation between the carboxylateanions and per-NH₃ ⁺--CD. Dehydrationfrom both charged host and guestis the origin of entropic gains. The mechanism forcomplexation of a charged host withan oppositely charged guest involving the cooperativework of inclusion and Coulombinteractions and positive entropy change due todehydration upon complexation isgenerally applied for related systems such asenantioselective complexation ofRu(phen)₃ ²⁺ with per-COO^---CDand of Ru(phen)₃ ²⁺with DNA.     

Cationic Closo Carboranes—Promising Weakly Coordinating Ions

The unexplored carbon rich cationic closo carboranes, C₃B_n?3H_n⁺¹ (n=5, 6, 7, 10, 12) are investigated theoretically. The position isomers were calculated at the B3LYP/6‐31G* level, and the charge distribution in the cluster is estimated by NBO analysis. The criterion of ring‐cap orbital overlap compatibility along with the number of B? C, C? C, and B? B bonds help in explaining the stability order in each category. The most stable isomer is the one with maximum ring‐cap orbital overlap and largest number of B? C bonds. The order of relative stability among the trigonal bipyramid is 1c > 1b > 1a ′, where the stability is proportional to the number of CH caps over the small three‐membered ring. The C₃B₃H₆⁺ isomer with the one allyl C3 group ( 2b ) is more favorable than the one with a cyclopropenyl group ( 2a ). Among the C₃B₄H₇⁺ isomers the stability order is 3e > 3d > 3c > 3b > 3a , which mostly depends on the ring‐cap orbital overlap. In the bicapped square antiprism (4) where there is large number of isomers, the order follows the rule of ring cap compatibility and the number of B? C bonds. The order of 5e > 5d > 5c > 5b > 5a obtained from the calculations is in perfect agreement with the above sited rules. Equations (1) – (5) devised for estimating the stability of isomers of C₃B_n?3H_n⁺ indicate an increase in stability with cage size. The mono‐positive charge of the isomers is distributed throughout the cage, making them suitable candidates as weakly electrophillic cations. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1542–1551, 2001     

Radical and cationic polymerizations of 3‐ethyl‐3‐methacryloyloxymethyloxetane

3‐Ethyl‐3‐methacryloyloxymethyloxetane (EMO) was easily polymerized by dimethyl 2,2′‐azobisisobutyrate (MAIB) as the radical initiator through the opening of the vinyl group. The initial polymerization rate (R_p) at 50 °C in benzene was given by R_p = k[MAIB]^0.55 [EMO]^1.2. The overall activation energy of the polymerization was estimated to be 87 kJ/mol. The number‐average molecular weight (M?_n) of the resulting poly(EMO)s was in the range of 1–3.3 × 10⁵. The polymerization system was found to involve electron spin resonance (ESR) observable propagating poly(EMO) radicals under practical polymerization conditions. ESR‐determined rate constants of propagation (k_p) and termination (k_t) at 60 °C are 120 and 2.41 × 10⁵ L/mol s, respectively—much lower than those of the usual methacrylate esters such as methyl methacrylate and glycidyl methacrylate. The radical copolymerization of EMO (M₁) with styrene (M₂) at 60 °C gave the following copolymerization parameters: r₁ = 0.53, r₂ = 0.43, Q₁ = 0.87, and e₁ = +0.42. EMO was also observed to be polymerized by BF₃OEt₂ as the cationic initiator through the opening of the oxetane ring. The M?_n of the resulting polymer was in the range of 650–3100. The cationic polymerization of radically formed poly(EMO) provided a crosslinked polymer showing distinguishably different thermal behaviors from those of the radical and cationic poly(EMO)s. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1269–1279, 2001