Uses of Near-Infrared Spectroscopy in Pharmaceutical Analysis

Abstract

Near-infrared (near-IR, NIR) spectroscopy has been a regularly used technique in agriculture and textile manufacturing for some years [1–61. However, the pharmaceutical industry has been slow to accept near-JR as an everyday analytical process. One reason may be its lack of primary absorption bands. All NIR absorbances are overtones of bands originating in the midrange infrared spectrum (4000–17000 nm). In addition, most of the near-JR spectrum of organic compounds (800–3500 nm) is attributable to combinations of the aforementioned over-tones. These “shortcomings” are more than compensated for by the attributes of near-IR instrumentation. Several excellent reviews have recently been published on the theory and instrumentation involved in near-IR reflectance analysis (NIRA) [7–10].     

Tuning the Solution Phase Photophysics of Two De Novo Designed Hydrogen Bond Sensitive 9-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-one Derivatives

Two new fluorophores, 6,7-dimethoxy-9-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-one (DMTCO) and 5-methyl-8,9-dihydro-5H-[1,3]dioxolo[4,5-b]carbazol-6(7H)-one (MDDCO), first of their kind, have been synthesized from the corresponding methoxy and methylenedioxy derivatives of 2,3,4,9-tetrahydro-1H-carbazol-1-one respectively. Comprehensive photophysical characterization of these compounds has been carried out in sixteen different homogeneous solvents and binary solvent mixtures. Both of these compounds are sensitive to solvent polarity, but the sensitivity is much higher in electronic excited state observed by steady-state and time-resolved fluorescence experiments than in ground state studied by UV–vis absorption spectroscopy. The fluorescence spectral shifts are linearly correlated with the empirical parameters of the protic solvents and also the quantitative influence of the empirical solvent parameters on the emission maxima of the compounds has been calculated. The change in dipole moment of the compounds in their excited state has been calculated from the shifts in corresponding emission maxima in pure solvents. A higher dipole moment change of both DMTCO and MDDCO in protic solvents is due to intermolecular hydrogen bonding which is further confirmed by the comparison of their behaviour in toluene-acetonitrile and toluene-methanol solvent mixtures. From structural features, MDDCO is more planar compared to DMTCO, which is reflected better in fluorescence quenching of the former with organic bases, N,N-dimethylaniline and N,N-diethylaniline. Laser flash photolysis experiments prove that the quenching interaction originates from photoinduced electron transfer from the bases to the compounds.     

Lattice dynamics of II–VI and III–V compounds

To study the lattice dynamics of II–VI and III–V compounds having zinc-blende structure in a model which incorporates three types of interactions: (i) central ion-ion forces (ii) bond-bending forces and (iii) long range Coulombic forces, has been developed. The model involves in total eight disposable parameters. The use of six critical point phonon frequencies, two elastic constants and the lattice equilibrium condition has been made to evaluate the consistent values of the parameters. The application of the present model has been made to calculate the phonon dispersion relations of ZnSe and InSb compounds. The comparison of theoretical results with the available experimental data has been made along the three symmetry directions [100], [110] and [111]. A reasonably good agreement is observed between theory and experiments.     

Application of Rapid Scanning Spectrometry to Atomic Spectroanalytical Analysis

Abstract

Determinations of metal content by single element atomic spectroscopy are well-established procedures in analytical laboratories. However, there has been considerable interest in methods for simultaneous multielement determinations as indicated by a recent review [1]. Correspondingly, much effort has been devoted to the development of detectors for multielement systems [2–8]. This review will report the application of rapid scanning spectrometers (RSS) to atomic spectroanalytical analysis. An instrument of this type can scan a selected wavelength window or region on a time scale ranging from a few microseconds to several seconds [4]. The scope of this review will be limited to RSS employing a mechanical means of rapid scanning, although much attention has been directed toward imaging devices such as the Vidicon tube and photodiode arrays [6–8]. The optical characteristics of the spectrometers, as well as the analytical results, will be discussed.     

On the Fate of Methanol and Ethanol in Cotton Plant

O-Methylester groups constitute a part in a variety of well-known organophosphorus insecticides. Such compounds, e.g. Dipterex and Rogor [1], were found to undergo in vivo [2–4] as well as in vitro [5]P—OCH₃ cleavage, thus liberating methanol. The degradation of methanol in mammals has been extensively studied [6, 7] and more recently its fate in the cotton leaf worm has been investigated [8].     

