EXCITED STATES OF DNA AND ITS COMPONENTS AT ROOM TEMPERATURE—IV. SPECTRAL, POLARIZATION AND QUANTUM YIELD STUDIES OF EMISSIONS FROM CpC AND POLY rC

Abstract— Corrected normalized emission spectra are reported for poly rC, CpC and CMP in neutral aqueous solution at room temperature. The emissions from CpC and poly rC show progressive and extensive depolarization across the emission band compared with CMP. Self-consistent analysis of the polarization and spectral data allows the resolution of red-shifted component emissions from the overall spectra and the evaluation of component polarizations. By comparison with experimental reference spectra three long wavelength components are identified in the poly rC emission and assigned as excimer fluorescence, monomer phosphorescence and excimer phosphorescence, whereas for CpC only two components are observed. The quantum yields are interpreted quantitatively in terms of the known stacking behavior of CpC and poly rC. with excimer emissions originating from the stacked fraction. Quantitative differences between CpC and poly rC are due to their different hypochromism and degree of stacking. Differences of polarization of excimer fluorescence are a consequence of different stacking geometries, and the directional properties of the transition moment suggest the excimer fluorescence is largely charge-resonance in nature. The behavior of the CpC/poly rC system is compared with ApA/ poly rA.     

EXCITED STATES OF DNA AND ITS COMPONENTS AT ROOM TEMPERATURE—III. SPECTRA, POLARISATION AND QUANTUM YIELDS OF EMISSIONS FROM ApA AND poly rA*

Abstract— Corrected normalised emission spectra from 300 to 480 nm and their polarisation are reported for neutral and poly rA at room temperature. Yields are 4 times (ApA) and 6 times (poly rA) greater than the monomer. Comparison of emission spectra and polarisation spectra demonstrates heterogeneity of emission and, following attempts at spectral synthesis, comparison with experimental reference spectra allows the observed total emission spectra to be resolved into four components assigned as I monomer-like emission, II excimer fluorescence, HI monomer phosphorescence, IV excimer phosphorescence; the polarisation of the excimer fluorescences of ApA and poly rA are deduced. The observations can be understood quantitatively using a simple stacking model with excimer emissions originating in the stacked components. Quantitative differences between ApA and poly rA are due to their different hypochromism and extent of stacking. Differences of polarisation are attributed to different stacking geometries, and the directional properties of the transition moment suggest that the excimer fluorescence is largely charge-resonance in nature.     

TRIPLET EXCITED STATES OF 4'',5''-PHOTOMONOADDUCTS OF 3- CARBETHOXYPSORALEN and 8-METHOXYPSORALEN WITH DNA NUCLEOSIDES

Abstract— Triplet absorption spectra, triplet extinction coefficient and intersystem crossing for 4',5'-monocycloadducts of 3-carbethoxypsoralen (3-CPs) with thymidine (dThd) and uridine (dUrd) in ethanol have been investigated in order to elucidate whether their triplet state properties could be the limitating step for a further photoreaction of 3-CPs monoadducts with DNA nucleosides. The comparison between the triplet characteristics of 4',5'-monoadducts of 3-CPs and those of 8-methoxypsoralen (8-MOP) shows that the quantum yield is much higher in the case of 3-CPs than for 8-MOP. The monofunctionality of 3-CPs cannot therefore be ascribed to the triplet excited states properties of its monoadducts. It is likely that steric hindrance introduced by the bulky carbethoxy group remains a reasonable explanation.     

EXCITED STATES OF FLAVINES – V. THE QUENCHING OF FLAVINE LUMINESCENCE BY INDOLES

Abstract— The quenching of the fluorescence of flavines by indoles in aqueous solution has been studied as a function of concentration, viscosity and temperature. The quenching shows a negative temperature dependence, and is in part diffusion controlled. Static and dynamic processes both contribute to quenching.
In the presence of alcohol or denaturants static quenching is inhibited and dynamic quenching supervenes. The effect of indoles on the flavine fluorescence lifetimes and phosphorescence characteristics is consistent with the quenching mechanism proposed.     

