A novel type of colony formation in marine planktonic diatoms revealed by atomic force microscopy

Diatoms have evolved a variety of colonial life forms in which cells are connected by organic threads, mucilage pads or silicate structures. In this study, we provide the first description of a novel strategy of colony formation among marine planktonic diatoms. Bacteriastrum jadranum is a chain‐forming centric diatom in which sibling cells are enclosed within the optically transparent organic matrix instead of fusing of silica between setae as it is the case in all other members of the family Chaetocerotaceae. This cell jacket structure was detected by staining procedures (Alcian Blue and Coomassie Brilliant Blue G), which showed that the polysaccharides are predominant matrix constituents and revealed that the jacket reaches the span of the setae. The scanning electron microscopy (SEM) observations showed distinguishable fibrillar network firmly associated with cells. Using atomic force microscopy (AFM), we were able to visualise and characterise the cell jacket structure at molecular resolution. At nanoscale resolution, the cell jacket appears as a cross‐linked fibrillar network organised into a recognisable structure. It is composed of non‐evenly distributed high density domains (patches) surrounded and interconnected by thicker fibrils. Inside the patches are the hexagonally shaped pores decreasing in size from the patch edge towards the center. The large pore openings found between the patches are formed by the robust branching fibrils and these represent the backbone of the fibrillar network. Such structure is porous, but at the same time highly flexible and mechanically stable. We conclude that the Bacteriastrum polysaccharide jacket represents an essential part of the cell, as such specific and unique patterns have never been found in self‐assembled polysaccharide gel networks, which are usually encountered in the marine environment

Students Remember Siniša Maričić (1926–2017): Upright to the End

Siniša Maričić, the father of Croatian biophysics, passed away on October 31, 2017. On this occasion, three of his students wish to share the memory of their teacher with the readers of the Croatica Chemica Acta. This work is licensed under a Creative Commons Attribution 4.0 International License

Učenici se sjećaju Siniše Maričića (1926.–2017.): Uspravan do kraja

Siniša Maričić umro je 31. listopada 2017. Tim su povodom troje njegovih učenika elektronskim putem razmijenili uspomene na dr. Maričića. Te uspomene ovdje žele podijeliti s čitateljima časopisa Croatica Chemica Acta. This work is licensed under a Creative Commons Attribution 4.0 International License

Nitrosoarene Dimerization on Two- and Three-dimensional Gold Surfaces

In the present study, we investigated nitrosoarene dimerization on an Au(111) and on the surface of gold nanoparticles (AuNPs). High-resolution STM images revealed that 8-thiocyanatoocty1-4-nitrosobenzoate (NCS(CH2)(8)OOCC6H4NO) forms well-ordered monolayer on an Au(111) surface displaying hexagonal 3 root 3 x 3 root 3 structure. AFM data indicated that this compound also dimerize on an Au(111) surface thus forming bilayers. On contrary, adsorption of 6-(4-nitrosophenoxy)hexane-l-thiol (HS(CH2)(6)OC6H4NO) on an Au(111) leads only to poorly organized.monolayer. Furthermore, it was found that nitrosoarene derivatives 8-thiocyanatooctyl-4-nitrosobenzoate (NCS(CH2)(8)OOCC6H4NO) and 3-thiocyanatopropyl-4-nitrosobenzoate (NCS(CH2)(3)OOCC6H4NO) are present as dimers on the surface of AuNPs. There is no appreciable quantity of dimeric species with free thiocyanate termini indicating interlinkage of AuNPs through azodioxide bonds. Besides the characteristic surface plasmon band, UV-vis spectra showed an additional red-shifted band that might have origin in aggregation of AuNPs. This was further supported by TEM revealing the appearence of larger aggregates in addition to smaller AuNPs

Diatom Polysaccharides: Extracellular Production, Isolation and Molecular Characterization

The extracellular polysaccharide production by marine diatoms is a significant route by which photosynthetically produced organic carbon enters the trophic web and may influence the physical environment in the sea as observed for example when massive aggregation events on basin scale occur. Many papers showed that the aldose signatures of marine DOM obtained from different seawater samples around the world is similar to that determined on cultured phytoplankton DOM and that the carbohydrate production could be very different among the species selected, growth and environmental conditions. These results are very important in order to understand the role of algal exudation in the aggregation processes observed in all of the seas and in general in carbon cycling in the euphotic zone. Many authors showed that cultured diatoms growth in P-limiting condition determines an increase of polysaccharides exudated by different diatoms species both pelagic and benthic

Elektrokemijska detekcija mikročestica gela u morskoj vodi

We present the first atomic force microscopy (AFM) images of the native marine gel network and a new type of electrochemical signals of individual gel microparticles in seawater. Gel microparticles in seawater are selectively detected through specific amperometric signals using a dropping mercury electrode (DME) as a sensor. We have demonstrated that organic microparticles naturally present in Northern Adriatic seawater can be detected as single particles and sorted at the DME/seawater interface according to their hydrophobicity and supramolecular organization.Prvi puta prikazana je nanostruktura morskog gela oslikana mikroskopijom atomskih sila i nova vrsta elektrokemijskih signala mikročestica gela u morskoj vodi. Čestice gela u morskoj vodi selektivno se detektiraju kao specifični amperometrijski signali primjenom živine kapajuće elektrode kao senzora. Svaki signal je rezultat sudara mikročestice gela s rastućom površinom živine elektrode. Primjenom amperometrijske tehnike i živine kapajuće elektrode kao senzora organske mikročestice detektiraju se na dinamičkoj međupovršini živina elektroda/morska voda temeljem svojstava hidrofobnosti i supramolekulske organizacije kao površinski-aktivne i gel čestice