Amino Hydrogen Research Articles

ESR spectral change of radicals produced in L-alanine-3,3,3-d3 and L-alanine-d4. -A new pathway to produce the de-hydrogen radical and the hydrogen exchange reactions of the de-amino radical-

Radicals produced in L-alanine-3,3,3-d3 and L-alanine-d4 by X-irradiation and their spectral change were investigated using X-band ESR. Apparently, two major radicals appeared. One is the radical formed by deamination from a protonated anion and the other is produced by the loss of an alpha hydrogen. Before the appearance of the de-hydrogen radical, the precursor radical with a singlet feature was observed at 148–158 K. The signal of the precursor decreased and that of the de-hydrogen radical increased with temperature. Because the feature of the precursor radical was a singlet, it will be produced by deprotonation of the alpha hydrogen from the deprotonated cation radical observed at 77–80 K. Protonation to the amine moiety of the deprotonated radical will be a new pathway to produce the de-hydrogen radical.In L-alanine-3,3,3-d3, the hydrogen exchange reaction between the alpha hydrogen in the de-amino radical and the beta deuterium in a neighboring molecule occurred at the first-order rate of 7 × 10−4 s−1 at 294 K. The activation energy was 25 kcal/mol. By annealing at 393 K, the spectral features have obviously changed by the hydrogen exchange reactions in the de-amino radicals. Finally, all the de-amino radicals changed to •CHCH3COOH(D) and the methyl deuterium in the de-hydrogen radicals changed to hydrogen by a hydrogen exchange reaction between the C-D deuteriums of the radical and the N–H hydrogens of a crystal molecule after 100 min of annealing at 393 K. Many of the N–H hydrogens in the crystalline molecules changed to deuterons leading to the deuteration of the amino hydrogens in the de-hydrogen radicals.

Molecular structure of noradrenaline according to gas-phase electron diffraction data and quantum chemical calculations

The structures of two main noradrenaline conformers were determined using gas-phase electron diffraction. These conformers are stabilized by intramolecular hydrogen bonds between the nitrogen atom of the amino group and hydrogen of hydroxyl group attached to an ethylamine carbon atom.

Loneliness and obesity in old women are associated with lower plasma oxytocin levels: The combined impact of mental and physical distress on the neuroendocrine system

The structures of two main noradrenaline conformers were determined using gas-phase electron diffraction. These conformers are stabilized by intramolecular hydrogen bonds between the nitrogen atom of the amino group and hydrogen of hydroxyl group attached to an ethylamine carbon atom.

Crystal structure of 4-[(1R,2S,5R)-2-isopropyl-5-methyl-cyclo-hex-yl] 2-methyl (2S,4S,5R)-1-[(2S,3R,5R)-5-meth-oxy-carbonyl-2-(2-methyl-phen-yl)pyrrolidine-3-carbon-yl]-5-(2-methyl-phen-yl)pyrrolidine-2,4-di-carboxyl-ate.

The title compound, C38H50N2O7, represents a chiral β-proline dipeptide. Corresponding stereogenic centres of constituting pyrrolidine units have opposite absolute configurations. The central amide fragment is planar within 0.1 Å and adopts a Z configuration along the N-CO bond. In the crystal, the hydrogen atoms of the methyl-ene groups form several short inter-molecular C-H⋯O contacts with the carbonyl oxygen atoms of an adjacent mol-ecule. The only active amino hydrogen atom is not involved in hydrogen bonding.

