Ozren Gamulin

FT-IR spectroscopy of lipoproteins—A comparative study

FT-IR spectra, in the frequency region 4000-600 cm(-1), of four major lipoprotein classes: very low density lipoprotein (VLDL), low density lipoprotein (LDL) and two subclasses of high density lipoproteins (HDL(2) and HDL(3)) were analyzed to obtain their detailed spectral characterization. Information about the protein domain of particle was obtained from the analysis of amide I band. The procedure of decomposition and curve fitting of this band confirms the data already known about the secondary structure of two different apolipoproteins: apo A-I in HDL(2) and HDL(3) and apo B-100 in LDL and VLDL. For information about the lipid composition and packing of the particular lipoprotein the well expressed lipid bands in the spectra were analyzed. Characterization of spectral details in the FT-IR spectrum of natural lipoprotein is necessary to study the influence of external compounds on its structure.

Raman Spectroscopic Assessment of Degree of Conversion of Bulk-Fill Resin Composites - Changes at 24 Hours Post Cure

OBJECTIVE The aim of this study was to determine degree of conversion (DC) of solid and flowable bulk-fill composites immediately and after 24 hours and investigate the variations of DC at surface and depths up to 4 mm. MATERIALS AND METHODS Eight bulk-fill composites (Tetric EvoCeram Bulk Fill [shades IVA and IVB], Quixfil, X-tra fil, Venus Bulk Fill, X-tra Base, SDR, Filtek Bulk Fill) were investigated, and two conventional composites (GrandioSO, X-Flow) were used as controls. The samples (n = 5) were cured for 20 seconds with irradiance of 1090 mW/cm(2). Raman spectroscopic measurements were made immediately after curing on sample surfaces and after 24 hours of dark storage at surface and at incremental depths up to 4 mm. Mean DC values were compared using repeated measures analysis of variance (ANOVA) and t-test for dependent samples. RESULTS Surface DC values immediately after curing ranged from 59.1%-71.8%, while the 24-hour postcure values ranged from 71.3%-86.1%. A significant increase of DC was observed 24 hours post cure for all bulk-fill composites, which amounted from 11.3% to 16.9%. Decrease of DC through depths up to 4 mm varied widely among bulk-fill composites and ranged from 2.9% to 19.7%. CONCLUSIONS All bulk-fill composites presented a considerable 24-hour postcure DC increase and clinically acceptable DC at depths up to 4 mm. Conventional control composites were sufficiently cured only up to 2 mm, despite significant postcure polymerization.

Investigation of Spermatozoa and Seminal Plasma by Fourier Transform Infrared Spectroscopy

Fourier transform infrared (FT-IR) spectra of human spermatozoa and seminal plasma were recorded and analyzed. The procedure that was established for sample preparation enabled acquisition of reproducible spectra. The parameter I1087/I966 for controlling spectra reproducibility was defined. The assignment of bands was carried out using an empirical approach and the origin of the “sperm specific doublet”, the bands at 968 cm−1 and 981 cm−1, was determined. The principal component regression (PCR) algorithm was used to define the specific spectral regions correlating to characteristics of spermatozoa, such as concentration, straight-line velocity (VSL), and beat cross frequency (BCF). Then, simple spectral parameters, such as band intensities and band ratios, were tested to determine which one best correlates to characteristics of spermatozoa. The region of the amide I band, between 1700 cm−1 and 1590 cm−1, was defined as a specific spectral region that correlates to the concentration of spermatozoa. The parameter that gave the linear dependence to the concentration of spermatozoa was the intensity of the amide I band. For VSL, the bands between 1119 cm−1 and 943 cm−1 were defined as the specific spectral region. The relative amount of nucleic acids with respect to proteins showed linear dependence on the straight-line velocity of spermatozoa. BCF showed the best correlation to the bands between 3678 cm−1 and 2749 cm−1, which largely represent lipids and proteins. These results suggest that FT-IR spectroscopy can serve as an adjunct to conventional histopathology studies.

cw laser crystallization of amorphous silicon: Thermal or athermal process

Hydrogenated amorphous silicon films have been deposited by dc magnetron sputtering on different substrates with different thicknesses and hydrogen concentration. The microscopic area of amorphous layers was crystallized by the focused beam of a cw laser. The laser threshold power for transition from the amorphous to crystalline state is dependent on the radius of the laser beam, film thickness, material of the substrate, and hydrogen concentration. These experimental results show that cw laser crystallization of amorphous silicon is a thermally induced process.

