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1.
J Chem Phys ; 150(9): 094709, 2019 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-30849892

RESUMO

This paper presents the first study of the rotations of rigid molecules in 3 dimensions at the air/water interface, using the femtosecond time resolved sum frequency generation (SFG) technique. For the purpose of this research, the aromatic dye molecule C153 was chosen as an example of a molecule having two functional groups that are SFG active, one being the hydrophilic -C=O group and the other the hydrophobic -CF3 group. From polarized SFG measurements, the orientations of the two chromophores with respect to the surface normal were obtained. On combining these results with the known relative orientation of the two chromophores in the molecule yields the absolute orientation of C153 at the air/water interface. It was found that the -CF3 axis projected towards the bulk air at an angle of 59° with respect to the interface normal and the -C=O group projected towards the bulk water at an angle of 144°. In order to observe the rotational motions of C153 at the air/water interface, the approach was used to perturb the ground electronic state equilibrium orientational distribution using a polarized resonant pump pulse, which preferentially excites ground state molecules that have their electronic S0 → S1 transition moment aligned closely to the electric field of the incident pump pulse. As a consequence of the photoselection perturbation, the orientational distribution of the remaining ground state molecules was not the equilibrium distribution. Similarly, the orientational distribution of the excited state molecules that were created by the polarized pump pulse was not in their final equilibrium orientational distribution. The rotational motions of the interfacial molecules towards equilibrium were obtained from time dependent measurements of the intensities of the SFG signal generated by the simultaneous incidence at the air/water interface of a visible probe pulse plus an IR probe pulse. In this way, the recovery times to achieve the orientational equilibrium of the two chromophores including the orientation of the normal of the C153 plane with respect to the interface were obtained. The photo-selection process shifts the average orientation angle of the hydrophilic -C=O group by an increase of 4° ± 0.6° with a rotational recovery time constant of 130 ± 20 ps, which is the time to return to an orientational equilibrium distribution. The hydrophobic -CF3 group undergoes a shift that increases its angle by 8° ± 1.5° with a rotational recovery time constant of 210 ± 38 ps. We find that the orientational change of the molecular normal is 4° ± 0.5° and has a rotational recovery time constant of 125 ± 26 ps. The interface-specific time-dependent polarized measurements allowed us to monitor the orientational motions of molecules at interfaces, both in 3 dimensions and in real time.

2.
Photochem Photobiol ; 93(5): 1165-1169, 2017 10.
Artigo em Inglês | MEDLINE | ID: mdl-28295380

RESUMO

In this manuscript, we demonstrate the control of film thickness and surface wettability in the photochemical immobilization of poly (vinyl alcohol) (PVA) to a self-assembled monolayer (SAM) containing a phthalimide chromophore. Surface attachment is characterized by ellipsometry and contact angle measurements. The wettability of the resulting films is shown to depend on the chemical composition of the polymer. The film thickness is shown to depend on the irradiation time and molecular weight of the polymer. Using a photomask, micropatterns of polymers can be grafted to the SAM. The photopatterned surface can be "developed" by coating with a thin layer of a mixture containing poly (styrene) (PS) and triphenylsulfonium triflate.

3.
Macromol Rapid Commun ; 38(2)2017 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-27873447

RESUMO

This report demonstrates the electroless deposition of Ni onto micropatterns of poly (acrylic acid) (PAA) photografted to phthalimide-terminated self-assembled monolayers (SAMs). PAA is spin-coated onto phthalimide SAMs and covered with a photomask. UV irradiation selectively binds PAA to exposed regions of the surface, allowing PAA on unexposed regions to be rinsed off. A Pd catalyst is then selectively adsorbed to regions of the surface where PAA is bound. The adsorbed catalyst selectively initiates Ni plating upon immersion of the substrate into a Ni(SO4 ) bath.


