Multivariate statistical analysis of mid-infrared spectra for a G1 allyl-terminated carbosilane dendrimer

doi:10.1016/j.saa.2012.02.090

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Volume 92, 15 June 2012, Pages 398-405

https://doi.org/10.1016/j.saa.2012.02.090 Get rights and content

Abstract

The FTIR spectra were measured for G1 allyl terminated carbosilane dendrimer over a temperature range of 25–200 °C to explore the temperature-dependent changes. The dendrimer spectra exhibited complicated patterns and thus were analyzed by both the exploratory principal component analysis (PCA) and two-dimensional (2D) correlation spectroscopy. Boltzmann fitting and score plots of PCA evidenced the phase transition temperature to be about 172 °C. Frequency variables, which strongly contributed to each principal component highlighted in their loadings plot, were linked to the frequencies assigned to vibrations of the CH₂ and CH₃ groups, as well as to vibrations of the SiCH groups. 2D correlation spectroscopy discerned all the sequences of group motion of dendrimer, indicating that during the heating process a reorganization of core structure takes place, followed by a conformational rearrangement of the terminal units.

Graphical abstract

Highlights

► New G1 allyl-terminated carbosilane dendrimer is characterized. ► FT-IR spectroscopy, PCA and 2D correlation spectroscopy were used to study the microstructural changes occurring at heating. ► The effect of temperature as a perturbing parameter gives new information about its effect on the structure and dynamics of macromolecular systems.

Introduction

The synthesis, modification, and possible application areas of diverse dendrimers and hyperbranched polymers have been intensively studied in the past decade owing to their unique structure and specific characteristics [1], [2]. Nowadays, particular attention is paid to the characterization of dendrimers since a deeper inside is necessary to understand the structure–properties relationship for these compounds. Thermal analysis methods find a wide range of current applications in pharmaceutical industry, for the design of new molecules, control of raw materials, stability, compatibility studies and development of new formulations.

Infrared (IR) spectroscopy is one of the most common spectroscopic techniques used by organic and inorganic chemists. Simply, it consists in the measurement of the absorption of different IR frequencies by a sample positioned in the path of an IR beam. Vibrational frequencies are very sensitive to small changes in the bonding and geometrical arrangement of atoms in molecules. Fourier transform infrared (FT-IR) spectroscopy offers the accessibility to intermolecular interactions in such systems, real-time conformational and structural changes during temperature variations, and orientational behavior. IR spectra are rather complicated because they contain many overlapping bands that cannot be differentiated exactly.

The principal component analysis (PCA) is a well-established technique in statistics and chemometrics that gives a precise mathematical estimation of changes along the object and variable vectors. PCA is the data mining method which reduces data dimensionality by redefining the axes so that they correspond with the directions of most variances, where these new axes or principal components (PCs) correspond with the eigenvectors of the original data's covariance matrix. By converting the data into the dimensionally reduced PCA space, the input data set is decomposed into two matrices of interest: scores and loadings. The loadings matrix defines the new axes of the dimensionally reduced data set, while the scores matrix describes the samples in the PC space. The use of a multivariate analysis with polymer systems has been limited. With PCA, the most important features of the FTIR spectra can be identified, and the peak shifts and non-symmetries in the peaks between the samples can be quickly determined.

Generalized 2D correlation spectroscopy, which was originally proposed by Noda in 1993, has been developed for the analysis of perturbation-induced spectral variations [3], [4], [5]. The basic concept of 2D correlation spectroscopy is the analysis of synchronicity and asynchronicity of the dynamic spectra, which are induced by an applied external perturbation. Namely, simultaneous or sequential changes of spectral intensities measured at different variables, i.e. wavenumbers during the application of the perturbation can be derived as synchronous or asynchronous correlations. So far, 2D correlation spectroscopy studies have been carried out for numerous types of perturbations such as temperature [6], [7], [8], [9], concentration [10], [11], [12], [13], [14], pH [15], [16], and pressure [17], [18]. One of the most important points of 2D correlation analysis lies in the fact that it is applicable to various types of systems as long as an external perturbation is described as a specific function.

In the present study, a first generation allyl-terminated carbosilane dendrimer was investigated by FTIR, PCA and 2D IR correlation spectroscopy. The sequential order of changes in the molecular environment and conformations of the functional groups was evidenced.

