Spectroscopic study of molecular associations between riboflavin and some (dihydro) β-carboline derivatives

The spectrophotometric and thermodynamic properties of molecular complexes of riboflavin (RFN) with some dihydro β-carboline derivatives have been investigated by using electronic absorption and fluorescence spectroscopic methods in aqueous solution. The molecular associations have been examined by means of eletronic absorption spectra, since in each, a new charge transfer-like band has been located, and also by observing the variation of the fluorescence emission of RFN on the solutions. The formation constants for the molecular complexes were determined from absorption data, using the Forster—Hammick—Wardley method. The quenching phenomenon observed in RFN fluorescence is related to the concentration of the dihydro β-carboline derivatives, allowing the calculation of the quenching constants for RFN—β-carboline complexes. Thermodynamic parameters have been determined from the values of association constants for the molecular complexes at various temperatures. The influence of substituents in the dihydro β-carboline molecule on the stability of the complexes formed was also investigated.     

Spectroscopic study of intermolecular complexes between FAD and some β-carboline derivatives

The formation of molecular complexes between flavine adenine dinucleotide (FAD) and some β-carboline derivatives [antidepressant drugs that have a pronounced inhibition of monoamine oxidase (MAO)] has been studied by using electronic absorption and fluorescence spectroscopic methods. Thermodynamic parameters have been determined from the values of association constants for the molecular complexes at various temperatures. The influence of substituents in the β-carboline molecule on the stability of the complexes formed was also investigated.     

Simultaneous determination of tetrahydro-β-carbolines and β-carbolines

Summary Reversed-phase ion-pair HPLC with fluorimetric detectors connected in series was studied for the simultaneous determination of two tetrahydro--carbolines and two -carbolines. After additon of internal standards the samples were reacted with fluorescamine, and then subjected to serial extractions to remove their precursor (tryptamine) from the analytical system. This treatment not only suppressed the artefactual formation of tetrahydro--carbolines and -carbolines during analysis, but also effectively purified them. Under optimum conditions, using trifluoroacetic acid as counter ion, all analytes were separated within 14 min and without major interfering peaks. The quantitative ranges were 0.25–80.0 ng mL^–1 for both tetrahydro--carbolines and 0.1–30.0 ng mL^–1 for both -carbolines. Replicate spiking experiments showed that recovery from most of the samples tested was over 90% and the relative standard deviation ranged from 0.7 to 10.4% within and between assays. The proposed method was applicable to various materials such as soy sauce, vinegar, ketchup, tabasco, beer, wine, sake, whisky, brandy, cows' milk, coffee, cocoa, cheese, cigarette smoke and urine.     

Spectroscopic and computational study of β-ethynylphenylene substituted zinc and free-base porphyrins

A series of tetraphenylporphyrins appended at the β-pyrrolic position with an ethynylphenylene- or ethynylpyridine-substituent have been subjected to spectroscopic and density functional theory (DFT) analyses. The mean absolute deviation between corresponding experimental and DFT-derived vibrational spectra is up to 10.2 cm(-1), suggesting that the DFT B3LYP/6-31G(d) method provides an accurate model of the β-substituted porphyrin systems. The configuration interactions that give rise to prominent electronic absorptions have been calculated using time-dependant DFT (TD-DFT) and have been rationalized with reference to the energy and topology of DFT calculated molecular orbitals. As the electron withdrawing capacity of the β-substituent increases the LUMO orbital gains appreciable amplitude over the substituent moiety and is stabilised. This represents a departure from the assumptions underpinning the Gouterman four-orbital model, resulting in atypical electronic absorption spectra. This phenomenon is also manifested in the enhancement patterns of the resonance Raman spectra insofar as B-band excitation engenders an enhancement of substituent based modes. These observations demonstrate that the β-substituent exerts an appreciable electronic influence on the porphyrin π-electron system and provides a means of introducing charge-transfer character to prominent electronic transitions.     

Synthesis of β-carbolines via a silver-mediated oxidation of tetrahydro-β-carbolines

The oxidation of tetrahydro-β-carbolines to β-carbolines using silver carbonate was developed as an alternative to current methods. The oxidation is extremely mild and provides the products in modest to good yields after purification. A number of functional groups are tolerated by this methodology, including reduction-sensitive groups which are often cleaved with other methods. Though the mechanism is not fully understood, the reaction proceeds in an open flask, is not sensitive to light or moisture, and provides a viable synthetic route to compounds that are not easily prepared via other methodologies.     

