Distribution of Mercury Species in the Water Column of the Stratified Krka River Estuary

Investigation of the mercury speciation (total/reactive and dissolved/ /particular forms) was carried out in waters of the highly stratified Krka River Estuary. The concentrations obtained are in satisfactory agreement with those obtained for other unpolluted aquatic environments (0.5-2.5 ng/L for total mercury, 0.1-0.8 ng/L for dissolved mercury and 0.04-0.75 pg/g for particulate mercury, 0 > 0.45 pm). Two or three discernible water layers (the upper fresh or brackish water layer, deeper saline layer and the in-between intermediate water layer) revealed different distribution of mercury species. In the upper freshwater layer with low salinity, the fraction of reactive mercury varied considerably with salinity changes (10-100% of the total), both during a single sampling campaign, as well as between particular sampling periods which coincided with different seasons and river regimes. This generally corresponded to the dissolved mercury fraction, confirming the insignificance of the organically bound dissolved mercury. In the bottom saline layer, mercury was mostly reactive (80-100% of the total), and even a part of the particulate mercury behaved as labile toward SnCl2 reduction. In the upper water layer (low-salinity), the largest fraction of mercury was bound to particles, which were mostly of biological origin (plankton), except in the lower part of the estuary, where the particles were of anthropogenic origin (municipal waste discharge from the city of Šibenik). Accumulation of mercury, both in reactive and particulate form, was observed at the halocline, e.g. at the fresh/saline water interface (FSI)

Surface adsorbed templates for directing the crystal growth of entacapone as monitored using process analytical techniques

Crystallization of entacapone (E-2-cyano-N,N-diethyl-3-(3,4-dihydroxy-5- nitrophenyl) propenamide) in acetone solution at the 500 mL scale using a self-assembled layer of the host material on Au(111) as a seeding template was studied and monitored using attenuated total reflectance (ATR)-UV-vis spectroscopy and focused beam reflectance measurement (FBRM). The data reveal that the template promotes crystal growth at lower supersaturations and at an increased rate when compared to experiments carried out without the template. Crystals prepared using the template are also found to have superior properties compared to crystals produced without the template. Notably, use of the template produces crystals with a much narrower size distribution, greatly increased perfection and a more equant crystal morphology. These observations are consistent with the template providing a sympathetic surface for the promotion of crystallization through an analogous mechanism to that associated with conventional seeding, but with the added advantage of conferring a well-ordered, easily reproducible and more robust process

Živa i radionuklidi u sedimentima Kaštelanskog zaljeva (Hrvatska) – Evaluacija povijetsi zagađivanja sedimenata

Mercury and radionuclides (natural U and its decay series products and artificial 137Cs) were measured in sediments of the Kaštela Bay (eastern Adriatic coast) in the vicinity of a former chloralkali plant. The depth distributions of radionuclides and mercury revealed that sediments in front of the factory represent a mixture of natural sediment and coal ash originating from the coal used in the factory power plant. Based on this data, the hypothesis that the coal ash from the factory power plant was dumped into the sea was confirmed, and it was estimated (from 137Cs depth profile) that the dumping happened between 1986 and 1991. Data on the artificial radionuclide 137Cs was shown to be very useful for evaluation of the sediment pollution history even in such very disturbed sediments. Future monitoring of mercury pollution and radionuclides in the Ka{tela Bay is suggested.U sedimentu Kaštelanskog zaljeva u blizini bivše tvornice klor-alkalija (pogon elektrolize tvornice "Jugovinil") mjereni su živa i radionuklidi (prirodni uran i njegovi raspadni produkti, te umjetni radionuklid 137Cs). Profili radionuklida i žive u sedimentu pokazali su da sediment ispred tvornice predstavlja smjesu prirodnog sedimenta i pepela iz ugljena koji je korišten u tvorničkoj energani. Temeljem dobivenih podataka potvrđena je hipoteza da je pepeo iz tvorničke energane odlagan u obalno more, te je procijenjeno (iz profila 137Cs u sedimentu) da se to dogodilo između 1986. i 1991. godine. Pokazalo se da su podaci o 137Cs u sedimentu vrlo korisni za evaluaciju historijata zagađivanja sedimenta čak i u slučaju tako poremećenih sedimenata. Sugerira se praćenje stanja zagađenja Kaštelanskog zaljeva živom i radionuklidima

