Spectroscopic examination of linear poly(ethylenimine) containing nucleic acid pendants as polynucleotide analogs

The NMR spectra and UV absorptions of polynucleotide analogs with a poly(ethylenimine) (PEI) backbone containing adenine, cytosine, and hypoxanthine pendants have been examined. As has been shown in single-stranded polynucleotides, these polymers also exhibited base stacking behavior in aqueous solution as well as in 2,2,2-trifluoroethanol. Such stacking resulted in significant UV hypochromicities and observed differences in the NMR spectra compared to the corresponding model compounds. From continuous variation mixing experiments, well-defined base pairing interactions were observed between complementary graft polymers in aqueous solutions. Enhanced UV hypochromicity due to such interactions was also observed.     

Preparation and spectroscopic studies of an inclusion complex of adenine with beta-cyclodextrin in solution and in the solid state

The interaction between adenine and beta-CD has been investigated in solution and in the solid state by several analytical techniques, primarily by 1H-NMR, 2D ROESY and fluorescence spectra, and secondarily by other important techniques, for example, Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The association constant and 1:1 nature of the complex between adenine and beta-CD in solution were determined by fluorescence spectroscopy. A spatial configuration for the complex in solution is proposed from analysis of the 1H-NMR and 2D ROESY data. The Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) data are consistent with the formation of an inclusion complex. In addition, a solid inclusion complex of adenine with beta-CD was synthesized by the coprecipitation method.     

The formation of heterodimers by vancomycin group antibiotics

The formation of heterodimers in mixtures of glycopeptide antibiotics has been detected by electrospray ionization mass spectrometry (ESI-MS), and dimerization constants have been determined. By using NMR spectroscopy, it has been shown that these heterodimers indeed exist in aqueous solution. The dimerization constants obtained by NMR spectroscopy are in good agreement with those determined by ESI-MS. Structural information on the heterodimer interface of some of the heterodimers is obtained by using two-dimensional NMR techniques and reveals that these heterodimers are similar in structure to the homodimers.     

Electronic structure of adenine and thymine base pairs studied by femtosecond electron-ion coincidence spectroscopy

Femtosecond pump-probe spectroscopy was combined with photoelectron-photoion coincidence detection to investigate the electronic structure and dynamics of isolated adenine (A) and thymine (T) dimers and the adenine-thymine (AT) base pair. The photoelectron spectra show that pipi* and npi* states are only weakly perturbed in the hydrogen-bound dimers as compared to the monomers. For cationic base pairs with internal energies greater than 1 eV, we observed considerable cluster fragmentation into protonated monomers. This process selectively removed signals from the npi* --> n-1 ionization channel in all dimers. The photoelectron spectra are compared to time-resolved mass spectra and confirm the assignment of short-lived pipi* and npi* populations in the adenine, thymine, and mixed AT dimers.     

FT-IR investigation of the acetamide state in AOT reversed micelles

The state of acetamide nanoparticles encapsulated in the hydrophilic core of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reversed micelles and dispersed in CCl ₄ has been investigated by Fourier transform infrared spectroscopy. The analysis of the vibrational spectra reveals even at the higher acetamide to AOT molar ratio some changes of the typical H-bonded structure of solid acetamide ascribable to their small size, confinement effects, and acetamide-AOT head group interactions. The stretching modes of acetamide CO and AOT sulfonate groups indicate unambiguously specific acetamide-AOT head group interactions.     

Photophysics of the acid and base forms of rhodamine B

Fluorescence lifetime measurements of rhodamine B in ethanol solution have confirmed the presence of two distinct species dependent on acidity. Rotational diffusion times of these species are identical and we propose that they are the acid and base forms of the dye. Species having identical spectra to these forms have also been obtained in concentration dependent studies and we believe that here, too, the equilibrium is acid—base rather than monomer—dimer as had been suggested.     

Switching binding sites: low-temperature NMR studies on adenosine-aspartic acid interactions

Low-temperature NMR experiments were performed on mixtures of adenine nucleosides and aspartic acid derivatives in a freonic solvent. By acquiring spectra at temperatures as low as 123 K, the regime of slow hydrogen bond exchange is reached and hydrogen-bonded complexes can be characterized in detail. With 2'-deoxyadenosine lacking a 2'-substituent, N-Boc-protected aspartic acid benzyl ester binds through its carboxylic acid side chain to the Watson-Crick site of the adenine base, forming a strong hydrogen bond with the proton located close to the center between the oxygen donor and adenine N1 nitrogen acceptor. However, in the case of 2'-O-silylated adenine ribofuranosides, noncovalent interactions of the 2'-substituent with protecting groups on the amino acid shift the binding mode toward a Hoogsteen geometry with only a moderately strong hydrogen bond involving adenine N7.     