Medium-sized and strained heterocycles from non-catalysed and gold-catalysed conversions of β-carbolines

2-Allyl-1-vinyl-β-carbolines and dihydropyrrolo-β-carbolines react with activated internal alkynes through novel rearrangement reactions leading to complex polycyclic structures. Favored reaction pathways depend on reaction conditions and on the presence of gold catalysts. In particular, upon reaction with 2 equiv. of the alkyne, new hexacyclic structures 10 are formed with total stereocontrol.     

Hydration of β-cyclodextrin: A molecular dynamics simulation study

We study by molecular dynamics simulations the hydration of -cyclodextrin. Our simulations show that within these barrel-shaped molecules hydrophobicity dominates, while at the top and bottom sides of the barrel interactions with water are mostly hydrophilic in nature. These results agree with crystallographic data at 120 K and, in particular, with the spontaneous hydration process of a cyclodextrin crystal in wet atmosphere. The predicted structure of the hydration shells is discussed and compared with previous molecular mechanics calculations which report an overall hydrophobic behavior. Moreover, the temperature dependence of the hydration process is discussed.     

Spectroscopic studies of inclusion complex of β-cyclodextrin and benzidine diammonium dipicrate

Formation of inclusion complex between benzidine diammonium dipicrate and β-cyclodextrin with stoichiometry 1:2 (guest–host) has been established by UV, ¹H NMR, ¹³C NMR, IR spectra and powder X-ray diffractometry. ¹H NMR studies are used to confirm the inclusion and to provide information on the geometry of dipicrate inside the cavity of β-cyclodextrin.     

Photosensitization of DNA by β-carbolines: kinetic analysis and photoproduct characterization

β-Carbolines (βCs) are a group of alkaloids present in many plants and animals. It has been suggested that these alkaloids participate in a variety of significant photosensitized processes. Despite their well-established natural occurrence, the main biological role of these alkaloids and the mechanisms involved are, to date, poorly understood. In the present work, we examined the capability of three important βCs (norharmane, harmane and harmine) and two of its derivatives (N-methyl-norharmane and N-methyl-harmane) to induce DNA damage upon UV-A excitation, correlating the type and extent of the damage with the photophysical characteristics and DNA binding properties of the compounds. The results indicate that DNA damage is mostly mediated by a direct type-I photoreaction of the protonated βCs after non-intercalative electrostatic binding. Reactive oxygen species such as singlet oxygen and superoxide are not involved to a major extent, as indicated by the only small influence of D(2)O and of superoxide dismutase on damage generation. An analysis with repair enzymes revealed that oxidative purine modifications such as 8-oxo-7,8-dihydroguanine, sites of base loss and single-strand breaks (SSB) are generated by all βCs, while only photoexcited harmine gives rise to the formation of cyclobutane pyrimidine dimers as well.     

NMR studies of conformations and molecular recognition of pyridinio-appended and nicotinamide-appended β-cyclodextrin

Abstract

The conformations of pyridinio-appended β-cyclodextrin (CDP⁺) and nicotinamide-appended β-cyclodextrin (CDNA⁺) were studied by NMR spectroscopy. The orientations of the pyridine residue of CDP⁺ and the nicotinamide residue of CDNA⁺ were determined by using a combination of NMR spectroscopic techniques. NMR spectra indicate that the shapes of the cavities of CDP⁺ and CDNA⁺ were changed after forming complexes. This change depended on the shape of the guest. CDNA⁺ could separate the ¹H resonances at the Cβ position of racemic tryptophan into two sets of resonances for each enantiomer.     

RCM-based approach to seven- and eight-member ring-fused β-carbolines

RCM-based new route to the synthesis of seven- and eight-member ring-fused β-carboline from Morita-Baylis-Hillman adduct or Barbier-allylation product of N-allyl-1-formyl-9H-β-carboline is described.     

