Selectivity – the hallmark of an analytical chemist: the current situation in the analytical sciences

In the scientific analytical chemical literature there is a problem in that there is a mix up of the two terms ”selectivity” and ”specificity” as indicators of the degree of interferences in analytical methods. This article gives an overview of the situation in the field of analytical sciences and ends with some recommendations in favour of using the term ”selectivity” only.     

Role of solvents in the gelation process: can light scattering studies shed some light?

Sol–gel reactions continue to be of interest for the preparation of nanostructured materials. Two chemical reactions that are important in the sol–gel process are the hydrolysis and condensation reactions. The rate of the these two reactions are affected by a number of factors such as reaction pH, temperature, humidity, amount of water, type of alkoxide, molar ratio of alkoxide to water, and nature of solvent. Moreover, there is a physical process, that of particle aggregation that is also important in the overall gelation process. The role of solvents in these chemical and physical processes is still not very clear. In order to clarify the role of solvents in the gelation process, small angle light scattering studies (SALS) were carried out. A model system chosen was a colloidal silica solution that contained preformed silica particles of 10–15 nm in diameter. SALS studies indicate that gelation times are independent of the nature of solvent.     

Features of molecular light scattering and structure of the chlorobenzene–o-dichlorobenzene solutions

Structural Chemistry - The total light scattering coefficient, degree of depolarization, refractive index, and density were measured in chlorobenzene–o-dichlorobenzene solutions. The...     

Asymmetrical flow field-flow fractionation with multi-angle light scattering and quasi elastic light scattering for characterization of poly(ethyleneglycol-b-ɛ-caprolactone) block copolymer self-assemblies used as drug carriers for photodynamic therapy

Poly(ethyleneoxide-b-?-caprolactone) (PEO-b-PCL) self-assemblies in water were characterized by asymmetrical flow field-flow fractionation (AsFlFFF), with on-line coupling with quasi-elastic light scattering (QELS), multi-angle light scattering (MALS), refractive index and UV/Vis detection. We report here the AsFlFFF analysis of three different nanoparticular self-assembled systems of PEO-PCL polymers in aqueous media, each polymer differing by the mass of the PEO and PCL fragments. Thus, self-assembled water samples of {PEO(2000)-b-PCL(2600)}, {PEO(5000)-b-PCL(1400)} and {PEO(5000)-b-PCL(4000)} were analyzed by AsFlFFF. In most cases, the size obtained by AsFlFFF was similar to the one characterized by DLS. However, in some instances, only AsFlFFF revealed the presence of several self-assemblies with very different sizes. These nanoparticles being used for the targeted delivery of photosensitizers in photodynamic therapy, it was important to fully characterize the samples in terms of size and size distribution, molecular weight, Ip, aggregation number and also to assess whether the photosensitizer was inside the nanoparticles. AsFlFFF proved to be a very efficient technique which enabled this study without any destruction of the nanoparticles.     

Dielectric response and quasielastic light scattering on freely suspended films of the SmC * α phase in an external transverse electric field

A theoretical analysis of dynamic properties of freely suspended films of a SmC^* _α phase in an external electric field is performed within the ‘clock’ model, where the interactions up to nextnearest neighbours are considered. It is shown, that for an N-layer film, N amplitude and N phase fluctuation modes are present. The relaxation rates of the amplitude modes are in the MHz region, whereas the phase modes are typically in the kHz region. Magnitudes of the dielectric response and quasielastic light scattering cross-sections for individual modes are calculated as a function of an electric field applied along the smectic layers.     

Traceability in measurement – time for an update?

 The present international definition of "traceability" is discussed and suggestions are made for a possible refinement of the definition.     

A supramolecular polymerisation model for the structurisation of DNA–lipid complexes

Complexes formed by DNA and lipid mixtures have great interest for the assessment of self-assembling mechanisms in open biological systems. X-ray diffraction has revealed that minor alterations of the cationic/neutral lipid composition produced major alterations to the liquid crystalline structure and the hydration of the complexes. We have extended to these systems by an approach based on the identification of a fundamental repeating unit that grows according to the general principles of supramolecular polymerisation and liquid crystallinity. Structural reorganisations that optimise the electrostatic and hydrophobic compensation are enhanced by competition between the rigidity of the polyelectrolyte and the cohesion of the lipid assembly. The non-hydrated hexagonal structure revealed by X-ray examination is represented by a dendritic-type supramolecular polymerisation of DNA units decorated by the aliphatic tails of dissociated liposomes. An increase in the cationic/neutral lipid component ratio enhances the stability of planar bilayers, favouring the formation of the partly hydrated lamellar structure revealed by X-ray diffraction.     

