Displaying publications 21 - 40 of 942 in total

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  1. Jamil W, Perveen S, Shah SA, Taha M, Ismail NH, Perveen S, et al.
    Molecules, 2014 Jun 25;19(7):8788-802.
    PMID: 24968334 DOI: 10.3390/molecules19078788
    Phenoxyacetohydrazide Schiff base analogs 1-28 have been synthesized and their in vitro β-glucouoronidase inhibition potential studied. Compounds 1 (IC50=9.20±0.32 µM), 5 (IC50=9.47±0.16 µM), 7 (IC50=14.7±0.19 µM), 8 (IC50=15.4±1.56 µM), 11 (IC50=19.6±0.62 µM), 12 (IC50=30.7±1.49 µM), 15 (IC50=12.0±0.16 µM), 21 (IC50=13.7±0.40 µM) and 22 (IC50=22.0±0.14 µM) showed promising β-glucuronidase inhibition activity, better than the standard (D-saccharic acid-1,4-lactone, IC50=48.4±1.25 µM).
  2. Baharara J, Namvar F, Mousavi M, Ramezani T, Mohamad R
    Molecules, 2014;19(9):13498-508.
    PMID: 25255752 DOI: 10.3390/molecules190913498
    Angiogenesis, which is required for physiological events, plays a crucial role in several pathological conditions, such as tumor growth and metastasis. The use of plant extracts is a cost effective and eco-friendly way to synthesize nanoparticles. In the present study, we investigated the anti-angiogenesis properties of silver nanoparticles synthesized using Saliva officinalis extract on chick chorioalantoic membrane. The production of nanoparticles was confirmed by the color change from yellow to brown observed after approximately 3 h at 37 °C. Then, the nanoparticles were characterized by UV-visible spectroscopy, FTIR, and TEM. The UV-visible spectroscopy results showed that the surface plasmon resonance band for AgNPs was around 430 nm. The intensity of the AgNP-specific absorption peak improved with an increase of 0.5 mL of extract into 10 mL of AgNO3 (2.5 mM). The FTIR results showed good interaction between the plant extracts and AgNPs. The TEM images of the samples revealed that the NPs varied in morphology and size from 1 to 40 nm; the average was recorded at 16.5 ± 1.2 nm. Forty Ross fertilized eggs were divided into four groups; the control and three experimental groups. On the 8th day, gelatin sponges containing albumin were placed on the chorioalantoic membrane and soaked with different concentrations of NPs. On the 12th day, all the cases were photographed using a photostereomicroscope. The number and the lengths of the vessels were measured using Image J software. The crown rump (CR) and weight of the embryo were also recorded. Then the hemoglobin content was measured using Drabkin's reagent kit for quantification of the blood vessel formation. According to the data analysis, the number and length of the blood vessels, as well as the CR and weight of the embryos reduced significantly compared to the control (p < 0.05), dose dependently. The total hemoglobin was quantified as an indicator of the blood vessel formation. The hemoglobin content in the treated samples with AgNPs decreased, which showed its inhibitory effect on angiogenesis.
  3. Sultan S, Noor MZ, Anouar el H, Shah SA, Salim F, Rahim R, et al.
    Molecules, 2014 Sep 03;19(9):13775-87.
    PMID: 25255760 DOI: 10.3390/molecules190913775
    The anti-inflammatory drug predinisolone (1) was reduced to 20β-hydroxyprednisolone (2) by the marine endophytic fungus Penicilium lapidosum isolated from an alga. The structural elucidation of 2 was achieved by 1D- and 2D-NMR, MS, IR data. Although, 2 is a known compound previously obtained through microbial transformation, the data provided failed to prove the C20 stereochemistry. To solve this issue, DFT and TD-DFT calculations have been carried out at the B3LYP/6-31+G (d,p) level of theory in gas and solvent phase. The absolute configuration of C20 was eventually assigned by combining experimental and calculated electronic circular dichroism spectra and 3JHH chemical coupling constants.
  4. Anarjan N, Nehdi IA, Sbihi HM, Al-Resayes SI, Malmiri HJ, Tan CP
    Molecules, 2014 Sep 10;19(9):14257-65.