Study of nucleic acid bases by the DADI method

The DADI spectra of the nucleic acid bases adenine (I), guanine (II), Uracil (III), thymine (IV), cytosine (V), and 5-methylcytosine (VI) have been studied. It has been established that the samples of nucleic acid bases investigated are characterized by a specific pattern of the DADI spectra which reflects the nature of the molecular ion due to the structure of the given base and, in the case of M⁺ for (IV) and (VI) also the tautomeric state. The possibility has been shown of using the information obtained for the quantitative determination of (VI) in a mixture of bases.Institute of Bioorganic Chemistry, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodynkh Soedinenii, No. 6, pp. 838–844, November–December, 1979.     

Study of nucleic acid bases by the DADI method

The DADI spectra of the nucleic acid bases adenine (I), guanine (II), Uracil (III), thymine (IV), cytosine (V), and 5-methylcytosine (VI) have been studied. It has been established that the samples of nucleic acid bases investigated are characterized by a specific pattern of the DADI spectra which reflects the nature of the molecular ion due to the structure of the given base and, in the case of M⁺ for (IV) and (VI) also the tautomeric state. The possibility has been shown of using the information obtained for the quantitative determination of (VI) in a mixture of bases.     

Ionization potentials and donor properties of nucleic acid bases and related compounds

The first vertical ionization potentials of guanine, adenine, hypoxanthine, xanthine, cytosine, thymine, uracil and purine have been determined by HeI photoelectron spectroscopy. The potentials increase in the above order and are assigned to ionization from the highest π level. The experimental results are compared with valence shell SCF calculations, and the correlation between the association constants of these molecules with riboflavin and their donor properties is discussed. Detailed spectra will be presented and discussed in a forthcoming paper.     

Surface enhanced Raman spectra of nucleic acid components adsorbed at a silver electrode

High-resolution vibrational spectra of nucleic acid components adsorbed on a silver electrode were obtained using a spectroelectrochemical method based on the large-intensity enhancement for Raman scattering at electrode surfaces.The laser surface Raman spectra of purine, adenine, adenosine, deoxyadenosine, adenine mononucleotides, adenylyl-3′, 5′-adenosine and polyriboadenylic acid were recorded in the range of 150–3500 cm^?1. The intensities of the vibrational bands were highly dependent upon the electrochemical preparation of the electrode, the applied potential and the nature of the adsorbate species. High-intensity spectra in rather dilute bulk solutions were obtained.The phosphate derivatives of adenosine exhibited strongly enhanced Raman scattering. Spectral band frequencies corresponded closely with normal Raman spectra of these molecules in solution. The adenine ring breathing mode at 740 cm^?1 and the adenine ring skeletal vibration at 1335 cm^?1 produced prominent Raman scattering. A strong band at about 240 cm^?1 for the adenine mononucleotides was attributed to silver/adsorbed phosphate group vibrations.     

Mass spectrometry of benzylamines and benzylamine derivatives

The mass spectra of benzylamine, N-ethylbenzylamine, N,N-dimethylbenzylamine, p-methoxybenzylamine and 4-hydroxy-3-methoxybenzylamine, and their acetamide and trimethyl- silyl (TMS) derivatives have been recorded. Low and high resolution spectroscopy were employed in conjunction with ion kinetic energy (IKE) determinations to establish the empirical formulae of the fragment ions and their modes of fragmentation. In the case of the acetamide derivatives the acyl group is lost by acetoxy elimination giving rise to the [M — 1] ion of the parent amine which then undergoes fragmentation very similar to the original amine. The TMS derivatives present more complex fragmentation patterns which involve rearrangement of the TMS side chain during decomposition. Consequently the acetamide derivative of an unknown aromatic amine is preferred for diagnostic purposes.     

Vinylsulfonylethyl derivatives of nucleic acid bases and their graft polymers on polyethyleneimine

Vinylsulfonylethyl (VSE) derivatives of the nucleic acid bases adenine, thymine, cytosine, and the nucleosides inosine and uridine have been prepared via a simple Michael reaction with divinyl sulfone. The VSE derivatives were grafted on a polyethyleneimine (PEI) backbone. PEI of different molecular weights (1400, 1800 and 50,000–100,000) were used and also two different molar ratios (1:1 and 1:2) of monomer to PEI were employed. From the ¹H-NMR and elemental analysis, it appeared that in almost all instances the grafting was quantitative. In one case, both 1-VSE-thymine and 9-VSE-adenine were grafted on the same PEI backbone. Interactions between some of these polymers were investigated by UV spectroscopy. The expected complementary base pairing was observed only in DMSO–ethylene glycol solvent system but not in DMSO. The adenine polymer showed a one-to-one interaction with the thymine polymer.     

Elementary peptide motifs in the gas phase: FTIR aggregation study of formamide, acetamide, N-methylformamide, and N-methylacetamide

Cold, isolated peptide model compounds and their aggregates are generated in pulsed supersonic jet expansions and detected by FTIR spectroscopy in the amide-A region, complemented by amide-I spectra. The most stable, symmetric dimer of formamide is unambiguously assigned in the gas phase for the first time, also by comparison to the analogous acetamide dimer. Efficient quenching of a hot-state Fermi resonance by cooling of the dimers is invoked. As the preferred relative orientation of the C=O and N-H groups in N-methylated formamide and acetamide is trans, these compounds show a fundamentally different dimerization pattern. Their most stable dimers, which would be analogous to those of formamide and acetamide, remain undetected as a consequence of kinetic control in the jet. Accurate benchmark quantities for multidimensional vibrational treatments of these peptide models are derived, and the influence of methyl groups on the N-H stretching dynamics is discussed.     