An electron paramagnetic resonance study of the tetragonally distorted [Formula: see text] ion in [Formula: see text] and [Formula: see text

Chromium-doped [Formula: see text] and [Formula: see text] have been studied by both EPR and ENDOR spectroscopy. [Formula: see text] ions enter the fluorite structure in distorted substitution cation sites. In both matrices the distortion observed is tetragonal. X- and Q-band EPR measurements at temperatures between 4 and 300 K allowed us to determine the ion symmetry and the following spin-Hamiltonian parameters: [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text]; and [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text]. For [Formula: see text], the weak superhyperfine interaction of [Formula: see text] with the surrounding [Formula: see text] ions has been studied by both EPR and ENDOR techniques for [Formula: see text]. No ENDOR signals were detected for [Formula: see text]. The results are tentatively explained in terms of a Jahn - Teller effect corresponding to [Formula: see text] coupling strongly stabilized by lattice stresses, although other possible origins for the distortion cannot be completely ruled out.     

Fiber-optic sensor based on evanescent wave absorbance around 2.7 μm for determining water content in polar organic solvents

The feasibility of sapphire fiber-optic sensors based on evanescent wave absorption spectroscopy in the infrared range for quantitative determination of water content in polar organic solvents has been investigated. Evanescent wave absorption spectra of sapphire fiber-optic sensors in glycerol, ethanol, and glycol with different water concentrations obtained and analyzed, respectively. Evanescent absorbance of the sensors in those organic solvents has been utilized to implement for in situ monitoring water concentration in organic solvents. The evanescent absorbance of sensors in glycerol and glycol has been found to vary linearly with water content in the range 0–30 % and in ethanol in the range 0–10 %, respectively. The fiber-optic sensors based on evanescent absorbance for monitoring water concentrations in those organic solvents are acceptably accurate, cost-effective, and reliable. Some methods to improve the accuracy of predicated water content in those organic solvents are also suggested. Overall, the results demonstrate that the sapphire fiber-optic sensor based on evanescent absorption spectroscopy is a promising candidate for prediction of water content in polar organic solvents in on-line and remote situation.     

Use of Hexafluoroacetone as an Analytical Tool for NMR

In recent years a number of papers have been published dealing with a new NMR technique which is useful for characterization of organic compounds which contain active hydrogen functional groups such as —OH, —NH₂, and -SH [1–6]. This method, which involves use of hexafluoroacetone (HFA) and ¹⁹F NMR, is very easy to use since no preliminary preparation of a derivative of the compound being studied is necessary. It has been found to be generally superior in convenience, range of applicability, and ability to distinguish between closely related compounds to other techniques for the study of reactive functional groups which have previously been reported [8–11].

The simple addition of a small amount (typically 1 to 5 mg) of the compound being studied to a solution of HFA in ethyl acetate at ambient temperature results in the in situ formation of a stable adduct according to the general equation     

Crazing in semicrystalline thermoplastics

The deformation processes in crystalline polymers have been studie ever since the discovery of chain folding in 1957. Since then, scientists have been intrigued by the different steps of the transformation of the folded-chain lamellar structure of single crystals or of macroscopically isotropic, often spherulitic, polymers into fibrous morphologies (see Refs. 1 and 2 for early reviews). The importance of molecular tilt, of inter- and intralamellar slip, and of micronecking were rapidly recognized [1–4]. In this paper, we discuss the analogies and differences with respect to crazing of glassy amorphous polymers. Obviously, there is an extensive body of literature on the micromechanics of crazing (see the reviews in Refs. 5–9). On the basis of these studies, it has been established that crazes in amorphous polymers are well-defined regions with approximately planar boundaries that extend perpendicular to the direction of maximum principal tensile stress and that contain highly stretched and voided material [7]. However, crazelike features have also been observed in many semicrystalline polymers (polyethylene [PE], isotactic polypropylene [IPP], isotatic polystyrene [IPS], polyoxymethylene [POM], polyamide 6 and 66 [PA6 and PA66], polycarbonate [PC], polyethylene terephthalate [PET], polybutylene terephthalate [PBT], polyvinylidene fluoride [PVDF], and polyether ether ketone [PEEK]). They are designated in the literature [3–10] as micronecks, true crazes, fibrillar deformation zones (DZs), or simply as crazes since they correspond well to the above definition.     

