Ana M. Amado

USE OF FTIR, FT-RAMAN AND 13C-NMR SPECTROSCOPY FOR IDENTIFICATION OF SOME SEAWEED PHYCOCOLLOIDS

Many seaweeds produce phycocolloids, stored in the cell wall. Members of the Rhodophyceae produce polysaccharides the main components of which are galactose (galactans)-agar and carrageenan. In addition, alginic acid is extracted from members of the Phaeophyceae. This is a binary polyuronide made up of mannuronic acid and guluronic acid. The wide uses of these phycocolloids are based on their gelling, viscosifying and emulsifying properties, which generate an increasing commercial and scientific interest. In this work, the FTIR and FT-RAMAN spectra of carrageenan and agar, obtained by alkaline extraction from different seaweeds (e.g. Mastocarpus stellatus, Chondrus crispus, Calliblepharis jubata, Chondracanthus acicularis, Chondracanthus teedei and Gracilaria gracilis), were recorded in order to identify the type of phycocolloid produced. The spectra of commercial carrageenan, alginic acid and agar samples (SIGMA and TAAB laboratories) were used as references. Special emphasis was given to the 500-1500 cm(-1) region, which presents several vibrational modes, sensitive to the type of polysaccharide and to the type of glycosidic linkage. The FT-Raman spectra present a higher resolution than FTIR spectra, this allowing the identification of a larger number of characteristic bands. In some cases, phycocolloids can be identified by FT-Raman spectroscopy alone.

Weak hydrogen bonding. Part 2. The hydrogen bonding nature of short C–H ⋯π contacts: crystallographic, spectroscopic and quantum mechanical studies of some terminal alkynes

In a number of crystalline terminal alkynes, the alkyne C–H groups form short intermolecular contacts with other alkyne or with aromatic moieties. A particularly short C–H ··· phenyl contact is found in (±)-3-phenylbut-1-yn-3-ol, with an H ··· midpoint separation of only 2.51 A. Crystallographic, spectroscopic and computational evidence is given to show that these contacts represent hydrogen-bond-type interactions. Quantum chemical calculations indicate hydrogen bond energies in the range 1–2.2 kcal mol–1. Interconnected contacts such as CC–H ··· CC–H ··· CC–H exhibit a pronounced cooperativity effect, with energy increases of ∼0.5 kcal mol–1 compared with isolated contacts. Based on these results, the role of the terminal alkyne group in cooperative hydrogen bond networks is described as topologically paralleling that of hydroxy groups.

Conformational and vibrational study of platinum(II) anticancer drugs : cis-diamminedichloroplatinum (II) as a case study

A conformational and vibrational analysis of cisplatin [cis-diamminedichloro-platinum(II)] (cDDP) is reported. Several theory methods (from Hartree-Fock to Moller-Plesset and density functional theory) combined with different all-electron basis sets are evaluated, in view of determining the best suited strategy for accurately representing this molecule. This choice is based on the best compromise between accuracy and computational requirements. Different scaling models of the cDDP vibrational modes were tested for obtaining the best scaling factors to be used in this type of inorganic systems. The structural parameters and vibrational results predicted by the calculations are compared with the corresponding experimental data, namely, x-ray structure, and Raman and inelastic neutron scattering spectra. Finally, a complete assignment of the cDDP vibrational spectra is presented.

Experimental and Theoretical Evidence of CH⋅⋅⋅O Hydrogen Bonding in Liquid 4-Fluorobenzaldehyde

The presence of C-H...O hydrogen bonds in liquid 4-fluorobenzaldehyde has been studied by a combination of theoretical and spectroscopic methods. Ab initio calculations yielded bond energies and preferred bonding geometries, and the calculated spectroscopic properties have been compared with the experimental results. The presence of C-H...O hydrogen bonds in the liquid phase is strongly supported by vibrational and NMR spectroscopic data. Particular attention is paid to the spectroscopic effects related to the predicted shortening of the C-H bond engaged in the C-H...O contact. The concentration-dependent intensity in the C-H stretching region is tentatively assigned to a blue-shift effect due to C-H...O hydrogen bonding.

A comparative analysis of phycocolloids produced by underutilized versus industrially utilized carrageenophytes (Gigartinales, Rhodophyta)