Assuntos
Resinas Acrílicas/química , Níquel/química , Adsorção , Catálise , Estrutura Molecular , Processos Fotoquímicos
4.
RSC Adv ; 4(90): 49342-49346, 2014 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-25396047

RESUMO

As an alternative to fluorescence-based DNA sequencing by synthesis (SBS), we report here an approach using an azido moiety (N3) that has an intense, narrow and unique Raman shift at 2125 cm-1, where virtually all biological molecules are transparent, as a label for SBS. We first demonstrated that the four 3'-O-azidomethyl nucleotide reversible terminators (3'-O-azidomethyl-dNTPs) displayed surface enhanced Raman scattering (SERS) at 2125 cm-1. Using these 4 nucleotide analogues as substrates, we then performed a complete 4-step SBS reaction. We used SERS to monitor the appearance of the azide-specific Raman peak at 2125 cm-1 as a result of polymerase extension by a single 3'-O-azidomethyl-dNTP into the growing DNA strand and disappearance of this Raman peak with cleavage of the azido label to permit the next nucleotide incorporation, thereby continuously determining the DNA sequence. Due to the small size of the azido label, the 3'-O-azidomethyl-dNTPs are efficient substrates for the DNA polymerase. In the SBS cycles, the natural nucleotides are restored after each incorporation and cleavage, producing a growing DNA strand that bears no modifications and will not impede further polymerase reactions. Thus, with further improvements in SERS for the azido moiety, this approach has the potential to provide an attractive alternative to fluorescence-based SBS.

5.
Phys Chem Chem Phys ; 16(39): 21330-9, 2014 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-25178254

RESUMO

Inelastic neutron scattering (INS) has been employed to investigate the quantum dynamics of water molecules permanently entrapped inside the cages of C60 fullerene molecules. This study of the supramolecular complex, H2O@C60, provides the unique opportunity to study isolated water molecules in a highly symmetric environment. Free from strong interactions, the water molecule has a high degree of rotational freedom enabling its nuclear spin isomers, ortho-H2O and para-H2O to be separately identified and studied. The INS technique mediates transitions between the ortho and para spin isomers and using three INS spectrometers, the rotational levels of H2O have been investigated, correlating well with the known levels in gaseous water. The slow process of nuclear spin conversion between ortho-H2O and para-H2O is revealed in the time dependence of the INS peak intensities over periods of many hours. Of particular interest to this study is the observed splitting of the ground state of ortho-H2O, raising the three-fold degeneracy into two states with degeneracy 2 and 1 respectively. This is attributed to a symmetry-breaking interaction of the water environment.

6.
Proc Natl Acad Sci U S A ; 111(35): 12684-8, 2014 Sep 02.
Artigo em Inglês | MEDLINE | ID: mdl-25136100

RESUMO

The transacting activator of transduction (TAT) protein plays a key role in the progression of AIDS. Studies have shown that a +8 charged sequence of amino acids in the protein, called the TAT peptide, enables the TAT protein to penetrate cell membranes. To probe mechanisms of binding and translocation of the TAT peptide into the cell, investigators have used phospholipid liposomes as cell membrane mimics. We have used the method of surface potential sensitive second harmonic generation (SHG), which is a label-free and interface-selective method, to study the binding of TAT to anionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-1'-rac-glycerol (POPG) and neutral 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposomes. It is the SHG sensitivity to the electrostatic field generated by a charged interface that enabled us to obtain the interfacial electrostatic potential. SHG together with the Poisson-Boltzmann equation yielded the dependence of the surface potential on the density of adsorbed TAT. We obtained the dissociation constants Kd for TAT binding to POPC and POPG liposomes and the maximum number of TATs that can bind to a given liposome surface. For POPC Kd was found to be 7.5 ± 2 µM, and for POPG Kd was 29.0 ± 4.0 µM. As TAT was added to the liposome solution the POPC surface potential changed from 0 mV to +37 mV, and for POPG it changed from -57 mV to -37 mV. A numerical calculation of Kd, which included all terms obtained from application of the Poisson-Boltzmann equation to the TAT liposome SHG data, was shown to be in good agreement with an approximated solution.