Research for improvement on the extract efficiency of lignans in traditional Chinese medicines by hybrid ionic liquids: As a case of Suhuang antitussive capsule

Recently, efficient extraction of natural products from traditional Chinese medicines (TCMs) by green solvents is deemed an essential area of green technology and attracts extensive attentions. In this work, a green protocol for simultaneous ultrasonic-extraction of the native compounds with different polarities of TCMs by using a hybrid ionic liquids (HILs)-water system was reported for the first time. As a case study, three superior ILs (1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]), and 1-allyl-3-methylimidazolium chloride ([AMIM]Cl)) were chosen as the compositions of the HILs system, and the TCMs Suhuang antitussive capsule (SH) containing different-polarity lignans was selected. Primarily, an ultra-performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry (UPLC-QqQ-MS/MS) method in the multiple reaction monitoring (MRM) mode was established for qualitative and quantitative analysis of 18 lignans. After majorization by uniform design experiment, the HILs prepared with [AMIM]Cl, [EMIM][BF4], and [EMIM][OAc] at a volume ratio of 1:5:5 could simultaneously extract multi-polarity lignans compared to single IL. Subsequently, the conditions of ultrasonic extraction employing with HILs and traditional organic solvent were optimized by the response surface methodology, respectively. The results indicated that the extract efficiency of the HILs system for target compounds was significantly improved compared with the traditional organic solvent-extraction, i.e. the content of total lignans in ethanol system was up to 47 mg/g, while that in the HILs system was up to 69 mg/g, with an increasing of 47%. Additionally, ¹H-NMR and ¹³C-NMR spectra were used to characterize the hydrogen-bond interactions in the HILs-lignan mixtures. Extraction with the HILs in TCMs is a new application schema of ILs, which not only avoids the use of volatile toxic organic solvents, but also shows the potential to be comprehensively applied for the extraction of bioactive compounds from TCMs.     

New concept of organic homo‐rank compounds and its application in estimating enthalpy of formation of mono‐substituted alkanes

Based on the topological characteristics of distance matrices and adjacency matrices of molecular graphs, a new concept of organic homo‐rank compounds was proposed. Based on this concept, compounds can be classified into new groups other than the traditional homologues. Furthermore, novel structure–property relationship approach named as homo‐rank compounds method can be developed. The feasibility of homo‐rank compounds method was explored by estimating the enthalpy of formation of organic compounds. The group contribution index (GCI_X) and group polarizability potential index (GPI_X) of substituents X were defined and determined for mono‐substituted alkanes RX (X includes 20 substituents). The research results show that the enthalpies of formation of organic homo‐rank compounds and their isomers can be correlated very well with the parameters GCI_X and GPI_X. Combining the method of homologues with that of homo‐rank compounds, a general and simple quantitative correlation equation (8) was established to estimate the enthalpy of formation for RX, and the calculation precision is within the chemical accuracy ‘1 kcal/mol’. For 242 samples of RX, the average absolute deviation between the experimental and the calculated values is 2.42 kJ/mol. In addition, the enthalpies of formation of more than 2800 samples of RX were estimated. The approaches of organic homo‐rank compounds and organic homologues are independent of but complementary to each other. The combination of these two methods can help us to understand the organic molecular structure–property relationships more deeply, and to investigate these relationships more conveniently and accurately. Copyright © 2015 John Wiley & Sons, Ltd.     

Automatic detection and branch switching methods for steady bifurcation in fluid mechanics

This paper deals with the computation of steady bifurcations in the framework of 2D incompressible Navier–Stokes flow. We first propose a numerical method to accurately detect the critical Reynolds number where this kind of bifurcation appears. From this singular value, we introduce a numerical tool to compute all the steady bifurcated branches. All these algorithms are based on the Asymptotic Numerical Method [1], [2]. The critical values are determined by using a bifurcation indicator [3], [4], [5] and the bifurcated branches are computed by using an augmented system which was first introduced in solid mechanics [4], [6]. Several numerical examples from 2D Navier–Stokes show the reliability and the efficiency of the proposed methods.     

