Synthesis and Crystal Structure of p-tert-Butylthiacalix[8]arene: A New Member of Thiacalixarenes

Even though it was obtained in poor yield, p-tert-butylthiacalix[8]arene (TC8A) has been synthesized as a new member of thiacalix[n]arenes by the terephthalate-induced cyclization of a mixture of acyclic oligomers, which was obtained by the reaction between p-tert-butylphenol and sulfur with CaO in ethylene glycol/diphenyl ether system. Slow evaporation of the chloroform solution of TC8A afforded guest-free crystals consisting of TC8A itself. The close-packed crystal structure of TC8A resembles that of p-tert-butylcalix[8]arene (C8A) closely, containing a plated loop molecular structure.This revised version was published online in July 2005 with a corrected issue number.     

QUATERNARY STRUCTURE OF PEA PHYTOCHROME I DIMER STUDIED WITH SMALL-ANGLE X-RAY SCATTERING and ROTARY-SHADOWING ELECTRON MICROSCOPY

Abstract— The quaternary structure of pea phytochrome type I (PI) dimer in the red-light-absorbing form was studied by small-angle X-ray scattering (SAXS) technique and rotary-shadowing electron microscopy. Structural parameters for PI 114 kDa chromopeptide dimer and its tryptically digested N-terminal 59 kDa chromopeptide monomer, such as average electron density, molecular volume and the second moment of electron density distribution, were determined in terms of SAXS using the contrast variation method. Furthermore, by means of model simulation for the scattering profiles of the chromopeptides, most plausible structural models for both peptides were constructed. The distance between the chromophoric domains was estimated to be about 70 A in the resultant model for 114 kDa chromopeptide dimer. Furthermore, the model was consistent with the electron-micrographic images of both the intact PI dimer and the PI 114 kDa chromopeptide dimer, so that the N-terminal 7 kDa fragment did not significantly contribute the low-resolution images of the dimer.     

KINETICS OF 4-THIOURIDYLATE-SENSITIZED PHOTOINACTIVATION OF RIBONUCLEASE A

Abstract —An action spectrum for the inactivation of ribonuclease A photosensitized with 4-thiouridylic acid follows the shape of the absorption spectrum of an RNase-thiouridylate complex or of the unbound nucleotide. The quantum yield is 3.3 times 10^-3. Statistical analysis of the data suggests that only the bound nucleotide participates in the photoinactivation. An Arrhenius plot for the first-order rate constants of inactivation gives a straight line in the range 0–40C and an apparent activation energy of photoinactivation of 5.7 kcal/mol. The 4-thiouridylate-sensitized photoinactivation of ribonuclease A is regarded as a kind of photodynamic action in which the substrate analogue plays the role of photosensitizer.     

Synthesis of new dihydropyrazines with DNA strand-breakage activity

Treatment of 1,2-cyclohexanedione with 1,2-diamines, e.g. ethylenediamine and cis-(and trans-)1,2-diaminocyclohexane, caused [4+2] cyclocondensation to give the corresponding dihydropyrazine derivatives (compounds 1-6). They exhibited stronger DNA strand-breakage activity than that of dihydropyrazines, which has already been reported in previous papers.     

A High Sensitivity Fluorescent Chemo-sensory System Based on β-Cyclodextrin Dimer Modified with Dansyl Moieties

-Cyclodextrin dimer linked with ethylenediamine at the upper rim of the cyclodextrin has been synthesized and then modified with two dansyl moieties inthe presence of N,N'-dicyclohexylcarbodiimide. The sensing ability and bindingproperty of the title compound were investigated for steroids and terpenoids. Thefluorescence intensity of this dimer was decreased when a host–guest complex was formed. The value I/I⁰, where I⁰ and I are fluorescence intensitiesin the absence and presence of a guest and I is I⁰- I, was used as a parameter of sensitivity. This host exhibited a much higher sensitivity and selective molecular recognition ability for bile acids such as ursodeoxycholic acid andchenodeoxycholic acid and terpenoids such as (-)-borneol than the dansyl-modifiedcyclodextrins reported previously including -cyclodextrin dimer. The behaviors of the appended moieties of the host during the formation of host–guest complexes were studied using induced circular dichroism (ICD) and fluorescence spectra. The ICD intensityof this dimer was decreased on accommodation of a guest and this spectral pattern of the title dimer was opposite to that of bis dansyl-modified -cyclodextrin monomer. Theguest-induced variations in the fluorescence and ICD intensities suggest that this dimer formed a 1 : 1 host–guest complex and the appended moieties act as a hydrophobic cap.     

New synthesis of 5-amino-5-deazaflavin derivatives by direct coupling of 5-deazaflavins and amines

5-Amino-5-deazaflavin derivatives are newly synthesized by direct coupling of 5-deazaflavins and amines. Some of them revealed potential activity toward tumor cells such as L1210 or KB cells.     

A synthesis of lumazine derivatives

Treatment of 6-amino-1,3-dimethyl-5-nitrosouracil (Ia) with dimethyl acetylenedicarboxylate (DMAD) in dimethylformamide (DMF) afforded 6,7-bis(dimethoxycarbonyl)-1,3-dimethyllumazine (II). Similarly, the reaction of 6-amino-1,3-dimethyl-5-phenylazouracil with DMAD gave also II. Hydrolysis of II with hydrochloric acid gave 1,3-dimethyllumazine-6-carboxylic acid (III). III was chlorinated with thionyl chloride and then aminated with ethanolic ammonia to give rise to 6-carbamoyl-1,3-dimethyllumazine (V). V was alternatively synthesized by the treatment of Ia with propiolamide in DMF.     

Fluorescent Molecular Recognition and Sensing System of Bis-Dansyl Modified γ-Cyclodextrins

Flexible hosts, 6A,6B-; 6A,6C-; 6A,6D-; and 6A,6E-bis dansylglycine-modified -cyclodextrins (-1, -2, -3, and -4, respectively) have been synthesized as a sensing molecule for organic guests including terpenoids and bile acids. These host compounds show a pure monomer fluorescence whose intensity is decreased or enhanced upon addition of guest species. The value I/I₀, where I and I₀ are fluorescence intensities in the presence and absence of a guest and I is I₀- I, was used as a parameter of sensitivity. These hosts exhibit highly sensitive and selective molecular recognition ability, particularly, for lithochoic acid, chenodeoxycholic acid, and ursodeoxycholic acid. The behaviors of the appended moieties of these hosts when host–guest complexation occurs are studied by induced circular dichroism (ICD) spectra and fluorescence spectral change on accommodation of a guest. The ICD pattern of these hosts alone or on accommodation of a guest is very similar, indicating that the behavior of the appended moieties are very similar. The guest-induced variations in the fluorescence or ICD intensity suggest that the appended moieties act as a hydrophobic cap that enables the cyclodextrin to form 1 : 1 host–guest complexes.     

Method to determine quadruple points of a two-component system containing a simple hydrate phase and behavior of the system near these points

A method for determining quadruple points of a two-component system containing a simple hydrate phase is proposed. This method utilizes the quasi-static change of the system along three-phase equilibrium lines and was proved to be able to determine the quadruple points as accurately as the conventional method. By using this method, even though some preparation is necessary, a quadruple point can be determined in just a single experimental run. The behavior of the system near the quadruple points was also examined experimentally, for both the quasi-static and the irreversible change cases. At the quadruple points, the temperature and pressure of the system were kept constant for a while, as at the triple point of water. In both cases, the representative point of the state of the system passed through the quadruple point on a p–T diagram.