Spectroscopic Study of the Interactions of Buflomedil to Serum Albumin and β-Cyclodextrin

The effects of buflomedil (BFM), a novel cerebrovascular medicine, on serum albumin and the feasibility of ??-cyclodextrin (??-CD) acting as a controlled releaser for BFM were investigated by molecular spectroscopy methods, including fluorescence emission, UV?Cvisible absorption, Fourier transform infrared (FT-IR), synchronous and three-dimensional fluorescence spectroscopies. The interaction of BFM with bovine serum albumin (BSA) was analyzed by fluorescence quenching and it was found that BFM had reacted with BSA in the ground state and had affected the secondary structure of BSA. The observed binding constant K _b, the number of binding sites n, the distance r between donor (BSA) and acceptor (BFM), the enthalpy change (??H ^?? ), Gibbs energy change (??G ^?? ) and entropy change (??S ^?? ) at different temperatures were calculated. The inclusion reaction between ??-CD and BFM was explored by the Lineweaver?CBurk equation. The inclusion constants and the thermodynamic parameters were determined. The mechanism of the inclusion reaction was discussed and the controlled release characteristics of ??-CD to BFM were considered at the molecule level.     

Comparing the peroxo/superoxo nature of the interaction between molecular O2 and β-diketiminato-copper and nickel complexes

Adducts resulting from the interaction between molecular oxygen and β-diketiminato-copper and nickel complexes have been recently described in the literature as peroxo and superoxo complexes, respectively. The nature of the interaction is analyzed by means of DDCI calculations and an orthogonal valence bond reading of the ground state wavefunction for each system. Our results reveal that there is not any substantial difference between these systems, both presenting a marked leading superoxo nature, which is in line with the fact that LCu-O(2) and LNi-O(2) adducts present similar O-O distances and quite close O-O stretching vibration modes.     

HPLC study of the host–guest complexation between fluorescent glutathione derivatives and β-cyclodextrin

RP-HPLC and the van’t Hoff law were used to study the association in which β-cyclodextrin forms inclusion complexes with aminothiol–phthaldialdehyde derivatives prepared from either glutathione (GSH) or γ-glutamylcysteine (γ-glucys) and either naphthalene-2,3-dicarboxaldehyde (NDA) or o-phthaldialdehyde (OPA). Elution was carried out at pH 8.5, the derivatization pH which gave the highest fluorescence signal during batch experiments. The variation of the retention factor (k) was monitored as a function of column temperature (10–35 °C) and β-cyclodextrin concentration (0–5 mM) in the mobile phase. Apparent binding constants, enthalpy and entropy were calculated from van’t Hoff plots for the complexation reaction. These data lay the groundwork for the improvement of high throughput GSH quantification methods using fluorimetry in biological and vegetal samples.     

Mass spectrometry and molecular modeling studies on the inclusion complexes between alendronate and β-cyclodextrin

Complexation of alendronate sodium (AlnNa) with β-cyclodextrin (β-CD) was studied by means of ESI-mass spectrometry. The experimental results show that stable 1:1 inclusion complexes between selected bisphosphonates and β-CD were formed. In addition, complexes with different stoichiometry were observed. DFT/B3LYP calculations were performed to elucidate the different inclusion behavior between alendronate and β-CD. Molecular modeling showed that the inclusion complex of Aln-β-CD where the two phosphonate groups bound to the central carbon atom of bisphosphonate were inserted into the cavity of β-CD from its “top” side was thermodynamically more favorable than when they were inserted from its “bottom” side; the complexation energy was ?74.05 versus ?60.85 kcal/mol. The calculations indicated that the formation of conventional hydrogen bonds was the main factor for non-covalent β-CD:Aln complex formation and stabilization in the gas phase.     

Spectroscopic study of hydrogen bonding in the enol form of β-diketones—I. Vibrational assignment and strength of the bond

The i.r. and Raman spectra of the trans-enol form of some β-diketones and their deuterated analogues in α position are examined in the 4000-50cm⁻¹ range and an approximate assignment is given for the fundamental vibrations. The ν_as(OH) and ν(CO) values suggest that the intramolecular H-bond strength increases in the order: hexafluoroacetylacetone < trifluoroacetylacetone < acetylacetone < α - Cl - acetylacetone < benzoylacetone < dibenzoylmethane < tetraacetylethane.The observed relative Raman intensities of the ν(CC) and ν(CC) bands also support this feature. The spectroscopic results show a great change in the internal modes of the β-diketones upon deuteration; this behaviour indicates a greater localization of the π-electron system of the chelate ring and a weakening of the H-bond on deuteration. The ν_s(OH) vibration seems to be involved in one of the in-plane ring deformational modes.