Advances in the determination of hindered amine light stabilizers – A review

Within this paper we discuss analytical strategies for the characterization and quantitation of hindered amine light stabilizers (HALS) an important sub-group of polymer additives. For the determination of monomeric HALS a range of mature and reliable techniques exists, allowing their determination in polymer extracts. If qualitative or semi-quantitative information suffices, certain techniques are capable of sampling directly from the polymer surface with limited or no sample preparation. Different strategies for the determination of complex oligomeric HALS in extracts from polymer samples are discussed. Here, approaches providing only a sum parameter including all HALS oligomers have been distinguished from more sophisticated technologies allowing the determination of single oligomers, their degradation and by-products. Particularly, the latter issue is facing increased interest as it provides important information for polymers aging studies. A tabulated overview provides comprehensive information on different analytical techniques suitable for HALS determination.     

Can the light scattering depolarization ratio of small particles be greater than 1/3?

According to the theory of light scattering by small randomly oriented particles, the depolarized ratio of the scattered intensities, I(vh)/I(vv), cannot exceed 1/3. Here we show that this conclusion does not hold for nonspherical plasmon resonant metal particles. Our analysis is based on the Rayleigh approximation and the exact T-matrix method as applied to spheroids and circular cylinders with semispherical ends. For small particles, the condition I(vh)/I(vv) >1/3 can be satisfied within the upper left quadrant of the complex relative dielectric permeability Real(eps) < -2 (rods) and within the upper unit semicircle centered at Real(eps) = -1 (disks). For gold nanorods with the axis ratio exceeding 2, the maximal theoretical values I(vh)/I(vv) lie between 1/3 and 3/4 at wavelengths of 550-650 nm. The extinction and static light scattering spectra (450-850 nm, at 90 degrees degrees) as well as the depolarized ratio of He-Ne laser light scattering were measured with gold nanospheres (the average diameters of 21, 29, and 46 nm) and nanorods (the longitudinal plasmon resonance peak positions at 655, 692, and 900 nm). The measured depolarization ratios of nanospheres (0.07-0.16) and nanorods (0.3-0.48) are in good agreement with theoretical calculations based on estimations of the average particle size and shape.     

Iranian chemist’s efforts to provide various effective methods for the synthesis of xanthenes

Xanthenes and their derivatives as very important classes of organic compounds are key structural elements of many biologically active compounds. These materials are important heterocyclic nucleus of various dyes and drugs. Because of their wide range of pharmacological, industrial and synthetic applications, many methods for the preparation of xanthenes are reported in the literature. In recent years, among the other chemists, introduction of new methods for the preparation of these types of compounds has attracted the attention of Iranian chemists. The result of these efforts is the introduction of appropriate, effective and efficient methods. In this paper, we have a brief review on these methods and their main advantages and important applicabilities.     

Primary reference materials for chemical composition analysis – Proposal for an operational definition

A metrologically motivated concept of a "Primary reference material (PRM)" for chemical composition analysis is proposed. This concept turns out to be essentially equivalent to that of a "Certified reference material (CRM)", as described in the relevant ISO Guides. Since the majority of actually available CRMs are far from realizing the theoretical concept, it is proposed to re-name and moderately revise the theoretical concept and to give it a new try to be put into practice.     

Requirements of the glow discharge techniques to the fundamentals – an exemplary approach

The importance of gaining knowledge on the fundamental processes in glow discharges in the field of the signal generation, the sputtering phenomena taking place in the case of solids and the analyte breakdown in the excitation of gases is treated. For gaining more knowledge on the plasma processes diagnostics including temperature and electron number density as well as gas and analyte atom and ion densities are required. For the sputtering process, it is shown at the hand of measurements with gas-jet enhanced sputtering and magnetically enhanced sputtering that selective sputtering may occur and that the influence of the analyte loading of the glow discharge plasma needs further study. For the case of the introduction of gaseous samples, the analyte distribution as well as the break-down mechanisms and kinetics in the case of molecular species ask for further study as shown by experiments with gas-sampling glow discharges.     

Determination of triadimenol based on the quenching effect on resonance light scattering from the triadimenol–deoxyribonucleic acid–hydrochloric acid system

Analysis of triadimenol was carried out using deoxyribonucleic acids (DNA) via the resonance light scattering (RLS) technique. After adding triadimenol into aqueous medium of pH 1.72, the RLS of DNA was remarkably quenched. A resonance light scattering peak at 310 nm was found, and the quenched intensity of RLS at this wavelength was proportional to the concentration of triadimenol. The linear range of the calibration curve was approximately 0–3 μg mL⁻¹ with a detection limit (S/N = 3) of 0.07 μg mL⁻¹. The triadimenol in samples of water, cucumber and human serum was determined. The results were satisfactory, and the recovery rates were in the range of 96.3–106.0%, 94.8–105.9% and 92.3–100.5%, respectively. The interaction mechanism was also studied.     

