A triptycene-based polymer of intrinsic microposity that displays enhanced surface area and hydrogen adsorption

A novel triptycene-based polymer of intrinsic microporosity (Trip-PIM) displays enhanced surface area (1065 m2 g(-1)) and reversibly adsorbs 1.65% hydrogen by mass at 1 bar/77 K and 2.71% at 10 bar/77 K.     

Interaction of the acid soap of triethanolamine stearate and stearic acid with water

Stearic acid and triethanolamine (TEA) in a molar ratio of 2:1 were mixed in aqueous solution at 80 degrees C and subsequently cooled to ambient temperature. The structural evolution of the resultant sample during storage was characterized by using light microscopy, Cryo-SEM, differential scanning calorimetery, pH, infrared spectroscopy, elemental analysis, and simultaneous small and wide-angle X-ray diffraction. It was found that a lamellar liquid crystalline phase was formed when stearic acid and TEA solution were mixed at 80 degrees C and multilamellar spheres of a few microns diameter were formed initially after cooling. A hydrolysis reaction (i.e., the reverse reaction of neutralization between stearic acid and TEA) occurred thereafter that caused the breakdown of the lamellar gel phase and the formation of platelet stearic acid crystals. Three polymorphs of stearic acid (defined following previous work as the A, C, and E forms) were formed as the result of hydrolysis reaction, which gave rise to a strong optically pearlescent appearance.     

The Fundamental Basis for Cyclopolymerization. V. A Kinetically Based Explanation for the Enhanced Rate

The enhanced rate of cyclopolymerization of divinyl monomers over that of the corresponding monovinyl monomers is considered. The relative polymerization rates of the following monovinyl-divinyl monomer pairs were determined: methyl methacrylate-methacrylic anhydride; 2-cyano-l-heptene-2,6-dicyano-l, 6-heptadiene; and 2-phenyl-l -hepteneh-2,6-diphenyl-1,6-heptadiene. An attempt was made to prepare methacrylic isobutyric anhydride as the monovinyl monomer to compare with methacrylic anhydride but its inherent instability precluded its isolation in pure state. The over-all rate of the divinyl monomer in every case was considerably greater than that of the corresponding monovinyl monomer, the ratios varying from two to ten. From the rate data obtained it was possible to estimate the effective concentration of the intramolecular double bond with respect to the radical, and values greater than 20 M at 50° were obtained in the case of 2,6-dicyano-l,6-heptadiene. This value compares favorably with a concentration of 21.8 M for liquid ethylene at -102°. These results can be interpreted most satisfactorily in terms of a concerted cyclization step which requires considerable preorientation prior to reaction. This favorable preorientation could be interpreted as an electronic interaction between the developing radical cite and the intramolecular double bond.     

Polymerization and Copolymerization Studies of Orthoacrylates: A Novel Class of Acrylic Esters

Although ortho-esters constitute a well-known class of organic compounds, the orthoacrylates were unknown prior to a report from these laboratories in 1972. To date, this novel class of acrylic esters has not been investigated as polymerization monomers. We report here polymerization and copolymerization studies of representative members of this class of compounds. Although the orthoacrylates studied did not polymerize in the presence of conventional cationic initiators nor radical initiators, they did respond to radical-initiated copolymerization with a variety of conventional vinyl monomers. Their corresponding reactivity ratios were determined, as well as the Q and e parameters. Monomer syntheses and characterization are reported, as well as structural and properties studies on the copolymers.     

Studies in Cyclocopolymerization. IX. A Systematic Kinetic Study on the Cyclocopolymerization of Vinyl Ethers with Maleic Anhydride in Different Solvents

Abstract

The kinetics of the AIBN-initiated copolymerization of divinyl ether (DVE) and ethyl vinyl ether (EVE) with maleic anhydride (MA) was extensively studied in seven different solvents. The yield at 100% conversion as a function of the feed composition when the total monomer concentration is kept constant gave a confirmation of the composition of these copolymers: DVE/MA=½ and EVE/MA=1/1. The study of the initial rate as a function of the feed composition made it possible to determine the relative values of the different propagation rate constants consistent with a mechanism by successive and selective additions: in the EVE-MA system, the addition of EVE is slower than the addition of MA; in the DVE-MA system, the addition of DVE is slower than the addition of the first MA molecule, while the addition of the second MA molecule is slower than the first one. The study of the dependence of the monomer concentration, of the AIBN concentration, and of the efficiency of the initiator, on the rate of polymerization, shows finally that the true order of the monomer concentration is close to 1 while its apparent order varies from 1 to 2. From all the kinetic data it was observed that the mechanism of these co polymerizations can be explained without reliving upon the concept of participation of the charge-transfer complex formed between the monomers. However, participation of the complex in a competing mechanism with the above cannot be completely excluded.     