    PMID: 25211006 DOI: 10.3390/molecules190914257
    The incorporation of lipophilic nutrients, such as astaxanthin (a fat soluble carotenoid) in nanodispersion systems can either increase the water solubility, stability and bioavailability or widen their applications in aqueous food and pharmaceutical formulations. In this research, gelatin and its combinations with sucrose oleate as a small molecular emulsifier, sodium caseinate (SC) as a protein and gum Arabic as a polysaccharide were used as stabilizer systems in the formation of astaxanthin nanodispersions via an emulsification-evaporation process. The results indicated that the addition of SC to gelatin in the stabilizer system could increase the chemical stability of astaxanthin nanodispersions significantly, while using a mixture of gelatin and sucrose oleate as a stabilizer led to production of nanodispersions with the smallest particle size (121.4±8.6 nm). It was also shown that a combination of gelatin and gum Arabic could produce optimal astaxanthin nanodispersions in terms of physical stability (minimum polydispersity index (PDI) and maximum zeta-potential). This study demonstrated that the mixture of surface active compounds showed higher emulsifying and stabilizing functionality compared to using them individually in the preparation of astaxanthin nanodispersions.
  5. Imran S, Taha M, Ismail NH, Khan KM, Naz F, Hussain M, et al.
    Molecules, 2014;19(8):11722-40.
    PMID: 25102118 DOI: 10.3390/molecules190811722
    In an effort to develop new antibacterial drugs, some novel bisindolylmethane derivatives containing Schiff base moieties were prepared and screened for their antibacterial activity. The synthesis of the bisindolylmethane Schiff base derivatives 3-26 was carried out in three steps. First, the nitro group of 3,3'-((4-nitrophenyl)-methylene)bis(1H-indole) (1) was reduced to give the amino substituted bisindolylmethane 2 without affecting the unsaturation of the bisindolylmethane moiety using nickel boride in situ generated. Reduction of compound 1 using various catalysts showed that combination of sodium borohydride and nickel acetate provides the highest yield for compound 2. Bisindolylmethane Schiff base derivatives were synthesized by coupling various benzaldehydes with amino substituted bisindolylmethane 2. All synthesized compounds were characterized by various spectroscopic methods. The bisindolylmethane Schiff base derivatives were evaluated against selected Gram-positive and Gram-negative bacterial strains. Derivatives having halogen and nitro substituent display weak to moderate antibacterial activity against Salmonella typhi, S. paratyphi A and S. paratyphi B.
  6. Ng CH, Rullah K, Aluwi MF, Abas F, Lam KW, Ismail IS, et al.
    Molecules, 2014;19(8):11645-59.
    PMID: 25100256 DOI: 10.3390/molecules190811645
    The natural product molecule 2,4,6-trihydroxy-3-geranyl-acetophenone (tHGA) isolated from the medicinal plant Melicope ptelefolia was shown to exhibit potent lipoxygenase (LOX) inhibitory activity. It is known that LOX plays an important role in inflammatory response as it catalyzes the oxidation of unsaturated fatty acids, such as linoleic acid to form hydroperoxides. The search for selective LOX inhibitors may provide new therapeutic approach for inflammatory diseases. Herein, we report the synthesis of tHGA analogs using simple Friedel-Craft acylation and alkylation reactions with the aim of obtaining a better insight into the structure-activity relationships of the compounds. All the synthesized analogs showed potent soybean 15-LOX inhibitory activity in a dose-dependent manner (IC50 = 10.31-27.61 μM) where compound 3e was two-fold more active than tHGA. Molecular docking was then applied to reveal the important binding interactions of compound 3e in soybean 15-LOX binding site. The findings suggest that the presence of longer acyl bearing aliphatic chain (5Cs) and aromatic groups could significantly affect the enzymatic activity.
  7. Zia-Ul-Haq M, Riaz M, De Feo V, Jaafar HZ, Moga M
    Molecules, 2014 Jul 28;19(8):10998-1029.
    PMID: 25072202 DOI: 10.3390/molecules190810998
    Rubus fruticosus L. is a shrub famous for its fruit called blackberry fruit or more commonly blackberry. The fruit has medicinal, cosmetic and nutritive value. It is a concentrated source of valuable nutrients, as well as bioactive constituents of therapeutic interest highlighting its importance as a functional food. Besides use as a fresh fruit, it is also used as ingredient in cooked dishes, salads and bakery products like jams, snacks, desserts, and fruit preserves. R. fruticosus contains vitamins, steroids and lipids in seed oil and minerals, flavonoids, glycosides, terpenes, acids and tannins in aerial parts that possess diverse pharmacological activities such as antioxidant, anti-carcinogenic, anti-inflammatory, antimicrobial anti-diabetic, anti-diarrheal, and antiviral. Various agrogeoclimatological factors like cultivar, environmental conditions of the area, agronomic practices employed, harvest time, post-harvest storage and processing techniques all influence the nutritional composition of blackberry fruit. This review focuses on the nutrients and chemical constituents as well as medicinal properties of different parts of R. fruticosus. Various cultivars and their physicochemical characteristics, polyphenolic content and ascorbic acid content are also discussed. The information in the present work will serve as baseline data and may lead to new biomedical applications of R. fruticosus as functional food.
