Seasonal variations in the yield, gelling properties, and chemical composition of agars from Gracilaria eucheumoides and Gelidiella acerosa (Rhodophyta) from the Philippines

The yield, physical, and chemical properties of agars from two Philippine red seaweeds, Gracilaria eucheumoides and Gelidiella acerosa, were investigated on a bimonthly basis. The yield of agar from Gracilaria eucheumoides was at a maximum during the early rainy season (May, 29%) and at a minimum during the summer month of March (20%). In Gelidiella acerosa, a peak in agar yield was also recorded in May (21%), with generally higher yields recorded during the rainy than in the dry season. Agar gel strengths fluctuated from 225 to 430 g cm−2 and from 160 to 820 g cm−2 for Gracilaria eucheumoides and Gelidiella acerosa, respectively, and both agars exhibited strongest gels in July. Significant seasonal variations were observed in the gelling and melting temperatures of agar from Gracilaria eucheumoides, but not from Gelidiella acerosa. Sulphate content only varied slightly in agar samples from Gracilaria eucheumoides, while a higher sulphate content was found in Gelidiella acerosaagar during the dry season. Moreover, the sulphate content in G. acerosa agar fluctuated inversely with the 3,6-anhydrogalactose content. A FT-IR analysis showed a fairly constant spectrum for temporal Gracilaria eucheumoides agar while peaks attributed to S–O vibrations intensified in Gelidiella acerosa samples which were recorded to contain high sulphate residues and possess low gel strengths. Diagnosis of the FT-IR spectra in the 1000–400 cm−1frequency range was also conducted in comparison with agarose and Gracilaria chilensis agar

1,4-Benzenedimethanethiol Interaction with Au(110), Ag(111), Cu(100), and Cu(111) Surfaces: Self-Assembly and Dissociation Processes

In this work, we study systematically the evaporative adsorption under high vacuum conditions of 1,4-benzenedimethanethiol (BDMT) onto different metal surfaces: Ag(111), Au(110), Cu(100), and Cu(111). The study is carried out by photoemission using synchrotron radiation. In the case of Ag(111) and Au(110), at low exposures, a lying down BDMT phase is formed, with both S atoms attached to Ag and Au. A standing up phase is attained after a large exposure, above several hundred thousand Langmuir. However, also a mixed complex over layer appears to be formed, attributable to molecules sticking on top of the SAM. In the case of Au(110), heating leads to BDMT desorption with some degree of SC bond scission, and some S atoms are left in different adsorption sites with mainly two different core level binding energies. On Ag(111), after heating the sample, BDMT desorbs and also sulfidation of Ag occurs. In the case of Cu(100) and Cu(111), SC bond cleavage occurs already after initial adsorption. Lost S from BDMT molecules is adsorbed on Cu. Surface passivation occurs and only then BDMT adsorption takes place, with an interface with Cu enriched with sulfur