Zeolite X with potassium diformate as a sustained-release antibacterial agent

A reaction of 800 mesh stellerite and a concentration of 15% hydrochloric acid in a solid to liquid ratio of 1:3 was carried out for 2 h at \(80^{\circ }\hbox {C}\). Most of its impurities were removed. It can be used as precursors for the preparation of high quality zeolite. Zeolite X which is octahedral crystal shape as cube, 96% of the degree of crystallinity has been synthesized hydrothermally from \(n(\hbox {SiO}_{2}/\hbox {Al}_{2}\hbox {O}_{3})=3, n(\hbox {Na}_{2}\hbox {O}/\hbox {SiO}_{2})=1.14\) and \(n(\hbox {H}_{2}\hbox {O/Na}_{2}\hbox {O})=37\) by controlling reaction temperature and time. The synthesis included zeolite X as carriers, chitosan as intermediates, a mass ratio of zeolite X:chitosan:potassium diformate \(=\) 3:1:2 in weight for 2 h at \(40^{\circ }\hbox {C}\). X-ray photoelectron spectroscopy analysis showed hydrogen bond formation by the chitosan amino hydrogen, potassium diformate oxygen and zeolite X oxygen or hydrogen bond formation by free hydroxyl group of zeolite X and oxygen of chitosan’s C–O, indicating effective grafting. Zeolite X sustained-release antibacterial agent was prepared with an inhibition rate of 78.16% by the antibacterial.

Effect of three-day Glutathione introduction on hydrogen sulfide metabolism in liver of rats under experimental nephropathy conditions

Topicality. Scientists are becoming more interested in the exchange of sulfur-containing amino acids and hydrogen sulfide (H 2 S) metabolism and glutathione. But the effect of tripeptide on the H 2 S metabolism by nephropathy is not studied enough. Aim. To study the effect of tree-day glutathione introduction on the system of H 2 S-producing enzymes, concentration and production in the liver of rats under conditions of experimental nephropathy. Materials and methods. The experiment was conducted on albino mature male rats. The animals in experimental group were administered a single intraperitoneal dose of folic acid (250 mg/kg). Glutathione was introduced intragastral (100 mg/kg) during 3 days after intoxication. Results and discussion. Under conditions of experimental nephropathy, there was a decrease in concentration of hydrogen sulfide by 37.92 % and the production of hydrogen sulfide by 34.84 % compared with the control group. The introduction of glutathione led to an increase in these indicators by 36.32 % and 48.4 % compared with the animals with nephropathy. The activity of cystathionine-γ-lyase (CSE), cystathionine-β-synthase (CBS) and cysteinaminotransferase (CAT) in the liver of rats with nephropathy was reduced by 38.98 %, 33.73 % and 26.76 % compared with animal control group. Glutathione increased the activity of CSE and CBS by 31 % and 33.55 % compared with a group of animals with nephropathy. The activity of cystathionine aminotransferase in the conditions of tripeptide increased by 49.3 % introduction and exceeded the date of the control group. Conclusions. The activity of H 2 S-producing enzymes in experimental nephropathy in the liver of rats is decreased. The introduction of glutathione increased the content of hydrogen sulfide and promoted the growth of the activity of H 2 S-producing enzymes in the liver of rats with nephropathy. As reasons for this effect, the possibility of including tripeptide as a source of cysteine in the synthesis of hydrogen sulfide is considered.

Synthesis, Crystal Structure and Photophysical Properties of Two Reduced Schiff Bases Derived from 5-Aminoisophthalic Acid

Two reduced Schiff bases, namely 5-[(2-hydroxybenzyl)amino]isophthalic acid (1) and 5-[(pyridin-4-ylmethyl)amino]isophthalic acid (2), were synthesized in two-step method using 5-aminoisophthalic acid as the starting material, and were characterized by single-crystal X-ray diffraction, elemental analysis, infrared, 1H NMR, mass, absorption and fluorescence spectra. Both 1 and 2 crystallize in monoclinic system with space groups P21/c for 1 and P21/n for 2. Photophysical properties of both 1 and 2 are significantly different from those of raw material 5-aminoisophthalic acid due to stronger p → π conjugation when one amino hydrogen atom in 5-aminoisophthalic acid is substituted with electron-donor group. 1 displays a very strong narrow-band blue fluorescence with the maximum peak at 439 nm, a high quantum efficiency up to 64%, and a narrow full width at half maximum of 35 nm, while 2 has a broader and weaker fluorescence with the peak at 418 nm and FHWM of about 50 nm. Two reduced Schiff bases with blue fluorescence were synthesized from 5-aminoisophthalic acid in two-step method including formation of the corresponding Schiff bases and further reduction by NaBH4.