Determination of Dissolved Monomethylmercury in Saline, Estuarine and Fresh Waters of Croatia

Measurements of dissolved monomethylmercury (MeHg) (which included both the dissolved part and the part leached from the particles by addition of 2 M HCl) were carried out in natural waters of various origin and composition (fresh, estuarine saline and brackish water, saline coastal water and groundwater). Following a proper water sampling procedure, MeHg was leached by hydrochloric acid, preconcentrated on a sulphydryl cotton fibre (SCF), eluated with hydrochloric acid, decomposed, and detected as Hg0 by a cold vapour atomic absorption spectrometry (CVAAS). The MeHg concentrations determined in the water samples of the Krka River Estuary, groundwaters (landfill »Jakuševec«, in the vicinity of Zagreb), and the Kaštela Bay were: 3.5 × 10-14 to 7.5 × 10-13 mol dm-3, 2.0 × 10-13 to 3.0 × 10-12 mol dm-3, and 1.0 × 10-12 to 2.0 × 10-11 mol dm-3, respectively. The concentration of MeHg in the water column of the Krka River Estuary is inversely related to reactive mercury. The MeHg maximum is just above a fresh/saline water interface (FSI), whereas maximums of the reactive and total mercury are below and/or inside the FSI. Winds and other meteorological conditions exert significant influence upon the distribution of MeHg concentrations in the water column. The performance of the modified analytical procedure was improved, yielding a high recovery efficiency of MeHg (85-96%), reproducibility better than 15% (CV) and the limit of detection of 3.5 × 10-14 mol dm-3, i.e. 0.007 ng L-1 (3 σ of the blank) for water sample of 3 L

Utjecaj kompleksacije piroksikama s ciklodekstrinima na oblikovanje gela

The aim of this work was to evaluate the role of cyclodextrins in topical drug formulations. Solid piroxicam (PX) complexes with beta-cyclodextrin (beta-CD) and randomly methylated beta-cyclodextrin (RAMEB) were prepared by freeze-drying and characterized using differential scanning calorimetry (DSC), X-ray powder diffractometry (XRPD), Fourier transform infrared spectroscopy (FTIR) and near infrared spectroscopy (NIR). A physical mixture of PX and cyclodextrins was characterized by enhanced dissolution properties compared to the dissolution profile of the pure drug due to in situ complex formation. Formation of the PX-cyclodextrin inclusion complex additionally improved the drug dissolution properties. Influence of CDs on drug permeation from the water dispersion and the prepared hydroxypropyl methylcellulose (HPMC) gels was investigated. Permeation of the drug involved three consecutive processes: dissolution of the solid phase, diffusion across the swollen polymer matrix and drug permeation through the membrane. Complexation increased PX diffusion by increasing the amount of diffusible species in the donor phase. Slower drug diffusion through the HPMC matrix was the rate limiting step in the overall diffusion process. Possible interaction between the hydrophilic polymer and cyclodextrin may result in physicochemical changes, especially in a change of rheological parameters.Svrha rada bila je ispitati utjecaj kompleksacije piroksikama s ciklodekstrinima na oblikovanje pripravaka za topičku primjenu lijeka. Kompleksi piroksikama s β- i nasumično metiliranim β-ciklodekstrinom u krutom stanju pripremljeni su metodom sušenja smrzavanjem i karakterizirani su diferencijalnom pretražnom kalorimetrijom, difrakcijom X-zraka na prahu, infracrvenom spektroskopijom s Fourierovim transformacijama, te spektroskopijom u niskom infracrvenom području. Fizička smjesa lijeka s ciklodekstrinima karakterizirana je poboljšanom topljivošću u usporedbi sa čistim lijekom zbog stvaranja kompleksa in situ. Kompleksacija piroksikama sa ciklodekstrinima dodatno je poboljšala topljivost lijeka u liofiliziranom kompleksu. Ispitan je utjecaj ciklodekstrina na permeaciju lijekova iz vodenih disperzija i pripremljenih gelova s hidroksipropil metilcelulozom. Permeacija lijekova uključuje više uzastopnih procesa: otapanje krute faze, difuziju lijeka kroz izbubreni polimerni matriks, te difuziju lijeka kroz polupropusnu membranu. Kompleksacija piroksikama s ciklodekstrinima povećala je difuzibilnost lijeka uslijed porasta količine lijeka raspoloživog za difuziju. Difuzija lijeka kroz izbubreni polimerni matriks hidroksipropil metilceluloze pokazala se ključnim procesom koji određuje ukupnu difuziju lijeka. Interakcija hidrofilnog polimera s ciklodekstrinima utjecala je na fizikalno-kemijska svojstva gela, posebice na reološke parametere

