Amino acids are the basic “building blocks” of peptides and proteins and play important roles in the physiological processes of all species. In this study, we simulated the Raman spectrum of Glycine, Tyrosine and Phenylalanine using General Atomic and Molecular Electronic Structure System (GAMESS) and Gaussian, two computational codes that perform calculations of electronic and vibrational properties of molecules. Through our work, strong bands with N-H and O-H bonds and with benzyl ring were pinpointed and identified. Our work presents insights into the importance of intermolecular bonding of amino acids in the life and physiological processes, including metabolism, signal transduction, and neurotransmission etc.
A pump-probe photothermal mirror (PTM) method has been developed to determine the thermal diffusivity of opaque solid samples. The method involves the detection of the distortion of a probe beam whose reflection profile is affected by the photoelastic deformation of a polished material surface induced by the absorption of a focused pump field. We have measured the time dependence of the PTM signal of Ti, Al, Cu, Sn, Ag, and Ni samples. We show theoretically and experimentally that the time derivative of the signal in the first microseconds is proportional to the square root of the thermal diffusivity coefficient. The method affords a simple calibration and efficient interpretation of experimental data for a sensitive determination of the thermal diffusivity coefficient for materials. We demonstrate the applicability of the technique by measuring the thermal diffusivities of wadsleyite (β-Mg2SiO4) and diopside (MgCaSi2O6), two important minerals relevant to geophysical studies.
We report on pump-probe mode-mismatched photothermal lens experiments of metallic nanoparticles water solutions.
We show that metallic nanoparticles colloids exhibit nonlinear absorption effects related to attraction or repulsion forces
that result from the interaction with the electromagnetic radiation. Gold and iron oxide nanoparticles show a double
peak Z-scan shape that is associated to the presence of attraction forces. We calibrate the experiment using the linear
absorption values of the samples obtaining their corresponding nonlinear absorption coefficients.
We report on a mode-mismatched pump-probe photothermal lens experiment aimed at determination of the thermal diffusivity coefficient of optical samples. In the scheme, the probe beam is collimated and the pump beam is focused. Using a Fresnel diffraction approximation, we show that under these conditions the time dependence of the signal does not depend on the Rayleigh parameters and waist positions of the light beams. This fact allows a more simple and reliable calibration of the experiment in comparison to other schemes. We conduct studies on liquid and solid samples that confirm the predictions of the model. Using the proposed method, we measure the thermal diffusivity coefficient of distilled water, ethanol, methanol, chloroform, nitrobenzene, ethylene glycol, and a solid piece of acrylic plastic. The results are in good agreement with previous measurements.
Fast Fourier transform spectroscopy has proved to be a powerful method for study of the secondary structure of proteins
since peak positions and their relative amplitude are affected by the number of hydrogen bridges that sustain this
secondary structure. However, to our best knowledge, the method has not been used yet for identification of proteins
within a complex matrix like a blood sample. The principal reason is the apparent similarity of protein infrared spectra
with actual differences usually masked by the solvent contribution and other interactions. In this paper, we propose a
novel machine learning based method that uses protein spectra for classification and identification of such proteins
within a given sample. The proposed method uses principal component analysis (PCA) to identify most important linear
combinations of original spectral components and then employs support vector machine (SVM) classification model
applied on such identified combinations to categorize proteins into one of given groups. Our experiments have been
performed on the set of four different proteins, namely: Bovine Serum Albumin, Leptin, Insulin-like Growth Factor 2
and Osteopontin. Our proposed method of applying principal component analysis along with support vector machines
exhibits excellent classification accuracy when identifying proteins using their infrared spectra.
We report on a new application of laser induced breakdown spectroscopy (LIBS) for the diagnosis of diseases such as
ovarian cancer. We perform detection of ovarian cancer biomarker CA 125 based on LIBS measurements. Immunoconjugated
Silicon particles are incubated with the affinity agarose beads carrying CA125 molecules. In the competitive
affinity method Si particles carrying IgG molecules are pre-incubated with CA125. This pre-incubation decreases the
numbers of free IgG molecules available for consequent interaction with the affinity beads. Thus less Si particles are
attached to the agarose beads and consequently smaller Si peak area is measured by LIBS. We demonstrate a limit-ofdetection
about 30 ppb for model protein avidin. We use two-element coded micro-particles to yield spectroscopic
emission code using LIBS. We show that LIBS-based data collecting technique provides methodology for identification
of biomarkers and cost-effective device for future clinical applications.
We report on a pump-probe photothermal lens experiment aimed for the measurement of thermal diffusivity
coefficient of organic samples in the CW regime. We show that when the probe beam is collimated and the pump
beam is focused the time dependence of the signal does not depend on the sample position. This effect allows simple
determination of the thermal diffusivity coefficient and its effective calibration using reference samples. We use this
method to determine the thermal diffusivity of distilled water, methanol, chloroform, nitrobenzene and other organic
solvents.
