Dragosav Mutavdžić

Changes in peroxidase activity and isoenzymes in spruce needles after exposure to different concentrations of cadmium.

We studied the guaiacol peroxidase activity, isoenzyme pattern and metal content in the needles of 2-year-old spruce grown on soils supplemented with cadmium concentrations from 1 to 21 mg kg(-1). Following exposure to cadmium, an initial increase and subsequent decrease in the activity of the soluble fraction was observed. A parallel change of their isoenzyme pattern occurred. An increase of the cell wall-bound peroxidase activity under prolonged metal treatment was evident. The results obtained show that peroxidase activity and isoenzyme pattern could be used to evaluate the capacity of one part of the defense system in spruce seedlings to withstand metal stress.

Atomic Force Microscopy Stiffness Tomography on Living Arabidopsis thaliana Cells Reveals the Mechanical Properties of Surface and Deep Cell-Wall Layers during Growth

Cell-wall mechanical properties play a key role in the growth and the protection of plants. However, little is known about genuine wall mechanical properties and their growth-related dynamics at subcellular resolution and in living cells. Here, we used atomic force microscopy (AFM) stiffness tomography to explore stiffness distribution in the cell wall of suspension-cultured Arabidopsis thaliana as a model of primary, growing cell wall. For the first time that we know of, this new imaging technique was performed on living single cells of a higher plant, permitting monitoring of the stiffness distribution in cell-wall layers as a function of the depth and its evolution during the different growth phases. The mechanical measurements were correlated with changes in the composition of the cell wall, which were revealed by Fourier-transform infrared (FTIR) spectroscopy. In the beginning and end of cell growth, the average stiffness of the cell wall was low and the wall was mechanically homogenous, whereas in the exponential growth phase, the average wall stiffness increased, with increasing heterogeneity. In this phase, the difference between the superficial and deep wall stiffness was highest. FTIR spectra revealed a relative increase in the polysaccharide/lignin content.

Luminescent carbon nanoparticles: effects of chemical functionalization, and evaluation of Ag+ sensing properties

Luminescent carbon-based nanoparticles, addressed as carbon dots (CDs), were synthesized at relatively low temperature from lactose following an easy and inexpensive procedure. Modification of their surface was done by functionalization with mercaptosuccinic acid (MSA) (CDs–MSA). Transmission electron microscopy images showed regular spherical nanoparticles of 5 nm diameter. Raw and functionalized (CDs–MSA) CDs were highly fluorescent at 448 and 472 nm, with relative high quantum yield (Φ = 0.21 and 0.46 respectively). At the maximum fluorescence of CDs–MSA the intensity was quenched by addition of Ag+ ions by a static mechanism with a Stern–Volmer constant of 3.7 × 103 M−1. The analysis of the emission spectra showed that the CD–MSA complex was stable after this process. The quenching profiles showed that only 44% of the CD–MSA fluorophores are accessible to Ag+. The main figures of merit were detection and quantification limits of 385.8 nM and 1.2 μM respectively, and the precision as relative standard deviation was 1.76%. No interference was observed when other metal ions were present indicating a high selectivity for Ag+ detection. The results showed that CDs–MSA can be used for efficient quantification of Ag+ in silver nanoparticle dissolution.

Application of Asymmetric Model in Analysis of Fluorescence Spectra of Biologically Important Molecules

Having a valid mathematical model for structureless emission band shapes is important when deconvoluting fluorescence spectra of complex molecules. We propose a new asymmetric model for emission spectra of five organic molecules containing aromatic ring: catechol, coniferyl alcohol, hydroquinone, phenylalanine and tryptophan. For each molecule, a series of emission spectra, varying in excitation wavelength, were fitted with the new model as well as with two other analytical expressions: log-normal, described previously in the literature, and sigmoid-exponential. Their deconvolution into two, three and four Gaussian components was also performed, in order to estimate the number of symmetric components needed to obtain a better fitting quality than that of the asymmetric models. Four subtypes of the new model, as well as the log-normal one, did not differ significantly in their fitting errors, while the sigmoid-exponential model showed a significantly worse fit. Spectra of two mixtures: hydroquinone–coniferyl alcohol and hydroquinone–tryptophan were deconvoluted into two asymmetric and four Gaussian components. Positions of asymmetric components of mixtures matched those of separate molecules, while Gaussian did not. Component analysis of a polymer molecule, lignin, was also performed. In this more complex case asymmetric and Gaussian components also grouped in alternating positions.

Determination of the size of quantum dots by fluorescence spectroscopy

There has been a lack of quick, simple and reliable methods for determination of nanoparticle size. An investigation of the size of hydrophobic (CdSe) and hydrophilic (CdSe/ZnS) quantum dots was performed by using the maximum position of the corresponding fluorescence spectrum. It has been found that fluorescence spectroscopy is a simple and reliable methodology to estimate the size of both quantum dot types. For a given solution, the homogeneity of the size of quantum dots is correlated to the relationship between the fluorescence maximum position (FMP) and the quantum dot size. This methodology can be extended to the other fluorescent nanoparticles. The employment of evolving factor analysis and multivariate curve resolution-alternating least squares for decomposition of the series of quantum dots fluorescence spectra recorded by a specific measuring procedure reveals the number of quantum dot fractions having different diameters. The size of the quantum dots in a particular group is defined by the FMP of the corresponding component in the decomposed spectrum. These results show that a combination of the fluorescence and appropriate statistical method for decomposition of the emission spectra of nanoparticles may be a quick and trusted method for the screening of the inhomogeneity of their solution.

