Thermal Behavior and Slow Relaxation Dynamics in Amorphous Efavirenz: A Study by DSC, XRPD, TSDC, and DRS.

The analysis of the thermal behavior of efavirenz showed a high glass-forming ability and good glass stability of this glass-forming liquid at room temperature. No polymorphic forms were formed either by cold crystallization or by recrystallization from solvent acetone. The determination of the dynamic fragility by the differential scanning calorimetry, thermally stimulated depolarization currents (TSDC), and dielectric relaxation spectroscopy (DRS) techniques is unanimous in suggesting efavirenz as a moderately fragile liquid.

A Cationic Smart Copolymer for DNA Binding.

A new block copolymer with a temperature-responsive block and a cationic block was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization, with good control of its size and composition. The first block is composed by di(ethylene glycol) methyl ether methacrylate (DEGMA) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA), with the ratio DEGMA/OEGMA being used to choose the volume phase transition temperature of the polymer in water, tunable from ca. 25 to above 90 °C.

Polymeric nanoparticles: A study on the preparation variables and characterization methods.

Since the emergence of Nanotechnology in the past decades, the development and design of nanomaterials has become an important field of research. An emerging component in this field is nanomedicine, wherein nanoscale materials are being developed for use as imaging agents or for drug delivery applications. Much work is currently focused in the preparation of well-defined nanomaterials in terms of size and shape.

Stabilizing Unstable Amorphous Menthol through Inclusion in Mesoporous Silica Hosts.

The amorphization of the readily crystallizable therapeutic ingredient and food additive, menthol, was successfully achieved by inclusion of neat menthol in mesoporous silica matrixes of 3.2 and 5.9 nm size pores.

Dipolar Reorientations in Amorphous Nimesulide: A TSDC and DSC Study.

Background: The preparation of APIs in the amorphous solid form can be a means of circumventing problems arising from poor solubility and low dissolution rate of the crystalline drugs. However, molecular mobility can be responsible for the glass instability, so that the kinetic characterization of the different relaxations that subsist in the amorphous solid is useful to allow define the conditions for greater stability of the glassy pharmaceutical. Our purpose is to use the experimental techniques of differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC) to study the thermal behavior of the pharmaceutical drug nimesulide and its slow molecular mobility in the amorphous solid state.

The slow relaxation dynamics in active pharmaceutical ingredients studied by DSC and TSDC: Voriconazole, miconazole and itraconazole.

The slow molecular mobility of three active pharmaceutical drugs (voriconazole, miconazole and itraconazole) has been studied by differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). This study yielded the main kinetic features of the secondary relaxations and of the main (glass transition) relaxation, in particular their distribution of relaxation times. The dynamic fragility of the three glass formers was determined from DSC data (using two different procedures) and from TSDC data.

Phasor Representation of Monomer-Excimer Kinetics: General Results and Application to Pyrene.

Phasor plots of the fluorescence intensity decay (plots of the Fourier sine transform versus the Fourier cosine transform, for one or several angular frequencies) are being increasingly used in studies of homogeneous and heterogeneous systems. In this work, the phasor approach is applied to monomer-excimer kinetics. The results obtained allow a clear visualization of the information contained in the decays.

Dipolar motions and ionic conduction in an ibuprofen derived ionic liquid.

It was demonstrated that the combination of the almost water insoluble active pharmaceutical ingredient (API) ibuprofen with the biocompatible 1-ethanol-3-methylimidazolium [C2OHMIM] cation of an ionic liquid (IL) leads to a highly water miscible IL-API with a solubility increased by around 5 orders of magnitude. Its phase transformations, as crystallization and glass transition, are highly sensitive to the water content, the latter shifting to higher temperatures upon dehydration. By dielectric relaxation spectroscopy the dynamical behavior of anhydrous [C2OHMIM][Ibu] and with 18.

The Slow Molecular Mobility in Amorphous Ketoprofen and Ibuprofen.