Dissolution of chitosan nanocrystals in aqueous media of different acidity. Molecular dynamic study

The process of dissolution of chitosan nanocrystals with molecular mass of polymer up to 12.8 kDa in aqueous media of various pH was studied by molecular dynamic simulations with the use of the improved force field GROMOS 56ACARBO_CHT specially developed for the chitosan polymers description. The effect of the media acidity and polymer molecular weight on the dissolution process kinetics has been studied and the regression expressions for kinetic parameters were established. The calculated solution viscosity, Mark–Houwink–Sakurada equation parameters, and pH values of the dissolution beginning are in good agreement with the available experimental data. The uniform/non-uniform distribution of protonated amino groups and hydrogen bonds along the polymeric chains is found to be of key importance parameter for the dissolution process which can be considered as a criterion of dissolution ability.

Hydrogen-bonding network in anhydrous chitosan from neutron crystallography and periodic density functional theory calculations

The hydrogen-bonding network in anhydrous chitosan crystal was studied using a combination of neutron crystallography and quantum chemical calculation. The locations of the hydroxyl hydrogen were directly resolved using Fourier omit maps applied to neutron diffraction data, whereas the amino hydrogen atoms were determined based on geometrical optimization using periodic density functional theory (DFT) calculation. Energy optimization of the hydrogen positions based on DFT calculation allowed the measurement of the hydrogen-bond energies. In the chitosan crystal, the hydroxyl groups mostly play a role as hydrogen-bond donors while the amino moiety behaves as a strong acceptor but a poor donor.

Hydrogenation of 4-chloronitrobenzenes over palladium and platinum catalysts supported on beta zeolite and γ-alumina

Liquid-phase hydrogenation of 4-chloronitrobenzene (4-CNB) to 4-chloroaniline (4-CAN) under mild reaction conditions (0.6 MPa, 25 °C, methanol-diethyl ether, 1:1 vol.) over palladium and platinum catalysts containing 1 mass% of metal supported on beta zeolite (M/B) or γ-alumina (M/A) was studied. The catalysts were prepared by the incipient wetness method using amino nitrate complexes and hydrogen as the reducing agent. SEM, adsorption–desorption nitrogen isotherms, XRD, TEM, and hydrogen chemisorption techniques were used for their characterization. The techniques employed revealed the presence of relatively large metal particles (approximately 15 nm; about 3% of metal dispersion). Stability of the catalysts during the hydrogenation was high; no catalyst changes were observed after two recycle runs. Hydrogenation over M/A catalysts was found to be faster than that over M/B catalysts in the methanol–diethyl ether mixture. Selectivity of only about 75% to 4-CAN was achieved over the M/A catalyst in methanol. Positive effect of the acid support (beta zeolite) and low polarity of the reaction environment (diethyl ether) are reflected in the high selectivity to 4-CAN; of about 99% at virtually 100% conversion of 4-CNB.

A new perfluoromethyl aminoenone derivative and the role of the hydrogen bonding in the intra- and intermolecular interactions