PHOTOPRODUCTS OF BROMOURACIL-LABELED DNA AND THE STRUCTURE OF 5-BROMODEOXYURIDYLYL-(3' → 5')-THYMIDINE PHOTOPRODUCT

Abstract— –An attempt was made to identify some of the ultraviolet (u.v.) photoproducts of 5-bromouracil-labeled DNA (BrU-DNA). Two synthetic dinucleotides, 5-bromodeoxyuridylyl-(3' →5 ')-thymidine (BrdUpT) and 5-bromodeoxyuridylyl-(3' → 5')-deoxycytidine (BrdUpdC), were prepared. Each gave a single u.v. photoproduct which in turn gave a single acid hydrolysis product. 2-¹⁴C-BrU-DNA. prepared from E. coli B3, was irradiated (275–280 nm), hydrolyzed, and paper chromatographed in four systems. Comparison with the two synthetic photoproducts showed that if present at all, BrdUpT and BrdUpdC photoproducts could account for no more than 10 and 3.5 per cent respectively of the total photoproducts. At 55 per cent conversion of BrU into photoproducts, the major ¹⁴C-photoproduct was uracil (78 per cent); the remaining 22 per cent was made up of at least six products, three of which were reversed by 232 nm irradiation.
The debrominated cyclobutane structure proposed by Haug for BrdUpT photoproduct has been shown to be incorrect. It was found to contain one atom of bromine per molecule. On the basis of nuclear magnetic resonance and u.v. spectra, two possible structures are proposed for the photoproduct, each containing an eight-membered ring.     

NONLINEAR POLARIZATION SPECTROSCOPY (FREQUENCY DOMAIN) STUDIES OF EXCITED STATE PROCESSES: THE B800–850ANTENNA OF RHODOBACTER SPHAEROIDES

Nonlinear polarization spectroscopy in the frequency domain allows rate constant determinations of fast electronic energy and phase relaxations together with characterization of the type of line broadening. Application of this method to the B850 component of the isolated B800–850antenna ofRhodobacter sphaeroides at room temperature shows that B850 is inhomogeneously broadened, with homogeneous widths between 30 and 200 cm^?1, depending on the spectral position of the subforms. The corresponding phase relaxation times are clearly in the subpicosecond range. There is also indication of an up-to-now unspecified1–5 ps energy relaxation channel per subunit.     

EXCITED STATES OF SIX-MEMBERED N-HETEROCYCLES. FLUORESCENCE, PHOSPHORESCENCE AND ACID-BASE EQUILIBRIA OF FIVE MONO- AND DIAZA-PHENANTHRENES IN THE LOWEST EXCITED (τ,τ) STATES

Abstract— Acid-base equilibria of five azaphenanthrenes (1-and 4-aza; 1,10-, 1,7-, and 4,7-diaza) in the two lowest excited (τ,τ) states have been determined by Förster's cycle. Pure electronic levels of the free bases and their conjugate acids have been located from the absorption, fluorescence and phosphorescence spectra. In diazaphenanthrenes the increase of the first pK_a and the decrease of the second pK_a under excitation has been observed, and an explanation is offered. In many cases the reactivity of the molecule excited to the lowest triplet state differs considerably from that in the ground state. The Pariser-Pam-Pople (PPP) calculations of the free bases have been performed. From the theoretical results, the changes of the net charge on nitrogen atoms under excitation and the magnitude of the S-T splitting in the L_a and L_b states have been discussed and compared with experiment.     

Hydrolytic reactions of guanosyl-(3',3')-uridine and guanosyl-(3',3')-(2',5'-di-O-methyluridine)