Assuntos
Síndrome da Imunodeficiência Adquirida/virologia , HIV-1/metabolismo , Modelos Químicos , Mimetismo Molecular , Análise Espectral Raman/métodos , Produtos do Gene tat do Vírus da Imunodeficiência Humana/metabolismo , Síndrome da Imunodeficiência Adquirida/metabolismo , Coloides/metabolismo , Sistemas de Liberação de Medicamentos , Humanos , Lasers , Lipossomos/metabolismo , Membranas Artificiais , Fosfolipídeos/metabolismo , Ligação Proteica , Propriedades de Superfície , Água/metabolismo
7.
Photochem Photobiol Sci ; 13(2): 407-11, 2014 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-24398916

RESUMO

Fluorescent chlorophyll catabolites (FCCs) are fleeting intermediates of chlorophyll breakdown, which is seen as an enzyme controlled detoxification process of the chlorophylls in plants. However, some plants accumulate large amounts of persistent FCCs, such as in senescent leaves and in peels of yellow bananas. The photophysical properties of such a persistent FCC (Me-sFCC) were investigated in detail. FCCs absorb in the near UV spectral region and show blue fluorescence (max at 437 nm). The Me-sFCC fluorescence had a quantum yield of 0.21 (lifetime 1.6 ns). Photoexcited Me-sFCC intersystem crosses into the triplet state (quantum yield 0.6) and generates efficiently singlet oxygen (quantum yield 0.59). The efficient generation of singlet oxygen makes fluorescent chlorophyll catabolites phototoxic, but might also be useful as a (stress) signal and for defense of the plant tissue against infection by pathogens.


Assuntos
Clorofila/metabolismo , Fluorescência , Musa/química , Processos Fotoquímicos , Fármacos Fotossensibilizantes/metabolismo , Oxigênio Singlete/química , Clorofila/química , Cor , Musa/metabolismo , Fármacos Fotossensibilizantes/química
8.
Photochem Photobiol ; 90(2): 394-401, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24256104

RESUMO

Small molecules representing common synthetic polymers were subjected to photochemically induced hydrogen abstraction by benzophenone. Reactions were monitored using (1) H NMR to query the factors that influence preferential abstraction of protons in unique chemical environments. Differences in bond dissociation energies do not fully explain the observed hydrogen abstraction preferences. To that end, we identify contributions to abstraction from prereactive complexation, radical stability, steric effects and charge transfer effects. Using representative small molecule model compounds in lieu of polymeric materials is a novel approach to understanding photochemical reaction in polymers; however, it cannot probe the contributions of macromolecular effects--e.g. polymer rigidity or side chain and backbone mobility--to preferential hydrogen abstraction.


Assuntos
Hidrogênio/química , Modelos Químicos , Mimetismo Molecular , Polímeros/química , Espectroscopia de Prótons por Ressonância Magnética
9.
Photochem Photobiol ; 90(2): 338-43, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-23998198

RESUMO

Recent studies suggest that aliphatic ß-nitro alcohols may represent a useful class of compounds for use as in vivo therapeutic corneoscleral cross-linking agents with higher order nitroalcohols (HONAs) showing enhanced efficacy over the mono-nitroalcohols. The current study was undertaken in order to evaluate the chemical stability of these compounds during storage conditions. Two mono-nitroalcohols (2-nitroethanol=2ne and 2-nitro-1-propanol = 2 nprop) and two HONAs, a nitrodiol (2-methyl-2-nitro-1,3-propanediol = MNPD), and a nitrotriol (2-hydroxymethyl-2-nitro-1,3-propanediol = HNPD) were monitored for chemical stability by (1)H-NMR for up to 7 months. Each compound was studied at two concentrations (1% and 10%) either in unbuffered H2O or 0.2 m NaH2 PO4/Na2 HPO4 (pH = 5), and at 0 °C and room temperature (RT) for a total of eight conditions for each compound. The (1)H-NMR spectra for the starting material were compared to subsequent spectra. Under all four of the conditions studied, both the nitrodiol (MNPD) and nitrotriol (HNPD) were stable for the duration of 7 months. 2nprop became unstable under all conditions at 3 months. 2ne was the most unstable of all the compounds tested. HONAs exhibit excellent chemical stability under long-term storage conditions. In contrast, the nitromonols tested are significantly less stable. These findings are relevant to the translation of this technology into clinical use.