Zn2+-胆红素络合物的超快激发态动力学研究

胆红素(Bilirubin, BR)是脊椎动物分解代谢血红素的最终产物之一,具有抗氧化和消炎等作用。体内保持正常含量的胆红素对人类的健康起着非常重要的作用,被认为有利于预防癌症、中风、糖尿病和心血管等疾病的发生[1-2]。然而胆红素过量则被认为是肝功能障碍的征兆,同时也是引起新生儿严重脑损伤的原因[3]。因此,对人体中胆红素含量的快速精准检测具有十分重要的应用价值。目前为止,用于检测血清样品中胆红素含量的方法主要有重氮法、过氧化物酶法、光纤传感检测法和荧光光谱法等[4]。其中,荧光光谱法具有检测迅速和操作简便的优势[5],吸引了越来越多研究人员的关注。但是,由于胆红素自身的荧光量子产率通常低至10-4量级[6],直接荧光测量难度很大,因此通常采用间接方式解决胆红素含量测量的难题。例如, Wabaidur等[7]通过胆红素猝灭Ru(bopy)2+₃荧光的方式来测量胆红素的含量;Aparna等[8]通过胆红素猝灭铜纳米团簇荧光的方式来测量胆红素的含量;Iwatani等[9]通过UnaG蛋白结合胆红素增强荧光的方式来测量胆红素的含量。UnaG与胆红素具有极高的亲和力,且自身几乎不发射荧光,其与胆红素结合后,会将胆红素的荧光提高三个数量级[10],可以用作人体内的荧光传感器[11]。然而,由于蛋白的制备和保存的成本十分高昂,人们更希望使用有机小分子或无机分子对胆红素的荧光进行增强。例如,Yang等[12]发现Zn2+有助于显著增强胆红素的荧光,Kotal等[13]提出了将Zn2+用于胆红素代谢物（尿胆素原）含量测量的方法。为了研究Zn2+增强胆红素荧光的机理并用于胆红素含量的测量,研究首先使用了稳态荧光光谱和紫外-可见吸收光谱表征了不同Zn2+浓度下胆红素的光学特性,并采用相对法测量了其量子产率。通过分析Zn2+-胆红素络合物在不同探测波长下的激发谱,提出了该络合物具有两个发光基团的设想。为了进一步验证关于发光基团的设想,使用了飞秒瞬态吸收光谱的手段研究分析了Zn2+-胆红素络合物的超快光动力学过程,分析结果与之前发表的对胆红素和Zn2+配位方式的结论有很好的吻合。根据瞬态吸收光谱和稳态荧光光谱的数据以及所提出的模型,得到了在有无Zn2+条件下胆红素的平均激发态寿命,进一步计算出了其辐射跃迁速率和非辐射跃迁速率的理论值。通过数据对比,得出了络合物相对单纯胆红素有更大的消光系数而具有更高的辐射跃迁速率的结论,同时发现胆红素与Zn2+的配位方式增加了胆红素以锥型交叉退激发态的效率。     

Excellence – energy – ethics

Dear pss readers, As the previous year approached its end, news on three excellent prize winnings and nominations of pss authors and editors reached us: Gerhard Abstreiter of TU Munich will receive the Stern–Gerlach Medal 2014, the highest prize of the German Physical Society for experimental physics, honoring his work on low‐dimensional electron systems in semiconductor hetero‐ and nanostructures. His Review@RRL on InGaAs nanowires on silicon is opening the 2014 volume of pss (RRL) [1]. It is a welcome addition to our recent successful Focus Issue on Semiconductor Nanowires [2]. Our long‐term Editorial Advisory Board member, Wiley author and Guest Editor, Rainer Waser of RWTH Aachen and Research Centre Jülich, is one of the 11 winners of the highly prestigious Leibniz Prize for his outstanding research on nanoelectronics, especially oxides, ferroelectrics and resistive switching [3, 4]. Last but not least, one of the three nominated teams for the German Future Prize has been led by Wolfgang Schnick , LMU Munich, and Peter J. Schmidt , Philips Lumileds Aachen. Their groundbreaking work on new phosphor materials in white light emitting diodes (LEDs) for solid‐state lighting [5] goes back to a highly‐cited pss (a) article from 2005 [6] (see figure). The technology is now being commercialized and expected to enable energy savings on a grand scale in the coming years. Speaking of energy, research results related to this global challenge have been important throughout the year, touching areas such as thermoelectrics [7], efficiency of organic LEDs [8] and photovoltaics [9]. The latter field is even better represented since the recent introduction of our section rrl solar, covering solar cell materials or device development and characterization (see Editorial [10]). The full‐paper sister journals pss (a) and (b) presented an unprecedented number of high‐profile special issues in 2013 [11–15]. With heartfelt gratitude we look back onto fruitful collaboration with highly engaged guest editors, who helped bring to light issues such as the “Advanced Concepts for Silicon Based Photovoltaics” [11], the “Quantum Criticality and Novel Phases” [12], the “Disorder in Order: A special issue on amorphous materials” [13], the “Substrate Interactions in Heterogeneous Catalysis” [14], and the “Quantum Transport at the Molecular Scale” [15] among other interesting topical issues and sections. Both contributors and fine articles are too numerous to do justice to all of them here. We must restrict ourselves to a general invitation to browse this content, only hinting a few possible starting points, such as topological insulators [16], molecular electronics [17] and quantum phase transitions [18].

     

Migration of triplet excitations of complex molecules in disordered media and in systems with a confined geometry

The paper presents the results of analysis of migration of a triplet excitation in inhomogeneous media such as mixed molecular crystals, solid solutions of organic compounds in low-molecular solvents and polymers, as well as porous matrices activated by complex molecules. The experimental data obtained under conditions of steady-state excitation and time resolution are analyzed within different approaches used for describing the energy transport in disordered systems.     