The structure of a new perfluoromethyl derivative, (Z)-4,4,4-trifluoro-1-(2-hydroxyphenyl)-3-(methylamino)-2-buten-1-one (1), was investigated in both crystalline state and solution since the prototropy enable the existence of three tautomeric species in equilibrium. The preference in the configurational E/Z arrangement is strongly dependent on the intramolecular hydrogen bond interactions. The vibrational and electronic spectra of 1 were discussed and assigned by using DFT calculations. The crystal, solved by single-crystal X-ray diffraction, shows the prevalence of the tautomer aminoenone over the imino-enol and imino-ketone forms. Therefore, an almost planar molecular conformation is observed due to the formation of two intramolecular amino and phenolic hydrogen bonds to the same carbonyl oxygen acceptor atom that stabilize the Z configuration. The molecular packing is held by the OH⋯O(keto) and NH⋯O hydrogen bonds, F⋯F, CH⋯π and π-stacking interactions that contribute to the crystal stabilization. The intra and intermolecular contacts were also characterized by Natural Bond Orbital (NBO) analysis and Atoms in Molecules (AIM) approach. Hirshfeld surfaces and their associated fingerprint plots were generated for 1 and for a related structure, to visualize different intermolecular interactions and their relative contributions to the total surface.

QM/MM Study of the Reaction Catalyzed by Alkyladenine DNA Glycosylase: Examination of the Substrate Specificity of a DNA Repair Enzyme.

Human alkyladenine DNA glycosylase (AAG) functions as part of the base excision repair pathway to excise structurally diverse oxidized and alkylated DNA purines. Specifically, AAG uses a water molecule activated by a general base and a nonspecific active site lined with aromatic residues to cleave the N-glycosidic bond. Despite broad substrate specificity, AAG does not target the natural purines (adenine (A) and guanine (G)). Using the ONIOM(QM:MM) methodology, we provide fundamental atomic level details of AAG bound to DNA-containing a neutral substrate (hypoxanthine (Hx)), a nonsubstrate (G), or a cationic substrate (7-methylguanine (7MeG)) and probe changes in the reaction pathway that occur when AAG targets different nucleotides. We reveal that subtle differences in protein-DNA contacts upon binding different substrates within the flexible AAG active site can significantly affect the deglycosylation reaction. Notably, we predict that AAG excises Hx in a concerted mechanism that is facilitated through correct alignment of the (E125) general base due to hydrogen bonding with a neighboring aromatic amino acid (Y127). Hx departure is further stabilized by π-π interactions with aromatic amino acids and hydrogen bonds with active site water. Despite possessing a similar structure to Hx, G is not excised since the additional exocyclic amino group leads to misalignment of the general base due to disruption of the key E125-Y127 hydrogen bond, the catalytically unfavorable placement of water within the active site, and weakened π-contacts between aromatic amino acids and the nucleobase. In contrast, cationic 7MeG does not occupy the same position within the AAG active site as G due to steric clashes with the additional N7 methyl group, which results in the correct alignment of the general base and permits nucleobase excision as observed for neutral Hx. Overall, our structural data rationalizes the observed substrate specificity of AAG and contributes to our fundamental understanding of enzymes with flexible active sites and broad substrate specificities.

Trinuclear clusters containing 2-aminopyridinate/pyrimidinate ligands as electrocatalysts for proton reduction

Triiron and triruthenium clusters containing capping 2-aminopyridinate/pyrimidinate ligands are developed as functional models of the [FeFe]-hydrogenase for electrocatalytic reduction of protons to hydrogen. The 48-electron clusters Fe3(CO)9(μ3-pyNH)(μ-H) (1), Fe3(CO)9(μ3-pymNH)(μ-H) (2), Ru3(CO)9(μ3-pyNH)(μ-H) (3) and Ru3(CO)9(μ3-pymNH)(μ-H) (4) (pyNH = 2-aminopyridinate, pymNH = 2-aminopyrimidinate) are prepared from reactions of M3(CO)12 (M = Fe or Ru) with the corresponding heterocyclic amine at elevated temperatures. Each contains a hydride and a residual amino hydrogen in close proximity (ca. 2.8 Å). The triiron 2-aminopyridinate cluster 1 does not protonate by TsOH·H2O (used as the proton source during catalysis), whereas its ruthenium analogue 3 undergoes slow protonation across a ruthenium-ruthenium bond. The 2-aminopyrimidinate clusters 2 and 4 undergo rapid protonation at the ring nitrogen. In MeCN, the triiron clusters show a single irreversible reduction wave (Ep = −1.61 V for 1; Ep = −1.47 V for 2) in the cathodic region of their CVs, while the triruthenium clusters display a pair of irreversible cathodic waves (Ep = −2.01 and −2.15 V for 1; Ep = −1.93 and −2.09 V for 2). All catalyze proton reduction in the presence of TsOH·H2O but different mechanisms are proposed. The triiron clusters are more efficient toward proton reduction and operate at reduced overpotentials as compared to their triruthenium analogues. Introduction of a potential proton relay in these clusters neither increases the efficiency nor reduces the overpotential of catalysis which is in sharp contrast with the results observed for hydrogenase biomimetics.