Hydrolytic reactions of guanosyl-(3',3')-uridine and guanosyl-(3',3')-(2',5'-di-O-methyluridine) have been followed by RP HPLC over a wide pH range at 363.2 K in order to elucidate the role of the 2'-hydroxyl group as a hydrogen-bond donor upon departure of the 3'-uridine moiety. Under neutral and basic conditions, guanosyl-(3',3')-uridine undergoes hydroxide ion-catalyzed cleavage (first order in [OH(-)]) of the P-O3' bonds, giving uridine and guanosine 2',3'-cyclic monophosphates, which are subsequently hydrolyzed to a mixture of 2'- and 3'-monophosphates. This bond rupture is 23 times as fast as the corresponding cleavage of the P-O3' bond of guanosyl-(3',3')-(2',5'-di-O-methyluridine) to yield 2',5'-O-dimethyluridine and guanosine 2',3'-cyclic phosphate. Under acidic conditions, where the reactivity differences are smaller, depurination and isomerization compete with the cleavage. The effect of Zn(2+) on the cleavage of the P-O3' bonds of guanosyl-(3',3')-uridine is modest: about 6-fold acceleration was observed at [Zn(2+)] = 5 mmol L(-)(1) and pH 5.6. With guanosyl-(3',3')-(2',5'-di-O-methyluridine) the rate-acceleration effect is greater: a 37-fold acceleration was observed. The mechanisms of the partial reactions, in particular the effects of the 2'-hydroxyl group on the departure of the 3'-linked nucleoside, are discussed.     

3'-nitrophenylpropyloxycarbonyl (NPPOC) protecting groups for high-fidelity automated 5' --> 3' photochemical DNA synthesis

[structure: see text]. The most powerful DNA microarrays would be prepared by photolithography with free 3'-ends that could be processed enzymatically. A photoremovable group that could be removed in quantitative yield would ensure high purity of the synthesized probes. We have developed new pyrimidine building blocks for 5' --> 3' DNA synthesis with high cycle yields using the NPPOC (3'-nitrophenylpropyloxycarbonyl) protecting group. These phosphoramidites were proved in automated photochemical DNA synthesis on a modified synthesizer.     

SYNTHESIS AND SPECTRAL STUDIES OF(μ-PHENYLTHIO) (μ-ALKYLTHIO) HEXACARBONYLDIIRON COMPLEXES

Through reductive reaction between PhL1 and μ-S2 Fe (CO/6,tollowed by nucleophilicsubstitution of the intermediate (μ-PhS} (μ-LIS} Fe2 (CO)6 toward RX,nine Fe-S clus-ter complexes of (μ-PhS)(μ-RS)Fe2(CO)6 series have been synthesized.The influence of RX structures on the activities in nucleophilic substitution has been examined and possible steroisomers and isomer ratios of the complexes determined.In addition,the regular variations of isomer's CH3-S and CH2-S which are caused by the anisotropic effects of C-O and orientations of unshared electron pairs on sulfurs,have also been preliminarily discussed.     

CHARACTERIZATION OF THE (6-4) PHOTOPRODUCT OF 2'-DEOXYCYTIDYLYL-(3'->5')-THYMIDINE AND OF ITS DEWAR VALENCE ISOMER

Far-UV irradiation of dCpT in aqueous solution was found to generate the corresponding pyrimidine (6-4) pyrimidone photoadduct and the related Dewar valence isomer. The two photoproducts of dCpT were found to undergo deamination in aqueous solution, giving rise to the corresponding dUpT derivatives at a relatively slow rate. It was also shown that the Dewar isomer is much more alkali-labile than its (6-4) precursor.     

CRYSTAL AND MOLECULAR STRUCTURE OF 1-PHENYL-3-METHYL-4-( 3' -PHENYL-1', 3' -ACEDION)-PYRAZOLONE-5

<正> A new 4-acetyl pyrazolone chelating agent C_(19)H_(16)N_2O_3 Mr=320. 348 has been synthesized. The molecular composition is different from β-Diketon and "Double β-Diketon". There are conjugated metiple bonds composed of three carbonyl groups in the molecule. A single crystal of approximate dimensions 0.1 × 0.2 × 0.5mm was mounted on an NICOLET R3M/E four-circle diffractomcter with graphite monochromated MoKa     

SYNTHESIS,SPECTRAL STUDIES,AND ANTIMICROBIAL ACTIVITIES OF [N-(UN)ALKYLATED-2-ARYLINDOL-3-YL]THIOCARBOXAMIDES

A series of [N-(un)alkylated-2-arylindol-3-yl]thiocarboxamides(6) have been synthesized by the condensation of alkyl [N-(un)alkylated-2-arylindol-3-yl]dithiocarboxylates (5) with appropriate secondary amines in absolute alcohol. Compound 5 was prepared by the reaction of N-(un)alkylated-2-arylindoles with carbon disulphide in the presence of potassium-t-butoxide followed by alkyl iodide under nitrogen atmosphere. All of the compounds have been characterized on the basis of their elemental and spectral data and have been screened for their antibacterial and antifungal activities. Some of the synthesized compounds have shown promising activity.     