Section snippets

Materials

The dendrimer used is a first generation allyl-terminated carbosilane dendrimer (Fig. 1). The generation is attributed to the number of silicon shells instead of the branching degree. It has been synthesized at the University of Alcalá, according to reported methods [19], [20], and has the following characteristics: chemical formula C₄₀H₇₆Si₅; ¹H NMR (CDCl₃): δ = 1.29 ppm (attributed to the middle CH₂ group of the branch single bond SiCH2CH2CH2Si) and 0.57 ppm (assigned to the CH₂ groups directly bonded to

FT-IR spectra

The IR spectra of the studied dendrimer are shown in Fig. 2. In the 2700–3150 cm⁻¹ region, assigned to stretching vibrations of CH bonds, three strong bands at 2880, 2911, and 2952 cm⁻¹, two weak bands at 3076 and 2792 cm⁻¹ and two shoulders at 2993 and 2966 cm⁻¹ are observed.

The positions of the ν_as(CH₂) and ν_s(CH₂) bands are sensitive to the conformation of hydrocarbon chains [22]. If a hydrocarbon chain is in a solid crystalline state with all-trans conformation, the peaks of the ν_as(CH₂) and ν_s

Conclusions

The present study demonstrated that IR spectroscopy coupled with PCA and 2D correlation spectroscopy represent powerful tools in analyzing the structure and properties of the carbosilane dendrimer. A detailed classification of the frequencies was realized by combining the PCA method with 2D correlation spectroscopy.

The modifications occurred in the 3100–2700 cm⁻¹ and 1600–400 cm⁻¹ spectral regions and revealed the conformational and/or structural changes with temperature.

The dependencies of band

Acknowledgments

This study was financially supported by European Social Fund – “Cristofor I. Simionescu” Postdoctoral Fellowship Programme (ID POSDRU/89/1.5/S/55216), Sectoral Operational Programme Human Resources Development 2007–2013.

References (29)

L.-X. Wang et al.
J. Mol. Struct.
(2006)
H. Shinzawa et al.
J. Mol. Struct.
(2006)
M.C. Popescu et al.
Spectrochim. Acta. A. Mol. Biomol. Spectrosc.
(2011)
S. Ma et al.
J. Mol. Struct.
(2006)
L. Smeller et al.
Vib. Spectrosc.
(1999)
I. Noda et al.
Vib. Spectrosc.
(1999)
H.S. Shin et al.
Vib. Spectrosc.
(2005)
V.L. Furer et al.
Spectrochim. Acta A
(2008)
D.A. Tomalia et al.
Angew. Chem. Int. Ed. Engl.
(1990)
G.R. Newkome
Advances in Dendritic Macromolecules
(1994)

I. Noda

Appl. Spectrosc.

(1993)

I. Noda

Appl. Spectrosc.

(2000)

I. Noda et al.

Two-dimensional Correlation Spectroscopy

(2004)

M.-C. Popescu et al.

J. Phys. Chem. B

(2006)

Cited by (8)