Carrageenan (E-407) and semi-refined carrageenan (E-407a) are some of the main additives used by the food industry for their gelling, emulsifying, thickening, and stabilizing properties. These are natural ingredients, which have been used for decades in food applications and are generally regarded as safe. Internationally, sub-tropical carrageenophytes (e.g., Kappaphycus alvarezii) are cultivated extensively as a source of raw materials for industrial extraction, and their use as potential candidates in integrated multitrophic aquaculture is tentative. We analyzed carrageenan yield (as a percentage of dry weight) and chemical composition (by Fourier transform infrared attenuated total reflection and Fourier transform-Raman) of extracts produced by several carrageenophytes (Gigartinales, Rhodophyta), from different origins, e.g., K. alvarezii (Tanzania, Indonesia, the Philippines, Panama, and Mexico), Kappaphycus striatum (Madagascar), Eucheuma denticulatum (Tanzania, the Philippines, and Madagascar), Betaphycus gelatinum (the Philippines), Chondracanthus chamissoi, and Sarcothalia crispata (Chile). For comparison, some underutilized carrageenophytes were also analyzed, e.g., Chondrus crispus, Mastocarpus stellatus, Gigartina pistillata, Chondracanthus teedei var. lusitanicus, Chondracanthus acicularis, Calliblepharis jubata, Gymnogongrus crenulatus, and Ahnfeltiopsis devoniensis (Portuguese carrageenophytes). The main findings were that the highest carrageenan yield was obtained from K. striatum (Madagascar) with 75.6 (percent dry weight (% DW)); B. gelatinum and K. alvarezii (both from the Philippines) had yields of 71.0% and 68.0% (% DW), respectively; and G. pistillata (Portugal) 65.4% (% DW). Spectroscopic analysis of the phycocolloids allowed determination of a wide range of carrageenan types, e.g., pure iota carrageenan, several kappa–iota hybrid carrageenans with different iota/kappa ratios, and kappa–beta, xi–theta, and xi–lambda hybrid carrageenans.

Pt(II) vs Pd(II) Polyamine Complexes as New Anticancer Drugs: A Structure- Activity Study

Two homologous trinuclear polyamine chelates with either Pt(II) (Ia) or Pd(II) (Ib) were screened for their anticancer properties. Their growth-inhibition activity towards a human tongue epithelioma (HSC-3) was assessed in vitro, and the effect of the cation alteration was determined (IC50=32 μM for Ib vs 66 μM for Ia).

Use of Effective Core Potential Calculations for the Conformational and Vibrational Study of Platinum(II) Anticancer Drugs. cis-Diamminedichloroplatinum(II) as a Case Study

In the light of the recognized anticancer properties of cisplatin-type inorganic systems, the exact knowledge of their conformational preferences is of the utmost importance for understanding their biological activity. The present study reports the use of theoretical (quantum mechanical) calculations for achieving this goal. An alternative calculation method to the use of the AE basis sets, both accurate and computationally feasible, was presently tested for the conformational and vibrational study of cis-diamminedichloroplatinum(II). Effective core potentials (ECPs) were used, within the HF methodology and, within the B3LYP and mPW1PW DFT protocols. The DFT methods (particularly mPW1PW) were found to be the best choice for describing cDDP (as compared to the HF methodology).

Interactions of Copper (II) Chloride with β‐Cyclodextrin in Aqueous Solutions

The interaction between copper (II) chloride and the carbohydrate β‐cyclodextrin (β‐CD) has been studied in aqueous solutions (298.15 K and 310.15 K) using measurements of diffusion coefficients and electrical conductivity. Significant effects on the electrical conductivity were observed in the presence of the β‐CD, suggesting interactions between this carbohydrate and copper chloride. Support for this came from diffusion coefficient measurements. These studies have been complemented by molecular mechanics calculations.

Selection of substituted benzaldehyde conformers by the cyclodextrin inclusion process: a Raman spectroscopic study

Raman spectra of benzaldehyde (B), 4-Methoxybenzaldehyde (4MeOB), 3-methoxybenzaldehyde (3MeOB), 3-methylbenzaldehyde (3MB) and 3-chlorobenzaldehyde (3CB) included in α-, β- and γ-cyclodextrins (α-, β- and γCD) were recorded. The effects of the inclusion process on the conformational isomerism and on the hydrogen bond interactions of the guests were studied by monitoring sensitive modes, such as the C O and CH stretching modes, among others. Overall, the spectral observations suggest that the inclusion in the small αCD cavity imposes structural restrictions on the guest not observed with the larger βCD and γCD. For the 4MeOB molecule, only the most stable form is included in αCD, whereas for 3CB, the most stable form is completely absent from the αCD complex. Clear evidence of hydrogen bonding interactions with the carbonyl oxygen atom was observed for the 4MeOB·αCD complex. In addition, the presence of a C—H···OC hydrogen bond in the B·αCD structure is suggested by the changes observed in the region of the CH stretching modes. Copyright

H/D and D/H exchange rates in α-cyclodextrin and α-cyclodextrin inclusion compounds Raman spectroscopic study

The H/D and D/H exchange rates of hydroxy groups in crystalline α-cyclodextrin (CD) exposed to H 2 O and D 2 O vapour, respectively, have been studied by monitoring the relative integrated Raman intensities of the O–H and O–D stretching bands. The time-dependent Raman intensities suggest a fast diffusion-controlled H 2 O/D 2 O equilibrium process in shorter times, followed by a much slower H/D exchange for the longer times. The deuteriation process is found to be ca. 10 times slower than the reverse process, in excellent agreement with the expected isotopic effect in an exchange mechanism whose rate-determining step involves the cleavage of a O–H(–D) bond of a water molecule. The slow H/D exchange rate observed for α-CD hexahydrate in comparison with the β-CD dodecahydrate is explained by its structural rigidity, also evident from the discrete bands observed in the O–H and O–D stretching region. This structural rigidity is no longer present in the inclusion compounds of α-CD with an aromatic guest, which exhibit an H/D exchange rate much faster than the pure α-CD hexahydrate.