Raman study of light-induced changes in silicon-hydrogen bond stretching vibration in aSi:H

Abstract Amorphous hydrogenated silicon films prepared by a dc magnetron sputtering method was soaked by light of an argon ion laser and studied “in situ” by Raman spectroscopy in order to resolve the apparent inconsistency in the assignments of the silicon—hydrogen bond stretching vibrations. The bond-stretching frequency region between 1850 and 2250 cm −1 was decomposed in two Gaussian-shaped bands. The laser—induced changes at the power density from 20 to 500 W/cm 2 show: a) the continious increase of the integrated intensity of the band at about 2100 cm −1 compared to the band at about 2000 cm −1 ; b) the frequency shift of both bands to the lower values; c) the linewidth decrease of the band at about 2000 cm −1 , and d) linewidth increase of the band at about 2100 cm −1 . Contrary to the previous proposals that in the stretching region of the Raman spectra only two bands exist, our data show the existence of four vibrational bands.

Porous Silicon Covered with Silver Nanoparticles as Surface-Enhanced Raman Scattering (SERS) Substrate for Ultra-Low Concentration Detection

Microporous and macro-mesoporous silicon templates for surface-enhanced Raman scattering (SERS) substrates were produced by anodization of low doped p-type silicon wafers. By immersion plating in AgNO3, the templates were covered with silver metallic film consisting of different silver nanostructures. Scanning electron microscopy (SEM) micrographs of these SERS substrates showed diverse morphology with significant difference in an average size and size distribution of silver nanoparticles. Ultraviolet–visible–near-infrared (UV-Vis-NIR) reflection spectroscopy showed plasmonic absorption at 398 and 469 nm, which is in accordance with the SEM findings. The activity of the SERS substrates was tested using rhodamine 6G (R6G) dye molecules and 514.5 nm laser excitation. Contrary to the microporous silicon template, the SERS substrate prepared from macro-mesoporous silicon template showed significantly broader size distribution of irregular silver nanoparticles as well as localized surface plasmon resonance closer to excitation laser wavelength. Such silver morphology has high SERS sensitivity that enables ultralow concentration detection of R6G dye molecules up to 10−15 M. To our knowledge, this is the lowest concentration detected of R6G dye molecules on porous silicon-based SERS substrates, which might even indicate possible single molecule detection.

FTIR spectroscopy reveals lipid droplets in drug resistant laryngeal carcinoma cells through detection of increased ester vibrational bands intensity

The major obstacle to successful chemotherapy of cancer patients is drug resistance. Previously we explored the molecular mechanisms of curcumin cross-resistance in carboplatin resistant human laryngeal carcinoma 7T cells. Following curcumin treatment we found a reduction in curcumin accumulation, and reduced induction of reactive oxygen species (ROS) and their downstream effects, compared to parental HEp-2 cells. In order to shed more light on mechanisms involved in drug resistance of 7T cells, in the present study we applied Fourier transform infrared (FTIR) spectroscopy, a technique that provides information about the nature and quantities of all molecules present in the cell. By comparing the spectra from parental HEp-2 cells and their 7T subline, we found an increase in the intensity of ester vibrational bands in 7T cells. This implied an increase in the amount of cholesteryl esters in resistant cells, which we confirmed by an enzymatic assay. Since cholesteryl esters are localized in lipid droplets, we confirmed their higher quantity and serum dependency in 7T cells compared to HEp-2 cells. Moreover, treatment with oleic acid induced more lipid droplets in 7T when compared to HEp-2 cells, as shown by flow cytometry. We can conclude that along with previously determined molecular mechanisms of curcumin resistance in 7T cells, these cells exhibit an increased content of cholesteryl esters and lipid droplets, suggesting an alteration in cellular lipid metabolism as a possible additional mechanism of drug resistance. Furthermore, our results suggest the use of FTIR spectroscopy as a promising technique in drug resistance research.

