The design of cone-fixed calix[4]arene analogs by takingsyn-[2.n]metacyclophanes as a building block

Rigidified calix[4]arene analogs were synthesized fromsyn-[2.n]metacyclophanes as a building block. Their structure was firmly locked in the cone conformation. An enlarged calix[4]arene analog was obtained after the cyclobutane ring cleavage of the parent analog by Birch reduction. Several ionophores have been derived from the analogs and been found to select the larger ions during the extraction of alkali metals, transition metals, and lanthanoids. The ionophore having oligoethylene glycol units showed an effective catalytic activity for S_N2 reactions such as ester synthesis, Williamson ether synthesis, and Finkelstein reaction in several media.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Molecular assembly of C2-symmetric Bis-(2S)-2-methyldodecanoylamides of alpha,omega-alkylidenediamines into coiled coil and twisted ribbon aggregates

A series of 10 didodecanoylamides of alpha,omega-alkylidenediamines bridged by a straight carbon chain varying in length from 0 to 9 carbons was examined as possible gelator molecules of organic liquids to gain information on the relationships between the spacial arrangement of two amide groups in a molecule and their effects on the microscopic structures of the gel. The structural characteristics of these amides are parallel and antiparallel arrangements of two amide carbonyl groups, which depend on the even and odd numbers of a bridging zigzag carbon chain. The linear alkyl chain moieties and a center carbon chain of diamides intermolecularly interact with each other within the van der Waals contact. Two amide moieties of an even number carbon chain diamide intermolecularly interact with each other by using two pairs of hydrogen bonds with two other molecules in a plane, which formed ribbonlike self-complementarily assembled aggregates. On the other hand, a diamide of an odd number carbon chain forms four independent hydrogen bonds with four other molecules not in a plane, which assembled into woven aggregates. Asymmetric introduction of a methyl group at the alpha-position of the amide groups successfully twists the two side chain van der Waals cores of the chiral diamides in the fixed direction, giving helically twisted ribbon and coiled coil aggregates. The helically twisted ribbon and coiled coil aggregates of these chiral diamides were directly observed by CD, SEM, and TEM, providing a basis for the design of a sophisticated small molecular gelator of a tailor-made shape.     

Regioselective nucleophilic addition of triphenylphosphine to the nitrosylruthenium alkynyl complexes having a hydrotris(pyrazol-1-yl)borate: formation of phosphonio-alkenyl, alkynyl, and allenyl species

A nitrosylruthenium alkynyl complex of TpRuCl(C[triple bond]CPh)(NO)(1a) was reacted with PPh3 in the presence of HBF4.Et2O at room temperature to give a beta-phosphonio-alkenyl complex (E)-[TpRuCl{CH=C(PPh3)Ph}(NO)]BF4(2.BF4). On the other hand, for gamma-hydroxyalkynyl complexes TpRuCl{C[triple bond]CC(R)2OH}(NO)(R = Me (1b), Ph (1c), H (1d)), similar treatments with PPh3 were found to give gamma-phosphonio-alkynyl [TpRuCl{C[triple bond]CC(Me)2PPh3}(NO)]BF4(3.BF4),alpha-phosphonio-allenyl [TpRuCl{C(PPh3)=C=CPh2}(NO)]BF4(4.BF4), and a novel product of gamma-hydroxy-beta-phosphonio-alkenyl (E)-[TpRuCl{CH=C(PPh3)CH2OH}(NO)]BF4(5.BF4), respectively. Dominant factors for the selectivity in affording 3-5 were associated with the steric congestion and electronic properties at the gamma-carbons, along with those around the metal fragment. From the bis(alkynyl) complex TpRu(C[triple bond]CPh)2(NO)6, a bis(beta-phosphonio-alkenyl)(E,E)-[TpRu{CH=C(PPh3)Ph}2(NO)](BF4)2{7.(BF4)2} was produced at room temperature. However, similar reactions at 0 degrees C gave an alkynyl beta-phosphonio-alkenyl complex (E)-[TpRu(C[triple bondCPh){CH=C(PPh3)Ph}(NO)]BF4(8.BF4) as a sole product, of which additional hydration in the presence of HBF4.Et2O afforded a [small beta]-phosphonio-alkenyl ketonyl (E)-[TpRu{CH2C(O)Ph}{CH=C(PPh3)Ph}(NO)]BF(.9BF4). Five complexes, 2-5 and 7 were crystallographically characterized.     