We report on Fourier transform spectra of deuterated proteins: Bovine Serum Albumin, Leptin, Insulin-like Growth
Factor II, monoclonal antibody to ovarian cancer antigen CA125 and Osteopontin. The spectra exhibit changes in
the relative amplitude and spectral width of certain peaks. New peaks not present in the non-deuterated sample are
also observed. Ways for improving the deuteration of proteins by varying the temperature and dilution time are
discussed. We propose the use of deuterated proteins to increase the sensitivity of immunoassays aimed for early
diagnostic of diseases most notably cancer.
We report on laser-induced breakdown spectroscopy (LIBS) of whole blood and other organic fluids. LIBS spectra, in
the region 200-970 nm, are measured by recording the radiation emitted by the samples following their ablation in a
helium environment. We show that these spectra, although very complex, reveal the presence of elements such as
nitrogen, hydrogen, oxygen and carbon and that of important metallic elements such as iron, magnesium, calcium,
potassium, and sodium. We compare the measured LIBS spectra of whole blood to that of pure carbon and pure iron
and find that in the 200-300 nm region. Nearly 90% of the peaks can be assigned to only these two elements. We also
report on similar studies of methanol, ethanol, isopropanol and water solutions of protein molecules of interest to cancer
research. We show that using simple numerical algorithms, it is possible to distinguish between complex organic
compounds that have nearly the same chemical composition.
We present a two-beam mode-mismatched thermal lens method for pulse excitation aimed for the
determination of one- and two-photon absorption coefficient with high sensitivity. In this scheme the
excitation beam is focused onto the sample in the presence of a collimated CW probe light of low power. The
Z-scan signature is single peaked with a width that depends on the number of photons involved in the
absorption. We show that the method is at least two orders of magnitude more sensitive than the well-known
open Z-scan transmission method commonly used for multi-photon absorption measurement. Using the proposed method we measure a two photon absorption coefficient for nitrobenzene of β=1.12 10-10 cm/W for nanosecond pulses and a wavelength of 532 nm.
We report on the optical characterization and measurement of oxygen singlet quantum yield of Chlorophyll and Chlorin e6 in water-ethanol mixtures by direct observation of thermal relaxation using time resolved thermal lens method. The analysis of the time-resolved curve allows the determination of the quantum yield of singlet oxygen formation. The quantum yield is deduced from the relative magnitudes of the fast and slow components.
We report on a new source of coherent red-light with perspective applications in laser photodynamic therapy. The red light is generated through stimulated Raman scattering (SRS) process by acetone of a frequency-doubled Nd:YAG nanosecond laser radiation (532 nm). The Stokes transition is found at 630 nm and with spectral line narrowing similar to the pump one. When pumping using the radiation from a Rhodamine-6G Dye laser (560 - 575 nm), tuning between 640 and 670 nm is demonstrated. Conversion efficiencies up to 50% are reported.
We describe a new kind of fiber optics device, which detects directly sound and other perturbations with high sensitivity. The fiber works as a sound transducer able to detect human voice of low power levels. The phase changes, induced by sound waves in the propagating through the fiber light beam, generate amplitude changes after the beam is diffracted at the exit end of the fiber. A specially designed electronic system processes the signal which can be used for sound reproduction and detection. The system can also be used as an all purposes detector for the registration of subsonic and ultrasonic acoustic waves, direct pressure, temperature changes and other external fields.
We report the quadratic hyperpolarizability βs of newly synthesized chirals carboxylates salts. These nonlinear optical coefficients have been measured using Hyper-Rayleigh scattering (HRS) technique in solution. Before nonlinear measurements, the different compounds under study were characterized by resonance magnetic nuclear of protons and absorption spectra. They were shown to be completely transparent to the absorption in the UV-Visible and near-infrared region of the spectrum: spectra of solutions in methanol, recorded on an ATI-UNICAM spectrometer in range 250 - 1100 nm show no absorption above 350 - 400 nm. HRS measurements are made by using methanol as solvent and the values of the nonresonant hyperpolarisabilities obtained are of the same order of magnitude that that of the paranitroaniline and are located beween 30x10-30 esu and 60x10-30 esu.