Crystallographic and spectroscopic characterization of 5-chloro-pyridine-2,3-di-amine.

The two ortho-amino groups of the title compound, C5H6ClN3, twist out of the plane of the mol-ecule to minimize intra-molecular inter-action between the amino hydrogen atoms. In the crystal, the amino groups and the pyridine N atom engage in inter-molecular hydrogen bonding. The mol-ecules pack into spiral hydrogen-bonded columns with offset face-to-face π-stacking.

Decomposing protein-DNA binding and recognition using simplified protein models.

We analyze the role of different physicochemical factors in protein/DNA binding and recognition by comparing the results from all-atom molecular dynamics simulations with simulations using simplified protein models. These models enable us to separate the role of specific amino acid side chains, formal amino acid charges and hydrogen bonding from the effects of the low-dielectric volume occupied by the protein. Comparisons are made on the basis of the conformation of DNA after protein binding, the ionic distribution around the complex and the sequence specificity. The results for four transcription factors, binding in either the minor or major grooves of DNA, show that the protein volume and formal charges, with one exception, play a predominant role in binding. Adding hydrogen bonding and a very small number of key amino acid side chains at the all-atom level yields results in DNA conformations and sequence recognition close to those seen in the reference all-atom simulations.

In silico analysis of non-synonymous single nucleotide polymorphisms in human DAZL gene associated with male infertility

ABSTRACTIn living systems the most frequent type of genetic mutation is the single nucleotide polymorphism (SNP). Non-synonymous SNPs (nsSNPs) or missense mutations arise in coding regions of a particular gene. nsSNPs result in a single amino acid substitution which may have effects on the structure and/or function of proteins. Spermatogenesis is a complex process where haploid spermatozoa are formed. The deleted in azoospermia like (DAZL) gene has a relationship with male infertility and dysfunction of DAZL may decrease the sperm count which leads to oligozoospermia or azoospermia. Various computational methods were used to analyze the genetic variations of DAZL affecting the structure and/or function. In the present study, N109T was assigned as the most deleterious or disease related nsSNP by SIFT, MutPred, PolyPhen 2.0, I-Mutant, and MuStab tools. The ConSurf tool showed that functional amino acid residues which are conserved in Human DAZL include the N109T nsSNP. The secondary and tertiary structure was predicted using PSIPRED and MUSTER. Our study shows that the N109T variant may directly or indirectly weaken amino acid interactions and hydrogen bond networks of the DAZL protein, which we predicted may result in altered DAZL protein function. Further, computational analysis of free energy change due to this point mutation using GROMOS96 indicated decreased stability of the DAZL protein. The N109T variant in an infertile male population may provide a genetic marker for mutational analysis of DAZL.Abbreviations: DAZL: deleted in azoospermia like; dbSNP: database of single nucleotide polymorphism; nsSNPs: non-synonymous SNPs; AA: amino acid; SIFT: sorting intolerant from tolerant; PolyPhen-2: polymorphism phenotyping v2; MUSTER: multi-sources threader; PDB: protein data bank; MuStab: predicting mutant protein stability change; PSIPRED: PSI-blast based secondary structure prediction

Formation and Occurrence of N-Chloro-2,2-dichloroacetamide, a Previously Overlooked Nitrogenous Disinfection Byproduct in Chlorinated Drinking Waters.