Spin relaxation in the phosphorescent triplet state of several pyridyl carbonyl compounds

Spin relaxation is observed in benzophenone, isomers of benzoylpyridines and dipyridyl ketones. Models are used to describe optically detected echo shapes observed by transient techniques in the phosphorescent triplet state. Framed after the density matrix approach, the echo shapes were found to adequately fit the analytical expressions. Hahn spin echo, Carr-Purcell multiple echo, and rotary echo pulse sequences were used to study the nuclear contribution to the electron spin dephasing and the proximity effect of the nitrogen nuclei to the localized triplet excitation in the carbonyl portion of the molecule.     

Raman spectra of flavins: avoidance of interference from fluorescence

Raman spectra of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) in neutral aqueous solutions have been observed with excitations at 600.0, 363.8, 351.1, 337.1, and 257.3 nm. It has been suggested that, in general, an excitation in the absorption band of the second or the third longest waveleng (instead of the first) is an effective means for observing a resonance Raman spectrum of a chromophore without fluorescence disturbance.     

The practical synthesis of (2S)-7-methoxy-1,2,3,4-tetrahydro-2-naphthylamine via optical resolution of 2-(3-methoxybenzyl)succinic acid

We describe the practical synthetic route for (2S)-7-methoxy-1,2,3,4-tetrahydro-2-naphthylamine 1(2S)-2-amino-7-methoxytetraline; (S)-AMT]. (2R)-2-(3-Methoxybenzyl)succinic acid [(R)-1] was obtained by the optical resolution of 2-(3-methoxybenzyl)succinic acid (1) as the salt of (1R,2S)-2-(benzylamino)cyclohexylmethanol (7), and (R)-1 was converted to the optically active (2S)-7-methoxy-1,2,3,4-tetrahydro-2-naphthoic acid [(S)-2] by the intramolecular Friedel-Crafts reaction followed by catalytic hydrogenation. (S)-AMT was obtained from the acid (S)-2 by Hofmann rearrangement without racemization.     

In situ chemical aminoacylation with amino acid thioesters linked to a peptide nucleic acid

tRNA-specific chemical aminoacylation was achieved with nonnatural amino acids. A nonnatural amino acid was activated as a thioester derivative, and the latter was linked through a spacer to the N-terminal of a 9-mer peptide nucleic acid that is complementary to the 3'-terminal region of yeast phenylalanine tRNA. Efficient aminoacylation was observed when the amino acid thioester-spacer-PNA conjugate was mixed with the tRNA. The PNA-assisted aminoacylation was also successful in an Escherichia coli in vitro protein synthesizing system that contained an orthogonalized tRNA. The in situ aminoacylation/in vitro translation gave a mutant protein in which the nonnatural amino acid was incorporated into the position directed by a CGGG 4-base codon/anticodon pair.     

Synthesis of a [3.3]biphenylophane, and its photophysical and photochemical properties studied by emission and transient absorption measurements

[3.3](4,4′)Biphenylophane (BPP) is synthesized, and the photophysical and photochemical properties are studied by means of emission and transient absorption measurements. BPP emits excimer fluorescence at 295 and 77 K, and phosphorescence from the locally-excited (LE) triplet state at 77 K. Based on the transient absorption spectra of BPP, it is found that the excimeric triplet state of BPP is produced along with the LE triplet at 295 and 77 K. The triplet excimer of BPP is shown to be formed via intersystem crossing from the singlet excimer state, and concluded to be non-phosphorescent.