Intermolecular interactions and electrostatic properties of the β-hydroquinone apohost: implications for supramolecular chemistry

The crystal structure of the β-polymorph of hydroquinone (β-HQ), the apohost of a large family of clathrates, is reported with a specific focus on intermolecular interactions and the electrostatic nature of its cavity. Hirshfeld surface analysis reveals subtle close contacts between two interconnecting HQ networks, and the local packing and related close contacts were examined by breakdown of the fingerprint plot. An experimental multipole model containing anisotropic thermal parameters for hydrogen atoms has been successfully refined against 15(2) K single microcrystal synchrotron X-ray diffraction data. The experimental electron density model has been compared with a theoretical electron density calculated with the molecule embedded in its own crystal field. Hirshfeld charges, interaction energies and the electrostatic potential calculated for both models are qualitatively in good agreement, but small differences in the electrostatic potential persist due to charge transfer from all hydrogen atoms to the oxygen atoms in the theoretical model. The electrostatic potential in the center of the cavity is positive, very shallow and highly symmetric, suggesting that the inclusion of polar molecules in the void will involve a balance between opposing effects. The electric field is by symmetry zero in the center of the cavity, increasing to a value of 0.0185 e/?(2) (0.27 V/?) 1 ? along the 3-fold axis and 0.0105 e/?(2) (0.15 V/?) 1 ? along the perpendicular direction. While these values are substantial in a macroscopic context, they are quite small for a molecular cavity and are not expected to strongly polarize a guest molecule.     

Bengal gram seed husk as an adsorbent for the removal of dyes from aqueous solutions – Column studies

A continuous fixed bed (column) study was carried out by using seed husk of Bengal gram (Cicer arietinum) (SHBG) as a biosorbent for the removal of direct dye, Congo red (CR) from aqueous solutions. The effects of important factors, such as the value of initial pH, the flow rate, the influent concentration of CR, bed depth, particle size of SHBG, foreign ions and regeneration of CR were studied. The effect of similar type of direct dyes like direct turquoise blue 86 (DTB) and direct black 38 (DB) on the adsorption of CR in column containing SHBG is also studied by keeping other parameters constant. The studies confirmed that the breakthrough curves were dependent on flow rate, initial dye concentration, size of SHBG, initial pH of solution of CR and bed depth. The bed depth service time analysis (BDST) model was applied at different bed depths to predict the breakthrough curves. The model is found suitable for describing the biosorption process of the dynamic behaviour of the SHBG column and the data were in good agreement with BDST model. When the flow rate was 0.67 mL/min and the influent concentration of CR was mg L⁻¹, the column capacity was 6.572 mg g⁻¹. The removal capacity of SHBG was more in case of CR (6.572 mg g⁻¹) compared to other similar direct dyes of DTB (1.984 mg g⁻¹) and DB (1.612 mg g⁻¹). The removal of CR was enhanced in the presence of foreign ion potassium (8.308 mg g⁻¹) and decreased in the presence of calcium (5.58 mg g⁻¹). 120 ml of acetone is required for the completion of regeneration of the column and the total amount of CR recovered in this case. All the results suggested SHBG as a potential adsorbent for removal of CR from aqueous solution so that the rate of bio-sorption process is rapid.     

The light at the end of the tunnel—second generation HPMA conjugates for cancer treatment

It is almost four decades since N-(2-hydroxypropyl)methacrylamide (HPMA)-based copolymers arose as drug carriers. Although fundamentals have been established and significant advantages have been proved, the commercialization of this platform technology was hampered due to modest outcome of clinical trial initiated with PK1, the symbol of first generation polymer-drug conjugates. In this review, we illustrate the exciting progress and approaches offered by more effective 2nd generation HPMA-based polymer-drug conjugates in cancer treatment. For example, a new synthetic strategy endorses inert HPMA polymer with biodegradability, which permitted to prepare high molecular weight HPMA-drug conjugates with simple linear architecture while maintaining good biocompatibility. As expected, extended long-circulating pharmacokinetics and enhanced antitumor activities were achieved in several preclinical investigations. In addition, greater inhibition of tumor growth in combination regimes exhibits the remarkable capability and flexibility of HPMA-based macromolecular therapeutics. The review also discusses the main challenges and strategies for further translation development of 2nd generation HPMA-based polymer-drug conjugates.     

Model to describe light scattering by polymer film containing droplets with inhomogeneous anchoring of liquid crystal molecules at the polymer–droplet interface: asymmetry effect in the angular distribution of light

A model to describe light scattering by polymer film containing of monolayer of liquid crystal droplets with inhomogeneous anchoring of liquid crystal molecules at the polymer-droplet interface is developed. It is based on the interference approximation of the wave scattering theory. The director field distribution in the droplet volume is determined by solving the free energy density minimization problem using the relaxation method. The spatial distribution of droplets in the layer is described by the hard disks model. The amplitude scattering matrices of individual droplets are found in the anomalous diffraction approximation. The algorithm for numerical analysis of the characteristics of light scattered in a polymer film containing droplets at homogeneous and inhomogeneous surface anchoring is described in terms of the partial filling factors of the monolayer film. Electrically controllable symmetry breaking effect of angular distribution of light scattered by films containing droplets with inhomogeneous anchoring at the polymer-droplet interface is described and experimentally confirmed.