  8. Loo JL, Khoramnia A, Lai OM, Long K, Ghazali HM
    Molecules, 2014 Jun 23;19(6):8556-70.
    PMID: 24959682 DOI: 10.3390/molecules19068556
    Mycelium-bound lipase (MBL), from a locally isolated Geotrichum candidum strain, was produced and characterized as a natural immobilized lipase. A time course study of its lipolytic activity in 1 L liquid broth revealed the maximum MBL activity at 4 h for mycelium cells harvested after 54 h. The yield and specific activity of MBL were 3.87 g/L dry weight and 508.33 U/g protein, respectively, while less than 0.2 U/mL lipase activity was detected in the culture supernatant. Prolonged incubation caused release of the bound lipase into the growth medium. The growth pattern of G. candidum, and production and properties of MBL were not affected by the scale. The stability of mycelia harboring lipase (MBL), harvested and lyophilized after 54 h, studied at 4 °C depicted a loss of 4.3% and 30% in MBL activity after 1 and 8 months, while the activity of free lipase was totally lost after 14 days of storage. The MBL from G. candidum displayed high substrate selectivity for unsaturated fatty acids containing a cis-9 double bond, even in crude form. This unique specificity of MBL could be a direct, simple and inexpensive way in the fats and oil industry for the selective hydrolysis or transesterification of cis-9 fatty acid residues in natural triacylglycerols.
  9. Saminathan M, Tan HY, Sieo CC, Abdullah N, Wong CM, Abdulmalek E, et al.
    Molecules, 2014 Jun 12;19(6):7990-8010.
    PMID: 24927368 DOI: 10.3390/molecules19067990
    Condensed tannins (CTs) form insoluble complexes with proteins and are able to protect them from degradation, which could lead to rumen bypass proteins. Depending on their degrees of polymerization (DP) and molecular weights, CT fractions vary in their capability to bind proteins. In this study, purified condensed tannins (CTs) from a Leucaena leucocephala hybrid were fractionated into five different molecular weight fractions. The structures of the CT fractions were investigated using 13C-NMR. The DP of the CT fractions were determined using a modified vanillin assay and their molecular weights were determined using Q-TOF LC-MS. The protein-binding affinities of the respective CT fractions were determined using a protein precipitation assay. The DP of the five CT fractions (fractions F1-F5) measured by the vanillin assay in acetic acid ranged from 4.86 to 1.56. The 13C-NMR results showed that the CT fractions possessed monomer unit structural heterogeneity. The number-average molecular weights (Mn) of the different fractions were 1265.8, 1028.6, 652.2, 562.2, and 469.6 for fractions F1, F2, F3, F4, and F5, respectively. The b values representing the CT quantities needed to bind half of the maximum precipitable bovine serum albumin increased with decreasing molecular weight--from fraction F1 to fraction F5 with values of 0.216, 0.295, 0.359, 0.425, and 0.460, respectively. This indicated that higher molecular weight fractions of CTs from L. leucocephala have higher protein-binding affinities than those with lower molecular weights.
  10. Ahmed S, Gul S, Idris F, Hussain A, Zia-Ul-Haq M, Jaafar HZ, et al.
    Molecules, 2014;19(8):11385-94.
    PMID: 25090125 DOI: 10.3390/molecules190811385
    Human plasma inhibits arachidonic acid metabolism and platelet aggregation. This helps human form a haemostatic control system that prevents the progress of certain aggregatory or inflammatory reactions. Whether this property of plasma is unique to human or extends to other species is not well known. It is speculated that this protective ability of plasma remains evolutionarily conserved in different mammals. In order to confirm this, the effect of plasma from 12 different mammalian species was investigated for its inhibitory potential against arachidonic acid metabolism and platelet aggregation. Metabolism of arachidonic acid by cyclooxygenase and lipoxygenase pathways was studies using radio-immuno assay and thin layer chromatography while platelet aggregation in the plasma of various mammals was monitored following turbedmetric method in a dual channel aggregometer. Results indicate that inhibition of AA metabolism and platelet aggregation is a common feature of plasma obtained from different mammalian species, although there exists large interspecies variation. This shows that besides human, other mammals also possess general protective mechanisms against various aggregatory and inflammatory conditions and this anti-inflammatory property of the plasma is evolutionarily conserved in mammalian species. The most likely candidates responsible for these properties of plasma include haptoglobin, albumin and lipoproteins.