Haloacetamides (HAMs) are a class of newly identified nitrogenous disinfection byproducts (N-DBPs) whose occurrence in drinking waters has recently been reported in several DBP surveys. As the most prominent HAM species, it is commonly acknowledged that 2,2-dichloroacetamide (DCAM) is mainly generated from dichloroacetonitrile (DCAN) hydrolysis because the concentrations of these two compounds are often well correlated. Instead of DCAM, a previously unreported N-DBP, N-chloro-2,2-dichloroacetamide (N-Cl-DCAM), was confirmed in this study as the actual DCAN degradation product in chlorinated drinking waters. It is suspected that N-Cl-DCAM has been erroneously identified as DCAM, because its nitrogen-bound chlorine is readily reduced by most commonly used quenching agents. This hypothesis is supported by kinetic studies that indicate almost instantaneous N-chlorination of DCAM even at low chlorine residuals. Therefore, it is unlikely that DCAM can persist as a long-lived DCAN decomposition product in systems using free chlorine as a residual disinfectant. Instead, chlorination of DCAM will lead to the formation of an equal amount of N-Cl-DCAM by forming a hydrogen bond between hypochlorite oxygen and amino hydrogen. Alternatively, N-Cl-DCAM can be produced directly from DCAN chlorination via nucleophilic addition of hypochlorite on the nitrile carbon. Due to its relatively low pKa value, N-Cl-DCAM tends to deprotonate under typical drinking water pH conditions, and the anionic form of N-Cl-DCAM was found to be very stable in the absence of chlorine. N-Cl-DCAM can, however, undergo acid-catalyzed decomposition to form the corresponding dichloroacetic acid (DCAA) when chlorine is present, although those acidic conditions that favor N-Cl-DCAM degradation are generally atypical for finished drinking waters. For these reasons, N-Cl-DCAM is predicted to have very long half-lives in most distribution systems that use free chlorine. Furthermore, an analytical method using ultra performance liquid chromatography (UPLC)/negative electrospray ionization (ESI-)/quadrupole time-of-flight mass spectrometry (qTOF) was developed for the detection of a family of seven N-chloro-haloacetamides (N-Cl-HAMs). Combined with solid phase extraction (SPE), the occurrence of N-Cl-DCAM and its two brominated analogues (i.e., N-chloro-2,2-bromochloroacetamide and N-chloro-2,2-dibromoacetamide) was quantitatively determined for the first time in 11 real tap water samples. The discovery of N-Cl-DCAM or, more broadly speaking, N-Cl-HAMs in chlorinated drinking waters is of significance because they are organic chloramines, a family of compounds that is perceived to be more toxicologically potent than halonitriles (e.g., DCAN) and haloamides (e.g., DCAM), and therefore they may pose greater risks to drinking water consumers given their widespread occurrence and high stability.

Fibrillar Collagens.

Fibrillar collagens (types I, II, III, V, XI, XXIV and XXVII) constitute a sub-group within the collagen family (of which there are 28 types in humans) whose functions are to provide three-dimensional frameworks for tissues and organs. These networks confer mechanical strength as well as signalling and organizing functions through binding to cellular receptors and other components of the extracellular matrix (ECM). Here we describe the structure and assembly of fibrillar collagens, and their procollagen precursors, from the molecular to the tissue level. We show how the structure of the collagen triple-helix is influenced by the amino acid sequence, hydrogen bonding and post-translational modifications, such as prolyl 4-hydroxylation. The numerous steps in the biosynthesis of the fibrillar collagens are reviewed with particular attention to the role of prolyl 3-hydroxylation, collagen chaperones, trimerization of procollagen chains and proteolytic maturation. The multiple steps controlling fibril assembly are then discussed with a focus on the cellular control of this process in vivo. Our current understanding of the molecular packing in collagen fibrils, from different tissues, is then summarized on the basis of data from X-ray diffraction and electron microscopy. These results provide structural insights into how collagen fibrils interact with cell receptors, other fibrillar and non-fibrillar collagens and other ECM components, as well as enzymes involved in cross-linking and degradation.

