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The first and second dissociation constants of amino acids (glycine, L-proline, L-valine, α-alanine, β-alanine, L-asparagine, L-methionine, L-leucine, L-threonine, L-glutamine, L-serine and L-histidine) were determined pH-metrically In water + urea (0-8 M urea) mixtures at 298 K. Solubilities of amino acids in water + urea mixtures and the interaction constants of amino acids with urea were also determined pH-metrically. The Gibbs energies of transfer ΔG0tt (1) and ΔG 0 t, (2) for the reactions, RH2 + + H2O ⇌ RH± + H3O+ (1) and RH± + H2O ⇌ R- + H3O+ (2) were coupled with Gibbs energies of transfer for neutral amino acids [ΔG 0 t(RH±) and H+-ions [ΔG 0, (H+)] (determined previously) to get the Gibbs energies of transfer of RH2 + [ΔG0 t (RH2 +)] and R- [ΔG0, (R -)] from water to water+urea mixtures. ΔG0 t (H+) were also calculated directly and utilized. ΔG0 t(RH2 +) and ΔG 0 t (R-) are negative and positive respectively. These give the quantitative measure of ion-solvent interactions of the cations and anions of the amino acids. The Interaction constants of amino acids with urea were calculated. The results were discussed in terms of structural changes of water in presence of urea in water + urea mixtures, changed basicities of the solvent mixtures and solute-solvent interactions. However interaction of urea with amino acids appears not to be responsible for the denaturation of proteins but the destruction of the tetrahedral structure of H2O by urea is responsible for the alteration of protein folding and protein structure leading to denaturation. Direct mechanism involving microscopic properties suggests that no structure breaking of water by urea but a number of indirect evidences suggest urea to be the structure breaker of water.

Jain R.,Central Forensic Science Laboratory | Singh R.,Central University of Rajasthan
TrAC - Trends in Analytical Chemistry | Year: 2016

Analysis of cannabinoids in biological and other matrices is of paramount importance in forensic toxicology, since they are the most widely abused drugs over the globe. Generally, extraction of cannabinoids from biological matrices is achieved by liquid-liquid extraction (LLE) and solid-phase extraction (SPE). However, great attention has now been paid towards modern microextraction techniques in order to improve the quality and sensitivity of analytical methods. Microextraction techniques are environmentally benign, rapid, sensitive, inexpensive, offer high extraction efficiency and enrichment factors. This review provides an overview of microextraction techniques applied for the determination of cannabinoids and their metabolites in oral fluid, hair, urine and other matrices of forensic importance. After a complete revision of microextraction techniques for cannabinoids, they have been classified into two categories: (i) solid based e.g. solid-phase microextraction (SPME) etc., and (ii) solvent based e.g. dispersive liquid-liquid microextraction (DLLME). © 2016 Elsevier B.V.

Jain R.,Central Forensic Science Laboratory | Singh R.,Central University of Rajasthan
TrAC - Trends in Analytical Chemistry | Year: 2016

Of the several techniques available for micro-extraction, dispersive liquid-liquid micro-extraction (DLLME) has attracted the interest of forensic toxicologists in recent years. DLLME is a simple, fast, inexpensive and environmentally benign micro-extraction technique with high enrichment factors and extraction efficiencies. It becomes a versatile micro-extraction method with the use of a broad range of analytical instruments. DLLME has found a wide range of applications in the field of forensic toxicology, such as analysis of narcotic substances, drugs of abuse, hallucinogens, cannabinoids, metals and pesticides. Furthermore, the capability of DLLME for simultaneous derivatization and extraction and its coupling with injection-port silylation (IPS) simplify and accelerate the analysis of polar analytes by gas chromatography-mass spectrometry (GC-MS). This review focuses on various applications and operating procedures of DLLME for various classes of drugs and poisons of forensic interest. In addition, viability of future trends for the application of DLLME in forensic toxicology has been addressed. © 2015 Elsevier B.V.