  11. Nazarbahjat N, Nordin N, Abdullah Z, Abdulla MA, Yehye WA, Halim SN, et al.
    Molecules, 2014;19(8):11520-37.
    PMID: 25093989 DOI: 10.3390/molecules190811520
    New thiosemicarbazide derivatives 2-6 were synthesised by reacting 2-(ethylsulfanyl)benzohydrazide with various aryl isothiocyanates. The cyclisation of compounds 2-6 under reflux conditions in a basic medium (aqueous NaOH, 4 N) yielded compounds 7-11 that contain a 1,2,4-triazole ring. All of the synthesised compounds were screened for their antioxidant activities. Compounds 2, 3, and 7 showed better radical scavenging in a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, with IC50 values of 1.08, 0.22, and 0.74 µg/mL, respectively, compared to gallic acid (IC50, 1.2 µg/mL). Compound 3 also showed superior results in a ferric reducing antioxidant power (FRAP) assay (3054 µM/100 g) compared to those of ascorbic acid (1207 µM/100 g).
  12. Karimian H, Mohan S, Moghadamtousi SZ, Fadaeinasab M, Razavi M, Arya A, et al.
    Molecules, 2014 Jul 03;19(7):9478-501.
    PMID: 24995928 DOI: 10.3390/molecules19079478
    Tanacetum polycephalum (L.) Schultz-Bip (Mokhaleseh) has been traditionally used in the treatment of headaches, migraines, hyperlipidemia and diabetes. The present study aimed to evaluate its anticancer properties and possible mechanism of action using MCF7 as an in vitro model. T. polycephalum leaves were extracted using hexane, chloroform and methanol solvents and the cytotoxicity was evaluated using the MTT assay. Detection of the early apoptotic cells was investigated using acridine orange/propidium iodide staining. An Annexin-V-FITC assay was carried out to observe the phosphatidylserine externalization as a marker for apoptotic cells. High content screening was applied to analyze the cell membrane permeability, nuclear condensation, mitochondrial membrane potential (MMP) and cytochrome c release. Apoptosis was confirmed by using caspase-8, caspase-9 and DNA laddering assays. In addition, Bax/Bcl-2 expressions and cell cycle arrest also have been investigated. MTT assay revealed significant cytotoxicity of T. Polycephalum hexane extract (TPHE) on MCF7 cells with the IC50 value of 6.42±0.35 µg/mL. Significant increase in chromatin condensation was also observed via fluorescence analysis. Treatment of MCF7 cells with TPHE encouraged apoptosis through reduction of MMP by down-regulation of Bcl-2 and up-regulation of Bax, triggering the cytochrome c leakage from mitochondria to the cytosol. The treated MCF7 cells significantly arrested at G1 phase. The chromatographic analysis elicited that the major active compound in this extract is 8β-hydroxy-4β,15-dihydrozaluzanin C. Taken together, the results presented in this study demonstrated that the hexane extract of T. Polycephalum inhibits the proliferation of MCF7 cells, resulting in the cell cycle arrest and apoptosis, which was explained to be through the mitochondrial pathway.
  13. Cheong KW, Mirhosseini H, Hamid NS, Osman A, Basri M, Tan CP
    Molecules, 2014 Jun 24;19(6):8691-706.
    PMID: 24962400 DOI: 10.3390/molecules19068691
    This study was conducted to investigate the effect of main emulsion components namely, modified starch, propylene glycol alginate (PGA), sucrose laurate and sucrose stearate on creaming index, cloudiness, average droplet size and conductivity of soursop beverage emulsions. Generally, the use of different emulsifiers or a mixture of emulsifiers has a significant (p < 0.05) effect on the response variables studied. The addition of PGA had a significant (p < 0.05) effect on the creaming index at 55 °C, while PGA-stabilized (PGA1) emulsions showed low creaming stability at both 25 °C and 55 °C. Conversely, the utilization of PGA either as a mixture or sole emulsifier, showed significantly (p < 0.05) higher cloudiness, as larger average droplet size will affect the refractive index of the oil and aqueous phases. Additionally, the cloudiness was directly proportional to the mean droplet size of the dispersed phase. The inclusion of PGA into the formulation could have disrupted the properties of the interfacial film, thus resulting in larger droplet size. While unadsorbed ionized PGA could have contributed to higher conductivity of emulsions prepared at low pH. Generally, emulsions prepared using sucrose monoesters or as a mixture with modified starch emulsions have significantly (p < 0.05) lower creaming index and conductivity values, but higher cloudiness and average droplet size.