Direction of the polymorphic form of entacapone using an electrochemical tuneable surface template

The ability to direct the surface crystallisation of different polymorphs of entacapone by tuning the electrochemical potential of Au(100) templates is demonstrated. Under quiescent conditions, without polarization (at open circuit potential), entacapone crystallises in its stable form A on the template surface and concomitantly in its metastable form D in the bulk solution. When Au(100) is negatively polarized (-150 mV), form D is still formed in the bulk solution but the metastable form α is found to crystallise at the edges of the template. Both crystals of form A and α were observed to grow epitaxially over the Au template surface. The electrochemical templating effect is consistent with the polarisation changing the structure of the initially adsorbed layers of supersaturated solution at the template surface which directs the nuclei formation and the subsequent crystal growth processes. This study demonstrates, for the first time, the direction of polymorphic form using a low field polarized nucleation template

Role of Molecular, Crystal, and Surface Chemistry in Directing the Crystallization of Entacapone Polymorphs on the Au(111) Template Surface

The pharmaceutical compound entacapone ((E)-2-cyano-3-(3,4-dihydroxy-5-nitrophenyl)-N,N-diethylprop-2-enamide) is important in the treatment of Parkinson’s disease, exhibiting interesting polymorphic behavior upon crystallization from solution. It consistently produces its stable form A with a uniform crystal size distribution on the surface of an Au(111) template while concomitantly forming its metastable form D within the same bulk solution. Molecular modeling using empirical atomistic force-fields reveals more complex molecular and intermolecular structures for form D compared to form A, with the crystal chemistry of both polymorphs being dominated by van der Waals and π–π stacking interactions with lower contributions (ca. 20%) from hydrogen bonding and electrostatic interactions. Comparative lattice energies and convergence for the polymorphs are consistent with the observed concomitant polymorphic behavior. Synthon characterization reveals an elongated needle-like morphology for form D crystals in contrast to the more equant form A crystals with the surface chemistry of the latter exposing the molecules’ cyano groups on its {010} and {011} habit faces. Density functional theory modeling of surface adsorption reveals preferential interactions between Au and the synthon GA interactions of form A on the Au surface. Molecular dynamics modeling of the entacapone/gold interface reveals the entacapone molecular structure within the first adsorbed layer to show nearly identical interaction distances, for both the molecules within form A or D with respect to the Au surface, while in the second and third layers when entacapone molecule–molecule interactions overtake the interactions between those of molecule–Au, the intermolecular structures are found to be closer to the form A structure than form D. In these layers, synthon GA (form A) could be reproduced with just two small azimuthal rotations (5° and 15°) whereas the closest alignment to a form D synthon requires larger azimuthal rotations (15° and 40°). The cyano functional group interactions with the Au template dominate interfacial interactions with these groups being aligned parallel to the Au surface and with nearest neighbor distances to Au atoms more closely matching those in form A than form D. The overall polymorph direction pathway thus encompasses consideration of molecular, crystal, and surface chemistry factors