Sharma K.,Vivekananda Mahavidyalaya | Sharma S.P.,Central Forensic Science Laboratory | Lahiri S.C.,Central Forensic Science Laboratory
Alcohol | Year: 2010

Numerous methods like distillation followed by iodometric titrations, gas chromatograph (GC)-flame ionization detector, gas chromatograph-mass spectrophotometer, GC-Headspace, Breath analyzer, and biosensors including alcohol dehydrogenase (enzymatic) have been used to determine blood alcohol concentration (BAC). In the present study, horizontal attenuated total reflectance-Fourier transform infrared spectroscopy had been used to determine BAC in whole blood. The asymmetric stretching frequency of C-C-O group of ethanol in water (1,045cm-1) had been used to calculate BAC using Beer's Law. A seven-point calibration curve of ethanol was drawn in the concentration range 24-790mg dL-1. The curve showed good linearity over the concentration range used (r2=0.999, standard deviation=0.0023). The method is accurate, reproducible, rapid, simple, and nondestructive in nature. © 2010 Elsevier Inc.

Sharma K.,Vivekananda Mahavidyalaya | Lahiri S.C.,Central Forensic Science Laboratory
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2011

1,3-Dinitrobenzene formed colored 1:1 complexes with aliphatic amines (chromogenic agents) like isopropylamine,ethylenediamine, tetraethylenepentamine and bis(3-aminopropyl)amine in DMSO having absorption maxima at 563 nm, 584 nm, 580.5 nm and 555 nm respectively. The complexes were stable for more than 24 h. The accurate association constants K AD and other thermodynamic parameters were determined with D and A usually in stoichiometric ratios. But in case of m-DNB and bis(3-aminopropyl)amine, the association constants K AD and the thermodynamic parameters were also determined using Benesi-Hildebrand equation to show the variations of K AD under different conditions. ΔG° values were found to be negative in all cases resulting from exothermic enthalpy changes and favourable entropy changes. The energies of transition for the CT complexes hν CT found experimentally were considerably different from the energies of transition (from HOMO of donor to LUMO of acceptor) calculated using AM1 but the differences were considerably reduced using DFT calculations. The vertical electron affinity of m-DNB was calculated using the method suggested by Mulliken. However, no FTIR measurements of the complexes could be made due to experimental limitations. © 2011 Elsevier B.V. All rights reserved.

Methyldopa is a much used antihypertensive drug. It is the subject matter of study mostly for the determination and estimation of methyldopa in pharmaceutical properties. These considerations led us to study the charge-transfer interactions between methyldopa, a centrally acting antihypertensive agent of limited use with the known acceptors like o-chloranil (o-ClN), chloranilic acid (ClA) and dichlorodicyanobenzoquinone (DDQ). Methyldopa (MDP) formed beautifully colored complexes (having absorption maxima at 581 nm and 368 nm; 519 nm; 583.5 nm, 547 nm and 346 nm, respectively) with the acceptors mentioned before. The physico-chemical properties of the complexes were studied using UV-visible spectrophotometry and FTIR measurements. The composition, the accurate association constants and thermodynamics of the complexes were determined spectrophotometrically. Attempts were made to interpret the thermodynamics of complexes in terms of IDV, EAV and hν CT. Solid CT complexes between MDP + o-ClN, MDP + ClA and MDP + DDQ were prepared and FTIR spectra of the complexes were studied. The energies hν CT of the charge-transfer complexes and vertical ionization potential IDV of methyldopa were compared with the theoretical values of hν CT obtained from HOMO and LUMO of the donors and acceptors calculated using Density Function Theory utilizing different basis sets. The agreement between the results can be regarded to be reasonable. Oscillator strengths and dipole strengths of the complexes were determined theoretically and experimentally and the limitations of the calculations were outlined. © 2012 Elsevier B.V. All rights reserved.

Verma R.S.,Central Forensic Science Laboratory | Middha D.,Central Forensic Science Laboratory
Chromatographia | Year: 2010

A liquid chromatographic tandem mass spectrometric validated method was developed for the detection of chemicals attributing color, flavor, taste and medicinal properties to saffron (Crocus sativus L. stigma). Ultrasonic extractions of saffron stigmas were followed by LC procedure with Pinnacle II Cyano (5 μm 150 × 2.1 mm) column and acetonitrile: water (70:30, v/v) as mobile phase. Deprotonated ions formed by a turbo ion spray in negative MS mode were used to detect the analytes. MS-MS detection was by monitoring precursors (m/z) fragmentations; of 149 → 113 (safranal), 327 → 283 (crocetin), 329 → 167 (picrocrocin), 355 → 327 (dimethyl crocetin), 489 → 327 (crocin E), 535 → 489 (carotenes), 651 → 327 (crocin C), 813 → 652 (crocin B), 975 → 651 (crocin A) and 1,137 → 813 (crocin F). The method was validated for linearity, precision, repeatability and specificity. © 2009 Vieweg+Teubner | GWV Fachverlage GmbH.