Solid-state synthesis of poly(3',4'-dimethoxy-2,2':5',2"- terthiophene): comparison with poly(terthiophene) and poly(3',4'-ethylenedioxy-2,2':5',2"- terthiophene)

A new terthiophene monomer: 3',4'-dimethoxy-2,2':5',2"-terthiophene (TMT) was synthesized and characterized by 1H-NMR, 13C-NMR and FTIR. The solid-state oxidative polymerizations of TMT were performed in various ratios of oxidant (FeCl?) to monomer (TMT). The resulting polymers were characterized by 1H-NMR, FTIR, UV-vis-NIR, GPC, X-ray diffraction, CV, as well as TGA and conductivity measurements. The structure and properties of poly (TMT) were compared with those of polyterthiophene [poly(TT)] and poly (3',4'-ethylenedioxy-2,2':5',2"-terthiophene) [poly(TET)] prepared under the same polymerization conditions. After comparative analysis with poly(TT) and poly(TET), the effects of the dimethoxy substituent and FeCl? on the structural and physicochemical properties of the poly(TMT)s were discussed in depth. The comparison suggested that the dimethoxy-substituted polymer did not display higher crystallinity, thermal stability, conductivity and electrochemical activity than ethylenedioxy substituted one. The results also showed that the effect of FeCl? on poly(TMT) was similar that seen with the poly(TT), in which the oxidation degree, electrochemical activity and conductivity increased steadily with increasing [FeCl?/[TT] ratio. Furthermore, the poly(TMT) and poly(TT) are mostly made up of dimers with a small amount of higher molecular weight components.     

Total synthesis of 2',3',4',5',5' '-(2)h(5)-ribonucleosides: the key building blocks for NMR structure elucidation of large RNA

The diastereospecific chemical syntheses of uridine-2',3',4',5',5' '-(2)H(5) (21a), adenosine-2',3',4',5',5' '-(2)H(5) (21b), cytidine-2',3',4',5',5' '-(2)H(5)(2)H(5) (21c), and guanosine-2',3',4',5',5' '-(2)H(5) (21d) (>97 atom % (2)H at C2', C3', C4', and C5'/C5' ') have been achieved for their use in the solution NMR structure determination of oligo-RNA by the Uppsala "NMR-window" concept (refs 4a-c, 5a, 6), in which a small (1)H segment is NMR-visible, while the rest is made NMR-invisible by incorporation of the deuterated blocks 21a-d. The deuterated ribonucleosides 21a-d have been prepared by the condensation of appropriately protected aglycone with 1-O-acetyl-2,3,5-tri-O-(4-toluoyl)-alpha/beta-D-ribofuranose-2,3,4,5,5'-(2)H(5) (19), which has been obtained via diastereospecific deuterium incorporation at the C2 center of appropriate D-ribose-(2)H(4) derivatives either through an oxidation-reduction-inversion sequence or a one-step deuterium-proton exchange in high overall yield (44% and 24%, respectively).     

SYNTHETIC,SPECTRAL AND BIOLOGICAL STUDIES OF ORGANOSILICON (IV) COMPLEXES WITH SCHIFF BASES OF SULFA DRUGS

Abstract

In the present paper synthetic and structural studies of six-coordinated Me₂Si(NN)₂ type of organosilicon(IV) complexes of Schiff bases (NN) have been described. The complexes were characterized by elemental analyses, conductance measurements, molecular weight determinations and electronic, infrared, ¹H, ¹³C and ²⁹Si NMR spectral studies. A few representative complexes were also screened for antimicrobial activity and found to be quite active in this respect.