Fingerprint detection and using intercalated CdSe nanoparticles on non-porous surfaces

A fluorescent nanocomposite based on the inclusion of CdSe quantum dots in porous phosphate heterostructures, functionalized with amino groups (PPH-NH2@CdSe), was synthesized, characterized and used for fingerprint detection. The main scopes of this work were first to develop a friendly chemical powder for detecting latent fingerprints, especially in non-porous surfaces; their further intercalation in PPH structure enables not to spread the fluorescent nanoparticles, for that reason very good fluorescent images can be obtained. The fingerprints, obtained on different non-porous surfaces such as iron tweezers, mobile telephone screen and magnetic band of a credit card, treated with this powder emit a pale orange luminescence under ultraviolet excitation. A further image processing consists of contrast enhancement that allows obtaining positive matches according to the information supplied from a police database, and showed to be more effective than that obtained with the non-processed images. Experimental results illustrate the effectiveness of proposed methods.

The relationship of physicochemical properties to the antioxidative activity of free amino acids in Fenton system.

Herein we compared antioxidative activities (AA) of 25 free L-amino acids (FAA) against Fenton system-mediated hydroxyl radical (HO(•)) production in aqueous solution, and examined the relation between AA and a set of physicochemical properties. The rank order according to AA was: Trp > norleucine > Phe, Leu > Ile > His >3,4-dihydroxyphenylalanine, Arg > Val > Lys, Tyr, Pro > hydroxyproline > α-aminobutyric acid > Gln, Thr, Ser > Glu, Ala, Gly, Asn, Asp. Sulfur-containing FAA generated different secondary reactive products, which were discriminated by the means of electron paramagnetic resonance spin-trapping spectroscopy. AA showed a general positive correlation with hydrophobicity. However, when taken separately, uncharged FAA exhibited strong positive correlation of AA with hydrophobicity whereas charged FAA showed negative or no significant correlation depending on the scale applied. A general strong negative correlation was found between AA and polarity. Steric parameters and hydration numbers correlated positively with AA of nonpolar side-chain FAA. In addition, a decrease of temperature which promotes hydrophobic hydration resulted in increased AA. This implies that HO(•)-provoked oxidation of FAA is strongly affected by hydrophobic hydration. Our findings are important for the understanding of oxidation processes in natural and waste waters.

ZnS:Mn nanoparticles functionalized by PAMAM-OH dendrimer based fluorescence ratiometric probe for cadmium

We report a nanocomposite of ZnS:Mn quantum dots and a third generation PAMAM-OH dendrimer (ZnS:Mn@PAMAM-OH(G=3)) which was rationalized to be used as ratiometric nanosensor for Cd(2+) in aqueous solution. The nanoparticles exhibited a bright yellow-orange emission with peaks at 448 and 595 nm. The structure of ZnS:Mn was not changed after coupling with PAMAM-OH, which was evidenced by the analysis of the emission spectra of the compounds. The results confirm that the prepared fluorescence nanoparticles could selectively detect Cd(2+) in aqueous solution with a limit of detection of 24.34 μM and RSD 4.07%, obtained by using the ratio I448/I595. The method was applied to different water samples.

Solvatochromism of symmetrical 2,6-distyrylpyridines. An experimental and theoretical study

Seven symmetrical 2,6-distyrylpyridines, phenyl-substituted with hydrogen-bond donors, hydrogen-bond acceptors, halogens and hydrophobic moieties were synthesized and their spectroscopic characterization was done. Solvent effects on the absorption and fluorescence spectra were analyzed and quantified using the Kamlet-Taft and Catalán approach. The obtained results were rationalized by comparison of electrostatic potentials of the molecules in the ground and in excited state and by comparison of the frontier molecular orbitals (HOMO and LUMO), derived from quantum-mechanical calculations (HF, DFT, MP2). Analysis of the results revealed an important influence of non-specific (dispersive) interactions on the solvatochromic behavior of the compounds. 1D and 2D NMR data, in silico obtained conformational assembly of the compound, and the NMR analysis of molecular flexibility in solution (NAMFIS), were used to estimate population of conformers and to deconvolute the UV-Vis spectrum of representative derivative; inferring that the conformational assembly is more complex than was assumed in so far published literature data for this class of compounds. Along with this, the emission spectra of the representative compounds were decomposed by the Multivariate Curve Resolution analysis.

Total phenol content and total antioxidant activity drop during Tacitus bellus direct shoot organogenesis

Changes in total phenolics content (TPC) and total antioxidant activity (TAA) in different morphogenic stages of Tacitus bellus (L.) Moran and J. Meyrán (Crassulaceae) direct shoot organogenesis in vitro were examined. A HPLC method was used for the assessment of changes in phenolic profile. Significant decrease in TPC and TAA, as well as the decline of the amount of specific phenolic compounds coincided with the initiation of shoot organogenesis. Additional decrease in TPC and TAA, and the disappearance of procyanidin glycoside, occurred associated with shoot development. Performed correlation analysis suggests phenolics as the main component of nonenzymatic antioxidant system involved in T. bellus direct shoot organogenesis, it argues in favor of involvement of specific phenolics in the regulation of early stages of T. bellus direct shoot organogenesis and indicates different fine regulatory mechanisms of early and late stages of shoot organogenesis.