Recently new photosensitizers, chlorophyll "a and b" derivatives, for photodynamic therapy (PDT) have been presented. It already passed complete pre-clinical investigations. This prompted us to carry out an extensive study of photophysical properties of chlorine derivatives, important both for optimization of their clinic applications and for study of mechanisms of chlorine PDT&. The fresh leaves of Bauhinia megalandra (Caesalpinaceae) were extracted with methanol by percolation, and re-extract with a mixture of methanol-water (1:1), the insoluble fraction was then separated by column chromatography [RP18/hexane-ethylacetate (9:1)] to obtain four fractions named 1 to 4. These compounds were identified by NMR data. We found that 3 and 4 efficiently generates singlet oxygen when irradiated with visible light. Detection of the singlet oxygen was fulfilled by its reaction with histidine and detected by bleaching p-nitrosodimethylaniline under 440 nm irradiation. The quantum yields of singlet oxygen determined by us were 0.088 (1), 0.151 (2), 0.219 (3) and 0.301 (4). We measured absorption and fluorescence spectra of compounds 1 to 4 (Mg-chlorophyll-a, Pheophytin, Mg-chlorophyll-b and chlorophyll-b respectively) in different media and in aqueous solutions of human serum albumin. The association constant of the compounds 1, 2, 3 and 4 in the presence of HSA were estimated. The binding and quenching studies suggest that only 1 and 3 may serve as a useful fluorescence probe for structure/function studies of different chlorophyll binding proteins. No photoinduced binding was observed after irradiation by all the studied compounds in presence of human serum albumin.
We study the effects of a thermal lens generated by a pump beam on the propagation of a low power TEM00 probe beam. We show that the thermal lens affects the probe beam waist position and waist radius. The waist position is displaced forward and backward depending on the sign of the refractive index thermal gradient. We show that the waist position does not coincide with the focal plane of the thermal lens. Our results suggest that the absorption coefficient of the sample can be found measuring the time-dependent waist radius of the probe beam.
We have developed a method which yields the real and the imaginary parts of third-order susceptibility of material media. We have applied this method to determine the nonlinear refractive index (n2) of new synthesized organic materials in the picosecond regime (30 ps pulse duration at 1064 nm wavelength). The results obtained show the efficiency of this technique for measuring low values of the nonlinear refraction coefficient n2 in diluted materials.
We present a pump-probe mode-mismatched thermal lens method for pulse excitation aimed to the measurement of one- and multi-photon absorption coefficient with high sensitivity. Short pulses of light are used as pump source while the probe field is a collimated CW light of low power. The method is used for the measurement of absorption of distilled water and ethanol. Absorption coefficient as small as 10-8 cm-1 can be measured with the described technique.
The quenching of fluorescence due to the high values of the fluence of the excitation field is studied for three different samples of Rhodamine 6G: ethanol and glycerol solutions and a film of the dye deposited over a silica substrate. High level of quenching is reported for the ethanol solution, while the effect is barely observed for the glycerol solution. The film sample does not exhibit the quenching effect. We also report correlation between the presence of quenching of the fluorescence and the fluence dependence of the fluorescence decay. The results confirm the validity of a model, which suggests this dependence as an explanation of the quenching effect.
We report on a novel pump-probe thermal lens method with nearly collimated beams developed for the measurement of absorption coefficients of the order of 10-9 cm-1. This method allows the us of samples of path- lengths 100 cm and larger.
We measure the absorption spectrum of an ethanol solution of Rhodamine 101 in the spectral region 555 nm - 585 nm as a function of the incident light fluence. Distortions of the absorption spectra are observed at high fluence values. Besides the observation of the light induced spectral broadening, we report the splitting of the spectrum into two peaks as predicted by the optical Stark effect theory.
We propose a new method for the measurement of nonlinear susceptibility of an optical material based on the recording of the total distortions of the wave-front of a light wave propagating through the medium. We compare the method with the usual Z-scan and EZ-scan techniques and demonstrate theoretically and experimentally the better sensitivity of the new method.
The evolution of the spatial profile of a thermal lens induced by a cw low power laser beam in an absorbing dye solution is directly visualized in real time using glow- coherence light interferometry. Both spatial characteristics and response times of the lens are measured. Preliminary comparisons between experimental result and thermal diffusion theory are presented. The accuracy of measured refractive index in the thermal lens profile is better than 10-6.
A method for the measurement of the nonlinear refraction and absorption in optical materials studying the distortions of the wavefront of light beams is proposed. Using a one-shot CCD camera, the beam profile changes are recorded for different cell positions. Usual Z-scan, eclipse Z-scan and the total profile distortion signals can be extracted from these data. Proportionality between the measured total signal and the induced phase shift is demonstrated. A comparison between this signal and the usual Z-scan signal is performed.
Spatial characteristics of a thermal lens induced by a Gaussian beam in an absorbing liquid are studied using a nonlinear geometrical optics approximation. We show that the thermal lens in the vicinity of the sample cell is a focal point of light and a ring-of-light foci located in a plane displaced with respect to the focal point. The distance between the focal point and the ring-of-light foci decreases when the light power is increased. Experiments performed on an ethanol solution of iodine confirm the existence of this microscopic structure. The distance between the focal point and the ring of foci was measured for samples of different absorption coefficients. A good agreement between theory and experiment was obtained.
Theoretical and experimental studies of the structure of the thermal lens generated in a liquid by a Gaussian electromagnetic field are performed. It is shown that the light induced thermal lens can be considered a focal source of light plus a ring of light sources located on different planes.
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