Conformational analysis, inter-molecular interactions, electronic properties and vibrational spectroscopic studies on cis-4-hydroxy-d-proline

Figures & data

Figure 1. Global minimum structure of CHDP monomer obtained at B3LYP/6-31+G(d,p) level.

Figure 2. PES scan curve of CHDP along dihedral (C6-C3-C9-O12) at B3LYP/6-31+G(d,p) level.

Figure 3. Various conformers of CHDP obtained from PES scan along C6-C3-C9-O12 dihedral.

Table 1. Conformation analysis of CHDP at B3LYP/6-31+G(d,p) level

Dihedral (C6–C3–C9–O12)	Conformer (Figure 3)	ΔE (kcal/mol)	Ring dihedral (C3–C7–C6–C2)	Nf (%)
0	a	2.5	27	0.7
20	b	2.3	28	1.0
40	c	1.5	29	3.9
60	d	0.4	30	24.0
80		0	31	47.0
100	e	0.5	28	21.0
120	f	2.0	27	1.7
140	g	3.2	19	0.2
160	h	3.2	21	0.2
180	i	2.8	24	0.4

Figure 4. HOMO, LUMO, and MESP surfaces of CHDP calculated at B3LYP/6-31+G(d,p) level.

Figure 5. Atomic charges on CHDP monomer obtained by MPA and NPA schemes at B3LYP/6-31+G(d,p) level.

Figure 6. Optimized structures of CHDP dimer at B3LYP/6-31+G(d,p) level.

Note: Inter-molecular interactions are displayed by dotted blue lines.

Table 2. QTAIM parameters calculated for inter-molecular interactions in CHDP dimer

	A⋯B	Bond-distance	ρ	∇^2ρ	V	G	H	ΔE
a	O34⋯H13	1.645	0.0498	0.1397	−0.0381	0.0365	−0.0016	12.0
	O11⋯H36	1.653	0.0488	0.1379	−0.0371	0.0358	−0.0013	11.6
b	O32⋯H13	1.765	0.0355	0.1099	−0.0255	0.0265	0.0010	8.0
	O11⋯H26	2.837	0.0045	0.0179	−0.0027	0.0036	0.0009	0.9
	O11⋯H28	2.518	0.0091	0.0305	−0.0059	0.0068	0.0009	1.9

Note: All parameters are in a.u., Bond-distance in Angstrom, and ΔE is in kcal/mol.

Table 3. Second-order perturbation theory analysis of Fock matrix for various lone pairs’ interactions in the NBO basis^* for CHDP dimer

a			b
Donor (i)	Acceptor (j)	E^(2) (kcal/mol)	Donor (i)	Acceptor (j)	E^(2) (kcal/mol)
n1(O34)	σ^*(C31–O35)	6.71	n1(O11)	σ^*(C22-H28)	0.71
n2(O34)	σ^*(C31–C32)	18.00	n2(O11)	σ^*(C22–H28)	0.73
n2(O34)	σ^*(C31–O35)	18.33	n1(O11)	σ^*(C23–H26)	0.27
n1(O11)	σ^*(C8–O12)	6.54	n2(O11)	σ^*(C23–H26)	0.08
n2(O11)	σ^*(C8–O3)	17.71	n1(O32)	σ^*(O12–H13)	9.51
n2(O11)	σ^*(C8–O12)	18.75	n2(O32)	σ^*(O12–H13)	13.56

* E⁽²⁾ = −n_i F_ij²/ΔE where F_ij = <i | F | j> and ΔE = E_i − E_j.

Figure 7. Experimental FT-IR spectra (a) KBr disc, (b) Nujol mull, and calculated IR spectra, (c) monomer, (d) dimer of CHDP at B3LYP/6-31+G(d,p) level.