  14. Hajjouli S, Chateauvieux S, Teiten MH, Orlikova B, Schumacher M, Dicato M, et al.
    Molecules, 2014 Sep 16;19(9):14649-66.
    PMID: 25230121 DOI: 10.3390/molecules190914649
    Eurycomanone and eurycomanol are two quassinoids from the roots of Eurycoma longifolia Jack. The aim of this study was to assess the bioactivity of these compounds in Jurkat and K562 human leukemia cell models compared to peripheral blood mononuclear cells from healthy donors. Both eurycomanone and eurycomanol inhibited Jurkat and K562 cell viability and proliferation without affecting healthy cells. Interestingly, eurycomanone inhibited NF-κB signaling through inhibition of IκBα phosphorylation and upstream mitogen activated protein kinase (MAPK) signaling, but not eurycomanol. In conclusion, both quassinoids present differential toxicity towards leukemia cells, and the presence of the α,β-unsaturated ketone in eurycomanone could be prerequisite for the NF-κB inhibition.
  15. Tay PY, Tan CP, Abas F, Yim HS, Ho CW
    Molecules, 2014 Aug 14;19(8):12304-19.
    PMID: 25153858 DOI: 10.3390/molecules190812304
    The effects of ethanol concentration (0%-100%, v/v), solid-to-solvent ratio (1:10-1:60, w/v) and extraction time (30-180 min) on the extraction of polyphenols from agarwood (Aquilaria crassna) were examined. Total phenolic content (TPC), total flavonoid content (TFC) and total flavanol (TF) assays and HPLC-DAD were used for the determination and quantification of polyphenols, flavanol gallates (epigallocatechin gallate--EGCG and epicatechin gallate--ECG) and a benzophenone (iriflophenone 3-C-β-glucoside) from the crude polyphenol extract (CPE) of A. crassna. 2,2'-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity was used to evaluate the antioxidant capacity of the CPE. Experimental results concluded that ethanol concentration and solid-to-solvent ratio had significant effects (p<0.05) on the yields of polyphenol and antioxidant capacity. Extraction time had an insignificant influence on the recovery of EGCG, ECG and iriflophenone 3-C-β-glucoside, as well as radical scavenging capacity from the CPE. The extraction parameters that exhibited maximum yields were 40% (v/v) ethanol, 1:60 (w/v) for 30 min where the TPC, TFC, TF, DPPH, EGCG, ECG and iriflophenone 3-C-β-glucoside levels achieved were 183.5 mg GAE/g DW, 249.0 mg QE/g DW, 4.9 mg CE/g DW, 93.7%, 29.1 mg EGCG/g DW, 44.3 mg ECG/g DW and 39.9 mg iriflophenone 3-C-β-glucoside/g DW respectively. The IC50 of the CPE was 24.6 mg/L.
  16. Ho SK, Tan CP, Thoo YY, Abas F, Ho CW
    Molecules, 2014 Aug 19;19(8):12640-59.
    PMID: 25153876 DOI: 10.3390/molecules190812640
    Ultrasound-assisted extraction (UAE) with ethanol was used to extract the compounds responsible for the antioxidant activities of Misai Kucing (Orthosiphon stamineus). Response surface methodology (RSM) was used to optimize four independent variables: ethanol concentration (%), amplitude (%), duty cycle (W/s) and extraction time (min). Antioxidant compounds were determined by total phenolic content and total flavonoid content to be 1.4 g gallic acid equivalent/100 g DW and 45 g catechin equivalent/100 g DW, respectively. Antioxidant activities were evaluated using the 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS•+) radical scavenging capacity assay and the 2,2-diphenyl-1-picrylhydrazyl (DPPH•) radical scavenging capacity assay to be 1,961.3 and 2,423.3 µmol Trolox Equivalent Antioxidant Capacity (TEAC)/100 g DW, respectively. Based on the optimal conditions, experimental values were reported to be close to the predicted value by RSM modeling (p>0.05), indicating the suitability of UAE for extracting the antioxidants of Misai Kucing. Rosmarinic acid, kaempferol-rutinoside and sinesetine were identified by high performance liquid chromatography-mass spectrometry.