Conversion and temperature rise of remineralizing composites reinforced with inert fillers.

OBJECTIVES Remineralizing experimental composites based on amorphous calcium phosphate (ACP) were investigated. The impact of curing time (20 and 40s), curing depth (1, 2, 3 and 4mm) and addition of inert fillers (barium glass and silica) on the conversion and temperature rise during curing were examined. METHODS Five ACP-composites and two control composites were prepared based on the light-curable EBPADMA-TEGDMA-HEMA resin. For temperature measurements, a commercial composite was used as an additional control. Conversion was assessed using FT-Raman spectroscopy by comparing the relative change of the band at 1640 cm(-1) before and after polymerization. The temperature rise during curing was recorded in real-time using a T-type thermocouple. RESULTS At 1mm depth, the ACP-composites attained significantly higher conversion (77.8-87.3%) than the control composites based on the same resin (60.5-66.3%). The addition of inert fillers resulted in approximately 5% lower conversion at clinically relevant depths (up to 2mm) for the curing time of 40s. Conversion decline through depths depended on the added inert fillers. Conversion values higher than 80% of the maximum conversion were observed for all of the ACP-composites at depths up to 3mm, when cured for 40s. Significantly higher total temperature rise for the ACP-composites (11.5-13.1 °C) was measured compared to the control composites (8.6-10.8 °C) and the commercial control (8.7 °C). CONCLUSIONS The admixture of inert fillers represents a promising strategy for further development of ACP-composites, as it reduced the temperature rise while negligibly impairing the conversion. CLINICAL SIGNIFICANCE High conversions of ACP-composites are favorable in terms of mechanical properties and biocompatibility. However, high conversions were accompanied with high temperature rise, which might present a pulpal hazard.

Formation of CdS Nanocrystals in SiO2 by Ion Implantation

We present a systematic study of the influence of ion dose and post-implantation annealing on the synthesis and growth of CdS nanocrystals in a SiO{sub 2} matrix. Nanocrystals were obtained after implantation of monoenergetic Cd and S ions and subsequent annealing in a very wide range of annealing temperatures, T{sub a}. The average size, as determined from the blue shift of band gap E{sub g}, varied from 3.5-4.5 to 10 nm, depending on implantation and annealing parameters. For the highest dose, 10{sup 17} ions/cm{sup 2}, the synthesis of CdS phase starts already during implantation. For T{sub a} above 700 C, large nanocrystals (9-10 nm) prevail for all doses. High energy optical transitions, identified as the E{sub 1A} and E{sub 1B} transitions of hexagonal CdS, were also observed after annealings at higher temperature.

Impedance changes during setting of amorphous calcium phosphate composites.

OBJECTIVES To investigate the electrical properties of experimental light-curable composite materials based on amorphous calcium phosphate (ACP) with the admixture of silanized barium glass and silica fillers. METHODS Short-term setting was investigated by impedance measurements at a frequency of 1kHz, while for the long-term setting the impedance spectra were measured consecutively over a frequency range of 0.05Hz to 1MHz for 24h. The analysis of electrical resistivity changes during curing allowed the extraction of relevant kinetic parameters. The impedance results were correlated to the degree of conversion assessed by Raman spectroscopy, water content determined by gravimetry, light transmittance measured by CCD spectrometer and microstructural features observed by scanning electron microscopy. RESULTS ACP-based composites have shown higher immediate degree of conversion and less post-cure polymerization than the control composites, but lower polymerization rate. The polymerization rate assessed by impedance measurements correlated well with the light transmittance. The differences in the electrical conductivity values observed among the materials were correlated to the amount of water introduced into composites by the ACP filler. High correlation was found between the degree of conversion and electrical resistivity. Equivalent circuit modeling revealed two electrical contributions for the ACP-based composites and a single contribution for the control composites. SIGNIFICANCE The impedance spectroscopy has proven a valuable method for gaining insight into various features of ACP-based composites. Better understanding of the properties of ACP-based composites should further the development of these promising bioactive materials.