Self-Assembled Monolayers prepared from alkanethiols or dialkyl disulfides on Au: evidence of influence of the anchoring group

Mainly based on electrochemical investigations, this work provides evidence of discrimination between self-assembled monolayers (SAMs) prepared from alkanethiols or symmetrical dialkyl disulfides on gold. Gravimetric experiments carried out by quartz crystal microbalance during the elaboration of ferrocene based SAMs (from alkanethiols FcC15SH and dialkyl disulfides FcC15SSC15Fc), showed significant differences between monolayers made from the two precursors. The recorded mass was almost 60 % more important with FcC15SH by comparison with FcC15SSC15Fc. The resulting cyclic voltammograms also highlighted a 60 % difference concerning the surface coverage of ferrocene heads. Moreover, dialkyl disulfide and thiol anchoring groups led to symmetrical and dissymmetrical peaks, respectively, suggesting not insignificant differences concerning interactions between adsorbed species into the two kinds of elaborated monolayers. These observations were confirmed on SAMs obtained from other precursors possessing shorter chain length or another functional moiety

Free and immobilized matrix molecules: impairing ionization by quenching secondary ion formation in laser desorption MS

Within the last 25 years, matrix-assisted laser desorption ionization (MALDI) has become a powerful analytical tool in mass spectrometry (MS). While the method has been successfully applied to characterize large organic molecules such as proteins, sugars and polymers, its utilization for small molecules (≤ 600 Da) is significantly impaired by the coformation of matrix ions. Reducing or eliminating matrix-related signals has been subject of many studies. Some of which propose the enhancement of so-called matrix suppression effects, while others suggest the replacement of matrix molecules by materials such as microporous silicon. Alternatively, the immobilization of matrix molecules by utilizing them as self-assembled monolayers (SAMs) has been discussed. In continuation of this research, the current manuscript focuses on the elucidation of ion formation processes occurring on the surface of light absorbing SAMs. Ion yields obtained by free and immobilized matrix molecules as well as those generated by matrix-free gold film-assisted laser desorption ionization (GF-LDI) were compared. Experiments showed that the formation of strong analyte signals essentially required the presence of free matrix molecules, while the immobilization of the latter severely impaired ionization. The observed effect inversely correlated with the surface coverage of SAMs determined by cyclic voltammetry (CV). Based on these findings, the MS signal generated on light absorbing SAMs could be used supplementary to CV for determining the surface coverage of light absorbing SAMs

Selective detection of alkaloids in MALDI-TOF: the introduction of a novel matrix molecule

The current manuscript presents 3-[5′-(methylthio)-2,2′-bithiophen-5-ylthio]propanenitrile (MT3P), as a novel matrix molecule, which facilitates the selective ionization of alkaloids in matrix-assisted laser desorption/ionization mass spectrometry. Exhibiting strong ionizing properties at low levels of laser energy, MT3P was evaluated on 55 compounds belonging to various chemical families. The observed molecular ion yields induced by MT3P were compared with those obtained by commercially available matrices such as 1,8-dihydroxy-9,10-dihydroanthracen-9-one, α-cyano-4-hydroxycinnamic acid, 2,2′:5′,2″-terthiophene and 2,5-dihydroxybenzoic acid. In conclusion, MT3P displayed excellent ionization properties for 23 out of 25 investigated alkaloids, while showing little to no interaction with compounds from different chemical origin. Further, in comparison to other tested matrices, MT3P generally facilitated better ionization of alkaloids. Eventually, levels of laser energy were adjusted to obtain spectra with significantly reduced matrix noise

Effect of hydrogen-interactions on electrochemical behavior of bithiophene self-assembled monolayers containing amide moieties

Herein, we evaluated the influence of hydrogen interactions in bithiophene self-assembled monolayers on gold. We have elaborated SAMs from different thiol derivatives in which the number and position of amide functionality is varied to compare their electrochemical behavior. Preliminary, optimal conditions of the monolayer formation from our synthesized compounds were determined (thiol concentrations and incubation times). Electrochemical studies of the SAMs highlight a pronounced influence of the hydrogen bond when located in the outer extremity (electrochemical stability, interactions). The behavior observed with SAMs containing two amide moieties emphasizes the important impact of the number of hydrogen bonds inside the organic layer. (C) 2011 Elsevier B.V. All rights reserved

Potential of as a Nutritional Supplement in Malnourished HIV-Infected Adults in Sub-Saharan Africa: A Randomised, Single-Blind Study

Background Malnutrition is a major global public health issue and its impact on communities and individuals is more dramatic in Sub-Saharan Africa, where it is compounded by widespread poverty and generalized high prevalence of human immunodeficiency virus (HIV). Therefore, malnutrition should be addressed through a multisectorial approach, and malnourished individuals should have access to nutritional rehabilitation molecules that are affordable, accessible, rich in nutrient and efficient. We thus assessed the efficacy of two affordable and accessible nutritional supplements, spirulina platensis versus soya beans among malnourished HIV-infected adults. Methods Undernourished patients, naïve of, but eligible to antiretroviral treatment (ART), aged 18 to 35 years were enrolled and randomly assigned to two groups. The first group received spirulina (Group A) as food supplement and the second received soya beans (Group B). Patients were initiated ART simultaneously with supplements. Food supplements were auto-administered daily, the quantity being calculated according to weight to provide 1.5 g/kg body weight of proteins with 25% from supplements (spirulina and soya beans). Patients were monitored at baseline and followed-up during twelve weeks for anthropometric parameters, body composition, haemoglobin and serum albumin, CD4 count and viral load. Results Fifty-two patients were enrolled (Group A: 26 and Group B: 26). The mean age was 26.4 ± 4.9 years (Group A) and 28.7 ± 4.8 (Group B) with no significant difference between groups ( P = 0.10). After 12 weeks, weight and BMI significantly improved in both groups ( P < 0.001 within each group). The mean gain in weight and BMI in Group A and B were 4.8 vs. 6.5 kg, ( P = 0.68) and 1.3 vs. 1.90 Kg/m 2 , ( P = 0.82) respectively. In terms of body composition, fat free mass (FFM) did not significantly increase within each group (40.5 vs. 42.2 Kg, P = 0.56 for Group A; 39.2 vs. 39.0 Kg, P = 0.22 for Group B). But when compared between the two groups at the end of the trial, FFM was significantly higher in the spirulina group (42.2 vs. 39.0 Kg, P = 0.01). The haemoglobin level rose significantly within groups ( P < 0.001 for each group) with no difference between groups ( P = 0.77). Serum albumin level did not increase significantly within groups ( P < 0.90 vs. P < 0.82) with no difference between groups ( P = 0.39). The increase in CD4 cell count within groups was significant ( P < 0.01 in both groups), with a significantly higher CD4 count in the spirulina group compared to subjects on soya beans at the end of the study ( P = 0.02). Within each group, HIV viral load significantly reduced at the end of the study ( P < 0.001 and P = 0.04 for spirulina and soya beans groups respectively). Between the groups, the viral load was similar at baseline but significantly reduced in the spirulina group at the end of the study ( P = 0.02). Conclusion We therefore conclude in this preliminary study, firstly, that both spirulina and soja improve on nutritional status of malnourished HIV-infected patients but in terms of quality of nutritional improvement, subjects on spirulina were better off than subjects on soya beans. Secondly, nutritional rehabilitation improves on immune status with a consequent drop in viral load but further investigations on the antiviral effects of this alga and its clinical implications are strongly needed