Aharonov–Bohm effects in magnetohydrodynamics

It is shown that an Aharonov–Bohm (AB) effect exists in magnetohydrodynamics (MHD). This effect is best described in terms of the MHD variational variables (Kats, 2004; Yahalom and Lynden-Bell, 2008; Yahalom, 2010) [1], [10], [12]. If a MHD flow has a non-trivial topology some of the functions appearing in the MHD Lagrangian are non-single-valued. These functions have properties similar to the phases in the AB celebrated effect (Aharonov and Bohm, 1959; van Oudenaarden et al., 1998) [2], [3]. While the manifestation of the quantum AB effect is in interference fringe patterns (Tonomura et al., 1982) [4], the manifestation of the MHD Aharonov–Bohm effects are through new dynamical conservation laws.     

Line Shape of Spontaneous Resonance Hyper-Raman Scattering of Intense Optical Fields

The splitting of the line of resonance scattered light from atomic systems, being a mong the most interesting phenomena in resonance nonlinear optics has received considerable attention during the past decade [1–11]. It is known by now that the number of lines into which the spontaneous scattered light spectrum splits, grows up with increasing the number N of strongly coupled atomic (or molecular) levels as N(N-1)+1 [10, 11]. But while the character of resonance fluorescence (RF) from a two- and three-level systems has been extensively studied [1–91], the number of papers devoted to the spectral structure of scattered light from systems with N>3 is scarce. In reality there is only one work [12], known to us, which treat s certain aspects of the spectrum of RF from a four-level system irradiated by three strong light fields at exact resonance.     

A charge-conservative approach for simulating electrohydrodynamic two-phase flows using volume-of-fluid

In the present study we propose a charge-conservative scheme to solve two-phase electrohydrodynamic (EHD) problems using the volume-of-fluid (VOF) method. EHD problems are usually simplified by assuming that the fluids involved are purely dielectric (insulators) or purely conducting. Gases can be considered as perfect insulators but pure dielectric liquids do not exist in nature and insulating liquids have to be approximated using the “Taylor–Melcher leaky dielectric model” [1], [2] in which a leakage of charge through the liquid due to ohmic conduction is allowed. It is also a customary assumption to neglect the convection of charge against the ohmic conduction. The scheme proposed in this article can deal with any EHD problem since it does not rely on any of the above simplifications. An unrestricted EHD solver requires not only to incorporate electric forces in the Navier–Stokes equations, but also to consider the charge migration due to both conduction and convection in the electric charge conservation equation [3]. The conducting or insulating nature of the fluids arise on their own as a result of their electric and fluid mechanical properties. The EHD solver has been built as an extension to Gerris, a free software solver for the solution of incompressible fluid motion using an adaptive VOF method on octree meshes developed by Popinet [4], [5].     

A gradient stable scheme for a phase field model for the moving contact line problem

In this paper, an efficient numerical scheme is designed for a phase field model for the moving contact line problem, which consists of a coupled system of the Cahn–Hilliard and Navier–Stokes equations with the generalized Navier boundary condition [1], [2], [4]. The nonlinear version of the scheme is semi-implicit in time and is based on a convex splitting of the Cahn–Hilliard free energy (including the boundary energy) together with a projection method for the Navier–Stokes equations. We show, under certain conditions, the scheme has the total energy decaying property and is unconditionally stable. The linearized scheme is easy to implement and introduces only mild CFL time constraint. Numerical tests are carried out to verify the accuracy and stability of the scheme. The behavior of the solution near the contact line is examined. It is verified that, when the interface intersects with the boundary, the consistent splitting scheme [21], [22] for the Navier Stokes equations has the better accuracy for pressure.     

Second-Order Data Obtained by Time-Resolved Room Temperature Phosphorescence. A New Approach for PARAFAC Multicomponent Analysis

A second-order multivariate calibration approach, based on a combination of PARAFAC with time-resolved room temperature phosphorescence (RTP), has been applied to resolve a binary mixture of Phenanthrene and 1,10-Phenanthroline, as model compounds. The RTP signals were obtained in aqueous β-cyclodextrin solutions, in the presence of several heavy atom containing compounds. No deoxygenation was necessary to obtain the phosphorescence signals, which adds simplicity to the method. The resolution of the model compounds was possible in base to the differences in the delay-time of the RTP signals of the investigated analytes, opening a new approach for second-order data generation and subsequent second order multivariate calibration.