Pairing of Isolated Nucleobases: Double Resonance Laser Spectroscopy of Adenine–Thymine

The vibronic spectrum of the adenine–thymine (A–T) base pair was obtained by one‐color resonant two‐photon ionization (R2PI) spectroscopy in a free jet of thermally evaporated A and T under conditions favorable for formation of small clusters. The onset of the spectrum at 35 064 cm^?1 exhibits a large red shift relative to the π–π* origin of 9H‐adenine at 36 105 cm^?1. The IR–UV spectrum was assigned to cluster structures with HNH???O?C/N???HN hydrogen bonding by comparison with the IR spectra of A and T monomers and with ab initio calculated vibrational spectra of the most stable A–T isomers. The Watson–Crick A–T base pair is not the most stable base‐pair structure at different levels of ab initio theory, and its vibrational spectrum is not in agreement with the observed experimental spectrum. Experiments with methylated A and T were performed to further support the structural assignment.     

Three-state conical intersections in nucleic acid bases

The involvement of three-state conical intersections in the photophysics and radiationless decay processes of the nucleobases has been investigated using multireference configuration interaction methods. Three-state conical intersections have been located for the pyrimidine base, uracil, and the purine base, adenine. In uracil, a three-state degeneracy between the S(0), S(1), and S(2) states has been located at 6.2 eV above the ground-state minimum energy. This energy is 0.4 eV higher than vertical excitation to S(2) and at least 1.3 eV higher than the two-state conical intersections found previously. In adenine, two different three-state degeneracies between the S(1), S(2), and S(3) states have been located at energies close to the vertical excitation energies. The energetics of these three-state conical intersections suggest they can play a role in a radiationless decay pathway present in adenine. The existence of two different seams of three-state conical intersections indicates that these features are common and complicate the potential energy surfaces of adenine and possibly many other aromatic molecules.     

Interaction of some complementary constituents of nucleic acids in aqueous solution: UV and IR hypochromicities

Ultraviolet spectra of mixtures of monomeric units of nucleic acids and dinucleoside monophosphates, containing the complementary nucleobases adenine and uracil, have been obtained in aqueous solution. Hypochromicity of spectra of the mixtures with respect to free components has been determined, introducing the correction corresponding to selfassociation of these compounds. Hypochromicity of mixtures can be considered an experimental evidence of the existence of heteroassociation processes.Infrared spectra of some complementary constituents of nucleic acids in aqueous solution also reveal hypochromic effects, which provide information about the molecular groups involved in the heteroassociation.     

Transient absorption spectra and quenching of coumarin excited states by nucleic acid bases.

Triplet-triplet absorption spectra of coumarin show different profiles and maxima in ethanol from those in water, which are very similar to those reported in benzene. Long-lived transient species other than triplet states were generated as initial photoproducts between coumarins and nucleic acid bases. The excited singlet and triplet states of coumarins were quenched by nucleic acid bases. Adenine base quenched the excited singlet state of coumarins more efficiently than thymine base. However, photocycloadducts of furocoumarins are formed predominantly with thymine, and not with adenine. Moreover, it is reported that the poly[dA-dT].poly[dA-dT] sequence region is the most favourable site for the photocycloaddition reaction of furocoumarins. The results imply that adenine contributes to singlet-state photocycloaddition reaction of furocoumarins with thymine, probably through an adenine-furocoumarin-thymine termolecular interaction.     

Synthesis and characterization of new polyesters based on 2,5-bis[(4-chloro carboxyanilino) carbonyl] pyridine and aromatic diols

<正>Six new polyesters 7a-f were synthesized through the solution polycondensation reaction of diacid chloride 5 with six aromatic diols 6a-f in N,N-dimethyl acetamide(DMAc) as solvent in the presence of pyridine as base.The polycondensation reaction produced a series of novel polyester containing pyridyl moiety in the main chain in high yields with inherent viscosities between 0.35 and 0.54 dL/g.The resulted polymers were fully characterized by means of FT-IR spectroscopy,elemental analyses,inherent viscosity and solubility tests.Thermal properties of these polymers were investigated by using thermal gravimetric analysis(TGA) and differentional thermal gravimetric(DTG).The glass-transition temperatures of these polyesters were recorded between 130 and 170℃by differential scanning calorimetry(DSC) and the 10%weight loss temperatures were ranging from 390 to 450℃under nitrogen.     

利用原位红外光谱技术研究2,6二甲基苯酚在金电极上的电化学聚合机理

利用原位LPSIRS技术获得氢氧化钠甲醇溶液中2,6-二甲基苯酚在金电极上电聚合的红外光谱信息, 从而推测2,6-二甲基苯酚在金电极上电聚合机理是一系列交替着的离子、游离基步骤。