The slow molecular dynamics in two active pharmaceutical drugs, ketoprofen and ibuprofen, have been studied by differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). This study allowed finding the main kinetic features of the fast secondary (γ) relaxation, of the Johari-Goldstein relaxation, and of the main (glass transition) relaxation, in particular their distribution of relaxation times. The fragility index of the two glass formers was determined based on data from DSC and from TSDC.

Fluorescence Phasor Plots Using Time Domain Data: Effect of the Instrument Response Function.

Phasor plots of the fluorescence intensity decay (plots of the Fourier sine transform vs the Fourier cosine transform, for one or several angular frequencies) are being increasingly used, namely, in fluorescence lifetime imaging microscopy (FLIM) of cells, tissues, and surfaces, but are also relevant for the characterization of homogeneous (e.g., solution) systems.

Portuguese tin-glazed earthenware from the 17th century. Part 2: A spectroscopic characterization of pigments, glazes and pastes of the three main production centers.

Sherds representative of the three Portuguese faience production centers of the 17th century - Lisbon, Coimbra and Vila Nova were studied with the use of mostly non-invasive spectroscopies, namely: ground state diffuse reflectance absorption (GSDR), micro-Raman, Fourier-transform infrared (FT-IR) and proton induced X-ray (PIXE) or X-ray fluorescence emission (XRF). X-ray diffraction (XRD) experiments were also performed. The obtained results evidence a clear similarity in the pastes of the pottery produced Vila Nova and some of the ceramic pastes from Lisbon, in accordance with documental sources that described the use of Lisbon clays by Vila Nova potters, at least since mid 17th century.

The segmental and chain relaxation modes in high-cis-polyisoprene as studied by thermally stimulated currents.

The technique of Thermally Stimulated Currents is used to study the slow molecular mobility in a series of poly (1,4-cis-isoprene) samples with different molecular weights, Mw, and low polydispersity. The technique revealed a high resolution power, particularly useful in the study of the lower molecular weight samples where the chain and the segmental relaxations strongly overlap. The dynamic crossover that is reported for the normal mode by varying the molecular weight is clearly revealed by the thermally stimulated depolarization currents results through the temperature location, TMn, of the normal mode peak, the values of the relaxation time at TMn, τ(TMn), and the value of the fragility index of the normal mode, mn.

Influence of excited-state absorption on time-resolved luminescence: general formalism and application to the phosphorescence of polycyclic aromatic hydrocarbons.

The luminescence decay of a species in an absorbing medium whose optical thickness changes with time, as occurs with triplet-triplet absorption following excitation cut-off, is studied theoretically and experimentally. A general luminescence decay function based on a distribution of optical thicknesses is presented. A simple decay function previously used empirically is shown to result from an exponential distribution of optical thicknesses.

Confinement effects on the dynamic behavior of poly(D,L-lactic acid) upon incorporation in α-cyclodextrin.

Inclusion complexes (ICs) composed of α-cyclodextrin (α-CD) and poly(D,L-lactic acid) (PDLLA), with 10/24 (IC1) and 15/46 (IC2) (% w/w) of PDLLA incorporated/initial PDLLA weight percentage, were prepared and characterized mainly by dielectric relaxation spectroscopy (DRS). Bulk PDLLA was also analyzed for comparison. DRS was revealed to be a suitable tool to distinguish the dynamical response of the PDLLA regions constrained in between α-CD channels from the fraction incorporated inside channels.

Temperature dependence of the phosphorescence and of the thermally activated delayed fluorescence of C and C in amorphous polymer matrices. Is a second triplet involved?

The phosphorescence and thermally activated delayed fluorescence (TADF) lifetimes of C and C in two different glassy hydrocarbon polymers, one aliphatic (cyclic polyolefin) and one aromatic (polystyrene), were measured between -200 and 100 ºC. The temperature dependence of the lifetimes is equally well described by a three-state mechanism (ground state, S, and two excited states in thermal equilibrium, T and S, the lifetime of T being temperature dependent) and by a four-state mechanism (ground state, S, and three excited states in thermal equilibrium, T, T and S, all with temperature-independent lifetimes). The estimated S-T and T-T energy gaps (four-state mechanism) are in good agreement with spectroscopic measurements.