Assuntos
Álcoois/farmacologia , Córnea/efeitos dos fármacos , Nitrocompostos/química , Esclera/efeitos dos fármacos , Álcoois/química , Álcoois/uso terapêutico , Humanos , Ceratocone/terapia , Espectroscopia de Prótons por Ressonância Magnética
10.
Photochem Photobiol ; 90(2): 439-47, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24134493

RESUMO

We synthesized two molecular systems, in which an endofullerene C60 , incarcerating one hydrogen molecule (H2 @C60 ) and a nitroxide radical are connected by a folded 310 -helical peptide. The difference between the two molecules is the direction of the peptide orientation. The nuclear spin relaxation rates and the para → ortho conversion rate of the incarcerated hydrogen molecule were determined by (1) H NMR spectroscopy. The experimental results were analyzed using DFT-optimized molecular models. The relaxation rates and the conversion rates of the two peptides fall in the expected distance range. One of the two peptides is particularly rigid and thus ideal to keep the H2 @C60 /nitroxide separation, r, as large and controlled as possible, which results in particularly low relaxation and conversion rates. Despite the very similar optimized distance, however, the rates measured with the other peptide are considerably higher and thus are compatible with a shorter effective distance. The results strengthen the outcome of previous investigations that while the para → ortho conversion rates satisfactorily obey the Wigner's theory, the nuclear spin relaxation rates are in excellent agreement with the Solomon-Bloembergen equation predicting a 1/r(6) dependence.


Assuntos
Fulerenos/química , Hidrogênio/química , Óxidos de Nitrogênio/química , Peptídeos/química , Conformação Molecular , Espectroscopia de Prótons por Ressonância Magnética
11.
Org Lett ; 15(18): 4746-9, 2013 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-24004381

RESUMO

Relaxation rates of endo-H2O in H2O@Open-C60 in the presence of a nitroxide radical and of their nitroxide derivatives have been measured and are compared with effects for endo-H2 in similar cages. T1 relaxation enhancement of the endo-H2O and H2 induced by either intra- or intermolecular interaction is relatively insensitive to the presence of a cage opening. Enhancement of intermolecular relaxation is observed, however, when the cage opening has an OH group.

12.
J Chem Phys ; 139(6): 064309, 2013 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-23947857

RESUMO

In the supramolecular complex H2@C60, the lightest of molecules, H2, is encapsulated inside the most highly symmetric molecule C60. The elegance and apparent simplicity of H2@C60 conceal highly intricate quantum dynamics of the coupled translational and rotational motions of the guest molecule in a nearly spherical nanoscale cavity, which embodies some of the most fundamental concepts of quantum mechanics. Here we present the first rigorous and highly accurate quantum calculations of the inelastic neutron scattering (INS) spectra of this prototypical endohedral fullerene complex and their temperature dependence. The calculations enable complete assignment of the recently reported experimental INS spectra of H2@C60 measured at several temperatures. We also derive a new and unexpected selection rule for the INS spectroscopy of H2 in a near-spherical confinement, which explains why the INS transitions between certain translation-rotation eigenstates of H2 in C60 have zero intensity and do not appear in the spectra.

13.
J Org Chem ; 78(18): 9161-5, 2013 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-23944866

RESUMO

A photoinitiator for free-radical polymerization based on a thioxanthone chromophore containing two acetic acid functions was synthesized and characterized. Photophysical studies such as fluorescence, phosphorescence, and laser flash photolysis in addition to photopolymerization of acrylates were performed to elucidate the radical generation mechanism involving intramolecular electron transfer from the triplet state followed by decarboxylation. We found that the position of the acetic acid substituent is critical for the photoreactivity. In most solvents and acrylic monomers, if the acetic acid functionality is at the 1-position, the singlet excited states are deactivated rapidly before electron transfer can occur, resulting in negligible photoreactivity. The excited-state deactivation probably involves intramolecular H-bonding deactivation. The intramolecular H-bonding is disrupted by solvents that support intermolecular H-bonding, such as DMF and DMSO, leading to efficient intramolecular photoreaction.