Morphine, codeine and thebaine formed charge transfer complexes with acceptors like hydroquinone, benzoquinone, naphthaquinone, picric acid, chloranil and dinitrobenzene as evidenced from the shifting of absorption maxima and change in optical densities in the UV regions. The evidence of complex formation was observed from the optical densities of the complex in the visible region when D>>A and where D and A do not absorb. The evidence of complex formation was also adduced from FT-IR measurements for morphine + naphthaquinone, codeine + naphthaquinone and thebaine + naphthaquinone complexes. The formations of CT complexes with those acceptors arc confirmed from the plots of hvCT against ID V (vertical ionization potential) of the drugs. From the values CT transition energies, the vertical ionization potentials (ID V) of morphine, codeine and thebaine were estimated to be 7.228 ± 0.396, 7.236 ± 0.399 and 7.233 ± 0.405 eV respectively. The almost equal values are due to structural similarities of the drugs. The degrees of overlap in the ground state of the complexes were also calculated. The association constants and thermodynamics of the complexes (e.g. ΔG0, ΔH0 and ΔS0) were determined spectrophotometrically from the o.d measurements at 298, 303, 306 and 310 K using D and A in stoichiometric ratios, a condition necessary for the accurate determination of the association constants. The complexes are fairly stable.

Dubey P.,CFSL | Shukla S.K.,Central Forensic Science Laboratory | Gupta K.C.,Indian Institute of Technology Roorkee
Australian Journal of Forensic Sciences | Year: 2013

Ketamine is a drug of abuse and is gaining popularity as a date rape drug. There are no field test kits available especially for ketamine. Scott's test has been used for the detection of cocaine for a very long time. It is based upon the formation of an insoluble complex of the cobalt thiocyanate ion with a free nitrogen base of cocaine. However, this test has been known for a large number of false positives when tested for cocaine. The authors have modified Scott's test by basifying the original solution and the addition of ethylene glycol for the detection of ketamine hydrochloride in the presence of lignocaine and cocaine. The test was done on more than 100 common drugs of abuse, medicines, cutting agents, excipients and other substances and was found to be specific only for ketamine. The EDX and FTIR analysis was further carried to establish the presence of ketamine in the complex. There were no false positives for the test and hence it could be incorporated for routine drug screening in toxicological and forensic drug laboratories, as well as frontline drug enforcement agencies. © 2013 Copyright Taylor and Francis Group, LLC.

Charge-transfer (CT) or electron donor-acceptor (EDA) complex formation between organic donors and acceptors has been extensively studied by spectrophotometry and other methods. High performance thin layer chromatography (HPTLC), although extensively used for the identification and quantification of drugs and explosives, has not been used until now to determine the extent of association and the association constants K DA of charge transfer or EDA complexes between donor (D) and acceptor (A). This paper describes the use of the HPTLC technique with scanning densitometry to identify and determine the association constants K DA of charge-transfer complexes of N,N-diethylaniline (DEA) with different nitro explosives, namely 1,4-dinitrobenzene (DNB), 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT), in chloroform. Advantages of the HPTLC method are highlighted. The association constants K DA of the complexes determined using the HPTLC method have been verified and validated spectrophotometrically when the concentrations of D and A are in their stoichiometric ratio. The thermodynamics of the complex formation reaction were obtained spectrophotometrically from measurements of the association constants K da at five different temperatures ranging from 293 to 313 K, when D and A are in their stoichiometric ratio and also when A ≥ D. The vertical ionization potential (I D V) and vertical electron affinity (E A V) of DEA were also calculated using Mulliken's theory employing the semi-empirical AM1 method. © Springer Science+Business Media, LLC 2011.

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