Absolute configuration and total synthesis of a novel antimalarial lipopeptide by the de novo preparation of chiral nonproteinogenic amino acids

The absolute configuration (via degradation and Marfey's derivatization studies) and the total synthesis of a novel antimalarial lipid-peptide isolated from Streptomyces sp. (IC(50) = 0.8 μM, Plasmodium falciparum 3D7) is disclosed. To this end, versatile stereocontrolled routes to nonproteinogenic amino acids (via catalytic Mannich, Sharpless methods) and enantiomeric trans fatty acids (via Evans alkylation, Kocienski-Julia olefination) have been developed.     

Role of bridge energetics on the preference for hole or electron transfer leading to charge recombination in donor-bridge-acceptor molecules

The impact of donor-acceptor electronic coupling and bridge energetics on the preference for hole or electron transfer leading to charge recombination in a series of donor-bridge-acceptor (D-B-A) molecules was examined. In these systems, the donor is 3,5-dimethyl-4-(9-anthracenyl)-julolidine (DMJ-An) and acceptor is naphthalene-1,8:4,5-bis(dicarboximide) (NI), while the bridges are either oligo(p-phenyleneethynylene) (PE(n)P, where n = 1-3) 1-3 or oligo(2,7-fluorenone) (FN(n), where n = 1-3) 4-6. Photoexcitation of 1-3 and 4-6 produces DMJ(+?)-An-PE(n)P-NI(-?) and DMJ(+?)-An-FN(n)-NI(-?), respectively, which undergo radical pair intersystem crossing followed by charge recombination to yield both (3*)An and (3*)NI, which are observed by time-resolved electron paramagnetic resonance (TREPR) spectroscopy. (3*)NI is produced by hole transfer from DMJ(+?) to NI(-?), while (3*)An is produced by electron transfer from NI(-?) to DMJ(+?), using the agency of the bridge HOMOs and LUMOs, respectively. By monitoring the initial population of (3*)NI and (3*)An in 1-6, the data show that charge recombination occurs preferentially by selective hole transfer when the bridge is PE(n)P, while it occurs by preferential electron transfer when the bridge is FN(n). Over time, the initial population of (3*)NI decreases, while that of (3*)An increases, indicating that triplet-triplet energy transfer (TEnT) occurs. The observed distance dependence of TEnT from (3*)NI to An is weakly exponential with a decay parameter β = 0.08 ?(-1) for the PE(n)P series and β = 0.03 ?(-1) for the FN(n) series. In the PE(n)P series, this weak distance dependence is attributed to a transition from the superexchange regime to hopping transport as the energy gap for triplet energy injection onto the bridge becomes significantly smaller as n increases, while in the FN(n) series the corresponding energy gap is small for all n resulting in triplet energy transport by the hopping mechanism.     

A cascade thermal isomerisation of cyclobutane di-(carbomethoxy) Δ2-1,2,3-triazolines with intramolecular 1,3-dipolar cycloreversion as the key step

Unprecedented thermal isomerisation of the strained Δ²-1,2,3-triazolines led to the formation of products possessing a novel 1,2,7-triaza-[3.3.0]octa-2-ene ring system incorporated in a norbornane framework. Experimental evidence and quantum chemical calculations have been used to support a postulated reaction mechanism involving as the first step, a rare example of intramolecular 1,3-dipolar cycloreversion. Subsequently, several steps involving 1,3-dipolar ring closure, hydrogen shifts and an intramolecular addition are postulated leading to the observed product of this deep-seated isomerisation. The influence of changing substituents on the product outcome of this novel reaction cascade was also studied.     

Exponential distance dependence of photoinitiated stepwise electron transfer in donor-bridge-acceptor molecules: implications for wirelike behavior

Donor-bridge-acceptor (D-B-A) systems in which a 3,5-dimethyl-4-(9-anthracenyl)julolidine (DMJ-An) chromophore and a naphthalene-1,8:4,5-bis(dicarboximide) (NI) acceptor are linked by oligomeric 2,7-fluorenone (FN(n)) bridges (n = 1-3) have been synthesized. Selective photoexcitation of DMJ-An quantitatively produces DMJ(+?)-An(-?), and An(-?) acts as a high-potential electron donor. Femtosecond transient absorption spectroscopy in the visible and mid-IR regions showed that electron transfer occurs quantitatively in the sequence: DMJ(+?)-An(-?)-FN(n)-NI → DMJ(+?)-An-FN(n)(-?)-NI → DMJ(+?)-An-FN(n)-NI(-?). The charge-shift reaction from An(-?) to NI(-?) exhibits an exponential distance dependence in the nonpolar solvent toluene with an attenuation factor (β) of 0.34 ?(-1), which would normally be attributed to electron tunneling by the superexchange mechanism. However, the FN(n)(-?) radical anion was directly observed spectroscopically as an intermediate in the charge-separation mechanism, thereby demonstrating conclusively that the overall charge separation involves the incoherent hopping (stepwise) mechanism. Kinetic modeling of the data showed that the observed exponential distance dependence is largely due to electron injection onto the first FN unit followed by charge hopping between the FN units of the bridge biased by the distance-dependent electrostatic attraction of the two charges in D(+?)-B(-?)-A. This work shows that wirelike behavior does not necessarily result from building a stepwise, energetically downhill redox gradient into a D-B-A molecule.