Assuntos
Fármacos Fotossensibilizantes/química , Quinonas/química , Xantonas/química , Radicais Livres/química , Estrutura Molecular , Processos Fotoquímicos , Raios Ultravioleta
14.
Philos Trans A Math Phys Eng Sci ; 371(1998): 20110628, 2013 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-23918710

RESUMO

Spectroscopic studies of recently synthesized endofullerenes, in which H2, H2O and other atoms and small molecules are trapped in cages of carbon atoms, have shown that although the trapped molecules interact relatively weakly with the internal environment they are nevertheless susceptible to appropriately applied external perturbations. These properties have been exploited to isolate and study samples of H2 in C60 and other fullerenes that are highly enriched in the para spin isomer. Several strategies for spin-isomer enrichment, potential extensions to other endofullerenes and possible applications of these materials are discussed.

15.
Philos Trans A Math Phys Eng Sci ; 371(1998): 20110630, 2013 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-23918712

RESUMO

We report rigorous quantum calculations of the inelastic neutron scattering (INS) spectra of HD@C60, over a range of temperatures from 0 to 240 K and for two incident neutron wavelengths used in recent experimental investigations. The computations were performed using our newly developed methodology, which incorporates the coupled five-dimensional translation-rotation (T-R) eigenstates of the guest molecule as the initial and final states of the INS transitions, and yields highly detailed spectra. Depending on the incident neutron wavelength, the number of computed INS transitions varies from almost 500 to over 2000. The low-temperature INS spectra display the fingerprints of the coupling between the translational and rotational motions of the entrapped HD molecule, which is responsible for the characteristic splitting patterns of the T-R energy levels. INS transitions from the ground T-R state of HD to certain sublevels of excited T-R multiplets have zero intensity and are absent from the spectra. This surprising finding is explained by the new INS selection rule introduced here. The calculated spectra exhibit strong temperature dependence. As the temperature increases, numerous new peaks appear, arising from the transitions originating in excited T-R states which become populated. Our calculations show that the higher temperature features typically comprise two or more transitions close in energy and with similar intensities, interspersed with numerous other transitions whose intensities are negligible. This implies that accurately calculated energies and intensities of INS transitions which our methodology provides will be indispensable for reliable interpretation and assignment of the experimental spectra of HD@C60 and related systems at higher temperatures.

16.
Philos Trans A Math Phys Eng Sci ; 371(1998): 20110634, 2013 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-23918714

RESUMO

We have investigated the structure and nuclear magnetic resonance (NMR) spectroscopic properties of some dihydrogen endofullerene nitroxides by means of density-functional theory (DFT) calculations. Quantum versus classical roto-translational dynamics of H2 have been characterized and compared. Geometrical parameters and hyperfine couplings calculated by DFT have been input to the Solomon-Bloembergen equations to predict the enhancement of the NMR longitudinal relaxation of H2 due to coupling with the unpaired electron. Estimating the rotational correlation time via computed molecular volumes leads to a fair agreement with experiment for the simplest derivative; the estimate is considerably improved by recourse to the calculation of the diffusion tensor. For the other more flexible congeners, the agreement is less good, which may be due to an insufficient sampling of the conformational space. In all cases, relaxation by Fermi contact and Curie mechanisms is predicted to be negligible.

17.
Philos Trans A Math Phys Eng Sci ; 371(1998): 20120475, 2013 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-23918718

RESUMO

The photoexcitation of functionalized fullerenes to their paramagnetic triplet electronic state can be studied by pulsed electron paramagnetic resonance (EPR) spectroscopy, whereas the interactions of this state with the surrounding nuclear spins can be observed by a related technique: electron nuclear double resonance (ENDOR). In this study, we present EPR and ENDOR studies on a functionalized exohedral fullerene system, dimethyl[9-hydro (C60-Ih)[5,6]fulleren-1(9H)-yl]phosphonate (DMHFP), where the triplet electron spin has been used to hyperpolarize, couple and measure two nuclear spins. We go on to discuss the extension of these methods to study a new class of endohedral fullerenes filled with small molecules, such as H2@C60, and we relate the results to density functional calculations.