Flotation separation of chalcopyrite from molybdenite with sodium thioglycolate: Mechanistic insights from experiments and MD simulations
2024, Separation and Purification Technology
The pivotal roles of Cu and Mo in industrial applications accentuate the importance of effectively separating and recovering chalcopyrite and molybdenite. They commonly exist together in natural environments, necessitating their segregation prior to engaging in smelting processes. The separation is mainly accomplished through flotation. The inadequate comprehension of the mechanisms of thiol depressants, commonly used in the separation of chalcopyrite and molybdenite, poses challenges to both resource recovery and the development of depressants. Based on the bulk flotation practice of copper-molybdenum sulfide minerals, this study investigated the separation effect and mechanism of sodium thioglycolate (STG) on xanthate-treated chalcopyrite and molybdenite. Flotation and contact angle tests validate that STG enhances the hydrophilicity of chalcopyrite surfaces, leading to an 83.79% flotation separation efficiency for molybdenite. Various methodologies were employed to explore the mechanism of the depressant, encompassing open-circuit potential measurements, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, infrared and ultraviolet spectroscopy, time-of-flight secondary ion mass spectrometry, classical molecular dynamics and ab initio molecular dynamics simulations. The stable adsorption layer of STG is established by the interaction of thiol groups from STG with Cu and Fe sites on the chalcopyrite surface, resulting in the formation of Cu(I)-S and Fe(III)-S structures. The adsorption density of STG layer on the chalcopyrite surface is four times greater than that on molybdenite. Additionally, following the adsorption of STG, the previously adsorbed xanthate chalcopyrite surface is desorbed with an efficiency of 65.88%. These findings contribute to the elucidation of the mechanistic understanding of thiol-containing depressants in the flotation separation process of copper-molybdenum sulfide minerals and establish a basis for the prospective advancement of mineral processing reagents.
Calorimetric and infrared studies of carbosilane dendrimers of the third generation with ethyleneoxide terminal groups
2015, Thermochimica Acta
In the present work, temperature dependences of heat capacities of carbosilane dendrimers of the third generation with ethyleneoxide terminal groups, denoted as G3[(OCH₂CH₂)₁OCH₃]₃₂ and G3[(OCH₂CH₂)₃OCH₃]₃₂, have been measured in the temperature ranges from T = 6 to 520 K by precision adiabatic calorimetry (AC) and differential scanning calorimetry (DSC). In the above temperature range the physical transformations, such as glass transition and anomalies, have been detected, and their standard thermodynamic characteristics have been determined and analyzed. Complementary temperature-dependent infrared (IR) studies of carbosilane dendrimer G3[(OCH₂CH₂)₁OCH₃]₃₂ have been performed in the range from T = 4 to 298 K in order to study the nature of the revealed transformations. The standard thermodynamic functions of dendrimers under study, namely, heat capacity $C_{p}^{0} (T)$ , enthalpy H°(T) − H°(0), entropy S°(T) − S°(0), and Gibbs energy G°(T) − H°(0) have been calculated for the range from T → 0 to 520 K. The standard thermodynamic properties of the investigated dendrimers have been discussed and compared with literature data for carbosilane dendrimers with different functional terminal groups.
Frontiers of two-dimensional correlation spectroscopy. Part 1. New concepts and noteworthy developments
2014, Journal of Molecular Structure
Citation Excerpt :
Park et al. [74] used PCA to guide the way that dataset is segmented in the study of temperature effect on self-assembled thin films. In a similar manner, Popescu and Simionescu [75] used PCA scores to segment the temperature dependent IR spectra. Tang et al. [76] also used PCA scores to segment data blocks.
A comprehensive survey review of new and noteworthy developments, which are advancing forward the frontiers in the field of 2D correlation spectroscopy during the last four years, is compiled. This review covers books, proceedings, and review articles published on 2D correlation spectroscopy, a number of significant conceptual developments in the field, data pretreatment methods and other pertinent topics, as well as patent and publication trends and citation activities. Developments discussed include projection 2D correlation analysis, concatenated 2D correlation, and correlation under multiple perturbation effects, as well as orthogonal sample design, predicting 2D correlation spectra, manipulating and comparing 2D spectra, correlation strategy based on segmented data blocks, such as moving-window analysis, features like determination of sequential order and enhanced spectral resolution, statistical 2D spectroscopy using covariance and other statistical metrics, hetero-correlation analysis, and sample–sample correlation technique. Data pretreatment operations prior to 2D correlation analysis are discussed, including the correction for physical effects, background and baseline subtraction, selection of reference spectrum, normalization and scaling of data, derivatives spectra and deconvolution technique, and smoothing and noise reduction. Other pertinent topics include chemometrics and statistical considerations, peak position shift phenomena, variable sampling increments, computation and software, display schemes, such as color coded format, slice and power spectra, tabulation, and other schemes.
Frontiers of two-dimensional correlation spectroscopy. Part 2. Perturbation methods, fields of applications, and types of analytical probes
2014, Journal of Molecular Structure
Citation Excerpt :
Jing and Wu [232] studied the temperature-induced coil-to-globule and sol–gel phase transitions of hydroxypropylcellulose aqueous solution by 2D IR and NIR. Popescu and Simionescu [226] reported the 2D IR study of the phase transition of allyl-terminated carbosilane dendrimer. Sui et al. [131] applied 2D correlation to derivative thermogravimetry to study the decomposition reaction of polyester–urethane adhesive with different doses of γ-ray irradiation.
Noteworthy experimental practices, which are advancing forward the frontiers of the field of two-dimensional (2D) correlation spectroscopy, are reviewed with the focus on various perturbation methods currently practiced to induce spectral changes, pertinent examples of applications in various fields, and types of analytical probes employed. Types of perturbation methods found in the published literature are very diverse, encompassing both dynamic and static effects. Although a sizable portion of publications report the use of dynamic perturbatuions, much greater number of studies employ static effect, especially that of temperature. Fields of applications covered by the literature are also very broad, ranging from fundamental research to practical applications in a number of physical, chemical and biological systems, such as synthetic polymers, composites and biomolecules. Aside from IR spectroscopy, which is the most commonly used tool, many other analytical probes are used in 2D correlation analysis. The ever expanding trend in depth, breadth and versatility of 2D correlation spectroscopy techniques and their broad applications all point to the robust and healthy state of the field.
A near infrared spectroscopic study of the structural modifications of lime (Tilia cordata Mill.) wood during hydro-thermal treatment
2013, Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
Citation Excerpt :
The 2D correlation spectroscopy can also discern the specific order taking place under external perturbation. For simplifying the Noda’s rule, the relatively straightforward method proposed by Sun et al. [27,28] was used. Using this approach, (see Table 2).
The modifications and/or degradation of lime (Tillia cordata) wood components during wood heat treatment under low temperature at about 140 °C and 10% percentage of relative humidity were evaluated. The aim of this study was to obtain results by simple NIR coupled with second derivative, principal component analysis and two dimensional correlation spectroscopy in order to better understand how these techniques are able to evaluate structural differences resulted under hydro-thermal treatment of the wood over a period of 504 h. The NIR spectra of treated samples were compared with the reference one. Due to the broad bands in the NIR spectra, the assignment and modifications occurring during treatment is difficult, therefore the second derivative principal component analysis were applied. Principal component analysis by first two components was able to differentiate the samples series, PC1 being considered as the time axis, and PC2 as the axis representing the structural modification of wood components.
2D NIR correlation spectroscopy was able to estimate the sequential order of the groups variations under the hydro-thermal treatment time as external perturbation, indicating as first moment changes the OH and CO groups from carbohydrates and lignin, followed by C_arH, CH and CH₂ groups from lignin, cellulose and hemicelluloses.
Analysis of alkali ultrasonication pretreatment in bioethanol production from cotton gin trash using FT-IR spectroscopy and principal component analysis
2014, Bioresources and Bioprocessing