Table 4. Vibrational analysis of CHDP at B3LYP/6-31+G(d,p) level

Monomer			Dimer						FT-IR value		Assignments (PED ≥ 10%)
Cal.	Scal.	IR Int.	Cal.	Scal.	IR Int.	Cal.	Scal.	IR Int.	KBr disc	Nujol mull
3,831	3,656	32.9	3,831	3,644	37.1	3,831	3,644	28.0			ν(OH)G1 (98)
3,749	3,578	66.2	3,152	3,002	4,249.6	3,152	3,002	4,249.6			ν(OH)G2 (99)
3,555	3,393	17.1	3,568	3,395	5.86	3,559	3,386	15.2			ν(NH) (91)
3,136	2,993	17.6	3,147	2,997	4.9	3,138	2,988	65.2	3,212	3,212	ν(CH) (97)
3,076	2,935	15.5	3,090	2,943	20.4	3,080	2,933	35.9	3,016	3,016	ν(CH) (88)
3,072	2,932	45.3	3,073	2,927	75.8	3,037	2,892	32.3	2,976	2,995	ν(CH) (98)
3,026	2,888	19.6	3,026	2,883	43.2	2,965	2,825	49.3	2,951	2,962	ν(CH) (96)
1,806	1,723	300.9	1,758	1,684	700.9	1,703	1,632	23.0	1,629	1,629	ν(CO)G2 (76)
1,529	1,459	5.4	1,491	1,432	1.8	1,471	1,413	35.3	1,564	1,563	ν(CO)G2 (75) + δ(COO) (25)
1,465	1,398	3.6	1,456	1,398	94.5	1,442	1,385	14.9	1,433	1,434	ω (CHH) (68) + δ(CHH) (23)
1,423	1,358	12.4	1,422	1,366	3.6	1,420	1,364	4.8			δ(CHH) (65) + ω(CHH) (25)
1,383	1,320	6.1	1,392	1,338	27.8	1,371	1,318	23.6	1,384	1,384	δ(CCH) (87)
1,357	1,295	24.9	1,355	1,303	50.7	1,355	1,303	13.2	1,353	1,354	δ(CHH) (66)
1,336	1,275	23.2	1,348	1,296	2.7	1,348	1,296	21.7	1,313	1,313	δ(NCC) (54) + ω (CHC) (10)
1,313	1,253	14.4	1,313	1,263	109.2	1,308	1,259	59.2	1,298	1,298	δ(NCH) (27) + δ(CCH) (25)
1,294	1,235	21.1	1,292	1,243	112.5	1,286	1,238	39.3			δ(OCH)G2 (17)
1,285	1,227	11.8	1,282	1,234	32.0	1,275	1,227	80.5			δ(CNC) (40) + ν(CC) (33)
1,266	1,208	5.0	1,263	1,216	23.9	1,262	1,215	28.2	1,266	1,266	δ(CNC) (46) + ν(CC) (34)
1,207	1,152	21.2	1,211	1,167	8.8	1,207	1,163	16.3	1,198		δ(CNC) (27) + ν(CC) (25) + ν(CO)G2 (18) + δ(OCH)G2 (10)
1,184	1,129	15.6	1,185	1,142	8.2	1,182	1,139	21.9	1,178	1,178	δ(CNC) (15) + δ(CHO)G2 (12) + ν(CC) (12)
1,172	1,119	20.4	1,156	1,114	25.2	1,133	1,093	18.0			δ(CNC) (18) + δ(CCH) (13) + ν(NC) (13) + δ(CCC) (10)
1,117	1,066	202.5	1,116	1,077	32.5	1,101	1,063	62.8	1,089	1,089	ν(NC) (25)
1,094	1,044	27.6	1,096	1,058	48.6	1,095	1,057	60.7	1,071	1,071	δ(R2) (19) + ν(CC) (15)
1,060	1,011	66.6	1,072	1,035	48.2	1,064	1,028	58.2	1,041	1,042	δ(CNC) (16) + ω(CO)G2 (12)
1,022	975	60.9	1,022	988	25.4	1,020	986	22.5	1,003	1,003	δ(CNC) (22) + ν(NC) (6)
981	936	20.1	993	961	1.3	986	954	10.7	976	976	ν(NC) (21) + ν(CC) (25)
944	901	2.8	949	919	5.1	945	915	4.9	920		ω(NHH) (10)
901	860	3.4	901	874	8.0	891	864	8.8	869	870	τ(R2) (11)
845	806	13.7	860	835	11.7	849	825	7.2	811	811	τ(R2) (59)
788	752	63.6	822	799	35.2	802	780	72.2	736	734	ω(COH)G2 (36) + δ(R1) (28)
729	695	44.3	755	736	34.4	742	724	7.2	681	681	τ(R2) (22) + δ(COO)G2 (11)
641	611	87.7	653	639	88.0	646	633	8.7	620	620	δ(CCC) (17) + δ(R1) (15) + ω(COH)G2 (12)
614	586	53.1	621	609	50.1	602	591	14.4			τ(R2) (45) + τ(R1) (16)
584	557	21.6	558	550	8.3	535	528	10.1			τ(R2) (25)
526	502	27.0	495	490	7.4	479	475	10.0	483	482	ω(COH)G2 (41) + ρ(OCO) (10)
476	454	8.3	460	457	25.7	427	425	11.4			ω(CHC) (19) + δ (OCH)G2 (17)

Notes: Experimental FTIR values are also included. All frequencies are in cm⁻¹ and IR intensities are in a.u.

Abbreviations: ν—stretching, ρ—rocking, ω—wagging, δ—bending, τ—torsion, R1, R2—rings, G1, G2—OH and COOH groups.

Table 5. Electronic and thermodynamic parameters of CHDP monomer and dimer calculated at B3LYP/6-31+G(d,p) level

Electronic	Monomer	Dimer	Thermodynamic	Monomer	Dimer
I (eV)	6.4	6.47	ZPE (kcal/mol)	93.3	187.7
A (eV)	0.47	0.73	E (kcal/mol)	98.8	199.5
Eg (eV)	6.01	5.75	Cv (cal/mol K)	32.3	68.1
μ (Debye)	1.11	1.92	S (cal/mol K)	93.4	149.8