18.
Chemphyschem ; 14(13): 3121-30, 2013 Sep 16.
Artigo em Inglês | MEDLINE | ID: mdl-23788291

RESUMO

We present a solid-state NMR study of H2 molecules confined inside the cavity of C70 fullerene cages over a wide range of temperatures (300 K to 4 K). The proton NMR spectra are consistent with a model in which the dipole-dipole coupling between the ortho-H2 protons is averaged over the rotational/translational states of the confined quantum rotor, with an additional chemical shift anisotropy δ(H)(CSA)=10.1 ppm induced by the carbon cage. The magnitude of the chemical shift anisotropy is consistent with DFT estimates of the chemical shielding tensor field within the cage. The experimental NMR data indicate that the ground state of endohedral ortho-H2 in C70 is doubly degenerate and polarized transverse to the principal axis of the cage. The NMR spectra indicate significant magnetic alignment of the C70 long axes along the magnetic field, at temperatures below ~10 K.

19.
J Phys Chem A ; 117(25): 5232-40, 2013 Jun 27.
Artigo em Inglês | MEDLINE | ID: mdl-23768193

RESUMO

X-band EPR spectra of singlet O2((1)Δg) and triplet O2((3)Σg(-)) were observed in the gas phase under low molecular-oxygen pressures PO2 = 0.175-0.625 Torr, T = 293-323 K. O2((1)Δg) was produced by quenching of photogenerated triplet sensitizers naphthalene C8H10, perdeuterated naphthalene, and perfluoronaphthalene in the gas phase. The EPR spectrum of O2((1)Δg) was also observed under microwave discharge. Integrated intensities and line widths of individual components of the EPR spectrum of O2((3)Σg(-)) were used as internal standards for estimating the concentration of O2 species and PO2 in the EPR cavity. Time-resolved (TR) EPR experiments of C8H10 were the main focus of this Article. Pulsed irradiation of C8H10 in the presence of O2((3)Σg(-)) allowed us to determine the kinetics of formation and decay for each of the four components of the O2((1)Δg) EPR signal, which lasted for only a few seconds. We found that the kinetics of EPR-component decay fit nicely to a biexponential kinetics law. The TR EPR 2D spectrum of the third component of the O2((1)Δg) EPR spectrum was examined in experiments using C8H10. This spectrum vividly presents the time evolution of an EPR component. The largest EPR signal and the longest lifetime of O2((1)Δg), τ = 0.4 s, were observed at medium pressure PO2 = 0.4 Torr, T = 293 K. The mechanism of O2((1)Δg) decay in the presence of photosensitizers is discussed. EPR spectra of O2((1)Δg) evidence that the spin-rotational states of O2((1)Δg) are populated according to Boltzmann distribution in the studied time range of 10-100 ms. We believe that this is the first report dealing with the dependence of O2((1)Δg) EPR line width on PO2 and T.


Assuntos
Naftalenos/química , Oxigênio/química , Fármacos Fotossensibilizantes/química , Oxigênio Singlete/química , Espectroscopia de Ressonância de Spin Eletrônica , Cinética , Micro-Ondas , Processos Fotoquímicos
20.
Proc Natl Acad Sci U S A ; 110(15): 5756-8, 2013 Apr 09.
Artigo em Inglês | MEDLINE | ID: mdl-23530200

RESUMO

A method is described in which the interference of radiated second-harmonic electric fields generated by a pair of oriented molecules intercalated into double-stranded DNA is controlled and measured. The results show that the relative molecular orientation of the two molecules significantly changes the magnitude of the observed second-harmonic generation intensity, which is described by a simple model that accounts for the interferences of the radiated fields. The technique presented shows promise for future experiments investigating structural changes induced by the formation of a DNA-biomolecule complex.


Assuntos
Biofísica/métodos , DNA/química , Daunorrubicina/farmacologia , Ligantes , Modelos Estatísticos , Conformação de Ácido Nucleico , Óptica e Fotônica , Oscilometria/métodos , Espectrofotometria/métodos
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