View all citing articles on Scopus

View full text

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Multivariate statistical analysis of mid-infrared spectra for a G1 allyl-terminated carbosilane dendrimer

Abstract

Graphical abstract

Highlights

Introduction

Section snippets

Materials

FT-IR spectra

Conclusions

Acknowledgments

J. Mol. Struct.

J. Mol. Struct.

Spectrochim. Acta. A. Mol. Biomol. Spectrosc.

J. Mol. Struct.

Vib. Spectrosc.

Vib. Spectrosc.

Vib. Spectrosc.

Spectrochim. Acta A

Angew. Chem. Int. Ed. Engl.

Advances in Dendritic Macromolecules

Appl. Spectrosc.

Appl. Spectrosc.

Two-dimensional Correlation Spectroscopy

J. Phys. Chem. B

Flotation separation of chalcopyrite from molybdenite with sodium thioglycolate: Mechanistic insights from experiments and MD simulations

Calorimetric and infrared studies of carbosilane dendrimers of the third generation with ethyleneoxide terminal groups

Frontiers of two-dimensional correlation spectroscopy. Part 1. New concepts and noteworthy developments

Frontiers of two-dimensional correlation spectroscopy. Part 2. Perturbation methods, fields of applications, and types of analytical probes

A near infrared spectroscopic study of the structural modifications of lime (Tilia cordata Mill.) wood during hydro-thermal treatment

Analysis of alkali ultrasonication pretreatment in bioethanol production from cotton gin trash using FT-IR spectroscopy and principal component analysis