Computational prediction of the effects of non-synonymous single nucleotide polymorphisms in the human Quinone Oxidoreductase 1 (NQO1)

The human NAD(P)H Quinone Oxidoreductase 1 (NQO1) gene codes for a flavoenzyme which protects cells from oxidative stress and also regulates ubiquitin-independent proteasomal degradation of several proteins including p53. Polymorphisms in NQO1 are associated with several diseases but of the thousand SNPs reported till date, only a few elevate risk. Thus during an epidemiological investigation, studying a few selected SNPs could be more justified. Computational approaches help in the identification of non-synonymous single nucleotide polymorphisms (nsSNPs) that affect protein functions and impact disease risk. The present study evaluates the structure and functional effect of all known nsSNPs of NQO1. NQO1 SNP information and their corresponding protein sequences were collected from dbSNP and UniProt databases respectively. Genomic analysis of the 75 nsSNPs was initiated using SIFT, Polyphen, SNP & GO, PROVEAN, MutPred, I-Mutant 2.0 and nsSNPAnalyzer. Protein structural analysis of select amino acid variants was performed using Phyre2, RaptorX and Swiss-PDB Viewer, molecular dynamics using GROMOS96 and root mean square deviation (RMSD) values were calculated using UCSF Chimera. We identified eight deleterious substitutions - rs11555215 (R119P), rs368942932 (L7R), rs554822773 (L113P), rs749792989 (W116L), rs764253929 (G160R), rs769655604 (W106R), rs775472154 (F102V) and rs777649241 (D41G). The NQO1 variants -R119P and G160R, were the most energetically unfavorable substitutions and could destabilize the amino acid interactions and hydrogen bond networks. The study concludes that screening for these variants especially rs11555215 and rs764253929 may be useful in understanding disease pathogenesis and developing molecular diagnostics involving the NQO1 pathways.

Engineering the Excited-State Dynamics of 3-Aminoquinoline by Chemical Modification and Temperature Variation.

The role of the amino group in the excited-state dynamics of 3-aminoquinoline (3AQ) has been investigated by comparison with its synthetic derivative 3-(piperidin-1-yl)quinoline (3PQ). The absence of amino hydrogen atoms in 3PQ eliminates, to a large extent, the complexity of the excited-state processes observed in 3AQ. The polarity of the medium is found to be the most important determinant in the nonradiative rate constants of 3PQ, unlike in 3AQ where hydrogen bonding plays the most significant role. The nonradiative rate constants decrease with increase in micropolarity. This trend is opposite to what is usually observed with dipolar states. Temperature dependence of the fluorescence spectra and lifetime has been studied to understand this unexpected observation. An unusual redshift in the emission of 3AQ and 3PQ is observed in nonpolar media at low temperatures. This is surprising, as a process involving a barrier is expected to be hindered at low temperatures and be manifested in a blueshift of the spectra, due to the predominance of the locally excited (LE) state. Moreover, the variation of emission maxima of 3AQ with temperature is sigmoidal in nature, indicating the involvement of two distinct states. The counterintuitive observation of the predominance of the state with comparatively lower emission energy, at low temperatures, establishes the following: the photophysics in 3AQ is dominated by a LE state at room temperature in nonpolar media. This state is associated with rapid flip-flop of the amino group, which provides an efficient nonradiative channel of deactivation. At low temperatures, this flip-flop is hindered and the molecule can undergo intramolecular charge transfer (ICT), whereby the lower energy state is populated. In the case of 3PQ, the ICT state is the only one present, owing to the tertiary amino group.