  17. Al-Majedy YK, Kadhum AA, Al-Amiery AA, Mohamad AB
    Molecules, 2014 Aug 07;19(8):11791-9.
    PMID: 25105917 DOI: 10.3390/molecules190811791
    Some novel coumarins were synthesized starting from 4-hydroxycoumarin and methyl bromoacetate. The structures of the newly obtained compounds were confirmed by elemental analysis, mass, IR and NMR spectra.
  18. Aziz AN, Taha M, Ismail NH, Anouar el H, Yousuf S, Jamil W, et al.
    Molecules, 2014 Jun 19;19(6):8414-33.
    PMID: 24950444 DOI: 10.3390/molecules19068414
    Schiff bases of 3,4-dimethoxybenzenamine 1-25 were synthesized and evaluated for their antioxidant activity. All the synthesized compounds were characterized by various spectroscopic techniques. In addition, the characterizations of compounds 13, 15 and 16 were supported by crystal X-ray determinations and their geometrical parameters were compared with theoretical DFT calculations at the B3LYP level of theory. Furthermore, the X-ray crystal data of two non-crystalline compounds 8 and 18 were theoretically calculated and compared with the practical values of compounds 13, 15, 16 and found a good agreement. The compounds showed good DPPH scavenging activity ranging from 10.12 to 84.34 μM where compounds 1-4 and 6 showed stronger activity than the standard n-propyl gallate. For the superoxide anion radical assay, compounds 1-3 showed better activity than the standard.
  19. Sekeli R, Abdullah JO, Namasivayam P, Muda P, Abu Bakar UK, Yeong WC, et al.
    Molecules, 2014 Jun 19;19(6):8350-62.
    PMID: 24950439 DOI: 10.3390/molecules19068350
    The purpose of this study was to evaluate the effectiveness of using RNA interference in down regulating the expression of 1-aminocyclopropane-1-carboxylic acid oxidase gene in Eksotika papaya. One-month old embryogenic calli were separately transformed with Agrobacterium strain LBA 4404 harbouring the three different RNAi pOpOff2 constructs bearing the 1-aminocyclopropane-1-carboxylic acid oxidase gene. A total of 176 putative transformed lines were produced from 15,000 calli transformed, selected, then regenerated on medium supplemented with kanamycin. Integration and expression of the targeted gene in putatively transformed lines were verified by PCR and real-time RT-PCR. Confined field evaluation of a total of 31 putative transgenic lines planted showed a knockdown expression of the targeted ACO1 and ACO2 genes in 13 lines, which required more than 8 days to achieve the full yellow colour (Index 6). Fruits harvested from lines pRNAiACO2 L2-9 and pRNAiACO1 L2 exhibited about 20 and 14 days extended post-harvest shelf life to reach Index 6, respectively. The total soluble solids contents of the fruits ranged from 11 to 14° Brix, a range similar to fruits from non-transformed, wild type seed-derived plants.
  20. Fun HK, Chantrapromma S, Ong LH
    Molecules, 2014 Jul 11;19(7):10137-49.
    PMID: 25019557 DOI: 10.3390/molecules190710137
    Crystals of 1,6-hexanedioic acid (I) undergo a temperature-dependent reversible phase transition from monoclinic P21/c at a temperature higher than the critical temperature (Tc) 130 K to another monoclinic P21/c at temperature lower than Tc. The phase transition is of first order, involving a discontinuity and a tripling of the b-axis at Tc whereas the other unit cell parameters vary continuously. The transition is described by the phenomenological Landau theory. The crystal structure analyses for data collected at 297(2) K and 120.0(1) K show that there is half of a molecule of (I) in the asymmetric unit at 297(2) K whereas there are one and a half molecules of (I) in the asymmetric unit at 120.0(1) K. At both temperatures, 297(2) and 120.0(1) K, intermolecular O-H···O hydrogen bonds link the molecules of I into infinite 1D chains along [101] direction. However there are significantly more O-H···O hydrogen bonds presented in the 120.0(1) K polymorph, thereby indicating this phase transition is negotiated via hydrogen bonds. The relationship of the conformational changes and hydrogen bonding for these two polymorphs are explained in detail.
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