Functional Films from Silica/Polymer Nanoparticles.

High performance functional coatings, based on hybrid organic/inorganic materials, are being developed to combine the polymer flexibility and ease of processing with the mechanical properties and versatility of inorganic materials. By incorporating silica nanoparticles (SiNPs) in the polymeric matrices, it is possible to obtain hybrid polymer films with increased tensile strength and impact resistance, without decreasing the flexural properties of the polymer matrix. The SiNPs can further be used as carriers to impart other functionalities (optical, ) to the hybrid films.

Controlled release of singlet oxygen using diphenylanthracene functionalized polymer nanoparticles.

Functionalized polymer nanoparticles react and store molecular oxygen for several weeks in the form of endoperoxides. On-demand controlled release of singlet oxygen by the particles is achieved by thermolysis.

Photochemical properties of squarylium cyanine dyes.

This study presents several new squarylium dyes derived from benzothiazole and benzoselenazole with several structural variations, namely the nature of the heteroaromatic ring and the length of the N,N'-dialkyl groups. Before being investigated in connection with their effect on living cells and/or tissues, these novel compounds were characterized, namely with respect to the determination of their main photophysical parameters. Therefore, a study of the ground state absorption, fluorescence emission (quantum yields and lifetimes) and singlet oxygen generation quantum yields was performed for all the compounds synthesized in order to evaluate their efficiency as photosensitizers.

Methods for the analysis of complex fluorescence decays: sum of Becquerel functions versus sum of exponentials.

Ensemble fluorescence decays are usually analyzed with a sum of exponentials. However, broad continuous distributions of lifetimes, either unimodal or multimodal, occur in many situations. A simple and flexible fitting function for these cases that encompasses the exponential is the Becquerel function.

Portuguese tin-glazed earthenware from the 17th century. Part 1: pigments and glazes characterization.

Two sherds representative of the Portuguese faience production of the first and second halves of the 17th century were studied carefully with the use of non-invasive spectroscopies, namely: Ground State Diffuse Reflectance Absorption (GSDR), micro-Raman, Fourier-Transform Infrared (FT-IR), Laser Induced Luminescence (LIL) and Proton Induced X-ray (PIXE). These results were compared with the ones obtained for a Chinese Ming porcelain, Wanli period (16th/beginning of the 17th centuries), which served as an influence for the initial Lisbon's faience production. By combining information of the different non-destructive spectroscopic techniques used in this work, it was possible to conclude that: Co(3)O(4) (Co II and Co III) can be found in the silicate matrix and is the blue pigment in the "Especieiro" sample (1st half of the 17th C.

Surface photochemistry: alloxazine within nanochannels of Na+ and H + ZSM-5 zeolites.

This work reports the surface photochemistry study of alloxazine adsorbed within nanochannels of MFI zeolites, namely in a series of Na+ and H+ ZSM-5 zeolites where the hydrophobic and hydrophilic character of the host varies systematically. Laser-induced room temperature and 77 K luminescence of air-equilibrated solid powdered samples of alloxazine adsorbed onto the two sets of zeolites, which we will name NaZSM-5 and HZSM-5, revealed the existence of a single emission of alloxazine as a broad band centred at about 450 nm in some cases, while in others an emission with a maximum at about 510 nm was detected. The decay times of the alloxazine emission vary greatly going from solution to entrapment within the nanochannels of the ZSM-5 zeolites.

How fast is a fast equilibrium? A new view of reversible reactions.

Reversible reactions are described in terms of kinetic cycles. From this description, two useful parameters arise: 1) average cycle duration and 2) average number of cycles. The latter applies to cycles with at least one unstable species.